STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Jun. 30, 2024

STOCK-BASED COMPENSATION

Stock-Based Compensation Expense

Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Research and development	$	238	$	826	$	614	$	2,059
General and administrative		484		958		1,194		2,035
Total stock-based compensation	$	722	$	1,784	$	1,808	$	4,094

Weighted-Average Fair Value Valuation Assumptions

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Three Months Ended June 30,						Six Months Ended June 30,
	2024			2023			2024			2023
Employee Stock Options:
Risk-free interest rate		4.56	%		3.49	%		4.07	%		3.93	%
Expected term (in years)		6.08			6.08			6.08			6.08
Dividend yield		—			—			—			—
Volatility		79.55	%		78.45	%		77.69	%		77.19	%
Weighted-average fair value of stock options granted	$	1.04		$	0.27		$	2.17		$	0.33

Summary of Stock Option Activity Under Equity Incentive Plan

The following table summarizes stock option activity under the Company’s equity incentive plans:

	Outstanding Options Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value (in millions):
Balances, December 31, 2022	562,878	$	115.50	7.09	$	—
Granted	236,651	$	7.25
Exercised	(192)	$	7.20
Cancelled	(285,273)	$	88.62
Balances, December 31, 2023	514,064	$	80.62	7.03	$	—
Granted	129,864	$	3.10
Exercised	—	$	—
Cancelled	(67,840)	$	24.89
Balances, June 30, 2024	576,088	$	69.71	—	$	—
Vested and expected to vest, June 30, 2024	576,088	$	69.71	6.77	$	—
Exercisable at June 30, 2024	343,922	$	106.30	5.24	$	—