A Randomized, Double-blind, Placebo-controlled, Phase II Study with and Without Enzastaurin in Combination with Docetaxel-based Chemotherapy in Patients with Castration-resistant Metastatic Prostate Cancer

Purpose: Enzastaurin is an oral serine/threonine kinase inhibitor that inhibits the beta isoform of protein kinase C and which may have therapeutic activity in prostate cancer. We explored the efficacy of docetaxel/prednisone with or without enzastaurin in patients with castration-resistant metastatic prostate cancer.

Methods: A nonrandomized safety cohort consisting of 14 patients was followed by a double-blind randomized Phase II trial. Patients received standard doses of docetaxel (75 mg/m(2)) with prednisone 10 mg daily with or without 500 mg/day of enzastaurin.

Results: There was no difference in the objective response rate between the enzastaurin and placebo arms (placebo: 7 [15.2 %]; enzastaurin: 6 [15.0 %]; P = 1.00). The median PFS was 229 days for patients in the enzastaurin arm versus 213 days for the placebo arm (P = 0.524). The 1-year overall survival rates were almost identical, with 76.7 % and 75.1 % in the enzastaurin and placebo arms, respectively. Therapy was well tolerated although the combination of enzastaurin and docetaxel was more myelosuppressive than with docetaxel alone.

Conclusions: The clinical activity of docetaxel/prednisone plus enzastaurin cannot be distinguished from docetaxel/prednisone alone, given the limitations of a randomized Phase II design. Although the toxicity profile was favorable for the enzastaurin-containing regimen, there is no compelling rationale to move this combination forward for the treatment of castration-resistant metastatic prostate cancer.