Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Tables)

9 Months Ended

Sep. 30, 2019

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	706,640		3.82
Exercised	(50,047	)	1.30
Cancelled/Expired	(95,379	)	9.83
Outstanding at September 30, 2019	1,844,061		$	5.71	8.8	$	—
Vested and exercisable at September 30, 2019	682,462		$	6.51	8.4	$	—

Summary of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense for the three and nine months ended September 30, 2019 and 2018 as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Research and development	$	58,619	$	43,363	$	169,209	$	131,900
General and administrative	305,841		9,762		820,312		28,651
Total stock-based compensation expense	$	364,460	$	53,125	$	989,521	$	160,551

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 September 30,			Nine Months Ended September 30,
	2019		2018	2019		2018
Risk-free interest rate	1.8	%	—	2.4	%	2.5	%
Expected volatility	65.6-68.2%		—	64.3-68.2%		63.0	%
Expected term (in years)	6.1		—	5.1		4.0
Expected dividend yield	0.0	%	—	0.0	%	0.0	%

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consist of the following:



	September 30, 2019
Stock options issued and outstanding	1,844,061
Authorized for future stock awards, option grants, or employee stock purchase program	305,593
Common Warrants	4,224,494
Total	6,374,148