Uptake of adenoviral vectors via fibroblast growth factor receptors involves intracellular pathways that differ from the targeting ligand

Target-specific delivery of adenoviral gene therapy vectors has been achiev ed by introducing basic fibroblast growth factor (FGF2) onto viral capsids. FGF2-retargeted vectors enter the cell through high-affinity FGF receptors while normal adenoviral receptor interactions are ablated. In addition, FG F2-mediated targeting permits a higher level of transgene expression and in vivo efficacy. We now present studies on the intracellular pathways and me chanisms of transduction by FGF2-retargeted adenovirus. FGF2. retargeting r esults in increased virion entry. Nuclear delivery is also increased, but t o a level that is directly proportional to virion entry. In addition, after entry, the retargeted particle rapidly localizes to the nucleus in a time frame similar to that of adenovirus alone. Transgene expression is always e nhanced with FGF2-mediated delivery, whether overall transduction of the po pulation is increased, equivalent, or decreased relative to nontargeted ade noviral vectors. However, the increase in transgene expression does not cor relate quantitatively with enhanced cellular entry, indicating that other f actors may influence transgene expression levels. The increase in transgene expression occurs only when the FGF2-retargeting moiety is physically comp lexed with the adenoviral vector, indicating a requirement for a spatial li nk between the ligand and the virus particle. The FGF2-adenoviral complex a ctivates the FGF receptor-mediated proliferative signaling cascade, but thi s signal transduction is not required for the enhanced level of gene expres sion observed after FGF2-mediated delivery. These findings emphasize that, in addition to altering receptor tropism, the influence of FGF2 retargeting extends to intracellular adenoviral trafficking pathways. Although the inc reased delivery of virions into the cell and nucleus contributes to the enh anced transgene expression observed with FGF2 retargeting, other as yet und efined cellular mechanisms also contribute to this process.