Ren, Z.; Bernasocchi, T.; Kurmi, K.; Guo, C.; Jiang, K.; Zaniewski, E.; Lam, G.; Islam, K. N.; Joshi, S.; Li, X.; Smidt, I.; Morris, R.; Ordway, B.; Bossuyt, V.; Wang, G. X.; Chou, S.-H.; Zou, L.; Sanidas, I.; Spring, L. M.; Lawrence, M.; Rheinbay, E.; Haas, W.; Mostoslavsky, R.; Haigis, M. C.; Ellisen, L. W.

Chemoresistance is the leading cause of poor prognosis in triple-negative breast cancer (TNBC), yet the underlying mechanisms remain unknown. To reveal metabolic drivers of de novo chemoresistance in TNBC, we analyzed pretreatment primary tumor biopsies, employing quantitative proteomics and metabolomics. Chemoresistant TNBCs exhibit hallmarks of oxidative phosphorylation (OXPHOS) and altered nucleotide metabolism linked to overexpression of the mitochondrial sirtuin, SIRT5. Through gain- and loss-of-function studies and stable isotope tracing, we demonstrate that SIRT5 induces a coordinated metabolic switch that redirects glycolysis to the pentose phosphate pathway, thereby augmenting nucleotide pools, while enhancing glutaminolysis to support OXPHOS. Mechanistically, SIRT5 enhances conversion of 6-phospho-D-gluconate to ribulose-5-phosphate through demalonylation of 6-phosphogluconate dehydrogenase (6-PGD), and coordinately activates oncogenic c-MYC to promote glutamine utilization and dependence. Concurrently, SIRT5-induced nucleotide deregulation induces replication stress and hypersensitivity to ATR checkpoint activation, and ATR inhibition synergistically reverses chemoresistance in TNBC. Thus, elevated SIRT5 orchestrates a coordinated metabolic switch to expand nucleotide pools and drive chemoresistance, while producing ATR checkpoint dependence that represents a metabolic vulnerability of SIRT5-overexpressing TNBC.