3036 - Ferroptotic Potentiation of Radiation for the Treatment of Pancreatic Ductal Adenocarcinoma
Presenter(s)
J. Carmicheal1, A. Seas2, N. File3, P. Atri2, S. Kaur2, C. Lin4, and S. Batra2; 1University of Nebraska Medical Center, College of Medicine, Omaha, NE, 2University of Nebraska Medical Center, Omaha, NE, 3School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom, 4Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE
Purpose/Objective(s): Pancreatic ductal adenocarcinoma (PDAC) is an incredibly lethal malignancy. This high mortality is due in part to the inadequacy of current treatments. Novel methods to increase the therapeutic efficacy are needed. The significance of this study lies in the investigation of a novel sensitization mechanism that can be used to potentiate radiation therapy (RT). Production of reactive oxygen species (ROS) within a cell, can result in a lethal buildup of peroxidated lipid species in the cell membrane, inducing ferroptosis (an iron dependent form of cell death). Glutathione peroxidase 4 (GPX4) converts lethal lipid peroxides to nontoxic lipid alcohols. Inhibition of the cysteine-glutamate antiporter, system Xc (complex of SLC3A2 and SLC7A11), prevents the renewal of GPX4 activity. Importantly, system Xc can be inhibited pharmacologically, e.g. Erastin. PDAC is under a considerable amount of oxidative stress due to its high proliferation rate, iron dependence, and hypoxic environment. This makes it dependent on antioxidative processes and susceptible to inhibition of these pathways. Additionally, a mechanism by which RT induces cellular damage is via ROS production. Thus, we hypothesized that pharmacologic inhibition of system Xc will allow for the buildup of ROS mediated lipid peroxidation leading to ferroptosis potentiation of RT for the treatment of PDAC.
Materials/Methods: GPX4 and SLC7A11 expression in PDAC patients compared to healthy controls was assessed in publicly available data sets. IHC of GPX4 and SLC7A11 was conducted on tissue from healthy controls, PDAC, and irradiated patients. mRNA and protein levels of key ferroptosis genes were assessed, pre and post RT, in five human PDAC cell lines. Cellular proliferation in the setting of system Xc inhibition (via Erastin) alone, and in conjunction with RT, was determined via MTT, clonogenic assay, and 3D organoid models. ROS and free iron generation was evaluated. Xenograph mouse models were utilized to determine in vivo efficacy of combination treatment.
Results: GPX4 and system SLC7A11 expression levels were elevated in PDAC compared to healthy controls. IHC staining showed high GPX4 expression in PDAC and post RT compared to normal controls. Expression of GPX4 and SLC7A11 at the protein level is high in all cancer cell lines tested. mRNA microarray analysis showed all cell lines assessed increase GPX4 expression after receiving 2Gy, with 3/4 showing GPX4 in the top 10 most up regulated genes. In vitro ROS and free iron were increased with combination treatment compared to either modality alone. The combination of RT and Erastin had a synergistic effect to induce cell death in vitro as well as a significant improvement in tumor response in xenograph mouse models of PDAC.
Conclusion: This study demonstrates that system Xc is an actionable target for the initiation of ferroptosis in PDAC and can be used as a novel method for RT sensitization.