Carboxybetaine Modified Polyethylenimine As Non-viral Gene Vectors

Gene therapy is promising for the effective treatments of genetic diseases such ashaemophilia, muscular dystrophy and cystic fibrosis as well as acquired diseases includingcardiovascular, infectious diseases, wound healing and cancers. However, the lack of genevectors which are biologically safe and efficient is the bottleneck of gene therapy. Cationicpolymer-based gene vectors have attracted a great amount of attention for gene delivery as aresult of their advantages, such as good reproducibility and low price, no limit of gene size,ease of use and modification. Polyethenimne (PEI) is one of the most widely studied cationicgene vectors, especially branched PEI25kDa (bPEI25kDa, PEI25kDa for short) withstrong―proton sponge‖effect, high positive charge density and therefore high transfectionefficiency for PEI25kDa/pDNA, which is considered as a―golden standard‖for cationicpolymer-based gene vectors.But PEI25kDa also has some serve problems, for example poor biocompatibility andhigh toxicity, which have restricted its research and application in clinical treatment. Areflection of its poor biocompatibility is that because of a surplus of positive charge on thesurface, gene complexes based on PEI25kDa have strong non-specific interaction withnegatively charged proteins in serum, causing aggregation of complexes and consequently adecrease in transfection efficiency. Hence, modification for PEI25kDa, which can improvebiocompatibility and reducing toxicity while keeping or even enhancing transfectionefficiency, has become a main topic of PEI25kDa for researchers currently. In recent years,due to their high resistance to protein adsorption and good biocompatibility, zwitterioniccompounds have attracted much attention as new anti-protein-adsorption materials.Modifying PEI25kDa with zwitterionic compounds provides new ideas for designing andsynthetizing novel PEI-based gene vectors with high transfection efficiency and low toxicity.In this paper, zwitterionic monomers-carboxybetaine acrylamide (CBAA) had beensynthetized. A large amount of CBAA monomers were grafted to PEI25kDa through MichaelAddition between vinyl group of CBAA and primary amines in PEI25kDa. PEI-g-CBAAconjugates with different graft ratios were prepared by controlling the feed ratios between PEI 25kDa and CBAA. Using unmodified PEI25kDa as a contrast, the properties ofPEI-g-CBAA as potential gene vectors were discussed, such as its binding and complexingabilities with pDNA, proton buffering capacity, protein adsorption, cytotoxicity and in vitrotransfection efficiency of PEI-g-CBAA/pDNA. The effect of graft ratios of CBAA on theproperties of gene vectors was also studied. The results show that, PEI25kDa modified byCBAA has potential as novel non-viral gene vectors with high transfection efficiency and lowcytotoxicity.