CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 44,541	$ 33,229
Short-term investments		4,499
Prepaid expenses and other current assets	2,477	3,627
Total current assets	47,018	41,355
Property and equipment, net	38	44
Operating lease right-of-use assets	882	930
Other assets	70	70
Total assets	48,008	42,399
Current liabilities:
Accounts payable	185	329
Accrued expenses	4,398	6,072
Operating lease liability	196	191
Other current liability	217	435
Total current liabilities	4,996	7,027
Warrant liability, long-term		6,983
Future tranche right liability, long-term		118,803
Operating lease liability, net of current portion	708	758
Total liabilities	5,704	133,571
Commitments and contingencies (Note 13)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 46,537 and 38,291 at March 31, 2021 and December 31, 2020, respectively	46	38
Additional paid-in capital	760,072	742,342
Accumulated deficit	(717,814)	(833,552)
Total stockholders' equity (deficit)	42,304	(91,172)
Total liabilities and stockholders' equity (deficit)	48,008	42,399
Series B1 Redeemable Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock
Series A Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock