Abstract B024: Multiplexed 3D atlas of state transitions and potential prognostic role of poly- ADP ribose glycohydrolase (PARG) in chronic pancreatitis and PDAC

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC), a disease predominantly associated with chronic inflammation, ranks as the third-leading cause of cancer-related mortality. The limited efficacy of current PDAC therapies is, in part, attributed to the challenges posed by late- stage diagnosis, highlighting the urgent need for early detection techniques to improve treatment outcomes. Sustained pancreatic inflammation induces the production of reactive oxygen species, leading to the activation of the DNA damage repair network, including enzymes such as poly-ADP ribose glycohydrolase (PARG). PARG is crucial for degrading poly-ADP ribose (PAR) chains catalyzed by PARP and, thus, regulating key cellular responses to DNA damage. However, the role of PARG in the molecular etiology of pancreatic diseases remains unclear. As a first step, we conducted a single-cell spatial analysis on a multiplex immunofluorescence cyclic dataset focusing on pathways involved in: immune and stromal alterations influencing cell-state transitions; differentiation; and critical cellular signaling pathways. Specifically, we evaluated the expression patterns of DNA damage enzymes (i.e., PARG), to elucidate their potential roles in the transformation from chronic inflammation to malignancy. Method: The human pancreatitis tissue microarray (TMA), consisting of 6 normal, 36 pancreatitis, 36 pancreatic intraepithelial neoplasia (PanINs), and 6 PDAC samples in duplicate, obtained from patients with pancreatitis or pancreatic cancer diagnosed at Oregon Health and Science University. We generated a comprehensive 48-plex image dataset that was processed through unsupervised clustering and manual gating to identify common cell types across different stages of pancreatic disease, including epithelial, stromal, immune, and endothelial. Result and conclusion: We observed moderate to strong cytoplasmic PARG expression in pancreatitis samples compared to normal tissue (p < 0.001), which significantly decreased in PanINs (p < 0.001) and PDAC samples (p < 0.001). Notably, the PARG expression was primarily in CK19-positive epithelial cells. Further evaluation showed that DNA damage markers, such as pRPA and γH2AX, increased as the disease progressed from pancreatitis to PanINs to PDAC. Therefore, there was an inverse correlation between PARG expression and DNA damage marker expression in cells exhibiting DNA damage. Additionally, PARG expression was inversely correlated with proliferating cells, marked by Ki67 and PCNA, at the single-cell level. In conclusion, our single-cell spatial analysis supports the notion that PARG expression correlates with resolution of DNA damage and that its reduced expression associates with disease progression and cellular proliferation. Overall, these findings support early phase clinical trials using PARG inhibitors in the oncologic space, and as a potential target for early detection of PDAC and treatment of other pancreatic diseases. Mechanistically, PARG loss may provide a setting for faulty DNA repair and thus, an accumulation of driver mutations. Citation Format: Vidhi M Shah, Jennifer Eng, Koei Chin, Brett C. Sheppard, Jonathan R. Brody, Rosalie C. Sears. Multiplexed 3D atlas of state transitions and potential prognostic role of poly- ADP ribose glycohydrolase (PARG) in chronic pancreatitis and PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B024.