Rational, structure-based inhibitor design, synthesis and evaluation as a first step towards the discovery of new anti-tuberculosis drugs

Background: Mycobacterium tuberculosis and M. bovis are the main causes of tuberculosis (TB) in humans and animals respectively. The World Health Organisation (WHO) reported that 1.5M people (including 251K with HIV) died from TB and 10M fell ill in 2018, the highest of any infectious disease. Increasing occurrences of drug resistance to the drugs used to treat TB include strains showing extreme drug resistance (XDR-TB) have been observed. DEFRA reported that 2,805 herds of cattle in Great Britain tested positive for bovine TB in the 12 months to Sept 2018, with 305K cattle having to be slaughtered in GB over the last decade at the cost of £500M. Methods of treating or eradicating TB are therefore crucial to both human and animal health. Mycobacteria have an unusual and more complex cell wall structure than other Gram-positive bacteria. The exterior surface of the bacterium is formed from a hydrophobic, waxy coat of mycolic acids (~C60 long chain fatty acids) (Alderwick et al. Cold Spring Harb Perspect Med. 2015, 5, a021113) that acts as a pseudo-outer membrane. This sits on a polysaccharide structure, arabinogalactan that contains several rare sugars (galactofuranose/arabinofuranose/rhamnose) which is then attached to the peptidoglycan layer. This 'stealth' coat masks the bacteria from its host's defences and allows them to colonize mammalian tissues and form biofilms without triggering a host response. We can selectively target several enzymes unique to Mycobacteria with inhibitors/drugs with a reduced chance of off-target toxicity. Research Project: This will involve the design, synthesis and evaluation of new compounds as putative inhibitors of selected target enzymes: InhA (an enoyl reductase) involved in mycolic acid
biosynthesis; UGM and GlfT2 involved in galactan biosynthesis. There are high resolution X-ray structures available for these enzymes allowing new inhibitor designs to be tested in silico using protein-ligand docking programs including GOLD or OEDocking prior to their synthesis. For InhA, the clinically important mutations that cause resistance are known and new compounds can be docked against these mutants to test if their binding will be impacted. The majority of TB cases are in the third world, therefore new drugs need to be easy to produce and be orally active to minimise their cost.The research will focus on one/two of the enzymes mentioned above. The student will express the enzyme(s) from vectors available in the group and synthesize their assay substrates as necessary. Initial test compounds will be designed by docking existing small molecule/fragment libraries (size