Development of optimized AAV3 serotype vectors: Mechanism of high-efficiency transduction of human liver cancer cells

Our recent studies have revealed that among the 10 different commonly used AAV serotypes, AAV3 vectors transduce human liver cancer cells extremely efficiently because these cells express high levels of human hepatocyte growth factor receptor (hHGFR), and AAV3 utilizes hHGFR as a cellular co-receptor for viral entry. In this report, we provide further evidence that both extracellular as well as intracellular kinase domains of hHGFR are involved in AAV3 vector entry and AAV3-mediated transgene expression. We also document that AAV3 vectors are targeted for degradation by the host cell proteasome machinery, and that site-directed mutagenesis of surface exposed tyrosine (Y) to phenylalanine (F) residues on AAV3 capsids significantly improves the transduction efficiency of Y701F, Y705F and Y731F mutant AAV3 vectors. The transduction efficiency of the Y705+731F double-mutant vector is significantly higher than each of the single-mutants in liver cancer cells in vitro. In immuno-deficient mouse xenograft models, direct intra-tumor injection of AAV3 vectors also led to high-efficiency transduction of human liver tumor cells in vivo. We also document here that the optimized tyrosine-mutant AAV3 vectors lead to increased transduction efficiency following both intra-tumor and tail-vein injections in vivo. The optimized tyrosine-mutant AAV3 serotype vectors containing pro-apoptotic genes should prove useful for the potential gene therapy of human liver cancers.