Stereoisomeric Dipeptide Monoester Prodrugs of Gancyclovir for the Treatment of Ocular Herpes: Synthesis, Aqueous Stability and Transporter Interaction

Abstract

Purpose: : To synthesize the stereoisomeric peptide monoester prodrugs of Gancyclovir for the treatement of Ocular Herpes Simplex virus infections and to study their aqueous and enzymatic stability and interactions with various influx transporters.

Methods: : The stereoisomeric peptide prodrugs L-Val-D-Val-Gancyclovir (LDGCV), D-Val-L-Val- Gancyclovir (DLGCV), L-Val-L-Val- Gancyclovir (LLGCV), D-Val-D-Val- Gancyclovir (DDGCV) and the amino acid prodrugs D-Val-Gancyclovir (DGCV), and L-Val-Gancyclovir (LGCV) were synthesized and identified using LC-MS/MS and NMR in our laboratory. MDCK and SIRC cell lines were used as model cell lines to study the interaction of these prodrugs with Peptide Transporter (PEPT) and Amino Acid transporters (LAT, B_o⁺, and b₀⁺). The aqueous stability studies of these prodrugs were performed in Dulbecco’s phosphate buffered Saline (DPBS) at different pH (6.5, 7.4 and 8.5) at 34⁰C for 10 days. Transport of Radioactive Gly-Sar was measured in presence of the prodrugs in SIRC cells. All stability samples were analyzed using HPLC.

Results: : No measurable degradation was observed for LDGCV, DGCV at pH 7.4. However, the degradation rate was found to be higher at alkaline pH. The stability in increasing order for the prodrugs was found to be DDGCV>LDGCV>DLGCV>LLGCV. The interaction of these prodrugs with PEPT was confirmed by their significant inhibition of [³H] Gly-Sar uptake as well as transport. All prodrugs other than DDGCV and DGCV were found to interact with PEPT1. LGCV, LDGCV and DLGCV were found to interact with LAT. Only LGCV was found to interact with b₀⁺ transporter where as only LDGCV and DLGCV were found to interact with B₀⁺ transporter.

Conclusions: : Our results clearly indicate that stereoisomeric dipeptide monoester prodrugs of GCV can not only enhance the aqueous and enzymatic stability but also retain their affinity towards Peptide transporter. Hence these can be a better substitute to conventional peptide prodrugs of GCV for the treatment of Ocular Herpes. This work has been supported by a grant from Missouri Life Science Research Board. (Award No: 0017025)

Keywords: cornea: epithelium • cornea: stroma and keratocytes