Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Stock Incentive Plan Compensation [Abstract]

The Company estimates the fair value of stock options with performance and service conditions on the date of grant using the Black-Scholes valuation model. The assumptions used in the Black-Scholes model are presented below:



	Year Ended December 31,
	2017		2016
Risk-free interest rate	1.27 to 2.36	%	1.22 to 1.63	%
Expected volatility	117 to 144	%	113 to 123	%
Expected term (in years)	2.0 to 9.1		6.0
Expected dividend yield	0	%	0	%

Allocation of Stock-Based Compensation Expenses

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



	Year Ended December 31,
	2017		2016

Research and development	$	171,000	$	138,000
General and administrative		529,000		1,857,000
Total stock-based compensation	$	700,000	$	1,995,000

Summary of Stock Option Activity

Stock option transactions during the years ended December 31, 2017 and 2016 are presented below:



					Weighted
					Average
			Weighted		Remaining
			Average		Contractual		Aggregate
			Exercise		Term		Intrinsic
	Shares		Price		(Years)		Value
Outstanding at December 31, 2015		66,964	$	86.52		9.29
Granted		26,419		26.48
Forfeited/Cancelled		(18,493)		89.95
Outstanding at December 31, 2016		74,890		64.50		8.65
Granted		1,070,572		1.22
Forfeited/Cancelled		(29,597)		87.87
Outstanding at December 31, 2017		1,115,865	$	3.17		8.98	$	118,000
Vested and expected to vest at December 31, 2017		830,752	$	3.94		8.71	$	90,000
Exercisable at December 31, 2017		136,142	$	13.18		4.02	$	14,000

Shares Reserved for Future Issuance

As of December 31, 2017, the Company had reserved shares of its common stock for future issuance as follows:



	Shares Reserved
Stock options outstanding		1,115,865
Employee stock purchase plan		21,016
Available for future grants under the 2016 Plan		4,758
Warrants		8,531,918
Total shares reserved		9,673,557