Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 18,146	$ 16,557
Marketable securities	43,445	49,543
Prepaid expenses and other current assets	1,847	1,393
Total current assets	63,438	67,493
Restricted cash	1,413	1,413
Property and equipment, net	3,779	3,805
Intangible asset, net	11	11
Total assets	68,641	72,722
Current liabilities:
Accounts payable	1,387	1,424
Accrued expenses and other current liabilities	1,519	4,303
Current portion of loans payable, net	12,460	12,425
Deferred rent	63	61
Total current liabilities	15,429	18,213
Loans payable, net	12,595	15,725
Capital leases, net of current portion	28	31
Deferred rent, net of current portion	2,992	3,006
Warrant liability	10	10
Other long term liabilities	1,270	1,104
Total liabilities	32,324	38,089
Commitments and contingencies (Note 6)
Stockholders’ equity:
Common stock—$0.001 par value; 100,000,000 shares authorized, 67,603,736 and 62,310,795 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	68	62
Preferred stock—$0.001 par value; 5,000,000 shares authorized, none issued or outstanding at March 31, 2018 and December 31, 2017
Additional paid-in capital	402,806	392,103
Accumulated deficit	(366,511)	(357,490)
Accumulated other comprehensive loss	(46)	(42)
Total stockholders’ equity	36,317	34,633
Total liabilities and stockholders’ equity	$ 68,641	$ 72,722