NRF2 mutation confers malignant potential and resistance to chemoradiation therapy in advanced esophageal squamous cancer

NRF2 Regulation by Noncoding RNAs in Cancers: The Present Knowledge and the Way Forward

Simple Summary

The NRF2 pathway represents one of the most intriguing pathways that promotes chemo- and radioresistance of neoplastic cells. Increasing findings suggest that the NRF2 signaling can be modulated by multiple epigenetic factors such as noncoding RNAs, which influence a large number of oncogenic mechanisms, both at transcriptional and at post-transcriptional levels. As a consequence, the identification and characterization of specific noncoding RNAs as biomarkers related to oxidative stress may help to clarify the relationship between them and NRF2 signaling in the tumor context, in terms of positive and negative modulation, also referring to their intersection with other NRF2 crosstalking pathways. In this review, we summarize the recent updates on NRF2 network regulation by noncoding RNAs in tumors, thus paving the way toward the potential translational role of these small RNAs as key tumor biomarkers of neoplastic processes.

Abstract

Nuclear factor erythroid 2-related factor 2 (NRF2) is the key transcription factor triggered by oxidative stress that moves in cells of the antioxidant response element (ARE)-antioxidant gene network against reactive oxygen species (ROS) cellular damage. In tumors, the NRF2 pathway represents one of the most intriguing pathways that promotes chemo- and radioresistance of neoplastic cells and its activity is regulated by genetic and epigenetic mechanisms; some of these being poorly investigated in cancer. The noncoding RNA (ncRNA) network is governed by microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) and modulates a variety of cellular mechanisms linked to cancer onset and progression, both at transcriptional and post-transcriptional levels. In recent years, the scientific findings about the effects of ncRNA landscape variations on NRF2 machines are rapidly increasing and need to be continuously updated. Here, we review the latest knowledge about the link between NRF2 and ncRNA networks in cancer, thus focusing on their potential translational significance as key tumor biomarkers.

NRF2 and the Ambiguous Consequences of Its Activation during Initiation and the Subsequent Stages of Tumourigenesis

NF-E2 p45-related factor 2 (NRF2, encoded in the human by NFE2L2) mediates short-term adaptation to thiol-reactive stressors. In normal cells, activation of NRF2 by a thiol-reactive stressor helps prevent, for a limited period of time, the initiation of cancer by chemical carcinogens through induction of genes encoding drug-metabolising enzymes. However, in many tumour types, NRF2 is permanently upregulated. In such cases, its overexpressed target genes support the promotion and progression of cancer by suppressing oxidative stress, because they constitutively increase the capacity to scavenge reactive oxygen species (ROS), and they support cell proliferation by increasing ribonucleotide synthesis, serine biosynthesis and autophagy. Herein, we describe cancer chemoprevention and the discovery of the essential role played by NRF2 in orchestrating protection against chemical carcinogenesis. We similarly describe the discoveries of somatic mutations in NFE2L2 and the gene encoding the principal NRF2 repressor, Kelch-like ECH-associated protein 1 (KEAP1) along with that encoding a component of the E3 ubiquitin-ligase complex Cullin 3 (CUL3), which result in permanent activation of NRF2, and the recognition that such mutations occur frequently in many types of cancer. Notably, mutations in NFE2L2, KEAP1 and CUL3 that cause persistent upregulation of NRF2 often co-exist with mutations that activate KRAS and the PI3K-PKB/Akt pathway, suggesting NRF2 supports growth of tumours in which KRAS or PKB/Akt are hyperactive. Besides somatic mutations, NRF2 activation in human tumours can occur by other means, such as alternative splicing that results in a NRF2 protein which lacks the KEAP1-binding domain or overexpression of other KEAP1-binding partners that compete with NRF2. Lastly, as NRF2 upregulation is associated with resistance to cancer chemotherapy and radiotherapy, we describe strategies that might be employed to suppress growth and overcome drug resistance in tumours with overactive NRF2.

Redox Potential of Antioxidants in Cancer Progression and Prevention

The benevolent and detrimental effects of antioxidants are much debated in clinical trials and cancer research. Several antioxidant enzymes and molecules are overexpressed in oxidative stress conditions that can damage cellular proteins, lipids, and DNA. Natural antioxidants remove excess free radical intermediates by reducing hydrogen donors or quenching singlet oxygen and delaying oxidative reactions in actively growing cancer cells. These reducing agents have the potential to hinder cancer progression only when administered at the right proportions along with chemo-/radiotherapies. Antioxidants and enzymes affect signal transduction and energy metabolism pathways for the maintenance of cellular redox status. A decline in antioxidant capacity arising from genetic mutations may increase the mitochondrial flux of free radicals resulting in misfiring of cellular signalling pathways. Often, a metabolic reprogramming arising from these mutations in metabolic enzymes leads to the overproduction of so called ’oncometabolites’ in a state of ‘pseudohypoxia’. This can inactivate several of the intracellular molecules involved in epigenetic and redox regulations, thereby increasing oxidative stress giving rise to growth advantages for cancerous cells. Undeniably, these are cell-type and Reactive Oxygen Species (ROS) specific, which is manifested as changes in the enzyme activation, differences in gene expression, cellular functions as well as cell death mechanisms. Photodynamic therapy (PDT) using light-activated photosensitizing molecules that can regulate cellular redox balance in accordance with the changes in endogenous ROS production is a solution for many of these challenges in cancer therapy.

The NRF2, Thioredoxin, and Glutathione System in Tumorigenesis and Anticancer Therapies

Cancer remains an elusive, highly complex disease and a global burden. Constant change by acquired mutations and metabolic reprogramming contribute to the high inter- and intratumor heterogeneity of malignant cells, their selective growth advantage, and their resistance to anticancer therapies. In the modern era of integrative biomedicine, realizing that a personalized approach could benefit therapy treatments and patients' prognosis, we should focus on cancer-driving advantageous modifications. Namely, reactive oxygen species (ROS), known to act as regulators of cellular metabolism and growth, exhibit both negative and positive activities, as do antioxidants with potential anticancer effects. Such complexity of oxidative homeostasis is sometimes overseen in the case of studies evaluating the effects of potential anticancer antioxidants. While cancer cells often produce more ROS due to their increased growth-favoring demands, numerous conventional anticancer therapies exploit this feature to ensure selective cancer cell death triggered by excessive ROS levels, also causing serious side effects. The activation of the cellular NRF2 (nuclear factor erythroid 2 like 2) pathway and induction of cytoprotective genes accompanies an increase in ROS levels. A plethora of specific targets, including those involved in thioredoxin (TRX) and glutathione (GSH) systems, are activated by NRF2. In this paper, we briefly review preclinical research findings on the interrelated roles of the NRF2 pathway and TRX and GSH systems, with focus given to clinical findings and their relevance in carcinogenesis and anticancer treatments.

Nuclear Factor Erythroid 2-Related Factor 2 in Regulating Cancer Metabolism

Significance: Nuclear factor erythroid 2 (NFE2)-related factor 2 (NFE2L2, or NRF2) is a transcription factor predominantly affecting the expression of antioxidant genes. NRF2 plays a significant role in the control of redox balance, which is crucial in cancer cells. NRF2 activation regulates numerous cancer hallmarks, including metabolism, cancer stem cell characteristics, tumor aggressiveness, invasion, and metastasis formation. We review the molecular characteristics of the NRF2 pathway and discuss its interactions with the cancer hallmarks previously listed. Recent Advances: The noncanonical activation of NRF2 was recently discovered, and members of this pathway are involved in carcinogenesis. Further, cancer-related changes (e.g., metabolic flexibility) that support cancer progression were found to be redox- and NRF2 dependent. Critical Issues: NRF2 undergoes Janus-faced behavior in cancers. The pro- or antineoplastic effects of NRF2 are context dependent and essentially based on the specific molecular characteristics of the cancer in question. Therefore, systematic investigation of NRF2 signaling is necessary to clarify its role in cancer etiology. The biggest challenge in the NRF2 field is to determine which cancers can be targeted for better clinical outcomes. Further, large-scale genomic and transcriptomic studies are missing to correlate the clinical outcome with the activity of the NRF2 system. Future Directions: To exploit NRF2 in a clinical setting in the future, the druggable members of the NRF2 pathway should be identified. In addition, it will be important to study how the modulation of the NRF2 system interferes with cytostatic drugs and their combinations.

Geldanamycin-Derived HSP90 Inhibitors Are Synthetic Lethal with NRF2

Activating mutations in KEAP1-NRF2 are frequently found in tumors of the lung, esophagus, and liver, where they are associated with aggressive growth, resistance to cancer therapies, and low overall survival. Despite the fact that NRF2 is a validated driver of tumorigenesis and chemotherapeutic resistance, there are currently no approved drugs which can inhibit its activity. Therefore, there is an urgent clinical need to identify NRF2-selective cancer therapies. To this end, we developed a novel synthetic lethal assay, based on fluorescently labeled isogenic wild-type and Keap1 knockout cell lines, in order to screen for compounds which selectively kill cells in an NRF2-dependent manner. Through this approach, we identified three compounds based on the geldanamycin scaffold which display synthetic lethality with NRF2. Mechanistically, we show that products of NRF2 target genes metabolize the quinone-containing geldanamycin compounds into more potent HSP90 inhibitors, which enhances their cytotoxicity while simultaneously restricting the synthetic lethal effect to cells with aberrant NRF2 activity. As all three of the geldanamycin-derived compounds have been used in clinical trials, they represent ideal candidates for drug repositioning to target the currently untreatable NRF2 activity in cancer.

Stigmasterol sensitizes endometrial cancer cells to chemotherapy by repressing Nrf2 signal pathway

Background

Chemoresistance reduces the 5-year survival rate of endometrial cancer patient, which is the current major obstacle for cancer therapy. Increasing evidence state that Nrf2 contributes to chemoresistance in several kinds of cancer. However, its role in endometrial cancer cells remains unclarified.

Methods

Immunohistochemistry staining was used to detect the expression of Nrf2 in normal patient and endometrial cancer patient. Stable transfection Ishikawa cell line with high level of Nrf2 was established to evaluate its role in chemoresistance. Dot blot assays were used to assess global hydroxymethylation level after stigmasterol treatment. Cellular growth profile was detected by CCK8 assay. Western blot was used to evaluate the changes of the target molecules after various treatments.

Results

Nrf2 is overexpressed in endometrial cancer tissues compared with the normal endometrium. Overexpression of Nrf2 resulted in decrease sensitivity to cisplatin. In addition, stigmasterol has been identified as a novel Nrf2 inhibitor. It enhanced the sensitivity of endometrial cancer cells to cisplatin, and the underlying mechanism is that stigmasterol declines the Nrf2 protein level.

Conclusions

Our findings identified stigmasterol as a new potential inhibitor of Nrf2 and highlight a critical role of stigmasterol in overcoming chemoresistance in endometrial cancer therapy.

Role of Nrf2 and mitochondria in cancer stem cells; in carcinogenesis, tumor progression, and chemoresistance

Cancer stem cells (CSCs) are rare sub-population in tumor mass with self-renewal and differentiation abilities; CSCs are considered as the main cells which are responsible for tumor metastasis, cancer recurrence, and chemo/radio-resistance. CSCs are believed to contain low mitochondria in quantity, high concentration of nuclear factor erythroid 2-related factor 2 (Nrf2), and low reactive oxygen species (ROS) levels. Mitochondria regulate certain cellular functions, including controlling of cellular energetics, calcium signaling, cell growth and cell differentiation, cell cycle regulation, and cell death. Also, mitochondria are the main sources of intrinsic ROS production. Dysfunction of CSCs mitochondria due to oxidative phosphorylation is reported in several pathological conditions, including metabolic disorders, age-related diseases, and various types of cancers. ROS levels play a significant role in cellular signal transduction and CSCs' identity and differentiation capability. Nrf2 is a master transcription factor that plays critical functions in maintaining cellular redox hemostasis by regulating several antioxidant and detoxification pathways. Recently, the critical function of Nrf2 in CSCs has been revealed by several studies. Nrf2 is an essential molecule in the maintenance of CSCs' stemness and self-renewal in response to different oxidative stresses such as chemotherapy-induced elevation of ROS. Nrf2 enables these cells to recover from chemotherapy damages, and promotes establishment of invasion and dissemination. In this study, we have summarized the role of Nrf2 and mitochondria function CSCs, which promote cancer development. The significant role of Nrf2 in the regulation of mitochondrial function and ROS levels suggests this molecule as a potential target to eradicate CSCs.

Genetic Heterogeneity of Esophageal Squamous Cell Carcinoma with Inherited Family History

Background

Esophageal squamous cell carcinoma (ESCC) is a common malignant tumor with significant geographical variation and familial aggregation. However, the potentially different mechanisms underlying tumorigenesis in patients with ESCC with and without a family history of the disease remain unclear. In this study, the genes mutated in familial and nonfamilial ESCC were analyzed. Further, we aimed to explore the genes related to ESCC and attempt to identify potential patients in families with a history of ESCC.

Methods

Next-generation sequencing technology was used to examine germline mutations and mutation profiles in 36 matched tumor-normal ESCC specimens. Additionally, tumor mutational burden (TMB) values were measured in two cohorts.

Results

We identified four novel germline mutations in patients with familial ESCC, in BAX (c.121dupG: p.E41G), CDKN2A (c.374dupA: p.D125E), TP53 (c.856G>A: p.E286K), and CHEK1 (c.923+1G>A). Mutation profiles revealed that patients with and without a family history of ESCC had similar high-frequency gene mutation profiles, among which TP53 was the most commonly mutated gene. Additionally, tumor-specific mutated genes in patients with a positive family history of ESCC were APC, AKT3, DPYD, EP300, NFE2L2, PPP2R1A, RUNX1, and VEGFA, while those in patients without a family history of ESCC were CXCR4, PIK3R2, SMARCA4, and TTF1. Moreover, patients with positive family history had significantly higher TMB values (7.8 ± 4.1 vs 5.0 ± 2.4, for patients with and without a family history, respectively; P = 0.038).

Conclusion

Our results identified mutation profiles in patients with familial and nonfamilial ESCC, and identified germline mutations in patients with positive history. TMB values may be informative for immunotherapy approaches in familial ESCC.

GULP1 regulates the NRF2-KEAP1 signaling axis in urothelial carcinoma

Disruption of the KEAP1-NRF2 pathway results in the transactivation of NRF2 target genes, consequently inducing cell proliferation and other phenotypic changes in cancer cells. Here, we demonstrated that GULP1 was a KEAP1-binding protein that maintained actin cytoskeleton architecture and helped KEAP1 to sequester NRF2 in the cytoplasm. In urothelial carcinoma of the bladder (UCB), silencing of GULP1 facilitated the nuclear accumulation of NRF2, led to constitutive activation of NRF2 signaling, and conferred resistance to the platinum drug cisplatin. Knockdown of GULP1 in UCB cells promoted tumor cell proliferation in vitro and enhanced tumor growth in vivo. In primary UCB, GULP1 silencing was more prevalent in muscle-invasive UCB compared to nonmuscle-invasive UCB. GULP1 knockdown cells showed resistance to cisplatin treatment. In parallel with decreased GULP1 expression, we observed increased expression of NRF2, HMOX1, and other candidate antioxidant genes in cisplatin-resistant cells. Furthermore, low or no expression of GULP1 was observed in most cisplatin nonresponder cases. Silencing of GULP1 was associated with GULP1 promoter hypermethylation in cell lines and primary tumors, and a high frequency of GULP1 promoter methylation was observed in multiple sets of primary clinical UCB samples. Together, our findings demonstrate that GULP1 is a KEAP1-binding protein that regulates KEAP1-NRF2 signaling in UCB and that promoter hypermethylation of GULP1 is a potential mechanism of GULP1 silencing.

Nrf2 promotes esophageal squamous cell carcinoma (ESCC) resistance to radiotherapy through the CaMKIIα-associated activation of autophagy

BACKGROUND

NF-E2-related factor 2 (Nrf2) is involved in the radiation resistance of esophageal squamous cell carcinoma (ESCC), but the underlying molecular mechanism is unclear. The purpose of our study was to explore the role of Nrf2 in the radiation resistance of ESCC and the potential molecular mechanism.

RESULTS

Nrf2 expression was introduced into Ec109 and KYSE-30 ESCC cells with lentivirus. CCK-8 and colony formation assays were used to evaluate the effect of Nrf2 on radioresistance in culture. The autophagy level was assessed by western blotting, flow cytometry, and confocal fluorescence microscopy. The effect of Nrf2 on the transcription of Ca2 +/calmodulin-dependent protein kinase II α (CaMKIIα) was studied by chromatin immunoprecipitation. We found that the overexpression of Nrf2 increased the radiation resistance of ESCC cells. Mechanistically, Nrf2 triggered the radiation resistance of ESCC cells by targeting CaMKIIα and subsequently activating autophagy. In addition, we found that Nrf2 directly regulated the transcription of CaMKIIα by binding to its promoter region. The effect of Nrf2 on radiation resistance was also explored in both a xenograft mouse model and ESCC patient samples. Consistent with the results of the in vitro study, high Nrf2 expression level resulted in in vivo radioresistance in an Ec109-derived xenograft mouse model. Furthermore, we also demonstrated that upregulations of both Nrf2 and CaMKIIα was closely related to lower survival rates of ESCC patients.

CONCLUSIONS

Our study reveals that Nrf2 promotes the radiation resistance of ESCC by targeting CaMKIIα and subsequently activating autophagy, which is characterized by the suppression of phosphorylated mTOR and p62, activation of Beclin 1, and transformation of LC3-I to LC3-II.

Molecular Mechanisms Underlying Hepatocellular Carcinoma Induction by Aberrant NRF2 Activation-Mediated Transcription Networks: Interaction of NRF2-KEAP1 Controls the Fate of Hepatocarcinogenesis

NF-E2-related factor 2 (NRF2) is a basic leucine zipper transcription factor, a master regulator of redox homeostasis regulating a variety of genes for antioxidant and detoxification enzymes. NRF2 was, therefore, initially thought to protect the liver from oxidative stress. Recent studies, however, have revealed that mutations in NRF2 cause aberrant accumulation of NRF2 in the nucleus and exert the upregulation of NRF2 target genes. Moreover, among all molecular changes in hepatocellular carcinoma (HCC), NRF2 activation has been revealed as a more prominent pathway contributing to the progression of precancerous lesions to malignancy. Nevertheless, how its activation leads to poor prognosis in HCC patients remains unclear. In this review, we provide an overview of how aberrant activation of NRF2 triggers HCC development. We also summarize the emerging roles of other NRF family members in liver cancer development.

The role of natural products in revealing NRF2 function

Covering: up to 2020The transcription factor NRF2 is one of the body's major defense mechanisms, driving transcription of >300 antioxidant response element (ARE)-regulated genes that are involved in many critical cellular processes including redox regulation, proteostasis, xenobiotic detoxification, and primary metabolism. The transcription factor NRF2 and natural products have an intimately entwined history, as the discovery of NRF2 and much of its rich biology were revealed using natural products both intentionally and unintentionally. In addition, in the last decade a more sinister aspect of NRF2 biology has been revealed. NRF2 is normally present at very low cellular levels and only activated when needed, however, it has been recently revealed that chronic, high levels of NRF2 can lead to diseases such as diabetes and cancer, and may play a role in other diseases. Again, this "dark side" of NRF2 was revealed and studied largely using a natural product, the quassinoid, brusatol. In the present review, we provide an overview of NRF2 structure and function to orient the general reader, we will discuss the history of NRF2 and NRF2-activating compounds and the biology these have revealed, and we will delve into the dark side of NRF2 and contemporary issues related to the dark side biology and the role of natural products in dissecting this biology.

Heterogeneous genomic aberrations in esophageal squamous cell carcinoma: a review

Esophageal cancer (EC) causes hundreds of thousands of deaths a year worldwide, especially the major subtype esophageal squamous cell carcinoma (ESCC). With the advent of next-generation sequencing and the availability of commercial microarrays, abnormities in genetic levels have been revealed in various independent researches. High frequencies of structure variations (SVs), single nucleotide variations (SNVs) and copy-number alterations (CNAs) in ESCCs are uncovered, and ESCC shows high levels of inter- and intratumor heterogeneity, implying diverse evolutionary trajectories. This review tries to explain the pathogenesis of ESCC on the scope of most often mutated genes based on prior studies, hopes to offer some hints for diagnosis and therapy in clinic.

Whole-genome sequencing of 508 patients identifies key molecular features associated with poor prognosis in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a poor-prognosis cancer type with limited understanding of its molecular etiology. Using 508 ESCC genomes, we identified five novel significantly mutated genes and uncovered mutational signature clusters associated with metastasis and patients' outcomes. Several functional assays implicated that NFE2L2 may act as a tumor suppressor in ESCC and that mutations in NFE2L2 probably impaired its tumor-suppressive function, or even conferred oncogenic activities. Additionally, we found that the NFE2L2 mutations were significantly associated with worse prognosis of ESCC. We also identified potential noncoding driver mutations including hotspot mutations in the promoter region of SLC35E2 that were correlated with worse survival. Approximately 5.9% and 15.2% of patients had high tumor mutation burden or actionable mutations, respectively, and may benefit from immunotherapy or targeted therapies. We found clinically relevant coding and noncoding genomic alterations and revealed three major subtypes that robustly predicted patients' outcomes. Collectively, we report the largest dataset of genomic profiling of ESCC useful for developing ESCC-specific biomarkers for diagnosis and treatment.

Treatment-related complications in patients with esophageal cancer: A systematic review and network meta-analysis

BACKGROUND

The aim of this review was to compare the available treatments of esophageal cancer, in terms of pulmonary, cardiovascular complications, anastomotic leakage, and esophagitis after treatment in patients with esophageal squamous cell carcinoma (SCC).

METHODS

Medline, Web of Science, Scopus, the Cochrane Library and Embase were searched. The randomized controlled trials (RCT) that had compared the treatment -related complications of treatments for esophageal SCC were included. We included 39 randomized control trials in a network meta-analysis. The Chi2-test was used to assess of heterogeneity. The loop-specific and design-by-treatment interaction methods were used for assessment of consistency assumption. The risk ratio with 95% confidence interval (CI) was used to report the effect-sizes in the network meta-analysis.

RESULTS

The pulmonary complication, cardiac complication, anastomotic leakage, and esophagitis were reported in 31, 11, 17, and 15 RCTs respectively. Video-assisted thoracoscopy + laparoscopy (VATS) was rank as the first and second treatment in terms of lower risk for pulmonary complication and anastomotic leakage. There was no statistically significant difference between treatments in terms of lower risk of cardiovascular complications. However, Surgery + Cisplatin + Fluorouracil (SCF) was ranked as better treatment. 3-dimensional conformal radiotherapy + Docetaxel + Cisplatin (3DCRTDC) was the best treatment in terms of lower risk for esophagitis.

CONCLUSION

According to the results of this study, it seems the risk of pulmonary, cardiovascular, anastomotic leakage and esophagitis complications for VATS, SCF, surgery + radiotherapy (SRT), and 3DCRTDC was lower than other treatments respectively in the networks.

Keap1 deletion accelerates mutant K-ras/p53-driven cholangiocarcinoma

The activation of the Kelch-like ECH-associated protein 1 (Keap1)-NF-E2-related factor 2 (Nrf2) pathway contributes to cancer progression in addition to oxidative stress responses. Loss-of-function Keap1 mutations were reported to activate Nrf2, leading to cancer progression. We examined the effects of Keap1 deletion in a cholangiocarcinoma mouse model using a mutant K-ras/p53 mouse. Introduction of the Keap1 deletion into liver-specific mutant K-ras/p53 expression resulted in the formation of invasive cholangiocarcinoma. Comprehensive analyses of the gene expression profiles identified broad upregulation of Nrf2-target genes such as Nqo1 and Gstm1 in the Keap1-deleted mutant K-ras/p53 expressing livers, accompanied by upregulation of cholangiocyte-related genes. Among these genes, the transcriptional factor Sox9 was highly expressed in the dysplastic bile duct. The Keap-Nrf2-Sox9 axis might serve as a novel therapeutic target for cholangiocarcinoma.NEW & NOTEWORTHY The Keap1-Nrf2 system has a wide variety of effects in addition to the oxidative stress response in cancer cells. Addition of the liver-specific Keap1 deletion to mice harboring mutant K-ras and p53 accelerated cholangiocarcinoma formation, together with the hallmarks of Nrf2 activation. This process involved the expansion of Sox9-positive cells, indicating increased differentiation toward the cholangiocyte phenotype.

Metabolic features of cancer cells in NRF2 addiction status

The KEAP1-NRF2 system is a sulfur-employing defense mechanism against oxidative and electrophilic stress. NRF2 is a potent transcription activator for genes mediating sulfur-involving redox reactions, and KEAP1 controls the NRF2 activity in response to the stimuli by utilizing reactivity of sulfur atoms. In many human cancer cells, the KEAP1-mediated regulation of NRF2 activity is abrogated, resulting in the persistent activation of NRF2. Persistently activated NRF2 drives malignant progression of cancers by increasing therapeutic resistance and promoting aggressive tumorigenesis, a state termed as NRF2 addiction. In NRF2-addicted cancer cell, NRF2 contributes to metabolic reprogramming in cooperation with other oncogenic pathways. In particular, NRF2 strongly activates cystine uptake coupled with glutamate excretion and glutathione synthesis, which increases consumption of intracellular glutamate. Decreased availability of glutamate limits anaplerosis of the TCA cycle, resulting in low mitochondrial respiration, and nitrogen source, resulting in the high dependency on exogenous non-essential amino acids. The highly enhanced glutathione synthesis is also likely to alter sulfur metabolism, which can contribute to the maintenance of the mitochondrial membrane potential in normal cells. The potent antioxidant and detoxification capacity supported by abundant production of glutathione is achieved at the expense of central carbon metabolism and requires skewed metabolic flow of sulfur. These metabolic features of NRF2 addiction status provide clues for novel therapeutic strategies to target NRF2-addicted cancer cells.

Cullin 3 and Its Role in Tumorigenesis

Cullin 3 (Cul3) family of ubiquitin ligases comprises three components, the RING finger protein RBX1, the Cul3 scaffold, and a Bric-a-brac/Tramtrack/Broad complex (BTB) protein. The BTB protein serves as a bridge to connect Cul3 to substrate and is functionally equivalent to the combination of substrate adaptor and linker in other Cullin complexes. Human genome encodes for ~180 BTB proteins, implying a broad spectrum of ubiquitination signals and substrate repertoire. Accordingly, Cul3 ubiquitin ligases are involved in diverse cellular processes, including cell division, differentiation, cytoskeleton remodeling, stress responses, and nerve cell functions. Emerging evidence has pointed to the prominent role of Cul3 ubiquitin ligases in cancer. This chapter will describe recent advances on the roles of Cul3 E3 ligase complexes in regulating various cancer hallmarks and therapeutic responses and the mutation/dysregulation of Cul3 substrate adaptors in cancer. In particular, we will focus on several extensively studied substrate adaptors, such as Keap1, SPOP, KLHL20, and LZTR1, and will also discuss other recently identified Cul3 adaptors with oncogenic or tumor-suppressive functions. We conclude that Cul3 ubiquitin ligases represent master regulators of human malignancies and highlight the importance of developing modulating agents for oncogenic/tumor-suppressive Cul3 E3 ligase complexes to prevent or intervene tumorigenesis.

Genome-wide global identification of NRF2 binding sites in A549 non-small cell lung cancer cells by ChIP-Seq reveals NRF2 regulation of genes involved in focal adhesion pathways

Nuclear factor erythroid-derived-2-like 2(NRF2) regulates its downstream genes through binding with antioxidant responsive elements in their promoter regions. Hyperactivation of NRF2 results in oncogenesis and drug resistance in various cancers including non-small cell lung cancer (NSCLC). However, identification of the genes and pathways regulated by NRF2 in NSCLC warrants further investigation. We investigated the global NRF2 genomic binding sites using the high-throughput ChIP-Seq technique in KEAP1 (Kelch-like ECH-associated protein 1)-mutated A549 (NSCLC) cells. We next carried out an integrated analysis of the ChIP-Seq data with transcriptomic data from A549 cells with NRF2-knockdown and RNA-Seq data from TCGA patients with altered KEAP1 to identify downstream and clinically-correlated genes respectively. Furthermore, we applied transcription factor enrichment analysis, generated a protein-protein interaction network, and used kinase enrichment analysis. Moreover, functional annotation of NRF2 binding sites using DAVID v7 identified the genes involved in focal adhesion. Putative focal adhesion genes regulated by NRF2 were validated using qRT-PCR. Further, we selected one novel conserved focal adhesion gene regulated by NRF2–LAMC1 (laminin subunit gamma 1) and validated it using a reporter assay. Overall, the identification of NRF2 target genes paves the way for identifying the molecular mechanism of NRF2 signaling in NSCLC development and therapy. Moreover, our data highlight the complexity of the pathways regulated by NRF2 in lung tumorigenesis.

Nrf2 Activation Ameliorates Hepatotoxicity Induced by a Heme Synthesis Inhibitor

Transcription factor Nrf2 protects hepatocytes against various toxicants by upregulating cytoprotective genes. The heme synthesis inhibitor 3, 5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) leads to liver injury around the portal vein, unlike other groups of toxicants that cause hemorrhage and necrosis in the centrilobular area. To examine whether and how Nrf2 protects livers from the injury, we fed DDC to Nrf2 knockout (Nrf2KO), wild-type (WT), Keap1flox/flox (Keap1-knockdown; Keap1KD), and liver-specific Keap1 knockout (Keap1-Alb) mice, as these lines of mice exhibit stepwise increases in Nrf2 protein expression levels. Liver-specific Keap1::Nrf2 double-knockout (Keap1::Nrf2-Alb) mice were also exploited to examine the contribution of Nrf2. Two weeks after DDC feeding, Keap1-Alb mice were fully recovered from body weight loss, but the WT and Nrf2KO mice were not. The liver-to-body-weight ratio of Keap1-Alb mice was significantly larger than that of WT and Nrf2KO mice. Two indicators of hepatotoxicity, alanine aminotransferase and bilirubin in plasma, were both elevated in WT mice, but downregulated in Keap1-Alb mice after the DDC-feeding. DDC-induced porphyrin accumulation was reduced in the livers of Keap1-Alb and Keap1KD mice compared with that of WT mice. When assessed by the Nqo1 level, Nrf2 expression was further enhanced by DDC in Keap1-Alb mice, suggesting that DDC may have a Keap1 independent potential to activate Nrf2. Genetic activation of Nrf2 in Keap1-Alb mice increased the extracellular excretion of porphyrins, but contrary to our expectation, hepatic damages in Nrf2KO mice appeared to be similar to that of WT mice. Based on these observations, we conclude that Nrf2 activation protects livers against DDC-elicited hepatotoxicity.

Esophageal carcinoma: Towards targeted therapies

BACKGROUND

Patients with esophageal cancer are confronted with high mortality rates. Whether it is esophageal squamous cell carcinoma (ESCC) or esophageal adenocarcinoma (EAC), patients usually present at advanced stages, with treatment options traditionally involving chemotherapy in metastatic settings. With the comprehensive genomic characterization of esophageal cancers, targeted therapies are gaining interest and agents such as ramucirumab, trastuzumab and pembrolizumab are already being used for the treatment of EAC.

CONCLUSIONS

Pembrolizumab has recently been FDA-approved for PD-L1 positive, locally advanced or metastatic ESCC. Despite comprehensive molecular characterization, however, available targed therapies for ESCC are still lagging behind. Herein, we discuss current trends towards more targeted therapies in esophageal cancers, taking into consideration unique features of ESCCs and EACs. Patients progressing on standard therapies should be subjected to genomic profiling and considered for clinical trials aimed at testing targeted therapies. Future targeted therapies may include CDK4/6 inhibitors, PARP inhibitors and inhibitors targeting the NRF2 and Wnt signaling pathways. Ultimately, optimized biomarker assays and next generation sequencing platforms may allow for the identification of subcategories of ESCC and EAC patients that will benefit from selective targeted therapies and/or combinations thereof.

The expression of p-p62 and nuclear Nrf2 in esophageal squamous cell carcinoma and association with radioresistance

Background

The roles of p62‐Keap1‐Nrf2 pathway in the radioresistance of esophageal squamous cell carcinoma (ESCC) have not yet been revealed. This study aimed to clarify the expression and correlation of p‐p62 and nuclear Nrf2 and their association with radioresistance in ESCC.

Methods

This study included 164 cases of inoperable locally advanced ESCC. All patients received concurrent chemoradiotherapy (CCRT). Immunohistochemical staining was used to detect the expression of p‐p62 and nuclear Nrf2. The results were analyzed independently by two pathologists.

Results

There was no significant relationship between p‐p62 or nuclear Nrf2 and patients' clinical characteristics. Compared to patients with low expression of p‐p62, patients with high expression of p‐p62 showed lower objective response rate (ORR). Similarly, patients with high expression of nuclear Nrf2 exhibited lower ORR compared to those with low expression of nuclear Nrf2. The expression of p‐p62 was positively correlated with that of nuclear Nrf2. Moreover, the correlation coefficient between them was higher among patients showing no response to CCRT. Univariate analysis revealed that higher expression of p‐p62 or nuclear Nrf2 was significantly associated with poorer PFS and OS. Multivariate analysis indicated that the expression of nuclear Nrf2 and treatment response were independent prognostic factors for PFS. Sex, treatment response, expression of p‐p62 and nuclear Nrf2 were independent prognostic factors for OS.

Conclusion

Higher expression of p‐p62 and nuclear Nrf2 are associated with lower ORR as well as poorer prognosis, which indicates that p62‐Keap1‐Nrf2 pathway might play an essential role in the radioresistance of ESCC.

Key points

The expression of p‐p62 and nuclear Nrf2 in ESCC show a significant relationship with patients' responses to CCRT and influence the prognosis of ESCC.

p62‐Keap1‐Nrf2 pathway might be a new target for radiosensitization in ESCC.

Cullin Ring Ubiquitin Ligases (CRLs) in Cancer: Responses to Ionizing Radiation (IR) Treatment

Treatment with ionizing radiation (IR) remains the cornerstone of therapy for multiple cancer types, including disseminated and aggressive diseases in the palliative setting. Radiotherapy efficacy could be improved in combination with drugs that regulate the ubiquitin-proteasome system (UPS), many of which are currently being tested in clinical trials. The UPS operates through the covalent attachment of ATP-activated ubiquitin molecules onto substrates following the transfer of ubiquitin from an E1, to an E2, and then to the substrate via an E3 enzyme. The specificity of ubiquitin ligation is dictated by E3 ligases, which select substrates to be ubiquitylated. Among the E3s, cullin ring ubiquitin ligases (CRLs) represent prototypical multi-subunit E3s, which use the cullin subunit as a central assembling scaffold. CRLs have crucial roles in controlling the cell cycle, hypoxia signaling, reactive oxygen species clearance and DNA repair; pivotal factors regulating the cancer and normal tissue response to IR. Here, we summarize the findings on the involvement of CRLs in the response of cancer cells to IR, and we discuss the therapeutic approaches to target the CRLs which could be exploited in the clinic.

Genome-Wide CRISPR Screen Reveals Autophagy Disruption as the Convergence Mechanism That Regulates the NRF2 Transcription Factor

The nuclear factor (erythroid 2)-like 2 (NRF2 or NFE2L2) transcription factor regulates the expression of many genes that are critical in maintaining cellular homeostasis. Its deregulation has been implicated in many diseases, including cancer and metabolic and neurodegenerative diseases. While several mechanisms by which NRF2 can be activated have gradually been identified over time, a more complete regulatory network of NRF2 is still lacking. Here we show through a genome-wide clustered regularly interspaced short palindromic repeat (CRISPR) screen that a total of 273 genes, when knocked out, will lead to sustained NRF2 activation. Pathway analysis revealed a significant overrepresentation of genes (18 of the 273 genes) involved in autophagy. Molecular validation of a subset of the enriched genes identified 8 high-confidence genes that negatively regulate NRF2 activity irrespective of cell type: ATG12, ATG7, GOSR1, IFT172, NRXN2, RAB6A, VPS37A, and the well-known negative regulator of NRF2, KEAP1 Of these, ATG12, ATG7, KEAP1, and VPS37A are known to be involved in autophagic processes. Our results present a comprehensive list of NRF2 negative regulators and reveal an intimate link between autophagy and NRF2 regulation.

Paired whole exome and transcriptome analyses for the Immunogenomic changes during concurrent chemoradiotherapy in esophageal squamous cell carcinoma

BACKGROUND

The immunogenomic changes triggered by concurrent chemoradiation therapy (CCRT), a standard neoadjuvant treatment for locally advanced esophageal squamous cell carcinoma (ESCC), are unknown. We aimed to analyze the early immunogenomic changes in ESCC induced by CCRT and to correlate them with clinical outcomes.

METHODS

We collected biopsy samples from 40 patients with ESCC and the surgical candidates were treated with 5-fluorouracil (5-FU)/Cisplatin and concurrent radiation therapy. Endoscopic biopsy was performed before and after one treatment cycle of 5-FU/Cisplatin and 5 to 18 fractions of radiation. We analyzed immunogenomic changes using paired whole-exome sequencing (n = 29) and paired whole-transcriptome sequencing (WTS, n = 23). Multiplex immunohistochemistry (IHC) was conducted in four representative pair samples.

RESULTS

Fourteen out of 23 WTS samples (60.8%) showed increased immune scores after CCRT, as calculated by ESTIMATE. The rate of progression-free survival was higher in patients with increased immune scores compared with the remaining patients (83.1% vs. 57.1%, p = 0.25). Tumor mutation burden and neoantigen load were significantly reduced after CCRT (p < 0.001). We observed no specific correlation with non-synonymous mutations and no changes in the single-nucleotide variant spectrum after CCRT. Post-CCRT samples were enriched in gene sets related to immune signaling pathways, such as interferon gamma signaling and CD28 co-stimulation. Multiplex IHC showed an incremental trend in the proportion of CD4 positive cells in cytokeratin positive region after CCRT. However, CD8, CD20, FOXP1, PD-L1 showed no definitive trend. Proportion of immune cells calculated by CIBERSORT, showed that significant increase in neutrophils after CCRT.

CONCLUSIONS

We have comprehensively analyzed the early immunogenomic changes induced in ESCC by CCRT and correlated them with clinical outcomes. Our results provide a potential basis for combining immunotherapy with CCRT for the treatment of ESCC.

Potential Applications of NRF2 Inhibitors in Cancer Therapy

The NRF2/KEAP1 pathway represents one of the most important cell defense mechanisms against exogenous or endogenous stressors. Indeed, by increasing the expression of several cytoprotective genes, the transcription factor NRF2 can shelter cells and tissues from multiple sources of damage including xenobiotic, electrophilic, metabolic, and oxidative stress. Importantly, the aberrant activation or accumulation of NRF2, a common event in many tumors, confers a selective advantage to cancer cells and is associated to malignant progression, therapy resistance, and poor prognosis. Hence, in the last years, NRF2 has emerged as a promising target in cancer treatment and many efforts have been made to identify therapeutic strategies aimed at disrupting its prooncogenic role. By summarizing the results from past and recent studies, in this review, we provide an overview concerning the NRF2/KEAP1 pathway, its biological impact in solid and hematologic malignancies, and the molecular mechanisms causing NRF2 hyperactivation in cancer cells. Finally, we also describe some of the most promising therapeutic approaches that have been successfully employed to counteract NRF2 activity in tumors, with a particular emphasis on the development of natural compounds and the adoption of drug repurposing strategies.

Emerging Therapeutic Targets in Oncologic Photodynamic Therapy

Background:

Reactive oxygen species sustain tumorigenesis and cancer progression through deregulated redox signalling which also sensitizes cancer cells to therapy. Photodynamic therapy (PDT) is a promising anti-cancer therapy based on a provoked singlet oxygen burst, exhibiting a better toxicological profile than chemo- and radiotherapy. Important gaps in the knowledge on underlining molecular mechanisms impede on its translation towards clinical applications.

Aims and Methods:

The main objective of this review is to critically analyse the knowledge lately gained on therapeutic targets related to redox and inflammatory networks underlining PDT and its outcome in terms of cell death and resistance to therapy. Emerging therapeutic targets and pharmaceutical tools will be documented based on the identified molecular background of PDT.

Results:

Cellular responses and molecular networks in cancer cells exposed to the PDT-triggered singlet oxygen burst and the associated stresses are analysed using a systems medicine approach, addressing both cell death and repair mechanisms. In the context of immunogenic cell death, therapeutic tools for boosting anti-tumor immunity will be outlined. Finally, the transcription factor NRF2, which is a major coordinator of cytoprotective responses, is presented as a promising pharmacologic target for developing co-therapies designed to increase PDT efficacy.

Conclusion:

There is an urgent need to perform in-depth molecular investigations in the field of PDT and to correlate them with clinical data through a systems medicine approach for highlighting the complex biological signature of PDT. This will definitely guide translation of PDT to clinic and the development of new therapeutic strategies aimed at improving PDT.

Combined Modality Therapy for Management of Esophageal Cancer: Current Approach Based on Experiences from East and West

Human evolutionary genetic divergence and distinctive environmental exposures have contributed to the development of clinicopathologic variations of esophageal cancer in Eastern and Western countries. Different treatment strategies have derived from the disparate regional experiences. Treatment strategy is more standardized in the West. Trimodality treatment with neoadjuvant chemoradiation followed by surgery is widely accepted as the standard treatment of locally advanced esophageal adenocarcinoma and esophageal squamous cell carcinoma. Trimodality treatment has not been adopted in many Eastern countries, and standard treatment is neoadjuvant chemotherapy. Several randomized trials are ongoing that may alter the standard management of esophageal cancer worldwide.

The discovery and characterization of K-563, a novel inhibitor of the Keap1/Nrf2 pathway produced by Streptomyces sp

Keap1/Nrf2 pathway regulates the antioxidant stress response, detoxification response, and energy metabolism. Previous reports found that aberrant Keap1/Nrf2 pathway activation due to Kelch‐like ECH‐associated protein 1 (Keap1) mutations or Nuclear factor E2‐related factor 2 (Nrf2) mutations induced resistance of cancer cells to chemotherapy and accelerated cell growth via the supply of nutrients. Therefore, Keap1/Nrf2 pathway activation is associated with a poor prognosis in many cancers. These previous findings suggested that inhibition of Keap1/Nrf2 pathway could be a target for anti‐cancer therapies. To discover a small‐molecule Keap1/Nrf2 pathway inhibitor, we conducted high‐throughput screening in Keap1 mutant human lung cancer A549 cells using a transcriptional reporter assay. Through this screening, we identified the novel Keap1/Nrf2 pathway inhibitor K‐563, which was isolated from actinomycete Streptomyces sp. K‐563 suppressed the expression of Keap1/Nrf2 pathway downstream target genes or the downstream target protein, which induced suppression of GSH production, and activated reactive oxygen species production in A549 cells. K‐563 also inhibited the expression of downstream target genes in other Keap1‐ or Nrf2‐mutated cancer cells. Furthermore, K‐563 exerted anti‐proliferative activities in these mutated cancer cells. These in vitro analyses showed that K‐563 was able to inhibit cell growth in Keap1‐ or Nrf2‐mutated cancer cells by Keap1/Nrf2 pathway inhibition. K‐563 also exerted synergistic combinational effects with lung cancer chemotherapeutic agents. An in vivo study in mice xenotransplanted with A549 cells to further explore the therapeutic potential of K‐563 revealed that it also inhibited Keap1/Nrf2 pathway in lung cancer tumors. K‐563, a novel Keap1/Nrf2 pathway inhibitor, may be a lead compound for development as an anti‐cancer agent.

The Nrf2/HO-1 axis can be a prognostic factor in clear cell renal cell carcinoma

Objective

To study the protein expression level of Nrf2/HO-1 in clear cell renal cell carcinoma (ccRCC) and adjacent normal tissue and to explore its relationship with clinicopathological characteristics and prognosis in ccRCC patients.

Materials and methods

In total, 152 ccRCC patients with available follow-up and clinical data were enrolled, and sample microarrays were prepared for immunohistochemistry studies. The human ccRCC cell lines 786-O, OS-RC-2, A498, and ACHN were cultured for immunofluorescence. The protein concentrations of five ccRCC patients’ tumor and adjacent normal renal tissues were prepared for Western blotting. Chi-squared tests, Fisher’s exact test, Kaplan–Meier analyses, log-rank tests, and Cox regression were performed for statistical analyses.

Results

The immunoreactivity results showed that the Nrf2 and HO-1 proteins were found in consistent locations in vitro and were expressed both in ccRCC and adjacent normal tissues. The two proteins were localized in the cytoplasm and nucleus of RCC tumor cells and in adjacent normal tissue cells. The expression levels of Nrf2 and HO-1 were significantly higher in ccRCC tissues than in the adjacent normal tissues. The Nrf2 protein level was found to be significantly correlated with the tumor size. Additionally, higher protein expression levels of Nrf2 and HO-1 were also correlated with worse overall survival outcomes and could potentially be used to predict the prognosis of ccRCC patients.

Conclusion

Our study provides an important theoretical basis for evaluating the clinical prognosis of ccRCC patients, which implies that the Nrf2/HO-1 axis can be a prognostic factor in ccRCC.

The Regulation of NRF2 by Nutrient-Responsive Signaling and Its Role in Anabolic Cancer Metabolism

SIGNIFICANCE

The stress responsive transcription factor nuclear factor erythroid 2 p45-related factor 2, or NRF2, regulates the expression of many cytoprotective enzymes to mitigate oxidative stress under physiological conditions. NRF2 is activated in response to oxidative stress, growth factor signaling, and changes in nutrient status. In addition, somatic mutations that disrupt the interaction between NRF2 and its negative regulator Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated 1 (KEAP1) commonly occur in cancer and are thought to promote tumorigenesis. Recent Advances: While it is well established that aberrant NRF2 activation results in enhanced antioxidant capacity in cancer cells, recent exciting findings demonstrate a role for NRF2-mediated metabolic deregulation that supports cancer cell proliferation.

CRITICAL ISSUES

In this review, we describe how the NRF2-KEAP1 signaling pathway is altered in cancer, how NRF2 is regulated by changes in cellular metabolism, and how NRF2 reprograms cellular metabolism to support proliferation.

FUTURE DIRECTIONS

Future studies will delineate the NRF2-regulated processes critical for metabolic adaptation to nutrient availability, cellular proliferation, and tumorigenesis. Antioxid. Redox Signal. 00, 000-000.

Molecular landscape of esophageal cancer: implications for early detection and personalized therapy

Esophageal cancer (EC) is one of the most lethal cancers and a public health concern worldwide, owing to late diagnosis and lack of efficient treatment. Esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC) are main histopathological subtypes of EC that show striking differences in geographical distribution, possibly due to differences in exposure to risk factors and lifestyles. ESCC and EAC are distinct diseases in terms of cell of origin, epidemiology, and molecular architecture of tumor cells. Past efforts aimed at translating potential molecular candidates into clinical practice proved to be challenging, underscoring the need for identifying novel candidates for early diagnosis and therapy of EC. Several major international efforts have brought about important advances in identifying molecular landscapes of ESCC and EAC toward understanding molecular mechanisms and critical molecular events driving the progression and pathological features of the disease. In our review, we summarize recent advances in the areas of genomics and epigenomics of ESCC and EAC, their mutational signatures and immunotherapy. We also discuss implications of recent advances in characterizing the genome and epigenome of EC for the discovery of diagnostic/prognostic biomarkers and development of new targets for personalized treatment and prevention.

Hyperactivity of the transcription factor Nrf2 causes metabolic reprogramming in mouse esophagus

Mutations in the genes encoding nuclear factor (erythroid-derived 2)-like 2 (NRF2), Kelch-like ECH-associated protein 1 (KEAP1), and cullin 3 (CUL3) are commonly observed in human esophageal squamous cell carcinoma (ESCC) and result in activation of the NRF2 signaling pathway. Moreover, hyperactivity of the transcription factor Nrf2 has been found to cause esophageal hyperproliferation and hyperkeratosis in mice. However, the underlying mechanism is unclear. In this study, we aimed to understand the molecular mechanisms of esophageal hyperproliferation in mice due to hyperactive Nrf2. Esophageal tissues were obtained from genetically modified mice that differed in the status of the Nrf2 gene and genes in the same pathway (Nrf2 ^-/-, Keap1 ^-/-, K5Cre;Pkm2^fl/fl;Keap1 ^-/-, and WT) and analyzed for metabolomic profiles, Nrf2 ChIP-seq, and gene expression. We found that hyperactive Nrf2 causes metabolic reprogramming and up-regulation of metabolic genes in the mouse esophagus. One of the glycolysis genes encoding pyruvate kinase M2 (Pkm2) was not only differentially up-regulated, but also glycosylated and oligomerized, resulting in increased ATP biosynthesis. However, constitutive knockout of Pkm2 failed to inhibit this esophageal phenotype in vivo, and this failure may have been due to compensation by Pkm1 up-regulation. Transient inhibition of NRF2 or glycolysis inhibited the growth of human ESCC cells in which NRF2 is hyperactive in vitro In summary, hyperactive Nrf2 causes metabolic reprogramming in the mouse esophagus through its transcriptional regulation of metabolic genes. Blocking glycolysis transiently inhibits cell proliferation and may therefore have therapeutically beneficial effects on NRF2^high ESCC in humans.

Identification of distinct mutational patterns and new driver genes in oesophageal squamous cell carcinomas and adenocarcinomas

OBJECTIVES

Oesophageal squamous cell carcinoma (OSCC) and adenocarcinoma (OAC) are distinct cancers in terms of a number of clinical and epidemiological characteristics, complicating the design of clinical trials and biomarker developments. We analysed 1048 oesophageal tumour-germline pairs from both subtypes, to characterise their genomic features, and biological and clinical significance.

DESIGN

Previously exome-sequenced samples were re-analysed to identify significantly mutated genes (SMGs) and mutational signatures. The biological functions of novel SMGs were investigated using cell line and xenograft models. We further performed whole-genome bisulfite sequencing and chromatin immunoprecipitation (ChIP)-seq to characterise epigenetic alterations.

RESULTS

OSCC and OAC displayed nearly mutually exclusive sets of driver genes, indicating that they follow independent developmental paths. The combined sample size allowed the statistical identification of a number of novel subtype-specific SMGs, mutational signatures and prognostic biomarkers. Particularly, we identified a novel mutational signature similar to Catalogue Of Somatic Mutations In Cancer (COSMIC)signature 16, which has prognostic value in OSCC. Two newly discovered SMGs, CUL3 and ZFP36L2, were validated as important tumour-suppressors specific to the OSCC subtype. We further identified their additional loss-of-function mechanisms. CUL3 was homozygously deleted specifically in OSCC and other squamous cell cancers (SCCs). Notably, ZFP36L2 is associated with super-enhancer in healthy oesophageal mucosa; DNA hypermethylation in its super-enhancer reduced active histone markers in squamous cancer cells, suggesting an epigenetic inactivation of a super-enhancer-associated SCC suppressor.

CONCLUSIONS

These data comprehensively contrast differences between OSCC and OAC at both genomic and epigenomic levels, and reveal novel molecular features for further delineating the pathophysiological mechanisms and treatment strategies for these cancers.

Design and development of Nrf2 modulators for cancer chemoprevention and therapy: a review

A major cell defense mechanism against oxidative and xenobiotic stress is mediated by the Nrf2/Keap1 signaling pathway. The Nrf2/Keap1 pathway regulates gene expression of many cytoprotective and detoxifying enzymes, thus playing a pivotal role in maintaining redox cellular homeostasis. Many diseases including cancer have been closely related to impaired Nrf2 activity. Targeting Nrf2 and modulating its activity represents a novel modern strategy for cancer chemoprevention and therapy. In this review, different design strategies used for the development of Nrf2 modulators are described in detail. Moreover, the main focus is on important and recently developed Nrf2 activators and inhibitors, their in vitro and in vivo studies, and their potential use as chemopreventive agents and/or cancer therapeutics.

Cancer Cell Metabolism Featuring Nrf2

Although the major role of Nrf2 has long been established as a transcription factor for providing cellular protection against oxidative stress, multiple pieces of research and reviews now claim exactly the opposite. The dilemma - "to activate or inhibit" the protein requires an immediate answer, which evidently links cellular metabolism to the causes and purpose of cancer. Profusely growing cancerous cells have prolific energy requirements, which can only be fulfilled by modulating cellular metabolism. This review highlights the cause and effect of Nrf2 modulation in cancer that in turn channelize cellular metabolism, thereby fulfilling the energy requirements of cancer cells. The present work also highlights the purpose of genetic mutations in Nrf2, in relation to cellular metabolism in cancer cells, thus pointing out a newer approach where parallel mutations may be the key factor to decide whether to activate or inhibit Nrf2.

A catalogue of somatic NRF2 gain-of-function mutations in cancer

Identification and characterization of somatic mutations in cancer have important prognostication and treatment implications. Genes encoding the Nuclear factor (erythroid-derived 2)-like 2 (NRF2) transcription factor and its negative regulator, Kelch-like ECH-associated protein 1 (KEAP1), are frequently mutated in cancer. These mutations drive constitutive NRF2 activation and correlate with poor prognosis. Despite its apparent significance, a comprehensive catalogue of somatic NRF2 mutations across different tumor types is still lacking. Here, we catalogue NRF2 mutations in The Cancer Genome Atlas (TCGA) database. 226 unique NRF2-mutant tumors were identified from 10,364 cases. NRF2 mutations were found in 21 out of the 33 tumor types. A total of 11 hotspots were identified. Of these, mutation to the R34 position was most frequent. Notably, R34 and D29 mutations were overrepresented in bladder, lung, and uterine cancers. Analyses of corresponding RNA sequencing data using a de novo derived gene expression classifier showed that the R34 mutations drive constitutive NRF2 activation with a selection pressure biased against the formation of R34L. Of all R34 mutants, R34L conferred the least degree of protein stabilization, suggesting a pro-tumor NRF2 half-life threshold. Our findings offer a comprehensive catalogue of NRF2 mutations in cancer that can help prognostication and NRF2 research.

xCT inhibition sensitizes tumors to γ-radiation via glutathione reduction

About 3 million US cancer patients and 1.7 million EU cancer patients received multiple doses of radiation therapy (RT) in 2012, with treatment duration limited by normal adjacent tissue damage. Tumor-specific sensitization could allow treatment with lower radiation doses, reducing normal tissue damage. This is a longstanding, largely unrealized therapeutic goal. The cystine:glutamate exchanger xCT is expressed on poor prognosis subsets of most solid tumors, but not on most normal cells. xCT provides cells with environmental cystine for enhanced glutathione synthesis. Glutathione is used to control reactive oxygen species (ROS), which are therapeutic effectors of RT. We tested whether xCT inhibition would sensitize xCT⁺ tumor cells to ionizing radiation. We found that pretreatment with the xCT inhibitor erastin potently sensitized xCT⁺ but not xCT^- cells, in vitro and in xenograft. Similarly, targeted gene inactivation also sensitized cells, and both modes of sensitization were overcome by glutathione supplementation. Sensitization prolongs DNA damage signaling, increases genome instability, and enhances cell death, revealing an unforeseen role for cysteine in genome integrity maintenance. We conclude that an xCT-specific therapeutic would provide tumor-specific sensitization to RT, allowing treatment with lower radiation doses, and producing far fewer side effects than other proposed sensitizers. Our data speaks to the need for the rapid development of such a drug.

Identification of serum biomarkers of chemoradiosensitivity in esophageal cancer via the targeted metabolomics approach

AIM

To identify the serum metabolomics signature that is correlated with the chemoradiosensitivity of esophageal squamous cell carcinoma (ESCC).

MATERIALS & METHODS

Untargeted and targeted metabolomics analysis of serum samples from 26 ESCC patients, which were collected before the neoadjuvant chemoradiotherapy, was performed.

RESULTS

On receiving the results of untargeted metabolomics analysis, we performed the targeted metabolomics analysis of the six metabolites (arabitol, betaine, glycine, L-serine, L-arginine and L-aspartate). The serum levels of the four metabolites (arabitol, glycine, L-serine and L-arginine) were significantly lower in the patients who achieved pathological complete response with neoadjuvant chemoradiotherapy compared with the patients who did not achieve pathological complete response (p = 0.0086, 0.0345, 0.0106 and 0.0373, respectively).

CONCLUSION

The serum levels of metabolites might be useful for predicting the chemoradiosensitivity of ESCC patients.

The KEAP1-NRF2 System: a Thiol-Based Sensor-Effector Apparatus for Maintaining Redox Homeostasis

The Kelch-like ECH-associated protein 1-NF-E2-related factor 2 (KEAP1-NRF2) system forms the major node of cellular and organismal defense against oxidative and electrophilic stresses of both exogenous and endogenous origins. KEAP1 acts as a cysteine thiol-rich sensor of redox insults, whereas NRF2 is a transcription factor that robustly transduces chemical signals to regulate a battery of cytoprotective genes. KEAP1 represses NRF2 activity under quiescent conditions, whereas NRF2 is liberated from KEAP1-mediated repression on exposure to stresses. The rapid inducibility of a response based on a derepression mechanism is an important feature of the KEAP1-NRF2 system. Recent studies have unveiled the complexities of the functional contributions of the KEAP1-NRF2 system and defined its broader involvement in biological processes, including cell proliferation and differentiation, as well as cytoprotection. In this review, we describe historical milestones in the initial characterization of the KEAP1-NRF2 system and provide a comprehensive overview of the molecular mechanisms governing the functions of KEAP1 and NRF2, as well as their roles in physiology and pathology. We also refer to the clinical significance of the KEAP1-NRF2 system as an important prophylactic and therapeutic target for various diseases, particularly aging-related disorders. We believe that controlled harnessing of the KEAP1-NRF2 system is a key to healthy aging and well-being in humans.

Topoisomerase II Poisons for Glioblastoma; Existing Challenges and Opportunities to Personalize Therapy

Despite advances in surgery, radiotherapy, and chemotherapy, glioblastoma (GBM) remains a malignancy with poor prognosis. The molecular profile of GBM is diverse across patients, and individual responses to therapy are highly variable. Yet, patients diagnosed with GBM are treated with a rather uniform paradigm. Exploiting these molecular differences and inter-individual responses to therapy may present an opportunity to improve the otherwise bleak prognosis of patients with GBM. This review aims to examine one group of chemotherapeutics: Topoisomerase 2 (TOP2) poisons, a class of drugs that enables TOP2 to induce DNA damage, but interferes with its ability to repair it. These potent chemotherapeutic agents are currently used for a number of malignancies and have shown promise in the treatment of GBM. Despite their robust efficacy in vitro, some of these agents have fallen short of achieving similar results in clinical trials for this tumor. In this review, we explore reasons for this discrepancy, focusing on drug delivery and individual susceptibility differences as challenges for effective TOP2-targeting for GBM. We critically review the evidence implicating genes in susceptibility to TOP2 poisons and categorize this evidence as experimental, correlative or both. This is important as mere experimental evidence does not necessarily lead to identification of genes that serve as good biomarkers of susceptibility for personalizing the use of these drugs.

Expression of Keap1 and Nrf2 in diffuse large B-cell lymphoma and its clinical significance

The present study investigated the expression and clinical significance of kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid-2-related factor-2 (Nrf2) expression in diffuse large B-cell lymphoma (DLBCL). These proteins were detected by immunohistochemistry in 39 DLBCL cases and 17 cases of reactive lymph node hyperplasia, and their association with the clinicopathological features of DLBCL patients was analyzed. In DLBCL, the percentage of cells with positive staining for Keap1 and Nrf2 was 46.2 and 35.9%, respectively, which was significantly higher than that in reactive lymph node hyperplasia (17.7 and 5.9%, respectively). There was no correlation between Keap1 and Nrf2 expression according to a Spearman rank correlation analysis (r=0.272; P>0.05). Keap1 and Nrf2 expression was associated with the international prognostic index and Ann-Arbor clinical stage (P<0.05), and Keap1 and Nrf2 expression was higher in DLBCL patients with stage III–IV (68.4 and 52.6%, respectively) compared with in those with stage I–II (25.0 and 20.0%, respectively). The aberrant expression of Keap1 and Nrf2 in DLBCL suggests that these factors may have crucial roles in the development and progression of the disease, and may therefore be used as prognostic indicators.

A network meta-analysis of the treatments for esophageal squamous cell carcinoma in terms of survival

We aimed to compare treatments for patients with esophageal squamous cell carcinoma (SCC) in terms of survival. Medline, Web of Science, Scopus, the Cochrane Library and Embase were searched. Randomized controlled trials (RCT) that had compared esophageal SCC treatments were included. The hazard ratio (HR) with 95% credible interval (CrI) was used to summarize the effect measures in the Bayesian network meta-analysis. Out of 23,256 references, 43 RCTs with 34 treatments were included. Carboplatin and paclitaxel plus radiotherapy plus surgery (carbo-pacli + RT + S) compared with surgery alone decreased risk of death (HR = 0.49; 95% CrI: 0.26, 0.90). The HRs for carbo-pacli + RT + S versus surgery plus cisplatin and fluorouracil and surgery plus cisplatin and vindesine were 0.44 (0.22, 0.86) and 0.41 (0.20, 0.83), respectively. Among all treatments in network, carbo-pacli + RT + S ranked as first treatment. It seems carbo-pacli + RT + S was a better treatment among available treatments in network in terms of survival in patients with esophageal SCC.

Targeted therapy of esophageal squamous cell carcinoma: the NRF2 signaling pathway as target

Esophageal squamous cell carcinoma (ESCC) is a deadly disease that requires extensive research. Here, we review the current understanding of the functions of the nuclear factor erythroid-derived 2-like 2 (NRF2) signaling pathway in the esophagus. Genomic data suggest that gene mutations and several other mechanisms result in NRF2 hyperactivation in human ESCC. As a consequence, NRF2^high ESCC is more resistant to chemoradiotherapy and associated with poorer survival than NRF2^low ESCC. Mechanistically, we believe NRF2, functioning as a transcription factor, causes an esophageal phenotype through regulation of gene transcription. We discuss metabolism, mitochondria, proteasomes, and several signaling pathways as downstream players that may contribute to an esophageal phenotype due to NRF2 hyperactivation. Finally, strategies are proposed to target the NRF2 signaling pathway for therapy of NRF2^high ESCC.

Suppression of lung inflammation by the methanol extract of Spilanthes acmella Murray is related to differential regulation of NF-κB and Nrf2

ETHNOPHARMACOLOGICAL RELEVANCE

Although Spilanthes acmella has been used to relieve inflammation, fever, pain, or infection in traditional Asian medicine, experimental evidence supporting these functions is scarce. Here, we examined an anti-inflammatory function and a possible underlying mechanism of S. acmella Murray (SAM).

MATERIALS AND METHOD

The methanol extract of SAM was fingerprinted by HPLC. C57BL/6 mice were administered with a single intratracheal (i.t.) LPS and 2 h later with a single i.t. SAM. The effect of SAM on lung inflammation was assessed by histology, semi-quantitative RT-PCR, and MPO assay of lung tissue. The effects of SAM on a pro-inflammatory factor NF-κB and an anti-inflammatory factor Nrf2 were analyzed by immunoblotting of nuclear proteins and by semi-quantitative RT-PCR analysis of mRNA of the genes governed by these transcription factors. V5-Nrf2 was precipitated by an anti-V5 antibody and the ubiquitinated V5-Nrf2 was revealed by immunoblotting of HA-tagged ubiquitin.

RESULTS

The i.t. SAM robustly diminished a neutrophilic lung inflammation induced by i.t. LPS treatment of mice. In RAW 264.7 cells, SAM suppressed the nuclear localization of NF-κB and the expression of NF-κB-dependent cytokine genes. SAM increased the level of Nrf2 in the nucleus and the expression of Nrf2-dependent genes while suppressing ubiquitination of Nrf2.

CONCLUSION

Our results suggest that SAM can suppress a neutrophilic inflammation in mouse lungs, which is associated with suppressed NF-κB and activated Nrf2. Our results provide experimental evidence supporting the anti-inflammatory function of S. acmella.

Role of NRF2 in protection of the gastrointestinal tract against oxidative stress

The gastrointestinal tract is exposed to a variety of noxious factors, such as Helicobacter pylori, nonsteroidal anti-inflammatory drugs, gastric acid, ischemia-reperfusion, and mental stresses. Theses stressors generate free radicals within gastrointestinal tissues, causing organ injury and functional disturbance. Although the gastrointestinal tract can withstand such oxidative stresses to some extent by enhancing its antioxidant system via nuclear factor erythroid 2-related factor 2-Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1-mediated pathways, acute or chronic exposure to oxidative stress can cause several gastrointestinal tract disorders, such as inflammation, ulcers, cancers, and various functional disturbances. Recent studies have demonstrated that some natural compounds and drugs can upregulate the nuclear factor erythroid 2-related factor 2-mediated antioxidant system, ameliorating or preventing these disorders. Although these compounds may be useful as chemopreventive agents, sufficient evidence for their clinical efficacy has not yet been provided. In addition, it is important to note that excessive nuclear factor erythroid 2-related factor 2 stimulation can be harmful to human health, especially from the standpoint of tumor biology.

Targeting the KEAP1/NRF2 pathway to manipulate the expression of oncogenic and oncosuppressive miRNAs in human leukemia

The Kelch-like ECH-associated protein 1 (KEAP1)/nuclear factor E2-related factor 2 (NRF2L2, best known as NRF2) pathway plays a pivotal cytoprotective role in the regulation of cellular responses to oxidative stress. We report that NRF2 modulates the expression of microRNA-125B and microRNA-29B in acute myeloid leukemia. The regulation of microRNA in leukemia can now be added to the growing list of prosurvival functions of NRF2.

Nrf2 and Keap1 abnormalities in esophageal squamous cell carcinoma and association with the effect of chemoradiotherapy

BACKGROUND

The Keap1-Nrf2 pathway is a key antioxidant and redox signaling cascade. Pathway abnormalities enhance the reactive oxygen species scavenging ability of cancer cells; thus the pathway is involved in carcinogenesis and resistance to chemoradiotherapy (CRT). This retrospective study was conducted to examine the status of the Keap1-Nrf2 pathway in locally advanced esophageal squamous cell carcinoma (ESCC) and to analyze its prognostic value in patients receiving CRT.

METHODS

Nrf2 and Keap1 expression were immunohistochemically examined in 152 ESCC and 31 normal esophageal mucosae. All ESCC specimens were obtained from patients with locally advanced ESCC who underwent CRT.

RESULTS

Strong staining of nuclear and cytoplasmic Nrf2 and limited or absent Keap1 expression was uncommon in normal tissues, but frequently observed in ESCC. Interaction between Nrf2 and Keap1 in normal mucosae is negatively correlated, while in tumors there is no negative correlation, indicating that there is little to no interaction between Nrf2 and Keap1 in ESCC. Positive Nrf2 expression in the nucleus was of diagnostic value for predicting ESCC from normal esophageal mucosae, and was significantly associated with poorer clinical response and poor progression-free survival after CRT. The value of Keap1 expression for diagnosis and predicting CRT outcomes was marginal. These different influences of Keap1 and Nrf2 on ESCC indicated that the signaling of this pathway was disturbed and displayed a Keap1-independent pattern.

CONCLUSION

Aberrant signaling via the Keap1-Nrf2 pathway was common in ESCC and was associated with response and survival after CRT.

NRF2 addiction in cancer cells

The Kelch‐like ECH‐associated protein 1/nuclear factor erythroid‐derived 2‐like 2 (KEAP1‐NRF2) system is a pivotal defense mechanism against oxidative and electrophilic stress. Although transient NRF2 activation in response to stress is beneficial for health, persistent NRF2 activation in cancer cells has deleterious effects on cancer‐bearing hosts by conferring therapeutic resistance and aggressive tumorigenic activity on cancer cells. Because NRF2 increases the antioxidant and detoxification capability of cancer cells, persistently high levels of NRF2 activity enhance therapeutic resistance of cancer cells. NRF2 also drives metabolic reprogramming to establish cellular metabolic processes that are advantageous for cell proliferation in cooperation with other oncogenic pathways. As a result of these advantages, cancer cells with persistent activation of NRF2 often develop “NRF2 addiction” and show malignant phenotypes leading to poor prognoses in cancer patients. Inhibition of NRF2 is a promising therapeutic approach for NRF2‐addicted cancers and NRF2 inhibitors are being actively developed. However, giving systemic NRF2 inhibitors might have undesirable effects on cancer‐bearing hosts, considering the central roles of NRF2 in cytoprotection. To avoid these side‐effects, new therapeutic targets besides NRF2 for NRF2‐addicted cancers have been actively explored. This review introduces recent studies describing the development and characterization of NRF2‐addicted cancers, as well as their potential therapeutic targets. Expected advances in diagnostic and therapeutic interventions for NRF2‐addicted cancers are also discussed.