The Application Of Novel Agents And Combination Strategies In The Treatment Of Multiple Myeloma

Objective: To investigate the combination of bendamustine and histonedeacetyltransferase inhibitor (HDACi) entinostat in inhibiting drugsensitive/resistant MM cell lines, and potential mechanisms. To study the effect ofbendamustine and cladribine in inhibiting drug sensitive/resistant multiplemyeloma (MM) cell lines, and potential mechanisms.Methods：(1) MTS-based proliferation assays were used to determine cell viabilityin response to bendamustine, cladribine, or entinostat.(2) Cells undergoingapoptosis were evaluated with flow cytometric analysis and a specific ELISA toquantitatively measure cytoplasmic histone-associated DNA fragments.(3) Cellcycle progression was examined by flow cytometric analysis.(4) Western blotanalyses were performed to determine the expression and activation of proteins.(5)Giemsa staining was used to evaluate morphologic alteration of mitoticcatastrophe and apoptosis.Results：(1) HDACi entinostat significantly enhances bendamustine-inducedapoptosis via activation of caspase-dependent signaling pathway, and DNAdamage response via induction of P-H2A.X and/or P-CHK2in bothdexamethasone-sensitive and–resistant MM cells, and subsequently promotes thecells undergoing mitotic catastrophe.(2) Bendamustine and cladribine have effectof inhibiting proliferation, and inducing apoptosis and cell cycle arrest in bothdexamethasone-sensitive and–resistant MM cell lines. This effect mainly resultsfrom inducing activation of caspase-dependent apoptotic pathways, and alteringDNA damage or cell cycle associated protein expression.Conclusions: Bendamustine/cladribine alone and the combination ofbendamustine and HDACi entinostat have potentials to inhibit growth of bothdexamethasone-sensitive and–resistant MM cells. Our study may provide novel strategies to overcome chemotherapy resistance, and establish the theoretical basisfor in vivo study and clinical trials in the future.