A study of thermoresponsive poly(N-isopropylacrylamide)/polyarginine bioconjugate non-viral transgene vectors

A thermoresponsive poly(N-isopropylacrylamide)/poly(l-arginine)bioconjugate (PNIPArg) was prepared by radical polymerization and EDC-activated coupling. The lower critical solution temperature (LCST) of PNIPArg aqueous solution determined by turbidimetry was around 35.2 °C. The transmission electron microscope (TEM) showed that the PNIPArg/DNA complexes appeared uniform nanospheres with size about 50–120 nm. Variable temperature circular dichroism (CD) and gel electrophoresis results revealed that the association and dissociation of PNIPArg/DNA complexes could be tuned by varying temperature; polyarginine (PArg) showed no temperature-controllable change of DNA condensate. Incorporation of PNIPAAm considerably decreased the cytotoxicity of PArg. The transfection level of PNIPArg and PArg was evaluated with COS-1 cells using two different reporter genes, pGL3-Control encoding luciferase and pEGP-C1 encoding green fluorescent protein (GFP). The transfection efficiency of PNIPArg incubated at 37 °C for 22 h, 20 °C for 2 h and 37 °C for 24 h was enhanced to a different extent depending on PNIPArg/DNA ratios compared to that incubated at 37 °C for 48 h. Encouragingly, at PNIPArg/DNA mass ratio of 3/1, the transfection efficiency of PNIPArg obtained with variable temperature route was equivalent to that of LipofectamineTM 2000.