Ebselen, a multi-target compound: its effects on biological processes and diseases

Selenization of Small Molecule Drugs: A New Player on the Board

There is an urgent need to develop safer and more effective modalities for the treatment of a wide range of pathologies due to the increasing rates of drug resistance, undesired side effects, poor clinical outcomes, etc. Throughout the years, selenium (Se) has attracted a great deal of attention due to its important role in human health. Besides, a growing body of work has unveiled that the inclusion of Se motifs into a great number of molecules is a promising strategy for obtaining novel therapeutic agents. In the current Perspective, we have gathered the most recent literature related to the incorporation of different Se moieties into the scaffolds of a wide range of known drugs and their feasible pharmaceutical applications. In addition, we highlight different representative examples as well as provide our perspective on Se drugs and the possible future directions, promises, opportunities, and challenges of this ground-breaking area of research.

Ebselen: A Promising Repurposing Drug to Treat Infections Caused by Multidrug-Resistant Microorganisms

Bacterial multiresistance to drugs is a rapidly growing global phenomenon. New resistance mechanisms have been described in different bacterial pathogens, threatening the effective treatment of even common infectious diseases. The problem worsens in infections associated with biofilms because, in addition to the pathogen's multiresistance, the biofilm provides a barrier that prevents antimicrobial access. Several "non-antibiotic" drugs have antimicrobial activity, even though it is not their primary therapeutic purpose. However, due to the urgent need to develop effective antimicrobials to treat diseases caused by multidrug-resistant pathogens, there has been an increase in research into "non-antibiotic" drugs to offer an alternative therapy through the so-called drug repositioning or repurposing. The prospect of new uses for existing drugs has the advantage of reducing the time and effort required to develop new compounds. Moreover, many drugs are already well characterized regarding toxicity and pharmacokinetic/pharmacodynamic properties. Ebselen has shown promise for use as a repurposing drug for antimicrobial purposes. It is a synthetic organoselenium with anti-inflammatory, antioxidant, and cytoprotective activity. A very attractive factor for using ebselen is that, in addition to potent antimicrobial activity, its minimum inhibitory concentration is very low for microbial pathogens.

Discovery of the sEH Inhibitor Epoxykynin as a Potent Kynurenine Pathway Modulator

Disease-related phenotypic assays enable unbiased discovery of novel bioactive small molecules and may provide novel insights into physiological systems and unprecedented molecular modes of action (MMOA). Herein, we report the identification and characterization of epoxykynin, a potent inhibitor of the soluble epoxide hydrolase (sEH). Epoxykynin was discovered by means of a cellular assay monitoring modulation of kynurenine (Kyn) levels in BxPC-3 cells upon stimulation with the cytokine interferon-γ (IFN-γ) and subsequent target identification employing affinity-based chemical proteomics. Increased Kyn levels are associated with immune suppression in the tumor microenvironment and, thus, the Kyn pathway and its key player indoleamine 2,3-dioxygenase 1 (IDO1) are appealing targets in immuno-oncology. However, targeting IDO1 directly has led to limited success in clinical investigations, demonstrating that alternative approaches to reduce Kyn levels are in high demand. We uncover a cross-talk between sEH and the Kyn pathway that may provide new opportunities to revert cancer-induced immune tolerance.

Should ebselen be considered for the treatment of mercury intoxication? A minireview

Mercury is a ubiquitous environmental contaminant and can be found in inorganic (Hg0, Hg+ and Hg2+) and organic forms (chiefly CH3Hg+ or MeHg+). The main route of human, mammals and bird exposure occurs via predatory fish ingestion. Occupational exposure to Hg0 (and Hg2+) can also occur; furthermore, in gold mining areas the exposure to inorganic Hg can also be high. The toxicity of electrophilic forms of Hg (E+Hg) is mediated by disruption of thiol (-SH)- or selenol (-SeH)-containing proteins. The therapeutic approaches to treat methylmercury (MeHg+), Hg0 and Hg2+ are limited. Here we discuss the potential use of ebselen as a potential therapeutic agent to lower the body burden of Hg in man. Ebselen is a safe drug for humans and has been tested in clinical trials (for instance, brain ischemia, noise-induce hearing loss, diabetes complications, bipolar disorders) at doses varying from 400 to 3600 mg per day. Two clinical trials with ebselen in moderate and severe COVID are also approved. Ebselen can be metabolized to an intermediate with -SeH (selenol) functional group, which has a greater affinity to electrophilic Hg (E+Hg) forms than the available thiol-containing therapeutic agents. Accordingly, as observed in vitro and rodent models in vivo, Ebselen exhibited protective effects against MeHg+, indicating its potential as a therapeutic agent to treat MeHg+ overexposure. The combined use of ebselen with thiol-containing molecules (e.g. N-acetylcysteine and enaramide)) is also commented, because they can have synergistic protective effects against MeHg+.

Ebselen, Iron Uptake Inhibitor, Alleviates Iron Overload-Induced Senescence-Like Neuronal Cells SH-SY5Y via Suppressing the mTORC1 Signaling Pathway

Increasing evidence highlights that excessive iron accumulation in the brain plays a vital role in neuronal senescence and is implicated in the pathogenesis of age-related neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Therefore, the chemical compounds that eliminate an iron overload may provide better protection against oxidative stress conditions that cause the accumulation of senescent cells during brain aging. Ebselen has been identified as a strongly useful compound in the research on redox biology mechanisms. We hypothesized that ebselen could alleviate an iron overload-induced oxidative stress and consequently reverses the senescence-like phenotypes in the neuronal cells. In the present study, SH-SY5Y cells were treated with ferric ammonium citrate (FAC) before ebselen, and the evaluation of the cellular iron homeostasis, the indicators of oxidative stress, and the onset of senescence phenotypes and mechanisms were carried out accordingly. Our findings showed that ebselen ameliorated the FAC-mediated iron overload by decreasing the expression of divalent metal transporter 1 (DMT1) and ferritin light chain (FT-L) proteins. In contrast, it increased the expression of ferroportin 1 (FPN1) protein and its correlation led to a decrease in the expression of the cytosolic labile iron pool (LIP). Furthermore, ebselen significantly reduced reactive oxygen species (ROS) and rescued the mitochondrial membrane potential (ΔΨm). Notably, ebselen restored the biomarkers of cellular senescence by reducing the number of senescence-associated β-galactosidase (SA-β-gal) positive cells and senescence-associated secretory phenotypes (SASP). This also suppressed the expression of p53 protein targeting DNA damage response (DDR)/p21 cyclin-dependent kinase (CDK) inhibitor through a mTORC1 signaling pathway. Potentially, ebselen could be a therapeutic agent for treating brain aging and AD by mitigating iron accumulation and restoring senescence in SH-SY5Y cells.

Emerging role of inositol monophosphatase in cancer

Inositol monophosphatase (IMPase) is an enzyme with two homologs-IMPA1 and IMPA2-that is responsible for dephosphorylating myo-inositol monophosphate to generate myo-inositol. IMPase has been extensively studied in neuropsychiatric diseases and is regarded as a susceptibility gene. Recently, emerging evidence has implied that IMPase is linked to cancer development and progression and correlates with patient survival outcomes. Interestingly, whether it acts as a tumor-promoter or tumor-suppressor is inconsistent among different research studies. In this review, we summarize the latest findings on IMPase in cancer, focusing on exploring the underlying mechanisms for its pro- and anticancer roles. In addition, we discuss the potential methods of IMPase regulation in cancer cells and the possible approaches for IMPase intervention in clinical practice.

Optimized Ebselen-Based Inhibitors of Bacterial Ureases with Nontypical Mode of Action

Screening of 25 analogs of Ebselen, diversified at the N-aromatic residue, led to the identification of the most potent inhibitors of Sporosarcina pasteurii urease reported to date. The presence of a dihalogenated phenyl ring caused exceptional activity of these 1,2-benzisoselenazol-3(2H)-ones, with K_i value in a low picomolar range (<20 pM). The affinity was attributed to the increased π-π and π-cation interactions of the dihalogenated phenyl ring with αHis323 and αArg339 during the initial step of binding. Complementary biological studies with selected compounds on the inhibition of ureolysis in whole Proteus mirabilis cells showed a very good potency (IC₅₀ < 25 nM in phosphate-buffered saline (PBS) buffer and IC₉₀ < 50 nM in a urine model) for monosubstituted N-phenyl derivatives. The crystal structure of S. pasteurii urease inhibited by one of the most active analogs revealed the recurrent selenation of the Cys322 thiolate, yielding an unprecedented Cys322-S-Se-Se chemical moiety.

Antibacterial Activity of Ebselen

Ebselen is a low-molecular-weight organoselenium compound that has been broadly studied for its antioxidant, anti-inflammatory, and cytoprotective properties. These advantageous properties were initially associated with mimicking the activity of selenoprotein glutathione peroxidase, but the biomedical impact of this compound appear to be far more complex. Ebselen serves as a substrate or inhibitor with multiple protein/enzyme targets, whereas inhibition typically originates from the covalent modification of cysteine residues by opening the benzisoselenazolone ring and S-Se bond formation. The inhibition of enzymes of various classes and origins has been associated with substantial antimicrobial potential among other activities. In this contribution, we summarize the current state of the art regarding the antibacterial activity of ebselen. This activity, alone and in combination with commercial pharmaceuticals, against pathogens, including those resistant to drugs, is presented, together with the molecular mechanism behind the reactivity. The specific inactivation of thioredoxin reductase, bacterial toxins, and other resistance factors is considered to have certain therapeutic implications. Synergistic action and sensitization to common antibiotics assisted with the use of ebselen appear to be promising directions in the treatment of persistent infections.

Synthesis of new chiral N-heterocyclic diselenides and their application in the alkoxyselenylation reaction

Novel chiral diselenides based on a cyclic or bicyclic backbone were applied in the highly diastereoselective methoxyselenylation of styrene.