Activation of benznidazole by trypanosomal type I nitroreductases results in glyoxal formation.
Benznidazole, a 2-nitroimidazole, is the front-line treatment used against American trypanosomiasis, a parasitic infection caused by Trypanosoma cruzi. Despite nearly 40 years of use, the trypanocidal activity of this prodrug is not fully understood. It has been proposed that benznidazole activation leads to the formation of reductive metabolites that can cause a series of deleterious effects, including DNA damage and thiol depletion. Here, we show that the key step in benznidazole activation involves an NADH-dependent trypanosomal type I nitroreductase. This catalyzes an oxygen-insensitive reaction with the interaction of enzyme, reductant, and prodrug occurring through a ping-pong mechanism. Liquid chromatography/mass spectrometry (LC/MS) analysis of the resultant metabolites identified 4,5-dihydro-4,5-dihydroxyimidazole as the major product of a reductive pathway proceeding through hydroxylamine and hydroxy intermediates. The breakdown of this product released the reactive dialdehyde glyoxal, which, in the presence of guanosine, generated guanosine-glyoxal adducts. These experiments indicate that the reduction of benznidazole by type I nitroreductase activity leads to the formation of highly reactive metabolites and that the expression of this enzyme is key to the trypanocidal properties displayed by the prodrug.
Queen Mary Pre-Clinical Drug Discovery Group, School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
Belinda S
BS
Hall
Shane R
SR
Wilkinson
D001711:Biotransformation; D014355:Chagas Disease / Q000188:drug therapy* / Q000469:parasitology; D002853:Chromatography, Liquid; D004249:DNA Damage / Q000187:drug effects; D006037:Glyoxal / Q000378:metabolism; D006151:Guanosine / Q000378:metabolism; D006801:Humans; D019811:Hydroxylamine / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism; D007700:Kinetics; D013058:Mass Spectrometry; D009243:NAD / Q000378:metabolism; D009593:Nitroimidazoles / Q000378:metabolism* / Q000494:pharmacology; D009601:Nitroreductases / Q000378:metabolism*; D011355:Prodrugs / Q000378:metabolism* / Q000494:pharmacology; D015800:Protozoan Proteins / Q000378:metabolism; D013053:Spectrophotometry; D014344:Trypanocidal Agents / Q000378:metabolism* / Q000494:pharmacology; D014346:Trypanosoma brucei brucei / Q000187:drug effects* / Q000201:enzymology; D014349:Trypanosoma cruzi / Q000187:drug effects* / Q000201:enzymology; D014353:Trypanosomiasis, African / Q000188:drug therapy / Q000469:parasitology
D007093:Imidazoles; D009593:Nitroimidazoles; D011355:Prodrugs; D015800:Protozoan Proteins; D014344:Trypanocidal Agents; D009243:NAD; D006151:Guanosine; D019811:Hydroxylamine; D006037:Glyoxal; C029492:aromatic NADH-dependent nitroreductase; D009601:Nitroreductases; C009999:benzonidazole