Mechanistic Study of PEG-asparaginase-Induced Liver Injury

Project Summary PEGylated asparaginase (PEG-ASNase) is one of the main drugs used for the treatment of pediatric acute lymphoblastic leukemia (ALL). Although PEG-ASNase is safe and effective to treat pediatric ALL, its use in adults is limited due to dose-limiting liver injury that negatively impacts therapeutic efficacy. Therefore, strategies that can mitigate the risk of PEG-ASNase liver injury are urgently needed. Our preliminary data show that (1) our murine model of PEG-ASNase liver injury recapitulates clinical features, (2) PEG-ASNase activates ATGL, leading to white adipose tissue (WAT) lipolysis and hepatic lipid peroxidation and apoptosis; (3) PEG-ASNase sensitizes hepatocytes to lipotoxicity; (4) Inhibiting adipocyte ATGL genetically or pharmacologically protects against PEG-ASNase-induced liver injury; (5) PEG-ASNase induces eIF2α phosphorylation in WAT and triggers adipocyte lipolysis, which can be attenuated by GCN2 inhibition; (6) PEG- ASNase induces CTSS expression and activates ERK in WAT; (7) in vivo CTSS inhibition attenuates PEG- ASNase-induced liver injury and ATGL activation; and (8) RNA-seq analysis identified that the PEG-ASNase- responsive hepatocyte lipotoxicity is associated with upregulation of Cyp2e1. Based on these observations, we hypothesize that that (1) PEG-ASNase-induced liver injury is due to ATGL activation and subsequent WAT lipolysis. (2) Mechanistically, we postulate that PEG-ASNase-driven WAT lipolysis is dependent on GCN2-mediated p-eIF2α and AAR activation, with CTSS induction by PEG- ASNase leading to ATGL activation. (3) Additionally, we propose that PEG-ASNase sensitizes hepatocytes to lipotoxicity by inducing Cyp2e1, leading to elevated ROS production and cell death. We propose three specific aims to test our hypotheses: 1) To demonstrate that inhibition of ATGL-mediated WAT lipolysis attenuates PEG-ASNase-induced liver injury; 2) to show that the PEG-ASNase responsive ATGL activation and liver injury are mediated by GCN2-dependent induction of cathepsin S (CTSS); and 3) to investigate whether the PEG-ASNase responsive induction of Cyp2e1 sensitizes hepatocytes to lipotoxicity. The proposed work will identify a novel mechanism of drug-induced liver injury caused by the anti-leukemia drug PEG-ASNase involving drug-induced activation of ATGL and the onset of adipose tissue lipolysis leading to hepatic steatosis. The three aims are not interdependent but are logically related with a singular focus on elucidating the mechanism of PEG-ASNase-induced liver injury. The long-term goal of this project is to identify approaches leading to the safe use of PEG-ASNase and to extend the therapeutic benefit of PEG-ASNase to adult ALL patients.