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Biomacromolecules 2008, 9, 444–455
Controlled Delivery of Plasmid DNA and siRNA to Intracellular Targets Using Ketalized Polyethylenimine Min Suk Shim† and Young Jik Kwon*,‡ Department of Macromolecular Science and Engineering and Department of Biomedical Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106-7207 Received June 30, 2007; Revised Manuscript Received September 27, 2007
A new polyethylenimine (PEI)-derived biodegradable polymer was synthesized as a nonviral gene carrier. Branches of PEI were ketalized, and capabilities of nucleic acid condensation and delivery efficiency of the modified polymers were compared with ones of unketalized PEI. Ketalized PEI was able to efficiently compact both plasmid DNA and siRNA into nucleic acids/ketalized PEI polyplexes with a range of 80–200 nm in diameter. Nucleic acids were efficiently dissociated from the polyplexes made of ketalized PEI upon hydrolysis. In vitro study also demonstrated that ketalization enhanced transfection efficiency of the polyplexes while reducing cytotoxicity, even at high N/P ratios. Interestingly, transfection efficiency was found to be inversely proportional to molecular weights of ketalized PEI, while RNA interference was observed in the opposite way. This study implies that selective delivery of plasmid DNA and siRNA to the nucleus and the cytoplasm can be achieved by tailoring the structures of polymeric gene carriers.
Introduction Therapeutic goals of gene therapy can be achieved by introducing missing genes, elevating expression of existing genes, and/or silencing disease genes. However, developing efficient and safe gene carriers remains a major challenge. Among many forms of carriers, nonviral vectors have been of great interest in research and clinical trials.1,2 Among various cationic polymers, including poly(L-lysine),3,4 imidazolecontaining polymers,5,6 and polyamidoamine (PAMAM) dendrimers,7 polyethylenimine (PEI) has been widely used for nonviral gene delivery due to its superior transfection efficiency.8,9 PEI condenses nucleic acids into highly compacted polyplexes, which protect their cargos from nucleases and acidic environments in the endosome and/or lysosome. A strong buffering capacity of PEI over a wide range of pH contributes to the cytosolic release of nucleic acids via hypothetical proton sponge effect.10 In general, high molecular weight PEI has intolerable cytotoxicity and limited uses in clinical trials due to its nonbiodegradability.11 On the contrary, low molecular weight PEI (
