Polyethylene glycol-conjugated copolymers for plasmid DNA delivery

Polymeric gene delivery systems have been developed as an alternative for viral gene delivery systems to overcome the problems in the use of viral gene carriers. Polymeric carriers have many advantages as gene carriers such as low cytotoxicity, low immunogenicity, moderate transfection efficiency, no size-limit, low cost, and reproducibility. In the efforts to develop safe and efficient polymeric gene carriers, polyethylene glycol (PEG) has widely been used because of its excellent characteristics. PEG-conjugated copolymers have advantages for gene delivery: (1) The PEG-conjugated copolymers show low cytotoxicity to cells in vitro and in vivo, (2) PEG increases water-solubility of the polymer/DNA complex, (3) PEG reduces the interaction of the polymer/DNA complex with serum proteins and increases circulation time of the complex, 4) PEG can be used as a spacer between a targeting ligand and a cationic polymer. A targeting ligand at the end of a PEG chain is not disturbed by the interaction of a cationic polymer with plasmid DNA, and the PEG spacer increases the accessibility of the ligand to its receptor. In this review, PEG copolymers as gene carriers are introduced, and their characteristics are discussed.