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 Improving the effectiveness of gene delivery systems are crucial problems in biomedical science. A delivery vehicle (vector), of either viral or non-viral origin, must be used to carry the foreign gene into a cell. Side reactions provoked by the viral vectors, e.g., immune response and insertional mutagenesis, have prompted efforts to improve non-viral delivery systems (vectors). Polyethylenimine (PEI) is a well-known cationic polymer, which has high transfection efficiency owing to its buffering capacity. But it has been reported that PEI is cytotoxic in many cell lines. Polyethylenimine (PEI), a readily available synthetic polycation was introduced for transfection a few years ago. The effect of various chemical modifications of nitrogen atoms on the efficiency of polyethylenimines (PEIs) as synthetic vectors for the delivery of plasmid DNA into several cell lines has been investigated. In the present study our research group has started a couple of new approaches for modifying the structure of PEI in order to increase its transfection efficiency and decrease its cytotoxicity. The first approach was to alkylate the surface nitrogen of PEI (10 KDa) and then top them up with various oligoamines followed by addition of sugar. Therefore, we synthesized modified PEI denderimers and used them as new gene carriers. Polyethylenimine was reacted with bromoacetic acid derivatives with different lengths followed by addition of ethylendiamine, diethylentriamine, spermidine and spermine oligoamines to the carboxyl end of the chains. The second approache was the modification of PEI with peptide sequences which can help the endocytosis and endosomal escape of the nanoperticles. Briefly, various peptide sequences including either Lysine/Histidine, Arginine/Histidine or Serine/Histidine will be added on the top of alkylated-PEI followed by the evaluation of transfection efficiency and cytotoxicity. These polymers were complexed with plasmid DNA at different N/P ratios and the resulting nanoparticles were characterized by dynamic light scattering, gel retardation and transmission electron microscopy (TEM) to determine particle sizes, complex formation and complex shape, respectively. Cytotoxicity and transfection efficiency of the polymers were also tested in cultured Neuro2A cell line. pCMV-RLU and luminometer was employed to quantify the level of transgene expression in Neuro2A cells.


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