Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Our stock-based compensation expense for the last three fiscal years was as follows:


	2015		2014		2013
Research and development expense	$	1,873,848	$	608,840	$	1,219,308
General and administrative expense		2,370,560		1,426,058		1,389,362

Total stock-based compensation expense and effect on net loss	$	4,244,408	$	2,034,898	$	2,608,670

Schedule of Fair Value Option Award, Assumptions

The weighted-average assumptions used for the last three fiscal years are as follows:


	2015			2014			2013
Expected term (years)(1)		5.7			4.2			5.1
Risk-free interest rate(2)		1.8	%		1.3	%		1.2	%
Expected volatility(3)		75.2	%		78.7	%		89.3	%
Expected dividend yield(4)		0	%		0	%		0	%

(1)

The expected term represents the period during which our stock-based awards are expected to be outstanding. We estimated this amount based on historical experience of similar awards, giving consideration to the contractual terms of the awards, vesting requirements, and expectation of future employee behavior, including post-vesting terminations.

(2)	The risk-free interest rate is based on U.S. Treasury debt securities with maturities close to the expected term of the option as of the date of grant.

(3)	Expected volatility is based on historical volatility over the most recent historical period equal to the length of the expected term of the option as of the date of grant.

(4)	We have neither declared nor paid dividends on any share of common stock and we do not expect to do so in the foreseeable future.

Stock Option Activity

A summary of our stock option activity and related information for the last three fiscal years is as follows:


	Outstanding Options
	Number of Shares			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term		Aggregate Intrinsic Value(1)
Balance at December 31, 2012		447,359		$	19.59		5.1	$	2,175
Granted		—
Exercised		(3,452	)	$	1.00			$	2,214
Cancelled (forfeited and expired)		(15,649	)	$	13.06

Balance at December 31, 2013		428,258		$	19.97		4.3	$	—
Granted		—
Exercised		—			—				—
Cancelled (forfeited and expired)		(125,529	)	$	24.30

Balance at December 31, 2014		302,729		$	18.18		3.3	$	—
Granted		2,595,000		$	0.69
Exercised		—			—				—
Cancelled (forfeited and expired)		(818,600	)	$	1.57

Balance at December 31, 2015		2,079,129		$	2.89		8.6	$	1,800

Exercisable at December 31, 2015		399,129		$	12.14		4.9	$	360

Vested and expected to vest(2)		1,873,521		$	3.134		8.5	$	1,620

(1)

Aggregate intrinsic value represents the value of the closing price per share of our common stock on the last trading day of the fiscal period in excess of the exercise price multiplied by the number of options outstanding or exercisable, except for the “Exercised” line, which uses the closing price on the date exercised.

(2)	Number of shares includes options vested and those expected to vest net of estimated forfeitures.

Summary of Changes in Unvested Options

The following is a summary of changes in unvested options:


Unvested Options	Number of Options			Weighted Average Grant Date Fair Value
Unvested options at December 31, 2014		—			—
Granted(1)		2,595,000		$	0.45
Vested		(135,000	)	$	0.44
Cancelled		(38,600	)	$	14.62

Unvested options at December 31, 2015		1,680,000		$	9.97

Weighted Average Exercise Price and Remaining Term Information about Significant Option Groups Outstanding

The following table presents weighted average exercise price and remaining term information about significant option groups outstanding at December 31, 2015:


Options Outstanding at December 31, 2015
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Term (Yrs.)		Weighted Average Exercise Price		Aggregate Intrinsic Value at December 31, 2015
Less than $10.00		1,815,300		9.5	$	0.69	$	1,800
$10.00 - $19.99		140,870		4.0	$	11.79		—
$20.00 - $29.99		106,159		1.1	$	23.27		—
$30.00 - $39.99		16,800		0.1	$	36.95		—

		2,079,129		8.6	$	2.9	$	1,800


Vested Options Outstanding at December 31, 2015
Range of Exercise Prices	Number Outstanding		Weighted Average Exercise Price
Less than $10.00		135,300	$	0.70
$10.00 - $19.99		140,870	$	11.79
$20.00 - $29.99		106,159	$	23.27
$30.00 - $39.99		16,800	$	36.95

		399,129	$	12.14

Summary of Restricted Stock Unit Activity

A summary of our restricted stock unit activity for the year ended December 31, 2015 is as follows:


	Number of RSUs			Weighted Average Grant Date Fair Value
Unvested at January 1, 2015		3,374,940		$	1.55
Granted(1)		7,540,768		$	1.10
Vested		(1,510,257	)	$	1.41
Cancelled		(1,154,100	)	$	1.22

Unvested at December 31, 2015		8,251,351		$	1.21

(1)

All 2,595,000 options granted in 2015 vest upon the attainment of certain performance goals established by the Compensation Committee or the Single Member Committee established under our 2006 Equity Incentive Plan and our 2013 Equity Incentive Plan. A total of 7,540,768 restricted units were granted in 2015. 349,518 of these restricted stock units vest and convert into shares of our common stock after one year from the date of grant. 2,331,250 of these restricted stock units vest and convert into shares of our common stock over a three year period from the date of grant: one-third of the award will vest on each grant date anniversary following the grant. The remaining restricted units granted vest upon the attainment of certain performance goals established by the Compensation Committee or the Single Member Committee established under our 2006 Equity Incentive Plan and our 2013 Equity Incentive Plan.