Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2023

Stock-Based Compensation [Abstract]

Components of Stock-Based Compensation Expense

Following is the stock-based compensation expense related to common stock options, restricted common stock, common stock warrants and deferred stock units:

	Three Months Ended March 31,
	2023		2022
Research and development	$	270	$	225
General and administrative		392		633
Total stock-based compensation expense	$	662	$	858

Stock Option Activity

The following table summarizes the stock option activity in the Company’s equity incentive plans, including non-plan grants to Company executives, from December 31, 2022 through March 31, 2023:

	Shares			Weighted Average Exercise Price
Outstanding, December 31, 2022		5,745,561		$	2.90
Granted		800,000			1.11
Exercised		—			—
Options forfeited/cancelled		(18,803	)		3.59
Outstanding, March 31, 2023		6,526,758		$	2.67

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The fair value of all other options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

	Three Months Ended March 31,			Three Months Ended March 31,
	2023			2022
Risk-free interest rate		3.76	%		1.23	%
Expected life of the options	5.5 years			5.5 years
Expected volatility of the underlying stock		86	%		95	%
Expected dividend rate		0	%		0	%