The Company recorded total stock-based compensation expense related to stock options, restricted stock units and it's employee stock purchase plan awarded under the Company's 2010 Stock Incentive Plan, as amended and restated effective as of October 12, 20217 (the 2010 Plan), 2017 Employee Stock Purchase Plan (2017 Plan) and grants made pursuant to the Nasdaq inducement grant exception in accordance with Nasdaq Listing Rule 5635(c)(4) (the "Nasdaq Inducement Grant Exception") in the following expense categories in the accompanying consolidated statements of operations as follows:


	Three Months Ended June 30,			Six Months Ended June 30,
		2024		2023		2024		2023
Cost of product sales		$	33	$	12	$	50	$	18
Research and development		5		126		62		281
General and administrative		2,697		1,365		4,079		2,726
		$	2,735	$	1,503	$	4,191	$	3,025

The Company issues stock-based awards pursuant to the 2010 Plan and the Nasdaq Inducement Grant Exception. The Company has issued service-based, performance-based, and market-based stock options that generally have a contractual life of up to 10 years and may be exercisable in cash or as otherwise determined by the Company's board of directors or committee thereof. Vesting generally occurs over a period of not greater than four years. Performance-based options may vest upon the achievement of certain milestones. As of June 30, 2024, all of the performance conditions related to performance-based stock options issued by the Company had been achieved. Market-based options may vest upon the achievement of certain market-based objectives relating to the trading price of the Company's common stock.

The following table summarizes the activity related to stock option grants to employees and non-employees for the six months ended June 30, 2024:


	Shares	Weighted average exercise price per share		Weighted average remaining contractual life
Outstanding at December 31, 2023	8,527,626	$	5.03	6.55
Granted	1,685,601	1.56
Exercised	—	—
Expired	(846,640)	9.73
Forfeited	(68,276)	1.90
Outstanding at June 30, 2024	9,298,311	$	4.00	7.34
Exercisable at June 30, 2024	4,926,384	$	3.97	6.07

During the six months ended June 30, 2024, service-based stock options to purchase 1,685,601 shares of common stock were granted to employees and generally vest over four years. The stock options had an estimated weighted

average grant date fair value of $1.06. The grant date fair value of each service-based and performance-based option grant was estimated at the time of grant using the Black-Scholes option-pricing model. The grant date fair value of each market-based stock option grant was estimated at the time of grant using a Monte Carlo simulation.

The aggregate intrinsic value of stock options outstanding and stock options exercisable, other than market-based stock options, as of June 30, 2024 was $0 and $0, respectively. At June 30, 2024, the unrecognized compensation cost related to unvested stock options, other than market-based stock options, expected to vest was $4,209. This unrecognized compensation will be recognized over an estimated weighted-average amortization period of 2.6 years.

Included in the table above are 569,345 market-based options outstanding granted in 2022. These options generally become eligible to vest over four years, subject to the achievement of certain market-based objectives relating to the trading price of the common stock. Stock-based compensation for these awards is recognized over the derived service period of approximately 2 years. The grant date fair value of each stock option grant, as well as the derived service period for these awards, was estimated at the time of grant using a Monte Carlo simulation. During the six months ended June 30, 2024, no market-based options vested upon the achievement of certain market-based objectives relating to the trading price of the Company's common stock.

Included in the table above are 711,500 options outstanding granted outside the 2010 Plan. The grants were made pursuant to the Nasdaq Inducement Grant Exception.


	Six Months Ended June 30,
	2024		2023
Risk free interest rate	4.26	%	3.97	%
Expected term (in years)	5.9		6.08
Expected volatility	75.02	%	75.31	%
Annual dividend yield	0.00	%	0.00	%

The Company has issued service-based and performance-based restricted stock units (RSUs). Vesting generally occurs over a period not greater than four years. Vesting of the performance-based RSUs is subject to the achievement of certain milestones in connection with the Company's development programs.

The following table summarizes the activity related to RSUs granted to employees for the six months ended June 30, 2024:


			Shares
Balance at December 31, 2023			1,897,421
Granted			3,574,200
Vested and settled			(638,204)
Expired/forfeited/canceled			(95,542)
Balance at June 30, 2024			4,737,875
Expected to vest at June 30, 2024			4,737,875

During the six months ended June 30, 2024, the Company granted 3,574,200 RSUs at a weighted-average grant date fair value of $1.82, all of which were service-based RSUs, provided, that, in the event certain financial metrics are achieved any then unvested RSUs shall become fully-vested subject to the recipients continued service through such date. No performance-based RSUs were granted in the six months ended June 30, 2024. As of December 31, 2023, the milestone associated with the previously granted performance based-RSUs was achieved. At June 30, 2024, the unrecognized compensation cost related to unvested service-based RSUs expected to vest was $6,612, to be recognized over an estimated weighted-average amortization period of 3.33 years.

Under the 2017 Plan, shares of Common Stock may be purchased by eligible employees who elect to participate in the 2017 Plan at 85% of the lower of the fair market value of Common Stock on the first or last day of designated offering periods. During the six months ended June 30, 2024, the Company issued 160,711 shares of Common Stock to employees.


	Six Months Ended June 30,
	2024		2023
Risk free interest rate	0.05	%	0.05	%
Expected term (in years)	0.5		0.5
Expected volatility	65.06	%	71.43	%
Annual dividend yield	—	%	—	%