Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2021

Stock-based Compensation

Assumptions used in the black-Scholes model

The assumptions used in the Black-Scholes model are presented below:

	Three Months Ended
	March 31, 2021	March 31, 2020
Risk-free interest rate	0.93% -- 1.29%	1.48% -- 1.51%
Expected volatility	93.37%	90.43%
Expected term (in years)	5.50 to 7.00	5.75 to 6.25
Expected dividend yield	0%	0%

Allocation of Stock-Based Compensation Expenses

The tables below summarize the total stock-based compensation expense included in the Company’s consolidated statements of operations for the periods presented:

	Three Months Ended March 31,
	2021		2020
Research and development	$	353,000	$	337,000
General and administrative		489,000		707,000
Total stock-based compensation	$	842,000	$	1,044,000

Summary of Stock Option Activity

Stock option transactions during the three months ended March 31, 2021 are presented below:

	Options Outstanding
				Weighted
				Average
		Weighted		Remaining
		Average		Contractual	Aggregate
		Exercise		Term	Intrinsic
	Shares	Price		(Years)	Value
Outstanding at December 31, 2020	1,668,926	$	6.30	8.32		—
Granted	549,750		5.14	—		—
Exercised	(46,134)		3.34	—	$	82,000
Forfeited/Cancelled	(5,599)		94.92	—		—
Outstanding at March 31, 2021	2,166,943	$	5.84	8.56	$	2,311,000
Vested and expected to vest at March 31, 2021	2,166,943	$	5.84	8.56	$	2,311,000
Exercisable at March 31, 2021	435,646	$	13.83	6.60	$	452,000

Shares Reserved for Future Issuance

As of March 31, 2021, the Company had reserved shares of its common stock for future issuance as follows:

	Shares Reserved
Stock options outstanding	2,166,943
Unvested restricted stock units	70,000
Employee stock purchase plan	9,748
Available for future grants under the 2016 Plan	527,947
Warrants outstanding	16,647,219
Total shares reserved	19,421,857