Brusatol enhances the efficacy of chemotherapy by inhibiting the Nrf2-mediated defense mechanism

Perspectives on the Clinical Development of NRF2-Targeting Drugs

The transcription factor NRF2 (nuclear factor erythroid 2-related factor 2) triggers homeostatic responses against a plethora of environmental or endogenous deviations in redox metabolism, inflammation, proteostasis, etc. Therefore, pharmacological activation of NRF2 is a promising therapeutic strategy for several chronic diseases that are underlined by low-grade oxidative inflammation and dysregulation of redox metabolism, such as neurodegenerative, cardiovascular, and metabolic diseases. While NRF2 activation is useful in inhibiting carcinogenesis, its inhibition is needed in constituted tumors where NRF2 provides a survival advantage in the challenging tumor niche. This review describes the electrophilic and non-electrophilic NRF2 activators with clinical projection in various chronic diseases. We also analyze the status of NRF2 inhibitors, which are for the moment in a proof-of-concept stage. Advanced in silico screening and medicinal chemistry are expected to provide new or repurposing small molecules with increased potential for fostering the development of targeted NRF2 modulators. The nuclear factor erythroid 2 (NFE2)-related factor 2 (NRF2) is rapidly degraded by proteasomes under a basal condition in a Keap1-dependent manner. ROS oxidatively modifies Keap1 to release NRF2 and allow its nuclear translocation. Here it binds to the antioxidant response element to regulate gene transcription. An alternative mechanism controlling NRF2 stability is glycogen synthase kinase 3 (GSK-3)-induced phosphorylation. Indicated in blue are NRF2-activating and NRF2-inhibiting drugs.

Friend or Foe: Xenobiotic Activation of Nrf2 in Disease Control and Cardioprotection

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that governs a highly conserved pathway central to the protection of cells against various oxidative stresses. However, the biological impact of xenobiotic intervention of Nrf2 in physiological and pathophysiological conditions remains debatable. Activation of Nrf2 in cancer cells has been shown to elevate drug resistance and increase cell survival and proliferation, while inhibition of Nrf2 sensitizes cancer cells to drug treatment. On the other hand, activation of Nrf2 in normal healthy cells has been explored as a rather successful strategy for cancer chemoprevention. Selective activation of Nrf2 in off-target cells has recently been investigated as an approach for protecting off-target tissues from untoward drug toxicity. Specifically, induction of antioxidant response element genes via Nrf2 activation in cardiac cells is being explored as a means to limit the well-documented cardiotoxicity accompanied by cancer treatment with commonly prescribed anthracycline drugs. In addition to cancers, Nrf2 has been implicated in many other diseases including Alzheimer's and Parkinson's Diseases, diabetes, and cardiovascular disease. In this review, we discuss the roles of Nrf2 and its downstream target genes in the treatment of various diseases, and its recently explored potential for increasing the benefit: risk ratio of commonly utilized cancer treatments.

NRF2-Dependent Bioactivation of Mitomycin C as a Novel Strategy To Target KEAP1-NRF2 Pathway Activation in Human Cancer

Activating mutations in the KEAP1-NRF2 pathway are found in approximately 25% of lung tumors, where the hijacking of NRF2's cytoprotective functions results in aggressive tumor growth, chemoresistance, and a poor prognosis for patients. There are currently no approved drugs which target aberrant NRF2 activation, which means that there is an urgent clinical need to target this orphan oncogenic pathway in human tumors. In this study, we used an isogenic pair of wild-type and Keap1 knockout cells to screen a range of chemotherapeutic and pathway-targeted anticancer drugs in order to identify compounds which display enhanced toxicity toward cells with high levels of Nrf2 activity. Through this approach, complemented by validation across a panel of eight human cancer cell lines from a range of different tissues, we identified the DNA-damaging agent mitomycin C to be significantly more toxic in cells with aberrant Nrf2 activation. Mechanistically, we found that the NRF2 target genes for cytochrome P450 reductase, NQO1, and enzymes in the pentose phosphate pathway are all responsible for the NRF2-dependent enhanced bioactivation of mitomycin C. As mitomycin C is already approved for clinical use, it represents as excellent drug repositioning candidate to target the currently untreatable NRF2 activation in human tumors.

Apoptotic activities of brusatol in human non-small cell lung cancer cells: Involvement of ROS-mediated mitochondrial-dependent pathway and inhibition of Nrf2-mediated antioxidant response

Brusatol occurs as a characteristic bioactive principle of Brucea javanica (L.) Merr., a traditional medicinal herb frequently employed to tackle cancer in China. This work endeavored to unravel the potential anti-cancer activity and action mechanism of brusatol against non-small cell lung cancer (NSCLC) cell lines. The findings indicated that brusatol remarkably inhibited the growth of wild-type NSCLC cell lines (A549 and H1650) and epidermal growth factor receptor-mutant cell lines (PC9 and HCC827) in a dose- and time-related fashion, and profoundly inhibited the clonogenic capability and migratory capacity of PC9 cells. Treatment with brusatol resulted in significant apoptosis in PC9 cells, as evidenced by Hoechst 33342 staining and flow cytometric analysis. The apoptotic effect was closely related to induction of G0-G1 cell cycle arrest, stimulation of reactive oxygen species (ROS) and malondialdehyde, decrease of glutathione levels and disruption of mitochondrial membrane potential. Furthermore, pretreatment with N-acetylcysteine, a typical ROS scavenger, markedly ameliorated the brusatol-induced inhibition of PC9 cells. Western blotting assay indicated that brusatol pronouncedly suppressed the expression levels of mitochondrial apoptotic pathway-associated proteins Bcl-2 and Bcl-xl, accentuated the expression of Bax and Bak, and upregulated the protein expression of XIAP, cleaved caspase-3/pro caspase-3, cleaved caspase-8/pro caspase-8, and cleaved PARP/total PARP. In addition, brusatol significantly suppressed the expression of Nrf2 and HO-1, and abrogated tBHQ-induced Nrf2 activation. Combinational administration of brusatol with four chemotherapeutic agents exhibited marked synergetic effect on PC9 cells. Together, the inhibition of PC9 cells proliferation by brusatol might be intimately associated with the modulation of ROS-mediated mitochondrial-dependent pathway and inhibition of Nrf2-mediated antioxidant response. This novel insight might provide further evidence to buttress the antineoplastic efficacy of B. javanica, and support a role for brusatol as a promising anti-cancer candidate or adjuvant to current chemotherapeutic medication in the therapy of EGFR-mutant NSCLC.

Perillaldehyde Ameliorates Aspergillus fumigatus Keratitis by Activating the Nrf2/HO-1 Signaling Pathway and Inhibiting Dectin-1-Mediated Inflammation

Purpose

The purpose of this study was to investigate the therapeutic effect of perillaldehyde (PAE) on Aspergillus fumigatus (A. fumigatus) keratitis.

Methods

Human corneal epithelial cells (HCECs) were pretreated with PAE and stimulated with A. fumigatus mycelium. C57BL/6 mice were infected with A. fumigatus and treated with or without PAE 1 day after infection. Clinical scores, PCR, ELISA, and Western blotting were used to detect the expression of pro-inflammatory mediators, dendritic cell-associated c-type lectin-1 (Dectin-1), nuclear factor (erythroid-derived 2) like 2 (Nrf2), and heme oxygenase (HO-1). Nrf2 expression in HCECs pretreated with PAE was observed by immunofluorescence. NIMP-R14 protein expression and localization in mouse corneas were observed by immunofluorescence staining after treatment with PAE. Corneal colony counting, time-kill tests, and mycelial transformation inhibition tests were used to evaluate the antifungal effect of PAE.

Results

C57BL/6 mice treated with PAE at 1 day after infection had a lower clinical score and decreased IL-1β, TNF-α, IL-6, Dectin-1, and MPO levels. PAE treatment significantly reduced neutrophil recruitments to the corneal stroma. Compared with the DMSO-treated group, PAE treatment significantly decreased mRNA and protein levels of pro-inflammatory cytokines and Dectin-1 in HCECs. PAE pretreatment before A. fumigatus stimulation obviously elevated the mRNA and protein levels of components of the Nrf2/HO-1 axis. HCECs pretreated with PAE before infection showed a weakened ability to inhibit inflammation in the presence of brusatol (BT; an Nrf2 inhibitor) or ZnPP (an HO-1 inhibitor). PAE treatment significantly reduced the fungal load of C57BL/6 mouse corneas and inhibited fungal growth in vitro.

Conclusions

These data proved that PAE may ameliorate A. fumigatus keratitis by activating the Nrf2/HO-1 signaling pathway and inhibiting the Dectin-1 mediated inflammatory response and neutrophil recruitment. Furthermore, PAE exerts direct fungicidal activity on A. fumigatus.

The KEAP1-NRF2 System as a Molecular Target of Cancer Treatment

Simple Summary

Nuclear factor erythroid-derived 2-like 2 (encoded by the Nfe2l2 gene; NRF2) is a transcription factor that regulates a variety of cytoprotective genes, including antioxidant enzymes, detoxification enzymes, inflammation-related proteins, drug transporters and metabolic enzymes. NRF2 is regulated by unique molecular mechanisms that stem from Kelch-like ECH-associated protein 1 (KEAP1) in response to oxidative and electrophilic stresses. It has been shown that disturbance or perturbation of the NRF2 activation causes and/or exacerbates many kinds of diseases. On the contrary, aberrant activations of NRF2 also provoke intriguing pathologic features, especially in cancers. Cancer cells with high NRF2 activity have been referred to as NRF2-addicted cancers, which are frequently found in lung cancers. In this review, we summarize the current accomplishments of the KEAP1–NRF2 pathway analyses in special reference to the therapeutic target of cancer therapy. The concept of synthetic lethality provides a new therapeutic approach for NRF2-addicted cancers.

Abstract

The Kelch-like ECH-associated protein 1 (KEAP1)—Nuclear factor erythroid-derived 2-like 2 (encoded by the Nfe2l2 gene; NRF2) system attracts extensive interest from scientists in basic and clinical cancer research fields, as NRF2 exhibits activity as both an oncogene and tumor suppressor, depending on the context. Especially unique and malignant, NRF2-addicted cancers exhibit high levels of NRF2 expression. Somatic mutations identified in the NRF2 or KEAP1 genes of NRF2-addicted cancers cause the stabilization and accumulation of NRF2. NRF2-addicted cancers hijack the intrinsic roles that NRF2 plays in cytoprotection, including antioxidative and anti-electrophilic responses, as well as metabolic reprogramming, and acquire a marked advantage to survive under severe and limited microenvironments. Therefore, NRF2 inhibitors are expected to have therapeutic effects in patients with NRF2-addicted cancers. In contrast, NRF2 activation in host immune cells exerts significant suppression of cancer cell growth, indicating that NRF2 inducers also have the potential to be therapeutics for cancers. Thus, the KEAP1–NRF2 system makes a broad range of contributions to both cancer development and suppression. These observations thus demonstrate that both NRF2 inhibitors and inducers are useful for the treatment of cancers with high NRF2 activity.

Malformations and mortality in zebrafish early stages associated with elevated caspase activity after 24 h exposure to MS-222

Tricaine methanesulfonate (MS-222) is a commonly used anaesthetic agent for immobilization of aquatic species. However, delayed development and malformations have been observed in 24 hpf (hours post-fertilization) zebrafish embryos after long-term immobilization. Still, no comprehensive study has been described regarding zebrafish exposure to MS-222 during the first hours of development, which are one of the most sensitive life stages to toxicants. Therefore, this research aimed to assess the toxicity of a 24 h exposure to MS-222 on zebrafish embryonic development. Based on the MS-222 LC₅₀, early blastula stage embryos (~2 hpf) were exposed to 0, 12.5, 25 and 50 mg L^-1 for 24 h and then allowed to develop up to 144 hpf. The chromatographic analysis showed that this anaesthetic agent bioaccumulates in 26 hpf zebrafish larvae in a concentration-dependent manner. In addition, increased mortalities and skeletal abnormalities were observed at 144 hpf, namely in the highest tested concentration. Yet, no craniofacial anomalies were observed either by alcian blue or calcein staining methods. Independently of the tested concentration, decreased speed and distance travelled were perceived in 144 hpf larvae. At the biochemical level, decreased in vivo reactive oxygen species (ROS) generation and apoptosis was observed. Additionally, catalase activity was increased at 26 hpf while results of mRNA expression showed a decreased gclc transcript content at the same time-point. Overall, data obtained highlight the toxicological risk of MS-222 and support ROS-mediated cell death signalling changes through the elevation of catalase activity as an adaptative or protective response.

Development of Potential Antitumor Agents from the Scaffolds of Plant-Derived Terpenoid Lactones

Naturally occurring terpenoid lactones and their synthetic derivatives have attracted increasing interest for their promising antitumor activity and potential utilization in the discovery and design of new antitumor agents. In the present perspective article, selected plant-derived five-membered γ-lactones and six-membered δ-lactones that occur with terpenoid scaffolds are reviewed, with their structures, cancer cell line cytotoxicity and in vivo antitumor activity, structure-activity relationships, mechanism of action, and the potential for developing cancer chemotherapeutic agents discussed in each case. The compounds presented include artemisinin (ART, 1), parthenolide (PTL, 2), thapsigargin (TPG, 3), andrographolide (AGL, 4), ginkgolide B (GKL B, 5), jolkinolide B (JKL B, 6), nagilactone E (NGL E, 7), triptolide (TPL, 8), bruceantin (BRC, 9), dichapetalin A (DCT A, 10), and limonin (LMN, 11), and their naturally occurring analogues and synthetic derivatives. It is hoped that this contribution will be supportive of the future development of additional efficacious anticancer agents derived from natural products.

Clinical Implications of KEAP1-NFE2L2 Mutations in NSCLC

The KEAP1-NFE2L2 pathway is an important modulator of cell homeostasis. Mutations in this pathway are common in NSCLC and have been associated with enhanced tumor growth and aggressiveness. In addition, tumors with mutations in the KEAP1-NFE2L2 pathway have been reported in preclinical and clinical studies to convey refractoriness to cancer-directed therapy such as radiation, chemotherapy, and targeted therapy. The role of immunotherapy in this patient population is less clear, and there are conflicting studies on the efficacy of immune checkpoint inhibitors in KEAP1-NFE2L2-mutant NSCLC. Here, we review the current clinical evidence on several classes of anticancer therapeutics in KEAP1-NFE2L2-mutant tumors. Furthermore, we provide an overview of the landscape of the current clinical trials in this patient population, highlighting the work being done with mTORC1, mTORC2, and glutaminase inhibition.

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.

The PI3K pathway preserves metabolic health through MARCO-dependent lipid uptake by adipose tissue macrophages

Adipose tissue macrophages (ATMs) display tremendous heterogeneity depending on signals in their local microenvironment and contribute to the pathogenesis of obesity. The phosphoinositide 3-kinase (PI3K) signalling pathway, antagonized by the phosphatase and tensin homologue (PTEN), is important for metabolic responses to obesity. We hypothesized that fluctuations in macrophage-intrinsic PI3K activity via PTEN could alter the trajectory of metabolic disease by driving distinct ATM populations. Using mice harbouring macrophage-specific PTEN deletion or bone marrow chimeras carrying additional PTEN copies, we demonstrate that sustained PI3K activity in macrophages preserves metabolic health in obesity by preventing lipotoxicity. Myeloid PI3K signalling promotes a beneficial ATM population characterized by lipid uptake, catabolism and high expression of the scavenger macrophage receptor with collagenous structure (MARCO). Dual MARCO and myeloid PTEN deficiencies prevent the generation of lipid-buffering ATMs, reversing the beneficial actions of elevated myeloid PI3K activity in metabolic disease. Thus, macrophage-intrinsic PI3K signalling boosts metabolic health by driving ATM programmes associated with MARCO-dependent lipid uptake.

Kaempferol inhibits Nrf2 signalling pathway via downregulation of Nrf2 mRNA and induces apoptosis in NSCLC cells

Chemoprevention failure is considered to be the most emerging problem that makes non-small cell lung cancer (NSCLC) as one of the deadliest malignancies in the world. In NSCLC cells, Nuclear factor erythroid 2-related factor 2 (Nrf2), a redox sensitive transcription factor, promotes cancer cell survival and fosters mechanism for drug resistance. Here we report identification of Kaempferol, a dietary flavonoid, as a potent Nrf2 inhibitor using Nrf2 reporter assay in NSCLC cells (A549 and NCIH460). Kaempferol selectively reduces Nrf2 mRNA and protein levels and lower level of nuclear Nrf2 downregulates transcription of Nrf2 target genes (NQO1, HO1, AKR1C1 and GST). Kaempferol (25 μM) mediated downregulation of GST, NQO1 and HO1 expression is also observed even after stimulation of Nrf2 by tert-butylhydroquinone (tBHQ). Again, Kaempferol incubation does not change the levels of NFκBp65 and phospho NFκBp65, suggesting it hampers Nrf2 signalling pathway in these cells. Nrf2 inhibition by Kaempferol induces ROS accumulation after 48 h of treatment and makes NSCLC cells sensitive to apoptosis at physiological concentration. Taken together, our study demonstrates that Kaempferol is a potent inhibitor of Nrf2 and can be used as a natural sensitizer and anti-cancer agent for lung cancer therapeutics.

BRG1 protects the heart from acute myocardial infarction by reducing oxidative damage through the activation of the NRF2/HO1 signaling pathway

Brahma-related gene 1 (BRG1) regulates the chromatin structure and expression of cardiac genes. Although BRG1 is downregulated in adult cardiomyocytes, it is reactivated during cardiac stress. The role of BRG1 in acute myocardial infarction (AMI) has not been clearly defined. This study assessed the protective role of BRG1 in AMI using cell cultures and an animal model and explored the underlying molecular events. The results showed that in the peri-infarct zone, expression of BRG1 protein was significantly increased relative to the sham group, which was accompanied by NRF2 and HO1 upregulation and KEAP1 downregulation. BRG1 overexpression through adenoviral intramyocardial injection into AMI mice reduced the infarct size and improved cardiac functions with upregulation of NRF2 and its target HO1 and attenuated oxidative damage and cell apoptosis. However, shRNA-mediated Brg1 knockdown had the opposite effects. These results were further confirmed in cultured primary neonatal rat cardiomyocytes (NRCMs) with oxygen-glucose deprivation (OGD). Moreover, the selective NRF2 inhibitor brusatol could partially reverse cardiomyocyte antioxidant ability and BRG1 overexpression-induced cardiac protection in vitro. In addition, co-immunoprecipitation and immunofluorescence data showed that BRG1 overexpression significantly promoted the BRG1/NRF2 co-localization in cardiomyocytes. The chromatin immunoprecipitation-qPCR revealed BRG1 interaction with the Ho1 promoter and BRG1 overexpression could induce BRG1 binding to the Ho1 promoter during the OGD. In conclusion, this study demonstrated that BRG1 upregulation during AMI in vitro and in vivo increased the NRF2 level and NRF2 nuclear accumulation for HO1 expression to alleviate cardiac myocyte oxidative stress and upregulate cardiomyocyte viability. The BRG1-NRF2-HO1 pathway may represent a novel therapeutic target in the prevention of cardiac dysfunction in AMI patients.

UNG2 deacetylation confers cancer cell resistance to hydrogen peroxide-induced cytotoxicity

Cancer therapeutics produce reactive oxygen species (ROS) that damage the cancer genome and lead to cell death. However, cancer cells can resist ROS-induced cytotoxicity and survive. We show that nuclear-localized uracil-DNA N-glycosylase isoform 2 (UNG2) has a critical role in preventing ROS-induced DNA damage and enabling cancer-cell resistance. Under physiological conditions, UNG2 is targeted for rapid degradation via an interaction with the E3 ligase UHRF1. In response to ROS, however, UNG2 protein in cancer cells exhibits a remarkably extended half-life. Upon ROS exposure, UNG2 is deacetylated at lysine 78 by histone deacetylases, which prevents the UNG2-UHRF1 interaction. Accumulated UNG2 protein can thus excise the base damaged by ROS and enable the cell to survive these otherwise toxic conditions. Consequently, combining HDAC inhibitors (to permit UNG2 degradation) with genotoxic agents (to produce cytotoxic cellular levels of ROS) leads to a robust synergistic killing effect in cancer cells in vitro. Altogether, these data support the application of a novel approach to cancer treatment based on promoting UNG2 degradation by altering its acetylation status using an HDAC inhibitor.

Gasotransmitter synthesis and signalling in the renal glomerulus. Implications for glomerular diseases

Glomerular injury is a hallmark of kidney diseases such as diabetic nephropathy, IgA nephropathy or other forms of glomerulonephritis. Glomerular endothelial cells, mesangial cells, glomerular epithelial cells (podocytes) and, in an inflammatory context, infiltrating immune cells crosstalk to mediate signalling processes in the glomerulus. Under physiological conditions, mesangial cells act by the control of extracellular matrix production and degradation, by the synthesis of growth factors and by preserving a well-defined crosstalk with glomerular podocytes and endothelial cells to regulate glomerular structure and function. It is well known that mesangial cells are able to amplify an inflammatory process by the formation of cytokines, reactive oxygen species (ROS) and nitric oxide (NO). This exaggerated reaction may result in a vicious cycle with subsequent damage of neighboured podocytes and endothelial cells, loss of the filtration barrier and, finally destruction of the whole glomerulus. Unfortunately, all efforts to develop new therapies for the treatment of glomerular diseases by controlling unbridled ROS or NO production directly had so far no success. However, on-going research on ROS and NO defined these autacoids more as important signalling molecules than as endogenously produced cytotoxic compounds. New findings on signalling activities of ROS, NO but also hydrogen sulfide (H₂S) and carbon monoxide (CO) supported this paradigm shift. Because of their similar chemical properties and their similar signal transduction capacities, NO, H₂S and CO are meanwhile designated as the group of gasotransmitters. In this review, we describe the current knowledge of the signalling properties of gasotransmitters with a focus on glomerular cells and their role in glomerular diseases.

Melatonin-Nrf2 Signaling Activates Peroxisomal Activities in Porcine Cumulus Cell-Oocyte Complexes

Melatonin and Nrf2 signaling synergistically improve mammalian oocyte maturation and embryonic development. Furthermore, previous studies have suggested an interplay between peroxisomes and Nrf2 signaling in cells, but it is still unclear whether peroxisomes are involved in oocyte maturation. The aim of the present study was to identify the possible roles of peroxisomes in the melatonin-Nrf2 signaling pathway during in vitro maturation (IVM) of porcine oocytes. Porcine oocytes were treated with melatonin (10^-9 M) and brusatol, a Nrf2 specific inhibitor, in order to investigate the mechanism. Then, the rates of maturation and related gene and protein expression were analyzed. During oocyte maturation, melatonin upregulated the expression of gene and protein related to Nrf2 signaling and peroxisomal activities; RNA sequencing partially validated these results. Our results demonstrate that melatonin can activate Nrf2 signaling by binding to melatonin receptor 2, resulting in the upregulation of catalase. Moreover, peroxisomes were also found to be activated in response to melatonin treatment, causing the activation of catalase; together with Nrf2 signaling, peroxisomes synergistically prevented the generation of reactive oxygen species and enhanced oocyte quality. Thus, we suggest that a crosstalk might exist between Nrf2 signaling and peroxisomal activities in porcine oocytes.

Emerging role of NRF2 in ROS-mediated tumor chemoresistance

Chemoresistance is a central cause for the tumor management failure. Cancer cells disrupt the redox homeostasis through reactive oxygen species (ROS) regulatory mechanisms, leading to tumor progression and chemoresistance. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of neutralizing cellular ROS and restoring redox balance. Understanding the role of NRF2 in ROS-mediated chemoresistance can be helpful in the development of chemotherapy strategies with better efficiency. In this review, we sum up the roles of ROS in the development of chemoresistance to classical chemotherapy agents including cisplatin, 5-fluorouracil, gemcitabine, oxaliplatin, paclitaxel, and doxorubicin, and how to overcome ROS-mediated tumor chemoresistance by targeting NRF2. Finally, we propose that targeting NRF2 might be a promising strategy to resist ROS-driven chemoresistance and acquire better efficacy in cancer treatment.

NRF2 as a regulator of cell metabolism and inflammation in cancer

Nuclear factor erythroid 2-related factor 2 (NRF2) is a master transcriptional regulator of genes whose products defend our cells for toxic and oxidative insults. Although NRF2 activation may reduce cancer risk by suppressing oxidative stress and tumor-promoting inflammation, many cancers exhibit elevated NRF2 activity either due to mutations that disrupt the negative control of NRF2 activity or other factors. Importantly, NRF2 activation is associated with poor prognosis and NRF2 has turned out to be a key activator of cancer-supportive anabolic metabolism. In this review, we summarize the diverse roles played by NRF2 in cancer focusing on metabolic reprogramming and tumor-promoting inflammation.

Mechanistic Analysis of an Extracellular Signal-Regulated Kinase 2-Interacting Compound that Inhibits Mutant BRAF-Expressing Melanoma Cells by Inducing Oxidative Stress

Constitutively active extracellular signal–regulated kinase (ERK) 1/2 signaling promotes cancer cell proliferation and survival. We previously described a class of compounds containing a 1,1-dioxido-2,5-dihydrothiophen-3-yl 4-benzenesulfonate scaffold that targeted ERK2 substrate docking sites and selectively inhibited ERK1/2-dependent functions, including activator protein-1–mediated transcription and growth of cancer cells containing active ERK1/2 due to mutations in Ras G-proteins or BRAF, Proto-oncogene B-RAF (Rapidly Acclerated Fibrosarcoma) kinase. The current study identified chemical features required for biologic activity and global effects on gene and protein levels in A375 melanoma cells containing mutant BRAF (V600E). Saturation transfer difference-NMR and mass spectrometry analyses revealed interactions between a lead compound (SF-3-030) and ERK2, including the formation of a covalent adduct on cysteine 252 that is located near the docking site for ERK/FXF (DEF) motif for substrate recruitment. Cells treated with SF-3-030 showed rapid changes in immediate early gene levels, including DEF motif–containing ERK1/2 substrates in the Fos family. Analysis of transcriptome and proteome changes showed that the SF-3-030 effects overlapped with ATP-competitive or catalytic site inhibitors of MAPK/ERK Kinase 1/2 (MEK1/2) or ERK1/2. Like other ERK1/2 pathway inhibitors, SF-3-030 induced reactive oxygen species (ROS) and genes associated with oxidative stress, including nuclear factor erythroid 2–related factor 2 (NRF2). Whereas the addition of the ROS inhibitor N-acetyl cysteine reversed SF-3-030–induced ROS and inhibition of A375 cell proliferation, the addition of NRF2 inhibitors has little effect on cell proliferation. These studies provide mechanistic information on a novel chemical scaffold that selectively regulates ERK1/2-targeted transcription factors and inhibits the proliferation of A375 melanoma cells through a ROS-dependent mechanism.

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.

Nrf2 in Neoplastic and Non-Neoplastic Liver Diseases

Simple Summary

Although the Keap1-Nrf2 pathway represents a powerful cell defense mechanism against a variety of toxic insults, its role in acute or chronic liver damage and tumor development is not completely understood. This review addresses how Nrf2 is involved in liver pathophysiology and critically discusses the contrasting results emerging from the literature. The aim of the present report is to stimulate further investigation on the role of Nrf2 that could lead to define the best strategies to therapeutically target this pathway.

Abstract

Activation of the Keap1/Nrf2 pathway, the most important cell defense signal, triggered to neutralize the harmful effects of electrophilic and oxidative stress, plays a crucial role in cell survival. Therefore, its ability to attenuate acute and chronic liver damage, where oxidative stress represents the key player, is not surprising. On the other hand, while Nrf2 promotes proliferation in cancer cells, its role in non-neoplastic hepatocytes is a matter of debate. Another topic of uncertainty concerns the nature of the mechanisms of Nrf2 activation in hepatocarcinogenesis. Indeed, it remains unclear what is the main mechanism behind the sustained activation of the Keap1/Nrf2 pathway in hepatocarcinogenesis. This raises doubts about the best strategies to therapeutically target this pathway. In this review, we will analyze and discuss our present knowledge concerning the role of Nrf2 in hepatic physiology and pathology, including hepatocellular carcinoma. In particular, we will critically examine and discuss some findings originating from animal models that raise questions that still need to be adequately answered.

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.

NRF2 regulates the sensitivity of human NSCLC cells to cystine deprivation-induced ferroptosis via FOCAD-FAK signaling pathway

Transcription factor nuclear factor-erythroid 2-like 2 (NRF2) mainly regulates cellular antioxidant response, redox homeostasis and metabolic balance. Our previous study illustrated the translational significance of NRF2-mediated transcriptional repression, and the transcription of FOCAD gene might be negatively regulated by NRF2. However, the detailed mechanism and the related significance remain unclear. In this study, we mainly explored the effect of NRF2-FOCAD signaling pathway on ferroptosis regulation in human non-small-cell lung carcinoma (NSCLC) model. Our results confirmed the negative regulation relationship between NRF2 and FOCAD, which was dependent on NRF2-Replication Protein A1 (RPA1)-Antioxidant Response Elements (ARE) complex. In addition, FOCAD promoted the activity of focal adhesion kinase (FAK), which further enhanced the sensitivity of NSCLC cells to cysteine deprivation-induced ferroptosis via promoting the tricarboxylic acid (TCA) cycle and the activity of Complex I in mitochondrial electron transport chain (ETC). However, FOCAD didn't affect GPX4 inhibition-induced ferroptosis. Moreover, the treatment with the combination of NRF2 inhibitor (brusatol) and erastin showed better therapeutic action against NSCLC in vitro and in vivo than single treatment, and the improved therapeutic function partially depended on the activation of FOCAD-FAK signal. Taken together, our study indicates the close association of NRF2-FOCAD-FAK signaling pathway with cysteine deprivation-induced ferroptosis, and elucidates a novel insight into the ferroptosis-based therapeutic approach for the patients with NSCLC.

Brusatol: A potential anti-tumor quassinoid from Brucea javanica

Brusatol, a triterpene lactone compound mainly from Brucea javanica, sensitizes a broad spectrum of cancer cells. It is known as a specific inhibitor of nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway. In this review, we provide a comprehensive overview on the antitumor effect and molecular mechanisms of brusatol in vitro and in vivo. This review also covers pharmacokinetics studies, modification of dosages forms of brusatol. Increasing evidences have validated the value of brusatol as a chemotherapeutic agent in cancers, which may contribute to drug development and clinical application.

High NRF2 Levels Correlate with Poor Prognosis in Colorectal Cancer Patients and with Sensitivity to the Kinase Inhibitor AT9283 In Vitro

Aberrant hyperactivation of nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2) is a common event in many tumour types and associates with resistance to therapy and poor patient prognosis; however, its relevance in colorectal tumours is not well-established. Measuring the expression of surrogate genes for NRF2 activity in silico, in combination with validation in patients' samples, we show that the NRF2 pathway is upregulated in colorectal tumours and that high levels of nuclear NRF2 correlate with a poor patient prognosis. These results highlight the need to overcome the protection provided by NRF2 and present an opportunity to selectively kill cancer cells with hyperactive NRF2. Exploiting the CRISPR/Cas9 technology, we generated colorectal cancer cell lines with hyperactive NRF2 and used them to perform a drug screen. We identified AT9283, an Aurora kinase inhibitor, for its selectivity towards killing cancer cells with hyperactive NRF2 as a consequence to either genetic or pharmacological activation. Our results show that hyperactivation of NRF2 in colorectal cancer cells might present a vulnerability that could potentially be therapeutically exploited by using the Aurora kinase inhibitor AT9283.

Identification of a 3-β-homoalanine conjugate of brusatol with reduced toxicity in mice

Brusatol, a quassinoid natural product, is effective against multiple diseases including hematologic malignancies, as we reported recently by targeting the PI3Kγ isoform, but toxicity limits its further development. Herein, we report the synthesis of a series of conjugates of brusatol with amino acids and short peptides at its enolic hydroxyl at C-3. A number of conjugates with smaller amino acids and peptides demonstrated activities comparable to brusatol. Through in vitro and in vivo evaluations, we identified UPB-26, a conjugate of brusatol with a L- β-homoalanine, which exhibits good chemical stability at physiological pH's (SGF and SIF), moderate rate of conversion to brusatol in both human and rat plasmas, improved mouse liver microsomal stability, and most encouragingly, enhanced safety compared to brusatol in mice upon IP administration.

NRF2 preserves genomic integrity by facilitating ATR activation and G2 cell cycle arrest

Nuclear factor erythroid 2-related factor 2 (NRF2) is a well-characterized transcription factor that protects cells against oxidative and electrophilic stresses. Emerging evidence has suggested that NRF2 protects cells against DNA damage by mechanisms other than antioxidation, yet the mechanism remains poorly understood. Here, we demonstrate that knockout of NRF2 in cells results in hypersensitivity to ionizing radiation (IR) in the presence or absence of reactive oxygen species (ROS). Under ROS scavenging conditions, induction of DNA double-strand breaks (DSBs) increases the NRF2 protein level and recruits NRF2 to DNA damage sites where it interacts with ATR, resulting in activation of the ATR-CHK1-CDC2 signaling pathway. In turn, this leads to G2 cell cycle arrest and the promotion of homologous recombination repair of DSBs, thereby preserving genome stability. The inhibition of NRF2 by brusatol increased the radiosensitivity of tumor cells in xenografts by perturbing ATR and CHK1 activation. Collectively, our results reveal a novel function of NRF2 as an ATR activator in the regulation of the cellular response to DSBs. This shift in perspective should help furnish a more complete understanding of the function of NRF2 and the DNA damage response.

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.

Cytotoxic effect of specific T cells from mice with experimental autoimmune uveitis on murine photoreceptor cells

AIM

To investigate the cytotoxic effect of specific T cells from mice with experimental autoimmune uveitis (EAU) as well as their secreted interferon (IFN)-γ and interleukin (IL)-17A on murine photoreceptor (661W) cells.

METHODS

An EAU model was established in female mice by injection of interphotoreceptor retinoid binding protein (IRBP) emulsion supplemented with complete Freund's adjuvant (CFA) and Mycobacterium tuberculosis (TB). On day 12 after induction of EAU, specific T cells from spleen and lymph node tissues were isolated and cultured for 4d and the levels of IFN-γ and IL-17A in the supernatants were determined by enzyme-linked immunosorbent assays (ELISAs). T cells and their supernatants were added to 661W cells to observe the alteration of cell morphology; IFN-γ and IL-17A were separately added to 661W cells to observe the effect of IFN-γ and IL-17A on cell proliferation.

RESULTS

The levels of IFN-γ and IL-17A in the T cell supernatants were 1568.64±38.79 pg/mL and 1456.57±46.98 pg/mL, respectively. The supernatants apparently inhibited 661W cell proliferation (P<0.05). T cells could also attach to the surface of 661W cells, and IFN-γ showed a more serious cytotoxic effect on 661W cells than IL-17A, inhibiting cell proliferation (P<0.01).

CONCLUSION

IFN-γ and IL-17A from T cells of EAU mice model can exert cytotoxic effects on murine photoreceptor cell proliferation, and IFN-γ shows more serious cytotoxic effects on murine photoreceptor cells than IL-17A.

Protection of procyanidin B2 on mitochondrial dynamics in sepsis associated acute kidney injury via promoting Nrf2 nuclear translocation

In septic acute kidney injury (SAKI), the positive feedback between damaged mitochondria and accumulation of reactive oxygen species results in cell and tissue damage through multiple mechanisms. Removing the damaged mitochondria or neutralizing the reactive oxygen species has been considered beneficial to alleviating cell damage. The antioxidant Procyanidin B2 has been reported to inhibits reactive oxygen species and thereby reduces cell injury. However, it is unclear whether this effect is associated with clearance of damaged mitochondria. Here, we evaluated the efficacy of procyanidin B2 on SAKI, and focused on its effects on mitochondrial dynamics and removing damaged mitochondria via mitophagy. The results showed that the renal function, renal tubular cell vacuolization and oxidative stress were decreased in SAKI mice treated with procyanidin B2, moreover, skewed mitochondrial fusion/fission, mitochondrial mediated apoptosis and impaired mitophagy were improved in SAKI mice treated with procyanidin B2. In mechanism, the improvement of procyanidin B2 on mitochondrial dynamics were associated with increased nuclear translocation of the transcription factor, Nrf2. In summary, our findings highlighted that the protective efficacy of procyanidin B2 in reducing cellular damage in SAKI, and mechanisms improving mitochondrial dynamics and quality control at least in part by promoting Nrf2 translocation into the nucleus.

Cellular Responses to Platinum-Based Anticancer Drugs and UVC: Role of p53 and Implications for Cancer Therapy

Chemotherapy is intended to induce cancer cell death through apoptosis and other avenues. Unfortunately, as discussed in this article, moderate doses of genotoxic drugs such as cisplatin typical of those achieved in the clinic often invoke a cytostatic/dormancy rather than cytotoxic/apoptosis response in solid tumour-derived cell lines. This is commonly manifested by an extended apoptotic threshold, with extensive apoptosis only being seen after very high/supralethal doses of such agents. The dormancy response can be associated with senescence-like features, polyploidy and/or multinucleation, depending in part on the p53 status of the cells. In most solid tumour-derived cells, dormancy represents a long-term survival mechanism, ultimately contributing to disease recurrence. This review highlights the nonlinearity of key aspects of the molecular and cellular responses to bulky DNA lesions in human cells treated with chemotherapeutic drugs (e.g., cisplatin) or ultraviolet light-C (a widely used tool for unraveling details of the DNA damage-response) as a function of the level of genotoxic stress. Such data highlight the growing realization that targeting dormant cancer cells, which frequently emerge following conventional anticancer treatments, may represent a novel strategy to prevent or, at least, significantly suppress cancer recurrence.

NF-E2-Related Factor 2 Regulates Interferon Receptor Expression and Alters Macrophage Polarization in Lupus

OBJECTIVE

Pristane-induced lupus is associated with nonresolving inflammation and deficiency of proresolving macrophages. Proresolving nonclassic macrophages (NCMs) are less responsive to type I interferon (IFN) than classic macrophages (CMs; which are proinflammatory), reflecting their relative expression levels of the type I IFN receptor (IFNAR). This study was undertaken to investigate the regulation of IFNAR expression in macrophages.

METHODS

We carried out gene expression profiling of purified CMs and NCMs from mice treated with pristane (which develop lupus) or mineral oil (non-lupus controls). Macrophage differentiation and IFNAR expression were examined in mice treated with NF-E2-related factor 2 (Nrf2) activators and inhibitors and in Nrf2-deficient mice. Nrf2 activity was also assessed in blood cells from patients with systemic lupus erythematosus (SLE). Significant differences were determined by Student's t-test.

RESULTS

RNA sequencing revealed increased expression of genes regulated by the transcription factor Nrf2 in NCMs from mineral oil-treated versus pristane-treated mice and in NCMs versus CMs. The Nrf2 activator CDDO-imidazole (CDDO-Im) decreased CMs (P < 0.0001) and promoted the development of proresolving NCMs (P = 0.06), whereas the Nrf2 inhibitor brusatol increased CMs (P < 0.05) and decreased NCMs (P < 0.001). CDDO-Im decreased Ifnar1 (P < 0.001) and IFN-stimulated gene (ISG) expression in macrophages and alleviated oxidative stress (P < 0.05), whereas brusatol had the opposite effect (P < 0.01). Moreover, Ifnar1 and ISG expression levels were higher in Nrf2-knockout mice than controls (P < 0.05). As seen in mice with lupus, SLE patients showed evidence of low Nrf2 activity.

CONCLUSION

Our findings indicate that Nrf2 activation favors the resolution of chronic inflammation in lupus. Since autoantibody production and lupus nephritis depend on IFNAR signaling, the ability of Nrf2 activators to repolarize macrophages and reduce the INF signature suggests that these agents may warrant consideration for treating lupus.

Nrf2 Inhibitor, Brusatol in Combination with Trastuzumab Exerts Synergistic Antitumor Activity in HER2-Positive Cancers by Inhibiting Nrf2/HO-1 and HER2-AKT/ERK1/2 Pathways

The HER2-targeting antibody trastuzumab has shown effectiveness in treating HER2-positive breast and gastric cancers; however, its responses are limited. Currently, Nrf2 has been deemed as a key transcription factor in promoting cancer progression and resistance by crosstalk with other proliferative signaling pathways. Brusatol as a novel Nrf2 inhibitor has been deemed as an efficacious and safe drug candidate in cancer therapy. In this study, we firstly reported that brusatol exerted the growth-inhibitory effects on HER2-positive cancer cells by regressing Nrf2/HO-1 and HER2-AKT/ERK1/2 signaling pathways in these cells. More importantly, we found that brusatol synergistically enhanced the antitumor activity of trastuzumab against HER2-positive SK-OV-3 and BT-474 cells, which may be attributed to the inhibition of Nrf2/HO-1 and HER2-AKT/ERK1/2 signaling pathways. Furthermore, the synergistic effects were also observed in BT-474 and SK-OV-3 tumor xenografts. In addition, our results showed that trastuzumab markedly enhanced brusatol-induced ROS accumulation and apoptosis level, which could further explain the synergistic effects. To conclude, the study provided a new insight on exploring Nrf2 inhibition in combination with HER2-targeted trastuzumab as a potential clinical treatment regimen in treating HER2-positive cancers.

Antiproliferative Activity of Ursolic Acid in MDA-MB-231 Human Breast Cancer Cells through Nrf2 Pathway Regulation

The potential mechanisms of action of ursolic acid (UA) in regulating cell proliferation in MDA-MB-231 human breast cancer cells through Nrf2 pathway were investigated. UA significantly inhibited the proliferation of MDA-MB-231 cells at a dose ≥10 μM in a dose-dependent manner, and no cytotoxicity was observed at concentrations below 29.87 ± 2.60 μM. The expressions of Nrf2 and p-Nrf2, in whole cell and nucleus, and NQO1 were inhibited by UA treatment, whereas the Keap1 expression was upregulated. No significant difference was observed in the Nrf2 mRNA levels, indicating that UA reduced Nrf2 expression not through mRNA but through a post-translational mechanism. Additionally, EGF-induced p-Nrf2 and its downstream NQO1 and SOD1 enzymes were abolished by UA. However, EGF or p-EGFR had no effect on the expressions of Keap1. These results suggested that the proliferative inhibitory effect of UA might be partially through downregulating Nrf2 via the Keap1/Nrf2 pathway and EGFR/Nrf2 pathway in MDA-MB-231 cells.

Brusatol suppresses STAT3-driven metastasis by downregulating epithelial-mesenchymal transition in hepatocellular carcinoma

Introduction

Epithelial-mesenchymal transition (EMT) is a process of transdifferentiation where epithelial cells attain mesenchymal phenotype to gain invasive properties and thus, can contribute to metastasis of tumor cells.

Objectives

The antimetastatic and antitumor efficacy of brusatol (BT) was investigated in a hepatocellular carcinoma (HCC) model.

Methods

We evaluated the action of BT on EMT process using various biological assays in HCC cell lines and its effect on tumorigenesis in an orthotopic mouse model.

Results

We found that BT treatment restored the expression of Occludin, E-cadherin (epithelial markers) while suppressing the levels of different mesenchymal markers in HCC cells and tumor tissues. Moreover, we observed a decline in the expression of transcription factors (Snail, Twist). Since the expression of these two factors can be regulated by STAT3 signaling, we deciphered the influence of BT on modulation of this pathway. BT suppressed the phosphorylation of STAT3^Y705 and STAT3 depletion using siRNA resulted in the restoration of epithelial markers. Importantly, BT (1mg/kg) reduced the tumor burden in orthotopic mouse model with a concurrent decline in lung metastasis.

Conclusions

Overall, our results demonstrate that BT interferes with STAT3 induced metastasis by altering the expression of EMT-related proteins in HCC model.

Microenvironmental Activation of Nrf2 Restricts the Progression of Nrf2-Activated Malignant Tumors

The transcription factor Nrf2 activates transcription of cytoprotective genes during oxidative and electrophilic insults. Nrf2 activity is regulated by Keap1 in a stress-dependent manner in normal cells, and somatic loss-of-function mutations of Keap1 are known to induce constitutive Nrf2 activation, especially in lung adenocarcinomas, conferring survival and proliferative benefits to tumors. Therefore, several therapeutic strategies that aim to inhibit Nrf2 in tumors have been developed for the treatment of Nrf2-activated cancers. Here we addressed whether targeting Nrf2 activation in the microenvironment can suppress the progression of Nrf2-activated tumors. We combined two types of Keap1-flox mice expressing variable levels of Keap1 with a Kras-driven adenocarcinoma model to generate Keap1-deficient lung tumors surrounded by normal or Keap1-knockdown host cells. In this model system, activation of Nrf2 in the microenvironment prolonged the survival of Nrf2-activated tumor-bearing mice. The Nrf2-activated microenvironment suppressed tumor burden; in particular, preinvasive lesion formation was significantly suppressed. Notably, loss of Nrf2 in bone marrow-derived cells in Nrf2-activated host cells appeared to counteract the suppression of Nrf2-activated cancer progression. Thus, these results demonstrate that microenvironmental Nrf2 activation suppresses the progression of malignant Nrf2-activated tumors and that Nrf2 activation in immune cells at least partially contributes to these suppressive effects. SIGNIFICANCE: This study clarifies the importance of Nrf2 activation in the tumor microenvironment and in the host for the suppression of malignant Nrf2-activated cancers and proposes new cancer therapies utilizing inducers of Nrf2.

A ruthenium(II)-curcumin compound modulates NRF2 expression balancing the cancer cell death/survival outcome according to p53 status

Abstract

Background

Tumor progression and tumor response to anticancer therapies may be affected by activation of oncogenic pathways such as the antioxidant one induced by NRF2 (nuclear factor erythroid 2-related factor 2) transcription factor and the pathways modified by deregulation of oncosuppressor p53. Often, oncogenic pathways may crosstalk between them increasing tumor progression and resistance to anticancer therapies. Therefore, understanding that interplay is critical to improve cancer cell response to therapies. In this study we aimed at evaluating NRF2 and p53 in several cancer cell lines carrying different endogenous p53 status, using a novel curcumin compound since curcumin has been shown to target both NRF2 and p53 and have anti-tumor activity.

Methods

We performed biochemical and molecular studies by using pharmacologic of genetic inhibition of NRF2 to evaluate the effect of curcumin compound in cancer cell lines of different tumor types bearing wild-type (wt) p53, mutant (mut) p53 or p53 null status.

Results

We found that the curcumin compound induced a certain degree of cell death in all tested cancer cell lines, independently of the p53 status. At molecular level, the curcumin compound induced NRF2 activation, mutp53 degradation and/or wtp53 activation. Pharmacologic or genetic NRF2 inhibition further increased the curcumin-induced cell death in both mutp53- and wtp53-carrying cancer cell lines while it did not increase cell death in p53 null cells, suggesting a cytoprotective role for NRF2 and a critical role for functional p53 to achieve an efficient cancer cell response to therapy.

Conclusions

These findings underline the prosurvival role of curcumin-induced NRF2 expression in cancer cells even when cells underwent mutp53 downregulation and/or wtp53 activation. Thus, NRF2 inhibition increased cell demise particularly in cancer cells carrying p53 either wild-type or mutant suggesting that p53 is crucial for efficient cancer cell death. These results may represent a paradigm for better understanding the cancer cell response to therapies in order to design more efficient combined anticancer therapies targeting both NRF2 and p53.

Loss-of-function mutations in KEAP1 drive lung cancer progression via KEAP1/NRF2 pathway activation

BACKGROUND AND PURPOSE

Targeted therapy and immunotherapy have led to dramatic change in the treatment of lung cancer, however, the overall 5-year survival rate of lung cancer patients is still suboptimal. It is important to exploit new potential of molecularly targeted therapies. High-frequency somatic mutations in KEAP1/NRF2 (27.9%) have been identified in lung squamous cell carcinoma. In this research, we explored the role of KEAP1 somatic mutations in the development of LSCC and whether a nuclear factor erythroid 2-related factor 2(NRF2) inhibitor be potential to target lung cancer carrying KEAP1/NRF2 mutations.

METHODS

Lung cancer cell lines A549 and H460 with loss-of-function mutations in KEAP1 stably transfected with wild-type (WT) KEAP1 or somatic mutations in KEAP1 were used to investigate the functions of somatic mutations in KEAP1. Flow cytometry, plate clone formation experiments, and scratch tests were used to examine reactive oxygen species, proliferation, and migration of these cell lines.

RESULTS

The expression of NRF2 and its target genes increased, and tumor cell proliferation, migration, and tumor growth were accelerated in A549 and H460 cells stably transfected with KEAP1 mutants compared to control cells with a loss-of-function KEAP1 mutation and stably transfected with WT KEAP1 in both in vitro and in vivo studies. The proliferation of A549 cell line trasfected with the R320Q KEAP1 mutant was inhibited more apparent than that of the A549 cell line trasfected with WT KEAP1 after treatment with NRF2 inhibitor ML385.

CONCLUSION

Somatic mutations of KEAP1 identified from patients with LSCC likely promote tumorigenesis mediated by activation of the KEAP1/NRF2 antioxidant stress response pathway. NRF2 inhibition with ML385 could inhibit the proliferation of tumor cells with KEAP1 mutation. Video abstract.

Targeting IDH1-Mutated Malignancies with NRF2 Blockade

BACKGROUND

Neomorphic IDH1 mutations disrupt the redox balance by promoting reactive oxygen species (ROS) production. However, the mechanism by which IDH1-mutant cells maintain ROS homeostasis remains elusive. It is also not known whether reprogrammed ROS homeostasis establishes targetable vulnerability in IDH1-mutated cancers.

METHODS

We investigated ROS homeostasis in wild-type (GSC827, GSC923, GSC627, and GSC711) and IDH1-mutated cells (IDH1R132C- and IDH1R132H-transduced U87, U251; MGG152, and TS603 cells). We analyzed the stability and transcriptional activity of NRF2 in IDH1-mutated cells. The oxidative DNA damage was analyzed using NRF2-targeting small interfering RNA. Moreover, we evaluated the effect of the NRF2 inhibitor brusatol in an IDH1-mutated subcutaneous xenograft nude mouse model (control group, n = 5; brusatol-treated group, n = 6). All statistical tests were two-sided.

RESULTS

We showed that IDH1-mutated cells develop a dependency on the NRF2 antioxidative pathway. Genetic or pharmacologic blockade of NRF2 not only disrupted ROS homeostasis (mean [SD] ROS levels increased by 317 [42.1]%, P = .001, in IDH1R132C and by 286. 5 [48.7]%, P = .003, in IDH1R132H cells) but also enhanced oxidative DNA damage and decreased proliferation of IDH1-mutated cells. Brusatol selectively suppressed IDH1-mutated cancer progression in vivo (mean [SD] final tumor volume was 761.6 [391.6] mm3 in the control and 246.2 [215] mm3 in the brusatol-treated group, P = .02).

CONCLUSIONS

IDH1 mutation reprograms ROS homeostasis in cancer cells, which leads to dependency on the NRF2 antioxidant pathway for ROS scavenging. NRF2 blockade might be a novel therapeutic approach to treat malignancies with IDH1 mutation.

Ischemic postconditioning attenuates acute kidney injury following intestinal ischemia-reperfusion through Nrf2-regulated autophagy, anti-oxidation, and anti-inflammation in mice

Intestinal ischemia-reperfusion (IIR) often occurs during and following major cardiovascular or gut surgery and causes significant organ including kidney injuries. This study was to investigate the protective effect of intestinal ischemic postconditioning (IPo) on IIR-induced acute kidney injury (AKI) and the underling cellular signaling mechanisms with focus on the Nrf2/HO-1. Adult C57BL/6J mice were subjected to IIR with or without IPo. IIR was established by clamping the superior mesenteric artery (SMA) for 45 minutes followed by 120 minutes reperfusion. Outcome measures were: (i) Intestinal and renal histopathology; (ii) Renal function; (iii) Cellular signaling changes; (iv) Oxidative stress and inflammatory responses. IPo significantly attenuated IIR-induced kidney injury. Furthermore, IPo significantly increased both nuclear Nrf2 and HO-1 expression in the kidney, upregulated autophagic flux, inhibited IIR-induced inflammation and reduced oxidative stress. The protective effect of IPo was abolished by the administration of Nrf2 inhibitor (Brusatol) or Nrf2 siRNA. Conversely, a Nrf2 activator t-BHQ has a similar protective effect to that of IPo. Our data indicate that IPo protects the kidney injury induced by IIR, which was likely mediated through the Nrf2/HO-1 cellular signaling activation.

Inhibitory effects of brusatol delivered using glycosaminoglycan‑placental chondroitin sulfate A‑modified nanoparticles on the proliferation, migration and invasion of cancer cells

Breakthroughs in cancer management result from the development of drugs that can be used for early diagnosis and effective treatment. Surgery, chemotherapy, radiotherapy and hormone therapy are the main anticancer therapies. However, traditional cancer chemotherapy is associated with serious systemic side effects. Nanoparticles (NPs) provide an effective solution for cancer treatment via the targeted delivery of drugs to cancer cells, while minimizing injury to normal cells. Glycosaminoglycan-placental chondroitin sulfate A (plCSA) is expressed in a number of tumor cells and trophoblasts. A plCSA-binding peptide (plCSA-BP) was isolated from malaria protein VAR2CSA, which can effectively promote the binding of lipid polymer NPs to tumor cells, thereby significantly enhancing the anticancer effect of encapsulated drugs. Brusatol is an important compound derived from Brucea javanica that exerts a multitude of biological effects, including inhibiting tumor cell growth, reducing the reproduction of malaria parasites, reducing inflammation and resisting virus invasion. In the present study, brusatol-loaded NPs (BNPs) or coumarin 6 NPs (CNPs), plCSA-BP and scrambled control peptide-bound BNPs or CNPs were prepared. Ovarian cancer cells (SKOV3), endometrial cancer cells (HEC-1-A) and lung cancer cells (A549) were treated with the NPs. The uptake of plCSA-CNPs by tumor cells was found to be markedly higher compared with that of other types of NPs. Further studies demonstrated that the plCSA-BNPs promoted the apoptosis of cancer cells more effectively and inhibited their proliferation, invasion and migration, accompanied by downregulation of matrix metalloproteinase (MMP)-2, MMP-9 and B-cell CLL/lymphoma 2 (BCL2) levels, but upregulation of BCL2-associated X protein BAX and cleaved caspase-3 levels. The results demonstrated the potential of brusatol delivered by plCSA-modified NPs as a chemotherapeutic agent for the targeted therapy of tumors by regulating the BCL2, BAX, cleaved caspase-3, MMP-2 and MMP-9 pathways, and indicated that it may be an effective and safe strategy for the treatment of various tumors.

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.

Quassinoid analogs with enhanced efficacy for treatment of hematologic malignancies target the PI3Kγ isoform

Development of novel PI3K inhibitors is an important strategy to overcome their resistance and poor tolerability in clinical trials. The quassinoid family member Brusatol shows specific inhibitory activity against hematologic malignancies. However, the mechanism of its anti-cancer activity is unknown. We investigated the anti-cancer activity of Brusatol on multiple hematologic malignancies derived cell lines. The results demonstrated that the PI3Kγ isoform was identified as a direct target of Brusatol, and inhibition was dramatically reduced on cells with lower PI3Kγ levels. Novel synthetic analogs were also developed and tested in vitro and in vivo. They shared comparable or superior potency in their ability to inhibit malignant hematologic cell lines, and in a xenograft transplant mouse model. One unique analog had minimal toxicity to normal human cells and in a mouse model. These new analogs have enhanced potential for development as a new class of PI3K inhibitors for treatment of hematologic malignancies.

Pei et al. demonstrate that PI3Kγ isoform is a direct target of Brusatol, a natural compound with inhibitory activity against hematologic malignancies. They further develop several Brusatol analogs with superior in vitro and in vivo anti-cancer activity.

Anticancer effects of brusatol in nasopharyngeal carcinoma through suppression of the Akt/mTOR signaling pathway

PURPOSE

Brusatol, a natural quassinoid that is isolated from a traditional Chinese herbal medicine known as Bruceae Fructus, possesses biological activity in various types of human cancers, but its effects in nasopharyngeal carcinoma (NPC) have not been reported. This study aimed to explore the effect and molecular mechanism of brusatol in NPC in vivo and in vitro.

METHODS

The antiproliferative effect of brusatol was assessed by MTT and colony formation assays. Apoptosis was determined by flow cytometry. The expression of mitochondrial apoptosis, cell cycle arrest, and Akt/mTOR pathway proteins were determined by western blot analysis. Further in vivo confirmation was performed in a nude mouse model.

RESULTS

Brusatol showed antiproliferative activity against four human NPC cell lines (CNE-1, CNE-2, 5-8F, and 6-10B) in a dose-dependent manner. This antiproliferative effect was accompanied by mitochondrial apoptosis and cell cycle arrest through the modulation of several key molecular targets, such as Bcl-xl, Bcl-2, Bad, Bax, PARP, Caspase-9, Caspase-7, Caspase-3, Cdc25c, Cyclin B1, Cdc2 p34, and Cyclin D1. In addition, we found that brusatol inhibited the activation of Akt, mTOR, 4EBP1, and S6K, suggesting that the Akt/mTOR pathway is a key underlying mechanism by which brusatol inhibits growth and promotes apoptosis. Further in vivo nude mouse models proved that brusatol significantly inhibited the growth of CNE-1 xenografts with no significant toxicity.

CONCLUSIONS

These observations indicate that brusatol is a promising antitumor drug candidate or a supplement to current chemotherapeutic therapies to treat NPC.

Copper-imidazo[1,2-a]pyridines induce intrinsic apoptosis and modulate the expression of mutated p53, haem-oxygenase-1 and apoptotic inhibitory proteins in HT-29 colorectal cancer cells

Metastatic colorectal cancer responds poorly to treatment and is a leading cause of cancer related deaths. Worldwide, chemotherapy of metastatic colorectal cancer remains plagued by poor efficacy, development of resistance and serious adverse effects. Copper-imidazo[1,2-a]pyridines were previously shown by our group to be selectively active against several cancer cell lines, with three complexes, JD46(27), JD47(29), and JD88(21), showing IC₅₀ values between 0.8 and 1.8 μM against HT-29 cells. Here, we report that treatment with the copper complexes resulted in fragmented nuclei suggestive of apoptotic cell death, which was confirmed by increased annexin V binding and caspase-3/7 activity. The copper complexes caused a loss of mitochondrial membrane potential and increased caspase-9 activity. The absence of caspase-8 activity indicated activation of the intrinsic pathway. Proteomic analysis revealed that copper-imidazo[1,2-a]pyridines decreased the expression of phosphorylated forms of p53 [phospho-p53(S15), phospho-p53(S46) and phospho-p53(S392)]. The expression of inhibitor of apoptosis proteins, XIAP, cIAP1, livin, and the antiapoptotic proteins, Bcl-2 and Bcl-x, was decreased. HO/HMOX/HSP32, expression was notably increased, which suggested the accumulation of reactive oxygen species. Increased expression of TRAIL-R2/DR5 death receptor indicated the possible dual activation of both the extrinsic and intrinsic apoptotic pathways; however, caspase-8 activation could not be demonstrated. In conclusion, the copper-imidazo[1,2-a]pyridines were effective inducers of apoptotic cell death at low micromolar concentrations and changed the expression levels of proteins important for cell survival and cell death. These copper complexes may be useful tools to better understand the complexity of signalling networks in cancer cell death in response to cell stress.

Molecular mechanisms and systemic targeting of NRF2 dysregulation in cancer

NF-E2-related factor 2 (NRF2) is a master regulator of redox homeostasis and provides cellular protection against oxidants and electrophiles by inducing the expression of a wide array of phase II cytoprotective genes. Until now, a number of NRF2 activators have been developed for treatment of chronic diseases and some are under evaluation in the clinical studies. On the other hand, accumulating evidence indicates that NRF2 confers chemoresistance and radioresistance, and its expression is correlated with poor prognosis in cancer patients. Studies in the last decade demonstrate that diverse mechanisms such as somatic mutations, accumulation of KEAP1 binding proteins, transcriptional dysregulation, oncogene activation, and accumulation of reactive metabolites contribute to NRF2 activation in cancer. In the present review, we illustrate the molecular mechanisms governing the function of NRF2 and explain how they are hijacked in cancer. We also provide some examples of NRF2 inhibitors together with a brief explanation of their mechanisms of action.

The Effects of Dietary Supplements that Overactivate the Nrf2/ARE System

Background:

Inflammation is one of the most misunderstood aspects of human health. People have been encouraged to eat foods that have a high antioxidant capacity, and in vitro tests for total antioxidant capacity emerged. They were based on measuring the destruction of oxidized test compounds in direct reactions with the antioxidants in foods. Many dietary supplements arrived in the market. They contained purified antioxidants, such as resveratrol and EGCG that were and still are widely assumed by many to be quite healthy at any dose.

Methods:

The literature on inflammation and the Nrf2/ARE antioxidant system was searched systematically. Articles from prestigious, peer-reviewed journals were obtained and read. The information obtained from them was used to write this review article.

Results:

Over 150 articles and books were read. The information obtained from them showed that very few dietary antioxidants exert their effects by reacting directly with Reactive Oxygen and Nitrogen Species (RONS). Instead, most of the effective antioxidants activate the endogenous Nrf2/ARE antioxidant system. This helps prevent smoldering inflammation and the diseases that it can cause. However, when overactivated or activated constitutively, the Nrf2/ARE antioxidant system can cause some of these diseases, including many types of multidrug resistant cancer, autoimmune, neurodegenerative and cardiovascular diseases.

Conclusion:

Even though green tea, as well as many fruits, vegetables and spices are quite healthy, dietary supplements that deliver much higher doses of antioxidants may not be. People who are diagnosed with cancer and plan to start chemotherapy and/or radiotherapy should probably avoid such supplements. This is because multidrug resistant tumors can hijack and overactivate the Nrf2/ARE antioxidant system.