Effect of physicochemical properties of polyplexes composed of chemically modified PL derivatives on transfection efficiency in vitro

Chemically modified poly-L-lysine (PL) derivatives with two essential features, which we have previously reported, have been used to examine the effect of physico-chemical properties of their complexes with plasmid DNA on expression efficacy in in vitro gene transfection by osmotic shock procedure. PL derivatives having either Nepsilon-trimethyl lysine or 13.9% serine residue showed no transfection efficiency. Only when PL was modified in both ways, giving Nepsilon-trimethyl poly(L-lysine-co-L-serine), markedly enhance gene expression was observed. The cellular uptake and localization of DNA in the cells were similar for each cationic polypeptide. The trimethylated polypeptide formed the loosest complexes of DNA among all of the polypeptides used, judging from the loss of EtBr fluorescence. It resulted in more effective DNA release from the complexes by adding heparin, and in the significant gene expression in in vitro transcription/translation systems, as compared with the other polypeptides. The gene transfection efficiency was found to depend on the physicochemical properties of the complexes, such as absence of aggregation, moderate compaction and easy dissociation, which allow the efficient transcription.