Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 37,665	$ 20,194
Restricted cash	361	361
Prepaid expenses and other current assets	413	184
Total current assets	38,439	20,739
Property, equipment and leasehold improvements, net	630	938
Other assets	411	115
Total assets	39,480	21,792
Current liabilities:
Accounts payable	556	521
Loan payable, current portion	416	395
Derivative warrant liability	2,695	1,907
Deferred rent, current portion	134	115
Accrued expenses	1,704	374
Total current liabilities	5,505	3,312
Loan payable, net of current portion	960	1,275
Deferred rent, net of current portion	175	276
Total liabilities	6,640	4,863
Commitments and contingencies
Stockholders' equity:
Common stock, $0.00001 par value, authorized 100,000,000 shares, issued and outstanding 32,033,197 at September 30, 2016; and authorized 50,000,000 shares, issued and outstanding 27,555,948 shares at December 31, 2015	1	1
Additional paid-in capital	184,411	150,497
Accumulated deficit	(151,572)	(133,569)
Total stockholders' equity	32,840	16,929
Total liabilities and stockholders' equity	$ 39,480	$ 21,792