Bendamustine Is Effective in p53-Deficient B-Cell Neoplasms and Requires Oxidative Stress and Caspase-Independent Signaling

Purpose: Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) are two incurable B-cell lymphoid neoplasms characterized by distinct clinical presentation and evolution. Bendamustine hydrochloride is a multifunctional, alkylating agent with a purine-like ring system that exhibits activity in multiple cancer models, including CLL and MCL, but whose mechanism is only partially described. Our aim was to analyze the apoptotic pathways activated by bendamustine in CLL and MCL together with the relevance of p53 mutation in determining the response to this drug. Experimental Design: Thirteen CLL/MCL cell lines and primary tumor cells from 8 MCL and 25 CLL patients were cultured for up to 24 h with bendamustine followed by cytotoxic assays, flow cytometry, immunofluorescence, and Western blot analysis of p53 response pathway and apoptosis-related factors. Results: Bendamustine displayed cytotoxic activity on most CLL and MCL primary cells and cell lines irrespective of ZAP-70 expression and p53 status. Bendamustine was found to act synergistically with nucleoside analogues in both CLL and MCL, this combination being effective in p53 mutated cases resistant to standard chemotherapy. Bendamustine cytotoxicity was mediated by the generation of reactive oxygen species and triggering of the intrinsic apoptotic pathway involving up-regulation of PUMA and NOXA, conformational activation of BAX and BAK, and cytosolic release of caspase-related and caspase-unrelated mitochondrial apoptogenic proteins. Conclusions: Our findings support the use of bendamustine as a therapeutic agent, alone or in combination, for CLL and MCL with p53 alterations and describe the molecular basis of its activity in these entities.