Towards the discovery of direct inhibitors of Mycobacterium tuberculosis and Mycobacterium abscessus InhA by protein-templated fragment ligations – TagInhA

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) affects 10 million people each year and the emergence of resistant TB augurs for a growing incidence. In the last 60 years, only three new drugs were approved for TB treatment, for which resistances are already emerging. Therefore, there is a crucial need for new chemotherapeutic agents capable of eradicating TB. Enzymes belonging to the type II fatty acid synthase system (FAS-II) are involved in the biosynthesis of mycolic acids, cell envelope components essential for mycobacterial survival. Among them, InhA is the primary target of isoniazid (INH), one of the most effective compounds to treat TB. INH acts as a prodrug requiring activation by the catalase-peroxidase KatG, whose mutations are the major cause for INH resistance. Different classes of direct inhibitors of InhA requiring no prior activation by KatG have been discovered but none of them was approved for clinical use so far. M. abscessus (Mab), another mycobacterium, is responsible for severe lung infections, especially in patients with lung disorders such as cystic fibrosis. The current treatment causes significant side effects and its success is also challenged by antibiotic resistance. Mab also integrates a FAS-II system, which includes an InhA enzyme but INH is unfortunately poorly active against Mab. The major goal of this project is to capitalize on methods involving pre-organization of fragments based on a protein template, such as Kinetic Target-Guided Synthesis (KTGS) and Dynamic Combinatorial Chemistry (DCC) combined to X-ray crystallography, to discover new potent inhibitors of Mtb- and Mab-InhA. Our aim will be to develop the screening of fragments that will assemble by KTGS and DCC and to proceed with their optimization. In each of these two steps, we will characterize the inhibition of the enzyme and growth of Mtb and Mab by the identified/optimized compounds and verify their lack of cytotoxicity in several human cell lines. Finally, the mechanism of action and pharmacokinetic properties of the most effective compounds will be studied.