Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

Share-based Payment Arrangement [Abstract]

Summary of Stock Options Activity under Plans

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	$	—

Summary of Assumptions used to Determine Fair Value of Stock Options Granted

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:

Risk-free interest rate	2.0% - 3.6%
Expected volatility	90.7% - 101.3%
Expected dividend yield	—%
Expected life (years)	5.5 - 6.3 years

Summary of Restricted Stock Units Activity

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

Schedule of Stock-based Compensation Expense

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