PT  - JOURNAL ARTICLE
AU  - Siccardi, Dario
AU  - Kandalaft, Lana E.
AU  - Gumbleton, Mark
AU  - McGuigan, Christopher
TI  - Stereoselective and Concentration-Dependent Polarized Epithelial Permeability of a Series of Phosphoramidate Triester Prodrugs of d4T: An in Vitro Study in Caco-2 and Madin-Darby Canine Kidney Cell Monolayers
AID  - 10.1124/jpet.103.056135
DP  - 2003 Dec 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1112--1119
VI  - 307
IP  - 3
4099  - http://jpet.aspetjournals.org/content/307/3/1112.short
4100  - http://jpet.aspetjournals.org/content/307/3/1112.full
SO  - J Pharmacol Exp Ther2003 Dec 01; 307
AB  - Nucleoside analogs are successful, widely used antiviral and anticancer therapeutics. Nucleotide prodrugs (i.e., pronucleotide) have increasingly been used to improve in vivo efficacy of nucleoside analogs. In this study, we evaluated the permeability of a series of phosphoramidate triester prodrugs of the anti-HIV drug 2′,3′-didehydro-2′,3′-dideoxythymidine across monolayers of Caco-2, Madin-Darby canine kidney (MDCKII) epithelial cell line, and its recombinant clone containing the human MDR1/P-gp gene (MDR1-MDCKII). Transport was studied in the apical-to-basolateral (A-B) and the basolateral-to-apical directions (B-A). The impact upon transport of differences in stereochemistry at the chiral phosphate center was evaluated. In the Caco-2 and MDCK models the A-B permeability was lower than expected based on the lipophilicity of the compounds, suggesting the involvement of a polarized efflux system and/or metabolic degradation in limiting the absorption of these ester-based prodrugs. Average permeability values through cell monolayers obtained in the A-B direction were lower than in the B-A direction. The inclusion of the P-glycoprotein (P-gp) inhibitor verapamil in the transport medium markedly increased the permeability in the A-B direction, whereas decreasing it in the opposite direction, suggesting an efflux mechanism mainly mediated by P-gp. Stereoselective permeability was significant for the most lipophilic compounds, where the diastereoisomer possessing the slower eluting time on a reverse-phase high-performance liquid chromatography column was transported through Caco-2 and MDCK monolayers at higher rate. The American Society for Pharmacology and Experimental Therapeutics