Polysaccharides in Gene Delivery

Gene therapy, which involves insertion and expression of a therapeutic gene into cells followed by production of the required proteins, emerged as a new paradigm in medicine with enormous therapeutic potential. In 2000, gene therapy research came into the picture by successful treatment of a genetic disease called X-linked severe combined immunodeficiency. However, adverse events such as T cell leukemia, which developed in some patients in clinical trials, raised many questions regarding associated risks. 

Among cationic polymers, cationic polysaccharides secured an important position in this research area. Cationic polysaccharides most widely used for this purpose are chitosan, dextran, cyclodextrin (CD), pullulan and schizophyllan. These pol3aners act through the formation of an electrostatic complex, but they also create some problems like undesired interaction with blood components, low transfection efficiency and failure from endosomal escape, etc. Various modifications have been proposed to solve all these issues. 

Inside the endosome the pH (5.0-6.2) is more acidic and poses the problem of nucleic acid degradation. In the case of viral vectors, their inherent property to undergo conformational changes in the coat proteins promotes endosomal membrane fusion, which helps in protecting them from the endosomal environment, but in the case of nonviral vectors, lysosomotropic agents like chloroquine, membrane-destabilizing peptides such as synthetic N-terminal peptides of rhinovirus VP-1 or influenza virus HA-2 are attached to the cationic complex to mediate endosomal release. 

Apart from polyplexes, various nanoscale assemblies of cationic polysaccharides are also proposed to promote the surface-mediated delivery of DNA to cells. These approaches are classified into one of two broad categories (i) methods based upon the physical adsorption of preformed polyplex on polymeric surfaces like PLGA or collagen films and these polyplex functionalized films promoted surface-mediated transfection of cells in vitro and in vivof (ii) methods for layer-by-layer adsorption of DNA and cationic polymers on surfaces to fabricate multilayered thin films. Recently, degradable carbohydrate-based nanogels were proposed for codelivery of pDNA and therapeutic proteins. These systems were designed to possess stimuli-sensitive characteristics where the temperature-sensitive property of nanogels allowed the facile encapsulation of biomaterials, while 

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The most commonly used cationic polysaccharides in gene delivery, such as chitosan, CD, dextran, carbohydrate copolymers, etc., are discussed exhaustively in this section. The chemical structures of the listed pol3miers are given in Figure 9.2. 

In another study, dendritic amidoamine side chains of different generations were covalently attached to the polysaccharide chitosan in an attempt to combine the biological activity of chitosan in gene delivery. 

The subject of this review is complexes of DNA with synthetic cationic polymers and their application in gene delivery [1 ]. Linear, graft, and comb polymers (flexible, i.e., non-conjugated polymers) are its focus. This review is not meant to be exhaustive but to give representative examples of the various types (chemical structure, architecture, etc.) of synthetic cationic polymers or polyampholytes that can be used to complex DNA. Other interesting synthetic architectures such dendrimers [5-7], dendritic structures/polymers [8, 9], and hyperbranched polymers [10-12] will not be addressed because there are numerous recent valuable reports about their complexes with DNA. Natural or partially synthetic polymers such as polysaccharides (chitosan [13], dextran [14,15], etc.) and peptides [16, 17] for DNA complexation or delivery will not be mentioned. 

Azzam T, Domb AJ (2005) Cationic polysaccharides for gene delivery. In Amiji MM (ed) Polymeric gene delivery-principles and applications. CRC, Boca Raton, pp 279-299... 

Hydrogels prepared via homogeneous esterification of dextran with unsaturated carboxylic acids are advanced polysaccharide-based products useful for drug delivery systems and protective encapsulants, e.g. of viruses used in gene therapy [173]. Very promising in this regard is the dextran maleic acid monoester [174], which can be obtained by conversion of dextran in DMF/LiCl with the maleic anhydride in the presence of TEA. The DS of the products can be easily controlled with the amount of anhydride applied but... 

Ouchi, T., Murata, J-I. and Ohya, Y. (1999) Gene delivery by quaternary chitosan with antennary galactose residues, in Polysaccharide Applications Cosmetics and Pharmaceuticals (eds M.A. El-Nokaly and H.A. Soini), American Chemical Society, Washington DC, pp. 15-23. 

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