Abstract 1621: Investigate PARP1-dependent cell death in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is one of the most prevalent types of liver cancer, representing the third-leading cause of cancer-related mortality worldwide. It is typically characterized by an environment of high oxidative stress and persistent DNA damage. The persistent DNA damage in HCC triggers and initiates the ADP-ribosylation signalling pathway, which locates the DNA lesion sites for the recruitment of proteins involved in DNA damage repair. While ADP-ribosylation is critical for DNA damage repair, the impact of disrupting the homeostasis of ADP-ribosylation on HCC remains poorly understood. To explore the impact of dysregulated ADP-ribosylation in HCC, a degron-mediated gene silencing system was employed in HCC cell lines with PARG and ARH3 knockout (KO). With the addition of doxycycline (Dox) and Auxin (IAA), the degron-tagged PARG was degraded, establishing the PARG and ARH3 KO environment. Acute loss of PARG and ARH3 resulted in PARP1 hyperactivation, leading to PAR accumulation in the cells, followed by massive cell death in a time-dependent manner. The PARP1-dependent cell death induced by PARG and ARH3 KO was confirmed using the PARP1 KO model and the supplementation of a PARP1 inhibitor to cells. While activation of apoptosis and parthanatos (canonical PARP1-dependent cell death pathways) was observed, targeting the key enzymes in these pathways failed to suppress PARG and ARH3 KO-mediated cell death, indicating that the underlying mechanism is yet to be identified. Nevertheless, an interconnection between the NAD cycle and PARP1-dependent cell death was also examined. Supplementation of the metabolite in the NAD cycle suppresses PARP1-dependent cell death. Interestingly, targeting the rate-limiting enzyme in the NAD salvage pathway using CRISPR-Cas9-mediated KO or NAMPT inhibitor could suppress cell death. Altogether, these results extend the understanding of PARP1-dependent cell death mediated by the loss of PARG and ARH3 and provide insights into the therapeutic development for targeting the homeostasis of ADP-ribosylation in HCC. Citation Format: Chun Yin YU, Hoi Tang MA. Investigate PARP1-dependent cell death in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1621.