Development of small molecule selenium-based inhibitors as anti-toxin agents for the treatment of Clostrodium difficile infection (CDI)

• Applicant: Dr. Sebastian Loscher
• Subject Area: Biological and Biomimetic Chemistry ; Pharmacy ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 349476693

In past decades the excessive use of antibiotics has caused numerous problems in human health such as raising resistances. One of them is the burden of a C. difficile infection caused by the antibiotic agents which are known to disrupts the natural gut microbiota allowing resistant C. difficile strains to thrive. Present standard of care treatment of CDI is again additional dosage of antibiotics never allowing the natural microbiome to recover leading to a high reoccurrence rate of about 25%. The major virulence factor of the opportunistic anaerobic bacteria C. diff. is called toxin B (TcdB) and it bears a cysteine protease domain (CPD) which autocatalytically frees a toxic glycosyltransferase domain upon endocytosis. This domain irreversibly glycosylates members of the small GTPase families leading to cell lysis, severe diarrhea and sepsis. The described project targets the major C. difficile virulence factor TcdB with small molecule inhibitors to shut down the CPD activity which in turn allows the patients natural microbiome to revive over time leading to natural cleaning of the infection.An initial HTS revealed hits with sub-micromolar activity against the purified toxin. Besides some phenols and enamides, an organo-selenium compound called ebselen appeared in the screen with single digit nanomolar activity against the purified enzyme. Testing ebselen in a CDI mouse model clearly showed that it protects epithelial cells in the gut from lysis during infection in a dose dependent manner. Another benefit from targeting TcdB was verified in phase III clinical trials by Merck using a monoclonal antibody against TcdB. Their study showed a significant decrease in the reoccurrence rate in humans after standard of care antibiotic treatment against CDI in combination with their antibody. Another benefit of ebselen based compounds is the already known clear pharmacokinetic profile of the parent in humans.This project is a new approach to target one of Clostrodium difficiles exotoxin with small molecule inhibitors. The planned inhibitors are based on the organo-selenium compound ebselen which proofed active in different in vitro and in vivo models.The project is focused on building a library of organo-selenium compounds around the core ebselen scaffold potentially being specific towards the CPD only and potentially more soluble for a higher oral availability. Potential overall structure and perspective substituents of this scaffold will be based on docking results in collaboration. The proposed work will not only explore the chemical space around the core ebselen scaffold but is also going to investigate the mode of action of this compound type in different infection models in more detail. This project also wants to consider formulation studies for specific gut delivery. The lead compound as well as promising derivatives will be tested in different in vitro systems and potential drug candidates will be verified in existing mouse models.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Matthew Bogyo, Ph.D.