CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 36,602	$ 33,229
Short-term investments		4,499
Prepaid expenses and other current assets	1,697	3,627
Total current assets	38,299	41,355
Property and equipment, net	27	44
Operating lease right-of-use assets	784	930
Other assets	70	70
Total assets	39,180	42,399
Current liabilities:
Accounts payable	276	329
Accrued expenses	5,085	6,072
Operating lease liability	205	191
Other current liability		435
Total current liabilities	5,566	7,027
Warrant liability, long-term		6,983
Future tranche right liability, long-term		118,803
Operating lease liability, net of current portion	603	758
Total liabilities	6,169	133,571
Commitments and contingencies (Note 13)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 52,115 and 38,291 at June 30, 2021 and December 31, 2020, respectively	53	38
Additional paid-in capital	764,300	742,342
Accumulated deficit	(731,342)	(833,552)
Total stockholders' equity (deficit)	33,011	(91,172)
Total liabilities and stockholders' equity (deficit)	39,180	42,399
Series B1 Redeemable Convertible Preferred Stock
TEMPORARY EQUITY
Preferred stock
Series A Preferred Stock [Member]
Stockholders' equity (deficit):
Preferred stock