A small-molecule antivirulence agent for treating Clostridium difficile infection

A high-throughput screen against the Clostridium difficile toxin B cysteine protease domain identified a drug in clinical trials that reduced C. difficile pathology in a mouse model. A tough drug for a C. difficile problem Clostridium difficile infection (CDI) is an emerging disease threat caused by use of broad-spectrum antibiotics. CDI is the leading cause of hospital-acquired diarrhea, and with nearly half a million cases diagnosed in the United States each year, it places a yearly estimated burden of more than $4 billion on the U.S. healthcare system. A shift away from standard antibiotics is required to successfully contain this pathogen. Using a screen targeting bacterial virulence factors, Oresic Bender and colleagues identified a lead compound already in human clinical trials. The compound showed potent protective effects in a mouse model of CDI, supporting its translation into clinical studies as a new non-antibiotic treatment for CDI. Clostridium difficile infection (CDI) is a worldwide health threat that is typically triggered by the use of broad-spectrum antibiotics, which disrupt the natural gut microbiota and allow this Gram-positive anaerobic pathogen to thrive. The increased incidence and severity of disease coupled with decreased response, high recurrence rates, and emergence of multiple antibiotic-resistant strains have created an urgent need for new therapies. We describe pharmacological targeting of the cysteine protease domain (CPD) within the C. difficile major virulence factor toxin B (TcdB). Through a targeted screen with an activity-based probe for this protease domain, we identified a number of potent CPD inhibitors, including one bioactive compound, ebselen, which is currently in human clinical trials for a clinically unrelated indication. This drug showed activity against both major virulence factors, TcdA and TcdB, in biochemical and cell-based studies. Treatment in a mouse model of CDI that closely resembles the human infection confirmed a therapeutic benefit in the form of reduced disease pathology in host tissues that correlated with inhibition of the release of the toxic glucosyltransferase domain (GTD). Our results show that this non-antibiotic drug can modulate the pathology of disease and therefore could potentially be developed as a therapeutic for the treatment of CDI.