Selective agents against C. difficile infection

DESCRIPTION provided by applicant The overall goal of this project is to develop a selective antibiotic against Clostridium difficile the major agent responsible for antibiotic induced diarrhea and colitis The pathogen can be carried in healthy individuals and is kept at bay by gut symbionts Antibiotic treatment suppresses the normal flora but spores of C difficile survive germinate and cause disease Treatment with metronidazole vancomycin or fidaxomicin kills not only the pathogen but also the symbionts which may result in relapse Ideally one would like to have a therapeutic which is selective against C difficile as it would allow the normal flora to restore in the course of treating the pathogen preventing relapse Based on genomic studies bacteria share a core of genes and in addition to those there may be up to essential genes specific to a given species genus We reasoned that the existence of a large number of specific targets presents an opportunity to discover antimicrobials acting selectively against C difficile The pathogen is an anaerobe while HTS normally requires aerobic conditions As a result current therapeutics for treating the infection come from other programs and are not selective We developed an anaerobic HTS and performed a first direct screen against C difficile Given the historically high success rate of discovering antibiotics from natural products we screened a library of extracts from soil bacteria This library comes from an untapped resource uncultured bacteria and is rich in novel compounds The library had been screened against S aureus and E coli producing hit rates of and respectively We reasoned that the remaining andquot inactiveandquot strains may harbor compounds active against particular species that were missed in the primary screen A pilot screen of extracts resulted in a hit rate of against C difficile Preliminary analysis of these extracts showed that two were selective against C difficile when tested against a small panel of gut commensals and contained compounds with novel masses In the proposed project we will follow up on these hits and screen additional extracts from the andquot inactiveandquot library Hits will be de replicated by LC MS which will indicate the degree of novelty and tested against representatives of the main groups of gut symbionts Clostridium selective compounds passing dereplication will be tested for potency resistance frequency cytotoxicity and penetration into intestinal epithelial cells Compounds that are not absorbed and thus retained at the site of infection will be given priority Structure determination will confirm novelty and provde information on the suitability of compounds for further development Whole genome sequencing of resistant mutants will indicate the likely target Maximum tolerated dose and bioavailability of leads will be determined in hamsters which will inform the design of a C difficile efficacy study The goal of Phase I is to identify two to three lead compounds with efficacy in a hamster model of C difficile infection This will form a solid basis for a Phase II application aimed at preclincal development towards an IND PUBLIC HEALTH RELEVANCE C difficile infection CDI has become a major cause of infectious diarrhea and colitis in healthcare settings and in the community It is widely agreed that new antibiotics are needed to treat this disease and the proposed study will address this need