Stock Options (Tables)

9 Months Ended

Sep. 30, 2017

Stock Options [Abstract]

Stock-Based Compensation Expense

The Company’s stock-based compensation expense was recognized in operating expense as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	(unaudited)				(unaudited)
Stock-Based Compensation
Research and development	$	702,284	$	567,452	$	2,090,076	$	1,609,683
General and administrative		868,630		665,579		2,547,066		2,419,643
Total	$	1,570,914	$	1,233,031	$	4,637,142	$	4,029,326

Assumptions Used to Value Stock Options and Warrants Granted

The fair value of options and warrants granted during the three months ended September 30, 2017 and 2016 was estimated using the Black-Scholes option valuation model utilizing the following assumptions:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	Weighted Average			Weighted Average			Weighted Average			Weighted Average
	(unaudited)						(unaudited)
Volatility		86.98	%		71.80	%		88.82	%		77.96	%
Risk-Free Interest Rate		1.83	%		1.19	%		1.89	%		1.38	%
Expected Term in Years		6.03			6.07			5.99			6.02
Dividend Rate		0.00	%		0.00	%		0.00	%		0.00	%
Fair Value of Option on Grant Date	$	7.22		$	6.78		$	6.76		$	5.24

Stock Option Activity

The following table summarizes the number of options outstanding and the weighted average exercise price:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years		Aggregate Intrinsic Value
Options outstanding at December 31, 2016		5,316,511		$	5.84
Granted		1,165,400			9.16
Exercised		(30,666	)		3.00
Forfeited		(63,750	)		8.21
Options outstanding at September 30, 2017		6,387,495		$	6.44		7.32	$	27,951,302
Vested and expected to vest at September 30, 2017		6,387,495		$	6.44		7.32	$	27,951,302
Exercisable at September 30, 2017		3,898,218		$	5.02		6.40	$	22,525,438