Abstract 4774: Adaptation to chronic oxidative stress promotes metabolic rewiring to maintain redox balance in HER2+ breast tumors
Authors: Mirabelli Caitlynn Nicole , Selva Rachel La , Annis Matthew , Najyb Ouafa , Hébert Steven , Kleinman Claudia , St-Pierre Julie , Siegel Peter , Ursini-Siegel Josie 
Published: April 2023

Abstract
Breast cancer is the most commonly diagnosed malignancy in women worldwide. Breast tumors possess a high degree of intra- and inter-tumoral heterogeneity, enabling the emergence of aggressive, therapy-resistant tumors. One contributor to breast tumor heterogeneity is reactive oxygen species (ROS), which are unstable oxygen-containing molecules that modify proteins, lipids, and DNA. Our lab has developed unique models of HER2+ breast cancer that evolved in vivo under conditions of low (ROSLOW) and high (ROSHIGH) chronic oxidative stress to acquire more aggressive properties. As such, we became interested in understanding the underlying mechanisms by which breast cancer cells capitalize on sustained oxidative stress to acquire more aggressive properties. We show that, relative to their parental and ROSLOW counterparts, ROSHIGH-evolved tumors are better able to maintain redox balance by coping with ROS-induced damage in vivo and following H2O2 treatment in vitro. Moreover, ROSHIGH-evolved breast cancer cells lose their aggressive phenotype in vitro, implying a necessary microenvironmental contribution. RNAseq analysis of parental and aggressive breast cancers further identified glycolytic and hypoxic transcriptional signatures that were preferentially induced in breast cancers that adapted to chronic oxidative stress. Therefore, we hypothesized that breast cancer cells conditioned to cope with chronic oxidative stress may re-wire their glucose metabolism to support ROS buffering, which may be facilitated by a hypoxic tumor microenvironment. Notably, ROSHIGH-evolved tumors are insensitive to inhibition of glycolysis using 2-deoxyglucose (2-DG); however, we show that they are specifically sensitized to inhibition of glutathione synthesis, and this sensitivity is exacerbated when treated in combination with 2-DG. As well, we show through glucose tracing that ROSHIGH-evolved tumors exhibit increased incorporation of glucose-derived carbons into glutathione. This data confirms that breast tumor adaptation to chronic oxidative stress promotes metabolic re-wiring to support ROS scavenging. To begin interrogating the role hypoxia plays in this phenotype, we assessed cell proliferation and levels of hypoxia-responsive genes following hypoxia exposure in our breast cancer models in vitro. Relative to their parental counterparts, breast cancer cells that adapted to chronic oxidative stress exhibit enhanced proliferation in hypoxia and are better able to upregulate hypoxia-responsive genes, even in response to modest changes in oxygen levels. Overall, our study shows that tumor adaptation under chronic oxidative stress promotes metabolic rewiring which may be facilitated by a hypoxic microenvironment.
Citation Format: Caitlynn Nicole Mirabelli, Rachel La Selva, Matthew Annis, Ouafa Najyb, Steven Hébert, Claudia Kleinman, Julie St-Pierre, Peter Siegel, Josie Ursini-Siegel. Adaptation to chronic oxidative stress promotes metabolic rewiring to maintain redox balance in HER2+ breast tumors. [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 4774.