BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 79,741	$ 61,729
Receivables	3,330	1,864
Prepaid expenses and other current assets	22,421	20,692
Total current assets	105,492	84,285
Property and equipment, net	1,110	1,097
Deposits	130	128
Right-of-use asset	2,272
Other non-current assets	110	9,541
Total assets	109,114	95,051
Current liabilities:
Accounts payable	906	707
Accrued expenses	10,846	8,763
Lease liability - current portion	774
Deferred rent - current portion		13
Total current liabilities	12,526	9,483
Lease liability - noncurrent portion	1,578
Deferred rent - noncurrent portion		4
Total liabilities	14,104	9,487
Commitments and contingencies (Note 9)
Preferred stock, $0.001 par value, 30,000,000 shares authorized
Stockholders' equity:
Common stock, $0.001 par value; 250,000,000 shares authorized; 181,803,320 and 161,066,136 shares issued and outstanding at December 31, 2019 and 2018, respectively	182	161
Additional paid-in capital	778,953	651,732
Accumulated deficit	(684,125)	(566,329)
Total stockholders' equity	95,010	85,564
Total liabilities and stockholders' equity	109,114	$ 95,051
Series 1 Preferred Stock
Current liabilities:
Series 1 preferred stock, $1,200 stated value; 250,000 designated; 0 shares issued and outstanding at December 31, 2019 and 2018; liquidation value of $0 million at December 31, 2019 and 2018