Stacking and mobility of cationic amphiphiles in the complex with DNA and DNA transfection activity of the complex

Abstract

Cationic amphiphiles, which have a quaternary ammonium head, hydrocarbon tails and a glutamic acid connector with methylene and/or phenylene spacer, have been used to deliver DNA into eukaryotic cells. The relationship between the mobility of various synthetic cationic amphiphiles complexed with DNA and their DNA transfer activities has been examined. When plasmid DNA was added to liposomes formed with cationic amphiphiles and treated with DNase I, DNA was found to be completely resistant to digestion suggesting that DNA is enclosed in the liposomal vesicle formed by the amphiphiles. CD spectra due to a chiral phenylene chromophore of the amphiphiles showed that the amphiphile–DNA complexes with higher transfection activity exhibited disordering of stacking of the amphiphiles by formation of the complex at the culture temperature. Study of the NMR signal of protons in the methylene and terminal methyl groups of the hydrocarbon chain of the amphiphiles indicates that the mobility of the chain was restricted by the binding of the cationic headgroup to DNA at lower than the phase transition temperature of the amphiphiles. Based on these results and those on the gene transfer activity of the complexes, we discuss the relationship between the amphiphile–DNA interaction in the complex and the gene transfection activity of the complex, and conclude that the most important requirement for efficient gene transfection is that amphiphiles in the complex are in a fluid bilayer at the culture temperature of the cells.