Gene delivery system

There are other potential drawbacks that may limit the usefulness of retroviruses in gene therapy. For example, retroviruses are generally 

Adenoviral vectors for use in gene therapy are typically based on serotype 5, with the majority of the Ela and Elb regions deleted to prevent virus replication. The E3 region can also he deleted to provide additional space for the insertion of up to 7.5 kh of exogenous DNA. This is larger than the amount that can be inserted into retroviral vectors, but is still too small to be of use in all gene therapy applications. 

The main advantages of adenoviral vectors is that the efficiency of transduction is high, as is the level of gene expression, although this is only transient and can deteriorate rapidly within a few weeks  

Despite these apparent drawbacks, the adenovirus remains a popular vector for gene therapy due to its high gene transfer efficiency and high level of expression in a wide variety of cell types. Some effort has been made to modify the inflammatory and immunogenic properties of the adenovirus capsid, but so far little progress has been made. 

AAV vectors have not been studied to the same extent as adenoviral or retroviral systems, however they appear to be associated with fewer safety risks than the other viral systems. This is due to the elimination of all sequences coding for viral proteins, thereby greatly reducing the risk of an immune reaction against the vector. There remain, however, the potential problems of insertional mutagenesis and the generation of replication competent virus. 

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

Pharmaceutical Gene Delivery Systems, edited by Alain Rolland and Sean M. Sullivan... 

Polymers as Drugs, Conjugates and Gene Delivery Systems... 

In this chapter, we describe the synthetic strategy for bio-inorganic conjugates which can be used as drug or gene delivery systems and their efficient cellular uptake mechanism. 

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Kurosaki T, Kitahara T, Fumoto S, Nishida K, Nakamura J, Niidome T, Kodama Y, Nakagawa H, To H, Sasaki H (2009) Ternary complexes of pDNA, polyethylenimine, and gamma-polyglutamic acid for gene delivery systems. Biomaterials 30 2846-2853... 

Koppu S, Oh YJ, Edrada-Ebel R, Blatchford DR, Tetley L, Tate RJ, Dufes C (2010) Tumor regression after systemic administration of a novel tumor-targeted gene delivery system carrying a therapeutic plasmid DNA. J Control Release 143 215-221... 

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Huang R, Ke W, Liu Y, Jiang C, Pei Y (2008) The use of lactoferrin as a ligand for targeting the polyamidoamine-based gene delivery system to the brain. Biomaterials 29 238-246... 

Hatakeyama H, Akita H, Kogure K, Oishi M, Nagasaki Y, Kihira Y, Ueno M, Kobayashi H, Kikuchi H, Harashima H (2007) Development of a novel systemic gene delivery system for cancer therapy with a tumor-specific cleavable PEG-lipid. Gene Ther 14 68-77... 

Duncan, R., Ringsdorf, H. and Satchi-Fainaro, R. Polymer Therapeutics Polymers as Drugs, Drug and Protein Conjugates and Gene Delivery Systems Past, Present and Future Opportunities. Vol. 192, pp. 1-8. 

Some 24 per cent of all gene therapy clinical trials undertaken to date have employed retroviral vectors as gene delivery systems. Retroviruses are enveloped viruses. Their genome consists of ssRNA of approximately 5-8 kb. Upon entry into sensitive cells, the viral RNA is reverse transcribed and eventually yields double-stranded DNA. This subsequently integrates into the host cell genome (Box 14.1). The basic retroviral genome contains a minimum of three structural genes ... 

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 ... 

No matter what their composition, such synthetic gene delivery systems also meet various biological barriers to efficient cellular gene delivery. Viral vector-based systems are far less prone to such problems, as the viral carrier has evolved in nature to overcome such obstacles. Obstacles relate to ... 

Some attempts have been made to rationally increase the efficiency of endosomal escape. One such avenue entails the incorporation of selected hydrophobic (viral) peptides into the gene delivery systems. Many viruses naturally enter animal cells via receptor-mediated endocytosis. These viruses have evolved efficient means of endosomal escape, usually relying upon membrane-disrupting peptides derived from the viral coat proteins. 

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. 

CNTs can also be encapsulated with DNA molecules. As shown in Fig. 9.1, a DNA molecule could be spontaneously inserted into a SWNT in a water solution via molecular dynamics simulation (Gao et al., 2003). The van der Waals and hydrophobic forces were very key factors for the insertion process, with the former playing a more dominant role in the course of DNA entering into the hole of CNT. Experiment also confirmed that Pt-labeled DNA molecules can be encapsulated into multi-walled carbon nanotubes in water solution at 400 K and 3 Bar as shown in Fig. 9.2 (Cui et al., 2004). The CNTs filled with DNA molecules have potential in applications such as gene delivery system, and electronic sequencing, nanomotor, etc. 

Pan B, Cui D, Sheng Y, Ozkan CS, Gao F, et al. (2007). Dendrimer-modified magnetic nanoparticles enhance efficiency of gene delivery system. Cancer Res. 67 8156-8163. 

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Longmuir KJ, Haynes SM, Dickinson ME, et al. Optimization of a peptide/ non-cationic lipid gene delivery system for effective microinjection into chicken embryo in vivo. Mol Ther 2001 4 66-74. 

Weissig V, Lasch J, Erdos G, Meyer HW, Rowe TC, Hughes J. DQAsomes a novel potential drug and gene delivery system made from Dequalinium. Pharm Res 1998 15(2) 334-337. 

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