Kansara Viral, Hao Yi, Mitra Ashim K
Department of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, MO, USA.
J Ocul Pharmacol Ther. 2007 Aug;23(4):321-34. doi: 10.1089/jop.2006.0150.
The overall aim of this research work was to evaluate a series of dipeptide monoester prodrugs of an antiviral agent, ganciclovir (GCV), for oligopeptide transporter-targeted transscleral drug delivery to rabbit retina.
The permeability and enzymatic hydrolysis of dipeptide monoester GCV prodrugs were evaluated using freshly excized rabbit retinal pigment epithelium (RPE)-choroidsclera (RCS) and sclera tissue preparations. Affinity and transport mechanism of these prodrugs and their translocation across RCS were investigated through competitive inhibition studies of [(3)H]glycylsarcosine with the prodrugs.
The transport of glycylsarcosine was found to be saturable (K(m) = 1.21 +/- 0.41 mM, V(max) = 15.89 +/- 1.54 pmoles/min/cm(2)), pH, temperature, and energy dependant. Dipeptides, angiotensin converting enzyme inhibitors, and a beta-lactum antibiotic strongly inhibited the transport of glycylsarcosine indicating the functional presence of oligopeptide transport (OPT) system on the RPE. Dipeptide prodrugs (valine-valine-GCV, glycine-valine-GCV, and tyrosine-valine-GCV), and valine-GCV demonstrate a high enzymatic stability and affinity toward the retinal OPT system. The transport of the prodrugs was significantly inhibited ( approximately 50%) in the presence of glycylsarcosine. The rank order of scleral permeability was Gly-Val-GCV approximately GCV>Val-GCV>Tyr-Val-GCV approximately Val-Val-GCV. The RCS permeability values of Val-GCV (3.29 +/- 0.09 x 10(6)cm/s), Val-Val-GCV (4.14 +/- 0.33 x 10(6)cm/s), Gly-Val-GCV (3.40 +/- 0.47 x 10(6)cm/s) and Tyr-Val-GCV (3.08 +/- 0.29 x 10(6)cm/s) were two-fold higher than that of GCV (1.61 +/- 0.06 x 10(6)cm/s).
The dipeptide monoester GCV prodrugs, owning to higher lipophilicity and OPT-mediated translocation across RPE, appear to be promising candidates in the treatment of ocular cytomegalovirus infections following an episcleral administration.
本研究工作的总体目标是评估一系列抗病毒药物更昔洛韦（GCV）的二肽单酯前药，用于靶向寡肽转运体的经巩膜药物递送至兔视网膜。
使用新鲜摘除的兔视网膜色素上皮（RPE）-脉络膜巩膜（RCS）和巩膜组织制剂评估二肽单酯GCV前药的渗透性和酶促水解。通过用前药对[³H]甘氨酰肌氨酸进行竞争性抑制研究，研究这些前药的亲和力、转运机制及其在RCS中的转运。
发现甘氨酰肌氨酸的转运是可饱和的（Km = 1.21±0.41 mM，Vmax = 15.89±1.54 pmoles/min/cm²），依赖于pH、温度和能量。二肽、血管紧张素转换酶抑制剂和一种β-内酰胺抗生素强烈抑制甘氨酰肌氨酸的转运，表明RPE上存在寡肽转运（OPT）系统。二肽前药（缬氨酸-缬氨酸-GCV、甘氨酸-缬氨酸-GCV和酪氨酸-缬氨酸-GCV）以及缬氨酸-GCV表现出高酶稳定性和对视网膜OPT系统的亲和力。在存在甘氨酰肌氨酸的情况下，前药的转运受到显著抑制（约50%）。巩膜渗透性的顺序为甘氨酸-缬氨酸-GCV≈GCV>缬氨酸-GCV>酪氨酸-缬氨酸-GCV≈缬氨酸-缬氨酸-GCV。缬氨酸-GCV（3.29±0.09×10⁶cm/s）、缬氨酸-缬氨酸-GCV（4.14±0.33×10⁶cm/s）、甘氨酸-缬氨酸-GCV（3.40±0.47×10⁶cm/s）和酪氨酸-缬氨酸-GCV（3.08±0.29×10⁶cm/s）的RCS渗透性值比GCV（1.61±0.06×10⁶cm/s）高两倍。
二肽单酯GCV前药由于具有更高的亲脂性以及OPT介导的跨RPE转运，似乎是经巩膜给药治疗眼部巨细胞病毒感染的有前景的候选药物。
