BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 46,122	$ 68,204
Receivables	208	145
Prepaid expenses and other current assets	1,484	1,948
Total current assets	47,814	70,297
Property and equipment, net	654	801
Deposits	128	128
Other non-current assets	513	528
Total assets	49,109	71,754
Current liabilities:
Accounts payable	1,953	422
Accrued expenses	7,803	6,357
Deferred revenue - current portion	1,700	800
Deferred rent - current portion	244	212
Total current liabilities	11,700	7,791
Deferred revenue		1,933
Deferred rent	665	851
Warrant liabilities	247	11,776
Other long-term liabilities	20	20
Total liabilities	12,632	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; 102,683,984 and 100,159,618 shares issued and outstanding at September 30, 2014 and December 31, 2013, respectively	103	100
Additional paid-in capital - common stock	398,585	386,511
Additional paid-in capital - warrants issued		3,603
Accumulated deficit	(362,211)	(340,831)
Total stockholders' equity	36,477	49,383
Total liabilities and stockholders' equity	$ 49,109	$ 71,754