Inhibition of DNA cross-linking by mitomycin C by peroxidase-mediated oxidation of mitomycin C hydroquinone.
Mitomycin C requires reductive activation to cross-link DNA and express anticancer activity. Reduction of mitomycin C (40 microm) by sodium borohydride (200 microm) in 20 mm Tris-HCl, 1 mm EDTA at 37 degrees C, pH 7.4, gives a 50-60% yield of the reactive intermediate mitomycin C hydroquinone. The hydroquinone decays with first order kinetics or pseudo first order kinetics with a t(12) of approximately 15 s under these conditions. The cross-linking of T7 DNA in this system followed matching kinetics, with the conversion of mitomycin C hydroquinone to leuco-aziridinomitosene appearing to be the rate-determining step. Several peroxidases were found to oxidize mitomycin C hydroquinone to mitomycin C and to block DNA cross-linking to various degrees. Concentrations of the various peroxidases that largely blocked DNA cross-linking, regenerated 10-70% mitomycin C from the reduced material. Thus, significant quantities of products other than mitomycin C were produced by the peroxidase-mediated oxidation of mitomycin C hydroquinone or products derived therefrom. Variations in the sensitivity of cells to mitomycin C have been attributed to differing levels of activating enzymes, export pumps, and DNA repair. Mitomycin C hydroquinone-oxidizing enzymes give rise to a new mechanism by which oxic/hypoxic toxicity differentials and resistance can occur.
Penketh
P G
PG
Department of Pharmacology and Developmental Therapeutics Program, Cancer Center, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Hodnick
W F
WF
Belcourt
M F
MF
Shyam
K
K
Sherman
D H
DH
Sartorelli
A C
AC
D001894:Borohydrides / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000378:metabolism*; D006873:Hydroquinones / Q000378:metabolism*; D016685:Mitomycin / Q000378:metabolism*; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000502:physiology*
D001894:Borohydrides; D006873:Hydroquinones; D016685:Mitomycin; C025364:sodium borohydride; D004247:DNA; D010544:Peroxidases; C031927:hydroquinone