Target Discovery for New Antitubercular Drugs Using a Large Dataset of Growth Inhibitors from PubChem

The number of drugs available for treatment of active tuberculosis is diminishing due to increased multidrug resistance selection in Mycobacterium tuberculosis leading to multiple (MDR) and extensively (XDR) resistant strains. Also, TB is treated with multiple drugs to minimize further resistance development, mandating a sustained effort to identify new lead compounds for treating drug-resistant TB and shortening time to cure for all TB infections. High throughput screening, a well-known approach to discovery of new leads, is conducted in two basic modes 1) using whole cells and screening for inhibition of growth, or whole cell reporter cells that signal when a specific pathway is perturbed, and 2) in vitro non-cell based enzyme or other functional assays for direct ligand-target binding. Combining high throughput screening for inhibitors of growth (to identify and chemically assess inhibitors active on whole cells), followed by target identification abrogates the problem of discovering new leads in non-cell based systems that are inactive on whole cells due to issues with target access (e.g., uptake). High throughput screening of 341,778 compounds by the National Institutes of Health identified 8,950 primary hit, growth inhibitors of M. tuberculosis. Final evaluation based on reproducibility, potency, medicinal chemistry inspection, and cytotoxicity on tissue culture cells identified 1,113 priority compounds. These data were deposited in PubChem, making data available to TB research labs for follow up studies on target identification. This effort led to the identification of compounds targeting Pks13, MmpL3, DprE1, AspS, EthA, GuaB2, nonreplicating cells, and VKOR (Vitamin K epoxide reductase).