Introduction: As the prognosis of metastatic gastric cancer patients is extremely poor, development of novel effective treatment is necessary. Pexa-Vec (pexastimogene devacirpvec; JX-594) engineered from the Wyeth vaccine strain has emerged as an attractive oncolytic virotherapy in cancer treatment. The aim of this study is to investigate the efficacy of Pexa-Vec against human gastric cancer cell lines and to identify potential biomarkers of oncolytic virotherapy. Method: Forty-nine human gastric cancer cell lines and normal human umbilical vein endothelial cell (HUVEC), FHs 173We, human embryonic kindey 293(HEK 293), and Hela cell line as control were used in this study. For evaluation of cytopathic effect, gastric cancer cells were infected with JX594 (M.O.I [multiplicity of infection]= 0.1-5), then incubated at 37°C. Cell viability was measured 72 hours postinfection using MTT assay. Viral plaque assay was used for quantification of Pexa-Vec infection. Copy number variation (CNV), single nucleotide variation (SNV), gene expression using whole exome sequencing (WES,) and RNA sequencing of 49 gastric cancer cell lines were analyzed. In addition, expression levels for TK and EGFR family were confirmed by Western blot, and secreted VEGF (vascular endothelial growth factor) levels in conditioned media of gastric cancer were measured using ELISA (enzyme-linked immunosorbent assay). Result: Cytopathic effect of Pexa-Vec was observed in all 49 gastric cancer cell lines. Median ED 50 (effective dose 50) was 0.37 pfu/cell (range 0.02-6.18) in gastric cancer cells and 0.30 pfu/cell (range 0.14-1.67) in normal control cells. Interestingly, EBV-infected cells (YCCEL1/YCC-10, SNU 719) showed relative resistance to Pexa-Vec when compared with other cells (ED 50; 4.34 [range 2.49-6.18]) vs 0.36 pfu/cell (range 0.02-5.00, p=0.003). Plaque assay was performed to quantify Pexa-Vec viral infection of gastric cancer cell lines, but the plaques were too small and diffuse to quantify. Increase in virus M.O.I. seemed to be correlated with increase in plaque numbers, yet this did not explain the association with the degree of TK expression in gastric cancer cells. In addition, EGFR, HER2, HER3, and secreted VEGF expressions were not related to the cytotoxicity of Pexa-Vec (R=-0.19, p=0.19; R=0.06, p=0.537; R=0.18, p=0.232; R=-0.067, p=0.69). From RNA sequencing data, VEGF B expression showed negative correlation with antitumor acitivity of Pexa-Vec (R=- 0.295, p=0.04). Conclusion: Pexa-Vec showed moderate antitumor effects in gastric cancer cell lines in vitro compared with other cancer types. Interestingly, EBV-infected gastric cancer cells showed relatively lower efficacy. In our study, correlation was not observed between TK and EGFR expression levels and cytopathic effects. Therefore, we need to further investigate the mechanisms of action of Pexa-Vec for development of metastatic gastric cancer treatment.

Citation Format: Jee Hung Kim, Woo Sun Kwon, Tae Soo Kim, Kyu Hyun Park, Joong Bae Ahn, Namhee Lee, Ji Won Choi, Hyun Cheol Chung, Sun Young Rha. Antitumor effect of oncolytic vaccinia virus in gastric cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B132.