pH-Responsive Charge-Conversional Poly(ethylene imine)-Poly(l-lysine)-Poly(l-glutamic acid) with Self-Assembly and Endosome Buffering Ability for Gene Delivery Systems.

Poly(ethylene imine)-poly(l-lysine)-poly(l-glutamic acid) (PKE) polymers with various glutamic acid portions were synthesized by ring opening polymerization of l-lysine N -carboxyanhydride (NCA) and l-glutamic acid NCA from poly(ethylene imine) 1.8 kDa (PEI 1.8k ) as a macroinitiator. It was found that their glutamic acid residues could buffer endosomal pH. PK 5 E 9 polymer could form nanoparticles by self-assembly and nanosized polyplexes, possessing pH-responsive charge-conversion properties. PK 5 E 9 or its polyplex nanoparticles showed polyhedral structures with bumpy surfaces. Its cytotoxicity was marginal at both pH 7.4 and 6.0, and its transfection efficiency was highly increased at pH 6.0. The improved transfection efficiency in acidic conditions was thought to be induced by elevated cellular uptake of the polyplexes via charge-conversion from negative to positive charges. Its transfection was also found to be mediated by endosomal escape through endosome buffering by bafilomycin A1-treated transfection. In conclusion, PK 5 E 9 polymer with self-assembly and endosome buffering ability was found to possess potentials for efficient gene delivery systems in acidic conditions via charge conversion, which may be applied for tumor microenvironment-targeting.