Acquired BRAFi Resistance Increases Melanoma Cell Sensitivity to Metabolic Targeting with Metformin

The use of BRAF inhibitors (BRAFi) for the targeted inhibition of the MAPK pathway represents a cornerstone of treatment for BRAFV600E-mutant melanoma. However, the rapid emergence of drug resistance remains a major clinical challenge. Mounting evidence indicates that therapy resistance is driven by both phenotypic plasticity and metabolic reprogramming. This study aimed to investigate the molecular, phenotypic, and metabolic adaptations underlying acquired resistance to the BRAFi GSK2118436 in A375 melanoma cells. BRAFi-resistant cells (A375-R) displayed cross-resistance to additional BRAFi and MEK inhibitors and clear features of epithelial–mesenchymal transition (EMT), including decreased E-cadherin, increased vimentin, and inhibitor-dependent spheroid compaction. Among the multiple metabolic modulators evaluated, inhibitors of mitochondrial respiration—particularly metformin and antimycin A—selectively impaired viability, clonogenicity, sphere formation and 3D growth of resistant cells. Importantly, while simultaneous BRAFi–metformin combination caused mostly antagonist effects, a sequential regimen (BRAFi followed by metformin) elicited additive/synergistic cytotoxicity in both 2D and 3D models. Collectively, these findings show that BRAFi resistance is driven by coordinated EMT and metabolic rewiring toward OXPHOS dependency and suggest that sequential metabolic targeting is an effective strategy to overcome therapy resistance in melanoma.