Abstract 660: Investigating the mechanism of the abscopal effect in combined IRE and anti-PD-1 therapy against PDAC

Abstract Introduction: Pancreatic ductal adenocarcinoma (PDAC) is characterized by a high potential for metastatic dissemination, contributing to its poor 5-year survival. Irreversible electroporation (IRE) is an interventional technique that employs short, high-voltage electric pulses to induce cell death. This study was aimed at investigating the abscopal effect of combined IRE and anti-PD-1 therapy in the setting of liver metastasis and possible mechanisms action. Methods: Female C57BL/6 mice were inoculated with murine Kras* PDAC cells in the pancreas and the liver. The primary tumor in the pancreas was treated with IRE while the distal liver metastasis was untreated by IRE. Following six intraperitoneal doses of anti-PD-1 (100 µg/100 µL/injection, administered every other day), all mice were euthanized 14 days after IRE. Both the IRE-treated pancreatic tumors and the liver metastases were collected for pathological analysis. Tumor tissue microarrays were prepared, and multiplex immunofluorescence staining was performed using the Lunaphore COMET™ system. Additionally, to evaluate the impact of IRE on macrophage phagocytosis of pancreatic tumor cells, macrophages were co-cultured with either control or IRE-treated CFSE-pre-stained pancreatic tumor cells, and phagocytosis effect was assessed using flow cytometry. To explore the impact of IRE on gene expression pathways, Kras* PDAC cells were treated with IRE (400 V, 20 pulses), and cells were collected 4 hours post-treatment. Total RNA was extracted for RNA sequencing analysis. Results: Results from the PDAC liver metastasis mouse model demonstrated enhanced antitumor activity in both the IRE-treated pancreatic tumors and the untreated liver metastases following combined IRE and anti-PD-1 treatments. Multiplex immunofluorescence analysis of both tumor types revealed a significant accumulation of F4/80+ macrophages in the interface between necrotic tissue (caused by IRE) and viable tumor tissue. Additionally, CD8+GzmB+ T cells and B220+ B cells were significantly increased in the tumor tissues of mice treated with the combination of IRE and αPD-1. In vitro macrophage phagocytosis assays further demonstrated that macrophages were more effective at phagocytosing IRE-treated Kras* PDAC cells compared to untreated control cells. Moreover, RNA sequencing of KRAS* PDAC cells treated with IRE (400 V, 20 pulses) identified 908 differentially expressed genes (DEGs) (fold change > 2, FDR < 0.01) compared to untreated controls. Ingenuity Pathway Analysis revealed that these DEGs were associated with TNFα signaling via the NFκB pathway and IL6-JAK-STAT3 signaling, highlighting the expression of key inflammatory genes essential for immune responses. Conclusions: These findings indicate that combining IRE with PD-1 blockade enhances a robust antitumor immune response, resulting in systemic antitumor activity and a strong abscopal effect. Citation Format: Qizhen Cao, Yitao Tang, Nicholas A. Egan, Ping Pan, James P. Long, Huamin Wang, Jared K. Burks, Han Liang, Weiyi Peng, Chun Li. Investigating the mechanism of the abscopal effect in combined IRE and anti-PD-1 therapy against PDAC [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 660.