An in vivo gene expressing system induced by external thermal stimuli

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A thermo-responsive polymer was synthesized from N-isopropyl acrylamide, 2-(dimethylamino)ethyl methacrylate, and butylmethacrylate. This copolymer possessed a phase transition temperature at 25℃. Behaviors of its complexation with plasmid DNA were analyzed. When this polymer was complxed with DNA at a N/P charge ratio of 4, zeta-potencial of the formed complex was +14.1mV. Binding affinity of this polymer to DNA was revealed to change on temperature stimuli ; lower affinity at higher temperature. This induced change of affinity could contribute to DNA release from the complex on temperature drop. This affinity change for this polymer was larger than that obtained in previously studied polymers that synthesized with lower contents of 2-(dimethylamino)ethyl methacrylate and butylmethacrylate than the polymer of the present study.In vitro gene expression assay revealed that this thermo-responsive polymer exhibited thermo-responsive gene expression ; two-fold gene expression upon cooling at 20℃ for 3h. This polymer showed much higher level of gene expression than the previously studied polymer. Furthermore, cytotoxicity of this polymer complex was considerably low such as 80% bioactivity compared to the untreated control. These all results indicated that well controlled DNA binding change using the thermo-responsive copolymer as a synthetic gene vector contributed to obtain high and temperature-controlled in vitro gene expression with low cytotoxicity.