Characterization of a Targeted Gene Carrier, Lactose-Polyethylene Glycol-Grafted Poly-L-Lysine, and Its Complex with Plasmid DNA

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Abstract
The physicochemical properties and gene transfer ability of lactose-polyethylene glycol-grafted poly-L-lysine (Lac-PEG-PLL) were investigated. A dye displacement assay showed that plasmid DNA self-assembled with Lac-PEG-PLL, and condensation began at a < 1:1 charge ratio of plasmid DNA to polymer. In atomic force microscopy, spontaneously assembled Lac-PEG-PLL/DNA complexes revealed a compact structure, with a size of about 100-200 nm. Circular dichroism spectra of Lac-PEG-PLL/DNA complexes revealed that the secondary structure of DNA was altered by complex formation and was similar to that of the poly-L-lysine/DNA complex. Lac-PEG-PLL was shown to protect DNA against nuclease action in a DNase I protection assay. The cytotoxicity test demonstrated that the complex composed of plasmid DNA and Lac-PEG-PLL had little influence on the viability of HepG2 cells, especially in comparison with that of poly-L-lysine/DNA complexes. In conclusion, our copolymer, Lac-PEG-PLI, formed complexes with plasmid DNA (on average, 150 nm), gave little cytotoxicity, and showed increased efficiency of gene transfer into hepatoma cells in vitro.