ABSTRACT
Figure 34.1 Scheme of PEI-PEG-TAT synthesis.One of the most often used polymers for formation of polyplex nanoparticles for gene therapy is positively charged polyethylenimine [6]. Due to the negatively charged cell surface, nanoparticles having a positively charged surface generally display better association and internalization rates [9]. The cationic surface charge of polyplexes needs to be concealed to ensure the existence of the nanoparticles in the circulation for extended time periods sufficient to reach target tissues. For this reason, they are PEGylated [10, 11]. The PEGylation results in the formation of a hydrophilic corona around the PEI/DNA core [12] and reduces interactions of the polyplex with plasma proteins and erythrocytes
[13]. Grafting of PEI with PEG chains reduces the z-potential of PEI-based polyplexes to less than +3 mV even at the high N/P ratio (polymer nitrogen to DNA phosphate ratio) of 50 [14]. Quite often cell-penetrating peptides, like TAT-derived peptides, are included into non-cell-specific PEI-PEG-containing polyplexes to enhance their efficacy [15-18]. These block copolymers complexed with DNA demonstrated good transfection efficacy not only in vitro but also in vivo. For these reasons, polyplexes with PEI-PEG-TAT synthetic part are mainly considered in this chapter (a scheme of PEI-PEG-TAT synthesis can be seen in Fig. 34.1). Notably, the experimental approaches described here can be applied for many other types of polyplexes without changes or with slight modifications.
