Radiosensitization of glioma cells by TP53-induced glycolysis and apoptosis regulator knockdown is dependent on thioredoxin-1 nuclear translocation

The Relationship Between the Molecular Phenotypes of Brain Gliomas and the Imaging Features and Sensitivity of Radiotherapy and Chemotherapy

Gliomas are the most common primary malignant tumors of the brain, accounting for about 80% of all central nervous system malignancies. With the development of molecular biology, the molecular phenotypes of gliomas have been shown to be closely related to the process of diagnosis and treatment. The molecular phenotype of glioma also plays an important role in guiding treatment plans and evaluating treatment effects and prognosis. However, due to the heterogeneity of the tumors and the trauma associated with the surgical removal of tumor tissue, the application of molecular phenotyping in glioma is limited. With the development of imaging technology, functional magnetic resonance imaging (MRI) can provide structural and function information about tumors in a noninvasive and radiation-free manner. MRI is very important for the diagnosis of intracranial lesions. In recent years, with the development of the technology for tumor molecular diagnosis and imaging, the use of molecular phenotype information and imaging procedures to evaluate the treatment outcome of tumors has become a hot topic. By reviewing the related literature on glioma treatment and molecular typing that has been published in the past 20 years, and referring to the latest 2020 NCCN treatment guidelines, summarizing the imaging characteristic and sensitivity of radiotherapy and chemotherapy of different molecular phenotypes of glioma. In this article, we briefly review the imaging characteristics of different molecular phenotypes in gliomas and their relationship with radiosensitivity and chemosensitivity of gliomas.

Inhibition of the thioredoxin system for radiosensitization therapy of cancer

Radiotherapy (RT) stands as a cornerstone in the clinical armamentarium against various cancers due to its proven efficacy. However, the intrinsic radiation resistance exhibited by cancer cells, coupled with the adverse effects of RT on normal tissues, often compromises its therapeutic potential and leads to unwanted side effects. This comprehensive review aims to consolidate our understanding of how radiosensitizers inhibit the thioredoxin (Trx) system in cellular contexts. Notable radiosensitizers, including gold nanoparticles (GNPs), gold triethylphosphine cyanide ([Au(SCN) (PEt3)]), auranofin, ceria nanoparticles (CONPs), curcumin and its derivatives, piperlongamide, indolequinone derivatives, micheliolide, motexafin gadolinium, and ethane selenide selenidazole derivatives (SeDs), are meticulously elucidated in terms of their applications in radiotherapy. In this review, the sensitization mechanisms and the current research progress of these radiosensitizers are discussed in detail, with the overall aim of providing valuable insights for the judicious application of Trx system inhibitors in the field of cancer radiosensitization therapy.

Thioredoxin reductase: An emerging pharmacologic target for radiosensitization of cancer

Novel agents are required to increase the radiosensitivity of cancer and improve the outcome of radiotherapy. Thioredoxin (Trx) and thioredoxin reductase (TrxR) reduce the oxidized cysteine thiols in several proteins, which regulate cellular redox, survival, proliferation, DNA synthesis, transcription factor activity and apoptosis. TrxR is essential for maintaining a conducive redox state for tumor growth, survival and resistance to therapy. Therefore, it is an appealing pharmacological target for the radiosensitization of tumors. Ionizing radiation (IR) is known to cause cytotoxicity through ROS, oxidative stress and DNA damage. Inhibition of thioredoxin system augments IR induced oxidative stress and potentiates cytotoxic effects. However, TrxR also regulates several critical cellular processes in normal cells. Here, we highlight the pre-clinical research and pharmacological studies to surmise possible utility of different TrxR inhibitors for radiosensitization. This review provides a succinct perspective on the role of TrxR inhibitors during the radiotherapy of cancer.

Structure, regulation, and biological functions of TIGAR and its role in diseases

TIGAR (TP53-induced glycolysis and apoptosis regulator) is the downstream target gene of p53, contains a functional sequence similar to 6-phosphofructose kinase/fructose-2, 6-bisphosphatase (PFKFB) bisphosphatase domain. TIGAR is mainly located in the cytoplasm; in response to stress, TIGAR is translocated to nucleus and organelles, including mitochondria and endoplasmic reticulum to regulate cell function. P53 family members (p53, p63, and p73), some transcription factors (SP1 and CREB), and noncoding miRNAs (miR-144, miR-885-5p, and miR-101) regulate the transcription of TIGAR. TIGAR mainly functions as fructose-2,6-bisphosphatase to hydrolyze fructose-1,6-diphosphate and fructose-2,6-diphosphate to inhibit glycolysis. TIGAR in turn facilitates pentose phosphate pathway flux to produce nicotinamide adenine dinucleotide phosphate (NADPH) and ribose, thereby promoting DNA repair, and reducing intracellular reactive oxygen species. TIGAR thus maintains energy metabolism balance, regulates autophagy and stem cell differentiation, and promotes cell survival. Meanwhile, TIGAR also has a nonenzymatic function and can interact with retinoblastoma protein, protein kinase B, nuclear factor-kappa B, hexokinase 2, and ATP5A1 to mediate cell cycle arrest, inflammatory response, and mitochondrial protection. TIGAR might be a potential target for the prevention and treatment of cardiovascular and neurological diseases, as well as cancers.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

NAD+ depletion radiosensitizes 2-DG-treated glioma cells by abolishing metabolic adaptation

Two-deoxy-d-glucose (2-DG) mediated glucose restriction (GR) has been applied as a potential therapeutic strategy for tumor clinical treatments. However, increasing evidences have indicated that 2-DG alone is inefficient in killing tumor cells, and the effect of 2-DG on modifying tumor radio-responses also remains controversial. In this study, we found that 2-DG triggered metabolic adaption in U87 glioma cells by up-regulating nicotinamide phosphoribosyltransferase (NAMPT) and cellular NAD+ content, which abolished 2-DG-induced potential radiosensitizing effect in glioma cells. Strikingly, NAD+ depletion evoked notable oxidative stress by NADPH reduction and hence re-radiosensitized 2-DG-treated glioma cells. Furthermore, isocitrate dehydrogenase-1 (IDH1) mutant U87 glioma cells with deficiency in the rate-limiting enzyme of Preiss-Handler pathway nicotinate phosphoribosyltransferase (Naprt1) revealed notable 2-DG-induced oxidative stress and radiosensitization. Our findings implied that targeting NAD+ could radiosensitize gliomas with GR, and 2-DG administration could be benefit for tumor patients with IDH1 mutation.

The Effect of TIGAR Knockdown on Apoptotic and Epithelial-Mesenchymal Markers Expression in Doxorubicin-Resistant Non-Small Cell Lung Cancer A549 Cell Lines

Resistance to chemotherapeutic drugs is a critical problem in cancer therapy, but the underlying mechanism has not been fully elucidated. TP53-induced glycolysis regulatory phosphatase (TIGAR), an important glycolysis and apoptosis regulator, plays a crucial role in cancer cell survival by protecting cells against oxidative stress-induced apoptosis. In the present study, we investigated whether TIGAR is involved in epithelial-mesenchymal transition (EMT) in doxorubicin (DOX)-resistant human non-small cell lung cancer (NSCLC), A549/DOX cells. We found that the expression of TIGAR was significantly higher in A549/DOX cells than in the parent A549 cell lines. siRNA-mediated TIGAR knockdown reduced migration, viability and colony survival of doxorubicin-resistant lung cancer cells. Also, TIGAR knockdown decreased pro-survival protein Bcl-2 and increased pro-apoptotic Bax and cleaved poly (ADP-ribose) polymerase (PARP). Moreover, TIGAR depletion significantly up-regulated both caspase-3 and caspase-9 expression. Furthermore, TIGAR depletion up-regulated the expression of E-cadherin and down-regulated the expression of vimentin. These results indicate that TIGAR knockdown may inhibit EMT in doxorubicin (DOX)-resistant human NSCLC and may represent a therapeutic target for a non-small lung cancer cells chemoresistance.

Thioredoxin, Glutathione and Related Molecules in Tumors of the Nervous System

BACKGROUND

Central Nervous System (CNS) tumors have a poor survival prognosis due to their invasive and heterogeneous nature, in addition to the resistance to multiple treatments.

OBJECTIVE

In this paper, the main aspects of brain tumor biology and pathogenesis are reviewed both for primary tumors of the brain, (i.e., gliomas) and for metastasis from other malignant tumors, namely lung cancer, breast cancer and malignant melanoma which account for a high percentage of overall malignant brain tumors. We review the role of antioxidant systems, namely the thioredoxin and glutathione systems, in the genesis and/or progression of brain tumors.

METHODS

Although overexpression of Thioredoxin Reductase (TrxR) and Thioredoxin (Trx) is often linked to increased malignancy rate of brain tumors, and higher expression of Glutathione (GSH) and Glutathione S-Transferases (GST) are associated to resistance to therapy, several knowledge gaps still exist regarding for example, the role of Peroxiredoxins (Prx), and Glutaredoxins (Grx).

CONCLUSION

Due to their central role in redox homeostasis and ROS scavenging, redox systems are potential targets for new antitumorals and examples of innovative therapeutics aiming at improving success rates in brain tumor treatment are discussed.

TIGAR/AP-1 axis accelerates the division of Lgr5- reserve intestinal stem cells to reestablish intestinal architecture after lethal radiation

During radiologic or nuclear accidents, high-dose ionizing radiation (IR) can cause gastrointestinal syndrome (GIS), a deadly disorder that urgently needs effective therapy. Unfortunately, current treatments based on natural products and antioxidants have shown very limited effects in alleviating deadly GIS. Reserve intestinal stem cells (ISCs) and secretory progenitor cells are both reported to replenish damaged cells and contribute to crypt regeneration. However, the suppressed β-catenin/c-MYC axis within these slow-cycling cells leads to limited regenerative response to restore intestinal integrity during fatal accidental injury. Current study demonstrates that post-IR overexpression of TIGAR, a critical downstream target of c-MYC in mouse intestine, mounts a hyperplastic response in Bmi1-creERT⁺ reserve ISCs, and thus rescues mice from lethal IR exposure. Critically, by eliminating damaging reactive oxygen species (ROS) yet retaining the proliferative ROS signals, TIGAR-overexpression enhances the activity of activator protein 1, which is indispensable for initiating reserve-ISC division after lethal radiation. In addition, it is identified that TIGAR-induction exclusively gears the Lgr5⁻ subpopulation of reserve ISCs to regenerate crypts, and intestinal TIGAR-overexpression displays equivalent intestinal reconstruction to reserve-ISC-restricted TIGAR-induction. Our findings imply that precise administrations toward Lgr5⁻ reserve ISCs are promising strategies for unpredictable lethal injury, and TIGAR can be employed as a therapeutic target for unexpected radiation-induced GIS.

IDH1-R132H mutation radiosensitizes U87MG glioma cells via epigenetic downregulation of TIGAR

Isocitrate dehydrogenase 1 (IDH1) is the most frequently mutated gene in World Health Organization grade II–III and secondary glioma. The majority of IDH1 mutation cases involve the substitution from arginine to histidine at codon 132 (IDH1-R132H). Although the oncogenic role of IDH1-R132H has been confirmed, patients with IDH1-R132H brain tumors exhibit a better response to radiotherapy compared with those with wild-type (WT) IDH1. In the present study, the potential mechanism of radiosensitization mediated by IDH1-R132H was investigated by overexpressing IDH1-R132H in U87MG glioma cells. The results demonstrated decreased clonogenic capacity of IDH1-R132H-expressing cells, as well as delayed repair of DNA double-strand breaks compared with IDH1-WT. Data from The Cancer Genome Atlas were analyzed, which demonstrated that the expression of TP53-induced glycolysis and apoptosis regulator (TIGAR) was lower in patients with glioma harboring IDH1 mutations compared with that in patients with IDH1-WT. TIGAR-knockdown increases the radiosensitivity of glioma cells; in U87MG cells, IDH1-R132H suppressed TIGAR expression. Chromatin immunoprecipitation assays revealed increased levels of repressive H3K9me3 markers at the TIGAR promoter in IDH1-R132H compared with IDH1-WT. These data indicated that IDH1-R132H may overcome radioresistance in glioma cells through epigenetic suppression of TIGAR expression. However, these favorable effects were not observed in U87MG glioma stem-like cells. The results of the present study provide an improved understanding of the functionality of IDH1 mutations in glioma cells, which may improve the therapeutic efficacy of radiotherapy.

TIGAR promotes growth, survival and metastasis through oxidation resistance and AKT activation in glioblastoma

Glioblastoma has a poor prognosis and is one of the most lethal types of cancer in the world. TP53 induced glycolysis regulatory phosphatase (TIGAR) is upregulated in various types of cancer. Therefore, the present study investigated the role of TIGAR in glioblastoma. TIGAR expression was measured in glioma samples and cell lines using immunohistochemistry and western blotting. Reduced nicotinamide adenine dinucleotide phosphate (NADPH), glutathione, malondialdehyde and intracellular reactive oxygen species levels were detected to measure oxidative stress in U-87MG cells following short hairpin RNA (shRNA)-mediated knockdown of TIGAR. Cell viability was determined using an MTT assay for TIGAR-overexpression vector- and TIGAR-shRNA-transfected U-87MG cells. Apoptosis was assessed to evaluate whether TIGAR knockdown sensitized cells to the antitumor effects of temozolomide (TMZ). Migration, invasion and epithelial-mesenchymal transition (EMT) were further assessed using Transwell and western blotting assays. A co-immunoprecipitation assay was used to detect the interaction between TIGAR and protein kinase B (AKT). The results of the present study revealed that TIGAR was positively associated with poor survival and was upregulated in glioblastoma. TIGAR knockdown significantly increased oxidative stress, decreased cell proliferation and exacerbated TMZ-induced apoptosis in U-87MG cells. Additionally, TIGAR knockdown decreased migration, invasion and EMT, and treatment of TIGAR-shRNA-transfected cells with NADPH had no effect on metastasis. In addition, TIGAR promoted AKT activation and bound to AKT. In conclusion, the present study demonstrated that TIGAR may promote glioblastoma growth and progression through oxidation resistance and AKT activation.

Knockdown of the TP53-Induced Glycolysis and Apoptosis Regulator (TIGAR) Sensitizes Glioma Cells to Hypoxia, Irradiation and Temozolomide

The TP53-induced glycolysis and apoptosis regulator (TIGAR) has been shown to decrease glycolysis, to activate the pentose phosphate pathway, and to provide protection against oxidative damage. Hypoxic regions are considered characteristic of glioblastoma and linked with resistance to current treatment strategies. Here, we established that LNT-229 glioma cell lines stably expressed shRNA constructs targeting TIGAR, and exposed them to hypoxia, irradiation and temozolomide. The disruption of TIGAR enhanced levels of reactive oxygen species and cell death under hypoxic conditions, as well as the effectiveness of irradiation and temozolomide. In addition, TIGAR was upregulated by HIF-1α. As a component of a complex network, TIGAR contributes to the metabolic adjustments that arise from either spontaneous or therapy-induced changes in tumor microenvironment.

TIGAR knockdown enhanced the anticancer effect of aescin via regulating autophagy and apoptosis in colorectal cancer cells

Our previous study showed that TP53-induced glycolysis and apoptosis regulator (TIGAR) regulated ROS, autophagy, and apoptosis in response to hypoxia and chemotherapeutic drugs. Aescin, a triterpene saponin, exerts anticancer effects and increases ROS levels. The ROS is a key upstream signaling to activate autophagy. Whether there is a crosstalk between TIGAR and aescin in regulating ROS, autophagy, and apoptosis is unknown. In this study, we found that aescin inhibited cell viability and colony formation, and induced DNA damage, cell cycle arrest, and apoptosis in cancer cell lines HCT-116 and HCT-8 cells. Concurrently, aescin increased the expression of TIGAR, ROS levels, and autophagy activation. Knockdown of TIGAR enhanced the anticancer effects of aescin in vitro and in vivo, whereas overexpression of TIGAR or replenishing TIGAR downstream products, NADPH and ribose, attenuated aescin-induced apoptosis. Furthermore, aescin-induced ROS elevation and autophagy activation were further strengthened by TIGAR knockdown in HCT-116 cells. However, autophagy inhibition by knockdown of autophagy-related gene ATG5 or 3-methyladenine (3-MA) exaggerated aescin-induced apoptosis when TIGAR was knocked down. In conclusion, TIGAR plays a dual role in determining cancer cell fate via inhibiting both apoptosis and autophagy in response to aescin, which indicated that inhibition of TIGAR and/or autophagy may be a junctional therapeutic target in treatment of cancers with aescin.

Prognostic value of TIGAR and LC3B protein expression in nasopharyngeal carcinoma

Purpose

Autophagy, the process responsible for degrading cytoplasmic organelles to sustain cellular metabolism, has been associated with cancer initiation and progression. As TP53-induced glycolysis and apoptosis regulator (TIGAR) is among the important genes that can regulate autophagy, we aimed to investigate the correlation between the expression levels of TIGAR and the autophagy-related protein microtubule-associated protein 1 light chain 3 (LC3B), as well as their association with clinical outcomes, in nasopharyngeal carcinoma (NPC) patients.

Methods

We detected the expressions of TIGAR and LC3B in 182 NPC tissue samples via immunohistochemical staining.

Results

A significant correlation between TIGAR and LC3B expressions was identified (P=0.045). Moreover, survival analysis showed that TIGAR− or LC3B+ expression was associated with improved overall survival, local regional failure-free survival, distant failure-free survival, and failure-free survival rates, compared with TIGAR+ or LC3B− expression, respectively. Meanwhile, when combining TIGAR with LC3B expression in terms of prognostic value, patients with TIGAR+/LC3B− expression were significantly disadvantaged with regard to overall survival, local regional failure-free survival, distant failure-free survival, and failure-free survival compared with other groups based on the log-rank test and Cox regression analyses (all P<0.05).

Conclusion

TIGAR and LC3B may be novel biomarkers for predicting the prognosis of NPC patients and could be utilized as potential targets for future therapeutics aimed at treating NPC patients.

The diverse role of TIGAR in cellular homeostasis and cancer

TP53-induced glycolysis and apoptosis regulator (TIGAR) is a p53 target protein that plays critical roles in glycolysis and redox balance. Accumulating evidence shows that TIGAR is highly expressed in cancer. TIGAR redirects glycolysis and promotes carcinoma growth by providing metabolic intermediates and reductive power derived from pentose phosphate pathway (PPP). The expression of TIGAR in cancer is positively associated with chemotherapy resistance, suggesting that TIGAR could be a novel therapeutic target. In this review, we briefly presented the function of TIGAR in metabolic homeostasis in normal and cancer cells. Finally, we discussed the future directions of TIGAR research in cancer.

Met is involved in TIGAR-regulated metastasis of non-small-cell lung cancer

TIGAR is a p53 target gene that is known to protect cells from ROS-induced apoptosis by promoting the pentose phosphate pathway. The role of TIGAR in tumor cell invasion and metastasis remains elusive. Here we found that downregulation of TIGAR reduced the invasion and metastasis of NSCLC cells in vitro and in vivo. Immunohistochemical analysis of 72 NSCLC patients showed that TIGAR and Met protein expression was positively correlated with late stages of lung cancer. Besides, patients with high co-expression of TIGAR and Met presented a significantly worse survival. In addition, we found that Met signaling pathway is involved in TIGAR-induced invasion and metastasis. Our study indicates that TIGAR/Met pathway may be a novel target for NSCLC therapy. It is necessary to evaluate the expression of TIGAR before Met inhibitors are used for NSCLC treatment.

Cancer metabolism: New insights into classic characteristics

Initial studies of cancer metabolism in the early 1920s found that cancer cells were phenotypically characterized by aerobic glycolysis, in that these cells favor glucose uptake and lactate production, even in the presence of oxygen. This property, called the Warburg effect, is considered a hallmark of cancer. The mechanism by which these cells acquire aerobic glycolysis has been uncovered. Acidic extracellular fluid, secreted by cancer cells, induces a malignant phenotype, including invasion and metastasis. Cancer cells survival depends on a critical balance of redox status, which is regulated by amino acid metabolism. Glutamine is extremely important for oxidative phosphorylation and redox regulation. Cells highly dependent on glutamine and that cannot survive with glutamine are called glutamine-addicted cells. Metabolic reprogramming has been observed in cancer stem cells, which have the property of self-renewal and are resistant to chemotherapy and radiotherapy. These findings suggest that studies of cancer metabolism can reveal methods of preventing cancer recurrence and metastasis.

TIGAR knockdown radiosensitizes TrxR1-overexpressing glioma in vitro and in vivo via inhibiting Trx1 nuclear transport

The up-regulation of thioredoxin reductase-1 (TrxR1) is detected in more than half of gliomas, which is significantly associated with increased malignancy grade and recurrence rate. The biological functions of NADPH-dependent TrxR1 are mainly associated with reduced thioredoxin-1 (Trx1) which plays critical roles in cellular redox signaling and tumour radio-resistance. Our previous work has proved that TP53 induced glycolysis and apoptosis regulator (TIGAR) knockdown could notably radiosensitize glioma cells. However, whether TrxR1-overexpressing glioma cells could be re-radiosensitized by TIGAR silence is still far from clear. In the present study, TrxR1 was stably over-expressed in U-87MG and T98G glioma cells. Both in vitro and in vivo data demonstrated that the radiosensitivity of glioma cells was considerably diminished by TrxR1 overexpression. TIGAR abrogation was able to radiosensitize TrxR1-overexpressing gliomas by inhibiting IR-induced Trx1 nuclear transport. Post-radiotherapy, TIGAR low-expression predicted significant longer survival time for animals suffering from TrxR1-overexpessing xenografts, which suggested that TIGAR abrogation might be a promising strategy for radiosensitizing TrxR1-overexpressing glial tumours.

The protein PprI provides protection against radiation injury in human and mouse cells

Severe acute radiation injuries are both very lethal and exceptionally difficult to treat. Though the radioresistant bacterium D. radiodurans was first characterized in 1956, genes and proteins key to its radioprotection have not yet to be applied in radiation injury therapy for humans. In this work, we express the D. radiodurans protein PprI in Pichia pastoris yeast cells transfected with the designed vector plasmid pHBM905A-pprI. We then treat human umbilical endothelial vein cells and BALB/c mouse cells with the yeast-derived PprI and elucidate the radioprotective effects the protein provides upon gamma irradiation. We see that PprI significantly increases the survival rate, antioxidant viability, and DNA-repair capacity in irradiated cells and decreases concomitant apoptosis rates and counts of damage-indicative γH2AX foci. Furthermore, we find that PprI reduces mortality and enhances bone marrow cell clone formation and white blood cell and platelet counts in irradiated mice. PprI also seems to alleviate pathological injuries to multiple organs and improve antioxidant viability in some tissues. Our results thus suggest that PprI has crucial radioprotective effects on irradiated human and mouse cells.