Peptides are short, sequence and length specific oligomers composed of small amino acid residues. Nature has refined these peptide sequences and their endogenous function through evolution. In addition, peptides have played an important role in medicine, which has lead to further research into developing peptides as lead pharmaceuticals (therapeutic peptides). Unfortunately, therapeutic peptides are inferior as drug candidates due to their low oral bioavailability; immunogenicity and potential to be attacked by peptidases. Fortunately, peptides can be modified by steric constraints, cyclization, and/or replacement of the peptide backbone itself creating a mimic (peptidomimetic) of the original peptide. Peptidomimetics are deliberately designed to have increased protease resistance, reduced immunogenicity and improved bioavailability when compared to the original endogenous peptide. One such peptide, Magainin is a O One such peptide, Magainin is a well-studied, a-helical peptide found in African clawed frogs. This peptide has antibiotic properties (against pathogenic bacteria), which partly arises from the hydrophilic portion of the peptide having basic amino acid side chains periodically disposed on one side of the a-helix. This property of magainin causes its attraction to negatively charged bacteria cell membranes. Unfortunately, as in the case of other antibiotics, pathogenic bacteria have developed effective countermeasures against magainin. We designed a peptidomimetic based on magainin and implemented a plan to determine what type of molecules could be assembled for a magainin mimic. We successfully utilized molecular modeling (Monte Carlo conformational search), as well as results from previous experiments to elucidate what type of molecules, as well as how many molecules would be necessary to create a novel helical-like magainin peptidomimetic. It was discovered that C2 symmetric diamines would be best at generating the helical-like motif and the amino acid lysine to generate the basic side chain. The next step was the successful connection of two C2 symmetric molecules via a urea linkage and then one more connection to a lysine (a-amino group) residue, creating a short sequence of oligoureas (trimers). Finally, attempts to connect the oligoureas trimers were attempted using a solid-phase synthesis approach to generate a functional magainin mimic.

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The world-wide transdermal drug delivery market is quite large, but only a small number of agents have FDA approval. The primary reason for such limited development is the difficulty in permeating the stratum corneum layer of human skin. In our study, we developed a novel percutaneous delivery enhancing approach. Magainin peptide was previously shown to disrupt vesicles from stratum corneum lipid components and this ability of magainin allows us to propose that magainin can increase skin permeability. Therefore, we tested the hypothesis that magainin, a pore-forming peptide, can increase skin permeability by disrupting stratum corneum lipid structure and that magainin¡¯s enhancement requires co-administration of a surfactant chemical enhancer to increase magainin penetration into the skin. In support of these hypotheses, synergistic enhancement of transdermal permeation can be observed with magainin peptide in combination of N-lauroyl sarcosine (NLS) in 50% ethanol-PBS solution. The exposure to NLS in 50% ethanol solution increased in vitro skin permeability to fluorescein 15 fold and the addition of magainin synergistically increased skin permeability 47 fold. In contrast, skin permeability was unaffected by exposure to magainin without co-enhancement by NLS-ethanol. To elucidate the mechanism of this synergistic effect, several characterization methods such as differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction were applied. These analyses showed that NLS-ethanol disrupted stratum corneum lipid structure and that the combination of magainin and NLS-ethanol disrupted stratum corneum lipids even further. Furthermore, confocal microscopy showed that magainin in the presence of NLS-ethanol penetrated deeply and extensively into stratum corneum, whereas magainin alone penetrated poorly into the skin. Together, these data suggest that NLS-ethanol increased magainin penetration into stratum corneum, which further increased stratum corneum lipid disruption and skin permeability. Finally, skin permeability was enhanced by changing the charge of magainin peptide via pH change. We modulated pH from 5 to 11 to change the magainin charge from positive to neutral, which decreased skin permeability to a negatively charged fluorescein and increased skin permeability to a positively charged granisetron. This suggests that an attractive interaction between the drug and magainin peptide improves transdermal flux.