Mitochondrial ACSS1 links acetate metabolism to pyrimidine biosynthesis in nutrient-stressed B-cell lymphomas.

Acetate serves as an alternative carbon source in nutrient-limited tumors, yet its role in supporting nucleotide biosynthesis remains poorly understood. Here, we identify the mitochondrial enzyme ACSS1 as a key metabolic driver in mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), and chronic lymphocytic leukemia (CLL). ACSS1 is frequently overexpressed and catalyzes the conversion of acetate to mitochondrial acetyl-CoA, sustaining oxidative metabolism and biosynthesis under nutrient stress. Genetic silencing of ACSS1 impairs mitochondrial respiration and disrupts acetate incorporation into acetyl-CoA, TCA cycle intermediates, glutamate, and aspartate, while markedly reducing 13C-acetate labeling of dihydroorotate and orotate, intermediates in de novo pyrimidine synthesis. Untargeted metabolomics reveal enrichment of pyrimidine biosynthesis pathways in ACSS1-high cells. Notably, acetate or uridine supplementation rescues the growth of ACSS1-deficient cells, confirming a functional link between acetate metabolism and nucleotide synthesis. Importantly, in vivo studies using two different MCL xenografts demonstrate that ACSS1 knockdown profoundly suppresses tumor growth, indicating that ACSS1 is required not only for metabolic adaptation of lymphoma cells in vitro but also in vivo. Collectively, our results uncover an ACSS1-dependent mitochondrial acetate-pyrimidine axis that sustains lymphoma growth and represents a previously unrecognized therapeutic vulnerability.