BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 104,713	$ 60,392
Collaboration receivable	79
Prepaid expenses and other current assets	1,313	424
Total current assets	106,105	60,816
Property and equipment, net	1,141	253
Deposits	91	87
Other non current assets	771	364
Total assets	108,108	61,520
Current liabilities:
Accounts payable	1,727	1,031
Accrued expenses	10,821	2,538
Deferred revenue - current portion	800
Deferred rent - current portion	15	43
Total current liabilities	13,363	3,612
Deferred revenue	3,533
Deferred rent	180	44
Warrant liabilities	19,425	27,311
Total liabilities	36,501	30,967
Commitments and contingencies (note 8)
Stockholders' equity:
Common stock, $0.001 par value; 250,000,000 shares authorized; 69,206,044 and 48,466,562 shares issued and outstanding at December 31, 2011 and 2010, respectively	69	48
Preferred stock, $0.001 par value; 30,000,000 shares authorized and no shares issued and outstanding
Additional paid-in capital - common stock	246,519	131,530
Additional paid-in capital - warrants issued	12,611	22,789
Deficit accumulated during the development stage	(187,592)	(123,814)
Total stockholders' equity	71,607	30,553
Total liabilities and stockholders' equity	$ 108,108	$ 61,520