Molecular actions of ebselen--an antiinflammatory antioxidant

An Efficient One-Pot Synthesis of 2-Amino-1,3,4-Selenadiazoles

An efficient one-pot synthesis of 2-amino-1,3,4-selenadiazoles from isoselenocyanates, hydrazine hydrate and aromatic aldehydes has been developed. This approach provides a simple, mild and facile way to construct various derivatives in moderate to good yields (57–82%). A plausible mechanism is proposed for the formation of the target products.

Comprehensive modeling of the antioxidant mechanism of ebselen

Three possible catalytic cycles for ebselen have been comprehensively modeled by theoretical calculations using density functional theory (DFT) at a mixed basis set level; the 6-31G(d) basis set for hydrocarbon fragments and the 6-31[Formula: see text]G(d,p) basis set for other atoms. The 2[Formula: see text] cycle is the main pathway in the glutathione peroxidase (GPx) cycle (cycle A), and IM3[Formula: see text]TS3 is the rate controlling process. The 1[Formula: see text]1 cycle is the main pathway for the oxidation cycle (cycle B), and the rate controlling step is the [Formula: see text] step. Ebselen reacts with the selenol 3 to form the diselenide 9, and this is the rate controlling step for cycle C. The extremely high energy barrier for the IM9[Formula: see text]TS9 process indicates that cycle C is unlikely to occur in vivo. Although cycle B is favored based on the energy analysis, with a maximum energy barrier of only 26.68[Formula: see text]kcal/mol at the mixed basis set level, it is generally unlikely to have very high concentrations of peroxides present in vivo. The results indicate that in order to improve the antioxidant activity of ebselen, it would be necessary to suitably modify the molecular structure of ebselen to reduce the energy barrier of the IM3[Formula: see text]TS3 process.

Development of a Sensitive Bioluminogenic Probe for Imaging Highly Reactive Oxygen Species in Living Rats

A sensitive bioluminogenic probe for highly reactive oxygen species (hROS), SO3 H-APL, was developed based on the concept of dual control of bioluminescence emission by means of bioluminescent enzyme-induced electron transfer (BioLeT) and modulation of cell-membrane permeability. This probe enables non-invasive visualization of physiologically relevant amounts of hROS generated deep inside the body of living rats for the first time. It is expected to serve as a practical analytical tool for investigating a wide range of biological functions of hROS in vivo. The design concept should be applicable to other in vivo bioluminogenic probes.

Different dose-dependent effects of ebselen in sciatic nerve ischemia-reperfusion injury in rats

Ebselen is an organoselenium compound which has strong antioxidant and anti-inflammatory effects. We investigated the neuroprotective role of ebselen pretreatment in rats with experimental sciatic nerve ischemia-reperfusion (I/R) injury. Adult male Sprague Dawley rats were divided into four groups (N = 7 in each group). Before sciatic nerve I/R was induced, ebselen was injected intraperitoneally at doses of 15 and 30 mg/kg. After a 2 h ischemia and a 3 h reperfusion period, sciatic nerve tissues were excised. Tissue levels of malondialdehyde (MDA) and nitric oxide (NO), and activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) were measured. Sciatic nerve tissues were also examined histopathologically. The 15 mg/kg dose of ebselen reduced sciatic nerve damage and apoptosis (p<0.01), levels of MDA, NO, and inducible nitric oxide synthase (iNOS) positive cells (p<0.01, p<0.05, respectively), and increased SOD, GPx, and CAT activities (p<0.001, p<0.01, p<0.05, respectively) compared with the I/R group that did not receive ebselen. Conversely, the 30 mg/kg dose of ebselen increased sciatic nerve damage, apoptosis, iNOS positive cells (p<0.01, p<0.05, p<0.001) and MDA and NO levels (p<0.05, p<0.01) and decreased SOD, GPx, and CAT activities (p<0.05) compared with the sham group. The results of this study suggest that ebselen may cause different effects depending on the dose employed. Ebselen may be protective against sciatic nerve I/R injury via antioxidant and antiapoptotic activities at a 15 mg/kg dose, conversely higher doses may cause detrimental effects.

NOX2 As a Target for Drug Development: Indications, Possible Complications, and Progress

SIGNIFICANCE

NOX2 is important for host defense, and yet is implicated in a large number of diseases in which inflammation plays a role in pathogenesis. These include acute and chronic lung inflammatory diseases, stroke, traumatic brain injury, and neurodegenerative diseases, including Alzheimer's and Parkinson's Diseases.

RECENT ADVANCES

Recent drug development programs have targeted several NOX isoforms that are implicated in a variety of diseases. The focus has been primarily on NOX4 and NOX1 rather than on NOX2, due, in part, to concerns about possible immunosuppressive side effects. Nevertheless, NOX2 clearly contributes to the pathogenesis of many inflammatory diseases, and its inhibition is predicted to provide a novel therapeutic approach.

CRITICAL ISSUES

Possible side effects that might arise from targeting NOX2 are discussed, including the possibility that such inhibition will contribute to increased infections and/or autoimmune disorders. The state of the field with regard to existing NOX2 inhibitors and targeted development of novel inhibitors is also summarized.

FUTURE DIRECTIONS

NOX2 inhibitors show particular promise for the treatment of inflammatory diseases, both acute and chronic. Theoretical side effects include pro-inflammatory and autoimmune complications and should be considered in any therapeutic program, but in our opinion, available data do not indicate that they are sufficiently likely to eliminate NOX2 as a drug target, particularly when weighed against the seriousness of many NOX2-related indications. Model studies demonstrating efficacy with minimal side effects are needed to encourage future development of NOX2 inhibitors as therapeutic agents.

Repurposing Clinical Molecule Ebselen to Combat Drug Resistant Pathogens

Without a doubt, our current antimicrobials are losing the battle in the fight against newly-emerged multidrug-resistant pathogens. There is a pressing, unmet need for novel antimicrobials and novel approaches to develop them; however, it is becoming increasingly difficult and costly to develop new antimicrobials. One strategy to reduce the time and cost associated with antimicrobial innovation is drug repurposing, which is to find new applications outside the scope of the original medical indication of the drug. Ebselen, an organoselenium clinical molecule, possesses potent antimicrobial activity against clinical multidrug-resistant Gram-positive pathogens, including Staphylococcus, Streptococcus, and Enterococcus, but not against Gram-negative pathogens. Moreover, the activity of ebselen against Gram-positive pathogens exceeded those activities determined for vancomycin and linezolid, drugs of choice for treatment of Enterococcus and Staphylococcus infections. The minimum inhibitory concentrations of ebselen at which 90% of clinical isolates of Enterococcus and Staphylococcus were inhibited (MIC₉₀) were found to be 0.5 and 0.25 mg/L, respectively. Ebselen showed significant clearance of intracellular methicillin-resistant S. aureus (MRSA) in comparison to vancomycin and linezolid. We demonstrated that ebselen inhibits the bacterial translation process without affecting mitochondrial biogenesis. Additionally, ebselen was found to exhibit excellent activity in vivo in a Caenorhabditis elegans MRSA-infected whole animal model. Finally, ebselen showed synergistic activities with conventional antimicrobials against MRSA. Taken together, our results demonstrate that ebselen, with its potent antimicrobial activity and safety profiles, can be potentially used to treat multidrug resistant Gram-positive bacterial infections alone or in combination with other antibiotics and should be further clinically evaluated.

Repurposing ebselen for treatment of multidrug-resistant staphylococcal infections

Novel antimicrobials and new approaches to developing them are urgently needed. Repurposing already-approved drugs with well-characterized toxicology and pharmacology is a novel way to reduce the time, cost, and risk associated with antibiotic innovation. Ebselen, an organoselenium compound, is known to be clinically safe and has a well-known pharmacology profile. It has shown potent bactericidal activity against multidrug-resistant clinical isolates of staphylococcus aureus, including methicillin- and vancomycin-resistant S. aureus (MRSA and VRSA). We demonstrated that ebselen acts through inhibition of protein synthesis and subsequently inhibited toxin production in MRSA. Additionally, ebselen was remarkably active and significantly reduced established staphylococcal biofilms. The therapeutic efficacy of ebselen was evaluated in a mouse model of staphylococcal skin infections. Ebselen 1% and 2% significantly reduced the bacterial load and the levels of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1 beta (IL-1β), and monocyte chemo attractant protein-1 (MCP-1) in MRSA USA300 skin lesions. Furthermore, it acts synergistically with traditional antimicrobials. This study provides evidence that ebselen has great potential for topical treatment of MRSA skin infections and lays the foundation for further analysis and development of ebselen as a potential treatment for multidrug-resistant staphylococcal infections.

17β-Estradiol Stimulates Generation of Reactive Species Oxygen and Nitric Oxide in Ovarian Adenocarcinoma Cells (OVCAR 3)

BACKGROUND

Experimental and epidemiological evidence supports a role for steroid hormones in the pathogenesis of ovarian cancer. Among steroid hormones, 17β-estradiol (E2) has the most potent effect on proliferation, apoptosis and metastasis.

OBJECTIVES

In the present study, we investigated the effect of E2 on production of ROS and NO in ovarian cancer cells.

MATERIALS AND METHODS

Ovarian adenocarcinoma cell line (OVCAR-3) was cultured and treated with various concentrations of E2, antioxidants (N-acetyle cysteine and Ebselen) and ICI182780 as an estrogen receptor antagonist. MTT test was performed to evaluate cell viability. NO and ROS levels were measured by Griess and DCFH-DA methods, respectively.

RESULTS

ROS levels as well as NO levels were increased in OVCAR-3 cells treated with E2. The increase in ROS production was in parallel with increased cell viability which indicates that estrogen-induced ROS can participate in cancer progression. ICI182780 abolished E2-induced ROS production. Progesterone was also effective in reducing ROS and NO generation.

CONCLUSIONS

NO and ROS are important molecules in signaling networks in cell. These molecules can be used as therapeutic targets for prevention and treatment of ovary cancer and other estrogen-induced malignancies.

Ebselen by modulating oxidative stress improves hypoxia-induced macroglial Müller cell and vascular injury in the retina

Oxidative stress is an important contributor to glial and vascular cell damage in ischemic retinopathies. We hypothesized that ebselen via its ability to reduce reactive oxygen species (ROS) and augment nuclear factor-like 2 (Nrf2) anti-oxidants would attenuate hypoxia-induced damage to macroglial Müller cells and also lessen retinal vasculopathy. Primary cultures of rat Müller cells were exposed to normoxia (21% O2), hypoxia (0.5% O2) and ebselen (2.5 μM) for up to 72 h. Oxygen-induced retinopathy (OIR) was induced in C57BL/6J mice while control mice were housed in room air. Mice received vehicle (saline, 5% dimethyl sulfoxide) or ebselen (10 mg/kg) each day between postnatal days 6-18. In cultured Müller cells, flow cytometry for dihydroethidium revealed that ebselen reduced the hypoxia-induced increase in ROS levels, whilst increasing the expression of Nrf2-regulated anti-oxidant genes, heme oxygenase 1, glutathione peroxidase-1, NAD(P)H dehydrogenase quinone oxidoreductase 1 and glutamate-cysteine ligase. Moreover, in Müller cells, ebselen reduced the hypoxia-induced increase in protein levels of pro-angiogenic and pro-inflammatory factors including vascular endothelial growth factor, interleukin-6, monocyte chemoattractant-protein 1 and intercellular adhesion molecule-1, and the mRNA levels of glial fibrillary acidic protein (GFAP), a marker of Müller cell injury. Ebselen improved OIR by attenuating capillary vaso-obliteration and neovascularization and a concomitant reduction in Müller cell gliosis and GFAP. We conclude that ebselen protects against hypoxia-induced injury of retinal Müller cells and the microvasculature, which is linked to its ability to reduce oxidative stress, vascular damaging factors and inflammation. Agents such as ebselen may be potential treatments for retinopathies that feature oxidative stress-mediated damage to glia and the microvasculature.

Crystal structure of 1-bromo-2-(phenyl-selen-yl)benzene

In the title compound, C12H9BrSe, the Se atom exhibits a bent geometry, with a C-Se-C bond angle of 99.19 (6)°. The ortho Se and Br atoms are slightly displaced from opposite faces of the mean plane of the benzene ring [by 0.129 (2) and 0.052 (2) Å, respectively]. The planes of the benzene and phenyl rings form a dihedral angle of 72.69 (5)°. In the crystal, π-stacking inter-actions between inversion-related phenyl rings are observed, with a centroid-centroid distance of 3.630 (1) Å.

Antinociceptive and anti-hyperalgesic effects of bis(4-methylbenzoyl) diselenide in mice: evidence for the mechanism of action

CONTEXT

The organoselenium compounds have been described to demonstrate several biological activities, including pain management.

OBJECTIVE

This study investigated the antinociceptive, hyperalgesic, and toxic effects of oral administration of bis(4-methylbenzoyl) diselenide (BMD) in mice.

MATERIALS AND METHODS

The antinociceptive and anti-hyperalgesic effects of BMD (1, 5, 10, 25, and 50 mg/kg, p.o.) were evaluated using models of nociception: formalin, capsaicin, bradykinin (BK), cinnamaldehyde, phorbol myristate acetate (PMA), 8-bromo-cAM, and glutamate-induced nociception; and mechanical hyperalgesia induced by carrageenan (Cg) or complete Freund's adjuvant (CFA). The acute toxicity was evaluated by biochemical markers for hepatic and renal damages.

RESULTS

BMD significantly inhibited the licking time of the injected paw in the early and late phases of a formalin test with ED50 values of 14.2 and 10.8 mg/kg, respectively. This compound reduced nociception produced by capsaicin (ED50 of 32.5 mg/kg), BK (ED50 of 24.6 mg/kg), glutamate (ED50 of 28.7 mg/kg), cinnamaldehyde (ED50 of 18.9 mg/kg), PMA (ED50 of 9.6 mg/kg), and 8-bromo-cAMP (ED50 of 24.8 mg/kg). In the glutamate test, the pretreatment with nitric oxide (NO) precursor, L-arginine, reversed antinociception caused by BMD or N(ω)-nitro-L-arginine (L-NOARG), but the effect of BMD was not abolished by naloxone. Mechanical hyperalgesia induced by Cg and CFA was attenuated by BMD, 70 ± 4% and 65 ± 4%, respectively. Furthermore, a single oral dose of BMD did not change plasma aspartate (AST) and alanine aminotransferase (ALT) activities or urea and creatinine levels.

CONCLUSION

BMD demonstrated as a promising compound because of the antinociceptive and anti-hyperalgesic properties in mice.

Ebselen as a potent covalent inhibitor of New Delhi metallo-β-lactamase (NDM-1)

We identified a potent NDM-1 inhibitor that formed a S–Se bond with the Cys²²¹ residue at the active site, thereby exhibiting a new inhibition mechanism with broad spectrum inhibitory potential.

Biological activity of selenorganic compounds at heavy metal salts intoxication

Possible mechanisms of the antitoxic action of organoselenium compounds in heavy metal poisoning have been considered. Heavy metal toxicity associated with intensification of free radical oxidation, suppression of the antioxidant system, damage to macromolecules, mitochondria and the genetic material can cause apoptotic cell death or the development of carcinogenesis. Organic selenium compounds are effective antioxidants during heavy metal poisoning; they exhibit higher bioavailability in mammals than inorganic ones and they are able to activate antioxidant defense, bind heavy metal ions and reactive oxygen species formed during metal-induced oxidative stress. One of promising organoselenium compounds is diacetophenonyl selenide (DAPS-25), which is characterized by antioxidant and antitoxic activity, under conditions including heavy metal intoxication

Ebselen inhibits hepatitis C virus NS3 helicase binding to nucleic acid and prevents viral replication

The hepatitis C virus (HCV) nonstructural protein 3 (NS3) is both a protease, which cleaves viral and host proteins, and a helicase that separates nucleic acid strands, using ATP hydrolysis to fuel the reaction. Many antiviral drugs, and compounds in clinical trials, target the NS3 protease, but few helicase inhibitors that function as antivirals have been reported. This study focuses on the analysis of the mechanism by which ebselen (2-phenyl-1,2-benzisoselenazol-3-one), a compound previously shown to be a HCV antiviral agent, inhibits the NS3 helicase. Ebselen inhibited the abilities of NS3 to unwind nucleic acids, to bind nucleic acids, and to hydrolyze ATP, and about 1 μM ebselen was sufficient to inhibit each of these activities by 50%. However, ebselen had no effect on the activity of the NS3 protease, even at 100 times higher ebselen concentrations. At concentrations below 10 μM, the ability of ebselen to inhibit HCV helicase was reversible, but prolonged incubation of HCV helicase with higher ebselen concentrations led to irreversible inhibition and the formation of covalent adducts between ebselen and all 14 cysteines present in HCV helicase. Ebselen analogues with sulfur replacing the selenium were just as potent HCV helicase inhibitors as ebselen, but the length of the linker between the phenyl and benzisoselenazol rings was critical. Modifications of the phenyl ring also affected compound potency over 30-fold, and ebselen was a far more potent helicase inhibitor than other, structurally unrelated, thiol-modifying agents. Ebselen analogues were also more effective antiviral agents, and they were less toxic to hepatocytes than ebselen. Although the above structure-activity relationship studies suggest that ebselen targets a specific site on NS3, we were unable to confirm binding to either the NS3 ATP binding site or nucleic acid binding cleft by examining the effects of ebselen on NS3 proteins lacking key cysteines.

A mitochondrial switch promotes tumor metastasis

Metastatic progression of cancer is associated with poor outcome, and here we examine metabolic changes underlying this process. Although aerobic glycolysis is known to promote metastasis, we have now identified a different switch primarily affecting mitochondria. The switch involves overload of the electron transport chain (ETC) with preserved mitochondrial functions but increased mitochondrial superoxide production. It provides a metastatic advantage phenocopied by partial ETC inhibition, another situation associated with enhanced superoxide production. Both cases involved protein tyrosine kinases Src and Pyk2 as downstream effectors. Thus, two different events, ETC overload and partial ETC inhibition, promote superoxide-dependent tumor cell migration, invasion, clonogenicity, and metastasis. Consequently, specific scavenging of mitochondrial superoxide with mitoTEMPO blocked tumor cell migration and prevented spontaneous tumor metastasis in murine and human tumor models.

Advances and strategies in NADPH oxidase inhibitors and activators patents

The NADPH oxidase (NOX) enzymes were identified as a family of seven isoforms contributing to the production of reactive oxygen species. During the past 15 years, this class of enzymes has increasingly gained interest from the academic and pharmaceutical laboratories. Extensive research efforts focused on the decryption of their mechanism of action has shown that Nox enzymes are the most important source of reactive oxygen species and key contributors in the pathogenesis of several diseases. Recent publications and patents suggest that NOX modulators may provide major opportunities in many diseases as novel therapeutics. This review covers application patents and current state-of-the-art on Nox modulators from 2005 to December 2013 and examines the different approaches patented to modulate the activity of Nox enzymes.

H2O2 generation by bacillus Calmette-Guérin induces the cellular oxidative stress response required for bacillus Calmette-Guérin direct effects on urothelial carcinoma biology

PURPOSE

Exposure of urothelial carcinoma cells to bacillus Calmette-Guérin affects cellular redox status and tumor cell biology but the mechanism(s) remain unclear. We examined free radical production by bacillus Calmette-Guérin in tumor cells in response to the bacillus using global profiling of reactive oxygen species/reactive nitrogen species. The relationship between free radical generation and downstream cellular events was evaluated.

MATERIALS AND METHODS

Using fluorescent probes we performed global profiling of reactive oxygen species/reactive nitrogen species in heat killed and viable bacillus Calmette-Guérin, and in the 253J and T24 urothelial carcinoma cell lines after exposure to the bacillus. Inhibition of bacillus Calmette-Guérin internalization and H2O2 pharmacological scavenging were studied for their effect on cellular reactive oxygen species/reactive nitrogen species generation and various physiological end points.

RESULTS

Viable bacillus Calmette-Guérin produced H2O2 and O2(-) but nitric oxide was not generated. Loss of viability decreased H2O2 production by 50% compared to viable bacillus. Bacillus Calmette-Guérin internalization was necessary for the bacillus to induce reactive oxygen species/reactive nitrogen species generation in urothelial carcinoma cells. Pharmacological H2O2 scavenging reversed reactive oxygen species/reactive nitrogen species mediated signaling in urothelial carcinoma cells. Bacillus Calmette-Guérin dependent alterations in tumor biology, including intracellular signaling, gene expression and cytotoxicity, depended on free radical generation.

CONCLUSIONS

This study demonstrates the importance of free radical generation by bacillus Calmette-Guérin and intracellular generation of cellular oxidative stress on the urothelial carcinoma cell response to the bacillus. Manipulating the cellular oxidative stress induced by bacillus Calmette-Guérin represents a potential target to increase the efficacy of the bacillus.

Ebselen and congeners inhibit NADPH oxidase 2-dependent superoxide generation by interrupting the binding of regulatory subunits

NADPH oxidases (Nox) are a primary source of reactive oxygen species (ROS), which function in normal physiology and, when overproduced, in pathophysiology. Recent studies using mice deficient in Nox2 identify this isoform as a novel target against Nox2-implicated inflammatory diseases. Nox2 activation depends on the binding of the proline-rich domain of its heterodimeric partner p22phox to p47phox. A high-throughput screen that monitored this interaction via fluorescence polarization identified ebselen and several of its analogs as inhibitors. Medicinal chemistry was performed to explore structure-activity relationships and to optimize potency. Ebselen and analogs potently inhibited Nox1 and Nox2 activity but were less effective against other isoforms. Ebselen also blocked translocation of p47phox to neutrophil membranes. Thus, ebselen and its analogs represent a class of compounds that inhibit ROS generation by interrupting the assembly of Nox2-activating regulatory subunits.

Thiol peroxidases ameliorate LRRK2 mutant-induced mitochondrial and dopaminergic neuronal degeneration in Drosophila

Mutations in leucine-rich repeat kinase 2 (LRRK2) are common causes of familial Parkinson's disease (PD). LRRK2 has been shown to bind peroxiredoxin-3 (PRDX3), the most important scavenger of hydrogen peroxide in the mitochondria, in vitro. Here, we examined the interactions of LRRK2 and PRDX3 in Drosophila models by crossing transgenic LRRK2 and PRDX3 flies. As proof of principle experiments, we subsequently challenged LRRK2 and LRRK2/PRDX3 flies with a peroxidase mimic, Ebselen. We demonstrated that co-expression of PRDX3 with the LRRK2 kinase mutant G2019S in bigenic Drosophila ameliorated the G2019S mutant-induced reduction in peroxidase capacity, loss of dopaminergic neurons, shortened lifespan and mitochondrial defects of flight muscles in monogenic flies expressing the G2019S alone. Challenges with Ebselen recapitulated similar rescue of these phenotypic features in mutant-expressing Drosophila. The peroxidase mimic preserved neuronal and mitochondrial and neuronal integrity and improved mobility and survival in mutant-expressing Drosophila. Taken together, our study provides the first in vivo evidence to suggest that phosphoinhibition of endogenous peroxidases could be a mechanism in LRRK2-induced oxidant-mediated neurotoxicity. Our therapeutic experiments also highlight the potential of thiol peroxidases as neuroprotective agents in PD patients carrying LRRK2 mutations.

High-throughput screening using the differential radial capillary action of ligand assay identifies ebselen as an inhibitor of diguanylate cyclases

The rise of bacterial resistance to traditional antibiotics has motivated recent efforts to identify new drug candidates that target virulence factors or their regulatory pathways. One such antivirulence target is the cyclic-di-GMP (cdiGMP) signaling pathway, which regulates biofilm formation, motility, and pathogenesis. Pseudomonas aeruginosa is an important opportunistic pathogen that utilizes cdiGMP-regulated polysaccharides, including alginate and pellicle polysaccharide (PEL), to mediate virulence and antibiotic resistance. CdiGMP activates PEL and alginate biosynthesis by binding to specific receptors including PelD and Alg44. Mutations that abrogate cdiGMP binding to these receptors prevent polysaccharide production. Identification of small molecules that can inhibit cdiGMP binding to the allosteric sites on these proteins could mimic binding defective mutants and potentially reduce biofilm formation or alginate secretion. Here, we report the development of a rapid and quantitative high-throughput screen for inhibitors of protein-cdiGMP interactions based on the differential radial capillary action of ligand assay (DRaCALA). Using this approach, we identified ebselen as an inhibitor of cdiGMP binding to receptors containing an RxxD domain including PelD and diguanylate cyclases (DGC). Ebselen reduces diguanylate cyclase activity by covalently modifying cysteine residues. Ebselen oxide, the selenone analogue of ebselen, also inhibits cdiGMP binding through the same covalent mechanism. Ebselen and ebselen oxide inhibit cdiGMP regulation of biofilm formation and flagella-mediated motility in P. aeruginosa through inhibition of diguanylate cyclases. The identification of ebselen provides a proof-of-principle that a DRaCALA high-throughput screening approach can be used to identify bioactive agents that reverse regulation of cdiGMP signaling by targeting cdiGMP-binding domains.

Ebselen induces reactive oxygen species (ROS)-mediated cytotoxicity in Saccharomyces cerevisiae with inhibition of glutamate dehydrogenase being a target

Ebselen is a synthetic, lipid-soluble seleno-organic compound. The high electrophilicity of ebselen enables it to react with multiple cysteine residues of various proteins. Despite extensive research on ebselen, its target molecules and mechanism of action remains less understood. We performed biochemical as well as in vivo experiments employing budding yeast as a model organism to understand the mode of action of ebselen. The growth curve analysis and FACS (florescence activated cell sorting) assays revealed that ebselen exerts growth inhibitory effects on yeast cells by causing a delay in cell cycle progression. We observed that ebselen exposure causes an increase in intracellular ROS levels and mitochondrial membrane potential, and that these effects were reversed by addition of antioxidants such as reduced glutathione (GSH) or N-acetyl-l-cysteine (NAC). Interestingly, a significant increase in ROS levels was noticed in gdh3-deleted cells compared to wild-type cells. Furthermore, we showed that ebselen inhibits GDH function by interacting with its cysteine residues, leading to the formation of inactive hexameric GDH. Two-dimensional gel electrophoresis revealed protein targets of ebselen including CPR1, the yeast homolog of Cyclophilin A. Additionally, ebselen treatment leads to the inhibition of yeast sporulation. These results indicate a novel direct connection between ebselen and redox homeostasis.

Organochalcogen peroxidase mimetics as potential drugs: a long story of a promise still unfulfilled

Organochalcogen compounds have attracted the interest of a multitude of studies to design potential therapeutic agents mimicking the peroxidase activity of selenium-based glutathione peroxidases (GPx's). Starting from the pioneering ebselen, various compounds have been synthesized over the years, which may be traced in three major classes of molecules: cyclic selenenyl amides, diaryl diselenides, and aromatic or aliphatic monoselenides. These compounds share common features and determinants needed to exert an efficient GPx-like activity, such as polarizing groups in close proximity to selenium and steric effects. Nonetheless, the reactivity of selenium, and tellurium as well, poses serious problems for the predictability of the biological effects of these compounds in vivo when used as potential drugs. These molecules, indeed, interfere with thiols of redox-regulated proteins and enzymes, leading to unexpected biological effects. The various chemical aspects of the reaction mechanism of peroxidase mimetics are surveyed here, focusing on experimental evidence and quantum mechanics calculations of organochalcogen representatives of the various classes.

12/15-lipoxygenase contributes to platelet-derived growth factor-induced activation of signal transducer and activator of transcription 3

We showed previously that the small molecule indirubin-3′-monoxime (I3MO) prevents vascular smooth muscle cell (VSMC) proliferation by selectively inhibiting signal transducer and activator of transcription 3 (STAT3). Looking for the underlying upstream molecular mechanism, we here reveal the important role of reactive oxygen species (ROS) for PDGF-induced STAT3 activation in VSMC. We show that neither NADPH-dependent oxidases (Noxes) nor mitochondria, but rather 12/15-lipoxygenase (12/15-LO) are pivotal ROS sources involved in the redox-regulated signal transduction from PDGFR to STAT3. Accordingly, pharmacological and genetic interference with 12/15-LO activity selectively inhibited PDGF-induced Src activation and STAT3 phosphorylation. I3MO is able to blunt PDGF-induced ROS and 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) production, indicating an inhibitory action of I3MO on 12/15-LO and consequently on STAT3. We identify 12/15-LO as a hitherto unrecognized signaling hub in PDGF-triggered STAT3 activation and show for the first time a negative impact of I3MO on 12/15-LO.

Glucose deprivation increases monocarboxylate transporter 1 (MCT1) expression and MCT1-dependent tumor cell migration

The glycolytic end-product lactate is a pleiotropic tumor growth-promoting factor. Its activities primarily depend on its uptake, a process facilitated by the lactate-proton symporter monocarboxylate transporter 1 (MCT1). Therefore, targeting the transporter or its chaperon protein CD147/basigin, itself involved in the aggressive malignant phenotype, is an attractive therapeutic option for cancer, but basic information is still lacking regarding the regulation of the expression, interaction and activities of both proteins. In this study, we found that glucose deprivation dose-dependently upregulates MCT1 and CD147 protein expression and their interaction in oxidative tumor cells. While this posttranslational induction could be recapitulated using glycolysis inhibition, hypoxia, oxidative phosphorylation (OXPHOS) inhibitor rotenone or hydrogen peroxide, it was blocked with alternative oxidative substrates and specific antioxidants, pointing out at a mitochondrial control. Indeed, we found that the stabilization of MCT1 and CD147 proteins upon glucose removal depends on mitochondrial impairment and the associated generation of reactive oxygen species. When glucose was a limited resource (a situation occurring naturally or during the treatment of many tumors), MCT1-CD147 heterocomplexes accumulated, including in cell protrusions of the plasma membrane. It endowed oxidative tumor cells with increased migratory capacities towards glucose. Migration increased in cells overexpressing MCT1 and CD147, but it was inhibited in glucose-starved cells provided with an alternative oxidative fuel, treated with an antioxidant, lacking MCT1 expression, or submitted to pharmacological MCT1 inhibition. While our study identifies the mitochondrion as a glucose sensor promoting tumor cell migration, MCT1 is also revealed as a transducer of this response, providing a new rationale for the use of MCT1 inhibitors in cancer.

Exploring the mode of action of ebselen in Trypanosoma brucei hexokinase inhibition

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Trypanosoma brucei hexokinase 1 is irreversibly inhibited by ebselen.

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Mutation of Cys residues did not change hexamer abundance.

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Active variants bearing Cys mutations were inhibited by ebselen.

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ESI–MS/MS indicated that the essential Cys327 was oxidized by ebselen.

Glycolysis is essential to Trypanosoma brucei, the causative agent of African sleeping sickness, suggesting enzymes in the pathway could be targets for drug development. Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one, EbSe) was identified in a screen as a potent inhibitor of T. brucei hexokinase 1 (TbHK1), the first enzyme in the pathway. EbSe has a history of promiscuity as an enzyme inhibitor, inactivating proteins through seleno-sulfide conjugation with Cys residues. Indeed, dilution of TbHK1 and inhibitor following incubation did not temper inhibition suggesting conjugate formation. Using mass spectrometry to analyze EbSe-based modifications revealed that two Cys residues (C327 and C369) were oxidized after treatment. Site-directed mutagenesis of C327 led to enzyme inactivation indicating that C327 was essential for catalysis. C369 was not essential, suggesting that EbSe inhibition of TbHK1 was the consequence of modification of C327 via thiol oxidation. Additionally, neither EbSe treatment nor mutation of the nine TbHK1 Cys residues appreciably altered enzyme quaternary structure.

In vitro glutathione peroxidase mimicry of ebselen is linked to its oxidation of critical thiols on key cerebral suphydryl proteins - A novel component of its GPx-mimic antioxidant mechanism emerging from its thiol-modulated toxicology and pharmacology

The antioxidant mechanism of ebselen in rats brain is largely linked with its glutathione peroxidase (GPx) rather than its peroxiredoxin mimicry ability. However, the precise molecular dynamics between the GPx-mimicry of ebselen and thiol utilization is yet to be fully clarified and thus still open. Herein, we investigated the influence of dithiothreitol (DTT) on the antioxidant action of ebselen against oxidant-induced cerebral lipid peroxidation and deoxyribose degradation. Furthermore, the critical inhibitory concentrations of ebselen on the activities of sulphydryl enzymes such as cerebral sodium pump, δ-aminolevulinic acid dehydratase (δ-ALAD) and lactate dehydrogenase (LDH) were also investigated. We observe that ebselen (at ≥42 μM) markedly inhibited lipid peroxidation in the presence and absence of DTT, whereas it inhibited deoxyribose degradation only in the presence of DTT. Furthermore, under in vitro conditions, ebselen inhibited the thiol containing enzymes; cerebral sodium pump (at ≥40 μM), δ-ALAD (≥10 μM) and LDH (≥1 μM) which were either prevented or reversed by DTT. However, the inhibition of the activities of these sulphydryl proteins in diabetic animals was prevented by ebselen. Summarily, it is apparent that the effective in vitro inhibitory doses of ebselen on the activity of the sulphydryl proteins are far less than its antioxidant doses. In addition, the presence of DTT is evidently a critical requirement for ebselen to effect its antioxidant action against deoxyribose degeradation and not lipid peroxidation. Consequently, we conclude that ebselen possibly utilizes available thiols on sulphydryl proteins to effect its GPx mimicry antioxidant action against lipid peroxidation in rat brain homogenate.

Ebsulfur is a benzisothiazolone cytocidal inhibitor targeting the trypanothione reductase of Trypanosoma brucei

Trypanosoma brucei is the causing agent of African trypanosomiasis. These parasites possess a unique thiol redox system required for DNA synthesis and defense against oxidative stress. It includes trypanothione and trypanothione reductase (TryR) instead of the thioredoxin and glutaredoxin systems of mammalian hosts. Here, we show that the benzisothiazolone compound ebsulfur (EbS), a sulfur analogue of ebselen, is a potent inhibitor of T. brucei growth with a favorable selectivity index over mammalian cells. EbS inhibited the TryR activity and decreased non-protein thiol levels in cultured parasites. The inhibition of TryR by EbS was irreversible and NADPH-dependent. EbS formed a complex with TryR and caused oxidation and inactivation of the enzyme. EbS was more toxic for T. brucei than for Trypanosoma cruzi, probably due to lower levels of TryR and trypanothione in T. brucei. Furthermore, inhibition of TryR produced high intracellular reactive oxygen species. Hydrogen peroxide, known to be constitutively high in T. brucei, enhanced the EbS inhibition of TryR. The elevation of reactive oxygen species production in parasites caused by EbS induced a programmed cell death. Soluble EbS analogues were synthesized and cured T. brucei brucei infection in mice when used together with nifurtimox. Altogether, EbS and EbS analogues disrupt the trypanothione system, hampering the defense against oxidative stress. Thus, EbS is a promising lead for development of drugs against African trypanosomiasis.

In vitroevaluation of glutathione peroxidase (GPx)-like activity and antioxidant properties of some Ebselen analogues

Four analogues of Ebselen were synthesized and their glutathione peroxidase activity and antioxidant property evaluated and compared to Ebselen. Among the studied compounds, only diselenide [3] exhibited both glutathione peroxidase activity and radical-scavenging capability. Compounds [3] and [4] showed a strong inhibitory effect (53% and 43%, respectively) on the lipid peroxidation of linoleic acid compared to Ebselen and selenide derivatives ([1] and [2]) which were less active (28%, 26% and 18% inhibition, respectively). A concentration-dependent inhibitory effect was also found in the model of the formation of ABTS*+ radical cation: 65% and 89% inhibition for compound [3] at 10(-4) M and 5 x 10(-5) M, respectively, and 68% and 90% for compound [4], compared to 14% and 52% inhibition for Ebselen and the diselenides [1] and [2] (29%, 46% and 45%, 68%, respectively). By EPR spin trapping technique, the following inhibitory profile of the Ebselen analogues was observed towards the formation of thiyl radicals: Ebselen = [3]>[1]>[2]>[4]. Studies with compound [3] are in progress on oxidative stress cell models.

Kinetic characterization of ebselen, chelerythrine and apomorphine as glutaminase inhibitors

Glutaminase catalyzes the hydrolysis of glutamine to glutamate and plays a central role in the proliferation of neoplastic cells via glutaminolysis, as well as in the generation of excitotoxic glutamate in central nervous system disorders such as HIV-associated dementia (HAD) and multiple sclerosis. Both glutaminase siRNA and glutaminase inhibition have been shown to be effective in in vitro models of cancer and HAD, suggesting a potential role for small molecule glutaminase inhibitors. However, there are no potent, selective inhibitors of glutaminase currently available. The two prototypical glutaminase inhibitors, BPTES and DON, are either insoluble or non-specific. In a search for more drug-like glutaminase inhibitors, we conducted a screen of 1280 in vivo active drugs (Library of Pharmacologically Active Compounds (LOPAC(1280))) and identified ebselen, chelerythrine and (R)-apomorphine. The newly identified inhibitors exhibited 10 to 1500-fold greater affinities than DON and BPTES and over 100-fold increased efficiency of inhibition. Although non-selective, it is noteworthy that the affinity of ebselen for glutaminase is more potent than any other activity yet described. It is possible that the previously reported biological activity seen with these compounds is due, in part, to glutaminase inhibition. Ebselen, chelerythrine and apomorphine complement the armamentarium of compounds to explore the role of glutaminase in disease.

A safe lithium mimetic for bipolar disorder

Lithium is the most effective mood stabilizer for the treatment of bipolar disorder, but it is toxic at only twice the therapeutic dosage and has many undesirable side effects. It is likely that a small molecule could be found with lithium-like efficacy but without toxicity through target-based drug discovery; however, lithium’s therapeutic target remains equivocal. Inositol monophosphatase is a possible target but no bioavailable inhibitors exist. Here we report that the antioxidant ebselen inhibits inositol monophosphatase and induces lithium-like effects on mouse behaviour, which are reversed with inositol, consistent with a mechanism involving inhibition of inositol recycling. Ebselen is part of the National Institutes of Health Clinical Collection, a chemical library of bioavailable drugs considered clinically safe but without proven use. Therefore, ebselen represents a lithium mimetic with the potential both to validate inositol monophosphatase inhibition as a treatment for bipolar disorder and to serve as a treatment itself.

The protective effect of ebselen on radiocontrast-induced nephrotoxicity

AIM

Radiocontrast-induced nephropathy has become one of the most important causes of renal acute failure. The most effective management of reducing the incidence of contrast nephropathy is to understand and prevent its causes. We aimed to investigate the protective role of ebselen against radiocontrast-induced nephrotoxicity in terms of tissue oxidant/antioxidant parameters and light microscopy in rats.

METHODS

Albino Wistar rats were randomly separated into four groups. The Group 1 rats were treated with sodium chloride as the control group, Group 2 with radiocontrast, Group 3 with radiocontrast plus ebselen, and Group 4 with ebselen alone. After 24 h, the animals over the experimental period were euthanized and blood samples were analyzed for blood urea nitrogen (BUN) and serum creatinine (Cr) levels. Kidney sections were analyzed for malondialdehyde (MDA) levels and superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities, as well as histopathological changes.

RESULTS

In the radiocontrast group, BUN, MDA, and GSH-Px levels increased while SOD activity decreased compared with the control group. These decays were improved by ebselen administration in the radiocontrast group. Significant histological deteriorations were observed in the radiocontrast group. We noted improvement in the histologic findings with ebselen administration.

CONCLUSION

These results indicate that ebselen might produce a protective mechanism against radiocontrast-induced nephrotoxicity.

Antimalarial screening via large-scale purification of Plasmodium falciparum Ca2+-ATPase 6 and in vitro studies

The most severe form of human malaria is caused by the parasite Plasmodium falciparum. Despite the current need, there is no effective vaccine and parasites are becoming resistant to most of the antimalarials available. Therefore, there is an urgent need to discover new drugs from targets that have not yet suffered from drug pressure with the aim of overcoming the problem of new emerging resistance. Membrane transporters, such as P. falciparum Ca(2+)-ATPase 6 (PfATP6), the P. falciparum sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA), have been proposed as potentially good antimalarial targets. The present investigation focuses on: (a) the large-scale purification of PfATP6 for maintenance of its enzymatic activity; (b) screening for PfATP6 inhibitors from a compound library; and (c) the selection of the best inhibitors for further tests on P. falciparum growth in vitro. We managed to heterologously express in yeast and purify an active form of PfATP6 as previously described, although in larger amounts. In addition to some classical SERCA inhibitors, a chemical library of 1680 molecules was screened. From these, we selected a pool of the 20 most potent inhibitors of PfATP6, presenting half maximal inhibitory concentration values in the range 1-9 μm. From these, eight were chosen for evaluation of their effect on P. falciparum growth in vitro, and the best compound presented a half maximal inhibitory concentration of ~ 2 μm. We verified the absence of an inhibitory effect of most of the compounds on mammalian SERCA1a, representing a potential advantage in terms of human toxicity. The present study describes a multidisciplinary approach allowing the selection of promising PfATP6-specific inhibitors with good antimalarial activity.