Development of a novel chimeric oncolytic viral platform, CF33 and its derivatives, for peritoneal-directed CF33-OV treatment of gastric cancer peritoneal carcinomatosis.

428 Background: Peritoneal carcinomatosis (PC) is a deadly end-stage manifestation of gastric cancer (GC). CF33, a chimeric oncolytic virus, and its genetically modified derivatives have shown exclusive cancer selectivity and oncolytic potency against various solid tumors. Intravenous and intratumoral CF33-hNIS and CF33-hNIS-antiPDL1 have entered phase I trials to treat triple-negative breast cancer and unresectable solid tumors. Here, we investigated the antitumor activities of CF33-OVs against GCPC. Methods: We infected six GC cell lines, including both intestinal-type (AGS and MKN-74) and diffuse-type (KATO III, MKN-45, SNU-1, and SNU-16) with CF33, CF33-GFP, or CF33-hNIS-antiPDL1 at various multiplicities (MOI 0.01, 0.1, 1.0 and 10.0) to examine viral proliferation and cytotoxicity by using standard plaque assay and cell proliferation assay. We performed immunofluorescence imaging and flow cytometric analysis to verify virus-encoded gene expression and blockade of PD-L1 binding by virus-encoded anti-PD-L1 scFv. A mouse model of peritoneal dissemination xenograft of SNU-16-ffluc cells was set up to evaluate the antitumor activity of intraperitoneal (IP) CF33-hNIS-antiPDL1 treatment (3x10 5 pfu x 3 doses). Results: CF33-OVs showed dose-dependent infection, replication, and killing of human GC cell lines. Immunofluorescence imaging showed virus-encoded GFP, hNIS, and anti-PD-L1 scFv expression in CF33-OV-infected GC cells. GC cell surface PD-L1 binding was blocked by virus-encoded anti-PD-L1 scFv. In the xenograft model, IP CF33-hNIS-antiPDL1 treatment significantly reduced peritoneal tumors (p<0.0001), decreased amount of ascites (62.5% PBS vs. 25% CF33-hNIS-antiPLD1), and prolonged animal survival (p<0.01). Conclusions: CF33-OVs demonstrate effective antitumor activity and can deliver functional proteins in vitro and in vivo. CF33-hNIS-antiPDL1 treatment induced sustained regression of GCPC and prolonged survival. These promising preclinical results support peritoneal-directed strategies with CF33-hNIS-antiPDL1 in GCPC patients.