Mutual influence of backbone proline substitution and lipophilic tail character on the biological activity of simplified analogues of caspofungin.

The echinocandins represent the most recent class of antifungal drugs. Previous structure-activity relationship studies on these lipopeptides have relied mainly upon semisynthetic derivatives due to their complex chemical structures. A successful strategy for the rapid enantioselective synthesis of the branched fatty acid chain of caspofungin and analogues was developed to synthesize several simplified analogues of caspofungin. The specific minimum inhibitory activity of each mimic was determined against a panel of Candida strains. This approach gave access to new fully synthetic derived caspofungin mimics with high and selective antifungal activities against Candida strains. In addition, the data suggested an important role of the hydroxy proline residue in the bioactive conformation of the macrocyclic peptide ring structure.

Synthesis and evaluation of novel macrocyclic antifungal peptides.

Echinocandins are a novel class of macrocyclic antifungal peptides that act by inhibiting the ß-(1,3)-D-glucan synthase complex, which is not present in mammalian cells. Due to the large number of hydroxyl groups present in these complex macrocyclic lipopeptides, most structure-activity relationship studies have relied upon semisynthetic derivatives. In order to probe the influence of the cyclic peptide backbone on the antifungal activity we developed a successful strategy for the synthesis of novel echinocandins analogues by on-resin ring closing metathesis or disulfide formation. The specific minimum inhibitory activity of each mimic was determined against Candida albicans. Our results indicate that ring size is an important factor for antifungal activity.

Manipulation of innate immunity by a bacterial secreted peptide: lantibiotic nisin Z is selectively immunomodulatory.

Innate immunity is triggered by a variety of bacterial molecules, resulting in both protective and potentially harmful pro-inflammatory responses. Further, innate immunity also provides a mechanism for the maintenance of homeostasis between the host immune system and symbiotic or non-pathogenic microorganisms. However, the bacterial factors that mediate these protective effects have been incompletely defined. Here, it was demonstrated that the lantiobiotic nisin Z is able to modulate host immune responses and mediate protective host immunity. Nisin Z induced the secretion of the chemokines MCP-1, IL-8 and Gro-α, and significantly reduced TNF-α induction in response to bacterial LPS in human PBMC. The results correlated with the ability of nisin Z to confer protection against both the Gram-positive organism Staphylococcus aureus, and the Gram-negatives Salmonella enterica sv. Typhimurium and Escherichia coli in murine challenge models. Mechanistic studies revealed that nisin Z modulates host immunity through similar mechanisms as natural host defense peptides, engaging multiple signal transduction pathways and growth factor receptors. The results presented herein demonstrate that, in addition to nisin Z, other bacterial cationic peptides and, in particular, the lantibiotics, could represent a new class of secreted bacterial molecule with immunomodulatory activities.