CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 23,496	$ 39,058
Restricted cash	13,938	13,938
Receivables	0	4
Prepaid expenses and other current assets	750	799
Total current assets	38,184	53,799
Property and equipment, net	7,889	8,460
Right-of-use assets	2,023	2,136
Deposits	42	42
Other non-current assets	500	500
Total assets	48,638	64,937
Current liabilities:
Accounts payable	1,380	1,389
Current portion of long-term debt	10,988	16,765
Accrued expenses	4,120	5,454
Lease liabilities, current	575	558
Total current liabilities	17,063	24,166
Lease liabilities, non-current	2,038	2,188
Other non-current liabilities	28	28
Total liabilities	19,129	26,382
Commitments and contingencies (Note 9)
Stockholders' equity
Common stock $0.001 par value; 420,000,000 shares authorized, 240,627,055 shares issued and outstanding at March 31, 2023 and 420,000,000 shares authorized, 240,410,761 shares issued and outstanding at December 31, 2022	241	240
Additional paid-in capital	919,943	918,942
Accumulated deficit	(890,675)	(880,627)
Total stockholders' equity	29,509	38,555
Total liabilities and stockholders' equity	$ 48,638	$ 64,937