Abstract PS2-11-18: Acetyl coA-fuels lipid storage to support triple negative breast cancer chemoresistance

Abstract Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype in which neoadjuvant chemotherapy (NACT) is the backbone of standard of care. Unfortunately, ∼45% of patients have residual tumor burden following NACT, strongly associated with poor prognoses. Our group previously demonstrated that mitochondrial oxidative phosphorylation (oxphos) is upregulated and is a therapeutic vulnerability in chemo-refractory TNBC. We used metabolomic flux tracing to show a heightened contribution of glucose oxidation to the tricarboxylic acid (TCA) cycle in residual human TNBC cells refractory to several conventional chemotherapies (PMID: 36813854). Subsequently, we found significantly elevated abundance of citrate and acetyl-coA (AcCoA) in residual cells, and glucose-derived heavy carbon was more strongly incorporated into both metabolites in residual relative to naïve cells. Both citrate and AcCoA are TCA cycle intermediates and can both contribute to fatty acid synthesis (FAS). Indeed, we observed drastic lipidomic remodeling, largely characterized by elevation of triglycerides, long chain fatty acids, and poly unsaturated fatty acids (PUFAs) in cultured human cells as well as in orthotopic PDX tumors following chemotherapy relative to their treatment naïve counterparts. This was accompanied by significant increase in the number of lipid droplets (LDs) in residual cells. Our analyses of publicly available human TNBC proteomic and transcriptomic data (PMID: 36001024) affirmed the significant association of fatty acid metabolism with TNBC chemoresistance, as well as its upregulation in treated tumors relative to their treatment naïve counterparts. Mining those data led us to ATP citrate lyase (ACLY), the rate limiting enzyme for cytosolic AcCoA production from citrate. Given these data, we hypothesized that ACLY converts excess citrate, generated by heightened mitochondrial respiration, to AcCoA to promote lipid production and storage to support TNBC chemoresistance. Western blotting revealed protein levels of ACLY and its activating phosphorylation mark Ser455 increased in human TNBC cells surviving treatment with doxorubicin and carboplatin. ACLY knockdown or inhibition with BMS-303141 potently reduced chemotherapy-induced accumulation of AcCoA and LDs and elicited substantial lipidomic changes consistent with increased PUFAs. Cell growth experiments examining TNBC cells treated with conventional NACT agents and ACLY inhibition or knockout showed significantly impaired growth in combination-treated cells compared to cells given either of the single agents. These data indicate that NACT can cause accumulation of AcCoA, heightened LDs, and lipidomic rewiring through ACLY. ACLY is a novel functional dependence of chemo-refractory TNBC cells and may represent a useful therapeutic target. Notably, perturbation of ACLY in nontumor mammary epithelial cells did not alter ACLY expression, ACLY phosphorylation at Ser455, or increase LDs and mice treated with BMS-303141 exhibited no overt signs of toxicity. We posit that TNBC cells adapt to the stress of NACT by upregulating lipid synthesis and storage in conjunction with glucose catabolism, enhancing metabolic flexibility and cell survival. Citation Format: K. E. Pendleton. Acetyl coA-fuels lipid storage to support triple negative breast cancer chemoresistance abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-11-18.