Cosibelimab Induces Encouraging Response Rate in cSCC, Warranting FDA BLA Submission


Topline results from an international phase 1 study of cosibelimab are encouraging and may lead to the submission of a biologics license application to the FDA.

Treatment with cosibelimab, achieved a promising objective response rate (ORR) in patients with metastatic cutaneous squamous cell carcinoma, meeting the primary end point of a phase 1 study, according to topline results announced in a press release.1

Cosibelimab (formerly CK-301) is a fully human monoclonal antibody of IgG1 subtype that connects to PD-L1 to block the interaction between PD-L1 and B7.1 receptors. By blocking this interaction, the suppressive effects of PD-L1 on anti-tumor CD8-positive T cells are removed and cytotoxic T cell response can be restored.

“We are thrilled to report these topline results from our pivotal trial of cosibelimab in metastatic cutaneous squamous cell carcinoma. We believe the strong ORR result is attributable to cosibelimab’s differentiated, 2-fold mechanism of action of engaging both T-cells and natural killer cells, while also demonstrates a potential favorable safety profile through its binding to PD-L1, reported in literature as associated with lower rates of severe or worse adverse events as compared to PD-1 therapy. We extend our sincere thanks to the patients, caregivers, investigators, and their site staff for their dedication to this trial, particularly during these challenging times globally. We look forward to a detailed presentation of the data at an upcoming medical meeting,” said James F. Oliviero, president, and chief executive officer of Checkpoint Therapeutics, in a press release.

In the phase 1, open-label, multicenter, dose-escalation study (NCT03212404), treatment with cosibelimab will be evaluated in approximately 500 patients with advanced cancers including cSCC, non–small cell lung cancer, colorectal cancer, endometrial cancer, small cell lung cancer, malignant pleural mesothelioma, head and neck squamous cell carcinoma, Merkel cell carcinoma, melanoma, renal cell carcinoma urothelial carcinoma, Hodgkin lymphoma, and B-cell non-Hodgkin lymphoma.2

The ORR observed with cosibelimab in the cSCC cohort of 78 patients was 47.4% (95% CI, 36.0%-59.1%), according to independent central review and per RECIST v1.1 criteria. The median duration of response (DOR) has not yet been reached, and responses were ongoing in 76% of patients.

Safety was assessed in 201 patients from the overall study population. Most of the treatment-emergent adverse events observed during the study were grade 1 or 2 in severity.

“These impressive results demonstrate that cosibelimab, a novel PD-L1 antibody with a unique 2-fold mechanism of action, has the potential to offer physicians a new treatment option that provides compelling efficacy, complemented by a favorable tolerability profile, for patients living with this devastating disease,” said study co-investigator, Professor Philip Clingan, medical oncologist, Southern Medical Day Care Centre, in a press release.

Based on the positive study results, the company plans to submit a biologics license application to the FDA and a marketing authorization application to the European Medicines Agency. There is also potential for the company to submit marketing applications to regulatory bodies worldwide.

The study is actively recruiting at 29 centers across Europe, Africa, Australia, and Asia. Those enrolled to part 2 of the study will be assessed for the primary end point of ORR and the secondary end points of confirmed best overall response, DOR, ORR, and DOR per modified RECIST v1.1, overall survival, pharmacokinetics, and the number of patients with anti-CK-301 antibodies.

To be eligible for inclusion, patients are required to have a histologically or cytologically confirmed advanced cancer, and ECOG performance status of 0 to1, at least 1 measurable lesion based on RECIST v1.1, adequate hematological, hepatic, and renal function. All patients must use effective contraception throughout the study if there is a risk of conception.

Those excluded from the study are patients who are previously treated with an anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, anti-CTLA-4 antibody, or any other antibody or drug specifically targeting T-cell co-stimulation or immune checkpoint pathway, or who received prior chemotherapy, radioactive, biological cancer therapy, or tyrosine kinase inhibitor therapy within 4 weeks of the study. Patients who have a history of hypersensitivity to other monoclonal antibodies are ineligible to enroll in the study as are those with a prior malignancy within the previous 2 years, or those who have a history of or active diseases that may interfere with study treatment.


1. Checkpoint Therapeutics announces positive topline results from the registration-enabling trial of cosibelimab in metastatic cutaneous squamous cell carcinoma. News release. Checkpoint Therapeutics, Inc. January 25, 2022. Accessed January 31, 2022.

2. Phase 1 study of CK-301 (cosibelimab) as a single agent in subjects with advanced cancers. Accessed January 31, 2022.

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