Diglycosyl diselenides alter redox homeostasis and glucose consumption of infective African trypanosomes

Restyling an old scaffold: Ebsulfur analogs with improved activity and selectivity against the infective stage of trypanosomes

Several species of trypanosomatids cause fatal and disabling diseases in humans and livestock animals. The current chemotherapy is limited and new drug candidates with improved efficacy and safety are needed. The benziso-thiazolone (e.g. Ebsulfur, EbS) and -selenazolone (e.g. Ebselen, EbSe) have been extensively investigated for their promising action towards transmissible and non-transmissible diseases. Here, we synthetized 23 benzisothiazolones and tested their anti-trypanosomatid activity against the clinically relevant stages of three major trypanosomatid species (Trypanosoma brucei brucei, Trypanosoma cruzi and Leishmania infantum). Several compounds presented nM or low μM activity and, at least a two-digit selectivity against Trypanosoma sp. but most proved inactive towards L. infantum. Structure-activity relationship analysis reveals that the chemotype of the top hits consisted of phenyl and benzyl rings occupying the N2 position of the benzisothiazolone scaffold and harboring polar substituents in the para position. Most compounds from these two clusters induced a rapid redox unbalance in the intracellular pool of low molecular weight thiols. None of the hits, but EbSe and EbS, affected Trypanothione synthetase activity (the enzyme producing the major low molecular weight thiol of trypanosomatids). However, at large enzyme:compound ratios, some inhibited irreversibly (and covalently) Trypanothione reductase (the enzyme maintaining trypanothione in a reduced state). Some hits exerted a minor effect on the rate of glucose consumption. Preliminary assessment of therapeutic efficacy in a murine infection model of acute African trypanosomiasis, the top candidate could not reduce parasite burden (monitored by in vivo imaging) but extended animal survival.

Organoselenium Compounds in Medicinal Chemistry

The chemical and biological interest in this element and the molecules bearing selenium has been exponentially growing over the years. Selenium, formerly designated as a toxin, becomes a vital trace element for life that appears as selenocysteine and its dimeric form, selenocystine, in the active sites of selenoproteins, which catalyze a wide variety of reactions, including the detoxification of reactive oxygen species and modulation of redox activities. From the point of view of drug developments, organoselenium drugs are isosteres of sulfur-containing and oxygen-containing drugs with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. This statement is the paramount relevance considering the big number of clinically employed compounds bearing sulfur or oxygen atoms in their structures including nucleosides and carbohydrates. Thus, in this article we have focused on the relevant features of the application of selenium in medicinal chemistry. With the increasing interest in selenium chemistry, we have attempted to highlight the most significant published data on this subject, mainly concentrating the analysis on the last years. In consequence, the recent advances of relevant pharmacological organoselenium compounds are discussed.

Modern optical approaches in redox biology: Genetically encoded sensors and Raman spectroscopy

The objective of the current review is to summarize the current state of optical methods in redox biology. It consists of two parts, the first is dedicated to genetically encoded fluorescent indicators and the second to Raman spectroscopy. In the first part, we provide a detailed classification of the currently available redox biosensors based on their target analytes. We thoroughly discuss the main architecture types of these proteins, the underlying engineering strategies for their development, the biochemical properties of existing tools and their advantages and disadvantages from a practical point of view. Particular attention is paid to fluorescence lifetime imaging microscopy as a possible readout technique, since it is less prone to certain artifacts than traditional intensiometric measurements. In the second part, the characteristic Raman peaks of the most important redox intermediates are listed, and examples of how this knowledge can be implemented in biological studies are given. This part covers such fields as estimation of the redox states and concentrations of Fe-S clusters, cytochromes, other heme-containing proteins, oxidative derivatives of thiols, lipids, and nucleotides. Finally, we touch on the issue of multiparameter imaging, in which biosensors are combined with other visualization methods for simultaneous assessment of several cellular parameters.

Selenosugars targeting the infective stage of Trypanosoma brucei with high selectivity

Earlier evidences showed that diglycosyl diselenides are active against the infective stage of African trypanosomes (top hits IC50 0.5 and 1.5 μM) but poorly selective (selectivity index <10). Here we extended the study to 33 new seleno-glycoconjugates with the aim to improve potency and selectivity. Three selenoglycosides and three glycosyl selenenylsulfides displayed IC50 against bloodstream Trypanosoma brucei in the sub-μM range (IC50 0.35-0.77 μM) and four of them showed an improved selectivity (selectivity index >38-folds vs. murine and human macrohages). For the glycosyl selenylsulfides, the anti-trypanosomal activity was not significantly influenced by the nature of the moiety attached to the sulfur atom. Except for a quinoline-, and to a minor extent a nitro-derivative, the most selective hits induced a rapid (within 60 min) and marked perturbation of the LMWT-redox homeostasis. The formation of selenenylsulfide glycoconjugates with free thiols has been identified as a potential mechanism involved in this process.

Multi-target Compounds against Trypanosomatid Parasites and Mycobacterium tuberculosis

Multi-target drug treatment has become popular as a substitute for traditional monotherapy. Monotherapy can lead to resistance and side effects. Multi-target drug discovery is gaining importance as data on bioactivity becomes more abundant. The design of multi-target drugs is expected to be an important development in the pharmaceutical industry in the near future. This review presents multi-target compounds against trypanosomatid parasites (Trypanosoma cruzi, T. brucei, and Leishmania sp.) and tuberculosis (Mycobacterium tuberculosis), which mainly affect populations in socioeconomically unfavorable conditions. The article analyzes the studies, including their chemical structures, viral strains, and molecular docking studies, when available. The objective of this review is to establish a foundation for designing new multi-target inhibitors for these diseases.

Mode of action of p-quinone derivatives with trypanocidal activity studied by experimental and in silico models

Quinones are attractive pharmacological scaffolds for developing new agents for the treatment of different transmissible and non-transmissible human diseases due to their capacity to alter the cell redox homeostasis. The bioactivity and potential mode of action of 19 p-quinone derivatives fused to different aromatic rings (carbo or heterocycles) and harboring distinct substituents were investigated in infective Trypanosoma brucei brucei. All the compounds, except for a furanequinone (EC₅₀₌38 μM), proved to be similarly or even more potent (EC₅₀ = 0.5-5.5 μM) than the clinical drug nifurtimox (EC₅₀ = 5.3 μM). Three furanequinones and one thiazolequinone displayed a higher selectivity than nifurtimox. Two of these selective hits resulted potent inhibitors of T. cruzi proliferation (EC₅₀₌0.8-1.1 μM) but proved inactive against Leishmania infantum amastigotes. Most of the p-quinones induced a rapid and marked intracellular oxidation in T. b. brucei. DFT calculations on the oxidized quinone (Q), semiquinone (Q^•-) and hydroquinone (QH₂) suggest that all quinones have negative ΔG for the formation of Q^•-. Qualitative and quantitative structure-activity relationship analyses in two or three dimensions of different electronic and biophysical descriptors of quinones and their corresponding bioactivities (killing potency and oxidative capacity) were performed. Charge distribution over the quinone ring carbons of Q and Q^.- and the frontier orbitals energies of SUMO (Q^.-) and LUMO (Q) correlate with their oxidative and trypanocidal activity. QSAR analysis also highlighted that both bromine substitution in the p-quinone ring and a bulky phenyl group attached to the furane and thiazole rings (which generates a negative charge due to the π electron system polarized by the nearby heteroatoms) are favorable for activity. By combining experimental and in silico procedures, this study disclosed important information about p-quinones that may help to rationally tune their electronic properties and biological activities.

Small molecules containing chalcogen elements (S, Se, Te) as new warhead to fight neglected tropical diseases

Neglected tropical diseases (NTDs) encompass a group of infectious diseases with a protozoan etiology, high incidence, and prevalence in developing countries. As a result, economic factors constitute one of the main obstacles to their management. Endemic countries have high levels of poverty, deprivation and marginalization which affect patients and limit their access to proper medical care. As a matter of fact, statistics remain uncollected in some affected areas due to non-reporting cases. World Health Organization and other organizations proposed a plan for the eradication and control of the vector, although many of these plans were halted by the COVID-19 pandemic. Despite of the available drugs to treat these pathologies, it exists a lack of effectiveness against several parasite strains. Treatment protocols for diseases such as American trypanosomiasis (Chagas disease), leishmaniasis, and human African trypanosomiasis (HAT) have not achieved the desired results. Unfortunately, these drugs present limitations such as side effects, toxicity, teratogenicity, renal, and hepatic impairment, as well as high costs that have hindered the control and eradication of these diseases. This review focuses on the analysis of a collection of scientific shreds of evidence with the aim of identifying novel chalcogen-derived molecules with biological activity against Chagas disease, leishmaniasis and HAT. Compounds illustrated in each figure share the distinction of containing at least one chalcogen element. Sulfur (S), selenium (Se), and tellurium (Te) have been grouped and analyzed in accordance with their design strategy, chemical synthesis process and biological activity. After an exhaustive revision of the related literature on S, Se, and Te compounds, 183 compounds presenting excellent biological performance were gathered against the different causative agents of CD, leishmaniasis and HAT.

Evaluation of the Anti-Leishmania mexicana and -Trypanosoma brucei Activity and Mode of Action of 4,4'-(Arylmethylene)bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)

Trypanosomiasis and leishmaniasis are neglected infections caused by trypanosomatid parasites. The first-line treatments have many adverse effects, high costs, and are prone to resistance development, hence the necessity for new chemotherapeutic options. In line with this, twenty five 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) derivatives were synthesized and evaluated in vitro for their anti-trypanosomatid activity. Ten and five compounds from this series showed IC50 ≤ 10 µM against the promastigote and the bloodstream stage of Leishmania mexicana and Trypanosoma brucei brucei, respectively. Overall, derivatives with pyrazole rings substituted with electron-withdrawing groups proved more active than those with electron-donating groups. The hits proved moderately selective towards L. mexicana and T. brucei (selectivity index, SI, compared to murine macrophages = 5−26). The exception was one derivative displaying an SI (>111−189) against T. brucei that surpassed, by >6-fold, the selectivity of the clinical drug nifurtimox (SI = 13−28.5). Despite sharing a common scaffold, the hits differed in their mechanism of action, with halogenated derivatives inducing a rapid and marked intracellular oxidative milieu in infective T. brucei. Notably, most of the hits presented better absorption, distribution, metabolism, and excretion (ADME) properties than the reference drugs. Several of the bioactive molecules herein identified represent a promising starting point for further improvement of their trypanosomatid potency and selectivity.

Drug-like molecules with anti-trypanothione synthetase activity identified by high throughput screening

Trypanothione synthetase (TryS) catalyses the synthesis of N¹,N⁸-bis(glutathionyl)spermidine (trypanothione), which is the main low molecular mass thiol supporting several redox functions in trypanosomatids. TryS attracts attention as molecular target for drug development against pathogens causing severe and fatal diseases in mammals. A drug discovery campaign aimed to identify and characterise new inhibitors of TryS with promising biological activity was conducted. A large compound library (n = 51,624), most of them bearing drug-like properties, was primarily screened against TryS from Trypanosoma brucei (TbTryS). With a true-hit rate of 0.056%, several of the TbTryS hits (IC₅₀ from 1.2 to 36 µM) also targeted the homologue enzyme from Leishmania infantum and Trypanosoma cruzi (IC₅₀ values from 2.6 to 40 µM). Calmidazolium chloride and Ebselen stand out for their multi-species anti-TryS activity at low µM concentrations (IC₅₀ from 2.6 to 13.8 µM). The moieties carboxy piperidine amide and amide methyl thiazole phenyl were identified as novel TbTryS inhibitor scaffolds. Several of the TryS hits presented one-digit µM EC₅₀ against T. cruzi and L. donovani amastigotes but proved cytotoxic against the human osteosarcoma and macrophage host cells (selectivity index ≤ 3). In contrast, seven hits showed a significantly higher selectivity against T. b. brucei (selectivity index from 11 to 182). Non-invasive redox assays confirmed that Ebselen, a multi-TryS inhibitor, induces an intracellular oxidative milieu in bloodstream T. b. brucei. Kinetic and mass spectrometry analysis revealed that Ebselen is a slow-binding inhibitor that modifies irreversible a highly conserved cysteine residue from the TryS’s synthetase domain. The most potent TbTryS inhibitor (a singleton containing an adamantine moiety) exerted a non-covalent, non-competitive (with any of the substrates) inhibition of the enzyme. These data feed the drug discovery pipeline for trypanosomatids with novel and valuable information on chemical entities with drug potential.

Selenium and protozoan parasitic infections: selenocompounds and selenoproteins potential

The current drug treatments against protozoan parasitic diseases including Chagas, malaria, leishmaniasis, and toxoplasmosis represent good examples of drug resistance mechanisms and have shown diverse side effects. Therefore, the identification of novel therapeutic strategies and drug compounds against such life-threatening diseases is urgent. According to the successful usage of selenium (Se) compounds-based therapy against some diseases, this therapeutic strategy has been recently further underlined against these parasitic diseases by targeting different parasite´s essential pathways. On the other hand, due to the important functions played by parasite selenoproteins in their biology (such as modulating the host immune response), they can be also considered as a novel therapeutic strategy by designing specific inhibitors against these important proteins. In addition, the immunomodulatory potentiality of these compounds to trigger T helper type 1 (Th1) cells and cytokine-mediated immune response for the substantial induction of proinflammatory cytokines, thus, Se, selenoproteins, and parasite selenoproteins could be further investigated to find possible vaccine antigens. Herein, we collect and present the results of some studies regarding Se-based therapy against protozoan parasitic diseases and highlight relevant information and some viewpoints that might be insightful to advance toward more effective studies in the future.

New phosphoramidates containing selenium as leishmanicidal agents

This work reports the synthesis, characterization by FTIR, ¹H, ¹³C and ⁷⁹Se NMR, mass spectrometry and elemental analysis techniques as well as the in vitro evaluation of the leishmanicidal activity of thirteen new selenophosphoramidate derivatives. Among the new compounds, four of them (compounds 1f, 1g, 2f and 2g), which exhibited the best profile, were tested against infected macrophages and were selected for further studies related their leishmanicidal mechanism. In this regard, trypanothione redox-system alteration was determined. Compound 1g, under similar conditions, was more effective than the corresponding references. In addition, theoretical calculations showed that this compound also presents most physico-chemical and pharmacokinetic properties within the ranges expected for orally available drugs. It is believed that selenophophoramidate functionalities may represent a scaffold to be explored toward the development of new agents for leishmania treatment.

Glucose 6-Phosphate Dehydrogenase from Trypanosomes: Selectivity for Steroids and Chemical Validation in Bloodstream Trypanosoma brucei

Glucose 6-phosphate dehydrogenase (G6PDH) fulfills an essential role in cell physiology by catalyzing the production of NADPH+ and of a precursor for the de novo synthesis of ribose 5-phosphate. In trypanosomatids, G6PDH is essential for in vitro proliferation, antioxidant defense and, thereby, drug resistance mechanisms. So far, 16α-brominated epiandrosterone represents the most potent hit targeting trypanosomal G6PDH. Here, we extended the investigations on this important drug target and its inhibition by using a small subset of androstane derivatives. In Trypanosoma cruzi, immunofluorescence revealed a cytoplasmic distribution of G6PDH and the absence of signal in major organelles. Cytochemical assays confirmed parasitic G6PDH as the molecular target of epiandrosterone. Structure-activity analysis for a set of new (dehydro)epiandrosterone derivatives revealed that bromination at position 16α of the cyclopentane moiety yielded more potent T. cruzi G6PDH inhibitors than the corresponding β-substituted analogues. For the 16α brominated compounds, the inclusion of an acetoxy group at position 3 either proved detrimental or enhanced the activity of the epiandrosterone or the dehydroepiandrosterone derivatives, respectively. Most derivatives presented single digit μM EC50 against infective T. brucei and the killing mechanism involved an early thiol-redox unbalance. This data suggests that infective African trypanosomes lack efficient NADPH+-synthesizing pathways, beyond the Pentose Phosphate, to maintain thiol-redox homeostasis.

New Amides Containing Selenium as Potent Leishmanicidal Agents Targeting Trypanothione Reductase

Two new series of 28 selenocyanate and diselenide derivatives containing amide moieties were designed, synthesized, and evaluated for their leishmanicidal activity against Leishmania infantum axenic amastigotes, and selectivity was assessed in human THP-1 cells. Eleven compounds exhibited excellent leishmanicidal activity with EC₅₀ values lower than the reference drug miltefosine (EC₅₀ = 2.84 μM). In addition, for six of them the selectivity index ranged from 9 to >1,442, greater than both references used. The most potent and selective compounds were compounds 2h, 2k, and 2m that displayed EC₅₀ values of 0.52, 1.19, and 0.50 μM, respectively, and a high selectivity index (SI) when tested against THP-1 monocytic cells (SI = >1,442, >672, and >1,100, respectively). These derivatives showed an efficacy similar to that of the reference drugs but much better SI values. They also showed interesting activity values against infected macrophages. Trypanothione reductase (TryR) activity and intracellular thiol level measurement assays were performed for the three best compounds in an attempt to elucidate their mechanism of action. Despite that the new analogs exhibited comparable or better inhibitory activities than the reference TryR inhibitors, more studies are necessary to confirm this result. In summary, our findings suggest that the three compounds described here could constitute leading leishmanicidal drug candidates.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

A tryparedoxin-coupled biosensor reveals a mitochondrial trypanothione metabolism in trypanosomes

Trypanosomes have a trypanothione redox metabolism that provides the reducing equivalents for numerous essential processes, most being mediated by tryparedoxin (Tpx). While the biosynthesis and reduction of trypanothione are cytosolic, the molecular basis of the thiol redox homeostasis in the single mitochondrion of these parasites has remained largely unknown. Here we expressed Tpx-roGFP2, roGFP2-hGrx1 or roGFP2 in either the cytosol or mitochondrion of Trypanosoma brucei. We show that the novel Tpx-roGFP2 is a superior probe for the trypanothione redox couple and that the mitochondrial matrix harbors a trypanothione system. Inhibition of trypanothione biosynthesis by the anti-trypanosomal drug Eflornithine impairs the ability of the cytosol and mitochondrion to cope with exogenous oxidative stresses, indicating a direct link between both thiol systems. Tpx depletion abolishes the cytosolic, but only partially affects the mitochondrial sensor response to H₂O₂. This strongly suggests that the mitochondrion harbors some Tpx and, another, as yet unidentified, oxidoreductase.

A simple, robust, and affordable bioluminescent assay for drug discovery against infective African trypanosomes

African trypanosomiasis is a major problem for human and animal health in endemic countries, where it threatens millions of people and affects economic development. New drugs are needed to overcome the toxicity, administration, low efficacy, and resistance issues of the current chemotherapy. Robust, simple, and economical high-throughput, whole-cell-based assays are required to accelerate the identification of novel chemical entities. With this aim, we generated a bioluminescent cell line of the bloodstream stage of Trypanosoma brucei brucei and established a screening assay. Trypanosomes were stably transfected to constitutively express a thermostable red-shifted luciferase. The growth phenotype and drug sensitivity of the reporter cell line were essentially identical to that of the parental cell line. The endogenous luciferase activity, measured by a simple bioluminescence assay, proved to be proportional to parasite number and metabolic status. The assay, optimized to detect highly potent compounds in a 96-well-plate format, was validated by screening a small compound library (inter-assay values for Z' factor and coefficient variation were 0.77 and 5.8%, respectively). With a hit-confirmation ratio of ~97%, the assay was potent enough to identify several hits with EC₅₀  ≤ 10 μM. Preliminary tests indicated that the assay can be scaled up to a 384-well-plate format without compromising its robustness. In summary, we have generated reporter trypanosomes and a simple, robust, and affordable bioluminescence screening assay with great potential to speed up the early-phase drug discovery against African trypanosomes.

Novel distamycin analogues that block the cell cycle of African trypanosomes with high selectivity and potency

Polyamides-based compounds related to the Streptomycetal distamycin and netropsin are potent cytostatic molecules that bind to AT-rich regions of the minor groove of the DNA, hence interfering with DNA replication and transcription. Recently, derivatives belonging to this scaffold have been reported to halt the proliferation of deadly African trypanosomes by different and unrelated mechanisms. Here we describe the synthesis and preliminary characterization of the anti-trypanosomal mode of action of new potent and selective distamycin analogues. Two tri-heterocyclic derivatives containing a central N-methyl pyrrole ring (16 and 17) displayed high activity (EC₅₀ < 20 nM) and selectivity (selectivity index >5000 with respect to mammalian macrophages) against the infective form of T. brucei. Both compounds caused cell cycle arrest by blocking the replication of the mitochondrial DNA but without affecting its integrity. This mode of action clearly differs from that reported for classical minor groove binder (MGB) drugs, which induce the degradation of the mitochondrial DNA. In line with this, in vitro assays suggest that 16 and 17 have a comparatively lower affinity for different template DNAs than the MGB drug diminazene. Therapeutic efficacy studies and stability assays suggest that the pharmacological properties of the hits should be optimized. The compounds can be rated as excellent scaffolds for the design of highly potent and selective anti-T. brucei agents.

Bivalent glycoconjugates based on 1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-dione ("bimane") as a central scaffold

The heteroaromatic fused diazabicyclic "bimane" ring system, discovered four decades ago, is endowed with remarkable chemical and photophysical properties. No carbohydrate derivatives of bimanes have, however, been described thus far. Here we report on the syntheses of a range of bimanes decorated with various glycosyl residues. Mono- and disaccharide residues were attached to syn- or anti-bimane central cores via thio-, disulfido- or selenoglycosidic linkages to obtain novel fluorescent or nonfluorescent glycoconjugates. Cu(I)-catalyzed cycloaddition of glycosyl azides to a bimane diethynyl derivative furnished further bivalent glycoconjugates with sugar residues linked to the central bimane core via 1,2,3-triazole rings. We have determined the crystal and molecular structures of several glycosylated and non-glycosylated bimanes and report fluorescence data for the new compounds.

New heterobimetallic ferrocenyl derivatives: Evaluation of their potential as prospective agents against trypanosomatid parasites and Mycobacterium tuberculosis

Searching for prospective agents against infectious diseases, four new ferrocenyl derivatives, [M(L)(dppf)4](PF₆), with M = Pd(II) or Pt(II), dppf = 1,1'-bis(dipheny1phosphino) ferrocene and HL = tropolone (HTrop) or hinokitiol (HHino), were synthesized and characterized. Complexes and ligands were evaluated against the bloodstream form of T. brucei, L. infantum amastigotes, M. tuberculosis (MTB) sensitive strain and MTB clinical isolates. Complexes showed a significant increase of the anti-T. brucei activity with respect to the free ligands (>28- and >46-fold for Trop and 6- and 22-fold for Hino coordinated to Pt-dppf and Pd-dppf, respectively), yielding IC₅₀ values < 5 μM. The complexes proved to be more potent than the antitrypanosomal drug Nifurtimox. The new ferrocenyl derivatives were more selective towards the parasite than the free ligands. The Pt compounds were less toxic on J774 murine macrophages (mammalian cell model), than the Pd ones, showing selectivity index values (SI = IC₅₀ murine macrophage/IC₅₀T. brucei) up to 23. Generation of the {M-dppf} compounds lead to a slightly positive impact on the anti-leishmanial potency. Although the ferrocenyl derivatives were more active on sensitive MTB than the free ligands (MIC₉₀ = 9.88-14.73 μM), they showed low selectivity towards the pathogen. Related to the mechanism of action, the antiparasitic effect cannot be ascribed to an interference of the compounds with the thiol-redox homeostasis of the pathogen. Fluorescence measurements pointed at DNA as a probable target of the new compounds. [Pt(Trop)(dppf)](PF₆) and [Pt(Hino)(dppf)](PF₆) could be considered prospective anti-T. brucei agents that deserve further research.

Aralkyl selenoglycosides and related selenosugars in acetylated form activate protein phosphatase-1 and -2A

Aralkyl and aryl selenoglycosides as well as glycosyl selenocarboxylate derivatives were assayed on the activity of protein phosphatase-1 (PP1) and -2A (PP2A) catalytic subunits (PP1c and PP2Ac) in search of compounds for PP1c and PP2Ac effectors. The majority of tested selenoglycosides activated both PP1c and PP2Ac by ∼2-4-fold in a phosphatase assay with phosphorylated myosin light chain substrate when the hydroxyl groups of the glycosyl moiety were acetylated, but they were without any effects in the non-acetylated forms. A peptide from the myosin phosphatase target subunit-1 (MYPT1^23-38) that included an RVxF PP1c-binding motif attenuated activation of PP1c by 2-Trifluoromethylbenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (TFM-BASG) and 4-Bromobenzyl 2,3,4,6-tetra-O-acetyl-1-seleno-β-d-glucopyranoside (Br-BASG). MYPT1^23-38 stimulated PP2Ac and contributed to PP2Ac activation exerted by either Br-BASG or TFM-BASG. Br-BASG and TFM-BASG suppressed partially binding of PP1c to MYPT1 in surface plasmon resonance based binding experiments. Molecular docking predicted that the hydrophobic binding surfaces in PP1c for interaction with either the RVxF residues of PP1c-interactors or selenoglycosides are partially overlapped. Br-BASG and TFM-BASG caused a moderate increase in the phosphatase activity of HeLa cells in 1 h, and suppressed cell viability in 24 h incubations. In conclusion, our present study identified selenoglycosides as novel activators of PP1 and PP2A as well as provided insights into the structural background of their interactions establishing a molecular model for future design of more efficient phosphatase activator molecules.