Abstract 5158: Estrogen receptor β agonists: A novel therapeutic strategy for breast cancer

Background: Estrogen receptor (ER) positive breast cancer accounts 80% of all breast cancer subtypes. ER exists as ERα and ERβ, which are encoded by ESR1 and ESR2 genes, respectively. ERα stimulates the growth of breast cancer cells, while ERβ suppresses cancer cells. We hypothesize that activation of the ERβ may inhibit the viability of cancer cells in ER positive breast cancer without any effect on ERα. Material and Methods: Quantitative RT-PCR was performed with the DNase-treated RNA isolated from various breast cancer cell lines using gene-specific primers spanning exon-exon junctions that include introns in the corresponding genomic sequence to avoid genomic DNA amplification. Gene expression was calculated by ΔΔCt method using GAPDH as an internal control. Immuno-blot analyses were performed on lysates prepared from cells in log phase of growth. Proteins were detected by Enhanced Chemi-Luminescence (ECL) method. Viability of cells treated with ERβ specific agonists was determined by using CellTiter-Glo® 2.0 assay. HEK 293T cells were co-transfected with ERE-luciferase, Renila luciferase, and ESR1/ESR2 plasmids. Following treatment with ERβ agonists or estradiol, Dual Luciferase activity was measured with the lysates prepared from the cells. For clinical correlation, an IRB-approved single institution retrospective analysis was performed for 37 patients with metastatic HER2-negative ER-positive breast cancer to determine the mRNA expression levels of the genes including CCND1, MYC, IGF-1, Bcl-2, MMP-1, FN1; IGFBP-4, E2F4, CXCL12, PGR, EBAG9, and TRIM25 and correlated with ERα and ERβ. Descriptive analysis of gene expression was done using Spearman correlation coefficients and Cox proportional hazards regression. Results: Our experiments show that ERβ is expressed in ER positive breast cancer cell lines and that drugs which selectively activate ERβ, without activating ERα, inhibit the viability of these cells. One such compound has been invented at our institution is a highly selective activator of ERβ. Clinically, we found that ESR2 is positively correlated with CXCL12 (rho = 0.54, p (rho = -0.45, p = 0.005), ESR1 (rho = -0.35, rho = 0.033). We did not find a correlation between ESR2 and Overall Survival in this data set. Conclusion: ERβ agonist is highly selective to treat ER positive breast cancer. We are in the process of testing this compound in murine xenografts of human breast cancer cell lines. If the experiments planned in this project indicate that this is a viable strategy for breast cancer, we will plan to move forward to early trials in human patients in the future. Citation Format: Mathew Cherian, Jharna Datta, Mahmoud Kassem, Natalie Willingham, Jasmine Manouchehri, Joel David, Mirisha Sheth, Alexa Magner, Rahul Mal, Evan Morgan, Jeffrey VanDeusen, Sagar Sardesai, Nicole Williams, Daniel Stover, Maryam Lustberg, Robert Wesolowski, Bhuvaneswari Ramaswamy, Ramesh Ganju. Estrogen receptor β agonists: A novel therapeutic strategy for breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5158.