Phase I study of resminostat, an HDAC inhibitor, combined with S-1 in patients with pre-treated biliary tract or pancreatic cancer

Resminostat is an oral hydroxamate inhibitor of class I, IIb, and IV histone deacetylases. S-1 is widely used to treat biliary tract cancer and pancreatic cancer in Japan. We performed a phase I study of resminostat combined with S-1 as second-line or later therapy in Japanese patients with biliary tract or pancreatic cancer. A total of 27 patients were enrolled. We determined the optimal regimen for resminostat/S-1 therapy in part 1, and investigated its safety and efficacy in part 2. In part 1, 17 patients were enrolled. One DLT (anorexia and stomatitis, respectively) occurred with each of regimens 2 and 3. In part 2, an additional 10 patients received regimen 3, which was selected in part 1. Regimen 3 was resminostat (200 mg/day on Days 1 to 5 and Days 8 to 12: 5 days on/2 days off) plus S-1 (80–120 mg/day according to body surface area on Days 1 to 14) repeated every 21 days. A total of 16 patients (13 with biliary tract cancer and 3 with pancreatic cancer) received regimen 3 and it was well tolerated. The most frequent treatment-related adverse events were thrombocytopenia and anorexia (11 patients each, 69%). The disease control rate was 81.3% (84.6% for biliary tract cancer and 66.7% for pancreatic cancer, respectively). Median progression-free survival was 3.1 months (5.5 and 2.3 months), while median overall survival was 8.8 months (10.2 and 4.7 months). In conclusion, regimen 3 was well tolerated by patients with pre-treated biliary tract or pancreatic cancer.