Screening and biological activities of pedopeptins, novel inhibitors of LPS produced by soil bacteria.

Lipopolysaccharide (LPS) is a strong endotoxin and is delivered to the cell surface signaling receptor, Toll-like receptor 4 and MD-2 complex, via soluble cluster of differentiation (CD) 14 or membranous CD14, resulting in the induction of the inflammatory response. To obtain new compounds that block LPS binding to CD14, we designed a high-throughput screening based on time-resolved intermolecular fluorescence resonance energy transfer. This cell-free screening system successfully led to the discovery of novel inhibitors of LPS-CD14 interaction from the library of the secondary metabolites of microorganisms. We identified the novel compounds pedopeptin A, B and C from a culture broth of Pedobacter sp. SANK 72003. Pedopeptins blocked LPS binding to CD14 in vitro with IC50 values of 20, 11 and 47 nM, respectively, and also inhibited LPS binding to the cells expressing CD14, leading to the suppression of cytokine production. Moreover, they showed antimicrobial activities against Escherichia coli with minimum inhibitory concentration ranging from 2 to 4 μg ml(-1).