Abstract 2339: Fulvestrant regulation of SIRT1 and SIRT3 expression in breast cancer cells
Authors: De Oliveira Karla A. , Sengupta Surojeet , Jin Lu , Clarke Robert 
Published: June 2022

Abstract
Estrogen receptor positive (ER+) breast cancers (BC) that do not respond to endocrine therapies exhibit lower response rates to chemotherapy than other subtypes, implying that endocrine resistance may confer cross-resistance to cytotoxic drugs and contribute to the poor responses to chemotherapy in recurrent ER+ disease. Endocrine therapies can reduce glucose (GLC) and glutamine uptake and total cellular ATP production in BC cells, and the ability of cells to bypass this metabolic stress is fundamental to how endocrine therapies regulate BC growth in a way that leads to acquired endocrine resistance and cross-resistance to other drugs. Sirtuins are NAD+-dependent deacylases. SIRT1 deacetylates histones and various transcription factors, and regulates GLC metabolism through TORC2, PGC1α, FOXO1. SIRT3, activated by caloric restriction, modulates mitochondrial adaptation to low energy input. SIRT3 destabilizes HIF-1α, and then regulates glycoytic gene expression. The role of SIRT3 in epigenetic regulation has been reported. Using Differential Dependency Network analysis to compare the wiring of the SIRTs and key metabolism-related genes in matched antiestrogen- sensitive vs. resistant BC cells, guided by gene related to the nicotinate and nicotinamide metabolism, and associated with clinical outcome in ER+ patients treated with an endocrine therapy, we identifyed several novel signaling hubs including: CDKN2A (p16) Hub, linking SIRT3 to cell proliferation; TP53 Hub, linking SIRT5 to clinical resistance to aromatase inhibitors, cell survival and proliferation; ATM Hub that comprises ATM/SIRT2/SIRT4/HIF1A and may functionally link endocrine resistance to chemoresistance, consistent with the relatively poor responses of ER+ BC to cytotoxic drugs. Hence, 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 enabled by epigenetically maintained changes in genes that control metabolism. Using endocrine sensitive (LCC1) and resistant (LCC9) BC cells, we confirmed the higher expression of SIRT1 and 3 in LCC9, compared to LCC1 cells. We further showed an upregulation of SIRT3 expression within 24 hrs of Fulvestrant (1 µM) treament (p=0.0176) in LCC1, but no effect was observed in LCC9 cells. Conversely, treatment with 17β-estradiol (10 nM) did not significantly affect SIRT3 expression in either LCC1 or LCC9 cells. SIRT 1 expression in LCC1 cells was not regulated by ICI within 72 hrs of treatment. In ER+ BC patients, lower expression of SIRT3 is associated with poor relapse free survival (RFS) (HR=0.57; CI=0.43-0.76); p= 7.7x 10-5) whereas higher expression of SIRT5 is associated with poor RFS (HR=2.5; CI=0.99-6.59; p=4.4x10-2). We will use transfection assays for knockdown/overexpression of SIRTs to investigate their roles in therapy resistance.
Citation Format: Karla A. De Oliveira, Surojeet Sengupta, Lu Jin, Robert Clarke. Fulvestrant regulation of SIRT1 and SIRT3 expression in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2339.