Fighting Melanoma Drug Resistance: Synergistic Effects of Metformin and PLX4032 in Patient-Derived Cells

Introduction Malignant melanoma often harbors the BRAFV600E mutation, rendering it initially responsive to PLX4032 (PLX), a BRAF inhibitor. However, drug resistance commonly arises within six months of treatment. Our previous study demonstrated that PLX resistance of two patient-derived melanoma cell lines is related to oxidative phosphorylation. Therefore, our hypothesis is that metformin—an antidiabetic drug known to inhibit mitochondrial respiration—could represent a promising strategy to overcome resistance in BRAF-mutant melanoma. Methods Experiments were conducted on PLX-resistant MeOV (BRAFV600E) and MeTA (BRAFV600D) metastatic melanoma cells (Garbarino et al., 2022) treated with metformin (10 mM) and/or PLX (1.5 µM) for up to 120 h. Cell responses were assessed through MTT assays (viability/proliferation), X-Gal staining (senescence), LPO staining (lipid peroxidation), and clonogenic assays. Results Metformin sensitized both MeTA and MeOV cells to PLX, with a more rapid and marked effect in MeTA cells, which showed a 20% drop in metabolically-active cells within 24 h. Moreover, an induction of cellular senescence and lipid peroxidation was observed in both populations. Noteworthy, metformin alone reduced clonogenic potential in both models while its combination with PLX was able to strongly inhibit clonogenicity only in MeTA cells, indicating a synergistic response. Conclusions These findings suggest that metformin may overcome PLX resistance in BRAF-mutant melanoma. Its ability to induce senescence, reduce viability, and suppress clonogenic growth—especially in MeTA cells—highlights a metabolic vulnerability of resistant metastatic melanoma that could be therapeutically targeted.