Oxidative damage DNA: 8-oxoGua and 8-oxodG as molecular markers of cancer

Impact of weight loss induced by gastric bypass or caloric restriction on oxidative stress and genomic damage in obese Zucker rats

BACKGROUND

Evidence on bariatric surgery induced weight loss and its possible impact on cancer risk is limited, but also controversial. We used obese Zucker(fa/fa) and lean Zucker(fa/+) to investigate the association between obesity, oxidative stress and genomic damage after weight loss induced either by Roux-en-Y gastric bypass surgery (RYGB) or caloric restriction.

METHODS

Male Zucker(fa/fa) rats underwent RYGB (n=15) or sham surgery (n=17). Five shams were food restricted and body weight matched (BWM) to RYGB. Twelve Zucker(fa/+) rats served as lean controls. Body weight and food intake were measured daily. An oral glucose tolerance test was performed on day 27. DHE staining and western blots of HSP70 and HO-1 were used to evaluate oxidative stress and anti-3-nitrotyrosine antibody staining for nitrative stress detection in colon and kidney. Lipid peroxidation products in urine were quantified by TBARS assay. LC/MS/MS was applied to measure urinary excretion of 8-oxoGua (oxidized DNA derived base), 8-oxodG (oxidized DNA derived nucleoside) and 8-oxoGuo (oxidized RNA derived nucleoside). DNA double strand breaks (DSBs) and cell proliferation (PCNA) were detected by immunohistochemistry.

RESULTS

Sham-operated rats showed impaired glucose tolerance, elevated plasma insulin levels as well as elevated oxidative stress and nitrative stress markers, which were less severe after weight loss by RYGB or caloric restriction. Cell proliferation showed similar trends but no significant alteration. DNA DSBs were more frequent in sham-operated compared to all other groups. DNA damage in Zucker(fa/fa) rats positively correlated with basal plasma insulin values (Spearman's correlation coefficient for colon, 0.634 and for kidney, 0.525).

CONCLUSIONS

RYGB and caloric restriction were sufficient to significantly reduce elevated oxidative/nitrative stress and genomic damage in obese Zucker(fa/fa) rats. Further investigations are needed to elucidate the underlying mechanism of these genome protective effects.

Altered Levels of Salivary 8-oxo-7-hydrodeoxyguanosine in Breast Cancer

Oxidative stress has been implicated in the pathogenesis of breast cancer (BC). To determine whether BC is associated with altered salivary redox homeostasis, we performed a case-control study assessing the relationship between BC and 8-oxo-7-hydrodeoxyguanosine (8-oxodG), a marker for oxidative damage to DNA. Enzyme-linked immunosorbent assay for 8-oxodG was used on whole, unstimulated saliva of 134 BC patients and 226 healthy controls. Associations of the redox data were assessed by analysis of variance and logistic regression analysis. Our results revealed that there were 1) significantly lower mean levels of salivary 8-oxodG in BC patients versus controls ( P = 0.0005), 2) significantly lower levels among participants who did not receive radiotherapy and/or chemotherapy as compared with controls ( P < 0.0001), 3) significantly lower levels among BC patients who did not receive these treatments than among those who did ( P < 0.02), 4) and no significant differences in mean 8-oxodG levels among BC patients positive or negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 ( P ≥ 0.08). Our results suggest that BC is associated with decreased levels of oxidatively modified DNA in saliva. Knowledge Transfer Statement: The results of our current case-control study indicate that the molecular biomarker of oxidative stress 8-oxo-7-hydrodeoxyguanosine, measured from saliva, is associated with breast cancer. Our findings may provide the basis for future studies on molecular biomarkers of oxidative stress and breast cancer using saliva as an accessible and noninvasive tissue.

Effects of Marsdenia tenacissima polysaccharide on the immune regulation and tumor growth in H22 tumor-bearing mice

One water-soluble polysaccharide (Marsdenia tenacissima polysaccharide, MTP), with an average molecular weight of 4.9 × 10(4) Da, was isolated from the dried rattan of M. tenacissima. MTP contained 93.8% carbohydrates, 5.6% proteins and 21.3% uronic acid, and were composed of arabinose, mannose, galactose, xylose, glucuronic acid at a molar ratio of 9.1, 17.7, 30.2, 22.4 and 20.6. The experiments on the animals showed that MTP could increase the serum hemolysin, promote the formation of antibody-forming cells and improve the phagocytosis of mononuclear macrophage in normal mice. Meanwhile, MTP could also inhibit the growth of tumor in H22 tumor-bearing mice dose-dependently, and increase the spleen index, thymus index and serum albumin level in the mice. In addition, MTP could elevate the serum level of TNF-α and IL-2, increase the activity of GSH-Px, CAT and SOD in the liver tissue, and reduce the content of VEGF and MDA. These results suggest that MTP can regulate the immune function in mice and suppress the growth of tumor in H22 tumor-bearing mice, and its antitumor activity may be related to its antioxidant and immunomodulatory effects.

Association of APE1 Gene Asp148Glu Variant with Digestive Cancer: A Meta-Analysis

Background

Apurinic/apyrimidinic endonuclease-1 (APE1) is a rate-limiting enzyme in DNA base excision repair and has been implicated in carcinogenesis. In this study, we summarize available data to examine the susceptibility of APE1 gene Asp148Glu variant to digestive cancer via a meta-analysis.

Material/Methods

Study selection and data abstraction were conducted independently by 2 authors. Random-effects model was utilized to pool effect estimates. Heterogeneity and publication bias were addressed.

Results

Sixteen articles involving 4916 digestive cancer patients and 7748 controls were qualified for this meta-analysis. Overall association showed an indicative association between Asp148Glu variant and digestive cancer under allelic (odds ratio or OR=1.11; 95% confidence interval or CI: 0.99–1.25; P=0.074) and dominant (OR=1.18; 95% CI: 1.00–1.40; P=0.056) models, with strong evidence of heterogeneity. Deviation from Hardy-Weinberg equilibrium was an obvious source of heterogeneity. In subgroup analyses by cancer sites, this variant was significantly associated with the increased risk for hepatocellular cancer under allelic (OR=1.50; 95% CI: 1.25–1.80; P<0.001) and homozygous genotypic (OR=1.55; 95% CI: 1.02–2.29; P=0.028) models. There were low probabilities of publication bias for the above comparisons.

Conclusions

The results of this meta-analysis collectively suggest that APE1 gene Asp148Glu variant is not a risk-conferring factor for digestive cancer. Further large and well-designed studies are required.

Impaired self-renewal and increased colitis and dysplastic lesions in colonic mucosa of AKR1B8-deficient mice

PURPOSE

Ulcerative colitis and colitis-associated colorectal cancer (CAC) is a serious health issue, but etiopathological factors remain unclear. Aldo-keto reductase 1B10 (AKR1B10) is specifically expressed in the colonic epithelium, but downregulated in colorectal cancer. This study was aimed to investigate the etiopathogenic role of AKR1B10 in ulcerative colitis and CAC.

EXPERIMENTAL DESIGN

Ulcerative colitis and CAC biopsies (paraffin-embedded sections) and frozen tissues were collected to examine AKR1B10 expression. Aldo-keto reductase 1B8 (the ortholog of human AKR1B10) knockout (AKR1B8(-/-)) mice were produced to estimate its role in the susceptibility and severity of chronic colitis and associated dysplastic lesions, induced by dextran sulfate sodium (DSS) at a low dose (2%). Genome-wide exome sequencing was used to profile DNA damage in DSS-induced colitis and tumors.

RESULTS

AKR1B10 expression was markedly diminished in over 90% of ulcerative colitis and CAC tissues. AKR1B8 deficiency led to reduced lipid synthesis from butyrate and diminished proliferation of colonic epithelial cells. The DSS-treated AKR1B8(-/-) mice demonstrated impaired injury repair of colonic epithelium and more severe bleeding, inflammation, and ulceration. These AKR1B8(-/-) mice had more severe oxidative stress and DNA damage, and dysplasias were more frequent and at a higher grade in the AKR1B8(-/-) mice than in wild-type mice. Palpable masses were seen in the AKR1B8(-/-) mice only, not in wild-type.

CONCLUSIONS

AKR1B8 is a critical protein in the proliferation and injury repair of the colonic epithelium and in the pathogenesis of ulcerative colitis and CAC, being a new etiopathogenic factor of these diseases.

Potential survival markers in cancer patients undergoing chemotherapy

Due to the importance of the identification of chemotherapy outcome prognostic factors, we attempted to establish the potential of oxidative stress/DNA damage parameters such as prognostic markers. The aim of the study was to determine whether platinum derivative-based chemotherapy in cancer patients (n = 66) is responsible for systemic oxidatively damaged DNA and whether damage biomarkers, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and the modified base 8-oxo-7,8-dihydroguanine (8-oxo-Gua), in urine and DNA may be used as a prognostic factor for the outcome of chemotherapy. All the aforementioned modifications were analyzed using techniques involving high-performance liquid chromatography/electrochemical detection (HPLC/EC) or HPLC/gas chromatography-mass spectrometry (GC-MS). Among all the analyzed parameters, the significantly decreased levels of 8-oxo-Gua in urine collected from a subgroup of patients 24 h after the first infusion of the drug, as compared with the baseline levels, correlated with a significantly longer overall survival (OS) (60 months after therapy) than in the subgroup without any decrease of this parameter after therapy (median OS = 24 months, p = 0.007). Moreover, a significantly longer OS was also observed in a group with increased urine levels of 8-oxo-dG after chemotherapy (38.6 vs. 20.5 months, p = 0.03). The results of our study suggest that patients with decreased 8-oxo-Gua levels and increased 8-oxo-dG levels in urine 24 h after the first dose should be considered as better responders to the administered chemotherapy, with a lower risk of death. The conclusion may permit the use of these parameters as markers for predicting the clinical outcome of platinum derivative-based chemotherapy.

Increased oxidative DNA damage and decreased expression of base excision repair proteins in airway epithelial cells of women who cook with biomass fuels

To investigate whether biomass burning causes oxidative DNA damage and alters the expression of DNA base excision repair (BER) proteins in airway cells, sputum samples were collected from 80 premenopausal rural biomass-users and 70 age-matched control women who cooked with liquefied petroleum gas. Compared with control the airway cells of biomass-users showed increased DNA damage in alkaline comet assay. Biomass-users showed higher percentage of cells expressing oxidative DNA damage marker 8-oxoguanine and lower percentages of BER proteins OGG1 and APE1 by immunocytochemical staining. Reactive oxygen species (ROS) generation was doubled and level of superoxide dismutase was depleted significantly among biomass-users. The concentrations of particulate matters were higher in biomass-using households which positively correlated with ROS generation and negatively with BER proteins expressions. ROS generation was positively correlated with 8-oxoguanine and negatively with BER proteins suggesting cooking with biomass is a risk for genotoxicity among rural women in their child-bearing age.

SERMs attenuate estrogen-induced malignant transformation of human mammary epithelial cells by upregulating detoxification of oxidative metabolites

The risk of developing hormone-dependent cancers with long-term exposure to estrogens is attributed both to proliferative, hormonal actions at the estrogen receptor (ER) and to chemical carcinogenesis elicited by genotoxic, oxidative estrogen metabolites. Nontumorigenic MCF-10A human breast epithelial cells are classified as ER(-) and undergo estrogen-induced malignant transformation. Selective estrogen receptor modulators (SERM), in use for breast cancer chemoprevention and for postmenopausal osteoporosis, were observed to inhibit malignant transformation, as measured by anchorage-independent colony growth. This chemopreventive activity was observed to correlate with reduced levels of oxidative estrogen metabolites, cellular reactive oxygen species (ROS), and DNA oxidation. The ability of raloxifene, desmethylarzoxifene (DMA), and bazedoxifene to inhibit this chemical carcinogenesis pathway was not shared by 4-hydroxytamoxifen. Regulation of phase II rather than phase I metabolic enzymes was implicated mechanistically: raloxifene and DMA were observed to upregulate sulfotransferase (SULT 1E1) and glucuronidase (UGT 1A1). The results support upregulation of phase II metabolism in detoxification of catechol estrogen metabolites leading to attenuated ROS formation as a mechanism for inhibition of malignant transformation by a subset of clinically important SERMs.

NEIL2 protects against oxidative DNA damage induced by sidestream smoke in human cells

Secondhand smoke (SHS) is a confirmed lung carcinogen that introduces thousands of toxic chemicals into the lungs. SHS contains chemicals that have been implicated in causing oxidative DNA damage in the airway epithelium. Although DNA repair is considered a key defensive mechanism against various environmental attacks, such as cigarette smoking, the associations of individual repair enzymes with susceptibility to lung cancer are largely unknown. This study investigated the role of NEIL2, a DNA glycosylase excising oxidative base lesions, in human lung cells treated with sidestream smoke (SSS), the main component of SHS. To do so, we generated NEIL2 knockdown cells using siRNA-technology and exposed them to SSS-laden medium. Representative SSS chemical compounds in the medium were analyzed by mass spectrometry. An increased production of reactive oxygen species (ROS) in SSS-exposed cells was detected through the fluorescent detection and the induction of HIF-1α. The long amplicon–quantitative PCR (LA-QPCR) assay detected significant dose-dependent increases of oxidative DNA damage in the HPRT gene of cultured human pulmonary fibroblasts (hPF) and BEAS-2B epithelial cells exposed to SSS for 24 h. These data suggest that SSS exposure increased oxidative stress, which could contribute to SSS-mediated toxicity. siRNA knockdown of NEIL2 in hPF and HEK 293 cells exposed to SSS for 24 h resulted in significantly more oxidative DNA damage in HPRT and POLB than in cells with control siRNA. Taken together, our data strongly suggest that decreased repair of oxidative DNA base lesions due to an impaired NEIL2 expression in non-smokers exposed to SSS would lead to accumulation of mutations in genomic DNA of lung cells over time, thus contributing to the onset of SSS-induced lung cancer.

Urinary excretion of oxidative damage markers in a rat model of vascularized composite allotransplantation

BACKGROUND

Vascularized composite allotransplantation is an emerging field of transplantation that provides a potential treatment for complex tissue defects after traumatic loss or tumor resection and for the repair of congenital abnormalities. However, vascularized composite allotransplantation recipients have suffered from acute and chronic graft rejection that is associated with oxidative stress. This study investigated the oxidative damage in a rat vascularized composite allotransplantation model by measuring three urinary biomarkers, 8-oxo-7,8-dihydroguanine (8-oxoGua), 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), and malondialdehyde.

METHODS

Rats received two different immunosuppressants, including cyclosporine A and mycophenolate mofetil after transplantation, with one group also receiving mesenchymal stem cells before transplantation. Urine was collected and analyzed for 8-oxo-7,8-dihydroguanine, 8-oxo-7,8-dihydro-2'-deoxyguanosine, and malondialdehyde by liquid chromatography coupled to tandem mass spectometry methods.

RESULTS

Rats undergoing vascularized composite allotransplantation had higher urinary levels of 8-oxo-7,8-dihydroguanine, 8-oxo-7,8-dihydro-2'-deoxyguanosine, and malondialdehyde compared with rats undergoing syngeneic transplantation. Cyclosporine A/mycophenolate mofetil following treatment prolonged the allograft survival in a dose-dependent manner. Compared with rats undergoing vascularized composite allotransplantation with cyclosporine A/mycophenolate mofetil treatment alone, rats undergoing mesenchymal stem cell combined treatment showed the longest allograft survival, and had approximately 50 percent lower urinary levels of malondialdehyde together with approximately 2.7-times higher levels of 8-oxo-7,8-dihydroguanine.

CONCLUSIONS

Mesenchymal stem cell combined treatment efficiently managed oxidative stress in rats undergoing vascularized composite allotransplantation, and urinary 8-oxo-7,8-dihydroguanine and malondialdehyde could be regarded as good responders to the mesenchymal stem cell therapy.

Oxidized DNA induces an adaptive response in human fibroblasts

Cell-free DNA (cfDNA) released from dying cells contains a substantial proportion of oxidized nucleotides, thus, forming cfDNA(OX). The levels of cfDNA(OX) are increased in the serum of patients with chronic diseases. Oxidation of DNA turns it into a stress signal. The samples of genomic DNA (gDNA) oxidized by Н2О2in vitro (gDNA(OX)) induce effects similar to that of DNA released from damaged cells. Here we describe the effects of gDNA(OX) on human fibroblasts cultivated in the stressful conditions of serum withdrawal. In these cells, gDNA(OX) evokes an adaptive response that leads to an increase in the rates of survival in serum starving cell populations as well as in populations irradiated at the dose of 1.2Gy. These effects are not seen in control populations of fibroblasts treated with non-modified gDNA. In particular, the exposure to gDNA(OX) leads to a decrease in the expression of the proliferation marker Ki-67 and an increase in levels of РСNА, a decrease in the proportion of subG1- and G2/M cells, a decrease in proportion of cells with double strand breaks (DSBs). Both gDNA(OX) and gDNA suppress the expression of DNA sensors TLR9 and AIM2 and up-regulate nuclear factor-erythroid 2 p45-related factor 2 (NRF2), while only gDNA(OX) inhibits NF-κB signaling. gDNA(OX) is a model for oxidized cfDNA(OX) that is released from the dying tumor cells and being carried to the distant organs. The systemic effects of oxidized DNA have to be taken into account when treating tumors. In particular, the damaged DNA released from irradiated cells may be responsible for an abscopal effects and a bystander mediated adaptive response seen in some cancer patients. These results indicate the necessity for the further study of the effects of oxidized DNA in both in vitro and in vivo systems.

Oxidized extracellular DNA as a stress signal in human cells

The term "cell-free DNA" (cfDNA) was recently coined for DNA fragments from plasma/serum, while DNA present in in vitro cell culture media is known as extracellular DNA (ecDNA). Under oxidative stress conditions, the levels of oxidative modification of cellular DNA and the rate of cell death increase. Dying cells release their damaged DNA, thus, contributing oxidized DNA fragments to the pool of cfDNA/ecDNA. Oxidized cell-free DNA could serve as a stress signal that promotes irradiation-induced bystander effect. Evidence points to TLR9 as a possible candidate for oxidized DNA sensor. An exposure to oxidized ecDNA stimulates a synthesis of reactive oxygen species (ROS) that evokes an adaptive response that includes transposition of the homologous loci within the nucleus, polymerization and the formation of the stress fibers of the actin, as well as activation of the ribosomal gene expression, and nuclear translocation of NF-E2 related factor-2 (NRF2) that, in turn, mediates induction of phase II detoxifying and antioxidant enzymes. In conclusion, the oxidized DNA is a stress signal released in response to oxidative stress in the cultured cells and, possibly, in the human body; in particular, it might contribute to systemic abscopal effects of localized irradiation treatments.

Eicosanoids and adipokines in breast cancer: from molecular mechanisms to clinical considerations

Chronic inflammation is one of the foremost risk factors for different types of malignancies, including breast cancer. Additional risk factors of this pathology in postmenopausal women are weight gain, obesity, estrogen secretion, and an imbalance in the production of adipokines, such as leptin and adiponectin. Various signaling products of transcription factor, nuclear factor-kappaB, in particular inflammatory eicosanoids, reactive oxygen species (ROS), and cytokines, are thought to be involved in chronic inflammation-induced cancer. Together, these key components have an influence on inflammatory reactions in malignant tissue damage when their levels are deregulated endogenously. Prostaglandins (PGs) are well recognized in inflammation and cancer, and they are solely biosynthesized through cyclooxygenases (COXs) from arachidonic acid. Concurrently, ROS give rise to bioactive isoprostanes from arachidonic acid precursors that are also involved in acute and chronic inflammation, but their specific characteristics in breast cancer are less demonstrated. Higher aromatase activity, a cytochrome P-450 enzyme, is intimately connected to tumor growth in the breast through estrogen synthesis, and is interrelated to COXs that catalyze the formation of both inflammatory and anti-inflammatory PGs such as PGE(2), PGF(2α), PGD(2), and PGJ(2) synchronously under the influence of specific mediators and downstream enzymes. Some of the latter compounds upsurge the intracellular cyclic adenosine monophosphate concentration and appear to be associated with estrogen synthesis. This review discusses the role of COX- and ROS-catalyzed eicosanoids and adipokines in breast cancer, and therefore ranges from their molecular mechanisms to clinical aspects to understand the impact of inflammation.

Quantification of 8-oxodGuo lesions in double-stranded DNA using a photoelectrochemical DNA sensor

Exposure of DNA to oxidative stress conditions results in the generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). 8-OxodGuo is genotoxic if left unrepaired. We quantified 8-oxodGuo lesions in double-stranded DNA films by using a photoelectrochemical DNA sensor in conjunction with a specific covalent labeling method. A lesion-containing DNA film was assembled on a SnO(2) nanoparticle modified indium tin oxide electrode through layer-by-layer electrostatic adsorption. The lesions were covalently labeled with a biotin conjugated spermine derivative, and ruthenium tris(bipyridine) labeled streptavidin was introduced as the signal reporter molecule. Photocurrent increased with the number of lesions in the strand and decreased as the film was diluted with intact DNA. Quantification of 8-oxodGuo was achieved with an estimated detection limit of ∼1 lesion in 650 bases or 1.6 fmol of 8-oxodGuo on the electrode. Incubation of the film with a DNA base excision repair enzyme, E. coli formamidopyrimidine-DNA glycosylase (Fpg), resulted in complete loss of the signal, indicating efficient excision of the isolated lesions in the nucleotide. Oxidatively generated DNA damage to a double-stranded calf thymus DNA film by the Fenton reaction was then assessed. One 8-oxodGuo lesion in 520 bases was detected in DNA exposed to 50 μM Fe(2+)/200 μM H(2)O(2). Treatment with Fpg reduced the photocurrent by 50%, indicating only partial excision of 8-oxodGuo. This suggests that tandem lesions, which are resistant to Fpg excision, are generated by the Fenton reaction. Unlike repair enzyme dependent methods, the sensor recognizes 8-oxodGuo in tandem lesions and can avoid underestimating DNA damage.

Urinary 8-oxoguanine as a predictor of survival in patients undergoing radiotherapy

BACKGROUND

Because of the importance to identify prognostic indicator for radiotherapy, herein we decided to check whether the parameters which describe oxidative stress/DNA damage may be used as a marker of the therapy. The aim of this work was to investigate whether fractionated radiotherapy of patients with cancer (n = 99) is responsible for oxidative DNA damage on the level of the whole organism and whether the biomarkers of the damage such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and its modified base 8-oxo-7,8-dihydroguanine (8-oxo-Gua) in urine and DNA may be used as a predictor of radiotherapy success.

METHODS

All the aforementioned modifications were analyzed using techniques which involve high-performance liquid chromatography/electrochemical detection (HPLC/EC) or HPLC/gas chromatography-mass spectroscopy (GC-MS).

RESULTS

Of all analyzed parameters only patients with significantly elevated urinary excretion of the 8-oxo-Gua with concomitant unchanged level of 8-oxo-dG in leukocytes DNA in the samples collected 24 hours after the first fraction in comparison to the initial level have significantly increased survival time (60 months after the treatment, survival of 50% of the patients who fulfill the above mentioned criteria, in comparison with 10% of the patients who did not).

CONCLUSIONS

Results of our work suggest that patients with higher urinary 8-oxo-Gua and concomitant stable level of 8-oxo-dG in leukocytes DNA, after 24 hours of the first dose should be regarded as better responder to radiotherapy as being at lower risk of mortality.

IMPACT

The above mentioned statement could make it possible to use these parameters as markers to predict the clinical success.

Hydrogen peroxide fuels aging, inflammation, cancer metabolism and metastasis: the seed and soil also needs "fertilizer"

In 1889, Dr. Stephen Paget proposed the "seed and soil" hypothesis, which states that cancer cells (the seeds) need the proper microenvironment (the soil) for them to grow, spread and metastasize systemically. In this hypothesis, Dr. Paget rightfully recognized that the tumor microenvironment has an important role to play in cancer progression and metastasis. In this regard, a series of recent studies have elegantly shown that the production of hydrogen peroxide, by both cancer cells and cancer-associated fibroblasts, may provide the necessary "fertilizer," by driving accelerated aging, DNA damage, inflammation and cancer metabolism, in the tumor microenvironment. By secreting hydrogen peroxide, cancer cells and fibroblasts are mimicking the behavior of immune cells (macrophages/neutrophils), driving local and systemic inflammation, via the innate immune response (NFκB). Thus, we should consider using various therapeutic strategies (such as catalase and/or other anti-oxidants) to neutralize the production of cancer-associated hydrogen peroxide, thereby preventing tumor-stroma co-evolution and metastasis. The implications of these findings for overcoming chemo-resistance in cancer cells are also discussed in the context of hydrogen peroxide production and cancer metabolism.