Selenium-containing chrysin and quercetin derivatives: attractive scaffolds for cancer therapy

Novel selenylated imidazo[1,2-a]pyridines for breast cancer chemotherapy: Inhibition of cell proliferation by Akt-mediated regulation, DNA cleavage and apoptosis

A novel series of selenylated imidazo[1,2-a]pyridines were designed and synthesized with a view to a promising activity against breast cancer cell. The compounds, 7-methyl-3-(naphthalene-1-ylselanyl)-2-phenylimidazo[1,2-a]pyridine, named IP-Se-05, and 3-((2-methoxyphenyl)selanyl)-7-methyl-2-phenylimidazo[1,2-a]pyridine, named IP-Se-06, showed high cytotoxicity for MCF-7 cells (IC₅₀ = 26.0 μM and 12.5 μM, respectively). Both the compounds inhibited the cell proliferation and caused decrease in the number of cells in the G2/M phase of cell cycle. IP-Se-05 and IP-Se-06 were also evaluated for effects on CT-DNA and DNA of MCF-7 cells. The compounds intercalated into CT-DNA and both treatments caused cleavage of DNA in cells. In addition, the compounds induced cell death by apoptosis. However, the presence of (2-methoxyphenyl) selenyl moiety at the imidazo[1,2-a]pyridine (IP-Se-06) appears to have a better antitumor effect with higher cytotoxicity at a lower concentration and caused less necrosis. Overall, the current study established IP-Se-06 more than IP-Se-05 as a potential prototype compound to be employed as an antiproliferative agent for the treatment of breast cancer.

Novel pyrimidinic selenourea induces DNA damage, cell cycle arrest, and apoptosis in human breast carcinoma

Novel pyrimidinic selenoureas were synthesized and evaluated against tumour and normal cell lines. Among these, the compound named 3j initially showed relevant cytotoxicity and selectivity for tumour cells. Three analogues of 3j were designed and synthesized keeping in view the structural requirements of this compound. Almost all the tested compounds displayed considerable cytotoxicity. However, 8a, one of the 3j analogues, was shown to be highly selective and cytotoxic, especially for breast carcinoma cells (MCF-7) (IC₅₀ = 3.9 μM). Furthermore, 8a caused DNA damage, inhibited cell proliferation, was able to arrest cell cycle in S phase, and induced cell death by apoptosis in human breast carcinoma cells. Moreover, predictions of pharmacokinetic properties showed that 8a may present good absorption and permeation characteristics for oral administration. Overall, the current study established 8a as a potential drug prototype to be employed as a DNA interactive cytotoxic agent for the treatment of breast cancer.

Synthesis of 28a-homoselenolupanes and 28a-homoselenolupane saponins

A practical synthesis of 28a-homo-28a-selenolupane triterpenes and the corresponding selenosaponins containing d-mannose, l-arabinose, l-rhamnose, and d-idose moieties is described. Selenium containing triterpenes were obtained from the readily available 3-O-allyl-homobetulin mesylate by nucleophilic substitution with the selenocyanate ion which upon reduction of the -SeCN group afforded the free selenol. Glycosylation using classical Schmidt donors gave 1,2-trans selenosaponins as the main product as well as minute amounts of 1,2-cis isomers. This is one of the very few examples of the synthesis of selenoglycosides by direct glycosylation of free selenols. The studied selenol showed high resistance to air oxidation resulting in good stability during the synthesis of selenolupane derivatives. Cytotoxic activities of new homoselenolupane derivatives were also evaluated in vitro and revealed that some triterpenes exhibited an interesting profile against human cancer cell lines.

Chalcogen-containing phenolics as antiproliferative agents

Aim: The increasing number of cancer cases has stimulated researchers to seek for novel approaches. We have combined two bioactive moieties: a polyphenolic scaffold and an organoselenium motif. Four different families (isothiocyanates/thioureas, and their selenium isosters) derived from dopamine, (±)-norepinephrine and R-epinephrine were accessed. Results: Heterocumulenes derived from dopamine and β-O-methylnoradrenaline were strong antiproliferative agents (GI50<10 μM). Selenoureas derived from β-O-methylnoradrenaline bearing electron-withdrawing groups (halogen, -NO2, -Ph) on the phenyl ring, were also strong antiproliferative agents, besides exhibiting good antiradical and glutathione peroxidase-like activities. Up to a 14-fold increased activity was achieved compared with classical chemotherapeutic agents, exhibiting also different mechanisms of action (cell cycle assays). Redox analysis on HeLa cells suggested an increase of ROS levels after the incubation period. Conclusion: the combination of organoselenium and phenolic moieties might provide valuable lead compounds with relevant antiproliferative properties.

Copper-Catalyzed Decarboxylative/Click Cascade Reaction: Regioselective Assembly of 5-Selenotriazole Anticancer Agents

A simple and efficient Cu-catalyzed decarboxylative/click reaction for the preparation of 1,4-disubstituted 5-arylselanyl-1,2,3-triazoles from propiolic acids, diselenides, and azides has been developed. The mechanistic study revealed that the intermolecular AAC reaction of an alkynyl selenium intermediate occurred. The resulting multisubstituted 5-seleno-1,2,3-triazoles were tested for in vitro anticancer activity by MTT assay, and compounds 4f, 4h, and 4p showed potent cancer cell-growth inhibition activities.

Organoselenium compounds as mimics of selenoproteins and thiol modifier agents

Selenium is an essential trace element for animals and its role in the chemistry of life relies on a unique functional group: the selenol (-SeH) group. The selenol group participates in critical redox reactions. The antioxidant enzymes glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) exemplify important selenoproteins. The selenol group shares several chemical properties with the thiol group (-SH), but it is much more reactive than the sulfur analogue. The substitution of S by Se has been exploited in organic synthesis for a long time, but in the last 4 decades the re-discovery of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) and the demonstration that it has antioxidant and therapeutic properties has renovated interest in the field. The ability of ebselen to mimic the reaction catalyzed by GPx has been viewed as the most important molecular mechanism of action of this class of compound. The term GPx-like or thiol peroxidase-like reaction was previously coined in the field and it is now accepted as the most important chemical attribute of organoselenium compounds. Here, we will critically review the literature on the capacity of organoselenium compounds to mimic selenoproteins (particularly GPx) and discuss some of the bottlenecks in the field. Although the GPx-like activity of organoselenium compounds contributes to their pharmacological effects, the superestimation of the GPx-like activity has to be questioned. The ability of these compounds to oxidize the thiol groups of proteins (the thiol modifier effects of organoselenium compounds) and to spare selenoproteins from inactivation by soft-electrophiles (MeHg⁺, Hg²⁺, Cd²⁺, etc.) might be more relevant for the explanation of their pharmacological effects than their GPx-like activity. In our view, the exploitation of the thiol modifier properties of organoselenium compounds can be harnessed more rationally than the use of low mass molecular structures to mimic the activity of high mass macromolecules that have been shaped by millions to billions of years of evolution.

Ultrasound-promoted copper-catalyzed synthesis of bis-arylselanyl chrysin derivatives with boosted antioxidant and anticancer activities

Herein we report the use of ultrasonic irradiation (US) in the synthesis of six new semi-synthetic selenium-containing chrysin derivatives by a simple and effective methodology utilizing CuI as catalyst, in good to excellent yields (60-89%). It was observed that US accelerates the reaction compared to conventional heating with excellent selectivity for diselenylated products. Compounds were tested for their antioxidant and anticancer activities in vitro and it was observed that the presence of selenium in the A-ring of chrysin enhanced both antioxidant and anticancer properties. Semi-synthetic 6,8-bis(o-tolylselanyl)-chrysin 3b has the best radical scavenging activity of DPPH (I_max: 39.79µM) and ABTS⁺ (IC₅₀: 6.5µM) radicals. Similarly, in the Reactive Species (RS) assay, 3b showed high antioxidant activity in mice cortex (IC₅₀: 5.67µM), whereas 6,8-bis(p-anisoylselanyl)-chrysin 3c was the more active in the hippocampus (IC₅₀: 5.63µM). The Se-chrysins were effective in prevention of lipid peroxidation, highlighting 6,8-bis(p-fluorophenylselanyl)-chrysin 3d in cortex (IC₅₀: 0.54µM) and 3b in hippocampus (IC₅₀: 0.27µM). In addition, 3d was effective in inhibiting human lung adenocarcinoma (A549) cells growth, with a IC₅₀ of 19.9µM after 72h of treatment, while 6,8-bis(p-anisoylselanyl)-chrysin 3c presented the higher antiproliferative activity after 48h of treatment (IC₅₀ of 41.4µM).

Research Progress in the Modification of Quercetin Leading to Anticancer Agents

The flavonoid quercetin (3,3′,4′,5,7-pentahydroxyflavone) is widely distributed in plants, foods, and beverages. This polyphenol compound exhibits varied biological actions such as antioxidant, radical-scavenging, anti-inflammatory, antibacterial, antiviral, gastroprotective, immune-modulator, and finds also application in the treatment of obesity, cardiovascular diseases and diabetes. Besides, quercetin can prevent neurological disorders and exerts protection against mitochondrial damages. Various in vitro studies have assessed the anticancer effects of quercetin, although there are no conclusive data regarding its mode of action. However, low bioavailability, poor aqueous solubility as well as rapid body clearance, fast metabolism and enzymatic degradation hamper the use of quercetin as therapeutic agent, so intense research efforts have been focused on the modification of the quercetin scaffold to obtain analogs with potentially improved properties for clinical applications. This review gives an overview of the developments in the synthesis and anticancer-related activities of quercetin derivatives reported from 2012 to 2016.

Recent advances in gossypol derivatives and analogs: a chemistry and biology view

Gossypol as a natural occurring polyphenol has been studied in a wide range of therapeutic contexts for a long time. The chemical modifications on gossypol were limited due to the unique chemical properties of polyphenols. The design and synthesis of gossypol derivatives and the exploration of their biological activities are the interest of the synthetic chemists, medicinal chemists and pharmacologists. Thus, the progress of diverse gossypol derivatives and analogs' synthesis, biological activities, mechanism elucidation and drug discovery based on gossypol scaffold is summarized.

Rational design and optimization of selenophenes with basic side chains as novel potent selective estrogen receptor modulators (SERMs) for breast cancer therapy

To increase the diversity of estrogen receptor (ER) ligands having novel structures and activities, series of selenophene derivatives with a basic side chain (BSC) were synthesized and their biological activity as subtype-selective antagonists for the ER was explored. Compared with the selenophenes without a BSC, most compounds showed an increase in binding affinity, and several compounds displayed enhanced antagonist potency and antiproliferative activity. Especially, compound 16c exhibited excellent transcriptional activity for ERα (IC50 = 13 nM) which made this compound the most potent antagonist for ERα of the whole series and is 66-fold better than the best selenophene compound without a BSC. Moreover, several compounds showed values of IC50 better than that of 4-hydroxytamoxifen in breast cancer MCF-7 cells. The modeling study indicated that the basic side chain might contribute to their increased antagonist potency and antiproliferative activity. These new ligands have the potential to be further developed as novel agents to improve therapeutics that target the estrogen receptor.

Selenophenes: Introducing a New Element into the Core of Non-Steroidal Estrogen Receptor Ligands

The importance of the heterocyclic core elements with peripheral phenolic and alkyl substituents as a dominant structural motif of ligands for the estrogen receptor (ER) has been well recognized. In this study we expanded the structural diversity of core elements by preparing selenium-containing heterocycles and exploring the activities of these selenophenes on the two ERs, ERα and ERβ. Careful structure-activity relationship (SAR) analysis of their ER binding affinities showed that most selenophenes are ERβ-selective, with the position of the phenol substituents on the selenophene core and the nature of these substituents having a marked effect on their binding affinities. The compound bis(2-fluoro-4-hydroxyphenyl)selenophene (2 f) has the highest relative binding affinity (RBA) of 24.3 for ERβ. In transcription assays, most selenophenes were found to exhibit partial to full agonist activity for both ER subtypes, with compounds bis(2-methyl-4-hydroxyphenyl)selenophene (2 b), bis(4-fluoro-3-hydroxyphenyl)3-bromoselenophene (6 f), and 2,3,5-tris(hydroxyphenyl)thiophenes (8 b and 8 d) profiling as superagonists for ERα; however, several compounds display a range of ERα or ERβ antagonistic activities. A few selenophenes exhibited antiproliferative activity, with compound 8 c showing antiproliferative effects similar to that of 4-hydroxytamoxifen in breast cancer MCF-7 cells while being nontoxic to normal VERO cells. These new ligands could act as models for the development of novel agents leading to improved therapeutics that target the estrogen receptor.

Selenocompounds in Cancer Therapy: An Overview

In vitro and in vivo experimental models clearly demonstrate the efficacy of Se compounds as anticancer agents, contingent upon chemical structures and concentrations of test molecules, as well as on the experimental model under investigation that together influence cellular availability of compounds, their molecular dynamics and mechanism of action. The latter includes direct and indirect redox effects on cellular targets by the activation and altered compartmentalization of molecular oxygen, and the interaction with protein thiols and Se proteins. As such, Se compounds interfere with the redox homeostasis and signaling of cancer cells to produce anticancer effects that include alterations in key regulatory elements of energy metabolism and cell cycle checkpoints that ultimately influence differentiation, proliferation, senescence, and death pathways. Cys-containing proteins and Se proteins involved in the response to Se compounds as sensors and transducers of anticancer signals, i.e., the pharmacoproteome of Se compounds, are described and include critical elements in the different phases of cancer onset and progression from initiation and escape of immune surveillance to tumor growth, angiogenesis, and metastasis. The efficacy and mode of action on these compounds vary depending on the inorganic and organic form of Se used as either supplement or pharmacological agent. In this regard, differences in experimental/clinical protocols provide options for either chemoprevention or therapy in different human cancers.

Novel synthesised flavone derivatives provide significant insight into the structural features required for enhanced anti-proliferative activity

Synthesis and antiproliferative evaluation of a library of 76 methoxy and hydroxy flavones, and their 4-thio analogues showed that the novel thioflavones 15f and 16f exhibit 7–46 fold greater anti-proliferative potency than the natural flavone chrysin (2d).

Selenadiazole derivatives as theranostic agents for simultaneous cancer chemo-/radiotherapy by targeting thioredoxin reductase

Herein we have identified selenadiazole derivatives as effective and safe theranostic agents for simultaneous cancer chemo-/radiotherapy.