Diaziquone-glutathione conjugates: characterization and mechanisms of formation.
The antitumor agent diaziquone (AZQ) reacts with reduced glutathione (GSH) in aqueous solutions and under aerobic conditions to give rise to the glutathionyl and hydroxyl free radicals, as well as the AZQ semiquinone. Under anaerobic conditions, the only radical observed was the glutathionyl radical. These radicals are quickly abrogated when superoxide dismutase and catalase are coincubated. Separately, superoxide dismutase favors the formation of thiyl radicals while catalase favors the formation of hydroxyl radicals and AZQ semiquinone. The metal chelator diethylenetriaminepentaacetic acid favors the production of hydroxyl radicals and AZQ semiquinone. The reaction of AZQ with GSH at pH 7.2 and 5.5 results in a variety of conjugates. These conjugates include addition of glutathione to both aziridines, displacement of the aziridines by GSH, and a combination of both. The majority of the conjugates are formed by nucleophilic attack of GSH to the AZQ aziridines or by 1,4-Michael addition to the AZQ quinone or a combination of both. There may be a small free radical component in conjugate formation, but the majority of the free radicals observed are from redox reactions that involve the oxidation of glutathione and the reduction and autoxidation of AZQ to produce oxygen radicals and hydrogen peroxide, a process that is enhanced by trace metal ions.
Gutierrez
P L
PL
University of Maryland Cancer Center, Baltimore 21201, USA.
Siva
S
S
D000970:Antineoplastic Agents / Q000737:chemistry*; D000975:Antioxidants / Q000494:pharmacology; D001388:Aziridines / Q000737:chemistry*; D016227:Benzoquinones / Q000737:chemistry*; D002374:Catalase / Q000494:pharmacology; D004347:Drug Interactions; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D005978:Glutathione / Q000737:chemistry*; D010101:Oxygen Consumption; D013482:Superoxide Dismutase / Q000494:pharmacology
D000970:Antineoplastic Agents; D000975:Antioxidants; D001388:Aziridines; D016227:Benzoquinones; D005609:Free Radicals; D002374:Catalase; D013482:Superoxide Dismutase; C029108:diaziquone; D005978:Glutathione