Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2012

Stock-Based Compensation Expense Related to Common Stock Options, Common Stock, Restricted Common Stock and Common Stock Warrants

Following is the stock-based compensation expense related to common stock options, common stock, restricted common stock and common stock warrants:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
	(in thousands)
Research and development	$	248	$	270	$	756	$	1,407
General and administrative		571		379		1,414		1,281
Total stock-based compensation expense	$	819	$	649	$	2,170	$	2,688

Summary of Stock Option Activity

The following table summarizes the stock option activity in the Company’s equity incentive plans, including non-plan grants to Company executives, from December 31, 2011 through September 30, 2012:

	Shares			Weighted Average Exercise Price
Outstanding, December 31, 2011		3,091,474		$	6.83
Granted		730,000			2.16
Exercised		(51,830	)		2.31
Options forfeited/cancelled		(228,014	)		7.65
Outstanding, September 30, 2012		3,541,630		$	5.88

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The following weighted average assumptions were used:

	Nine Months Ended September 30,						Cumulative Period from Inception (July 10, 2000) to September 30,
	2012			2011			2012
Risk-free interest rate		0.84	%		1.91	%		1.87	%
Expected life of the options		5.4 years			5.1 years			5.1 years
Expected volatility of the underlying stock		117	%		121	%		119	%
Expected dividend rate		0	%		0	%		0	%