Endosomolytic peptide

Meyer M, Philipp A, Oskuee R, Schmidt C, Wagner E (2008) Breathing life into polycations functionalization with pH-responsive endosomolytic peptides and polyethylene glycol enables siRNA delivery. J Am Chem Soc 130 3272-3273... 

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. 

The transition from coated vesicle to early endosome is accompanied by acidification of the vesicular lumen that continues into the late endosomal and lysosomal compartments, reaching a final pH in the perinuclear lysosome of approximately 4.5. Such acidification associated with endosome maturation provides the means by which certain viruses gain access to the cytosol. Acid-induced conformational changes in the viral proteins trigger translocation across the endosomal membrane via a fusion process. By taking advantage of the endosomal acidification, pH-sensitive liposomes, adenovirus and endosomolytic peptides have been used to facilitate the release of plasmids into the cytoplasm prior to lysosomal degradation. 

The polyelectrolytic properties of chitosan may further be used to form complexes with DNA plasmid, which are protected from enzymatic degra-dation. 5 MacLaughlin et al. foxmd that plasmid-chitosan complexes with a 1 2 ionic charge ratio were stable in vitro Furthermore, they foxmd that the chitosan complexes, when containing the endosomolytic peptide GM225.1, led to transgene expression in small intestine of rabbits, while naked plasmids yielded no expression. 

Synthetic peptide-based gene delivery systems consisting of a lysine-rich DNA binding motif and endosomolytic motif have been developed for in vivo gene delivery. One example of such a gene delivery system comprises ... 

Lysosomotropic agents, such as chloroquine and sucrose, have been used to enhance DNA/vector release into the cytoplasm in vitro [187]. Viral DNA vectors have evolved the ability to escape acidified endosomes. To mimic this property, replication-defective adenoviruses were administered with transferrin-polylysine DNA vectors, resulting in greater gene expression [188,189]. More recently, endosomolytic structures have been attached to DNA vectors in lieu of using whole viruses. HA-2, the fusogenic peptide of the influenza virus... 

V.H. Ho, N.K.H. Slater, R. Chen, Ph-responsive endosomolytic pseudo-peptides for drug delivery to multicellular spheroids tumour models, Biomaterials 32 (2011) 2953-2958. 

This was the basis for the development of a second generation DPC, named ARC-520, which is currently in phase II clinical trial for the treatment of hepatitis B (Table 14.2). In ARC-520, the previous endosomolytic PBAVE polymer was replaced with a melittin-like peptide (MLP) with a well-defined structure. In addition, there is no chemical link between the siRNA and the polymer. Thus, ARC-520 consists of two individual components cholesterol-siRNA conjugates and hepatocyte-targeting membrane-active peptides linked to the MLP polymer. 

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