Targeting the Glyoxalase Pathway Enhances TRAIL Efficacy in Cancer Cells by Downregulating the Expression of Antiapoptotic Molecules

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.

Time-Dependent Changes in Protein Composition of Medial Prefrontal Cortex in Rats with Neuropathic Pain

Chronic pain is associated with time-dependent structural and functional reorganization of the prefrontal cortex that may reflect adaptive pain compensatory and/or maladaptive pain-promoting mechanisms. However, the molecular underpinnings of these changes and whether there are time-dependent relationships to pain progression are not well characterized. In this study, we analyzed protein composition in the medial prefrontal cortex (mPFC) of rats at two timepoints after spinal nerve ligation (SNL) using two-dimensional gel electrophoresis (2D-ELFO) and liquid chromatography with tandem mass spectrometry (LC–MS/MS). SNL, but not sham-operated, rats developed persistent tactile allodynia and thermal hyperalgesia, confirming the presence of experimental neuropathic pain. Two weeks after SNL (early timepoint), we identified 11 proteins involved in signal transduction, protein transport, cell homeostasis, metabolism, and apoptosis, as well as heat-shock proteins and chaperones that were upregulated by more than 1.5-fold compared to the sham-operated rats. Interestingly, there were only four significantly altered proteins identified at 8 weeks after SNL (late timepoint). These findings demonstrate extensive time-dependent modifications of protein expression in the rat mPFC under a chronic neuropathic pain state that might underlie the evolution of chronic pain characterized by early pain-compensatory and later aberrant mechanisms.

Glyoxalase pathway is required for normal liver-stage proliferation of Plasmodium berghei

The glyoxalase system is a ubiquitous detoxification pathway of methylglyoxal, a cytotoxic byproduct of glycolysis. Actively proliferating cells, such as cancer cells, depend on their energy metabolism for glycolysis. Therefore, the glyoxalase system has been evaluated as a target of anticancer drugs. The malaria sporozoite, which is the infective stage of the malaria parasite, actively proliferates and produces thousands of merozoites within 2-3 days in hepatocytes. This is the first step of infection in mammalian hosts. The glyoxalase system appears to play an important role in this active proliferation stage of the malaria parasite in hepatocytes. In this study, we aimed to dissect the role of the glyoxalase system in malaria parasite proliferation in hepatocytes to examine its potential as a target of malaria prevention using a reverse genetics approach. The malaria parasite possesses a glyoxalase system, comprised of glyoxalases and GloI-like protein, in the cytosol and apicoplast. We generated cytosolic glyoxalase II (cgloII) knockout, apicoplast targeted glyoxalase gloII (tgloII) knockout, and cgloII and tgloII double-knockout parasites and performed their phenotypic analysis. We did not observe any defects in the cgloII or tgloII knockout parasites. In contrast, we observed approximately 90% inhibition of the liver-stage proliferation of cgloII and tgloII double-knockout parasites in vivo. These findings suggest that although the glyoxalase system is dispensable, it plays an important role in parasite proliferation in hepatocytes. Additionally, the results indicate a complementary relationship between the cytosolic and apicoplast glyoxalase pathways. We expect that the parasite utilizes a system similar to that observed in cancer cells to enable its rapid proliferation in hepatocytes; this process could be targeted in the development of novel strategies to prevent malaria.

Genomic GLO1 deletion modulates TXNIP expression, glucose metabolism, and redox homeostasis while accelerating human A375 malignant melanoma tumor growth

Glyoxalase 1 (encoded by GLO1) is a glutathione-dependent enzyme detoxifying the glycolytic byproduct methylglyoxal (MG), an oncometabolite involved in metabolic reprogramming. Recently, we have demonstrated that GLO1 is overexpressed in human malignant melanoma cells and patient tumors and substantiated a novel role of GLO1 as a molecular determinant of invasion and metastasis in melanoma. Here, employing NanoString™ gene expression profiling (nCounter™ 'PanCancer Progression Panel'), we report that CRISPR/Cas 9-based GLO1 deletion from human A375 malignant melanoma cells alters glucose metabolism and redox homeostasis, observable together with acceleration of tumorigenesis. Nanostring™ analysis identified TXNIP (encoding thioredoxin-interacting protein), a master regulator of cellular energy metabolism and redox homeostasis, displaying the most pronounced expression change in response to GLO1 elimination, confirmed by RT-qPCR and immunoblot analysis. TXNIP was also upregulated in CRISPR/Cas9-engineered DU145 prostate carcinoma cells lacking GLO1, and treatment with MG or a pharmacological GLO1 inhibitor (TLSC702) mimicked GLO1_KO status, suggesting that GLO1 controls TXNIP expression through regulation of MG. GLO1_KO status was characterized by (i) altered oxidative stress response gene expression, (ii) attenuation of glucose uptake and metabolism with downregulation of gene expression (GLUT1, GFAT1, GFAT2, LDHA) and depletion of related key metabolites (glucose-6-phosphate, UDP-N-acetylglucosamine), and (iii) immune checkpoint modulation (PDL1). While confirming our earlier finding that GLO1 deletion limits invasion and metastasis with modulation of EMT-related genes (e.g. TGFBI, MMP9, ANGPTL4, TLR4, SERPINF1), we observed that GLO1_KO melanoma cells displayed a shortened population doubling time, cell cycle alteration with increased M-phase population, and enhanced anchorage-independent growth, a phenotype supported by expression analysis (CXCL8, CD24, IL1A, CDKN1A). Concordantly, an accelerated growth rate of GLO1_KO tumors, accompanied by TXNIP overexpression and metabolic reprogramming, was observable in a SCID mouse melanoma xenograft model, demonstrating that A375 melanoma tumor growth and metastasis can be dysregulated in opposing ways as a consequence of GLO1 elimination.

Genetic Target Modulation Employing CRISPR/Cas9 Identifies Glyoxalase 1 as a Novel Molecular Determinant of Invasion and Metastasis in A375 Human Malignant Melanoma Cells In Vitro and In Vivo

Metabolic reprogramming is a molecular hallmark of cancer. Recently, we have reported the overexpression of glyoxalase 1 (encoded by GLO1), a glutathione-dependent enzyme involved in detoxification of the reactive glycolytic byproduct methylglyoxal, in human malignant melanoma cell culture models and clinical samples. However, the specific role of GLO1 in melanomagenesis remains largely unexplored. Here, using genetic target modulation, we report the identification of GLO1 as a novel molecular determinant of invasion and metastasis in malignant melanoma. First, A375 human malignant melanoma cells with GLO1 deletion (A375-GLO1_KO) were engineered using CRISPR/Cas9, and genetic rescue clones were generated by stable transfection of KO clones employing a CMV-driven GLO1 construct (A375-GLO1_R). After confirming GLO1 target modulation at the mRNA and protein levels (RT-qPCR, immunodetection, enzymatic activity), phenotypic characterization indicated that deletion of GLO1 does not impact proliferative capacity while causing significant sensitization to methylglyoxal-, chemotherapy-, and starvation-induced cytotoxic stress. Employing differential gene expression array analysis (A375-GLO1_KO versus A375-GLO1_WT), pronounced modulation of epithelial--mesenchymal transition (EMT)-related genes [upregulated: CDH1, OCLN, IL1RN, PDGFRB, SNAI3; (downregulated): BMP1, CDH2, CTNNB1, FN1, FTH1, FZD7, MELTF, MMP2, MMP9, MYC, PTGS2, SNAI2, TFRC, TWIST1, VIM, WNT5A, ZEB1, and ZEB2 (up to tenfold; p < 0.05)] was observed-all of which are consistent with EMT suppression as a result of GLO1 deletion. Importantly, these expression changes were largely reversed upon genetic rescue employing A375-GLO1_R cells. Differential expression of MMP9 as a function of GLO1 status was further substantiated by enzymatic activity and ELISA analysis; phenotypic assessment revealed the pronounced attenuation of morphological potential, transwell migration, and matrigel 3D-invasion capacity displayed by A375-GLO1_KO cells, reversed again in genetic rescue clones. Strikingly, in a SCID mouse metastasis model, lung tumor burden imposed by A375-GLO1_KO cells was strongly attenuated as compared to A375-GLO1_WT cells. Taken together, these prototype data provide evidence in support of a novel function of GLO1 in melanoma cell invasiveness and metastasis, and ongoing investigations explore the function and therapeutic potential of GLO1 as a novel melanoma target.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Piperlongumine, a Novel TrxR1 Inhibitor, Induces Apoptosis in Hepatocellular Carcinoma Cells by ROS-Mediated ER Stress

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the third leading cause of cancer-related deaths globally. Despite advances in diagnosis and treatment, the incidence and mortality of HCC continue to rise. Piperlongumine (PL), an alkaloid isolated from the fruit of the long pepper, is known to selectively kill tumor tissues while sparing their normal counterparts. However, the killing effects of PL on HCC and the underlying mechanism of PL are not clear. We report that PL may interact with thioredoxin reductase 1 (TrxR1), an important selenocysteine (Sec)-containing antioxidant enzyme, and induce reactive oxygen species (ROS)-mediated apoptosis in HCC cells. Our results suggest that PL induces a lethal endoplasmic reticulum (ER) stress response in HCC cells by targeting TrxR1 and increasing intracellular ROS levels. Notably, PL treatment reduces TrxR1 activity and tumor cell burden in vivo. Additionally, TrxR1 is significantly upregulated in existing HCC databases and available HCC clinical specimens. Taken together, these results suggest PL as a novel anticancer candidate for the treatment of HCC. More importantly, this study reveals that TrxR1 might be an effective target in treating HCC.

Developing TRAIL/TRAIL death receptor-based cancer therapies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can initiate the apoptosis pathway by binding to its associated death receptors DR4 and DR5. The activation of the TRAIL pathway in inducing tumor-selective apoptosis leads to the development of TRAIL-based cancer therapies, which include recombinant forms of TRAIL, TRAIL receptor agonists, and other therapeutic agents. Importantly, TRAIL, DR4, and DR5 can all be induced by synthetic and natural agents that activate the TRAIL apoptosis pathway in cancer cells. Thus, understanding the regulation of the TRAIL apoptosis pathway can aid in the development of TRAIL-based therapies for the treatment of human cancer.

MMSET I acts as an oncoprotein and regulates GLO1 expression in t(4;14) multiple myeloma cells

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. T(4;14) MM overexpresses multiple myeloma SET domain-containing protein (MMSET). MMSET has three major isoforms: the full-length form MMSET II and the short isoforms REIIBP and MMSET I. Here we show that the short isoform MMSET I is an oncoprotein that promoted cell survival and tumorigenesis in vitro and in vivo. Gene expression array analysis indicated that MMSET I increased glyoxalase I (GLO1) expression. Chromatin immunoprecipitation (ChIP) coupled with qPCR indicated that MMSET I bound upstream of the GLO1 transcription start site. Ectopic overexpression of MMSET I or its mutants showed MMSET I depended on its C terminus to regulate GLO1 expression. GLO1 knockdown (KD) induced apoptosis and reduced colony formation. MMSET I or GLO1 KD reduced the levels of anti-apoptosis factors such as MCL1 and BCL2. Ectopic overexpression of GLO1 resulted in the significant rescue of KMS11 cells from MMSET I KD-induced apoptosis and glycolysis inhibition. This suggested that GLO1 may be of functional importance target downstream of MMSET I. Cumulatively, our study suggests that MMSET I is an oncoprotein and potential therapeutic target for t(4;14) MM.

A cancer vaccine with dendritic cells differentiated with GM-CSF and IFNα and pulsed with a squaric acid treated cell lysate improves T cell priming and tumor growth control in a mouse model

Introduction: Ovarian cancer is one of the most lethal gynecologic cancers. Relapses after remission are common, hence novel strategies are urgently needed. Our group has previously developed a vaccination approach based on dendritic cells pulsed with HOCl-oxidized tumor lysates. Here we investigate the improvement of this vaccine strategy using squaric acid treatment of cancer cells during tumor lysate preparation and by differentiating dendritic cells in the presence of GM-CSF and IFNα.

Methods: Induction of cell death by squaric acid treatment was assessed with propidium iodide (PI) and Annexin V in ID8 tumor cells. High mobility group box 1 (HMGB1) immunogenic status was analyzed using a western blot-based method, as previously described. For immunological tests, ID8 cells expressing ovalbumin (ova-ID8) were treated with squaric acid before cell lysis. DCs prepared with the canonical GM-CSF and IL-4 differentiation cocktail or IFNα and GM-CSF were pulsed with tumor cell lysates and further matured in the presence of IFNγ and LPS (4-DCs and α-DCs respectively). DCs were then used in co-culture assays with ova-specific T cells and IFNγ and IL-4 secretion measured by ELISA. DC phenotypes were characterized by FACS. Finally, DCs were tested in an ovarian cancer mouse model measuring body weight and animal survival.

Results: Squaric acid treatment of mouse ovarian cancer cells induced tumor cell death as well as preserve HMGB1, a crucial Damage-associated molecular pattern (DAMP) signal, in its active reduced form. Squaric acid treatment of ID8-ova cells increased IFNγ and decreased IL-4 production from ova-specific T cells in co-culture experiments, promoting a more immunogenic cytokine secretion pattern. DCs differentiated in the presence of IFNα induced a considerable decrease in IL-4 production compared to canonical 4-DCs, without affecting IFNγ release. DC phenotyping demonstrated a more mature and immunogenic phenotype for IFNα-differentiated DCs. Vaccination in tumor-bearing mice showed that IFNα-differentiated DCs pulsed with squaric acid-treated lysates were the most potent at delaying tumor growth, improving animal survival.

Conclusion: We identified squaric acid as a novel immunogenic treatment of tumor cells for cancer vaccines particularly efficient in prolonging animal survival when used in combination with IFNα-differentiated DCs. These promising results support future efforts for the clinical translation of this approach.

Methylglyoxal displays colorectal cancer-promoting properties in the murine models of azoxymethane and CT26 isografts

Methylglyoxal (MG), a highly reactive carbonyl species (RCS) with pro-oxidant and proinflammatory properties, may be a colon tumor-promoting factor in food and biological systems. In the present study, we found that consumption of MG significantly deteriorated azoxymethane (AOM)-induced colonic preneoplastic lesions in ICR mice, in which biomarkers of oxidative stress and inflammation within the body and feces induced by MG-fueled carbonyl stress may have played important roles. Interestingly, exposure to MG also led to increases in the serum low-density lipoprotein (LDL)/high-density lipoprotein (HDL) ratio and fecal bile acid levels in mice, which may be critical factors involved in MG-induced colonic lesions. Additionally, MG treatment (50mg/kg body weight (BW); intraperitoneally) promoted tumor growth of CT26 isografts in mice partly by carbonyl stress-evoked protumorigenic responses, including low-grade inflammation and oxidative stress. Furthermore, primary tumor cells isolated from mice with MG-induced CT26 isografts had greater proliferative and migratory activities as well as stem-like properties compared to those isolated from the vehicle controls. Excitingly, enhanced expression or activation of proteins that modulate cell survival, proliferation, or migration/invasion was also observed in those cells. In conclusion, it is conceivable that MG-induced carbonyl stress may be the pivotal promoter involved in colon cancer progression.

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.

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.

Multiple roles of glyoxalase 1-mediated suppression of methylglyoxal glycation in cancer biology-Involvement in tumour suppression, tumour growth, multidrug resistance and target for chemotherapy

Glyoxalase 1 (Glo1) is part of the glyoxalase system in the cytoplasm of all human cells. It catalyses the glutathione-dependent removal of the endogenous reactive dicarbonyl metabolite, methylglyoxal (MG). MG is formed mainly as a side product of anaerobic glycolysis. It modifies protein and DNA to form mainly hydroimidazolone MG-H1 and imidazopurinone MGdG adducts, respectively. Abnormal accumulation of MG, dicarbonyl stress, increases adduct levels which may induce apoptosis and replication catastrophe. In the non-malignant state, Glo1 is a tumour suppressor protein and small molecule inducers of Glo1 expression may find use in cancer prevention. Increased Glo1 expression is permissive for growth of tumours with high glycolytic activity and is thereby a biomarker of tumour growth. High Glo1 expression is a cause of multi-drug resistance. It is produced by over-activation of the Nrf2 pathway and GLO1 amplification. Glo1 inhibitors are antitumour agents, inducing apoptosis and necrosis, and anoikis. Tumour stem cells and tumours with high flux of MG formation and Glo1 expression are sensitive to Glo1 inhibitor therapy. It is likely that MG-induced cell death contributes to the mechanism of action of current antitumour agents. Common refractory tumours have high prevalence of Glo1 overexpression for which Glo1 inhibitors may improve therapy.

Methylglyoxal-induced apoptosis is dependent on the suppression of c-FLIPL expression via down-regulation of p65 in endothelial cells

Methylglyoxal (MGO) is a reactive dicarbonyl metabolite of glucose, and its plasma levels are elevated in patients with diabetes. Studies have shown that MGO combines with the amino and sulphhydryl groups of proteins to form stable advanced glycation end products (AGEs), which are associated with vascular endothelial cell (EC) injury and may contribute to the progression of atherosclerosis. In this study, MGO induced apoptosis in a dose-dependent manner in HUVECs, which was attenuated by pre-treatment with z-VAD, a pan caspase inhibitor. Treatment with MGO increased ROS levels, followed by dose-dependent down-regulation of c-FLIP_L . In addition, pre-treatment with the ROS scavenger NAC prevented the MGO-induced down-regulation of p65 and c-FLIP_L , and the forced expression of c-FLIP_L attenuated MGO-mediated apoptosis. Furthermore, MGO-induced apoptotic cell death in endothelium isolated from mouse aortas. Finally, MGO was found to induce apoptosis by down-regulating p65 expression at both the transcriptional and posttranslational levels, and thus, to inhibit c-FLIP_L mRNA expression by suppressing NF-κB transcriptional activity. Collectively, this study showed that MGO-induced apoptosis is dependent on c-FLIP_L down-regulation via ROS-mediated down-regulation of p65 expression in endothelial cells.

Blockage of Glyoxalase I Inhibits Colorectal Tumorigenesis and Tumor Growth via Upregulation of STAT1, p53, and Bax and Downregulation of c-Myc and Bcl-2

GlyoxalaseI (GLOI) is an enzyme that catalyzes methylglyoxal metabolism. Overexpression of GLOI has been documented in numerous tumor tissues, including colorectal cancer (CRC). The antitumor effects of GLOI depletion have been demonstrated in some types of cancer, but its role in CRC and the mechanisms underlying this activity remain largely unknown. Our purpose was to investigate the antitumor effects of depleted GLOI on CRC in vitro and in vivo. RNA interference was used to deplete GLOI activity in four CRC cell lines. The cells' proliferation, apoptosis, migration, and invasion were assessed by using the Cell Counting Kit-8, plate colony formation assay, flow cytometry, and transwell assays. Protein and mRNA levels were analyzed by western blot and quantitative real-time PCR (qRT-PCR), respectively. The antitumor effect of GLOI depletion in vivo was investigated in a SW620 xenograft tumor model in BALB/c nude mice. Our results show that GLOI is over-expressed in the CRC cell lines. GLOI depletion inhibited the proliferation, colony formation, migration, and invasion and induced apoptosis of all CRC cells compared with the controls. The levels of signal transducer and activator of transcription 1 (STAT1), p53, and Bcl-2 assaciated X protein (Bax) were upregulated by GLOI depletion, while cellular homologue of avian myelocytomatosis virus oncogene (c-Myc) and B cell lymphoma/lewkmia-2 (Bcl-2) were downregulated. Moreover, the growth of SW620-induced CRC tumors in BALB/c nude mice was significantly attenuated by GLOI depletion. The expression levels of STAT1, p53, and Bax were increased and those of c-Myc and Bcl-2 were decreased in the GLOI-depleted tumors. Our findings demonstrate that GLOI depletion has an antitumor effect through the STAT1 or p53 signaling pathways in CRC, suggesting that GLOI is a potential therapeutic target.

Effects of methylglyoxal and glyoxalase I inhibition on breast cancer cells proliferation, invasion, and apoptosis through modulation of MAPKs, MMP9, and Bcl-2

Emerging evidence indicates that methylglyoxal (MG) can inhibit tumorigenesis. Glyoxalase I (GLOI), a MG degradation enzyme, is implicated in the progression of human malignancies. However, little is known about the roles of MG and GLOI in breast cancer. Our purpose was to investigate the anticancer effects of MG and inhibition of GLOI on breast cancer cells and the underlying mechanisms of these effects. Our findings demonstrate that cell viability, migration, invasion, colony formation, and tubule formation were significantly restrained by addition of MG or inhibition of GLOI, while apoptosis was significantly increased. Furthermore, the expression of p-JNK, p-ERK, and p-p38 was markedly upregulated by addition of MG or inhibition of GLOI, whereas MMP-9 and Bcl-2 expression levels were dramatically decreased. These effects were augmented by combined treatment with MG and inhibition of GLOI. Collectively, these data indicate that MG or inhibition of GLOI induces anticancer effects in breast cancer cells and that these effects are potentiated by combination of the 2. These effects were modulated by activation of the MAPK family and downregulation of Bcl-2 and MMP-9. These findings may provide a new approach for the treatment of breast cancer.

Silencing of survivin by YM155 induces apoptosis and growth arrest in hepatocellular carcinoma cells

Survivin overactivation is a frequent event in human hepatocellular carcinoma (HCC), due to its function in the induction of hepatocyte proliferation and apoptotic dysfunction. Recently, a novel survivin inhibitor named YM155, has demonstrated broad antitumor effects against various malignant tumors. Therefore, the present study aimed to explore how this agent may impact on HCC and elucidate its underlying mechanism of action. Immunohistochemical analysis was performed on 8 specimens of human HCC, to assess the protein expression of survivin and phosphorylated retinoblastoma tumor suppressor (p-Rb). In addition, in vitro, HepG2 and Huh7 human HCC cell lines were exposed to 100 µM YM155 for up to 72 h and the cell viability was subsequently determined using MTT assay. Furthermore, the apoptotic status of YM155-treated HCC cells was investigated by flow cytometry, and the protein levels of survivin, procaspase-3 and p-Rb in YM155-treated HCC cells were assessed by immunoblotting analysis. The results demonstrated that HCC specimens expressed high levels of survivin and p-Rb protein compared with those of adjacent noncancerous liver tissues. In vitro, YM155 significantly induced HCC cell apoptosis and growth arrest. At the protein level, YM155 markedly inhibited survivin and p-Rb expression, and elevated procaspase-3. YM155 demonstrated significant antitumor effects on HCC cells in the present study. These effects were associated with its anti-proliferative and apoptosis-induction activities. YM155 requires further investigation as a novel agent for potential use as a therapeutic strategy for the treatment of HCC.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Glyoxalase I is differentially expressed in cutaneous neoplasms and contributes to the progression of squamous cell carcinoma

Glyoxalase I (GLO1) is a methylglyoxal detoxification enzyme being implicated in the progression of multiple malignancies. However, currently, the role of GLO1 in human nonmelanoma skin tumors remains unclear. To explore the expression of GLO1 in cutaneous neoplasms and its role in the pathogenesis of skin cancers, we determined the GLO1 expression in multiple subtypes of cutaneous neoplasms and cell lines harboring different tumorigenicity. Also, the GLO1 siRNA transfection was performed in squamous cell carcinoma (SCC)-13 cells or SCC in the xenograft model. The results show that GLO1 was overexpressed by SCC, basal cell carcinoma, and verrucous carcinoma but weakly expressed by several benign neoplasms. Human papilloma virus 16 E6/E7-transfected keratinocytes expressed more GLO1 than did normal keratinocytes, although both of them had lower levels of GLO1 than SCC-13 cells. Moreover, the knockdown of GLO1 by siRNA was related to enhanced apoptosis of SCC-13 cells in the presence of tumor necrosis factor-related apoptosis-inducing ligand and inhibited cell invasion and migration, which was mirrored by the suppressed growth of SCC xenografts in mice. Finally, the GLO1 regulation of SCC-13 cells might be relevant to methylglyoxal-induced p53 translocation. Therefore, GLO1 is prevailingly expressed in cutaneous neoplasms of higher malignancy and contributes to the progression of SCC.

A novel HDAC inhibitor OBP-801 and a PI3K inhibitor LY294002 synergistically induce apoptosis via the suppression of survivin and XIAP in renal cell carcinoma

Renal cell carcinoma (RCC) is resistant to traditional cancer therapies such as radiation therapy and chemotherapy. The use of targeted therapies has improved the clinical outcomes of patients with metastatic RCC. However, most patients acquire resistance against targeted therapies over time. We report that the combination of the novel histone deacetylase (HDAC) inhibitor OBP-801, also known as YM753 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 synergistically inhibits cell growth and induces apoptosis in RCC cells. This combination activated caspase-3, -8 and -9 and the pan-caspase inhibitor zVAD-fmk significantly reduced the apoptotic response to the treatment with OBP-801 and LY294002. Moreover, the combined treatment induced intracellular reactive oxygen species (ROS) and the radical scavenger N-acetyl-L-cysteine (NAC) blocked the intracellular ROS and apoptosis induced by OBP-801 and LY294002. The co-treatment with OBP-801 and LY294002 markedly decreased survivin and the X-linked inhibitor of apoptosis protein (XIAP) protein levels, but Bcl-2 family members were not altered by the OBP-801/LY294002 co-treatment. These alterations were restored by NAC treatment. The transient transfection of survivin and XIAP reduced the apoptotic response to the OBP-801/LY294002 co-treatment. Additionally, OBP-801 was significantly more effective than SAHA, another HDAC inhibitor, in the combination with LY294002 against 786-O cells. Taken together, these results strongly suggest the combination of OBP-801 and LY294002 to be a promising treatment for RCC.