Abstract 967: γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple negative breast cancer (TNBC) MBA-MB-231 and MDA-MB-453 cells is associated with a reduction in epithelial-to-mesenchymal transition (EMT)

Abstract

Abstract Triple-negative breast cancers (TNBC) are a subset of breast cancer that is highly aggressive and has a poor prognosis. The TNBC subtype has no effective molecular targeted therapies. Gene expression studies have identified a subset of TNBC that is enriched with androgen receptors (AR) and androgen receptor signaling. AR levels are most abundant in the luminal AR (LAR) molecular subtype of TNBC, but other non-LAR molecular TNBC subtypes also display high levels of AR expression and activity. Interference with androgen signaling in TNBC with AR-inhibiting drugs have shown a reduction in epithelial-to-mesenchymal transition (EMT), which is a process by which epithelial cells lose their cell polarity and cell-cell adhesion and gain migratory and invasive properties to become mesenchymal-like stem cells. Approximately one-third of TNBC expressed AR, and evaluation of AR-positive TNBC primary tumors shows nuclear localization of AR, an indication of transcriptionally active receptors. Previous studies have shown that AR inhibition or AR knockdown significantly reduces migration and invasion and EMT in different TNBC cell lines. γ-Tocotrienol is a member of the vitamin E family of compounds that displays potent anticancer effects and have little or no effect on normal cell viability. Studies show that treatment with 0-7 µM γ-tocotrienol reduced AR levels, proliferation, migration and invasion in a dose-responsive manner in TNBC MDA-MB-231 and MDA MB-453 cell lines. Results also show that treatment with 5 µM (MDA-MB-231) and 7 µM (MDA-MB-453) γ-tocotrienol induced a reversal in EMT cell biomarkers, as well as reversal in EMT morphological and behavioral characteristics in these TNBC cell lines. Western blot analysis show that similar treatment with γ-tocotrienol significantly decreased DHT-induced N-cadherin (mesenchymal cell biomarker) and increased expression in cytokeratin 18 and E-cadherin (epithelial cell biomarkers) in these cells. AR signaling is known to play an important role in stimulating DHT-induced EMT by stimulating the STAT3/Snail signaling pathway in MDA-MB231. However, results in the present study shows that γ-tocotrienol treatment significantly inhibited activation of STAT3 and Snail proteins. Additional immunocytochemistry experiments showed that γ-tocotrienol treatment significantly inhibited DHT-induced cytoskeleton changes in TNBC MDA-MB-231 and MDA MB-453 cell lines. In conclusion, these results demonstrated that γ-tocotrienol treatment inhibits AR expression and DHT-dependent EMT and cytoskeleton changes in TNBC cells. These findings suggest that AR may be a potential therapeutic target for treating both LAR and non-LAR TNBC subtypes. This study was supported in part by funding from the Louisiana Cancer Foundation. Citation Format: Nayef Aldabaan, Tasmin A. Sultana, Paul W. Sylvester. γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple negative breast cancer (TNBC) MBA-MB-231 and MDA-MB-453 cells is associated with a reduction in epithelial-to-mesenchymal transition (EMT) [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 967.