Transglutaminase 2 inhibitor abrogates renal cell carcinoma in xenograft models

Novel combinatorial autophagy inhibition therapy for triple negative breast cancers

BACKGROUND

Triple negative breast cancer (TNBC) has the worst prognosis among breast cancer subtypes. It is characterized by lack of estrogen, progesterone and human epidermal growth factor 2 receptors, and thus, have limited therapeutic options. Autophagy has been found to be correlated with poor prognosis and aggressive behaviour in TNBC. This study aimed to target autophagy in TNBC via a novel approach to inhibit TNBC progression.

METHODS

Immunoblotting and confocal microscopy were carried out to examine the effect of tumor microenvironmental stressors on autophagy. Cellular proliferation and migration assays were used to test the effect of different autophagy inhibitors and standard chemotherapy alone or in combination. In vivo xenograft mouse model was utilized to assess the effect of autophagy inhibitors alone or in combination with Paclitaxel. High resolution mass spectrometry based proteomic analysis was performed to explore the mechanisms behind chemoresistance in TNBC. Lastly, immunohistochemistry was done to assess the correlation between autophagy related proteins and clinical characteristics in TNBC tissue specimens.

RESULTS

Metabolic stressors were found to induce autophagy in TNBC cell lines. Autophagy initiation inhibitors, SAR405 and MRT68921, showed marked synergy in their anti-proliferative activity in both chemosensitive and chemoresistant TNBC cell models. Paradoxically, positive expression of autophagosome marker LC3 was shown to be associated with better overall survival of TNBC patients.

CONCLUSION

In this study, a novel combination between different autophagy inhibitors was identified which inhibited tumor cell proliferation in both chemosensitive and chemoresistant TNBC cells and could result in development of a novel treatment modality against TNBC.

Discovery of novel 1H-benzo[d]imidazole-4,7-dione based transglutaminase 2 inhibitors as p53 stabilizing anticancer agents in renal cell carcinoma

Overexpression of transglutaminase 2 (TGase 2; TG2) has been implicated in the progression of renal cell carcinoma (RCC) through the inactivation of p53 by forming a protein complex. Because most p53 in RCC has no mutations, apoptosis can be increased by inhibiting the binding between TG2 and p53 to increase the stability of p53. In the present study, a novel TG2 inhibitor was discovered by investigating the structure of 1H-benzo[d]imidazole-4,7-dione as a simpler chemotype based on the amino-1,4-benzoquinone moiety of streptonigrin, a previously reported inhibitor. Through structure-activity relationship (SAR) studies, compound 8j (MD102) was discovered as a potent TG2 inhibitor with an IC50 value of 0.35 µM, p53 stabilization effect and anticancer effects in the ACHN and Caki-1 RCC cell lines with sulforhodamine B (SRB) GI50 values of 2.15 µM and 1.98 µM, respectively. The binding property of compound 8j (MD102) with TG2 was confirmed to be reversible in a competitive enzyme assay, and the binding interaction was expected to be formed at the β-sandwich domain, a p53 binding site, in the SPR binding assay with mutant proteins. The mode of binding of compound 8j (MD102) to the β-sandwich domain of TG2 was analyzed by molecular docking using the crystal structure of the active conformation of human TG2. Compound 8j (MD102) induced a decrease in the downstream signaling of p-AKT and p-mTOR through the stabilization of p53 by TG2 inhibition, resulting in tumor cell apoptosis. In a xenograft animal model using ACHN cancer cells, oral administration and intraperitoneal injection of compound 8j (MD102) showed an inhibitory effect on tumor growth, confirming increased levels of p53 and decreased levels of Ki-67 in tumor tissues through immunohistochemical (IHC) tissue staining. These results indicated that the inhibition of TG2 by compound 8j (MD102) could enhance p53 stabilization, thereby ultimately showing anticancer effects in RCC. Compound 8j (MD102), a novel TG2 inhibitor, can be further applied for the development of an anticancer candidate drug targeting RCC.

Inhibition of autophagy initiation: A novel strategy for oral squamous cell carcinomas

BACKGROUND

Oral squamous cell carcinoma (OSCC) is one of the most common forms of oral cancer and is known to have poor prognostic outcomes. Autophagy is known to be associated with aggressive tumor biology of OSCC. Hence, this study aimed to develop a novel therapeutic strategy against OSCC by targeting the autophagic pathway.

METHODS

Immunoblotting, and confocal microscopy were used to examine the effect of tumor microenvironmental stressors on the autophagy activity. Cellular proliferation and migration assays were performed to assess the anti-cancer activity of standard chemotherapy and autophagy initiation inhibitors, either alone or in combination. High resolution mass-spectrometry based proteomic analysis was utilized to understand the mechanisms behind chemoresistance in OSCC models. Finally, immunohistochemistry was performed to determine associations between autophagy markers and clinicopathological characteristics.

RESULTS

Tumor microenvironmental stressors were shown to induce autophagy activity in OSCC cell lines. Novel combinations of chemotherapy and autophagy inhibitors as well as different classes of autophagy inhibitors were identified. Combination of MRT68921 and SAR405 demonstrated marked synergy in their anti-proliferative activity and also showed synergy with chemotherapy in chemoresistant OSCC cell models. Autophagy was identified as one of the key pathways involved in mediating chemoresistance in OSCC. Furthermore, TGM2 was identified as a key upstream regulator of chemoresistance in OSCC models. Finally, positive staining for autophagosome marker LC3 was shown to be associated with low histological grade OSCC.

CONCLUSION

In conclusion, this study identified a combination of novel autophagy inhibitors which can potently inhibit proliferation of both chemosensitive as well as chemoresistant OSCC cells and could be developed as a novel therapy against advanced OSCC tumors.

Discovery and Characterization of PROTACs Targeting Tissue Transglutaminase (TG2)

Tissue transglutaminase (TG2) is a multifunctional enzyme involved in the cross-linking of extracellular matrix proteins, formation of complexes with fibronectin (FN) and integrins, and GTP hydrolysis. TG2 is activated in several pathological conditions, including cancer. We recently described a novel series of ligands that bind to TG2 and inhibit its interaction with FN. Because TG2 acts via multiple mechanisms, we set out to pursue a targeted protein degradation strategy to abolish TG2's myriad functions. Here, we report the synthesis and characterization of a series of VHL-based degraders that reduce TG2 in ovarian cancer cells in a proteasome-dependent manner. Degradation of TG2 resulted in significantly reduced cancer cell adhesion and migration in vitro in scratch-wound and migration assays. These results strongly indicate that further development of more potent and in vivo efficient TG2 degraders could be a new strategy for reducing the dissemination of ovarian and other cancers.

The transglutaminase 2 cancer cell survival factor maintains mTOR activity to drive an aggressive cancer phenotype

Transglutaminase 2 (TG2) is an important cancer stem-like cell survival protein that is highly expressed in epidermal squamous cell carcinoma and drives an aggressive cancer phenotype. In the present study, we show that TG2 knockdown or inactivation results in a reduction in mammalian target of rapamycin (mTOR) level and activity in epidermal cancer stem-like cells which are associated with reduced spheroid formation, invasion, and migration, and reduced cancer stem cell and epithelial-mesenchymal transition (EMT) marker expression. Similar changes were observed in both cultured cells and tumors. mTOR knockdown or treatment with rapamycin phenocopies the reduction in spheroid formation, invasion, and migration, and cancer stem cell and EMT marker expression. Moreover, mTOR appears to be a necessary mediator of TG2 action, as a forced expression of constitutively active mTOR in TG2 knockdown cells partially restores the aggressive cancer phenotype and cancer stem cell and EMT marker expression. Tumor studies show that rapamycin reduces tumor growth and cancer stem cell marker expression and EMT. These studies suggest that TG2 stimulates mTOR activity to stimulate cancer cell stemness and EMT and drive aggressive tumor growth.

Transglutaminase 2 regulates terminal erythroid differentiation via cross-linking activity

Transglutaminase 2 (TGM2) is a versatile enzyme that modulates cell survival and differentiation. However, its role in terminal erythroid differentiation is poorly understood. In this study, we investigated the function of TGM2 in primary fetal liver erythroid differentiation. We predicted TGM2 as an upstream regulator via ingenuity pathway analysis (IPA), and found that its expression was increased at both RNA and protein level during terminal erythroid differentiation. TGM2 cross-linking activity inhibitors GK921 and Z-DON suppressed erythroid maturation and enucleation, while its GTPase inhibitor LDN27219 had no such effect. Z-DON treatment arrested differentiation at basophilic erythroblast stage, and interfered with cell cycle progression. RT-PCR demonstrated decreased GATA-1 and KLF1, and disarranged cyclin, CDKI and E2F family genes expression after Z-DON treatment. In conclusion, TGM2 regulates terminal erythroid differentiation through its cross-linking enzyme activity.

A Multidisciplinary Approach Establishes a Link between Transglutaminase 2 and the Kv10.1 Voltage-Dependent K+ Channel in Breast Cancer

Since the multifunctionality of transglutaminase 2 (TG2) includes extra- and intracellular functions, we investigated the effects of intracellular administration of TG2 inhibitors in three breast cancer cell lines, MDA-MB-231, MDA-MB-436 and MDA-MB-468, which are representative of different triple-negative phenotypes, using a patch-clamp technique. The first cell line has a highly voltage-dependent a membrane current, which is low in the second and almost absent in the third one. While applying a voltage protocol to responsive single cells, injection of TG2 inhibitors triggered a significant decrease of the current in MDA-MB-231 that we attributed to voltage-dependent K⁺ channels using the specific inhibitors 4-aminopyridine and astemizole. Since the Kv10.1 channel plays a dominant role as a marker of cell migration and survival in breast cancer, we investigated its relationship with TG2 by immunoprecipitation. Our data reveal their physical interaction affects membrane currents in MDA-MB-231 but not in the less sensitive MDA-MB-436 cells. We further correlated the efficacy of TG2 inhibition with metabolic changes in the supernatants of treated cells, resulting in increased concentration of methyl- and dimethylamines, representing possible response markers. In conclusion, our findings highlight the interference of TG2 inhibitors with the Kv10.1 channel as a potential therapeutic tool depending on the specific features of cancer cells.

Immune subtyping for pancreatic cancer with implication in clinical outcomes and improving immunotherapy

Background

Emerging evidence has shown that intra-tumor immune features are associated with response to immune checkpoint blockade (ICB) therapy. Accordingly, patient stratification is needed for identifying target patients and designing strategies to improve the efficacy of ICB therapy. We aimed to depict the specific immune features of patients with pancreatic cancer and explore the implication of immune diversity in prognostic prediction and individualized immunotherapy.

Methods

From transcriptional profiles of 383 tumor samples in TCGA, ICGC, and GEO database, robust immune subtypes which had different response immunotherapy, including ICB therapy, were identified by consensus clustering with five gene modules. DEGs analysis and tumor microarray were used to screen and demonstrate potential targets for improving ICB therapy.

Results

Three subtypes of pancreatic cancer, namely cluster 1–3 (C1–C3), characterized with distinct immune features and prognosis, were generated. Of that, subtype C1 was an immune-cold type in lack of immune regulators, subtype C2, with an immunosuppression-dominated phenotype characterized by robust TGFβ signaling and stromal reaction, showed the worst prognosis, subtype C3 was an immune-hot type, with massive immune cell infiltration and in abundance of immune regulators. The disparity of immune features uncovered the discrepant applicability of anti-PD-1/PD-L1 therapy and potential sensitivity to other alternative immunotherapy for each subtype. Patients in C3 were more suitable for anti-PD-1/PD-L1 therapy, while patients in the other two clusters may need combined strategies targeted on other immune checkpoints or oncogenic pathways. A promising target for improving anti-PD-1/PD-L1 treatment, TGM2, was screened out and its role in the regulation of PD-L1 was investigated for the first time.

Conclusion

Collectively, immune features of pancreatic cancer contribute to distinct immunosuppressive mechanisms that are responsible for individualized immunotherapy. Despite pancreatic cancer being considered as a poor immunogenic cancer type, the derived immune subtypes may have implications in tailored designing of immunotherapy for the patients. TGM2 has potential synergistic roles with ICB therapy.

Transglutaminase 2-Mediated p53 Depletion Promotes Angiogenesis by Increasing HIF-1α-p300 Binding in Renal Cell Carcinoma

Angiogenesis and the expression of vascular endothelial growth factor (VEGF) are increased in renal cell carcinoma (RCC). Transglutaminase 2 (TGase 2), which promotes angiogenesis in endothelial cells during wound healing, is upregulated in RCC. Tumor angiogenesis involves three domains: cancer cells, the extracellular matrix, and endothelial cells. TGase 2 stabilizes VEGF in the extracellular matrix and promotes VEGFR-2 nuclear translocation in endothelial cells. However, the role of TGase 2 in angiogenesis in the cancer cell domain remains unclear. Hypoxia-inducible factor (HIF)-1α-mediated VEGF production underlies the induction of angiogenesis in cancer cells. In this study, we show that p53 downregulated HIF-1α in RCC, and p53 overexpression decreased VEGF production. Increased TGase 2 promoted angiogenesis by inducing p53 degradation, leading to the activation of HIF-1α. The interaction of HIF-1α and p53 with the cofactor p300 is required for stable transcriptional activation. We found that TGase 2-mediated p53 depletion increased the availability of p300 for HIF-1α-p300 binding. A preclinical xenograft model suggested that TGase 2 inhibition can reverse angiogenesis in RCC.

Inhibition of Transglutaminase 2 but Not of MDM2 Has a Significant Therapeutic Effect on Renal Cell Carcinoma

More than 50% of human cancers harbor TP53 mutations and increased expression of Mouse double minute 2 homolog(MDM2), which contribute to cancer progression and drug resistance. Renal cell carcinoma (RCC) has an unusually high incidence of wild-type p53, with a mutation rate of less than 4%. MDM2 is master regulator of apoptosis in cancer cells, which is triggered through proteasomal degradation of wild-type p53. Recently, we found that p53 protein levels in RCC are regulated by autophagic degradation. Transglutaminase 2 (TGase 2) was responsible for p53 degradation through this pathway. Knocking down TGase 2 increased p53-mediated apoptosis in RCC. Therefore, we asked whether depleting p53 from RCC cells occurs via MDM2-mediated proteasomal degradation or via TGase 2-mediated autophagic degradation. In vitro gene knockdown experiments revealed that stability of p53 in RCC was inversely related to levels of both MDM2 and TGase 2 protein. Therefore, we examined the therapeutic efficacy of inhibitors of TGase 2 and MDM2 in an in vivo model of RCC. The results showed that inhibiting TGase 2 but not MDM2 had efficient anticancer effects.

A Precision Strategy to Cure Renal Cell Carcinoma by Targeting Transglutaminase 2

In a recent report, no significance of transglutaminase 2 (TGase 2) was noted in the analyses of expression differences between normal and clear cell renal cell carcinoma (ccRCC), although we found that knock down of TGase 2 induced significant p53-mediated cell death in ccRCC. Generally, to find effective therapeutic targets, we need to identify targets that belong specifically to a cancer phenotype that can be differentiated from a normal phenotype. Here, we offer precise reasons why TGase 2 may be the first therapeutic target for ccRCC, according to several lines of evidence. TGase 2 is negatively regulated by von Hippel-Lindau tumor suppressor protein (pVHL) and positively regulated by hypoxia-inducible factor 1-α (HIF-1α) in renal cell carcinoma (RCC). Therefore, most of ccRCC presents high level expression of TGase 2 because over 90% of ccRCC showed VHL inactivity through mutation and methylation. Cell death, angiogenesis and drug resistance were specifically regulated by TGase 2 through p53 depletion in ccRCC because over 90% of ccRCC express wild type p53, which is a cell death inducer as well as a HIF-1α suppressor. Although there have been no detailed studies of the physiological role of TGase 2 in multi-omics analyses of ccRCC, a life-long study of the physiological roles of TGase 2 led to the discovery of the first target as well as the first therapeutic treatment for ccRCC in the clinical field.

Transglutaminase 2 takes center stage as a cancer cell survival factor and therapy target

Transglutaminase 2 (TG2) has emerged as a key cancer cell survival factor that drives epithelial to mesenchymal transition, angiogenesis, metastasis, inflammation, drug resistance, cancer stem cell survival and stemness, and invasion and migration. TG2 can exist in a GTP-bound signaling-active conformation or in a transamidase-active conformation. The GTP bound conformation of TG2 contributes to cell survival and the transamidase conformation can contribute to cell survival or death. We present evidence suggesting that TG2 has a role in human cancer, summarize what is known about the TG2 mechanism of action in a range of cancer types, and discuss TG2 as a cancer therapy target.

Transglutaminase 2: The Maestro of the Oncogenic Mediators in Renal Cell Carcinoma

Transglutaminase 2 (TG2) is a multifunctional crosslinking enzyme that displays transamidation, protein disulfide isomerase, protein kinase, as well as GTPase and ATPase activities. TG2 can also act as an adhesion molecule involved in the syndecan and integrin receptor signaling. In recent years, TG2 was implicated in cancer progression, survival, invasion, migration, and stemness of many cancer types, including renal cell carcinoma (RCC). Von Hippel-Lindau mutations leading to the subsequent activation of Hypoxia Inducible Factor (HIF)-1-mediated signaling pathways, survival signaling via the PI3K/Akt pathway resulting in Epithelial Mesenchymal Transition (EMT) metastasis and angiogenesis are the main factors in RCC progression. A number of studies have shown that TG2 was important in HIF-1- and PI3K-mediated signaling, VHL and p53 stabilization, glycolytic metabolism and migratory phenotype in RCC. This review focuses on the role of TG2 in the regulation of molecular pathways nurturing not only the development and propagation of RCC, but also drug-resistance and metastatic potential.

Transglutaminase 2 Promotes Autophagy by LC3 Induction through p53 Depletion in Cancer Cell

Transglutaminase 2 (TGase 2) plays a key role in p53 regulation, depleting p53 tumor suppressor through autophagy in renal cell carcinoma. We found that microtubule-associated protein 1A/1B-light chain 3 (LC3), a hallmark of autophagy, were tightly associated with the level of TGase 2 in cancer cells. TGase 2 overexpression increased LC3 levels, and TGase 2 knockdown decreased LC3 levels in cancer cells. Transcript abundance of LC3 was inversely correlated with level of wild type p53. TGase 2 knockdown using siRNA, or TGase 2 inhibition using GK921 significantly reduced autophagy through reduction of LC3 transcription, which was followed by restoration of p53 levels in cancer cells. TGase 2 overexpression promoted the autophagy process by LC3 induction, which was correlated with p53 depletion in cancer cells. Rapamycin-resistant cancer cells also showed higher expression of LC3 compared to the rapamycin-sensitive cancer cells, which was tightly correlated with TGase 2 levels. TGase 2 knockdown or TGase 2 inhibition sensitized rapamycin-resistant cancer cells to drug treatment. In summary, TGase 2 induces drug resistance by potentiating autophagy through LC3 induction via p53 regulation in cancer.

Renal Cell Carcinoma Is Abrogated by p53 Stabilization through Transglutaminase 2 Inhibition

In general, expression of transglutaminase 2 (TGase 2) is upregulated in renal cell carcinoma (RCC), resulting in p53 instability. Previous studies show that TGase 2 binds to p53 and transports it to the autophagosome. Knockdown or inhibition of TGase 2 in RCC induces p53-mediated apoptosis. Here, we screened a chemical library for TGase 2 inhibitors and identified streptonigrin as a potential therapeutic compound for RCC. Surface plasmon resonance and mass spectroscopy were used to measure streptonigrin binding to TGase 2. Mass spectrometry analysis revealed that streptonigrin binds to the N-terminus of TGase 2 (amino acids 95–116), which is associated with inhibition of TGase 2 activity in vitro and with p53 stabilization in RCC. The anti-cancer effects of streptonigrin on RCC cell lines were demonstrated in cell proliferation and cell death assays. In addition, a single dose of streptonigrin (0.2 mg/kg) showed marked anti-tumor effects in a preclinical RCC model by stabilizing p53. Inhibition of TGase 2 using streptonigrin increased p53 stability, which resulted in p53-mediated apoptosis of RCC. Thus, targeting TGase 2 may be a new therapeutic approach to RCC.

New Insights into Development of Transglutaminase 2 Inhibitors as Pharmaceutical Lead Compounds

Transglutaminase 2 (EC 2.3.2.13; TG2 or TGase 2) plays important roles in the pathogenesis of many diseases, including cancers, neurodegeneration, and inflammatory disorders. Under normal conditions, however, mice lacking TGase 2 exhibit no obvious abnormal phenotype. TGase 2 expression is induced by chemical, physical, and viral stresses through tissue-protective signaling pathways. After stress dissipates, expression is normalized by feedback mechanisms. Dysregulation of TGase 2 expression under pathologic conditions, however, can potentiate pathogenesis and aggravate disease severity. Consistent with this, TGase 2 knockout mice exhibit reversal of disease phenotypes in neurodegenerative and chronic inflammatory disease models. Accordingly, TGase 2 is considered to be a potential therapeutic target. Based on structure–activity relationship assays performed over the past few decades, TGase 2 inhibitors have been developed that target the enzyme’s active site, but clinically applicable inhibitors are not yet available. The recently described the small molecule GK921, which lacks a group that can react with the active site of TGase 2, and efficiently inhibits the enzyme’s activity. Mechanistic studies revealed that GK921 binds at an allosteric binding site in the N-terminus of TGase 2 (amino acids (a.a.) 81–116), triggering a conformational change that inactivates the enzyme. Because the binding site of GK921 overlaps with the p53-binding site of TGase 2, the drug induces apoptosis in renal cell carcinoma by stabilizing p53. In this review, we discuss the possibility of developing TGase 2 inhibitors that target the allosteric binding site of TGase 2.

Allosteric inhibition site of transglutaminase 2 is unveiled in the N terminus

Previously we have demonstrated transglutaminase 2 (TGase 2) inhibition abrogated renal cell carcinoma (RCC) using GK921 (3-(phenylethynyl)-2-(2-(pyridin-2-yl)ethoxy)pyrido[3,2-b]pyrazine), although the mechanism of TGase 2 inhibition remains unsolved. Recently, we found that the increase of TGase 2 expression is required for p53 depletion in RCC by transporting the TGase 2 (1-139 a.a)-p53 complex to the autophagosome, through TGase 2 (472-687 a.a) binding p62. In this study, mass analysis revealed that GK921 bound to the N terminus of TGase 2 (81-116 a.a), which stabilized p53 by blocking TGase 2 binding. This suggests that RCC survival can be stopped by p53-induced cell death through blocking the p53-TGase 2 complex formation using GK921. Although GK921 does not bind to the active site of TGase 2, GK921 binding to the N terminus of TGase 2 also inactivated TGase 2 activity through acceleration of non-covalent self-polymerization of TGase 2 via conformational change. This suggests that TGase 2 has an allosteric binding site (81-116 a.a) which changes the conformation of TGase 2 enough to accelerate inactivation through self-polymer formation.

The diamond anniversary of tissue transglutaminase: a protein of many talents

Tissue transglutaminase (tTG) is capable of binding and hydrolyzing GTP, as well as catalyzing an enzymatic transamidation reaction that crosslinks primary amines to glutamine residues. tTG adopts two vastly different conformations, depending on whether it is functioning as a GTP-binding protein or a crosslinking enzyme. It has been shown to have important roles in several different aspects of cancer progression, making it an attractive target for therapeutic intervention. Here, we highlight many of the major findings involving tTG since its discovery 60 years ago, and describe recent drug discovery efforts that target specific activities or conformations of this unique protein.

Restoration of type 1 iodothyronine deiodinase expression in renal cancer cells downregulates oncoproteins and affects key metabolic pathways as well as anti-oxidative system

Type 1 iodothyronine deiodinase (DIO1) contributes to deiodination of 3,5,3’,5’-tetraiodo-L-thyronine (thyroxine, T4) yielding of 3,5,3’-triiodothyronine (T3), a powerful regulator of cell differentiation, proliferation, and metabolism. Our previous work showed that loss of DIO1 enhances proliferation and migration of renal cancer cells. However, the global effects of DIO1 expression in various tissues affected by cancer remain unknown. Here, the effects of stable DIO1 re-expression were analyzed on the proteome of renal cancer cells, followed by quantitative real-time PCR validation in two renal cancer-derived cell lines. DIO1-induced changes in intracellular concentrations of thyroid hormones were quantified by L-MS/MS and correlations between expression of DIO1 and potential target genes were determined in tissue samples from renal cancer patients. Stable re-expression of DIO1, resulted in 26 downregulated proteins while 59 proteins were overexpressed in renal cancer cells. The ‘downregulated’ group consisted mainly of oncoproteins (e.g. STAT3, ANPEP, TGFBI, TGM2) that promote proliferation, migration and invasion. Furthermore, DIO1 re-expression enhanced concentrations of two subunits of thyroid hormone transporter (SLC7A5, SLC3A2), enzymes of key pathways of cellular energy metabolism (e.g. TKT, NAMPT, IDH2), sex steroid metabolism and anti-oxidative response (AKR1C2, AKR1B10). DIO1 expression resulted in elevated intracellular concentration of T4. Expression of DIO1-affected genes strongly correlated with DIO1 transcript levels in tissue samples from renal cancer patients as well as with their poor survival. This first study addressing effects of deiodinase re-expression on proteome of cancer cells demonstrates that induced DIO1 re-expression in renal cancer robustly downregulates oncoproteins, affects key metabolic pathways, and triggers proteins involved in anti-oxidative protection. This data supports the notion that suppressed DIO1 expression and changes in local availability of thyroid hormones might favor a shift from a differentiated to a more proliferation-prone state of cancer tissues and cell lines.

Transglutaminase 2 Inhibition Reverses Mesenchymal Transdifferentiation of Glioma Stem Cells by Regulating C/EBPβ Signaling

Necrosis is a hallmark of glioblastoma (GBM) and is responsible for poor prognosis and resistance to conventional therapies. However, the molecular mechanisms underlying necrotic microenvironment-induced malignancy of GBM have not been elucidated. Here, we report that transglutaminase 2 (TGM2) is upregulated in the perinecrotic region of GBM and triggered mesenchymal (MES) transdifferentiation of glioma stem cells (GSC) by regulating master transcription factors (TF), such as C/EBPβ, TAZ, and STAT3. TGM2 expression was induced by macrophages/microglia-derived cytokines via NF-κB activation and further degraded DNA damage-inducible transcript 3 (GADD153) to induce C/EBPβ expression, resulting in expression of the MES transcriptome. Downregulation of TGM2 decreased sphere-forming ability, tumor size, and radioresistance and survival in a xenograft mouse model through a loss of the MES signature. A TGM2-specific inhibitor GK921 blocked MES transdifferentiation and showed significant therapeutic efficacy in mouse models of GSC. Moreover, TGM2 expression was significantly increased in recurrent MES patients and inversely correlated with patient prognosis. Collectively, our results indicate that TGM2 is a key molecular switch of necrosis-induced MES transdifferentiation and an important therapeutic target for MES GBM. Cancer Res; 77(18); 4973-84. ©2017 AACR.

The prognostic value of BAP1, PBRM1, pS6, PTEN, TGase2, PD-L1, CA9, PSMA, and Ki-67 tissue markers in localized renal cell carcinoma: A retrospective study of tissue microarrays using immunohistochemistry

OBJECTIVE

To assess the prognostic roles of BAP1, PBRM1, pS6, PTEN, TGase2, PD-L1, CA9, PSMA, and Ki-67 tissue biomarkers in localized renal cell carcinoma (RCC).

METHODS

Patients who underwent a nephrectomy during 1992-2015 and had a primary specimen of their kidney tumor were included. The nine tissue biomarkers were immunohistochemically stained on tissue microarrays of RCC, and the semi-quantitative H-score, including intensity score, was used to grade the sample. The Cox proportional hazards model was used to evaluate tissue markers significant for overall survival (OS), cancer-specific survival (CSS), and recurrence-free survival (RFS) after adjusting for significant clinicopathological parameters.

RESULTS

Samples from 351 RCC patients were included. The mean age of the patients was 53.9 years; the rates of pathologic T1-2/≥T3 stage, Fuhrman 1+2/3+4 grade, recurrence, and death were 269/65(80.5/19.5%), 222/107 (67.5/32.5%), 6.6%, and 10.5%, respectively. Median OS, CSS, and RFS were 220.6, 220.6, and 147.1 months, respectively. The multivariable analysis showed that pathologic T stage and Fuhrman nuclear grade were significantly associated with OS and CSS. Pathologic T stage and tumor size were associated with RFS. After adjusting for these significant prognostic clinicopathological factors, Ki-67 was significantly associated with OS (hazard ratio [HR], 2.7), CSS (HR, 3.82), and RFS (HR, 4.85) and pS6 was associated with CSS (HR, 8.63) and RFS (HR, 8.51) in the multivariable model (p<0.05).

CONCLUSION

pS6 and Ki-67 are significant prognostic factors of RCC; however, BAP1, PBRM1, TGase 2, PD-L1, CA9, PTEN loss, and PSMA markers did not show this association.

Recent Progress in the Development of Transglutaminase 2 (TGase2) Inhibitors

Transglutaminase 2 (TGase2, TG2) activity has been implicated in the pathogenesis of a number of unrelated disorders, including celiac, neurological, and renal diseases, and various forms of cancer. It has been suggested that TGase2 activity, such as cross-linking, deamidation, and GTP-related activity, is associated with each disease. Continuing efforts to develop small molecule TG2 inhibitors are ongoing. To develop a new class of TG2 inhibitors, the factors impeding the development of TG2 inhibitors have been identified. Additionally, the conformational effect of TG2 enzyme in regard to its pathological roles, in vitro screening methods, recently discovered TG2 inhibitors, and preclinical evaluations are discussed with a brief summary of current TG2 inhibitor pipelines under the clinical setting.

Synthesis and evaluation of in vitro antiproliferative activity of new ethyl 3-(arylethynyl)quinoxaline-2-carboxylate and pyrido[4,3-b]quinoxalin-1(2H)-one derivatives

We report a novel series of quinoxaline derivatives from which agents with antiproliferative activity have been identified. Two ethyl 3-(arylethynyl)quinoxaline-2-carboxylates demonstrated substantial antiproliferative activity against both human non-small cell lung carcinoma (A549) and glioblastoma (U87-MG) cell lines. Pyrido[4,3-b]quinoxalin-1(2H)-ones demonstrated poor activity against A549 and U87-MG cell lines. Three of the derivatives in ethyl 3-(arylethynyl)quinoxaline-2-carboxylate series demonstrated substantial antiproliferative activity. The arylethynyl derivative 2a and 2d proved to be the most cytotoxic with an IC₅₀ value of 3.3 μM for both A549 and U87-MG cell lines.

Transglutaminase-2: evolution from pedestrian protein to a promising therapeutic target

The ability of cancer cells to metastasize represents the most devastating feature of cancer. Currently, there are no specific biomarkers or therapeutic targets that can be used to predict the risk or to treat metastatic cancer. Many recent reports have demonstrated elevated expression of transglutaminase 2 (TG2) in multiple drug-resistant and metastatic cancer cells. TG2 is a multifunctional protein mostly known for catalyzing Ca²⁺-dependent -acyl transferase reaction to form protein crosslinks. Besides this transamidase activity, many Ca²⁺-independent and non-enzymatic activities of TG2 have been identified. Both, the enzymatic and non-enzymatic activities of TG2 have been implicated in diverse pathophysiological processes such as wound healing, cell growth, cell survival, extracellular matrix modification, apoptosis, and autophagy. Tumors have been frequently referred to as 'wounds that never heal'. Based on the observation that TG2 plays an important role in wound healing and inflammation is known to facilitate cancer growth and progression, we discuss the evidence that TG2 can reprogram inflammatory signaling networks that play fundamental roles in cancer progression. TG2-regulated signaling bestows on cancer cells the ability to proliferate, to resist cell death, to invade, to reprogram glucose metabolism and to metastasize, the attributes that are considered important hallmarks of cancer. Therefore, inhibiting TG2 may offer a novel therapeutic approach for managing and treatment of metastatic cancer. Strategies to inhibit TG2-regulated pathways will also be discussed.

Renal cell carcinoma escapes death by p53 depletion through transglutaminase 2-chaperoned autophagy

In renal cell carcinoma, transglutaminase 2 (TGase 2) crosslinks p53 in autophagosomes, resulting in p53 depletion and the tumor's evasion of apoptosis. Inhibition of TGase 2 stabilizes p53 and induces tumor cells to enter apoptosis. This study explored the mechanism of TGase 2-dependent p53 degradation. We found that TGase 2 competes with human double minute 2 homolog (HDM2) for binding to p53; promotes autophagy-dependent p53 degradation in renal cell carcinoma (RCC) cell lines under starvation; and binds to p53 and p62 simultaneously without ubiquitin-dependent recognition of p62. The bound complex does not have crosslinking activity. A binding assay using a series of deletion mutants of p62, p53 and TGase 2 revealed that the PB1 (Phox and Bem1p-1) domain of p62 (residues 85-110) directly interacts with the β-barrel domains of TGase 2 (residues 592-687), whereas the HDM2-binding domain (transactivation domain, residues 15-26) of p53 interacts with the N terminus of TGase 2 (residues 1-139). In addition to the increase in p53 stability due to TGase 2 inhibition, the administration of a DNA-damaging anti-cancer drug such as doxorubicin-induced apoptosis in RCC cell lines and synergistically reduced tumor volume in a xenograft model. Combination therapy with a TGase 2 inhibitor and a DNA-damaging agent may represent an effective therapeutic approach for treating RCC.

CHIP-mediated degradation of transglutaminase 2 negatively regulates tumor growth and angiogenesis in renal cancer

The multifunctional enzyme transglutaminase 2 (TG2) primarily catalyzes cross-linking reactions of proteins via (γ-glutamyl) lysine bonds. Several recent findings indicate that altered regulation of intracellular TG2 levels affects renal cancer. Elevated TG2 expression is observed in renal cancer. However, the molecular mechanism underlying TG2 degradation is not completely understood. Carboxyl-terminus of Hsp70-interacting protein (CHIP) functions as an ubiquitin E3 ligase. Previous studies reveal that CHIP deficiency mice displayed a reduced life span with accelerated aging in kidney tissues. Here we show that CHIP promotes polyubiquitination of TG2 and its subsequent proteasomal degradation. In addition, TG2 upregulation contributes to enhanced kidney tumorigenesis. Furthermore, CHIP-mediated TG2 downregulation is critical for the suppression of kidney tumor growth and angiogenesis. Notably, our findings are further supported by decreased CHIP expression in human renal cancer tissues and renal cancer cells. The present work reveals that CHIP-mediated TG2 ubiquitination and proteasomal degradation represent a novel regulatory mechanism that controls intracellular TG2 levels. Alterations in this pathway result in TG2 hyperexpression and consequently contribute to renal cancer.

Axl receptor tyrosine kinase is a potential therapeutic target in renal cell carcinoma

Background:

Axl plays multiple roles in tumourigenesis in several cancers. Here we evaluated the expression and biological function of Axl in renal cell carcinoma (RCC).

Methods:

Axl expression was analysed in a tissue microarray of 174 RCC samples by immunostaining and a panel of 11 normal tumour pairs of human RCC tissues by western blot, as well as in RCC cell lines by both western blot and quantitative PCR. The effects of Axl knockdown in RCC cells on cell growth and signalling were investigated. The efficacy of a humanised Axl targeting monoclonal antibody hMAb173 was tested in histoculture and tumour xenograft.

Results:

We have determined by immunohistochemistry (IHC) that Axl is expressed in 59% of RCC array samples with moderate to high in 20% but not expressed in normal kidney tissue. Western blot analysis of 11 pairs of tumour and adjacent normal tissue show high Axl expression in 73% of the tumours but not normal tissue. Axl is also expressed in RCC cell lines in which Axl knockdown reduces cell viability and PI3K/Akt signalling. The Axl antibody hMAb173 significantly induced RCC cell apoptosis in histoculture and inhibited the growth of RCC tumour in vivo by 78%. The hMAb173-treated tumours also had significantly reduced Axl protein levels, inhibited PI3K signalling, decreased proliferation, and induced apoptosis.

Conclusions:

Axl is highly expressed in RCC and critical for RCC cell survival. Targeting Axl is a potential approach for RCC treatment.

The increased transglutaminase 2 expression levels during initial tumorigenesis predict increased risk of metastasis and decreased disease-free and cancer-specific survivals in renal cell carcinoma

PURPOSE

The aim of this study was to investigate the role of transglutaminase 2(TG2) in renal cell carcinoma (RCC) by comparing the immunohistochemistry staining of primary and metastatic tumor tissues.

METHODS

A total of 33 metastatic RCC(mRCC) and 33 non-metastatic RCC (nmRCC) patients who were matched as closely as possible based on gender, age, nuclear grade and pathologic T stage were retrospectively investigated. TG2 immunohistochemistry staining was performed on paraffin-embedded primary tumor tissues from both patient groups and on metastatic tissues from mRCC patients. The tissues were scored from 0 to 7 according to the TG2 staining. Furthermore, the patients were stratified into two groups using median primary tumor staining score as the cutoff value: Group 1 (high risk, n = 41) and Group 2(low risk, n = 22). The clinical, histopathological and survival outcomes were compared between these risk groups using Chi-square test, t test, Mann-Whitney U test and Kaplan-Meier survival analyses.

RESULTS

The median TG2 score for primary tumor was 5 for the entire study population. The median primary tumor TG2 score of the mRCC patients was significantly higher compared to the nmRCC patients (6 vs. 4, p < 0.001). The TG2 score between the primary and metastatic tissues of mRCC patients was not significantly different (6 vs. 7, p = 0.086). The percentage of metastatic patients was significantly higher in Group 1 compared to Group 2 (68.3 vs. 18.2 %, p < 0.001). Kaplan-Meier analyses showed that 5-year disease-free (34.9 vs. 92.9 %, p = 0.001) and cancer-specific (47.4 vs. 86.5 %, p = 0.04) survival rates were significantly lower in high-risk group.

CONCLUSIONS

The increased expression of TG2 in primary tumor predicts metastasis in RCC patients and is also associated with a decrease in disease-free and cancer-specific survival outcomes.