Androgen receptor and fatty acid oxidation cooperate in ferroptosis evasion in BRAFi resistant melanoma

Melanoma accounts for over 85% of all skin cancer deaths. Current therapies including drugs targeting BRAF and MEK significantly improve the prognosis of metastatic melanoma patients, yet innate or acquired resistance challenges long-term responses. We have shown previously that fatty acid beta-oxidation (FAO) is up-regulated during the acquisition of BRAF-inhibitor (BRAFi) resistance and that the FDA approved drug ranolazine, by targeting FAO attenuates the development of acquired resistance. However, how ranolazine-induced metabolic rewiring increases cell death is unclear. Here we identify ranolazine as a ferroptosis inducer in BRAFi-resistant melanoma, in which FAO serves as a ferroptosis surveillance mechanism. Accordingly, in progressed tumours of BRAFi treated patients up-regulation of FAO regulators correlates with increased expression of ferroptosis markers. BRAFi resistant cells are heavily poised for execution of ferroptosis; they display reduced glutathione levels, higher levels of long-chain polyunsaturated fatty acid (PUFA) membrane-incorporation, and increased membrane-resident phospholipid oxidation, all of which is amplified by ranolazine. Counteracting ranolazine action is MBOAT1/2 mediated phospholipid remodelling, which initiates reduced PUFA membrane-incorporation as ferroptosis surveillance mechanism. We show that the androgen receptor (AR), which is a determinant of BRAFi resistance, controls MBOAT1/2 expression, thereby contributing to ferroptosis resistance. In BRAFi resistant tumours and cell lines, we confirm AR upregulation predominantly in the MITF^low/AXL^high undifferentiated/neural-crest like state, but it also occurs in the MITF^high/AXL^low differentiated melanocytic state. The AR antagonist enzalutamide sensitises AR expressing melanoma cells to RSL3 and erastin independent of phenotype state, but in FAO^high BRAFi relapsed tumours AR up-regulation correlates with the undifferentiated/neural-crest like (UD/NC) state, and enzalutamide synergises with ranolazine in ferroptosis-induction in UD/NC cells. Thus, therapeutically combining ranolazine with the AR inhibitor enzalutamide to induce ferroptosis can circumvent dedifferentiation related BRAFi resistance and could increase therapeutic activity and long-term efficacy.