title: Everolimus enhances the cytotoxicity of bendamustine in multiple myeloma cells through a network of pro-apoptotic and cell-cycle-progression regulatory proteins.
abstract: Bendamustine is a bifunctional alkylating agent with some efficacy in the treatment of newly diagnosed and relapsed/refractory multiple myeloma (MM). Everolimus, an mammalian target of rapamycin (mTOR) inhibitor, is a additional promising chemotherapeutic agent that has efficacy in a variety of cancers. We investigated the individual and combinational cytotoxic effects of these drugs in MM cell lines (RPMI8226 and MM1.S) and primary MM cells. Our results demonstrated a synergistic effect of these drugs, which was effective for both p53-wild-type and p-53-deleted MM cells, but was minimal in mononuclear cells from a healthy donor. Combination treatment with the two agents inhibited proliferation and promoted cytotoxicity and apoptosis as assessed by Annexin-V/PI staining, caspase-3 degradation, and PARP cleavage. Cell death was associated with the up-regulation of the pro-apoptotic protein Bax and the down-regulation of the anti-apoptotic proteins Mcl-1 and survivin. The combination drug treatment also promoted a decrease in the levels of the downstream target proteins of the mTOR pathway, p70s6k, and 4EBP-1, as well as an increase in the level of phosphorylation of the tumor suppressor protein p53 in MM1.S cells. p21 was also down-regulated upon treatment with the two drugs, suggesting a mechanism of sensitization through the release of cell cycle arrest. Our results demonstrate a network of regulatory factors that may contribute to the synergistic cytotoxicity of everolimus and bendamustine, and provide a rationale for application for the combinatorial treatment of MM with alkylating agents and mTOR inhibitors in future clinical practice.
authors.affiliation: Department of Hematology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou 510080, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Lu
authors.forename: Juan
authors.initials: J
authors.lastname: Li
authors.forename: Jingxuan
authors.initials: J
authors.lastname: Pan
authors.forename: Beihui
authors.initials: B
authors.lastname: Huang
authors.forename: Junru
authors.initials: J
authors.lastname: Liu
authors.forename: Dong
authors.initials: D
authors.lastname: Zheng
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D000069461:Bendamustine Hydrochloride; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D000068338:Everolimus; D006801:Humans; D009101:Multiple Myeloma / Q000378:metabolism / Q000473:pathology*; D009588:Nitrogen Mustard Compounds / Q000494:pharmacology*; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D009588:Nitrogen Mustard Compounds; D000069461:Bendamustine Hydrochloride; D000068338:Everolimus; D020123:Sirolimus
keywords: apoptosis; bendamustine; everolimus; myeloma; synergy