Cell Penetrating -Peptides

The cell-penetrating peptides (CPPs), also called protein transduction domains, were discovered in 1988 almost simultaneously by two research teams. However, interest in CPPs began only in 1994, when it was found that the HIV-l-trans-activating protein (Tat protein) can be covalently attached to very different cargoes, such as low molecular weight compounds, peptides, proteins, polysaccharides, oligonucleotides, nucleic 

Several reports have now shown that fluorescent-labeled polycationic / -peptides (a Tat (47-57) yS-peptide analog (165) [260] as well as homooligomers of y9 -HArg (166) [261] and of yS -HLys (167) [261, 262] with seven to eight residues) are also able to translocate rapidly across human cell membranes in a temperature-independent manner and to accumulate in the nucleus. 

FI=fluorescein FITC=fluoresceinisothiocyanat Adoa=8-amino-3,6-cioxooctanoic acid 

These y9 -peptides are not expected to adopt a 3i4-helical conformation in an aqueous environment because of the destabihzing effect of cationic charges. The circular dichroism spectrum of a non-labeled analog of 165 does not display the characteristic signature of the 3i4-helix in aqueous solution however it is highly hehcoidal in MeOH. 

These oligomers for which synthetic routes have been developed, are formally obtained by either the introduction of a peptide bond isostere (e.g. y9-thiopeptides [263], 

Example 1 Oligomers of a-Amlnooxy Acids as Peptide Mimetics 

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Villa R., Folini M., Lualdi S., Veronese S., Daidone M.C., Zaffaroni N. Inhibition of telomerase activity by a cell-penetrating peptide nucleic acid construct in human melanoma cells. FEB.S. Lett. 2000 473 241-248. 

Richard J.P., Melikov K., Vives E., Ramos C., Verbeure B., Gait M.J., Chemo-mordik L.V., Lebleu B. Cell-penetrating peptides. J. Biol. Chem. 2003 278 585-590. 

Fig. 13 Left. ELP carrier N-terminally fused to a cell-penetrating peptide and C-terminally fused to a therapeutic peptide. Right Amino acid sequences for several cell-penetrating peptides (see text for details). Reprinted from [83] with permission from Elsevier, cop)mght 2010...

Lundberg, P. and Langel, U. (2006). Uptake mechanisms of cell-penetrating peptides derived from the Alzheimer s disease associated gamma-secretase complex. Int. J. Pept. Res. Therap. 12, 105-114. 

Trehin R, Nielsen HM, Jahnke HG, Krauss U, Beck-Sickinger AG, Merkle HP (2004) Metabolic cleavage of cell-penetrating peptides in contact with epithelial models human calcitonin (hCT)-derived peptides, Tat(47-57) and penetratin(43-58). Biochem J 382(Pt 3) 945-956. 

Proteasome inhibitors have been instrumental in identifying numerous protein substrates and in elucidating the importance of the proteasome/ubiquitin pathway in many biological processes. Initially, non-specific cell-penetrating peptide aldehydes were used for this purpose. More recently, it became possible to synthesize compounds with increased potency and selectivity (Adams et al. 1998 Elofsson et al. 1999). Furthermore, based on the crystal structure of the yeast and bovine liver CP (Groll et al. 1997 Unno et al. 2002), molecular modeling can now be used to engineer improved inhibitors. 

Temsamani J, Vidal P. The use of cell-penetrating peptides for drug delivery. Drug Discov Today 2004 9 1012. 

Richard JP, et al. Cell-penetrating peptides - a reevaluation of the mechanism of cellular uptake. J Biol Chem 2003 278 585. 

Figure 2 Proposed pathways for liposomal entry into the cell enhanced by peptides. These include direct cell entry suggested as the mechanism of entry by cell-penetrating peptides and receptor-mediated endocytosis by caveolae- and clathrin-dependent endocytosis.

Hallbrink M, Floren A, Elmquist A, et al. Cargo delivery kinetics of cell-penetrating peptides. Biochim Biophys Acta 2001 1515 101-109. 

Marty C, Meylan C, Schott H, et al. Enhanced heparan sulfate proteoglycan-mediated uptake of cell-penetrating peptide-modified liposomes. Cell Mol Life Sci 2004 61 (14) 1785-1794. 

Meade BR, Dowdy SF (2007) Exogenous siRNA delivery using peptide transduction domains/cell penetrating peptides. Adv Drug Deliv Rev 59 134-140... 

Duchardt, F., Fotin-Mleczek, M., Schwarz, H., Fischer, R., Brock, R. A comprehensive model for the cellular uptake of cationic cell-penetrating peptides. Traffic 2007, 8, 848-66. 

Cell penetrating peptides + SynB5 / pAnt-(43-58) AMT Blood to brain [50]... 

Drin, G., et al. 2003. Studies on the internalisation mechanism of cationic cell-penetrating peptides. J Biol Chem 278 31192. 

Lundin P, Johansson H, Guterstam P, Holm T, Hansen M, Langel U, EL Andaloussi S (2008) Distinct uptake routes of cell-penetrating peptide conjugates. Bioconjug Chem 19 2535-2542... 

Mae M, Andaloussi SE, Lehto T, Langel U (2009) Chemically modified cell-penetrating peptides for the delivery of nucleic acids. Expert Opin Drug Deliv 6 1195-1205... 

The cytotoxicity of other metal complexes was also investigated. Neundorf, Schatzschneider, and coworkers found that the cymantrene derivative of the branched cell-penetrating peptide hCT(18-32)-k7 mentioned in Sect. 2.2.1 shows high cytotoxicity (IC50 = 36 pM) against the MCF-7 cell line, while the cymantrene complex as well as the peptide alone is nontoxic [47]. Likewise, the attached... 

Already in 1965, Ryser and Hancock provided evidence that histones and polyamino acids could greatly enhance albumin uptake by cultured tumor cells (6). More recently, several polybasic peptides (so-called protein transduction domains, PTDs or cell-penetrating peptides, CPPs) have been shown to efficiently mediate uptake of nucleic acids, bioactive peptides, phage particles, and liposomes into a wide variety of mammalian cells. The initially proposed ability of CPPs to penetrate plasma membranes via a temperature-independent, non-endocytotic pathway was later shown to be a fixation artifact, and it is currently widely accepted that CPP-mediated macromolecular delivery follows energy-dependent endocytotic pathways that in most cases depend on the expression of cell-surface heparan sulfate proteoglycans (HSPGs) (7). 

Key Words Cell penetrating peptides Peptide nucleic acids Splicing correction. 

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