In March 2020, the Company's Board of Directors and stockholders approved the 2020 Stock Option and Grant Plan (“2020 Plan”). Holders of stock options under the 2020 Plan shall be entitled to exercise the vested portion of the stock option during the term of the grant. If a qualified exit, as defined in the 2020 Plan, occurs before the stock option vests, then all of the holders' unvested options shall vest immediately.

In October 2020, the Company's Board of Directors and stockholders approved the 2020 Equity Incentive Plan (“2020 Equity Plan”). Following the adoption of the 2020 Equity Plan, no further options are available to be issued under the 2020 Plan. Stock-based awards granted under the 2020 Equity Plan generally vest over a four-year period and expire ten years from the grant date. Shares available for grant under the 2020 Equity Plan will cumulatively increase by 5 percent of the number of shares of common stock issued and outstanding on January 1st each year until 2030. At June 30, 2024, the Company had 3,024,020 shares available for future grant under the 2020 Equity Plan.

The following table sets forth the activity for the Company’s stock options during the six months ended June 30, 2024:


	Number of Options			Weighted- average exercise price per share		Weighted- average remaining contractual term (in years)		Aggregate intrinsic value
Outstanding at December 31, 2023		6,886,889		$	4.58		6.7	$	—
Granted		108,000			0.49		—		—
Cancelled		(1,439,703	)		4.22		—		—
Outstanding at June 30, 2024		5,555,186		$	4.59		6.7	$	—
Vested and expected to vest at June 30, 2024		5,270,540		$	4.55		6.7	$	—
Vested and exercisable at June 30, 2024		4,420,549		$	5.05		6.3	$	—

The weighted-average grant date fair value of all stock-based awards granted for the six months ended June 30, 2024 was $0.38 per share. The intrinsic value at June 30, 2024 and December 31, 2023 was based on the closing price of the Company’s common stock on these dates of $0.47 and $0.72 per share, respectively.

In November 2022, the Company's Board of Directors approved the 2022 Inducement Plan (the “Inducement Plan”), which allows for the grant of equity awards to be made to a new employee where the equity award is a material inducement to an employee entering into employment with the Company. The Inducement Plan was adopted by the Company's Board of Directors without stockholder approval pursuant to Nasdaq Listing Rule 5635(c)(4). A total of 250,000 shares of the Company's common stock have been reserved for issuance under the Inducement Plan. As of June 30, 2024, no shares have been issued under the Inducement Plan.

In January 2024, the Company granted 855,000 restricted stock units, or RSUs, to its employees under the 2020 Equity Plan. The weighted average grant date fair value of the time-based RSUs was $0.71 for the six months ended June 30, 2024.The RSUs vest 33% after one-year from the grant date and 17% every six-months thereafter. For the three and six months ended June 30, 2024, the Company recognized $47,000 and $94,000 expense related to the RSUs, respectively.

The following table sets forth the activity for the Company’s RSUs during the six months ended June 30, 2024:


	Restricted Stock Units			Weighted- average grant date fair value
Total nonvested units at December 31, 2023		—		$	—
Granted		855,000			0.71
Vested		(17,499	)		0.71
Cancelled		(132,501	)		0.71
Total nonvested units at June 30, 2024		705,000		$	0.71

The grant date fair value of stock-based awards vested during the six months ended June 30, 2024 and 2023 was $2.2 million and $3.5 million, respectively. Total unrecognized compensation expense related to unvested options granted under the Company’s stock-based compensation plan was $2.6 million at June 30, 2024, which is expected to be recognized over a weighted average period of 1.5 years. The Company recorded stock-based compensation expense related to the issuance of stock as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
Research and development	$	188	$	686	$	817	$	1,370
General and administrative		703		753		1,433		1,503
Total stock-based compensation	$	891	$	1,439	$	2,250	$	2,873

The Company uses a Black-Scholes option pricing model to determine fair value of its stock options. The Black-Scholes option pricing model includes various assumptions, including the fair value of common shares, expected life of stock options, the expected volatility based on the historical volatility of a publicly traded set of peer companies and the expected risk-free interest rate based on the implied yield on a U.S. Treasury security.

The fair values of the options granted were estimated using the following assumptions:


	Six Months Ended
	June 30,
	2024			2023
Risk-free interest rate		4.2	%		3.8	%
Expected term (in years)		5.3			6.0
Expected volatility		99.3	%		91.0	%
Expected dividend yield		—			—