Abstract 5915: Overexpression of tumor suppressor p53 gene by oncolytic adenovirus boosts immune responses in human pancreatic ductal adenocarcinoma cells

Background: Pancreatic ductal adenocarcinoma (PDAC) is the worst prognosis disease with an overall 5-year survival rate of less than 5%. Although immune checkpoint therapy has been emerged as a novel antitumor therapy, PDAC is less sensitive to immunotherapy due to small number of infiltrating T cells. Recently, oncolytic virotherapy has been shown to promote intratumoral T cell infiltration as an immunogenic antitumor therapy. In the current study, we explored whether overexpression of the wild-type p53 tumor suppressor gene could synergize with oncolysis for induction of immunogenic cell death in human PDAC cells. Methods: OBP-702 is a tumor-specific replication-competent oncolytic adenovirus, in which the hTERT promoter drives the expression of the viral E1A and E1B genes for tumor-specific viral replication and the Egr-1 promoter induces wild-type p53 expression. We used 4 PDAC cell lines (MIA PaCa-2, Capan-1, BxPC-3, Panc-1). Molecular mechanisms of OBP-702-mediated cell death was investigated. Migration and invasion properties were assessed using transwell chamber assay. In addition, virus-induced immunogenic cell death was assessed by analyzing the level of extracellular ATP and high-mobility group box protein B1 (HMGB1). In vivo antitumor effect of OBP-702 was assessed using an orthotopic BxPC-3 xenograft tumor model. Results: At 72 hours after virus infection, OBP-702 induced profound antitumor effect in all human PDAC cells. OBP-702 induced autophagy- and apoptosis-related cell deaths. In migration and invasion assays, MIA Paca-2 and Capan-1 cells were low-invasive type, and Panc-1 and BxPC-3 cells were high-invasive type. OBP-702 inhibited migration and invasion properties of high-invasive type PDAC cells At 24 and 48 hours after virus infection, the secretion of ATP was significantly higher in OBP-702-infected PDAC cells compared to p53-null virus-infected cells. Moreover, OBP-702 significantly induced the higher amount of extracellular HMGB1 in all PDAC cells. Finally, OBP-702 significantly suppressed tumor growth in an orthotopic BxPC-3 xenograft tumor model compared to p53-null virus. Conclusions: Our data suggest that oncolytic adenovirus-mediated p53 overexpression induces more profound immunogenic cell death to boost the immune responses in PDAC. This additional immunological function of p53 is quite attractive and warrants clinical trials combined with immune checkpoint inhibitors. Citation Format: Hiroyuki Araki, Hiroshi Tazawa, Takeshi