Oral enzastaurin in prostate cancer: A two-cohort phase II trial in patients with PSA progression in the non-metastatic castrate state and following docetaxel-based chemotherapy for castrate metastatic disease

Purpose: Enzastaurin is an oral serine/threonine kinase inhibitor of the beta isoform of protein kinase C that may have therapeutic activity in prostate cancer. We explored the efficacy of enzastaurin on two cohorts of patients with prostate cancer progression in the castrate state. Patients and Methods: A two-cohort phase II trial was conducted, with both groups participating simultaneously. Cohort 1 consisted of patients with non-metastatic castrate prostate-specific antigen progressive disease. Cohort 2 consisted of patients with castrate metastatic disease with progression following docetaxel-based chemotherapy. Patients in both cohorts received 500 mg/day enzastaurin. Results: Therapy was well tolerated in both cohorts. One complete response was observed in Cohort 1, with limited activity in the majority of patients. In Cohort 2, no objective responses were seen and the median progression-free survival (11 weeks [90% confidence interval: 7.6, 11.7]) did not differ from the historical control. Conclusions: Enzastaurin as a single agent has limited activity in castrate progressive prostate cancer. Evaluation in combination with docetaxel is ongoing.