Abstract 5711: Therapeutic induction of tumor-selective ferroptosis in models of pancreatic cancer

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDA) is an aggressive cancer with few therapeutic options. Oncogenic signaling from mutant Kras, the driving oncogene of PDA, drives ROS production, making PDA cells reliant on ROS detoxification processes. To detoxify ROS, mammalian cells use thiols derived from the semi-essential amino acid cysteine, which is imported from exogenous pools of cystine via the system xC− cystine/glutamate antiporter. We found that cysteine depletion in multiple human PDA lines induced a rapid, oxidative, iron-dependent form of non-apoptotic cell death called ferroptosis. Confirming work in other systems, we found that glutathione depletion was necessary for the induction of ferroptosis in PDA cells. However, depletion of glutathione alone was not sufficient to induce ferroptosis, indicating that modulation of other cysteine-dependent processes must also play a role in ferroptosis. Using carbon-labelled cystine, we determined that extracellular cystine is quickly incorporated into coenzyme A. Furthermore, dual inhibition of both CoA and GSH synthesis combined to induce ferroptosis, and CoA treatment rescued the induction of ferroptosis following cysteine depletion. To assess whether cysteine depletion could be useful for targeting pancreatic tumors in vivo, we utilized both genetic and pharmacological approaches. First, we generated a dual recombinase mouse model in which the system xC- gene Slc7a11 can be acutely, systemically deleted in mice with established K-ras/p53 mutant PDA. Acute deletion of Slc7a11 in mice with established PDA led to tumor stabilizations/regressions and increased overall survival, and this was fully reversed by co-treatment with the membrane-permeable cysteine analog NAC. Second, we treated the well validated KPC genetic model of PDA with cyst(e)inase, an engineered enzyme that breaks down cysteine and cystine in circulation. Tumor-bearing KPC mice treated with cyst(e)inase also exhibited tumor responses. In both the genetic and pharmacological models, we observed tumor-selective necrosis and confirmed the induction of ferroptosis using several orthogonal techniques, including electron microscopy, immunohistochemistry, histopathology, and laser capture microdissection/RNA sequencing. These data demonstrate the potential therapeutic utility of targeting cystine import in pancreatic cancer. Citation Format: Michael Badgley, Kathleen DelGiorno, Geoffrey Wahl, Costas Lyssiotis, Kenneth P. Olive. Therapeutic induction of tumor-selective ferroptosis in models of pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5711.