The Company approved the 2013 Equity Incentive Plan in October 2013, which was amended in June 2016 and June 2018 (the Amended 2013 Plan). The Amended 2013 Plan provided for the granting of stock options, restricted stock units (RSU), stock appreciation rights, and stock units to certain employees, members of the board of directors and consultants of the Company.

In May 2023, the Company's Board of Directors approved the 2023 Equity Incentive Plan (the 2023 Equity Plan) to replace the Amended 2013 Plan. On June 30, 2023, the Company's stockholders approved the 2023 Equity Plan at the Company's 2023 annual meeting of stockholders. Pursuant to the 2023 Equity Plan, the Company will not make any further grants under the Amended 2013 Plan following June 30, 2023, though awards previously granted under the Amended 2013 Plan will remain outstanding. The 2023 Equity Plan is effective for a period of ten years after June 30, 2023, and a total of 5,450,000 shares of the Company’s common stock, in addition to shares of the Company’s common stock that are subject to awards granted under the Amended 2013 Plan that are outstanding as of such date and that are subsequently forfeited, cancelled, or expire before being exercised or settled in full, are authorized for issuance under the 2023 Equity Plan. As of September 30, 2024, there were 3,542,805 shares of common stock available for grant under the 2023 Equity Plan.

In 2022, the Company granted cash awards under the Management Cash Incentive Plan, as amended (the Management Cash Incentive Plan). The Management Cash Incentive Plan, which was adopted in 2016, provides participants with the opportunity to earn cash incentive awards for the achievement of goals relating to the performance of the Company. The cash awards, which are equal in value to the amount by which the then value of the Company’s common stock on the Nasdaq Capital Market (Nasdaq) exceeds the base values, vest in four annual installments from the date of grant based on continued service and entitle employees to receive a cash payment on the earlier of (i) four years from the date of grant, or (ii) a change of control. As of September 30, 2024, $0.3 million was accrued as compensation expense for vested cash awards. There was no unrecognized expense as of September 30, 2024.

In 2022, the Company granted performance cash settled bonus awards (CSBUs) under the Management Cash Incentive Plan. As the performance criteria had been met, the awards, which are equal in value to the closing price per share of the Company's common stock on Nasdaq on the payment date, will vest in four annual installments from the date of grant based on continued service, and entitle employees to receive cash payments for each vested CSBU, on the earlier of (i) four years from the date of grant or (ii) a change of control. As of September 30, 2024, $3.0 million was accrued as compensation expense for CSBUs as the Performance Criteria was met in February 2023. There was no unrecognized expense as of September 30, 2024.

The Company recognizes stock-based compensation expense over the requisite service period. The Company's share-based awards are accounted for as equity instruments, except for cash awards and CSBUs, which are accounted for as liabilities. The amounts included in the consolidated statements of operations relating to stock-based compensation associated with the two equity incentive plans, cash awards, and CSBUs are as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development expenses	$	1,711,231	$	403,904	$	3,609,590	$	3,457,642
General and administrative expenses		1,514,563		385,313	$	3,100,572	$	3,095,470
Total stock-based compensation expense	$	3,225,794	$	789,217	$	6,710,162	$	6,553,112

The table below summarizes activity relating to stock options under the incentive plans for the nine months ended September 30, 2024:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Contractual Term (Years)		Aggregate Intrinsic Value(a)
Outstanding at December 31, 2023		5,868,816		$	6.40	6.44		$	3,996
Granted		2,376,328		$	3.67				—
Expired		(179,897	)	$	7.90				—
Forfeitures		(31,506	)	$	4.49				—
Outstanding at September 30, 2024		8,033,741		$	5.57		6.94	$	7,387,843
Exercisable at September 30, 2024		5,116,768		$	6.23		5.76	$	3,509,500

(a)

The aggregate intrinsic value in the above table was calculated on the positive difference, if any, between the closing price per share of the Company’s common stock on September 30, 2024 of $5.39 and the per share exercise price of the underlying options.

As of September 30, 2024, unamortized stock-based compensation for stock options outstanding was $8.9 million and is expected to be recognized over a weighted average period of 2.5 years. Total unrecognized compensation cost will be adjusted for future forfeitures, if necessary.

The table below summarizes activity relating to restricted stock units (RSUs) for the nine months ended September 30, 2024:


	Number of Shares			Weighted-Average Grant Date Fair Value
Outstanding at December 31, 2023		944,497		$	5.30
Settled in common stock		(340,488	)		5.10
Outstanding at September 30, 2024		604,009		$	5.41

There were no RSUs granted during the nine months ended September 30, 2024. The total grant date fair value of RSUs vested was $1.7 million for the nine months ended September 30, 2024. As of September 30, 2024, the outstanding RSUs had unamortized stock-based compensation of $2.5 million with a weighted-average remaining recognition period of 1.8 years and an aggregate intrinsic value of $3.3 million.

At September 30, 2024, the Company had 2,921,164 shares available for issuance under the 2016 Employee Stock Purchase Plan (2016 ESPP). A summary of the weighted-average grant-date fair value and total stock-based compensation expense recognized related to the 2016 ESPP are as follows:


	Nine Months Ended September 30,
	2024		2023
Weighted-average grant-date fair value per share	$	1.32	$	3.09
Total stock-based compensation expense	$	14,199	$	38,931