Bioactivation of antituberculosis thioamide and thiourea prodrugs by bacterial and mammalian flavin monooxygenases
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Updated: Jun 8, 2026

System for Efficacy and Cytotoxicity Screening of Inhibitors Targeting Intracellular Mycobacterium tuberculosis
Published on: April 5, 2017
Clinton R Nishida1, Paul R Ortiz de Montellano
1Department of Pharmaceutical Chemistry, University of California, 600 16th Street, San Francisco, CA 94158-2517, USA.
Abstract:
The thioamide and thiourea class of antituberculosis agents encompasses prodrugs that are oxidatively converted to their active forms by the flavin monooxygenase EtaA of Mycobacterium tuberculosis. Reactive intermediates produced in the EtaA-catalyzed transformations of ethionamide and prothionamide result in NAD(+)/NADH adducts that inhibit the enoyl CoA reductase InhA, the ultimate target of these drugs. In the case of thiacetazone and isoxyl, EtaA produces electrophilic metabolites that mediate the antibacterial activity of these agents. The oxidation of the thioamide/thiourea drugs by the human flavin monooxygenases yields similar reactive metabolites that contribute to the toxicities associated with these second line antituberculosis drugs.
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