Antileishmanial activity of imidothiocarbamates and imidoselenocarbamates

The repertoire of iron superoxide dismutases from Leishmania infantum as targets in the search for therapeutic agents against leishmaniasis

Species of Leishmania and Trypanosoma genera are the causative agents of relevant parasitic diseases. Survival inside their hosts requires the existence of a potent antioxidant enzymatic machinery. Four iron superoxide dismutases have been described in trypanosomatids (FeSODA, FeSODB1, FeSODB2, and FeSODC) that hold a potential as therapeutic targets. Nonetheless, very few studies have been developed that make use of the purified enzymes. Moreover, FeSODC remains uncharacterised in Leishmania. In this work, for the first time, we describe the purification and enzymatic activity of recombinant versions of the four Leishmania FeSOD isoforms and establish an improved strategy for developing inhibitors. We propose a novel parameter [(V*cyt. c - Vcyt. c)/Vcyt. c] which, in contrast to that used in the classical cytochrome c reduction assay, correlates linearly with enzyme concentration. As a proof of concept, we determine the IC50 values of two ruthenium carbosilane metallodendrimers against these isoforms.

Thia- and Seleno-Michael Reactions for the Synthesis of Carbonic Anhydrases Inhibitors

Novel chalcogen-containing amides and esters bearing the benzenesulfonamide moiety have been synthesised upon nucleophilic conjugate addition of thiols and selenols to suitable electron-deficient alkenes. The activity of the synthesised compounds as Carbonic Anhydrases inhibitors has been investigated in vitro and the inhibition mechanism has been elucidated by X-rays studies.

Novel Schiff bases of Vanillin: potent inhibitors of macrophage harbored Leishmania tropica

Due to limited chemotherapeutic options for leishmaniasis, novel synthetic compounds are gaining attention for evaluation against leishmaniasis. This study aimed to synthesize the compound's Schiff bases of Vanillin to investigate and evaluate their anti-leishmanial potentials against intracellular protozoan parasites Leishmania tropica. In the current study, the phenomena of synergism by designing Schiff bases with Vanillin enhances their desired importance. A total of five compounds Schiff bases of Vanillin were synthesized using different aromatic amines and Vanillin. The structural analysis of all the compounds was done through FT-IR (Fourier Transformer-Infrared), thin layer chromatography, and spectroscopic techniques such as 13C-NMR, mass spectrometry, and 1H-NMR. The antimicrobial properties of all the compounds ZI-1, ZI-2, BS-1, KH-1, and FA-2 against promastigotes and amastigotes forms of L. tropica were analyzed at three different concentrations 25, 50, and 100 µg/ml. The in-vitro MTT assay was performed to calculate the percent inhibition, IC50 values, and their cytotoxicity. The highest percent inhibition values against promastigote form of L. tropica were BS-1 53.78% at 25 µg/ml, ZI-2 66.95% at 50 µg/ml, and again ZI-2 76.92% at 100 µg/ml. Similarly, the highest percent inhibition values against intracellular amastigote stage were BS-1 55.77% at 25 µg/ml, ZI-2 67.78% at 50 µg/ml and again ZI-2 84.93% 100 µg/ml. The highest potency was recorded for BS-1 in both stages, with IC50 values of 9.83 and 4.27 µg/ml against promastigotes and intracellular amastigotes, respectively. The percent hemolysis as toxicity; the lowest percent hemolysis was recorded for ZI-1 at three different concentrations of 25, 50, 100 µg/ml of 2.60, 3.50, and 6.31, respectively. These results suggested that all the compounds exhibited anti-leishmanial activity, with BS-1 as the most potent. Further studies are suggested to increase the activity of compounds with structural modifications by the addition of some other synergistic, novel, and analogue compounds.

In vitro Leishmanicidal and Trypanosomicidal Properties of Imidazole-Containing Azine and Benzoazine Derivatives

Leishmaniasis and Chagas diseases are two of the most important parasitic diseases in the world. Both belong to the category of Neglected Tropical Diseases, and they cannot be prevented by vaccination. Their treatments are founded in outdated drugs that possess many pernicious side-effects and they're not easy to administer. With the aim of discovering new compounds that could serve as anti-trypanosomal drugs, an antiparasitic study of a synthetic compound family has been conducted. A series of new 1,4-bis(alkylamino)- and 1-alkylamino-4-chloroazine and benzoazine derivatives 1-4 containing imidazole rings have been synthesized and identified. Their structures showed a possible interest based on previous work. Their in vitro anti-Leishmania infantum, anti-L. braziliensis, anti-L. donovani and anti-T. cruzi activity were tested, as well as the inhibition of Fe-SOD enzymes. It was found that some of them exhibited quite relevant values indicative of being worthy of future more detailed studies, as most of them showed activity to more than only one parasite species, especially compound 3 c was active for the three studied Leishmania species and also for T. cruzi, which is a very interesting trait as it covers a wide spectrum.

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.

Axenic amastigotes of Leishmania species as a suitable model for in vitro studies

Leishmania spp. are etiological agents of infection diseases, which in some cases can be fatal. The main forms of their biological cycle, promastigotes and amastigotes, can be maintained in vitro. While promastigotes are easier to maintain, amastigotes are more complex and can be obtained through different ways, including infection assays of tissues or in vitro cells, and differentiation from promastigotes to axenic amastigotes. Several protocols have been proposed for in vitro differentiation for at least 12 Leishmania spp. of both subgenera, Leishmania and Viannia. In this review we propose a critical summary of axenic amastigotes induction, as well as the impact of these strategies on metabolic pathways and regulatory networks analyzed by omics approaches. The parameters used by different research groups show considerable variations in temperature, pH and induction stages, as highlighted here for Leishmania (Viannia) braziliensis. Therefore, a consensus on strategies for inducing amastigogenesis is necessary to improve accuracy and even define stage-specific biomarkers. In fact, the axenic amastigote model has contributed to elucidate several aspects of the parasite cycle, however, since it does not reproduce the intracellular environment, its use requires several precautions. In addition, we present a discussion about using axenic amastigotes for drug screening, suggesting the need of a more sensitive methodology to verify cell viability in these tests. Collectively, this review explores the advantages and limitations found in studies with axenic amastigotes, done for more than 30 years, and discuss the gaps that impair their use as a suitable model for in vitro studies.

3,5-Dimethyl-4-isoxazoyl selenocyanate as promising agent for the treatment of Leishmania infantum-infected mice

Compounds 1 and 2 (selenocyanate and diselenide derivatives, respectively) were evaluated for their potential use in vivo against visceral leishmaniasis (VL). Both entities showed low cytoxicity in vitro in Vero and Caco-2 cell lines. However, the compounds were not suitable for their oral administration, since they exhibited poor values of intestinal permeability in vitro. Microsomal stability assays did not show any metabolite for compound 1 after 120 min, whereas 2 was highly metabolized by the enzyme CYP450. Thus, the in vivo efficacy of compound 1 was assessed in a murine model of L. infantum VL. The daily i.v. administration of 1 mg/kg of compound 1 during 5 consecutive days reduced parasite load in liver, spleen and bone marrow (99.2%, 91.7% and 61.4%, respectively) compared to non-treated mice. To the best of our knowledge, this is the first time that a selenium compound has been tested in vivo against VL. Thus, this work evidences the possible usefulness of selenocyanate derivatives for the treatment of this disease.

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.

Selenium as an interesting option for the treatment of Chagas disease: A review

Chagas disease is one of the most prevalent tropical neglected diseases and causes high mortality and morbidity in endemic countries. Current treatments for this disease, nifurtimox and benznidazole, are ineffective in the chronic phase of the disease and produce severe adverse effects. Therefore, novel therapies are urgently required. The trace element selenium has an important role in human health, due to its antioxidant, antiinflammatory and pro-immune properties. Actually, its deficiency has been related to several diseases and supplementation with this element has been proven to be beneficial for multiple pathologies. Furthermore, the usefulness of organic-selenium compounds has been studied in many disorders, showing promising results. The aim of this review is to analyse the available literature regarding the role of selenium in Chagas disease in order to determine whether its use could be beneficial for the management of this pathology.

Prolyl Oligopeptidase From Leishmania infantum: Biochemical Characterization and Involvement in Macrophage Infection

Leishmania infantum is a flagellated protozoan and one of the main causative agents of visceral leishmaniasis. This disease usually affects the human reticuloendothelial system, can cause death and available therapies may lead to serious side effects. Since it is a neglected tropical disease, the incentives for the development of new drugs are insufficient. It is important to know Leishmania virulence factors that contribute most to the disease in order to develop drugs. In the present work, we have produced L. infantum prolyl oligopeptidase (rPOPLi) in Escherichia coli, and investigated its biochemical properties as well as the effect of POP inhibitors on its enzymatic activity and on the inhibition of the macrophage infection by L. infantum. The optimal activity occurred at pH 7.5 and 37°C in the presence of DTT, the latter increased rPOPLi catalytic efficiency 5-fold on the substrate N-Suc-Gly-Pro-Leu-Gly-Pro-AMC. The enzyme was inhibited by TPCK, TLCK and by two POP specific inhibitors, Z-Pro-prolinal (ZPP, IC₅₀ 4.2 nM) and S17092 (IC₅₀ 3.5 nM). Besides being a cytoplasmic enzyme, POPLi is also found in punctuate structures within the parasite cytoplasm or associated with the parasite plasma membrane in amastigotes and promastigotes, respectively. Interestingly, S17092 and ZPP prevented parasite invasion in murine macrophages, supporting the involvement of POPLi in the invasive process of L. infantum. These data suggest POPLi as a virulence factor that offers potential as a target for designing new antileishmanial drugs.

Synthesis and Leishmanicidal Activity of Novel Urea, Thiourea, and Selenourea Derivatives of Diselenides

A novel series of thirty-one N-substituted urea, thiourea, and selenourea derivatives containing diphenyldiselenide entities were synthesized, fully characterized by spectroscopic and analytical methods, and screened for their in vitro leishmanicidal activities. The cytotoxic activity of these derivatives was tested against Leishmania infantum axenic amastigotes, and selectivity was assessed in human THP-1 cells. Thirteen of the synthesized compounds showed a significant antileishmanial activity, with 50% effective concentration (EC₅₀) values lower than that for the reference drug miltefosine (EC₅₀, 2.84 μM). In addition, the derivatives 9, 11, 42, and 47, with EC₅₀ between 1.1 and 1.95 μM, also displayed excellent selectivity (selectivity index ranged from 12.4 to 22.7) and were tested against infected macrophages. Compound 11, a derivative with a cyclohexyl chain, exhibited the highest activity against intracellular amastigotes, with EC₅₀ values similar to those observed for the standard drug edelfosine. Structure-activity relationship analyses revealed that N-aliphatic substitution in urea and selenourea is recommended for the leishmanicidal activity of these analogs. Preliminary studies of the mechanism of action for the hit compounds was carried out by measuring their ability to inhibit trypanothione reductase. Even though the obtained results suggest that this enzyme is not the target for most of these derivatives, their activity comparable to that of the standards and lack of toxicity in THP-1 cells highlight the potential of these compounds to be optimized for leishmaniasis treatment.

In vitro antileishmanial activity of fisetin flavonoid via inhibition of glutathione biosynthesis and arginase activity in Leishmania infantum

With the increasing emergence of drug resistant Leishmania sp. in recent years, combination therapy has been considered as a useful way to treat and control of Leishmaniasis. The present study was designed to evaluate the antileishmanial effects of the fisetin alone and combination of fisetin plus Meglumine antimoniate (Fi-MA) against Leishmania infantum. The IC50 values for fisetin were obtained 0.283 and 0.102 μM against promastigotes and amastigote forms, respectively. Meglumine antimoniate (MA, Glucantime) as control drug also revealed IC50 values of 0.247 and 0.105 μM for promastigotes and amastigotes of L. infantum, respectively. In order to determine the mode of action of fisetin and Meglumine antimoniate (MA, Glucantime), the activities of arginase (ARG), catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) were measured. Moreover, intracellular glutathione (GSH) and nitric oxide (NO) levels in L. infantum-infected macrophages and L. infantum promastigotes which were treated with IC50 concentrations of fisetin, MA and Fi-MA were investigated. Our results showed that MA decreased CAT and SOD activity and increased NO levels in L. infantum-infected macrophages. In promastigotes, MA inhibited parasite SOD activity and reduced parasite NO production. The decreased levels of most of the antioxidant enzymes, accompanying by the raised level of NO in treated macrophages with MA, were observed to regain their normal profiles due to Fi-MA treatment. Furthermore, fisetin could prevent the growth of promastigotes by inhibition of ARG activity and reduction of GSH levels and NO production. In conclusion, these findings showed that fisetin improves MA side effects.

Library of Seleno-Compounds as Novel Agents against Leishmania Species

The in vitro leishmanicidal activities of a series of 48 recently synthesized selenium derivatives against Leishmania infantum and Leishmania braziliensis parasites were tested using promastigotes and intracellular amastigote forms. The cytotoxicity of the tested compounds for J774.2 macrophage cells was also measured in order to establish their selectivity. Six of the tested compounds (compounds 8, 10, 11, 15, 45, and 48) showed selectivity indexes higher than those of the reference drug, meglumine antimonate (Glucantime), for both Leishmania species; in the case of L. braziliensis, compound 20 was also remarkably selective. Moreover, data on infection rates and amastigote numbers per macrophage showed that compounds 8, 10, 11, 15, 45, and 48 were the most active against both Leishmania species studied. The observed changes in the excretion product profile of parasites treated with these six compounds were also consistent with substantial cytoplasmic alterations. On the other hand, the most active compounds were potent inhibitors of Fe superoxide dismutase (Fe-SOD) in the two parasite species considered, whereas their impact on human CuZn-SOD was low. The high activity, low toxicity, stability, low cost of the starting materials, and straightforward synthesis make these compounds appropriate molecules for the development of affordable antileishmanicidal agents.

Novel Heteroaryl Selenocyanates and Diselenides as Potent Antileishmanial Agents

A series of new selenocyanates and diselenides bearing interesting bioactive scaffolds (quinoline, quinoxaline, acridine, chromene, furane, isosazole, etc.) was synthesized, and their in vitro leishmanicidal activities against Leishmania infantum amastigotes along with their cytotoxicities in human THP-1 cells were determined. Interestingly, most tested compounds were active in the low micromolar range and led us to identify four lead compounds (1h, 2d, 2e, and 2f) with 50% effective dose (ED50) values ranging from 0.45 to 1.27 μM and selectivity indexes of >25 for all of them, much higher than those observed for the reference drugs. These active derivatives were evaluated against infected macrophages, and in order to gain preliminary knowledge about their possible mechanism of action, the inhibition of trypanothione reductase (TryR) was measured. Among these novel structures, compounds 1h (3,5-dimethyl-4-isoxazolyl selenocyanate) and 2d [3,3'-(diselenodiyldimethanediyl)bis(2-bromothiophene)] exhibited good association between TryR inhibitory activity and antileishmanial potency, pointing to 1h, for its excellent theoretical ADME (absorption, distribution, metabolism, and excretion) properties, as the most promising lead molecule for leishmancidal drug design.

A catalyst- and solvent-free thermal multicomponent approach for the construction of diverse and polysubstituted 2-aminopyridines and their antibacterial activity

A multicomponent approach for the synthesis of polysubstituted 2-aminopyridines under catalyst- and solvent-free thermal conditions has been established.

Molecular descriptors calculation as a tool in the analysis of the antileishmanial activity achieved by two series of diselenide derivatives. An insight into its potential action mechanism

A molecular modeling study has been carried out on two previously reported series of symmetric diselenide derivatives that show remarkable antileishmanial in vitro activity against Leishmania infantum intracellular amastigotes and in infected macrophages (THP-1 cells), in addition to showing favorable selectivity indices. Series 1 consists of compounds that can be considered as central scaffold constructed with a diaryl/dialkylaryl diselenide central nucleus, decorated with different substituents located on the aryl rings. Series 2 consists of compounds constructed over a diaryl diselenide central nucleus, decorated in 4 and 4' positions with an aryl or heteroaryl sulfonamide fragment, thus forming the diselenosulfonamide derivatives. With regard to the diselenosulfonamide derivatives (2 series), the activity can be related, as a first approximation, with (a) the ability to release bis(4-aminophenyl) diselenide, the common fragment which can be ultimately responsible for the activity of the compounds. (b) the anti-parasitic activity achieved by the sulfonamide pharmacophore present in the analyzed derivatives. The data that support this connection include the topography of the molecules, the conformational behavior of the compounds, which influences the bond order, as well as the accessibility of the hydrolysis point, and possibly the hydrophobicity and polarizability of the compounds.

Organocatalyzed oxidative N-annulation for diverse and polyfunctionalized pyridines

A variety of polyfunctionalized pyridines were synthesized from readily available ketones with α,β-unsaturated aldehydes and ammonium acetate under a mild organocatalyst.

Novel hybrid selenosulfonamides as potent antileishmanial agents

Diselenide and sulfonamide derivatives have recently attracted considerable interest as leishmanicidal agents in drug discovery. In this study, a novel series of sixteen hybrid selenosulfonamides has been synthesized and screened for their in vitro activity against Leishmania infantum intracellular amastigotes and THP-1 cells. These assays revealed that most of the compounds exhibited antileishmanial activity in the low micromolar range and led us to identify three lead compounds (derivatives 2, 7 and 14) with IC50 values ranging from 0.83 to 1.47 μM and selectivity indexes (SI) over 17, much higher than those observed for the reference drugs miltefosine and edelfosine. When evaluated against intracellular amastigotes, hybrid compound 7 emerged as the most active compound (IC50 = 2.8 μM), showing higher activity and much less toxicity against THP-1 cells than edelfosine. These compounds could potentially serve as templates for future drug-optimization and drug-development efforts for their use as therapeutic agents in developing countries.

Simple colorimetric trypanothione reductase-based assay for high-throughput screening of drugs against Leishmania intracellular amastigotes

Critical to the search for new anti-leishmanial drugs is the availability of high-throughput screening (HTS) methods to test chemical compounds against the relevant stage for pathogenesis, the intracellular amastigotes. Recent progress in automated microscopy and genetic recombination has produced powerful tools for drug discovery. Nevertheless, a simple and efficient test for measuring drug activity against Leishmania clinical isolates is lacking. Here we describe a quantitative colorimetric assay in which the activity of a Leishmania native enzyme is used to assess parasite viability. Enzymatic reduction of disulfide trypanothione, monitored by a microtiter plate reader, was used to quantify the growth of Leishmania parasites. An excellent correlation was found between the optical density at 412 nm and the number of parasites inoculated. Pharmacological validation of the assay was performed against the conventional alamarBlue method for promastigotes and standard microscopy for intracellular amastigotes. The activity of a selected-compound panel, including several anti-leishmanial reference drugs, demonstrated high consistency between the newly developed assay and the reference method and corroborated previously published data. Quality assessment with standard measures confirmed the robustness and reproducibility of the assay, which performed in compliance with HTS requirements. This simple and rapid assay provides a reliable, accurate method for screening anti-leishmanial agents, with high throughput. The basic equipment and manipulation required to perform the assay make it easy to implement, simplifying the method for scoring inhibitor assays.

Phthalazine derivatives containing imidazole rings behave as Fe-SOD inhibitors and show remarkable anti-T. cruzi activity in immunodeficient-mouse mode of infection

A series of new phthalazine derivatives 1-4 containing imidazole rings were prepared. The monoalkylamino substituted derivatives 2 and 4 were more active in vitro against T. cruzi and less toxic against Vero cells than both their disubstituted analogues and the reference drug benznidazole. Compounds 2 and 4 highly inhibited the antioxidant parasite enzyme Fe-SOD, and molecular modeling suggested that they interact with the H-bonding system of the iron atom moiety. In vivo tests on the acute phase of Chagas disease gave parasitemia inhibition values twice those of benznidazole, and a remarkable decrease in the reactivation of parasitemia was found in the chronic phase for immunodeficient mice. Glucose metabolism studies showed that compounds 1-4 did not affect the succinate pathway but originated important changes in the excretion of pyruvate metabolites. The morphological alterations found in epimastigotes treated with 1-4 confirmed extensive cytoplasm damage and a high mortality rate of parasites.

Cytotoxic and proapototic activities of imidoselenocarbamate derivatives are dependent on the release of methylselenol

In the search for new molecules with potential antiangiogenic activity, we found that several imidoselenocarbamate derivatives effectively suppressed the expression of vascular endothelial growth factor (VEGF) induced by hypoxia in NCI-H157 tumor cells. Mechanistic studies indicated that these compounds inhibited STAT3 phosphorylation triggered by hypoxia, suggesting that inhibition of STAT3 function may play a role in VEGF inhibition. Moreover, these molecules showed interesting proapoptotic and antiproliferative effects. Both the presence of selenium, but not sulfur, and the nature of the radical substituents were important for activity. Interestingly, under hypoxic conditions, several methyl imidoselenocarbamate derivatives released methylselenol, a highly reactive and cytotoxic gas, which was responsible for their biological activities. The kinetics of the release of methylselenol by these molecules was highly dependent on the nature of the substituent radicals and correlated with their early proapoptotic activity. Our results support the notion that pharmacological activities reported for methyl imidoselenocarbamate derivatives are dependent on the release of methylselenol. Given the well-known antitumor activities of this compound, imidoselenocarbamate derivatives represent a promising approach to develop new drugs that release methylselenol in a controlled way.

In vitro and in vivo studies of the trypanocidal activity of four terpenoid derivatives against Trypanosoma cruzi

Four terpenoid derivatives were examined for their activity against Trypanosoma cruzi. Our results show that two compounds were very active in vitro against both extra- and intracellular forms. These compounds, non-toxic for the host cells, are more effective than the reference drug benznidazole. The capacity to infect cells was negatively affected and the number of amastigotes and trypomastigotes was reduced. A wide range of ultrastructural alterations was found in the epimastigote forms treated with these compounds. Some metabolic changes occurred presumably at the level of succinate and acetate production, perhaps caused by the disturbance of the enzymes involved in sugar metabolism inside the mitochondria. In vivo results were consistent with those observed in vitro. The parasitic load was significantly lower than in the control assay with benznidazole. The effects of these products showed the reduction of the anti-T. cruzi antibodies level during the chronic stage.

Selenium compounds, apoptosis and other types of cell death: an overview for cancer therapy

Selenium (Se) is an essential trace element involved in different physiological functions of the human body and plays a role in cancer prevention and treatment. Induction of apoptosis is considered an important cellular event that can account for the cancer preventive effects of Se. The mechanisms of Se-induced apoptosis are associated with the chemical forms of Se and their metabolism as well as the type of cancer studied. So, some selenocompounds, such as SeO₂ involve the activation of caspase-3 while sodium selenite induces apoptosis in the absence of the activation of caspases. Modulation of mitochondrial functions has been reported to play a key role in the regulation of apoptosis and also to be one of the targets of Se compounds. Other mechanisms for apoptosis induction are the modulation of glutathione and reactive oxygen species levels, which may function as intracellular messengers to regulate signaling pathways, or the regulation of kinase, among others. Emerging evidence indicates the overlaps between the apoptosis and other types of cell death such as autophagy. In this review we report different processes of cell death induced by Se compounds in cancer treatment and prevention.

Benzaldehyde thiosemicarbazone derived from limonene complexed with copper induced mitochondrial dysfunction in Leishmania amazonensis

Background

Leishmaniasis is a major health problem that affects more than 12 million people. Treatment presents several problems, including high toxicity and many adverse effects, leading to the discontinuation of treatment and emergence of resistant strains.

Methodology/Principal Findings

We evaluated the in vitro antileishmanial activity of benzaldehyde thiosemicarbazone derived from limonene complexed with copper, termed BenzCo, against Leishmania amazonensis. BenzCo inhibited the growth of the promastigote and axenic amastigote forms, with IC₅₀ concentrations of 3.8 and 9.5 µM, respectively, with 72 h of incubation. Intracellular amastigotes were inhibited by the compound, with an IC₅₀ of 10.7 µM. BenzCo altered the shape, size, and ultrastructure of the parasites. Mitochondrial membrane depolarization was observed in protozoa treated with BenzCo but caused no alterations in the plasma membrane. Additionally, BenzCo induced lipoperoxidation and the production of mitochondrial superoxide anion radicals in promastigotes and axenic amastigotes of Leishmania amazonensis.

Conclusion/Significance

Our studies indicated that the antileishmania activity of BenzCo might be associated with mitochondrial dysfunction and oxidative damage, leading to parasite death.

Leishmanicidal activity of nine novel flavonoids from Delphinium staphisagria

Objectives. To evaluate the in vitro leishmanicidal activity of nine flavonoid derivatives from Delphinium staphisagria against L. infantum and L. braziliensis. Design and Methods. The in vitro activity of compounds 1–9 was assayed on extracellular promastigote and axenic amastigote forms and on intracellular amastigote forms of the parasites. Infectivity and cytotoxicity tests were carried on J774.2 macrophage cells using Glucantime as the reference drug. The mechanisms of action were analysed performing metabolite excretion and transmission electronic microscope ultrastructural alteration studies. Results. Nine flavonoids showed leishmanicidal activity against promastigote as well as amastigote forms of Leishmania infantum and L. braziliensis. These compounds were nontoxic to mammalian cells and were effective at similar concentrations up to or lower than that of the reference drug (Glucantime). The results showed that 2^″-acetylpetiolaroside (compound 8) was clearly the most active. Conclusion. This study has demonstrated that flavonoid derivatives are active against L. infantum and L. braziliensis.

Leishmania major protein disulfide isomerase as a drug target: enzymatic and functional characterization

Leishmaniasis is a major health problem worldwide and tools available for their control are limited. Effective vaccines are still lacking, drugs are toxic and expensive, and parasites develop resistance to chemotherapy. In this context, new antimicrobials are urgently needed to control the disease in both human and animal. Here, we report the enzymatic and functional characterization of a Leishmania virulence factor, Leishmania major Protein disulfide isomerase (LmPDI) that could constitute a potential drug target. LmPDI possesses domain structure organization similar to other PDI family members (a, a', b, b' and c domains), and it displays the three enzymatic and functional activities specific of PDI family members: isomerase, reductase and chaperone. These results suggest that LmPDI plays a key role in assisting Leishmania protein folding via its capacity to catalyze formation, breakage, and rearrangement of disulfide bonds in nascent polypeptides. Moreover, Bacitracin, a reductase activity inhibitor, and Ribostamycin, a chaperone activity inhibitor, were tested in LmPDI enzymatic assays and versus Leishmania promastigote in vitro cultures and Leishmania amastigote multiplication inside infected THP-1-derived macrophages. Bacitracin inhibited both isomerase and reductase activities, while Ribostamycin had no effect on the chaperone activity. Interestingly, Bacitracin blocked in vitro promastigote growth as well as amastigote multiplication inside macrophages with EC(50) values of 39 μM. These results suggest that LmPDI may constitute an interesting target for the development of new anti-Leishmania drugs.

In vitro leishmanicidal activity of imidazole- or pyrazole-based benzo[g]phthalazine derivatives against Leishmania infantum and Leishmania braziliensis species

OBJECTIVES

To evaluate the in vitro leishmanicidal activity of imidazole-based (1-4) and pyrazole-based (5-6) benzo[g]phthalazine derivatives against Leishmania infantum and Leishmania braziliensis.

METHODS

The in vitro activity of compounds 1-6 was assayed on extracellular promastigote and axenic amastigote forms, and on intracellular amastigote forms of the parasites. Infectivity and cytotoxicity tests were performed on J774.2 macrophage cells using meglumine antimoniate (Glucantime) as the reference drug. The mechanisms of action were analysed by iron superoxide dismutase (Fe-SOD) and copper/zinc superoxide dismutase (CuZn-SOD) inhibition, metabolite excretion and transmission electronic microscopy (TEM).

RESULTS

Compounds 1-6 were more active and less toxic than meglumine antimoniate. Data on infection rates and amastigote mean numbers showed that 2, 4 and 6 were more active than 1, 3 and 5 in both L. infantum and L. braziliensis. The inhibitory effect of these compounds on the antioxidant enzyme Fe-SOD of promastigote forms of the parasites was remarkable, whereas inhibition of human CuZn-SOD was negligible. The ultrastructural alterations observed in treated promastigote forms confirmed the greater cell damage caused by the most active compounds 2, 4 and 6. The modifications observed by (1)H-NMR in the nature and amounts of catabolites excreted by the parasites after treatment with 1-6 suggested that the catabolic mechanisms could depend on the structure of the side chains linked to the benzo[g]phthalazine moiety.

CONCLUSIONS

All the compounds assayed were active in vitro against the two Leishmania species and were less toxic against mammalian cells than the reference drug, but the monosubstituted compounds were significantly more effective and less toxic than their disubstituted counterparts.

Luciferase-expressing Leishmania infantum allows the monitoring of amastigote population size, in vivo, ex vivo and in vitro

Here we engineered transgenic Leishmania infantum that express luciferase, the objectives being to more easily monitor in real time their establishment either in BALB/c mice—the liver and spleen being mainly studied—or in vitro. Whatever stationary phase L. infantum promastigotes population—wild type or engineered to express luciferase—the parasite burden was similar in the liver and the spleen at day 30 post the intravenous inoculation of BALB/c mice. Imaging of L. infantum hosting BALB/C mice provided sensitivity in the range of 20,000 to 40,000 amastigotes/mg tissue, two tissues—liver and spleen—being monitored. Once sampled and processed ex vivo for their luciferin-dependent bioluminescence the threshold sensitivity was shown to range from 1,000 to 6,000 amastigotes/mg tissue. This model further proved to be valuable for in vivo measurement of the efficiency of drugs such as miltefosine and may, therefore, additionally be used to evaluate vaccine-induced protection.

Leishmania infantum/L. chagasi parasites are inoculated in the skin of mammals by sand flies. Though most often these L. infantum-mammal interactions are asymptomatic, they can proceed, in some individuals, to a systemic disease known as visceral leishmaniasis. If left untreated this disease is fatal. The lack of protective or curative vaccines and the limited number of parasite-targeting drugs were incentive to set up experimental conditions that could allow easy monitoring of the fluctuation of the population size of parasites in living laboratory animals. Thus, in the present report, we depict two distinct readout assays that rely on a population of L. infantum we genetically engineered for stably expressing the firefly luciferase gene. These transgenic parasites were either inoculated to BALB/c mice or added to a culture of monocytic cells. Post intravenous inoculation, BALB/c mice were imaged over time, with special attention being given to the liver and the spleen. The sensitivity of this technique ranged from 20,000 to 40,000 parasites/mg of tissue and from 1,000 to 6,000 parasites/mg tissue, for in vivo and ex vivo measurements, respectively. Though preliminary, the data, relying on monocytic cells, are promising for further in vitro screening of small compound libraries.