Emerging Screening Approaches in the Development of Nrf2-Keap1 Protein-Protein Interaction Inhibitors

The emerging role of deubiquitylating enzyme USP21 as a potential therapeutic target in cancer

Although certain members of the Ubiquitin-specific peptidases (USPs) have been recognized as promising therapeutic targets for various diseases, research progress regarding USP21 has been relatively sluggish in its early stages. USP21 is a crucial member of the USPs subfamily, involved in diverse cellular processes such as apoptosis, DNA repair, and signal transduction. Research findings from the past decade demonstrate that USP21 mediates the deubiquitination of multiple well-known target proteins associated with critical cellular processes relevant to both disease and homeostasis, particularly in various cancers.This reviewcomprehensively summarizes the structure and biological functions of USP21 with an emphasis on its role in tumorigenesis, and elucidates the advances on the discovery of tens of small-molecule inhibitors targeting USP21, which suggests that targeting USP21 may represent a potential strategy for cancer therapy.

The Emerging Role of Ubiquitin-Specific Protease 36 (USP36) in Cancer and Beyond

The balance between ubiquitination and deubiquitination is instrumental in the regulation of protein stability and maintenance of cellular homeostasis. The deubiquitinating enzyme, ubiquitin-specific protease 36 (USP36), a member of the USP family, plays a crucial role in this dynamic equilibrium by hydrolyzing and removing ubiquitin chains from target proteins and facilitating their proteasome-dependent degradation. The multifaceted functions of USP36 have been implicated in various disease processes, including cancer, infections, and inflammation, via the modulation of numerous cellular events, including gene transcription regulation, cell cycle regulation, immune responses, signal transduction, tumor growth, and inflammatory processes. The objective of this review is to provide a comprehensive summary of the current state of research on the roles of USP36 in different pathological conditions. By synthesizing the findings from previous studies, we have aimed to increase our understanding of the mechanisms underlying these diseases and identify potential therapeutic targets for their treatment.

Phenothiazines: Nrf2 activation and antioxidant effects

Phenothiazines (PTZs) are an emerging group of molecules showing effectiveness toward redox signaling and reduction of oxidative injury to cells, via the activation on Kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2 (Nrf2). Although several electrophilic and indirect Nrf2 activators have been reported, the risk of "off-target" effect due to the complexity of their molecular mechanisms of action, has aroused research interest toward non-electrophilic and direct modulators of Nrf2 pathway, such as PTZs. This review represents the first overview on the roles of PTZs as non-electrophilic Nrf2 activator and free radical scavengers, as well as on their potential therapeutic effects in oxidative stress-mediated diseases. Here, we provide a collective and comprehensive information on the PTZs ability to scavenge free radicals and activate the Nrf2 signaling pathway, with the aim to broaden the knowledge of their therapeutic potentials and to stimulate innovative research ideas.

New Insights into Antioxidant Peptides: An Overview of Efficient Screening, Evaluation Models, Molecular Mechanisms, and Applications

Antioxidant peptides are currently a hotspot in food science, pharmaceuticals, and cosmetics. In different fields, the screening, activity evaluation, mechanisms, and applications of antioxidant peptides are the pivotal areas of research. Among these topics, the efficient screening of antioxidant peptides stands at the forefront of cutting-edge research. To this end, efficient screening with novel technologies has significantly accelerated the research process, gradually replacing the traditional approach. After the novel antioxidant peptides are screened and identified, a time-consuming activity evaluation is another indispensable procedure, especially in in vivo models. Cellular and rodent models have been widely used for activity evaluation, whilst non-rodent models provide an efficient solution, even with the potential for high-throughput screening. Meanwhile, further research of molecular mechanisms can elucidate the essence underlying the activity, which is related to several signaling pathways, including Keap1-Nrf2/ARE, mitochondria-dependent apoptosis, TGF-β/SMAD, AMPK/SIRT1/PGC-1α, PI3K/Akt/mTOR, and NF-κB. Last but not least, antioxidant peptides have broad applications in food manufacture, therapy, and the cosmetics industry, which requires a systematic review. This review introduces novel technologies for the efficient screening of antioxidant peptides, categorized with a new vision. A wide range of activity evaluation assays, encompassing cellular models, as well as rodent and non-rodent models, are provided in a comprehensive manner. In addition, recent advances in molecular mechanisms are analyzed with specific cases. Finally, the applications of antioxidant peptides in food production, therapy, and cosmetics are systematically reviewed.

Ameliorative inhibition of sirtuin 6 by imidazole derivative triggers oxidative stress-mediated apoptosis associated with Nrf2/Keap1 signaling in non-small cell lung cancer cell lines

Background: Redox homeostasis is the vital regulatory system with respect to antioxidative response and detoxification. The imbalance of redox homeostasis causes oxidative stress. Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2, also called Nfe2l2)/Kelchlike ECH-associated protein 1 (Keap1) signaling is the major regulator of redox homeostasis. Nrf2/Keap1 signaling is reported to be involved in cancer cell growth and survival. A high level of Nrf2 in cancers is associated with poor prognosis, resistance to therapeutics, and rapid proliferation, framing Nrf2 as an interesting target in cancer biology. Sirtuins (SIRT1-7) are class III histone deacetylases with NAD + dependent deacetylase activity that have a remarkable impact on antioxidant and redox signaling (ARS) linked with Nrf2 deacetylation thereby increasing its transcription by epigenetic modifications which has been identified as a crucial event in cancer progression under the influence of oxidative stress in various transformed cells. SIRT6 plays an important role in the cytoprotective effect of multiple diseases, including cancer. This study aimed to inhibit SIRT6 using an imidazole derivative, Ethyl 2-[5-(4-chlorophenyl)-2-methyl-1-H-Imidazole-4-yl] acetate, to assess its impact on Nrf2/Keap1 signaling in A549 and NCI-H460 cell lines. Method: Half maximal inhibitory concentration (IC50) of Ethyl 2-[5-(4-chlorophenyl)-2-methyl-1-H-Imidazole-4-yl] acetate was fixed by cell viability assay. The changes in the gene expression of important regulators involved in this study were examined using quantitative real-time PCR (qRT-PCR) and protein expression changes were confirmed by Western blotting. The changes in the antioxidant molecules are determined by biochemical assays. Further, morphological studies were performed to observe the generation of reactive oxygen species, mitochondrial damage, and apoptosis. Results: We inhibited SIRT6 using Ethyl 2-[5-(4-chlorophenyl)-2-methyl-1-H-Imidazole-4-yl] acetate and demonstrated that SIRT6 inhibition impacts the modulation of antioxidant and redox signaling. The level of antioxidant enzymes and percentage of reactive oxygen species scavenging activity were depleted. The morphological studies showed ROS generation, mitochondrial damage, nuclear damage, and apoptosis. The molecular examination of apoptotic factors confirmed apoptotic cell death. Further, molecular studies confirmed the changes in Nrf2 and Keap1 expression during SIRT6 inhibition. Conclusion: The overall study suggests that SIRT6 inhibition by imidazole derivative disrupts Nrf2/Keap1 signaling leading to oxidative stress and apoptosis induction.

Structural Characteristics and Antioxidant Mechanism of Donkey-Hide Gelatin Peptides by Molecular Dynamics Simulation

This study aimed to explore the structural characteristics and antioxidant mechanism of donkey-hide gelatin peptides. After hydrolysis and ultrafiltration treatment, five gelatin peptides with different molecular weights (MWs) were obtained. Amino acid analysis showed that gelatin peptides with different MWs contained a large number of amino acids, including G, P, E, N, A, and R, and differences were noted in the content of various amino acids. Fourier transform infrared spectroscopy and circular dichroism revealed that these gelatin peptides differed in terms of the peak strength of functional groups and number of secondary structures. Moreover, 26 pentapeptides/hexapeptides were identified. Among them, we investigated by molecular docking how PGPAP, which has the best antioxidant activity, may interact with the Keap1 protein. The results showed that the PGPAP-Keap1 complex had a stable conformation, and Arg415, Gly462, Phe478, and Tyr572 were the key residues involved in the binding of the peptide PGPAP to Keap1. Our results demonstrated that PGPAP could serve as a bioactive peptide with antioxidant activity.

Technologies of targeting histone deacetylase in drug discovery: Current progress and emerging prospects

Histone deacetylases (HDACs) catalyze the hydrolysis of acetyl-l-lysine side chains in histones and non-histones, which are key to epigenetic regulation in humans. Targeting HDACs has emerged as a promising strategy for treating various types of cancer, including myeloma and hematologic malignancies. At present, numerous small molecule inhibitors targeting HDACs are actively being investigated in clinical trials. Despite their potential efficacy in cancer treatment, HDAC inhibitors suffer from multi-directional selectivity and preclinical resistance issues. Hence, developing novel inhibitors based on cutting-edge medicinal chemistry techniques is essential to overcome these limitations and improve clinical outcomes. This manuscript presents an extensive overview of the properties and biological functions of HDACs in cancer, provides an overview of the current state of development and limitations of clinical HDAC inhibitors, and analyzes a range of innovative medicinal chemistry techniques that are applied. These techniques include selective inhibitors, dual-target inhibitors, proteolysis targeting chimeras, and protein-protein interaction inhibitors.

Lysine-specific demethylase 7A (KDM7A): A potential target for disease therapy

Histone demethylation is a kind of epigenetic modification mediated by a variety of enzymes and participates in regulating multiple physiological and pathological events. Lysine-specific demethylase 7A is a kind of α-ketoglutarate- and Fe(II)-dependent demethylase belonging to the PHF2/8 subfamily of the JmjC demethylases. KDM7A is mainly localized in the nucleus and contributes to transcriptional activation via removing mono- and di-methyl groups from the lysine residues 9 and 27 of Histone H3. Mounting studies support that KDM7A is not only necessary for normal embryonic, neural, and skeletal development, but also associated with cancer, inflammation, osteoporosis, and other diseases. Herein, the structure of KDM7A is described by comparing the similarities and differences of its amino acid sequences of KDM7A and other Histone demethylases; the functions of KDM7A in homeostasis and dyshomeostasis are summarized via documenting its content and related signaling; the currently known KDM7A-specific inhibitors and their structural relationship are listed based on their structure optimization and pharmacological activities; and the challenges and opportunities in exploring functions and developing targeted agents of KDM7A are also prospected via presenting encountered problems and potential solutions, which will provide an insight in functional exploration and drug discovery for KDM7A-related diseases.

In vitro and in silico perspectives on the activation of antioxidant responsive element by citrus-derived flavonoids

Introduction

Oxidative stress plays an essential role in the pathogenesis of chronic diseases. Disrupting the Keap1-Nrf2 pathway by binding Keap1 is identified as a potential strategy to prevent oxidative stress-related chronic diseases. Therefore, of special interest is the utilization of dietary antioxidations from citrus, including narirutin, naringenin, hesperetin, hesperidin, naringin, neohesperidin dihydrochalcone, neohesperidin, and nobiletin, has been exploited as a prospective way to treat or prevent several human pathologies as Keap1-Nrf2 inhibitors for modulation of antioxidant properties.

Methods

To probe into the structural foundation of the molecular identification of citrus-derived antioxidations, we calculated the antioxidant responsive element activation ability of citrus-derived flavonoids after binding with Keap1. Also, the quantum chemistry properties and binding mode were performed theoretically with frontier molecular orbitals, molecular electrostatic potential analysis, molecular docking, and absorption, distribution, metabolism, excretion (ADME) calculation.

Results and discussion

Experimental findings combining computational assays revealed that the tested citrus-derived flavonoids can be grouped into strong agonists and weak agonists. The citrus-derived antioxidations were well housed in the bound zone of Keap1 via stable hydrogen bonding and hydrophobic interaction. Eventually, three of eight antioxidations were identified after ADME and physicochemical evaluations. The citrus-derived flavonoids were identified as potential dietary antioxidants of the Keap1-Nrf2 interaction, and can be used to improve oxidative stress-related chronic diseases.

Hangover-Relieving Effect of Ginseng Berry Kombucha Fermented by Saccharomyces cerevisiae and Gluconobacter oxydans in Ethanol-Treated Cells and Mice Model

This study aimed to evaluate the hangover relieving effect of ginseng berry kombucha (GBK) fermented with Saccharomyces cerevisiae and Gluconobacter oxydans in in vitro and in vivo models. The antioxidant activity and oxidative stress inhibitory effect of GBK were evaluated in ethanol-treated human liver HepG2 cells. In addition, biochemical and behavioral analyses of ethanol treated male ICR mice were performed to confirm the anti-hangover effect of GBK. The radical scavenging activity of GBK was increased by fermentation, and the total ginsenoside content of GBK was 70.24 μg/mL. In HepG2 cells, in which oxidative stress was induced using ethanol, GBK significantly increased the expression of antioxidant enzymes by upregulating the Nrf2/Keap1 pathway. Moreover, GBK (15 and 30 mg/kg) significantly reduced blood ethanol and acetaldehyde concentrations in ethanol-treated mice. GBK significantly increased the levels of alcohol-metabolizing enzymes, including alcohol dehydrogenase and acetaldehyde dehydrogenase. The balance beam test and elevated plus maze test revealed that high-dose GBK significantly ameliorated ethanol-induced behavioral changes. Collectively, GBK exerted a protective effect against ethanol-induced liver damage by regulating the Nrf2/Keap1 pathway.

Structural basis of Nrf2 activation by flavonolignans from silymarin

Several properties of silymarin (SM) extract have been attributed to their three major flavonolignans (silybin, silychristin, and silydianin) and their 2,3-dehydro derivatives (2,3-dehydrosilybin, 2,3-dehydrosilychristin, and 2,3-dehydrosilydianin). Experimental findings have suggested that the antioxidative and protective activities of these compounds could be due to their ability to activate nuclear factor erythroid 2-related factor 2 (Nrf2). The mechanism by which SM compounds exert their effect has been suggested to be by disrupting the complex between Nrf2 and Kelch-like ECH-associated protein 1 (Keap1). However, information about the structural and energetic basis of the inhibitory mechanism of SM compounds on the Nrf2-Keap1 pathway is lacking. We evaluated the binding properties of SM compounds because experimental findings have pointed to them as potential activators of Nrf2. Our study combined docking and molecular dynamics (MD) simulations with the Poisson-Boltzmann and generalized Born and surface area (MMPBSA and MMGBSA) methods and quantum mechanics-molecular mechanics (QMMM) calculations to investigate Keap1-ligand interactions. Our results predicted that silybin_A and 2,3-dehydrosilybin bind to Keap1, forming interactions with the same pockets as those observed for the cocrystallized Keap1-Cpd16 complex but with more favorable binding free energies. These findings indicate that both natural compounds are potential activators of Nrf2.

NRF2 in dermo-cosmetic: From scientific knowledge to skin care products

The skin is the organ that is most susceptible to the impact of the exposome. Located at the interface with the external environment, it protects internal organs through the barrier function of the epidermis. It must adapt to the consequences of the harmful effects of solar radiation, the various chemical constituents of atmospheric pollution, and wounds associated with mechanical damage: oxidation, cytotoxicity, inflammation, and so forth. In this biological context, a capacity to adapt to the various stresses caused by the exposome is essential; otherwise, more or less serious conditions may develop accelerated aging, pigmentation disorders, atopy, psoriasis, and skin cancers. Nrf2-controlled pathways play a key role at this level. Nrf2 is a transcription factor that controls genes involved in oxidative stress protection and detoxification of chemicals. Its involvement in UV protection, reduction of inflammation in processes associated with healing, epidermal differentiation for barrier function, and hair regrowth, has been demonstrated. The modulation of Nrf2 in the skin may therefore constitute a skin protection or care strategy for certain dermatological stresses and disorders initiated or aggravated by the exposome. Nrf2 inducers can act through different modes of action. Keap1-dependent mechanisms include modification of the cysteine residues of Keap1 by (pro)electrophiles or prooxidants, and disruption of the Keap1-Nrf2 complex. Indirect mechanisms are suggested for numerous phytochemicals, acting on upstream pathways, or via hormesis. While developing novel and safe Nrf2 modulators for skin care may be challenging, new avenues can arise from natural compounds-based molecular modeling and emerging concepts such as epigenetic regulation.

KEAP1-NRF2 protein-protein interaction inhibitors: Design, pharmacological properties and therapeutic potential

The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is considered the master regulator of the phase II antioxidant response. It controls a plethora of cytoprotective genes related to oxidative stress, inflammation, and protein homeostasis, among other processes. Activation of these pathways has been described in numerous pathologies including cancer, cardiovascular, respiratory, renal, digestive, metabolic, autoimmune, and neurodegenerative diseases. Considering the increasing interest of discovering novel NRF2 activators due to its clinical application, initial efforts were devoted to the development of electrophilic drugs able to induce NRF2 nuclear accumulation by targeting its natural repressor protein Kelch-like ECH-associated protein 1 (KEAP1) through covalent modifications on cysteine residues. However, off-target effects of these drugs prompted the development of an innovative strategy, the search of KEAP1-NRF2 protein-protein interaction (PPI) inhibitors. These innovative activators are proposed to target NRF2 in a more selective way, leading to potentially improved drugs with the application for a variety of diseases that are currently under investigation. In this review, we summarize known KEAP1-NRF2 PPI inhibitors to date and the bases of their design highlighting the most important features of their respective interactions. We also discuss the preclinical pharmacological properties described for the most promising compounds.

Dehydroeburicoic Acid, a Dual Inhibitor against Oxidative Stress in Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a complicated disease which can lead to hepatocellular carcinoma; however, there is a lack of satisfactory therapeutics. Dehydroeburicoic acid (DEA) (1), a triterpenoid isolated from Antrodia cinnamomea, has been reported to act against ALD, but its mechanisms of action are still not clear. In this study, we report for the first time the use of DEA (1) as a dual inhibitor of the Keap1-Nrf2 protein-protein interaction (PPI) and GSK3β in an in vitro ALD cell model. DEA (1) engages Keap1 to disrupt the Keap1-Nrf2 PPI and inhibits GSK3β to restore Nrf2 activity in a Keap1-independent fashion. DEA (1) promotes Nrf2 nuclear translocation to activate downstream antioxidant genes. Importantly, DEA (1) restores the mitochondrial dysfunction induced by ethanol and generates antioxidant activity in the ALD cell model with minimal toxicity. We anticipate that DEA (1) could be a potential scaffold for the further development of clinical agents for treating ALD.

Use of Physiologically Based Kinetic Modeling-Based Reverse Dosimetry to Predict In Vivo Nrf2 Activation by EGCG and Its Colonic Metabolites in Humans

(-)-Epigallocatechin gallate (EGCG) is prone to microbial metabolism when reaching the colon. This study aimed to develop a human physiologically based kinetic (PBK) model for EGCG, with sub-models for its colonic metabolites gallic acid and pyrogallol. Results show that the developed PBK model could adequately predict in vivo time-dependent blood concentrations of EGCG after either the single or repeated oral administration of EGCG under both fasting and non-fasting conditions. The predicted in vivo blood C_max of EGCG indicates that the Nrf2 activation is limited, while concentrations of its metabolites in the intestinal tract may reach levels that are higher than that of EGCG and also high enough to activate Nrf2 gene transcription. Taken together, combining in vitro data with a human PBK model allowed the prediction of a dose-response curve for EGCG-induced Nrf2-mediated gene expression in humans and provided insights into the contribution of gut microbial metabolites to this effect.

Harnessing the Therapeutic Potential of the Nrf2/Bach1 Signaling Pathway in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative movement disorder characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Although a complex interplay of multiple environmental and genetic factors has been implicated, the etiology of neuronal death in PD remains unresolved. Various mechanisms of neuronal degeneration in PD have been proposed, including oxidative stress, mitochondrial dysfunction, neuroinflammation, α-synuclein proteostasis, disruption of calcium homeostasis, and other cell death pathways. While many drugs individually targeting these pathways have shown promise in preclinical PD models, this promise has not yet translated into neuroprotective therapies in human PD. This has consequently spurred efforts to identify alternative targets with multipronged therapeutic approaches. A promising therapeutic target that could modulate multiple etiological pathways involves drug-induced activation of a coordinated genetic program regulated by the transcription factor, nuclear factor E2-related factor 2 (Nrf2). Nrf2 regulates the transcription of over 250 genes, creating a multifaceted network that integrates cellular activities by expressing cytoprotective genes, promoting the resolution of inflammation, restoring redox and protein homeostasis, stimulating energy metabolism, and facilitating repair. However, FDA-approved electrophilic Nrf2 activators cause irreversible alkylation of cysteine residues in various cellular proteins resulting in side effects. We propose that the transcriptional repressor of BTB and CNC homology 1 (Bach1), which antagonizes Nrf2, could serve as a promising complementary target for the activation of both Nrf2-dependent and Nrf2-independent neuroprotective pathways. This review presents the current knowledge on the Nrf2/Bach1 signaling pathway, its role in various cellular processes, and the benefits of simultaneously inhibiting Bach1 and stabilizing Nrf2 using non-electrophilic small molecules as a novel therapeutic approach for PD.

Molecular docking analysis of melamine with nuclear factor erythroid 2-related factor 2 and succinate dehydrogenase

Melamine consumption causes oxidative stress by an unknown mechanism. Therefore, it is of interest to analyze the interaction of melamine with two important proteins involved in oxidative stress biology namely, nuclear factor erythroid 2-related factor 2 and succinate dehydrogenase. The molecular docking data shows the melamine binding with these two proteins at critical residues. These interactions can be logically perceived for the causation of melamine induced oxidative stress.

Nrf2 signaling activation by a small molecule activator compound 16 inhibits hydrogen peroxide-induced oxidative injury and death in osteoblasts

We explored the potential activity of compound 16 (Cpd16), a novel small molecule Nrf2 activator, in hydrogen peroxide (H₂O₂)-stimulated osteoblasts. In the primary murine/human osteoblasts and MC3T3-E1 murine osteoblastic cells, Cpd16 treatment at micro-molar concentrations caused disassociation of Keap1-Nrf2 and Nrf2 cascade activation. Cpd16 induced stabilization of Nrf2 protein and its nuclear translocation, thereby increasing the antioxidant response elements (ARE) reporter activity and Nrf2 response genes transcription in murine and human osteoblasts. Significantly, Cpd16 mitigated oxidative injury in H₂O₂-stimulited osteoblasts. H₂O₂-provoked apoptosis as well as programmed necrosis in osteoblasts were significantly alleviated by the novel Nrf2 activator. Cpd16-induced Nrf2 activation and osteoblasts protection were stronger than other known Nrf2 activators. Dexamethasone- and nicotine-caused oxidative stress and death in osteoblasts were attenuated by Cpd16 as well. Cpd16-induced osteoblast cytoprotection was abolished by Nrf2 short hairpin RNA or knockout, but was mimicked by Keap1 knockout. Keap1 Cys151S mutation abolished Cpd16-induced Nrf2 cascade activation and osteoblasts protection against H₂O₂. Importantly, weekly Cpd16 administration largely ameliorated trabecular bone loss in ovariectomy mice. Together, Cpd16 alleviates H₂O₂-induced oxidative stress and death in osteoblasts by activating Nrf2 cascade.

Oxidative Stress and Ginsenosides: An Update on the Molecular Mechanisms

Ginsenosides are a class of active components extracted from ginseng plants (such as Panax ginseng, Panax quinquefolium, and Panax notoginseng). Ginsenosides have significant protective effects on the nervous system, cardiovascular system, and immune system, so they have been widely used in the treatment of related diseases. Entry of a variety of endogenous or exogenous harmful substances into the body can lead to an imbalance between the antioxidant defense system and reactive oxygen species, thus producing toxic effects on a variety of tissues and cells. In addition, oxidative stress can alter multiple signaling pathways, including the Keap1/Nrf2/ARE, PI3K/AKT, Wnt/β-catenin, and NF-κB pathways. With the deepening of research in this field, various ginsenoside monomers have been reported to exert antioxidant effects through multiple signaling pathways and thus have good application prospects. This article summarized the research advancements regarding the antioxidative effects and related mechanisms of ginsenosides, providing a theoretical basis for experimental research on and clinical treatment with ginsenosides.

The Interplay between Autophagy and Redox Signaling in Cardiovascular Diseases

Reactive oxygen and nitrogen species produced at low levels under normal cellular metabolism act as important signal molecules. However, at increased production, they cause damage associated with oxidative stress, which can lead to the development of many diseases, such as cardiovascular, metabolic, neurodegenerative, diabetes, and cancer. The defense systems used to maintain normal redox homeostasis plays an important role in cellular responses to oxidative stress. The key players here are Nrf2-regulated redox signaling and autophagy. A tight interface has been described between these two processes under stress conditions and their role in oxidative stress-induced diseases progression. In this review, we focus on the role of Nrf2 as a key player in redox regulation in cell response to oxidative stress. We also summarize the current knowledge about the autophagy regulation and the role of redox signaling in this process. In line with the focus of our review, we describe in more detail information about the interplay between Nrf2 and autophagy pathways in myocardium and the role of these processes in cardiovascular disease development.

Novel Prenylated Indole Alkaloids with Neuroprotection on SH-SY5Y Cells against Oxidative Stress Targeting Keap1–Nrf2

Oxidative stress has been implicated in the etiology of Parkinson’s disease (PD). Molecules non-covalently binding to the Keap1–Nrf2 complex could be a promising therapeutic approach for PD. Herein, two novel prenylated indole alkaloids asperpenazine (1), and asperpendoline (2) with a scarce skeleton of pyrimido[1,6-a]indole were discovered from the co-cultivated fungi of Aspergillus ochraceus MCCC 3A00521 and Penicillium sp. HUBU 0120. Compound 2 exhibited potential neuroprotective activity on SH-SY5Y cells against oxidative stress. Molecular mechanism research demonstrated that 2 inhibited Keap1 expression, resulting in the translocation of Nrf2 from the cytoplasm to the nucleus, activating the downstream genes expression of HO-1 and NQO1, leading to the reduction in reactive oxygen species (ROS) and the augment of glutathione. Molecular docking and dynamic simulation analyses manifested that 2 interacted with Keap1 (PDB ID: 1X2R) via forming typical hydrogen and hydrophobic bonds with residues and presented less fluctuation of RMSD and RMSF during a natural physiological condition.

Targeting Nrf2/Keap1 signaling pathway by bioactive natural agents: Possible therapeutic strategy to combat liver disease

BACKGROUND

Nuclear factor erythroid 2-related factor (Nrf2), a stress-activated transcription factor, has been documented to induce a defense mechanism against oxidative stress damage, and growing evidence considers this signaling pathway a key pharmacological target for the treatment of liver diseases.

PURPOSE

The present review highlights the role of phytochemical compounds in activating Nrf2 and mitigate toxicant-induced stress on liver injury.

METHODS

A comprehensive search of published articles was carried out to focus on original publications related to Nrf2 activators against liver disease using various literature databases, including the scientific Databases of Science Direct, Web of Science, Pubmed, Google, EMBASE, and Scientific Information (SID).

RESULTS

Nrf2 activators exhibited promising effects in resisting a variety of liver diseases induced by different toxicants in preclinical experiments and in vitro studies by regulating cell proliferation and apoptosis as well as an antioxidant defense mechanism. We found that the phytochemical compounds, such as curcumin, naringenin, sulforaphane, diallyl disulfide, mangiferin, oleanolic acid, umbelliferone, daphnetin, quercetin, isorhamnetin-3-O-galactoside, hesperidin, diammonium glycyrrhizinate, corilagin, shikonin, farrerol, and chenpi, had the potential to improve the Nrf2-ARE signaling thereby combat hepatotoxicity.

CONCLUSION

Nrf2 activators may offer a novel potential strategy for the prevention and treatment of liver diseases. More extensive studies are essential to identify the underlying mechanisms and establish future therapeutic potentials of these signaling modulators. Further clinical trials are warranted to determine the safety and effectiveness of Nrf2 activators for hepatopathy.

MicroRNAs Involved in Oxidative Stress Processes Regulating Physiological and Pathological Responses

Oxidative stress influences several physiological and pathological cellular events, including cell differentiation, excessive growth, proliferation, apoptosis, and the inflammatory response. Therefore, oxidative stress is involved in the pathogenesis of various diseases, including pulmonary fibrosis, epilepsy, hypertension, atherosclerosis, Parkinson's disease, cardiovascular disease, and Alzheimer's disease. Recent studies have shown that several microRNAs (miRNAs) are involved in developing various diseases caused by oxidative stress and that miRNAs may be helpful to determine the inflammatory characteristics of immune responses during infection and disease. This review describes the known effects of miRNAs on reactive oxygen species to induce oxidative stress and the miRNA regulatory mechanisms involved in the uncoupling of Keap1-Nrf2 complexes. Finally, we summarized the functions of miRNAs in several antioxidant genes. Understanding the crosstalk between miRNAs and oxidative stress-inducing factors during physiological and pathological cellular events may have implications for designing more effective treatments for immune diseases.

Elevated O-GlcNAcylation Promotes Malignant Phenotypes of Hypopharyngeal Squamous Cell Carcinoma by Stabilizing Nrf2 through Regulation of the PI3K/Akt Pathway

BACKGROUND AND PURPOSE

O-GlcNAcylation is a significant protein posttranslational modification with O-linked β-N-acetylglucosamine (GlcNAc) for intracellular signaling. Elevated O-GlcNAcylation contributes to cell proliferation, cell migration, cell apoptosis and signal transduction in various cancers. However, the expression level and functional role of O-GlcNAcylation in Hypopharyngeal Squamous Cell Carcinoma (HSCC) is not clearly elucidated. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a master transcriptional factor that has been found to be aberrantly activated in HSCC. Here, we provide a molecular rationale between O-GlcNAcylation and Nrf2 in HSCC patients.

METHODS

The protein levels of O-GlcNAcylation and Nrf2 in HSCC tissues were detected by immunohistochemistry technique and western blot analysis. Then, O-GlcNAcylation knockdown HSCC cells were applied in this study. Cell proliferation was detected by CCK8, colony-forming analysis, and cell cycle assays. Cell migration and invasion ability was evaluated by transwell assays. Cell apoptosis was measured by TUNEL analysis.

RESULTS

O-GlcNAcylation was obviously up-regulated in HSCC tissues, which correlated with tumor size and lymph node metastasis. In addition, the protein level of Nrf2 was found to positively correlate with the expression of O-GlcNAcylation both in vivo and in vitro. Knockdown of O-GlcNAcylation significantly inhibited HSCC cell growth, suppressed cell migration, and promoted cell apoptosis, whereas overexpression of Nrf2 reversed these phenotypes. Mechanismly, the upregulation of O-GlcNAcylation promoted the phosphorylation of Akt, leading to the stabilization of Nrf2; this could be attenuated by inhibition of the PI3K/Akt signaling pathway.

CONCLUSION

Here, we provide a molecular association between O-GlcNAcylation and Nrf2 in HSCC patients, thus providing valuable therapeutic targets for the disease.

Targeting MCL-1 in cancer: current status and perspectives

Myeloid leukemia 1 (MCL-1) is an antiapoptotic protein of the BCL-2 family that prevents apoptosis by binding to the pro-apoptotic BCL-2 proteins. Overexpression of MCL-1 is frequently observed in many tumor types and is closely associated with tumorigenesis, poor prognosis and drug resistance. The central role of MCL-1 in regulating the mitochondrial apoptotic pathway makes it an attractive target for cancer therapy. Significant progress has been made with regard to MCL-1 inhibitors, some of which have entered clinical trials. Here, we discuss the mechanism by which MCL-1 regulates cancer cell apoptosis and review the progress related to MCL-1 small molecule inhibitors and their role in cancer therapy.

Identification of novel inhibitors of Keap1/Nrf2 by a promising method combining protein-protein interaction-oriented library and machine learning

Protein–protein interactions (PPIs) are prospective but challenging targets for drug discovery, because screening using traditional small-molecule libraries often fails to identify hits. Recently, we developed a PPI-oriented library comprising 12,593 small-to-medium-sized newly synthesized molecules. This study validates a promising combined method using PPI-oriented library and ligand-based virtual screening (LBVS) to discover novel PPI inhibitory compounds for Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2). We performed LBVS with two random forest models against our PPI library and the following time-resolved fluorescence resonance energy transfer (TR-FRET) assays of 620 compounds identified 15 specific hit compounds. The high hit rates for the entire PPI library (estimated 0.56–1.3%) and the LBVS (maximum 5.4%) compared to a conventional screening library showed the utility of the library and the efficiency of LBVS. All the hit compounds possessed novel structures with Tanimoto similarity ≤ 0.26 to known Keap1/Nrf2 inhibitors and aqueous solubility (AlogP < 5). Reasonable binding modes were predicted using 3D alignment of five hit compounds and a Keap1/Nrf2 peptide crystal structure. Our results represent a new, efficient method combining the PPI library and LBVS to identify novel PPI inhibitory ligands with expanded chemical space.

Transcriptional network constituted of CBP, Ku70, NOX2, and BAX prevents the cell death of necrosis, paraptosis, and apoptosis in human melanoma

CREB-binding protein (CBP) is an acetyltransferase known to play multiple roles in the transcriptions of genes involving oxidative metabolism, cell cycle, DNA damage checkpoints, and cell death. In this study, CBP was found to positively regulate the expression of Ku70, and both CBP and Ku70 were found to negatively regulate the expression of NOX2, therefore, mitigating the intracellular ROS in human melanoma. Knocking down CBP or Ku70 induced necrotic and paraptotic cell death as indicated by high-level intracellular ROS, cytoplasmic vacuolization, and cell cycle arrest in the S phase. In addition, chromosomal condensations were also observed in the cells proceeding necrotic and paraptotic cell death, which was found to be related to the BAX-associated intrinsic pathway of apoptotic cell death, when Ku70 was decreased either by CBP depletion or by Ku70 depletion directly. Our results, therefore, supported the idea that CBP, Ku70, BAX, and NOX2 have formed a transcriptional network in the prevention of cell death of necrosis, paraptosis, and apoptosis in human melanoma.

Targeting Bromodomain and Extraterminal Proteins for Drug Discovery: From Current Progress to Technological Development

Bromodomain and extraterminal (BET) proteins bind acetylated lysine residues in histones and nonhistone proteins via tandem bromodomains and regulate chromatin dynamics, cellular processes, and disease procession. Thus targeting BET proteins is a promising strategy for treating various diseases, especially malignant tumors and chronic inflammation. Many pan-BET small-molecule inhibitors have been described, and some of them are in clinical evaluation. Nevertheless, the limited clinical efficacy of the current BET inhibitors is also evident and has inspired the development of new technologies to improve their clinical outcomes and minimize unwanted side effects. In this Review, we summarize the latest protein characteristics and biological functions of BRD4 as an example of BET proteins, analyze the clinical development status and preclinical resistance mechanisms, and discuss recent advances in BRD4-selective inhibitors, dual-target BET inhibitors, proteolysis targeting chimera degraders, and protein-protein interaction inhibitors.

Endogenous Mechanisms of Neuroprotection: To Boost or Not to Boost

Postmitotic cells, like neurons, must live through a lifetime. For this reason, organisms/cells have evolved with self-repair mechanisms that allow them to have a long life. The discovery workflow of neuroprotectors during the last years has focused on blocking the pathophysiological mechanisms that lead to neuronal loss in neurodegeneration. Unfortunately, only a few strategies from these studies were able to slow down or prevent neurodegeneration. There is compelling evidence demonstrating that endorsing the self-healing mechanisms that organisms/cells endogenously have, commonly referred to as cellular resilience, can arm neurons and promote their self-healing. Although enhancing these mechanisms has not yet received sufficient attention, these pathways open up new therapeutic avenues to prevent neuronal death and ameliorate neurodegeneration. Here, we highlight the main endogenous mechanisms of protection and describe their role in promoting neuron survival during neurodegeneration.

Novel target for treating Alzheimer's Diseases: Crosstalk between the Nrf2 pathway and autophagy

In mammals, the Keap1-Nrf2-ARE pathway (henceforth, "the Nrf2 pathway") and autophagy are major intracellular defence systems that combat oxidative damage and maintain homeostasis. p62/SQSTM1, a ubiquitin-binding autophagy receptor protein, links the Nrf2 pathway and autophagy. Phosphorylation of p62 dramatically enhances its affinity for Keap1, which induces Keap1 to release Nrf2, and the p62-Keap1 heterodimer recruits LC3 and mediates the permanent degradation of Keap1 in the selective autophagy pathway. Eventually, Nrf2 accumulates in the cytoplasm and then translocates into the nucleus to activate the transcription of downstream genes that encode antioxidant enzymes, which protect cells from oxidative damage. Since Nrf2 also upregulates the expression of the p62 gene, a p62-Keap1-Nrf2 positive feedback loop is created that further enhances the protective effect on cells. Studies have shown that the p62-activated noncanonical Nrf2 pathway is an important marker of neurodegenerative diseases. The p62-Keap1-Nrf2 positive feedback loop and the Nrf2 pathway are involved in eliminating the ROS and protein aggregates induced by AD. Therefore, maintaining the homeostasis of the p62-Keap1-Nrf2 positive feedback loop, which is a bridge between the Nrf2 pathway and autophagy, may be a potential target for the treatment of AD.

Discovery of 2-oxy-2-phenylacetic acid substituted naphthalene sulfonamide derivatives as potent KEAP1-NRF2 protein-protein interaction inhibitors for inflammatory conditions

Nuclear factor erythroid 2-related factor 2 (NRF2) is a pleiotropic transcription factor which regulates the constitutive and inducible transcription of a wide array of genes and confers protection against a variety of pathologies. Directly disrupting Kelch-like ECH-associated protein 1 (KEAP1)-NRF2 protein-protein interaction (PPI) has been explored as a promising strategy to activate NRF2. We reported here the first identification of a series of 2-oxy-2-phenylacetic acid substituted naphthalene sulfonamide derivatives as potent KEAP1-NRF2 inhibitors. Our efforts led to the potent small molecule KEAP1-NRF2 inhibitor, 20c, which exhibited a K_d of 24 nM to KEAP1 and an IC₅₀ of 75 nM in disrupting KEAP1-NRF2 interaction. Subsequent biological studies provided consistent evidence across mouse macrophage cell-based and in vivo models that 20c induced NRF2 target gene expression and enhanced downstream antioxidant and anti-inflammatory activities. Our study not only demonstrated that small molecule KEAP1-NRF2 PPI inhibitors can be potential preventive and therapeutic agents for diseases and conditions involving oxidative stress and inflammation but also enriched the chemical diversity of the KEAP1-NRF2 inhibitors.

Penehyclidine hydrochloride inhibits renal ischemia/reperfusion-induced acute lung injury by activating the Nrf2 pathway

The nuclear factor (NF)-κB and NOD-like receptor protein 3 (NLRP3) pathways promote inflammatory signaling that injures the kidneys, whereas the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway promotes anti-inflammatory signaling that inhibits oxidative damage. Penehyclidine hydrochloride (PHC) inhibits NF-κB and activates Nrf2 signaling. We investigated whether PHC induces communication between the Nrf2 and NF-κB/NLRP3 pathways, thereby protecting against renal ischemia/reperfusion (rI/R)-induced lung inflammation. Rat alveolar macrophages (NR8383 cells) were stimulated for 24 h with PHC with or without brusatol (a Nrf2 antagonist), after which they were treated for 4 h with tert-butyl hydroperoxide (10 mM). PHC Nrf2-dependently alleviated tert-butyl hydroperoxide-induced reactive oxygen species production in alveolar macrophages. Additionally, wild-type and Nrf2^-/- rats were each divided into four groups: (1) sham, (2) PHC (1 mg/kg), (3) rI/R and (4) rI/R + PHC (1 mg/kg). PHC markedly induced the Nrf2 and adenosine monophosphate-activated protein kinase pathways and suppressed rI/R-induced NF-κB and NLRP3 activation in the lungs. Nrf2 deficiency diminished the ability of PHC to ameliorate rI/R-induced histopathological alterations and reactive oxygen species release in the lungs; however, PHC inhibited NLRP3 signaling Nrf2-dependently, while it inhibited NF-κB signaling Nrf2-independently. Our findings demonstrate the beneficial effects of PHC on rI/R-induced lung inflammation.

Recent progress in Keap1-Nrf2 protein-protein interaction inhibitors

Therapeutic targeting the protein-protein interaction (PPI) of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its main regulator, Kelch-like ECH-Associating protein 1 (Keap1) has been emerged as a feasible way to combat oxidative stress related diseases, due to the key role of Nrf2 in oxidative stress regulation. In recent years, many efforts have been made to develop potent Keap1-Nrf2 inhibitors with new chemical structures. Various molecules with diverse chemical structures have been reported and some compounds exhibit high potency. This review summarizes peptide and small molecule Keap1-Nrf2 inhibitors reported recently. We also highlight the pharmacological effects and discuss the possible therapeutic application of Keap1-Nrf2 inhibitors.

Flavolignans from Silymarin as Nrf2 Bioactivators and Their Therapeutic Applications

Silymarin (SM) is a mixture of flavolignans extracted from the seeds of species derived from Silybum marianum, commonly known as milk thistle or St. Mary'sthistle. These species have been widely used in the treatment of liver disorders in traditional medicine since ancient times. Several properties had been attributed to the major SM flavolignans components, identified as silybin, isosilybin, silychristin, isosilychristin, and silydianin. Previous research reported antioxidant and protective activities, which are probably related to the activation of the nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf2), known as a master regulator of the cytoprotector response. Nrf2 is a redox-sensitive nuclear transcription factor able to induce the downstream-associated genes. The disruption of Nrf2 signaling has been associated with different pathological conditions. Some identified phytochemicals from SM had shown to participate in the Nrf2 signaling pathway; in particular, they have been suggested as activators that disrupt interactions in the Keap1-Nrf2 system, but also as antioxidants or with additional actions regarding Nrf2 regulation. Thus, the study of these molecules makes them appear attractive as novel targets for the treatment or prevention of several diseases.

Recent progress in the development of small molecule Nrf2 activators: a patent review (2017-present)

Introduction: The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is the first line of defense against a plethora of environmental or endogenous deviations in redox metabolism, proteostasis, inflammation, etc. Therefore, pharmacological activation of Nrf2 is a potential therapeutic approach for several diseases related to oxidative stress and inflammation, such as cancer, cardiovascular, and neurodegenerative diseases.Areas covered: The authors first describe the biological function of Nrf2 and the molecular regulatory mechanism of Keap1-Nrf2-ARE ((Kelch-like ECH-Associating protein 1)-Nrf2-(antioxidant response element)). Then, they review recent progress of covalent activators and non-covalent Keap1-Nrf2 protein-protein interaction (PPI) inhibitors from patents and publications in 2017-present, consisting of new chemical molecules, structure optimization of reported activators and progress in preclinical or clinical trials.Expert opinion: Despite significant achievements in the development of Nrf2 activators, the selectivity is the primary consideration. Due to reacting with redox-sensitive cysteines in proteins except for Keap1, electrophilic activators often exhibit off-target effects. For Keap1-Nrf2 PPI inhibitors, how to enhance in vivo efficacy and/or penetrate blood-brain barrier (BBB) to reach central nervous system (CNS) is also challenging. Fragment-based drug discovery (FBDD), carboxylic acid bioisosteric replacement and prodrug approach might be used to circumvent this challenge. Moreover, the possibility of cancer risk caused by Nrf2 activation needs to be considered carefully.

Mimicking Strategy for Protein-Protein Interaction Inhibitor Discovery by Virtual Screening

As protein–protein interactions (PPIs) are highly involved in most cellular processes, the discovery of PPI inhibitors that mimic the structure of the natural protein partners is a promising strategy toward the discovery of PPI inhibitors. In this review, we discuss recent advances in the application of virtual screening for identifying mimics of protein partners. The classification and function of the mimicking protein partner inhibitor discovery by virtual screening are described. We anticipate that this review would be of interest to medicinal chemists and chemical biologists working in the field of protein–protein interaction inhibitors or probes.

Investigation of Molecular Details of Keap1-Nrf2 Inhibitors Using Molecular Dynamics and Umbrella Sampling Techniques

In this study, we investigate the atomistic details of Keap1-Nrf2 inhibitors by in-depth modeling techniques, including molecular dynamics (MD) simulations, and the path-based free energy method of umbrella sampling (US). The protein–protein interaction (PPI) of Keap1-Nrf2 is implicated in several neurodegenerative diseases like cancer, diabetes, and cardiomyopathy. A better understanding of the five sub-pocket binding sites for Nrf2 (ETGE and DLG motifs) inside the Kelch domain would expedite the inhibitor design process. We selected four protein–ligand complexes with distinct co-crystal ligands and binding occupancies inside the Nrf2 binding site. We performed 100 ns of MD simulation for each complex and analyzed the trajectories. From the results, it is evident that one ligand (1VV) has flipped inside the binding pocket, whereas the remaining three were stable. We found that Coulombic (Arg483, Arg415, Ser363, Ser508, and Ser602) and Lennard–Jones (Tyr525, Tyr334, and Tyr572) interactions played a significant role in complex stability. The obtained binding free energy values from US simulations were consistent with the potencies of simulated ligands. US simulation highlight the importance of basic and aromatic residues in the binding pocket. A detailed description of the dissociation process brings valuable insight into the interaction of the four selected protein–ligand complexes, which could help in the future to design more potent PPI inhibitors.