A Water-Soluble Phospholipid Polymer as a New Biocompatible Synthetic DNA Carrier

The purpose of this work was the preparation of a water-soluble DNA complex with a biocompatible phospholipid polymer for delivering DNA into a target cell. The phospholipid polymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-2-aminoethyl methacrylate (AEMA)] (poly(MPC-co-AEMA)), was synthesized and the functions of poly(MPC-co-AEMA) as a DNA carrier were compared with those of a conventional cationic DNA carrier such as poly(l-lysine). We investigated the toxicity of these polymers and the water solubility, structures, and nuclease resistance of the associated DNA/polymer complexes. An evaluation of toxicity in a colony forming test using Chinese hamster fibroblast cells (V-79 cells) indicated that the toxicity of poly(MPC-co-AEMA) is about 40% of that of poly(l-lysine). In the case of a salmon sperm DNA/poly(l-lysine) complex, a water-insoluble precipitate formed. In contrast, the DNA/poly(MPC-co-AEMA) complex was completely water-soluble. Although the DNA/poly(l-lysine) complex did not provide a CD spectrum, the DNA/poly(MPC-co-AEMA) complex did. DNase I hardly degraded the DNA in the DNA/poly(MPC-co-AEMA) complex. To demonstrate the transient expression of β-galactosidase, a plasmid DNA/poly(MPC-co-AEMA) complex was incubated with V-79 cells with chloroquine treatment. Under a phase-contrast microscope after 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside (X-gal) staining, more stained cells due to the transient expression of β-galactosidase were observed in a sample with the poly(MPC-co-AEMA) complex than in a sample with the poly(l-lysine) complex. From these results came the following conclusions: poly(MPC-co-AEMA) is a useful water-soluble polymer that can form a complex with DNA, and DNA/poly(MPC-co-AEMA) has good potential for DNA delivery into cells.