Preferred Stock, Common Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Summary of Warrants Activity

  A summary of the Company’s warrant activity is as follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual
	Shares			Price		Term (Years)
Outstanding at December 31, 2015		118,881		$	16.73		4.35
Issued		3,227,876		$	2.81		5.04
Exercised		(22,881	)	$	5.90		8.00
Expired/Forfeited	—			—		—
Outstanding at December 31, 2016		3,323,876		$	3.29		4.96

Summary of Stock Option Activity

A summary of the Company’s stock option activity under the 2007 Plan and 2013 Plan is as follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual		Aggregate
	Shares			Price		Term (Years)		IntrinsicValue
Outstanding at December 31, 2015		1,037,500		$	7.19		8.04	$	342,200
Granted		941,624		$	3.26		9.12	—
Exercised	—			—		—		—
Expired/Forfeited/Exchanged		(703,500	)		7.65		7.46	—
Outstanding at December 31, 2016		1,275,624		$	4.04		8.34	$	191,160
Vested and expected to vest at December 31, 2016		1,275,624		$	4.04		8.34	$	191,160
Exercisable at December 31, 2016		584,663		$	4.86		7.42	$	191,160

Summary of Nonvested Options Activity

The Company had the following nonvested options under the 2007 Plan and 2013 Plan:

	Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested at December 31, 2015		507,421		$	7.60
Granted		941,624		$	2.04
Vested		(340,663	)	$	4.53
Expired/Forfeited/Exchanged		(417,421	)	—
Nonvested at December 31, 2016		690,961		$	3.34

Summary of Estimated Fair Value of Employee Stock Purchase Plan Award

The estimated fair value of the shares to be acquired under the ESPP was determined on the initiation date of each six month purchase period using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for ESPP shares to be purchased during the year ended December 31, 2016 and 2015:

	Year Ended December 31,
	2016		2015
Risk free interest rate	0.47% - 0.50%		0.08% - 0.26%
Expected term	6 months		6 months
Expected volatility of common stock	83.83% - 212.80%		62.91% - 69.64%
Expected dividend yield		0.0%		0.0%

Summary of Estimated Fair Value of Stock Option Award

The estimated fair value of each option award granted was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for options grants during the two years ended December 31, 2016:

	Year Ended December 31,
	2016		2015
Risk free interest rate	1.25% - 1.58%		1.50% - 1.87%
Expected option term	5.3 - 6.0 years		5.5 - 6.0 years
Expected volatility of common stock	74.44 - 75.91%		71.99% - 76.74%
Expected dividend yield		0.0%		0.0%

Summary of Recognized Non-Cash Stock-Based Compensation Expense

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Year Ended December 31,
	2016		2015
Research and development	$	698,032	$	579,078
General and administrative		1,008,492		925,278
Total stock-based compensation expense	$	1,706,524	$	1,504,356

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consists of the following at December 31, 2016 and 2015:

	December 31,
	2016		2015
Stock options issued and outstanding		1,275,624		1,037,500
Authorized for future option grants		628,801		78,854
Warrants to purchase common stock		3,323,876		118,881
Authorized for employee stock purchase plan		37,463		41,530
Total common stock reserved for future issuance		5,265,764		1,276,765