Retinoic acid synergizes ATO-mediated cytotoxicity by precluding Nrf2 activity in AML cells.

BACKGROUND: Standard therapy for acute promyelocytic leukaemia (APL) includes retinoic acid (all-trans retinoic acid (ATRA)), which promotes differentiation of promyelocytic blasts. Although co-administration of arsenic trioxide (ATO) with ATRA has emerged as an effective option to treat APL, the molecular basis of this effect remains unclear. METHODS: Four leukaemia cancer human models (HL60, THP-1, NBR4 and NBR4-R2 cells) were treated either with ATO alone or ATO plus ATRA. Cancer cell survival was monitored by trypan blue exclusion and DEVDase activity assays. Gene and protein expression changes were assessed by RT-PCR and western blot. RESULTS: ATO induced an antioxidant response characterised by Nrf2 nuclear translocation and enhanced transcription of downstream target genes (that is, HO-1, NQO1, GCLM, ferritin). In cells exposed to ATO plus ATRA, the Nrf2 nuclear translocation was prevented and cytotoxicity was enhanced. HO-1 overexpression reversed partially the cytotoxicity by ATRA-ATO in HL60 cells. The inhibitory effects of ATRA on ATO-mediated responses were not observed in either the ATRA-resistant NB4-R2 cells or in NB4 cells pre-incubated with the RARα antagonist Ro-41-52-53. CONCLUSIONS: The augmented cytotoxicity observed in leukaemia cells following combined ATO-ATRA treatment is likely due to inhibition of Nrf2 activity, thus explaining the efficacy of combined ATO-ATRA treatment in the APL therapy.

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.

Antiproliferative effects of phenylaminonaphthoquinones are increased by ascorbate and associated with the appearance of a senescent phenotype in human bladder cancer cells.

Quinone-containing molecules have been developed against cancer mainly for their redox cycling ability leading to reactive oxygen species (ROS) formation. We have previously shown that donor-acceptor phenylaminonaphthoquinones are biologically active against a panel of cancer cells. In this report, we explored the mechanisms involved in cancer cell growth inhibition caused by two phenylaminonaphthoquinones, namely Q7 and Q9, with or without ascorbate (ASC). The results show that Q7 and Q9 are both redox cyclers able to form ROS, which strongly inhibit the proliferation of T24 cells. Q9 was a better redox cycler than Q7 because of marked stabilization of the semiquinone radical species arising from its reduction by ascorbate. Indeed, ASC dramatically enhances the inhibitory effect of Q9 on cell proliferation. Q9 plus ASC impairs the cell cycle, causing a decrease in the number of cells in the G2/M phase without involving other cell cycle regulating key proteins. Moreover, Q9 plus ASC influences the MAPK signaling pathways, provoking the appearance of a senescent cancer cell phenotype and ultimately leading to necrotic-like cell death. Because cellular senescence limits the replicative capacity of cells, our results suggest that induction of senescence may be exploited as a basis for new approaches to cancer therapy.

Gut microbiota-derived propionate reduces cancer cell proliferation in the liver.

BACKGROUND: Metabolites released by the gut microbiota may influence host metabolism and immunity. We have tested the hypothesis that inulin-type fructans (ITF), by promoting microbial production of short-chain fatty acids (SCFA), influence cancer cell proliferation outside the gut. METHODS: Mice transplanted with Bcr-Abl-transfected BaF3 cells, received ITF in their drinking water. Gut microbiota was analysed by 16S rDNA polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and qPCR. Serum Short-chain fatty acids were quantified by UHPLC-MS. Cell proliferation was evaluated in vivo, by molecular biology and histology, and in vitro. RESULTS: Inulin-type fructans treatment reduces hepatic BaF3 cell infiltration, lessens inflammation and increases portal propionate concentration. In vitro, propionate reduces BaF3 cell growth through a cAMP level-dependent pathway. Furthermore, the activation of free fatty acid receptor 2 (FFA2), a Gi/Gq-protein-coupled receptor also known as GPR43 and that binds propionate, lessens the proliferation of BaF3 and other human cancer cell lines. CONCLUSION: We show for the first time that the fermentation of nutrients such as ITF into propionate can counteract malignant cell proliferation in the liver tissue. Our results support the interest of FFA2 activation as a new strategy for cancer therapeutics. This study highlights the importance of research focusing on gut microbes-host interactions for managing systemic and severe diseases such as leukaemia.

Inhibition of cell proliferation and migration by oxidative stress from ascorbate-driven juglone redox cycling in human bladder-derived T24 cells.

The effects of juglone on T24 cells were assessed in the presence and absence of ascorbate. The EC(50) value for juglone at 24 h decreased from 28.5 µM to 6.3 µM in the presence of ascorbate. In juglone-treated cells, ascorbate increased ROS formation (4-fold) and depleted GSH (65%). N-acetylcysteine or catalase restricted the juglone/ascorbate-mediated effects, highlighting the role of oxidative stress in juglone cytotoxicity. Juglone alone or associated with ascorbate did not cause caspase-3 activation or PARP cleavage, suggesting necrosis-like cell death. DNA damage and the mild ER stress caused by juglone were both enhanced by ascorbate. In cells treated with juglone (1-5 µM), a concentration-dependent decrease in cell proliferation was observed. Ascorbate did not impair cell proliferation but its association with juglone led to a clonogenic death state. The motility of ascorbate-treated cells was not affected. Juglone slightly restricted motility, but cells lost their ability to migrate most noticeably when treated with juglone plus ascorbate. We postulate that juglone kills cells by a necrosis-like mechanism inhibiting cell proliferation and the motility of T24 cells. These effects are enhanced in the presence of ascorbate.

Molecular chaperone Hsp90 as a target for oxidant-based anticancer therapies.

Hsp90 is a molecular chaperone involved in the stabilization of many oncoproteins that are required for the acquisition and maintenance of the so-called six major hallmarks of cancer cells. Various strategies have, therefore, been developed to inhibit the chaperone activity of Hsp90 and induce cancer cell death through the destabilization of its client proteins. Among these strategies, we have shown that generation of oxidative stress leads to the cleavage and deactivation of Hsp90. Because cancer cells are often deficient in antioxidant enzymes and exhibit higher basal levels of reactive oxygen species (ROS) than their normal counterparts, inducing a selective oxidative stress may be a promising approach for cancer treatment. Thus, many redox-modulating agents have, therefore, been developed or are undergoing clinical trials and Hsp90 represents a new target for oxidative stress-generating agents. The purpose of this article is to review the current state of knowledge about Hsp90 and the use of oxidative stress-generating agents in cancer treatment. We will illustrate the review with some of our results concerning the effects of oxidative stress on Hsp90 using various oxidative stress-generating systems based on different quinones in combination with a well-known reducing agent (i.e., ascorbate). Our results show that oxidative stress provokes the cleavage of Hsp90 in CML cells, as well as the degradation of its client protein Bcr-Abl and the deactivation of its downstream signaling pathways, namely MAPK and STAT5. Overall, these results highlight the potential interest of using oxidative stress to target Hsp90.

Redox-active quinones and ascorbate: an innovative cancer therapy that exploits the vulnerability of cancer cells to oxidative stress.

Cancer cells are particularly vulnerable to treatments impairing redox homeostasis. Reactive oxygen species (ROS) can indeed play an important role in the initiation and progression of cancer, and advanced stage tumors frequently exhibit high basal levels of ROS that stimulate cell proliferation and promote genetic instability. In addition, an inverse correlation between histological grade and antioxidant enzyme activities is frequently observed in human tumors, further supporting the existence of a redox dysregulation in cancer cells. This biochemical property can be exploited by using redox-modulating compounds, which represent an interesting approach to induce cancer cell death. Thus, we have developed a new strategy based on the use of pharmacologic concentrations of ascorbate and redox-active quinones. Ascorbate-driven quinone redox cycling leads to ROS formation and provoke an oxidative stress that preferentially kill cancer cells and spare healthy tissues. Cancer cell death occurs through necrosis and the underlying mechanism implies an energetic impairment (ATP depletion) that is likely due to glycolysis inhibition. Additional mechanisms that participate to cell death include calcium equilibrium impairment and oxidative cleavage of protein chaperone Hsp90. Given the low systemic toxicity of ascorbate and the impairment of crucial survival pathways when associated with redox-active quinones, these combinations could represent an original approach that could be combined to standard cancer therapy.

In situ modulation of oxidative stress: a novel and efficient strategy to kill cancer cells.

Cancer cells show an up-regulation of glycolysis, they readily take up vitamin C, and they appear more susceptible to an oxidative stress than the surrounding normal cells. Here we compare, analyse and discuss these particular hallmarks by performing experiments in murine hepatomas (TLT cells) and freshly isolated mouse hepatocytes. The results show that rates of lactate formation are higher in TLT cells as compared to mouse hepatocytes, but their ATP content represents less than 25% of that in normal cells. The uptake of vitamin C is more important in hepatoma cells as compared to normal hepatocytes. This uptake mainly occurs through GLUT1 transporters. Hepatoma cells have less than 10% of antioxidant enzyme activities as compared to normal hepatocytes. This decrease includes not only the major antioxidant enzymes, namely catalase, superoxide dismutase and glutathione peroxidase, but also the GSH content. Moreover, catalase is almost not expressed in hepatoma cells as shown by western blot analysis. We explored therefore a selective exposure of cancer cells to an oxidative stress induced by pro-oxidant mixtures containing pharmacological doses of vitamin C and a redox active compound such as menadione (vitamin K(3)). Indeed, the combination of vitamin C (which accumulates in hepatoma cells) and a quinone undergoing a redox cycling (vitamin K(3)) leads to an oxidative stress that kills cancer cells in a selective manner. This differential sensitivity between cancer cells and normal cells may have important clinical applications, as it has been observed with other pro-oxidants like Arsenic trioxide, isothiocyanates, Adaphostin.

The controversial place of vitamin C in cancer treatment.

In 2008, we celebrate the 80th anniversary of the discovery of vitamin C. Since then, we know that vitamin C possesses few pharmacological actions although it is still perceived by the public as a "miracle-pill" capable to heal a variety of illnesses. Cancer is one of the most common diseases for which a beneficial role of vitamin C has been claimed. Thus, its dietary use has been proposed in cancer prevention for several years. Apart from this nutritional aspect, an extensive and often confusing literature exists about the use of vitamin C in cancer that has considerably discredited its use. Nevertheless, recent pharmacokinetic data suggest that pharmacologic concentrations of vitamin C can be achieved by intravenous injections. Since these concentrations exhibit anticancer activities in vitro, this raises the controversial question of the re-evaluation of vitamin C in cancer treatment. Therefore, the purpose of this commentary is to make a critical review of our current knowledge of vitamin C, focusing on the rationale that could support its use in cancer therapy.

Targeting cancer cells by an oxidant-based therapy.

Despite the progress achieved in chemo- and radiotherapy, cancer is still a leading life-threatening pathology. In that sense, there is a need for novel therapeutic strategies based on our current knowledge of cancer biology. Among the phenotypical features of cancer cells, two of them are of particular interest: their nearly universal glycolytic phenotype and their sensitivity towards an oxidative stress, both resulting from the combination of high anabolic needs and hypoxic growth conditions. By using menadione (vitamin K3) and ascorbate (vitamin C), we took advantage of these features to develop an original approach that consists in the exposure of cancer cells to an oxidant insult. When used in combination, these compounds exhibit a synergistic action and are devoid of major toxicity in vivo. Thus, this review is dedicated to the analysis of the molecular pathways by which this promising combination exerts its antitumoural effect.