Metformin Targets AMPK/mTORC1 And MTORC2 Pathway In Multiple Myeloma

Background: In recent years,outcome of multiple myeloma had greatly improved by using novel target agents,such as bortezomib containing therapy.But it still an incurable disease.Metformin is a traditional drug in the treatment of diabetes.Recently,it is proved to have the effect of anti-tumor in many cancers,including myeloma(MM).However,the molecular mechanisms have not been clearly elucidated.Methods: RPMI8226 and U266 humman myeloma cell lines were used in vitro.Cell viability was assessed with CCK8 and cell proliferation was measured by Ed U uptake assay.Cell cycle distribution and apoptosis were analyzed by flow cytometry.Transmission electron micrographic was used to show the autophagosomes.The activation of AMPK and inhibition of m TORC1/C2 pathways were examined by Western blot.AMPK knockdown into RPMI8226 cells and U266 cells were performed using Lipofectamine 2000 reagent.NOD-SCID murine xenograft myeloma model was applied to test the in vivo efficiency of metforminResults: Metformin effectively inhibited the proliferation of myeloma cell lines.The autophagy induction and G0/G1 cell cycle arrest might contribute to the effect of metformin in anti-myeloma.The study suggested that both m TOR complex 1(m TORC1)and m TOR complex 2(m TORC2)mediated downstream molecular signaling pathway were simultaneously suppressed.The further study confirmed that the activated AMPK directly phosphorylates and activates tuberous sclerosis complex 2(TSC2),which lead to inactivation of the mammalian target of rapamycin(m TOR).The xenograft mouse model further confirmed that metformin inhibited tumor growth by up-regulation AMPK and down-regulation m TOR.Conclusions: Metformin inhibits the proliferation of myeloma by inducing autophagy and cell cycle arrest.The molecular mechanism might inhibit both m TORC1 and m TORC2 pathways through AMPK activation.We hope our study will provide the theoretical basis for the treatment of MM using metformin as a safe and efficient targeting drugs.