Stock Options (Tables)

6 Months Ended

Jun. 30, 2016

Stock Options [Abstract]

Stock-Based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2015		2016		2015
	(unaudited)				(unaudited)
Stock-Based Compensation
Research and development	$	544,702	$	265,029	$	1,042,232	$	428,541
General and administrative		836,292		318,486		1,754,064		526,143
Total	$	1,380,994	$	583,515	$	2,796,296	$	954,684

Assumptions Used in Valuing Stock Options and Warrants Granted

The fair value of options and warrants granted during the three and six months ended June 30, 2016 and 2015 was estimated using the Black-Scholes option valuation model utilizing the following assumptions:

	Three Months Ended June 30,						Six Months  Ended June 30,
	2016			2015			2016			2015
	Weighted Average			Weighted Average			Weighted Average			Weighted Average
	(unaudited)						(unaudited)
Volatility		71.80	%		79.80	%		78.50	%		79.80	%
Risk-Free Interest Rate		1.29	%		1.58	%		1.39	%		1.79	%
Expected Term in Years		5.68			6.08			6.01			6.07
Dividend Rate		0.00	%		0.00	%		0.00	%		0.00	%
Fair Value of Option on Grant Date	$	5.81		$	4.39		$	5.11		$	4.28

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, 2015		4,302,267		$	5.19
Granted		976,400			7.56
Exercised		(7,375	)		3.55
Forfeited		(133,517	)		5.79
Expirations		-			-
Options outstanding at June 30, 2016		5,137,775		$	5.62		8.00	$	23,960,058
Vested and expected to vest at June 30, 2016		5,035,892		$	5.58		7.98	$	23,679,976
Exercisable at June 30, 2016		2,617,577		$	3.97		7.10	$	16,226,531