Exhibit 12.1

COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES

The following table sets forth our ratio of earnings to fixed charges for each of the periods indicated (in thousands):

	Year Ended December 31,
	2013			2012		2011			2010			2009
Earnings:
Net income (loss)	$	(21,452	)	$	16,200	$	(18,765	)	$	(22,898	)	$	(30,288	)
Fixed charges		607			620		828			805			934
Total Earnings	$	(20,845	)	$	16,820	$	(17,937	)	$	(22,093	)	$	(29,354	)
Fixed Charges:
Interest expense	$	6		$	7	$	46		$	6		$	36
Portion of rent expense representative of interest		601			613		782			799			898
Total Fixed Charges	$	607		$	620	$	828		$	805		$	934
Ratio of Earnings to Fixed Charges (1)		—			27.1		—			—			—

(1) For purposes of computing the ratio of earnings to fixed charges, earnings consist of net income (loss) plus fixed charges. Fixed charges consist of interest expense, amortization of debt expense and discount or premium related to indebtedness, whether expensed or capitalized, and that portion of rental payments under operating leases we believe to be representative of interest. Earnings were insufficient to cover fixed charges by $21.5 million, $18.8 million, $22.9 million and $30.3 million for the years ended December 31, 2013, 2011, 2010, and 2009, respectively. Earnings for the year ended December 31, 2012 included recognition of $35.4 million of collaborative research and development revenue as a result of the termination of the Company’s agreements with Nycomed, Pfizer and Hospira. Excluding the recognition of $35.4 million of deferred revenue, earnings would have been insufficient to cover fixed charges by $19.2 million for the year ended December 31, 2012.