Stockholders' Equity and Stock-Based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2020

Stockholders' Equity and Stock-Based Compensation Expense

Summary of outstanding warrants to purchase shares of common stock

The Company reviewed the authoritative accounting guidance and determined that the warrants meet the criteria to be accounted for as permanent equity. As of June 30, 2020, outstanding warrants to purchase shares of the Company’s common stock are as follows:

Shares Underlying Outstanding Warrants	Exercise Price		Expiration Date
1,322,510	$	2.50	April 22, 2025
12,677,490	$	2.50	June 11, 2025
14,000,000

Summary of Stock option activity under the 2015 and 2018 Plan

				Weighted-
		Weighted-		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Options	Price		Term (Years)	Value (in thousands)
Outstanding as of December 31, 2019	2,388,400	$	6.20	8.44	$	906
Granted	958,900		4.59
Exercised	—		—
Forfeited	(90,763)		5.34
Outstanding as of June 30, 2020	3,256,537	$	5.75	8.37	$	38
Exercisable as of June 30, 2020	1,261,829	$	5.78	7.33	$	—

Schedule of stock-based compensation expense

Stock-based compensation expense was classified in the consolidated statement of operations as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
Research and development	$	349	$	191	$	698	$	423
General and administrative		401		408		837		754
Total stock-based compensation expense	$	750	$	599	$	1,535	$	1,177