Abstract 711: γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple-negative breast cancer (TNBC) MDA-MB-453 cells is associated with a reduction in cellular proliferation and viability
Authors: Sultana Tasmin A. , Aldabaan Nayef , Sylvester Paul W. 
Published: June 2022

Abstract
Targeted therapy for triple-negative breast cancer (TNBC) remains challenging due to poor understanding of its molecular etiology. Previous studies have shown that androgen receptors (AR) are widely expressed in approximately one-third of TNBC, and are referred to as luminal androgen receptors (LAR). AR has recently emerged as a prognostic and treatment-predictive biomarker in breast cancer. However, the role of AR in TNBC remained elusive. Treatment with AR-antagonist have been shown to suppress AR activation and signaling in TNBC and results in a corresponding reduction in tumor cell proliferation and survival due to the initiation of apoptosis in these tumor cells. γ-Tocotrienol (γT3) is a natural isoform of vitamin E that displays potent anticancer activity. Results show that treatment with 0-7 μM γT3 induces a dose-responsive significant decrease, whereas treatment with 35 nM dihydrotestosterone (DHT) results in a significant increase of AR expression and corresponding increase in growth of MDA-MB-453 TNBC cells. Combined treatment of 7 μM γT3 with 35 nM DHT significantly inhibits DHT-induced proliferation and AR activation in MDA-MB-453 cells. Western blot analysis shows that combined treatment with γT3 and DHT induced a significant decrease in phosphorylated ERK1/2 (active form) expression, but had no effect on total ERK1/2 levels in MDA-MB-453 TNBC cells. Flow cytometry analysis shows that γT3 treatment was also found to induce G0/G1 cell cycle arrest and significantly increased the number of apoptotic and necrotic cells, as compared to MDA-MB-453 TNBC cells in the vehicle-treated control group. Western blot analysis shows that γT3 treatment also inhibited DHT-induced elevations in CDK2, CDK4, CDK6 and cyclin D1 expression (cell cycle progression biomarkers) and induces a significant increase in the expression of tumor suppressor protein, p53, in MDA-MB-453 TNBC cells. Similar treatment with 7 µM γT3 induces a corresponding significant increase in apoptosis biomarker expression of cleaved caspase-3 and Bax in MDA-MB-453 TNBC cells. In summary, results from these studies demonstrated that γT3 treatment inhibits AR expression, activation and signaling, as well as DHT-dependent cell proliferation and viability in TNBC. These finding also suggest that the LAR may be a potential therapeutic target for the treatment TNBC. This study was supported in part by funding from the Louisiana Cancer Foundation.
Citation Format: Tasmin A. Sultana, Nayef Aldabaan, Paul W. Sylvester. γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple-negative breast cancer (TNBC) MDA-MB-453 cells is associated with a reduction in cellular proliferation and viability [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 711.