Selenium-based pharmacological agents: an update

Perfluoroalkyl Selenoxides, Selenones and Selenoximines: General Preparation and Properties

A selective access to perfluoroalkyl selenoxides, via Oxone® as oxidant or to selenones by using a Polyoxometalate-based Ionic Liquid (POM-IL) as a catalyst for the oxidation step is described. The reaction works with various perfluoralkyl chains and substituents with satisfactory to excellent yields. A two-step one-pot reaction from selenocyanates was performed to gain access to perfluoroalkyl selenoxides. The previously unknown perfluoroalkyl selenoximines family was also prepared with good yields. Having unlocked two strategies for the synthesis of fluoroalkylated Se^IV and Se^VI compounds, we then evaluated the Hansch-Leo lipophilicity parameters of these groups. Finally, asymmetric aryl perfluoroalkyl selenoximines were resolved to determine their absolute configurations.

Investigation of chalcogen bioisosteric replacement in a series of heterocyclic inhibitors of tryptophan 2,3-dioxygenase

Selenium is an underexplored element that can be used for bioisosteric replacement of lower molecular weight chalcogens such as oxygen and sulfur. More studies regarding the impact of selenium substitution in different chemical scaffolds are needed to fully grasp this element's potential. Herein, we decided to evaluate the impact of selenium incorporation in a series of tryptophan 2,3-dioxygenase (TDO2) inhibitors, a target of interest in cancer immunotherapy. First, we synthesized the different chalcogen isosteres through Suzuki-Miyaura type coupling. Next, we evaluated the isosteres' affinity and selectivity for TDO2, as well as their lipophilicity, microsomal stability and cellular toxicity on TDO2-expressing cell lines. Overall, chalcogen isosteric replacements did not disturb the on-target activity but allowed for a modulation of the compounds' lipophilicity, toxicity and stability profiles. The present work contributes to our understanding of oxygen/sulfur/selenium isostery towards increasing structural options in medicinal chemistry for the development of novel and distinctive drug candidates.

3,3'-Diselenodipropionic acid (DSePA): A redox active multifunctional molecule of biological relevance

BACKGROUND

Extensive research is being carried out globally to design and develop new selenium compounds for various biological applications such as antioxidants, radio-protectors, anti-carcinogenic agents, biocides, etc. In this pursuit, 3,3'-diselenodipropionic acid (DSePA), a synthetic organoselenium compound, has received considerable attention for its biological activities.

SCOPE OF REVIEW

This review intends to give a comprehensive account of research on DSePA so as to facilitate further research activities on this organoselenium compound and to realize its full potential in different areas of biological and pharmacological sciences.

MAJOR CONCLUSIONS

It is an interesting diselenide structurally related to selenocystine. It shows moderate glutathione peroxidase (GPx)-like activity and is an excellent scavenger of reactive oxygen species (ROS). Exposure to radiation, as envisaged during radiation therapy, has been associated with normal tissue side effects and also with the decrease in selenium levels in the body. In vitro and in vivo evaluation of DSePA has confirmed its ability to reduce radiation induced side effects into normal tissues. Administration of DSePA through intraperitoneal (IP) or oral route to mice in a dose range of 2 to 2.5 mg/kg body weight has shown survival advantage against whole body irradiation and a significant protection to lung tissue against thoracic irradiation. Pharmacokinetic profiling of DSePA suggests its maximum absorption in the lung.

GENERAL SIGNIFICANCE

Research work on DSePA reported in fifteen years or so indicates that it is a promising multifunctional organoselenium compound exhibiting many important activities of biological relevance apart from radioprotection.

2,2′-Dipyridyl diselenide (Py2Se2) induces G1 arrest and apoptosis in human lung carcinoma (A549) cells through ROS scavenging and reductive stress

This study demonstrates the cytotoxic activity and the underlying mechanisms of a synthetic organoselenium compound containing pyridine and diselenide moieties.

Selenium and hydrogen selenide: essential micronutrient and the fourth gasotransmitter?

Selenium (Se) is an essential micronutrient required by organisms of diverse lineage. Dietary Se is converted to hydrogen selenide either enzymatically or by endogenous antioxidant proteins. This convergent biochemical step crucially underlies the subsequent biological activity of Se and argues for inclusion of hydrogen selenide as the fourth endogenous gasotransmitter alongside nitric oxide, carbon monoxide and hydrogen sulfide.Endogenously generated hydrogen selenide is incorporated into numerous 'selenoprotein' oxidoreductase enzymes, essential for maintaining redox-status homeostasis in health and disease. Direct effects of endogenous hydrogen selenide on cellular and molecular targets are currently unknown. Given exogenously, hydrogen selenide acts as a modulator of metabolism via transient inhibition of mitochondrial cytochrome C oxidase. Here we provide an overview of Se biology, its impact on several physiological systems (immune, endocrine, cardiovascular and metabolic) and its utility as a supplement in acute and critical illness states. We further explore the evidence base supporting its role as the fourth gasotransmitter and propose a strategic case towards generation of novel selenomimetic therapeutics.

Cytoprotective and antioxidant properties of organic selenides for the myelin-forming cells, oligodendrocytes

Here a new series of twenty-one organoselenides, of potential protective activity, were synthesized and tested for their intrinsic cytotoxicity, anti-apoptotic and antioxidant capacities in oligodendrocytes. Most of the organoselenides were able to decrease the ROS levels, revealing antioxidant properties. Compounds 5b and 7b showed a high glutathione peroxidase (GPx)-like activities, which were 1.5 folds more active than ebselen. Remarkably, compound 5a diminished the formation of the oligodendrocytes SubG1 peak in a concentration-dependent manner, indicating its anti-apoptotic properties. Furthermore, based on the SwissADME web interface, we performed an in-silico structure-activity relationship to explore the drug-likeness of these organoselenides, predicting the pharmacokinetic parameters for compounds of interest that could cross the blood-brain barrier. Collectively, we present new organoselenide compounds with cytoprotective and antioxidant properties that can be considered as promising drug candidates for myelin diseases.

Natural product-based synthesis of novel anti-infective isothiocyanate- and isoselenocyanate-functionalized amphilectane diterpenes

The marine natural product (-)-8,15-diisocyano-11(20)-amphilectene (1), isolated from the Caribbean sponge Svenzea flava, was used as scaffold to synthetize five new products, all of which were tested against laboratory strains of Plasmodium falciparum and Mycobacterium tuberculosis H37Rv. The scaffold contains two isocyanide units that are amenable to chemical manipulation, enabling them to be elaborated into a small library of sulfur and selenium compounds. Although most of the analogs prepared were less potent than the parent compound, 5 was nearly equipotent showing IC50 values of 0.0066 μM and 0.0025 μM, respectively, against two strains (Dd2 and 3D7) of the malaria parasite. On the other hand, when assayed against the tuberculosis bacterium, analogs 5 and 6 were found to be more potent than 1.

Design, synthesis, in vitro antimicrobial and cytotoxic evaluation of novel 1,2,3-selena/thiadiazolyltetrazole derivatives

A new series of 2,5-disubstituted tetrazoles and 1,2,3-selena/thiadiazolyl-2H-tetrazole derivatives were synthesized and evaluated for theirin vitroantimicrobial and cytotoxic activities against pathogenic strains.

Pharmacokinetics, antitumor and cardioprotective effects of liposome-encapsulated phenylaminoethyl selenide in human prostate cancer rodent models

PURPOSE

Cardiotoxicity associated with the use of doxorubicin (DOX), and other chemotherapeutics, limits their clinical potential. This study determined the pharmacokinetics and antitumor and cardioprotective activity of free and liposome encapsulated phenyl-2-aminoethyl-selenide (PAESe).

METHODS

The pharmacokinetics of free PAESe and PAESe encapsulated in liposomes (SSL-PAESe) were determined in rats using liquid chromatography tandem mass-spectrometry. The antitumor and cardioprotective effects were determined in a mouse xenograft model of human prostate (PC-3) cancer and cardiomyocytes (H9C2).

RESULTS

The encapsulation of PAESe in liposomes increased the circulation half-life and area under the drug concentration time profile, and decreased total systemic clearance significantly compared to free PAESe. Free- and SSL-PAESe improved survival, decreased weight-loss and prevented cardiac hypertrophy significantly in tumor bearing and healthy mice following treatment with DOX at 5 and 12.5 mg/kg. In vitro studies revealed PAESe treatment altered formation of reactive oxygen species (ROS), cardiac hypertrophy and gene expression, i.e., atrial natriuretic peptide and myosin heavy chain complex beta, in H9C2 cells.

CONCLUSIONS

Treatment with free and SSL-PAESe exhibited antitumor activity in a prostate xenograft model and mitigated DOX-mediated cardiotoxicity.

Selenoprotein dSelK in Drosophila elevates release of Ca2+ from endoplasmic reticulum by upregulating expression of inositol 1,4,5-tris-phosphate receptor

dSelK (G-rich), a homolog of human and mouse SelK, is one of three selenoproteins in Drosophila melanogaster. It is the only trans-membrane selenoprotein in D. melanogaster integrated into both the endoplasmic reticulum (ER) membrane and the Golgi apparatus. The gene expression profile of Drosophila Schneider 2 (S2) cells after the dsRNA interference (dsRNAi) targeting of dSelK was examined with the GeneChip Drosophila Genome 2.0 Array (Affymetrix), a high-density oligonucleotide microarray encompassing nearly the full Drosophila genome. The results showed that the transcriptional expression of eight genes whose proteins are located on (or related to) the ER or the Golgi apparatus was highly induced or repressed by the dsRNAi treatment. The mRNA levels of the inositol 1,4,5-tris-phosphate receptor (IP3 receptor), whose gene product is integrated into the ER membrane and regulates the release of Ca2+ from the ER to the cytosol, were significantly downregulated. In contrast, the expression of inositol 1,4,5-tris-phosphate kinase 1, which is a cytosolic protein with opposing functions to the IP3 receptor, was significantly upregulated. Quantitative real-time PCR verified these results. The concentration of intracellular free Ca2+ of the Drosophila S2 cells was significantly decreased after the knockdown of dSelK, whereas overexpression of dSelK significantly increased the intracellular free Ca2+ concentration. These results indicate that dSelK in D. melanogaster is involved in regulating the release of Ca2+ from the ER to the cytosol and may play important roles in the signal transduction pathways involving Ca2+ mobilization.

Therapeutic potential of selenium and tellurium compounds: opportunities yet unrealised

Despite being disparaged for their malodorous and toxic demeanour, compounds of selenium, a bio-essential element, and tellurium, offer possibilities as therapeutic agents. Herein, their potential use as drugs, for example, as anti-viral, anti-microbial, anti-inflammatory agents, etc., will be surveyed along with a summary of the established biological functions of selenium. The natural biological functions of tellurium remain to be discovered.

The antioxidant phenylaminoethyl selenide reduces doxorubicin-induced cardiotoxicity in a xenograft model of human prostate cancer

Anthracyclines are potent anticancer agents, but cardiotoxicity mediated by free radical generation limits their clinical use. This study evaluated the anticancer activity of phenyl-2-aminoethyl selenide (PAESe) and its potential to reduce doxorubicin (DOX)-induced cardiotoxicity. Growth inhibitory effects of PAESe with DOX, and vincristine, clinically used anticancer agents, and tert-butylhydroperoxide (TBHP), a known oxidant, on the growth of human prostate carcinoma (PC-3) cells was determined. PAESe (≤1μm) did not alter the growth of PC-3 cells, however, concomitant use of PAESe decreased the oxidative-mediated cytotoxicity of TBHP, but had limited effect on vincristine or DOX activity. Further, PAESe decreased the formation of intracellular reactive oxygen species from TBHP and DOX. The effect of PAESe on the activity of DOX was determined using a tumor (PC-3) xenograft model in mice. PAESe did not alter DOX antitumor activity and showed evidence of direct antitumor activity relative to controls. DOX treatment decreased mice body weight significantly, whereas concomitant administration of PAESe and DOX was similar to controls. Most importantly, PAESe decreased DOX-mediated infiltration of neutrophil and macrophages into the myocardium. These data suggest PAESe had in vivo antitumor activity and in combination with DOX decreased early signs of cardiotoxicity while preserving its antitumor activity.

New development of synthesis and reactivity of seleno- and tellurophenes

Due to the many new and remarkable findings and applications that have been published in recent years in seleno- and tellurophene chemistry, this review revisits the different aspects of this chemistry, including synthesis, reactivity and applications in the field of heterocycles.

3-Alkynyl selenophene protects against carbon-tetrachloride-induced and 2-nitropropane-induced hepatic damage in rats

The aim of this study was to investigate the protective effect of 3-alkynyl selenophene (3-ASP) on acute liver injury induced by carbon tetrachloride (CCl(4)) and 2-nitropropane (2-NP) in rats. On the first day of treatment, the animals received 3-ASP (25 mg/kg, p.o.). On the second day, the rats received CCl(4) (1 mg/kg, i.p.) or 2-NP (100 mg/kg, p.o.). Twenty-four hours after CCl(4) or 2-NP administration, the animals were euthanized, and their plasma and liver were removed for biochemical and histological analyses. The histological analysis revealed extensive injury in the liver of CCl(4)-exposed and 2-NP-exposed rats, which was attenuated by 3-ASP. 3-ASP significantly attenuated (1) the increase in plasmatic aspartate and alanine aminotransferase activities and lipid peroxidation levels induced by CCl(4) and 2-NP; (2) the inhibition of δ-aminolevulinic dehydratase activity caused by 2-NP; and (3) the decrease in ascorbic acid (AA) levels and catalase (CAT) activity caused by CCl(4). AA levels and CAT activity remained unaltered in the liver of rats exposed to 2-NP. The protective effect of 3-ASP on acute liver injury induced by CCl(4) and 2-NP in rats was demonstrated.

Hypolipidaemic activity of orally administered diphenyl diselenide in Triton WR-1339-induced hyperlipidaemia in mice

Objectives

A significant association between the trace element selenium and hyper-cholesterolaemia has been reported. This study was designed to investigate a potential hypolipidaemic effect of diphenyl diselenide ((PhSe)2) in Triton WR-1339-induced hyperlipidaemia in mice.

Methods

Triton was administered intraperitoneally (400 mg/kg) to overnight-fasted mice to develop acute hyperlipidaemia. (PhSe)2 was administered orally (10 mg/kg) 30 min before Triton. At 24 h after Triton injection, blood samples were collected to measure plasma lipid levels. The hepatic thiobarbituric acid reactive substances and ascorbic acid levels as well as catalase and glutathione peroxidase activity were recorded.

Key findings

(PhSe)2 administration significantly lowered total cholesterol, non-high-density lipoprotein-cholesterol and triglycerides, whilst it increased high-density lipoprotein-cholesterol levels in plasma of hyperlipidaemic mice. Neither oxidative stress nor the antioxidant effect of (PhSe)2 was observed in the mouse liver in this experimental protocol.

Conclusions

These findings indicated that (PhSe)2 was able to lower plasma lipid concentrations. Further studies are needed to elucidate the exact mechanism by which (PhSe)2 exerted its hypolipidaemic effect in the management of hyperlipidaemia and atherosclerosis.

Synthesis and biological evaluation of novel selenonucleosides

A series of novel selenonucleoside analogues with 1,4-oxaselenane as the carbohydrate fragment has been synthesized from their corresponding dimesylated seconucleosides treated with NaHSe solution and subsequent deprotection. The synthesized selenonucleoside analogues were evaluated as potential antitumor agents.

Isoselenocyanates: a powerful tool for the synthesis of selenium-containing heterocycles

Selenium-containing heterocyclic compounds have been well recognized, not only because of their remarkable reactivities and chemical properties, but also because of their diverse pharmaceutical applications. In this context, isoselenocyanates have been emerged as a powerful tool for the synthesis of selenium-containing heterocycles, since they are easy to prepare and store and are safe to handle. In this review the recent advances in the development of synthesis methods for selenium-containing heterocycles from isoselenocyanates are presented and discussed.

Effects of selenium supplementation on cardiovascular disease incidence and mortality: secondary analyses in a randomized clinical trial

Despite the documented antioxidant and chemopreventive properties of selenium, studies of selenium intake and supplementation and cardiovascular disease have yielded inconsistent findings. The authors examined the effect of selenium supplementation (200 microg daily) on cardiovascular disease incidence and mortality through the entire blinded phase of the Nutritional Prevention of Cancer Trial (1983-1996) among participants who were free of cardiovascular disease at baseline (randomized to selenium: n = 504; randomized to placebo: n = 500). Selenium supplementation was not significantly associated with any of the cardiovascular disease endpoints during 7.6 years of follow-up (all cardiovascular disease: hazard ratio (HR) = 1.03, 95% confidence interval (CI): 0.78, 1.37; myocardial infarction: HR = 0.94, 95% CI: 0.61, 1.44; stroke: HR = 1.02, 95% CI: 0.63, 1.65; all cardiovascular disease mortality: HR = 1.22, 95% CI: 0.76, 1.95). The lack of significant association with cardiovascular disease endpoints was also confirmed when analyses were further stratified by tertiles of baseline plasma selenium concentrations. These findings indicate no overall effect of selenium supplementation on the primary prevention of cardiovascular disease in this population.

Acute liver damage induced by 2-nitropropane in rats: Effect of diphenyl diselenide on antioxidant defenses

The effect of post-treatment with diphenyl diselenide on liver damage induced by 2-nitropropane (2-NP) was examined in male rats. Rats were pre-treated with a single dose of 2-NP (100 mg/kg body weight dissolved in canola oil). Afterward, the animals were post-treated with a dose of diphenyl diselenide (10, 50 or 100 micromol/kg). The parameters that indicate tissue damage such as liver histopathology, plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), urea and creatinine were determined. Since the liver damage induced by 2-NP is related to oxidative damage, lipid peroxidation, superoxide dismutase (SOD), catalase (CAT) and ascorbic acid level were also evaluated. Diphenyl diselenide (50 and 100 micromol/kg) effectively restored the increase of ALT and AST activities and urea level when compared to the 2-NP group. At the higher dose, diphenyl diselenide decreased GGT activity. Treatment with diphenyl diselenide, at all doses, effectively ameliorated the increase of hepatic and renal lipid peroxidation when compared to 2-NP group. 2-NP reduced CAT activity and neither alter SOD activity nor ascorbic acid level. This study points out the involvement of CAT activity in 2-NP-induced acute liver damage and suggests that the post-treatment with diphenyl diselenide was effective in restoring the hepatic damage induced by 2-NP.

Preparation of 2,3-dihydroselenolo[2,3-b]pyridines and related compounds by free-radical means

Photolysis of the thiohydroximate ester derivative 21 of 2-carboethoxy-2-(2-(benzylseleno)pyridin-3-yl)tridecylcarboxylic acid (20) affords 2-dodecyl-2-carboethoxy-2,3-dihydroselenolo[2,3-b]pyridine (22) in 89% yield in a process presumably involving intramolecular homolytic substitution by a tertiary alkyl radical at selenium with loss of a benzyl radical. Alternatively, rearrangement of O-(omega-haloalkyl)esters 34 of 2-carboethoxy-N-hydroxypyridine-2-selone affords azonianaphthalenium halides 37 in 79% yield.