Expression of Peptide Transporters on the Rabbit Retina: A Strategy to Improve Retinal Delivery of Ganciclovir

The objective of this study was to investigate functional expression of peptide transporters on the rabbit retina. In vivo and ex vivo retina / choroidal uptake studies were carried out with New Zealand albino rabbits. [3H]Gly-Sar was used as the model peptide transporter substrate. [3H]Gly-Sar solutions, in the presence and absence of specific inhibitors, were added to the vitreal side of the retina. Results indicate that retinal uptake of [3H]Gly-Sar was significantly inhibited in the presence of other known peptide transporter substrates, such as Gly-Pro and cephalexin. Importantly, valganciclovir, a peptidomimetic prodrug of ganciclovir, also inhibited uptake of [3H]Gly-Sar. These studies therefore, indicate that peptide transporters are functionally expressed on the rabbit retina and retinal concentrations of GCV may be enhanced by targeting these transporters through prodrug derivatization.