Gene Delivery System Using Thermo-responsive Polymers

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A thermo-responsive copolymer, poly(N-isopropylacrylamjde (IPAAm)-co-2-(dimethylamino)ethyl methacrylate (DMAEMA)-co-butylmethacrylate (BMA)) was synthesized, and its in vitro gene transfection efficiency at different incubation temperatures was evaluated. A copolymer containing 8 mol% of DMAEMA and 11 mol% of BMA (P(IP-8DA-11BM)) had a lower critical solution temperature (LCST) at 21℃, therefore, the copolymer was insoluble above 21℃ and soluble below 21℃. This copolymer was complexed with plasmid DNA. Transfection efficiency of polymer-plasmid complexes was evaluated in COS-1 cells using pCMV-βgal plasmid, encoding for β-galactosidase as a reporter gene. Transfection efficiency of PDMAEMA homopolymer incubated at 37℃ for 48h was higher than that incubated at 20℃ for 3h and 37℃ for 45h. In contrast, transfection efficiency of P(IP-8DA-11BM) incubated at 20℃ for 3h and 37℃ for 45h was much higher than that incubated at 37℃ for 48h. This gene expression enhancement was increased to 8.6-fold by optimizing incubation period of the complex with cells. Such increased transfection efficiency by lowering temperature is considered to be due to appropriate formation/dissociation control of P(IP-8DA-11BM)-DNA complexes.