Gene Therapy with Plasmid DNA

Gene therapy is a promising therapeutic modality for the treatment of inherited as well as acquired genetic disorders. It can be defined as the use of nucleic acid transfer, either RNA or DNA, to treat or prevent a disease. Although initially most research on gene therapy has focused on the development of viral-mediated approaches to deliver therapeutic genes to cells both ex vivo and in vivo, nonviral gene medicines have emerged as a potentially safe and effective gene therapy method for the treatment of a wide variety of acquired and inherited disorders. Compared to viral vectors, this delivery system has received great attention due to their several favorable properties, including low toxicity and immunogenicity, resistance to nuclease, and their efficiency is independent on size of the genetic cargo. One of the simplest approaches of delivery is direct gene transfer with naked plasmid DNA to the organs of interest. Plasmid DNAs (pDNAs), which carry recombinant genes of interest, are used for introducing genes to cells and organs. Various physical methods, for example, gene gun, electroporation, sonoporation, and laser irradiation increase the efficiency of the naked DNA incorporation. Synthetic gene delivery vectors such as cationic lipids and cationic polymers have the advantage of protecting the DNA against degradation by endogenous DNase in vivo, and can be targeted to a specific cellular site in some special cases. Varieties of lipid-based systems have been designed, mostly containing cationic lipids of different structures. Vectors containing polymers, either synthetic or natural, have also been developed. Although significant progress has been made, nonviral vectors are still limited in their efficiency and by some cytotoxicity inherited in the bacterial pDNA, which hosts the gene of interest. Understanding mechanisms and means to overcome the cellular barriers for the DNA delivery will undoubtedly promote further development of pDNA-mediated gene delivery. Great advancement has recently been made in the delivery of oligonucleotides, including siRNA, by nonviral vectors. This is because the nuclear membrane is not a delivery barrier for most of the oligonucleotides. Keywords: gene therapy; lipoplex; lipopolyplex; nonviral gene delivery; polyplex