Electron transport chain inhibition increases cellular dependence on purine transport and salvage

Mitochondria house many metabolic pathways required for homeostasis and growth. To explore how human cells respond to mitochondrial dysfunction, we performed metabolomics in fibroblasts from patients with various mitochondrial disorders and cancer cells with electron transport chain (ETC) blockade. These analyses revealed extensive perturbations in purine metabolism, and stable isotope tracing demonstrated that ETC defects suppress de novo purine synthesis while enhancing purine salvage. In human lung cancer, tumors with markers of low oxidative mitochondrial metabolism exhibit enhanced expression of the salvage enzyme hypoxanthine phosphoribosyl transferase 1 (HPRT1) and high levels of the HPRT1 product inosine monophosphate. Mechanistically, ETC blockade activates the pentose phosphate pathway, providing phosphoribosyl diphosphate to drive purine salvage supplied by uptake of extracellular bases. Blocking HPRT1 sensitizes cancer cells to ETC inhibition. These findings demonstrate how cells remodel purine metabolism upon ETC blockade and uncover a new metabolic vulnerability in tumors with low respiration. [Display omitted] •ETC inhibition rewires purine metabolism•Cytosolic NAD(H) imbalance induces purine accumulation in ETC-deficient cells•HPRT1-mediated purine salvage supports NSCLC growth during ETC inhibition•Purine uptake is required to supply salvage upon ETC inhibition Wu et al. report that mitochondrial electron transport chain impairment induces a metabolic shift from de novo purine biosynthesis to purine salvage. Cancer cells with low electron transport chain activity require purine uptake and salvage to grow in culture and in vivo.