Synthesis and in vitro evaluation of novel star-shaped block copolymers (Blocked star vectors) for efficient gene delivery

Novel 4-branched diblock copolymers consisting of cationic chains as an inner domain and nonionic chains as an outer domain were prepared by iniferter-based living radial polymerization and evaluated as a polymeric transfectant. The cationic polymerization of 3-(N,N-dimethylamino)propyl acrylamide (DMAPAAm) using 1,2,4,5-tetrakis(N,N-diethyldithiocarbamylmethyl)benzene as a 4-functional iniferter followed by the nonionic block polymerization of N,N-dimethylacrylamide (DMAAm) afforded 4-branched diblock copolymers with controlled compositions. By changing the solution or irradiation conditions, 4-branched PDMAPAAms with molecular weights of 10 000, 20 000, and 50 000 were synthesized. In addition, by graft polymerization, PDMAPAAm-PDMAAm blocked copolymers with copolymer composition (unit ratio of DMAAm/DMAPAAm) ranging from 0.18 to 1.0 for each cationic polymer were synthesized. All polymers were shown to interact with and condense plasmid DNA to yield polyrner/DNA complexes (polyplexes). A transfection study on COS-1 cells showed that the polyplexes from block copolymers with cationic chain length of approximately 50 000 and a nonionic chain length of 30 000, which were approximately 200 nm in diameter and very stable in aqueous media, had the most efficient luciferase activity with minimal cellular cytotoxicity under a charge ratio of 20 (vector/pDNA). The PDMAPAAm-PDMAAmblocked, star-shaped polymers are an attractive novel class of nonviral gene delivery systems.