Development and Evaluation of Inhibitors of the C. difficile Enzyme, FabK, as Microbiome-Sparing Antibacterials
Abstract
Clostridioides difficile (C. difficile) is a bacterium that is responsible for an infection of the lower bowel resulting in diarrhea and, potentially, life-threatening colon inflammation. C. difficile infection (CDI) has been historically associated with the treatment of hospitalized patients using broad-spectrum antibacterial drugs. These drugs eradicate the non-pathogenic, or beneficial, bacteria in the lower bowel, allowing C. difficile to overgrow and cause infection. Interestingly, the first-line antibacterial agent used to treat CDI, vancomycin, also has activity against the other, non-pathogenic gut bacteria, which prevents the re-growth of these bacteria and results in a high rate of infection recurrence, up to 35% of patients in some settings. In the United States, CDI occurs in about 500,000 people every year, causing more than 29,000 deaths and resulting in healthcare costs exceeding $4.5 billion. The situation has become so dire that the U.S. Centers for Disease Control and Prevention (CDC) has now declared C. difficile to be an “urgent health threat.” The recent emergence of epidemic, hypervirulent strains of C. difficile, such as NAP1/027, and strains associated with infections in the community, versus the typical hospital settings, have further compounded the situation. There is clearly an urgent need to identify new antibacterials that are narrow spectrum, selectively targeting C. difficile while sparing the non-pathogenic bacteria in the human gut. This proposal addresses the need for C. difficile selective therapies by focusing on a hitherto unexplored antibacterial target in this organism, the fatty acid synthesis pathway (FAS-II). The bacterial FAS-II pathway is distinct from the mammalian fatty acid synthesis pathway (FAS-I) and presents a promising target for antibacterial drug discovery. The FAS-II pathway provides fatty acids that the bacteria use as cell membrane components and for the formation of spores (dormant structures that are highly resistant to adverse environmental conditions and antibacterial drugs). Inhibitors of FabI, a critical enzyme in FAS-II, have been characterized, including the agent triclosan, found in many household items. C. difficile expresses an isozyme of FabI called FabK that is structurally and mechanistically distinct. We have generated strong preliminary data demonstrating that C. difficile FabK (CdFabK) is essential, druggable, and that inhibition of CdFabK by our lead compounds causes a selective antibacterial effect, inhibits spore formation, and cures mice infected with severe CDI caused by a NAP1 strain. We have also shown that CdFabK inhibition is not overcome by fatty acids taken up from the host. These findings represent an important foundation for development of clinically useful inhibitors targeted to FabK for treatment of CDI and preventing infection recurrence. While our current lead demonstrates activity in mice, further optimization is required to improve the compound, including increasing solubility, decreasing protein binding, improving antibacterial activity, and overcoming the ability of some non-NAP1 C. difficile strains to pump the compound out of the cell (efflux). Our long-term goal is to advance inhibitors of the CdFabK enzyme as clinical candidates for treatment of resistant and recurrent CDI. The objectives of this application, and the next steps toward the achievement of our goal, are (i) to optimize the physicochemical properties of the lead compound series; (ii) to identify novel classes of CdFabK inhibitors; and (iii) to show that these CdFabK inhibitors exhibit activity in animals without disrupting the beneficial bacteria, while decreasing the spore formation that leads to recurrent infection. Project Relevance to Peer Reviewed Medical Research Program Interests: (1) Topic Area – Antimicrobial Resistance. The compounds under study are effective against a highly resistant and pathogenic strain of C. difficile, NAP1,
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010296
Entities
People
- Kirk E Hevener
Organizations
- United States Army
- University of Tennessee Health Science Center