Complex I drives glutamine-dependent TCA cycle to support viability of MYChigh breast cancer cells.

In many cancers, stably elevated MYC levels drive sustained activation of anabolic programs and the cell cycle, creating opportunities for the synthetic-lethal targeting of MYChigh tumors. Enhanced mitochondrial respiration is a hallmark of MYC overexpressing cancer cells. Mitochondrial respiration sustains the TCA cycle by regenerating NAD+ through complex I-mediated oxidation of NADH, supporting the anabolic demand of MYC-driven cells. Metabolic carbon tracing reveals that MYC shifts the TCA cycle carbon source from glucose to glutamine. Inhibition of the glutamine-fueled TCA cycle using NAD+-depleting complex I inhibitors promotes MYC-dependent synthetic lethality in breast cancer cells. In mouse models of MYChigh tumors, combined inhibition of complex I and glutaminolysis produces persistent suppression of tumor growth. Altogether, the elevated respiration of MYChigh cells supports a glutamine carbon-enriched TCA cycle that meets anabolic demand, rendering MYChigh tumors selectively vulnerable to mitochondrial respiration and glutaminolysis inhibitors.