FASN targeting by G28UCM impairs mitochondrial fatty acid synthesis and reveals a FASN-SDHB synthetic interaction.

Metabolic reprogramming in cancer relies on lipid synthesis and mitochondrial function, yet how these processes, other than citrate flux and β-oxidation, intersect remains unclear. While inhibitors of lipogenic pathways have been developed as potential therapeutic agents in cancer therapy, their impact on oxidative metabolism is underexplored. Here, we identify the fatty acid synthase (FASN) inhibitor G28UCM as a compound that additionally destabilizes mitochondrial fatty acid synthase (mtFAS) and succinate dehydrogenase subunit B (SDHB), thereby targeting cytosolic and mitochondrial metabolism. Unexpectedly, the decreased abundance of SDHB was linked to disruption of mtFAS, most notably downregulation of Lipoyl Synthase (LIAS). G28UCM induced profound metabolic stress, including pseudohypoxia, oxidative stress, endoplasmic reticulum stress, and ferroptosis. In contrast, genetic depletion of FASN failed to reproduce these effects. In addition to investigating the mechanism of action of G28UCM, our study revealed a genetic interaction between FASN and SDHB, establishing that their dual but not single loss of function is sufficient to impair tumor growth. The synthetic interaction was conserved across prostate cancer, neuroendocrine tumors, and renal carcinoma cell models, including patient-derived cells, and combined inhibition of FASN and SDH markedly suppressed tumor progression in a breast cancer mouse model. Our findings point to new therapeutic opportunities for FASN inhibition beyond tumor initiation, with particular relevance to cancers associated with malignant SDHB mutations.