Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2017

Summary of Estimated Fair Value of Stock Option Award

The estimated fair value of each stock 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 option grants during the three and six months ended June 30, 2017 and 2016:

	Three Months Ended June 30.				Six Months Ended June 30,
	2017		2016		2017		2016
Common Stock Options
Risk free interest rate		1.93%		1.41%	1.93%-2.16%		1.25%-1.58%
Expected option term	5.5 years		5.5 years		5.5-6.0 years		5.3-6.0 years
Expected volatility of common stock		98.23%		75.03%	94.05%-98.23%		74.44%-75.91%
Expected dividend yield		0.0%		0.0%		0.0%		0.0%

Summary of Estimated Fair Value of Employee Stock Purchase Plan Award

The estimated fair value of each ESPP award was determined on the date of grant using the Black Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three and six months ended June 30, 2017 and 2016:

	Three and Six Months Ended June 30,
	2017	2016
Employee Stock Purchase Plan
Risk free interest rate	0.79%		0.50%
Expected term	6.0 months	6.0 months
Expected volatility of common stock	99.23%		83.83%
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:

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Research and development	$	219,345	$	151,148	$	426,203	$	309,937
General and administrative		245,526		275,982		502,826		536,105
Total stock-based compensation expense	$	464,871	$	427,130	$	929,029	$	846,042