A phase I study of vorinostat combined with bortezomib in Japanese patients with relapsed or refractory multiple myeloma.

This study was undertaken to evaluate safety and pharmacokinetics and to determine treatment doses of vorinostat plus bortezomib in Japanese patients with relapsed or refractory multiple myeloma (MM). Of 9 originally enrolled patients, 2 were refractory to bortezomib, and both experienced dose-limiting toxicity (DLT), prompting a protocol amendment to exclude bortezomib-refractory individuals. Patients not considered bortezomib refractory (N = 7) received 21-day cycles of 1.3 mg/m(2) intravenous bortezomib (Days 1, 4, 8, and 11) and oral vorinostat 400 mg (Days 1 through 14) and were further evaluated. Vorinostat and bortezomib treatment doses were determined by DLT and safety, tolerability, and treatment response were assessed. Of 7 enrolled patients, 6 were evaluated, and one developed DLTs. The most common adverse events were leukopenia, neutropenia, thrombocytopenia, diarrhea, nausea, decreased appetite, and vomiting. Combination of vorinostat plus bortezomib did not increase vorinostat exposure at Day 11 [AUC0-24 h ratio (95% CI) = 1.08 (0.80, 1.45)]; geometric mean AUC0-24 h ratio for bortezomib (90% CI) was 1.96 (1.24-3.12). Objective therapeutic response occurred in 3 patients, including 1 complete response and 2 partial responses. Vorinostat 400 mg plus bortezomib 1.3 mg/m(2) was safe and well-tolerated in Japanese patients with relapsed or refractory MM not considered bortezomib refractory (NCT00858234).