130. Insertion of Transgenes into the E3 or L3 Region To Allow Tumor Selective Expression from Armed Oncolytic Adenoviruses

The ability to arm oncolytic vectors with transgenes gives researchers a mechanism for potential improvements in the vector potency. However, depending on the method for transgene insertion, the growth and selectivity of the oncolytic vector may be affected, ultimately reducing the efficacy of the vector. Here, a novel approach of inserting transgenes into various regions of the Ad5 genome that utilizes the Ad5 transcriptional machinery to allow high levels of transgene expression with minimal effect on the growth, cytotoxicity or selectivity of the vectors is described.A tumor-selective replication-competent vector backbone in which E1A expression is controlled by the human E2F promoter to restrict virus replication to pRb-pathway defective cells was used. The cDNA for a nontoxic, secreted protein transgene was inserted into either the E3 or L3 region of the viral genome. In the E3 region, the gp19K or the 14.7K genes were used as insertion sites. In the L3 region, a novel use of splice acceptor sites was utilized to insert the cDNA either after the 23K gene or between the hexon and 23K genes.No effect was observed on virus production for any virus tested compared to the parental unarmed virus. The insertion site of the transgene did not affect the cytotoxicity of the vectors compared to the parental vector, with similar levels of cell killing seen in the SW780 bladder cancer cell line. Tumor-selective killing of these vectors was also unaffected.Transgene expression did vary amongst the vectors, the highest expression levels from the virus with transgene inserted after 23K in L3. Expression levels where at least 10-fold higher compared to a non-replicating Ad5 vector that expressed the transgene from the constitutive CMV promoter. This observation was expected as the L3 transcript is one of the most abundant in an infected cell. Insertion of the transgene into the E3 14.7K gene resulted expression levels 2-to 3-fold higher than the non-replicating Ad5 vector. Transgene expression was markedly reduced from all vectors in cells in which DNA replication was blocked, demonstrating the tumor-selective nature of the transgene expression at these insertion sites.These studies show that by utilizing the adenoviral transcriptional machinery and the novel splice acceptor sites, transgenes can be inserted into several different loci and can be expressed to various high levels in a tumor-specific manner with minimal effect on the vector growth and efficacy.