Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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 June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
	in thousands
Research and development	$	134	$	154	$	403	$	379
General and administrative		382		493		775		1,126
Total stock-based compensation expense	$	516	$	647	$	1,178	$	1,505

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 June 30, 2023:

	Shares			Weighted Average Exercise Price
Outstanding, December 31, 2022		5,745,561		$	2.90
Granted		800,000			1.11
Exercised		—			—
Options forfeited/cancelled		(258,804	)		2.45
Outstanding, June 30, 2023		6,286,757		$	2.69

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:

	Six Months Ended June 30,			Six Months Ended June 30,
	2023			2022
Risk-free interest rate		3.76	%		1.56	%
Expected life of the options	5.5 years			5.6 years
Expected volatility of the underlying stock		86	%		94	%
Expected dividend rate		0	%		0	%