Metformin suppressed epithelial-mesenchymal transition, cisplatin resistance and metastatic potential of ovarian cancer via inhibiting TGF-β1/Smads

Background: Ovarian cancer (OC) is a lethal gynecologic malignancy, in which cisplatin (cDDP) chemoresistance and metastasis are major causes of therapeutic failure. Metformin, a first-line anti-diabetic agent, has exhibited anti-tumor potential in various cancers. However, its precise role in modulating chemosensitivity and metastatic behavior in OC, and the underlying mechanisms, remain to be fully elucidated. Methods: The human OC cell line SKOV3 and its cDDP-resistant variant SKOV3/cDDP were employed. Cell viability and the half-maximal inhibitory concentration (IC50) of cDDP were determined by cell counting kit-8 (CCK-8) assay. Clonogenic ability, migratory and invasive potentials were assessed using colony formation, wound healing, and transwell assays, respectively. The protein expression of epithelial-mesenchymal transition (EMT) markers (E-cadherin, N-cadherin), EMT-related transcription factors (Snail, Slug, Zeb-1), and components of transforming growth factor beta 1/Smads (TGF-β1/Smads) pathway were analyzed by western blot and enzyme-linked immunosorbent assay. Rescue experiments were conducted by co-treating cells with metformin and TGF-β1. Results: Metformin dose-dependently inhibited cell viability and clonogenic survival in both SKOV3 and SKOV3/cDDP cells. It significantly enhanced chemosensitivity of OC cells to cDDP, as evidenced by a marked reduction of IC50 value. Metformin also potently suppressed cell migratory and invasive potentials. Mechanistic investigations revealed that metformin up-regulated epithelial marker E-cadherin and down-regulated mesenchymal marker N-cadherin. Concurrently, it suppressed the expression of pivotal EMT-transcription factors (Snail, Slug, Zeb-1), alongside the disruption of mesenchymal-like cell cytoskeleton. Mechanistically, metformin exerted multi-level suppression of TGF-β1/Smads axis, evidenced by inhibiting TGF-β1 secretion, downregulating the expression and phosphorylation of TGF-β receptor I/II, and reducing the protein level, phosphorylation and nuclear translocation of Smad2/3/4. Crucially, the suppressive effects of metformin on EMT, chemoresistance, and metastatic potential were impaired by exogenous TGF-β1. Conclusions: Our findings demonstrated that metformin counteracted EMT, cDDP resistance and metastatic potential in OC via TGF-β1/Smads pathway, supporting the therapeutic potential of repurposing metformin as a promising adjunctive treatment.