Phase Ia/Ib Talazoparib + Tazemetostat for mCRPC

This is a Phase 1a/1b clinical trial to assess safety, tolerability and preliminary clinical activity of the combination of talazoparib with tazemetostat in metastatic castration-resistant prostate cancer (mCRPC) patients. The U.S. Food and Drug Administration (FDA) has not approved talazoparib or tazemetostat for metastatic castration-resistant prostate cancer (mCRPC) but they have been approved for other uses. Talazoparib has been approved for use in breast cancer, and tazemetostat has been approved for use in certain types of sarcoma and lymphoma. Talazoparib is an orally administered molecularly targeted chemotherapy drug called a "PARP inhibitor", which acts to block the ability of cancer cells to repair certain forms of damage to their DNA - the accumulation of damaged DNA causes certain cancer cells to die. Other PARP inhibitors are already approved for use in prostate cancer patients with specific gene mutations detected in their blood or in their cancer, and talazoparib is currently being studied for treatment of prostate cancer in other clinical trials. Tazemetostat is an orally administered molecularly targeted chemotherapy drug called an "EZH2 inhibitor", which acts to block the production of proteins encoded by DNA in the cancer cells that are important in cancer growth and survival. Tazemetostat is also being studied for the treatment of prostate cancer in other clinical trials. In the laboratory setting, tazemetostat causes changes in protein levels in prostate cancer cells that make them sensitive to dying in the presence of PARP inhibitors. The research study procedures include screening for eligibility and study treatment including evaluations and follow up visits. The study design involves two parts. The first part is called the "dose escalation" to find a safe dose for the combination of talazoparib and tazemetostat. The second part is called the "dose expansion" where additional participants are treated at the safe dose identified in the first part of the study. Participants will receive study treatment for as long as they do not have serious side effects and their disease does not get worse. Participants will be followed after completion of study treatment for up to 24 months. It is expected that about 38 people will take part in this research study. Funding for this research is provided by a grant awarded by the non-profit Prostate Cancer Foundation along with Pfizer, Inc. In addition, Pfizer is supporting the study by providing the study drug talazoparib. Epizyme, Inc. is supporting the study by providing the study drug tazemetostat.