Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (15,816)	$ (34,044)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	0	577
Stock-based compensation expense	726	1,775
Amortization of premium on marketable securities	44	1,055
Non-cash loss on termination of lease	0	137
Gain on sale of equipment	0	(147)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	141	(231)
Accounts payable	(2,372)	(9,762)
Other liabilities	1,769	(1,432)
Net cash used in operating activities	(15,508)	(42,072)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	0	(7)
Proceeds from sale of property and equipment	0	173
Purchases of available-for-sale marketable securities	0	(3,671)
Proceeds from sales and maturities of marketable securities	7,712	66,094
Net cash provided by investing activities	7,712	62,589
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of pre-funded warrants for the purchase of common stock, net of issuance costs	16,567	0
Repurchase and retirement of common stock, amount	(3,000)	0
Net cash provided by financing activities	13,567	0
Net change in cash and cash equivalents	5,771	20,517
Cash and cash equivalents at beginning of period	36,640	8,305
Effect of exchange rates on cash	47	58
Cash and cash equivalents at end of period	42,458	28,880
Supplemental non-cash disclosure: NONCASH INVESTING AND FINANCING ACTIVITY:
Non-cash gain on sale of fixed assets	0	14
Operating right-of-use asset obtained in exchange for operating lease liability	0	824
Derecognition of operating right-of-use asset and operating lease liability upon termination of lease	0	714
Unrealized (loss) gain on available-for-sale securities	$ 56	$ (14)