Nucleoside Ester Prodrug Substrate Specificity of Liver

Carboxylesterases are among the best characterized prodrug-hydrolyzing enzymes involved in the activation of several ther-apeutic carbamate and ester prodrugs. The broad specificity of these enzymes makes them amenable for designing prodrugs. Porcine liver carboxylesterase 1 specificity for amino acid esters of three nucleoside analogs [floxuridine, gemcitabine, and 2-bromo-5,6-dichloro-1-(-D-ribofuranosyl) benzimidazole] was evaluated to assess optimal structural preferences for prodrug design. The amino acid promoiety and the esterifica-tion site influenced carboxylesterase hydrolysis rates up to 1164-fold and the binding affinity up to 26-fold. Carboxylester-ase (CES) 1 exhibited high-catalytic efficiency hydrolyzing pro-drugs containing a phenylalanyl moiety but was over 100-fold less efficient with valyl or isoleucyl prodrugs, regardless of th