Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 53,001	$ 68,204
Receivables	32	145
Prepaid expenses and other current assets	991	1,948
Total current assets	54,024	70,297
Property and equipment, net	683	801
Deposits	128	128
Other non-current assets	513	528
Total assets	55,348	71,754
Current liabilities:
Accounts payable	447	422
Accrued expenses	7,773	6,357
Deferred revenue - current portion	2,333	800
Deferred rent - current portion	235	212
Total current liabilities	10,788	7,791
Deferred revenue		1,933
Deferred rent	730	851
Warrant liabilities	6,094	11,776
Other long-term liabilities	20	20
Total liabilities	17,632	22,371
Commitments and contingencies (note 8)
Stockholders' equity:
Preferred stock, $0.001 par value; 30,000,000 shares authorized and no shares issued and outstanding
Common stock, $0.001 par value; 250,000,000 shares authorized; 100,725,066 and 100,159,618 shares issued and outstanding at June 30, 2014 and December 31, 2013, respectively	101	100
Additional paid-in capital - common stock	390,192	386,511
Additional paid-in capital - warrants issued	3,541	3,603
Accumulated deficit	(356,118)	(340,831)
Total stockholders' equity	37,716	49,383
Total liabilities and stockholders' equity	$ 55,348	$ 71,754