The Phase 3 Study of the Prostate Cancer Vaccine Prostvac Has Been Discontinued
An independent Data Monitoring Committee (DMC) recommended that the Phase 3 PROSPECT study of Prostvac in men with metastatic hormone-resistant prostate cancer (mCRPC) should be discontinued due to inadequate results. Prostvac did not improve overall survival. The PROSPECT trial (NCT01322490) was a randomized, double-blind, and placebo-controlled Phase 3 trial that included 1,298 mCRPC patients from 200 sites in 15 countries. These men had minimal or no symptoms associated with their mCRPC. The trial evaluated whether Prostvac, alone or in combination with granulocyte macrophage colony-stimulating factor (GM-CSF), could improve overall survival compared to a placebo. GM-CSF is a cytokine or signaling molecule that can also stimulate the immune system. It stimulates the production of granulocytes and monocytes, two types of cells in the immune system that are important for fighting infections.
Previous studies evaluating more than 2,000 participants suggested that Prostvac immunotherapy was well-tolerated. In a Phase 2 trial, this immunotherapy showed potential in prolonging survival in men with advanced prostate cancer. However, the interim analysis for the Phase 3 PROSPECT trial suggested that Prostvac may not be as effective as hoped. It is hoped that combination therapies including Prostvac may be more effective. Copenhagen, Denmark-based Bavarian Nordic’s hopes of salvaging Prostvac now rest on whether it can boost the effect of other immuno-oncology agents, notably Bristol-Myers’ PD-1 and CTLA-4 checkpoint inhibitors Opdivo and Yervoy. Publicly, Bavarian Nordic has not given up hope that the cancer vaccine can complement these drugs. For further details, see the Sept. 15th FierceBiotech article and Sept. 21st Prostate Cancer News Today.
Prostvac had been in late stage Phase III development (PROSPECT trial) for metastatic, hormone-resistant prostate cancer patients who are either asymptomatic or minimally symptomatic. It is a therapeutic pox virus cancer vaccine directed at PSA-producing cells. It is administered with or without GM-CSF (granulocyte macrophage colony-stimulating factor, a protein secreted by immune system cells that functions as a white blood cell growth factor. Prostvac immunotherapy (administered by s.c. injections) is intended to trigger a specific and targeted immune response against prostate cancer cells and tissue by using virus-based immunotherapies that carry the tumor-associated antigen PSA (prostate-specific antigen) along with 3 natural human immune-enhancing costimulatory molecules collectively designated as TRICOM (LFA-3, ICAM-1, and B7.1 When PSA-TRICOM is presented to the immune system in Prostvac, cytotoxic T lymphocytes (CTLs) are generated that may recognize and kill PSA-expressing cancer cells.