Triple negative tumors accumulate significantly less methylglyoxal specific adducts than other human breast cancer subtypes

G2A as a key modulator of carbonyl stress and apoptosis resistance in glucose-loaded cancer cells

Cancer cells exhibit high glycolytic activity, metabolizing glucose as their primary energy substrate. Toxic metabolites produced during glycolysis, such as methylglyoxal, induce carbonyl stress (CS), promoting inflammation and oxidative stress. The elevated glucose metabolism in cancer cells creates this toxic environment. However, little research has focused on the molecules mediating these reactions and stresses, and their role in selecting and enriching apoptosis-resistant cells. This study investigated the impact of constitutively suppressing oxidized lipid receptor G2A (GPR132) expression on the relationship between CS and oxidative stress in glucose-loaded cancer cells. G2A has recently attracted attention as a tumor promoter. However, our study shows that G2A suppression under glucose loading significantly reduces CS and associated oxidative stress, thereby enhancing cancer cell survival. This suggests a new mechanism contrary to conventional thinking, involving the acute induction of glyoxalase 1 (Glo1). G2A may thus play a role in selecting and enriching apoptosis-resistant cell populations under high glucose conditions by regulating Glo1 expression. These findings improve our understanding of the adaptive capacity of cancer cells to glucose toxicity.

Free Methylglyoxal as a Metabolic New Biomarker of Tumor Cell Proliferation in Cancers

BACKGROUND

A fundamental property of cancer cells is their metabolic reprogramming, allowing them to increase glucose uptake and glycolysis. Using a rat colon adenocarcinoma model, we previously showed that blood levels of free methylglyoxal (MG), a side-product of glycolysis, remained normal in animals grafted with a non-growing tumor cell clone, while MG levels were significantly increased and positively correlated with tumor growth in animals grafted with a tumorigenic cell clone issued from the same tumor.

METHODS

We measured free MG in the blood of cancerous non-diabetic patients and compared the results to healthy subjects and non-cancerous diabetic patients. We also measured free MG in tumors and in the corresponding non-cancer tissues, and the peripheral blood.

RESULTS

We show that free MG levels in the peripheral blood of cancer patients are significantly increased in comparison with free MG levels in the peripheral blood of healthy controls (p < 0.0001), and similar to those in the peripheral blood of hyperglycemic diabetic patients (p = 0.965). In addition, we show that repeated free MG level measurement could be used for the therapeutic monitoring of cancer patients. Moreover, we confirmed that free MG is produced by tumor cells at significantly higher levels than cells from their corresponding tissues (p < 0.0001), and is subsequently released in the peripheral blood.

CONCLUSIONS

Free MG measured in the blood could be a new metabolic biomarker useful for the diagnostic, prognostic and follow-up of non-diabetic patients with cancers, such as bronchus carcinoma, pancreatic carcinoma and glioblastoma, for which there are presently no available useful biomarkers.

Dietary glycation compounds - implications for human health

The term "glycation compounds" comprises a wide range of structurally diverse compounds that are formed endogenously and in food via the Maillard reaction, a chemical reaction between reducing sugars and amino acids. Glycation compounds produced endogenously are considered to contribute to a range of diseases. This has led to the hypothesis that glycation compounds present in food may also cause adverse effects and thus pose a nutritional risk to human health. In this work, the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG) summarized data on formation, occurrence, exposure and toxicity of glycation compounds (Part A) and systematically assessed potential associations between dietary intake of defined glycation compounds and disease, including allergy, diabetes, cardiovascular and renal disease, gut/gastrotoxicity, brain/cognitive impairment and cancer (Part B). A systematic search in Pubmed (Medline), Scopus and Web of Science using a combination of keywords defining individual glycation compounds and relevant disease patterns linked to the subject area of food, nutrition and diet retrieved 253 original publications relevant to the research question. Of these, only 192 were found to comply with previously defined quality criteria and were thus considered suitable to assess potential health risks of dietary glycation compounds. For each adverse health effect considered in this assessment, however, only limited numbers of human, animal and in vitro studies were identified. While studies in humans were often limited due to small cohort size, short study duration, and confounders, experimental studies in animals that allow for controlled exposure to individual glycation compounds provided some evidence for impaired glucose tolerance, insulin resistance, cardiovascular effects and renal injury in response to oral exposure to dicarbonyl compounds, albeit at dose levels by far exceeding estimated human exposures. The overall database was generally inconsistent or inconclusive. Based on this systematic review, the SKLM concludes that there is at present no convincing evidence for a causal association between dietary intake of glycation compounds and adverse health effects.

Dietary and serum advanced glycation end-products and clinical outcomes in breast cancer

One in five women with breast cancer will relapse despite ideal treatment. Body weight and physical activity are strongly associated with recurrence risk, thus lifestyle modification is an attractive strategy to improve prognosis. Trials of dietary modification in breast cancer are promising but the role of specific diets is unclear, as is whether high-quality diet without weight loss can impact prognosis. Advanced glycation end-products (AGEs) are compounds produced in the body during sugar metabolism. Exogenous AGEs, such as those found in food, combined with endogenous AGEs, make up the total body AGE load. AGEs deposit in tissues over time impacting cell signaling pathways and altering protein functions. AGEs can be measured or estimated in the diet and measured in blood through their metabolites. Studies demonstrate an association between AGEs and breast cancer risk and prognosis. Here, we review the clinical data on dietary and serum AGEs in breast cancer.

Resistance to Gemcitabine in Pancreatic Cancer Is Connected to Methylglyoxal Stress and Heat Shock Response

Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease with poor prognosis. Gemcitabine is the first-line therapy for PDAC, but gemcitabine resistance is a major impediment to achieving satisfactory clinical outcomes. This study investigated whether methylglyoxal (MG), an oncometabolite spontaneously formed as a by-product of glycolysis, notably favors PDAC resistance to gemcitabine. We observed that human PDAC tumors expressing elevated levels of glycolytic enzymes together with high levels of glyoxalase 1 (GLO1), the major MG-detoxifying enzyme, present with a poor prognosis. Next, we showed that glycolysis and subsequent MG stress are triggered in PDAC cells rendered resistant to gemcitabine when compared with parental cells. In fact, acquired resistance, following short and long-term gemcitabine challenges, correlated with the upregulation of GLUT1, LDHA, GLO1, and the accumulation of MG protein adducts. We showed that MG-mediated activation of heat shock response is, at least in part, the molecular mechanism underlying survival in gemcitabine-treated PDAC cells. This novel adverse effect of gemcitabine, i.e., induction of MG stress and HSR activation, is efficiently reversed using potent MG scavengers such as metformin and aminoguanidine. We propose that the MG blockade could be exploited to resensitize resistant PDAC tumors and to improve patient outcomes using gemcitabine therapy.

Leveraging histone glycation for cancer diagnostics and therapeutics

Cancer cells undergo metabolic reprogramming to rely mostly on aerobic glycolysis (the Warburg effect). The increased glycolytic intake enhances the intracellular levels of reactive sugars and sugar metabolites. These reactive species can covalently modify macromolecules in a process termed glycation. Histones are particularly susceptible to glycation, resulting in substantial alterations to chromatin structure, function, and transcriptional output. Growing evidence suggests a link between dysregulated metabolism of tumors and cancer proliferation through epigenetic changes. This review discusses recent advances in the understanding of histone glycation, its impact on the epigenetic landscape and cellular fate, and its role in cancer. In addition, we investigate the possibility of using histone glycation as biomarkers and targets for anticancer therapeutics.

Glycation Leads to Increased Invasion of Glioblastoma Cells

Glioblastoma (GBM) is a highly aggressive and invasive brain tumor with a poor prognosis despite extensive treatment. The switch to aerobic glycolysis, known as the Warburg effect, in cancer cells leads to an increased production of methylglyoxal (MGO), a potent glycation agent with pro-tumorigenic characteristics. MGO non-enzymatically reacts with proteins, DNA, and lipids, leading to alterations in the signaling pathways, genomic instability, and cellular dysfunction. In this study, we investigated the impact of MGO on the LN229 and U251 (WHO grade IV, GBM) cell lines and the U343 (WHO grade III) glioma cell line, along with primary human astrocytes (hA). The results showed that increasing concentrations of MGO led to glycation, the accumulation of advanced glycation end-products, and decreasing cell viability in all cell lines. The invasiveness of the GBM cell lines increased under the influence of physiological MGO concentrations (0.3 mmol/L), resulting in a more aggressive phenotype, whereas glycation decreased the invasion potential of hA. In addition, glycation had differential effects on the ECM components that are involved in the invasion progress, upregulating TGFβ, brevican, and tenascin C in the GBM cell lines LN229 and U251. These findings highlight the importance of further studies on the prevention of glycation through MGO scavengers or glyoxalase 1 activators as a potential therapeutic strategy against glioma and GBM.

Methylglyoxal: a novel upstream regulator of DNA methylation

BACKGROUND

Aerobic glycolysis, also known as the Warburg effect, is predominantly upregulated in a variety of solid tumors, including breast cancer. We have previously reported that methylglyoxal (MG), a very reactive by-product of glycolysis, unexpectedly enhanced the metastatic potential in triple negative breast cancer (TNBC) cells. MG and MG-derived glycation products have been associated with various diseases, such as diabetes, neurodegenerative disorders, and cancer. Glyoxalase 1 (GLO1) exerts an anti-glycation defense by detoxifying MG to D-lactate.

METHODS

Here, we used our validated model consisting of stable GLO1 depletion to induce MG stress in TNBC cells. Using genome-scale DNA methylation analysis, we report that this condition resulted in DNA hypermethylation in TNBC cells and xenografts.

RESULTS

GLO1-depleted breast cancer cells showed elevated expression of DNMT3B methyltransferase and significant loss of metastasis-related tumor suppressor genes, as assessed using integrated analysis of methylome and transcriptome data. Interestingly, MG scavengers revealed to be as potent as typical DNA demethylating agents at triggering the re-expression of representative silenced genes. Importantly, we delineated an epigenomic MG signature that effectively stratified TNBC patients based on survival.

CONCLUSION

This study emphasizes the importance of MG oncometabolite, occurring downstream of the Warburg effect, as a novel epigenetic regulator and proposes MG scavengers to reverse altered patterns of gene expression in TNBC.

Glyoxalase 1 as a Therapeutic Target in Cancer and Cancer Stem Cells

Methylglyoxal (MG) is a dicarbonyl compound formed in cells mainly by the spontaneous degradation of the triose phosphate intermediates of glycolysis. MG is a powerful precursor of advanced glycation end products, which lead to strong dicarbonyl and oxidative stress. Although divergent functions of MG have been observed depending on its concentration, MG is considered to be a potential anti-tumor factor due to its cytotoxic effects within the oncologic domain. MG detoxification is carried out by the glyoxalase system. Glyoxalase 1 (Glo1), the ubiquitous glutathione-dependent enzyme responsible for MG degradation, is considered to be a tumor promoting factor due to it catalyzing the removal of cytotoxic MG. Indeed, various cancer types exhibit increased expression and activity of Glo1 that closely correlate with tumor cell growth and metastasis. Furthermore, mounting evidence suggests that Glo1 contributes to cancer stem cell survival. In this review, we discuss the role of Glo1 in the malignant progression of cancer and its possible use as a promising therapeutic target for tumor therapy. We also summarize therapeutic outcomes of Glo1 inhibitors as prospective treatments for the prevention of cancer.

Design, Synthesis and Biological Evaluation of 1,4-Benzenesulfonamide Derivatives as Glyoxalase I Inhibitors

Background

Glyoxalase system is one of the defense cellular mechanisms that protect cells against endogenous harmful metabolites, mainly methylglyoxal (MG), through conversion of cytotoxic methylglyoxal into the non-toxic lactic acid. Glyoxalase system comprises of two enzymes glyoxalase I, glyoxalase II, and a catalytic amount of reduced glutathione. Cancerous cells overexpress glyoxalase I, making it a target for cancer therapy. Many studies have been conducted to identify potent Glx-I inhibitors.

Methods

Aiming to discover and develop novel Glx-I inhibitors, a series of 1,4-benzenesulfonamide derivatives were designed, synthesized, and biologically evaluated in vitro against human Glx-I enzyme. Seventeen compounds were designed based on the hit compound that was obtained from searching the National Cancer Institute (NCI) database. The synthesis of the target compounds (13-29) was accomplished utilizing an azo coupling reaction of aniline derivatives and activated substituted aromatic compounds. To understand the binding mode of the active compounds at the active site of Glx-I, docking studies were performed.

Results

Structure activity relationship (SAR) studies were accomplished which led to the identification of several compounds that showed potent inhibitory activity with IC50 values below 10 μM. Among the compounds tested, compounds (E)-2-hydroxy-5-((4-sulfamoylphenyl)diazenyl)benzoic acid (26) and (E)-4-((8-hydroxyquinolin-5-yl)diazenyl) benzenesulfonamide (28) displayed potent Glx-I inhibitory activity with IC50 values of 0.39 μM and 1.36 µM, respectively. Docking studies of compounds 26 and 28 were carried out to illustrate the binding mode of the molecules into the Glx-I active site.

Conclusion

Our results show that compounds 26 and 28 displayed potent Glx-I inhibitory activity and can bind the Glx-I well. These findings should lead us to discover new classes of compounds with better Glx-I inhibition.

Food-Related Carbonyl Stress in Cardiometabolic and Cancer Risk Linked to Unhealthy Modern Diet

Carbonyl stress is a condition characterized by an increase in the steady-state levels of reactive carbonyl species (RCS) that leads to accumulation of their irreversible covalent adducts with biological molecules. RCS are generated by the oxidative cleavage and cellular metabolism of lipids and sugars. In addition to causing damage directly, the RCS adducts, advanced glycation end-products (AGEs) and advanced lipoxidation end-products (ALEs), cause additional harm by eliciting chronic inflammation through receptor-mediated mechanisms. Hyperglycemia- and dyslipidemia-induced carbonyl stress plays a role in diabetic cardiovascular complications and diabetes-related cancer risk. Moreover, the increased dietary exposure to AGEs/ALEs could mediate the impact of the modern, highly processed diet on cardiometabolic and cancer risk. Finally, the transient carbonyl stress resulting from supraphysiological postprandial spikes in blood glucose and lipid levels may play a role in acute proinflammatory and proatherogenic changes occurring after a calorie dense meal. These findings underline the potential importance of carbonyl stress as a mediator of the cardiometabolic and cancer risk linked to today’s unhealthy diet. In this review, current knowledge in this field is discussed along with future research courses to offer new insights and open new avenues for therapeutic interventions to prevent diet-associated cardiometabolic disorders and cancer.

Diet and Obesity-Induced Methylglyoxal Production and Links to Metabolic Disease

The obesity rate in the United States is 42.4% and has become a national epidemic. Obesity is a complex condition that is influenced by socioeconomic status, ethnicity, genetics, age, and diet. Increased consumption of a Western diet, one that is high in processed foods, red meat, and sugar content, is associated with elevated obesity rates. Factors that increase obesity risk, such as socioeconomic status, also increase consumption of a Western diet because of a limited access to healthier options and greater affordability of processed foods. Obesity is a public health threat because it increases the risk of several pathologies, including atherosclerosis, diabetes, and cancer. The molecular mechanisms linking obesity to disease onset and progression are not well understood, but a proposed mechanism is physiological changes caused by altered lipid peroxidation, glycolysis, and protein metabolism. These metabolic pathways give rise to reactive molecules such as the abundant electrophile methylglyoxal (MG), which covalently modifies nucleic acids and proteins. MG-adducts are associated with obesity-linked pathologies and may have potential for biomonitoring to determine the risk of disease onset and progression. MG-adducts may also play a role in disease progression because they are mutagenic and directly impact protein stability and function. In this review, we discuss how obesity drives metabolic alterations, how these alterations lead to MG production, the association of MG-adducts with disease, and the potential impact of MG-adducts on cellular function.

Glyoxalase 1 and protein kinase Cλ as potential therapeutic targets for late-stage breast cancer

Cancer cells upregulate the expression levels of glycolytic enzymes in order to reach the increased glycolysis required. One such upregulated glycolytic enzyme is glyoxalase 1 (GLO 1), which catalyzes the conversion of toxic methylglyoxal to nontoxic S-D-lactoylglutathione. Protein kinase Cλ (PKCλ) is also upregulated in various types of cancer and is involved in cancer progression. In the present study, the association between enhanced glycolysis and PKCλ in breast cancer was investigated. In human breast cancer, high GLO 1 expression was associated with high PKCλ expression at the protein (P<0.01) and mRNA levels (P<0.01). Furthermore, Wilcoxon and Cox regression model analysis revealed that patients with stage III-IV tumors with high GLO 1 and PKCλ expression had poor overall survival compared with patients expressing lower levels of these genes [P=0.040 (Gehan-Breslow generalized Wilcoxon test) and P=0.031 (hazard ratio, 2.36; 95% confidence interval, 1.08-5.16), respectively]. Treatment of MDA-MB-157 and MDA-MB-468 human basal-like breast cancer cells with TLSC702 (a GLO 1 inhibitor) and/or aurothiomalate (a PKCλ inhibitor) reduced both cell viability and tumor-sphere formation. These results suggested that GLO 1 and PKCλ were cooperatively involved in cancer progression and contributed to a poor prognosis in breast cancer. In conclusion, GLO 1 and PKCλ serve as potentially effective therapeutic targets for treatment of late-stage human breast cancer.

The Dual-Role of Methylglyoxal in Tumor Progression - Novel Therapeutic Approaches

One of the hallmarks of cancer cells is their metabolic reprogramming, which includes the preference for the use of anaerobic glycolysis to produce energy, even in presence of normal oxygen levels. This phenomenon, known as “Warburg effect”, leads to the increased production of reactive intermediates. Among these Methylglyoxal (MGO), a reactive dicarbonyl known as the major precursor of the advanced glycated end products (AGEs), is attracting great attention. It has been well established that endogenous MGO levels are increased in several types of cancer, however the MGO contribution in tumor progression is still debated. Although an anti-cancer role was initially attributed to MGO due to its cytotoxicity, emerging evidence has highlighted its pro-tumorigenic role in several types of cancer. These apparently conflicting results are explained by the hormetic potential of MGO, in which lower doses of MGO are able to establish an adaptive response in cancer cells while higher doses cause cellular apoptosis. Therefore, the extent of MGO accumulation and the tumor context are crucial to establish MGO contribution to cancer progression. Several therapeutic approaches have been proposed and are currently under investigation to inhibit the pro-tumorigenic action of MGO. In this review, we provide an overview of the early and latest evidence regarding the role of MGO in cancer, in order to define its contribution in tumor progression, and the therapeutic strategies aimed to counteract the tumor growth.

Diabetes and Pancreatic Cancer-A Dangerous Liaison Relying on Carbonyl Stress

Both type 2 (T2DM) and type 1 (T1DM) diabetes mellitus confer an increased risk of pancreatic cancer in humans. The magnitude and temporal trajectory of the risk conferred by the two forms of diabetes are similar, suggesting a common mechanism. Carbonyl stress is a hallmark of hyperglycemia and dyslipidemia, which accompanies T2DM, prediabetes, and obesity. Accumulating evidence demonstrates that diabetes promotes pancreatic ductal adenocarcinoma (PDAC) in experimental models of T2DM, a finding recently confirmed in a T1DM model. The carbonyl stress markers advanced glycation end-products (AGEs), the levels of which are increased in diabetes, were shown to markedly accelerate tumor development in a mouse model of Kras-driven PDAC. Consistently, inhibition of AGE formation by trapping their carbonyl precursors (i.e., reactive carbonyl species, RCS) prevented the PDAC-promoting effect of diabetes. Considering the growing attention on carbonyl stress in the onset and progression of several cancers, including breast, lung and colorectal cancer, this review discusses the mechanisms by which glucose and lipid imbalances induce a status of carbonyl stress, the oncogenic pathways activated by AGEs and their precursors RCS, and the potential use of carbonyl-scavenging agents and AGE inhibitors in PDAC prevention and treatment, particularly in high-risk diabetic individuals.

LncRNA OIP5-AS1 Promotes Breast Cancer Progression by Regulating miR-216a-5p/GLO1

BACKGROUND

Breast cancer is a familiar malignant tumor, which is a great threat to women's life. Long noncoding RNA Opa interacting protein 5-antisense RNA 1 (OIP5-AS1) has been reported to be associated with numerous cancers. This study aimed to explore the role of OIP5-AS1 and the mechanism of its action in the progression of breast cancer.

METHODS

The expression of OIP5-AS1 and miR-216a-5p was detected by quantitative real-time polymerase chain reaction. Cell proliferation, apoptosis, migration, or invasion was assessed by 4-5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide, flow cytometry, or transwell assay, respectively. The binding sites were predicted by bioinformatics tool starBase2.0 (http://starbase.sysu.edu.cn/starbase2/index.php). The interaction between miR-216a-5p and OIP5-AS1 or glyoxalase 1 (GLO1) was confirmed by dual-luciferase reporter assay. The expression of GLO1 was quantified by Western blot. Nude mouse tumorigenicity assays were conducted to verify the role of OIP5-AS1 in vivo.

RESULTS

OIP5-AS1 and GLO1 were highly expressed in both clinical tumor tissues and cell lines, whereas miR-216a-5p was downregulated. Knockdown of OIP5-AS1 suppressed proliferation, migration, and invasion but promoted apoptosis of breast cancer cells. MiR-216a-5p was a target of OIP5-AS1 and interacted with GLO1. MiR-216a-5p inhibition or GLO1 overexpression reversed the effects of OIP5-AS1 knockdown on the development of breast cancer cells. OIP5-AS1 knockdown depleted tumor growth in vivo.

CONCLUSIONS

OIP5-AS1 knockdown suppressed the progression of breast cancer by inducing GLO1 expression via competitively binding to miR-216a-5p, suggesting that OIP5-AS1 was a hopeful biomarker for the therapy of breast cancer.

Glyoxalase 1 expression analysis by immunohistochemistry in breast cancer

Glyoxalase-1 (GLO-1) is the key enzyme in aldehyde defence in cancer cells. We here evaluated the prognostic impact and association with clinico-pathological parameters and relapse-free as well as overall survival in tumor samples from 187 breast cancer patients. The determined GLO1-immunoreactive score (GLO1-IRS) did not correlate with parameters such as grading, size, hormone receptors or ki67. However, an association of GLO1-IRS with the advanced glycation end product N^ε-(carboxymethyl)lysine (p = 0.07) and HER2 (p = 0.06), and a strong correlation with VEGF (p = 0.008) was found. In survival analysis, no significant impact of GLO-1 IRS could be deduced for all patients. However, GLO1-IRS correlated with treatment by radiotherapy (p = 0.008) and high GLO1-IRS predicted a shorter relapse free survival after radiotherapy (log-rank p = 0.067). METABRIC- and TCGA expression-data were analyzed for correlation of regulatory genes of the NF-κB-pathway (RELA, RELB, IRAK1), the oxidative-stress associated transcription factor nrf2 (NFE2L2), the receptor for AGEs (AGER, RAGE) as well as enzymes associated with aldehyde defense. Here, RELA, RELB and NFE2L2 correlated significantly with GLO1 expression, but there were conflicting results between the two data sources. In conclusion, GLO1 was highly expressed in cancer cells, correlated surprisingly weak with survival, but we could show a positive association with the AGE CML as well as VEGF. Gene expression data suggest a regulation of GLO-1 mRNA via both, inflammation (NF-kB) and oxidative stress (NFE2L2) in tumors.

Diabetes promotes invasive pancreatic cancer by increasing systemic and tumour carbonyl stress in KrasG12D/+ mice

Background

Type 1 and 2 diabetes confer an increased risk of pancreatic cancer (PaC) of similar magnitude, suggesting a common mechanism. The recent finding that PaC incidence increases linearly with increasing fasting glucose levels supports a central role for hyperglycaemia, which is known to cause carbonyl stress and advanced glycation end-product (AGE) accumulation through increased glycolytic activity and non-enzymatic reactions. This study investigated the impact of hyperglycaemia on invasive tumour development and the underlying mechanisms involved.

Methods

Pdx1-Cre;LSL-Kras^G12D/+ mice were interbred with mitosis luciferase reporter mice, rendered diabetic with streptozotocin and treated or not with carnosinol (FL-926-16), a selective scavenger of reactive carbonyl species (RCS) and, as such, an inhibitor of AGE formation. Mice were monitored for tumour development by in vivo bioluminescence imaging. At the end of the study, pancreatic tissue was collected for histology/immunohistochemistry and molecular analyses. Mechanistic studies were performed in pancreatic ductal adenocarcinoma cell lines challenged with high glucose, glycolysis- and glycoxidation-derived RCS, their protein adducts AGEs and sera from diabetic patients.

Results

Cumulative incidence of invasive PaC at 22 weeks of age was 75% in untreated diabetic vs 25% in FL-926-16-gtreated diabetic and 8.3% in non-diabetic mice. FL-926-16 treatment suppressed systemic and pancreatic carbonyl stress, extracellular signal-regulated kinases (ERK) 1/2 activation, and nuclear translocation of Yes-associated protein (YAP) in pancreas. In vitro, RCS scavenging and AGE elimination completely inhibited cell proliferation stimulated by high glucose, and YAP proved essential in mediating the effects of both glucose-derived RCS and their protein adducts AGEs. However, RCS and AGEs induced YAP activity through distinct pathways, causing reduction of Large Tumour Suppressor Kinase 1 and activation of the Epidermal Growth Factor Receptor/ERK signalling pathway, respectively.

Conclusions

An RCS scavenger and AGE inhibitor prevented the accelerating effect of diabetes on PainINs progression to invasive PaC, showing that hyperglycaemia promotes PaC mainly through increased carbonyl stress. In vitro experiments demonstrated that both circulating RCS/AGEs and tumour cell-derived carbonyl stress generated by excess glucose metabolism induce proliferation by YAP activation, hence providing a molecular mechanism underlying the link between diabetes and PaC (and cancer in general).

Circulating free methylglyoxal as a metabolic tumor biomarker in a rat colon adenocarcinoma model

Since the 1956 hypothesis of Otto Warburg, aerobic glycolysis has been recognized as a metabolic hallmark of cancer. Because methylglyoxal (MG) is a naturally occurring waste metabolite of glycolysis, we measured blood levels of this molecule in colon cancer-bearing rats. To compare the blood levels of free MG in cancerous and healthy animals,the present study used a dedicated tumor graft model consisting of the subcutaneous administration in syngenic BD-IX rats of a tumorigenic cell clone (PROb) and another non-tumorigenic clone (REGb) derived from the same tumor. Rats grafted with the PROb growing tumor cell clone exhibited a statistically significant increase in free MG blood levels (P=0.003), whereas rats transplanted with the REGb non-growing tumor cell clone exhibited normal MG values. The present study (first of three parts) suggests that cancer cells can produce and release free MG at higher levels than normal cells, making MG a putative novel metabolic biomarker of cancer.

Hypermetabolism of glutathione, glutamate and ornithine via redox imbalance in methylglyoxal-induced peritoneal injury rats

Peritoneal dialysis (PD) is a blood purification treatment for patients with reduced renal function. However, the peritoneum is exposed to oxidative stress during PD and long-term PD results in peritoneal damage, leading to the termination of PD. Methylglyoxal (MGO) contained in commercial PD fluids is a source of strong oxidative stress. The aim of this study was to clarify the mechanism of MGO-induced peritoneal injury using metabolome analysis in rats. We prepared peritoneal fibrosis rats by intraperitoneal administration of PD fluids containing MGO for 21 days. As a result, MGO-induced excessive proliferation of mesenchymal cells with an accumulation of advanced glycation end-products (AGEs) at the surface of the thickened peritoneum in rats. The effluent levels of methionine sulfoxide, an oxidative stress marker and glutathione peroxidase activity were increased in the MGO-treated rats. The levels of glutathione, glutamate, aspartate, ornithine and AGEs were also increased in these rats. MGO upregulated the gene expression of transporters and enzymes related to the metabolism of glutathione, glutamate and ornithine in the peritoneum. These results suggest that MGO may induce peritoneal injury with mesenchymal cell proliferation via increased redox metabolism, directly or through the formation of AGEs during PD.

Methylglyoxal, a potent inducer of AGEs, connects between diabetes and cancer

Diabetes is one of the most frequent diseases throughout the world and its incidence is predicted to exponentially progress in the future. This metabolic disorder is associated with major complications such as neuropathy, retinopathy, atherosclerosis, and diabetic nephropathy, the severity of which correlates with hyperglycemia, suggesting that they are triggered by high glucose condition. Reducing sugars and reactive carbonyl species such as methylglyoxal (MGO) lead to glycation of proteins, lipids and DNA and the gradual accumulation of advanced glycation end products (AGEs) in cells and tissues. While AGEs are clearly implicated in the pathogenesis of diabetes complications, their potential involvement during malignant tumor development, progression and resistance to therapy is an emerging concept. Meta-analysis studies established that patients with diabetes are at higher risk of developing cancer and show a higher mortality rate than cancer patients free of diabetes. In this review, we highlight the potential connection between hyperglycemia-associated AGEs formation on the one hand and the recent evidence of pro-tumoral effects of MGO stress on the other hand. We also discuss the marked interest in anti-glycation compounds in view of their strategic use to treat diabetic complications but also to protect against augmented cancer risk in patients with diabetes.

Methylglyoxal, a glycolysis metabolite, triggers metastasis through MEK/ERK/SMAD1 pathway activation in breast cancer

BACKGROUND

Elevated aerobic glycolysis rate is a biochemical alteration associated with malignant transformation and cancer progression. This metabolic shift unavoidably generates methylglyoxal (MG), a potent inducer of dicarbonyl stress through the formation of advanced glycation end products (AGEs). We have previously shown that the silencing of glyoxalase 1 (GLO1), the main MG detoxifying enzyme, generates endogenous dicarbonyl stress resulting in enhanced growth and metastasis in vivo. However, the molecular mechanisms through which MG stress promotes metastasis development remain to be unveiled.

METHODS

In this study, we used RNA sequencing analysis to investigate gene-expression profiling of GLO1-depleted breast cancer cells and we validated the regulated expression of selected genes of interest by RT-qPCR. Using in vitro and in vivo assays, we demonstrated the acquisition of a pro-metastatic phenotype related to dicarbonyl stress in MDA-MB-231, MDA-MB-468 and MCF7 breast cancer cellular models. Hyperactivation of MEK/ERK/SMAD1 pathway was evidenced using western blotting upon endogenous MG stress and exogenous MG treatment conditions. MEK and SMAD1 regulation of MG pro-metastatic signature genes in breast cancer cells was demonstrated by RT-qPCR.

RESULTS

High-throughput transcriptome profiling of GLO1-depleted breast cancer cells highlighted a pro-metastatic signature that establishes novel connections between MG dicarbonyl stress, extracellular matrix (ECM) remodeling by neoplastic cells and enhanced cell migration. Mechanistically, we showed that these metastasis-related processes are functionally linked to MEK/ERK/SMAD1 cascade activation in breast cancer cells. We showed that sustained MEK/ERK activation in GLO1-depleted cells notably occurred through the down-regulation of the expression of dual specificity phosphatases in MG-stressed breast cancer cells. The use of carnosine and aminoguanidine, two potent MG scavengers, reversed MG stress effects in in vitro and in vivo experimental settings.

CONCLUSIONS

These results uncover for the first time the key role of MG dicarbonyl stress in the induction of ECM remodeling and the activation of migratory signaling pathways, both in favor of enhanced metastatic dissemination of breast cancer cells. Importantly, the efficient inhibition of mitogen-activated protein kinase (MAPK) signaling using MG scavengers further emphasizes the need to investigate their therapeutic potential across different malignancies.

Glyoxalase 1 gene is highly expressed in basal-like human breast cancers and contributes to survival of ALDH1-positive breast cancer stem cells

Glyoxalase 1 (GLO1) is a ubiquitous enzyme involved in the detoxification of methylglyoxal, a cytotoxic byproduct of glycolysis that induces apoptosis. In this study, we found that GLO1 gene expression correlates with neoplasm histologic grade (χ 2 test, p = 0.002) and is elevated in human basal-like breast cancer tissues. Approximately 90% of basal-like cancers were grade 3 tumors highly expressing both GLO1 and the cancer stem cell marker ALDH1A3. ALDH1high cells derived from the MDA-MB 157 and MDA-MB 468 human basal-like breast cancer cell lines showed elevated GLO1 activity. GLO1 inhibition using TLSC702 suppressed ALDH1high cell viability as well as the formation of tumor-spheres by ALDH1high cells. GLO1 knockdown using specific siRNAs also suppressed ALDH1high cell viability, and both TLSC702 and GLO1 siRNA induced apoptosis in ALDH1high cells. These results suggest GLO1 is essential for the survival of ALDH1-positive breast cancer stem cells. We therefore conclude that GLO1 is a potential therapeutic target for treatment of basal-like breast cancers.

Methylglyoxal at metronomic doses sensitizes breast cancer cells to doxorubicin and cisplatin causing synergistic induction of programmed cell death and inhibition of stemness

Potent anticancer activity coupled with absence of toxicity at therapeutic dose established the glycolytic metabolite, methylglyoxal, as a promising candidate against malignant neoplasia. In this preclinical study we illustrate the applicability of methylglyoxal in formulating an optimally designed combination regimen with chemotherapeutic drugs against breast cancer. Results demonstrated a synergistic augmentation in doxorubicin and cisplatin mediated cytotoxicity in human breast cancer cell lines MDA MB 231 & MCF 7 with methylglyoxal co-treatment at metronomic concentrations. The cell death due to combination treatment was significantly prevented by N-Acetylcysteine and the synergistic effects were attenuated in presence of inhibitors for apoptosis and necroptosis, in MDA MB 231 and MCF 7 cells, respectively. Additionally, acridine orange staining and immunoblotting with LC3B antibody indicated the suppression of doxorubicin induced autophagy flux with methylglyoxal co-treatment. This report documents for the first time the preferential targeting of breast cancer stem cells by methylglyoxal. Combination treatment with doxorubicin or cisplatin hindered mammosphere forming efficiency and inclusively eliminated both cancer stem as well as non-stem cancer cells. The synergistic effect was validated in Ehrlich mammary carcinoma cell induced murine ascites model and the combination advantage in vivo was achieved without any additional deleterious effect to liver and kidney. Our present study evidences the implications of methylglyoxal inclusion in adjuvant multimodal chemotherapeutics against breast cancer and offers noteworthy insights into the possible outcome.

Glyoxalase 1 sustains the metastatic phenotype of prostate cancer cells via EMT control

Metastasis is the primary cause of death in prostate cancer (PCa) patients. Effective therapeutic intervention in metastatic PCa is undermined by our poor understanding of its molecular aetiology. Defining the mechanisms underlying PCa metastasis may lead to insights into how to decrease morbidity and mortality in this disease. Glyoxalase 1 (Glo1) is the detoxification enzyme of methylglyoxal (MG), a potent precursor of advanced glycation end products (AGEs). Hydroimidazolone (MG-H1) and argpyrimidine (AP) are AGEs originating from MG-mediated post-translational modification of proteins at arginine residues. AP is involved in the control of epithelial to mesenchymal transition (EMT), a crucial determinant of cancer metastasis and invasion, whose regulation mechanisms in malignant cells are still emerging. Here, we uncover a novel mechanism linking Glo1 to the maintenance of the metastatic phenotype of PCa cells by controlling EMT by engaging the tumour suppressor miR-101, MG-H1-AP and TGF-β1/Smad signalling. Moreover, circulating levels of Glo1, miR-101, MG-H1-AP and TGF-β1 in patients with metastatic compared with non-metastatic PCa support our in vitro results, demonstrating their clinical relevance. We suggest that Glo1, together with miR-101, might be potential therapeutic targets for metastatic PCa, possibly by metformin administration.

A novel monoclonal antibody targeting carboxymethyllysine, an advanced glycation end product in atherosclerosis and pancreatic cancer

Advanced glycation end products are formed by non-enzymatic reactions between proteins and carbohydrates, causing irreversible lysine and arginine alterations that severely affect protein structure and function. The resulting modifications induce inflammation by binding to scavenger receptors. An increase in advanced glycation end products is observed in a number of diseases e.g. atherosclerosis and cancer. Since advanced glycation end products also are present in healthy individuals, their detection and quantification are of great importance for usage as potential biomarkers. Current methods for advanced glycation end product detection are though limited and solely measure total glycation. This study describes a new epitope-mapped single chain variable fragment, D1-B2, against carboxymethyllysine, produced from a phage library that was constructed from mouse immunizations. The phage library was selected against advanced glycation end product targets using a phage display platform. Characterization of its binding pattern was performed using large synthetic glycated peptide and protein libraries displayed on microarray slides. D1-B2 showed a preference for an aspartic acid, three positions N-terminally from a carboxymethyllysine residue and also bound to a broad collection of glycated proteins. Positive immunohistochemical staining of mouse atherosclerotic plaques and of a tissue microarray of human pancreatic tumors confirmed the usability of the new scFv for advanced glycation end product detection in tissues. This study demonstrates a promising methodology for high-throughput generation of epitope-mapped monoclonal antibodies against AGE.

Glyoxalases in Urological Malignancies

Urological cancers include a spectrum of malignancies affecting organs of the reproductive and/or urinary systems, such as prostate, kidney, bladder, and testis. Despite improved primary prevention, detection and treatment, urological cancers are still characterized by an increasing incidence and mortality worldwide. While advances have been made towards understanding the molecular bases of these diseases, a complete understanding of the pathological mechanisms remains an unmet research goal that is essential for defining safer pharmacological therapies and prognostic factors, especially for the metastatic stage of these malignancies for which no effective therapies are currently being used. Glyoxalases, consisting of glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2), are enzymes that catalyze the glutathione-dependent metabolism of cytotoxic methylglyoxal (MG), thus protecting against cellular damage and apoptosis. They are generally overexpressed in numerous cancers as a survival strategy by providing a safeguard through enhancement of MG detoxification. Increasing evidence suggests that glyoxalases, especially Glo1, play an important role in the initiation and progression of urological malignancies. In this review, we highlight the critical role of glyoxalases as regulators of tumorigenesis in the prostate through modulation of various critical signaling pathways, and provide an overview of the current knowledge on glyoxalases in bladder, kidney and testis cancers. We also discuss the promise and challenges for Glo1 inhibitors as future anti-prostate cancer (PCa) therapeutics and the potential of glyoxalases as biomarkers for PCa diagnosis.

Interdependence of GLO I and PKM2 in the Metabolic shift to escape apoptosis in GLO I-dependent cancer cells

Many cancer cells undergo metabolic reprogramming known as the Warburg effect, which is characterized by a greater dependence on glycolysis for ATP generation, even under normoxic conditions. Glyoxalase I (GLO I) is a rate-limiting enzyme involved in the detoxification of cytotoxic methylglyoxal formed in glycolysis and which is known to be highly expressed in many cancer cells. Thus, specific inhibitors of GLO I are expected to be effective anticancer drugs. We previously discovered a novel GLO I inhibitor named TLSC702. Although the strong inhibitory activity of TLSC702 was observed in the in vitro enzyme assay, higher concentrations were required to induce apoptosis at the cellular level. One of the proposed reasons for this difference is that cancer cells alter the energy metabolism leading them to become more dependent on mitochondrial respiration than glycolysis (Metabolic shift) to avoid apoptosis induction. Thus, we assumed that combination of TLSC702 with shikonin-a specific inhibitor of pyruvate kinase M2 (PKM2) that acts as a driver of TCA cycle by supplying pyruvate and which is known to be specifically expressed in cancer cells-would have anticancer effects. We herein show the anticancer effects of combination treatment with TLSC702 and shikonin, and a possible anticancer mechanism.

Do all roads lead to the Rome? The glycation perspective!

Oxidative, carbonyl, and glycative stress have gained substantial attention recently for their alleged influence on cancer progression. Oxidative stress can trigger variable transcription factors, such as nuclear factor erythroid-2-related factor (Nrf2), nuclear factor kappa B (NF-κB), protein-53 (p-53), activating protein-1 (AP-1), hypoxia-inducible factor-1α (HIF-1α), β-catenin/Wnt and peroxisome proliferator-activated receptor-γ (PPAR-γ). Activated transcription factors can lead to approximately 500 different alterations in gene expression, and can alter expression patterns of inflammatory cytokines, growth factors, regulatory cell cycle molecules, and anti-inflammatory molecules. These alterations of gene expression can induce a normal cell to become a tumor cell. Glycative stress resulting from advanced glycation end products (AGEs) and reactive dicarbonyls can significantly affect cancer progression. AGEs are fashioned from the multifaceted chemical reaction of reducing sugars with a compound containing an amino group. AGEs bind to and trigger the receptor for AGEs (RAGE) through AGE-RAGE interaction, which is a major modulator of inflammation allied tumors. Dicarbonyls like, GO (glyoxal), MG (methylglyoxal) and 3-DG (3-deoxyglucosone) fashioned throughout lipid peroxidation, glycolysis, and protein degradation are viewed as key precursors of AGEs. These dicarbonyls lead to the carbonyl stress in living organisms, possibly resulting in carbonyl impairment of proteins, carbohydrates, DNA, and lipoproteins. The damage caused by carbonyls results in numerous lesions, some of which are involved in cancer pathogenesis. In this review, the effects of oxidative, carbonyl and glycative stress on cancer initiation and progression are thoroughly discussed, including probable signaling pathways and the effects on tumorigenesis.

Up-regulation of the tumor promoter Glyoxalase-1 indicates poor prognosis in breast cancer

Glyoxalase 1 (Glo1) is an enzyme that plays a role to metabolize and inactivate methylglyoxal. Previous studies also have confirmed that Glo1 is closely related with tumorigenesis, metastasis, and drug-resistant, but its prognostic value in breast cancer has never been explored. In this study, we investigated the expression of Glo1 in breast cancer cell lines and tissues using real-time PCR, western blot and immunohistochemical analysis. We found Glo1 was frequently up-regulated in human breast cancer cells and tissues, and high expression of Glo1 was associated with positive lymph node, lymphovascular invasion, and TNM stage (all P<0.05). The Kaplan-Meier survival curve demonstrated that patients with high Glo1 expression had a shorter overall survival (OS) and recurrence-free survival (RFS) (Both P<0.001) than those with low Glo1 expression. Moreover, the univariate and further multivariate analysis revealed that Glo1 expression was an independent prognostic factor for both OS and RFS of breast cancer patients. Next, with CCK-8 assay, cell apoptosis analysis, colony formation assay, transwell invasion/migration assay, and wound-healing assay, we validated knock-down of Glo1 suppressed invasion and migration and promoted apoptosis of breast cancer cells. Taken together, we demonstrated the tumor-promoter Glo1 may serve as a prognostic biomarker for breast cancer.

Hormetic potential of methylglyoxal, a side-product of glycolysis, in switching tumours from growth to death

Metabolic reprogramming toward aerobic glycolysis unavoidably favours methylglyoxal (MG) and advanced glycation end products (AGEs) formation in cancer cells. MG was initially considered a highly cytotoxic molecule with potential anti-cancer value. However, we have recently demonstrated that MG enhanced tumour growth and metastasis. In an attempt to understand this dual role, we explored MG-mediated dicarbonyl stress status in four breast and glioblastoma cancer cell lines in relation with their glycolytic phenotype and MG detoxifying capacity. In glycolytic cancer cells cultured in high glucose, we observed a significant increase of the conversion of MG to D-lactate through the glyoxalase system. Moreover, upon exogenous MG challenge, glycolytic cells showed elevated amounts of intracellular MG and induced de novo GLO1 detoxifying enzyme and Nrf2 expression. Thus, supporting the adaptive nature of glycolytic cancer cells to MG dicarbonyl stress when compared to non-glycolytic ones. Finally and consistent with the pro-tumoural role of MG, we showed that low doses of MG induced AGEs formation and tumour growth in vivo, both of which can be reversed using a MG scavenger. Our study represents the first demonstration of a hormetic effect of MG defined by a low-dose stimulation and a high-dose inhibition of tumour growth.

Synergistic inhibition of colon cancer growth by the combination of methylglyoxal and silencing of glyoxalase I mediated by the STAT1 pathway

Methylglyoxal (MG), an extremely reactive glucose metabolite, exhibits antitumor activity. Glyoxalase I (GLOI), which catalyzes MG metabolism, is associated with the progression of human malignancies. While the roles of MG or GLOI have been demonstrated in some types of cancer, their effects in colon cancer and the mechanisms underlying these effects remain largely unknown. For this study, MG and GLOI levels were manipulated in colon cancer cells and the effects on their viability, proliferation, apoptosis, migration, and invasion in vitro were quantified by Cell Counting Kit-8, colony formation assay, flow cytometry, and transwell assays. The expression levels of STAT1 pathway–associated proteins and mRNAs in these cells were quantified by western blot and qRT-PCR, respectively. The antitumor effects of MG and silencing of GLOI were investigated in vivo in a SW620 colon cancer xenograft model in BALB/c nude mice. Our findings demonstrate that MG in combination with silencing of GLOI synergistically inhibited the cancer cells’ proliferation, colony formation, migration, and invasion and induced apoptosis in vitro compared with the controls. Furthermore, these treatments up-regulated STAT1 and Bax while down-regulating Bcl-2 in vitro. MG treatment alone or in combination with silencing of GLOI also reduced the growth of the SW620 tumors in mice by up-regulation of STAT1 and Bax and down-regulation of Bcl-2. Taken together, our findings suggest that MG in combination with silencing of GLOI merits further evaluation as a targeted therapeutic strategy for colon cancer.

Glyoxalase 1 expression is associated with an unfavorable prognosis of oropharyngeal squamous cell carcinoma

Background

Glyoxalase 1 is a key enzyme in the detoxification of reactive metabolites such as methylglyoxal and induced Glyoxalase 1 expression has been demonstrated for several human malignancies. However, the regulation and clinical relevance of Glyoxalase 1 in the context of head and neck squamous cell carcinoma has not been addressed so far.

Methods

Argpyrimidine modification as a surrogate for methylglyoxal accumulation and Glyoxalase 1 expression in tumor cells was assessed by immunohistochemical staining of tissue microarrays with specimens from oropharyngeal squamous cell carcinoma patients (n = 154). Prognostic values of distinct Glyoxalase 1 staining patterns were demonstrated by Kaplan-Meier, univariate and multivariate Cox proportional hazard model analysis. The impact of exogenous methylglyoxal or a Glyoxalase 1 inhibitor on the viability of two established tumor cell lines was monitored by a colony-forming assay in vitro.

Results

Glyoxalase 1 expression in tumor cells of oropharyngeal squamous cell carcinoma patients was positively correlated with the presence of Argpyrimidine modification and administration of exogenous methylglyoxal induced Glyoxalase 1 protein levels in FaDu and Cal27 cells in vitro. Cal27 cells with lower basal and methylglyoxal-induced Glyoxalase 1 expression were more sensitive to the cytotoxic effect at high methylgyoxal concentrations and both cell lines showed a decrease in colony formation with increasing amounts of a Glyoxalase 1 inhibitor. A high and nuclear Glyoxalase 1 staining was significantly correlated with shorter progression-free and disease-specific survival, and served as an independent risk factor for an unfavorable prognosis of oropharyngeal squamous cell carcinoma patients.

Conclusions

Induced Glyoxalase 1 expression is a common feature in the pathogenesis of oropharyngeal squamous cell carcinoma and most likely represents an adaptive response to the accumulation of cytotoxic metabolites. Oropharyngeal squamous cell carcinoma patients with a high and nuclear Glyoxalase 1 staining pattern have a high risk for treatment failure, but might benefit from pharmacological targeting Glyoxalase 1 activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3367-5) contains supplementary material, which is available to authorized users.

Induction of mitochondrial apoptotic pathway in triple negative breast carcinoma cells by methylglyoxal via generation of reactive oxygen species

Triple negative breast cancer (TNBC) tends to form aggressive tumors associated with high mortality and morbidity which urge the need for development of new therapeutic strategies. Recently, the normal metabolite Methylglyoxal (MG) has been documented for its anti-proliferative activity against human breast cancer. However, the mode of action of MG against TNBC remains open to question. In our study, we investigated the anticancer activity of MG in MDA MB 231 and 4T1 TNBC cell lines and elucidated the underlying mechanisms. MG dose-dependently caused cell death, induced apoptosis, and generated ROS in both the TNBC cell lines. Furthermore, such effects were attenuated in presence of ROS scavenger N-Acetyl cysteine. MG triggered mitochondrial cytochrome c release in the cytosol and up-regulated Bax while down-regulated anti-apoptotic protein Bcl-2. Additionally, MG treatment down-regulated phospho-akt and inhibited the nuclear translocation of the p65 subunit of NF-κB. MG exhibited a tumor suppressive effect in BALB/c mouse 4T1 breast tumor model as well. The cytotoxic effect was studied using MTT assay. Apoptosis, ROS generation, and mitochondrial dysfunction was evaluated by flow cytometry as well as fluorescence microscopy. Western blot assay was performed to analyze proteins responsible for apoptosis. This study demonstrated MG as a potent anticancer agent against TNBC both in vitro and in vivo. The findings will furnish fresh insights into the treatment of this subgroup of breast cancer.

Piceatannol, a natural trans-stilbene compound, inhibits human glyoxalase I

Human glyoxalase I (GLO I), a rate-limiting enzyme for detoxification of methylglyoxal (MG), a by-product of glycolysis, is known to be a potential therapeutic target for cancer. Here, we searched new scaffolds from natural compounds for designing novel GLO I inhibitors and found trans-stilbene scaffold. We examined the inhibitory abilities to human GLO I of commercially available trans-stilbene compounds. Among them, piceatannol was found to have the most potent inhibitory activity against human GLO I. Piceatannol could inhibit the proliferation of human lung cancer NCI-H522 cells, which are dependent on GLO I for survival, in a dose- and time-dependent manner. In addition, piceatannol more significantly inhibited the proliferation of NCI-H522 cells than that of NCI-H460 cells, which are less dependent on GLO I. Importantly, overexpression of GLO I in NCI-H522 cells resulted in less sensitive to the antiproliferative activity of piceatannol. Taken together, this is the first report demonstrating that piceatannol inhibits GLO I activity and the GLO I-dependent proliferation of cancer cells. Furthermore, we determined a pharmacophore for novel inhibitors of human GLO I by computational simulation analyses of the binding mode of piceatannol to the enzyme hot spot in the active site. We suggest that piceatannol is a possible lead compound for the development of novel GLO I inhibitory anticancer drugs.

Methylglyoxal-Mediated Stress Correlates with High Metabolic Activity and Promotes Tumor Growth in Colorectal Cancer

Cancer cells generally rely on aerobic glycolysis as a major source of energy. Methylglyoxal (MG), a dicarbonyl compound that is produced as a side product during glycolysis, is highly reactive and induces the formation of advanced glycation end-products that are implicated in several pathologies including cancer. All mammalian cells have an enzymatic defense against MG composed by glyoxalases GLO1 and GLO2 that converts MG to d-lactate. Colorectal cancer (CRC) is one of the most frequently occurring cancers with high morbidity and mortality. In this study, we used immunohistochemistry to examine the level of MG protein adducts, in a series of 102 CRC human tumors divided into four clinical stages. We consistently detected a high level of MG adducts and low GLO1 activity in high stage tumors compared to low stage ones suggesting a pro-tumor role for dicarbonyl stress. Accordingly, GLO1 depletion in CRC cells promoted tumor growth in vivo that was efficiently reversed using carnosine, a potent MG scavenger. Our study represents the first demonstration that MG adducts accumulation is a consistent feature of high stage CRC tumors. Our data point to MG production and detoxification levels as an important molecular link between exacerbated glycolytic activity and CRC progression.

Accumulation of the advanced glycation end product carboxymethyl lysine in breast cancer is positively associated with estrogen receptor expression and unfavorable prognosis in estrogen receptor-negative cases

Advanced glycation end products (AGEs) accumulate as a result of high concentrations of reactive aldehydes, oxidative stress, and insufficient degradation of glycated proteins. AGEs are therefore accepted biomarkers for aging, diabetes, and several degenerative diseases. Due to the Warburg effect and increased oxidative stress, cancer cells frequently accumulate significant amounts of AGEs. As the accumulation of AGEs may reflect the metabolic state and receptor signaling, we evaluated the potential prognostic and predictive value of this biomarker. We used immunohistochemistry to determine the AGE Nε-carboxymethyl lysine (CML) in 213 mammary carcinoma samples and Western blotting to detect AGEs in cell cultures. Whereas no significant correlation between hormone receptor status and CML was observed in cell lines, CML accumulation in tumors was positively correlated with the presence of estrogen receptor alpha, the postmenopausal state, and age. A negative correlation was found for grade III carcinomas and triple-negative cases. In a retrospective Kaplan-Meier survival analysis, there was a statistical trend that high CML accumulation correlated with a more favorable prognosis (relapse-free survival, RFS) under tamoxifen treatment (p = 0.1). In estrogen receptor-negative cases, the high CML content was significantly correlated with an unfavorable outcome (RFS) of chemotherapy (p = 0.046). CML is a therefore a potentially predictive marker for the treatment of breast cancer patients with tamoxifen or chemotherapy.

γKlotho is a novel marker and cell survival factor in a subset of triple negative breast cancers

Over the last decade, breast cancer mortality has declined. However, triple negative breast cancer (TNBC) remains a challenging problem mostly due to early recurrence and lack of molecularly driven treatments. There is a critical need to identify subgroups of TNBC with common molecular features that can be therapeutically targeted. Here we show that in contrast to Klotho and βKlotho, the third member of the Klotho protein family, γKlotho, is overexpressed in more than 60% of TNBCs and correlates with poorer disease progression. Furthermore, we find that γKlotho is expressed in a subset of TNBC cell lines promoting cell growth. Importantly, we demonstrate that in these cells γKlotho is necessary for cell survival and that its depletion leads to constitutive ERK activation, cell cycle arrest and apoptosis. Interestingly, we observe increased oxidative stress in γKlotho-depleted cells suggesting that γKlotho enables cancer cells to cope with an oxidative environment and that cells become dependent on its expression to maintain this survival advantage. These findings indicate that γKlotho might be a potential marker for patients that would benefit from treatments that alter oxidative stress and constitutes a novel drug target for a subset of TN breast cancers.

Altered metabolite levels in cancer: implications for tumour biology and cancer therapy

Altered cell metabolism is a characteristic feature of many cancers. Aside from well-described changes in nutrient consumption and waste excretion, altered cancer cell metabolism also results in changes to intracellular metabolite concentrations. Increased levels of metabolites that result directly from genetic mutations and cancer-associated modifications in protein expression can promote cancer initiation and progression. Changes in the levels of specific metabolites, such as 2-hydroxyglutarate, fumarate, succinate, aspartate and reactive oxygen species, can result in altered cell signalling, enzyme activity and/or metabolic flux. In this Review, we discuss the mechanisms that lead to changes in metabolite concentrations in cancer cells, the consequences of these changes for the cells and how they might be exploited to improve cancer therapy.

Methylglyoxal, a glycolysis side-product, induces Hsp90 glycation and YAP-mediated tumor growth and metastasis

Metabolic reprogramming toward aerobic glycolysis unavoidably induces methylglyoxal (MG) formation in cancer cells. MG mediates the glycation of proteins to form advanced glycation end products (AGEs). We have recently demonstrated that MG-induced AGEs are a common feature of breast cancer. Little is known regarding the impact of MG-mediated carbonyl stress on tumor progression. Breast tumors with MG stress presented with high nuclear YAP, a key transcriptional co-activator regulating tumor growth and invasion. Elevated MG levels resulted in sustained YAP nuclear localization/activity that could be reverted using Carnosine, a scavenger for MG. MG treatment affected Hsp90 chaperone activity and decreased its binding to LATS1, a key kinase of the Hippo pathway. Cancer cells with high MG stress showed enhanced growth and metastatic potential in vivo. These findings reinforce the cumulative evidence pointing to hyperglycemia as a risk factor for cancer incidence and bring renewed interest in MG scavengers for cancer treatment.

Oxidative stress and glyoxalase I activity mediate dicarbonyl toxicity in MCF-7 mamma carcinoma cells and a tamoxifen resistant derivative

BACKGROUND

Acquired tamoxifen resistance is a significant problem in estrogen receptor positive breast cancer. In a cellular model, tamoxifen resistance was associated with increased sensitivity towards toxic dicarbonyls and reduced free sulfhydryl group content. We here analyzed the role of oxidative stress and glyoxalase I activity on dicarbonyl resistance and the significance of glyoxalase I expression for survival.

METHODS

Reactive oxygen species were determined by 2,7-dihydrochlorofluorescein diacetate. Inhibitors for NADPH-oxidase (diphenyleneiodonium), p38 MAPK (SB203580) and ERK1/2 (UO126) were applied to investigate interactions of these signaling molecules. N-acetyl cysteine was used to evaluate the effect of oxidative stress on cell viability, which was assessed by the resazurin assay. Gene expression was analyzed by real time qRT-PCR. Glyoxalase activity was inhibited by the specific inhibitor CS-0683 and siRNA. The relevance of glyoxalase 1 mRNA abundance on survival of breast cancer patients was evaluated by the KM-plotter web interface.

RESULTS

α-Oxo-aldehydes caused an immediate increase in reactive oxygen species where the tamoxifen resistant cell line (TamR) responded at lower concentrations than the MCF-7 parental cell line. Inhibitor studies placed ROS production by NADPH-oxidase downstream of p38 MAPK. The antioxidant N-acetyl cysteine (NAC) increased survival, whereas glyoxalase (GLO1) inhibition increased dicarbonyl toxicity. GLO1 mRNA abundance was correlated with unfavorable prognosis of breast cancer patients.

CONCLUSIONS

Dicarbonyl toxicity was mediated by oxidative stress and GLO1 activity determines aldehyde toxicity in tamoxifen resistant cells.

GENERAL SIGNIFICANCE

Glyoxalases might be predictive biomarkers for tamoxifen resistance and a putative target for the treatment of tamoxifen resistant breast cancer patients.

Improved Mitochondrial and Methylglyoxal-Related Metabolisms Support Hyperproliferation Induced by 50 Hz Magnetic Field in Neuroblastoma Cells

Extremely low frequency magnetic fields (ELF-MF) are common environmental agents that are suspected to promote later stages of tumorigenesis, especially in brain-derived malignancies. Even though ELF magnetic fields have been previously linked to increased proliferation in neuroblastoma cells, no previous work has studied whether ELF-MF exposure may change key biomolecular features, such as anti-glycative defence and energy re-programming, both of which are currently considered as crucial factors involved in the phenotype and progression of many malignancies. Our study investigated whether the hyperproliferation that is induced in SH-SY5Y human neuroblastoma cells by a 50 Hz, 1 mT ELF magnetic field is supported by an improved defense towards methylglyoxal (MG), which is an endogenous cancer-static and glycating α-oxoaldehyde, and by rewiring of energy metabolism. Our findings show that not only the ELF magnetic field interfered with the biology of neuron-derived malignant cells, by de-differentiating further the cellular phenotype and by increasing the proliferative activity, but also triggered cytoprotective mechanisms through the enhancement of the defense against MG, along with a more efficient management of metabolic energy, presumably to support the rapid cell outgrowth. Intriguingly, we also revealed that the MF-induced bioeffects took place after an initial imbalance of the cellular homeostasis, which most likely created a transient unstable milieu. The biochemical pathways and molecular targets revealed in this research could be exploited for future approaches aimed at limiting or suppressing the deleterious effects of ELF magnetic fields. J. Cell. Physiol. 231: 2014-2025, 2016. © 2016 Wiley Periodicals, Inc.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.