Abstract P3-11-08: Inhibition of Sirtuin 3 Sensitizes Breast Cancer Cells to Fulvestrant

Abstract Endocrine therapy can lead to nutrient deprivation by reducing glucose and glutamine uptake and total cellular ATP production. The ability of cells to bypass this metabolic stress is fundamental to how they regulate BC growth and acquire endocrine resistance. Sirtuins (SIRTs) are NAD+-dependent deacylases and regulate a widerange of intracellular processes including metabolism. SIRT3, activated by calorie restriction, modulates mitochondrial adaptation to low energy input. It has a key role in mitochondrial integrity and function, regulating cell survival, death and metabolic pathways, regulating the shift to amino-acid and fatty-acid catabolism. SIRT3 can maintain ROS levels at the appropriate levels for sustaining a proliferative phenotype, preventing apoptosis and promoting carcinogenesis. A role of SIRT3 in epigenetic regulation has also been reported. We used Differential Dependency Network analysis to compare the wiring of the SIRTs and key metabolism-related genes in matched antiestrogen- sensitive vs. resistant breast cancer (BC) cells, which identified several novel signaling hubs including CDKN2A (p16), linking SIRT3 to cell proliferation. The ability of SIRTs to sense and respond to changes in energy, coupled with their deacetylase/deacylase functions, could provide a mechanism for the cell to rewire signaling and maintain a newly acquired drug-resistant phenotype. Using endocrine sensitive (LCC1) and resistant (LCC9) BC cells, we confirmed the higher expression of SIRT3 in LCC9, compared to LCC1 cells. Upregulation of SIRT3 expression within 24 hrs of Fulvestrant (ICI 1 µM) treatment (p=0.0176) in LCC1 was shown, but no effect was observed in LCC9 cells. Conversely, treatment with 17β-estradiol (E2- 10 nM) did not significantly affect SIRT3 expression in either LCC1 or LCC9 cells. Inhibition of SIRT3 acitivity, using the LC0296 inhibitor (15 µM), reduced growth rate in LCC1 and SIRT3-silenced LCC9 cells under treatment with ICI (1 nM and 1 µM, respectively) (p< 0.0001, p< 0.001 respectively). Treatment with SIRTUIN 3 inhibitor and ICI induced apoptosis in LCC1 and SIRT3-silenced LCC9 cells compared to the untreated control and ICI only treated cells (p< 0.001). The combination SIRT3 inhibitor (15 µM) plus ICI (0.5 µM) increased ROS production in LCC9-SIRT3 silenced cells in 24 hours of treatment compared to the untreated control and ICI only treated cells (p< 0.001). SIRT3 inhibitor (15 µM) decreased LCC1 cell spheroid formation (p< 0.05), however it didn’t show additive effect to the effect of ICI (0.5 µM) in the same conditions. The combination of SIRT3 inhibitor (15 µM) and ICI (1 µM) reduced the growth of LCC9 SIRT3-silenced cells in detached condition compared to untreated control and ICI only treated cells (p< 0.001). The results show that SIRT3 may have a role in Fulvestrant response in BC cells; the mechanism is under investigation in our laboratory. Citation Format: Karla Andrade de Oliveira, Surojeet Sengupta, Lu Jin, Fabia de Oliveira Andrade, Melike Ozgu-Onal, Anil Yadav, Robert Clarke. Inhibition of Sirtuin 3 Sensitizes Breast Cancer Cells to Fulvestrant [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 P3-11-08.