Polycations, polyplexes

The neoangiogenic tumor vasculature overexpresses certain integrins and other surface markers, which can also be used for targeting of polyplexes. The RGD peptide motif has been successfully applied for integrin-targeted pDNA [125-128] and siRNA [129, 130] delivery. In many cases, the PEG motif-containing peptide was attached to the polycation via a PEG spacer. For RGD-PEG-PEI/pDNA polyplexes, an optimum grafting with RGD-PEG was required because transfection... 

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. 

Figuer 9.1 Schematic illustration of various polycation structures used for preparation of polyplexes (A) linear (PEI) (B) randomly branched (PEI) (C) dendrimer (PAMAM) (D) block and graft copolymers (Pluronic-g-PEI and PEO-g-PEI modified with a targeting moiety by one PEO end) (E) nanoscale cross-linked network (PEO-c7-PEI). 

Physicochemical properties of polyplexes greatly depend on the ratio of poly cation and DNA units in the mixture Z=[polycation units]/[DNA bases] referred to as composition of the mixture (Kabanov and Kabanov, 1995). In the case of polycations containing amino groups, the composition of the mixture is commonly expressed as N/P ratio, i.e., the ratio of the numbers of amino groups of the poly cation to phosphate groups of the DNA. It should be emphasized that the composition of the complex formed after mixing of the polycation and DNA solutions, [Pg.153]

Figure 9.4 Core-shell polyplex structures (A) cationic particles with a core from neutralized DNA and polycation and a corona from polycation chains adsorbed on the core (B) electroneutral particles ( polyion complex micelles or block ionomer complex ) with a core from neutralized DNA and poly cation and a corona from nonionic water soluble polymer.

Schematic illustration of various polycation structures used for preparation of polyplexes 151... 

Once internalized, the essential step for the polyplex is to escape rapidly the endosomal vesicle in order to release the nucleic acid in the cytosol and prevent its lysosomal degradation. As the endosomal and lysosomal pH presents values between 4.5 and 6.5 and therefore differs from the neutral pH of 7.4 in other biological compartments [58], some polycations containing protonable residues like PEI facilitate this step by the proton sponge effect [59, 60]. As not all cationic polymers display this attribute, another effective method for enhanced endosomal polyplex release is incorporation of specific endosomal membrane disrupting or pore-forming domains, such as lytic lipid moieties or endosomolytic peptides. 

Polymer. The field of nonviral gene delivery using cationic polymers is at its early stage compared to that of cationic lipid. However, this system is also known to have advantages over lipid-based systems in controlling the size, charge, and other physicochemical properties. Polycation-DNA complexes, also called as polyplexes, are formed by a cooperative... 

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... 

Boeckle, S., K. von Gersdorff, S. van der Piepen, C. Culmsee, E. Wagner, and M. Ogris. 2004. Purification of polyethylen-imine polyplexes highlights the role of free polycations in gene transfer. J. Gene Med. 6 1102-1111. 

Fig. 16 Ethidium bromide displacement assay of the DMAEC-a 18-SS-polyrotaxanes polyplex and the LPEI22k polyplex. The recorded fluorescent intensities (F.I.) were expressed relative to the fluorescence intensity of the DNA-EtBr solution in the absence of polycation, after subtracting the fluorescence of EtBr in the absence of DNA under the same buffer conditions...

Cationic polymers, such as poly(L-lysine) (PEL), polyethylenimine (PEI), chitosan, polyamidoamine (PAMAM) dendrimers, poly(2-dimethylamino) ethyl methacrylate, and polyphosphoesters, condense DNA to form compacted polyplexes. ° The size and the stability of polyplexes depend on the ratio of cations vs. anions, temperature, ionic strength, and the solvent. Stability of polyplexes can be enhanced by conjugating PEG to the polycations or by using PEG-containing block or graft polymers that form micelles. Small cationic peptides are also able to condense DNA, however, six-consecutive-cations is the minimal requirement to achieve this effectively. 

Among non-viral vectors, the lipoplex and polyplex systems [69,70], in which cationic Hpids and polycations, respectively, associate with DNA through an electrostatic interaction, are most widely studied for both in vitro and in vivo transfection. Their assets are that they can carry various size ranges of DNA, ease in manufacturing and mass production, a variety of chemical designs with smart fimctions, and their surface properties can be readily controlled by changing the charge ratio between the cationic polymer and DNA. 

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