The role of specific reductases in the intracellular activation and binding of 2-nitroimidazoles.
OBJECTIVE
To determine the relative effectiveness of specific cellular reductases for the activation and binding of 2-nitroimidazoles in vivo.


METHODS
Monkey kidney cells were transfected with recombinant plasmids to effect intracellular overexpression of P450 reductase and DT-diaphorase. The covalent binding of 2-nitroimidazoles to cellular macromolecules was measured as a function of time of cell incubation at various oxygen concentrations. The effect of allopurinol on cellular binding of radiolabeled 2-nitroimidazoles was also measured.


RESULTS
A 1,000-fold overexpression of DT-diaphorase resulted in a small but significant increase in 2-nitroimidazole binding rate. An 80-fold overexpression of cytochrome P450 reductase resulted in a 5-7-fold increase in the binding rate of 2-nitroimidazole. The inhibition of xanthine oxidase by allopurinol had no effect on 2-nitroimidazole binding rates. The amplification of P450 reductase activity within cells was always much larger than the resultant increase in 2-nitroimidazole binding rate, suggesting an enzyme kinetic process less than first order and possibly of 1/2-order.


CONCLUSIONS
These data suggest that cytochrome P450 reductase is the most important enzyme in these cells for reducing 2-nitroimidazoles to intermediates which can covalently bind to cellular macromolecules. Furthermore, since this cellular process demonstrates approximately 1/2-order kinetics, a tissue's capacity for binding 2-nitroimidazole drug in hypoxia should be proportional to the square root of its intracellular P450 reductase level.
Joseph
P
P
Department of Pharmacology, Fox Chase Cancer Center, Philadelphia, PA 19111.
Jaiswal
A K
AK
Stobbe
C C
CC
Chapman
J D
JD
D000818:Animals; D001711:Biotransformation; D002478:Cells, Cultured; D000882:Haplorhini; D007668:Kidney / Q000378:metabolism*; D008920:Misonidazole / Q000031:analogs & derivatives / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000502:physiology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000502:physiology*; D009593:Nitroimidazoles / Q000378:metabolism*
D009593:Nitroimidazoles; D008920:Misonidazole; D009251:NADPH-Ferrihemoprotein Reductase; D016660:NAD(P)H Dehydrogenase (Quinone); C009997:desmethylmisonidazole