Combination of the natural product mensacarcin with vemurafenib (Zelboraf) combats BRAF mutant and chemo-resistant melanoma in vitro by affecting cell metabolism and cellular migration

Melanoma is the most prevalent and aggressive form of skin cancer, often with a low survival rate due to rapid metastasis and a high occurrence of multi-drug resistance (MDR). In this study, we examine the combination treatment of the recently discovered cytotoxic bacterial metabolite mensacarcin and FDA approved therapeutic vemurafenib (Zelboraf). Vemurafenib is the standard regiment for BRAF V600E mutation positive patients with unresectable or metastatic malignant melanoma. On its own, menscarcin induces mitochondrial dysfunction in selected BRAF-mutant melanoma cell lines. In combination treatment, mensacarcin enhances vemurafenib's cytotoxicity via metabolic impairment. Specifically, it lowers cellular glucose uptake, decreases the oxygen consumption rate, reduces the abundance of glycolytic enzymes, and halts wound healing. Mensacarcin alone retains strong cytotoxic effects in three vemurafenib resistant cell lines SK-Mel-28PLXr, A375PLXr, and A2058PLXr with an average IC₅₀ of 1 μM, inducing apoptosis via the caspase-3/7 pathway. We also find that mensacarcin lowers metastatic migration in a wound healing assay and it alters the morphology of migrating cells on a nanofiber scaffold. Using extracellular matrix (ECM) mimicking fibers, mensacarcin treated cells exhibit a decrease in single cell maximum coil width and an increase in the protrusion length limiting cellular coiling behavior which may limit metastatic migration. In summary, the bacterial metabolite mensacarcin shows great promise as a melanoma drug lead in vitro: in combination with vemurafenib, the cytotoxic activity is enhanced, and alone, mensacarcin retains activity in BRAF inhibitor chemo-resistant melanoma cell lines, and features a unique, migratory limited single cell phenotype.