Abstract C117: Understanding the implications of CD36 expression in Hormone Receptor+/HER2- (HR+/HER2-) Drug Tolerant Persister breast cancer

Abstract Background In the HR+/HER2- subtype of breast cancer (BC), comprising approximately 70% of all BC cases, about one-third of patients develop late onset metastatic disease despite having no clinically detectable cancer in the interim. The cancer cells responsible for recurrence are known as drug-tolerant persisters (DTP). During clinical dormancy, these cells are exposed to estrogen deprivation via aromatase inhibition and, under similar hormone deprived (HD) conditions, preferentially utilize fatty acid metabolism. CD36, a critical protein in this pathway, represents a potential therapeutic target. Materials and Methods DTP cell populations were generated by treating hormone receptor positive (HR+) BC cells with ± 1 nM 17b-estradiol (E2) for 14 days. Cells were treated with or without inhibitors of CD36, fatty acid synthase (FASN), and the fatty acid transporter CPT1a. Assay endpoints included transcript and protein levels of fatty acid metabolism regulations (CD36, FASN, CPT1a), glycolysis, and oxidative respiration. CD36 overexpressing (OE), knockdown (KD), and control cell lines were cultured with or without exogeneous fatty acids (FA). Assay measured fatty acid uptake, growth response, functional metabolic activity, and levels of stored lipids and lipid metabolism proteins. Results Baseline CD36 expression varied across HR+/HER2- cell lines: MCF-7 (low), MDA-MB-415 (high), ZR75-1 (moderate), and T47D (moderate). CD36 expression was upregulated under HD conditions, as shown by qPCR and immunoblotting. Functional metabolic assays revealed that CD36 OE increased basal and maximal mitochondrial respiration, while KD impaired respiration. T47D-CD36-OE cells demonstrated higher neutral lipid uptake, decreased CPT1a protein expression, and enhanced mitochondrial respiration under both endogenous and exogenous FA inhibition. In contrast, T47D-CD36-KD cells demonstrated impaired basal and maximal respiration and increased CPT1a expression. Inhibition of CPT1a, CD36, FASN, and Complex 1 of the electron transport chain, assessed by Seahorse Assay, decreased mitochondrial respiration in DTPs, suggesting reliance on fatty acid oxidation for metabolic activity. Conclusions DTPs in HR+/HER- breast cancer preferentially utilize fatty acid oxidation under hormone-deprived conditions. CD36 OE drives increased respiration and lipid uptake, while reducing CPT1a expression, indicating a metabolic shift that supports persistence. These findings suggest that CD36 contributes to the survival and metabolic flexibility of DTPs and may represent a viable therapeutic target to disrupt dormancy and prevent late recurrence in hormone receptor-positive breast cancer. Citation Format: Alexys C. Gayne, Abigail E. Goen, Todd W. Miller, Kelli B. Pointer. Understanding the implications of CD36 expression in Hormone Receptor+/HER2- (HR+/HER2-) Drug Tolerant Persister breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr C117.