| Summary: | Tuberculosis is a worldwide health concern causing 10 illion new cases and 1.4 million deaths annually. Multi-drug resistance is a further issue limiting effective treatment, with the proportion of cases in this category rising each year.
InhA is a key enzyme in the Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis (Mb) fatty acid synthase II pathway responsible for production of long chain mycolic acids. These acids comprise a high proportion of the Mtb/Mb cell walls. The only first-line, clinically used drug targeting InhA is the prodrug Isoniazid which is losing effectiveness in the wake of growing drug resistance. This resistance is developing at its site of metabolism to the active NAD+ conjugate, the catalase-peroxidase KatG. By developing direct inhibitors of InhA, resistance due to mutations in KatG can be bypassed, regaining access to a clinically validated anti-TB target.
The Nottingham Managed chemical Compound Collection (NMCCC) was selected as a source of chemical diversity. It contains over 82,000 molecules pre-screened for drug-like properties and a further 3,000 molecules submitted from research projects carried out at the university. The NMCCC was subjected to virtual screening against InhA using the GOLDSuite software package and four compounds were selected for synthesis from among the highest scoring candidates. These four compounds were screened against InhA in single point isolated enzyme assays, showing minimal activity.
A further 144 high scoring compounds were purchased from the NMCCC and screened against InhA in isolated enzyme assays. Three of these were identified as hits with over 50% inhibition of InhA at 50 µM and taken forward for synthesis. Following synthesis, precipitation of these compounds was observed prior to repeat in vitro analysis, requiring extended effort to solvate. Reduced activity against InhA was observed when these compounds were retested, indicating the need for orthogonal screening to confirm any hit moving forward.
There remain 11 NMCCC hits with greater than 30% inhibition of InhA at 50 µM and cLogP below 3 to be investigated and four of these show a common binding mode.
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