Abstract
Mycobacterium tuberculosis (MTb) possesses two nonproton pumping type II NADH dehydrogenase (NDH-2) enzymes which are predicted to be jointly essential for respiratory metabolism. Furthermore, the structure of a closely related bacterial NDH-2 has been reported recently, allowing for the structure-based design of small-molecule inhibitors. Herein, we disclose MTb whole-cell structure–activity relationships (SARs) for a series of 2-mercapto-quinazolinones which target the ndh encoded NDH-2 with nanomolar potencies. The compounds were inactivated by glutathione-dependent adduct formation as well as quinazolinone oxidation in microsomes. Pharmacokinetic studies demonstrated modest bioavailability and compound exposures. Resistance to the compounds in MTb was conferred by promoter mutations in the alternative nonessential NDH-2 encoded by ndhA in MTb. Bioenergetic analyses revealed a decrease in oxygen consumption rates in response to inhibitor in cells in which membrane potential was uncoupled from ATP production, while inverted membrane vesicles showed mercapto-quinazolinone-dependent inhibition of ATP production when NADH was the electron donor to the respiratory chain. Enzyme kinetic studies further demonstrated noncompetitive inhibition, suggesting binding of this scaffold to an allosteric site. In summary, while the initial MTb SAR showed limited improvement in potency, these results, combined with structural information on the bacterial protein, will aid in the future discovery of new and improved NDH-2 inhibitors.
Highlights
Article whole-cell structure−activity relationships (SARs) for a series of 2-mercapto-quinazolinones which target the ndh encoded NDH-2 with nanomolar potencies
We describe the identification of a 2-mercaptoquinazoline scaffold identified from a Mycobacterium tuberculosis (MTb) whole cell screen, which had been previously reported to inhibit the mycobacterial type II NADH dehydrogenase,14 providing further evidence for its inhibition of the MTb type II NADH dehydrogenase (NDH-2)
MTb encodes two NDH-2 genes of which the one encoded by ndh plays a critical role for growth both in vitro and in vivo.15−17 NDH-2 catalyzes the transfer of electrons from NADH into the mycobacterial respiratory pathway and has been proposed to be targeted by a number of early stage inhibitors.16,18−20 In contrast, the proton pumping type I NADH dehydrogenase can be deleted without apparent effects on growth both in vitro or in vivo.15−17 As the current series was considered to have a promising druglike profile (Table 1), a focused optimization program was initiated
Summary
Article whole-cell structure−activity relationships (SARs) for a series of 2-mercapto-quinazolinones which target the ndh encoded NDH-2 with nanomolar potencies. The large number of TB patients, coupled with the chemotherapeutic burden, often leads to poor patient adherence and suboptimal treatment outcomes in the developing world, as well as the emergence of multidrug resistant TB (MDR-TB, defined as resistance to isoniazid (INH) and rifampicin (RIF)) and extensively drug-resistant tuberculosis (XDR-TB, defined as MDR-TB plus resistance to any fluoroquinolone and one of three second-line injectable drugs, capreomycin, kanamycin (Kan), and amikacin) To address this global TB health problem, an improved treatment regimen is needed which will reduce treatment duration and prevent relapse and the development of TB drug resistance.− achieving this goal will require discovery of multiple novel and mechanistically distinct antimycobacterial agents possessing reduced liabilities for investigation of new drug regimens that might shorten the duration of treatment and simplify management of the disease by improving adherence and reducing costs.−. MTb encodes two NDH-2 genes of which the one encoded by ndh plays a critical role for growth both in vitro and in vivo.− NDH-2 catalyzes the transfer of electrons from NADH into the mycobacterial respiratory pathway and has been proposed to be targeted by a number of early stage inhibitors.− In contrast, the proton pumping type I NADH dehydrogenase can be deleted without apparent effects on growth both in vitro or in vivo.− As the current series was considered to have a promising druglike profile (Table 1), a focused optimization program was initiated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
