Pexiganan acetate

The aim of this study was to probe the potential anti-H. pylori activity of the synthetic antimicrobial peptide pexiganan, which is an analog of the peptide magainin, and its nanoparticles (PNPs) that were prepared in our laboratory. To compare their antibacterial effects in vitro and in vivo, studies of H. pylori growth inhibition, kinetics and resistance assays were undertaken. The gastric mucoadhesive efficiency and H. pylori clearance efficiency of pexiganan and PNPs were evaluated in rats and mice infected with H. pylori. The eradication of H. pylori was determined using urease tests and a microbial culture method. We observed that PNPs adhered to gastric mucosa more effectively owing to a prolonged stay in the stomach, which resulted in a more effective H. pylori clearance. In addition, PNPs had greater anti-H. pylori effect than pexiganan in infected mice. The amount of pexiganan required to eradicate H. pylori was significantly less using PNPs than the corresponding pexiganan suspension. The results confirmed that PNPs improved peptide stability in the stomach and more effectively eradicated H. pylori from mice stomachs than pexiganan.

Purpose:The purpose of this study was to identify four major degradation products, which were formed during a stress study of pexiganan (a 22-mer peptide) in a 1% formulation.Methods:The degradation products were isolated and characterized by LC/MS, tryptic and aminopeptidase digests.Results:One of the degradation products was shown to be des-glyl-pexiganan. The other three are structural isomers of N-glyoxylyl-desgly1-pexiganan. These isomers undergo reversible inter-conversions, as well as decompose irreversibly to des-gly1-pexiganan. Thus, all the impurities were formed from a single oxidation product of pexiganan, N-glyoxylyl-des-gly1-pexiganan. The aldehyde group of the glyoxylyl residue and the NH-amide of the adjacent isoleucine residue form a piperazinedione derivative of des-gly1-pexiganan. This heterocyclic compound rearranges to other tautomers or back to the N-glyoxylyl compound (see Fig. 3). Tryptic digests of the three degradation products showed that their N-terminal segment produced N-glyoxylyl-I-G-K whereas the N-terminal segment of pexiganan produced G-I-G-K. All the other tryptic-digest segments were identical to those formed in pexiganan. The LC/MS of the N-terminal segment and of synthetic N-glyoxylyl-I-G-K were identical. The enzymatic resistance of the three impurities to undergo aminopeptidase-M cleavage further supported the conclusion that their N-terminal amino residues are substituted.Conclusions:After a year under stress conditions 1% pexiganan cream lost about 15% of the active component to oxidative-deamination, where the N-terminal glycine residue was oxidized to N-glyoxylyl-desgly1-pexiganan. The other nine epsilon-amino lysine-residues of the peptide stayed intact. This oxidation product inter-converted and formed two additional impurities, tautomers of piperazinedionyl-des-gly-pexiganan, and decomposed to des-gly1-pexiganan, the forth impurity.

Pexiganan acetate (MSI 78) is a synthetic cationic peptide (22 amino acids) with antibacterial activity. It is an analogue of magainin 2, which is a host defence peptide isolated from frog skin. The drug is thought to act by disturbing the permeability of the cell membrane or cell wall. Pexiganan acetate has good in vitro activity against Gram-positive and Gram-negative aerobes; 99% of strains were susceptible to the agent using a break-point of 64 mg/L. 89 to 97% of anaerobes were susceptible to pexiganan acetate using the same break-point. After 7 passages in vitro, there was no evidence of resistance to pexiganan acetate among 2 strains of Staphylococcus aureus. In 2 phase III multicentre randomised double-blind trials in diabetic patients with infected foot ulcers, both topical pexiganan acetate 1% and oral ofloxacin 800 mg/day achieved clinical cure or improvement in about 90% of patients. Eradication of pathogens in the 2 studies was achieved in 82% of ofloxacin recipients and 66% of pexiganan acetate recipients at the end of therapy. Limited data indicate that pexiganan acetate is well tolerated.