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Small-Molecule Inhibition of the C. difficile FAS-II Enzyme, FabK, Results in Selective Activity
Jesse A Jones1, Allan M Prior2, Ravi K R Marreddy3
1Department of Pharmaceutical Sciences, College of Pharmacy , University of Tennessee Health Science Center , Memphis , Tennessee 38163 , United States.
Abstract:
Clostridioides difficile infection (CDI) is a leading cause of significant morbidity, mortality, and healthcare-related costs in the United States. After standard therapy, recurrence rates remain high, and multiple recurrences are not uncommon. Causes include treatments employing broad-spectrum agents that disrupt the normal host microbiota, as well as treatment-resistant spore formation by C. difficile. Thus, novel druggable anti-C. difficile targets that promote narrow-spectrum eradication and inhibition of sporulation are desired. As a critical rate-limiting step within the FAS-II bacterial fatty acid synthesis pathway, which supplies precursory component phospholipids found in bacterial cytoplasmic and spore-mediated membranes, enoyl-acyl carrier protein (ACP) reductase II (FabK) represents such a target. FabK is essential in C. difficile (CdFabK) and is structurally and mechanistically distinct from other isozymes found in gut microbiota species, making CdFabK an attractive narrow-spectrum target. We report here the kinetic evaluation of CdFabK, the biochemical activity of a series of phenylimidazole analogues, and microbiological data suggesting these compounds' selective antibacterial activity against C. difficile versus several other prominent gut organisms. The compounds display promising, selective, low micromolar CdFabK inhibitory activity without significantly affecting the growth of other gut organisms, and the series prototype (1b) is shown to be competitive for the CdFabK cofactor and uncompetitive for the substrate. A series analogue (1g) shows maintained inhibitory activity while also possessing increased solubility. These findings represent the basis for future drug discovery efforts by characterizing the CdFabK enzyme while demonstrating its druggability and potential role as a narrow-spectrum antidifficile target.
Insights
Novel phenylimidazole compounds selectively inhibit Clostridioides difficile FabK, a key enzyme in fatty acid synthesis. This discovery offers a promising narrow-spectrum target for new anti-infective therapies against recurrent C. difficile infections.
Area of Science:
- Microbiology
- Drug Discovery
- Biochemistry
Background:
- Clostridioides difficile infection (CDI) presents significant morbidity, mortality, and healthcare costs, with high recurrence rates after standard therapies.
- Broad-spectrum antibiotics disrupt gut microbiota, and C. difficile spore formation contributes to treatment resistance, necessitating novel narrow-spectrum targets.
- The bacterial fatty acid synthesis II (FAS-II) pathway is crucial for bacterial membranes and spore formation, with enoyl-acyl carrier protein (ACP) reductase II (FabK) as a potential druggable target.
Purpose of the Study:
- To identify and characterize novel narrow-spectrum anti-C. difficile targets.
- To evaluate the druggability of Clostridioides difficile enoyl-acyl carrier protein (ACP) reductase II (CdFabK) as a therapeutic target.
- To discover and assess phenylimidazole analogues for selective inhibition of CdFabK.
Main Methods:
- Kinetic evaluation of purified CdFabK enzyme.
- Biochemical assessment of phenylimidazole analogues against CdFabK.
- Microbiological assays to determine selective antibacterial activity against C. difficile and other gut organisms.
Main Results:
- Phenylimidazole analogues demonstrated selective, low micromolar inhibitory activity against CdFabK.
- Compounds showed minimal impact on the growth of other prominent gut organisms, indicating narrow-spectrum potential.
- The series prototype (1b) exhibited competitive inhibition for the cofactor and uncompetitive inhibition for the substrate, while analogue (1g) maintained activity with improved solubility.
Conclusions:
- CdFabK is a druggable target for developing narrow-spectrum anti-C. difficile agents.
- Phenylimidazole analogues represent a promising starting point for novel anti-infective drug discovery against CDI.
- Targeting CdFabK offers a strategy to overcome limitations of current therapies, including recurrence and broad-spectrum effects.
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