Vol. 287, Issue 1, 408-415, October 1998

Targeted Delivery of Plasmid DNA to Hepatocytes In Vivo: Optimization of the Pharmacokinetics of Plasmid DNA/Galactosylated Poly(L-Lysine) Complexes by Controlling their Physicochemical Properties

Makiya Nishikawa, Shigeo Takemura, Yoshinobu Takakura and Mitsuru Hashida

Department of Drug Delivery Research, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan

In vivo receptor-mediated targeting of plasmid DNA to hepatocytes was achieved through optimizing the physicochemical and pharmacokinetic properties of a plasmid DNA/carrier complex. Galactosylated poly(L-lysine) (Gal-PLL) was synthesized using PLL with a molecular weight of 1,800, 13,000 or 29,000 without loss of the cationic charge. Plasmid DNA encoding chloramphenicol acetyltransferase was complexed with each Gal-PLL. A larger amount of PLL₁₈₀₀ is required for the complex formation than with PLL₁₃₀₀₀ and PLL₂₉₀₀₀, and increasing the number of galactose units on Gal-PLL resulted in reduced binding to plasmid DNA. The particle size and -potential of the complexes varied depending on the mixing ratio and Gal-PLL used. Then, plasmid DNA/Gal-PLL complexes having diameters of 200 nm or less and a weak negative charge were prepared. After i.v. injection of [³²P]plasmid DNA/Gal₁₃-PLL₁₃₀₀₀ and [³²P]plasmid DNA/Gal₂₆-PLL₂₉₀₀₀, almost 80% of the radioactivity rapidly accumulated in the liver, preferentially in the parenchymal cells. The hepatic uptake clearances (CL_liver) were much greater than any of the other tissue uptake clearances. Compared with these complexes, [³²P]plasmid DNA/Gal₅-PLL₁₈₀₀ and [³²P]plasmid DNA/Gal₅-PLL₁₃₀₀₀ had a smaller CL_liver, suggesting that both the molecular weight of PLL and the degree of galactose modification determine the hepatic targeting of plasmid DNA. In vitro and in vivo gene expression studies revealed that plasmid DNA/Gal₁₃-PLL₁₃₀₀₀ and plasmid DNA/Gal₂₆-PLL₂₉₀₀₀ complexes are superior to plasmid DNA/Gal₅-PLL₁₈₀₀ complex for introducing DNA into cells. These results demonstrated that an optimal design of a DNA/carrier complex based on physicochemical properties and a pharmacokinetic analysis of the distribution properties leads to successful in vivo gene delivery.