In this study, we describe the development and characterization of lactosylated poly-L-lysine as a potential carrier for targeting anti-viral drugs to the parenchymal liver cell: Poly-L-lysine (M(r) 38 000) was modified with 2 to 130 lactose residues per molecule poly-L-lysine. In vitro competition studies for the asialoglycoprotein receptor on parenchymal liver cells using I-125-asialoorosomucoid as radioligand revealed that mild modification of poly-L-lysine with only five lactose residues was sufficient for high affinity competition. In vivo studies showed that, after injection of poly-L-lysine modified with at least five lactose residues, about 70-80% of the injected dose was taken up by the liver. Preinjection of N-acetyl galactosamine almost completely blocked the hepatic uptake of lactosylated poly-L-lysine, indicating that galactose-recognizing receptors are involved. At 10 min following injection, the contribution of the various liver cell types to the hepatic uptake of lactosylated poly-L-lysine was determined; the parenchymal cell appeared to be responsible for more than 98% of the total liver uptake. To assess the applicability of lactosylated poly-L-lysine as an anti-viral drug carrier, it was derivatized with 4 to 15 residues of the antiviral drug 5-iodo 2'-deoxyuridine, 5'-monophosphate per molecule poly-L-lysine (4-16% by weight) via an acid-labile phosphamide bond. Maximally 0.7% of the conjugated 5-iodo 2'-deoxyuridine 5'-monophosphate was released after 1 h incubation of the drug/carrier conjugate with serum at 37 degrees C, thus establishing the stability of the conjugate in serum. The drug-carrier conjugate was rapidly cleared from the bloodstream within 1. min. Approximately 90% of the injected dose could be recovered in the liver. The parenchymal liver cell was responsible for 97% of the hepatic uptake. lit vitro studies on the kinetics of endocytosis of lactosylated poly-L-lysine, derivatized with 5-iodo 2'-deoxyuridine 5'-monophosphate, by parenchymal liver cells revealed that the ligand was immediately internalized and, after a 10-min lag phase, deacetylated. Internalization and degradation did not occur in the presence of 100 mM N-acetyl galactosamine. In conclusion, the bioavailability of 5-iodo 2'-deoxyuridine 5'-monophosphate to the parenchymal liver cell is dramatically enhanced as a result of the conjugation of the anti-viral drugs to lactosylated poly-L-lysine. Accordingly, lactosylated poly-L-lysine constitutes a suitable carrier for targeting anti-viral drugs to the parenchymal liver cell. It is suggested that 5-iodo 2'-deoxyuridine 5'-monophosphate, conjugated to lactosylated poly-L-lysine might constitute effective therapy against viral infections such as chronic hepatitis B, which involve the parenchymal liver cell. (C) Journal of Hepatology.
