On May 5, 2021, holders of a majority of the outstanding common stock executed a written consent approving the Fourth Amended and Restated 2018 Equity Incentive Plan ("2018 Fourth Amended Plan"), which provides for an automatic annual increase in the number of shares of common stock reserved for issuance. As of June 30, 2022, 10,726,193 shares were available for issuance under the 2018 Fourth Amended Plan.

On November 3, 2021, the Board of Directors approved and adopted the Company’s 2021 Inducement Plan ("2021 Inducement Plan") to provide for the reservation of 6,500,000 shares of the Company’s common stock to be used exclusively for the grant of awards to individuals not previously an employee or non-employee director of the Company. As of June 30, 2022, 2,594,880 shares were available for grant under the 2021 Inducement Plan.

The following table summarizes stock option activity, which includes Performance Awards, under the 2012 Plan, the 2015 Plan, the 2018 Fourth Amended Plan and the 2021 Inducement Plan during the six months ended June 30, 2022:


	Stock Options Outstanding			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2021		8,640,951		$	4.74
Options granted		8,828,368		$	0.84
Options exercised		—			—
Options forfeited/cancelled		(1,678,488	)	$	3.48
Options expired		(692,913	)	$	6.23
Balance at June 30, 2022		15,097,918		$	2.53		8.64	$	48
Vested and expected to vest at June 30, 2022		15,097,918		$	2.53		8.60	$	48
Vested and exercisable at June 30, 2022		3,113,396		$	5.72		4.74	$	—

The aggregate intrinsic value in the above table is calculated as the difference between the closing price of the Company's common stock at June 30, 2022 of $0.70 per share and the exercise price of stock options that had strike prices below the closing price. There were no stock options exercised during the six months ended June 30, 2022.

The Company uses the Black-Scholes option pricing model to estimate the fair value of each option grant on the date of grant or any other measurement date. The following table sets forth the assumptions used to determine the fair value of stock options granted during the six months ended June 30, 2022:

The weighted-average grant date fair value of options granted during the six months ended June 30, 2022 and 2021 was $0.77 per option and $2.13 per option, respectively.

The following table summarizes RSU activity for the six months ended June 30, 2022:


	Number of Shares			Weighted- Average Grant Date Fair Value
Balance at December 31, 2021		3,879,110		$	3.80
Granted		5,277,244		$	0.84
Vested		(604,689	)	$	4.04
Forfeited/cancelled		(1,048,215	)	$	3.49
Balance at June 30, 2022		7,503,450		$	1.74

In June 2020, the Company’s board of directors adopted the ESPP with 510,000 shares of common stock reserved for future issuance under the ESPP. The ESPP also provides for automatic annual increases in the number of shares of common stock reserved for issuance. As of June 30, 2022 there were 1,225,918 total shares of common stock reserved for future issuance.

The following table presents total stock-based compensation expense included in each functional line item in the accompanying condensed consolidated statements of operations (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	26	$	1,080	$	363	$	1,675
Selling, general and administrative		1,420		2,310		3,136		3,950
Discontinued operations		—		1,080		—		1,475
Total stock-based compensation expense	$	1,446	$	4,470	$	3,499	$	7,100

At June 30, 2022 there was $13.0 million of compensation cost related to unvested stock options expected to be recognized over a remaining weighted average vesting period of 3.26 and $11.5 million of compensation cost related to unvested RSUs expected to be recognized over a remaining weighted average vesting period of 3.46 years.