Polyplexes for Gene Delivery

The successful appUcation of gene therapy through DNA or siRNA transfection into the cell is still a great challenge in research. Polymer-based DNA or RNA delivery systems offer a great potential for the facilitation of cellular uptake. 

Polycationic dendritic polymers and related structures are a special class of cationic polymers and have gained significant attention in the last two decades, due to their relative ease of preparation, their globular shape, and their multifunctionality. So far, a number of different dendritic polymers have been introduced for gene/siRNA delivery poly(amido amine) (PAMAM), poly(propylene imine) (PPl), poly(L-lysine) (PLL), (PEI), and poly(glycerol amine) (PGA) [46]. 

In order to overcome the limitations associated with siRNA delivery in vivo, a group of dendritic nanocarriers derived either fromPG or PEI were synthesized and their silencing efficiency was evaluated. Among the nanocarriers evaluated in this study, the best siRNA transfection efficiency with regard to toxicity was observed for PG amine. In general, successful systemic delivery 

FIGURE 6.18 Proposed mechanism of gene transfection having the following elements formation of the DNA/siRNA polymer complex (polyplex), endocytosis of the polyplex, fusion of endosome and lysosome, release of the polyplex into the cytosol, incorporation of the polyplex into the nucleus, and transcription of the DNA into mRNA followed by release of the polyamine backbone into the cytosol. Alternatively, direct binding of siRNA to mRNA via RISC complex and knock down is possible. Source Fischer et al. [46], figure 1. Reproduced with permission of Springer. 

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Table 9.1 Selected poly cations used for preparation of polyplexes for gene delivery...

Danielsen, S., Strand, S., Davies, C.L., Stokke, B.T. Glycosaminoglycan destabilization of DNA—chitosan polyplexes for gene delivery depends on chitosan chain length and GAG properties. Biochim. Biophys. Acta 1721, 44-54 (2005)... 

In a related development, the water-soluble polyphosphazenes, [NP(OCH2CH2NMe2)2] and [NP(NHCH2CH2NMe2)2] form 80 nm particles (polyplexes) when complexed to plasmid DNA. These particles may be used for gene delivery experiments.236... 

The list of references and contributors is not exhaustive. The authors tried to provide the earliest references known to them that describe preparation of the polyplexes specifically for gene delivery. In most cases these papers were followed by advanced work from the same and other laboratories. Furthermore, in several cases, such as PLL, there are earlier references available that describe the biophysical studies on DNA/polycation complexes. Many of these papers are cited in the text when appropriate. 

Liu Y, Reineke TM (2006) Poly(glycoamidoamine)s for gene delivery stability of polyplexes and efficacy with cardiomyoblast cells. Bioconjug Chem 17(1) 101—108... 

Synthetic polymer. Among the cationic synthetic polymers used for gene delivery are polyethylenimine (PEI), polyamidoamine dendrimers, and poly(2-dimethylaminoethyl methacrylate).161-164 Depending on the flexibility (or rigidity) of the polymers, they form either a small (<100 nm) DNA polyplex or a large (>1 to 10 pm) DNA polyplex.165 More detailed physicochemical properties and their transfection efficacy are to be discussed. 

Polyplexes. When cationic polymers (polycations) are mixed with the highly negatively charged DNA, they condense into colloids called polyplexes (see Fig. 11. Id). Polyplexes serve as an important nonviral vector for gene delivery, and one polyplex formulation has advanced to the clinical trials.68... 

Cyclodextrin polyplexes, which are called CDplexes, were prepared from polycationic thiolated amphiphilic cyclodextrin and DNA for gene delivery (see Figure ll.lC). CDplexes also can be functionalized for cellular targeting, nuclear localization and visualization purposes. ... 

Polyplexes are formed from many cationic polymers such as histones, PEI, dendrimers (pDMAEM) or carbohydrate-based polymers such as chitosan and cyclodextrin. Polyplexes are smaller in size than lipoplexes, which is a major physicochemical property for gene delivery, especially in vivoJ... 

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