Stockholders’ Equity (Tables)

3 Months Ended

Mar. 31, 2019

Equity [Abstract]

Summary of Stock Option Activity Under 2018 Plan and 2006 Plan

A summary of the Company’s stock option activity under the 2018 Plan and 2006 Plan is as follows:

	Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding at January 1, 2019	1,282,847		$	6.90	9.2	$	—
Granted	503,260		4.25			—
Exercised	(41,521	)	1.30			127,054
Cancelled/Expired	(37,160	)	15.96			—
Outstanding at March 31, 2019	1,707,426		$	6.04	9.1	$	1,060,875
Vested and exercisable at March 31, 2019	508,459		$	6.70	8.4	$	732,751

Summary of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense for the three months ended March 31, 2019 and 2018 as follows:

	Three Months Ended March 31,
	2019		2018
Research and development	$	52,903	$	9,635
General and administrative	236,492		44,809
Total stock-based compensation expense	$	289,395	$	54,444

Schedule of Weighted-Average Assumptions in Black -Scholes Option Pricing Model

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

	Three Months Ended March 31,
	2019		2018
Risk-free interest rate	2.5	%	2.5	%
Expected volatility	64.3-67.3 %		63.0	%
Expected term (in years)	4.9		4.0
Expected dividend yield	0.0	%	0.0	%

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consist of the following:

	March 31, 2019
Stock options issued and outstanding	1,707,426
Authorized for future stock awards, option grants, or employee stock purchase program	494,682
Common Warrants	4,224,494
Total	6,426,602