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

Small molecule drug discovery for glioblastoma treatment based on bioinformatics and cheminformatics approaches

Background: Glioblastoma (GBM) is a common and highly aggressive brain tumor with a poor prognosis for patients. It is urgently needed to identify potential small molecule drugs that specifically target key genes associated with GBM development and prognosis. Methods: Differentially expressed genes (DEGs) between GBM and normal tissues were obtained by data mining the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases. Gene function annotation was performed to investigate the potential functions of the DEGs. A protein-protein interaction (PPI) network was constructed to explore hub genes associated with GBM. Bioinformatics analysis was used to screen the potential therapeutic and prognostic genes. Finally, potential small molecule drugs were predicted using the DGIdb database and verified using chemical informatics methods including absorption, distribution, metabolism, excretion, toxicity (ADMET), and molecular docking studies. Results: A total of 429 DEGs were identified, of which 19 hub genes were obtained through PPI analysis. The hub genes were confirmed as potential therapeutic targets by functional enrichment and mRNA expression. Survival analysis and protein expression confirmed centromere protein A (CENPA) as a prognostic target in GBM. Four small molecule drugs were predicted for the treatment of GBM. Conclusion: Our study suggests some promising potential therapeutic targets and small molecule drugs for the treatment of GBM, providing new ideas for further research and targeted drug development.

SN-38, an active metabolite of irinotecan, inhibits transcription of nuclear factor erythroid 2-related factor 2 and enhances drug sensitivity of colorectal cancer cells

Nuclear factor erythroid 2-related factor 2 (Nrf2) significantly contributes to drug resistance of cancer cells, and Nrf2 inhibitors have been vigorously pursued. Repurposing of existing drugs, especially anticancer drugs, is a straightforward and promising strategy to find clinically available Nrf2 inhibitors and effective drug combinations. Topoisomerase inhibitors SN-38 (an active metabolite of irinotecan), topotecan, mitoxantrone, and epirubicin were found to significantly suppress Nrf2 transcriptional activity in cancer cells. SN-38, the most potent one among them, significantly inhibited the transcription of Nrf2, as indicated by decreased mRNA level and binding of RNA polymerase II to NFE2L2 gene, while no impact on Nrf2 protein or mRNA degradation was observed. SN-38 synergized with Nrf2-sensitive anticancer drugs such as mitomycin C in killing colorectal cancer cells, and irinotecan and mitomycin C synergistically inhibited the growth of SW480 xenografts in nude mice. Our study identified SN-38 and three other topoisomerase inhibitors as Nrf2 inhibitors, revealed the Nrf2-inhibitory mechanism of SN-38, and indicate that clinically feasible drug combinations could be designed based on their interactions with Nrf2 signaling.

Modulators of the Nrf2 Signaling Pathway Enhance the Cytotoxic Effect of Standard Chemotherapeutic Drugs on Organoids of Metastatic Colorectal Cancer

The activity of known modulators of the Nrf2 signaling pathway (bardoxolone and brusatol) was studied on cultures of tumor organoids of metastatic colorectal cancer previously obtained from three patients. The effect of modulators was studied both as monotherapy and in combination with standard chemotherapy drugs used to treat colorectal cancer. The Nrf2 inhibitor brusatol and the Nrf2 activator bardoxolone have antitumor activity. Moreover, bardoxolone and brusatol also significantly enhance the effect of the chemotherapy drugs 5-fluorouracil, oxaliplatin, and irinotecan metabolite SN-38. Thus, bardoxolone and brusatol can be considered promising candidates for further preclinical and clinical studies in the treatment of colorectal cancer.

The Aurora kinase inhibitor AT9283 inhibits Burkitt lymphoma growth by regulating Warburg effect

Objective

To investigate the effect of the kinase inhibitor AT9283 on Burkitt lymphoma (BL) cells and elucidate the underlying mechanisms.

Methods

The effect of AT9283 on the proliferation of BL cell lines was tested using the MTT assay. Apoptosis and cell cycle were measured by flow cytometry. The proteins associated with the cell cycle, apoptosis, and the Warburg effect were detected using Western blotting. Alterations in glycolytic metabolism in terms of glucose intake and lactate concentrations were determined by glucose and lactate assays.

Results

The current study utilized the GEPIA, the Human Protein Atlas (HAP) database and immunohistochemistry to conduct analyses, which revealed a high expression of Aurora kinases and Warburg effect-related proteins in malignant B-cell lymphoma tissues. AT9283 significantly inhibited the cell proliferation of BL cells and induced G2/M arrest. Additionally, AT9283 induced apoptosis in BL cells and reversed the Warburg effect by increasing glucose uptake and reducing lactate production. Moreover, the protein expression of hexokinase 2, pyruvate kinase M2, and lactate dehydrogenase A was significantly suppressed by AT9283, possibly through the inhibition of c-Myc and HIF-1α protein expression.

Conclusion

The reversal of the Warburg effect in BL cells and the subsequent inhibition of cell proliferation and induction of apoptosis were observed by targeting Aurora A and Aurora B with AT9283. This finding may present new therapeutic options and targets for BL.

Electrophilic reactive aldehydes as a therapeutic target in colorectal cancer prevention and treatment

Colorectal cancer (CRC) is a major health problem worldwide. Dicarbonyl electrophiles, such as isolevuglandins (isoLGs), are generated from lipid peroxidation and form covalent adducts with amine-containing macromolecules. We have shown high levels of adducts of isoLGs in colonic epithelial cells of patients with CRC. We thus investigated the role of these reactive aldehydes in colorectal cancer development. We found that 2-hydroxybenzylamine (2-HOBA), a natural compound derived from buckwheat seeds that acts as a potent scavenger of electrophiles, is bioavailable in the colon of mice after supplementation in the drinking water and does not affect the colonic microbiome. 2-HOBA reduced the level of isoLG adducts to lysine as well as tumorigenesis in models of colitis-associated carcinogenesis and of sporadic CRC driven by specific deletion of the adenomatous polyposis coli gene in colonic epithelial cells. In parallel, we found that oncogenic NRF2 activation and signaling were decreased in the colon of 2-HOBA-treated mice. Additionally, the growth of xenografted human HCT116 CRC cells in nude mice was significantly attenuated by 2-HOBA supplementation. In conclusion, 2-HOBA represents a promising natural compound for the prevention and treatment of CRC.

Terminators or Guardians? Design, Synthesis, and Cytotoxicity Profiling of Chalcone-Sulfonamide Hybrids

With a "less is more" philosophy, a series of 15 chalcone-sulfonamide hybrids were designed anticipating synergistic anticancer activity. The aromatic sulfonamide moiety was included as a known direct inhibitor of carbonic anhydrase IX activity through its zinc chelating property. The chalcone moiety was incorporated as an electrophilic stressor to indirectly inhibit carbonic anhydrase IX cellular activity. Screening by the Developmental Therapeutics Program of the National Cancer Institute, NCI-60, revealed that 12 derivatives were potent inhibitors of cancer cell growth in multiple cell lines and were promoted to the five-dose screen. The cancer cell growth inhibition profile indicated sub- to two-digit micromolar potency (GI₅₀ down to 0.3 μM and LC₅₀ as low as 4 μM) against colorectal carcinoma cells, in particular. Unexpectedly, most compounds demonstrated low to moderate potency as direct inhibitors of carbonic anhydrase catalytic activity in vitro, with 4d being the most potent, having an average Ki value of 4 μM. Compound 4j showed ca. six-fold selectivity to carbonic anhydrase IX over the other tested isoforms in vitro. Cytotoxicity of both 4d and 4j in live HCT116, U251, and LOX IMVI cells under hypoxic conditions confirmed their targeting of carbonic anhydrase activity. Elevation of oxidative cellular stress was stipulated from the increase in Nrf2 and ROS levels in 4j-treated colorectal carcinoma, HCT116, cells compared to the control. Compound 4j arrested the cell cycle of HCT116 cells at the G1/S phase. In addition, both 4d and 4j showed up to 50-fold cancer cell selectivity compared to the non-cancerous HEK293T cells. Accordingly, this study presents 4d and 4j being new, synthetically accessible, simplistically designed derivatives as potential candidates to be further developed as anticancer therapeutics.

NRF2 and Bip Interconnection Mediates Resistance to the Organometallic Ruthenium-Cymene Bisdemethoxycurcumin Complex Cytotoxicity in Colon Cancer Cells

Organometallic ruthenium (Ru)(II)-cymene complexes display promising pharmacological properties and might represent alternative therapeutic agents in medical applications. Polyphenols, such as curcumin and curcuminoids, display beneficial properties in medicine, including chemoprevention. Here we analyzed the anticancer effect of a cationic Ruthenium (Ru)(II)-cymene Bisdemethoxycurcumin (Ru-bdcurc) complex. The experimental data show that Ru-bdcurc induced cell death of colon cancer cells in vitro. In response to treatment, cancer cells activated the endoplasmic reticulum (ER)-resident chaperone GRP78/BiP and NRF2, the master regulators of the unfolded protein response (UPR) and the antioxidant response, respectively. Pharmacologic targeting of either NRF2 or BiP potentiated the cytotoxic effect of Ru-bdcurc. We also found that NRF2 and UPR pathways were interconnected as the inhibition of NRF2 reduced BiP protein levels. Mechanistically, the increased Ru-bdcurc-induced cell death, following NRF2 or BiP inhibition, correlated with the upregulation of the UPR apoptotic marker CHOP and with increased H2AX phosphorylation, a marker of DNA damage. The findings reveal that BiP and NRF2 interconnection was a key regulator of colon cancer cells resistance to Ru-bdcurc cytotoxic effect. Targeting that interconnection overcame the protective mechanism and enhanced the antitumor effect of the Ru-bdcurc compound.

Role of NRF2 in Colorectal Cancer Prevention and Treatment

Nuclear factor erythroid 2-related factor 2 (NRF2) is a basic leucine zipper protein that participates in a complex regulatory network in the body. The activation of NRF2 can prevent and treat colorectal cancer (CRC). A variety of natural compounds can activate NRF2 to inhibit oxidative stress and inflammation to prevent the occurrence and development of CRC, inhibit the proliferation of CRC cells and induce their apoptosis. However, some studies have also shown that it also has negative effects on CRC, such as overexpression of NRF2 can promote the growth of colorectal tumors and increase the drug resistance of chemotherapeutic drugs such as 5-fluorouracil and oxaliplatin. Therefore, inhibition of NRF2 can also be helpful in the treatment of CRC. In this study, we analyze the current research progress of NRF2 in CRC from various aspects to provide new ideas for prevention and treatment based on the NRF2 signaling pathway in CRC.

Genetic alterations of Keap1 confers chemotherapeutic resistance through functional activation of Nrf2 and Notch pathway in head and neck squamous cell carcinoma

Keap1 mutations regulate Nrf2 activity and lead to chemoresistance in cancers. Yet the underlying molecular mechanisms of chemoresistance are poorly explored. By focusing and genotyping head and neck squamous cell carcinoma (HNSCC) that had available pathologic and clinical data, we provide evidence that Keap1 displays frequent alterations (17%) in HNSCC. Functional loss of Keap1 results in significant activation of Nrf2 and promotes cancer cell growth, proliferation, and elevated cancer stem cell (CSCs) self-renewal efficiency and resistance to oxidative stress. Furthermore, decreased Keap1 activity in these cells increased nuclear accumulation of Nrf2 and activation of the Notch pathway, causing enhanced transcriptional alterations of antioxidants, xenobiotic metabolism enzymes, and resistance to chemotherapeutic treatment. Limiting the Nrf2 activity by either Keap1 complementation or by Nrf2 silencing increased the sensitivity to chemotherapy in Keap1-mutated cells and repressed the CSC self-renewal activity. Our findings suggest that Keap1 mutations define a distinct disease phenotype and the Keap1-Nrf2 pathway is one of the leading molecular mechanisms for clinical chemotherapeutic resistance. Targeting this pathway may provide a potential and attractive personalized treatment strategy for overcoming chemotherapeutic resistance conferred by Keap1 mutations.

The tumor/normal tissue ratio of Keap1 protein is a predictor for lymphovascular invasion in colorectal cancer: A correlation study between the Nrf2 and KRas pathways

PURPOSE: Oxidative stress has impacts on the KRas and Nrf2/Keap1 pathways, which have multiple interactions with each other and play important roles in colorectal cancer (CRC). This study investigated the expressions of proteins in the KRas and Nrf2/Keap1 pathways and their associations with clinicopathological features in CRC.METHODS: The protein levels of Nrf2, Keap1, Bach1, p62, HO1, KRas, Erk, Raf1 and PI3K in both the tumor and normal tissues of 60 CRC subjects were determined by Western blot and their T/N (tumor/normal tissue) ratios were correlated with clinicopathological features.RESULTS: The T/N ratios of proteins in the KRas and Nrf2/Keap1 pathways had correlation patterns and proximity profiles in cluster dendrograms different in CRC with different status of lymphovascular invasion (LVI) or lymph node/distant metastases. The Keap1 protein T/N ratio was a significant predictor (odd ratio: 2.24; 95% confidence interval: 1.26 - 4.38) of LVI, which in turn predicted metastases (11.0; 3.49 - 39.8).CONCLUSION: The interactions between the KRas and Nrf2/Keap1 pathways may be affected differently by LVI and metastases, and the protein T/N ratio of Keap1 may be helpful for predicting LVI in CRC.

Targeting Nrf2 in ischemia-reperfusion alleviation: From signaling networks to therapeutic targeting

The nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of redox balance and it responds to various cell stresses that oxidative stress is the most well-known one. The Nrf2 should undergo nuclear translocation to exert its protective impacts and decrease ROS production. On the other hand, ischemic/reperfusion (I/R) injury is a pathological event resulting from low blood flow to an organ and followed by reperfusion. The I/R induces cell injury and organ dysfunction. The present review focuses on Nrf2 function in alleviation of I/R injury. Stimulating of Nrf2 signaling ameliorates I/R injury in various organs including lung, liver, brain, testis and heart. The Nrf2 enhances activity of antioxidant enzymes to reduce ROS production and prevent oxidative stress-mediated cell death. Besides, Nrf2 reduces inflammation via decreasing levels of pro-inflammatory factors including IL-6, IL-1β and TNF-α. Nrf2 signaling is beneficial in preventing apoptosis and increasing cell viability. Nrf2 induces autophagy to prevent apoptosis during I/R injury. Furthermore, it can interact with other molecular pathways including PI3K/Akt, NF-κB, miRNAs, lncRNAs and GSK-3β among others, to ameliorate I/R injury. The therapeutic agents, most of them are phytochemicals such as resveratrol, berberine and curcumin, induce Nrf2 signaling in I/R injury alleviation.

The synthetic triterpenoids CDDO-TFEA and CDDO-Me, but not CDDO, promote nuclear exclusion of BACH1 impairing its activity

The transcription factor BACH1 is a potential therapeutic target for a variety of chronic conditions linked to oxidative stress and inflammation, as well as cancer metastasis. However, only a few BACH1 degraders/inhibitors have been described. BACH1 is a transcriptional repressor of heme oxygenase 1 (HMOX1), which is positively regulated by transcription factor NRF2 and is highly inducible by derivatives of the synthetic oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO). Most of the therapeutic activities of these compounds are due to their anti-inflammatory and antioxidant properties, which are widely attributed to their ability to activate NRF2. However, with such a broad range of action, these compounds have other molecular targets that have not been fully identified and could also be of importance for their therapeutic profile. Herein we identified BACH1 as a target of two CDDO-derivatives (CDDO-Me and CDDO-TFEA), but not of CDDO. While both CDDO and CDDO-derivatives activate NRF2 similarly, only CDDO-Me and CDDO-TFEA inhibit BACH1, which explains the much higher potency of these CDDO-derivatives as HMOX1 inducers compared with unmodified CDDO. Notably, we demonstrate that CDDO-Me and CDDO-TFEA inhibit BACH1 via a novel mechanism that reduces BACH1 nuclear levels while accumulating its cytoplasmic form. In an in vitro model, both CDDO-derivatives impaired lung cancer cell invasion in a BACH1-dependent and NRF2-independent manner, while CDDO was inactive. Altogether, our study identifies CDDO-Me and CDDO-TFEA as dual KEAP1/BACH1 inhibitors, providing a rationale for further therapeutic uses of these drugs.

The Impact of NRF2 Inhibition on Drug-Induced Colon Cancer Cell Death and p53 Activity: A Pilot Study

Nuclear factor erythroid 2 (NF-E2) p45-related factor 2 (NRF2) protein is the master regulator of oxidative stress, which is at the basis of various chronic diseases including cancer. Hyperactivation of NRF2 in already established cancers can promote cell proliferation and resistance to therapies, such as in colorectal cancer (CRC), one of the most lethal and prevalent malignancies in industrialized countries with limited patient overall survival due to its escape mechanisms in both chemo- and targeted therapies. In this study, we generated stable NRF2 knockout colon cancer cells (NRF2-Cas9) to investigate the cell response to chemotherapeutic drugs with regard to p53 oncosuppressor, whose inhibition we previously showed to correlate with NRF2 pathway activation. Here, we found that NRF2 activation by sulforaphane (SFN) reduced cisplatin (CDDP)-induced cell death only in NRF2-proficient cells (NRF2-ctr) compared to NRF2-Cas9 cells. Mechanistically, we found that NRF2 activation protected NRF2-ctr cells from the drug-induced DNA damage and the apoptotic function of the unfolded protein response (UPR), in correlation with reduction of p53 activity, effects that were not observed in NRF2-Cas9 cells. Finally, we found that ZnCl2 supplementation rescued the cisplatin cytotoxic effects, as it impaired NRF2 activation, restoring p53 activity. These findings highlight NRF2′s key role in neutralizing the cytotoxic effects of chemotherapeutic drugs in correlation with reduced DNA damage and p53 activity. They also suggest that NRF2 inhibition could be a useful strategy for efficient anticancer chemotherapy and support the use of ZnCl2 to inhibit NRF2 pathway in combination therapies.

Pirin, an Nrf2-Regulated Protein, Is Overexpressed in Human Colorectal Tumors

The evolutionary conserved non-heme Fe-containing protein pirin has been implicated as an important factor in cell proliferation, migration, invasion, and tumour progression of melanoma, breast, lung, cervical, prostate, and oral cancers. Here we found that pirin is overexpressed in human colorectal cancer in comparison with matched normal tissue. The overexpression of pirin correlates with activation of transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) and increased expression of the classical Nrf2 target NAD(P)H:quinone oxidoreductase 1 (NQO1), but interestingly and unexpectedly, not with expression of the aldo-keto reductase (AKR) family members AKR1B10 and AKR1C1, which are considered to be the most overexpressed genes in response to Nrf2 activation in humans. Using pharmacologic and genetic approaches to either downregulate or upregulate Nrf2, we show that pirin is regulated by Nrf2 in human and mouse cells and in the mouse colon in vivo. The small molecule pirin inhibitor TPhA decreased the viability of human colorectal cancer (DLD1) cells, but this decrease was independent of the levels of pirin. Our study demonstrates the Nrf2-dependent regulation of pirin and encourages the pursuit for specific pirin inhibitors.

Nrf2 activation does not affect adenoma development in a mouse model of colorectal cancer

Transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) and its main negative regulator, Kelch-like ECH associated protein 1 (Keap1), are at the interface between redox and intermediary metabolism. Nrf2 activation is protective in models of human disease and has benefits in clinical trials. Consequently, the Keap1/Nrf2 protein complex is a drug target. However, in cancer Nrf2 plays a dual role, raising concerns that Nrf2 activators may promote growth of early neoplasms. To address this concern, we examined the role of Nrf2 in development of colorectal adenomas by employing genetic, pharmacological, and metabolomic approaches. We found that colorectal adenomas that form in Gstp-/-: ApcMin/+ mice are characterized by altered one-carbon metabolism and that genetic activation, but not disruption of Nrf2, enhances these metabolic alterations. However, this enhancement is modest compared to the magnitude of metabolic differences between tumor and peri-tumoral tissues, suggesting that the metabolic changes conferred by Nrf2 activation may have little contribution to the early stages of carcinogenesis. Indeed, neither genetic (by Keap1 knockdown) nor pharmacological Nrf2 activation, nor its disruption, affected colorectal adenoma formation in this model. We conclude that pharmacological Nrf2 activation is unlikely to impact the early stages of development of colorectal cancer.

NRF2 Mediates Therapeutic Resistance to Chemoradiation in Colorectal Cancer through a Metabolic Switch

Radiation resistance is a significant clinical problem in rectal cancer treatment, the mechanisms of which are poorly understood. NRF2 signalling is known to contribute to chemo/radioresistance in some cancers, but its role in therapeutic resistance in colorectal cancer (CRC) is unexplored. Using siRNA and CRiSPR/Cas9 isogenic CRC cell lines, we investigated the effect of the knockdown and upregulation of the NRF2 pathway on chemo-radiosensitivity. Poly (A) enriched RNA sequencing and geneset enrichment analysis (GSEA) were carried out on both sensitive and resistant cell models for mechanistic insights. Finally, a cohort of rectal patient samples was profiled to understand the clinical relevance of NRF2 signalling. Radioresistant cell lines were significantly radiosensitised by siRNA knockdown (SW1463, SER10 1.22, ANOVA p < 0.0001; HT55, SER10 1.17, ANOVA p < 0.01), but not the (already) radiosensitive HCT116. The constitutive activation of NRF2 via a CRISPR Cas9 NFE2L2 mutation, E79K, induced radioresistance in HCT116 (SER10 0.71, ANOVA, p < 0.0001). GSEA demonstrated significant opposing metabolic dependencies in NRF2 signalling, specifically, the downregulation of amino acid and protein synthesis with low levels of NRF2 and upregulation with over expression. In a clinical cohort of 127 rectal patients, using a validated mRNA signature, higher baseline NRF2 signalling was associated with incomplete responses to radiation higher final neoadjuvant rectal (NAR) score (OR 1.34, 95% C.I. 1.01-1.80, LRT p-value = 0.023), where high NAR indicates poor radiation response and poor long-term prognosis. This is the first demonstration of NRF2-mediated radiation resistance in colorectal cancer. NRF2 appears to regulate crucial metabolic pathways, which could be exploited for therapeutic interventions.

Kidney cancer biomarkers and targets for therapeutics: survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, p53, KRAS and AKT in renal cell carcinoma

The incidence of renal cell carcinoma (RCC) is increasing worldwide with an approximate 20% mortality rate. The challenge in RCC is the therapy-resistance. Cancer resistance to treatment employs multiple mechanisms due to cancer heterogeneity with multiple genetic and epigenetic alterations. These changes include aberrant overexpression of (1) anticancer cell death proteins (e.g., survivin/BIRC5), (2) DNA repair regulators (e.g., ERCC6) and (3) efflux pump proteins (e.g., ABCG2/BCRP); mutations and/or deregulation of key (4) oncogenes (e.g., MDM2, KRAS) and/or (5) tumor suppressor genes (e.g., TP5/p53); and (6) deregulation of redox-sensitive regulators (e.g., HIF, NRF2). Foci of tumor cells that have these genetic alterations and/or deregulation possess survival advantages and are selected for survival during treatment. We will review the significance of survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, TP5/p53, KRAS and AKT in treatment resistance as the potential therapeutic biomarkers and/or targets in RCC in parallel with our analized RCC-relevant TCGA genetic results from each of these gene/protein molecules. We then present our data to show the anticancer drug FL118 modulation of these protein targets and RCC cell/tumor growth. Finally, we include additional data to show a promising FL118 analogue (FL496) for treating the specialized type 2 papillary RCC.

Inhibition of the NRF2/KEAP1 Axis: A Promising Therapeutic Strategy to Alter Redox Balance of Cancer Cells

Significance: The nuclear factor erythroid 2-related factor 2/Kelch-like ECH-associated protein 1 (NRF2/KEAP1) pathway is a crucial and highly conserved defensive system that is required to maintain or restore the intracellular homeostasis in response to oxidative, electrophilic, and other types of stress conditions. The tight control of NRF2 function is maintained by a complex network of biological interactions between positive and negative regulators that ultimately ensure context-specific activation, culminating in the NRF2-driven transcription of cytoprotective genes. Recent Advances: Recent studies indicate that deregulated NRF2 activation is a frequent event in malignant tumors, wherein it is associated with metabolic reprogramming, increased antioxidant capacity, chemoresistance, and poor clinical outcome. On the other hand, the growing interest in the modulation of the cancer cells' redox balance identified NRF2 as an ideal therapeutic target. Critical Issues: For this reason, many efforts have been made to identify potent and selective NRF2 inhibitors that might be used as single agents or adjuvants of anticancer drugs with redox disrupting properties. Despite the lack of specific NRF2 inhibitors still represents a major clinical hurdle, the researchers have exploited alternative strategies to disrupt NRF2 signaling at different levels of its biological activation. Future Directions: Given its dualistic role in tumor initiation and progression, the identification of the appropriate biological context of NRF2 activation and the specific clinicopathological features of patients cohorts wherein its inactivation is expected to have clinical benefits, will represent a major goal in the field of cancer research. In this review, we will briefly describe the structure and function of the NRF2/ KEAP1 system and some of the most promising NRF2 inhibitors, with a particular emphasis on natural compounds and drug repurposing. Antioxid. Redox Signal. 34, 1428-1483.

Nuclear Factor Erythroid 2-related Factor 2 Knockout Suppresses the Development of Aggressive Colorectal Cancer Formation Induced by Azoxymethane/Dextran Sulfate Sodium-Treatment in Female Mice

Colon tumors develop more frequently in male than in female. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays differential roles in the stage of tumorigenesis. The purpose of this study was to investigate the role of Nrf2 on colitis-associated tumorigenesis using Nrf2 knockout (KO) female mice. Azoxymethane (AOM) and dextran sulfate sodium (DSS)-treated wild-type (WT) and Nrf2 KO female mice were sacrificed at week 2 and 16 after AOM injection. Severity of colitis, tumor incidence, and levels of inflammatory mediators were evaluated in AOM/DSS-treated WT and Nrf2 KO mice. Furthermore, qRT-PCR, Western blot abnalysis, and ELISA were performed in colon tissues. At week 2, AOM/DSS-induced colon tissue damages were significantly greater in Nrf2 KO than in WT mice. At week 16, tumor numbers (> 2 mm size) were significantly lower in both the proximal and distal colon in Nrf2 KO compared to WT. The overall incidences of adenoma/cancer of the proximal colon and submucosal invasive cancer of the distal colon were reduced by Nrf2 KO. The mRNA and protein expression levels of NF-κB-related mediators (i.e., iNOS and COX-2) and Nrf2-related antioxidants (i.e., heme oxygenase-1 and glutamate-cysteine ligase catalytic subunit) were significantly lower in the Nrf2 KO than in WT mice. Interestingly, the protein level of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) was higher in AOM/DSS-treated Nrf2 KO than in WT mice. Our results support the oncogenic effect of Nrf2 in the later stage of carcinogenesis and upregulation of tumor suppressor 15-PGDH might contribute to the repression of colitis-associated tumorigenesis in Nrf2 KO female mice.

P62/SQSTM1/Keap1/NRF2 Axis Reduces Cancer Cells Death-Sensitivity in Response to Zn(II)-Curcumin Complex

The hyperactivation of nuclear factor erythroid 2 p45-related factor 2 (NRF2), frequently found in many tumor types, can be responsible for cancer resistance to therapies and poor patient prognosis. Curcumin has been shown to activate NRF2 that has cytotprotective or protumorigenic roles according to tumor stage. The present study aimed at investigating whether the zinc–curcumin Zn(II)–curc compound, which we previously showed to display anticancer effects through multiple mechanisms, could induce NRF2 activation and to explore the underlying molecular mechanisms. Biochemical studies showed that Zn(II)–curc treatment increased the NRF2 protein levels along with its targets, heme oxygenase-1 (HO-1) and p62/SQSTM1, while markedly reduced the levels of Keap1 (Kelch-like ECH-associated protein 1), the NRF2 inhibitor, in the cancer cell lines analyzed. The silencing of either NRF2 or p62/SQSTM1 with specific siRNA demonstrated the crosstalk between the two molecules and that the knockdown of either molecule increased the cancer cell sensitivity to Zn(II)–curc-induced cell death. This suggests that the crosstalk between p62/SQSTM1 and NRF2 could be therapeutically exploited to increase cancer patient response to therapies.

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.