CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 27,810	$ 40,019
Short-term investments	3,196	2,774
Prepaid expenses and other current assets	2,681	3,475
Total current assets	33,687	46,268
Property and equipment, net	63	97
Operating lease right-of-use asset	965	1,054
Other assets	70	70
Total assets	34,785	47,489
Current liabilities:
Accounts payable	345	457
Accrued expenses	7,023	7,461
Operating lease liability	166	163
Future tranche right liability		46,436
Total current liabilities	7,534	54,517
Warrant liability, long-term	3,053	3,241
Future tranche right liability, long-term	41,074
Operating lease liability, net of current portion	815	899
Total liabilities	52,476	58,657
Commitments and contingencies
Stockholders' equity (deficit)
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 34,291 and 29,672 at June 30, 2020 and December 31, 2019, respectively	34	30
Additional paid-in capital	718,574	709,692
Accumulated deficit	(736,299)	(720,890)
Total stockholders' deficit	(17,691)	(11,168)
Total liabilities and stockholders' deficit	34,785	47,489
Series B1 redeemable convertible preferred stock
Stockholders' equity (deficit)
Preferred stock
Series A convertible preferred stock; Designated - 1,500 shares, Issued and outstanding - 1 share
Stockholders' equity (deficit)
Preferred stock