Abstract 3902: Glutathione as a potential marker of tamoxifen resistance in breast cancer

Abstract Glutathione (GSH) is an antioxidant with an important protective intracellular role against reactive oxygen species. Increased glutathione level is associated with higher rates of metastases and a more aggressive behavior in breast cancer. This study aims to study the molecular and metabolic changes in glutathione synthesis in tamoxifen resistant (TAM-R) MCF-7 breast cancer cell lines.Methods: Three tamoxifen resistant MCF-7 cell lines were produced by using two methods. The first was achieved by treating the cells with tamoxifen and gradually increasing the amount until reaching a predetermined concentration of tamoxifen. The second was achieved by giving multiple fixed concentrations of tamoxifen, the third model was produced from the second by treating the cells with continuous 1µM of tamoxifen. mRNA and metabolites were extracted from the cell lines. cDNA was synthesized from the extracted mRNA, and gene expression of glutathione synthetase (GSS) was measured using real-time PCR. Nuclear Magnetic Resonance technique with PABO probe was used for metabolic profiling of extracted metabolites from the resistant and sensitive MCF-7cells and Chenomix software for quantification. Additionally, Kaplan Meier plotter (https://kmplot.com/) was used to predict the significance of GSS gene expression to overall survival of breast cancer patients. Results: A significant increase in glutathione accompanied with significant decrease in cysteine levels were found in TAM-R cells compared to control TAM sensitive cells. However, there was a 2 times reduction in the expression of GSS in TAM-R cells. Correlation of GSS gene expression among ER +ve, PR +ve patients who received tamoxifen in their therapy showed that its down regulation is significantly linked to poor overall survival (p-value 0.022 and HR of 0.7). Conclusion: The significant increase of glutathione in TAM-R cells may contribute to their increased resistance to oxidative stress and exhibition of a more aggressive behavior. Moreover, the decrease in GSS expression is a strong indicator of decreased glutathione synthesis in TAM-R cells as a result of cysteine depletion in the cells that was correlated to poor overall survival among BC patients. However, high glutathione levels in TAM-R cells could be due to increased glutathione regeneration in TAM-R cell lines compared to control. Citation Format: Yazan I. Hamadneh, Mohammad AlWahsh, Jawad Alrawabdeh, Roland Hergenröder, Lina A. Dahabiyeh, Lama Hamadneh. Glutathione as a potential marker of tamoxifen resistance in breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3902.