Molecular weight-dependent gene transfection activity of unmodified and galactosylated polyethyleneimine on hepatoma cells and mouse liver

To optimize a receptor-mediated and cell-selective gene transfer with polyethyleneimine (PEI)-based vector, we synthesized three galactosylated PEIs (Gal-PEI) with different molecular weights (PEI₁₈₀₀, PEI_10,000, and PEI_70,000) and investigated their potential as a targetable vector to asialoglycoprotein receptor-positive cells. All PEI derivatives formed complexes with plasmid DNA (pDNA), whereas the particle size of the complex became smaller on increasing the molecular weight of PEI. Transfection efficiency in HepG2 cells with PEI was highest with PEI₁₈₀₀; efficiency was next highest with PEI_10,000, although the cellular association was similar. After galactosylation, Gal₁₉-PEI_10,000/pDNA and Gal₁₂₀-PEI_70,000/pDNA showed considerable agglutination with a galactose-recognizing lectin, but Gal₉-PEI₁₈₀₀ did not, suggesting that galactose units on the Gal₉-PEI₁₈₀₀-pDNA complex are not sufficiently available for recognition. Gal₁₉-PEI_10,000-pDNA and Gal₁₂₀-PEI_70,000-pDNA complexes showed galactose-inhibitable transgene expression in HepG2 cells. Transfection efficiency was greatest with Gal₁₉-PEI_10,000/pDNA, a result that highlights the importance of obtaining a balance between the cytotoxicity and the transfection activity, both of which are found to be a function of the molecular weight of PEI. After intraportal injection, however, Gal₁₅₃-PEI_70,000/pDNA having a low N/P ratio was most effective, suggesting that additional variables, such as the size of the complex, are important for in vivo gene transfer to hepatocytes.