On December 29, 2017, the 2017 Equity Incentive Plan was approved by the stockholders of the Company, which currently allows for issuance of up to approximately 22,000 shares of common stock underlying stock options granted prior to September 10, 2019. The 2017 Equity Incentive Plan was terminated upon the approval of the 2019 Incentive Plan subject to outstanding stock options granted under the 2017 Equity Incentive Plan that remain exercisable through maturity for the Company's employees and directors.

On September 10, 2019, the 2019 Equity Incentive Plan ("2019 Equity Plan") was approved by the stockholders of the Company. On June 20, 2023, an amendment to the 2019 Equity Plan was approved by the stockholders of the Company, which amended and restated the 2019 Equity Plan (as amended and restated, the "2023 Amended and Restated Equity Incentive Plan") to increase the number of shares of common stock authorized for issuance under the 2019 Equity Plan by 3,000,000 shares.

The 2023 Amended and Restated Equity Incentive Plan currently allows for issuance of up to approximately 6,036,000 shares of common stock in connection with the grant of stock-based awards, including stock options, restricted stock, restricted stock units, stock appreciation rights and other types of awards as deemed appropriate.

The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations for the three and nine months ended September 30, 2024 and 2023, respectively (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
Research and development	$	87	$	93	$	260	$	281
General and administrative	294		450		931		1,316
Total stock-based compensation	$	381	$	543	$	1,191	$	1,597


	Total Number of Shares (In Thousands)	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (In Years)	Aggregate Intrinsic Value (In Thousands)
Outstanding at December 31, 2023	1,607	$	5.92		$	—
Granted	671	0.53

Canceled	(325)	3.53
Outstanding at September 30, 2024	1,953	$	4.47	7.91	$	425
Options exercisable at September 30, 2024	950	$	7.17	7.00	$	—

The aggregate intrinsic values of outstanding and exercisable stock options at September 30, 2024 were calculated based on the closing price of the Company’s common stock as reported on the Nasdaq Capital Market on September 30, 2024 of $1.25 per share. The aggregate intrinsic value equals the positive difference between the closing fair market value of the Company’s common stock and the exercise price of the underlying stock options.

The Company uses the Black-Scholes option-pricing model to determine the fair value of all its stock options granted. The weighted average assumptions used during the three and nine months ended September 30, 2024 and 2023, respectively, were as follows:


	Three Months Ended September 30,		Nine Months Ended September 30,
	2024	2023	2024		2023
Risk free interest rate	n/a	n/a	4.01	%	3.78	%
Volatility	n/a	n/a	130.41	%	127.77	%
Expected lives (years)	n/a	n/a	6.19		6.20
Expected dividend yield	n/a	n/a	—	%	—	%

There were no options granted during each of the three months ended September 30, 2024 and 2023. The weighted-average grant date fair value of options granted during the nine months ended September 30, 2024 and 2023 was $0.48 and $2.88, respectively.

The Company’s expected common stock price volatility assumption is based upon the Company's own implied volatility in combination with the implied volatility of a basket of comparable companies. The expected life assumptions for employee grants were based upon the simplified method, which averages the contractual term of the Company’s options of ten years with the average vesting term of four years for an average of approximately six years. The expected life assumptions for non-employees were based upon the contractual term of the option. The dividend yield assumption is zero because the Company has never paid cash dividends and presently has no intention to do so. The risk-free interest rate used for each grant was also based upon prevailing short-term interest rates. The Company accounts for forfeitures as they occur.

As of September 30, 2024, there was $1.6 million of unrecognized compensation cost related to outstanding stock options that is expected to be recognized as a component of the Company’s operating expenses over a weighted-average period of 2.0 years.


	Shares (In Thousands)	Weighted Average Grant Date Fair Value
Unvested at December 31, 2023	338	$	2.99
Granted	429	$	0.52
Canceled	(123)	$	1.84
Unvested at September 30, 2024	644	$	1.57

As of September 30, 2024, there was $0.7 million of unrecognized compensation cost related to outstanding RSUs that is expected to be recognized as a component of the Company's operating expenses over a weighted-average period of 2.0 years. No RSUs vested during the nine months ended September 30, 2024.

On April 22, 2021, the Board of Directors adopted the 2021 Employee Stock Purchase Plan ("2021 ESPP") which was approved by the Company's stockholders on June 8, 2021 and authorized the issuance of up to 300,000 shares of common stock pursuant to the 2021 ESPP. The 2021 ESPP allows employees to contribute up to 20% of their cash earnings, subject to a maximum of $25,000 per year under Internal Revenue Service rules, to be used to purchase shares of the Company’s common stock on semi-annual purchase dates. The 2021 ESPP allows eligible employees to purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value of the common stock at the beginning or end of each six-month offering period during the term of the 2021 ESPP.

During the nine months ended September 30, 2024, 103,853 shares of common stock were purchased by employees under the 2021 ESPP for proceeds of approximately $0.1 million. There are currently 79,604 shares of common stock reserved for issuance under the 2021 ESPP as of September 30, 2024.