Stock Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2022

Summary of Stock-based Compensation Expense

Stock-based compensation expense included in the Company’s statements of operations and comprehensive loss is as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	135	$	303	$	305	$	550
General and administrative		425		657		872		1,277
Total	$	560	$	960	$	1,177	$	1,827

Summary of Stock Option Activity

A summary of the stock option activity under the 2011, 2017 and 2021 Plans during the six months ended June 30, 2022 is as follows:

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2021		6,765,837		$	2.81		7.6	$	3
Granted		—			—
Exercised		—			—
Forfeited		(1,316,712	)		2.54
Expired		(13,176	)		0.42
Outstanding at June 30, 2022		5,435,949			2.88		7.0	$	—
Exercisable at June 30, 2022		3,417,270		$	3.31		6.2	$	—

Restricted Stock Units (RSUs)

Summary of Nonvested RSUs

	Shares			Weighted-Average Grant Date Fair Value
Nonvested at December 31, 2021		—		$	—
Granted		2,998,500			0.40
Vested		—			—
Forfeited		(905,000	)		0.40
Nonvested at June 30, 2022		2,093,500		$	0.40

Employees and Directors

Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Estimate Fair Value of Stock Options

The fair value of each stock option granted to employees and directors during the three and six months ended June 30, 2021 was estimated on the date of grant using the Black-Scholes option-pricing model, with the following range of assumptions:

	Three Months Ended June 30, 2021	Six Months Ended June 30, 2021
Risk-free interest rate	0.9%-1.4%	0.4%-1.4%
Expected dividend yield	—%	—%
Expected term (in years)	5.4-7.0	5.0-7.0
Expected volatility	93%-94%	93%-94%