MAP (KLAL)

A diversity of cell-penetrating peptides (CPPs), is known, but so far the only common denominator for these peptides is the ability to gain cell entry in an energy-independent manner. The mechanism used by CPPs for cell entry is largely unknown, and data comparing the different peptides are lacking. In order to gain more information about the cell-penetrating process, as well as to quantitatively compare the uptake efficiency of different CPPs, we have studied the cellular uptake and cargo delivery kinetics of penetratin, transportan, Tat (48-60) and MAP (KLAL). The respective CPPs (labelled with the fluorescence quencher, 3-nitrotyrosine) are coupled to small a pentapeptide cargo (labelled with the 2-amino benzoic acid fluorophore) via a disulfide bond. The cellular uptake of the cargo is registered as an increase in fluorescence intensity when the disulfide bond of the CPP-S-S-cargo construct is reduced in the intracellular milieu. Our data show that MAP has the fastest uptake, followed by transportan, Tat(48-60) and, last, penetratin. Similarly, MAP has the highest cargo delivery efficiency, followed by transportan, Tat (48-60) and, last, penetratin. Since some CPPs have been found to be toxic at high concentration, we characterized the influence of CPPs on cellular 2-[(3)H]deoxyglucose-6-phosphate leakage. Measurements on this system show that the membrane-disturbing potential appears to be correlated with the hydrophobic moment of the peptides. In summary, the yield and kinetics of cellular cargo delivery for four different CPPs has been quantitatively characterized.

The absorption of drugs is limited by the epithelial barriers of the gastrointestinal tract. One of the strategies to improve drug delivery is the modulation of barrier function by the targeted opening of epithelial tight junctions. In our previous study the 18-mer amphiphilic PN159 peptide was found to be an effective tight junction modulator on intestinal epithelial and blood⁻brain barrier models. PN159, also known as KLAL or MAP, was described to interact with biological membranes as a cell-penetrating peptide. In the present work we demonstrated that the PN159 peptide as a penetration enhancer has a dual action on intestinal epithelial cells. The peptide safely and reversibly enhanced the permeability of Caco-2 monolayers by opening the intercellular junctions. The penetration of dextran molecules with different size and four efflux pump substrate drugs was increased several folds. We identified claudin-4 and -7 junctional proteins by docking studies as potential binding partners and targets of PN159 in the opening of the paracellular pathway. In addition to the tight junction modulator action, the peptide showed cell membrane permeabilizing and antimicrobial effects. This dual action is not general for cell-penetrating peptides (CPPs), since the other three CPPs tested did not show barrier opening effects.

A recently designed nanoconstruct was engineered using recombinant technology to contain a cell-penetrating peptide (CPP), i.e. Model Amphipathic Peptide (MAP), attached to a pH-sensitive masking peptide sequence. CPPs such as MAP exhibit unique internalization properties which enable them to deliver attached bioactive molecules, including proteins and peptides, into the cytosolic or nuclear compartment of cells. However, their application in drug delivery is limited due to lack of specificity, as they are widely distributed in most tissues following in vivo administration. In order to overcome this hurdle, a highly pH-sensitive histidine-glutamic acid (HE) copolymer sequence was linked to MAP to prevent non-specific internalization of the construct in non-target cells. Our results show that this nanoconstruct is highly pH-sensitive in a mildly acidic pH, exhibiting high binding and internalization at pH 6.8 and below, but low binding and internalization at pH>7. This unique sensitivity in the mildly acidic pH range can be applied to targeting the activation of membrane permeable properties in mildly acidic pH environments, such as the surface of tumor cells or in the early endosomes of target cells. Therefore, the design could lead to a significant advancement in the application of CPPs and in the therapeutic potential of the biotechnology field.