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Architectural and functional abnormalities of blood vessels are a common feature in tumors. A consequence of increased vascular permeability and concomitant aberrant blood flow is poor delivery of oxygen and drugs, which is associated with treatment resistance. In the present study, we describe a strategy to simultaneously visualize tissue oxygen concentration and microvascular permeability by using a hyperpolarized [sup.1]H-MRI, known as Overhauser enhanced MRI (OMRI), and an oxygen-sensitive contrast agent OX63. Substantial MRI signal enhancement was induced by dynamic nuclear polarization (DNP). The DNP achieved up to a 7,000% increase in MRI signal at an OX63 concentration of 1.5 mM compared with that under thermal equilibrium state. The extent of hyperpolarization is influenced mainly by the local concentration of OX63 and inversely by the tissue oxygen level. By collecting dynamic OMRI images at different hyperpolarization levels, local oxygen concentration and microvascular permeability of OX63 can be simultaneously determined. Application of this modality to murine tumors revealed that tumor regions with high vascular permeability were spatio-temporally coincident with hypoxia. Quantitative analysis of image data from individual animals showed an inverse correlation between tumor vascular leakage and median oxygen concentration. Immunohistochemical analyses of tumor tissues obtained from the same animals after OMRI experiments demonstrated that lack of integrity in tumor blood vessels was associated with increased tumor microvascular permeability. This dual imaging technique may be useful for the longitudinal assessment of changes in tumor vascular function and oxygenation in response to chemotherapy, radiotherapy, or antiangiogenic treatment. angiogenesis | dynamic nuclear polarization | hyperpolarized MRI | tumor hypoxia | DCE-MRI doi/ 10.1073/pnas.0908447106

In mammals, two homologous cytosolic regulatory proteins, iron regulatory protein 1 (also known as IRP1 and Aco1) and iron regulatory protein 2 (also known as IRP2 and Ireb2), sense cytosolic iron levels and posttranscriptionally regulate iron metabolism genes, including transferrin receptor 1 (TfR1) and ferritin H and L subunits, by binding to iron-responsive elements (IREs) within target transcripts. Mice that lack IRP2 develop microcytic anemia and neurodegeneration associated with functional cellular iron depletion caused by low TfR1 and high ferritin expression. IRP1 knockout ([IRP1.sup.-/-]) animals do not significantly misregulate iron metabolism, partly because IRP1 is an iron-sulfur protein that functions mainly as a cytosolic aconitase in mammalian tissues and IRP2 activity increases to compensate for loss of the IRE binding form of IRP1. The neurodegenerative disease of [IRP2.sup.-/-] animals progresses slowly as the animals age. In this study, we fed [IRP2.sup.-/-] mice a diet supplemented with a stable nitroxide, Tempol, and showed that the progression of neuromuscular impairment was markedly attenuated. In cell lines derived from [IRP2.sup.-/-] animals, and in the cerebellum, brainstem, and forebrain of animals maintained on the Tempol diet, IRP1 was converted from a cytosolic aconitase to an IRE binding protein that stabilized the TfR1 transcript and repressed ferritin synthesis. We suggest that Tempol protected [IRP2.sup.-/-] mice by disassembling the cytosolic iron-sulfur cluster of IRP1 and activating IRE binding activity, which stabilized the TfR1 transcript, repressed ferritin synthesis, and partially restored normal cellular iron homeostasis in the brain. anemia | axonopathy | ferritin | iron-sulfur cluster | transferrin receptor

Ascorbic acid is an essential nutrient commonly regarded as an antioxidant. In this study, we showed that ascorbate at pharmacologic concentrations was a prooxidant, generating hydrogenperoxide-dependent cytotoxicity toward a variety of cancer cells in vitro without adversely affecting normal cells. To test this action in vivo, normal oral tight control was bypassed by parenteral ascorbate administration. Real-time microdialysis sampling in mice bearing glioblastoma xenografts showed that a single pharmacologic dose of ascorbate produced sustained ascorbate radical and hydrogen peroxide formation selectively within interstitial fluids of tumors but not in blood. Moreover, a regimen of daily pharmacologic ascorbate treatment significantly decreased growth rates of ovarian (P < 0.005), pancreatic (P < 0.05), and glioblastoma (P < 0.001) tumors established in mice. Similar pharmacologic concentrations were readily achieved in humans given ascorbate intravenously. These data suggest that ascorbate as a prodrug may have benefits in cancers with poor prognosis and limited therapeutic options. cancer | hydrogen peroxide | oxidation | free radical | vitamin C

Ascorbate (ascorbic acid, vitamin C), in pharmacologic concentrations easily achieved in humans by i.v. administration, selectively kills some cancer cells but not normal cells. We proposed that pharmacologic ascorbate is a prodrug for preferential steady-state formation of ascorbate radical ([Asc*.sup.-]) and [H.sub.2][O.sub.2] in the extracellular space compared with blood. Here we test this hypothesis in vivo. Rats were administered parenteral (i.v. or i.p.) or oral ascorbate in typical human pharmacologic doses ([approximately equal to] 0.25-0.5 mg per gram of body weight). After i.v. injection, ascorbate baseline concentrations of 50-100 [micro]M in blood and extracellular fluid increased to peaks of >8 mM. After i.p. injection, peaks approached 3 mM in both fluids. By gavage, the same doses produced ascorbate concentrations of 8 mM. After parenteral dosing, [Asc*.sup.-] concentrations in extracellular fluid were 4-to 12-fold higher than those in blood, were as high as 250 nM, and were a function of ascorbate concentrations. By using the synthesized probe peroxyxanthone, [H.sub.2][O.sub.2] in extracellular fluid was detected only after parenteral administration of ascorbate and when [Asc*.sup.-] concentrations in extracellular fluid exceeded 100 nM. The data show that pharmacologic ascorbate is a prodrug for preferential steady-state formation of [Asc*.sup.-] and [H.sub.2][O.sub.2] in the extracellular space but not blood. These data provide a foundation for pursuing pharmacologic ascorbate as a prooxidant therapeutic agent in cancer and infections. ascorbic acid | cancer | vitamin C | pharmacokinetics

Human pharmacokinetics data indicate that i.v. ascorbic acid (ascorbate) in pharmacologic concentrations could have an unanticipated role in cancer treatment. Our goals here were to test whether ascorbate killed cancer cells selectively, and if so, to determine mechanisms, using clinically relevant conditions. Cell death in 10 cancer and 4 normal cell types was measured by using 1-h exposures. Normal cells were unaffected by 20 mM ascorbate, whereas 5 cancer lines had E[C.sub.50] values of cell death | ascorbate radical

Modulation of the cytotoxicity and mutagenicity of 4-hydroxyestradiol (4-OH[E.sub.2]), an oxidative metabolite of estrogen, by antioxidants was assessed in human MCF7 cells and TK-6 lymphoblast cells. The cytotoxicity of the catecholic estrogens was potentiated by depletion of intracellular glutathione and was independent of oxygen concentration. Agents such as the nitroxide Tempol can facilitate the oxidation of the semiquinone to the Q and enhanced 4-OH[E.sub.2] cytotoxicity. Conversely, reducing agents such as ascorbate, cysteine, and 1,4-dihydroxytetramethylpiperidine (THP) protected against cytotoxicity and decreased mutation induction, presumably by reducing the semiquinone to the hydroquinone. Our results support the proposition that oxidation of the semiquinone to the corresponding Q is crucial in eliciting the deleterious effects of catecholic estrogens. Furthermore, because the deleterious effects of 4-OH[E.sub.2] were abrogated by dietary and synthetic antioxidants, our results would support the chemopreventive use of diets rich in reducing substances (vitamins and added synthetic antioxidants) as a means of decreasing the risks associated with estrogen exposure and developing of breast cancer.

An efficient noninvasive method for in vivo imaging of tumor oxygenation by using a low-field magnetic resonance scanner and a paramagnetic contrast agent is described. The methodology is based on Overhauser enhanced magnetic resonance imaging (OMRI), a functional imaging technique. OMRI experiments were performed on tumor-bearing mice (squamous cell carcinoma) by i.v. administration of the contrast agent Oxo63 (a highly derivatized triarylmethyl radical) at nontoxic doses in the range of 2-7 mmol/kg either as a bolus or as a continuous infusion. Spatially resolved p[O.sub.2] (oxygen concentration) images from OMRI experiments of tumor-bearing mice exhibited heterogeneous oxygenation profiles and revealed regions of hypoxia in tumors (

Hydrogen peroxide and xanthine hypoxanthine oxidase were employed to analyze the synergy in mammalian cell cytotoxicity between active oxygen species and nitric oxide. Chinese hamster lung fibroblasts demonstrated poor survival tendencies when exposed to doses of xanthine/hypoxanthine oxidase. There was a degradation in dopamine absorption and its discharge when rat mesencephalic dopaminergic cells were doped in xanthine/hypoxanthine oxidase or hydrogen peroxide.

The dismutation of superoxides involves the mediation of five- or six-membered nitroxide compounds. An investigation was conducted to elucidate the mechanism by which these compounds catalyze dismutation. The results showed that nitroxide compounds mediate superoxide dismutation through the formation of an oxoammonium cation intermediate. Based on the results a pathway for superoxide dismutation is presented.

Ascorbic acid is an essential nutrient commonly regarded as an antioxidant. In this study, we showed that ascorbate at pharmacologic concentrations was a prooxidant, generating hydrogen-peroxide-dependent cytotoxicity toward a variety of cancer cells in vitro without adversely affecting normal cells. To test this action in vivo, normal oral tight control was bypassed by parenteral ascorbate administration. Real-time microdialysis sampling in mice bearing glioblastoma xenografts showed that a single pharmacologic dose of ascorbate produced sustained ascorbate radical and hydrogen peroxide formation selectively within interstitial fluids of tumors but not in blood. Moreover, a regimen of daily pharmacologic ascorbate treatment significantly decreased growth rates of ovarian (P < 0.005), pancreatic (P < 0.05), and glioblastoma (P < 0.001) tumors established in mice. Similar pharmacologic concentrations were readily achieved in humans given ascorbate intravenously. These data suggest that ascorbate as a prodrug may have benefits in cancers with poor prognosis and limited therapeutic options. [ABSTRACT FROM AUTHOR]

Ascorbate (ascorbic acid, vitamin C), in pharmacologic concentrations easily achieved in humans by i.v. administration, selectively kills some cancer cells but not normal cells. We proposed that pharmacologic ascorbate is a prodrug for preferential steady-state formation of ascorbate radical (Asc*-) and H2O2 in the extracellular space compared with blood. Here we test this hypothesis in vivo. Rats were administered parenteral (i.v. or i.p.) or oral ascorbate in typical human pharmacologic doses (≈0.25-0.5 mg per gram of body weight). After i.v. injection, ascorbate baseline concentrations of 50-100 μM in blood and extracellular fluid increased to peaks of >8 mM. After i.p. injection, peaks approached 3 mM in both fluids. By gavage, the same doses produced ascorbate concentrations of <150 μM in both fluids. In blood, Asc*- concentrations measured by EPR were undetectable with oral administration and always <50 nM with parenteral administration, even when corresponding ascorbate concentrations were >8 mM. After parenteral dosing, Asc*- concentrations in extracellular fluid were 4- to 12-fold higher than those in blood, were as high as 250 nM, and were a function of ascorbate concentrations. By using the synthesized probe peroxyxanthone, H2O2 in extracellular fluid was detected only after parenteral administration of ascorbate and when Asc*- concentrations in extracellular fluid exceeded 100 nM. The data show that pharmacologic ascorbate is a prodrug for preferential steady-state formation of Asc*- and H2O2 in the extracellular space but not blood. These data provide a foundation for pursuing pharmacologic ascorbate as a prooxidant therapeutic agent in cancer and infections. [ABSTRACT FROM AUTHOR]

Human pharmacokinetics data indicate that i.v. ascorbic acid (ascorbate) in pharmacologic concentrations could have an unanticipated role in cancer treatment. Our goals here were to test whether ascorbate killed cancer cells selectively, and if so, to determine mechanisms, using clinically relevant conditions. Cell death in 10 cancer and 4 normal cell types was measured by using 1-h exposures. Normal cells were unaffected by 20 mM ascorbate, whereas 5 cancer lines had EC50 values of <4 mM, a concentration easily achievable iv. Human lymphoma cells were studied in detail because of their sensitivity to ascorbate (EC50 of 0.5 mM) and suitability for addressing mechanisms. Extracellular but not intra- cellular ascorbate mediated cell death, which occurred by apoptosis and pyknosis/necrosis. Cell death was independent of metal chelators and absolutely dependent on H2O2 formation. Cell death from H2O2 added to cells was identical to that found when H2O2 was generated by ascorbate treatment. H2O2 generation was dependent on ascorbate concentration, incubation time, and the presence of 0.5-10% serum, and displayed a linear relationship with ascorbate radical formation. Although ascorbate addition to medium generated H2O2, ascorbate addition to blood generated no detectable H2O2 and only trace detectable ascorbate radical. Taken together, these data indicate that ascorbate at concentrations achieved only by i.v. administration may be a prodrug for formation of H2O2, and that blood can be a delivery system of the pro-drug to tissues. These findings give plausibility to i.v. ascorbic acid in cancer treatment, and have unexpected implications for treatment of infections where H2O2 may be beneficial. [ABSTRACT FROM AUTHOR]