Plasmid-based delivery

A current theme in plasmid-based delivery approaches is to mimic Nature s methods for nucleic acid delivery. To date, the best system to emulate Nature has been viral vectors. Briefly, most viral vectors escape immune surveillance, interact with cell membranes (e. g., receptor), internalize (via endocytosis), escape from endosomes, migrate to the nuclear envelope, enter the nucleus, and finally take over cellular functions. Plasmid-based systems (cationic liposomes and cationic polymers) can mimic portions of these events. This chapter will explore the barriers facing gene delivery vectors, with an emphasis of the pharmacokinetic behavior of these systems. In order to understand the in-vivo barrier, a brief review of physiology will be provided. 

Nonviral vector systems are usually either composed of a plasmid based expression cassette alone ( naked DNA), or are prepared with a synthetic amphipathic DNA-complexing agent (84, 88). Gene delivery systems based on nonviral vectors mainly comprise cationic liposomes, DNA-polymer-protein complexes, and mechanic administration of naked DNA. An idealized/optimized multifunctional nonviral gene delivery system is depicted in Figure 13.4. 

The major problem associated with plasmid based gene delivery to skeletal muscle is the relatively low efficiency of transfection. Recent developments have demonstrated improved delivery associated with the application of an electrical field to the muscle after injection of the plasmid DNA (109). It is clear that the application of naked DNA close to the site of pathology and away from degradative elements such as plasma is thus a viable strategy for gene delivery. However, this method is ineffective if DNA dosing to anatomically inaccessible sites (e.g., solid tumors in organs) is desired. 

Hagstrom, J.E. (2003). Plasmid-based gene delivery to target tissues in vivo the intravascular approach. Curr. Opin. Mol. Ther., 5(4), 338-344. 

Plasmid Based on Regulacor Inducer delivery Seleccion Use Reference... 

Figure 14.4 Fate of plasmid DNA after in vivo administration (modified with permission from Site-specific gene therapy design and use of plasmid-based gene medicines to control in vivo production, delivery and effect of therapeutic proteins, Eric Tomlinson (1998). In Peptide and Protein Drug Delivery, Alfred Benzon Symposium 43."...

Describe the pharmacodynamic and pharmacokinetic barriers to effective plasmid-based gene delivery. 

Describe the use of plasmid-based gene delivery for vaccination. 

Around 1990, the pulmonary delivery of liposomes was largely an academic exercise [43-46] and at best at an early stage of commercial development [47]. However, these and earlier efforts demonstrated the utility of liposomes, and interest has continued to flourish. This has been reinforced by greater acceptance of the dosage form, since there are now several injectable liposomal products on the market [e.g., Ambisome , Fungisome , Myocet ]. The specific use of lipid-based vehicles to deliver plasmid-based DN A has attracted much attention [48-51]. These developments have indirectly helped improve the quality and variety of... 

The elements of a nonviral gene delivery system include a gene coding for the therapeutic gene, a plasmid-based expression system, and a synthetic delivery system. 

Lee M, Nah JW et al (2001) Water-soluble and low molecular weight chitosan-based plasmid DNA delivery. Pharm Res 18 427 31... 

Compared to 66.5% of gene therapy clinical trials aiming at the treatment of cancer, only 2 of the 12 siRNA clinical trials are designed for cancer therapy, indicating the siRNA cancer therapy is still in its infancy. Same as the therapeutic application of pDNA, the major bottleneck for a successful siRNA therapy is the efficient delivery. Scientists have gained extensive experiences in the delivery of pDNA and these experiences can be utilized for the delivery of plasmid-based shRNA. However, the same experience cannot be transferred to siRNA directly since siRNA is very different from pDNA in terms of the molecular weight, molecular topography, and in vivo stability. In addition, compared to pDNA, siRNA is more difficult to be condensed into nanosized complex. Nevertheless, many nonviral vectors have been developed for siRNA delivery and one of them was recently approved for phase I clinical trial. 

Zhang L, Gao L, Zhao L, Guo B, Ji K, Tian Y, et al. Intratumoral delivery and suppression of prostate tumor growth by attenuated Salmonella enterica serovar typhi-murium carrying plasmid-based small interfering RNAs. Cancer Res 2007 67 5859-5864. 

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