Nitroreductase-mediated metabolic activation of 2-amino-4-(5-nitro-2-furyl)thiazole and binding to nucleic acids and proteins.

The reductive metabolism of 2-amino-4-(5-nitro-2-furyl)thiazole (ANFT), a rat urinary bladder and forestomach carcin ogen, was examined in vitro using rat liver tissues. ANFT was reduced by rat liver microsomes or cytosol on anaerobic incu bation with reduced nicotinamide adenine dinucleotide phos phate. The intermediate(s) produced during the microsomal reduction bound to microsomes and to exogenously added proteins or yeast transfer RNA (tRNA). The binding to tRNA was a function of the concentration of tRNA, microsomes, reduced nicotinamide adenine dinucleotide phosphate, and ANFT. At optimal conditions, up to 10 nmol [2-14C]ANFT metabolite(s) were bound per mg tRNA. Polyacrylamide gel electrophoresis, chromatography, and sensitivity to RNase treat ment of the adduci revealed covalent binding between [214C]ANFT metabolite(s) and tRNA. Similar covalent binding was observed with proteins. On microsomal reduction of [2-14C]ANFT, about 7% of the reduced metabolite was bound to a trichloroacetic acid-insoluble fraction, most of which was as sociated with proteins. Addition of mercaptoethanol, dithiothreitol, reduced glutathione, iodoacetamide, A/-ethylmaleimide, or p-chloromercuribenzoate to the incubation mixture significantly reduced the amount of protein binding, suggesting an involve ment of sulfhydryl groups in binding. These data demonstrate that reactive intermediate(s) are generated by anaerobic incu bation of ANFT with rat liver microsomes. It is suggested that the binding might involve interaction between the nitroso or Nhydroxylamino intermediate(s) and susceptible target sites in yeast tRNA or proteins.