Electrostatic Endocytosis

Plasmid DNA can be complexed electrostatically with cationic polymers. These complexes can be used for gene transfer [241]. Like the complexes of DNA with cationic lipids these complexes adhere to the cell surface with their cationic surface charges. Thereafter, they are internalized, presumably by adsorptive endocytosis. 

Fig. 4 Model of cellular uptake of Lac complexes. Complexes adhere to cells due to electrostatics (a) and enter through endocytosis (b, c). Low aM complexes remain trapped in the endosome (d). High aM complexes escape the endosome (e) where released DNA may form aggregates with cationic biomolecules (f) or the complexes are less able to dissociate and less DNA is available (g). Reproduced with permission from [21], Copyright 2005 John Wiley Sons Limited...

Another approach is to use polycation complexes, which can be electrostatically attracted and adsorbed to the negatively charged cell membranes and lead to electrostatically adsorptive endocytosis [155, 156], Eor example, cationized polymer conjugates [157], proteins [158, 159], and nanoparticles [96, 160, 161] exhibit enhanced cellular intemahzations when compared with their noncationized counterparts. Cationic charges, however, can cause severe serum inhibition and rapid clearance from the plasma compartment [162-164] for instance, a cationized antibody had a 58-fold increase in the systemic clearance from the plasma compartment... 

FIG. 15 Cellular entry and intracellular kinetics of the cationic lipid-DNA complexes. Cationic lipid-DOPE liposomes form electrostatic complexes with DNA, and, in this case, also transferrin (Tf) is incorporated. Cellular uptake by endocytosis and endosomal acidification can be blocked with cytochalasin B and bafilomycin A, respectively. DNA is proposed to be released at the level of endosomal wall after fusion of the carrier lipids with endosomal bilayer. This process is facilitated by the formation of inverted hexagonal DOPE phase as illustrated in the lower corner on the right. After its release to the cytoplasm DNA may enter the nucleus. (From Ref. 253. By permission of Nature Publishing Group.)... 

Fig. 4 Transfection process of TMC-Cys nanocomplexes (NC) including cell binding through electrostatic affinity and disulfide bonding, uptake via endocytosis, endosomal escape, intracellular plasmid DNA release, and nuclear transport of plasmid DNA [39]...

Fig. 1 Proposed model for the internalization of PTD-conjugated macromolecules into cells. Interaction of positively charged PTDs with negatively charged proteoglycans and glycosa-minoglycans plays an important role in the internalization. The electrostatic interaction is followed by energy- and temperature-dependent endocytotic pathways. This involves phago-cytotic and pinocytotic pathways clathrin-mediated endocytosis, caveolae-mediated endocytosis, and macropinocytosis...

Figure 1 Schematic of polycadon-pDNA binding, polyplex formation, and cellular deliveiy. (a) Polycations bind with pDNA via electrostatic interactions, (b) Smail nanoparticies (polyplexes) spontaneously form that associate with the cellular membrane, (c) Upon glycoprotein binding, polyplexes are internalized via endocytosis. (d) Endosomes carry the polyplexes into the cells, (e) The polyplexes must escape the endosomes to avoid degradation, (f) The polymeric delivery vector must reiease Its nucleic add cargo either in the cytoplasm or in the nucleus (depending in the desired destination) for effective delivery. It should be noted that delivery of other nucleic acid forms (i.e., siRNA) is thought to occur by similar pathways. Adapted from Reineke. T. M. J. Pofym. Sci. A Polym. Chem. 2006, 44,6895. ...

Endolysosomal Escape. Polyplexes bind to the surface of cells via nonspecific electrostatic interactions and are internalized via adsorptive pinocyto-sis. Alternatively, polyplexes derivatized with targeting ligands may bind to specific cell-snrface receptors, in which case they are often internalized by receptor-mediated endocytosis. In either case, the polyplexes become localized within endocytic vesicles, which isolate the polyplex from the rest of the cell. The endocytic pathway represents a hostile environment for polyplexes. The first vesicle, termed the early endosome, fuses with sorting endosomes from which the internalized material may be transported back to the membrane and ont of the cell by exocytosis. More generally, however, polyplexes are believed to be trafficked into late endosomes, vesicles that rapidly acidify to pH 5-6 becanse of the action of an ATPase proton-pump enzyme in the vesicle membrane. Polyplexes may subsequently be trafficked into lysosomes, which further acidify to... 

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