Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock Option Activity Under the 2012 and 2013 Plans

Stock option activity under the Company’s 2012 Equity Incentive Plan (the “2012 Plan”) and 2013 Equity Incentive Plan (the “2013 Plan”) for the three months ended March 31, 2019 is summarized as follows:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2018		3,339,471		$	1.03		8.1	$	—
Cancelled		(1,536,304	)		0.57		—		—

Outstanding at March 31, 2019		1,803,167		$	1.03		7.2	$	—

Vested and expected to vest at March 31, 2019		1,766,323		$	1.41		7.2	$	—

Exercisable at March 31, 2019		1,723,797		$	1.37		7.1	$	—

Summary of Stock-Based Compensation and Resricted stock awards

The allocation of stock-based compensation for all options granted and restricted stock awards is as follows:


	Three Months Ended March 31,
	2019			2018
	(in thousands)
Research and development	$	(38	)	$	96
General and administrative		145			307

Total stock-based compensation expense	$	107		$	403

Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants and non-employee stock options grants for the three months ended March 31, 2018 were as follows:


	Three Months Ended March 31, 2018
	Employees			Non-employees
Risk-free interest rate		2.70	%		1.97	%
Expected volatility		88.2	%		74.0	%
Expected term (in years)		6.08			6.08
Expected dividend yield		0.0	%		0.0	%