Phase I and pharmacokinetic study of bendamustine hydrochloride in relapsed or refractory indolent B‐cell non‐Hodgkin lymphoma and mantle cell lymphoma

Bendamustine is a cytotoxic agent with a novel mechanism of action. This phase I, dose‐escalation study evaluated the safety, tolerability, efficacy, and pharmacokinetics of bendamustine in Japanese patients with relapsed/refractory indolent B‐cell non‐Hodgkin lymphoma (B‐NHL) or mantle cell lymphoma (MCL) without major organ dysfunction. Bendamustine 90 or 120 mg/m² (dose escalation) was administered intravenously over 60 min on days 1 and 2 every 3 weeks for up to three cycles. Nine patients (eight indolent B‐NHL and one MCL) received per‐protocol treatment, three at 90 mg/m² and six at 120 mg/m². No dose‐limiting toxicities were observed; thus, the maximum‐tolerated dose was not reached. Grade 3/4 hematologic toxicities were neutropenia (33%) and leukopenia (33%). Non‐hematologic toxicities were grade 1/2 and included gastrointestinal events and fatigue. Peak plasma concentrations of bendamustine occurred near the end of infusion in both dose groups and were equivalent to therapeutic concentrations observed in vitro. Bendamustine was rapidly eliminated, with a mean elimination half‐life (t_1/2) of 29 min. Plasma concentrations of active metabolites M3 and M4 were approximately 4 and <1% of the plasma concentration of the parent molecule, with t_1/2 of 42 and 33 min, respectively. Two unconfirmed complete responses and six partial responses were observed for an overall response rate (ORR) of 89%. The recommended dose for this schedule in phase II trials is 120 mg/m². The acceptable safety profile and high ORR warrant further investigation of bendamustine in relapsed or refractory indolent B‐NHL and MCL. (ClinicalTrials.gov ID: NCT00389051). (Cancer Sci 2010)