Abstract 4985: Understanding the vulnerabilities in cancer cells upon inhibition of glutathione synthesis

• Published in: Cancer research (Chicago, Ill.) Ill.), 2017-07, Vol.77 (13_Supplement), p.4985-4985
• Main Authors: Harris, Isaac S., Endress, Jennifer E., Brugge, Joan S.
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2017-4985

A hallmark of cancer is the rewiring of cellular metabolic pathways, including those that mediate oxidative stress. Cancer initiation and progression, which demands increased production of ATP and synthesis of proteins, also results in elevated generation of toxic by-products such as reactive oxygen species (ROS). Cancer cells counteract ROS by increasing the production of antioxidants, which convert ROS into benign species. It has been shown that production of glutathione (GSH), the most abundant intracellular antioxidant, is necessary for many cancers to initiate malignant transformation. Whether inhibition of GSH synthesis can impact the survival of established malignant tumors remains poorly understood. In this study we investigated the extent to which GSH is required in cancer cells and across different subtypes of breast cancer. Profiling of an extensive panel of breast cancer cell lines demonstrated that the majority of cells are resistant to death after acute GSH depletion, while only luminal breast cancer cells are sensitive to chronic GSH depletion. To understand how most tumor cells are resistant to GSH depletion and oxidative stress, we conducted a small-molecule high-throughput screen interrogating more than 500 compounds in a 10-point dilution format. Importantly, screening plates were imaged and cell numbers quantified to avoid any false positives/negatives potentially associated with interrogating cellular metabolism using classical high throughput techniques, such as CellTiter-Glo. This screen revealed that depletion of glutathione sensitized breast cancer cells to inhibition of deubiquitinases, resulting in a drastic induction of a proteotoxic stress response. Furthermore, this sensitivity was found to be specific to malignant cells, as non-transformed cells were resistant to the combined treatments. It has been hypothesized that GSH, acting as an abundant thiol group, non-enzymatically reacts with ubiquitin and limits ubiquitination of proteins. Loss of glutathione, in combination with deubiquitinase inhibitors, leads to deregulation of ubiquitinated protein pools, and cancer cells undergo proteotoxic stress and cell death. These findings elucidate a novel vulnerability in cancers cells and shed light on an unexpected relationship between cancer metabolism and protein homeostasis. Citation Format: Isaac S. Harris, Jennifer E. Endress, Joan S. Brugge. Understanding the vulnerabilities in cancer cells upon inhibition of glutathione synthes