Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option Activity Under Company's Equity Incentive Plans

The following table summarizes stock option activity under the Company’s 2018 Plan and related information:

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (thousands)
Outstanding — December 31, 2021		2,603,630		$	7.70		7.46	$	—
Options granted ⁽¹⁾		10,270,911			1.34
Options forfeited and cancelled ⁽¹⁾		(4,148,455	)		4.96
Options expired		(47,319	)		13.27
Outstanding — December 31, 2022		8,678,767		$	1.42		7.47	$	1,051
Exercisable — December 31, 2022		4,317,076		$	2.38		5.94	$	—

(1)

Includes options that were cancelled and re-granted as part of the option modification from the special cash dividend, as further discussed above.

Summary of Weighted Average Valuation Assumptions Used to Estimate Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2022			2021
Employee Stock Options:
Expected term (in years)		6.02			6.00
Risk-free interest rate		3.00	%		0.84	%
Dividend yield		—			—
Volatility		92.58	%		93.25	%

Summary of Stock-Based Compensation Recognized

Total stock-based compensation recognized was as follows (in thousands):

	Year Ended December 31,
	2022		2021
Research and development	$	330	$	1,202
General and administrative⁽¹⁾		1,012		2,203
Total stock-based compensation	$	1,342	$	3,405

(1)

Included in general and administrative stock-based compensation for the years ended December 31, 2022 and 2021 is $30,000 and $0.3 million in expense related to 32,684 shares and 56,912 shares of common stock, respectively, issued to certain board members in lieu of their cash compensation.