Abstract 5098: Targeting fatty acid dependency in hormone receptor positive HER2 negative drug tolerant persister bone metastases

Abstract The HR + subtype constitutes 65% of breast cancer (BC) cases with a 1/3 of patients eventually developing metastatic disease, most often in bone. This implicates a drug-tolerant persister cancer cell (DTP) population as a source of disease recurrence. Mouse models of primary and metastatic dormancy along with human tumor transcriptional profiles suggest preferential use of fatty acids (FA) by DTPs, offering fatty acid inhibition as a potential therapeutic vulnerability. HR+ BC cells were treated ± 1 nM 17b-estradiol (E2) for 14 d to provide growing and DTP cell populations. Cells were then treated ± inhibitors of fatty acid transporter CPT1a or fatty acid synthase (FASN). Assay endpoints included levels of proteins and transcripts associated with fatty acid metabolism. CD36 over-expressing, shRNA knock-down, and control cell lines were cultured with exogenous FA adipocytes, or treated with adipocyte-condition medium; assay endpoints included fatty acid uptake, growth response, and levels of fat metabolism proteins and stored lipid. Luciferase-labeled xenografts were induced in NSG mice with E2, which was removed for 90 d to induce tumor regression and yield DTP populations both orthotopically and intra-tibially. Mice were randomized to treatment with vehicle or CD36 mAb and assayed for DTP burden by imaging. Tumors were harvested and molecular endpoints were assessed. DTPs had increased lipid uptake compared to E2-treated controls. Estrogen deprivation increased levels of fatty acid metabolism-associated proteins, and FASN inhibition induced CD36 upregulation, indicating a potential compensatory mechanism between sources of fatty acids. In DTPs, culture with FA supplementation, adipocyte-conditioned media, or adipocyte co-culture rescued growth to levels observed with E2, suggesting the abundance of FA may push DTP cells out of dormancy. Functional metabolic assays showed inhibition of FASN, CPT1a, or CD36 reduced the ability of DTPs to use fatty acid oxidation to drive respiration. Xenografts showed model-specific upregulation of FASN or CD36 after 90 d of E2 deprivation compared to baseline. Treatment of mice bearing MCF-7 primary and metastatic xenografts with a CD36-neutralizing mAb decreased DTP burden compared to vehicle control. Preclinical modeling suggests that DTPs have an increased dependence upon fatty acids (e.g., mammary fat pad, bone associated adipocytes, co-culture of adipocytes, or FA supplementation) than their proliferative counterparts, offering fatty acid inhibition as a therapeutic vulnerability, particularly for bone-tropic DTPs. Citation Format: Abigail E. Goen, Jonathan D. Marotti, Todd W. Miller. Targeting fatty acid dependency in hormone receptor positive HER2 negative drug tolerant persister bone metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5098.