Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2022

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	June 30, 2022
Common stock warrants		13,760
Common stock options and restricted stock units		3,048,636
Shares available under the 2015 equity incentive plan		961,351
Shares available under the 2022 inducement plan		128,200
Shares available under the employee stock purchase plan		819,975
		4,971,922

Summary of Stock Option Activity

The following table summarizes our stock option activity under all equity incentive plans for the six months ended June 30, 2022:

	Number of Outstanding Stock Options			Weighted- Average Exercise Price
Outstanding as of December 31, 2021		1,412,550		$	12.01
Granted		1,528,444		$	3.44
Exercises		(259	)	$	3.77
Canceled/forfeited/expired		(13,537	)	$	18.17
Outstanding as of June 30, 2022		2,927,198		$	7.51

Schedule of Restricted Stock Unit Activity

The following table summarizes our restricted stock unit activity under all equity incentive plans for the six months ended June 30, 2022:

	Number of Outstanding Restricted Stock Units			Weighted-Average Grant Date Fair Value
Balance as of December 31, 2021		7,500		$	4.08
Granted		116,438		$	5.13
Released		(2,500	)	$	4.13
Balance as of June 30, 2022		121,438		$	5.09

Schedule of Allocation of Stock-Based Compensation for All Options and Restricted Stock Units and Stock Issued Pursuant to Our Employee Stock Purchase Plan

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 June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	131	$	64	$	238	$	128
General and administrative		386		334		696		630
Total stock-based compensation expense	$	517	$	398	$	934	$	758

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:

	Three Months Ended June 30,						Six Months Ended June 30,
	2022			2021			2022			2021
Expected term (in years)	6.02 – 6.06			5.50 – 6.08			6.02 – 6.08			5.50 – 6.08
Risk-free interest rate	2.8%-3.0%			1.07% – 1.09%			1.7% – 3.0%			0.6% – 1.09%
Expected volatility	84.7% – 84.9%			87.4% – 88.29%			84.7% – 86.5%			88.3% – 104.8%
Expected dividend yield		0.0	%		0.0	%		0.0	%		0.0	%