Protamine Increases Transfection Efficiency and Cell Viability after Transfection with Calcium Phosphate Nanoparticles

64 Introduction As the expectations of gene therapy have been increasing in recent years, the development of an efficient gene transfer agent is a very important issue in biology and medicine. Viral vectors have good transfection efficiency, but are associated with cytotoxicity [1], immunogenicity [2] and potential recombination or complementation [3]. Systems such as liposomes [4-8], polymers [9-12] and inorganic nanoparticles [13-15] have been investigated as potent non-viral agents for gene transfer. However, most of these suffer from either low gene transfection efficiency or significant cytotoxicity. For an ideal transfer agent, cellular uptake, protection of nucleic acids from degradation and nuclear delivery should be associated with low cytotoxicity. Calcium phosphate nanoparticles are an attractive carrier system due to their good biocompatibility, their high biodegradability and their high affinity for nucleic acids [16]. Previously, we demonstrated that the transfection efficiency of DNA-loaded calcium phosphate nanoparticles was considerably higher with incorporation of DNA into multi-shell nanoparticles to prevent its degradation within the cell by nucleases [17]. Polyethylenimine (PEI) was used for gene delivery as a non-viral transfection agent with high cationic-charge density [18, 19]. PEI condenses DNA into positively charged particles (polyplexes), which penetrate through the negatively charged cell membrane by endocytosis. The ability of PEI to destabilize lysosomal membranes enables DNA to efficiently escape the degradation within the Protamine Increases Transfection Efficiency and Cell Viability after Transfection with Calcium Phosphate Nanoparticles