Investigational Drug-Libtayo Combo Demonstrates Clinical Activity in Metastatic Prostate Cancer

Data from an ongoing early-phase clinical trial shows that the combination of an investigational drug, REGN5678, and Libtayo (cemiplimab) elicited encouraging activity in patients with advanced metastatic castration-resistant prostate cancer.

“In past clinical trials, metastatic castration-resistant prostate cancer has been largely unresponsive to PD-1 inhibition and immunotherapy in general, leaving patients with inadequate treatment options, a poor prognosis and an expected survival of one to two years depending on the treatment history,” trial investigator Dr. Mark Stein, an associate professor of medical oncology at Columbia University Vagelos College of Physicians and Surgeons in New York City, said in a company-issued press release.

Patients are currently being enrolled onto this first-in-human phase 1/2 trial. Patients must have advanced metastatic castration-resistant prostate cancer and have disease progression after receiving multiple anti-androgen therapies, as well as chemotherapy.

The main goal of the phase 1 portion of the trial is to investigate the safety and tolerability of the investigational drug in combination with Libtayo, as well as the pharmacokinetics (how the drugs move within the body).

Additional goals include assessing the objective response rate, which in this case is being defined as a 50% or greater decline of prostate-specific antigen (PSA) from trial enrollment and/or tumor shrinkage.

PSA is a protein that is either produced by normal or cancerous cells within the prostate gland. Elevated blood levels of PSA often indicate the presence of prostate cancer. In men who have already had prostate cancer, PSA tests are performed to see if cancer has returned.

The preliminary data from 33 patients showed that the combination of REGN5678 and Libtayo is associated with eliciting anti-tumor activity. The patients have been assigned to eight separate dose-level groups. Although there is early evidence of anti-tumor activity, the findings showed that there was only one out of 17 patients in the lowest dose levels that achieved an adequate decrease in PSA levels.

"These initial data provide the first clinical evidence indicating that a costimulatory bispecific antibody may synergistically combine with an anti-PD-1 agent such as Libtayo to enable activity against a tumor class previously resistant to anti-PD-1 immunotherapy. We look forward to further investigating the safety and efficacy of this combination."

The trial is expected to include approximately 129 patients across several cancer centers in the United States, and is expected to be completed by July 2024.

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