Effect of a combination of atiprimod and the proteasome inhibitor bortezomib on apoptosis of mantle cell lymphoma in vitro and in vivo.

Abstract

e18529 Background: The proteasome inhibitor bortezomib (BTZ) induces apoptosis and sensitizes mantle cell lymphoma (MCL) cells to chemotherapy in relapsed or refractory MCL. Atiprimod (ATI), as a novel cationic amphophilic compound, displays significant anti-MCL effect in vitro and in xenograft mouse model. This study was to evaluate the effect of ATI and BTZ combination on MCL and to elucidate their therapeutic mechanisms. Methods: The established cells and freshly isolated MCL cells from refractory or relapsed MCL patients were incubated with ATI and/or BTZ and the effects on cell proliferation, cell cycle, and apoptosis were analyzed using 3H-thymidine incorporation assay, flow cytometry, immunoblotting, and MCL-bearing mouse model. Results: We found that ATI and BTZ synergistically induced the growth inhibition and apoptosis of both established MCL cells and freshly isolated tumor cells from relapsed or refractory MCL patients. Furthermore, ATI and BTZ induced apoptosis via two different signaling pathways. BTZ induced apoptosis via activation and cleavage of caspases-3, -8, -9, and PARP. The pan-caspase inhibitor Z-VAD-FMK completely blocked BTZ- but not ATI-induced apoptosis. ATI, but not BTZ, induced apoptosis by releasing apoptosis-inducing factor (AIF) from mitochondria to cytosol in MCL cells. Importantly, ATI plus BTZ synergistically delayed the tumor growth and prolonged the survival in MCL-bearing NOD-SCID mice. Conclusions: The results demonstrate that ATI and BTZ display synergistically therapeutic effects on MCL cells via activating two distinct apoptotic signaling pathways. The ATI and BTZ combination should be investigated in a clinical trial in patient with relapsed or refractory MCL. No significant financial relationships to disclose.