Non-viral delivery system

Although viral-mediated gene delivery systems currently predominate, a substantial number of current clinical trials use non-viral-based methods of gene delivery. General advantages quoted with respect to non-viral delivery systems include ... 

Successful gene therapy demands an effective system for therapeutic gene delivery into organs and tissues. Therefore gene delivery is based on the development of a non-viral delivery system. Such vector systems have the ability to introduce the alien genetic information into a cell. Carbon nanotubes can be used for creation of new vectors for gene transportation. 

Viruses are complex particles, entering the cells by fusion of their envelope to the plasma membrane or by endocytosis followed by the escape of the capsid by membrane fusion or lysis (Sodeik, 2000). The diameter of the viral particle could be several hundred nanometers, implying a very inefficient diffusional movement in the cytoplasm, based on those physicochemical considerations that were discussed above (Kasamatsu and Nakanishi, 1998). Despite these limitations, those viruses that replicate in the nucleus have evolved sophisticated mechanisms to ensure a highly efficient nuclear delivery of their genetic material. Since these mechanisms may provide a conceptual framework to design novel non-viral delivery systems, we shall review some of the key elements that account for the nuclear targeting of certain viruses. 

Encapsulation of DNA into neutral and anionic liposomes has also been explored as non-viral delivery system. An anionic liposome cannot efficiently bind negatively charged DNA due to repulsive electrostatic forces that occur between the anionic head group of the lipids and the phosphate backbone of DNA. Therefore, DNA must be encapsulated to use the anionic lipids as cell specific targeting. However, the size and shape of the DNA matrix limits it encapsulated form of applications [69]. 

The two classes of non-viral vector that are being investigated most actively are the cationic lipid-based vectors and the cationic polymer-based vectors. The cationic polymer-based vectors represent the newest class of non-viral delivery system to be developed and there are a number of groups working with these vectors. As this is such a new area of research there has yet to be any standardised definition of the terms involved in this field. Complexes formed between cationic polymers and DNA have been referred to as interpolyelectrolj1 e complexes, molecular conjugates, polylysine-DNA complexes, DNA-polylysine complexes, polyplexes and so on. In this review complexes formed between poly-(L-lysine) (pLL) and DNA are referred to as polylysine/DNA complexes or abbreviated to pLL/DNA complexes. Where polymers other dian poly(L-lysine) have been used the term polymer/DNA complex is used. The forward slash (/) is used to denote a non-covalent interaction, while a hyphen (-) is used to denote a covalent link. 

Key Players in Two Categories of Polymeric Non-viral Delivery Vehicle Systems Synthetic Polymers and Natural/Biodegradable Polymers... 

One reason can be found in their main characteristics, such as a well-defined size and structure, flexibility, monodispersity and multivalent molecular surface. In particular, cationic dendritic systems have been studied as non-viral delivery carriers of nucleic acids such as oligonucleotides, siRNA, mRNA or DNA and as antimicrobial systems. 

Table 17.3 Natural polymeric systems reported as non-viral delivery vectors in in vivofin vitro gene therapy to the brain. 

Peptoids have also shown great utility in their ability to complex with and deliver nucleic acids to cells, a critical step toward the development of antisense drugs, DNA vaccines, or gene-based therapeutics. Most non-viral nucleic acid delivery systems are based on cationic molecules that can form complexes with the polyan-... 

Davis, M.E., Non-viral gene delivery systems. Curr. Opin. Biotechnol. 2002, 13, 128-131. 

Li SD, Huang L (2006) Gene therapy progress and prospects non-viral gene therapy by systemic delivery. Gene Ther 13 1313-1319... 

Figure 14.10 Overview of cellular entry of (non-viral) gene delivery systems, with subsequent plasmid relocation to the nucleus. The delivery systems (e.g. lipoplexes and polyplexes) initially enter the cell via endocytosis (the invagination of a small section of plasma membrane to form small membrane-bound vesicles termed endosomes). Endosomes subsequently fuse with golgi-derived vesicles, forming lysosomes. Golgi-derived hydrolytic lysosomal enzymes then degrade the lysosomal contents. A proportion of the plasmid DNA must escape lysosomal destruction via entry into the cytoplasm. Some plasmids subsequently enter the nucleus. Refer to text for further details...

CNTs with different characteristics, which will lead to differences in the mechanism of CNT metabolism, degradation or dissolution, clearance and bioaccumulation. On the other hand, most non-viral gene delivery systems today suffer from both limited levels of gene expression and an unfavourable toxicity profile due to their highly cationic surface character. Therefore, opportunities for CNT-based gene transfer systems are still ample. 

Kataoka, K., Harashima, H., Gene delivery systems Viral vs. non-viral vectors. Adv Drug Deliv Rev 52, 151 (2001). 

A more selective inhibition of NFkB can be achieved by transfecting cells with DNA coding for the natural inhibitor IkBo or a mutant IkB protein that lacks 36 N-terminal amino acids, and consequently becomes proteolysis resistant. In this way expression of adhesion molecules and monocyte adhesion and transmigration can be inhibited [87,88], The potentials and limitations of these latter types of therapy are however not fully understood as yet. Different transfection systems (adenoviral, retroviral, non-viral) are available for gene delivery purposes, all with their own potentials and restrictions. 

Liu, E, Huang, L. (2002). Development of non-viral vectors for systemic gene delivery. Control Release, 78(1-3), 259-266. 

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