Abstract 4785: Disrupting redox regulated cancer stem cell state equilibrium by co-inhibition of glycolysis and thioredoxin/glutathione antioxidant pathways
Authors: Luo Ming , Shang Li , Brooks Michael , Jiagge Evelyn , Conley Sarah , Harouaka Ramdane , Zhu Yongyou , Merajver Sofia D. , Spitz Douglas R. , Wicha Max S. 
Published: July 2017

Abstract
Breast cancer stem cells (BCSCs) exist in a dynamic equilibrium of mesenchymal- (M) and epithelial-like (E) states that coordinately drive tumorigenesis, metastasis, and treatment resistance. Here, we show that BCSCs in both states display hyperactive aerobic glycolysis or oxidative phosphorylation (OXPHOS), depending on the availability of glucose. This metabolic plasticity is enabled by activation of genes regulating glycolysis and OXPHOS, as well as increased mitochondrial mass/activity. Despite their metabolic plasticity, E- and M-BCSCs exhibit markedly different vulnerabilities to inhibitors of glycolysis and redox metabolism. Glycolysis inhibition or hypoxia, by inducing oxidative stress, facilitates invasive M-BCSCs transition to their proliferative E state. This process is reversible by addition of the antioxidant N-acetyl-cysteine (NAC) and mediated by AMPK-dependent HIF1α stabilization, providing a molecular link between hypoxic/oxidant stress and BCSC phenotypic plasticity. Moreover, E-BCSCs are endowed with heightened thioredoxin (TXN) and glutathione (GSH) mediated antioxidant defenses, which are two major metabolic pathways to detoxify cellular hydrogen peroxide. We demonstrated that inhibition of the TXN pathway by Auranofin (AUR, an inhibitor of thioredoxin reductase) in SUM149 and human breast cancer xenograft tumor cells is sufficient to abrogate their tumorsphere forming activity and selectively deplete E-BCSCs by inducing their terminal differentiation and subsequent apoptosis. We also found that, although the inhibition of the GSH pathway by BSO (an inhibitor of GSH synthesis) was not sufficient to abrogate tumorsphere formation and E-BCSCs, co-inhibition of TXN and GSH pathways with low doses of AUR and BSO had a synergistic effect in suppressing tumorsphere forming activity, which could be rescued by NAC. Using patient-derived xenograft models of human triple negative breast cancer, we further validated that co-inhibition of glycolysis and TXN/GSH antioxidant pathways delivers synergistic antitumor effects to suppress tumor growth and regenerative potential by eliminating both M- and E-BCSCs. Hence, exploiting metabolic vulnerabilities of distinct BCSC states provides a potential therapeutic approach. As the CSC state equilibrium may be similarly regulated across a spectrum of tissue malignancies with diverse oncogenic drivers, the conceptual framework we build in this work to target metabolic vulnerabilities of distinct BCSC phenotypic states may have broad therapeutic applicability.
Citation Format: Ming Luo, Li Shang, Michael Brooks, Evelyn Jiagge, Sarah Conley, Ramdane Harouaka, Yongyou Zhu, Sofia D. Merajver, Douglas R. Spitz, Max S. Wicha. Disrupting redox regulated cancer stem cell state equilibrium by co-inhibition of glycolysis and thioredoxin/glutathione antioxidant pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4785. doi:10.1158/1538-7445.AM2017-4785