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 mug 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(TM). 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 degreesC in the posttransfection period, gene expression doubled over that for incubation temperature at 37 degreesC. 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. (C) 2004 Elsevier B.V. All rights reserved.