Previous investigations with E1-mutated adenoviruses indicated that tumor cells can possess E1A-like activity mediating viral replication. Recently, the human cellular factor YB-1 was identified to contribute to adenoviral replication. In this study, it could be demonstrated by utilization of a tetracycline-inducible anti-YB-1 short hairpin RNA (shRNA) expressing human cancer cell model that inhibition of nuclear YB-1 causes a dramatic decrease in ΔE1A adenovirus replication, i.e. YB-1-mediated E1A-like activity. In nuclear YB-1-positive cancer cells exhibiting the multidrug resistance (MDR) phenotype, the biological effect of YB-1-mediated ΔE1A adenovirus replication on the efficiency of the synthesis of “therapeutic” shRNAs directed against the MDR-associated MDR1 mRNA and the efficacy on specific target silencing was investigated. The data demonstrate that synthesis and biological activity of ΔE1A adenovirus-delivered “therapeutic” shRNAs is much more pronounced in the presence of the cellular factor YB-1, indicating that YB-1-mediated adenoviral replication enhanced the therapeutic efficiency of “therapeutic” shRNAs by increasing their expression level. Hence, it can be concluded that efficient delivery of “therapeutic” shRNAs by ΔE1A adenoviral vectors at very low “multiplicities of infection” (MOI) requires viral replication to reach a critical value necessary for “therapeutic” applications. Therewith, these findings have implications for the improvement of adenovirus-based gene therapeutic strategies with “therapeutic” shRNA. The data also offer the possibility of utilizing YB-1-dependent adenoviral replication as delivery technology for “therapeutic” shRNA molecules to generate “oncolytic” viruses with enhanced antitumor outcome.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA