BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 51,108	$ 70,946
Receivables	18	19
Prepaid expenses and other current assets	20,989	19,818
Total current assets	72,115	90,783
Property and equipment, net	1,244	1,211
Deposits	128	128
Other non-current assets	13,974	13,484
Total assets	87,461	105,606
Current liabilities:
Accounts payable	606	4,417
Accrued expenses	8,878	9,909
Contract liability - current portion	476	6,389
Deferred rent - current portion	102	141
Total current liabilities	10,062	20,856
Contract liability, net of current portion	49,037	35,139
Deferred rent, net of current portion	3	1
Derivative liabilities	2,469	2,424
Total liabilities	61,571	58,420
Commitments and contingencies (Note 5)
Preferred stock, $0.001 par value, 30,000,000 shares authorized
Stockholders' deficit:
Common stock, $0.001 par value; 250,000,000 shares authorized; 142,398,936 and 142,658,037 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	142	143
Additional paid-in capital	613,302	615,493
Accumulated deficit	(736,593)	(712,442)
Total stockholders' deficit	(123,149)	(96,806)
Total liabilities and stockholders' deficit	87,461	105,606
Series 1 Preferred Stock
Current liabilities:
Series 1 preferred stock, $1,200 stated value; 250,000 designated; 123,268 and 119,644 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively; liquidation value of $147.9 million and $143.6 million at March 31, 2018 and December 31, 2017, respectively	$ 149,039	$ 143,992