Adenoviral vectors for improved gene delivery to the inner ear

An important requirement for gene therapy in the inner ear is to achieve efficient gene delivery without damaging residual inner ear function. This can be achieved by delivering a high concentration of vector in a minimal volume. Adenovectors are well suited to meet these requirements since high quality concentrated vector with a high capacity for a gene payload can be produced. To reduce the number of vector particles and volume of delivery to the inner ear, we tested vectors with enhancements in cell binding and cell entry properties. We compared delivery of a marker gene to the inner ear using two different advanced generation serotype 5 adenovector designs. The first adenovector tested, AdRGD, has a restricted tropism of entry into cells. AdRGD is an Ad5 capsid vector with an arg-gly-asp (RGD) motif built into the adenovector fiber that has also been modified to abolish the fiber-CAR and penton-integrin interactions that provide the normal well characterized two-step entry pathway for adenovirus. The AdRGD vector has enhanced binding to alphanu integrins. The second vector, AdF2K, contains 7 lysine residues within the fiber knob and has been shown to have expanded tropism for cells in vitro and in vivo. AdF2K maintains its normal CAR and integrin receptors interactions and has an additional mechanism of entry via its ability to interact with heparan sulfate. Both vectors demonstrated effective delivery to the inner ear and more uniform labeling of the inner ear sensory epithelia than native capsid vector, when tested in vivo. Analysis of expression efficiency using quantitative PCR was tested in vitro on cultured macular organs and demonstrated that vector delivery with the AdF2K vector design yielded optimal delivery. The present study demonstrates that retargeting strategies can improve delivery to the inner ear.