Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 19,266	$ 35,495
Restricted cash	1,501	1,501
Accounts receivable, interest and other receivables	556	2
Prepaid expenses and other current assets	1,019	802
Assets held for sale	0	1,643
Total current assets	22,342	39,443
Operating lease right-of-use assets	0	645
Property and equipment, net	27	189
Other assets	4	307
Total assets	22,373	40,584
Current liabilities:
Accounts payable	521	891
Accrued expenses and other current liabilities	5,339	4,165
Warrant derivative liability	7,842	10,345
Private placement option liability	2,800	7,803
Current portion of lease liabilities	0	825
Liabilities held for sale	0	672
Total current liabilities	16,502	24,701
Long-term lease liabilities	0	344
Total liabilities	16,502	25,045
Commitments and contingencies
Redeemable preferred stock: $0.01 par value; 10,000,000 shares authorized, Series 1 redeemable convertible preferred stock, $0.01 par value, 1,517,500 shares authorized at September 30, 2021 and December 31, 2020; 452,000 shares issued and outstanding at September 30, 2021 and December 31, 2020	18,036	18,036
Stockholders’ deficit:
Common stock, $0.01 par value; 80,000,000 shares authorized at September 30, 2021 and December 31, 2020; 8,465,549 shares issued and 8,397,803 shares outstanding at September 30, 2021; 8,385,650 shares issued and 8,317,904 shares outstanding at December 31, 2020	84	84
Treasury stock: 67,746 shares held at September 30, 2021 and December 31, 2020	(5,056)	(5,056)
Additional paid-in capital	546,138	543,561
Accumulated other comprehensive loss	(348)	(339)
Accumulated deficit	(552,983)	(540,747)
Total stockholders’ deficit	(12,165)	(2,497)
Total liabilities, redeemable preferred stock and stockholders' deficit	$ 22,373	$ 40,584