| Introdution：Gefitinib (Iressa) and erlotinib (Tarceva) are reversible small-moleculeepidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI),which have shownhighly effective in the treatment of nonsmall cell lung cancer (NSCLC) patients withEGFR-activating mutations.Besides these drugs have been recommended as the standardfirst-line therapy in patients who are harboring EGFR-activating mutations. However,themajority of patients will eventually develop resistance and succumb to the disease., nearlyall responding patients eventually develop drug resistance after a median period of about10months. Thus, the reversion therapeutic resistance to EGFR-TKI strategies are urgentlyneeded to improve the survival of NSCLC patients.Various principal molecular mechanisms are involved, including secondary mutationsin the EGFR (EGFR T790M)、amplification of the N-Methyl-N′-nitro-N-nitroso-guanidine(MNNG) HOS transforming gene (MET) oncogene and epithelial mesenchymal transition(EMT). TGF-β is one of the major driving force of the EMT genetic program. It wasreported that the IL-6axis activation could be induced by TGF-β, further resulting in EMTand resistance to reversible TKI in lung cancer cells, while inhibiting the IL-6/STAT3signaling could restore EGFR-TKI sensitivity. So targeting EMT may reverse or preventacquisition of therapeutic resistance to EGFR inhibitors.Metformin is a widely used drug for diabetes and has arisen been studied as a potentialanticancer agent ever since the clinical evidence that the cancer risk and mortality arelessened in diabetics receiving metformin.Metformin exerts prominent antitumorproperties in tumor cells and mouse models. It forcefully inhibited the growth of lungcancer cells, and its combination with metformin and classical chemotherapeutic agents,including paclitaxel and cisplatin, significantly suppressed breast tumor growth andprolonged remission in a xenograft model. Intriguingly, metformin exposure significantly impeded the TGF-β promoted EMT process, reduced IL-6secretion, and suppressed STAT3activity.So we hypothesis that metformin may overcome TKI resistance by reversing EMTand inhibiting IL-6signaling pathways.Objectives：The epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) have been recommended as a standard therapy in patients with EGFR-activatingmutations. However, acquired resistance eventually limits the clinical effects andapplication of EGFR-TKI. Studies have shown that this acquired mechanism of drugresistance of TKIs could be abrogated by suppression of EMT and IL-6/STAT3pathway.This study aims to investigate the effect of metformin on sensitizing EGFR-TKI-resistanthuman lung cancer cells in vitro and in vivo through inhibition of IL-6signaling and EMTreversal.Methods：The effect of metformin on reversing TKI resistance was examined in vitroand in vivo using BrdU incorporation assay,invasion assay, immunostaining, flowcytometry analysis,3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium(MTT), Westernblot analysis and xenograft implantation.Results：In this study, metformin, a widely used antidiabetic agent, effectivelyincreased the sensitivity of TKI-resistant lung cancer cells to gefitinib or erlotinib.Metformin decreased IL-6signaling activation and reversed EMT in TKI-resistant cells,while adding IL-6to those cells bypassed the anti-TKI-resistance effect of metformin.Furthermore, addition or overexpression of IL-6to TKI-sensitive cells induced TKIresistance, which could be overcome by metformin. Finally, metformin-based combinatorialtherapy effectively blocked tumor growth in xenografts with TKI-resistant cancer cells,which was associated with decreased IL-6expression and secretion, EMT reversal anddecreased IL-6signaling activation in vivo.Conclusions：Metformin, generally considered remarkably inexpensive and non-toxic,might be used in combination with TKIs in NSCLC patients who harboring EGFRmutations to overcome TKI resistance and the mechanism could be abrogated bysuppression of EMT and IL-6/STAT3pathway. |
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