Time-dependent complex formation of dendritic poly(L-lysine) with plasmid DNA and correlation with in vitro transfection efficiencies.

Dendritic poly(L-lysine) of the 6th generation shows high transfection efficiency into several cultivated cells with low cytotoxicity. In order to understand the mechanism of complex formation with plasmid DNA, the complex was observed using atomic force microscopy. After mixing for 15 min, 1-2 microns assemblies of complexes composed of several small particles (50-200 nm) were observed. At the same time, individual small complexes of 50 to 500 nm were observed on a mica surface. After incubation for 2 h, only the large complexes were found on the mica surface. As a result of further dynamic light scattering analysis and measurement of the transfection efficiency at different time points, the transfection efficiency of KG6 was found to increase with increasing size of the DNA-complexes. This result indicates that large complexes of more than 1 micron are major species that contribute to transfection in vitro.