Polyplexes gene delivery

Schaffer DV, Fidelman NA, Dan N, Lauffenburger DA (2000) Vector unpacking as a potential barrier for receptor-mediated polyplex gene delivery. Biotechnol Bioeng 67 598-606... 

Burke RS, Pun SH (2008) Extracellular barriers to in vivo PEI and PEGylated PEI polyplex-mediated gene delivery to the liver. Bioconjug Chem 19 693-704... 

Moffatt S, Wiehle S, Cristiano RJ (2005) Tumor-specific gene delivery mediated by a novel peptide-polyethylenimine-DNA polyplex targeting aminopeptidase N/CD13. Hum Gene Ther 16 57-67... 

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...

Poly (ethylenimine) (PEI) has been demonstrated as an efficient gene delivery vehicle both in vitro and in vivo (161-163). Linear (22 kDa) and branched PEI formulations of varying molecular weights (0.6-800 kDa) have been reported. While polyplexes from higher molecular weight branched PEIs (70-800 kDa) were found to be more efficient in vitro but on intravenous administration the smaller and linear PEIs seem in general to be more efficient (171). However, questions as to the... 

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... 

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

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. 

The addition of NLS in a non viral gene delivery system is expected to favor the nuclear import (nuclear pores allow the passage of particles of 24 nm) by using the karyopherin and importin machinery. Where should the NLS be linked, on the pDNA or on the carrier For the latter strategy, polyplexes must not dissociate before their import in the cell nucleus. Both strategies have been prospected but with only limited success. 

The assembly of NLS in peptide-based gene delivery systems has been achieved by the non-covalent binding of plasmid to either free NLS embedded with polyplexes or to NLS linked to a cationic sequence, such as (PKKKRKV)4-K2o (Table 16.7), AKRARLSTSFNPVYPYEDES-K20 (Table 16.7) or H9-2 sequence (nls-H9-2) (Table 16.4). With nls-H9-2, the transfection efficiency with a formulation containing... 

As previously discussed, the protection of pDNA against degrading enzymes is a critical parameter for a non-viral carrier. Such ability is needed for the polyplex to protect the nucleic acid for an extended period of time in the blood while the polyplex circulates and distributes. Research conducted in 1999 by Richardson and coworkers [101] to study the ability of chitosan to protect against DNase degradation revealed that incubation of polyplexes prepared at NIP ratio of 3/1 in the presence of DNase I (8 U, 1 h incubation) protected pDNA from degradation. Other studies of chitosans as gene delivery vehicles confirm that the NIP ratio has to be at least 3/1 to 5/1 in order to provide a sufficient protective effect against DNases. 

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