Dwight Kaufman

Inhibition of oxygen-dependent radiation-induced damage by the nitroxide superoxide dismutase mimic, Tempol

Stable nitroxide radicals have been previously shown to function as superoxide dismutase (SOD)2 mimics and to protect mammalian cells against superoxide and hydrogen peroxide-mediated oxidative stress. These unique characteristics suggested that nitroxides, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), might protect mammalian cells against ionizing radiation. Treating Chinese hamster cells under aerobic conditions with 5, 10, 50, and 100 mM Tempol 10 min prior to X-rays resulted in radiation protection factors of 1.25, 1.30, 2.1, and 2.5, respectively. However, the reduced form of Tempol afforded no protection. Tempol treatment under hypoxic conditions did not provide radioprotection. Aerobic X-ray protection by Tempol could not be attributed to the induction of intracellular hypoxia, increase in intracellular glutathione, or induction of intracellular SOD mRNA. Tempol thus represents a new class of non-thiol-containing radiation protectors, which may be useful in elucidating the mechanism(s) of radiation-induced cellular damage and may have broad applications in protecting against oxidative stress.

The catecholic metal sequestering agent 1,2-dihydroxybenzene-3,5-disulfonate confers protection against oxidative cell damage

Tiron (1,2-dihydroxybenzene-3,5-disulfonate), a nontoxic chelator of a variety of metals, is used to alleviate acute metal overload in animals. It is also oxidized to the EPR-detectable semiquinone radical by various biologically relevant oxidants, such as .OH, O2-., alkyl, and alkoxyl radicals. Since Tiron reacts with potentially toxic intracellular species and is also a metal chelator, we evaluated its protective effects in V79 cells subjected to various types of oxidative damage and attempted to distinguish the protection due to direct detoxification of intracellular radicals from that resulting from chelation of redox-active transition metals. We found that Tiron protects Chinese hamster V79 cells against both O2.(-)-induced (and H2O2 via dismutation of O2.-) and H2O2-induced cytotoxicity as measured by clonogenic assays. In experiments where Tiron was incubated with V79 cells and rinsed prior to exposure to HX/XO or H2O2, cytoprotection was observed, indicating that it protects against intracellular oxidative damage. On the other hand, Tiron did not protect V79 cells against the damage caused by ionizing radiation under aerobic conditions, which is predominantly mediated by H., .OH, and hydrated electrons in a metal-independent fashion. We demonstrate also that in in vitro studies, Tiron protects supercoiled DNA from metal-mediated superoxide-dependent strand breaks. We conclude that Tiron is a potentially useful protecting agent against the lethal effects of oxidative stress and suggest that it offers protection by chelating redox-active transition metal ions, in contrast to earlier reports where the protection by this compound in cellular systems subjected to oxidative damage has been interpreted as due to radical scavenging alone.

Taxol in combination with doxorubicin or etoposide : possible antagonism in vitro

Background. Taxol is a novel chemotherapeutic agent that promotes microtubule assembly and stabilizes tubulin polymer formation. Clinical evaluation of its antineoplastic activity as a single agent and in combination with other chemotherapeutic drugs is in progress.

Nitroxide-mediated protection against X-ray- and neocarzinostatin-induced DNA damage

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.

Glutathione, a Determinant of Response to Cancer Treatment

The ability to cure a limited number of cancer types with drugs has existed for only the past 25 years. Although success has been limited primarily to lymphomas and leukemias and more recently, testicular cancer, analyses of common factors in successful treatment and of the reasons for failure in both the responsive tumor types and the much broader spectrum of malignancies in which chemotherapy usually plays at best a palliative role have allowed the establishment of a number of principles that may allow the rational design of curative treatment for most cancer.