The regulators of peroxisomal acyl-carnitine shuttle CROT and CRAT promote metastasis in melanoma

Circulating tumor cells (CTCs) are the key link between a primary tumor and distant metastases, but once in the bloodstream loss of adhesion induces cell death. To identify mechanisms relevant for melanoma CTC survival we performed RNAseq and discovered that detached melanoma cells and isolated melanoma CTCs rewire lipid metabolism by up-regulating fatty acid transport and fatty acid beta-oxidation (FAO) related genes. In melanoma patients high expression of fatty acid transporters and FAO enzymes significantly correlates with reduced progression free and overall survival. Amongst the highest expressed regulators in melanoma CTCs were the carnitine-transferases CROT and CRAT, which control the shuttle of peroxisome derived medium-chain fatty acids (MCFAs) towards mitochondria to fuel mitochondrial FAO. Knockdown of CROT or CRAT and short-term treatment with peroxisomal or mitochondrial FAO inhibitors thioridazine or ranolazine suppressed melanoma metastasis in mice. CROT and CRAT depletion could be rescued by MCFA supplementation, indicating that the peroxisomal supply of fatty acids is crucial for the survival of non-adherent melanoma cells. Our study identifies targeting the fatty acid based cross-talk between peroxisomes and mitochondria as a potential therapeutic opportunity to challenge melanoma progression. Moreover, the discovery of the anti-metastatic activity of the FDA-approved drug ranolazine carries translational potential.