Copolymers of Ethylene Imine and N-(2-Hydroxyethyl)-ethylene Imine as Tools To Study Effects of Polymer Structure on Physicochemical and Biological Properties of DNA Complexes

A series of five poly[(ethylene imine)-co-N-(2-hydroxyethyl-ethylene imine)] copolymers with similar molecular weights and different degrees of branching was established to study structure−function relationship with regard to physicochemical and biological properties as gene delivery systems. Copolymers were synthesized by acid-catalyzed ring-opening copolymerization of aziridine and N-(2-hydroxyethyl)-aziridine in aqueous solution and characterized by GPC-MALLS, 1H- and 13C NMR, IR, potentiometric titration, and ion exchange chromatography. Complexation of DNA was determined by agarose gel electrophoresis, and complex sizes were quantitated by PCS. Cytotoxicity of the copolymers in fibroblasts was assessed by MTT-assay, LDH-assay, and hemolysis. The transfection efficiency was determined using the reporter plasmid pGL3 in 3T3 mouse fibroblasts. The copolymers obtained by solution polymerization had relatively low molecular weights of about 2000 Da, and the degree of branching increased with increasing et...