Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2023

Summary of Common Stock Reserved for Future Issuance

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	March 31, 2023
Common stock warrants		13,760
Common stock options and restricted stock units		3,922,930
Shares available under the 2015 equity incentive plan		83,313
Shares available under the 2022 inducement plan		109,833
Shares available under the employee stock purchase plan		801,321
		4,931,157

Summary of Stock Option Activity

The following table summarizes our stock option activity under all equity incentive plans for the three months ended March 31, 2023:

	Number of Outstanding Stock Options			Weighted- Average Exercise Price
Outstanding as of December 31, 2022		2,956,170		$	7.45
Granted		938,485		$	2.20
Canceled/forfeited/expired		(71,052	)	$	4.37
Outstanding as of March 31, 2023		3,823,603		$	6.22

Schedule of Restricted Stock Units Activity

The following table summarizes our restricted stock unit activity under all equity incentive plans for the three months ended March 31, 2023:

	Number of Outstanding Restricted Stock Units			Weighted-Average Grant Date Fair Value
Balance as of December 31, 2022		121,438		$	5.09
Released		(22,111	)	$	5.39
Balance as of March 31, 2023		99,327		$	5.02

Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition and Restricted Stock Units

The allocation of stock-based compensation for all options and restricted stock units and stock issued pursuant to our employee stock purchase plan is as follows (in thousands):

	Three Months Ended March 31,
	2023		2022
Research and development	$	129	$	107
General and administrative		490		310
Total stock-based compensation expense	$	619	$	417

Employee Stock Option [Member]

Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

	March 31,
	2023			2022
Expected term (in years)	$	6.02		6.02 – 6.08
Risk-free interest rate		4.0	%	1.7% – 2.4%
Expected volatility		82.0	%	85.8% – 86.5%
Expected dividend yield		0.0	%		0.0	%