Association and dissociation characteristics of polymer/DNA complexes usedfor gene delivery

Purpose. The DNA association/dissociation properties of water-soluble catio nic methacrylate polymers with closely related structures (poly(2-dimethyla mino)ethyl methacrylate) [p(DMAEMA)], poly(2-(trimethylamino)ethyl methacry late chloride) [p(TMAEMA)]) and the frequently used transfectant poly(L-lys ine) were studied to gain a better insight into their transfection characte ristics. Methods. Association of DNA with different polymers and dissociation of the complexes, achieved by adding an excess of anionic polymers or salt, were studied by using spectroscopic techniques (fluorescence, circular dichroism (CD)), agarose gel etectrophoresis and an enzymatic assay (DNase I treatme nt). The transfection efficiency of the polyplexes was evaluated in tissue culture with OVCAR-3 cells. Results. Plasmid DNA complexed with either poly(L-lysine) or p(DMAEMA) was protected against digestion by DNase I. Fluorescence and CD spectroscopy as well as gel electrophoresis revealed that p(DMAEMA) with a relatively high molecular weight and poly(L-lysine) have similar DNA association/dissociat ion characteristics. Therefore, differences in transfection potential of th e polyplexes cannot be ascribed to differences in binding characteristics, but are probably caused by other factors. As compared with the other polyme rs, p(TMAEMA) has a high affinity for DNA as was concluded from the observa tion that poly(aspartic acid) was unable to fully dissociate complexes cont aining this polymer. This fact might very well explain the low transfection efficiency of these polyplexes. p(DMAEMA) with a relatively low molecular weight probably has a law affinity for DNA, which might explain both the fo rmation of DNA aggregates (psi-DNA) and the low transfection potential obta ined when using this polymer. Conclusions. DNA association/dissociation studies shed light on the preferr ed characteristics of polymeric transfectants.