Influence of Poly(Amino Acid) Composition on the Complexation of Plasmid DNA and Transfection Efficiency

Abstract

Random copolymers of poly[(Lys, Ala) 1: 1], poly[(Lys, Ala) 2: 1], poly[(Lys, Ala) 3: 1], poly[(Lys, Ser) 3: 1] and poly[(Arg, Ser) 3: 1] (ratios designate the feed comonomer composition), were complexed with plasmid DNA pRL CMV luc at different weight per weight DNA: polymer ratios. The physicochemical properties of the complexes were evaluated by gel retardation assay, Zeta potential measurements and photon correlation spectroscopy. The extent of DNA protection against nucleases was determined by a nuclease assay. Cell viability and transfection efficiency of the DNA/polymer complexes were determined by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-4-sulfophenyl)-2-H -tetrazolium) and luciferase assays, respectively. Regardless of the amino acid feed composition, neutral complexes were formed between 2: 1 and 1: 1 DNA: polymer ratios. The particle sizes of the complexes were in the range of 100-300 nm with complexes with more DNA gave a larger particle size than those with a higher proportion of polymer. Compared to other copolymers, lower amounts of poly[(Lys, Ser) 3: 1] were required to protect the DNA against degradation. The presence of arginine residues increased the transfection efficiency of the complexes by 2-3 orders of magnitude. Results suggest that the amino acid composition of the copolymers has an impact on protection of DNA against degradation by the nucleases, cytotoxicity and transfection efficiency.