Generation of free radicals from neocarzinostatin mediated by NADPH/cytochrome P-450 reductase via activation of enediyne chromophore.
Neocarzinostatin (NCS) is one of the most potent antitumor agents. It contains a chromophore of a unique enediyne structure as its prosthetic group. Here, we report the generation of free radicals from NCS by the NADPH/cytochrome (cyt) P-450 reductase system. Free radical species, which were generated in the reaction mixture of NCS/NADPH/cyt P-450 reductase, were identified by using electron spin resonance spin trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The spin adducts of superoxide and hydroxyl radical (DMPO-OOH and DMPO-OH, respectively) were generated in the reaction of NCS with the NADPH/cyt P-450 reductase system. From kinetic analyses of DMPO-OOH generation as a function of the concentration of NCS, the Vmax/Km value of the reaction was 0.4 x 10(6) M-1min-1. In addition, we identified thiyl radical generation in this system in the presence of glutathione. These results indicate that NCS is a potent generator of free radicals in cells where cyt P-450 reductase is available. Moreover, it seems that free radicals, generated by enzymatic activation of NCS, are involved in cytotoxicity of NCS as well as in DNA damage.
Sato
K
K
Department of Microbiology, Kumamoto University School of Medicine, Japan.
Akaike
T
T
Suga
M
M
Ando
M
M
Maeda
H
H
D000818:Animals; D016923:Cell Death / Q000187:drug effects; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D066298:In Vitro Techniques; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D013113:Spin Labels; D009353:Zinostatin / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology
D003497:Cyclic N-Oxides; D005609:Free Radicals; D017382:Reactive Oxygen Species; D013113:Spin Labels; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D009353:Zinostatin; D009251:NADPH-Ferrihemoprotein Reductase