Stock-Based Compensation Expense

6 Months Ended

Jun. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation Expense

5. Stock-Based Compensation Expense

A summary of the restricted stock unit activity under the Plans for the six months ended June 30, 2023 was as follows:

	Shares			Weighted- Average Grant Date Fair Value
Restricted stock units outstanding as of December 31, 2022		28,212		$	4.78
Granted		270,716		$	2.85
Vested		(7,041	)	$	4.78
Forfeited		(48,184	)	$	2.93
Restricted stock units outstanding as of June 30, 2023		243,703		$	3.00

A summary of the stock option activity under the Plans for the six months ended June 30, 2023 was as follows:

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		4,311,333		$	7.07		8.2	$	378
Granted		1,976,180			2.85
Exercised		(57,377	)		1.75
Cancelled		(358,323	)		8.13
Outstanding at June 30, 2023		5,871,813		$	5.63		8.5	$	3,090

The fair value of each stock option granted to employees, directors and non-employees was estimated on the date of grant using the Black-Scholes option-pricing model in the case of the options granted to executive officers, with the following weighted-average assumptions for the three and six months ended June 30, 2023 and 2022:

	Three Months Ended June 30,						Six Months Ended June 30,
	2023			2022			2023			2022
Risk-free interest rate		3.8	%		3.2	%		3.7	%		2.5	%
Expected dividend yield		—	%		—	%		—	%		—	%
Expected term (in years)		6.1			2.1			6.0			3.3
Expected volatility		82.0	%		80.6	%		82.9	%		80.7	%

The weighted-average fair value of options granted to employees, directors and non-employees during the three months ended June 30, 2023 and 2022 was $2.24 and $3.73, respectively, and $2.07 and $3.24 for the six months ended June 30, 2023 and 2022.

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	287	$	209	$	571	$	436
General and administrative		1,067		898		2,393		1,515
Total	$	1,354	$	1,107	$	2,964	$	1,951

Unrecognized share-based compensation related to stock-based options amounted to $9.9 million at June 30, 2023 and is expected to be recognized over a weighted average period of approximately 2.46 years. Unrecognized share-based compensation related to restricted stock units amounted to $0.7 million at June 30, 2023 and is expected to be recognized over a weighted average period of approximately 3.48 years.

At June 30, 2023, there were 1,182,286 shares available for grant under the Company’s 2020 Incentive Award Plan and 170,000 shares available for grant under the Company’s 2022 Inducement Award Plan.