Filed Pursuant to Rule 424(b)(3)
Registration No. 333-258301
Prospectus Supplement
(To Prospectus dated
August 6, 2021)
This prospectus supplement supplements and amends the prospectus dated August 6, 2021 (the Prospectus), as supplemented and
amended by (i) that certain prospectus supplement dated November 22, 2021 covering the offering, issuance and sale of up to a maximum aggregate offering price of $90,000,000 of our common stock that may be issued and sold under a sales
agreement with B. Riley Securities, Inc., BTIG, LLC and H.C. Wainwright & Co., LLC (the ATM Facility), and (ii) that certain prospectus supplement dated November 7, 2022 reducing the maximum aggregate offering price of
the ATM Facility to $70,000,000 (the Maximum Offering Price).
Effective as of June 13, 2023, we have reduced the Maximum
Offering Price to $12,000,000. As of the date of this prospectus supplement, 12,545,741 shares have been sold under the ATM Facility.
You
should read this prospectus supplement, together with additional information described under the headings Information Incorporated by Reference and Where You Can Find Additional Information in the Prospectus carefully before
you invest in our securities.
Investing in our securities involves a high degree of risk. Before making any investment in our securities, you should consider carefully
the risks and uncertainties described in the section entitled Risk Factors beginning on page 2 of the Prospectus.
The date of
this prospectus supplement is June 13, 2023.