BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 33,229	$ 40,019
Short-term investments	4,499	2,774
Prepaid expenses and other current assets	3,627	3,475
Total current assets	41,355	46,268
Property and equipment, net	44	97
Operating lease right-of-use assets	930	1,054
Other assets	70	70
Total assets	42,399	47,489
Current liabilities:
Accounts payable	329	457
Accrued expenses	6,072	7,461
Operating lease liability	191	163
Future tranche right liability		46,436
Other current liability	435
Total current liabilities	7,027	54,517
Warrant liability, long-term	6,983	3,241
Future tranche right liability, long-term	118,803
Operating lease liability, net of current portion	758	899
Total liabilities	133,571	58,657
Commitments and contingencies (Note 13)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 35,219 and 29,672 at December 31, 2020 and December 31, 2019, respectively	38	30
Additional paid-in capital	742,342	709,692
Accumulated deficit	(833,552)	(720,890)
Total stockholders' deficit	(91,172)	(11,168)
Total liabilities and stockholders' deficit	42,399	47,489
Series B1 Redeemable Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock
Series A Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock