RESUMO
Thioamide drugs, ethionamide (ETH) and prothionamide (PTH), are clinically effective in the treatment of Mycobacterium tuberculosis, M. leprae, and M. avium complex infections. Although generally considered second-line drugs for tuberculosis, their use has increased considerably as the number of multidrug resistant and extensively drug resistant tuberculosis cases continues to rise. Despite the widespread use of thioamide drugs to treat tuberculosis and leprosy, their precise mechanisms of action remain unknown. Using a cell-based activation method, we now have definitive evidence that both thioamides form covalent adducts with nicotinamide adenine dinucleotide (NAD) and that these adducts are tight-binding inhibitors of M. tuberculosis and M. leprae InhA. The crystal structures of the inhibited M. leprae and M. tuberculosis InhA complexes provide the molecular details of target-drug interactions. The purified ETH-NAD and PTH-NAD adducts both showed nanomolar Kis against M. tuberculosis and M. leprae InhA. Knowledge of the precise structures and mechanisms of action of these drugs provides insights into designing new drugs that can overcome drug resistance.
Assuntos
Etionamida/farmacologia , Hanseníase/tratamento farmacológico , Protionamida/farmacologia , Tuberculose/tratamento farmacológico , Antituberculosos/química , Antituberculosos/metabolismo , Antituberculosos/farmacologia , Proteínas de Bactérias/antagonistas & inibidores , Cristalografia por Raios X , Desenho de Fármacos , Farmacorresistência Bacteriana Múltipla , Etionamida/química , Etionamida/metabolismo , Humanos , Técnicas In Vitro , Hansenostáticos/química , Hansenostáticos/metabolismo , Hansenostáticos/farmacologia , Modelos Moleculares , Complexo Mycobacterium avium/efeitos dos fármacos , Complexo Mycobacterium avium/enzimologia , Infecção por Mycobacterium avium-intracellulare/tratamento farmacológico , Mycobacterium leprae/efeitos dos fármacos , Mycobacterium leprae/enzimologia , Mycobacterium tuberculosis/efeitos dos fármacos , Mycobacterium tuberculosis/enzimologia , NAD/química , NAD/metabolismo , Oxirredutases/antagonistas & inibidores , Protionamida/química , Protionamida/metabolismo , Tuberculose Resistente a Múltiplos Medicamentos/tratamento farmacológicoRESUMO
The tuberculostatic drug rifampicin has been described as a scavenger of reactive species. Additionally, the recent demonstration that oral therapy with a complex of rifampicin and horseradish peroxidase (HRP) was more effective than rifampicin alone, in an animal model of experimental leprosy, suggested the importance of redox reactions involving rifampicin and their relevance to the mechanism of action. Hence, we studied the oxidation of rifampicin catalyzed by HRP, since this enzyme may represent the prototype of peroxidation-mediated reactions. We found that the antibiotic is efficiently oxidized and that rifampicin-quinone is the product, in a reaction dependent on both HRP and hydrogen peroxide. The steady-state kinetic constants Km(app) (101+/-23 micromol/l), Vmax(app) (0.78+/-0.09 micromol/l.s(-1)) and kcat (5.1+/-0.6 s(-1)) were measured (n=4). The reaction rate was increased by the addition of co-substrates such as tetramethylbenzidine, salicylic acid, 5-aminosalicylic acid and paracetamol. This effect was explained by invoking an electron-transfer mechanism by which these drugs acted as mediators of rifampicin oxidation. We suggested that this drug interaction might be important at the inflammatory site.