Abstract 610: Metformin augments rituximab and chemotherapeutic agents-induced apoptosis via mTOR inhibition in rituximab-resistant B lymphoma cell lines

Abstract

Abstract With elusive mechanisms, a subgroup of NHL patients who treated with rituximab in combination with cytotoxic chemotherapeutic agents becomes unresponsive. Patients who relapsed lymphoma are known to have poorer outcome when treated with rituximab compared with treated without rituximab. Since activation of mTOR pathway has been recently suggested for progression of NHL, especially in salvage setting, we'd like to examine the effect of metformin which inhibits mTOR pathway in rituximab-resistant NHL. Three lymphoma cell lines (Raji, Raji-2R, Raji-4RH) were used, which were kindly given by Dr Czuczman MS from Rosewell Park Cancer Institute (Ref. Czuczmana MS et al. Clin Cancer Res 2008;14:1561, 2008;14:1550). These cells were treated with cisplatin, adriamycin, vincristine and rituximab in the absence or presence of metformin for 24, 48, 72 hrs. Cell growth and proliferation was evaluated by MTT assay and cell cycle progression was determined FACS analysis. To characterize molecular mechanisms involved in metformin-induced inhibition of cell proliferation, the level of BAX, BAK, Bcl-2, Bcl-XL, Mcl-1, AMPK, pAMPK, pACC, mTOR, p70S6K and S6K was determined by western blot analysis. Compared with rituximab-sensitive cell line (RSCL) which is parental lymphoma cell, Raji, rituximab-resistant cell lines (RRCLs), that are Raji-2R and Raji-4RH, have shown decreased cytotoxicity in response to chemotherapeutic agents including cisplatin, adriamycin and vincristine as well as rituximab. However, cytotoxic effect of these chemotherapeutic agents and rituximab was improved in combination of metformin in both RSCL and RRCLs. To us surprise, a better synergistic inhibition of cell proliferation was found in RRCLs as a result of combination of metformin and chemotherapeutic agents or rituximab, suggesting that intracellular signaling pathway induced by metformin might not be overlapped to that by chemotherapeutic agent and rituximab. Notably, it has known that in RRCLs, the level of proapototic proteins, BAX, BAK, is relatively low compared to in RSCL decreased, but the expression of anti-apoptotic protein and AMPK activity is increased and dysregulation of mTOR pathway is found. Our data showed that metformin restored dysregulation of mTOR pathway in RRCLs, since activation of p70S6K and S6K posphorylation was decreased. At the same time, expression of BAX and BAK was increased and that of anti-apoptotic proteins was decreased. Metformin enhances rituximab-induced and chemotherapy-induced apoptosis via mTOR inhibition in rituximab-resistant NHL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 610.