title: Nitroxide-mediated protection against X-ray- and neocarzinostatin-induced DNA damage.
abstract: The stable free radical Tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy) has been shown to protect against X-ray-induced cytotoxicity and hydrogen peroxide- or xanthine oxidase-induced cytotoxicity and mutagenicity. The ability of Tempol to protect against X-ray- or neocarzinostatin (NCS)-induced mutagenicity or DNA double-strand breaks (dsb) was studied in Chinese hamster cells. Tempol (50 mM) provided a protection factor of 2.7 against X-ray-induced mutagenicity in Chinese hamster ovary (CHO) AS52 cells, with a protection factor against cytotoxicity of 3.5. Using the field inversion gel electrophoresis technique of measuring DNA dsb, 50 mM Tempol provides a threefold reduction in DNA damage at an X-ray dose of 40 Gy. For NCS-induced damage, Tempol increased survival from 9% to 80% at 60 ng/mL NCS and reduced mutation induction by a factor of approximately 3. DNA dsb were reduced by a factor of approximately 7 at 500 ng/mL NCS. Tempol is representative of a class of stable nitroxide free radical compounds that have superoxide dismutase-mimetic activity, can oxidize metal ions such as ferrous iron that are complexed to DNA, and may also detoxify radiation-induced organoperoxide radicals by competitive scvenging. The NCS chromophore is reduced by sulfhydryls to an active form. Electron spin resonance (ESR) spectroscopy shows that 2-mercaptoethanol-activated NCS reacts with Tempol 3.5 times faster than does unactivated NCS. Thus, Tempol appears to inactivate the NCS chromophore before a substantial amount of DNA damage occurs.
authors.affiliation: Radiobiology Section, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: W G
authors.initials: WG
authors.lastname: DeGraff
authors.forename: M C
authors.initials: MC
authors.lastname: Krishna
authors.forename: D
authors.initials: D
authors.lastname: Kaufman
authors.forename: J B
authors.initials: JB
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects*; D006224:Cricetinae; D003497:Cyclic N-Oxides / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects* / Q000528:radiation effects*; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D007700:Kinetics; D016296:Mutagenesis; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D013113:Spin Labels; D014965:X-Rays; D009353:Zinostatin / Q000494:pharmacology*
chemical_list: D003497:Cyclic N-Oxides; D011837:Radiation-Protective Agents; D013113:Spin Labels; D004247:DNA; D009353:Zinostatin; C001803:tempol