Novel tricyclic compounds having acetylene groups at C-8a and cyano enones in rings A and C: highly potent anti-inflammatory and cytoprotective agents

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.

KEAP1, a cysteine-based sensor and a drug target for the prevention and treatment of chronic disease

Redox imbalance and persistent inflammation are the underlying causes of most chronic diseases. Mammalian cells have evolved elaborate mechanisms for restoring redox homeostasis and resolving acute inflammatory responses. One prominent mechanism is that of inducing the expression of antioxidant, anti-inflammatory and other cytoprotective proteins, while also suppressing the production of pro-inflammatory mediators, through the activation of transcription factor nuclear factor-erythroid 2 p45-related factor 2 (NRF2). At homeostatic conditions, NRF2 is a short-lived protein, which avidly binds to Kelch-like ECH-associated protein 1 (KEAP1). KEAP1 functions as (i) a substrate adaptor for a Cullin 3 (CUL3)-based E3 ubiquitin ligase that targets NRF2 for ubiquitination and proteasomal degradation, and (ii) a cysteine-based sensor for a myriad of physiological and pharmacological NRF2 activators. Here, we review the intricate molecular mechanisms by which KEAP1 senses electrophiles and oxidants. Chemical modification of specific cysteine sensors of KEAP1 results in loss of NRF2-repressor function and alterations in the expression of NRF2-target genes that encode large networks of diverse proteins, which collectively restore redox balance and resolve inflammation, thus ensuring a comprehensive cytoprotection. We focus on the cyclic cyanoenones, the most potent NRF2 activators, some of which are currently in clinical trials for various pathologies characterized by redox imbalance and inflammation.

Synthesis of New Dihydroquinopimaric Acid Analogs with Nitrile Groups as Apoptosis-Inducing Anticancer Agents

BACKGROUND

Cyan-containing compounds are of great interest as potential anticancer agents. Terpenoids can severe as a natural matrix for the development of promising derivatives with antitumor activity.

METHODS

The 2-cyanoethoxy methyl dihydroquinopimarate derivatives (5-9) were synthesized by the reaction of the intermediates (1-4) with acrylonitrile in the presence of alkali (30% KOH solution) using triethylbenzylammonium chloride. The cytotoxicity evaluation was carried out according to the National Cancer Institute (NCI) Protocol, while apoptosis was studied by flow cytometric analysis of Annexin V and 7-aminoactinomycin D staining and cell cycle was analyzed using the method of propidium iodide staining.

RESULTS

Synthesis of new dihydroquinopimaric acid derivatives with nitrile groups was carried out. The obtained cyanoethyl derivatives were converted into tetrazole, amine, oxadiazole and amidoxime analogs. The primary screening for antitumor activity showed the highest cytotoxic potency of the cyanoethyl-substituted compounds. The introduction of cyanoethyl groups at C-1, C-4 and C-1, C-4, C-20 positions of dihydroquinopimaric acid methyl ester provided antiproliferative effect towards the Jurkat, K562, U937, and HeLa tumor cell cultures (CC50=0.045-0.154µM). These nitrile derivatives are effective inducers of tumor cell apoptosis affecting the S and G2 phases of the cell cycle in a dose-dependent manner.

CONCLUSION

The cyanoethyl analogs of dihydroquinopimaric acid reported herein are apoptosis inducers and cytotoxic agents. These findings will be useful for the further design of more potent cytotoxic agents based on natural terpenes.

Essential Role of Keap1-Nrf2 Signaling in Mood Disorders: Overview and Future Perspective

Depression is one of the most common mood disorders with a high rate of relapse. Accumulating evidence suggests that the transcription factor Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1)-Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) system plays a key role in inflammation which is involved in depression. Preclinical studies demonstrated that the protein expressions of Keap1 and Nrf2 in the prefrontal cortex (PFC), CA3 and dentate gyrus (DG) of hippocampus in mice with depression-like phenotype were lower than control mice. In the learned helplessness paradigm, the protein levels of Keap1 and Nrf2 in the PFC and DG of hippocampus from rats with depression-like phenotype were also lower than control and resilient rats. Furthermore, rodents with depression-like phenotype have higher levels of pro-inflammatory cytokines. Interestingly, Nrf2 knock-out (KO) mice exhibit depression-like phenotype, and higher serum levels of pro-inflammatory cytokines compared with wild-type mice. Furthermore, Nrf2 KO mice have lower expression of brain-derived neurotrophic factor (BDNF) in the PFC, and CA3 and DG of hippocampus compared to wild-type mice. 7,8-Dihydroxyflavone, a TrkB agonist, showed antidepressant effects in Nrf2 KO mice, by stimulating BDNF-TrkB in the PFC, CA3, and DG. Pretreatment with sulforaphane, a naturally occurring Nrf2 activator, prevented depression-like phenotype in mice after inflammation, or chronic social defeat stress. Interestingly, dietary intake of 0.1% glucoraphanin (a precursor of sulforaphane) containing food during juvenile and adolescent stages of mice could prevent depression-like phenotype in adulthood after chronic social defeat stress. Moreover, the protein expressions of Keap1 and Nrf2 in the parietal cortex from major depressive disorder and bipolar disorder were lower than controls. These findings suggest that Keap1-Nrf2 system plays a key role in the stress resilience which is involved in the pathophysiology of mood disorders. It is, therefore, possible that dietary intake of cruciferous vegetables including glucoraphanin (or SFN) may prevent or minimize relapse from remission, induced by stress and/or inflammation in depressed patients. In the review, the author would like to discuss the role of Keap1-Nrf2 system in mood disorders.

C151 in KEAP1 is the main cysteine sensor for the cyanoenone class of NRF2 activators, irrespective of molecular size or shape

Numerous small molecules (termed inducers), many of which are electrophiles, upregulate cytoprotective responses and inhibit pro-inflammatory pathways by activating nuclear factor-erythroid 2 p45-related factor 2 (NRF2). Key to NRF2 activation is the ability to chemically modifying critical sensor cysteines in the main negative regulator of NRF2, Kelch-like ECH-associated protein 1 (KEAP1), of which C151, C273 and C288 are best characterized. This study aimed to establish the requirement for these cysteine sensor(s) for the biological activities of the most potent NRF2 activators known to date, the cyclic cyanoenones, some of which are in clinical trials. It was found that C151 in KEAP1 is the main cysteine sensor for this class of inducers, irrespective of molecular size or shape. Furthermore, in primary macrophage cells expressing C151S mutant KEAP1, at low concentrations, the tricyclic cyanoenone TBE-31 is inactive as an activator of NRF2 as well as an inhibitor of lipopolysaccharide-stimulated gene expression of the pro-inflammatory cytokines IL6 and IL1β. However, at high inducer concentrations, NRF2 activation proceeds in the absence of C151, albeit at a lower magnitude. Our findings highlight the intrinsic flexibility of KEAP1 and emphasize the critical importance of establishing the precise dose of NRF2 activators for maintaining on-target selectivity.

Pathogenic p62/SQSTM1 mutations impair energy metabolism through limitation of mitochondrial substrates

Abnormal mitochondrial function has been found in patients with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Mutations in the p62 gene (also known as SQSTM1) which encodes the p62 protein have been reported in both disorders supporting the idea of an ALS/FTD continuum. In this work the role of p62 in energy metabolism was studied in fibroblasts from FTD patients carrying two independent pathogenic mutations in the p62 gene, and in a p62-knock-down (p62 KD) human dopaminergic neuroblastoma cell line (SH-SY5Y). We found that p62 deficiency is associated with inhibited complex I mitochondrial respiration due to lack of NADH for the electron transport chain. This deficiency was also associated with increased levels of NADPH reflecting a higher activation of pentose phosphate pathway as this is accompanied with higher cytosolic reduced glutathione (GSH) levels. Complex I inhibition resulted in lower mitochondrial membrane potential and higher cytosolic ROS production. Pharmacological activation of transcription factor Nrf2 increased mitochondrial NADH levels and restored mitochondrial membrane potential in p62-deficient cells. Our results suggest that the phenotype is caused by a loss-of-function effect, because similar alterations were found both in the mutant fibroblasts and the p62 KD model. These findings highlight the implication of energy metabolism in pathophysiological events associated with p62 deficiency.

Aldo-keto reductases are biomarkers of NRF2 activity and are co-ordinately overexpressed in non-small cell lung cancer

BACKGROUND

Although the nuclear factor-erythroid 2-related factor 2 (NRF2) pathway is one of the most frequently dysregulated in cancer, it is not clear whether mutational status is a good predictor of NRF2 activity. Here we utilise four members of the aldo-keto reductase (AKR) superfamily as biomarkers to address this question.

METHODS

Twenty-three cell lines of diverse origin and NRF2-pathway mutational status were used to determine the relationship between AKR expression and NRF2 activity. AKR expression was evaluated in lung cancer biopsies and Cancer Genome Atlas (TCGA) and Oncomine data sets.

RESULTS

AKRs were expressed at a high basal level in cell lines carrying mutations in the NRF2 pathway. In non-mutant cell lines, co-ordinate induction of AKRs was consistently observed following activation of NRF2. Immunohistochemical analysis of lung tumour biopsies and interrogation of TCGA data revealed that AKRs are enriched in both squamous cell carcinomas (SCCs) and adenocarcinomas that contain somatic alterations in the NRF2 pathway but, in the case of SCC, AKRs were also enriched in most other tumours.

CONCLUSIONS

An AKR biomarker panel can be used to determine NRF2 status in tumours. Hyperactivation of the NRF2 pathway is far more prevalent in lung SCC than previously predicted by genomic analyses.

Antidepressant effects of TBE-31 and MCE-1, the novel Nrf2 activators, in an inflammation model of depression

The Nuclear factor (erythroid 2-derived)-like 2 (Nrf2) plays a key role in inflammation which is implicated in the pathophysiology of depression. The Nrf2 activators have antidepressant effects in animal models of depression. The present study was undertaken to examine whether TBE-31 [(±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octahydrophenanthrene-2,6-dicarbonitrile] and MCE-1 [(±)-3-ethynyl-3-methyl-6-oxocyclohexa-1,4-dienecarbonitrile], the novel Nrf2 activators, could show antidepressant effects in inflammation model of depression. We found that TBE-31 and MCE-1 significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration dependent manner. The Nrf2 siRNA, but not negative control of siRNA, significantly blocked the potentiating effects of TBE-31 and MCE-1 on neurite outgrowth in PC12 cells. Furthermore, oral administration of TBE-31 or MCE-1 significantly attenuated an increase in serum levels of tumor necrosis factor-α (TNF-α) after administration of lipopolysaccharide (LPS: 0.5mg/kg). In the tail-suspension test and forced swimming test, oral administration of TBE-31 or MCE-1 significantly attenuated an increase in the immobility time after LPS (0.5mg/kg) administration. These findings suggest that the novel Nrf2 activators such as TBE-31 and MCE-1 might be potential therapeutic drugs for inflammation-related depression.

The acetylenic tricyclic bis(cyano enone), TBE-31, targets microtubule dynamics and cell polarity in migrating cells

Cell migration is dependent on the microtubule network for structural support as well as for the proper delivery and positioning of polarity proteins at the leading edge of migrating cells. Identification of drugs that target cytoskeletal-dependent cell migration and protein transport in polarized migrating cells is important in understanding the cell biology of normal and tumor cells and can lead to new therapeutic targets in disease processes. Here, we show that the tricyclic compound TBE-31 directly binds to tubulin and interferes with microtubule dynamics, as assessed by end binding 1 (EB1) live cell imaging. Interestingly, this interference is independent of in vitro tubulin polymerization. Using immunofluorescence microscopy, we also observed that TBE-31 interferes with the polarity of migratory cells. The polarity proteins Rac1, IQGAP and Tiam1 were localized at the leading edge of DMSO-treated migrating cell, but were observed to be in multiple protrusions around the cell periphery of TBE-31-treated cells. Finally, we observed that TBE-31 inhibits the migration of Rat2 fibroblasts with an IC50 of 0.75 μM. Taken together, our results suggest that the inhibition of cell migration by TBE-31 may result from the improper maintenance of cell polarity of migrating cells.

New Monocyclic, Bicyclic, and Tricyclic Ethynylcyanodienones as Activators of the Keap1/Nrf2/ARE Pathway and Inhibitors of Inducible Nitric Oxide Synthase

A monocyclic compound 3 (3-ethynyl-3-methyl-6-oxocyclohexa-1,4-dienecarbonitrile) is a highly reactive Michael acceptor leading to reversible adducts with nucleophiles, which displays equal or greater potency than the pentacyclic triterpenoid CDDO in inflammation and carcinogenesis related assays. Recently, reversible covalent drugs, which bind with protein targets but not permanently, have been gaining attention because of their unique features. To explore such reversible covalent drugs, we have synthesized monocyclic, bicyclic, and tricyclic compounds containing 3 as an electrophilic fragment and evaluated them as activators of the Keap1/Nrf2/ARE pathway and inhibitors of iNOS. Notably, these compounds maintain the unique features of the chemical reactivity and biological potency of 3. Among them, a monocyclic compound 5 is the most potent in these assays while a tricyclic compound 14 displays a more robust and specific activation profile compared to 5. In conclusion, we demonstrate that 3 is a useful electrophilic fragment for exploring reversible covalent drugs.

Structure–activity relationship of terpenes with anti-inflammatory profile – a systematic review

Inflammation is a complex biological response that in spite of having available treatments, their side effects limit their usefulness. Because of this, natural products have been the subject of incessant studies, among which the class of terpenes stands out. They have been the source of study for the development of anti-inflammatory drugs, once their chemical diversity is well suited to provide skeleton for future anti-inflammatory drugs. This systematic review reports the studies present in the literature that evaluate the anti-inflammatory activity of terpenes suffering any change in their structures, assessing whether these changes also brought changes in their effects. The search terms anti-inflammatory agents, terpenes, and structure–activity relationship were used to retrieve English language articles in SCOPUS, PUBMED and EMBASE published between January 2002 and August 2013. Twenty-seven papers were found concerning the structural modification of terpenes with the evaluation of antiinflammatory activity. The data reviewed here suggest that modified terpenes are an interesting tool for the development of new anti-inflammatory drugs.

The acetylenic tricyclic bis(cyano enone), TBE-31 inhibits non-small cell lung cancer cell migration through direct binding with actin

The migratory and invasive potential of the epithelial-derived tumor cells depends on epithelial-to-mesenchymal transition (EMT) as well as the reorganization of the cell cytoskeleton. Here, we show that the tricyclic compound acetylenic tricyclic bis(cyano enone), TBE-31, directly binds to actin and inhibits linear and branched actin polymerization in vitro. Furthermore, we observed that TBE-31 inhibits stress fiber formation in fibroblasts as well as in non-small cell lung cancer cells during TGFβ-dependent EMT. Interestingly, TBE-31 does not interfere with TGFβ-dependent signaling or changes in E-cadherin and N-cadherin protein levels during EMT. Finally, we observed that TBE-31 inhibits fibroblast and non-small cell lung tumor cell migration with an IC50 of 1.0 and 2.5 μmol/L, respectively. Taken together, our results suggest that TBE-31 targets linear actin polymerization to alter cell morphology and inhibit cell migration.

Synthesis of a dicyano abietane, a key intermediate for the anti-inflammatory agent TBE-31

The synthesis of dicyano abietane 11, a potential precursor to the biologically active tricyclic bis-cyano enone 6 (TBE-31), was accomplished in eight steps from epoxide 13. The synthesis features a Lewis acid promoted stereoselective cyclization of epoxide 13 to generate the tricyclic ring system 12 in one step.

(±)-(4bS,8aR,10aS)-10a-Ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octa-hydro-phenanthrene-2,6-dicarbonitrile

The anti-inflammatory and cytoprotective tricyclic title compound, C(21)H(18)N(2)O(2), also known as TBE-31, crystallizes with two nearly superimposable mol-ecules in the asymmetric unit. In both mol-ecules, the three ring systems conform to an envelope-chair-planar arrangement. The central ring, in a cyclohexane chair conformation, contains an axial ethynyl group that bends slightly off from a nearby axial methyl group because of the 1,3-diaxial repulsion between the two groups. In the crystal, weak C-H⋯N and C-H⋯O inter-actions form chains along [001].

Highly potent activation of Nrf2 by topical tricyclic bis(cyano enone): implications for protection against UV radiation during thiopurine therapy

Chronic treatment with azathioprine, a highly effective anti-inflammatory and immunosuppressive agent, profoundly increases the risk for development of unusually aggressive cutaneous squamous cell carcinoma. Its ultimate metabolite, 6-thioguanine (6-TG) nucleotide, is incorporated in DNA of skin cells, and upon exposure to UVA radiation, causes oxidative stress, followed by damage of DNA and associated proteins. The acetylenic tricyclic bis(cyano enone) TBE-31 is a strong inhibitor of inflammation and a potent inducer of the Keap1/Nrf2/ARE pathway, which orchestrates the expression of a large network of cytoprotective genes. We now report that long-term (five days per week for four weeks) topical daily applications of small (200 nmol) quantities of TBE-31 cause a robust systemic induction of the Keap1/Nrf2/ARE pathway and decreases the 6-TG incorporation in DNA of skin, blood, and liver of azathioprine-treated mice, indicating extraordinary bioavailability and efficacy. In addition, TBE-31, at nanomolar concentrations, protects cells with 6-TG in their genomic DNA against oxidative stress caused by UVA radiation through induction of the Keap1/Nrf2/ARE pathway. At the same 6-TG DNA levels, Keap1-knockout cells, in which the pathway is constitutively upregulated, are highly resistant to UVA radiation-induced oxidative stress. The protective effects of both the Keap1-knockout genotype and TBE-31 are completely lost in the absence of transcription factor Nrf2. Our findings suggest that compounds of this kind are excellent candidates for mechanism-based chemoprotective agents against conditions in which oxidative stress and inflammation underlie disease pathogenesis. Moreover, their potential skin patch incorporation for transdermal delivery is an exciting possibility.

Tricyclic compounds containing nonenolizable cyano enones. A novel class of highly potent anti-inflammatory and cytoprotective agents

Forty-four novel tricycles containing nonenolizable cyano enones (TCEs) were designed and synthesized on the basis of a semisynthetic pentacyclic triterpenoid, bardoxolone methyl, which is currently being developed in phase II clinical trials for the treatment of severe chronic kidney disease in diabetic patients. Most of the TCEs having two different kinds of nonenolizable cyano enones in rings A and C are highly potent suppressors of induction of inducible nitric oxide synthase stimulated with interferon-γ and are highly potent inducers of the cytoprotective enzymes heme oxygenase-1 and NAD(P)H:quinone oxidoreductase-1. Among these compounds, (±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3,4b,7,8,8a,9,10,10a-octahydrophenanthrene-2,6-dicarbonitrile ((±)-31) is the most potent in these bioassays in our pool of drug candidates including semisynthetic triterpenoids and synthetic tricycles. These facts strongly suggest that an essential factor for potency is not a triterpenoid skeleton but the cyano enone functionality. Notably, TCE 31 reduces hepatic tumorigenesis induced with aflatoxin in rats. Further preclinical studies and detailed mechanism studies on 31 are in progress.

An exceptionally potent inducer of cytoprotective enzymes: elucidation of the structural features that determine inducer potency and reactivity with Keap1

The Keap1/Nrf2/ARE pathway controls a network of cytoprotective genes that defend against the damaging effects of oxidative and electrophilic stress, and inflammation. Induction of this pathway is a highly effective strategy in combating the risk of cancer and chronic degenerative diseases, including atherosclerosis and neurodegeneration. An acetylenic tricyclic bis(cyano enone) bearing two highly electrophilic Michael acceptors is an extremely potent inducer in cells and in vivo. We demonstrate spectroscopically that both cyano enone functions of the tricyclic molecule react with cysteine residues of Keap1 and activate transcription of cytoprotective genes. Novel monocyclic cyano enones, representing fragments of rings A and C of the tricyclic compound, reveal that the contribution to inducer potency of the ring C Michael acceptor is much greater than that of ring A, and that potency is further enhanced by spatial proximity of an acetylenic function. Critically, the simultaneous presence of two cyano enone functions in rings A and C within a rigid three-ring system results in exceptionally high inducer potency. Detailed understanding of the structural elements that contribute to the reactivity with the protein sensor Keap1 and to high potency of induction is essential for the development of specific and selective lead compounds as clinically relevant chemoprotective agents.

A novel acetylenic tricyclic bis-(cyano enone) potently induces phase 2 cytoprotective pathways and blocks liver carcinogenesis induced by aflatoxin

A novel acetylenic tricyclic bis-(cyano enone), TBE-31, is a lead compound in a series of tricyclic compounds with enone functionalities in rings A and C. Nanomolar concentrations of this potent multifunctional molecule suppress the induction of the inflammatory protein, inducible nitric oxide synthase, activate phase 2 cytoprotective enzymes in vitro and in vivo, block cell proliferation, and induce differentiation and apoptosis of leukemia cells. Oral administration of TBE-31 also significantly reduces formation of aflatoxin-DNA adducts and decreases size and number of aflatoxin-induced preneoplastic hepatic lesions in rats by >90%. Because of the two cyano enones in rings A and C, TBE-31 may directly interact with DTT and protein targets such as Keap1 that contain reactive cysteine residues. The above findings suggest that TBE-31 should also be tested for chemoprevention and chemotherapy in relevant models of cancer and against other chronic, degenerative diseases in which inflammation and oxidative stress contribute to disease pathogenesis.