Ebselen Diselenide Research Articles

Ebselen derivatives inhibit SARS-CoV-2 replication by inhibition of its essential proteins: PLpro and Mpro proteases, and nsp14 guanine N7-methyltransferase

Proteases encoded by SARS-CoV-2 constitute a promising target for new therapies against COVID-19. SARS-CoV-2 main protease (Mpro, 3CLpro) and papain-like protease (PLpro) are responsible for viral polyprotein cleavage—a process crucial for viral survival and replication. Recently it was shown that 2-phenylbenzisoselenazol-3(2H)-one (ebselen), an organoselenium anti-inflammatory small-molecule drug, is a potent, covalent inhibitor of both the proteases and its potency was evaluated in enzymatic and antiviral assays. In this study, we screened a collection of 34 ebselen and ebselen diselenide derivatives for SARS-CoV-2 PLpro and Mpro inhibitors. Our studies revealed that ebselen derivatives are potent inhibitors of both the proteases. We identified three PLpro and four Mpro inhibitors superior to ebselen. Independently, ebselen was shown to inhibit the N7-methyltransferase activity of SARS-CoV-2 nsp14 protein involved in viral RNA cap modification. Hence, selected compounds were also evaluated as nsp14 inhibitors. In the second part of our work, we employed 11 ebselen analogues—bis(2-carbamoylaryl)phenyl diselenides—in biological assays to evaluate their anti-SARS-CoV-2 activity in Vero E6 cells. We present their antiviral and cytoprotective activity and also low cytotoxicity. Our work shows that ebselen, its derivatives, and diselenide analogues constitute a promising platform for development of new antivirals targeting the SARS-CoV-2 virus.

Chemistry Related to the Catalytic Cycle of the Antioxidant Ebselen.

The antioxidant drug ebselen has been widely studied in both laboratories and in clinical trials. The catalytic mechanism by which it destroys hydrogen peroxide via reduction with glutathione or other thiols is complex and has been the subject of considerable debate. During reinvestigations of several key steps, we found that the seleninamide that comprises the first oxidation product of ebselen underwent facile reversible methanolysis to an unstable seleninate ester and two dimeric products. In its reaction with benzyl alcohol, the seleninamide produced a benzyl ester that reacted readily by selenoxide elimination, with formation of benzaldehyde. Oxidation of ebselen seleninic acid did not afford a selenonium seleninate salt as previously observed with benzene seleninic acid, but instead generated a mixture of the seleninic and selenonic acids. Thiolysis of ebselen with benzyl thiol was faster than oxidation by ca. an order of magnitude and produced a stable selenenyl sulfide. When glutathione was employed, the product rapidly disproportionated to glutathione disulfide and ebselen diselenide. Oxidation of the S-benzyl selenenyl sulfide, or thiolysis of the seleninamide with benzyl thiol, afforded a transient thiolseleninate that also readily underwent selenoxide elimination. The S-benzyl derivative disproportionated readily when catalyzed by the simultaneous presence of both the thiol and triethylamine. The phenylthio analogue disproportionated when exposed to ambient or UV (360 nm) light by a proposed radical mechanism. These observations provide additional insight into several reactions and intermediates related to ebselen.

In silico Studies on the Interaction between Mpro and PLpro From SARS-CoV-2 and Ebselen, its Metabolites and Derivatives.

The COVID‐19 pandemic caused by the SARS‐CoV‐2 has mobilized scientific attention in search of a treatment. The cysteine‐proteases, main protease (Mpro) and papain‐like protease (PLpro) are important targets for antiviral drugs. In this work, we simulate the interactions between the Mpro and PLpro with Ebselen, its metabolites and derivatives with the aim of finding molecules that can potentially inhibit these enzymes. The docking data demonstrate that there are two main interactions between the thiol (−SH) group of Cys (from the protease active sites) and the electrophilic centers of the organoselenium molecules, i. e. the interaction with the carbonyl group (O=C…SH) and the interaction with the Se moiety (Se…SH). Both interactions may lead to an adduct formation and enzyme inhibition. Density Functional Theory (DFT) calculations with Ebselen indicate that the energetics of the thiol nucleophilic attack is more favorable on Se than on the carbonyl group, which is in accordance with experimental data (Jin et al. Nature, 2020, 582, 289–293). Therefore, organoselenium molecules should be further explored as inhibitors of the SARS‐CoV‐2 proteases. Furthermore, we suggest that some metabolites of Ebselen (e. g. Ebselen diselenide and methylebselenoxide) and derivatives ethaselen and ebsulfur should be tested in vitro as inhibitors of virus replication and its proteases.

Inhibition of Anthracycline Alcohol Metabolite Formation in Human Heart Cytosol: A Potential Role for Several Promising Drugs.

The clinical efficacy of anthracyclines (e.g., doxorubicin and daunorubicin) in cancer therapy is limited by their severe cardiotoxicity, the etiology of which is still not fully understood. The development of anthracycline-induced cardiomyopathy has been found to correlate with myocardial formation and accumulation of anthracycline secondary alcohol metabolites (e.g., doxorubicinol and daunorubicinol) that are produced by distinct cytosolic NADPH-dependent reductases. The aim of the current study is to identify chemical compounds capable of inhibiting myocardial reductases implied in anthracycline reductive metabolism in an attempt to decrease the production of cardiotoxic C-13 alcohol metabolites. Among the variety of tested compounds (metal chelators, radical scavengers, antioxidants, β-blockers, nitrone spin traps, and lipid-lowering drugs), ebselen, cyclopentenone prostaglandins, nitric oxide donors, and short-chain coenzyme Q analogs resulted in being effective inhibitors of both doxorubicinol and daunorubicinol formation. In particular, ebselen (as well as ebselen diselenide, its storage form in the cells) was the most potent inhibitor of cardiotoxic anthracycline alcohol metabolites with 50% inhibition of doxorubicinol formation at 0.2 mol Eq of ebselen with respect to doxorubicin concentration. The high efficacy, together with its favorable pharmacological profile (low toxicity, lack of adverse effects, and metabolic stability) portends ebselen as a promising cardioprotective agent against anthracycline-induced cardiotoxicity.

Ebselen Reduces the Toxicity of Mechlorethamine in A-431 Cells via Inhibition of Apoptosis

A series of test compounds were evaluated for an ability to reduce the toxicity of the nitrogen mustard mechlorethamine (HN2) in vitro. The test compounds included resveratrol, pterostilbene, vitamin C, ebselen, ebselen diselenide, and ebselen-sulfur. Among them, ebselen demonstrated the highest degree of protection against HN2 toxicity. To this end, pretreatment of the cells with ebselen offered protection against the toxicant whereas no protection was observed when cells were first incubated with HN2 and then treated with ebselen. Significant increases in caspase 3 and caspase 9 activities were observed in response to HN2, and ebselen was found to reduce these effects. Taken together, the data presented here indicate that ebselen is an effective countermeasure to nitrogen mustard in vitro, which is worthy of future investigation in vivo.

Modeling the Oxidation of Ebselen and Other Organoselenium Compounds Using Explicit Solvent Networks

The oxidation of dimethylselenide, dimethyldiselenide, S-methylselenenyl-methylmercaptan, and truncated and full models of ebselen (N-phenyl-1,2-benzisoselenazol-3(2H)-one) by methyl hydrogen peroxide has been modeled using density functional theory (DFT) and solvent-assisted proton exchange (SAPE), a method of microsolvation that employs explicit solvent networks to facilitate proton transfer reactions. The calculated activation barriers for these systems were substantially lower in energy (DeltaG(double dagger) + DeltaG(solv) = 13 to 26 kcal/mol) than models that neglect the participation of solvent in proton exchange. The comparison of two- and three-water SAPE networks showed a reduction in the strain in the model system but without a substantial reduction in the activation barriers. Truncating the ebselen model to N-methylisoselenazol-3(2H)-one gave a larger activation barrier than ebselen or N-methyl-1,2-benzisoselenazol-3(2H)-one but provided an efficient means of determining an initial guess for larger transition-state models. The similar barriers obtained for ebselen and Me(2)Se(2) (DeltaG(double dagger) + DeltaG(solv) = 20.65 and 20.40 kcal/mol, respectively) were consistent with experimentally determined rate constants. The activation barrier for MeSeSMe (DeltaG(double dagger) + DeltaG(solv) = 21.25 kcal/mol) was similar to that of ebselen and Me(2)Se(2) despite its significantly lower experimental rate for oxidation of an ebselen selenenyl sulfide by hydrogen peroxide relative to ebselen and ebselen diselenide. The disparity is attributed to intramolecular Se-O interactions, which decrease the nucleophilicity of the selenium center of the selenenyl sulfide.

Density Functional Theory Study of the Reaction Mechanism and Energetics of the Reduction of Hydrogen Peroxide by Ebselen, Ebselen Diselenide, and Ebselen Selenol

Density functional theory calculations at the B3LYP/6-311++G(3df,3pd)//B3LYP/6-31G(d,p) level have been performed to elucidate the mechanism and reaction energetics for the reduction of hydrogen peroxide by ebselen, ebselen diselenide, ebselen selenol, and their sulfur analogues. The effects of solvation have been included with the CPCM model, and in the case of the selenol anion reaction, diffuse functions were used on heavy atoms for the geometry optimizations and thermochemical calculations. The topology of the electron density in each system was investigated using the quantum theory of atoms in molecules, and a detailed interpretation of the electronic charge and population data as well as the atomic energies is presented. Reaction free energy barriers for the oxidation of ebselen, ebselen diselenide, and ebselen selenol are 36.8, 38.4, and 32.5 kcal/mol, respectively, in good qualitative agreement with experiment. It is demonstrated that the oxidized selenium atom is significantly destabilized in all cases and that the exothermicity of the reactions is attributed to the peroxide oxygen atoms via reduction. The lower barrier to oxidation exhibited by the selenol is largely due to entropic effects in the reactant complex.

Modeling the Reduction of Hydrogen Peroxide by Glutathione Peroxidase Mimics

Theoretical calculations have been performed on three model reactions representing the reduction of hydrogen peroxide by ebselen, ebselen selenol, and ebselen diselenide. The reaction surfaces have been investigated at the B3PW91/6-311G(2df,p) level, and single-point energies were calculated using the 6-311++G(3df,3pd) basis set. Solvent effects were included implicitly with the conductor-like polarizable continuum model and in one case with explicit inclusion of three water molecules. Mechanistic information is gained from investigating the critical points using the quantum theory of atoms in molecules. The barriers for the reduction of hydrogen peroxide with the ebselen, ebselen selenol, and ebselen diselenide models are 56.7, 53.4, and 35.3 kcal/mol, respectively, suggesting that ebselen diselenide may be the most active antioxidant in the ebselen GPx redox pathway. Results are also compared to that of the sulfur analogues of the model compounds.

A Novel Antioxidant Mechanism of Ebselen Involving Ebselen Diselenide, a Substrate of Mammalian Thioredoxin and Thioredoxin Reductase

The antioxidant mechanism of ebselen involves recently discovered reductions by mammalian thioredoxin reductase (TrxR) and thioredoxin (Trx) forming ebselen selenol. Here we describe a previously unknown reaction; ebselen reacts with its selenol forming an ebselen diselenide with a rate constant of 372 m(-1)s(-1). The diselenide also was a substrate of TrxR forming the selenol with K(m) of 40 microm and k(cat) of 79 min(-1) (k(cat)/K(m) of 3.3 x 10(4) m(-1)s(-1)). Trx increased the reduction because of its fast reaction with diselenide (rate constant 1.7 x 10(3) m(-1)s(-1)). Diselenide stimulated the H2O2 reductase activity of TrxR, even more efficiently with Trx present. Because the mechanism of ebselen as an antioxidant has been assumed to involve glutathione peroxidase-like activity, we compared the H2O2 reductase activity of ebselen with the GSH and Trx systems. TrxR at 50 nm, far below the estimated physiological level, gave 8-fold higher activity compared with 1 mm GSH; addition of 5 microm Trx increased this difference to 13-fold. The rate constant of ebselen selenol reacting with H2O2 was estimated to be faster than 350 m(-1)s(-1). We propose novel mechanisms for ebselen antioxidant action involving ebselen selenol and diselenide formation, with the thioredoxin system rather than glutathione as the predominant effector and target.

Mechanism of protection of ebselen against paracetamol-induced toxicity in rat hepatocytes

The protective effect of ebselen (PZ 51), an anti-inflammatory agent, on paracetamolinduced (1 mM) cytotoxicity in hepatocytes freshly isolated from β-naphthoflavone-pretreated rats was studied. At a concentration of 50μM added simultaneously with paracetamol, ebselen prevented paracetamol-induced leakage of lactate dehydrogenase (LDH) almost completely and lipid peroxidation (LPO) and depletion of glutathione (GSH) substantially. These protective effects were even more pronounced at 100 μM concentration of ebselen. When added to the hepatocytes 1 hr before paracetamol, 50 μM of ebselen also prevented LDH leakage, LPO and GSH depletion. Reverse addition of paracetamol and ebselen did not result in protection. Simultaneous incubation of 100 μM ebselen and paracetamol inhibited GSH conjugation of paracetamol by more than 50%, however, without any effect on glucuronidation and sulfation of paracetamol. Ebselen was shown not to react directly with paracetamol nor to inhibit cytochrome P450 activity measured as 7-ethoxycoumarin 0-deethylase (ECD) activity in the hepatocytes. At mixing, synthetic ebselen selenol and synthetic N-acetyl- p-benzoquinone imine (NAPQI) were shown to form paracetamol and ebselen diselenide. No indication was found for the formation of an ebselen-paracetamol conjugate upon reacting synthetic NAPQI and synthetic ebselen selenol. Reduction of NAPQI, the reactive metabolite of paracetamol, by ebselen selenol is discussed in terms of the mechanism of cytoprotection.

Determination of the relative contributions of the diselenide and selenol forms of ebselen in the mechanism of its glutathione peroxidase-like activity

The molecular basis of the glutathione peroxidase activity of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) was investigated by the use of synthesised, authentic intermediates identical to those formed by the reaction of ebselen with glutathione. The second order rate constants for the reaction of ebselen (0.29 mM −1 min −1), ebselen-glutathione selenosulfide (≤0.01 mM −1 min −1), ebselen selenol (2.8 mM −1 min −1) and ebselen diselenide (0.32 mM −1 min −1) with hydrogen peroxide reveal that the selenol is particularly active in this respect. The determination of the relative amounts of ebselen selenol and diselenide under typical peroxidase assay conditions implies that the selenol is the predominant molecular species responsible for the glutathione - (70%) - and dithiothreitol - (96%) - dependent peroxidase activity of ebselen.