Antitumor efficacy of repurposed phenformin in preclinical models of epithelial ovarian cancer

Phenformin is a biguanide-class antidiabetic drug and has demonstrated anticancer activity in various malignancies. Epithelial ovarian cancer (EOC), which often develops chemoresistance, remains a lethal disease with a poor prognosis. While metformin has been widely studied, there is a need for more potent metabolic disruptors to overcome EOC progression. In this study, we examined the efficacy of phenformin in EOC with both in vitro and in vivo animal models. Cytotoxicity of phenformin was determined in chemo-sensitive (A2780, HeyA8, and SKOV3ip1) and chemo-resistant (A2780-CP20, HeyA8-MDR, and SKOV3-TR) EOC cell lines. Signaling pathways and apoptotic mechanisms affected by phenformin were analyzed by Western blot and intracellular ATP level assays. The in vivo efficacy of phenformin was examined with EOC cell line-derived orthotopic xenografts and patient-derived xenograft (PDX) mice models. Phenformin inhibited cell growth and induced apoptosis in all EOC cell lines, exhibiting superior cytotoxicity compared to metformin. Western blot analysis revealed that the AMPK–mTOR signaling pathway was significantly modulated by phenformin, characterized by AMPK activation and mTOR inhibition. In vivo efficacy studies with cell line-derived xenografts and PDX models demonstrated that phenformin significantly decreased tumor growth in both platinum-sensitive and platinum-resistant environments. Although phenformin enhanced chemotherapy-induced cytotoxicity in vitro , the primary antitumor benefit in vivo was driven by phenformin monotherapy. In conclusion, phenformin exerts potent antitumor effects against both chemo-sensitive and chemo-resistant EOC models through the inhibition of the AMPK–mTOR signaling pathway. Our findings suggest that phenformin might be a promising repurposed therapeutic candidate for EOC, particularly for chemo-resistant disease.