Corneal Absorption and Aqueous Humor Kinetics of Dipeptide Monoester Prodrugs of Ganciclovir(GCV), Val-GCV and GCV Utilizing Microdialysis Sampling Technique in the Rabbit Eye: Drug Delivery of GCV Through Peptide Transporter

Abstract

Purpose:: Overall aim of this study was to evaluate the corneal absorption and aqueous humor kinetics of dipeptide monoester prodrugs of GCV and compare these results with VGCV and GCV using corneal well infusion model utilizing microdialysis sampling technique.

Methods:: Cytotoxicity of prodrugs were conducted on rabbit Primary Corneal Epithelial Cells (rPCEC) in 96 well plates for 24hr using promega non-radioactive cell proliferation assay. For kinetic studies, a corneal well was placed over the anesthetized rabbit cornea, linear microdialysis probe was implanted in the anterior chamber of the eye. An infusion of two hundred microlitres of a 0.43% w/v (saturation concentration) solution of GCV and equimolar concentrations of dipeptide monoester prodrugs of GCV, Glycine-Valine-GCV (GVGCV), Valine-Valine-GCV (VVGCV), Tyrosine-Valine-GCV (YVGCV) and L-Valine-GCV (VGCV) were administered for 2hr. Samples were collected every twenty minutes throughout the infusion and post infusion phases. Samples were analyzed using reversed phase HPLC connected to a fluorescence detector. All relevant pharmacokinetic parameters were calculated using noncompartmental analyses with a pharmacokinetic software package, Win Nonlin, v2.1 (Pharsight, CA).

Results:: Cell proliferation assay of dipeptide monoester prodrugs of GCV showed no cytotoxicity to rPCEC cultures after 24hr treatment. Area under the concentration time profile (AUC) and maximum concentration (Cmax) of YVGCV were found to be higher than other prodrugs. AUC of total GCV obtained from YVGCV administration was found to be 12 fold more than AUC of GCV and 6.2 fold more than AUC obtained with total GCV from VGCV administartion. VVGCV also exhibited 3.2 times higher AUC relative to VGCV. Also, AUC and Cmax of regenerated GCV from YVGCV was 8.6 and 4.9 times more than GCV respectively. VVGCV did not produce higher concentrations of GCV. Elimination half life of regenerated GCV from YVGCV administration was observed to be 157 min.

Conclusions:: YVGCV exhibited superior corneal absorption and bioavailability in comparison with GCV, VVGCV, GVGCV and VGCV. Such facilitated absorption of prodrugs may be due to a combination of transcellular passive diffusion and peptide transporter (PEPT1) mediated transport across corneal epithelium

Keywords: aqueous • cornea: epithelium • ion transporters