
	Outstanding Options
	Number of Options	Weighted-Average Exercise Price
Outstanding at December 31, 2024	14,263,242	$	2.93
Granted	1,104,000	$	0.78
Exercised	(26,500)	$	0.76
Cancelled	(1,442,640)	$	8.05
Outstanding at June 30, 2025	13,898,102	$	2.23

The following table summarizes share-based compensation expense related to share-based payment awards granted pursuant to all of our equity compensation arrangements (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	253	$	954	$	584	$	1,561
General and administrative	698		1,035		1,309		1,744
Total share-based compensation expense	$	951	$	1,989	$	1,893	$	3,305

As of June 30, 2025, there was $9.0 million of total unrecognized compensation cost related to non-vested, share-based payment awards granted under all of our equity compensation plans. Total unrecognized compensation cost will be adjusted for forfeitures. We expect to recognize this compensation cost over a weighted-average period of 3.0 years.

On January 1, 2025, we began using the Black-Scholes option pricing model to estimate the fair value of each option grant on the grant date, in order to better align with our peers. Prior to 2025, we estimated the fair value of each option grant on the grant date using the Binomial option pricing model. In connection with our change in method of estimating the fair value per share, we also began estimating the expected term of each option grant based on the simplified method described in SEC Staff Accounting Bulletin No. 107, Share-Based Payment. We believe the simplified method is appropriate, as all of our stock option grants would be considered “plain-vanilla” and we have a limited history of option exercise activity.


	For the Six Months Ended June 30,
	2025		2024
Risk-free interest rate	4.1	%	4.4	%
Dividend yield	0.0	%	0.0	%
Volatility	105.7	%	103.7	%
Expected life (years)	6		10
Early exercise multiple (years)	—		2.2 - 2.8

We estimate the fair value of each purchase right granted under our Employee Stock Purchase Plan at the beginning of each new offering period using the Black-Scholes option pricing model. The following are the weighted-average assumptions for purchase rights under our ESPP. There was no new offering period during the six months ended June 30, 2024.