For stock options requiring an assessment of value during the six months ended June 30, 2025 and 2024, the fair value of each stock option award was estimated using the Black-Scholes option-pricing model utilizing the following assumptions:


		June 30, 2025
Risk-free interest rate		4.05% - 4.46%
Expected dividend yield		0%
Expected volatility		86.46% - 88.15%
Expected life		5.50 to 6.25 years

		June 30, 2024
Risk-free interest rate		3.83% - 4.43%
Expected dividend yield		0%
Expected volatility		50.1% - 109.86%
Expected life		5.50 to 8.91 years

A summary of stock option activity for the six months ended June 30, 2025 is as follows:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in Years)
Stock options outstanding at December 31, 2024		10,471,724		$	5.61		7.27
Granted		1,938,100			0.99		—
Exercised		—			—		—
Cancelled		(1,527,640	)		5.33		—
Stock options outstanding at June 30, 2025		10,882,184			4.83		7.06
Stock options exercisable at June 30, 2025		6,315,208		$	7.12		5.67

The aggregate intrinsic value of exercisable but unexercised in-the-money stock options at June 30, 2025 was less than $0.1 million based on a weighted average exercise price of $7.12 per share. The aggregate intrinsic value of options is calculated as the difference of the market close price of $0.68 on June 30, 2025, and the weighted average exercise price of $7.12, with a weighted average remaining contractual term of 5.67 years.

Stock-based compensation for the three and six months ended June 30, 2025 and 2024 was included in the Company’s condensed consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended June 30,				Six Months ended June 30,
(in thousands)	2025		2024		2025		2024
General and administrative	$	580	$	859	$	1,275	$	1,814
Research and development		683		896		1,326		1,887
Total stock-based compensation	$	1,263	$	1,755	$	2,601	$	3,701

As of June 30, 2025, total unrecognized stock-based compensation expense was $4.2 million, which is expected to be recognized as an operating expense in the Company’s condensed consolidated statements of operations and comprehensive loss over the weighted average remaining period of 2.24 years.

As of June 30, 2024, total unrecognized stock-based compensation expense was $9.2 million, which is expected to be recognized as an operating expense in the Company’s condensed consolidated statements of operations and comprehensive loss over the weighted average remaining period of 2.52 years.

During the three and six months ended June 30, 2025, the Company granted stock options to purchase 48,800 shares of common stock with a weighted average grant date fair value of $0.62 per share and stock options to purchase 1,938,100 shares of common stock with a weighted average grant date fair value of $0.99 per share, respectively.

During the three and six months ended June 30, 2024, the Company granted stock options to purchase 593,800 shares of common stock with a weighted average grant date fair value of $1.65 per share and stock options to purchase 2,463,300 shares of common stock with a weighted average grant date fair value of $1.93 per share, respectively.