10-Q

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

(Mark One)

☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended March 31, 2024

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission file number 001-34375

PLUS THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

Delaware	33-0827593
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)
4200 MARATHON BLVD., SUITE 200, AUSTIN, TX	78756
(Address of principal executive offices)	(Zip Code)

(737) 255-7194

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Title of each class	Trading Symbol(s)	Name of each exchange on which registered
Common Stock, par value $0.001	PSTV	Nasdaq Capital Market

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See definitions of “large accelerated filer,” “accelerated filer”, “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large Accelerated Filer	☐	Accelerated Filer	☐
Non-Accelerated Filer	☒	Smaller reporting company	☒
		Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financing accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

As of May 10, 2024 , there were 5,704,219 shares of the registrant’s common stock outstanding.

PLUS THERAPEUTICS, INC.

Table of Contents

			Page
PART I.	FINANCIAL INFORMATION
	Item 1.	Financial Statements (Unaudited)	4
		Condensed Balance Sheets	4
		Condensed Statements of Operations	5
		Condensed Statements of Stockholders’ Equity/(Deficit)	6
		Condensed Statements of Cash Flows	7
		Notes to Condensed Financial Statements	8
	Item 2.	Management’s Discussion and Analysis of Financial Condition and Results of Operations	18
	Item 3.	Quantitative and Qualitative Disclosures about Market Risk	28
	Item 4.	Controls and Procedures	28
PART II.	OTHER INFORMATION
	Item 1.	Legal Proceedings	29
	Item 1A.	Risk Factors	29
	Item 2.	Unregistered Sales of Equity Securities and Use of Proceeds	30
	Item 6.	Exhibits	31

2

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This Quarterly Report on Form 10-Q and the exhibits incorporated herein by reference contain “forward-looking statements” which are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Statements other than statements of historical fact constitute “forward-looking statements.” These forward-looking statements do not constitute guarantees of future performance. These forward-looking statements may be identified by terms such as “intend,” “expect,” “project,” “believe,” “anticipate,” “initiate,” “will,” “should,” “would,” “could,” “may,” “designed,” “potential,” “evaluate,” “hypothesize,” “plan,” “progressing,” “proceeding,” “exploring,” “opportunity,” “hopes,” “suggest,” and similar expressions, or the negative of such expressions. Such statements are based upon certain assumptions and assessments made by our management in light of their experience and their perception of historical trends, current conditions, expected future developments and other factors they believe to be appropriate.

These statements include, without limitation, statements about our anticipated expenditures, including research and development, and general and administrative expenses; our strategic collaborations and license agreements, intellectual property, U.S. Food and Drug Administration and European Medicines Agency approvals and interactions and government regulation; the potential size of the market for our product candidates; our research and development efforts; results from our pre-clinical and clinical studies and the implications of such results regarding the efficacy or safety of our product candidates; the safety profile, pathways, and efficacy of our product candidates and formulations; anticipated advantages of our product candidates over other products available in the market and being developed; the populations that will most benefit from our product candidates and indications that will be pursued with each product candidate; anticipated progress in our current and future clinical trials; plans and strategies to create novel technologies; our IP strategy; competition; future development and/or expansion of our product candidates and therapies in our markets; sources of competition for any of our product candidates; our pipeline; our ability to generate product or development revenue and the sources of such revenue; our ability to effectively manage our gross profit margins; our ability to obtain and maintain regulatory approvals; expectations as to our future performance; portions of the “Liquidity and Capital Resources” section of this report, including our potential need for additional financing and the availability thereof; our ability to continue as a going concern; our ability to remain listed on the Nasdaq Capital Market; our ability to repay or refinance some or all of our outstanding indebtedness and our ability to raise capital in the future; our ability to transfer the drug product manufacturing to a contract drug manufacturing organization; and the potential enhancement of our cash position through development, marketing, and licensing arrangements; and a material security breach or cybersecurity attack affecting our operations and property. The forward-looking statements included in this report are also subject to a number of additional material risks and uncertainties, including but not limited to the risks described under “Part I – Item 1A – Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2023, and under “Part II – Item 1A – Risk Factors” in this Quarterly Report on Form 10-Q. These risks and uncertainties could cause actual results to differ materially from expectations or those expressed in these forward-looking statements.

Our actual results may differ, including materially, from those anticipated in these forward-looking statements as a result of various factors, including, but not limited to, the following: the early stage of our product candidates and therapies, the results of our research and development activities, including uncertainties relating to the clinical trials of our product candidates and therapies; our liquidity and capital resources and our ability to raise additional cash, the outcome of our partnering/licensing efforts, risks associated with laws or regulatory requirements applicable to us, market conditions, product performance, potential litigation, and competition within the radiotherapeutics, and more generally, oncological medicine fields, among others. The forward-looking statements included in this report are also subject to a number of additional material risks and uncertainties, including but not limited to the risks described under “Part I – Item 1A – Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2023, and under “Part II – Item 1A – Risk Factors” in this Quarterly Report on Form 10-Q. These risks and uncertainties could cause actual results to differ materially from expectations or those expressed in these forward-looking statements.

We encourage you to read the risks described under “Part II – Item 1A – Risk Factors” in this report carefully. We caution you not to place undue reliance on the forward-looking statements contained in this report. These statements, like all statements in this report, speak only as of the date of this report (unless an earlier date is indicated) and the Company undertakes no obligation to update or revise the statements except as required by law. Such forward-looking statements are not guarantees of future performance.

3

PART I. FINANCIAL INFORMATION

Item 1. Financial Statements

PLUS THERAPEUTICS, INC.

CONDENSED BALANCE SHEETS

(UNAUDITED)

(in thousands, except share and par value data)

	March 31, 2024			December 31, 2023
Assets
Current assets:
Cash and cash equivalents	$	2,901		$	8,554
Investments		323			—
Other current assets		989			1,280
Total current assets		4,213			9,834
Property and equipment, net		800			906
Operating lease right-use-of assets		171			202
Goodwill		372			372
Intangible assets, net		33			42
Other assets		32			32
Total assets	$	5,621		$	11,388
Liabilities and Stockholders’ Equity
Current liabilities:
Accounts payable and accrued expenses	$	6,447		$	6,631
Operating lease liability		115			120
Deferred grant liability		247			—
Term loan obligation, current		3,590			3,976
Total current liabilities		10,399			10,727
Noncurrent operating lease liability		59			85
Deferred grant liability		—			1,924
Total liabilities		10,458			12,736
Commitments and contingencies (Note 8)
Stockholders’ deficit:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,952 shares issued and outstanding at March 31, 2024 and December 31, 2023, respectively		—			—
Common stock, $0.001 par value; 100,000,000 shares authorized; 4,522,656 and 4,264,231 issued and outstanding at March 31, 2024, and 4,522,656 issued and 4,444,097 outstanding as of December 31, 2023, respectively		5			5
Treasury stock (at cost, 258,425 and 78,559 shares as of March 31, 2024 and December 31, 2023, respectively)		(500	)		(126	)
Additional paid-in capital		479,420			479,274
Accumulated deficit		(483,762	)		(480,501	)
Total stockholders’ deficit		(4,837	)		(1,348	)
Total liabilities and stockholders’ deficit	$	5,621		$	11,388

See Accompanying Notes to these Condensed Financial Statements

4

PLUS THERAPEUTICS, INC.

CONDENSED STATEMENTS OF OPERATIONS

(UNAUDITED)

(in thousands, except share and per share data)

	For the Three Months Ended March 31,
	2024			2023
Grant revenue	$	1,677		$	506
Operating expenses:
Research and development		2,763			2,983
General and administrative		2,213			2,245
Total operating expenses		4,976			5,228
Operating loss		(3,299	)		(4,722	)
Other income (expense):
Interest income		72			51
Interest expense		(34	)		(134	)
Total other expense		38			(83	)
Net loss	$	(3,261	)	$	(4,805	)
Net loss per share, basic and diluted	$	(0.75	)	$	(2.07	)
Basic and diluted weighted average shares used in calculating net loss per share    attributable to common stockholders		4,321,731			2,320,017

See Accompanying Notes to these Condensed Financial Statements

5

PLUS THERAPEUTICS, INC.

CONDENSED STATEMENTS OF STOCKHOLDERS’ EQUITY/(DEFICIT)

(UNAUDITED)

(In thousands, except share data)

						Convertible																		Additional							Total
	Preferred stock					preferred stock					Common stock					Treasury Stock								paid-in			Accumulated				stockholders’
	Shares			Amount		Shares			Amount		Shares			Amount		Shares				Amount				capital			deficit				(deficit)/equity
Balance at December 31, 2022		—	$		—		1,952	$		—		2,240,092	$		2		—		$		—		$		473,628	$		(467,185	)	$		6,445
Stock-based compensation		—			—		—			—		—			—		—				—				140			—				140
Sale of common stock, net		—			—		—			—		168,164			—		—				—				895			—				895
Issuance of Series F preferred stock		1			—		—			—		—			—		—				—				1			—				1
Net loss		—			—		—			—		—			—		—				—				—			(4,805	)			(4,805	)
Balance at March 31, 2023		1	$		—		1,952	$		—		2,408,256	$		2		—		$		—		$		474,664	$		(471,990	)	$		2,676
Balance at December 31, 2023		—	$		—		1,952	$		—		4,522,656	$		5		(78,559	)	$		(126	)	$		479,274	$		(480,501	)	$		(1,348	)
Stock-based compensation		—			—		—			—		—			—		—				—				146			—				146
Purchase of treasury stock		—			—		—			—		—			—		(179,866	)			(374	)			—			—				(374	)
Net loss		—			—		—			—		—			—		—				—				—			(3,261	)			(3,261	)
Balance at March 31, 2024		—	$		—		1,952	$		—		4,522,656	$		5		(258,425	)	$		(500	)	$		479,420	$		(483,762	)	$		(4,837	)

See Accompanying Notes to these Condensed Financial Statements

6

PLUS THERAPEUTICS, INC.

CONDENSED STATEMENTS OF CASH FLOWS

(UNAUDITED)

(In thousands)

	For the Three Months Ended March 31,
	2024			2023
Cash flows used in operating activities:
Net loss	$	(3,261	)	$	(4,805	)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization		155			158
Amortization of deferred financing costs and debt discount		16			66
Share-based compensation expense		146			140
Accretion of discount on short-term investments		1			—
Reduction in the carrying amount of operating lease right-of-use assets		31			29
Loss on disposal of property and equipment		—			2
Increases (decreases) in cash caused by changes in operating assets and liabilities:
Other current assets		150			2,791
Accounts payable and accrued expenses		(43	)		(3,639	)
Change in operating lease liabilities		(31	)		(29	)
Deferred grant liability		(1,677	)		(506	)
Net cash used in operating activities		(4,513	)		(5,793	)
Cash flows used in investing activities:
Purchases of property and equipment		(40	)		(97	)
Purchase of short-term investments		(324	)		—
Net cash used in investing activities		(364	)		(97	)
Cash flows used in/provided by financing activities:
Principal payments of term loan obligation		(402	)		(402	)
Purchase of treasury stock		(374	)		—
Proceeds from sale of common stock, net		—			895
Net cash (used in) provided by financing activities		(776	)		493
Net decrease in cash and cash equivalents		(5,653	)		(5,397	)
Cash and cash equivalents at beginning of period		8,554			18,120
Cash and cash equivalents at end of period	$	2,901		$	12,723
Supplemental disclosure of cash flows information:
Cash paid during period for:
Interest	$	23		$	73
Supplemental schedule of non-cash investing and financing activities:
Unpaid offering cost	$	141		$	25
Right-of-use assets obtained in exchange for operating lease liability	$	—		$	51

See Accompanying Notes to these Condensed Financial Statements

7

PLUS THERAPEUTICS, INC.

NOTES TO CONDENSED FINANCIAL STATEMENTS

March 31, 2024

(UNAUDITED)

1. Basis of Presentation and New Accounting Standards

The accompanying unaudited condensed financial statements for the three months ended March 31, 2024 and 2023 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2023 has been derived from the audited financial statements at December 31, 2023, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc. (the “Company”) have been included. Operating results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, filed with the Securities and Exchange Commission on March 5, 2024.

Amendments to Certificate of Incorporation and Reverse Stock Split

At the Annual Meeting of Stockholders of the Company held on April 20, 2023 (the “Annual Meeting”), the stockholders of the Company approved an amendment to the Company’s Amended and Restated Certificate of Incorporation (the “Charter”) to implement a reverse stock split of the Company’s then issued and outstanding common stock, par value $0.001 per share, with the ratio to be determined by the Board of Directors (the “Board”) of the Company, within a range of not less than 1-for-3 and not greater than 1-for-15. Subsequently, on April 21, 2023, the Board determined to fix the ratio for the reverse stock split at 1-for-15, without any change to its par value (the "Reverse Stock Split").

On April 27, 2023, following stockholder and Board approval, the Company filed a Certificate of Amendment to its Charter (the “Amendment”), with the Secretary of State of the State of Delaware to effectuate the Reverse Stock Split. The Amendment became effective on May 1, 2023. Upon effectiveness of the Reverse Stock Split, the number of shares of the Company’s common stock (x) issued and outstanding decreased from approximately 37.4 million shares to approximately 2.5 million shares; (y) reserved for issuance upon exercise of outstanding warrants and options decreased from approximately 2.0 million shares to approximately 0.1 million shares, and (z) reserved but unallocated under the Company’s current equity incentive plans decreased from approximately 3.0 million shares of common stock to approximately 0.2 million shares of common stock. The Company’s common stock began trading on the Nasdaq Capital Market (“Nasdaq”) on a post-split basis on May 1, 2023. The Company’s 5,000,000 shares of authorized Preferred Stock were not affected by the Reverse Stock Split. No fractional shares were issued in connection with the Reverse Stock Split, and accordingly, the outstanding number of shares post Reverse Stock Split was adjusted down by approximately 1,310 (post-effect of the Reverse Stock Split) shares. Proportional adjustments for the Reverse Stock Split were made to the Company’s outstanding stock options, warrants and equity incentive plans for the period ended March 31, 2023 as presented in the condensed financial statements in this Quarterly Report on Form 10-Q. The Company’s financial statements, and all references thereto have been retroactively adjusted to reflect the Reverse Stock Split unless specifically stated otherwise.

Grant Revenue Recognition

In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as the Company does not consider there to be a transfer of control of goods or services. With respect to each grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies International Accounting Standards No. 20 ("IAS 20"), Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract.

The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of each grant, of whether each grant agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred.

8

Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.

Available-for-Sale Securities

The Company’s available-for-sale securities consist of U.S. government and agency securities. The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the condensed balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the condensed statements of operations and comprehensive income/loss and as a separate component of stockholders’ equity. Realized gains and losses are calculated on the specific identification method and recorded as interest income (loss). At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the decline in fair value below amortized cost is a result of credit losses or other factors, whether the Company expects to recover the amortized cost of the security, the Company’s intent to sell and if it is more likely than not that the Company will be required to sell the securities before the recovery of amortized cost. The Company records changes in allowance for expected credit loss in other income (expense). As of March 31, 2024, there were no available-for-sale securities in an unrealized loss position, and there has been no allowance for expected credit losses recorded during any of the periods presented.

Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Accretion of discounts are recorded in interest income in the condensed statements of operations and comprehensive income/loss.

During the three months ended March 31, 2024, the unrealized gain on the Company’s available-for-sale securities was less than $1,000, and not presented separately in the condensed statement of operations and comprehensive income/loss.

Recently Issued Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (ASU) No. 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosure. This ASU includes amendments that further enhance income tax disclosures, primarily through standardization and disaggregation of rate reconciliation categories and income taxes paid by jurisdiction. The ASU is effective for years beginning after December 15, 2024, but early adoption is permitted. This ASU should be applied on a prospective basis, although retrospective application is permitted. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

In November 2023, the FASB issued Accounting Standard Update (ASU) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. The new standard is intended to improve annual and interim reportable segment disclosure requirements regardless of number of reporting units, primarily through enhanced disclosures of significant expenses. The amendment requires public entities to disclose significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit and loss. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years starting after December 15, 2024. This ASU must be applied retrospectively to all prior periods presented. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

2. Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve reviewing assets for impairment and determining the assumptions used in measuring stock-based compensation expense.

3. Liquidity and Going Concern

The Company incurred a net loss of $3.3 million for the three months ended March 31, 2024. The Company had an accumulated deficit of $483.8 million as of March 31, 2024. Additionally, the Company used net cash of $4.5 million to fund its operating activities for the three months ended March 31, 2024.

To date, the Company’s operating losses have been funded primarily from outside sources of invested capital from issuance of its common and preferred stocks, proceeds from its term loan and grant funding. However, the Company has had, and will continue to have, an ongoing need to raise additional cash from outside sources to fund its future clinical development programs and other operations. There can be no assurance that the Company will be able to continue to raise additional capital in the future. The Company’s inability to raise additional cash would have a material and adverse impact on its operations and could cause the Company to default on its term loan. These factors raise substantial doubt about the Company’s ability to continue as a going concern.

9

On May 9, 2024, the Company closed a private placement of securities of the Company for aggregate gross proceeds of approximately $7.25 million, before deducting certain expenses payable by the Company, and excluding the proceeds, if any, from the exercise of warrants issued in the private placement. See Note 12 for further information regarding the private placement.

Nasdaq Listing Compliance

On March 8, 2024, the Company received a letter (the “Notice”) from the Listing Qualifications staff of Nasdaq, notifying the Company that it no longer complied with the requirement under Nasdaq Listing Rule 5550(b)(1) to maintain a minimum of $2.5 million in stockholders’ equity for continued listing on Nasdaq or the alternative requirements of having a market value of listed securities of $35 million or net income from continuing operations of $500,000 in the most recently completed fiscal year or two of the last three most recently completed fiscal years (the “Alternative Standards”). The Notice states that the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023, disclosed stockholders’ equity of ($1,348,000) as of December 31, 2023, and that, as of March 8, 2024, the Company did not meet the Alternative Standards.

On April 22, 2024, the Company provided Nasdaq with its plan to achieve and sustain compliance with the stockholders’ equity requirement and requested that Nasdaq grant the Company an extension of time until September 4, 2024, to provide evidence of compliance with the stockholders’ equity requirement. Nasdaq has not yet responded to the Company’s plan, and there can be no assurance that Nasdaq will grant an extension or that the Company will be able to comply with the applicable listing standards of Nasdaq.

The Company continues to seek additional capital from other financing alternatives and other sources in order to ensure adequate funding is available to allow the Company to continue research and product development activities at their current levels. If sufficient capital is not raised, the Company will at a minimum need to significantly reduce or curtail its research and development and other operations, and this would negatively affect its ability to achieve corporate growth goals.

Should the Company fail to raise additional cash from outside sources, it would have a material adverse impact on its operations.

The accompanying condensed financial statements have been prepared assuming the Company will continue to operate as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from uncertainty related to its ability to continue as a going concern.

4. Fair Value Measurements

Fair value measurements are market-based measurements, not entity-specific measurements. Therefore, fair value measurements are determined based on the assumptions that market participants would use in pricing the asset or liability. The Company follows a three-level hierarchy to prioritize the inputs used in the valuation techniques to derive fair values. The basis for fair value measurements for each level within the hierarchy is described below:

•Level 1: Quoted prices in active markets for identical assets or liabilities.

•Level 2: Quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs are observable in active markets.

•Level 3: Valuations derived from valuation techniques in which one or more significant inputs are unobservable in active markets.

The Company has investments in money market accounts, which are included in cash and cash equivalents on the balance sheets. Fair value inputs for these investments are considered Level 1 measurements within the fair value hierarchy since money market account fair values are known and observable through daily published floating net asset values.

The following table summarizes the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023, respectively (in thousands).

	Fair Value Measurements Using
March 31, 2024	Fair Value		Level 1		Level 2		Level 3
Money market	$	176	$	176	$	—	$	—
Treasury bills and government agency bonds		323		323		—		—
	$	499	$	499	$	—	$	—
	Fair Value Measurements Using
December 31, 2023	Fair Value		Level 1		Level 2		Level 3
Money market	$	5,449	$	5,449	$	—	$	—

10

5. Term Loan Obligations

On May 29, 2015, the Company entered into the Loan and Security Agreement (the “Loan and Security Agreement”), pursuant to which Oxford Finance, LLC (“Oxford”) funded an aggregate principal amount of $17.7 million (the “Term Loan”), subject to the terms and conditions set forth in the Loan and Security Agreement. The Term Loan accrues interest at a floating rate of at least 8.95% per annum, comprised of a three-month LIBOR rate with a floor of 1.00% plus 7.95%. Pursuant to the Loan and Security Agreement, as amended, the Company made interest only payments through May 1, 2021, and thereafter is required to make payments of principal and accrued interest in equal monthly installments sufficient to amortize the Term Loan through June 1, 2024, the maturity date. At maturity of the Term Loan, or earlier repayment in full following voluntary prepayment or upon acceleration, the Company is required to make a final payment in an aggregate amount equal to approximately $3.2 million.

From September 2017 to March 2020, the Company entered into a total of nine amendments to the Term Loan that, among other things, extended the interest only period, required repayment of $3.1 million using the proceeds received from sale of the Company’s former UK and Japan subsidiaries in April 2019, increased the final payment, increased the final payment fee upon maturity or early repayment of the Term Loan, increased the minimum liquidity covenant level to $2.0 million and deferred the start date of principal repayment from May 1, 2020 to May 1, 2021 and extended the term of the Term Loan from September 1, 2021 to June 1, 2024.

On June 28, 2023, the Company and Oxford entered into a tenth amendment to the Loan and Security Agreement, and revised the interest rate of the Loan to the greater of: (1) 8.95%, or (2) the sum of 1-month Secured Overnight Financing Rate and 8.05%, effective July 1, 2023.

The Term Loan, as amended, is collateralized by a security interest in substantially all of the Company’s existing and subsequently acquired assets, including its intellectual property assets, subject to certain exceptions set forth in the Loan and Security Agreement, as amended. The intellectual property asset collateral will be released upon the Company achieving a certain liquidity level when the total principal outstanding under the Loan and Security Agreement is less than $3.0 million. As of March 31, 2024, there was $0.4 million principal amount outstanding under the Term Loan, excluding the $3.2 million final payment fee, and the Company was in compliance with all of the debt covenants under the Loan and Security Agreement.

The Company’s interest expense for the three ended March 31, 2024 and 2023 was $34,000 and $0.1 million, respectively. Interest expense is calculated using the effective interest method; therefore it is inclusive of non-cash amortization in the amount of $21,000 and $0.1 million for the three ended March 31, 2024 and 2023, respectively, related to the amortization of the debt discount, capitalized loan costs, and accretion of final payment.

The Loan and Security Agreement, as amended, contains customary indemnification obligations and customary events of default, including, among other things, the Company’s failure to fulfill certain obligations under the Term Loan, as amended, and the occurrence of a material adverse change, which is defined as a material adverse change in the Company’s business, operations, or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the loan. In the event of default by the Company or a declaration of material adverse change by its lender, under the Term Loan, the lender would be entitled to exercise its remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Term Loan, which could materially harm the Company’s financial condition. As of March 31, 2024, the Company has not received any notification or indication from Oxford that it intends to invoke the material adverse change clause.

6. Loss per Share

Basic per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding as calculated using the treasury stock method. Potential common shares were related to outstanding but unexercised options, multiple series of convertible preferred stock, and warrants for all periods presented.

The following were excluded from the diluted loss per share calculation for the periods presented because their effect would be anti-dilutive:

	As of March 31,
	2024		2023
Outstanding stock options		303,133		134,283
Preferred stock		28,190		28,190
Outstanding warrants		142,733		142,733
Total		474,056		305,206

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7. Grant Revenue

On September 19, 2022, the Company entered into that certain CPRIT contract (“CPRIT Contract”), effective as of August 31, 2022, with CPRIT, pursuant to which CPRIT will provide the Company with a CPRIT grant (“CPRIT Grant”) over a three-year period to fund the continued development of rhenium (186Re) obisbemeda for the treatment of patients with leptomeningeal metastases (“LM”). The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements.

The CPRIT Contract will terminate on August 30, 2025, unless terminated earlier by (a) the mutual written consent of all parties to the CPRIT Contract, (b) CPRIT for an event of default by the Company, (c) CPRIT, if the funds allocated to the CPRIT Grant become legally unavailable during the term of the CPRIT Contract and CPRIT is unable to obtain additional funds for such purposes, and (d) the Company for convenience. CPRIT may require the Company to repay some or all of the disbursed CPRIT Grant proceeds (with interest not to exceed 5% annually) in the event of the early termination of the CPRIT Contract by CPRIT for an event of default by the Company or by the Company for convenience, or if the Company relocates its principal place of business outside of the state of Texas during the CPRIT Contract term or within three years after the final payment of the grant funds.

The Company retains ownership over any intellectual property developed under the CPRIT Contract (each, a “Project Result”). With respect to non-commercial use of any Project Result, the Company granted to CPRIT a nonexclusive, irrevocable, royalty-free, perpetual, worldwide license with right to sublicense any necessary additional intellectual property rights to exploit all Project Results by CPRIT, other governmental entities and agencies of the State of Texas, and private or independent institutions of higher education located in Texas, for education, research and other non-commercial purposes.

The Company recognized $1.7 million and $0.5 million in grant revenue from the CPRIT Contract during the three months ended March 31, 2024 and 2023, respectively.

8. Commitments and Contingencies

Leases

The Company leases laboratory, office and storage facilities in San Antonio, Texas, under operating lease agreements that expire in 2025. The Company also leases certain office space in Austin, Texas under a month-to-month operating lease agreement and certain office space in Charlottesville, Virginia (the “Charlottesville Lease”). The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods. On March 31, 2023, Company believed that it was reasonably certain that the Charlottesville Lease will be renewed through March 31, 2026, and as a result, it remeasured the related lease liability as of March 31, 2023 to be $80,000 using the then-in-effect discount rate of 12.76%. Effective July 1, 2023, the Company added additional office lease premises in Charlottesville, which was accounted for as a separate operating lease contract with a lease liability and corresponding right-of-use asset of $19,000, as a discount rate of 13.47%.

Piramal Master Services Agreement

On January 8, 2021, the Company entered into a Master Services Agreement (the “MSA”) with Piramal Pharma Solutions, Inc. (“Piramal”), for Piramal to perform certain services related to the development, manufacture, and supply of the Company’s rhenium (186Re) obisbemeda intermediate drug product. The MSA includes the transfer of analytical methods, development of microbiological methods, process transfer and optimization, intermediate drug product manufacturing, and stability studies for the Company, which has been initiated at Piramal’s facility located in Lexington, Kentucky.

The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice. Either party may terminate the MSA upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party.

Other commitments and contingencies

The Company has entered into agreements with various research organizations for pre-clinical and clinical development studies, which have provisions for cancellation. Under the terms of these agreements, the vendors provide a variety of services including conducting research, recruiting and enrolling patients, monitoring studies and data analysis. Payments under these agreements typically include fees for services and reimbursement of expenses. The timing of payments due under these agreements is estimated based on current study progress. As of March 31, 2024, the Company did not have any clinical research study obligations.

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Legal proceedings

From time to time, the Company is subject to legal proceedings and claims, whether asserted or unasserted, that arise in the ordinary course of business. Due to their nature, such legal proceedings involve inherent uncertainties including, but not limited to, court rulings, negotiations between affected parties and governmental actions. Management assesses the probability of loss for such contingencies and accrues a liability and/or discloses the relevant circumstances, as appropriate.

9. License Agreements

Biocept License Agreement

On September 7, 2023, the Company entered into a Non-Exclusive License and Services Agreement (the “Biocept Agreement”) with Biocept, Inc (“Biocept”), pursuant to which Biocept granted the Company a non-exclusive license to use the Biocept proprietary cell enumeration test, CNsideTM (“CNside”). In exchange for the license, the Company issued to Biocept 53,381 unregistered shares, the fair value of which was $75,000. The Biocept Agreement also provides that if Biocept fully transfers the technology to the Company, a tech transfer and validation fee of $300,000 will be payable. In addition, the Company was granted an option for an exclusive worldwide license for $1,000,000 on or before December 31, 2024, to process and perform cell enumeration testing for treatments for other patients including those on the Company’s radiotherapeutic drugs.

On October 16, 2023, Biocept filed a voluntary petition for relief under the provisions of Chapter 7 of Title 11 of the United States Bankruptcy Code. See Note 12 for further information regarding the Company’s acquisition of substantially all right, title and interest in CNside.

UT Health Science Center at San Antonio (“UTHSCSA”) License Agreement

On December 31, 2021, the Company entered into a Patent and Know-How License Agreement (the “UTHSCSA License Agreement”) with The University of Texas Health Science Center at San Antonio (“UTHSCSA”), pursuant to which UTHSCSA granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of biodegradable alginate microspheres (“BAM”) containing nanoliposomes loaded with imaging and/or therapeutic payloads.

NanoTx License Agreement

On March 29, 2020, the Company and NanoTx, Corp. (“NanoTx”) entered into a Patent and Know-How License Agreement, pursuant to which NanoTx granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of radiolabeled nanoliposomes.

The transaction terms included an upfront payment of $0.4 million in cash and $0.3 million in the Company's voting stock. The transaction terms also included success-based milestone and royalty payments contingent on key clinical, regulatory and sales milestones, as well as the requirement to pay 15% of any non-dilutive monetary awards or grants received from external agencies to support product development of the nanoliposome encapsulated BMEDA-chelated radioisotope, which includes grants from CPRIT. As of March 31, 2024, the Company accrued $0.5 million of payments due to NanoTx as a result of the CPRIT grant received (see Note 7, Grant Revenue of the condensed financial statements for additional information).

10. Stockholders’ Equity

Preferred Stock

The Company has authorized 5,000,000 shares of preferred stock, par value $0.001 per share. The Company’s Board is authorized to designate the terms and conditions of any preferred stock the Company issues without further action by the common stockholders.

Series F Preferred Stock

On March 3, 2023, the Company filed a certificate of designation (the “Certificate of Designation”) with the Secretary of State of the State of Delaware, effective as of the time of filing, designating the rights, preferences, privileges and restrictions of the Series F Preferred Stock, with the total authorization of one (1) share of Series F Preferred Stock. The Certificate of Designation provided that the share of Series F Preferred Stock would have 50,000,000 votes per share of Series F Preferred Stock and would vote together with the Company’s common stock, as a single class exclusively with respect to any proposal to amend the Company’s Charter to effect the Reverse Stock Split. On March 3, 2023, the Company entered into a subscription and investment representation agreement with Richard J. Hawkins, chairman of the board of the Company, who is an accredited investor (the “Series F Preferred Stock Purchaser”), pursuant to which the Company agreed to issue and sell one (1) share of the Company’s

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Series F Preferred Stock, par value $0.001 per share, to the Series F Preferred Stock Purchaser for $1,000 in cash. The sale closed on March 3, 2023.

At the Company’s 2023 annual meeting, the Series F Preferred Stock was voted, without action by the holder, on the proposal to approve the Reverse Stock Split in the same proportion as shares of common stock voted to approve the Reverse Stock Split. The Series F Preferred Stock otherwise had no voting rights except as otherwise required by the General Corporation Law of the State of Delaware.

The Series F Preferred Stock was not convertible into, or exchangeable for, shares of any other class or series of stock or other securities of the Company. The Series F Preferred Stock had no rights with respect to any distribution of assets of the Company, including upon a liquidation, bankruptcy, reorganization, merger, acquisition, sale, dissolution or winding up of the Company, whether voluntarily or involuntarily. The holder of the Series F Preferred Stock was not entitled to receive dividends of any kind.

The outstanding share of Series F Preferred Stock was redeemed in whole, automatically effective upon the approval by the Company’s stockholders of the Reverse Stock Split. Upon such redemption, the holder of the Series F Preferred Stock received consideration of $1,000 in cash.

Series B and C Preferred Stock

As of March 31, 2024, there were 938 outstanding shares of Series C Preferred Stock that can be converted into an aggregate of 27,792 shares of common stock, and 1,014 shares of Series B Convertible Preferred Stock that can be converted into an aggregate of 398 shares of common stock.

Warrants

On September 25, 2019, the Company completed an underwritten public offering. The Company issued 19,266 shares of its common stock, along with pre-funded warrants to purchase 180,733 shares of its common stock and Series U Warrants to purchase 230,000 shares of its common stock. The Series U Warrants have a term of five years from the issuance date. In addition, the Company issued warrants to H.C. Wainwright & Co., LLC, as representatives of the underwriters, to purchase 5,000 shares of its common stock with a term of five years from the issuance date, in the form of Series U Warrants (the “Representative Warrants”). As of March 31, 2024, there were 142,733 outstanding Series U Warrants and Representative Warrants which can be exercised into an aggregate of 142,733 shares of common stock at a weighted average exercise price of $34.10 per share.

Common Stock

Lincoln Park Purchase Agreement

On August 2, 2022, the Company entered into a purchase agreement (the “2022 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park Capital Fund (“Lincoln Park”) committed to purchase up to $50.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2022 Purchase Agreement, the Company has the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park is obligated to purchase up to $50.0 million of the Company’s common stock. Such sales of common stock by the Company are subject to certain limitations, and can occur from time to time, at the Company’s sole discretion, over the 36-month period commencing on August 17, 2022, subject to the satisfaction of certain conditions.

On May 16, 2022, the Company received stockholder approval for purposes of the Nasdaq listing rules to permit issuances of up to 57.5 million shares of the Company’s common stock (including the issuance of more than 19.99% of the Company’s common stock) to Lincoln Park, and it was pursuant to that approval that the Company entered into the 2022 Purchase Agreement.

Upon execution of the 2022 Purchase Agreement, the Company paid $0.1 million in cash as the initial commitment fee, and issued 32,846 shares as the initial commitment shares, to Lincoln Park as consideration for its irrevocable commitment to purchase shares of the Company’s common stock at its direction under the 2022 Purchase Agreement. The Company has agreed to pay an additional commitment fee, which it may elect to pay in cash and/or shares of its common stock, upon receipt of $25.0 million aggregate gross proceeds from sales of common stock to Lincoln Park under the 2022 Purchase Agreement.

On August 17, 2022, a registration statement (the “First Registration Statement”) was declared effective to cover the resale of up to 633,333 shares of the Company’s common stock comprised of (i) the 32,846 initial commitment shares, and (ii) up to 600,486 that the Company has reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time from and after the date of the prospectus. The Company sold approximately 527,166 shares under the First Registration Statement.

On August 18, 2023, a second registration statement (the “Second Registration Statement”) was declared effective to cover the resale of up to an additional 1,500,000

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shares of the Company’s common stock that the Company reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time. The Company sold 150,000 shares under the Second Registration Statement. The Company cannot sell more shares than registered under the Second Registration Statement under the 2022 Purchase Agreement without registering additional shares.

Actual sales of shares of common stock to Lincoln Park under the 2022 Purchase Agreement depend on a variety of factors to be determined by the Company from time to time, including, among others, market conditions, the trading price of the common stock and determinations by the Company as to the appropriate sources of funding for the Company and its operations. The net proceeds under the 2022 Purchase Agreement to the Company depend on the frequency and prices at which the Company sells shares of its stock to Lincoln Park.

During the period from August 17, 2022 to December 31, 2022, the Company issued 266,666 shares under the 2022 Purchase Agreement for net proceeds of approximately $3.2 million. The Company issued 410,500 shares under the 2022 Purchase Agreement for net proceeds of approximately $1.0 million from January 1, 2023 to December 31, 2023. The Company did not issue any common stock under the 2022 Purchase Agreement during the three months ended March 31, 2024.

At-the-market Issuances

On September 9, 2022, the Company entered into an Equity Distribution Agreement (the “September 2022 Distribution Agreement”) with Canaccord Genuity LLC (“Canaccord”), pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $5,000,000, depending on market demand, with Canaccord acting as an agent for sales. During the period from September 9, 2022 to December 31, 2022, the Company issued 68,758 shares of its common stock under the September 2022 Distribution Agreement for net proceeds of approximately $0.6 million. From January 1, 2023 through December 31, 2023, the Company issued 1,819,993 shares under the September 2022 Distribution Agreement for net proceeds of approximately $4.3 million. The Company has reached the capacity for sales of shares under the September 2022 Distribution Agreement and the agreement has terminated.

The Company was obligated to pay Canaccord a commission of up to 3.0% of the gross proceeds from the sale of its common stock under the September 2022 Distribution Agreement. The Company also agreed to reimburse Canaccord for its reasonable documented out-of-pocket expenses, including fees and disbursements of its counsel, in the amount of $50,000. In addition, the Company agreed to provide customary indemnification rights to Canaccord.

On January 14, 2022, the Company entered into an Equity Distribution Agreement (the “January 2022 Distribution Agreement”) with Canaccord, pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $5,000,000, with Canaccord acting as an agent for sales. The Company had no obligation to sell any of the Company’s shares and it could instruct Canaccord not to sell any shares if the sales could not be effected at or above the price designated by the Company from time to time and the Company could at any time suspend sales pursuant to the January 2022 Distribution Agreement. During the year ended December 31, 2023, the Company issued 460,151 shares under the January 2022 Distribution Agreement for net proceeds of approximately $4.8 million. The January 2022 Distribution Agreement has been terminated after all available registered shares were fully utilized.

Share Repurchase Program and Treasury Stock

On October 31, 2023, the Company announced that its Board has approved a share repurchase program (the “Share Repurchase Program”), with authorization to repurchase up to $500,000 of the outstanding shares of the Company’s common stock. The Company funded repurchases under the Share Repurchase Program with available cash.

During the year ended December 31, 2023, the Company purchased 78,559 of its common stock for approximately $0.1 million as treasury stock. The Company purchased 179,866 of its common shares for approximately $0.4 million as treasury stock during the three months ended March 31, 2024. As of March 31, 2024, no amount remained authorized for repurchase.

11. Stock-based Compensation

Under the Company’s 2015 New Employee Incentive Plan (the “2015 Plan”), awards may only be granted to employees who were not previously an employee or director of the Company, or following a bona fide period of non-employment, as a material inducement to entering into employment with the Company. As of March 31, 2024, there were 6,024 shares of common stock remaining and available for future issuances under the 2015 Plan.

The Company’s 2020 Stock Incentive Plan (the “2020 Plan”), which replaced the Company’s 2014 Equity Incentive Plan, provides for the award or sale of shares of common stock (including restricted stock), the award of stock units and stock appreciation rights,

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and the grant of both incentive stock options to purchase common stock to directors, officers, employees and consultants of the Company. The 2020 Plan, as amended, provides for the issuance of up to 236,667 shares of common stock, plus the number of shares available for issuance is increased to the extent that awards granted under the 2020 Plan and the Company’s 2014 Equity Incentive Plan are forfeited or expire (except as otherwise provided in the 2020 Plan). As of March 31, 2024, there were 17,582 shares remaining and available for future issuances under the 2020 Plan.

Generally, options issued under the 2020 Plan are subject to a two-year or four-year vesting schedule with 25% of the options vesting on the one year anniversary of the grant date followed by equal monthly installment vesting, and have a contractual term of 10 years.

A summary of activity for the three months ended March 31, 2024 is as follows:

	Options			Weighted Average  Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Balance as of December 31, 2023		140,109		$	37.48		8.07
Granted		163,025		$	2.03
Cancelled/forfeited		(1	)	$	289,125
Balance as of March 31, 2024		303,133		$	17.46		8.94	$	7,600
Vested and expected to vest at March 31, 2024		278,083		$	18.64		8.87	$	6,800
Exercisable at March 31, 2024		84,908		$	50.13		7.37	$	500

As of March 31, 2024, the total compensation cost related to non-vested stock options not yet recognized for all the Company’s plans is approximately $0.8 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 2.3 years.

12. Subsequent Events

May 2024 Private Placement

On May 5, 2024, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”) with certain investors, including certain of the Company’s directors and executive officers (“Company Insiders”) (collectively, the “Purchasers”), for the sale and issuance by the Company of its securities (the “Initial Subscription”). On May 8, 2024, the Company entered into a first amendment to the Securities Purchase Agreement (the “Amendment”) for the sale and issuance by the Company of additional securities to two of the Purchasers (the “Additional Subscription”, and together with the Initial Subscription, the “May 2024 Private Placement”). The Securities Purchase Agreement, as amended, provides for the sale and issuance by the Company of an aggregate of 3,591,532 shares (the “Private Placement Shares”) of the Company’s common stock or, at the election of each Purchaser, pre-funded warrants (the “Pre-Funded Warrants”), exercisable immediately at an exercise price of $0.001 per share (the “Pre-Funded Warrant Shares”), with each Private Placement Share or Pre-Funded Warrant accompanied by (i) a Series A common warrant (“Series A Warrants”) to purchase one share of common stock (the “Series A Warrant Shares”), for an aggregate of 3,591,532 Series A Warrants, and (ii) one Series B common warrant (“Series B Warrants”) to purchase one share of common stock (the “Series B Warrant Shares,” and together with the Series A Warrant Shares, the “Common Warrant Shares”), for an aggregate of 3,591,532 Series B Warrants.

The combined purchase price for each Private Placement Share and Pre-Funded Warrant from the Initial Subscription was $2.022, and $2.158 from the Additional Subscription, in each case together with one accompanying Series A Warrant and one accompanying Series B Warrant, provided, that the Company Insiders participated in the Initial Subscription at an offering price of $2.04 per Private Placement Share and accompanying Series A Warrant and Series B Warrant.

The exercise price of each Series A Warrant and Series B Warrant from the Initial Subscription is $1.772 per share and $1.908 per share in the Additional Subscription, provided that the exercise price for the Series A Warrants and Series B Warrants issued to the Company Insiders is $1.79 per share. Subject to certain ownership limitations, the Series A Warrants will be exercisable until the five-year anniversary of issuance. Subject to certain ownership limitations, the Series B Warrants will be exercisable until the one-year anniversary of the declaration of effectiveness of a registration statement to be filed with the Securities and Exchange Commission covering the resale of the Series B Warrant Shares underlying the Series B Warrants. The Pre-Funded Warrant will not expire until exercised in full.

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The May 2024 Private Offering closed on May 9, 2024 (the “May 2024 Private Placement Closing”). The aggregate gross proceeds at the May 2024 Private Placement Closing were approximately $7.25 million, before deducting certain expenses payable by the Company, and excluding the proceeds, if any, from the exercise of the Series A Warrant, the Series B Warrant, and Pre-Funded Warrant.

The Company is evaluating the accounting treatment of the Series A Warrants, Series B Warrants and the Pre-Funded Warrants under the authoritative accounting guidance.

Biocept Asset Purchase

On April 26, 2024, the Company acquired from Biocept, for a total cash payment of $400,000, substantially all of the right, title and interest in CNside, including (i) intellectual property, (ii) inventory and raw materials, and (iii) data, information, results and reports pertaining to the completed and on-going clinical studies involving the use of the CNside test (including, but not limited to, the FORSEE clinical study), related to the development, making, selling, and exporting or importing of CNside, after the Company’s bid was approved by the United States Bankruptcy Court for the District of Delaware.

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Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

The following discussion and analysis should be read in conjunction with the unaudited financial information and the notes thereto included herein, as well as the “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our audited financial statements and notes thereto contained in our Annual Report on Form 10-K for the year ended December 31, 2023, as filed on March 5, 2024. This discussion contains forward-looking statements that involve risks and uncertainties. Our actual results and the timing of selected events could differ materially from those anticipated in these forward-looking statements as a result of several factors, including those set forth under the caption “Cautionary Note Regarding Forward-Looking Statements” in this report, as well as under “Part I – Item 1A - Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2023, in other subsequent filings with the Securities and Exchange Commission, and elsewhere in this Quarterly Report on Form 10-Q. These statements, like all statements in this report, speak only as of the date of this report (unless another date is indicated), and the Company undertakes no obligation to update or revise these statements in light of future developments.

Our Management’s Discussion and Analysis of Financial Condition and Results of Operations, or MD&A, includes the following sections:

 Overview that discusses our operating results and some of the trends that affect our business.

 Results of Operations that includes a more detailed discussion of our revenue and expenses.

 Liquidity and Capital Resources that discusses key aspects of our statements of cash flows, changes in our financial position and our financial commitments.

Overview

Plus Therapeutics is a U.S. pharmaceutical company developing targeted radiotherapeutics with advanced platform technologies for central nervous system (“CNS”) cancers. Our novel radioactive drug formulations and therapeutic candidates are designed to deliver safe and effective doses of radiation to tumors. To achieve this, we have developed innovative approaches to drug formulation, including encapsulating radionuclides such as rhenium isotopes with nanoliposomes and microspheres. Our formulations are intended to achieve elevated patient absorbed radiation doses and extend retention times such that the clearance of the isotope occurs after significant and essentially complete radiation decay, which will contribute and provide less normal tissue/organ exposure and improved safety margins.

Traditional approaches to radiation therapy for cancer, such as external beam radiation, have many disadvantages including continuous treatment for four to six weeks (which is onerous for patients), that the radiation damages healthy cells and tissue, and that the amount of radiation delivered is very limited and, therefore, is frequently inadequate to fully destroy the cancer.

Our targeted radiotherapeutic platform and unique investigational drugs have the potential to overcome these disadvantages by directing higher, more powerful radiation doses at the tumor—and only the tumor—potentially in a single treatment. By minimizing radiation exposure to healthy tissues while simultaneously maximizing locoregional delivery and, thereby, efficacy, we hope to reduce the radiation toxicity for patients, improving their quality of life and life expectancy. Our radiotherapeutic platform, combined with advances in surgery, nuclear medicine, interventional radiology, and radiation oncology, affords us the opportunity to target a broad variety of cancer types.

Our lead radiotherapeutic candidate, rhenium (186Re) obisbemeda, is designed specifically for CNS cancers including recurrent glioblastoma (“GBM”), leptomeningeal metastases (“LM”), and pediatric brain cancers (“PBC”) by direct localized delivery utilizing approved standard-of-care tissue access such as with convection-enhanced delivery (“CED”) and intraventricular brain (Ommaya reservoir) catheters. Our acquired radiotherapeutic candidate, Rhenium-188 NanoLiposome Biodegradable Alginate Microsphere (“188RNL-BAM”) is designed to treat many solid organ cancers including primary and secondary liver cancers by intra-arterial injection.

Our headquarters and manufacturing facilities are in Texas and are in proximity to world-class cancer institutions and researchers. Our dedicated team of engineers, physicians, scientists, and other professionals are committed to advancing our targeted radiotherapeutic technology for the benefit of cancer patients and healthcare providers worldwide and our current pipeline is focused on treating rare and difficult-to-treat cancers with significant unmet medical needs.

In addition to our headquarters in Austin, we have an established, good manufacturing practice validated research and development and manufacturing facility in San Antonio, Texas, tailored to produce Current Good Manufacturing Practice (“cGMP”) rhenium (186Re) obisbemeda. We have built a robust supply chain through strategic partnerships that enable the development, manufacturing and future potential commercialization of our products. Our current supply chain and key partners are positioned to supply cGMP rhenium (186Re) obisbemeda for ongoing and planned Phase 2 and Phase 3 clinical trials in patients with GBM, LM and PBC.

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Pipeline

Our most advanced investigational drug, rhenium (186Re) obisbemeda, is a patented radiotherapy potentially useful for patients with CNS and other cancers. Preclinical study data describing the use of rhenium (186Re) obisbemeda for several cancer targets have been published in peer-reviewed journals and reported at a variety of medical society peer-reviewed meetings. Besides GBM, LM and PBC, rhenium (186Re) obisbemeda has been reported to have potential applications for head and neck cancer, ovarian cancer, breast cancer and peritoneal metastases.

The rhenium (186Re) obisbemeda technology was part of a licensed radiotherapeutic portfolio that we acquired from NanoTx, Corp. (“NanoTx”) on May 7, 2020. The licensed radiotherapeutic has been evaluated in preclinical studies for several cancer targets and we have an active $3.0 million award from U.S. National Institutes of Health/National Cancer Institute which is expected to provide financial support for the continued clinical development of rhenium (186Re) obisbemeda for recurrent GBM through the completion of a Phase 2 clinical trial, including enrollment of up to 55 patients.

On August 29, 2022, we announced feedback from a Type C meeting with the FDA regarding Chemistry, Manufacturing and Controls (“CMC”) practices. The meeting focused on our cGMP clinical and commercial manufacturing process for our lead investigational targeted radiotherapeutic, BMEDA-chelated rhenium (186Re) obisbemeda, for recurrent GBM.

The FDA indicated agreement with our proposed application of cGMP guidance for radiotherapeutics, small molecule drug products and liposome drug products for our novel rhenium (186Re) obisbemeda in support of ongoing and future GBM clinical trials, manufacturing scale up, and commercialization. Alignment with the FDA includes support of our proposed controls and release strategy for new drug substance and new drug product. Because this product is identical for recurrent GBM, LM, and PBC, we believe alignment will be consistent for rhenium (186Re) obisbemeda used in other clinical development programs, including LM and PBC.

Rhenium (186Re) obisbemeda versus External Beam Radiation Therapy for Recurrent GBM

Rhenium (186Re) obisbemeda is a novel injectable radiotherapy designed to deliver targeted, high dose radiation directly into GBM tumors in a safe, effective, and convenient manner that may ultimately prolong patient survival. Rhenium (186Re) obisbemeda is composed of the radionuclide Rhenium-186 and a nanoliposomal carrier, and is infused in a highly targeted, controlled fashion, directly into the tumor via precision brain mapping and CED catheters. Potential benefits of rhenium (186Re) obisbemeda compared to standard external beam radiotherapy or external beam radiation therapy (“EBRT”) include:

•The rhenium (186Re) obisbemeda radiation dose delivered to patients may be up to 20 times greater than what is possible with commonly used external beam radiation therapy (“EBRT”), which, unlike EBRT and proton beam devices, spares normal tissue and the brain from radiation exposure.

•Rhenium (186Re) obisbemeda can be visualized in real-time during administration, possibly giving clinicians better control of radiation dosing, distribution and retention.

•Rhenium (186Re) obisbemeda potentially more effectively treats a bulk tumor and microscopic disease that has already invaded healthy tissue.

•Rhenium (186Re) obisbemeda is infused directly into the targeted tumor by CED catheter insertion using MRI guided software to avoid critical patient neurological structures and neural pathways and also bypasses the blood brain barrier, which delivers the therapeutic product where it is needed. Importantly, it reduces radiation exposure to healthy cells, in contrast to EBRT, which passes through normal tissue to reach the tumor, continuing its path through the tumor, hence being less targeted and selective.

•Rhenium (186Re) obisbemeda is given during a single, short, in-patient hospital visit, and is available in all hospitals with nuclear medicine and neurosurgery, while EBRT requires out-patient visits five days a week for approximately four to six weeks.

ReSPECT-GBM Trial for Recurrent GBM

Recurrent GBM is the most common, complex, and aggressive primary brain cancer in adults. In the U.S., there are approximately 13,000 GBM cases diagnosed and approximately 10,000 patients succumb to the disease each year. The average length of overall survival (“OS”) for GBM patients is eight months, with a one-year survival rate of 40.8% and a five-year survival rate of only 6.8% and these estimates vary and are lower in some publications. GBM routinely presents with headaches, seizures, vision changes and other significant neurological complications, with a significant compromise in quality of life. Despite the best available medical treatments, the disease remains incurable. Even after efforts to manage the presenting signs and symptoms and completely resect the initial brain tumor, some microscopic disease almost always remains and tumor regrowth occurs within months. Approximately 90% or more of

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patients with primary GBM experience tumor recurrence. Complete surgical removal of GBM is usually not possible and GBM is often resistant or quickly develops resistance to most available current and investigational therapies. Even today, the treatment of GBM remains a significant challenge and it has been nearly a decade since the FDA approved a new therapy for this disease, and these more recent approvals have not improved GBM patients OS over past decades, and a significant unmet medical need persists.

For recurrent GBM, there are few currently approved treatments, which in the aggregate, provide only marginal survival benefit. Furthermore, these therapies are associated with significant side effects, which limit dosing and prolonged use.

While EBRT has been shown to be safe and has temporary efficacy in many malignancies including GBM, typically at absorbed, fractionated radiation dose of ~30 Gray in GBM, this maximum possible administered dose is always limited by toxicity to the normal tissues surrounding the malignancy and because EBRT requires fractionation to manage toxicity and maximum EBRT limits are typically reached before long-term efficacy reached. Because of this limitation, EBRT cannot provide a cure or long term control of GBM and GBM always recurs within months after EBRT. In contrast, locally delivered and targeted radiopharmaceuticals that precisely deliver radiation in the form of beta particles such as Iodine-131 for thyroid cancer, are known to be safe and effective and minimize exposure to normal cells and tissues especially with optimal administered dose and minimizing exposure to normal tissue. The locally delivered rhenium (186Re) obisbemeda is designed for and provides patient tolerability and safety. Though no rhenium (186Re) obisbemeda head-to-head trial with chemo, immune, EBRT or systemic radiopharmaceutical products have been conducted, patient tolerability and safety considerations have been reported as expected.

Interim results from our ongoing Phase 1/2a ReSPECT-GBM trial (ClinicalTrials.gov NCT01906385) show that the beta particle energy from our lead investigational drug rhenium (186Re) obisbemeda has provided preliminary positive data and utility in treating GBM and potential other malignancies. More specifically, the preliminary data from our Phase 1/2a ReSPECT-GBM trial suggests that radiation, in the form of high energy beta particles or electrons, can be effective against GBM. Thus far, we have been able to deliver up to 740 Gy of absorbed radiation to tumor tissue in humans, without significant or dose limiting toxicities and with what we believe has the capability to go higher if required. In comparison, current EBRT protocols for recurrent GBM typically recommend a total maximum radiation dose of about ~30-35 Gray.

In September 2020, the FDA granted both Orphan Drug designation and Fast Track designations to rhenium (186Re) obisbemeda for the treatment of patients with GBM.

Rhenium (186Re) obisbemeda is under clinical investigation in a multicenter, sequential cohort, open-label, volume and dose escalation study of the safety, tolerability, and distribution of rhenium (186Re) obisbemeda given by CED catheters to patients with recurrent or progressive malignant glioma after standard surgical, radiation, and/or chemotherapy treatment (NCT01906385). The study uses a standard, modified 3x3 Fibonacci dose escalation, followed by a planned Phase 2 expansion trial at the maximum tolerated dose (“MTD”) / maximum feasible dose (“MFD”) or non-dose limiting toxicity (“DLT”) if MTD is not reached, to determine efficacy. The trial is funded through Phase 2 in large part by a National Institute of Health/National Cancer Institute (“NIH/NCI”) grant. These investigations have not reached DLT or MTD/MFD and the study is in its eighth dosing administration cohort. Due to the observation of a preliminary efficacy signal, we have initiated in parallel a Phase 2, non-DLT dose trial pursuant to the currently funded NIH/NCI grant. This trial will begin at the current non-DLT rhenium (186Re) obisbemeda dose and will expand exploring higher radiation doses in larger volumes to treat larger tumors. Additionally, two or more rhenium (186Re) obisbemeda administrations, if indicated, will be evaluated, and reviewed with the FDA, as well as expanded safety, imaging and efficacy data to support a planned future registrational trial.

On September 6, 2022, we announced a summary of our Type C clinical meeting with the FDA that focused on the ReSPECT-GBM trial. The FDA agreed with us that the ReSPECT-GBM clinical trial should proceed to the planned Phase 2. The key focus areas of clinical investigation of the Phase 2 trial will be (1) further dose exploration, including both increased dosing and multiple doses, and (2) collecting additional safety and efficacy data to inform the design of a future registrational trial. Because no DLT administered doses were observed, the FDA and we also agreed to continue to dose cohort eight. There was further agreement with the FDA that in a planned future registrational trial, overall survival should be used as the primary endpoint. We agreed with the FDA to hold future meeting(s) to consider the use of external data to augment the use of a control arm in the registrational trial.

On January 18, 2023, we announced that the first patient has been dosed in the ReSPECT-GBM Phase 2b dose expansion clinical trial evaluating rhenium obisbemeda for the treatment of recurrent GBM. The Phase 2b trial is expected to enroll up to 31 total patients with small- to medium-sized tumors and is targeted for full enrollment by the end of 2024. We currently have four clinical sites, with the plan to add additional sites to support the trial, and expect an initial data read-out by the end of 2024.

In June 2023, we presented data regarding the safety and feasibility results from our Phase 1/2 Clinical Trial of 186RNL (Rhenium-186 Nanoliposome) (186Re) Obisbemeda in Recurrent Glioma: The ReSPECT-GBM Trial at the Society of Nuclear Medicine & Molecular Imaging Annual Meeting.

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On November 20, 2023, we announced positive data from the ongoing ReSPECT-GBM Phase 2 trial evaluating rhenium (186Re) obisbemeda, for the treatment of recurrent glioblastoma at the Society for NeuroOncology 28th Annual Meeting, which was held November 15-19, 2023 in Vancouver, Canada. Key findings included:

•Median overall survival (“mOS”) in 15 patients with recurrent glioblastoma (“rGBM”) from the Phase 2 study is 13 months, which is 63% better than current standard of care (bevacizumab monotherapy) of 8 months; 9 of the 15 patients remain alive.

•Median progression free survival (“mPFS”) is 11 months, compared to SOC at 4 months.

•Rhenium (186Re) obisbemeda continues to demonstrate a favorable safety profile, despite delivering up to 20x the dose of radiation (up to 740 Gy) typically delivered by EBRT for rGBM patients (up to 35 Gy).

•Imaging data presented by Andrew Brenner, MD, PhD is consistent with the efficacy signal of Rhenium (186Re) obisbemeda in rGBM.

On March 31, 2022, we entered into a Sales Order (the “Sales Order”) with Medidata Solutions, Inc. (“Medidata”), pursuant to which Medidata built a Synthetic Control Arm® platform that facilitates the use of historical clinical data to incorporate into our Phase 2 clinical trial of rhenium (186Re) obisbemeda in GBM. The Sales Order had a term of six (6) months. Work under this Sales Order has been completed. As part of this collaboration, we jointly submitted with Medidata a historical clinical trials control arm methodology abstract (“HCA”) to American Society of Clinical Oncology (“ASCO”) which was accepted for publication, further strengthening this collaboration and allowing applications to advance GBM development. We plan to use the HCA for breakthrough therapy designation and Phase 2 and/or a pivotal or registrational Phase 3 trial.

ReSPECT-LM Clinical Trial for LM

LM is a rare complication of cancer in which the disease spreads to the membranes (meninges) surrounding the brain and spinal cord. The incidence of LM is growing and occurs in approximately 5%, or more, of people with late-stage cancer, or 110,000 people in the U.S. each year. It is highly lethal with an average one-year survival of just 7%. All solid cancers, particularly breast, lung, GI, and melanoma, have the potential to spread to the leptomeninges.

The ReSPECT-LM Phase 1 clinical trial (ClinicalTrials.gov NCT05034497) was preceded with preclinical studies in which tolerance to doses of rhenium (186Re) obisbemeda as high as 1,075 Gy were shown in animal models with LM without significant observed toxicity. Furthermore, treatment led to a marked reduction in tumor burden in both C6 and MDA-231 LM models.

Upon receiving acceptance of our Investigational New Drug application and Fast Track designation by the FDA for rhenium (186Re) obisbemeda for the treatment of LM in November 2021, we initiated the trial and began screening patients for the ReSPECT-LM Phase 1 clinical trial in Q4 2021.

The ReSPECT-LM is a multi-center, sequential cohort, open-label, dose escalation study evaluating the safety, tolerability, and efficacy of a single-dose application of rhenium (186Re) obisbemeda administered through intrathecal infusion to the ventricle of patients with LM after standard surgical, radiation, and/or chemotherapy treatment. The primary endpoint of the study is the incidence and severity of adverse events and dose limiting toxicities, together with determining the maximum tolerated and recommended Phase 2 dose. Full enrollment in the Phase 1 trial is expected by the end of 2024, with the plan to add additional clinical sites to support the trial.

On September 19, 2022, we entered into a Cancer Research Grant Contract (the “CPRIT Contract”), effective as of August 31, 2022, with Cancer Prevention and Research Institute of Texas (“CPRIT”), pursuant to which CPRIT will provide us a grant of up to $17.6 million (the “CPRIT Grant”) over a three-year period to fund the continued development of rhenium (186Re) obisbemeda for the treatment of patients with LM through Phase 2 of the ReSPECT LM clinical trial. The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar from us for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements. To date, we have received approximately $7 million in milestone payments under the CPRIT Contract. We anticipate a continuing flow of milestone payments that throughout 2024 will include $6.9 million upon the continued progression of the Phase 2 of the ReSPECT LM clinical trial.

Interim results showed that a single treatment with rhenium (186Re) obisbemeda resulted in a consistent decreased cerebrospinal fluid (“CSF”) tumor cell count/ml and was tolerated by all LM patients. Rhenium (186Re) obisbemeda is an outpatient administration and treatment and is easily and safely administered through a standard intraventricular catheter (Ommaya Reservoir), distributed promptly throughout the CSF, and with durable retention in the leptomeninges at least through day seven. All patients have shown well tolerated

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prompt and durable rhenium (186Re) obisbemeda distribution throughout the subarachnoid space. On March 11, 2024, we announced we had completed Cohort 5 of the ReSPECT-LM Phase 1/2a dose escalation trial.

A total of 18 patients have received a single-dose of rhenium (186Re) obisbemeda in the ReSPECT-LM trial as of March 31, 2024. There have been no dose limiting toxicities observed to date with administered radiation doses up to 66.14 millicuries in Cohort 5, a ten-fold increase over Cohort 1. We plan to initiate dosing in Cohort 6 in the second quarter of 2024, pending Data Safety Monitoring Board (DSMB) approval. In addition, five new clinical trial sites were added to this trial over the last year, bringing the total number of sites to seven. We are planning a new multiple dosing ReSPECT-LM clinical trial in late 2024 or early 2025.

On August 10, 2023, we presented data from the ReSPECT-LM clinical trial of rhenium (186Re) obismeda at the Society for Neuro Oncology ASCO CNS Cancer Conference.

In November 2023, the FDA granted Orphan Drug designation to rhenium (186Re) obisbemeda for the treatment of patients with breast cancer with LM.

On December 12, 2023, we announced our partnership with K2bio to implement novel analysis for CSF tumor and molecular biomarkers for CNS cancers. Initial clinical specimen processing and testing began in the first quarter 2024 in our ongoing Phase 1 ReSPECT-LM trial of rhenium (186Re) obisbemeda in patients with LM.

ReSPECT-PBC Clinical Trial for Pediatric Brain Cancer

The average annual age adjusted mortality rate for children aged 0-14 for malignant brain (and other CNS) tumors is 0.71/100,000, making it the most common cause of death and cancer death in this age group. The 2021 World Health Organization Classification of CNS Tumors classifies gliomas, glioneuronal tumors, and neuronal tumors into six different families: (1) adult-type diffuse gliomas; (2) pediatric-type diffuse low-grade gliomas; (3) pediatric-type diffuse high-grade gliomas (“HGG”); (4) circumscribed astrocytic gliomas; (5) glioneuronal and neuronal tumors; and (6) ependymomas.

In August 2021, we announced plans for treating pediatric brain cancer at the 2021 American Association of Neurological Surgeons Annual Scientific Meeting. In July 2021, we reported that we had received FDA feedback pertaining to a pre-IND meeting briefing package in which the FDA stated that we are not required to perform any additional preclinical or toxicology studies.

Given the initial FDA feedback, receipt of adult GBM data and experience with rhenium (186Re) obisbemeda and follow-up communications with the FDA, we plan to submit a pediatric brain tumor IND to investigate the use of rhenium (186Re) obisbemeda in two pediatric brain cancers, high-grade glioma and ependymoma, by the third quarter of 2024.

Pediatric high-grade gliomas can be found almost anywhere within the CNS; however, they are most commonly found within the supratentorium. The highest incidence of supratentorial, high-grade gliomas in pediatrics appears to occur in children aged 15 to 19 years, with a median age of approximately nine years. Overall, pediatric high-grade glioma confers a three-year progression free survival (“PFS”) of 11 ± 3% and three-year OS of 22% ±5%. One-year PFS is as low as 40% in recent trials. Ependymomas are slow-growing central nervous system tumors that involve the ventricular system. Diagnosis is based on MRI and biopsy and survival rate depends on tumor grade and how much of the tumor can be removed. Grade II pathology was associated with significantly improved OS compared to Grade III (anaplastic) pathology (five-year OS = 71 ± 5% vs. 57 ± 10%; p = 0.026). Gross total resection compared to subtotal resection was associated with significantly improved OS (five-year OS = 75 ± 5% vs. 54 ± 8%; p = 0.002).

Overall, pediatric HGG and ependymoma are extremely difficult-to-treat pediatric brain tumors, frequently aggressive, and in recurrent settings, carry an extremely poor prognosis.

Rhenium-188 NanoLiposome Biodegradable Alginate Microsphere Technology

In January 2022, we announced that we licensed Biodegradable Alginate Microsphere (“BAM”) patents and technology from The University of Texas Health Science Center at San Antonio (“UTHSA”) to expand our tumor targeting capabilities and precision radiotherapeutics pipeline. We intend to combine our Rhenium NanoLiposome technology with the BAM technology to create a novel radioembolization technology. Initially, we intend to utilize the Rhenium-188 isotope, 188RNL-BAM for the intra-arterial embolization and local delivery of a high dose of targeted radiation for a variety of solid organ cancers such as hepatocellular cancer, hepatic metastases, pancreatic cancer and many others.

Preclinical data from an ex vivo embolization experiment in which Technetium99m-BAM was intra-arterially delivered to a bovine kidney perfusion model was presented at Society of Interventional Radiology Annual Scientific Meeting. The study concluded that the technology required for radiolabeling BAM could successfully deliver, embolize and retain radiation in the target organ. 188RNL-BAM

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is a preclinical investigational drug we intend to further develop and move into clinical trials. Specifically, in 2022 we transferred the 188RNL-BAM technology from UTHSA, and began planning to develop the drug product and complete early preclinical studies to support a future FDA IND submission. Our intended initial clinical target is liver cancer which is the sixth most common and third deadliest cancer worldwide. It is a rare disease with increasing U.S. annual incidence (42,000) and deaths (30,000).

Recent Developments

May 2024 Private Placement

See Liquidity and Capital Resources section below for details on closing of the May 2024 Private Placement.

Biocept Asset Purchase

On September 7, 2023, we entered into a Non-Exclusive License and Services Agreement (the “Biocept Agreement”) with Biocept, Inc (“Biocept”), pursuant to which Biocept granted us a non-exclusive license to use the Biocept proprietary cell enumeration test, CNsideTM (“CNside”). On October 16, 2023, Biocept filed a voluntary petition for relief under the provisions of Chapter 7 of Title 11 of the United States Bankruptcy Code.

On April 26, 2024, we acquired from Biocept, for a total cash payment of $400,000, substantially all of the right, title and interest in CNside, including (i) intellectual property, (ii) inventory and raw materials, and (iii) data, information, results and reports pertaining to the completed and on-going clinical studies involving the use of the CNside test (including, but not limited to, the FORSEE clinical study), related to the development, making, selling, and exporting or importing of CNside, after having its bid accepted by the United States Bankruptcy Court for the District of Delaware.

Department of Defense Grant

On April 22, 2024, we were selected by the Department of Defense (DoD) office of the Congressionally Directed Medical Research Programs (CDMRP) to receive a $3 million fund for research and development purposes (“DoD Award”). Transfers of funds under the DoD Award are expected to commence in the third quarter of 2024, pending execution of formal agreements, in order to support the planned expansion of our clinical trial for pediatric brain cancer.

Recent Financings

Refer to the “Liquidity and Capital Resources” section below for information on our recent financings.

Results of Operations

Grant Revenue

We recognized $1.7 million and $0.5 million of grant revenue during the three months ended March 31, 2024 and 2023, respectively, which represents CPRIT’s share of the costs incurred for our rhenium (186Re) obisbemeda development for the treatment of patients with LM.

Research and development expenses

Research and development expenses include costs associated with the design, development, testing, and enhancement of our product candidates, payment of regulatory fees, laboratory supplies, pre-clinical studies, and clinical studies.

The following table summarizes the components of our research and development expenses for the three months ended March 31, 2024 and 2023 (in thousands):

	Three Months Ended March 31,
	2024		2023
Research and development	$	2,746	$	2,963
Share-based compensation		17		20
Total research and development expenses	$	2,763	$	2,983

Research and development expenses decreased by approximately $0.2 million during the three months ended March 31, 2024 as compared to the same period in 2023. The decrease was due primarily to a reduction of $0.8 million of licenses fee to NanoTx, offset by an increase of approximately $0.3 million in clinical expenses related to the ReSPECT-LM trial, and an increase of approximately $0.2 million of professional research and development service fees.

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We expect aggregate research and development expenses to largely remain consistent during the remainder of 2024 as compared to the corresponding comparable period ended December 31, 2023.

General and administrative expenses

General and administrative expenses include costs for administrative personnel, legal and other professional expenses, and general corporate expenses. The following table summarizes the general and administrative expenses for the three months ended March 31, 2024 and 2023 (in thousands):

	Three Months Ended March 31,
	2024		2023
General and administrative	$	2,084	$	2,125
Share-based compensation		129		120
Total general and administrative expenses	$	2,213	$	2,245

General and administrative expenses remained consistent during the three months ended March 31, 2024, as compared to the same period in 2023.

We expect general and administrative expenditures to remain generally consistent during the remainder of 2024 as compared with the corresponding comparable period ended December 31, 2023.

Stock-based compensation expense

Stock-based compensation expense includes charges related to stock options issued to employees, directors and non-employees. We measure stock-based compensation expense based on the grant-date fair value of any awards granted to our employees. Such expense is recognized over the requisite service period.

The following table summarizes the components of our stock-based compensation expenses for the three months ended March 31, 2024 and 2023 (in thousands):

	Three Months Ended March 31,
	2024		2023
Research and development	$	17	$	20
General and administrative		129		120
Total share-based compensation	$	146	$	140

Our share-based compensation expenses, which are impacted by grants of share-based options, vesting schedule of such grants, as well as grant-date fair value of share-based awards, remained consistent for the three months ended March 31, 2024 and 2023.

Financing items

The following table summarizes interest income, interest expense, and other income and expense for the three months ended March 31, 2024 and 2023 (in thousands):

	Three Months Ended March 31,
	2024			2023
Interest income	$	72		$	51
Interest expense		(34	)		(134	)
Total	$	38		$	(83	)

The decrease in interest expense for the three months ended March 31, 2024 as compared to the same period in 2023 was primarily due to the repayment of debt principal of $1.6 million during the year ended December 31, 2023.

We expect interest expense in 2024 to decrease as compared with 2023 due to scheduled debt payoff by June 1, 2024.

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Liquidity and Capital Resources

Short-term and long-term liquidity

The following is a summary of our key liquidity measures at March 31, 2024 and December 31, 2023 (in thousands):

	March 31, 2024			December 31, 2023
Cash and cash equivalents	$	2,901		$	8,554
Current assets	$	4,213		$	9,834
Current liabilities		10,399			10,727
Working capital	$	(6,186	)	$	(893	)

We incurred net losses of $3.3 million for the three months ended March 31, 2024. We have an accumulated deficit of $483.8 million as of March 31, 2024. Additionally, we used net cash of $4.5 million to fund our operating activities for the three months ended March 31, 2024. These factors raise substantial doubt about our ability to continue as a going concern.

May 2024 Private Placement

In May 2024, we entered into a securities purchase agreement, which was subsequently amended, with certain investors, including certain of the Company’s directors and executive officers (the “Purchasers”), whereby we issued and sold in a private placement (the “May 2024 Private Placement”): (i) 3,591,532 shares of common stock (“Private Placement Share”), or, at the election of each Purchaser, pre-funded warrants (the “Pre-Funded Warrants”) exercisable immediately to purchase shares of common stock. Each Private Placement Share or Pre-Funded Warrant are accompanied by (i) a Series A common warrant (“Series A Warrants”) to purchase one share of common stock, for an aggregate of 3,591,532 Series A Warrants, and (ii) one Series B common warrant (“Series B Warrants”, and together with the Pre-Funded Warrants and Series A Warrants, the “Warrants”) to purchase one share of common stock, for an aggregate of 3,591,532 Series B Warrants. At the closing of the May 2024 Private Placement, we received aggregate upfront gross proceeds of approximately $7.25 million, before deducting fees and other expenses associated with the closing of the May 2024 Private Placement. If the Warrants are exercised in full we will receive additional gross proceeds of approximately $12.0 million. None of the Warrants issued in the May 2024 Private Placement have been exercised as of the filing of this report. Please see Note 12 to the unaudited condensed financial statements for further information regarding the private placement.

CPRIT Grant

On September 19, 2022, we entered into the CPRIT Contract, pursuant to which CPRIT will provide us with the CPRIT Grant of $17.6 million subject to the terms of the CPRIT Contract, to fund approximately two-thirds of the continued development of rhenium (186Re) obisbemeda for the treatment of patients with LM. We received $7.1 million of the available funding under the CPRIT Grant during 2022, 2023 and the three months ended March 31, 2024, of which we recognized $1.7 million, $4.9 million and $0.2 million of grant revenue during the three months ended March 31, 2024, and the years ended December 31, 2023 and 2022, respectively. The amounts recognized represents CPRIT’s share of the costs incurred for our rhenium (186Re) obisbemeda development for the treatment of patients with LM. As of March 31, 2024, we had $0.2 million of deferred revenue related to the CPRIT Grant.

Private Equity Lines

On September 9, 2022, we entered into an Equity Distribution Agreement (the “September 2022 Distribution Agreement”) with Canaccord Genuity LLC (“Canaccord”), pursuant to which we could issue and sell, from time to time, shares of our common stock in “at-the-market” offerings, having an aggregate offering price of up to $5,000,000, depending on market demand, with Canaccord acting as an agent for sales. During the period from September 9, 2022 to December 31, 2023, we issued 68,758 shares under the September 2022 Distribution Agreement for net proceeds of approximately $0.6 million. From January 1, 2023 through December 31, 2023, we issued 1,819,993 shares under the September 2022 Distribution Agreement for net proceeds of approximately $4.3 million. We have reached the capacity for sales of our shares under the September 2022 Distribution Agreement.

On August 2, 2022, we entered into a purchase agreement (the “2022 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park Capital Fund (“Lincoln Park”) committed to purchase up to $50.0 million of shares of our common stock. Under the terms and subject to the conditions of the 2022 Purchase Agreement, we have the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park is obligated to purchase up to $50.0 million of shares of our common stock, provided that we cannot sell more than 57.5 million shares pursuant to the 2022 Purchase Agreement. Sales of common stock by us are subject to certain limitations, and can occur from time to time, at our sole discretion, over the 36-month period commencing on August 17, 2022, subject to the satisfaction of certain conditions. Actual sales of shares of common stock to Lincoln Park under the 2022 Purchase Agreement depend on a variety of factors to be determined by us from time to time, including, among others, market conditions, the trading price of the common stock

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and our determinations as to the appropriate sources of funding for the Company and its operations. As consideration for Lincoln Park’s irrevocable commitment to purchase shares of our common stock upon the terms of and subject to satisfaction of the conditions set forth in the 2022 Purchase Agreement, we paid $0.1 million in cash as an Initial Commitment Fee and issued 32,846 as the initial commitment shares to Lincoln Park in consideration for its commitment to purchase shares of our common stock at our direction under the 2022 Purchase Agreement.

On August 17, 2022, a registration statement (the “First Registration Statement”) was declared effective covering the resale of up to 633,333 shares of our common stock comprised of (i) the 32,846 initial commitment shares, and (ii) up to 600,486 shares that we have reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement. An additional commitment fee equal to 2.5% of the remainder of the $50 million will be paid if and when we sell over $25.0 million of our common stock under the 2022 Purchase Agreement. The additional commitment fee may be paid in cash, common stock, or a combination thereof. We sold approximately 527,166 shares under the First Registration Statement.

On August 18, 2023, a second registration statement (the “Second Registration Statement”) was declared effective covering the resale of up to an additional 1,500,000 shares of our common stock that we reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time. We sold 150,000 shares under the Second Registration Statement. We cannot sell more shares than registered under the Second Registration Statement under the 2022 Purchase Agreement without registering additional shares.

During the period from August 17, 2022 to December 31, 2022, we issued 266,666 shares under the 2022 Purchase Agreement for net proceeds of approximately $3.2 million. We issued 410,500 shares under the 2022 Purchase Agreement for net proceeds of approximately $1.0 million from January 1, 2023 to December 31, 2023. No shares of common stock was purchased under the 2022 Purchase Agreement during the three months ended March 31, 2024.

On January 14, 2022, we entered into an Equity Distribution Agreement (the “January 2022 Distribution Agreement”) with Canaccord, pursuant to which we could issue and sell, from time to time, shares of our common stock in “at-the-market” offerings, having an aggregate offering price of up to $5,000,000, depending on market demand, with Canaccord acting as an agent for sales. During the year ended December 31, 2023, we issued 460,151 shares under the January 2022 Distribution Agreement for net proceeds of approximately $4.8 million. The January 2022 Distribution Agreement was terminated after all available registered shares were fully utilized.

Nasdaq Listing Compliance

On March 8, 2024, we received a letter (the “Notice”) from the Listing Qualifications staff of Nasdaq Capital Market (“Nasdaq”), notifying us that we no longer complied with the requirement under Nasdaq Listing Rule 5550(b)(1) to maintain a minimum of $2.5 million in stockholders’ equity for continued listing on Nasdaq or the alternative requirements of having a market value of listed securities of $35 million or net income from continuing operations of $500,000 in the most recently completed fiscal year or two of the last three most recently completed fiscal years (the “Alternative Standards”). The Notice states that our Annual Report on Form 10-K for the fiscal year ended December 31, 2023, disclosed stockholders’ equity of ($1,348,000) as of December 31, 2023, and that, as of March 8, 2024, we did not meet the Alternative Standards.

On April 22, 2024, we provided Nasdaq with our plan to achieve and sustain compliance with the stockholders’ equity requirement and requested that Nasdaq grant an extension of time until September 4, 2024, to provide evidence of our compliance with the stockholders’ equity requirement. Nasdaq has not yet responded to the plan we submitted, and there can be no assurance that Nasdaq will grant an extension or that we will be able to comply with the applicable listing standards of Nasdaq.

Funding and Material Cash Requirements

To date, our operating losses have been funded primarily from outside sources of invested capital from issuance of our common and preferred stocks, proceeds from our term loan with Oxford Finance, LLC (“Oxford”) and grant funding. However, the Company has had, and will continue to have, an ongoing need to raise additional cash from outside sources through a combination of equity offerings, debt financings and potential collaboration, license or development agreements to fund our future clinical development programs and other operations in the next twelve months from the filing of this report. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures, or declaring dividends. There can be no assurance that the Company will be able to continue to raise additional capital in the future. Our inability to raise additional cash would have a material adverse impact on our operations.

Our present and future funding and cash requirements will depend on many factors, including, among other things:

•the progress, timing and completion of our ongoing and planned clinical trials and nonclinical studies;

26

•our ability to receive, and the timing of receipt of, future regulatory approvals for our product candidates and the costs related thereto;

•our ability to receive, and the timing of receipt of, future regulatory approvals for our product candidates and the costs related thereto;

•the scope, progress, results and costs of our ongoing and planned operations;

•the costs associated with expanding our operations and building our sales and marketing capabilities;

•our ability to establish strategic collaborations;

•the cost and timing of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property rights and defending any intellectual property-related claims;

•the revenue, if any, received from commercial sales of our product candidates, if approved; and

•potential new product candidates that the Company identifies and attempt to develop.

The accompanying condensed financial statements have been prepared assuming that the Company will continue to operate as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from uncertainty related to our ability to continue as a going concern.

Cash (used in) provided by operating, investing, and financing activities for the three months ended March 31, 2024 and 2023 is summarized as follows (in thousands):

	Three Months Ended March 31,
	2024			2023
Net cash used in operating activities	$	(4,513	)	$	(5,793	)
Net cash used in investing activities		(364	)		(97	)
Net cash (used in) provided by financing activities		(776	)		493
Net decrease in cash and cash equivalents	$	(5,653	)	$	(5,397	)

Material Cash Obligations

Under the CPRIT Contract we receive matching funds for approximately two-thirds of the development costs for the development of rhenium (186Re) obisbemeda for the treatment of patients with LM, subject to various funding conditions. The CPRIT contract is effective for three years, unless otherwise terminated pursuant to the terms of the contract. CPRIT may require us to repay some or all of the disbursed CPRIT grant proceeds (with interest not to exceed 5% annually) in the event of the early termination of the CPRIT Contract.

Under our Term Loan with Oxford, we have ongoing principal and interest payment obligations and are required to make a final payment at maturity that in the aggregate will require approximately $3.6 million by June 1, 2024 (See Note 5, Term Loan Obligations of our condensed financial statements for more information). In addition, we are obligated to make operating lease payments for our office and laboratory space, and we may be required to make payments under certain of our other contractual agreements.

Other than as described above, we have no purchase commitments or long-term contractual obligations, except for lease obligations as of March 31, 2024. In addition, we have no off-balance sheet arrangements (as defined in the rules and regulations of the Securities and Exchange Commission) that have or are reasonably likely to have a current or future effect on our financial condition, changes in financial condition, revenues or expenses, results of operations, liquidity, capital expenditures or capital resources that is material to investors.

Operating activities

Net cash used in operating activities for the three months ended March 31, 2024 was $4.5 million compared to $5.8 million in the same period of 2023. Our operational cash use decreased $1.3 million during the three months ended March 31, 2024 as compared to the same period in 2023, due primarily to increased reimbursement under the CPRIT grant agreement for research and development costs related to the ReSPECT-LM program.

27

Investing activities

Net cash used in investing activities for the three months ended March 31, 2024 was related to purchase of short-term investments of $0.3 million and purchases of fixed assets of $40,000. Net cash used in investing activities for the three months ended March 31, 2023 was related to purchases of fixed assets of $0.1 million.

Financing Activities

Net cash used in financing activities for the three months ended March 31, 2024 was related to repurchase of treasury stock for approximately $0.4 million and repayment of principle balance under the Oxford loan of $0.4 million.

Net cash provided by financing activities for the three months ended March 31, 2023 was primarily related to sales of common stock of $0.9 million, net of offering cost through the September 2022 Distribution Agreement with Canaccord, and offset by repayment of principle balance under the Oxford loan of $0.4 million.

Critical Accounting Policies and Significant Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires us to make estimates and assumptions that affect the reported amounts of our assets, liabilities, revenues and expenses, and that affect our recognition and disclosure of contingent assets and liabilities.

While our estimates are based on assumptions we consider reasonable at the time they were made, our actual results may differ from our estimates, perhaps significantly. If results differ materially from our estimates, we will make adjustments to our financial statements prospectively as we become aware of the necessity for an adjustment.

Goodwill is reviewed for impairment annually or more frequently if indicators of impairment exist. We perform our impairment test annually during the fourth quarter. We operate in a single operating segment and reporting unit. We monitor the fluctuations in our share price and have experienced significant volatility during the year.

We believe it is important for you to understand our most critical accounting policies. Our critical accounting policies and estimates are discussed in our Annual Report on Form 10-K for the fiscal year ended December 31, 2023 and there have been no material changes during the three months ended March 31, 2024.

Item 3. Quantitative and Qualitative Disclosures about Market Risk

Not applicable.

Item 4. Controls and Procedures

Evaluation of Disclosure Controls and Procedures

We maintain “disclosure controls and procedures,” as such term is defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act of 1934, as amended (the “Exchange Act”), that are designed to ensure that information required to be disclosed in our reports that we file or furnish pursuant to the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the Securities and Exchange Commission’s rules and forms, and that such information is accumulated and communicated to our management, including our Chief Executive Officer (our principal executive officer) and Chief Financial Officer (our principal financial officer and principal accounting officer), as appropriate, to allow for timely decisions regarding required disclosure. In designing and evaluating the disclosure controls and procedures, management recognizes that any controls and procedures, no matter how well designed and operated, can provide only reasonable assurance of achieving the desired control objectives, and management necessarily is required to apply its judgment in evaluating the cost-benefit relationship of possible controls and procedures.

As required by Rule 13a-15(b) under the Exchange Act we carried out an evaluation, under the supervision and with the participation of our management, including our Chief Executive Officer (our principal executive officer) and Chief Financial Officer (our principal financial officer and principal accounting officer), of the effectiveness of our disclosure controls and procedures, as such term is defined under Rule 13a-15(e) and 15d-15(e) promulgated under the Exchange Act as of the end of the period covered by this Quarterly Report on Form 10-Q. Based on the foregoing, our Chief Executive Officer (our principal executive officer) and Chief Financial Officer (our principal financial officer and principal accounting officer) concluded that our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act) were effective at the reasonable assurance level as of the end of the period covered by this Quarterly Report on Form 10-Q.

We previously reported on our Form 10-Q for the quarter ended June 30, 2023, that the Company did not design and maintain effective internal controls over the application of appropriate accounting principles to significant and unusual grant revenue transactions. Specifically, controls over identification of significant and/or unusual transactions requiring technical analysis were not operating

28

effectively. Management evaluated the impact of this deficiency on our disclosure controls and procedures and concluded that the control deficiency represented a material weakness.

Since the identification of the material weakness, we have taken steps to remediate the material weakness mentioned above, including strengthening our review process related to significant and unusual transactions, such as multiple level of review of categorization of the research and development expenses eligible for grant revenue and supporting evidence of such expenses.

In the first quarter of fiscal 2024, the Company completed the testing of the design and operating effectiveness of the controls over application of appropriate accounting principles to significant and unusual grant revenue transaction. Management has determined that the controls are adequately designed and are operating effectively, and concluded that the material weakness identified in the Quarterly Report on Form 10-Q for the quarter ended June 30, 2023 had been remediated.

Changes in Internal Control over Financial Reporting

There have been no changes in our internal control over financial reporting during the quarter ended March 31, 2024, other than remediation of the material weakness discussed above, that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

PART II. OTHER INFORMATION

Item 1. Legal Proceedings

None.

Item 1A. Risk Factors

We have been notified by Nasdaq of our failure to comply with certain continued listing requirements and, if we are unable to regain compliance with all applicable continued listing requirements and standards of Nasdaq, our common stock could be delisted from Nasdaq.

Our common stock is currently listed on Nasdaq. In order to maintain that listing, we must satisfy continued listing requirements and standards. There can be no assurances that we will be able to comply with the applicable listing standards of Nasdaq.

On March 8, 2024, we received the Notice from Nasdaq, notifying us that we no longer complied with the requirement under Nasdaq Listing Rule 5550(b)(1) to maintain a minimum of $2.5 million in stockholders’ equity for continued listing on Nasdaq or the Alternative Requirements. The Notice states that our Annual Report on Form 10-K for the fiscal year ended December 31, 2023, disclosed stockholders’ equity of ($1.3 million) as of December 31, 2023, and that, as of March 8, 2024, we did not meet the Alternative Standards.

On April 22, 2024, we provided Nasdaq with our plan to achieve and sustain compliance with the stockholders’ equity requirement and requested that Nasdaq grant us an extension of time until September 4, 2024, to provide evidence of compliance with the stockholders’ equity requirement. Nasdaq has not yet responded to our plan, and there can be no assurance that Nasdaq will grant an extension or that we will be able to comply with the applicable listing standards of Nasdaq.

In the event that our common stock is delisted from Nasdaq, as a result of our failure to comply with the stockholders’ equity requirement, or as a result of Nasdaq not granting us an extension or due to our failure to continue to comply with any other requirement for continued listing on Nasdaq, we may have to pursue trading on a less recognized or accepted market, such as the over the counter markets, our stock may be traded as a “penny stock,” which would make transactions in our stock more difficult and cumbersome, and we may be unable to access capital on favorable terms or at all, as companies trading on alternative markets may be viewed as less attractive investments with higher associated risks, such that existing or prospective institutional investors may be less interested in, or prohibited from, investing in our common stock. This may also cause the market price of our common stock to decline.

We may issue additional shares of common stock or other equity securities without our stockholder approval, and holders of warrants and other securities convertible into shares of our common stock may choose to exercise their warrants and other securities requiring us to issue shares of common stock; all of these actions would dilute your ownership interest and may depress the market price of our common stock.

In May 2024, we entered into a securities purchase agreement with certain investors, including certain of the Company’s directors and executive officers, and issued and sold in a private placement: (i) an aggregate of 3,591,532 shares of common stock (or in lieu of shares of common stock, Pre-Funded Warrants), and (ii) Warrants to purchase up to 7,183,064 shares of common stock. If these Warrants are exercised, it will result in significant dilution to our stockholders. In the alternative, these Warrants may not be exercised, in which event

29

we are likely to seek alternative sources of financing to continue the clinical development of our product candidates. Please see Note 12 for further information regarding the May 2024 Private Placement and the terms of the Warrants.

In addition, outstanding securities convertible into our shares of common stock may be exercised and restricted stock units may vest resulting in the issuance of additional shares of common stock, which will result in further dilution to our stockholders.

Significant additional capital may be needed in the future to continue our planned operations, including further development of our product candidates, preparing IND or equivalent filings, conducting preclinical studies and clinical trials, commercialization efforts, expanded research and development activities and costs associated with operating a public company. To raise capital, we may sell common stock, convertible securities or other equity securities in one or more transactions at prices and in a manner we determine from time to time. If we sell common stock, convertible securities or other equity securities, investors may be materially diluted by subsequent sales. Such sales may also result in material dilution to our existing stockholders, and new investors could gain rights, preferences and privileges senior to the holders of our shares of common stock.

We may also issue additional shares of common stock or other equity securities of equal or senior rank in the future in connection with, among other things, future acquisitions or repayment of outstanding indebtedness, without stockholder approval, in a number of circumstances. The issuance of additional shares or other equity securities of equal or senior rank would have the following effects:

•existing stockholders’ proportionate ownership interest in us will decrease;

•the relative voting strength of each previously outstanding common stock may be diminished; and

•the market price of the common stock may decline.

Other than the risk factors set forth above, there have been no material changes to the risk factors disclosed in Part I, Item 1A, “Risk Factors” of our Annual Report on Form 10-K for the year ended December 31, 2023.

Item 2. Unregistered Sales of Equity Securities and Use of Proceeds

2(a): Unregistered Sales of Equity Securities and Use of Proceeds

None.

2(b): Use of Proceeds from Registered Securities

None.

2(c): Purchases of Equity Securities

The following table provides certain information with respect to the Company’s purchases of the Company’s common stock for the three months ended March 31, 2024:

	Company Purchases of Common stock
Period	Total number of shares purchased	Average price paid per share		Approximate dollar value of shares that may yet be purchased under plan or programs (1)
January 1, 2024 through January 31, 2024	102,194	$	2.02	$	157,000
February 1, 2024 through February 29, 2024	77,062	$	1.96	$	1,000
March 1, 2024 through March 31, 2024	610	$	2.01	$	0
Total	179,866	$	1.99	$	0

(1) On October 31, 2023, the Company announced that the Board authorized a $500,000 a share repurchase program (the “Share Repurchase Program”). Repurchases are funded from available cash and may be made at management’s discretion from time to time. As of March 31, 2024, there was no remaining amount available for future share repurchases under the Share Repurchase Program. The repurchase authorization will expire on October 31, 2024. Refer to Note 10. Stockholders’ Equity in Part I, Item 1 of this Quarterly Report on Form 10-Q for more information on the Share Repurchase Program.

30

Item 6. Exhibits

EXHIBIT INDEX

PLUS THERAPEUTICS, INC.

Exhibit Number	Exhibit Title	Filed with this Form 10-Q	Incorporated by Reference
			Form	File No.	Date Filed
3.1	Composite Certificate of Incorporation		10-K	001-34375  Exhibit 3.1	03/11/2016
3.2	Certificate of Amendment to Amended and Restated Certificate		8-K	001-34375  Exhibit 3.1	05/10/2016
3.3	Certificate of Amendment to Amended and Restated Certificate		8-K	001-34375  Exhibit 3.1	05/23/2018
3.4	Certificate of Amendment to Amended and Restated Certificate		8-K	001-34375  Exhibit 3.1	07/29/2019
3.5	Certificate of Amendment to Amended and Restated Certificate		8-K	001-34375  Exhibit 3.1	08/06/2019
3.6	Certificate of Amendment to Amended and Restated Certificate		8-K	001-34375  Exhibit 3.1	04/28/2023
3.7	Amended and Restated Bylaws of Plus Therapeutics, Inc.		8-K	001-34375 Exhibit 3.1	09/21/2021
3.8	Certificate of Designation of Preferences, Rights and Limitations of Series B Convertible Preferred Stock		8-K	001-34375 Exhibit 3.1	11/28/2017
3.9	Certificate of Designation of Preferences, Rights and Limitations of Series C Convertible Preferred Stock		8-K	001-34375 Exhibit 3.1	07/25/2018
3.10	Certificate of Designation of Series F Preferred Stock, dated March 3, 2023		8-K	001-34375 Exhibit 3.1	03/03/2023
4.1	Form of Series U Warrant		S-1/A	333-229485 Exhibit 4.37	09/16/2019
4.2	Form of Warrant Amendment Agreement		8-K	001-34375 Exhibit 4.1	04/23/2020
4.3	Form of Underwriters' Warrant Amendment Agreement		8-K	001-34375 Exhibit 4.1	10/05/2020
4.4	Form of Pre-Funded Warrant		8-K	001-34375 Exhibit 4.1	05/09/2024
4.5	Form of Series A Warrant		8-K	001-34375 Exhibit 4.2	05/09/2024
4.6	Form of Series B Warrant		8-K	001-34375 Exhibit 4.3	05/09/2024
10.1	Securities Purchase Agreement, dated May 5, 2024, by and among Plus Therapeutics, Inc. and the purchasers named therein		8-K	001-34375 Exhibit 10.1	05/09/2024

31

10.2	First Amendment to Securities Purchase Agreement, dated May 8, 2024, by and among Plus Therapeutics, Inc. and the purchasers named therein		8-K	001-34375 Exhibit 10.2	05/09/2024
31.1	Certification of Principal Executive Officer Pursuant to Securities Exchange Act Rule 13a-14(a), as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002	X
31.2	Certification of Principal Financial and Accounting Officer Pursuant to Securities Exchange Act Rule 13a-14(a), as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002	X
32.1*	Certifications Pursuant to 18 U.S.C. Section 1350/ Securities Exchange Act Rule 13a-14(b), as adopted pursuant to Section 906 of the Sarbanes - Oxley Act of 2002	X
101.INS	Inline XBRL Instance Document – the instance document does not appear in the Interactive Data File because its XBRL tags are embedded within the Inline XBRL document	X
101.SCH	Inline XBRL Schema Document	X
101.CAL	Inline XBRL Calculation Linkbase Document	X
101.DEF	Inline XBRL Definition Linkbase Document	X
101.LAB	Inline XBRL Label Linkbase Document	X
101.PRE	Inline XBRL Presentation Linkbase Document	X
104	Cover Page Interactive Data File (formatted as Inline XBRL and contained in Exhibit 101)	X

* In accordance with Item 601(b)(32)(ii) of Regulation S‑K and SEC Release No. 34‑47986, the certifications furnished in Exhibit 32.1 hereto is deemed to accompany this Form 10‑Q and will not be deemed “filed” for purposes of Section 18 of the Exchange Act or deemed to be incorporated by reference into any filing under the Exchange Act or the Securities Act of 1933 except to the extent that the Company specifically incorporates it by reference.

32

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

	PLUS THERAPEUTICS, INC.
	By:	/s/ Marc H. Hedrick
Dated: May 15, 2024		Marc H. Hedrick
		President & Chief Executive Officer (Duly Authorized Officer and Principal Executive Officer)
	By:	/s/ Andrew Sims
Dated: May 15, 2024		Andrew Sims
		Chief Financial Officer (Duly Authorized Officer and Principal Financial Officer and Principal Accounting Officer)

1

EX-31.1

EXHIBIT 31.1

Certification of Principal Executive Officer Pursuant to

Securities Exchange Act Rule 13a-14(a),

as Adopted Pursuant to

Section 302 of the Sarbanes-Oxley Act of 2002

I, Marc H. Hedrick, certify that:

1.I have reviewed this quarterly report on Form 10-Q of Plus Therapeutics, Inc.;

2.Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3.Based on my knowledge, the financial statements and other financial information included in this report fairly present in all material respects the financial condition, results of operations, and cash flows of the registrant as of, and for, the periods presented in this report;

4.The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a)designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b)designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c)evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d)disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5.The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a)all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

(b)any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 15, 2024

/s/ Marc H. Hedrick

Marc H. Hedrick,

President & Chief Executive Officer

EX-31.2

EXHIBIT 31.2

Certification of Principal Financial Officer Pursuant to

Securities Exchange Act Rule 13a-14(a),

as Adopted Pursuant to

Section 302 of the Sarbanes-Oxley Act of 2002

I, Andrew Sims, certify that:

1. I have reviewed this quarterly report on Form 10-Q of Plus Therapeutics, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements and other financial information included in this report fairly present in all material respects the financial condition, results of operations, and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a) all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

(b) any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 15, 2024

/s/ Andrew Sims

Andrew Sims

Chief Financial Officer

EX-32.1

EXHIBIT 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350/ SECURITIES EXCHANGE ACT RULE 13a-14(b), AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of Plus Therapeutics, Inc. for the quarterly period ended March 31, 2024 as filed with the Securities and Exchange Commission on the date hereof, Marc H. Hedrick, as President & Chief Executive Officer of Plus Therapeutics, Inc., and Andrew Sims, as VP of Finance and Chief Financial Officer of Plus Therapeutics, Inc., each hereby certifies, respectively, that:

1.The Form 10-Q report of Plus Therapeutics, Inc. that this certification accompanies fully complies with the requirements of Section 13(a) of the Securities Exchange Act of 1934.

2.The information contained in the Form 10-Q report of Plus Therapeutics, Inc. that this certification accompanies fairly presents, in all material respects, the financial condition and results of operations of Plus Therapeutics, Inc.

	By:	/s/ Marc H. Hedrick
Dated: May 15, 2024		Marc H. Hedrick
		President & Chief Executive Officer
	By:	/s/ Andrew Sims
Dated: May 15, 2024		Andrew Sims
		Chief Financial Officer & VP of Finance

XML

Document and Entity Information	3 Months Ended
	Mar. 31, 2024
Cover [Abstract]
Entity Registrant Name	PLUS THERAPEUTICS, INC.
Entity Central Index Key	0001095981
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Trading Symbol	PSTV
Title of 12(b) Security	Common Stock, par value $0.001
Security Exchange Name	NASDAQ
Entity File Number	001-34375
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	33-0827593
Entity Address, Address Line One	4200 MARATHON BLVD
Entity Address, Address Line Two	SUITE 200
Entity Address, City or Town	AUSTIN
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78756
City Area Code	737
Local Phone Number	255-7194

XML

CONDENSED BALANCE SHEETS (UNAUDITED) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 2,901,000	$ 8,554,000
Investments	323,000
Other current assets	989,000	1,280,000
Total current assets	4,213,000	9,834,000
Property and equipment, net	800,000	906,000
Operating lease right-use-of assets	171,000	202,000
Goodwill	372,000	372,000
Intangible assets, net	33,000	42,000
Other assets	32,000	32,000
Total assets	5,621,000	11,388,000
Current liabilities:
Accounts payable and accrued expenses	6,447,000	6,631,000
Operating lease liability	115,000	120,000
Deferred grant liability	247,000
Term loan obligation, current	3,590,000	3,976,000
Total current liabilities	10,399,000	10,727,000
Noncurrent operating lease liability	59,000	85,000
Deferred grant liability		1,924,000
Total liabilities	10,458,000	12,736,000
Commitments and contingencies (Note 8)
Stockholders' deficit:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; 1,952 shares issued and outstanding at March 31, 2024 and December 31, 2023, respectively
Common stock, $0.001 par value; 100,000,000 shares authorized; 4,522,656 and 4,264,231 issued and outstanding at March 31, 2024, and 4,522,656 issued and 4,444,097 outstanding as of December 31, 2023, respectively	5,000	5,000
Treasury stock (at cost, 258,425 and 78,559 shares as of March 31, 2024 and December 31, 2023, respectively)	(500,000)	(126,000)
Additional paid-in capital	479,420,000	479,274,000
Accumulated deficit	(483,762,000)	(480,501,000)
Total stockholders' deficit	(4,837,000)	(1,348,000)
Total liabilities and stockholders' deficit	$ 5,621,000	$ 11,388,000

XML

CONDENSED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Stockholders' deficit:
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	1,952	1,952
Preferred stock, shares outstanding (in shares)	1,952	1,952
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	4,522,656	4,522,656
Common stock, shares outstanding (in shares)	4,264,231	4,444,097
Treasury stock, shares	258,425	78,559

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CONDENSED STATEMENTS OF OPERATIONS (UNAUDITED) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 2,763,000	$ 2,983,000
General and administrative	2,213,000	2,245,000
Total operating expenses	4,976,000	5,228,000
Operating loss	(3,299,000)	(4,722,000)
Other income (expense):
Interest income	72,000	51,000
Interest expense	(34,000)	(134,000)
Total other expense	38,000	(83,000)
Net loss	$ (3,261,000)	$ (4,805,000)
Net loss per share, basic	$ (0.75)	$ (2.07)
Net loss per share, diluted	$ (0.75)	$ (2.07)
Basic weighted average shares used in calculating net loss per share attributable to common stockholders	4,321,731	2,320,017
Diluted weighted average shares used in calculating net loss per share attributable to common stockholders	4,321,731	2,320,017
Grant [Member]
Revenue	$ 1,677,000	$ 506,000

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CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY/(DEFICIT) (UNAUDITED) - USD ($)	Total	Series F Preferred Stock [Member]	Convertible Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member] Series F Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series F Preferred Stock [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2022	$ 6,445,000					$ 2,000	$ 473,628,000		$ (467,185,000)
Balance (in shares) at Dec. 31, 2022			1,952			2,240,092
Stock-based compensation	140,000						140,000
Issue and sale of stock, net	895,000	$ 1,000					895,000	$ 1,000
Issue and sale of share					1	168,164
Net loss	(4,805,000)								(4,805,000)
Balance at Mar. 31, 2023	2,676,000					$ 2,000	474,664,000		(471,990,000)
Balance (in shares) at Mar. 31, 2023			1,952	1		2,408,256
Balance at Dec. 31, 2022	6,445,000					$ 2,000	473,628,000		(467,185,000)
Balance (in shares) at Dec. 31, 2022			1,952			2,240,092
Balance at Dec. 31, 2023	(1,348,000)					$ 5,000	479,274,000		(480,501,000)	$ (126,000)
Balance (in shares) at Dec. 31, 2023			1,952			4,522,656				(78,559)
Stock-based compensation	146,000						146,000
Purchase of treasury stock	(374,000)									$ (374,000)
Purchase of treasury stock (in Shares)										(179,866)
Net loss	(3,261,000)								(3,261,000)
Balance at Mar. 31, 2024	$ (4,837,000)					$ 5,000	$ 479,420,000		$ (483,762,000)	$ (500,000)
Balance (in shares) at Mar. 31, 2024			1,952			4,522,656				(258,425)

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CONDENSED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Cash flows used in operating activities:
Net loss	$ (3,261)	$ (4,805)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	155	158
Amortization of deferred financing costs and debt discount	16	66
Share-based compensation expense	146	140
Accretion of discount on short-term investments	1
Reduction in the carrying amount of operating lease right-of-use assets	31	29
Loss on disposal of property and equipment		2
Increases (decreases) in cash caused by changes in operating assets and liabilities:
Other current assets	150	2,791
Accounts payable and accrued expenses	(43)	(3,639)
Change in operating lease liabilities	(31)	(29)
Deferred grant liability	(1,677)	(506)
Net cash used in operating activities	(4,513)	(5,793)
Cash flows used in investing activities:
Purchases of property and equipment	(40)	(97)
Purchase of short-term investments	(324)
Net cash used in investing activities	(364)	(97)
Cash flows used in/provided by financing activities:
Principal payments of term loan obligation	(402)	(402)
Purchase of treasury stock	(374)
Proceeds from sale of common stock, net		895
Net cash (used in) provided by financing activities	(776)	493
Net decrease in cash and cash equivalents	(5,653)	(5,397)
Cash and cash equivalents at beginning of period	8,554	18,120	$ 18,120
Cash and cash equivalents at end of period	2,901	12,723	$ 8,554
Cash paid during period for:
Interest	23	73
Supplemental schedule of non-cash investing and financing activities:
Unpaid offering cost	$ 141	25
Right-of-use assets obtained in exchange for operating lease liability		$ 51

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Basis of Presentation and New Accounting Standards

3 Months Ended

Mar. 31, 2024

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Basis of Presentation and New Accounting Standards

1. Basis of Presentation and New Accounting Standards

The accompanying unaudited condensed financial statements for the three months ended March 31, 2024 and 2023 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2023 has been derived from the audited financial statements at December 31, 2023, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc. (the “Company”) have been included. Operating results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, filed with the Securities and Exchange Commission on March 5, 2024.

Amendments to Certificate of Incorporation and Reverse Stock Split

At the Annual Meeting of Stockholders of the Company held on April 20, 2023 (the “Annual Meeting”), the stockholders of the Company approved an amendment to the Company’s Amended and Restated Certificate of Incorporation (the “Charter”) to implement a reverse stock split of the Company’s then issued and outstanding common stock, par value $0.001 per share, with the ratio to be determined by the Board of Directors (the “Board”) of the Company, within a range of not less than 1-for-3 and not greater than 1-for-15. Subsequently, on April 21, 2023, the Board determined to fix the ratio for the reverse stock split at 1-for-15, without any change to its par value (the "Reverse Stock Split").

On April 27, 2023, following stockholder and Board approval, the Company filed a Certificate of Amendment to its Charter (the “Amendment”), with the Secretary of State of the State of Delaware to effectuate the Reverse Stock Split. The Amendment became effective on May 1, 2023. Upon effectiveness of the Reverse Stock Split, the number of shares of the Company’s common stock (x) issued and outstanding decreased from approximately 37.4 million shares to approximately 2.5 million shares; (y) reserved for issuance upon exercise of outstanding warrants and options decreased from approximately 2.0 million shares to approximately 0.1 million shares, and (z) reserved but unallocated under the Company’s current equity incentive plans decreased from approximately 3.0 million shares of common stock to approximately 0.2 million shares of common stock. The Company’s common stock began trading on the Nasdaq Capital Market (“Nasdaq”) on a post-split basis on May 1, 2023. The Company’s 5,000,000 shares of authorized Preferred Stock were not affected by the Reverse Stock Split. No fractional shares were issued in connection with the Reverse Stock Split, and accordingly, the outstanding number of shares post Reverse Stock Split was adjusted down by approximately 1,310 (post-effect of the Reverse Stock Split) shares. Proportional adjustments for the Reverse Stock Split were made to the Company’s outstanding stock options, warrants and equity incentive plans for the period ended March 31, 2023 as presented in the condensed financial statements in this Quarterly Report on Form 10-Q. The Company’s financial statements, and all references thereto have been retroactively adjusted to reflect the Reverse Stock Split unless specifically stated otherwise.

Grant Revenue Recognition

In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as the Company does not consider there to be a transfer of control of goods or services. With respect to each grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies International Accounting Standards No. 20 ("IAS 20"), Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract.

The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of each grant, of whether each grant agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred.

Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.

Available-for-Sale Securities

The Company’s available-for-sale securities consist of U.S. government and agency securities. The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the condensed balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the condensed statements of operations and comprehensive income/loss and as a separate component of stockholders’ equity. Realized gains and losses are calculated on the specific identification method and recorded as interest income (loss). At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the decline in fair value below amortized cost is a result of credit losses or other factors, whether the Company expects to recover the amortized cost of the security, the Company’s intent to sell and if it is more likely than not that the Company will be required to sell the securities before the recovery of amortized cost. The Company records changes in allowance for expected credit loss in other income (expense). As of March 31, 2024, there were no available-for-sale securities in an unrealized loss position, and there has been no allowance for expected credit losses recorded during any of the periods presented.

Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Accretion of discounts are recorded in interest income in the condensed statements of operations and comprehensive income/loss.

During the three months ended March 31, 2024, the unrealized gain on the Company’s available-for-sale securities was less than $1,000, and not presented separately in the condensed statement of operations and comprehensive income/loss.

Recently Issued Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (ASU) No. 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosure. This ASU includes amendments that further enhance income tax disclosures, primarily through standardization and disaggregation of rate reconciliation categories and income taxes paid by jurisdiction. The ASU is effective for years beginning after December 15, 2024, but early adoption is permitted. This ASU should be applied on a prospective basis, although retrospective application is permitted. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

In November 2023, the FASB issued Accounting Standard Update (ASU) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. The new standard is intended to improve annual and interim reportable segment disclosure requirements regardless of number of reporting units, primarily through enhanced disclosures of significant expenses. The amendment requires public entities to disclose significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit and loss. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years starting after December 15, 2024. This ASU must be applied retrospectively to all prior periods presented. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

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Use of Estimates

3 Months Ended

Mar. 31, 2024

Use Of Estimates [Abstract]

Use of Estimates

2. Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve reviewing assets for impairment and determining the assumptions used in measuring stock-based compensation expense.

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Liquidity and Going Concern

3 Months Ended

Mar. 31, 2024

Liquidity [Abstract]

Liquidity and Going Concern

3. Liquidity and Going Concern

The Company incurred a net loss of $3.3 million for the three months ended March 31, 2024. The Company had an accumulated deficit of $483.8 million as of March 31, 2024. Additionally, the Company used net cash of $4.5 million to fund its operating activities for the three months ended March 31, 2024.

To date, the Company’s operating losses have been funded primarily from outside sources of invested capital from issuance of its common and preferred stocks, proceeds from its term loan and grant funding. However, the Company has had, and will continue to have, an ongoing need to raise additional cash from outside sources to fund its future clinical development programs and other operations. There can be no assurance that the Company will be able to continue to raise additional capital in the future. The Company’s inability to raise additional cash would have a material and adverse impact on its operations and could cause the Company to default on its term loan. These factors raise substantial doubt about the Company’s ability to continue as a going concern.

On May 9, 2024, the Company closed a private placement of securities of the Company for aggregate gross proceeds of approximately $7.25 million, before deducting certain expenses payable by the Company, and excluding the proceeds, if any, from the exercise of warrants issued in the private placement. See Note 12 for further information regarding the private placement.

Nasdaq Listing Compliance

On March 8, 2024, the Company received a letter (the “Notice”) from the Listing Qualifications staff of Nasdaq, notifying the Company that it no longer complied with the requirement under Nasdaq Listing Rule 5550(b)(1) to maintain a minimum of $2.5 million in stockholders’ equity for continued listing on Nasdaq or the alternative requirements of having a market value of listed securities of $35 million or net income from continuing operations of $500,000 in the most recently completed fiscal year or two of the last three most recently completed fiscal years (the “Alternative Standards”). The Notice states that the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023, disclosed stockholders’ equity of ($1,348,000) as of December 31, 2023, and that, as of March 8, 2024, the Company did not meet the Alternative Standards.

On April 22, 2024, the Company provided Nasdaq with its plan to achieve and sustain compliance with the stockholders’ equity requirement and requested that Nasdaq grant the Company an extension of time until September 4, 2024, to provide evidence of compliance with the stockholders’ equity requirement. Nasdaq has not yet responded to the Company’s plan, and there can be no assurance that Nasdaq will grant an extension or that the Company will be able to comply with the applicable listing standards of Nasdaq.

The Company continues to seek additional capital from other financing alternatives and other sources in order to ensure adequate funding is available to allow the Company to continue research and product development activities at their current levels. If sufficient capital is not raised, the Company will at a minimum need to significantly reduce or curtail its research and development and other operations, and this would negatively affect its ability to achieve corporate growth goals.

Should the Company fail to raise additional cash from outside sources, it would have a material adverse impact on its operations.

The accompanying condensed financial statements have been prepared assuming the Company will continue to operate as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result from uncertainty related to its ability to continue as a going concern.

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Fair Value Measurements

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

Fair value measurements are market-based measurements, not entity-specific measurements. Therefore, fair value measurements are determined based on the assumptions that market participants would use in pricing the asset or liability. The Company follows a three-level hierarchy to prioritize the inputs used in the valuation techniques to derive fair values. The basis for fair value measurements for each level within the hierarchy is described below:

•Level 1: Quoted prices in active markets for identical assets or liabilities.

•Level 2: Quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which all significant inputs are observable in active markets.

•Level 3: Valuations derived from valuation techniques in which one or more significant inputs are unobservable in active markets.

The Company has investments in money market accounts, which are included in cash and cash equivalents on the balance sheets. Fair value inputs for these investments are considered Level 1 measurements within the fair value hierarchy since money market account fair values are known and observable through daily published floating net asset values.

The following table summarizes the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023, respectively (in thousands).

	Fair Value Measurements Using
March 31, 2024	Fair Value		Level 1		Level 2		Level 3
Money market	$	176	$	176	$	—	$	—
Treasury bills and government agency bonds		323		323		—		—
	$	499	$	499	$	—	$	—
	Fair Value Measurements Using
December 31, 2023	Fair Value		Level 1		Level 2		Level 3
Money market	$	5,449	$	5,449	$	—	$	—

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Term Loan Obligations

3 Months Ended

Mar. 31, 2024

Debt Disclosure [Abstract]

Term Loan Obligations

5. Term Loan Obligations

On May 29, 2015, the Company entered into the Loan and Security Agreement (the “Loan and Security Agreement”), pursuant to which Oxford Finance, LLC (“Oxford”) funded an aggregate principal amount of $17.7 million (the “Term Loan”), subject to the terms and conditions set forth in the Loan and Security Agreement. The Term Loan accrues interest at a floating rate of at least 8.95% per annum, comprised of a three-month LIBOR rate with a floor of 1.00% plus 7.95%. Pursuant to the Loan and Security Agreement, as amended, the Company made interest only payments through May 1, 2021, and thereafter is required to make payments of principal and accrued interest in equal monthly installments sufficient to amortize the Term Loan through June 1, 2024, the maturity date. At maturity of the Term Loan, or earlier repayment in full following voluntary prepayment or upon acceleration, the Company is required to make a final payment in an aggregate amount equal to approximately $3.2 million.

From September 2017 to March 2020, the Company entered into a total of nine amendments to the Term Loan that, among other things, extended the interest only period, required repayment of $3.1 million using the proceeds received from sale of the Company’s former UK and Japan subsidiaries in April 2019, increased the final payment, increased the final payment fee upon maturity or early repayment of the Term Loan, increased the minimum liquidity covenant level to $2.0 million and deferred the start date of principal repayment from May 1, 2020 to May 1, 2021 and extended the term of the Term Loan from September 1, 2021 to June 1, 2024.

On June 28, 2023, the Company and Oxford entered into a tenth amendment to the Loan and Security Agreement, and revised the interest rate of the Loan to the greater of: (1) 8.95%, or (2) the sum of 1-month Secured Overnight Financing Rate and 8.05%, effective July 1, 2023.

The Term Loan, as amended, is collateralized by a security interest in substantially all of the Company’s existing and subsequently acquired assets, including its intellectual property assets, subject to certain exceptions set forth in the Loan and Security Agreement, as amended. The intellectual property asset collateral will be released upon the Company achieving a certain liquidity level when the total principal outstanding under the Loan and Security Agreement is less than $3.0 million. As of March 31, 2024, there was $0.4 million principal amount outstanding under the Term Loan, excluding the $3.2 million final payment fee, and the Company was in compliance with all of the debt covenants under the Loan and Security Agreement.

The Company’s interest expense for the three ended March 31, 2024 and 2023 was $34,000 and $0.1 million, respectively. Interest expense is calculated using the effective interest method; therefore it is inclusive of non-cash amortization in the amount of $21,000 and $0.1 million for the three ended March 31, 2024 and 2023, respectively, related to the amortization of the debt discount, capitalized loan costs, and accretion of final payment.

The Loan and Security Agreement, as amended, contains customary indemnification obligations and customary events of default, including, among other things, the Company’s failure to fulfill certain obligations under the Term Loan, as amended, and the occurrence of a material adverse change, which is defined as a material adverse change in the Company’s business, operations, or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the loan. In the event of default by the Company or a declaration of material adverse change by its lender, under the Term Loan, the lender would be entitled to exercise its remedies thereunder, including the right to accelerate the debt, upon which the Company may be required to repay all amounts then outstanding under the Term Loan, which could materially harm the Company’s financial condition. As of March 31, 2024, the Company has not received any notification or indication from Oxford that it intends to invoke the material adverse change clause.

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Loss per Share

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Loss per Share

6. Loss per Share

Basic per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted per share data is computed by dividing net income or loss applicable to common stockholders by the weighted average number of common shares outstanding during the period increased to include, if dilutive, the number of additional common shares that would have been outstanding as calculated using the treasury stock method. Potential common shares were related to outstanding but unexercised options, multiple series of convertible preferred stock, and warrants for all periods presented.

The following were excluded from the diluted loss per share calculation for the periods presented because their effect would be anti-dilutive:

	As of March 31,
	2024		2023
Outstanding stock options		303,133		134,283
Preferred stock		28,190		28,190
Outstanding warrants		142,733		142,733
Total		474,056		305,206

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Grant Revenue

3 Months Ended

Mar. 31, 2024

Revenue from Contract with Customer [Abstract]

Grant Revenue

7. Grant Revenue

On September 19, 2022, the Company entered into that certain CPRIT contract (“CPRIT Contract”), effective as of August 31, 2022, with CPRIT, pursuant to which CPRIT will provide the Company with a CPRIT grant (“CPRIT Grant”) over a three-year period to fund the continued development of rhenium (186Re) obisbemeda for the treatment of patients with leptomeningeal metastases (“LM”). The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements.

The CPRIT Contract will terminate on August 30, 2025, unless terminated earlier by (a) the mutual written consent of all parties to the CPRIT Contract, (b) CPRIT for an event of default by the Company, (c) CPRIT, if the funds allocated to the CPRIT Grant become legally unavailable during the term of the CPRIT Contract and CPRIT is unable to obtain additional funds for such purposes, and (d) the Company for convenience. CPRIT may require the Company to repay some or all of the disbursed CPRIT Grant proceeds (with interest not to exceed 5% annually) in the event of the early termination of the CPRIT Contract by CPRIT for an event of default by the Company or by the Company for convenience, or if the Company relocates its principal place of business outside of the state of Texas during the CPRIT Contract term or within three years after the final payment of the grant funds.

The Company retains ownership over any intellectual property developed under the CPRIT Contract (each, a “Project Result”). With respect to non-commercial use of any Project Result, the Company granted to CPRIT a nonexclusive, irrevocable, royalty-free, perpetual, worldwide license with right to sublicense any necessary additional intellectual property rights to exploit all Project Results by CPRIT, other governmental entities and agencies of the State of Texas, and private or independent institutions of higher education located in Texas, for education, research and other non-commercial purposes.

The Company recognized $1.7 million and $0.5 million in grant revenue from the CPRIT Contract during the three months ended March 31, 2024 and 2023, respectively.

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Commitments and Contingencies

3 Months Ended

Mar. 31, 2024

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. Commitments and Contingencies

Leases

The Company leases laboratory, office and storage facilities in San Antonio, Texas, under operating lease agreements that expire in 2025. The Company also leases certain office space in Austin, Texas under a month-to-month operating lease agreement and certain office space in Charlottesville, Virginia (the “Charlottesville Lease”). The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods. On March 31, 2023, Company believed that it was reasonably certain that the Charlottesville Lease will be renewed through March 31, 2026, and as a result, it remeasured the related lease liability as of March 31, 2023 to be $80,000 using the then-in-effect discount rate of 12.76%. Effective July 1, 2023, the Company added additional office lease premises in Charlottesville, which was accounted for as a separate operating lease contract with a lease liability and corresponding right-of-use asset of $19,000, as a discount rate of 13.47%.

Piramal Master Services Agreement

On January 8, 2021, the Company entered into a Master Services Agreement (the “MSA”) with Piramal Pharma Solutions, Inc. (“Piramal”), for Piramal to perform certain services related to the development, manufacture, and supply of the Company’s rhenium (186Re) obisbemeda intermediate drug product. The MSA includes the transfer of analytical methods, development of microbiological methods, process transfer and optimization, intermediate drug product manufacturing, and stability studies for the Company, which has been initiated at Piramal’s facility located in Lexington, Kentucky.

The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice. Either party may terminate the MSA upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party.

Other commitments and contingencies

The Company has entered into agreements with various research organizations for pre-clinical and clinical development studies, which have provisions for cancellation. Under the terms of these agreements, the vendors provide a variety of services including conducting research, recruiting and enrolling patients, monitoring studies and data analysis. Payments under these agreements typically include fees for services and reimbursement of expenses. The timing of payments due under these agreements is estimated based on current study progress. As of March 31, 2024, the Company did not have any clinical research study obligations.

Legal proceedings

From time to time, the Company is subject to legal proceedings and claims, whether asserted or unasserted, that arise in the ordinary course of business. Due to their nature, such legal proceedings involve inherent uncertainties including, but not limited to, court rulings, negotiations between affected parties and governmental actions. Management assesses the probability of loss for such contingencies and accrues a liability and/or discloses the relevant circumstances, as appropriate.

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License Agreements

3 Months Ended

Mar. 31, 2024

License Agreement [Abstract]

License Agreements

9. License Agreements

Biocept License Agreement

On September 7, 2023, the Company entered into a Non-Exclusive License and Services Agreement (the “Biocept Agreement”) with Biocept, Inc (“Biocept”), pursuant to which Biocept granted the Company a non-exclusive license to use the Biocept proprietary cell enumeration test, CNsideTM (“CNside”). In exchange for the license, the Company issued to Biocept 53,381 unregistered shares, the fair value of which was $75,000. The Biocept Agreement also provides that if Biocept fully transfers the technology to the Company, a tech transfer and validation fee of $300,000 will be payable. In addition, the Company was granted an option for an exclusive worldwide license for $1,000,000 on or before December 31, 2024, to process and perform cell enumeration testing for treatments for other patients including those on the Company’s radiotherapeutic drugs.

On October 16, 2023, Biocept filed a voluntary petition for relief under the provisions of Chapter 7 of Title 11 of the United States Bankruptcy Code. See Note 12 for further information regarding the Company’s acquisition of substantially all right, title and interest in CNside.

UT Health Science Center at San Antonio (“UTHSCSA”) License Agreement

On December 31, 2021, the Company entered into a Patent and Know-How License Agreement (the “UTHSCSA License Agreement”) with The University of Texas Health Science Center at San Antonio (“UTHSCSA”), pursuant to which UTHSCSA granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of biodegradable alginate microspheres (“BAM”) containing nanoliposomes loaded with imaging and/or therapeutic payloads.

NanoTx License Agreement

On March 29, 2020, the Company and NanoTx, Corp. (“NanoTx”) entered into a Patent and Know-How License Agreement, pursuant to which NanoTx granted the Company an irrevocable, perpetual, exclusive, fully paid-up license, with the right to sublicense and to make, develop, commercialize and otherwise exploit certain patents, know-how and technology related to the development of radiolabeled nanoliposomes.

The transaction terms included an upfront payment of $0.4 million in cash and $0.3 million in the Company's voting stock. The transaction terms also included success-based milestone and royalty payments contingent on key clinical, regulatory and sales milestones, as well as the requirement to pay 15% of any non-dilutive monetary awards or grants received from external agencies to support product development of the nanoliposome encapsulated BMEDA-chelated radioisotope, which includes grants from CPRIT. As of March 31, 2024, the Company accrued $0.5 million of payments due to NanoTx as a result of the CPRIT grant received (see Note 7, Grant Revenue of the condensed financial statements for additional information).

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Stockholders' Equity

3 Months Ended

Mar. 31, 2024

Stockholders Equity Note [Abstract]

Stockholders' Equity

10. Stockholders’ Equity

Preferred Stock

The Company has authorized 5,000,000 shares of preferred stock, par value $0.001 per share. The Company’s Board is authorized to designate the terms and conditions of any preferred stock the Company issues without further action by the common stockholders.

Series F Preferred Stock

On March 3, 2023, the Company filed a certificate of designation (the “Certificate of Designation”) with the Secretary of State of the State of Delaware, effective as of the time of filing, designating the rights, preferences, privileges and restrictions of the Series F Preferred Stock, with the total authorization of one (1) share of Series F Preferred Stock. The Certificate of Designation provided that the share of Series F Preferred Stock would have 50,000,000 votes per share of Series F Preferred Stock and would vote together with the Company’s common stock, as a single class exclusively with respect to any proposal to amend the Company’s Charter to effect the Reverse Stock Split. On March 3, 2023, the Company entered into a subscription and investment representation agreement with Richard J. Hawkins, chairman of the board of the Company, who is an accredited investor (the “Series F Preferred Stock Purchaser”), pursuant to which the Company agreed to issue and sell one (1) share of the Company’s

Series F Preferred Stock, par value $0.001 per share, to the Series F Preferred Stock Purchaser for $1,000 in cash. The sale closed on March 3, 2023.

At the Company’s 2023 annual meeting, the Series F Preferred Stock was voted, without action by the holder, on the proposal to approve the Reverse Stock Split in the same proportion as shares of common stock voted to approve the Reverse Stock Split. The Series F Preferred Stock otherwise had no voting rights except as otherwise required by the General Corporation Law of the State of Delaware.

The Series F Preferred Stock was not convertible into, or exchangeable for, shares of any other class or series of stock or other securities of the Company. The Series F Preferred Stock had no rights with respect to any distribution of assets of the Company, including upon a liquidation, bankruptcy, reorganization, merger, acquisition, sale, dissolution or winding up of the Company, whether voluntarily or involuntarily. The holder of the Series F Preferred Stock was not entitled to receive dividends of any kind.

The outstanding share of Series F Preferred Stock was redeemed in whole, automatically effective upon the approval by the Company’s stockholders of the Reverse Stock Split. Upon such redemption, the holder of the Series F Preferred Stock received consideration of $1,000 in cash.

Series B and C Preferred Stock

As of March 31, 2024, there were 938 outstanding shares of Series C Preferred Stock that can be converted into an aggregate of 27,792 shares of common stock, and 1,014 shares of Series B Convertible Preferred Stock that can be converted into an aggregate of 398 shares of common stock.

Warrants

On September 25, 2019, the Company completed an underwritten public offering. The Company issued 19,266 shares of its common stock, along with pre-funded warrants to purchase 180,733 shares of its common stock and Series U Warrants to purchase 230,000 shares of its common stock. The Series U Warrants have a term of five years from the issuance date. In addition, the Company issued warrants to H.C. Wainwright & Co., LLC, as representatives of the underwriters, to purchase 5,000 shares of its common stock with a term of five years from the issuance date, in the form of Series U Warrants (the “Representative Warrants”). As of March 31, 2024, there were 142,733 outstanding Series U Warrants and Representative Warrants which can be exercised into an aggregate of 142,733 shares of common stock at a weighted average exercise price of $34.10 per share.

Common Stock

Lincoln Park Purchase Agreement

On August 2, 2022, the Company entered into a purchase agreement (the “2022 Purchase Agreement”) and registration rights agreement pursuant to which Lincoln Park Capital Fund (“Lincoln Park”) committed to purchase up to $50.0 million of the Company’s common stock. Under the terms and subject to the conditions of the 2022 Purchase Agreement, the Company has the right, but not the obligation, to sell to Lincoln Park, and Lincoln Park is obligated to purchase up to $50.0 million of the Company’s common stock. Such sales of common stock by the Company are subject to certain limitations, and can occur from time to time, at the Company’s sole discretion, over the 36-month period commencing on August 17, 2022, subject to the satisfaction of certain conditions.

On May 16, 2022, the Company received stockholder approval for purposes of the Nasdaq listing rules to permit issuances of up to 57.5 million shares of the Company’s common stock (including the issuance of more than 19.99% of the Company’s common stock) to Lincoln Park, and it was pursuant to that approval that the Company entered into the 2022 Purchase Agreement.

Upon execution of the 2022 Purchase Agreement, the Company paid $0.1 million in cash as the initial commitment fee, and issued 32,846 shares as the initial commitment shares, to Lincoln Park as consideration for its irrevocable commitment to purchase shares of the Company’s common stock at its direction under the 2022 Purchase Agreement. The Company has agreed to pay an additional commitment fee, which it may elect to pay in cash and/or shares of its common stock, upon receipt of $25.0 million aggregate gross proceeds from sales of common stock to Lincoln Park under the 2022 Purchase Agreement.

On August 17, 2022, a registration statement (the “First Registration Statement”) was declared effective to cover the resale of up to 633,333 shares of the Company’s common stock comprised of (i) the 32,846 initial commitment shares, and (ii) up to 600,486 that the Company has reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time from and after the date of the prospectus. The Company sold approximately 527,166 shares under the First Registration Statement.

On August 18, 2023, a second registration statement (the “Second Registration Statement”) was declared effective to cover the resale of up to an additional 1,500,000

shares of the Company’s common stock that the Company reserved for issuance and sale to Lincoln Park under the 2022 Purchase Agreement from time to time. The Company sold 150,000 shares under the Second Registration Statement. The Company cannot sell more shares than registered under the Second Registration Statement under the 2022 Purchase Agreement without registering additional shares.

Actual sales of shares of common stock to Lincoln Park under the 2022 Purchase Agreement depend on a variety of factors to be determined by the Company from time to time, including, among others, market conditions, the trading price of the common stock and determinations by the Company as to the appropriate sources of funding for the Company and its operations. The net proceeds under the 2022 Purchase Agreement to the Company depend on the frequency and prices at which the Company sells shares of its stock to Lincoln Park.

During the period from August 17, 2022 to December 31, 2022, the Company issued 266,666 shares under the 2022 Purchase Agreement for net proceeds of approximately $3.2 million. The Company issued 410,500 shares under the 2022 Purchase Agreement for net proceeds of approximately $1.0 million from January 1, 2023 to December 31, 2023. The Company did not issue any common stock under the 2022 Purchase Agreement during the three months ended March 31, 2024.

At-the-market Issuances

On September 9, 2022, the Company entered into an Equity Distribution Agreement (the “September 2022 Distribution Agreement”) with Canaccord Genuity LLC (“Canaccord”), pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $5,000,000, depending on market demand, with Canaccord acting as an agent for sales. During the period from September 9, 2022 to December 31, 2022, the Company issued 68,758 shares of its common stock under the September 2022 Distribution Agreement for net proceeds of approximately $0.6 million. From January 1, 2023 through December 31, 2023, the Company issued 1,819,993 shares under the September 2022 Distribution Agreement for net proceeds of approximately $4.3 million. The Company has reached the capacity for sales of shares under the September 2022 Distribution Agreement and the agreement has terminated.

The Company was obligated to pay Canaccord a commission of up to 3.0% of the gross proceeds from the sale of its common stock under the September 2022 Distribution Agreement. The Company also agreed to reimburse Canaccord for its reasonable documented out-of-pocket expenses, including fees and disbursements of its counsel, in the amount of $50,000. In addition, the Company agreed to provide customary indemnification rights to Canaccord.

On January 14, 2022, the Company entered into an Equity Distribution Agreement (the “January 2022 Distribution Agreement”) with Canaccord, pursuant to which the Company could issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $5,000,000, with Canaccord acting as an agent for sales. The Company had no obligation to sell any of the Company’s shares and it could instruct Canaccord not to sell any shares if the sales could not be effected at or above the price designated by the Company from time to time and the Company could at any time suspend sales pursuant to the January 2022 Distribution Agreement. During the year ended December 31, 2023, the Company issued 460,151 shares under the January 2022 Distribution Agreement for net proceeds of approximately $4.8 million. The January 2022 Distribution Agreement has been terminated after all available registered shares were fully utilized.

Share Repurchase Program and Treasury Stock

On October 31, 2023, the Company announced that its Board has approved a share repurchase program (the “Share Repurchase Program”), with authorization to repurchase up to $500,000 of the outstanding shares of the Company’s common stock. The Company funded repurchases under the Share Repurchase Program with available cash.

During the year ended December 31, 2023, the Company purchased 78,559 of its common stock for approximately $0.1 million as treasury stock. The Company purchased 179,866 of its common shares for approximately $0.4 million as treasury stock during the three months ended March 31, 2024. As of March 31, 2024, no amount remained authorized for repurchase.

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Stock-based Compensation

3 Months Ended

Mar. 31, 2024

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

11. Stock-based Compensation

Under the Company’s 2015 New Employee Incentive Plan (the “2015 Plan”), awards may only be granted to employees who were not previously an employee or director of the Company, or following a bona fide period of non-employment, as a material inducement to entering into employment with the Company. As of March 31, 2024, there were 6,024 shares of common stock remaining and available for future issuances under the 2015 Plan.

The Company’s 2020 Stock Incentive Plan (the “2020 Plan”), which replaced the Company’s 2014 Equity Incentive Plan, provides for the award or sale of shares of common stock (including restricted stock), the award of stock units and stock appreciation rights,

and the grant of both incentive stock options to purchase common stock to directors, officers, employees and consultants of the Company. The 2020 Plan, as amended, provides for the issuance of up to 236,667 shares of common stock, plus the number of shares available for issuance is increased to the extent that awards granted under the 2020 Plan and the Company’s 2014 Equity Incentive Plan are forfeited or expire (except as otherwise provided in the 2020 Plan). As of March 31, 2024, there were 17,582 shares remaining and available for future issuances under the 2020 Plan.

Generally, options issued under the 2020 Plan are subject to a two-year or four-year vesting schedule with 25% of the options vesting on the one year anniversary of the grant date followed by equal monthly installment vesting, and have a contractual term of 10 years.

A summary of activity for the three months ended March 31, 2024 is as follows:

	Options			Weighted Average  Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Balance as of December 31, 2023		140,109		$	37.48		8.07
Granted		163,025		$	2.03
Cancelled/forfeited		(1	)	$	289,125
Balance as of March 31, 2024		303,133		$	17.46		8.94	$	7,600
Vested and expected to vest at March 31, 2024		278,083		$	18.64		8.87	$	6,800
Exercisable at March 31, 2024		84,908		$	50.13		7.37	$	500

As of March 31, 2024, the total compensation cost related to non-vested stock options not yet recognized for all the Company’s plans is approximately $0.8 million, which is expected to be recognized as a result of vesting under service conditions over a weighted average period of 2.3 years.

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Subsequent Events

3 Months Ended

Mar. 31, 2024

Subsequent Events [Abstract]

Subsequent Events

12. Subsequent Events

May 2024 Private Placement

On May 5, 2024, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”) with certain investors, including certain of the Company’s directors and executive officers (“Company Insiders”) (collectively, the “Purchasers”), for the sale and issuance by the Company of its securities (the “Initial Subscription”). On May 8, 2024, the Company entered into a first amendment to the Securities Purchase Agreement (the “Amendment”) for the sale and issuance by the Company of additional securities to two of the Purchasers (the “Additional Subscription”, and together with the Initial Subscription, the “May 2024 Private Placement”). The Securities Purchase Agreement, as amended, provides for the sale and issuance by the Company of an aggregate of 3,591,532 shares (the “Private Placement Shares”) of the Company’s common stock or, at the election of each Purchaser, pre-funded warrants (the “Pre-Funded Warrants”), exercisable immediately at an exercise price of $0.001 per share (the “Pre-Funded Warrant Shares”), with each Private Placement Share or Pre-Funded Warrant accompanied by (i) a Series A common warrant (“Series A Warrants”) to purchase one share of common stock (the “Series A Warrant Shares”), for an aggregate of 3,591,532 Series A Warrants, and (ii) one Series B common warrant (“Series B Warrants”) to purchase one share of common stock (the “Series B Warrant Shares,” and together with the Series A Warrant Shares, the “Common Warrant Shares”), for an aggregate of 3,591,532 Series B Warrants.

The combined purchase price for each Private Placement Share and Pre-Funded Warrant from the Initial Subscription was $2.022, and $2.158 from the Additional Subscription, in each case together with one accompanying Series A Warrant and one accompanying Series B Warrant, provided, that the Company Insiders participated in the Initial Subscription at an offering price of $2.04 per Private Placement Share and accompanying Series A Warrant and Series B Warrant.

The exercise price of each Series A Warrant and Series B Warrant from the Initial Subscription is $1.772 per share and $1.908 per share in the Additional Subscription, provided that the exercise price for the Series A Warrants and Series B Warrants issued to the Company Insiders is $1.79 per share. Subject to certain ownership limitations, the Series A Warrants will be exercisable until the five-year anniversary of issuance. Subject to certain ownership limitations, the Series B Warrants will be exercisable until the one-year anniversary of the declaration of effectiveness of a registration statement to be filed with the Securities and Exchange Commission covering the resale of the Series B Warrant Shares underlying the Series B Warrants. The Pre-Funded Warrant will not expire until exercised in full.

The May 2024 Private Offering closed on May 9, 2024 (the “May 2024 Private Placement Closing”). The aggregate gross proceeds at the May 2024 Private Placement Closing were approximately $7.25 million, before deducting certain expenses payable by the Company, and excluding the proceeds, if any, from the exercise of the Series A Warrant, the Series B Warrant, and Pre-Funded Warrant.

The Company is evaluating the accounting treatment of the Series A Warrants, Series B Warrants and the Pre-Funded Warrants under the authoritative accounting guidance.

Biocept Asset Purchase

On April 26, 2024, the Company acquired from Biocept, for a total cash payment of $400,000, substantially all of the right, title and interest in CNside, including (i) intellectual property, (ii) inventory and raw materials, and (iii) data, information, results and reports pertaining to the completed and on-going clinical studies involving the use of the CNside test (including, but not limited to, the FORSEE clinical study), related to the development, making, selling, and exporting or importing of CNside, after the Company’s bid was approved by the United States Bankruptcy Court for the District of Delaware.

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Basis of Presentation and New Accounting Standards (Policies)

3 Months Ended

Mar. 31, 2024

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Basis of Presentation and New Accounting Standards

The accompanying unaudited condensed financial statements for the three months ended March 31, 2024 and 2023 have been prepared in accordance with accounting principles generally accepted in the United States of America for interim financial information. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for annual financial statements. The condensed balance sheet at December 31, 2023 has been derived from the audited financial statements at December 31, 2023, but does not include all of the information and footnotes required by accounting principles generally accepted in the United States of America for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation of the financial position and results of operations of Plus Therapeutics, Inc. (the “Company”) have been included. Operating results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024. These financial statements should be read in conjunction with the financial statements and notes therein included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, filed with the Securities and Exchange Commission on March 5, 2024.

Grant Revenue Recognition

Grant Revenue Recognition

In applying the provisions of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”), the Company has determined that government grants are out of the scope of ASC 606 because the funding entities do not meet the definition of a “customer”, as defined by ASC 606, as the Company does not consider there to be a transfer of control of goods or services. With respect to each grant, the Company determines if it has a collaboration in accordance with ASC Topic 808, Collaborative Arrangements (“ASC 808”). For grants outside the scope of ASC 808, the Company applies International Accounting Standards No. 20 ("IAS 20"), Accounting for Government Grants and Disclosure of Government Assistance, by analogy, and revenue is recognized when the Company incurs expenses related to the grant for the amount the Company is entitled to under the provisions of the contract.

The Company also considers the guidance in ASC Topic 730, Research and Development, which requires an assessment, at the inception of each grant, of whether each grant agreement is a liability. If the Company is obligated to repay funds received regardless of the outcome of the related research and development activities, then the Company is required to estimate and recognize that liability. Alternatively, if the Company is not required to repay the funds, then payments received are recorded as revenue or contra-expense as the expenses are incurred.

Deferred grant liability represents grant funds received or receivable for which the allowable expenses have not yet been incurred as of the balance sheet date.

Available-for-Sale Securities

Available-for-Sale Securities

The Company’s available-for-sale securities consist of U.S. government and agency securities. The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the condensed balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the condensed statements of operations and comprehensive income/loss and as a separate component of stockholders’ equity. Realized gains and losses are calculated on the specific identification method and recorded as interest income (loss). At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the decline in fair value below amortized cost is a result of credit losses or other factors, whether the Company expects to recover the amortized cost of the security, the Company’s intent to sell and if it is more likely than not that the Company will be required to sell the securities before the recovery of amortized cost. The Company records changes in allowance for expected credit loss in other income (expense). As of March 31, 2024, there were no available-for-sale securities in an unrealized loss position, and there has been no allowance for expected credit losses recorded during any of the periods presented.

Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Accretion of discounts are recorded in interest income in the condensed statements of operations and comprehensive income/loss.

During the three months ended March 31, 2024, the unrealized gain on the Company’s available-for-sale securities was less than $1,000, and not presented separately in the condensed statement of operations and comprehensive income/loss.

Recently Issued Accounting Pronouncements

Recently Issued Accounting Pronouncements

In December 2023, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (ASU) No. 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosure. This ASU includes amendments that further enhance income tax disclosures, primarily through standardization and disaggregation of rate reconciliation categories and income taxes paid by jurisdiction. The ASU is effective for years beginning after December 15, 2024, but early adoption is permitted. This ASU should be applied on a prospective basis, although retrospective application is permitted. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

In November 2023, the FASB issued Accounting Standard Update (ASU) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. The new standard is intended to improve annual and interim reportable segment disclosure requirements regardless of number of reporting units, primarily through enhanced disclosures of significant expenses. The amendment requires public entities to disclose significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit and loss. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within those fiscal years starting after December 15, 2024. This ASU must be applied retrospectively to all prior periods presented. Management is currently evaluating the impact of the changes required by the new standard on the Company’s financial statements and related disclosures.

Use of Estimates

The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions affecting the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. The Company’s most significant estimates and critical accounting policies involve reviewing assets for impairment and determining the assumptions used in measuring stock-based compensation expense.

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Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

The following table summarizes the Company’s fair value hierarchy for its financial assets measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023, respectively (in thousands).

	Fair Value Measurements Using
March 31, 2024	Fair Value		Level 1		Level 2		Level 3
Money market	$	176	$	176	$	—	$	—
Treasury bills and government agency bonds		323		323		—		—
	$	499	$	499	$	—	$	—
	Fair Value Measurements Using
December 31, 2023	Fair Value		Level 1		Level 2		Level 3
Money market	$	5,449	$	5,449	$	—	$	—

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Loss per Share (Tables)

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share

The following were excluded from the diluted loss per share calculation for the periods presented because their effect would be anti-dilutive:

	As of March 31,
	2024		2023
Outstanding stock options		303,133		134,283
Preferred stock		28,190		28,190
Outstanding warrants		142,733		142,733
Total		474,056		305,206

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Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Option Activity

A summary of activity for the three months ended March 31, 2024 is as follows:

	Options			Weighted Average  Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Balance as of December 31, 2023		140,109		$	37.48		8.07
Granted		163,025		$	2.03
Cancelled/forfeited		(1	)	$	289,125
Balance as of March 31, 2024		303,133		$	17.46		8.94	$	7,600
Vested and expected to vest at March 31, 2024		278,083		$	18.64		8.87	$	6,800
Exercisable at March 31, 2024		84,908		$	50.13		7.37	$	500

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Basis of Presentation and New Accounting Standards (Additional Information) (Details) $ / shares in Units, $ in Thousands				3 Months Ended
	Apr. 27, 2023	Apr. 21, 2023	Apr. 20, 2023 $ / shares	Mar. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 $ / shares shares	May 01, 2023 shares	Apr. 30, 2023 shares
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.001	$ 0.001	$ 0.001
Stock split conversion ratio		0.06
Reverse stock split effective date	May 01, 2023
Common stock, shares issued (in shares)				4,522,656	4,522,656	2,500,000	37,400,000
Common stock, shares outstanding (in shares)				4,264,231	4,444,097	2,500,000	37,400,000
Preferred stock, shares authorized (in shares)				5,000,000	5,000,000
Common stock, reverse stock split, fractional shares issued				0
Stock issued during period reverse stock splits, shares				1,310
Equity Incentive Plans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock capital shares reserved for future issuance						200,000	3,000,000
Outstanding Warrants and Options [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common stock capital shares reserved for future issuance						100,000	2,000,000
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.33
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stock split conversion ratio			0.06
Unrealized gain on available-for-sale securities | $				$ 1,000

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Liquidity and Going Concern - Additional Information (Details) - USD ($)		3 Months Ended
	Mar. 08, 2024	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss		$ (3,261,000)	$ (4,805,000)
Accumulated deficit		(483,762,000)		$ (480,501,000)
Net cash used in operating activities		(4,513,000)	(5,793,000)
Stockholders' deficit		$ (4,837,000)	2,676,000	$ (1,348,000)	$ 6,445,000
Stockholders' equity requirement	$ 2,500,000		$ 895,000
Net income from continuing operations	500,000
Maintain minimum market value of listed securities	$ 35,000,000

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Fair Value Measurements - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 499
Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	176	$ 5,449
Treasury Bills and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	323
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	499
Level 1 [Member] | Money Market [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	176	$ 5,449
Level 1 [Member] | Treasury Bills and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 323

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Term Loan Obligations - Additional Information (Details) - USD ($)					3 Months Ended
	Jun. 28, 2023	Mar. 29, 2020	Mar. 28, 2020	May 29, 2015	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Line Items]
Interest expense					$ 34,000	$ 134,000
Non-cash amortization					$ 21,000	$ 100,000
LIBOR [Member] | Interest Rate Floor [Member]
Debt Instrument [Line Items]
Basis variable rate				1.00%
Term Loan [Member]
Debt Instrument [Line Items]
Origination date					May 29, 2015
Original loan amount				$ 17,700,000
Basis variable rate				7.95%
Maturity date		Jun. 01, 2024	Sep. 01, 2021	May 01, 2021
Fees amount associated with loan				$ 3,200,000	$ 3,200,000
Interest rate	8.95%
Minimum liquidity covenant					$ 2,000,000
Debt principal repayment start date		May 01, 2021	May 01, 2020
Debt instrument, covenant compliance					the Company was in compliance with all of the debt covenants under the Loan and Security Agreement
Term Loan [Member] | Loan and Security Agreement [Member] | Sale of the Japanese Subsidiary and Certain Assets [Member]
Debt Instrument [Line Items]
Payments for principal, interest and fees				$ 3,100,000
Term Loan [Member] | SOFR [Member]
Debt Instrument [Line Items]
Basis variable rate	8.05%
Term Loan [Member] | Minimum [Member]
Debt Instrument [Line Items]
Interest rate				8.95%
Term Loan [Member] | Maximum [Member]
Debt Instrument [Line Items]
Original loan amount					$ 3,000,000
Long term debt outstanding threshold amount					$ 400,000

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Loss per Share - Schedule of Antidilutive Securities Excluded from Diluted Income (Loss) per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	474,056	305,206
Outstanding Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	303,133	134,283
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	28,190	28,190
Outstanding Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive common shares excluded from the calculations of diluted loss per share (in shares)	142,733	142,733

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Grant Revenue - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended
	Sep. 19, 2022	Mar. 31, 2024	Mar. 31, 2023
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 1,677	$ 506
CPRIT Contract [Member]
Disaggregation of Revenue [Line Items]
Grant funding term	3 years
CPRIT grant funding term, description		The CPRIT Grant is subject to customary CPRIT funding conditions, including, but not limited to, a matching fund requirement (one dollar for every two dollars awarded by CPRIT), revenue sharing obligations upon commercialization of rhenium (186Re) obisbemeda based on specific dollar thresholds and tiered low single digit royalty rates until CPRIT receives the aggregate amount of 400% of the proceeds awarded under the CPRIT Grant, and certain reporting requirements.
Contract effective date	Aug. 31, 2022
Contract termination date	Aug. 30, 2025
Percentage of aggregate amount of proceeds awarded under CPRIT grant	400.00%
Percentage of grant proceeds with interest not exceed annually	5.00%
CPRIT Contract [Member] | Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 1,700	$ 500

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Commitments and Contingencies - Additional Information (Details) - USD ($)		3 Months Ended
	Jan. 08, 2021	Mar. 31, 2024	Dec. 31, 2023	Jul. 01, 2023	Mar. 31, 2023
Recorded Unconditional Purchase Obligation [Line Items]
Operating leases expiry year		2025
Operating lease right-use-of assets		$ 171,000	$ 202,000
Pre-clinical Research Study Obligations [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Contractual obligation		$ 0
Charlottesville [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Lessee, operating lease, term of contract		12 months
Lessee, operating lease, existence of option to extend [true false]		true
Lessee, operating lease, option to extend		The Charlottesville Lease has a term of 12 months and the Company has the ability to renew for three additional one-year periods.
Lessee, operating lease, renewal term		1 year
Lease liability					$ 80,000
Operating lease discount rate				13.47%	12.76%
Operating lease right-use-of assets				$ 19,000
Piramal Pharma Solutions, Inc. [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Master service agreement date	Jan. 08, 2021
Master services agreement initial term	5 years
Master services agreement terms, Description		The MSA has a term of five years and will automatically renew for successive one-year terms unless either party notifies the other no later than six months prior to the original term or any additional terms of its intention to not renew the MSA. The Company has the right to terminate the MSA for convenience upon thirty days’ prior written notice.

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Commitments and Contingencies - Summary of Future Minimum Annual Lease Payments under Operating Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Operating Leases
Less: current portion	$ (115)	$ (120)
Noncurrent operating lease liability	$ 59	$ 85

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License Agreements - Additional Information (Details) - USD ($)			3 Months Ended
	Sep. 07, 2023	Mar. 29, 2020	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Research and development expense			$ 2,763,000	$ 2,983,000
Voting stock, value			5,000		$ 5,000
Biocept Agreement [Member]
Shares issued	53,381
Research and development expense			75,000
Payment for tech transfer and validation fee	$ 300,000
Option for exclusive worldwide license	$ 1,000,000
Nano Tx Licenses Agreement [Member]
License fee payment in cash		$ 400,000
Voting stock, value		$ 300,000
Percentage of non-dilutive monetary awards required to pay		15.00%
Accrued payments due to NanoTx			$ 500,000

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Stockholders' Equity - Preferred Stock (Details)		3 Months Ended
	Mar. 03, 2023 USD ($) Votes $ / shares shares	Mar. 31, 2024 $ / shares shares	Dec. 31, 2023 $ / shares shares	Apr. 20, 2023 $ / shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		5,000,000	5,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Preferred stock, shares outstanding (in shares)		1,952	1,952
Common stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001	$ 0.001
Series B Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,014
Number of preferred stock, shares converted		398
Series C Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		938
Number of preferred stock, shares converted		27,792
Series F Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	1
Number Of Votes Per Share | Votes	50,000,000
Preferred stock, voting rights	no
Rights related to distribution of assets	no
Consideration paid to preferred stock holders | $	$ 1,000
Series F Convertible Preferred Stock [Member] | Subscription Agreement [Member]
Class of Stock [Line Items]
Common stock, par value (in dollars per share) | $ / shares	$ 0.001
Consideration to purchaser in cash | $	$ 1,000
Issue and sale of share	1
Sale closed date	Mar. 03, 2023

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Stockholders' Equity - Warrants (Details) - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Series U Warrants [Member]
Class of Stock [Line Items]
Issue and sale of share	230,000
Warrants expected term	5 years
Representative Warrants [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	5,000
Common Stock [Member]
Class of Stock [Line Items]
Issue and sale of share		168,164
Outstanding Warrants [Member] | Series U Warrants [Member]
Class of Stock [Line Items]
Warrant exercise price (in dollars per share)	$ 34.10
Class of warrant outstanding	142,733
Number of warrants exercised	142,733
Common Class A [Member]
Class of Stock [Line Items]
Issue and sale of share	19,266
Common Class B [Member]
Class of Stock [Line Items]
Number of securities called by warrant or right	180,733

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Stockholders' Equity - Common stock (Details) - USD ($)						3 Months Ended		4 Months Ended		7 Months Ended	12 Months Ended	19 Months Ended
	Mar. 08, 2024	Sep. 09, 2022	Aug. 02, 2022	May 16, 2022	Jan. 14, 2022	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2022	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2024	Oct. 31, 2023	Aug. 18, 2023	Aug. 17, 2022	Jul. 14, 2022
Class of Stock [Line Items]
Sale of common stock, net	$ 2,500,000						$ 895,000
Common stock, shares authorized (in shares)						100,000,000				100,000,000	100,000,000	100,000,000
Proceeds from sale of common stock, net							$ 895,000
Remained authorized amount for repurchase						$ 0				$ 0		$ 0
Common Stock [Member]
Class of Stock [Line Items]
Issue and sale of share							168,164
Number of stock repurchased						179,866					78,559
Treasury stock						$ 400,000				$ 400,000	$ 100,000	$ 400,000
Common Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Authorized amount of repurchase of stock													$ 500,000
2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				57,500,000
2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]
Class of Stock [Line Items]
Maximum value of shares to be issued under agreement			$ 50,000,000
Issue and sale of share						0			266,666	150,000	410,500
Period exercisable from the date of issuance						36 months
Number of maximum common shares can be resale															633,333
Initial commitment shares			32,846													32,846
Initial commitment fee paid in cash			$ 100,000
Aggregate gross proceeds from sales of common stock			$ 25,000,000
Proceeds from sale of common stock, net									$ 3,200,000		$ 1,000,000
2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Minimum [Member]
Class of Stock [Line Items]
Percentage issuance of common stock				19.99%
2022 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Number of maximum common shares can be resale														1,500,000
Number of shares reserved for issuance and sale															600,486
2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]
Class of Stock [Line Items]
Issue and sale of share												527,166
September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Reimburse of fee and disbursements expenses		$ 50,000
September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Issue and sale of share								68,758			1,819,993
Proceeds from sale of common stock, net								$ 600,000			$ 4,300,000
September 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Proceeds from sale of common stock, net		$ 5,000,000
Percentage of commission on gross proceeds from sale of common stock		3.00%
January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member]
Class of Stock [Line Items]
Issue and sale of share											460,151
Proceeds from sale of common stock, net											$ 4,800,000
January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Remaining availability under financing facility					$ 0
January 2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Proceeds from sale of common stock, net					$ 5,000,000

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Stock-based Compensation - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares to be issued (in shares)	163,025
Stock option contractual term	10 years
Stock option vesting percentage	25.00%
Total unamortized compensation cost related to outstanding unvested stock options and restricted stock awards | $	$ 0.8
Weighted average period for recognition of cost	2 years 3 months 18 days
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	2 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period	4 years
2015 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	6,024
2020 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining and available for future issuances (in shares)	17,582
Common stock shares to be issued (in shares)	236,667

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Stock-based Compensation - Stock Option Activity (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Options [Roll Forward]
Balance as of December 31, 2023 (in shares)	140,109
Granted (in shares)	163,025
Cancelled/forfeited (in shares)	(1)
Balance as of March 31, 2024 (in shares)	303,133	140,109
Vested and expected to vest at March 31, 2024 (in shares)	278,083
Exercisable at March 31, 2024 (in shares)	84,908
Weighted Average Exercise Price [Roll Forward]
Balance as of December 31, 2023 (in dollars per share)	$ 37.48
Granted (in dollars per share)	2.03
Cancelled/forfeited (in dollars per share)	289,125
Balance as of March 31, 2024 (in dollars per share)	17.46	$ 37.48
Vested and expected to vest at March 31, 2024 (in dollars per share)	18.64
Exercisable at March 31, 2024 (in dollars per share)	$ 50.13
Weighted Average Remaining Contractual Life (years) [Roll Forward]
Balance as of March 31, 2024	8 years 11 months 8 days	8 years 25 days
Vested and expected to vest at March 31, 2024	8 years 10 months 13 days
Exercisable at March 31, 2024	7 years 4 months 13 days
Aggregated Intrinsic Value [Roll Forward]
Balance as of March 31, 2024	$ 7,600
Vested and expected to vest as of March 31, 2024	6,800
Exercisable at March 31, 2024	500
Exercisable at March 31, 2024	$ 6,800