Improved packing of poly(ethylenimine)/DNA complexes increases transfection efficiency.

We have developed a modified poly(ethylenimine) (PEI) transfection procedure that significantly increases PEI's transfection efficiency. While the basic transfection procedure had a transfection efficiency of 37%, our modified procedure yielded a 53% transfection efficiency. The altered procedure gives improved results because of two simultaneous actions: free polycations are removed from the transfecting solutions, and the composition of the PEI complexes that are administered to cells has been modified. The reduction in the amount of free polycations in transfecting solutions reduced the toxicity sometimes associated with the administration of polycations to cellular environments. The structural modification of PEI/DNA transfecting complexes involves improved PEI packing around the delivered plasmid to yield a greater buffering capacity without a change in the complex's surface charge concentration. These structural properties were confirmed by titration and zeta potential analyses. Whether the modified PEI/DNA complexes are more effective because of increased cellular uptake or an enhanced ability to escape from endolysosomes has been addressed. The increase in transfection efficiency was obtained when the buffering capacity of the PEI/DNA was increased without a change in surface charge concentration, which implies that it is the property of enhanced lysosomal buffering that is responsible for successful PEI transfection.