Isoxyl Activation Is Required for Bacteriostatic Activity against Mycobacterium tuberculosis

• DOI: 10.1128/aac.00433-07
• Publication Date: 2007-09-05T00:54:30Z
• Authors: Jana Korduláková; Yves L. Janin; Avraham Liav; Nathalie Barilone; Tiago Dos Vultos; Jean Rauzier; Patrick J. Brennan; Brigitte Gicquel; Mary Jackson
• Keywords: 0301 basic medicine; [SDV.OT]Life Sciences [q-bio]/Other [q-bio.OT]; Molecular Structure; [SDV.OT] Life Sciences [q-bio]/Other [q-bio.OT]; Antitubercular Agents; Thiourea; Mycobacterium tuberculosis; Mixed Function Oxygenases; 3. Good health; 03 medical and health sciences; Bacterial Proteins; Mycolic Acids; Mutation

ABSTRACT

Isoxyl (ISO), a thiourea derivative that was successfully used for the clinical treatment of tuberculosis during the 1960s, is an inhibitor of the synthesis of oleic and mycolic acids in Mycobacterium tuberculosis . Its effect on oleic acid synthesis has been shown to be attributable to its inhibitory activity on the stearoyl-coenzyme A desaturase DesA3, but its enzymatic target(s) in the mycolic acid pathway remains to be identified. With the goal of elucidating the mode of action of ISO, we have isolated a number of spontaneous ISO-resistant mutants of M. tuberculosis and undertaken their genotypic characterization. We report here the characterization of a subset of these strains carrying mutations in the monooxygenase gene ethA . Through complementation studies, we demonstrate for the first time that the EthA-mediated oxidation of ISO is absolutely required for this prodrug to inhibit its lethal enzymatic target(s) in M. tuberculosis . An analysis of the metabolites resulting from the in vitro transformation of ISO by purified EthA revealed the occurrence of a formimidamide allowing the formulation of an activation pathway in which the oxidation of ISO catalyzed by EthA is followed by chemical transformations involving extrusion or elimination and, finally, hydrolysis.