Temperature-responsive polymeric carriers incorporating hydrophobic monomers for effective transfection in small doses

A series of thermoresponsive ternary random copolymers, poly[N-isopropylacrylamide (PIPAAm)-co-(dimethylamino)ethylmethacrylate (DMAEMA)-co-butylmethacrylate (BMA)], was synthesized and their in vitro gene transfection efficiency in cell culture was evaluated. A control copolymer containing 20 mol% DMAEMA units, IP-20D (mole ratio of IPAAm/DMAEMA/BMA=80/20/0 in feed, no BMA units) was inert in transfection. In contrast, copolymer IP-20D-10B (IPAAm/DMAEMA/BMA=70/20/10 in feed) effectively transfected plasmid DNA into COS-1 cell cultures even under small dosing conditions of 0.1 μg of plasmid DNA per well in a 96-well plate, suggesting that incorporation of the appropriate amount of hydrophobic unit is crucial to transfection efficiency. Gene expression was much more significant when transfected by the IP-20D-10B carrier in comparison with control homopolymer poly-DMAEMA, and almost equal to that of the highly competent lipid carrier, LipofectAMINE PLUS™. Furthermore, the transfection efficiency of IP-20D-10B is altered in a thermally responsive manner. By temporarily lowering the cell culture incubation temperature to 20°C in the posttransfection period, gene expression doubled over that for incubation temperature at 37°C. The DNA EtBr intercalation assay suggested that DNA affinity for IP-20D-10B is decreased by lowering incubation temperature, implying that the thermally regulated gene expression could provide more efficient DNA release from the polymeric carrier.