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.

Everolimus inhibits breast cancer cell growth through PI3K/AKT/mTOR signaling pathway

“…Our results reported that everolimus treatment decreased anti-apoptosis gene Bcl-2 and Bcl-w expression in breast cancer cells. Notably, everolimus induced dose-dependent changes to cell cycle regulation and modified the cell cycle response to enhance the cytotoxicity of bendamustine in multiple myeloma cells through a network of pro-apoptotic and cell-cycle-progression regulatory proteins ( 27 , 28 ). In this study, we found that everolimus not only induced apoptosis through regulation of apoptosis-related gene expression in breast cancer cells, but also arrested cell cycle at G0/G1 and S phase, which resulted in inhibition of breast cancer growth.…”

Inhibitory effect of the anthelmintic drug pyrvinium pamoate on T315I BCR-ABL-positive CML cells

“…The K562, KBM5, KBM5-T315I, 32D-BCR-ABL and 32D-T315I cells were cultured at 2x10 5 cells/well in 6-well plates, then cells were treated with increasing concentrations of pyrvinium pamoate, or with the fixed concentration for different time periods. Viable and dead cells were assessed by counting with a hemocytometer following trypan blue exclusion assay (23).…”

New perspectives in glioblastoma antiangiogenic therapy

“…Everolimus, a specific inhibitor of mTOR, is known to activate compensatory pathways, although favourable results were depicted in a few preclinical and clinical studies when used in combination with bendamustine or radiotherapy. Apoptosis pathways are activated through PI3K/AKT/PKB system downstream inducing phosphorylation of mTOR, not blocked by specific mTOR inhibitors [ 102 , 103 ]. Perifosine (KRX-0401), an AKT pathway inhibitor, was found to induce cytotoxicity and evade drug resistance in a study regarding myeloma.…”