Abstract P3-11-11: Impaired Succinate Metabolism Supports Endocrine Therapy Resistance in ER Positive Breast Cancers

Estrogen receptor positive (ER+) breast cancer is the most common subtype among all breast cancers and is responsible for most breast cancer related deaths. Endocrine therapies, such as selective estrogen receptor modulators (SERM) and aromatase inhibitors (AI), often given in combination with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, are initially effective but the majority of advanced ER+ breast cancers eventually become refractory to endocrine therapies. Therefore, understanding the underlying molecular mechanisms that enable or promote resistance to endocrine therapies may lead to novel therapeutic targets. Cancer cells consume greater quantities of glucose to meet their energy and anabolic demands to support cell growth and proliferation. In this study, we used breast cancer cell models that are endocrine therapy sensitive and resistant and investigated the metabolites by growing the cells in the presence of the stable glucose isotope, UC13-Glucose. We measured the C13-labelled metabolites of glycolysis and the TCA cycle. Glucose consumption was higher in endocrine therapy resistant MCF7/LCC9 (LCC9) cells compared with parental MCF7 (MCF7) and estrogen independent, endocrine therapy sensitive MCF7/LCC1 (LCC1) cells. Notably, in LCC9 cells the m+4 and m+6 isotopomer of C-13 labelled citrate was absent with a concurrent high succinate:fumarate ratio. Furthermore, in LCC9 cells, most of the fumarate was unlabeled suggesting that fumarate was not generated from glucose. These results suggest that the TCA cycle is impaired in LCC9 cells and the conversion of succinate to fumarate is dysregulated. Succinate dehydrogenase (SDH) enzyme is responsible for reversible catalytic conversion of succinate to fumarate. SDH is a multimeric protein comprised of four different subunits and SDH assembly factor 2 (SDHAF2), which is a tumor suppressor gene. Comparable SDH enzyme activity was observed in LCC9 and LCC1 cells. Intriguingly, when SDH activity was inhibited using dimethylmalonate, the LCC9 cells were re-sensitized to both Fulvestrant and 4-hydroxytamoxifen. Succinate accumulation was accompanied with HIF 1-alpha stabilization and SDH inhibition led to lower levels of HIF1-alpha. This indicated that SDH may function in the conversion of fumarate to succinate in LCC9 cells. Our study further investigates the source of fumarate in LCC9 cells. Overall, this study suggests that targeting succinate metabolism may help to restore sensitivity to Fulvestrant and tamoxifen in endocrine therapy resistance in ER+ breast cancer cells. Citation Format: Anil Yadav, Karla Andrade de Oliveira, Lu Jin, Robert Clarke, Surojeet Sengupta. Impaired Succinate Metabolism Supports Endocrine Therapy Resistance in ER Positive Breast Cancers [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-11-11.