Novel Peptide-based Antimicrobial Agents for the Treatment of Clostridium Difficile Associated Disease

摘要

Clostridium difficile is the main cause of nosocomial diarrhoea in developed countries. The incidence of disease due to this gram-positive bacterium has been increasing in recent years, with several outbreaks, including from strains such as 027 associated with increased severity and mortality [1]. The number of antibiotics for clinical treatment of Clostridium difficile infection is limited [2]. Antimicrobial peptides offer promise as novel anti-infective agents to which the development of resistance by microbes may be restricted [3]. We have developed a novel approach to combined delivery of antimicrobial peptides and agents that protect host epithelia from clostridial toxins for treatment of Clostridium difficile infection and disease and report here the synthesis and preliminary evaluation of the antimicrobial constituent of these multi-component delivery systems. There is a lack of development of new classes of antibiotic drugs. Many of the existing classes operate by targeting a specific aspect of microbial biochemistry. Consequently, microbes may easily evolve resistance mechanisms. Host defence peptides are molecular effectors of innate immunity in multicellular organisms. These cationic amphipathic peptides offer potential as novel therapeutic antimicrobial [3-5] and anticancer agents [6]. Their assets include potent and broad spectrum activity, low propensity to select resistant mutants and activity that does not rely upon bacterial division. However, to date, in clinical development host defence peptides have met a number of shortcomings, including lack of stability limiting their efficacy. The mode of action of these evolutionarily conserved mediators of innate immunity involves non-specific targeting of microbial function and structure such as anionic components of the microbial membrane [5]. Antimicrobial peptides can also be active against anaerobic bacteria, such as Clostridium species. Electrostatic properties, such as charge and hydrophobicity, and structural characteristics, such as alpha-helicity with segregation of polar and hydrophobic regions, of antimicrobial and host defence peptides impart selective action against membranes of pathogenic over host cells. Noncoded or uncommon amino acids such as occurring in fungal peptaibiotics [7] may be incorporated into synthetic antimicrobial peptide sequences to enhance hydrophobicity or promote alpha-helicity [8]. We have synthesized antimicrobial peptides bearing alphamethylalanine or alpha-aminoisobutyric acid (Aib) at the amino terminal, with the strategy of improving antimicrobial activity and stability over the parent peptide against the representative gram-positive bacterium Staphylococcus aureus. This approach contributes to the conversion of linear alpha-helical host defence peptides into peptidomimetics and should improve pharmacodynamic properties of these candidates. A method has been developed for combined delivery of antimicrobial peptides and antiinflammatory agents for treatment of Clostridium difficile infection and associated colitis.