BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 68,255	$ 76,054
Receivables		1,111
Prepaid expenses and other current assets	1,517	1,666
Total current assets	69,772	78,831
Property and equipment, net	10,311	10,941
Right of use asset	4,240	4,420
Deposits	42	42
Other non-current assets	626	631
Total assets	84,991	94,865
Current liabilities:
Accounts payable	605	1,368
Current portion of long-term debt	13,993	7,868
Accrued expenses	5,891	6,076
Lease liability - current portion	745	729
Total current liabilities	21,234	16,041
Long-term debt	10,323	16,250
Lease liability - non-current portion	4,312	4,518
Total liabilities	35,869	36,809
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock $0.001 par value; 350,000,000 shares authorized, 215,950,561 shares issued and outstanding at March 31, 2022 and 350,000,000 shares authorized, 216,127,443 shares issued and outstanding at December 31, 2021	216	216
Additional paid-in capital	901,546	900,693
Accumulated deficit	(852,640)	(842,852)
Total stockholders' equity	49,122	58,057
Total liabilities and stockholders' equity	$ 84,991	$ 94,865