An RNA-directed nucleoside anti-metabolite, 1-(3-C-ethynyl-beta-d-ribo-pentofuranosyl)cytosine (ECyd), elicits antitumor effect via TP53-induced Glycolysis and Apoptosis Regulator (TIGAR) downregulation

Is Nucleoredoxin a Master Regulator of Cellular Redox Homeostasis? Its Implication in Different Pathologies

Nucleoredoxin (NXN), an oxidoreductase enzyme, contributes to cellular redox homeostasis by regulating different signaling pathways in a redox-dependent manner. By interacting with seven proteins so far, namely disheveled (DVL), protein phosphatase 2A (PP2A), phosphofructokinase-1 (PFK1), translocation protein SEC63 homolog (SEC63), myeloid differentiation primary response gene-88 (MYD88), flightless-I (FLII), and calcium/calmodulin-dependent protein kinase II type alpha (CAMK2A), NXN is involved in the regulation of several key cellular processes, including proliferation, organogenesis, cell cycle progression, glycolysis, innate immunity and inflammation, motility, contraction, protein transport into the endoplasmic reticulum, neuronal plasticity, among others; as a result, NXN has been implicated in different pathologies, such as cancer, alcoholic and polycystic liver disease, liver fibrogenesis, obesity, Robinow syndrome, diabetes mellitus, Alzheimer’s disease, and retinitis pigmentosa. Together, this evidence places NXN as a strong candidate to be a master redox regulator of cell physiology and as the hub of different redox-sensitive signaling pathways and associated pathologies. This review summarizes and discusses the current insights on NXN-dependent redox regulation and its implication in different pathologies.

Advance of structural modification of nucleosides scaffold

With Remdesivir being approved by FDA as a drug for the treatment of Corona Virus Disease 2019 (COVID-19), nucleoside drugs have once again received widespread attention in the medical community. Herein, we summarized modification of traditional nucleoside framework (sugar + base), traizole nucleosides, nucleoside analogues assembled by other drugs, macromolecule-modified nucleosides, and their bioactivity rules. 2'-"Ara"-substituted by -F or -CN group, and 3'-"ara" substituted by acetylenyl group can greatly influence their anti-tumor activities. Dideoxy dehydrogenation of 2',3'-sites can enhance antiviral efficiencies. Acyclic nucleosides and L-type nucleosides mainly represented antiviral capabilities. 5-F Substituted uracil analogues exihibit anti-tumor effects, and the substrates substituted by -I, -CF3, bromovinyl group usually show antiviral activities. The sugar coupled with 1-N of triazolid usually displays anti-tumor efficiencies, while the sugar coupled with 2-N of triazolid mainly represents antiviral activities. The nucleoside analogues assembled by cholesterol, polyethylene glycol, fatty acid and phospholipid would improve their bioavailabilities and bioactivities, or reduce their toxicities.

TIGAR Promotes Tumorigenesis and Protects Tumor Cells From Oxidative and Metabolic Stresses in Gastric Cancer

Cancer cells adopt glycolysis to facilitate the generation of biosynthetic substrates demanded by cell proliferation and growth, and to adapt to stress conditions such as excessive reactive oxygen species (ROS) accumulation. TIGAR (TP53-induced glycolysis and apoptosis regulator) is a fructose-2,6-bisphosphatase that is regulated by p53. TIGAR functions to inhibit glycolysis and promote antioxidative activities, which assists the generation of NADPH to maintain the levels of GSH and thus reduces intracellular ROS. However, the functions of TIGAR in gastric cancer (GC) remain unclear. TIGAR expression levels were detected by immunoblotting and immunohistochemistry in gastric cancer samples, along with four established cell lines of GC. The functions of TIGAR were determined by utilizing shRNA-mediated knockdown experiments. The NADPH/NADP+ ratio, ROS, mitochondrial ATP production, and phosphorus oxygen ratios were determined in TIGAR-depleted cells. Xenograft experiment was conducted with BALB/c nude mice. TIGAR was up-regulated compared with corresponding non-cancerous tissues in primary GCs. TIGAR knockdown significantly reduced cell proliferation and increased apoptosis. TIGAR protected cancer cells from oxidative stress-caused damages, but also glycolysis defects. TIGAR also increased the production of NADPH in gastric cancer cells. TIGAR knockdown led to increased ROS production, elevated mitochondrial ATP production, and phosphorus oxygen ratios. The prognosis of high TIGAR expression patients was significantly poorer than those with low TIGAR expression. Taken together, TIGAR exhibits oncogenic features in GC, which can be evaluated as a target for intervention in the treatment of GC.

Targeting Strategies for Glucose Metabolic Pathways and T Cells in Colorectal Cancer

Colorectal cancer is a heterogeneous group of diseases that result from the accumulation of different sets of genomic alterations, together with epigenomic alterations, and it is influenced by tumor-host interactions, leading to tumor cell growth and glycolytic imbalances. This review summarizes recent findings that involve multiple signaling molecules and downstream genes in the dysregulated glycolytic pathway. This paper further discusses the role of the dysregulated glycolytic pathway in the tumor initiation, progression and the concomitant systemic immunosuppression commonly observed in colorectal cancer patients. Moreover, the relationship between colorectal cancer cells and T cells, especially CD8+ T cells, is discussed, while different aspects of metabolic pathway regulation in cancer cell proliferation are comprehensively defined. Furthermore, this study elaborates on metabolism in colorectal cancer, specifically key metabolic modulators together with regulators, glycolytic enzymes, and glucose deprivation induced by tumor cells and how they inhibit T-cell glycolysis and immunogenic functions. Moreover, metabolic pathways that are integral to T cell function, differentiation, and activation are described. Selective metabolic inhibitors or immunemodulation agents targeting these pathways may be clinically useful to increase effector T cell responses for colorectal cancer treatment. However, there is a need to identify specific antigens using a cancer patient-personalized approach and combination strategies with other therapeutic agents to effectively target tumor metabolic pathways.

Fructose 2,6-Bisphosphate in Cancer Cell Metabolism

For a long time, pioneers in the field of cancer cell metabolism, such as Otto Warburg, have focused on the idea that tumor cells maintain high glycolytic rates even with adequate oxygen supply, in what is known as aerobic glycolysis or the Warburg effect. Recent studies have reported a more complex situation, where the tumor ecosystem plays a more critical role in cancer progression. Cancer cells display extraordinary plasticity in adapting to changes in their tumor microenvironment, developing strategies to survive and proliferate. The proliferation of cancer cells needs a high rate of energy and metabolic substrates for biosynthesis of biomolecules. These requirements are met by the metabolic reprogramming of cancer cells and others present in the tumor microenvironment, which is essential for tumor survival and spread. Metabolic reprogramming involves a complex interplay between oncogenes, tumor suppressors, growth factors and local factors in the tumor microenvironment. These factors can induce overexpression and increased activity of glycolytic isoenzymes and proteins in stromal and cancer cells which are different from those expressed in normal cells. The fructose-6-phosphate/fructose-1,6-bisphosphate cycle, catalyzed by 6-phosphofructo-1-kinase/fructose 1,6-bisphosphatase (PFK1/FBPase1) isoenzymes, plays a key role in controlling glycolytic rates. PFK1/FBpase1 activities are allosterically regulated by fructose-2,6-bisphosphate, the product of the enzymatic activity of the dual kinase/phosphatase family of enzymes: 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase (PFKFB1-4) and TP53-induced glycolysis and apoptosis regulator (TIGAR), which show increased expression in a significant number of tumor types. In this review, the function of these isoenzymes in the regulation of metabolism, as well as the regulatory factors modulating their expression and activity in the tumor ecosystem are discussed. Targeting these isoenzymes, either directly or by inhibiting their activating factors, could be a promising approach for treating cancers.

miR-101 Enhances Cisplatin-Induced DNA Damage Through Decreasing Nicotinamide Adenine Dinucleotide Phosphate Levels by Directly Repressing Tp53-Induced Glycolysis and Apoptosis Regulator Expression in Prostate Cancer Cells

Tp53-induced glycolysis and apoptosis regulator (TIGAR) enhances the pentose phosphate pathway, thereby contributing directly to DNA repair due to generation of nicotinamide adenine dinucleotide phosphate (NADPH) and ribose-5-phosphate, two key precursors of DNA synthesis and repair. Targetscan database showed that miR-101 was predicted to potentially target TIGAR. Therefore, we speculated that miR-101 could enhance cisplatin-induced DNA damage by directly repressing TIGAR expression in prostate cancer cells. We found that upregulation of miR-101 inhibited viability, induced apoptosis, increased glycolysis rate and fructose-2,6-bisphosphate levels, decreased glucose-6-phosphate dehydrogenase expression and NADPH levels, and enhanced cisplatin-induced DNA damage in prostate cancer cells. We also demonstrated that TIGAR was a direct target of miR-101 by using luciferase activity assay. Furthermore, this study revealed that the roles of knockdown of TIGAR were similar to miR-101 upregulation in prostate cancer cells. Taken together, miR-101 inhibited viability, induced apoptosis, reprogramed glucose metabolism, and enhanced cisplatin-induced DNA damage through decreasing NADPH levels by directly suppressing the expression of TIGAR in prostate cancer cells.

TIGAR cooperated with glycolysis to inhibit the apoptosis of leukemia cells and associated with poor prognosis in patients with cytogenetically normal acute myeloid leukemia

Background

Cancer cells show increased glycolysis and take advantage of this metabolic pathway to generate ATP. The TP53-induced glycolysis and apoptosis regulator (TIGAR) inhibits aerobic glycolysis and protects tumor cells from intracellular reactive oxygen species (ROS)-associated apoptosis. However, the function of TIGAR in glycolysis and survival of acute myeloid leukemia cells remains unclear.

Methods

We analyzed TIGAR expression in cytogenetically normal (CN-) AML patients and the correlations with clinical and biological parameters. In vivo and in vitro, we tested whether glycolysis may induce TIGAR expression and evaluated the combination effect of glycolysis inhibitor and TIGAR knockdown on human leukemia cell proliferation.

Results

High TIGAR expression was an independent predictor of poor survival and high incidence of relapse in adult patients with CN-AML. TIGAR also showed high expression in multiple human leukemia cell lines and knockdown of TIGAR activated glycolysis through PFKFB3 upregulation in human leukemia cells. Knockdown of TIGAR inhibited the proliferation of human leukemia cells and sensitized leukemia cells to glycolysis inhibitor both in vitro and in vivo. Furthermore, TIGAR knockdown in combination with glycolysis inhibitor 2-DG led leukemia cells to apoptosis. In addition, the p53 activator Nutlin-3α showed a significant combinational effect with TIGAR knockdown in leukemia cells. However, TIGAR expression and its anti-apoptotic effects were uncoupled from overexpression of exogenous p53 in leukemia cells.

Conclusions

TIGAR might be a predictor of poor survival and high incidence of relapse in AML patients, and the combination of TIGAR inhibitors with anti-glycolytic agents may be novel therapies for the future clinical use in AML patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0360-4) contains supplementary material, which is available to authorized users.

A Nucleoside Anticancer Drug, 1-(3-C-Ethynyl-β-D-Ribo-Pentofuranosyl)Cytosine, Induces Depth-Dependent Enhancement of Tumor Cell Death in Spread-Out Bragg Peak (SOBP) of Proton Beam

The effect of 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (ECyd) on proton-induced cell death was evaluated in human lung carcinoma cell line A549 and Chinese hamster fibroblast cell line V79 to enhance relative biological effectiveness (RBE) within the spread-out Bragg peak (SOBP) of proton beams. Treatment with ECyd significantly enhanced the proton-induced loss of clonogenicity and increased senescence at the center, but not at the distal edge of SOBP. The p53-binding protein 1 foci formation assay showed that ECyd decelerated the rate of DNA double-strand break (DSB) repair at the center, but not the distal region of SOBP, suggesting that the ECyd-induced enhancement of proton-induced cell death is partially associated with the inhibition of DSB repair. This study demonstrated that ECyd enhances proton-induced cell killing at all positions of SOBP, except for the distal region and minimizes the site-dependent differences in RBE within SOBP. Thus, ECyd is a unique radiosensitizer for proton therapy that may be useful because it levels the biological dose within SOBP, which improves tumor control and reduces the risk of adverse effects at the distal edge of SOBP.

TRPV1 channels are involved in niacin-induced cutaneous vasodilation in mice

Niacin is effective in treating dyslipidemias but causes cutaneous vasodilation or flushing, a side effect that limits its clinical use. Blocking prostaglandins in humans reduces but does not consistently eliminate flushing, indicating additional mechanisms may contribute to flushing. The transient receptor potential vanilloid 1 (TRPV1) channel, when activated, causes cutaneous vasodilation and undergoes tachyphylaxis similar to that seen with niacin. Using a murine model, early phase niacin-induced flushing was examined and TRPV1 channel involvement demonstrated using pharmacologic blockade, desensitization, and genetic knockouts (TRPV1 KO). The TRPV1 antagonist AMG9810 reduced the magnitude of the initial and secondary peaks and the rapidity of the vasodilatory response (slope). TRPV1 desensitization by chronic capsaicin reduced the initial peak and slope. TRPV1 KO mice had a lower initial peak, secondary peak, and slope compared with wild-type mice. Chronic niacin reduced the initial peak, secondary peak, and slope in wild-type mice but had no effect in knockout mice. Furthermore, chronic niacin diminished the response to capsaicin in wild-type mice. Overall, these data demonstrate an important role for TRPV1 channels in niacin-induced flushing, both in the acute response and with chronic administration. That niacin-induced flushing is a complex cascade of events, which should inform pharmacological intervention against this side effect.

Identification of the TP53-induced glycolysis and apoptosis regulator in various stages of colorectal cancer patients

The TP53-induced glycolysis and apoptosis regulator (TIGAR) is a p53 target gene known to regulate glycolysis by acting as fructose bis-phosphatase (FBPase) and modulate reactive oxygen species. TIGAR expression has been implicated in oncogenesis and progression of several human cancers. However, TIGAR expression is not known in various stages of colorectal cancer (CRC). There is an increase in the colorectal cancer incidence in Saudi Arabia. We sought to analyze TIGAR expression in this ethnic group. The aim of this study was to investigate the TIGAR expression in colorectal cancer (CRC) patients from Saudi Arabia. Tissue microarray (TMA) was constructed from 22 matched colorectal tumor tissues and adjacent normal tissues. TIGAR expression was examined in TMA slide using immunohistochemistry. TIGAR mRNA was determined in 14 matched tumor tissue and adjacent normal tissue. TIGAR protein expression was also examined in CRC tumor tissues and cell lines. Statistical analyses (t-test) were applied to evaluate the significance of TIGAR expression. TIGAR mRNA level was upregulated significantly in stage II (p<0.01) and stage III (p<0.05) when compared to adjacent normal tissue. Immunohistochemical studies revealed that TIGAR expression was increased in colorectal cancer. Strong TIGAR positive staining was found in 68% (15/22) of the tumor samples with nuclear localization. TIGAR staining was found to be significantly increased in early stage (stage I and II) CRC (p<0.05) and late stage (stage III and IV) CRC (p<0.01). TIGAR protein was also found to be highly expressed in stage II and III colorectal cancer tissues and CRC cell lines. These findings indicate that TIGAR is highly expressed at the mRNA and protein levels in colorectal cancer with prominent nuclear localization. TIGAR expression may be used as a bio-marker for detection of colorectal cancer and can be used as a target for developing therapeutics for the treatment of colorectal cancer.

Oncogenic role of the TP53-induced glycolysis and apoptosis regulator in nasopharyngeal carcinoma through NF-κB pathway modulation

The TP53-induced glycolysis and apoptosis regulator (TIGAR) is a p53 target gene, which functions to suppress reactive oxygen species (ROS) damage and protect cells from apoptosis. In this study, we investigated the role of TIGAR in nasopharyngeal carcinoma (NPC) tumorigenesis. Imnunohistochemical analysis of the tissue specimens from nasopharyngeal carcinoma patients showed a higher expression level of TIGAR in tumor tissues, compared with normal nasopharyngeal epithelium. Knockdown of TIGAR by lentivirus-shRNA in CNE-2 or 5-8F cells resulted in decreased cell growth, colony formation, migration, invasion, and induced apoptosis. TIGAR overexpression exerted the opposite effects except for apoptosis reduction. In the xenograft tumor models, TIGAR knockdown reduced tumor growth rate and weight, whereas TIGAR overexpression showed the opposite effects. In addition, the NF-κB signaling pathway was decreased in TIGAR silenced cells. In conclusion, our data demonstrated that TIGAR acted as an oncogene in NPC tumorigenesis, and knockdown of TIGAR inhibited NPC tumor growth through the NF-κB pathway.

TP53-induced glycolysis and apoptosis regulator promotes proliferation and invasiveness of nasopharyngeal carcinoma cells

The TP53-induced glycolysis and apoptosis regulator (TIGAR) is the protein product of the p53 target gene, C12orf5. TIGAR blocks glycolysis and promotes cellular metabolism via the pentose phosphate pathway; it promotes the production of cellular nicotinamide adenine dinucleotide phosphate (NADPH), which leads to enhanced scavenging of intracellular reactive oxygen species, and inhibition of oxidative stress-induced apoptosis in normal cells. Our previous study identified a novel nucleoside analog that inhibited cellular growth and induced apoptosis in nasopharyngeal carcinoma (NPC) cell lines via downregulation of TIGAR expression. Furthermore, the growth inhibitory effects of c-Met tyrosine kinase inhibitors were ameliorated by the overexpression of TIGAR in the NPC cell lines. These results indicate a significant role for TIGAR expression in the survival of NPCs. The present study aimed to further define the function of TIGAR expression in NPC cells. In total, 36 formalin-fixed, paraffin-embedded NPC tissue samples were obtained for the immunohistochemical determination of TIGAR expression. The effects of TIGAR expression on cell proliferation, NADPH production and cellular invasiveness were also assessed in NPC cell lines. Overall, TIGAR was overexpressed in 27/36 (75%) of the NPC tissues compared with the adjacent non-cancer epithelial cells. Similarly, TIGAR overexpression was also observed in a panel of six NPC cell lines compared with normal NP460 hTert and Het1A cell lines. TIGAR overexpression led to increased cellular growth, NADPH production and invasiveness of the NPC cell lines, whereas a knockdown of TIGAR expression resulted in significant inhibition of cellular growth and invasiveness. The expression of the two mesenchymal markers, fibronectin and vimentin, was increased by TIGAR overexpression, but reduced following TIGAR-knockdown. The present study revealed that TIGAR overexpression led to increased cellular growth, NADPH production and invasiveness, and the maintenance of a mesenchymal phenotype, in NPC tissues.

TIGAR regulates glycolysis in ischemic kidney proximal tubules

Tp53-induced glycolysis and apoptosis regulator (TIGAR) activation blocks glycolytic ATP synthesis by inhibiting phosphofructokinase-1 activity. Our data indicate that TIGAR is selectively induced and activated in renal outermedullary proximal straight tubules (PSTs) after ischemia-reperfusion injury in a p53-dependent manner. Under severe ischemic conditions, TIGAR expression persisted through 48 h postinjury and induced loss of renal function and histological damage. Furthermore, TIGAR upregulation inhibited phosphofructokinase-1 activity, glucose 6-phosphate dehydrogenase (G6PD) activity, and induced ATP depletion, oxidative stress, autophagy, and apoptosis. Small interfering RNA-mediated TIGAR inhibition prevented the aforementioned malevolent effects and protected the kidneys from functional and histological damage. After mild ischemia, but not severe ischemia, G6PD activity and NADPH levels were restored, suggesting that TIGAR activation may redirect the glycolytic pathway into gluconeogenesis or the pentose phosphate pathway to produce NADPH. The increased level of NADPH maintained the level of GSH to scavenge ROS, resulting in a lower sensitivity of PST cells to injury. Under severe ischemia, G6PD activity and NADPH levels were reduced during reperfusion; however, blockade of TIGAR enhanced their levels and reduced oxidative stress and apoptosis. Collectively, these results demonstrate that inhibition of TIGAR may protect PST cells from energy depletion and apoptotic cell death in the setting of severe ischemia-reperfusion injury. However, under low ischemic burden, TIGAR activation induces the pentose phosphate pathway and autophagy as a protective mechanism.

TIGAR, TIGAR, burning bright

Cancers cells shift their metabolism towards glycolysis in order to help them support the biosynthetic demands necessary to sustain cell proliferation and growth, adapt to stress and avoid excessive reactive oxygen species (ROS) accumulation. While the p53 tumor suppressor protein is known to inhibit cell growth by inducing apoptosis, senescence and cell cycle arrest, recent studies have found that p53 is also able to influence cell metabolism. TIGAR is a p53 target that functions as a fructose-2,6-bisphosphatase, thereby lowering glycolytic flux and promoting antioxidant functions. By protecting cells from oxidative stress, TIGAR may mediate some of the tumor suppressor activity of p53 but could also contribute to tumorigenesis. Here we discuss the activities of TIGAR described so far, and the potential consequences of TIGAR expression on normal and tumor cells.

Phase II study of TAS-106 in patients with platinum-failure recurrent or metastatic head and neck cancer and nasopharyngeal cancer

TAS-106, a RNA polymerase inhibitor, was studied in solid tumors with potential clinical benefit and reasonable tolerability. We conducted a multicenter, international phase II trial of TAS-106 in salvage metastatic or recurrent head and neck squamous cell cancer (HNSCC) and nasopharyngeal cancer (NPC) patients. TAS-106 monotherapy was given at 6.5 mg/m² over 24-h continuous infusion every 3 weeks. Translational studies for blood and tissue were included. Twenty-seven enrolled patients experienced the most common drug-related adverse events of neutropenia, fatigue, non-neutropenic fever, injection site reaction, and skin rash/dermatitis. The greater than or equal to grade 3 adverse events included neutropenia (14.8%), febrile neutropenia (7.4%), pneumonia (7.4%), and peripheral neuropathy (3.7%). The overall response rate was 0% in both subgroups; five HNSCC patients had stable disease (median duration 99 days) and four NPC patients had stable disease (median duration of 92.5 days). Median progression-free survival (PFS) for HNSCC patients was 52 days (95% CI 43.0–99.0 days) and 48 days (95% CI 41.0–83.0 days) for NPC. Median overall survival (OS) for HNSCC patients was 175 days (95% CI 92.0–234.0 days) and 280 days (95% CI 107.0–462.0 days) for NPC. The TAS-106 plasma levels were equivalent between Asian and Caucasian patients. There was no significant correlation of tumor UCK2 protein expression levels to TAS-106 efficacy. TAS-106 was reasonably tolerated in patients with platinum-failure HNSCC and NPC. The administration schedule of 24-h continuous infusion prevented neurologic toxicity, but had myelosuppression as its main toxicity. There was no anti-tumor efficacy seen with TAS-106 monotherapy. Future studies will focus on TAS-106 combinations and mechanisms of drug resistance.

Synthesis and biological evaluation of (3'S)-3'-deoxy-3'-fluoro-3'-C-ethynylcytidine

The novel pyrimidine nucleoside, (3'S)-3'-deoxy-3'-fluoro-3'-C-ethynylcytidine (1) was synthesized from cytidine in seven steps. The key step in the synthesis was the introduction of the tertiary fluorine at the 3'-position. Compound 1 was evaluated in vitro against several RNA viruses.

Integrated analysis of multiple gene expression profiling datasets revealed novel gene signatures and molecular markers in nasopharyngeal carcinoma

PURPOSE

To identify the novel gene signatures and molecular markers of nasopharyngeal carcinoma (NPC) by integrated bioinformatics analysis of multiple gene expression profiling datasets.

EXPERIMENTAL DESIGN

Seven published gene expression profiling studies and one of our unpublished works were reanalyzed to identify the common significantly dysregulated (CSD) genes in NPC. Overrepresentation analysis of cytogenetic bands, Gene Ontology (GO) categories, pathways were used to explore CSD genes functionally associated with carcinogenesis. The protein expressions of selected CSD genes were examined by immunohistochemistry on tissue microarrays, and the correlations of their expressions with clinical outcomes were evaluated.

RESULTS

Using the criteria (genes reported deregulated in more than one study), a total of 962 genes were identified as the CSD genes in NPC. Four upregulated (BUB1B, CCND2, CENPF, and MAD2L1) and two downregulated (LTF and SLPI) genes were markedly reported in six studies. The enrichments of chromosome aberrations were 2q23, 2q31, 7p15, 12q15, 12q22, 18q11, and 18q12 in upregulated genes and 14q32 and 16q13 in downregulated genes. The activated GO categories and pathways related to proliferation, adhesion, invasion, and downregulated immune response had been functionally associated with NPC. SLPI significantly downregulated in nasopharyngeal adenocarcinoma. Furthermore, the high expression of BUB1B or CENPF was associated with poor overall survival of patients.

CONCLUSION

It was first clearly identified the dysregulated expression of BUB1B and SLPI in NPC tissues.

IMPACT

Further studies of the CSD genes as gene signatures and molecular markers of NPC might improve the understanding of the disease and identify new therapeutic targets.

TP53 induced glycolysis and apoptosis regulator (TIGAR) knockdown results in radiosensitization of glioma cells

BACKGROUND AND PURPOSE

The TP53 induced glycolysis and apoptosis regulator (TIGAR) functions to lower fructose-2,6-bisphosphate (Fru-2,6-P(2)) levels in cells, consequently decreasing glycolysis and leading to the scavenging of reactive oxygen species (ROS), which correlate with a higher resistance to cell death. The decrease in intracellular ROS levels in response to TIGAR may also play a role in the ability of p53 to protect from the accumulation of genomic lesions. Given these good prospects of TIGAR for metabolic regulation and p53-response modulation, we analyzed the effects of TIGAR knockdown in U87MG and T98G glioblastoma-derived cell lines.

METHODS/RESULTS

After TIGAR-knockdown in glioblastoma cell lines, different metabolic parameters were assayed, showing an increase in Fru-2,6-P(2), lactate and ROS levels, with a concomitant decrease in reduced glutathione (GSH) levels. In addition, cell growth was inhibited without evidence of apoptotic or autophagic cell death. In contrast, a clear senescent phenotype was observed. We also found that TIGAR protein levels were increased shortly after irradiation. In addition, avoiding radiotherapy-triggered TIGAR induction by gene silencing resulted in the loss of capacity of glioblastoma cells to form colonies in culture and the delay of DNA repair mechanisms, based in γ-H2AX foci, leading cells to undergo morphological changes compatible with a senescent phenotype. Thus, the results obtained raised the possibility to consider TIGAR as a therapeutic target to increase radiotherapy effects.

CONCLUSION

TIGAR abrogation provides a novel adjunctive therapeutic strategy against glial tumors by increasing radiation-induced cell impairment, thus allowing the use of lower radiotherapeutic doses.

Inhibition of c-Met downregulates TIGAR expression and reduces NADPH production leading to cell death

c-Met represents an important emerging therapeutic target in cancer. In this study, we demonstrate the mechanism by which c-Met tyrosine kinase inhibition inhibits tumor growth in a highly invasive Asian-prevalent head and neck cancer, nasopharyngeal cancer (NPC). c-Met tyrosine kinase inhibitors (TKIs; AM7 and c-Met TKI tool compound SU11274) downregulated c-Met phosphorylation, resulting in marked inhibition of NPC cell growth and invasion. Strikingly, inhibition of c-Met resulted in significant downregulation of TP53-induced Glycolysis and Apoptosis Regulator (TIGAR) and subsequent depletion of intracellular NADPH. Importantly, overexpression of TIGAR ameliorated the effects of c-Met kinase inhibition, confirming the importance of TIGAR downregulation in the growth inhibitory activity of c-Met TKI. The effects of c-Met inhibition on TIGAR and NADPH levels were observed with two different c-Met TKIs (AM7 and SU11274) and with multiple cell lines. As NADPH provides a crucial reducing power required for cell survival and proliferation, our findings reveal a novel mechanistic action of c-Met TKI, which may represent a key effect of c-Met kinase inhibition. Our data provide the first evidence linking c-Met, TIGAR and NADPH regulation in human cancer cells suggesting that inhibition of a tyrosine kinase/TIGAR/NADPH cascade may have therapeutic applicability in human cancers.