Intracellularly biorecognizable derivatives of 5-fluorouracil - Implications for site-specific delivery in the human condition

The release of 5-fluorouracil from polymer-based conjugates can be influenced by the type of linkages used to bind the drug to the polymer carrier. The use of specific oligopeptide sequences designed to be biorecognizable by intracellular enzymes is a promising approach for increasing the site-specific release of 5-fluorouracil from polymer-based conjugates. In this study, we investigated the biorecognizability of specific oligopeptide sequences linking 5-fluorouracil to a water-soluble copolymer carrier based on N-(2-hydroxypropyl)methacrylamide by human cathepsin B (EC 3.4.22.1), cathepsin H (EC 3.4.22.6), and a homogenate of the human colon adenocarcinoma cell line SW 480. The cathepsins were chosen based on the hypothesis that they were two principal lysosomal enzymes responsible for the release of 5-fluorouracil from these conjugates. Our results support this hypothesis; however, these two enzymes may not be the only lysosomal enzymes responsible for the release kinetics observed. While the results for cathepsin B corresponded well to our hypothesis, the cleavage via cathepsin H was lower than predicted, suggesting the presence of additional lysosomal enzymes with catalytic activity toward these 5-fluorouracil derivatives.