The Multifaceted Roles of NRF2 in Cancer: Friend or Foe?

Physiological concentrations of reactive oxygen species (ROS) play vital roles in various normal cellular processes, whereas excessive ROS generation is central to disease pathogenesis. The nuclear factor erythroid 2-related factor 2 (NRF2) is a critical transcription factor that regulates the cellular antioxidant systems in response to oxidative stress by governing the expression of genes encoding antioxidant enzymes that shield cells from diverse oxidative alterations. NRF2 and its negative regulator Kelch-like ECH-associated protein 1 (KEAP1) have been the focus of numerous investigations in elucidating whether NRF2 suppresses tumor promotion or conversely exerts pro-oncogenic effects. NRF2 has been found to participate in various pathological processes, including dysregulated cell proliferation, metabolic remodeling, and resistance to apoptosis. Herein, this review article will examine the intriguing role of phase separation in activating the NRF2 transcriptional activity and explore the NRF2 dual impacts on tumor immunology, cancer stem cells, metastasis, and long non-coding RNAs (LncRNAs). Taken together, this review aims to discuss the NRF2 multifaceted roles in both cancer prevention and promotion while also addressing the advantages, disadvantages, and limitations associated with modulating NRF2 therapeutically in cancer treatment.

Discovery of New 2-Phenylamino-3-acyl-1,4-naphthoquinones as Inhibitors of Cancer Cells Proliferation: Searching for Intra-Cellular Targets Playing a Role in Cancer Cells Survival

A series of 2-phenylamino-3-acyl-1,4-naphtoquinones were evaluated regarding their in vitro antiproliferative activities using DU-145, MCF-7 and T24 cancer cells. Such activities were discussed in terms of molecular descriptors such as half-wave potentials, hydrophobicity and molar refractivity. Compounds 4 and 11 displayed the highest antiproliferative activity against the three cancer cells and were therefore further investigated. The in silico prediction of drug likeness, using pkCSM and SwissADME explorer online, shows that compound 11 is a suitable lead molecule to be developed. Moreover, the expressions of key genes were studied in DU-145 cancer cells. They include genes involved in apoptosis (Bcl-2), tumor metabolism regulation (mTOR), redox homeostasis (GSR), cell cycle regulation (CDC25A), cell cycle progression (TP53), epigenetic (HDAC4), cell-cell communication (CCN2) and inflammatory pathways (TNF). Compound 11 displays an interesting profile because among these genes, mTOR was significantly less expressed as compared to control conditions. Molecular docking shows that compound 11 has good affinity with mTOR, unraveling a potential inhibitory effect on this protein. Due to the key role of mTOR on tumor metabolism, we suggest that impaired DU-145 cells proliferation by compound 11 is caused by a reduced mTOR expression (less mTOR protein) and inhibitory activity on mTOR protein.

Valeriana pilosa Roots Essential Oil: Chemical Composition, Antioxidant Activities, and Molecular Docking Studies on Enzymes Involved in Redox Biological Processes

Valeriana pilosa is usually employed in Peruvian folk medicine in the form of infusion to treat stomach pain, and has antispasmodic, relaxing, sleep-promoting, and sedative properties, as well as is an anti-inflammatory. In this study, Valeriana pilosa essential oil (VPEO) was obtained by hydrodistillation, analyzed by GC and GC/MS, and 47 compounds were identified. Major oil components were α-patchoulene (5.8%), α-humulene (6.1%), seychellene (7.6%), and patchoulol (20.8%). Furthermore, we assessed the in vitro antioxidant activities, molecular docking, and Ligand Efficiency studies on enzymes involved in cellular redox pathways such as CYP2C9, catalase, superoxide dismutase, and xanthine oxidase. Essential oil antioxidant activities were assessed by FRAP, ABTS•+, and DPPH• radical scavenging activity. VPEO displays high antioxidant activity as compared to essential oils of Valeriana jatamansi and Valeriana officinalis oil roots. In addition, molecular docking and ADMET prediction was employed to compare the absorption, metabolism, and toxicity properties of Valeriana pilosa compounds. In the molecular docking studies, limonene, p-cimene, carvone, α-cubebene, cyclosativene, α-guaiene, allo-aromadendrene, valencene, and eremophyllene were the compounds with the best docking score on CYP2C9 and xanthine oxidase. Thus, volatile components of Valeriana pilosa could be associated with the detected antioxidant activity, acting as putative inhibitors of CYP2C9 and xanthine oxidase.

Antifungal Activity and In Silico Studies on 2-Acylated Benzo- and Naphthohydroquinones

The high rates of morbidity and mortality due to fungal infections are associated with a limited antifungal arsenal and the high toxicity of drugs. Therefore, the identification of novel drug targets is challenging due to the several resemblances between fungal and human cells. Here, we report the in vitro antifungal evaluation of two acylphenols series, namely 2-acyl-1,4-benzo- and 2-acyl-1,4-naphthohydroquinones. The antifungal properties were assessed on diverse Candida and filamentous fungi strains through the halo of inhibition (HOI) and minimal inhibitory concentration (MIC). The antifungal activities of 2-acyl-1,4-benzohydroquinone derivatives were higher than those of the 2-acyl-1,4-naphthohydroquinone analogues. The evaluation indicates that 2-octanoylbenzohydroquinone 4 is the most active member of the 2-acylbenzohydroquinone series, with MIC values ranging from 2 to 16 μg/mL. In some fungal strains (i.e., Candida krusei and Rhizopus oryzae), such MIC values of compound 4 (2 and 4 μg/mL) were comparable to that obtained by amphotericin B (1 μg/mL). The compound 4 was evaluated for its antioxidant activity by means of FRAP, ABTS and DPPH assays, showing moderate activity as compared to standard antioxidants. Molecular docking studies of compound 4 and ADMET predictions make this compound a potential candidate for topical pharmacological use. The results obtained using the most active acylbenzohydroquinones are promising because some evaluated Candida strains are known to have decreased sensitivity to standard antifungal treatments.

Vitamin C (Ascorbate) and Redox Topics in Cancer

Significance: Vitamin C (ascorbate), in regard to its effectiveness against malignancies, has had a controversial history in cancer treatment. It has been shown that in vitro and in vivo anticancer efficacy of ascorbate relies on its pro-oxidant effect mainly from an increased generation of reactive oxygen species (ROS). A growing understanding of its anticancer activities and pharmacokinetic properties has prompted scientists to re-evaluate the significance of ascorbate in cancer treatment. Recent Advances: A recent resurge in ascorbate research emerged after discovering that, at high doses, ascorbate preferentially kills Kirsten-Ras (K-ras)- and B-raf oncogene (BRAF)-mutant cancer cells. In addition, some of the main hallmarks of cancer cells, such as redox homeostasis and oxygen-sensing regulation (through inhibition of hypoxia-inducible factor-1 alpha [HIF-1α] activity), are affected by vitamin C. Critical Issues: Currently, there is no clear consensus from the literature in regard to the beneficial effects of antioxidants. Results from both human and animal studies provide no clear evidence about the benefit of antioxidant treatment in preventing or suppressing cancer development. Since pro-oxidants may affect both normal and tumor cells, the extremely low toxicity of ascorbate represents a main advantage. This guarantees the safe inclusion of ascorbate in clinical protocols to treat cancer patients. Future Directions: Current research could focus on elucidating the wide array of reactions between ascorbate and reactive species, namely ROS, reactive nitrogen species as well as reactive sulfide species, and their intracellular molecular targets. Unraveling these mechanisms could allow researchers to assess what could be the optimal combination of ascorbate with standard treatments.

In Vitro Inhibition of Hsp90 Protein by Benzothiazoloquinazolinequinones Is Enhanced in The Presence of Ascorbate. A Preliminary In Vivo Antiproliferative Study

A series of benzo[g]benzothiazolo[2,3-b]quinazoline-7,12-quinones were prepared from 2-acylnaphthohydroquinones and 2-aminobenzothiazoles and were evaluated for their in vitro antiproliferative activity. After screening using the MTT reduction assay, their IC50 values were calculated on a panel of cancer cells (T24, DU-145, MCF-7). Current standard anticancer drugs were included as control, and their calculated IC50 values were 7.8 and 23.5 µM for 5-fluorouracil and tamoxifen, respectively. Non-cancer cells (AG1523) were included to assess cancer cell sensitivity and drug selectivity. Four members of the series, with IC50 values from 0.11 to 2.98 µM, were chosen for further assays. The selected quinones were evaluated regarding their effects on cancer cell proliferation (clonogenic assay) and on Hsp90 and poly(ADPribose)polymerase (PARP) protein integrity. The most active compound (i.e., 15) substantially inhibited colony forming unit (CFU) formation at 0.25 µM. In the presence of ascorbate, it induced an oxidative cleavage of Hsp90 but had no effect on PARP protein integrity. In an in vivo animal model, it discreetly increased the mean survival time (m.s.t.) of tumor-bearing mice. In light of these results, compound 15 represents a potential lead-molecule to be further developed.

Cancer Cell Sensitivity to Redox-Cycling Quinones is Influenced by NAD(P)H: Quinone Oxidoreductase 1 Polymorphism

BACKGROUND

Cancer cell sensitivity to drugs may be associated with disturbed antioxidant enzymes expression. We investigated mechanisms of resistance by using oxidative stress-resistant MCF-7 breast cancer cells (Resox cells). Since nicotinamide adenine dinucleotide phosphate (NAD(P)H): quinone oxidoreductase-1 (NQO1) is modified in tumors and oxidative stress-resistant cells, we studied its role in cells exposed to β-lapachone, menadione, and doxorubicin.

METHODS

Normal mammary epithelial 250MK, MCF-7, and Resox cells were employed. NQO1 expression and enzyme activity were determined by quantitative polymerase chain reaction (RT-PCR), immunoblotting, and biochemical assays. Dicoumarol and gene silencing (siRNA) were used to modulate NQO1 expression and to assess its potential drug-detoxifying role. MTT (3-(4,5-dimethylthia-zolyl-2)-2,5-diphenyltetrazolium bromide) or clonogenic assays were used to investigate cytotoxicity. NQO1 variants, NQO1*1 (wt), and NQO1*2 (C609T), were obtained by transfecting NQO1-null MDA-MB-231 cell line.

RESULTS

Resox cells have higher NQO1 expression than MCF-7 cells. In 250MK cells its expression was low but enzyme activity was higher suggesting a variant NQO1 form in MCF-7 cells. MCF-7 and Resox cells are heterozygous NQO1*1 (wt)/ NQO1*2 (C609T). Both NQO1 polymorphism and NQO1 overexpression are main determinants for cell resistance during oxidative stress. NQO1 overexpression increases cell sensitivity to β-lapachone whereas NQO1*2 polymorphism triggers quinone-based chemotherapies-sensitivity.

CONCLUSIONS

NQO1 influences cancer cells redox metabolism and their sensitivity to drugs. We suggest that determining NQO1 polymorphism may be important when considering the use of quinone-based chemotherapeutic drugs.

Half-Wave Potentials and In Vitro Cytotoxic Evaluation of 3-Acylated 2,5-Bis(phenylamino)-1,4-benzoquinones on Cancer Cells

A broad range of 3-acyl-2,5-bis(phenylamino)-1,4-benzoquinones were synthesized and their voltammetric values, as well as in vitro cancer cell cytotoxicities, were assessed. The members of this series were prepared from acylbenzoquinones and phenylamines, in moderate to good yields (47–74%), through a procedure involving a sequence of two in situ regioselective oxidative amination reactions. The cyclic voltammograms of the aminoquinones exhibit two one-electron reduction waves to the corresponding radical-anion and dianion, and two quasi-reversible oxidation peaks. The first and second half-wave potential values (E_1/2) of the members of the series were sensitive to the push-pull electronic effects of the substituents around the benzoquinone nucleus. The in vitro cytotoxic activities of the 3-acyl-2,5-bis(phenylamino)-1,4-benzoquinones against human cancer cells (bladder and prostate) and non-tumor human embryonic kidney cells were measured using the MTT colorimetric method. The substitution of both aniline groups, by either methoxy (electron donating effect) or fluorine (electron withdrawal effect), decreased the cytotoxicity in the aminoquinones. Among the members of the unsubstituted phenylamino series, two of the 18 compounds showed interesting anti-cancer activities. A preliminary assay, looking for changes in the expression of selected genes, was performed. In this context, the two compounds increased TNF gene expression, suggesting an association with an inflammatory-like response.

In Vitro Inhibition of Helicobacter pylori Growth by Redox Cycling Phenylaminojuglones

Infection by Helicobacter pylori increases 10 times the risk of developing gastric cancer. Juglone, a natural occurring 1,4-naphthoquinone, prevents H. pylori growth by interfering with some of its critical metabolic pathways. Here, we report the design, synthesis, and in vitro evaluation of a series of juglone derivatives, namely, 2/3-phenylaminojuglones, as potential H. pylori growth inhibitors. Results show that 5 out of 12 phenylaminojuglones (at 1.5 μg/mL) were 1.5-2.2-fold more active than juglone. Interestingly, most of the phenylaminojuglones (10 out of 12) were 1.1-2.8 fold more active than metronidazole, a known H. pylori growth inhibitor. The most active compound, namely, 2-((3,4,5-trimethoxyphenyl)amino)-5-hydroxynaphthalene-1,4-dione 7, showed significant higher halo of growth inhibitions (HGI = 32.25 mm) to that of juglone and metronidazole (HGI = 14.50 and 11.67 mm). Structural activity relationships of the series suggest that the nature and location of the nitrogen substituents in the juglone scaffold, likely due in part to their redox potential, may influence the antibacterial activity of the series.

Catalase down-regulation in cancer cells exposed to arsenic trioxide is involved in their increased sensitivity to a pro-oxidant treatment

Background

Pro-oxidant drugs have been proposed for treating certain cancers but the resistance developed by cancer cells to oxidative stress limits its potential use in clinics. To understand the mechanisms underlying resistance to oxidative stress, we found that the chronic exposure to an H₂O₂-generating system (ascorbate/menadione, Asc/Men) or catalase overexpression (CAT3 cells) increased the resistance of cancer cells to oxidative stress, likely by increasing the antioxidant status of cancer cells.

Methods

Modulation of catalase expression was performed by either protein overexpression or protein down-regulation using siRNA against catalase and aminotriazole as pharmacological inhibitor. The former approach was done by transfecting cells with a plasmid construct containing human catalase cDNA (CAT3 cells, derived from MCF-7 breast cancer cell line) or by generating resistant cells through chronic exposure to an oxidant injury (Resox cells). Cell survival was monitored by using the MTT reduction assay and further calculation of IC₅₀ values. Protein expression was done by Western blots procedures. The formation of reactive oxygen species was performed by flow cytometry. The transcriptional activity of human catalase promoter was assessed by using transfected cells with a plasmid containing the − 1518/+ 16 promoter domain.

Results

Using Resox and CAT3 cells (derived from MCF-7 breast cancer cell line) as models for cancer resistance to pro-oxidative treatment, we found that arsenic trioxide (ATO) remarkably sensitized Resox and CAT3 cells to Asc/Men treatment. Since catalase is a key antioxidant enzyme involved in detoxifying Asc/Men (as shown by siRNA-mediated catalase knockdown) that is overexpressed in resistant cells, we hypothesized that ATO might regulate the expression levels of catalase. Consistently, catalase protein level is decreased in Resox cells when incubated with ATO likely by a decreased transcriptional activity of the catalase promoter.

Conclusions

Our findings support the proposal that ATO should be administered in combination with pro-oxidant drugs to enhance cancer cell death in solid tumors.

Targeting Akt as strategy to kill cancer cells using 3-substituted 5-anilinobenzo[c]isoxazolequinones: A preliminary study

Several new 3-substituted 5-anilinobenzo[c]isoxazolequinones were synthesized from 1,4-benzoquinone and alkyl- or arylcarbaldehydes by a three-step synthetic sequence. The new compounds (3a-h) were tested in vitro in normal human fibroblasts and two cancer cell lines for their cytotoxic activity. The range of IC₅₀ values obtained for the compounds was from 3.4 to 74.2μM. Five members of the series (3b, 3d, 3e, 3f, 3g) were further selected and evaluated as inhibitors of the Hsp90 chaperoning function taking Akt as example of Hsp90 client proteins. We also evaluated the changes of intracellular levels of GSH and ATP as markers of cellular metabolic status in response to these compounds in T24 cells. One of such isoxazolquinones (3b) decreased the expression of Akt, PARP and Hsp90. Compounds 3b and 3d decreased the amount of ATP but caused no effect on GSH levels. These compounds also activated caspase-3 but an apoptosis-like type of cell death was unlike since PARP protein was not cleaved and caspase activation was substantially lower than its activation induced by staurosporine, a known caspase-3 activator in T24 cells. Taken together, preliminary results led to the discovery of an original lead compound (3b) which can be used as model to obtain new Akt inhibitors.

Catalase, a remarkable enzyme: targeting the oldest antioxidant enzyme to find a new cancer treatment approach

This review is centered on the antioxidant enzyme catalase and will present different aspects of this particular protein. Among them: historical discovery, biological functions, types of catalases and recent data with regard to molecular mechanisms regulating its expression. The main goal is to understand the biological consequences of chronic exposure of cells to hydrogen peroxide leading to cellular adaptation. Such issues are of the utmost importance with potential therapeutic extrapolation for various pathologies. Catalase is a key enzyme in the metabolism of H2O2 and reactive nitrogen species, and its expression and localization is markedly altered in tumors. The molecular mechanisms regulating the expression of catalase, the oldest known and first discovered antioxidant enzyme, are not completely elucidated. As cancer cells are characterized by an increased production of reactive oxygen species (ROS) and a rather altered expression of antioxidant enzymes, these characteristics represent an advantage in terms of cell proliferation. Meanwhile, they render cancer cells particularly sensitive to an oxidant insult. In this context, targeting the redox status of cancer cells by modulating catalase expression is emerging as a novel approach to potentiate chemotherapy.

Silibinin induces hepatic stellate cell cycle arrest via enhancing p53/p27 and inhibiting Akt downstream signaling protein expression

BACKGROUND

Proliferation of hepatic stellate cells (HSCs) plays a pivotal role in the progression of liver fibrosis consequent to chronic liver injury. Silibinin, a flavonoid compound, has been shown to possess anti-fibrogenic effects in animal models of liver fibrosis. This was attributed to an inhibition of cell proliferation of activated HSCs. The present study was to gain insight into the molecular pathways involved in silibinin anti-fibrogenic effect.

METHODS

The study was conducted on LX-2 human stellate cells treated with three concentrations of silibinin (10, 50 and 100 μmol/L) for 24 and 96 hours. At the end of the treatment cell viability and proliferation were evaluated. Protein expression of p27, p21, p53, Akt and phosphorylated-Akt was evaluated by Western blotting analysis and Ki-67 protein expression was by immunocytochemistry. Sirtuin activity was evaluated by chemiluminescence based assay.

RESULTS

Silibinin inhibits LX-2 cell proliferation in dose- and time-dependent manner; we showed that silibinin upregulated the protein expressions of p27 and p53. Such regulation was correlated to an inhibition of both downstream Akt and phosphorylated-Akt protein signaling and Ki-67 protein expression. Sirtuin activity also was correlated to silibinin-inhibited proliferation of LX-2 cells.

CONCLUSION

The anti-proliferative effect of silibinin on LX-2 human stellate cells is via the inhibition of the expressions of various cell cycle targets including p27, Akt and sirtuin signaling.

Synthetic approaches and in vitro cytotoxic evaluation of 2-acyl-3-(3,4,5-trimethoxyanilino)-1,4-naphthoquinones

2-Acyl-1,4-naphthoquinones react with 3,4,5-trimethoxyaniline, under aerobic conditions, to give benzophenanthridinequinone, benzocarbazole and 2-acyl-3-(3,4,5-trimethoxyanilino)-1,4-naphthoquinone derivatives.

Chromatin remodeling regulates catalase expression during cancer cells adaptation to chronic oxidative stress

Regulation of ROS metabolism plays a major role in cellular adaptation to oxidative stress in cancer cells, but the molecular mechanism that regulates catalase, a key antioxidant enzyme responsible for conversion of hydrogen peroxide to water and oxygen, remains to be elucidated. Therefore, we investigated the transcriptional regulatory mechanism controlling catalase expression in three human mammary cell lines: the normal mammary epithelial 250MK primary cells, the breast adenocarcinoma MCF-7 cells and an experimental model of MCF-7 cells resistant against oxidative stress resulting from chronic exposure to H₂O₂ (Resox), in which catalase was overexpressed. Here we identify a novel promoter region responsible for the regulation of catalase expression at -1518/-1226 locus and the key molecules that interact with this promoter and affect catalase transcription. We show that the AP-1 family member JunB and retinoic acid receptor alpha (RARα) mediate catalase transcriptional activation and repression, respectively, by controlling chromatin remodeling through a histone deacetylases-dependent mechanism. This regulatory mechanism plays an important role in redox adaptation to chronic exposure to H₂O₂ in breast cancer cells. Our study suggests that cancer adaptation to oxidative stress may be regulated by transcriptional factors through chromatin remodeling, and reveals a potential new mechanism to target cancer cells.

High hydrostatic pressure influences the in vitro response to xenobiotics in Dicentrarchus labrax liver

Hydrostatic pressure (HP) increases by about 1 atmosphere (0.1MPa) for each ten-meter depth increase in the water column. This thermodynamical parameter could well influence the response to and effects of xenobiotics in the deep-sea biota, but this possibility remains largely overlooked. To grasp the extent of HP adaptation in deep-sea fish, comparative studies with living cells of surface species exposed to chemicals at high HP are required. We initially conducted experiments with precision-cut liver slices of a deep-sea fish (Coryphaenoides rupestris), co-exposed for 15h to the aryl hydrocarbon receptor (AhR) agonist 3-methylcholanthrene at HP levels representative of the surface (0.1MPa) and deep-sea (5-15MPa; i.e., 500-1500m depth) environments. The transcript levels of a suite of stress-responsive genes, such as the AhR battery CYP1A, were subsequently measured (Lemaire et al., 2012; Environ. Sci. Technol. 46, 10310-10316). Strikingly, the AhR agonist-mediated increase of CYP1A mRNA content was pressure-dependently reduced in C. rupestris. Here, the same co-exposure scenario was applied for 6 or 15h to liver slices of a surface fish, Dicentrarchus labrax, a coastal species presumably not adapted to high HP. Precision-cut liver slices of D. labrax were also used in 1h co-exposure studies with the pro-oxidant tert-butylhydroperoxide (tBHP) as to investigate the pressure-dependence of the oxidative stress response (i.e., reactive oxygen production, glutathione and lipid peroxidation status). Liver cells remained viable in all experiments (adenosine triphosphate content). High HP precluded the AhR agonist-mediated increase of CYP1A mRNA expression in D. labrax, as well as that of glutathione peroxidase, and significantly reduced that of heat shock protein 70. High HP (1h) also tended per se to increase the level of oxidative stress in liver cells of the surface fish. Trends to an increased resistance to tBHP were also noted. Whether the latter observation truly reflects a protective response to oxidative stress will be addressed in future co-exposure studies with both surface and deep-sea fish liver cells, using additional pro-oxidant chemicals. Altogether, data on CYP1A inducibility with D. labrax and C. rupestris support the view that high HP represses AhR signaling in marine fishes, and that only species adapted to thrive in the deep-sea have evolved the molecular adaptations necessary to counteract to some extent this inhibition.

Regulation of catalase expression in healthy and cancerous cells

Catalase is an important antioxidant enzyme that dismutates hydrogen peroxide into water and molecular oxygen. The catalase gene has all the characteristics of a housekeeping gene (no TATA box, no initiator element sequence, high GC content in promoter) and a core promoter that is highly conserved among species. We demonstrate in this review that within this core promoter, the presence of DNA binding sites for transcription factors, such as NF-Y and Sp1, plays an essential role in the positive regulation of catalase expression. Additional transcription factors, such as FoxO3a, are also involved in this regulatory process. There is strong evidence that the protein Akt/PKB in the PI3K signaling pathway plays a major role in the expression of catalase by modulating the activity of FoxO3a. Over the past decade, other transcription factors (PPARγ, Oct-1, etc.), as well as genetic, epigenetic, and posttranscriptional processes, have emerged as crucial contributors to the regulation of catalase expression. Altered expression levels of catalase have been reported in cancer tissues compared to their normal counterparts. Deciphering the molecular mechanisms that regulate catalase expression could, therefore, be of crucial importance for the future development of pro-oxidant cancer chemotherapy.

AICAR induces Nrf2 activation by an AMPK-independent mechanism in hepatocarcinoma cells

Hepatocellular carcinoma is one of the most frequent tumor types worldwide and oxidative stress represents a major risk factor in pathogenesis of liver diseases leading to HCC. Nuclear factor erythroid 2-related factor (Nrf2) is a transcription factor activated by oxidative stress that governs the expression of many genes which constitute the antioxidant defenses of the cell. In addition, oxidative stress activates AMP-activated protein kinase (AMPK), which has emerged in recent years as a kinase that controls the redox-state of the cell. Since both AMPK and Nrf2 are involved in redox homeostasis, we investigated whether there was a crosstalk between the both signaling systems in hepatocarcinoma cells. Here, we demonstrated that AMPK activator AICAR, in contrary to the A769662 allosteric activator, induces Nrf2 activation and concomitantly modulates the basal redox state of the hepatocarcinoma cells. When the expression of Nrf2 is knocked down, AICAR failed to induce its effect on redox state. These data highlight a major role of Nrf2 signaling pathway in mediating the AICAR effect on basal oxidative state. Furthermore, we demonstrated that AICAR metabolization by the cell is required to induce Nrf2 activation while, the silencing of AMPK does not have any effect on Nrf2 activation. This suggests that AICAR-induced Nrf2 activation is independent of AMPK activity. In conclusion, we identified AICAR as a potent modulator of the redox state of human hepatocarcinoma cells, via the Nrf2 signaling pathway and in an AMPK-independent mechanism.

Substituted 3‑acyl‑2‑phenylamino‑1,4‑naphthoquinones intercalate into DNA and cause genotoxicity through the increased generation of reactive oxygen species culminating in cell death

Naphthoquinones interact with biological systems by generating reactive oxygen species (ROS) that can damage cancer cells. The cytotoxicity and the antitumor activity of 3‑acyl‑2‑phenylamino‑1,4‑naphthoquinones (DPB1‑DPB9) were evaluated in the MCF7 human breast cancer cell line and in male Ehrlich tumor‑bearing Balb/c mice. DPB4 was the most cytotoxic derivative against MCF7 cells (EC50 15 µM) and DPB6 was the least cytotoxic one (EC50 56 µM). The 1,4‑naphthoquinone derivatives were able to cause DNA damage and promote DNA fragmentation as shown by the plasmid DNA cleavage assay (FII form). In addition, 1,4‑naphthoquinone derivatives possibly interacted with DNA as intercalating agents, which was demonstrated by the changes caused in the fluorescence of the DNA‑ethidium bromide complexes. Cell death of MCF7 cells induced by 3‑acyl‑2‑phenylamino‑1,4‑naphthoquinones was mostly due to apoptosis. The DNA fragmentation and subsequent apoptosis may be correlated to the redox potential of the 1,4‑naphthoquinone derivatives that, once present in the cell nucleus, led to the increased generation of ROS. Finally, certain 1,4‑naphthoquinone derivatives and particularly DPB4 significantly inhibited the growth of Ehrlich ascites tumors in mice (73%).

Catalase expression in MCF-7 breast cancer cells is mainly controlled by PI3K/Akt/mTor signaling pathway

Catalase is an antioxidant enzyme that catalyzes mainly the transformation of hydrogen peroxide into water and oxygen. Although catalase is frequently down-regulated in tumors the underlying mechanism remains unclear. Few transcription factors have been reported to directly bind the human catalase promoter. Among them FoxO3a has been proposed as a positive regulator of catalase expression. Therefore, we decided to study the role of the transcription factor FoxO3a and the phosphatidylinositol-3 kinase (PI3K) signaling pathway, which regulates FoxO3a, in the expression of catalase. To this end, we developed an experimental model of mammary breast MCF-7 cancer cells that acquire resistance to oxidative stress, the so-called Resox cells, in which catalase is overexpressed as compared with MCF-7 parental cell line. In Resox cells, Akt expression is decreased but its phosphorylation is enhanced when compared with MCF-7 cells. A similar profile is observed for FoxO3a, with less total protein but more phosphorylated FoxO3a in Resox cells, correlating with its higher Akt activity. The modulation of FoxO3a expression by knockdown and overexpression strategies did not affect catalase expression, neither in MCF-7 nor in Resox cells. Inhibition of PI3K and mTOR by LY295002 and rapamycin, respectively, decreases the phosphorylation of downstream targets (i.e. GSK3β and p70S6K) and leads to an increase of catalase expression only in MCF-7 but not in Resox cells. In conclusion, FoxO3a does not appear to play a critical role in the regulation of catalase expression in both cancer cells. Only MCF-7 cells are sensitive and dependent on PI3K/Akt/mTOR signaling.

Role of oxidative stress in the pathogenesis of alcohol-induced liver disease

Chronic alcohol consumption is a well-known risk factor for liver disease, which represents a major cause of morbidity and mortality worldwide. The pathological process of alcohol-induced liver disease is characterized by a broad spectrum of morphological changes ranging from steatosis with minimal injury to more advanced liver damage, including steato-hepatitis and fibrosis/cirrhosis. Experimental and clinical studies increasingly show that the oxidative damage induced by ethanol contribute in many ways to the pathogenesis of alcohol hepatotoxicity. This article describes the contribution of oxidative mechanisms to liver damage by alcohol.

Eco-friendly synthesis and antiproliferative evaluation of some oxygen substituted diaryl ketones

A broad variety of oxygen-substituted diaryl ketones has been synthesized by solar energy-induced Friedel Crafts acylations of 1,4-benzo- and 1,4-naphthoquinones with benzaldehydes. The in vitro antiproliferative properties of the photoproducts were assessed on prostate (DU-145), bladder (T24) and breast (MCF7) human-derived tumor cell lines and compared to non-tumor mouse fibroblasts (Balb/3T3). Among the tested compounds, it was found that those containing a 3,4,5-trimethoxyphenyl A-ring, such as 12 and 22 are more active on DU-145, with EC₅₀ values of 1.2 and 5.9 μM, respectively. By comparing their effects on the three cancer cell lines, the analogue 22 has the best mean selective index (2.4).

Biological evaluation of 3-acyl-2-arylamino-1,4-naphthoquinones as inhibitors of Hsp90 chaperoning function

Hsp90 is a chaperone that plays a key function in cancer cells by stabilizing proteins responsible of cell growth and survival. Disruption of the Hsp90 chaperone machinery leads to the proteasomal degradation of its client proteins. Hsp90 appears then as an attractive target for the development of new anticancer molecules. We have shown that ascorbate- driven menadione-redox cycling inhibits Hsp90 activity by provoking an N-terminal cleavage of the protein, inducing the degradation of several of its client proteins. Since the mechanism involves an oxidative stress, we explored the effect of a series of diverse donor-acceptor 3-acyl-2-phenylamino 1,4-naphthoquinones on Hsp90 integrity, in the presence of ascorbate. Results show that quinone-derivatives that bear two electroactive groups (namely quinone and nitro) exhibit the highest inhibitory activity (Hsp90 cleavage and cell death). The biological activity of the series mainly relies on their redox capacity and their lipophilicity, which both modulate the ability of these compounds to induce a cytotoxic effect in K562 cells. As observed with other redox cycling quinones, the protein cleavage is blocked in the presence of N-terminal Hsp90 inhibitors suggesting that the availability or occupancy of nucleotide binding site in the N-terminal pocket of Hsp90 plays a critical role. In addition the survival of cancer cells and their metabolic and redox homeostasis were strongly impaired by the presence of ascorbate. Since these effects were similar to that obtained by ascorbate/menadione and they were blocked by the antioxidant N-acetylcyteine (NAC), it appears that oxidative stress is a major component of this cytotoxicity.

Role of AMPK activation in oxidative cell damage: Implications for alcohol-induced liver disease

Chronic alcohol consumption is a well-known risk factor for liver disease. Progression of alcohol-induced liver disease (ALD) is a multifactorial process that involves a number of genetic, nutritional and environmental factors. Experimental and clinical studies increasingly show that oxidative damage induced by ethanol contributes in many ways to the pathogenesis of alcohol hepatoxicity. Oxidative stress appears to activate AMP-activated protein kinase (AMPK) signaling system, which has emerged in recent years as a kinase that controls the redox-state and mitochondrial function. This review focuses on the most recent insights concerning the activation of AMPK by reactive oxygen species (ROS), and describes recent evidences supporting the hypothesis that AMPK signaling pathways play an important role in promoting cell viability under conditions of oxidative stress, such as during alcohol exposure. We suggest that AMPK activation by ROS can promote cell survival by inducing autophagy, mitochondrial biogenesis and expression of genes involved in antioxidant defense. Hence, increased intracellular concentrations of ROS may represent a general mechanism for enhancement of AMPK-mediated cellular adaptation, including maintenance of redox homeostasis. On the other hand, AMPK inhibition in the liver by ethanol appears to play a key role in the development of steatosis induced by chronic alcohol consumption. Although more studies are needed to assess the functions of AMPK during oxidative stress, AMPK may be a possible therapeutic target in the particular case of alcohol-induced liver disease.

Precision-cut liver slices to investigate responsiveness of deep-sea fish to contaminants at high pressure

While deep-sea fish accumulate high levels of persistent organic pollutants (POPs), the toxicity associated with this contamination remains unknown. Indeed, the recurrent collection of moribund individuals precludes experimental studies to investigate POP effects in this fauna. We show that precision-cut liver slices (PCLS), an in vitro tool commonly used in human and rodent toxicology, can overcome such limitation. This technology was applied to individuals of the deep-sea grenadier Coryphaenoides rupestris directly upon retrieval from 530-m depth in Trondheimsfjord (Norway). PCLS remained viable and functional for 15 h when maintained in an appropriate culture media at 4 °C. This allowed experimental exposure of liver slices to the model POP 3-methylcholanthrene (3-MC; 25 μM) at levels of hydrostatic pressure mimicking shallow (0.1 megapascal or MPa) and deep-sea (5-15 MPa; representative of 500-1500 m depth) environments. As in shallow water fish, 3-MC induced the transcription of the detoxification enzyme cytochrome P4501A (CYP1A; a biomarker of exposure to POPs). This induction was diminished at elevated pressure, suggesting a limited responsiveness of C. rupestris toward POPs in its native environment. This very first in vitro toxicological investigation on a deep-sea fish opens the route for understanding pollutants effects in this highly exposed fauna.

Restoring specific lactobacilli levels decreases inflammation and muscle atrophy markers in an acute leukemia mouse model

The gut microbiota has recently been proposed as a novel component in the regulation of host homeostasis and immunity. We have assessed for the first time the role of the gut microbiota in a mouse model of leukemia (transplantation of BaF3 cells containing ectopic expression of Bcr-Abl), characterized at the final stage by a loss of fat mass, muscle atrophy, anorexia and inflammation. The gut microbial 16S rDNA analysis, using PCR-Denaturating Gradient Gel Electrophoresis and quantitative PCR, reveals a dysbiosis and a selective modulation of Lactobacillus spp. (decrease of L. reuteri and L. johnsonii/gasseri in favor of L. murinus/animalis) in the BaF3 mice compared to the controls. The restoration of Lactobacillus species by oral supplementation with L. reuteri 100-23 and L. gasseri 311476 reduced the expression of atrophy markers (Atrogin-1, MuRF1, LC3, Cathepsin L) in the gastrocnemius and in the tibialis, a phenomenon correlated with a decrease of inflammatory cytokines (interleukin-6, monocyte chemoattractant protein-1, interleukin-4, granulocyte colony-stimulating factor, quantified by multiplex immuno-assay). These positive effects are strain- and/or species-specific since L. acidophilus NCFM supplementation does not impact on muscle atrophy markers and systemic inflammation. Altogether, these results suggest that the gut microbiota could constitute a novel therapeutic target in the management of leukemia-associated inflammation and related disorders in the muscle.

Tumor reoxygenation following administration of Mitogen-Activated Protein Kinase inhibitors: a rationale for combination with radiation therapy

BACKGROUND AND PURPOSE

The relevance of Mitogen Activated Protein Kinase (MAPK) inhibitors as co-treatments for radiation therapy is investigated, with special focus on a potential link between the MAPK pathway and tumor hypoxia, which is a critical determinant for response to therapy.

MATERIALS AND METHODS

The effects of two MAPK inhibitors, Sorafenib and PD0325901, were monitored daily using in vivo EPR (Electron Paramagnetic Resonance) oximetry in FSaII and TLT tumor models in order to identify a window of reoxygenation, during which tumor blood flow, oxygen consumption and radiation sensitivity were assessed.

RESULTS

Reoxygenation was shown after two days of treatments with Sorafenib or PD0325901 in two tumor models, which was further successfully exploited with Sorafenib for improving the radiation response of FSaII tumors by a factor of 1.5. The increase in tumor oxygenation was shown to be the result of two major factors: (i) an increase in blood flow for Sorafenib, that might be linked to its anti-angiogenic effect (vascular normalization), and (ii) a decrease in oxygen consumption for Sorafenib and PD0325901, due to an alteration of the mitochondrial activity.

CONCLUSION

We evidenced tumor reoxygenation in vivo following MAPK inhibition and suggest a rationale for the combination of radiation therapy with Sorafenib.

Evaluation of analgesic activities of tremetone derivatives isolated from the Chilean altiplano medicine Parastrephia lepidophylla

Parastrephia lepidophylla, family Asteraceae, has ancient use in traditional medicine in the region of Tarapacá, Chile. Bioguided fractionation of extracts of this plant was undertaken in the search for compounds with analgesic and antioxidant activity. Two benzofuran derivatives were isolated as the major components of this plant, identified as tremetone 1 and methoxytremetone 6. Remarkably, neither of these showed antioxidant activity, but tremetone 1 exhibited a morphine-like analgesic property. Reduction of this analgesic effect by naloxone suggests a direct effect on opiate receptors as a possible signaling pathway. However, both the low diffusion across lipid membranes (PAMPA assay) and the lipophilicity (Log P) shown by tremetone 1 make elusive the mechanism explaining its induced analgesia.

Evaluation of Analgesic Activities of Tremetone Derivatives Isolated from the Chilean Altiplano Medicine Parastrephia lepidophylla

Parastrephia lepidophylla, family Asteraceae, has ancient use in traditional medicine in the region of Tarapacá, Chile. Bioguided fractionation of extracts of this plant was undertaken in the search for compounds with analgesic and antioxidant activity. Two benzofuran derivatives were isolated as the major components of this plant, identified as tremetone 1 and methoxytremetone 6. Remarkably, neither of these showed antioxidant activity, but tremetone 1 exhibited a morphine-like analgesic property. Reduction of this analgesic effect by naloxone suggests a direct effect on opiate receptors as a possible signaling pathway. However, both the low diffusion across lipid membranes (PAMPA assay) and the lipophilicity (Log P) shown by tremetone 1 make elusive the mechanism explaining its induced analgesia.

Overexpression of GRP94 in breast cancer cells resistant to oxidative stress promotes high levels of cancer cell proliferation and migration: implications for tumor recurrence

Targeting the altered redox status of cancer cells is emerging as an interesting approach to potentiate chemotherapy. However, to maximize the effectiveness of this strategy and define the correct chemotherapeutic associations, it is important to understand the biological consequences of chronically exposing cancer cells to reactive oxygen species (ROS). Using an H(2)O(2)-generating system, we selected a ROS-resistant MCF-7 breast cancer cell line, namely Resox cells. By exploring different survival pathways that are usually induced during oxidative stress, we identified a constitutive overexpression of the endoplasmic reticulum chaperone, GRP94, in these cells, whereas levels of its cytoplasmic homolog HSP90, or GRP78, were not modified. This overexpression was not mediated by constitutive unfolded protein response (UPR) activation. The increase in GRP94 is tightly linked to an increase in cell proliferation and migration capacities, as shown by GRP94-silencing experiments. Interestingly, we also observed that GRP94 silencing inhibits migration and proliferation of the highly aggressive MDA-MB-231 cells. By immunohistochemistry, we showed that GRP94 expression was higher in recurrent human breast cancers than in their paired primary neoplasias. Similar to the situation in the Resox cells, this increase was not associated with an increase in UPR activation in recurrent tumors. In conclusion, this study suggests that GRP94 overexpression may be a hallmark of aggressiveness and recurrence in breast cancers.

Arsenic trioxide treatment decreases the oxygen consumption rate of tumor cells and radiosensitizes solid tumors

Arsenic trioxide (As(2)O(3)) is an effective therapeutic against acute promyelocytic leukemia and certain solid tumors. Because As(2)O(3) inhibits mitochondrial respiration in leukemia cells, we hypothesized that As(2)O(3) might enhance the radiosensitivity of solid tumors by increasing tumor oxygenation [partial pressure of oxygen (pO(2))] via a decrease in oxygen consumption. Two murine models of radioresistant hypoxic cancer were used to study the effects of As(2)O(3). We measured pO(2) and the oxygen consumption rate in vivo by electron paramagnetic resonance oximetry and (19)fluorine-MRI relaxometry. Tumor perfusion was assessed by Patent blue staining. In both models, As(2)O(3) inhibited mitochondrial respiration, leading to a rapid increase in pO(2). The decrease in oxygen consumption could be explained by an observed decrease in glutathione in As(2)O(3)-treated cells, as this could increase intracellular reactive oxygen species that can disrupt mitochondrial membrane potential. When tumors were irradiated during periods of As(2)O(3)-induced augmented oxygenation, radiosensitivity increased by 2.2-fold compared with control mice. Notably, this effect was abolished when temporarily clamped tumors were irradiated. Together, our findings show that As(2)O(3) acutely increases oxygen consumption and radiosensitizes tumors, providing a new rationale for clinical investigations of As(2)O(3) in irradiation protocols to treat solid tumors.

Intracellular ATP levels determine cell death fate of cancer cells exposed to both standard and redox chemotherapeutic agents

Cancer cells generally exhibit high levels of reactive oxygen species (ROS) that stimulate cell proliferation and promote genetic instability. Since this biochemical difference between normal and cancer cells represents a specific vulnerability that can be selectively targeted for cancer therapy, various ROS-generating agents are currently in clinical trials, either as single agents or in combination with standard therapy. However, little is known about the potential consequences of an increased oxidative stress for the efficacy of standard chemotherapeutic agents. In this context, we have assessed the influence of an oxidative stress generated by the combination of ascorbate and the redox-active quinone menadione on the capacity of melphalan, a common alkylating agent, to induce apoptosis in a chronic myelogenous leukemia cell line. Our data show that oxidative stress did not inhibit but rather promoted cancer cell killing by melphalan. Interestingly, we observed that, in the presence of oxidative stress, the type of cell death shifted from a caspase-3 dependent apoptosis to necrosis because of an ATP depletion which prevented caspase activation. Taken together, these data suggest that ROS-generating agents could be useful in combination with standard chemotherapy, even if all the molecular consequences of such an addition remain to be determined.

Catalase overexpression in mammary cancer cells leads to a less aggressive phenotype and an altered response to chemotherapy

Because reactive oxygen species (ROS) are naturally produced as a consequence of aerobic metabolism, cells have developed a sophisticated set of antioxidant molecules to prevent the toxic accumulation of these species. However, compared with normal cells, malignant cells often exhibit increased levels of intracellular ROS and altered levels of antioxidant molecules. The resulting endogenous oxidative stress favors tumor growth by promoting genetic instability, cell proliferation and angiogenesis. In this context, we assessed the influence of catalase overexpression on the sensitivity of breast cancer cells towards various anticancer treatments. Our data show that catalase overexpression in MCF-7 cells leads to a 7-fold increase in catalase activity but provokes a 40% decrease in the expression of both glutathione peroxidase and peroxiredoxin II. Interestingly, proliferation and migration capacities of MCF-7 cells were impaired by the overexpression of catalase, as compared to parental cells. Regarding their sensitivity to anticancer treatments, we observed that cells overexpressing catalase were more sensitive to paclitaxel, etoposide and arsenic trioxide. However, no effect was observed on the cytotoxic response to ionizing radiations, 5-fluorouracil, cisplatin or doxorubicin. Finally, we observed that catalase overexpression protects cancer cells against the pro-oxidant combination of ascorbate and menadione, suggesting that changes in the expression of antioxidant enzymes could be a mechanism of resistance of cancer cells towards redox-based chemotherapeutic drugs.

Studies on quinones. Part 46. Synthesis and in vitro antitumor evaluation of aminopyrimidoisoquinolinequinones

In the search of structure-activity relationship studies and to explore the antitumor effect associated with the pyrimidoisoquinolinequinone scaffold, several diversily substituted 8-aminopyrimido[4,5-c]isoquinolinequinones were regioselectively synthesized. Variation in the structure of the nitrogen substituent bonded to the 8-position of the pyrimidoisoquinolinequinone system led to a set of alkylamino-, phenylamino- and alkyphenylamino derivatives. The cytotoxic activity of the aminoquinone derivatives was evaluated in vitro using the MTT colorimetric method against one normal cell line (MRC-5 lung fibroblasts) and four human cancer cell lines (AGS human gastric adenocarcinoma; SK-MES-1 human lung cancer cells, and J82 human bladder carcinoma; HL-60 human leukemia) in 72-h drug exposure assays. Among the series, five compounds exhibited interesting antitumor activity against AGS human gastric adenocarcinoma and human lung cancer cells. The SAR studies revealed that both the nature of the nitrogen substituent into the quinone ring and the methyl group at the 6-position play key roles in the antitumor activity.

Ascorbate/menadione-induced oxidative stress kills cancer cells that express normal or mutated forms of the oncogenic protein Bcr-Abl. An in vitro and in vivo mechanistic study

Numerous studies suggest that generation of oxidative stress could be useful in cancer treatment. In this study, we evaluated, in vitro and in vivo, the antitumor potential of oxidative stress induced by ascorbate/menadione (asc/men). This combination of a reducing agent (ascorbate) and a redox active quinone (menadione) generates redox cycling leading to formation of reactive oxygen species (ROS). Asc/men was tested in several cell types including K562 cells (a stable human-derived leukemia cell line), freshly isolated leukocytes from patients with chronic myeloid leukemia, BaF3 cells (a murine pro-B cell line) transfected with Bcr-Abl and peripheral blood leukocytes derived from healthy donors. Although these latter cells were resistant to asc/men, survival of all the other cell lines was markedly reduced, including the BaF3 cells expressing either wild-type or mutated Bcr-Abl. In a standard in vivo model of subcutaneous tumor transplantation, asc/men provoked a significant delay in the proliferation of K562 and BaF3 cells expressing the T315I mutated form of Bcr-Abl. No effect of asc/men was observed when these latter cells were injected into blood of mice most probably because of the high antioxidant potential of red blood cells, as shown by in vitro experiments. We postulate that cancer cells are more sensitive to asc/men than healthy cells because of their lack of antioxidant enzymes, mainly catalase. The mechanism underlying this cytotoxicity involves the oxidative cleavage of Hsp90 with a subsequent loss of its chaperone function thus leading to degradation of wild-type and mutated Bcr-Abl protein.

An in vitro comparative study with furyl-1,4-quinones endowed with anticancer activities

We describe the biological activity of some furylbenzo- and naphthoquinones (furylquinones) on hepatocarcinoma cells and healthy rat liver slices. The effects of furylquinones on cancer cells (Transplantable Liver Tumor, TLT) were assessed by measuring cell death (membrane cell lysis); intracellular contents of ATP and GSH and the activity of caspase-3 were used to determine the type of cell death. Most of the furylquinones tested (at a concentration of 25 μg/ml) induced caspase-independent cell death but compound 4 had no cytotoxic effects. The levels of both ATP and GSH were severely affected by quinones 1, 2 and 5, while no effect was observed with compound 4. These cytotoxic properties of quinones are associated with physico-chemical properties as shown by the LUMO energies and lipophilicity. Interestingly, no cytotoxic effects of furylquinones were detected when the in vitro model of precision-cut liver slices (PCLS) was used. Indeed, although CYP2E1 activity was slightly affected, ATP and GSH levels as well as protein synthesis were not modified by furylquinones. Paracetamol, a well-known hepatotoxicant, reduced these parameters by more than 80% compared to control conditions. Taking into account the considerable incidence of adverse-effects induced by most current anticancer drugs, the selective cytotoxicity shown by compounds 1, 2 and 5, in particular that of 1, represents a safety factor that encourages the further development of these quinones as new drugs in cancer therapy.

Endoplasmic reticulum calcium release potentiates the ER stress and cell death caused by an oxidative stress in MCF-7 cells

Increase in cytosolic calcium concentration ([Ca2+](c)), release of endoplasmic reticulum (ER) calcium ([Ca2+](er)) and ER stress have been proposed to be involved in oxidative toxicity. Nevertheless, their relative involvements in the processes leading to cell death are not well defined. In this study, we investigated whether oxidative stress generated during ascorbate-driven menadione redox cycling (Asc/Men) could trigger these three events, and, if so, whether they contributed to Asc/Men cytoxicity in MCF-7 cells. Using microspectrofluorimetry, we demonstrated that Asc/Men-generated oxidative stress was associated with a slow and moderate increase in [Ca2+](c), largely preceding permeation of propidium iodide, and thus cell death. Asc/Men treatment was shown to partially deplete ER calcium stores after 90 min (decrease by 45% compared to control). This event was associated with ER stress activation, as shown by analysis of eIF2 phosphorylation and expression of the molecular chaperone GRP94. Thapsigargin (TG) was then used to study the effect of complete [Ca2+](er) emptying during the oxidative stress generated by Asc/Men. Surprisingly, the combination of TG and Asc/Men increased ER stress to a level considerably higher than that observed for either treatment alone, suggesting that [Ca2+](er) release alone is not sufficient to explain ER stress activation during oxidative stress. Finally, TG-mediated [Ca2+](er) release largely potentiated ER stress, DNA fragmentation and cell death caused by Asc/Men, supporting a role of ER stress in the process of Asc/Men cytotoxicity. Taken together, our results highlight the involvement of ER stress and [Ca2+](er) decrease in the process of oxidative stress-induced cell death in MCF-7 cells.

Comparison of methods for measuring oxygen consumption in tumor cells in vitro

The oxygen consumption rate of tumor cells affects tumor oxygenation and response to therapies. Highly sensitive methods for determining cellular oxygen consumption are, therefore, needed to identify treatments that can modulate this parameter. We compared the performances of three different methods for measuring cellular oxygen consumption: electron paramagnetic resonance (EPR) oximetry, the Clark electrode, and the MitoXpress fluorescent assay. To compare the assays, we used K562 cells in the presence of rotenone and hydrocortisone, compounds that are known to inhibit the mitochondrial electron transport chain to different extents. The EPR method was the only one that could identify both rotenone and hydrocortisone as inhibitors of tumor cell oxygen consumption. The Clark electrode and the fluorescence assay demonstrated a significant decrease in cellular oxygen consumption after administration of the most potent inhibitor (rotenone) but failed to show any significant effect of hydrocortisone. EPR oximetry is, therefore, the most sensitive method for identifying inhibitors of oxygen consumption on cell assays, whereas the Clark electrode offers the unique opportunity to add external compounds during experiments and still shows great sensitivity in studying enzyme and chemical reactions that consume oxygen (non-cell assays). Finally, the MitoXpress fluorescent assay has the advantage of a high-sample throughput and low bulk requirements but at the cost of a lower sensitivity.

Menadione reduction by pharmacological doses of ascorbate induces an oxidative stress that kills breast cancer cells

Oxidative stress generated by ascorbate-driven menadione redox cycling kills MCF7 cells by a concerted mechanism including glycolysis inhibition, loss of calcium homeostasis, DNA damage and changes in mitogen activated protein kinases (MAPK) activities. Cell death is mediated by necrosis rather than apoptosis or macroautophagy. Neither 3-methyladenine nor Z-VAD affects cytotoxicity by ascorbate/menadione (Asc/Men). BAPTA-AM, by restoring cellular capacity to reduce MTT, underlines the role of calcium in the necrotic process. Oxidative stress-mediated cell death is shown by the opposite effects of N-acetylcysteine and 3-aminotriazole. Moreover, oxidative stress induces DNA damage (protein poly-ADP-ribosylation and gamma-H2AX phosphorylation) and inhibits glycolysis. Asc/Men deactivates extracellular signal-regulated kinase (ERK) while activating p38, suggesting an additional mechanism to kill MCF7 cells. Since ascorbate is taken up by cancer cells and, due to their antioxidant enzyme deficiency, oxidative stress should affect cancer cells to a greater extent than normal cells. This differential sensitivity may have clinical applications.

Synthesis and antitumor evaluation of 8-phenylaminopyrimido[4,5-c]isoquinolinequinones

A series of 8-phenylaminopyrimido[4,5-c]isoquinoline-7,10-quinone derivatives were prepared by regioselective amination reaction of pyrimido[4,5-c]isoquinoline-7,10-quinones with arylamines in the presence of a Lewis acid catalyst. Preliminary evaluation of the members of the series against cancer cell lines and assays of activation of their cytotoxic activity on K562 cells with ascorbic acid are reported.

Part 2: influence of 2-euryfuryl-1,4-naphthoquinone and its peri-hydroxy derivatives on both cell death and metabolism of TLT cells, a murine hepatoma cell line. modulation of cytotoxicity by vitamin C

2-Euryfuryl-1,4-naphthoquinone C(1) and its 5- and 5,8-hydroxy derivatives C(2) and C(3), were tested for their cytotoxicity towards transplantable liver tumor (TLT) cells (a murine hepatoma cell line) in the absence and in the presence of vitamin C. Cell death, caspase-3 activity and two metabolic end-points, namely the intracellular content of ATP and glutathione (GSH), were employed to evaluate their cytotoxicity. In a range of concentration from 0 to 10 microg/ml C(1) and C(3) were non toxic against TLT cells, while compound C(2) killed about 50% of cells by necrosis. Interestingly, the presence of vitamin C did not enhance the cytolysis of C(2), but its addition exacerbated the effects of the three compounds on both ATP and GSH contents, the two metabolic end points selected in our study. Our assumption is that the electron donor effect of the peri-hydroxyl substituents on euryfurylnaphthoquinones and the hydrogen bond between the peri-hydroxy and quinone carbonyl groups influence the electron-acceptor capability of the quinone nucleus and thus modifies the electron transfer from ascorbate to the electroactive quinone nucleus. The combination of euryfurylnaphthoquinones with vitamin C may be of potential clinical interest, because cancer cells accumulate vitamin C, they are sensitive to an oxidant insult and they depend on glycolysis (ATP formation) for their survival.

Pharmacologic concentrations of ascorbate are achieved by parenteral administration and exhibit antitumoral effects

Recently, it has been proposed that pharmacologic concentrations of ascorbate (vitamin C) can be reached by intravenous injection. Because high doses of ascorbate have been described to possess anticancer effects, the therapeutic potential of these concentrations has been studied, both in vitro and in vivo. By using 2-h exposures, a protocol that mimics a parenteral use, we observed that pharmacologic concentrations of ascorbate killed various cancer cell lines very efficiently (EC(50) ranging from 3 to 7 mM). The mechanism of cytotoxicity is based on the production of extracellular hydrogen peroxide and involves intracellular transition metals. In agreement with what has been previously published, our in vivo results show that both intravenous and intraperitoneal administration of ascorbate induced pharmacologic concentrations (up to 20 mM) in blood. In contrast, the concentrations reached orally remained physiological. According to pharmacokinetic data, parenteral administration of ascorbate decreased the growth rate of a murine hepatoma, whereas oral administration of the same dosage did not. We also report that pharmacologic concentrations of ascorbate did not interfere with but rather reinforced the activity of five important chemotherapeutic drugs. Taken together, these results confirm that oral and parenteral administration of ascorbate are not comparable, the latter resulting in pharmacologic concentrations of ascorbate that exhibit interesting anticancer properties.

Oxidative stress in the thyroid gland: from harmlessness to hazard depending on the iodine content

In basal conditions, thyroid epithelial cells produce moderate amounts of reactive oxygen species (ROS) that are physiologically required for thyroid hormone synthesis. They are not necessarily toxic because they are continuously detoxified either in the process of hormone synthesis or by endogenous antioxidant systems. Using a rat model of goiter formation and iodine-induced involution, we found that compared with control thyroids, the oxidative stress, assessed by the detection of 4-hydroxynonenal, was strongly enhanced both in hyperplastic and involuting glands. The level of antioxidant defenses (glutathione peroxidases and peroxiredoxins) was also up-regulated in both groups, although somewhat less in the latter. Of note, increased oxidative stress came along with an inflammatory reaction, but only in involuting glands, suggesting that although antioxidant systems can adequately buffer a heavy load of ROS in goiter, it is not necessarily the case in involuting glands. The effects of 15-deoxy-Delta(12,14)-prostaglandin J2 (15dPGJ2), an endogenous ligand of peroxisome proliferated-activated receptor gamma (PPARgamma) with antiinflammatory properties, were then investigated in involuting glands. This drug strongly reduced both 4-hydroxynonenal staining and the inflammatory reaction, indicating that it can block iodine-induced cytotoxicity. When experiments were carried out with the PPARgamma antagonist, bisphenol A diglycidyl ether, 15dPGJ2-induced effects remained unchanged, suggesting that these effects were not mediated by PPARgamma. In conclusion, thyroid epithelial cells are well adapted to endogenously produced ROS in basal and goitrous conditions. In iodine-induced goiter involution, the increased oxidative stress is accompanied by inflammation that can be blocked by 15dPGJ2 through PPARgamma-independent protective effects.