A novel triazolic naphthofuranquinone induces autophagy in reservosomes and impairment of mitosis in Trypanosoma cruzi

A review on synthesis of furonaphthoquinones through lawsone derivatives annulation reactions and their biological properties

Furonaphthoquinones and their dihydro derivatives have attracted significant attention due to their diverse pharmacological activities. These compounds can be derived from natural sources, including various plants, or synthesized through chemical methods, resulting in a wide variety of structures with distinct biological properties. As a result, numerous methods have been developed over the past decades for the preparation of these compounds, particularly utilizing 2-hydroxy-1,4-naphthoquinone derivatives as key precursors. Considering these concepts, this review aims to offer a comprehensive overview of the chemical synthesis of linear and angular furonaphthoquinones, along with their dihydro derivatives derived from 2-hydroxy-1,4-naphthoquinones annulation reactions, and to explore their diverse biological activities.

Synthesis of Antiprotozoal 2-(4-Alkyloxyphenyl)-Imidazolines and Imidazoles and Their Evaluation on Leishmania mexicana and Trypanosoma cruzi

Twenty 2-(4-alkyloxyphenyl)-imidazolines and 2-(4-alkyloxyphenyl)-imidazoles were synthesized, with the former being synthesized in two steps by using MW and ultrasonication energy, resulting in good to excellent yields. Imidazoles were obtained in moderate yields by oxidizing imidazolines with MnO2 and MW energy. In response to the urgent need to treat neglected tropical diseases, a set of 2-(4-alkyloxyphenyl)- imidazolines and imidazoles was tested in vitro on Leishmania mexicana and Trypanosoma cruzi. The leishmanicidal activity of ten compounds was evaluated, showing an IC50 < 10 µg/mL. Among these compounds, 27-31 were the most active, with IC50 values < 1 µg/mL (similar to the reference drugs). In the evaluation on epimastigotes of T. cruzi, only 30 and 36 reached an IC50 < 1 µg/mL, showing better inhibition than both reference drugs. However, compounds 29, 33, and 35 also demonstrated attractive trypanocidal activities, with IC50 values < 10 µg/mL, similar to the values for benznidazole and nifurtimox.

Candimine from Hippeastrum escoipense (Amaryllidaceae): Anti-Trypanosoma cruzi activity and synergistic effect with benznidazole

BACKGROUND

Chagas disease (CD), caused by Trypanosoma cruzi, represents a health threat to around 20 million people worldwide. Side effects of benznidazole (Bzn) cause 15-20% of patients to discontinue their treatment. Evidence has increased in favor of the use of drug combinations to improve the efficacy and tolerance of the treatment. Natural products are well known to provide structures that could serve as new drugs or scaffolds for CD treatment. Spp of the Amaryllidoideae sub family of Amaryllidaceae family are known by their bioactives alkaloids, which have been reported by their antiparasitic activities.

PURPOSE

To evaluate the anti-T. cruzi activity of the isolated alkaloid candimine (Cnd) from Hippeastrum escoipense Slanis & Huaylla; and to assess the combination effect between Cnd and Bzn against different life stages of T. cruzi parasites.

METHODS

The chemical profile of H. escoipense alkaloids extract (AE-H. escoipense), including quantitation of Cnd was performed through GC/MS and UPLC-MS/MS techniques. Subsequently, Cnd was isolated using Shephadex LH-20. Then, the AE-H. escoipense and Cnd were tested against T. cruzi, (epimastigotes, trypomastigotes, and amastigotes) by in vitro proliferation and viability assays. The cytotoxicity was evaluated against Vero and HepG2 mammalian cells. The ultrastructural analysis was perform by transmission electron microscopy (TEM) and mitochondrial activity was carried out by MTT assay. Drug combination assay between Cnd and Bzn was evaluated using the Chou-Talalay method.

RESULTS

The AE-H. escoipense and Cnd showed high and specific anti-T. cruzi activity, comparable to Bzn. Cnd induces ultrastructural changes in T. cruzi, such as vacuolization, membrane blebs, and increased mitochondrial activity. Regarding the interaction between Cnd and Bzn, it generates synergism in the combinations of 0.25×IC₅₀ in epimastigotes, 2×IC₅₀ in trypomastigotes+amastigotes, and 0.25, 2, and 4×IC₅₀ in amastigotes.

CONCLUSION

The synergism between Cnd and Bzn indicates that the combination at the concentration of 4×IC₅₀ could be useful as an effective new therapy against CD in the chronic stage. Thus, Cnd isolated from the leaves of H. escoipense emerges as potential candidate for the development of a new drug for the treatment of CD.

Autophagy in protists and their hosts: When, how and why?

Pathogenic protists are a group of organisms responsible for causing a variety of human diseases including malaria, sleeping sickness, Chagas disease, leishmaniasis, and toxoplasmosis, among others. These diseases, which affect more than one billion people globally, mainly the poorest populations, are characterized by severe chronic stages and the lack of effective antiparasitic treatment. Parasitic protists display complex life-cycles and go through different cellular transformations in order to adapt to the different hosts they live in. Autophagy, a highly conserved cellular degradation process, has emerged as a key mechanism required for these differentiation processes, as well as other functions that are crucial to parasite fitness. In contrast to yeasts and mammals, protist autophagy is characterized by a modest number of conserved autophagy-related proteins (ATGs) that, even though, can drive the autophagosome formation and degradation. In addition, during their intracellular cycle, the interaction of these pathogens with the host autophagy system plays a crucial role resulting in a beneficial or harmful effect that is important for the outcome of the infection. In this review, we summarize the current state of knowledge on autophagy and other related mechanisms in pathogenic protists and their hosts. We sought to emphasize when, how, and why this process takes place, and the effects it may have on the parasitic cycle. A better understanding of the significance of autophagy for the protist life-cycle will potentially be helpful to design novel anti-parasitic strategies.

Chalcone Derivative Induces Flagellar Disruption and Autophagic Phenotype in Phytomonas serpens In Vitro

Phytomonas serpens is a trypanosomatid phytoparasite, found in a great variety of species, including tomato plants. It is a significant problem for agriculture, causing high economic loss. In order to reduce the vegetal infections, different strategies have been used. The biological activity of molecules obtained from natural sources has been widely investigated to treat trypanosomatids infections. Among these compounds, chalcones have been shown to have anti-parasitic and anti-inflammatory effects, being described as having a remarkable activity on trypanosomatids, especially in Leishmania species. Here, we evaluated the antiprotozoal activity of the chalcone derivative (NaF) on P. serpens promastigotes, while also assessing its mechanism of action. The results showed that treatment with the derivative NaF for 24 h promotes an important reduction in the parasite proliferation (IC50/24 h = 23.6 ± 4.6 µM). At IC50/24 h concentration, the compound induced an increase in reactive oxygen species (ROS) production and a shortening of the unique flagellum of the parasites. Electron microscopy evaluation reinforced the flagellar phenotype in treated promastigotes, and a dilated flagellar pocket was frequently observed. The treatment also promoted a prominent autophagic phenotype. An increased number of autophagosomes were detected, presenting different levels of cargo degradation, endoplasmic reticulum profiles surrounding different cellular structures, and the presence of concentric membranar structures inside the mitochondrion. Chalcone derivatives may present an opportunity to develop a treatment for the P. serpens infection, as they are easy to synthesize and are low in cost. In order to develop a new product, further studies are still necessary.

Natural naphthoquinones and their derivatives as potential drug molecules against trypanosome parasites

Over the past decades, a number of 1,4-naphthoquinones have been isolated from natural resources and several of naphthoquinone derivatives with diverse structural motif have been synthesized; they possess a multitude of biochemical properties and modulate numerous pharmacological roles that offer new targets for addressing the challenges pertaining to novel drug developments. Among natural naphthoquinones, lapachol, α-lapachone, β-lapachone, lawsone, juglone, and plumbagin have been evaluated for its potential as antitrypanosomal activities. The chemotherapeutic drugs available for combating human trypanosomiasis, that is, American trypanosomiasis and African trypanosomiasis caused by Trypanosoma cruzi and Trypanosoma brucei, respectively, and animal tripanosomosis caused by Trypanosoma evansi have a problem of drug resistance and several toxic effect. Therefore, search of alternative effective drug molecules, without toxic effects, have enthused the researchers for searching new drug entity with potential clinical efficacy. In the search for new antitrypanosomal compound, this review focuses on different natural quinones and their synthetic derivatives associated with antitrypanosomal studies. In this context, this review will be useful for the development of new antitrypanosomal drugs mainly based on different structural modification of natural and synthetic naphthoquinones.

Fexinidazole interferes with the growth and structural organization of Trypanosoma cruzi

Fexinidazole (FEX) is a heterocyclic compound and constitutes the first 100% oral treatment drug for African trypanosomiasis. Its effectiveness against Trypanosoma brucei encouraged the investigation of its antiparasitic potential against T. cruzi, the aetiological agent of Chagas disease. Although previous studies addressed the antitrypanosomal effects of FEX, none used electron microscopy to identify the main target structures of T. brucei or T. cruzi. In this work, we used microscopy techniques to analyze the ultrastructural alterations caused by FEX in different developmental stages of T. cruzi. In addition to inhibiting T. cruzi proliferation, with IC₅₀ of 1 µM for intracellular amastigotes, FEX promoted massive disorganization of reservosomes, the detachment of the plasma membrane, unpacking of nuclear heterochromatin, mitochondrial swelling, Golgi disruption and alterations in the kinetoplast-mitochondrion complex. Together, these observations point to FEX as a potential drug leader for further developing of chemotherapy against Chagas disease.

Different Drugs, Same End: Ultrastructural Hallmarks of Autophagy in Pathogenic Protozoa

Protozoan parasites interact with a wide variety of organisms ranging from bacteria to humans, representing one of the most common causes of parasitic diseases and an important public health problem affecting hundreds of millions of people worldwide. The current treatment for these parasitic diseases remains unsatisfactory and, in some cases, very limited. Treatment limitations together with the increased resistance of the pathogens represent a challenge for the improvement of the patient’s quality of life. The continuous search for alternative preclinical drugs is mandatory, but the mechanisms of action of several of these compounds have not been described. Electron microscopy is a powerful tool for the identification of drug targets in almost all cellular models. Interestingly, ultrastructural analysis showed that several classes of antiparasitic compounds induced similar autophagic phenotypes in trypanosomatids, trichomonadids, and apicomplexan parasites as well as in Giardia intestinalis and Entamoeba spp. with the presence of an increased number of autophagosomes as well as remarkable endoplasmic reticulum profiles surrounding different organelles. Autophagy is a physiological process of eukaryotes that maintains homeostasis by the self-digestion of nonfunctional organelles and/or macromolecules, limiting redundant and damaged cellular components. Here, we focus on protozoan autophagy to subvert drug effects, discussing its importance for successful chemotherapy.

Naphthoquinones and Derivatives for Chemotherapy: Perspectives and Limitations of their Anti-trypanosomatids Activities

Chagas disease, Sleeping sickness and Leishmaniasis, caused by trypanosomatids Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp., respectively, are considered neglected tropical diseases, and they especially affect impoverished populations in the developing world. The available chemotherapies are very limited, and a search for alternatives is still necessary. In folk medicine, natural naphthoquinones have been employed for the treatment of a great variety of illnesses, including parasitic infections. This review is focused on the anti-trypanosomatid activity and mechanistic analysis of naphthoquinones and derivatives. Among all the series of derivatives tested in vitro, naphthoquinone-derived 1,2,3-triazoles were very active on T. cruzi infective forms in blood bank conditions, as well as in amastigotes of Leishmania spp. naphthoquinones containing a CF₃ on a phenyl amine ring inhibited T. brucei proliferation in the nanomolar range, and naphthopterocarpanquinones stood out for their activity on a range of Leishmania species. Some of these compounds showed a promising selectivity index (SI) (30 to 1900), supporting further analysis in animal models. Indeed, high toxicity to the host and inactivation by blood components are crucial obstacles to be overcome to use naphthoquinones and/or their derivatives for chemotherapy. Multidisciplinary initiatives embracing medicinal chemistry, bioinformatics, biochemistry, and molecular and cellular biology need to be encouraged to allow the optimization of these compounds. Large scale automated tests are pivotal for the efficiency of the screening step, and subsequent evaluation of both the mechanism of action in vitro and pharmacokinetics in vivo is essential for the development of a novel, specific and safe derivative, minimizing adverse effects.

Novel N,N-di-alkylnaphthoimidazolium derivative of β-lapachone impaired Trypanosoma cruzi mitochondrial electron transport system

Trypanosoma cruzi is a protozoan parasite that causes Chagas disease, a neglected tropical disease that is endemic in Latin America and spreading worldwide due to globalization. The current treatments are based on benznidazole and nifurtimox; however, these drugs have important limitations and limited efficacy during the chronic phase, reinforcing the necessity of an alternative chemotherapy. For the last 30 years, our group has been evaluating the biological activity of naphthoquinones and derivatives on T. cruzi, and of the compounds tested, N1, N2 and N3 were found to be the most active in vitro. Here, we show the synthesis of a novel β-lapachone-derived naphthoimidazolium named N4 and assess its activity on T. cruzi stages and the mechanism of action. The new compound was very active on all parasite stages (IC₅₀/24 h in the range of 0.8-7.9 μM) and had a selectivity index of 5.4. Mechanistic analyses reveal that mitochondrial ROS production begins after short treatment starts and primarily affects the activity of complexes II-III. After 24 h treatment, a partial restoration of mitochondrial physiology (normal complexes II-III and IV activities and controlled H₂O₂ release) was observed; however, an extensive injury in its morphology was still detected. During treatment with N4, we also observed that trypanothione reductase activity increased in a time-dependent manner and concomitant with increased oxidative stress. Molecular docking calculations indicated the ubiquinone binding site of succinate dehydrogenase as an important interaction point with N4, as with the FMN binding site of dihydroorotate dehydrogenase. The results presented here may be a good starting point for the development of alternative treatments for Chagas disease and for understanding the mechanism of naphthoimidazoles in T. cruzi.

Autophagy in the control and pathogenesis of parasitic infections

Background

Autophagy has a crucial role in the defense against parasites. The interplay existing between host autophagy and parasites has varied outcomes due to the kind of host cell and microorganism. The presence of autophagic compartments disrupt a significant number of pathogens and are further cleared by xenophagy in an autolysosome. Another section of pathogens have the capacity to outwit the autophagic pathway to their own advantage.

Result

To comprehend the interaction between pathogens and the host cells, it is significant to distinguish between starvation-induced autophagy and other autophagic pathways. Subversion of host autophagy by parasites is likely due to differences in cellular pathways from those of ‘classical’ autophagy and that they are controlled by parasites in a peculiar way. In xenophagy clearance at the intracellular level, the pathogens are first ubiquitinated before autophagy receptors acknowledgement, followed by labeling with light chain 3 (LC3) protein. The LC3 in LC3-associated phagocytosis (LAP) is added directly into vacuole membrane and functions regardless of the ULK, an initiation complex. The activation of the ULK complex composed of ATG13, FIP200 and ATG101causes the initiation of host autophagic response. Again, the recognition of PAMPs by conserved PRRs marks the first line of defense against pathogens, involving Toll-like receptors (TLRs). These all important immune-related receptors have been reported recently to regulate autophagy.

Conclusion

In this review, we sum up recent advances in autophagy to acknowledge and understand the interplay between host and parasites, focusing on target proteins for the design of therapeutic drugs. The target host proteins on the initiation of the ULK complex and PRRs-mediated recognition of PAMPs may provide strong potential for the design of therapeutic drugs against parasitic infections.

Clearing or subverting the enemy: Role of autophagy in protozoan infections

The protozoan parasites are evolutionarily divergent, unicellular eukaryotic pathogens representing one of the essential sources of parasitic diseases. These parasites significantly affect the economy and cause public health burdens globally. Protozoan parasites share many cellular features and pathways with their respective host cells. This includes autophagy, a process responsible for self-degradation of the cell's components. There is conservation of the central structural and functional machinery for autophagy in most of the eukaryotic phyla, however, Plasmodium and Toxoplasma possess a decreased number of recognizable autophagy-related proteins (ATG). Plasmodium noticeably lacks clear orthologs of the initiating kinase ATG1/ULK1/2, and both Plasmodium and Toxoplasma lack proteins involved in the nucleation of autophagosomes. These organisms have essential apicoplast, a plastid-like non-photosynthetic organelle, which is an adaptation that is used in penetrating the host cell. Furthermore, available evidence suggests that Leishmania, an intracellular protozoan parasite, induces autophagy in macrophages. The autophagic pathway in Trypanosoma cruzi is activated during metacyclogenesis, a process responsible for the infective forms of parasites. Therefore, numerous pathogens have developed strategies to impair the autophagic mechanism in phagocytes. Regulating autophagy is essential to maintain cellular health as adjustments in the autophagy pathway have been linked to the progression of several physiological and pathological conditions in humans. In this review, we report current advances in autophagy in parasites and their host cells, focusing on the ramifications of these studies in the design of potential anti-protozoan therapeutics.

Autophagy: A necessary process during the Trypanosoma cruzi life-cycle

Autophagy is a well-conserved process of self-digestion of intracellular components. T. cruzi is a protozoan parasite with a complex life-cycle that involves insect vectors and mammalian hosts. Like other eukaryotic organisms, T. cruzi possesses an autophagic pathway that is activated during metacyclogenesis, the process that generates the infective forms of parasites. In addition, it has been demonstrated that mammalian autophagy has a role during host cell invasion by T. cruzi, and that T. cruzi can modulate this process to its own benefit. This review describes the latest findings concerning the participation of autophagy in both the T. cruzi differentiation processes and during the interaction of parasites within the host cells. Data to date suggest parasite autophagy is important for parasite survival and differentiation, which offers interesting prospects for therapeutic strategies. Additionally, the interruption of mammalian autophagy reduces the parasite infectivity, interfering with the intracellular cycle of T. cruzi inside the host. However, the impact on other stages of development, such as the intracellular replication of parasites is still not clearly understood. Further studies in this matter are necessaries to define the integral effect of autophagy on T. cruzi infection with both in vitro and in vivo approaches.

TrypanocidalActivity of Natural Sesquiterpenoids Involves Mitochondrial Dysfunction, ROS Production and Autophagic Phenotype in Trypanosomacruzi

Chagas disease is a neglected tropical disease that is caused by the protozoan Trypanosoma cruzi and represents a serious health problem, especially in Latin America. The clinical treatment of Chagas disease is based on two nitroderivatives that present severe side effects and important limitations. In folk medicine, natural products, including sesquiterpenoids, have been employed for the treatment of different parasitic diseases. In this study, the trypanocidal activity of compounds isolated from the Chilean plants Drimys winteri, Podanthus mitiqui and Maytenus boaria on three T. cruzi evolutive forms (epimastigote, trypomastigote and amastigote) was evaluated. Total extracts and seven isolated sesquiterpenoids were assayed on trypomastigotes and epimastigotes. Polygodial (Pgd) from D. winteri, total extract from P. mitiqui (PmTE) and the germacrane erioflorin (Efr) from P. mitiqui were the most bioactive substances. Pgd, Efr and PmTE also presented strong effects on intracellular amastigotes and low host toxicity. Many ultrastructural effects of these substances, including reservosome disruption, cytosolic vacuolization, autophagic phenotype and mitochondrial swelling (in the case of Pgd), were observed. Flow cytometric analysis demonstrated a reduction in mitochondrial membrane potential in treated epimastigotes and an increase in ROS production and high plasma membrane permeability after treatment with Pgd. The promising trypanocidal activity of these natural sesquiterpenoids may be a good starting point for the development of alternative treatmentsforChagas disease.

Experimental models in Chagas disease: a review of the methodologies applied for screening compounds against Trypanosoma cruzi

One of the main problems of Chagas disease (CD), the parasitic infection caused by Trypanosoma cruzi, is the lack of a completely satisfactory treatment, which is currently based on two old nitroheterocyclic drugs (i.e., nifurtimox and benznidazole) that show important limitations for treating patients. In this context, many laboratories look for alternative therapies potentially applicable to the treatment, and therefore, research in CD chemotherapy works in the design of experimental protocols for detecting molecules with activity against T. cruzi. Phenotypic assays are considered the most valuable strategy for screening these antiparasitic compounds. Among them, in vitro experiments are the first step to test potential anti-T. cruzi drugs directly on the different parasite forms (i.e., epimastigotes, trypomastigotes, and amastigotes) and to detect cytotoxicity. Once the putative trypanocidal drug has been identified in vitro, it must be moved to in vivo models of T. cruzi infection, to explore (i) acute toxicity, (ii) efficacy during the acute infection, and (iii) efficacy in the chronic disease. Moreover, in silico approaches for predicting activity have emerged as a supporting tool for drug screening procedures. Accordingly, this work reviews those in vitro, in vivo, and in silico methods that have been routinely applied during the last decades, aiming to discover trypanocidal compounds that contribute to developing more effective CD treatments.

New 1,2,3-triazole-based analogues of benznidazole for use against Trypanosoma cruzi infection: In vitro and in vivo evaluations

Chagas disease has spread throughout the world mainly because of the migration of infected individuals. In Brazil, only benznidazole (Bnz) is used; however, it is toxic and not active in the chronic phase, and cases of resistance are described. This work aimed at the synthesis and the trypanocidal evaluation in vitro and in vivo of six new Bnz analogues (3-8). They were designed by exploring the bioisosteric substitution between the amide group contained in Bnz and the 1,2,3-triazole ring. All the compounds were synthesized in good yields. With the exception of compound 7, the in vitro biological evaluation shows that all Bnz analogues were active against the amastigote form, whereas only compounds 3, 4, 5, and 8 were active against trypomastigote. Compounds 4 and 5 showed the most promising activities in vitro against the form of trypomastigote, being more active than Bnz. In vivo evaluation of compounds, 3-8 showed lower potency and higher toxicity than Bnz. Although the 1,2,3-triazole ring has been described in the literature as an amide bioisostere, its substitution here has reduced the activity of the compounds and made them more toxic. Thus, further molecular optimization could provide novel therapeutic agents for Chagas' disease.

Trypanosoma cruzi: death phenotypes induced by ortho-naphthoquinone substrates of the aldo-keto reductase (TcAKR). Role of this enzyme in the mechanism of action of β-lapachone

Several ortho-naphthoquinones (o-NQs) have trypanocidal activity against Trypanosoma cruzi, the aetiological agent of Chagas disease. Previously, we demonstrated that the aldo-keto reductase from this parasite (TcAKR) reduces o-NQs, such as β-lapachone (β-Lap) and 9,10-phenanthrenequinone (9,10-PQ), with concomitant reactive oxygen species (ROS) production. Recent characterization of TcAKR activity and expression in two T. cruzi strains, CL Brener and Nicaragua, showed that TcAKR expression is 2.2-fold higher in CL Brener than in Nicaragua. Here, we studied the trypanocidal effect and induction of several death phenotypes by β-Lap and 9,10-PQ in epimastigotes of these two strains. The CL Brener strain was more resistant to both o-NQs than Nicaragua, indicating that greater TcAKR activity is unlikely to be a major influence on o-NQ toxicity. Evaluation of changes in ROS production, mitochondrial membrane potential, phosphatidylserine exposure and monodansylcadaverine labelling evidenced that β-Lap and 9,10-PQ induce different death phenotypes depending on the combination of drug and T. cruzi strain analysed. To study whether TcAKR participates in o-NQ activation in intact parasites, β-Lap and 9,10-PQ trypanocidal effect was next evaluated in TcAKR-overexpressing parasites. Only β-Lap was more effective and induced greater ROS production in TcAKR-overexpressing epimastigotes than in controls, suggesting that TcAKR may participate in β-Lap activation.

Efficacy of 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinone derivatives against different Trypanosoma cruzi discrete type units: Identification of a promising hit compound

The limited efficacy of benznidazole (Bz) indicated by failures of current Phase II clinical trials emphasizes the urgent need to identify new drugs with improved safety and efficacy for treatment of Chagas disease (CD). Herein, we analyzed the efficacy of a series of 2-hydroxy-3-phenylsulfanylmethyl-[1,4]-naphthoquinones against different Trypanosoma cruzi discrete type units (DTUs) of relevant clinical forms of CD. Cytotoxic and trypanocidal effect of naphthoquinone derivatives were assessed in mammalian cells, trypomastigotes and intracellular amastigotes using, luminescent assays (CellTiter-Glo and T. cruzi Dm28c-luciferase) and/or counting with a light microscope. Reactive oxygen species (ROS) production and intracellular targets of promising compounds were assessed with 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) probe and ultrastructural analysis, respectively. ADMET properties were analyzed by in silico modeling. Most of the compounds showed low cytotoxic effect. Only two compounds (Compounds 2 and 11) had IC₅₀ values lower than Bz, showing higher susceptibility of bloodstream trypomastigotes. Compound 2 exhibited greater efficacy against trypomastigotes from different T. cruzi DTUs, even better than Bz against Brazil and CL strains. Ultrastructural analysis revealed changes in intracellular compartments, suggesting autophagy as one possible mechanism of action. Oxidative stress, induced by Compound 2, resulted in elevated level of ROS, leading to parasite death. Compound 2 was also effective against intracellular amastigotes, showing high selectivity index. ADMET analysis predicted good oral bioavailability, reduced drug metabolism and no carcinogenic potential for Compound 2. The data highlight Compound 2 as a hit compound and stimulate further structural and pharmacological optimization to potentiate its trypanocidal activity and selectivity.

The regulation of autophagy differentially affects Trypanosoma cruzi metacyclogenesis

Autophagy is a cellular process required for the removal of aged organelles and cytosolic components through lysosomal degradation. All types of eukaryotic cells from yeasts to mammalian cells have the machinery to activate autophagy as a result of many physiological and pathological situations. The most frequent stimulus of autophagy is starvation and the result, in this case, is the fast generation of utilizable food (e.g. amino acids and basic nutrients) to maintain the vital biological processes. In some organisms, starvation also triggers other associated processes such as differentiation. The protozoan parasite Trypanosoma cruzi undergoes a series of differentiation processes throughout its complex life cycle. Although not all autophagic genes have been identified in the T. cruzi genome, previous works have demonstrated the presence of essential autophagic-related proteins. Under starvation conditions, TcAtg8, which is the parasite homolog of Atg8/LC3 in other organisms, is located in autophagosome-like vesicles. In this work, we have characterized the autophagic pathway during T. cruzi differentiation from the epimastigote to metacyclic trypomastigote form, a process called metacyclogenesis. We demonstrated that autophagy is stimulated during metacyclogenesis and that the induction of autophagy promotes this process. Moreover, with exception of bafilomycin, other classical autophagy modulators have similar effects on T. cruzi autophagy. We also showed that spermidine and related polyamines can positively regulate parasite autophagy and differentiation. We concluded that both polyamine metabolism and autophagy are key processes during T. cruzi metacyclogenesis that could be exploited as drug targets to avoid the parasite cycle progression.

In spite of its old discovery, more than one hundred years ago, Trypanosoma cruzi, the causative agent of Chagas’ disease, is still prevalent in the world, infecting more than 6 million people mostly in Latin America, where this illness is endemic. Only two approved drugs, benznidazole and nifurtimox, are currently used for the treatment of Chagas’ disease. Although efficient for the acute phase, they are poorly effective in the chronic period of the disease and they cause many undesirable side effects. There is an urgent need for therapeutic alternatives. To this end, identifying and validating novel molecular targets is critically relevant. This study describes the effect of different inhibitors on the T. cruzi autophagic pathway, a process required for parasite differentiation. Herein, we demonstrate that the regulation of parasite autophagy exhibits similarities and differences with host cell autophagy. Our study provides new insights that could be used to avoid T. cruzi cycle progression in both insect and mammalian hosts.

Pheophorbide a, a compound isolated from the leaves of Arrabidaea chica, induces photodynamic inactivation of Trypanosoma cruzi

BACKGROUND

Approximately 6-7 million people are infected with Trypanosoma cruzi, the etiological agent of Chagas' disease. Only two therapeutic compounds have been found to be useful against this disease: nifurtimox and benznidazole. These drugs have been effective in the acute phase of the disease but less effective in the chronic phase; they also have many side effects. Thus, the search for new compounds with trypanocidal action is necessary. Natural products can be the source of many important substances for the development of drugs to treat this infection. The present study evaluated the biological activity of an extract and fractions of Arrabidaea chica against T. cruzi and observed morphological and ultrastructural characteristics of parasites exposed to the isolated compound pheophorbide a.

METHODS

The crude hydroethanolic extract of A. chica was prepared. Fractions were obtained by partition and separated by liquid chromatography.

RESULTS

We observed a progressive increase in activity against epimastigote, trypomastigote, and amastigote forms of the parasite over the course of the fractionation process. Interestingly, we isolated a compound known as a photosensitizer that is used in photodynamic therapy. This method of treatment involving a photosensitizer, activation light and molecular oxygen is of great importance due to its selectivity. Pheophorbide a had activity against the protozoan in the presence of light and caused morphological and ultrastructural changes, demonstrating its potential in photodynamic therapy.

CONCLUSIONS

Based on the ability of pheophorbide a to eliminate bloodstream forms of T. cruzi, we suggest its use in blood banks for hemoprophylaxis.

Synthesis and biological evaluation of N-alkyl naphthoimidazoles derived from β-lapachone against Trypanosoma cruzi bloodstream trypomastigotes

The QSAR study of 34 2-aryl-naphthoimidazoles screened so far revealed that σi is the most important factor for their lytic activity on the bloodstream trypomastigote forms of T. cruzi, the etiologic agent of Chagas disease. Based on this result, 16 new N-alkyl-naphthoimidazoles derived from 6,6-dimethyl-3,4,5,6-tetrahydrobenzo[7,8]chromene[5,6-d]imidazole (the product of the reaction of β-lapachone with paraformaldehyde) by its reaction with halo-alkanes were prepared and evaluated against the parasite and peritoneal macrophages. The N1-n-hexyl and N3-n-hexyl naphthoimidazoles were 2.2 and 3.2 times more active than the standard drug benznidazole with selectivity indices of 2.7 and 13.4, respectively.

Effects of a novel β-lapachone derivative on Trypanosoma cruzi: Parasite death involving apoptosis, autophagy and necrosis

Natural products comprise valuable sources for new antiparasitic drugs. Here we tested the effects of a novel β-lapachone derivative on Trypanosoma cruzi parasite survival and proliferation and used microscopy and cytometry techniques to approach the mechanism(s) underlying parasite death. The selectivity index determination indicate that the compound trypanocidal activity was over ten-fold more cytotoxic to epimastigotes than to macrophages or splenocytes. Scanning electron microscopy analysis revealed that the R72 β-lapachone derivative affected the T. cruzi morphology and surface topography. General plasma membrane waving and blebbing particularly on the cytostome region were observed in the R72-treated parasites. Transmission electron microscopy observations confirmed the surface damage at the cytostome opening vicinity. We also observed ultrastructural evidence of the autophagic mechanism termed macroautophagy. Some of the autophagosomes involved large portions of the parasite cytoplasm and their fusion/confluence may lead to necrotic parasite death. The remarkably enhanced frequency of autophagy triggering was confirmed by quantitating monodansylcadaverine labeling. Some cells displayed evidence of chromatin pycnosis and nuclear fragmentation were detected. This latter phenomenon was also indicated by DAPI staining of R72-treated cells. The apoptotis induction was suggested to take place in circa one-third of the parasites assessed by annexin V labeling measured by flow cytometry. TUNEL staining corroborated the apoptosis induction. Propidium iodide labeling indicate that at least 10% of the R72-treated parasites suffered necrosis within 24 h. The present data indicate that the β-lapachone derivative R72 selectively triggers T. cruzi cell death, involving both apoptosis and autophagy-induced necrosis.

Biological approaches to characterize the mode of action of two 5-nitroindazolinone prototypes on Trypanosoma cruzi bloodstream trypomastigotes

The phenotypic activity of two 5-nitroindazolinones, i.e. 2-benzyl-1-propyl (22) and 2-benzyl-1-butyl (24) derivatives, previously proposed as anti-Trypanosoma cruzi prototypes, was presently assayed on bloodstream trypomastigotes (BT) of the moderately drug-resistant Y strain. Further exploration of putative targets and cellular mechanisms involved in their activity was also carried out. Therefore, transmission electron microscopy, high-resolution respirometry and flow cytometry procedures were performed on BT treated for up to 24 h with the respective EC50 value of each derivative. Results demonstrated that although 22 and 24 were not as active as benznidazole in this in vitro assay on BT, both compounds triggered important damages in T. cruzi that lead to the parasite death. Ultrastructural alterations included shedding events, detachment of plasma membrane and nuclear envelope, loss of mitochondrial integrity, besides the occurrence of a large number of intracellular vesicles and profiles of endoplasmic reticulum surrounding cytoplasmic organelles such as mitochondrion. Moreover, both derivatives affected mitochondrion leading to this organelle dysfunction, as reflected by the inhibition in oxygen consumption and the loss of mitochondrial membrane potential. Altogether, the findings exposed in the present study propose autophagic processes and mitochondrial machinery as part of the mode of action of both 5-nitroindazolinones 22 and 24 on T. cruzi trypomastigotes.

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.

Antiparasitic evaluation of betulinic acid derivatives reveals effective and selective anti-Trypanosoma cruzi inhibitors

Betulinic acid is a pentacyclic triterpenoid with several biological properties already described, including antiparasitic activity. Here, the anti-Trypanosoma cruzi activity of betulinic acid and its semi-synthetic amide derivatives (BA1-BA8) was investigated. The anti-Trypanosoma cruzi activity and selectivity were enhanced in semi-synthetic derivatives, specially on derivatives BA5, BA6 and BA8. To understand the mechanism of action underlying betulinic acid anti-T. cruzi activity, we investigated ultrastructural changes by electron microscopy. Ultrastructural studies showed that trypomastigotes incubated with BA5 had membrane blebling, flagella retraction, atypical cytoplasmic vacuoles and Golgi cisternae dilatation. Flow cytometry analysis showed that parasite death is mainly caused by necrosis. Treatment with derivatives BA5, BA6 or BA8 reduced the invasion process, as well as intracellular parasite development in host cells, with a potency and selectivity similar to that observed in benznidazole-treated cells. More importantly, the combination of BA5 and benznidazole revealed synergistic effects on trypomastigote and amastigote forms of T. cruzi. In conclusion, we demonstrated that BA5 compound is an effective and selective anti-T. cruzi agent.

Molecular hybridization as a powerful tool towards multitarget quinoidal systems: synthesis, trypanocidal and antitumor activities of naphthoquinone-based 5-iodo-1,4-disubstituted-, 1,4- and 1,5-disubstituted-1,2,3-triazoles

Some of the hybrid compounds exhibited promising trypanocidal and anticancer activities.

Goulart MO, Cavalcanti BC, Pessoa C, Bruno MP, Corrêa JR, Emery FS, da Silva Júnior EN. Novel fluorescent lapachone-based BODIPY: synthesis, computational and electrochemical aspects, and subcellular localisation of a potent antitumour hybrid quinone

A fully characterized fluorescent lapachone-based BODIPY, a specific mitochondrial-staining agent, is reported.

On the investigation of hybrid quinones: synthesis, electrochemical studies and evaluation of trypanocidal activity

Thirty-eight compounds were evaluated against T. cruzi and six were found to be more potent against trypomastigotes than benznidazole.

Antileishmanial activity of the estrogen receptor modulator raloxifene

Background

The treatment of leishmaniasis relies mostly on parenteral drugs with potentially serious adverse effects. Additionally, parasite resistance in the treatment of leishmaniasis has been demonstrated for the majority of drugs available, making the search for more effective and less toxic drugs and treatment regimens a priority for the control of leishmaniasis. The aims of this study were to evaluate the antileishmanial activity of raloxifene in vitro and in vivo and to investigate its mechanism of action against Leishmania amazonensis.

Methodology/Principal Findings

Raloxifene was shown to possess antileishmanial activity in vitro against several species with EC₅₀ values ranging from 30.2 to 38.0 µM against promastigotes and from 8.8 to 16.2 µM against intracellular amastigotes. Raloxifene's mechanism of action was investigated through transmission electron microscopy and labeling with propidium iodide, DiSBAC₂(3), rhodamine 123 and monodansylcadaverine. Microscopic examinations showed that raloxifene treated parasites displayed autophagosomes and mitochondrial damage while the plasma membrane remained continuous. Nonetheless, plasma membrane potential was rapidly altered upon raloxifene treatment with initial hyperpolarization followed by depolarization. Loss of mitochondrial membrane potential was also verified. Treatment of L. amazonensis – infected BALB/c mice with raloxifene led to significant decrease in lesion size and parasite burden.

Conclusions/Significance

The results of this work extend the investigation of selective estrogen receptor modulators as potential candidates for leishmaniasis treatment. The antileishmanial activity of raloxifene was demonstrated in vitro and in vivo. Raloxifene produces functional disorder on the plasma membrane of L. amazonensis promastigotes and leads to functional and morphological disruption of mitochondria, which culminate in cell death.

Cutaneous and visceral leishmaniasis are part of the group we call neglected diseases. They are serious conditions that afflict millions in vast regions of the world. These diseases are very difficult to treat. This is due to the scanty choice of effective drugs together with their potentially severe side effects. One way of finding new treatments for these neglected conditions is to repurpose drugs that are already in use to treat other diseases. In this paper, we show that raloxifene, a drug that is used for the treatment of osteoporosis and also as an alternative in the treatment of breast cancer, is active against the causative agents of leishmaniasis and is effective in the treatment of cutaneous leishmaniasis in an experimental model. We also show that the antileishmanial mechanism of action of raloxifene is related to damage to the cell membrane and to the mitochondrion of the parasite.

Inhibition of NAD+-dependent histone deacetylases (sirtuins) causes growth arrest and activates both apoptosis and autophagy in the pathogenic protozoan Trypanosoma cruzi

Chagas disease, which is caused by the parasite Trypanosoma cruzi, affects approximately 7-8 million people in Latin America. The drugs available to treat this disease are ineffective against chronic phase disease and are associated with toxic side effects. Therefore, the development of new compounds that can kill T. cruzi at low concentrations is critically important. Herein, we report the effects of a novel 3-arylideneindolin-2-one that inhibits sirtuins, which are highly conserved proteins that are involved in a variety of physiological processes. The compound KH-TFMDI was tested against the epimastigote, trypomastigote and amastigote forms of T. cruzi, and its effects were evaluated using flow cytometry, light and electron microscopy. KH-TFMDI inhibited the replication of T. cruzi intracellular amastigotes with an IC50 of 0.5 ± 0.2 μM, which is significantly lower than the IC50 of benznidazole. The compound also lysed the highly infectious bloodstream trypomastigotes (BST) with LC50 values of 0.8 ± 0.3 μM at 4 °C and 2.5 ± 1.1 μM at 37 °C. KH-TFMDI inhibited cytokinesis and induced several morphological changes in the parasite, leading to its death by apoptosis and autophagy. This study highlights sirtuins as a potential new target for Chagas disease therapy.

A quinoxaline derivative as a potent chemotherapeutic agent, alone or in combination with benznidazole, against Trypanosoma cruzi

Background

Chagas’ disease is a condition caused by the protozoan Trypanosoma cruzi that affects millions of people, mainly in Latin America where it is considered endemic. The chemotherapy for Chagas disease remains a problem; the standard treatment currently relies on a single drug, benznidazole, which unfortunately induces several side effects and it is not successful in the cure of most of the chronic patients. In order to improve the drug armamentarium against Chagas’ disease, in the present study we describe the synthesis of the compound 3-chloro-7-methoxy-2-(methylsulfonyl) quinoxaline (quinoxaline 4) and its activity, alone or in combination with benznidazole, against Trypanosoma cruzi in vitro.

Methodology/Principal Findings

Quinoxaline 4 was found to be strongly active against Trypanosoma cruzi Y strain and more effective against the proliferative forms. The cytotoxicity against LLCMK₂ cells provided selective indices above one for all of the parasite forms. The drug induced very low hemolysis, but its anti-protozoan activity was partially inhibited when mouse blood was added in the experiment against trypomastigotes, an effect that was specifically related to blood cells. A synergistic effect between quinoxaline 4 and benznidazole was observed against epimastigotes and trypomastigotes, accompanied by an antagonistic interaction against LLCMK₂ cells. Quinoxaline 4 induced several ultrastructural alterations, including formations of vesicular bodies, profiles of reticulum endoplasmic surrounding organelles and disorganization of Golgi complex. These alterations were also companied by cell volume reduction and maintenance of cell membrane integrity of treated-parasites.

Conclusion/Significance

Our results demonstrated that quinoxaline 4, alone or in combination with benznidazole, has promising effects against all the main forms of T. cruzi. The compound at low concentrations induced several ultrastructural alterations and led the parasite to an autophagic-like cell death. Taken together these results may support the further development of a combination therapy as an alternative more effective in Chagas’ disease treatment.

The expected outcome of the Trypanosoma cruzi proteomic map: a review of its potential biological applications for drug target discovery

Chagas disease is a neglected tropical illness endemic to Latin America, and its treatment remains unsatisfactory. This disease is caused by the hemoflagellate protozoan Trypanosoma cruzi, which has a complex life cycle involving three evolutive forms in both vertebrate and invertebrate hosts. Targeting metabolic pathways in the parasite for rational drug design represents a promising research field. This research area requires high performance techniques and proteomics become a powerful tool in this context. Here, we review advances in the construction of proteomic maps of the different forms of T. cruzi, emphasizing their biological applications towards the identification of alternative candidates for drug intervention.

Trypanosoma cruzi mitochondrial swelling and membrane potential collapse as primary evidence of the mode of action of naphthoquinone analogues

BACKGROUND

Naphthoquinones (NQs) are privileged structures in medicinal chemistry due to the biological effects associated with the induction of oxidative stress. The present study evaluated the activities of sixteen NQs derivatives on Trypanosoma cruzi.

RESULTS

Fourteen NQs displayed higher activity against bloodstream trypomastigotes of T. cruzi than benznidazole. Further assays with NQ1, NQ8, NQ9 and NQ12 showed inhibition of the proliferation of axenic epimastigotes and intracelulluar amastigotes interiorized in macrophages and in heart muscle cells. NQ8 was the most active NQ against both proliferative forms of T. cruzi. In epimastigotes the four NQs induced mitochondrial swelling, vacuolization, and flagellar blebbing. The treatment with NQs also induced the appearance of large endoplasmic reticulum profiles surrounding different cellular structures and of myelin-like membranous contours, morphological characteristics of an autophagic process. At IC50 concentration, NQ8 totally disrupted the ΔΨm of about 20% of the parasites, suggesting the induction of a sub-population with metabolically inactive mitochondria. On the other hand, NQ1, NQ9 or NQ12 led only to a discrete decrease of TMRE + labeling at IC50 values. NQ8 led also to an increase in the percentage of parasites labeled with DHE, indicative of ROS production, possibly the cause of the observed mitochondrial swelling. The other three NQs behaved similarly to untreated controls.

CONCLUSIONS

NQ1, NQ8, NQ9 and NQ12 induce an autophagic phenotype in T. cruzi epimastigoted, as already observed with others NQs. The absence of oxidative stress in NQ1-, NQ9- and NQ12-treated parasites could be due to the existence of more than one mechanism of action involved in their trypanocidal activity, leaving ROS generation suppressed by the detoxification system of the parasite. The strong redox effect of NQ8 could be associated to the presence of the acetyl group in its structure facilitating quinone reduction, as previously demonstrated by electrochemical analysis. Further experiments using biochemical and molecular approaches are needed to better characterize ROS participation in the mechanism of action of these NQs.

Activities of psilostachyin A and cynaropicrin against Trypanosoma cruzi in vitro and in vivo

In vitro and in vivo activities against Trypanosoma cruzi were evaluated for two sesquiterpene lactones: psilostachyin A and cynaropicrin. Cynaropicrin had previously been shown to potently inhibit African trypanosomes in vivo, and psilostachyin A had been reported to show in vivo effects against T. cruzi, albeit in another test design. In vitro data showed that cynaropicrin was more effective than psilostachyin A. Ultrastructural alterations induced by cynaropicrin included shedding events, detachment of large portions of the plasma membrane, and vesicular bodies and large vacuoles containing membranous structures, suggestive of parasite autophagy. Acute toxicity studies showed that one of two mice died at a cynaropicrin dose of 400 mg/kg of body weight given intraperitoneally (i.p.). Although no major plasma biochemical alterations could be detected, histopathology demonstrated that the liver was the most affected organ in cynaropicrin-treated animals. Although cynaropicrin was as effective as benznidazole against trypomastigotes in vitro, the treatment (once or twice a day) of T. cruzi-infected mice (up to 50 mg/kg/day cynaropicrin) did not suppress parasitemia or protect against mortality induced by the Y and Colombiana strains. Psilostachyin A (0.5 to 50 mg/kg/day given once a day) was not effective in the acute model of T. cruzi infection (Y strain), reaching 100% animal mortality. Our data demonstrate that although it is very promising against African trypanosomes, cynaropicrin does not show efficacy compared to benznidazole in acute mouse models of T. cruzi infection.

In vitro and in vivo studies of the antiparasitic activity of sterol 14α-demethylase (CYP51) inhibitor VNI against drug-resistant strains of Trypanosoma cruzi

Chagas disease affects more than 10 million people worldwide, and yet, as it has historically been known as a disease of the poor, it remains highly neglected. Two currently available drugs exhibit severe toxicity and low effectiveness, especially in the chronic phase, while new drug discovery has been halted for years as a result of a lack of interest from pharmaceutical companies. Although attempts to repurpose the antifungal drugs posaconazole and ravuconazole (inhibitors of fungal sterol 14α-demethylase [CYP51]) are finally in progress, development of cheaper and more efficient, preferably Trypanosoma cruzi-specific, chemotherapies would be highly advantageous. We have recently reported that the experimental T. cruzi CYP51 inhibitor VNI cures with 100% survival and 100% parasitological clearance both acute and chronic murine infections with the Tulahuen strain of T. cruzi. In this work, we further explored the potential of VNI by assaying nitro-derivative-resistant T. cruzi strains, Y and Colombiana, in highly stringent protocols of acute infection. The data show high antiparasitic efficacy of VNI and its derivative (VNI/VNF) against both forms of T. cruzi that are relevant for mammalian host infection (bloodstream and amastigotes), with the in vivo potency, at 25 mg/kg twice a day (b.i.d.), similar to that of benznidazole (100 mg/kg/day). Transmission electron microscopy and reverse mutation tests were performed to explore cellular ultrastructural and mutagenic aspects of VNI, respectively. No mutagenic potential could be seen by the Ames test at up to 3.5 μM, and the main ultrastructural damage induced by VNI in T. cruzi was related to Golgi apparatus and endoplasmic reticulum organization, with membrane blebs presenting an autophagic phenotype. Thus, these preliminary studies confirm VNI as a very promising trypanocidal drug candidate for Chagas disease therapy.

Autophagy in trypanosomatids

Autophagy is a ubiquitous eukaryotic process that also occurs in trypanosomatid parasites, protist organisms belonging to the supergroup Excavata, distinct from the supergroup Opistokontha that includes mammals and fungi. Half of the known yeast and mammalian AuTophaGy (ATG) proteins were detected in trypanosomatids, although with low sequence conservation. Trypanosomatids such as Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. are responsible for serious tropical diseases in humans. The parasites are transmitted by insects and, consequently, have a complicated life cycle during which they undergo dramatic morphological and metabolic transformations to adapt to the different environments. Autophagy plays a major role during these transformations. Since inhibition of autophagy affects the transformation, survival and/or virulence of the parasites, the ATGs offer promise for development of drugs against tropical diseases. Furthermore, various trypanocidal drugs have been shown to trigger autophagy-like processes in the parasites. It is inferred that autophagy is used by the parasites in an-not always successful-attempt to cope with the stress caused by the toxic compounds.