Checkpoint Therapeutics, Inc. announced that the U.S. Food and Drug Administration ("FDA") has accepted for filing the Biologics License Application ("BLA") for cosibelimab, Checkpoint's investigational anti-PD-L1 antibody, as a treatment for patients with metastatic cutaneous squamous cell carcinoma ("cSCC") or locally advanced cSCC who are not candidates for curative surgery or radiation. The FDA has set a Prescription Drug User Fee Act ("PDUFA") goal date of January 3, 2024. In its BLA filing acceptance letter, the FDA indicated that no potential filing review issues have been identified, and that an advisory committee meeting to discuss the application is not currently planned.

The BLA submission is supported by the positive results from Checkpoint's registration-enabling clinical trial evaluating cosibelimab in patients with metastatic and locally advanced cSCC. In January 2022, Checkpoint announced that the metastatic cSCC cohort met its primary endpoint, with cosibelimab demonstrating a confirmed objective response rate ("ORR") of 47.4% (95% CI: 36.0, 59.1) based on independent central review of 78 patients enrolled in the cohort using Response Evaluation Criteria in Solid Tumors version 1.1 ("RECIST 1.1") criteria. The pivotal results were subsequently presented at the June 2022American Society of Clinical Oncology ("ASCO") Annual Meeting.

Also in June 2022, Checkpoint announced positive interim results from its locally advanced cSCC cohort, with cosibelimab demonstrating a confirmed ORR of 54.8% (95% CI: 36.0, 72.7) based on independent central review of 31 patients enrolled in the cohort. Based upon subsequent interactions with the FDA, the BLA under review includes both the metastatic and locally advanced cSCC indications. About Cutaneous Squamous Cell Carcinoma (cSCC) cSCC is the second most common type of skin cancer in the United States, with an estimated annual incidence of approximately 1.8 million cases according to the Skin Cancer Foundation.

Important risk factors for cSCC include chronic ultraviolet exposure and immunosuppressive conditions. While most cases are localized tumors amenable to curative resection, approximately 40,000 cases will become advanced, and an estimated 15,000 people will die from this disease each year. In addition to being a life-threatening disease, cSCC causes significant functional morbidities and cosmetic deformities based on tumors commonly arising in the head and neck region and invading blood vessels, nerves and vital organs such as the eye or ear.

The immune-suppressed population represents a challenging target in the treatment of advanced cSCC, as they present with a more aggressive disease and with a higher risk of developing immune-related toxicities from checkpoint inhibitor treatment. About Cosibelimab Cosibelimab is a potential best-in-class, high affinity, fully-human monoclonal antibody of IgG1 subtype that directly binds to programmed death ligand-1 ("PD-L1") and blocks the PD-L1 interaction with the programmed death receptor-1 ("PD- 1") and B7.1 receptors. Cosibelimab's primary mechanism of action is based on the inhibition of the interaction between PD-L1 and its receptors PD-1 and B7.1, which removes the suppressive effects of PD-L1 on anti-tumor CD8+ T-cells to restore the cytotoxic T cell response.

Cosibelimab is potentially differentiated from the currently marketed PD-1 and PD-L1 antibodies through sustained >99% target tumor occupancy to reactivate an antitumor immune response and the additional benefit of a functional Fc domain capable of inducing antibody-dependent cell-mediated cytotoxicity ("ADCC") for potential enhanced efficacy in certain tumor types.