Selective abrogation of S6K2 identifies lipid homeostasis as a survival vulnerability in MAPK inhibitor-resistant NRAS-mutant melanoma.

Although oncogenic NRAS activates mitogen-activated protein kinase (MAPK) signaling, inhibition of the MAPK pathway is not therapeutically efficacious in NRAS-mutant (NRAS(MUT)) tumors. Here, we report that selectively silencing the ribosomal protein S6 kinase 2 (S6K2) while preserving the activity of S6K1 perturbs lipid metabolism, enhances fatty acid unsaturation, and triggers lethal lipid peroxidation in NRAS(MUT) melanoma cells that are resistant to MAPK inhibition. S6K2 depletion induces endoplasmic reticulum stress and peroxisome proliferator-activated receptor α (PPARα) activation, triggering cell death selectively in MAPK inhibitor-resistant melanoma. We found that combining PPARα agonists and polyunsaturated fatty acids phenocopied the effects of S6K2 abrogation, blocking tumor growth in both patient-derived xenografts and immunocompetent murine melanoma models. Collectively, our study establishes S6K2 and its effector subnetwork as promising targets for NRAS(MUT) melanomas that are resistant to global MAPK pathway inhibitors.