Metformin Sensitizes Cisplatin-induced Apoptosis Through Regulating Nucleotide Excision Repair Pathway In Cisplatin-resistant Human Lung Cancer Cells

Abstract

Background: Lung cancer is a leading cause of cancer death globally. Platinum-based chemotherapeutic medications are essential for treating advanced NSCLC, despite that drug resistance severely limits its effectiveness. Objective: In this study, we investigated the cytotoxic effect of metformin on cisplatin-resistant NSCLC cells (A549/DDP) and its potential mechanisms. Methods: Anti-lung cancer efficacy of metformin, cisplatin, and metformin combined with cisplatin was examined in A549 and A549/DDP cells. The cell counting kit-8 (CCK-8) assay was applied for measuring cell proliferation. CalcuSyn software was used to calculate the combination index and estimate the synergistic effect of metformin and cisplatin on cell proliferation. The cell apoptosis was analyzed by flow cytometry and the expression of apoptosis-related proteins, Bcl-2, Bax and caspase-3 were analyzed using Western blot. Futhermore, the expression of key nucleotide excision repair (NER) proteins, ERCC1, XPF, and XPA, was also analyzed using Western blot. Results: We found that metformin had dose-dependent antiproliferative effects on A549/DDP and A549 cells. The combination of metformin and cisplatin had higher effectiveness in inhibiting A549/DDP and A549 cell growth than either of the two drugs alone. Flow cytometry analysis indicated that the combined treatment could cause more cell apoptosis than the single-drug treatment. Consistently, the combined treatment decreased the expression of Bcl-2 protein and elevated the expression of Bax, and cleaved caspase-3 proteins. The expression level of ERCC1, XPF, and XPA proteins were lower in the combined treatment than in either of metformin and cisplatin treatment alone. Conclusions: Our study suggested that metformin and cisplatin had synergistic antitumorigenic effects in A549/DDP cells. The combination of cisplatin and metformin could be promising drug candidates to sensitize cisplatin-induced apoptosis through regulating nucleotide excision repair pathways in lung cancer.