Mechanism of action of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the causative agent of Chagas' disease

Unveiling the Therapeutic Potential of Squalene Synthase: Deciphering Its Biochemical Mechanism, Disease Implications, and Intriguing Ties to Ferroptosis

Squalene synthase (SQS) has emerged as a promising therapeutic target for various diseases, including cancers, owing to its pivotal role in the mevalonate pathway and the antioxidant properties of squalene. Primarily, SQS orchestrates the head-to-head condensation reaction, catalyzing the fusion of two farnesyl pyrophosphate molecules, leading to the formation of squalene, which has been depicted as a highly effective oxygen-scavenging agent in in vitro studies. Recent studies have depicted this isoprenoid as a protective layer against ferroptosis due to its potential regulation of lipid peroxidation, as well as its protection against oxidative damage. Therefore, beyond its fundamental function, recent investigations have unveiled additional roles for SQS as a regulator of lipid peroxidation and programmed cell death pathways, such as ferroptosis-a type of cell death characterized by elevated levels of lipid peroxide, one of the forms of reactive oxygen species (ROS), and intracellular iron concentration. Notably, thorough explorations have shed light on the distinctive features that set SQS apart from other members within the isoprenoid synthase superfamily. Its unique biochemical structure, intricately intertwined with its reaction mechanism, has garnered significant attention. Moreover, considerable evidence substantiates the significance of SQS in various disease contexts, and its intriguing association with ferroptosis and lipid peroxidation. The objective of this report is to analyze the existing literature comprehensively, corroborating these findings, and provide an up-to-date perspective on the current understanding of SQS as a prospective therapeutic target, as well as its intricate relationship with ferroptosis. This review aims to consolidate the knowledge surrounding SQS, thereby contributing to the broader comprehension of its potential implications in disease management and therapeutic interventions.

Potential of sulfur-selenium isosteric replacement as a strategy for the development of new anti-chagasic drugs

Current treatment for Chagas disease is based on only two drugs: benznidazole and nifurtimox. Compounds containing sulfur (S) in their structure have shown promising results in vitro and in vivo against Trypanosoma cruzi, the parasite causing Chagas disease. Notably, some reports show that the isosteric replacement of S by selenium (Se) could be an interesting strategy for the development of new compounds for the treatment of Chagas disease. To date, the activity against T. cruzi of three Se- containing groups has been compared with their S counterparts: selenosemicarbazones, selenoquinones, and selenocyanates. More studies are needed to confirm the positive results of Se compounds. Therefore, we have investigated S compounds described in the literature tested against T. cruzi. We focused on those tested in vivo that allowed isosteric replacement to propose their Se counterparts as promising compounds for the future development of new drugs against Chagas disease.

New Approaches for the Treatment of Chagas Disease

Chagas disease, caused by the protozoan Trypanosoma cruzi is a neglected tropical disease with high prevalence (5.7 million in Latin America, WHO 2015), significant burden, and significant morbimortality mostly due to severe heart disorders during the chronic phase of infection. Chagas disease is endemic in Latin America, and medical care for the disease is the major expense for Brazil's Universal Healthcare System (Sistema Único de Saúde (SUS). The efficacy of the available drugs benznidazole and nifurtimox are low for the chronic phase of Chagas disease, the phase in which most patients are diagnosed, and there are frequent side effects, and drug resistance occurs. The rapid deployment of new drug regimens that are effective for the chronic phase treatment is low-cost and less toxic than the currently available therapy, which is a global priority. Repurposing drugs already in clinical use with other combinations would be the fastest and safest strategy for treating Chagas disease patients. We hypothesize that the combined treatment using repurposing drugs with benznidazole will be more efficacious than benznidazole alone. This needs to be tested further both in vitro and in animal models to understand the efficacy of the treatment before performing human clinical trials. We further hypothesize that producing nanoparticle formulation of the drugs can reduce their toxicity and improve therapeutic use.

Advances in preclinical approaches to Chagas disease drug discovery

Introduction: Chagas disease affects 8-10 million people worldwide, mainly in Latin America. The current therapy for Chagas disease is limited to nifurtimox and benznidazole, which are effective in treating only the acute phase of the disease but with severe side effects. Therefore, there is an unmet need for new drugs and for the exploration of innovative approaches which may lead to the discovery of new effective and safe drugs for its treatment. Areas covered: The authors report and discuss recent approaches including structure-based design that have led to the discovery of new promising small molecule candidates for Chagas disease which affect prime targets that intervene in the sterol pathway of T. cruzi. Other trypanosome targets, phenotypic screening, the use of artificial intelligence and the challenges with Chagas disease drug discovery are also discussed. Expert opinion: The application of recent scientific innovations to the field of Chagas disease have led to the discovery of new promising drug candidates for Chagas disease. Phenotypic screening brought new hits and opportunities for drug discovery. Artificial intelligence also has the potential to accelerate drug discovery in Chagas disease and further research into this is warranted.

Further insights of selenium-containing analogues of WC-9 against Trypanosoma cruzi

As a continuation of our project aimed at searching for new chemotherapeutic agents against American trypanosomiasis (Chagas disease), new selenocyanate derivatives were designed, synthesized and biologically evaluated against the clinically more relevant dividing form of Trypanosoma cruzi, the etiologic agent of this illness. In addition, in order to establish the role of each part of the selenocyanate moiety, different derivatives, in which the selenium atom or the cyano group were absent, were conceived, synthesized and biologically evaluated. In addition, in order to study the optimal position of the terminal phenoxy group, new regioisomers of WC-9 were synthesized and evaluated against T. cruzi. Finally, the resolution of a racemic mixture of a very potent conformationally rigid analogue of WC-9 was accomplished and further tested as growth inhibitors of T. cruzi proliferation. The results provide further insight into the role of the selenocyanate group in its antiparasitic activity.

In Vitro and In Vivo Activities of Sulfur-Containing Linear Bisphosphonates against Apicomplexan Parasites

We tested a series of sulfur-containing linear bisphosphonates against Toxoplasma gondii, the etiologic agent of toxoplasmosis. The most potent compound (compound 22; 1-[(n-decylsulfonyl)ethyl]-1,1-bisphosphonic acid) is a sulfone-containing compound, which had a 50% effective concentration (EC₅₀) of 0.11 ± 0.02 μM against intracellular tachyzoites. The compound showed low toxicity when tested in tissue culture with a selectivity index of >2,000. Compound 22 also showed high activity in vivo in a toxoplasmosis mouse model. The compound inhibited the Toxoplasma farnesyl diphosphate synthase (TgFPPS), but the concentration needed to inhibit 50% of the enzymatic activity (IC₅₀) was higher than the concentration that inhibited 50% of growth. We tested compound 22 against two other apicomplexan parasites, Plasmodium falciparum (EC₅₀ of 0.6 ± 0.01 μM), the agent of malaria, and Cryptosporidium parvum (EC₅₀ of ∼65 μM), the agent of cryptosporidiosis. Our results suggest that compound 22 is an excellent novel compound that could lead to the development of potent agents against apicomplexan parasites.

Activity of Fluorine-Containing Analogues of WC-9 and Structurally Related Analogues against Two Intracellular Parasites: Trypanosoma cruzi and Toxoplasma gondii

Two obligate intracellular parasites, Trypanosoma cruzi, the agent of Chagas disease, and Toxoplasma gondii, an agent of toxoplasmosis, upregulate the mevalonate pathway of their host cells upon infection, which suggests that this host pathway could be a potential drug target. In this work, a number of compounds structurally related to WC-9 (4-phenoxyphenoxyethyl thiocyanate), a known squalene synthase inhibitor, were designed, synthesized, and evaluated for their effect on T. cruzi and T. gondii growth in tissue culture cells. Two fluorine-containing derivatives, the 3-(3-fluorophenoxy)- and 3-(4-fluorophenoxy)phenoxyethyl thiocyanates, exhibited half-maximal effective concentration (EC50 ) values of 1.6 and 4.9 μm, respectively, against tachyzoites of T. gondii, whereas they showed similar potency to WC-9 against intracellular T. cruzi (EC50 values of 5.4 and 5.7 μm, respectively). In addition, 2-[3- (phenoxy)phenoxyethylthio]ethyl-1,1-bisphosphonate, which is a hybrid inhibitor containing 3-phenoxyphenoxy and bisphosphonate groups, has activity against T. gondii proliferation at sub-micromolar levels (EC50 =0.7 μm), which suggests a combined inhibitory effect of the two functional groups.

Quantitative Laser Biospeckle Method for the Evaluation of the Activity of Trypanosoma cruzi Using VDRL Plates and Digital Analysis

In this paper we report a quantitative laser Biospeckle method using VDRL plates to monitor the activity of Trypanosoma cruzi and the calibration conditions including three image processing algorithms and three programs (ImageJ and two programs designed in this work). Benznidazole was used as a test drug. Variable volume (constant density) and variable density (constant volume) were used for the quantitative evaluation of parasite activity in calibrated wells of the VDRL plate. The desiccation process within the well was monitored as a function of volume and of the activity of the Biospeckle pattern of the parasites as well as the quantitative effect of the surface parasite quantity (proportion of the object's plane). A statistical analysis was performed with ANOVA, Tukey post hoc and Descriptive Statistics using R and R Commander. Conditions of volume (100μl) and parasite density (2-4x104 parasites/well, in exponential growth phase), assay time (up to 204min), frame number (11 frames), algorithm and program (RCommander/SAGA) for image processing were selected to test the effect of variable concentrations of benznidazole (0.0195 to 20μg/mL / 0.075 to 76.8μM) at various times (1, 61, 128 and 204min) on the activity of the Biospeckle pattern. The flat wells of the VDRL plate were found to be suitable for the quantitative calibration of the activity of Trypanosoma cruzi using the appropriate algorithm and program. Under these conditions, benznidazole produces at 1min an instantaneous effect on the activity of the Biospeckle pattern of T. cruzi, which remains with a similar profile up to 1 hour. A second effect which is dependent on concentrations above 1.25μg/mL and is statistically different from the effect at lower concentrations causes a decrease in the activity of the Biospeckle pattern. This effect is better detected after 1 hour of drug action. This behavior may be explained by an instantaneous effect on a membrane protein of Trypanosoma cruzi that could mediate the translocation of benznidazole. At longer times the effect may possibly be explained by the required transformation of the pro-drug into the active drug.

Aryloxyethyl Thiocyanates Are Potent Growth Inhibitors of Trypanosoma cruzi and Toxoplasma gondii

As a part of our project aimed at searching for new safe chemotherapeutic agents against parasitic diseases, several compounds structurally related to the antiparasitic agent WC-9 (4-phenoxyphenoxyethyl thiocyanate), which were modified at the terminal phenyl ring, were designed, synthesized, and evaluated as growth inhibitors against Trypanosoma cruzi, the etiological agent of Chagas disease, and Toxoplasma gondii, the parasite responsible of toxoplasmosis. Most of the synthetic analogues exhibited similar antiparasitic activity and were slightly more potent than our lead WC-9. For example, two trifluoromethylated derivatives exhibited ED50 values of 10.0 and 9.2 μM against intracellular T. cruzi, whereas they showed potent action against tachyzoites of T. gondii (ED50 values of 1.6 and 1.9 μM against T. gondii). In addition, analogues of WC-9 in which the terminal aryl group is in the meta position with respect to the alkyl chain bearing the thiocyanate group showed potent inhibitory action against both T. cruzi and T. gondii at the very low micromolar range, which suggests that a para-phenyl substitution pattern is not necessary for biological activity.

Squalene synthase as a target for Chagas disease therapeutics

Trypanosomatid parasites are the causative agents of many neglected tropical diseases and there is currently considerable interest in targeting endogenous sterol biosynthesis in these organisms as a route to the development of novel anti-infective drugs. Here, we report the first x-ray crystallographic structures of the enzyme squalene synthase (SQS) from a trypanosomatid parasite, Trypanosoma cruzi, the causative agent of Chagas disease. We obtained five structures of T. cruzi SQS and eight structures of human SQS with four classes of inhibitors: the substrate-analog S-thiolo-farnesyl diphosphate, the quinuclidines E5700 and ER119884, several lipophilic bisphosphonates, and the thiocyanate WC-9, with the structures of the two very potent quinuclidines suggesting strategies for selective inhibitor development. We also show that the lipophilic bisphosphonates have low nM activity against T. cruzi and inhibit endogenous sterol biosynthesis and that E5700 acts synergistically with the azole drug, posaconazole. The determination of the structures of trypanosomatid and human SQS enzymes with a diverse set of inhibitors active in cells provides insights into SQS inhibition, of interest in the context of the development of drugs against Chagas disease.

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and affects eight million individuals, primarily in Latin America. Currently there is no cure for chronic T. cruzi infections. Unlike humans, this parasite use a variety of sterols (e.g. ergosterol, 24-ethyl-cholesta-5,7,22-trien-3 beta ol, and its 22-dihydro analogs), rather than cholesterol in their cell membranes, so inhibiting endogenous sterol biosynthesis is an important therapeutic target. Here, we report the first structure of the parasite's squalene synthase, which catalyzes the first committed step in sterol biosynthesis, as well as the structures of a broad range of squalene synthase inhibitors active against the clinically relevant intracellular stages, opening the way to new approaches to treating this neglected tropical disease.

Selection of molecular targets for drug development against trypanosomatids

Trypanosomatid parasites are a group of flagellated protozoa that includes the genera Leishmania and Trypanosoma, which are the causative agents of diseases (leishmaniases, sleeping sickness and Chagas disease) that cause considerable morbidity and mortality, affecting more than 27 million people worldwide. Today no effective vaccines for the prevention of these diseases exist, whereas current chemotherapy is ineffective, mainly due to toxic side effects of current drugs and to the emergence of drug resistance and lack of cost effectiveness. For these reasons, rational drug design and the search of good candidate drug targets is of prime importance. The search for drug targets requires a multidisciplinary approach. To this end, the completion of the genome project of many trypanosomatid species gives a vast amount of new information that can be exploited for the identification of good drug candidates with a prediction of "druggability" and divergence from mammalian host proteins. In addition, an important aspect in the search for good drug targets is the "target identification" and evaluation in a biological pathway, as well as the essentiality of the gene in the mammalian stage of the parasite, which is provided by basic research and genetic and proteomic approaches. In this chapter we will discuss how these bioinformatic tools and experimental evaluations can be integrated for the selection of candidate drug targets, and give examples of metabolic and signaling pathways in the parasitic protozoa that can be exploited for rational drug design.

Toxoplasma gondii relies on both host and parasite isoprenoids and can be rendered sensitive to atorvastatin

Intracellular pathogens have complex metabolic interactions with their host cells to ensure a steady supply of energy and anabolic building blocks for rapid growth. Here we use the obligate intracellular parasite Toxoplasma gondii to probe this interaction for isoprenoids, abundant lipidic compounds essential to many cellular processes including signaling, trafficking, energy metabolism, and protein translation. Synthesis of precursors for isoprenoids in Apicomplexa occurs in the apicoplast and is essential. To synthesize longer isoprenoids from these precursors, T. gondii expresses a bifunctional farnesyl diphosphate/geranylgeranyl diphosphate synthase (TgFPPS). In this work we construct and characterize T. gondii null mutants for this enzyme. Surprisingly, these mutants have only a mild growth phenotype and an isoprenoid composition similar to wild type parasites. However, when extracellular, the loss of the enzyme becomes phenotypically apparent. This strongly suggests that intracellular parasite salvage FPP and/or geranylgeranyl diphosphate (GGPP) from the host. We test this hypothesis using inhibitors of host cell isoprenoid synthesis. Mammals use the mevalonate pathway, which is susceptible to statins. We document strong synergy between statin treatment and pharmacological or genetic interference with the parasite isoprenoid pathway. Mice can be cured with atorvastatin (Lipitor) from a lethal infection with the TgFPPs mutant. We propose a double-hit strategy combining inhibitors of host and parasite pathways as a novel therapeutic approach against Apicomplexan parasites.

Toxoplasma gondii is an obligate intracellular parasite and is not able to replicate outside the host cell. The parasite lives in a specialized parasitophorous vacuole in contact with the host cytoplasm through the parasitophorous vacuole membrane. It is highly likely that a very active exchange of metabolites occurs between parasite and host cell. We present evidence for this exchange for isoprenoids, abundant lipidic compounds essential to many cellular processes including signaling, trafficking, energy metabolism, and protein translation. Our work shows that intracellular T. gondii tachyzoites are able to salvage farnesyl diphosphate (FPP) and/or geranylgeranyl diphosphate (GGPP) from the host, and the parasite is able to grow even when its endogenous production is shut down. However, when extracellular, the parasite depends entirely on its own production of isoprenoids. We propose to use a combination of inhibitors that would hit both the host and the parasite pathways as a novel therapeutic approach against Toxoplasma gondii that could also work against other Apicomplexan parasites.

Design, synthesis and biological evaluation of WC-9 analogs as antiparasitic agents

As a part of our project pointed at the search of new safe chemotherapeutic and chemoprophylactic agents against parasitic diseases, several compounds structurally related to 4-phenoxyphenoxyethyl thiocyanate (WC-9), which were modified at the terminal aromatic ring, were designed, synthesized and evaluated as antiproliferative agents against Trypanosoma cruzi, the parasite responsible of American trypanosomiasis (Chagas disease) and Toxoplasma gondii, the etiological agent of toxoplasmosis. Most of the synthetic analogs exhibited similar antiparasitic activity being slightly more potent than the reference compound WC-9. For example, the nitro derivative 13 showed an ED₅₀ value of 5.2 μM. Interestingly, the regioisomer of WC-9, compound 36 showed similar inhibitory action than WC-9 indicating that para-phenyl substitution pattern is not necessarily required for biological activity. The biological evaluation against T. gondii was also very promising. The ED₅₀ values corresponding for 13, 36 and 37 were at the very low micromolar level against tachyzoites of T. gondii.

Head-to-head prenyl tranferases: anti-infective drug targets

We report X-ray crystallographic structures of three inhibitors bound to dehydrosqualene synthase from Staphylococcus aureus: 1 (BPH-651), 2 (WC-9), and 3 (SQ-109). Compound 2 binds to the S2 site with its -SCN group surrounded by four hydrogen bond donors. With 1, we report two structures: in both, the quinuclidine headgroup binds in the allylic (S1) site with the side chain in S2, but in the presence of PPi and Mg(2+), the quinuclidine's cationic center interacts with PPi and three Mg(2+), mimicking a transition state involved in diphosphate ionization. With 3, there are again two structures. In one, the geranyl side chain binds to either S1 or S2 and the adamantane headgroup binds to S1. In the second, the side chain binds to S2 while the headgroup binds to S1. These results provide structural clues for the mechanism and inhibition of the head-to-head prenyl transferases and should aid future drug design.

New antibacterials for the treatment of toxoplasmosis; a patent review

INTRODUCTION

Toxoplasma gondii is an opportunistic protozoan parasite responsible for toxoplasmosis. T. gondii is able to infect a wide range of hosts, particularly humans and warm-blooded animals. Toxoplasmosis can be considered as one of the most prevalent parasitic diseases affecting close to one billion people worldwide, but its current chemotherapy is still deficient and is only effective in the acute phase of the disease.

AREAS COVERED

This review covers different approaches to toxoplasmosis chemotherapy focused on the metabolic differences between the host and the parasite. Selective action on different targets such as the isoprenoid pathway, dihydrofolate reductase, T. gondii adenosine kinase, different antibacterials, T. gondii histone deacetylase and calcium-dependent protein kinases is discussed.

EXPERT OPINION

A new and safe chemotherapy is needed, as T. gondii causes serious morbidity and mortality in pregnant women and immunodeficient patients undergoing chemotherapy. A particular drawback of the available treatments is the lack of efficacy against the tissue cyst of the parasite. During this review a broad scope of several attractive targets for drug design have been presented. In this context, the isoprenoid pathway, dihydrofolate reductase, T. gondii histone deacetylase are promising molecular targets.

Synthesis and biological evaluation of new 2-alkylaminoethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii targeting farnesyl diphosphate synthase

The effect of long-chain 2-alkylaminoethyl-1,1-bisphosphonates against proliferation of the clinically more relevant form of Trypanosoma cruzi, the etiologic agent of American trypanosomiasis (Chagas' disease), and against tachyzoites of Toxoplasma gondii was investigated. Particularly, compound 26 proved to be an extremely potent inhibitor against the intracellular form of T. cruzi, exhibiting IC(50) values at the nanomolar range. This cellular activity was associated with a strong inhibition of the enzymatic activity of T. cruzi farnesyl diphosphate synthase (TcFPPS), which constitutes a valid target for Chagas' disease chemotherapy. Compound 26 was an effective agent against T. cruzi (amastigotes) exhibiting an IC(50) value of 0.67 μM, while this compound showed an IC(50) value of 0.81 μM against the target enzyme TcFPPS. This drug was less effective against the enzymatic activity of T. cruzi solanesyl diphosphate synthase TcSPPS showing an IC(50) value of 3.2 μM. Interestingly, compound 26 was also very effective against T. gondii (tachyzoites) exhibiting IC(50) values of 6.23 μM. This cellular activity was also related to the inhibition of the enzymatic activity towards the target enzyme TgFPPS (IC(50)=0.093 μM) As bisphosphonate-containing compounds are FDA-approved drugs for the treatment of bone resorption disorders, their potential low toxicity makes them good candidates to control different tropical diseases.

Specific chemotherapy of Chagas disease: relevance, current limitations and new approaches

A critical review of the development of specific chemotherapeutic approaches for the management of American Trypanosomiasis or Chagas disease is presented, including controversies on the pathogenesis of the disease, the initial efforts that led to the development of currently available drugs (nifurtimox and benznidazole), limitations of these therapies and novel approaches for the development of anti-Trypanosoma cruzi drugs, based on our growing understanding of the biology of this parasite. Among the later, the most promising approaches are ergosterol biosynthesis inhibitors such as posaconazole and ravuconazole, poised to enter clinical trials for chronic Chagas disease in the short term; inhibitors of cruzipain, the main cysteine protease of T. cruzi, essential for its survival and proliferation in vitro and in vivo; bisphosphonates, metabolic stable pyrophosphate analogs that have trypanocidal activity through the inhibition of the parasite's farnesyl-pyrophosphate synthase or hexokinase; inhibitors of trypanothione synthesis and redox metabolism and inhibitors of hypoxanthine-guanine phosphoribosyl-transferase, an essential enzyme for purine salvage in T. cruzi and related organisms. Finally, the economic and political challenges faced by development of drugs for the treatment of neglected tropical diseases, which afflict almost exclusively poor populations in developing countries, are analyzed and recent potential solutions for this conundrum are discussed.

Synthetic Medicinal Chemistry in Chagas' Disease: Compounds at The Final Stage of "Hit-To-Lead" Phase

Chagas' disease, or American trypanosomosiasis, has been the most relevant illness produced by protozoa in Latin America. Synthetic medicinal chemistry efforts have provided an extensive number of chemodiverse hits at the "active-to-hit" stage. However, only a more limited number of these have been studied in vivo in models of Chagas' disease. Herein, we survey some of the cantidates able to surpass the "hit-to-lead" stage discussing their limitations or merit to enter in clinical trials in the short term.

Ergosterol biosynthesis and drug development for Chagas disease

This article presents an overview of the currently available drugs nifurtimox (NFX) and benznidazole (BZN) used against Trypanosoma cruzi, the aetiological agent of Chagas disease; herein we discuss their limitations along with potential alternatives with a focus on ergosterol biosynthesis inhibitors (EBI). These compounds are currently the most advanced candidates for new anti-T. cruzi agents given that they block de novo production of 24-alkyl-sterols, which are essential for parasite survival and cannot be replaced by a host's own cholesterol. Among these compounds, new triazole derivatives that inhibit the parasite's C14alpha sterol demethylase are the most promising, as they have been shown to have curative activity in murine models of acute and chronic Chagas disease and are active against NFX and BZN-resistant T. cruzi strains; among this class of compounds, posaconazole (Schering-Plough Research Institute) and ravuconazole (Eisai Company) are poised for clinical trials in Chagas disease patients in the short term. Other T. cruzi-specific EBI, with in vitro and in vivo potency, include squalene synthase, lanosterol synthase and squalene epoxidase-inhibitors as well as compounds with dual mechanisms of action (ergosterol biosynthesis inhibition and free radical generation), but they are less advanced in their development process. The main putative advantages of EBI over currently available therapies include their higher potency and selectivity in both acute and chronic infections, activity against NFX and BZN-resistant T. cruzi strains, and much better tolerability and safety profiles. Limitations may include complexity and cost of manufacture of the new compounds. As for any new drug, such compounds will require extensive clinical testing before being introduced for clinical use, and the complexity of such studies, particularly in chronic patients, will be compounded by the current limitations in the verification of true parasitological cures for T. cruzi infections.

Synthesis and biological evaluation of 2-alkylaminoethyl-1,1-bisphosphonic acids against Trypanosoma cruzi and Toxoplasma gondii targeting farnesyl diphosphate synthase

The effect of a series of 2-alkylaminoethyl-1,1-bisphosphonic acids against proliferation of the clinically more relevant form of Trypanosoma cruzi, the etiologic agent of American trypanosomiasis (Chagas' disease), and against tachyzoites of Toxoplasma gondii has been studied. Most of these drugs exhibited an extremely potent inhibitory action against the intracellular form of T. cruzi, exhibiting IC(50) values at the low micromolar level. This cellular activity was associated with a strong inhibition of the enzymatic activity of T. cruzi farnesyl diphosphate synthase (TcFPPS), which constitutes a valid target for Chagas' disease chemotherapy. Compound 17 was an effective agent against amastigotes exhibiting an IC(50) value of 0.84 microM, while this compound showed an IC(50) value of 0.49 microM against the target enzyme TcFPPS. Interestingly, compound 19 was very effective against both T. cruzi and T. gondii exhibiting IC(50) values of 4.1 microM and 2.6 microM, respectively. In this case, 19 inhibited at least two different enzymes of T. cruzi (TcFPPS and solanesyl diphosphate synthase (TcSPPS); 1.01 microM and 0.25 microM, respectively), while it inhibited TgFPPS in T. gondii. In general, this family of drugs was less effective against the activity of T. cruzi SPPS and against T. gondii growth in vitro. As bisphosphonate-containing compounds are FDA-approved drugs for the treatment of bone resorption disorders, their potential low toxicity makes them good candidates to control tropical diseases.

Synthesis, Cruzain Docking, and in vitro Studies of Aryl-4-Oxothiazolylhydrazones AgainstTrypanosoma cruzi

Research in recent years has demonstrated that the Trypanosoma cruzi cysteine protease cruzain (TCC) is a valid chemotherapeutic target. Herein we describe a small library of aryl-4-oxothiazolylhydrazones that have been tested in assays against T. cruzi cell cultures. The docking studies carried out suggest that these compounds are potential ligands for the TCC enzyme. The most promising compound of this series, N-(4-oxo-5-ethyl-2'-thiazolin-2-yl)-N'-phenylthio-(Z)-ethylidenehydrazone (6 f), was shown to be very active at non-cytotoxic concentrations in in vitro assays with mammalian cells and has a potency comparable with reference drugs such as nifurtimox (Nfx) and benznidazole (Bdz).

Cardiac manifestations of parasitic infections part 1: overview and immunopathogenesis

Parasitic infections produce a wide spectrum of cardiac manifestations. They may involve various anatomic structures of the heart and are manifested clinically as myocarditis, cardiomyopathies, pericarditis, or pulmonary hypertension in many resource-constrained settings. However, many parasitic infections involving the heart may also be currently diagnosed in developed countries due to growing worldwide travel, blood transfusions, and increasing numbers of immunosuppression states such as organ transplantation, use of immunosuppressive agents, or HIV/AIDS. Clinicians anywhere in the globe need to be aware of the potential cardiac manifestations of parasitic diseases. This is part one of a three-part series discussing parasites of the heart. In this section, we provide a general overview and immunopathogenesis of parasitic infections of the heart.

Fluorine-containing aryloxyethyl thiocyanate derivatives are potent inhibitors of Trypanosoma cruzi and Toxoplasma gondii proliferation

As a part of our project aimed at developing new safe chemotherapeutic and chemoprophylactic agents against tropical diseases, fluorine-containing drugs structurally related to 4-phenoxyphenoxyethyl thiocyanate (1) were designed, synthesized, and evaluated as antiproliferative agents against Trypanosoma cruzi, the parasite responsible of American trypanosomiasis (Chagas' disease), and Toxoplasma gondii, the etiological agent of toxoplasmosis. This thiocyanate derivative had previously proven to be an effective agent against T. cruzi proliferation. Fluorine-containing thiocyanate derivatives 2 and 3 were threefold more potent than our lead drug 1 against intracellular T. cruzi. The biological evaluation against T. gondii was also very promising. The IC(50) values corresponding to 2 and 3 were at the very low micromolar level against tachyzoites of T. gondii. Both of these drugs are interesting examples of effective antiparasitic agents that have outstanding potential not only as lead drugs but also to be used for further in vivo studies.

Inhibitory Effect of Umbelliferone Aminoalkyl Derivatives on Oxidosqualene Cyclases fromS. cerevisiae,T. cruzi,P. carinii,H. sapiens, andA. thaliana: a Structure–Activity Study

Eighteen coumarin derivatives were tested as inhibitors of oxidosqualene cyclases (OSCs) from Saccharomyces cerevisiae, Trypanosoma cruzi, Pneumocystis carinii, Homo sapiens, and Arabidopsis thaliana, all expressed in an OSC-defective strain of S. cerevisiae.35 All the compounds have an aminoalkyl chain bound to an aromatic nucleus; unconventional synthetic procedures (microwave- and ultrasound-promoted reactions) were successfully used to prepare some of them. The most interesting structure-dependent difference in inhibitory activities was observed with an N-oxide group replacement of the tertiary amino group at the end of the side chain. An interesting species specificity also emerged: T. cruzi OSC was the least sensitive enzyme; P. carinii and A. thaliana OSCs were the most sensitive. The remarkable activities of three compounds on the T. cruzi enzyme and of five of them on the P. carinii enzyme suggest the present series as a promising compound family for the development of novel antiparasitic agents.

Design, synthesis, and biological evaluation of phosphinopeptides against Trypanosoma cruzi targeting trypanothione biosynthesis

As a part of our project aimed at the search for new safe chemotherapeutic and chemoprophylactic agents against American trypanosomiasis (Chagas's disease), a series of phosphinopeptides structurally related to glutathione was designed, synthesized, and evaluated as antiproliferative agents against the parasite responsible for this disease, the hemoflagellated protozoan Trypanosoma cruzi. The rationale for the synthesis of these compounds was supported on the basis that the presence of the phosphinic acid moiety would mimic the tetrahedral transition state of trypanothione synthase (TryS), a typical C:N ligase, and the molecular target of these drugs. Of the designed compounds, 53 and 54 were potent growth inhibitors against the clinically more relevant form of T. cruzi (amastigotes) growing in myoblasts. The efficacy for these drugs was comparable to that exhibited by the well-known antiparasitic agent WC-9. The simple phosphinopeptide structure found as a pharmacophore in the present study constitutes a starting point for the development of straightforward optimized drugs.

In vitro and in vivo activities of E5700 and ER-119884, two novel orally active squalene synthase inhibitors, against Trypanosoma cruzi

Chagas' disease is a serious public health problem in Latin America, and no treatment is available for the prevalent chronic stage. Its causative agent, Trypanosoma cruzi, requires specific endogenous sterols for survival, and we have recently demonstrated that squalene synthase (SQS) is a promising target for antiparasitic chemotherapy. E5700 and ER-119884 are quinuclidine-based inhibitors of mammalian SQS that are currently in development as cholesterol- and triglyceride-lowering agents in humans. These compounds were found to be potent noncompetitive or mixed-type inhibitors of T. cruzi SQS with K(i) values in the low nanomolar to subnanomolar range in the absence or presence of 20 microM inorganic pyrophosphate. The antiproliferative 50% inhibitory concentrations of the compounds against extracellular epimastigotes and intracellular amastigotes were ca. 10 nM and 0.4 to 1.6 nM, respectively, with no effects on host cells. When treated with these compounds at the MIC, all of the parasite's sterols disappeared from the parasite cells. In vivo studies indicated that E5700 was able to provide full protection against death and completely arrested the development of parasitemia when given at a concentration of 50 mg/kg of body weight/day for 30 days, while ER-119884 provided only partial protection. This is the first report of an orally active SQS inhibitor that is capable of providing complete protection against fulminant, acute Chagas' disease.