• Journal of Pharmaceutical Investigation
• /
• v.24 no.4
• /
• pp.217-225
• /
• 1994

With the purpose of improving the therapeutic index of $[^3H]$ acyclovir (ACV) in the treatment of chronic hepatitis B infection, asialofetuin (AF) which after selective interaction with Ashwell's receptor specifically enters into hepatocytes, was chosen as a carrier system for hepatic targeting. This drug was first converted to its monophosphate (ACVMP), which was subsequently activated by water soluble carbodiimide to conjugate with ${\varepsilon}-NH_2$ groups of Iysine residues of AF. The molar ratio of ACVMP to AF in the conjugate was 3.9. In rats, elimination of ACVMP-AF conjugate after i.v. injection showed two phase elimination kinetics. Initial apparent elimination rate constant in rats was $0.191\;min^{-1}$ which was greater than that of ACV. The elimination rate constant from terminal phase was $0.021\;min^{-1}$. Area under the total radioactivities versus time curve was found to be several times larger in liver than in other organs (spleen, intestine, lung and kidney) after i.v. administration of the conjugate labelled in the drug moiety. The above results suggested that ACVMP-AF conjugate was rapidly taken up by hepatocytes and could be a useful hepatic targeting system.

• Journal of Pharmaceutical Investigation
• /
• v.27 no.1
• /
• pp.1-10
• /
• 1997

For the purpose of improving the chemotherapeutic index of acyclovir(ACV), it was conjugated with asialofetuin(AF), which has been reported to enter into hepatocytes. When $[H^3]$ acyclovir in itself or its conjugate were administered to rats, the latter was taken up more selectively by the liver than any other tissues. The stability of ACVMP-AF conjugate in phosphate buffer (pH 5.0) and rat liver homogenate showed a pseudo-first order profile. ACVMP-AF, however, was relatively stable in pH7.4 phosphate buffer and rat plasma. The conjugate was added to the isolated rat hepatocyte and cellular uptake was monitored by scintillation counting for up to 6 hours at $37^{\circ}C$. Hepatocytes incubated with the conjugate exhibited radioactivities significantly enhanced over control levels dose-dependently, i.e., a 3-40 fold increase in radioactivities was observed over controls at the conjugate concentrations of $0.1-10\;{\mu}g/ml$. The AUQ in the liver, kidney, spleen, intestine and lung was higher in treatment with ACVMP-AF than that in treatment with ACV. In treatment with ACVMP-AF, the weighted-average overall drug targeting efficiency(Te) for the liver was higher than in treatment with ACV(57.00 vs 13.31 %), and the weighted-average tissue exposure(Re) was 5.03 for the liver. These results indicated that ACVMP-AF conjugate was rapidly taken up by hepatocytes and could be an efficient and selective hepatic targeting system.

• Journal of Pharmaceutical Investigation
• /
• v.22 no.2
• /
• pp.155-161
• /
• 1992

Although glycosylated liposomes have attracted much attention as targeting delivery systems (DDS) of drugs to specific organs which have glycoside receptors, physical instability of liposomes greatly limits their practical application. In this case, proliposomes might be a potential answer to solve this problem. Utilizing the proliposomes as tageting DDS has been a goal of our series of works; we have tried to develop DDS which form liposomes uppon adding water and can deliver drugs to specific target organs/cells such as hepatocytes. In this paper, preparation of glycosylated liposomes and binding of the liposomes with lectin (agglutinin RCA 120) was studied. Asialoletuin (AF) was selected as a model compound which has galactose terminal and is favorable for binding with galactose receptor on the surface of hepatocytes. AF was obtained by splitting the terminal N-acetylneuraminic acid (NANA) of fetuin. Small unilamellar AF-liposomes were prepared by mixing aqueous solution of AF-palmitate with thin film of phosphatidyl choline and cholesterol (30:10 w/w) formed on the innersurface of the round bottomed flask. They were successively extruded through polycarbonate membranes (0.45 mm). Palmitoyl-AF not incorporated into the liposomal bilayer was separated from liposomes by a Sepharose 4B column equilibrated with 10 mM Tris-HCI buffered saline. Lectin (agglutinin RCA 120) was added to the suspension of AF-liposomes and incubated at $37^{\circ}C$ for 2 hr. After centrifugation, the unbound lectin in the supernatant was assayed for protein. The binding of the lectin to AF-liposomes (AF content 2.8 nmole) at $37^{\circ}C$ was linear at least upto 35 mg of lectin indicating high affinity association of the lectin to AF molecules of the liposomes.