Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 12,910	$ 21,464
Restricted cash	361	361
Marketable securities		11,577
Prepaid expenses and other current assets	535	451
Total current assets	13,806	33,853
Property, equipment and leasehold improvements, net	157	510
Other assets	82	421
Total assets	14,045	34,784
Current liabilities:
Accounts payable	988	1,011
Loan payable, current portion	452	423
Derivative warrant liability	4	1,314
Deferred rent, current portion	30	141
Accrued expenses	1,638	1,959
Total current liabilities	3,112	4,848
Loan payable, net of current portion	400	852
Deferred rent, net of current portion	367	135
Other liabilities	56
Total liabilities	3,935	5,835
Commitments and contingencies (Note 16)
Stockholders' equity:
Common stock, $0.00001 par value, authorized 100,000,000 shares; 34,274,776 shares issued and outstanding at December 31, 2017; 32,044,087 shares issued and outstanding at December 31, 2016	1	1
Additional paid-in capital	194,016	185,955
Accumulated deficit	(183,907)	(157,007)
Total stockholders' equity	10,110	28,949
Total liabilities and stockholders' equity	$ 14,045	$ 34,784