412. The Efficacy and Bio-Distribution of Oncolytic HSV-1 (G47Δ) in Mouse Orthotopic Esophageal Cancer Models

Abstract

Esophageal squamous cell carcinoma (ESCC) is one of the most lethal among cancer, because it easily metastasizes to the mediastinal lymph nodes and invades adjacent organs. The majority of patients with ESCC are diagnosed at advanced stages. Conventional treatments often result in unsatisfactory clinical outcome, therefore a novel therapeutic approach is urgently needed. Oncolytic viruses emerge as promising therapeutic agents. G47Δ, a third generation oncolytic herpes simplex virus type 1 (HSV-1), shows high replication capability and robust cytopathic effects in a variety of cancer cells. In this study, we examined the efficacy and bio-distribution of G47Δ using mouse ESCC models. A panel of human ESCC cell lines (KYSE70, KYSE180, KYSE220, T.Tn, and TE8) was susceptible to G47Δ by cytotoxicity assays. G47Δ showed moderate to good replication capability in all cell lines tested. Athymic mice harboring subcutaneous tumors (KYSE180, TE8) or orthotopic abdominal esophageal tumors (TE8-luc) were used for in vivo studies. When the subcutaneous tumors reached approximately 6 mm in diameter, they were inoculated twice (days 0 and 3) with G47Δ (4×104, 2×105, or 1×106 pfu) or mock, and the tumor size was measured (n=10). G47Δ was significantly more effective in inhibiting the growth of subcutaneous tumors than mock in both models. The orthotopic TE8-luc tumors were inoculated once with G47Δ (1×106 pfu) or mock under laparotomy 18 days after tumor implantation (n=10). The tumor size was evaluated by measuring photons emitted from the tumors every 3 days using the IVIS and Living Image Software (Xenogen). Tumors treated with G47Δ were significantly smaller than those with mock (p<0.01, Wilcoxon's test). In order to validate the result, the tumor weight was measured on day 31. G47Δ treated tumors were significantly smaller than mock treated tumors (p<0.01, Student's t test). For bio-distribution evaluation, wild type HSV-1 strain F (1×107 pfu) or G47Δ (1×107 pfu) were administered to HSV-1 sensitive A/J mice via oral route or by direct injection to abdominal esophagus under laparotomy. Mice were sacrificed at each time point (1, 3, 5, and 7 days after administration, n=3) and the amount of viral DNA in major organs was examined by quantitative PCR. DNA copy numbers of Strain F remained high in esophagus or dramatically increased in the brain, spinal cord and adrenal gland through day 7. In contrast, G47Δ DNA copy number decreased rapidly in the esophagus and was mostly undetectable in other organs. These results indicate that G47Δ is highly efficacious and safe in both orthotopic and subcutaneous ESCC models. G47Δ may be useful as a new therapeutic approach for ESCC.