608. VAI Deleted Adenovirus as an Oncolytic Agent Targeting Human EBV-Associated Tumours

Abstract

The EBV genome is frequently present in Burkitt's lymphomas, B-Cell lymphomas of immunocompromised patients, nasopharyngeal carcinomas, Hodgkin's disease, T-cell lymphomas, natural killer cell leukemia/lymphoma, smooth-muscle tumors and gastric cancer. More recently, there have been scattered reports linking EBV with conventional epithelial cancers of other primary sites including breast cancers, lung cancers, prostate cancers, liver cancers, colon cancers and lymphoepithelioma-like carcinoma of the esophagus. Given the ever-growing number of tumor types associated with EBV infection, it is therefore critically important to develop therapeutic strategies to treat EBV-associated tumors. Replication-selective oncolytic adenovirus is a promising new platform for anti-cancer therapy. Data from numerous clinical trials have demonstrated several attenuated oncolytic viral mutants to be safe and to replicate selectively in tumor cells with significant anti-tumor potency. Virus associated (VA) 1 and 2 RNA are two low molecular weight adenoviral RNAs that are synthesized late during the viral replication cycle and are required for efficient translation of late viral mRNAs. When the VA1 gene is deleted, replication is impeded in most cells (including HEK 293 cells). The Epstein Barr Virus (EBV) genome encodes two small, non-polyadenylated nuclear RNAs (EBER 1 and 2) that are uniformly expressed in most EBV-associated human tumors. EBER 1 and 2 can functionally substitute for the VA1 RNAs of adenovirus, enabling replication to proceed normally through complementation of VA1 deletion mutants. We hypothesized that VA1-deleted adenovirus would selectively replicate in EBV-positive tumor cells due to complementation by EBER 1, with poor or no replication in normal cells and EBV-negative tumor cells. Our data demonstrate that cytotoxicity of VA1 RNA deletion mutants was restricted to EBV-positive tumor cells (e.g. c666, AGS-EBV, Raji, Jiyoye). Cytopathic effects were much lower in EBV-negative tumor cells (Hep-2, AGS-ATCC, Panc-1). The replication of the VA1 deletion mutant virus was 14–25 times higher in EBV-positive tumor cells than in EBV-negative tumor cells and comparable with wild type adenovirus. The VA1 mutant did not replicate in normal cells in culture such as normal human bronchial epithelial cells (NHBE), and replicated poorly in prostate epithelial cells (PrEC). In vivo, VAI deleted adenovirus showed the same efficacy as wild type adenovirus in xenograft models of human EBV-positive tumor cells, but much lower cytotoxicity than wildtype adenovirus. Our data suggest that a VA1 RNA-deleted viral mutant is a promising replication-selective oncolytic virus specifically targeting EBV-associated cancers.