1017. Metabolically Biotinylated Viruses for Vector Targeting, Virus Purification, and Capsid Imaging

Abstract

Adenoviruses as oncolytic vectors have been investigated for almost a decade, and show great promise for the treatment of cancer. These vectors kill tumor cells as a result of the lytic replication cycle of the virus. A significant impediment to research with replicating adenovirus vectors is the lack of suitable animal models. As adenoviruses are very species-specific, researchers studying vectors based on human Adenovirus 5 were forced to use the highly artificial immunodeficient mouse-human tumor xenograft model, where the viruses could replicate within the human tumor cells. In this system, the replication of the adenovirus vector in normal tissues and the effect of the host immune system on the anti-tumor activity of the vector cannot be studied. We have developed an immunocompetent, semi-permissive animal model to study oncolytic adenovirus vectors. In this model, we induced subcutaneous tumors in immunocompetent cotton rats by injecting the animals with a suspension of LCRT cotton rat sarcoma cells. The cotton rat was shown by others to be semi-permissive to human adenovirus infection, and to exhibit pathology similar to that observed in humans with respiratory adenoviral infection. The LCRT cell line is derived from a spontaneously arisen mammary tumor. These cells support human adenovirus replication in vitro, as evidenced by expression of adenoviral late proteins and the production of progeny virus that can initiate a new infectious cycle. As a result, LCRT cells are destroyed upon infection even with low multiplicities of virus. When injected subcutaneously into cotton rats, LCRT cells form rapidly growing subcutaneous tumors that metastasize to the lung and to various lymph nodes. They show the characteristics of fibrosarcoma tumors, and usually contain a large necrotic center and rapidly dividing cells at the periphery. We injected pre-existing or nascent subcutaneous LCRT tumors with VRX-007, an oncolytic adenovirus overexpressing ADP. ADP is an adenoviral protein expressed at the culmination of infection that facilitates cell lysis and virus egress, thus speeding up the cell-to-cell dissemination of the vector. Injection of intact VRX-007 consistently caused a significant delay in tumor growth, while tumors injected with UV inactivated vector grew at a rate similar to that of vehicle injected tumors. We have also established the intravenous maximum tolerated dose of VRX-007 in cotton rats. Based upon these results, we propose subcutaneous LCRT tumor bearing cotton rats as a novel, immunocompetent, semi-permissive animal model for the testing of oncolytic adenovirus vectors.