ABSTRACT
A pharmacophore-based search led to the identification of thiazolopyridine ureas as a novel scaffold with antitubercular activity acting through inhibition of DNA Gyrase B (GyrB) ATPase. Evaluation of the binding mode of thiazolopyridines in a Mycobacterium tuberculosis (Mtb) GyrB homology model prompted exploration of the side chains at the thiazolopyridine ring C-5 position to access the ribose/solvent pocket. Potent compounds with GyrB IC50 ≤ 1 nM and Mtb MIC ≤ 0.1 µM were obtained with certain combinations of side chains at the C-5 position and heterocycles at the C-6 position of the thiazolopyridine core. Substitutions at C-5 also enabled optimization of the physicochemical properties. Representative compounds were cocrystallized with Streptococcus pneumoniae (Spn) ParE; these confirmed the binding modes predicted by the homology model. The target link to GyrB was confirmed by genetic mapping of the mutations conferring resistance to thiazolopyridine ureas. The compounds are bactericidal in vitro and efficacious in vivo in an acute murine model of tuberculosis.
Subject(s)
Antitubercular Agents/pharmacology , DNA Gyrase/metabolism , Mycobacterium tuberculosis/drug effects , Pyridines/pharmacology , Topoisomerase II Inhibitors/pharmacology , Tuberculosis/drug therapy , Urea/pharmacology , Animals , Antitubercular Agents/administration & dosage , Antitubercular Agents/chemistry , Disease Models, Animal , Dose-Response Relationship, Drug , Mice , Mice, Inbred BALB C , Models, Molecular , Molecular Structure , Mycobacterium tuberculosis/enzymology , Pyridines/administration & dosage , Pyridines/chemistry , Structure-Activity Relationship , Topoisomerase II Inhibitors/administration & dosage , Topoisomerase II Inhibitors/chemistry , Urea/analogs & derivatives , Urea/chemistryABSTRACT
The discovery of novel therapeutics for the treatment of tuberculosis involves routine testing in a mouse model over four weeks of daily dosing with test compounds. In this model, daily oral administration of rifampin (10 mg/kg) showed significantly lower plasma exposure on day 5 compared to day 1. The absence of PXR-mediated induction of mouse Cyp3a isoforms was confirmed in the present study by incubating liver microsomes prepared from control and rifampin treated mice with probe substrates of CYP3A. To test whether the reduction in exposure was due to Pgp-mediated efflux, verapamil, a known Pgp inhibitor, was dosed to the rifampin pre-treated mice which led to an increase in exposure to that obtained after a single dose of rifampin, suggesting the role of Pgp induction in reducing exposure to rifampin. To further confirm Pgp induction in rifampin treated mice, digoxin, a known substrate of Pgp, was administered to the rifampin pre-treated mice, and a significant drop in the digoxin exposure was observed compared to the control group. Collectively, our results show that repeated administration of rifampin in mice leads to a reduction in oral exposure due to induction of Pgp-mediated efflux of rifampin, and not via induction of CYP3A isoforms.
