Endosomal release

Zauner W, Blaas D, KuechlerE, Wagner E (1995) Rhinovirus-mediated endosomal release of transfection complexes. J Virol 69 1085-1092... 

Foster S, Duvall CL, Crownover EF et al (2010) Intracellular delivery of a protein antigen with an endosomal-releasing polymer enhances CD8 T-cell production and prophylactic vaccine efficacy. Bioconjug Chem 21 2205-2212... 

Electroporation, 294, 389, 397 Endosomal escape, 337 Endosomal release EBV, Epstein-Barr virus, 10 EBNA-1, 11... 

By means of PCI enhanced siRNA delivery was shown for the first time by Oliveira et al. They demonstrated a tenfold increased knockdown efficiency of the EGF receptor due to improved endosomal release by the activated PS meso-tetra-phenylporphine, which was, however, not integrated in the polyplex [155]. 

Kloeckner J, Boeckle S, Persson D et al (2006) DNA polyplexes based on degradable oligoethylenimine-derivatives combination with EGF receptor targeting and endosomal release functions. J Control Release 116 115-122... 

Fig. 6 Endosomal release of PEI/DNA polyplexes. Rupture of a single endosome filled with polyplexes consisting of DNA and PEI labeled by different fluorophores. The upper panel shows the DNA signal and reveals that the intact DNA remains in a confined area of the damaged endosome without diffusion in the cytosol. The lower panel shows the polymer signal whose fluorescence signal disappears due to diffusion into the cytosol. Scale bar 2 pm. Reproduced with permission from Elsevier B.V. [57]...

Chloroquine from Sigma-Aldrich to increase endosome release of CPP-ON conjugates. 

Co-treatment with 100 pM chloroquine may be included to improve endosomal release and to increase splicing correction. Chloroquine is required to achieve significant PNA or PMO nuclear delivery and splicing correction with Penetratin, (Arg)9 or Tat48 60 at low concentrations. It is not required with recently described basic CPPs as R6Pen (15) or (R-Ahx-R)4 (16). 

Macromolecules initially enter the cells inside membrane vesicles (endosomes). Release of the macromolecules from endocytic vesicles to the cytosol (endoso-mal escape) is a continuous process that takes a few hours. For example, activity of alkaline phosphatase toward intracellular targets could be detected only 1-3 h after the electroendocytic uptake (see Note 8). 

If the early endosomal release is not possible, another way to keep DNA intact in lysosome is to protect the DNA from lysosomal degradation. Cationic liposomes formulated with cholesterol believed to offer a useful role in keeping DNA intact (121,156,157). Straub-inger et al. (158) have demonstrated that the lysosomal enzymes work at lower pH, i.e., pH < 6. It was also shown that cholesterol-containing liposomes, which possess greater stability and lower ion-permeability compared with DOPE-containing liposomes, provide an improved stability to the lipid-DNA complex in the cytosol (158-160). It is easily conceivable that if the endosomal content passes onto lysosome before being released from endosomes, the lipid/DNA complex could remain secured in the lysosome. 

Within the Golgi, enzymes are targeted for endosomes (and eventually lysosomes) by addition of mannose 6-phosphate residues that bind to mannose 6-phosphate receptor proteins in the Golgi membrane. The mannose 6-phosphate receptors together with their bound acid hydrolases are incorporated into the clathrin-coated Golgi transport vesicles and released. The transport vesicles lose their clathrin coat and then fuse with the late endosomal membrane. The acidity of the endosome releases the acid hydrolases from the receptors into the vesicle lumen. The receptors are eventually recycled back to the Golgi. 

Moreover, in comparison to other cationic polymers like PEI, chitosan showed restricted transfection efficiency. This might be caused by the insufficient endosomal release of the complexes, due to the weak buffering capacity of chitosan [115]. Based on these findings, new strategies were developed like the elaboration... 

Pirollo et al. developed a nanoimmunoliposome modified with anti-TfR scFV to deliver siRNA to tumor cells. A fluorescein-labeled siRNA was delivered via systemic injection and it was specifically distributed into primary and metastatic tumor cells [110]. Later, the authors developed a similar nanoimmunoliposome for an anti-Her-2 siRNA. To enhance the endosomal release, a pH-sensitive histidine-lysine peptide was included in the complex. The in vitro results showed that the complexes can sensitize human cancer cells to che-motherapeutics. Furthermore, systemic delivery of the siRNA significantly inhibit tumor growth in a pancreatic cancer model [109]. 

---