1021. Development of a Syrian Hamster Animal Model To Study Replication Competent Adenovirus Vectors for Cancer Gene Therapy

Abstract

Replication-competent adenovirus vectors for cancer gene therapy are typically evaluated in immunodeficient nude or SCID mice bearing human xenograft tumors. However, the lack of an intact immune system in these animals lessens the relevance of these models to a clinical scenario. We have developed a novel Syrian hamster animal model for the study of oncolytic adenovirus vectors. Initially, we observed the expression of early and late adenovirus proteins in infected hamster cells at levels comparable to that seen in human A549 cells. Single step growth curves established that human adenovirus can replicate within and produce high virus yields in Syrian hamster cells. The yield per cell (burst size) was approximately 500 plaque forming units per cell, only one order of magnitude less than that obtained with A549 cells, one of the most permissive human cell lines known. We then confirmed that human adenovirus type 5 (Ad5) can replicate in the lungs of Syrian hamsters following endotracheal instillation. Three different Syrian hamster cancer cell lines were examined as subcutaneous tumor models in Syrian hamsters, and all three of these were found to form tumors following subcutaneous inoculation. Growth of these tumors was markedly suppressed following intratumoral injection with VRX-007, a replication-competent adenovirus vector developed in our laboratory, which overexpresses ADP (E3-11.6K). Furthermore, we found that VRX-007 replicates within tumors. Subcutaneous tumors formed by one of these hamster cell lines metastasized to the lungs and other organs. Intratumoral injection of VRX-007 suppressed the degree of metastasis. Histopathological analysis revealed areas of necrosis and degenerating tumor cells within tumors treated with VRX-007. These necrotic areas were located within viable areas of tumors, not in the central necrotic area, which most tumors contained. The necrotic regions were characterized as having a central core of debris which was primarily acellular, immediately surrounded by neutrophil infiltration and more peripherally surrounded by macrophages and fibroblasts. No such areas were observed within vehicle treated tumors. Our findings that Syrian hamster cells support productive adenovirus replication in vitro and that vectors developed in our laboratory show efficacy and replication in vivo demonstrate that the Syrian hamster can serve as a useful animal model to evaluate the safety and efficacy of oncolytic adenovirus vectors.