Degradable polyethylenimine-alt-poly(ethylene glycol) copolymers as novel gene carriers

Abstract

An ideal gene carrier requires both safety and transfection effciency. Polyethylenimine (PEI) is a well-known cationic polymer which has high transfection efficiency owing to its buffering capacity. But it has been reported that the PEI is cytotoxic in many cell lines and non-degradable. In this study, we synthesized degradable PEI-alt-poly(ethylene glycol) (PEG) copolymers using Michael-type addition reaction as a new gene carrier and characterized them. The copolymers were complexed with plasmid DNA and the resulting complexes were characterized by dynamic light scattering, gel retardation and atomic force microscopy to determine the particle sizes, complex formation and shape of complex, respectively. Cytotoxicity and transfection efficiency of the copolymers were also checked in cultured HeLa human cervix epithelial carcinoma cells, HepG2 human hepatoblastoma cell line and MG63 human osteosarcoma cells. The composition of PEG to PEI in the copolymers was around 1 and the molecular weight of the copolymer was from around 8000 to 12900. The copolymers degraded rapidly at 37¡É in 0.1M phosphate buffered saline (PBS; pH 7.4). The complete copolymer/DNA complex was formed at the N/P ratio of 12 and the complex to DNase I resistance was obtained. The particle sizes decreased with an increase of N/P ratio, molecular weight of PEG and had a minimum value around 75nm at the N/P ratio of 45 in the PEI-alt-PEG(700). Cytotoxicity study showed that the copolymers had no cytotoxic effects on cells even at high concentration of copolymers. Also, transfection efficiency was influenced by molecular weight of PEG, and in case of PEI-alt-PEG(258), the transfection efficiency was higher than PEI 25K in HepG2 and MG63 whereas it was lower than PEI 25K in HeLa. Furthermore, in vivo transfection, PEI-alt-PEG(258) mediate gene expression 10- to 100-fold more efficient in lung and liver than PEI 25K in both of intravenous and aerosol administration.