Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2012

Stock-Based Compensation Expense Related to Common Stock Options, 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 June 30,				Six Months Ended June 30,
	2012		2011		2012		2011
		(in thousands)
Research and development	$	359	$	614	$	508	$	1,138
General and administrative		520		714		844		901
Total stock-based compensation expense	$	879	$	1,328	$	1,352	$	2,039

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 June 30, 2012:

	Shares			Weighted Average Exercise Price
Outstanding, December 31, 2011		3,091,474		$	6.83
Granted		480,000			2.08
Exercised		(51,830	)		2.31
Options forfeited/cancelled		(228,014	)		7.65
Outstanding, June 30, 2012		3,291,630		$	6.15

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The following weighted average assumptions were used:

	Six Months Ended June 30,		Cumulative Period from Inception (July 10, 2000) to June 30,
	2012	2011	2012
Risk-free interest rate	0.91%	1.91%	1.98%
Expected life of the options	5.6 years	5.1 years	5.1 years
Expected volatility of the underlying stock	116%	121%	119%
Expected dividend rate	0%	0%	0%