Phase separation of siRNA–polycation complex and its effect on transfection efficiency

Abstract

Polycations and cationic lipids have been widely employed as non-viral vectors for siRNA delivery. However, the stability of siRNA–polycation complexes is still rarely reported. Using highly charged dendrimer poly(amidoamine) (PAMAM) as an example, we studied the complexation of siRNA with a polycation by laser light scattering and atomic force microscopy. PAMAM forms a complex of more than 100 nm in diameter with siRNA right after mixing. However, the complex is not stable. It experiences an interesting kinetic process of aggregation, followed by phase separation. The rate of phase separation is related to the chemical composition of the polycations. Gene expressions on A549 cells and Hela cells demonstrate that the transfection efficiency decreases with the kinetics of the complexes. Cross-linking of the primary amino group of the PAMAM stabilizes the siRNA complex and causes the transfection results to be steady with time.