Abstract 475: Autophagy inhibition enhances the antitumor effect of p53-armed oncolytic virotherapy against pancreatic cancer

Abstract Background: Autophagy is a survival mechanism that transports intracellular materials to lysosomes for degradation to provide energy or macromolecular precursors in response to cellular stresses such as hypoxia or starvation. Pancreatic ductal adenocarcinoma (PDAC) is characterized by high levels of autophagy, which plays a crucial role for cancer survival. Recently, autophagy has been shown to promote immune evasion by lysosomal degradation of MHC-1 expression and has been proposed as a therapeutic target in combination with immunotherapy. We have previously developed OBP-702, a tumor-specific replication-competent oncolytic adenovirus expressing the p53 tumor suppressor gene and demonstrated that OBP-702 exhibited direct cytotoxicity via p53-mediated induction of apoptosis and indirect immune activation via p53-mediated enhancement of immunogenic cell death (ICD). In this study, we examined the therapeutic potential of autophagy inhibition on the cytotoxicity and ICD of OBP-702 and MHC-I expression in PDAC cells. Methods: Murine PDAC cell line PAN02 was used in this study. The cytotoxic activity of autophagy inhibitor, chloroquine (CQ), and OBP-702 in monotherapy and combination therapy was analyzed using XTT assay. The combination index was calculated using CalcuSyn software. The apoptosis-inducing effect of CQ and OBP-702 in monotherapy and combination therapy was analyzed using apoptosis assay. The effect of CQ on virus-induced cell death and the molecular mechanism were investigated by Western blot analysis. The levels of extracellular ATP as ICD marker were analyzed following OBP-702 infection with or without CQ using ELISA assay. We further analyzed whether CQ enhances the expression level of MHC-1 by FACS analysis. Results: CQ and OBP-702 suppressed the viability of PAN02 cells in a dose-dependent manner. The calculation of combination index demonstrated that combination of CQ and OBP-702 showed profound synergistic effect, in which CQ enhanced the apoptosis-inducing effect of OBP-702. Moreover, CQ increased the levels of extracellular ATP followed by OBP-702 infection, suggesting that CQ enhances OBP-702-mediated ICD induction. CQ also increased the expression level of MHC-I on PAN02 cells. Conclusions: Our data suggest that autophagy inhibition by CQ enhances the induction of apoptosis and ICD by OBP-702 and the level of MHC-I expression on PDAC cells, probably promoting the antitumor immune responses against PDAC cells. Therefore, we are currently evaluating the combined effect of CQ and OBP-702 using the syngeneic PAN02 subcutaneous tumor models. Citation Format: Yosuke Takahashi, Hiroshi Tazawa, Satoru Kikuchi, Shinji Kuroda, Yasuo Urata, Shunsuke Kagawa Toshiyoshi Fujiwara. Autophagy inhibition enhances the antitumor effect of p53-armed oncolytic virotherapy against pancreatic cancer [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 475.