Optimization of novel inhibitors of mycolic acid synthesis as TB drug candidates.

Project Summary Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is responsible for staggering levels of morbidity and mortality, with ~1.7 million deaths and ~10 million new cases each year. The current TB regimens for drug susceptible strains, entailing multidrug cocktails for ≥4 months, leave much to be desired. The cost and logistics of administering standard of care regimens over many months and the inability of many patients to tolerate the debilitating side effects further complicate the clinical control of TB. The lingering negative impacts of the COVID pandemic on TB control efforts and increasing challenge of multidrug-resistant Mtb strains, which have only a ~50% treatment success rate, further highlight the urgent need for better antibiotics to tackle this problem. Even our definition of what “better” means has shifted based on recent appreciation of the heterogeneity of mycobacteria subpopulations that must be eradicated, including replicating and non-replicating bacilli residing both extracellularly and within host cells in diverse microenvironments. Thus, effective drug combinations must not only access mycobacteria within different niches and layers of granulomas but also be able to kill Mtb in many distinct metabolic states while minimizing the emergence of resistance. In order to meet this urgent need for game-changing new treatment options for TB, it is imperative to maintain a robust pipeline of new anti-TB drug candidates with the potential to meet these demanding performance criteria. This project seeks to address this need by building on our recent discovery of a first-in-class series of compounds that kill Mtb via inhibition of a well- validated but underexploited target enzyme essential for cell wall synthesis. Thus far, we have demonstrated sub-micromolar potency, enhanced potency against Mtb within macrophages, high specificity for Mtb, and high selectivity over mammalian cells. We have strong evidence that these compounds act via inhibition of an essential enzyme involved in mycolic acid biosynthesis for which there are currently no viable preclinical candidates. The first major goal of this project is hit-to-lead optimization and elucidation of structure-activity relationships, using whole cell potency and ADME/PK properties as key drivers of compound prioritization. Secondly, we will employ orthogonal approaches to further validate the target and ensure that optimized lead compounds remain on-target. Successful completion of this project will set the stage for subsequent lead optimization and in vivo efficacy studies of a promising new class of cell-wall targeting TB antibiotics.