New chemotherapy regimens and biomarkers for Chagas disease: the rationale and design of the TESEO study, an open-label, randomised, prospective, phase-2 clinical trial in the Plurinational State of Bolivia

INTRODUCTION

Chagas disease (CD) affects ~7 million people worldwide. Benznidazole (BZN) and nifurtimox (NFX) are the only approved drugs for CD chemotherapy. Although both drugs are highly effective in acute and paediatric infections, their efficacy in adults with chronic CD (CCD) is lower and variable. Moreover, the high incidence of adverse events (AEs) with both drugs has hampered their widespread use. Trials in CCD adults showed that quantitative PCR (qPCR) assays remain negative for 12 months after standard-of-care (SoC) BZN treatment in ~80% patients. BZN pharmacokinetic data and the nonsynchronous nature of the proliferative mammal-dwelling parasite stage suggested that a lower BZN/NFX dosing frequency, combined with standard or extended treatment duration, might have the same or better efficacy than either drug SoC, with fewer AEs.

METHODS AND ANALYSIS

New ThErapies and Biomarkers for ChagaS infEctiOn (TESEO) is an open-label, randomised, prospective, phase-2 clinical trial, with six treatment arms (75 patients/arm, 450 patients). Primary objectives are to compare the safety and efficacy of two new proposed chemotherapy regimens of BZN and NFX in adults with CCD with the current SoC for BZN and NFX, evaluated by qPCR and biomarkers for 36 months posttreatment and correlated with CD conventional serology. Recruitment of patients was initiated on 18 December 2019 and on 20 May 2021, 450 patients (study goal) were randomised among the six treatment arms. The treatment phase was finalised on 18 August 2021. Secondary objectives include evaluation of population pharmacokinetics of both drugs in all treatment arms, the incidence of AEs, and parasite genotyping.

ETHICS AND DISSEMINATION

The TESEO study was approved by the National Institutes of Health (NIH), U.S. Food and Drug Administration (FDA), federal regulatory agency of the Plurinational State of Bolivia and the Ethics Committees of the participating institutions. The results will be disseminated via publications in peer-reviewed journals, conferences and reports to the NIH, FDA and participating institutions.

TRIAL REGISTRATION NUMBER

NCT03981523.

Emerging agents for the treatment of Chagas disease: what is in the preclinical and clinical development pipeline?

INTRODUCTION

Chagas disease treatment relies on the lengthy administration of benznidazole and/or nifurtimox, which have frequent toxicity associated. The disease, caused by the parasite Trypanosoma cruzi, is mostly diagnosed at its chronic phase when life-threatening symptomatology manifest in approximately 30% of those infected. Considering that both available drugs have variable efficacy by then, and there are over 6 million people infected, there is a pressing need to find safer, more efficacious drugs.

AREAS COVERED

We provide an updated view of the path to achieve the aforementioned goal. From state-of-the-art in vitro and in vivo assays based on genetically engineered parasites that have allowed high throughput screenings of large chemical collections, to the unfulfilled requirement of having treatment-response biomarkers for the clinical evaluation of drugs. In between, we describe the most promising pre-clinical hits and the landscape of clinical trials with new drugs or new regimens of existing ones. Moreover, the use of monkey models to reduce the pre-clinical to clinical attrition rate is discussed.

EXPERT OPINION

In addition to the necessary research on new drugs and much awaited biomarkers of treatment efficacy, a key step will be to generalize access to diagnosis and treatment and maximize efforts to impede transmission.

Effect of Posaconazole in an in vitro model of cardiac fibrosis induced by Trypanosoma cruzi

Posaconazole (POS) is an inhibitor of ergosterol biosynthesis in clinical use for treating invasive fungal infections. POS has potent and selective anti-Trypanosoma cruzi activity and has been evaluated as a possible treatment for Chagas disease. Microtissues are a 3D culture system that has been shown to reproduce better tissue architecture and functionality than cell cultures in monolayer (2D). It has been used to evaluate chemotropic response as in vitro disease models. We previously developed an in vitro model that reproduces aspects of cardiac fibrosis observed in Chagas cardiomyopathy, using microtissues formed by primary cardiac cells infected by the T. cruzi, here called T. cruzi fibrotic cardiac microtissue (TCFCM). We also showed that the treatment of TCFCM with a TGF-β pathway inhibitor reduces fibrosis. Here, we aimed to evaluate the effect of POS in TCFCM, observing parasite load and molecules involved in fibrosis. To choose the concentration of POS to be used in TCFCM we first performed experiments in a monolayer of primary cardiac cell cultures and, based on the results, TCFCM was treated with 5 nM of POS for 96 h, starting at 144 h post-infection. Our previous studies showed that at this time the TCFCM had established fibrosis, resulting from T. cruzi infection. Treatment with POS of TCFCM reduced 50 % of parasite load as observed by real-time PCR and reduced markedly the fibrosis as observed by western blot and immunofluorescence, associated with a strong reduction in the expression of fibronectin and laminin (45 % and 54 %, respectively). POS treatment also changed the expression of proteins involved in the regulation of extracellular matrix proteins (TGF-β and TIMP-4, increased by 50 % and decreased by 58 %, respectively) in TCFCM. In conclusion, POS presented a potent trypanocidal effect both in 2D and in TCFCM, and the reduction of the parasite load was associated with a reduction of fibrosis in the absence of external immunological effectors.

Venezuela's humanitarian crisis, resurgence of vector-borne diseases, and implications for spillover in the region

In the past 5-10 years, Venezuela has faced a severe economic crisis, precipitated by political instability and declining oil revenue. Public health provision has been affected particularly. In this Review, we assess the impact of Venezuela's health-care crisis on vector-borne diseases, and the spillover into neighbouring countries. Between 2000 and 2015, Venezuela witnessed a 359% increase in malaria cases, followed by a 71% increase in 2017 (411 586 cases) compared with 2016 (240 613). Neighbouring countries, such as Brazil, have reported an escalating trend of imported malaria cases from Venezuela, from 1538 in 2014 to 3129 in 2017. In Venezuela, active Chagas disease transmission has been reported, with seroprevalence in children (<10 years), estimated to be as high as 12·5% in one community tested (n=64). Dengue incidence increased by more than four times between 1990 and 2016. The estimated incidence of chikungunya during its epidemic peak is 6975 cases per 100 000 people and that of Zika virus is 2057 cases per 100 000 people. The re-emergence of many vector-borne diseases represents a public health crisis in Venezuela and has the possibility of severely undermining regional disease elimination efforts. National, regional, and global authorities must take action to address these worsening epidemics and prevent their expansion beyond Venezuelan borders.

Ravuconazole self-emulsifying delivery system: in vitro activity against Trypanosoma cruzi amastigotes and in vivo toxicity

Self-emulsifying drug delivery systems (SEDDSs) are lipid-based anhydrous formulations composed of an isotropic mixture of oil, surfactant, and cosurfactants usually presented in gelatin capsules. Ravuconazole (Biopharmaceutics Classification System [BCS] Class II) is a poorly water-soluble drug, and a SEDDS type IIIA was designed to deliver it in a predissolved state, improving dissolution in gastrointestinal fluids. After emulsification, the droplets had mean hydrodynamic diameters <250 nm, zeta potential values in the range of −45 mV to −57 mV, and showed no signs of ravuconazole precipitation. Asymmetric flow field-flow fractionation with dynamic and multiangle laser light scattering was used to characterize these formulations in terms of size distribution and homogeneity. The fractograms obtained at 37°C showed a polydisperse profile for all blank and ravuconazole–SEDDS formulations but no large aggregates. SEDDS increased ravuconazole in vitro dissolution extent and rate (20%) compared to free drug (3%) in 6 h. The in vivo toxicity of blank SEDDS comprising Labrasol^® surfactant in different concentrations and preliminary safety tests in repeated-dose oral administration (20 days) showed a dose-dependent Labrasol toxicity in healthy mice. Ravuconazole–SEDDS at low surfactant content (10%, v/v) in Trypanosoma cruzi-infected mice was safe during the 20-day treatment. The anti-T. cruzi activity of free ravuconazole, ravuconazole–SEDDS and each excipient were evaluated in vitro at equivalent ravuconazole concentrations needed to inhibit 50% or 90% (IC₅₀ and IC₉₀), respectively of the intracellular amastigote form of the parasite in a cardiomyocyte cell line. The results showed a clear improvement of the ravuconazole anti-T. cruzi activity when associated with SEDDS. Based on our results, the repurposing of ravuconazole in SEDDS dosage form is a strategy that deserves further in vivo investigation in preclinical studies for the treatment of human T. cruzi infections.

Congenital Chagas' disease transmission in the United States: Diagnosis in adulthood

Two brothers with congenitally-acquired Chagas’ disease (CD) diagnosed during adulthood are reported. The patients were born in the USA to a mother from Bolivia who on subsequent assessment was found to be serologically positive for Trypanosoma cruzi. Serologic screening of all pregnant women who migrated from countries with endemic CD is strongly recommended.

Population pharmacokinetics of benznidazole in adult patients with Chagas disease

The aim of the present study was to build a population pharmacokinetic (popPK) model to characterize benznidazole (BNZ) pharmacokinetics in adults with chronic Chagas disease. This study was a prospective, open-label, single-center clinical trial approved by the local ethics committee. Patients received BNZ at 2.5 mg/kg of body weight/12 h (Abarax, Elea Laboratory, Argentina) for 60 days. Plasma BNZ samples were taken several times during the study and analyzed by high-performance liquid chromatography with UV-visible detection (HPLC-UV). The popPK analysis was done with NONMEMv.7.3. Demographic and biological data were tested as covariates. Intraindividual, interoccasion, and residual variabilities were modeled. Internal and external validations were completed to assess the robustness of the model. Later on, simulations were performed to generate BNZ concentration-time course profiles for different dosage regimens. A total of 358 plasma BNZ concentrations from 39 patients were included in the analysis. A one-compartment PK model characterized by clearance (CL/F) and the apparent volume of distribution (V/F), with first-order absorption (Ka) and elimination, adequately described the data (CL/F, 1.73 liters/h; V/F, 89.6 liters; and Ka, 1.15 h(-1)). No covariates were found to be significant for CL/F and V/F. Internal and external validations of the final model showed adequate results. Data from simulations revealed that a dose of 2.5 mg/kg/12 h might lead to overexposure in most patients. A lower dose (2.5 mg/kg/24 h) was able to achieve trough BNZ plasma concentrations within the accepted therapeutic range of 3 to 6 mg/liter. In summary, we developed a population PK model for BNZ in adults with chronic Chagas disease. Dosing simulations showed that a BNZ dose of 2.5 mg/kg/24 h will adequately keep BNZ trough plasma concentrations within the recommended target range for the majority of patients. (This study has been registered at EudraCT under number 2011-002900-34 and at ClinicalTrials.gov under number NCT01755403.).

Recent clinical trials for the etiological treatment of chronic chagas disease: advances, challenges and perspectives

Chagas disease, a chronic systemic parasitosis caused by the Kinetoplastid protozoon Trypanosoma cruzi, is the first cause of cardiac morbidity and mortality in poor rural and suburban areas of Latin America and the largest parasitic disease burden in the continent, now spreading worldwide due to international migrations. A recent change in the scientific paradigm on the pathogenesis of chronic Chagas disease has led to a consensus that all T. cruzi-seropositive patients should receive etiological treatment. This important scientific advance has spurred the rigorous evaluation of the safety and efficacy of currently available drugs (benznidazole and nifurtimox) as well as novel anti-T. cruzi drug candidates in chronic patients, who were previously excluded from such treatment. The first results indicate that benznidazole is effective in inducing a marked and sustained reduction in the circulating parasites' level in the majority of these patients, but adverse effects can lead to treatment discontinuation in 10-20% of cases. Ergosterol biosynthesis inhibitors, such as posaconazole and ravuconazole, are better tolerated but their efficacy at the doses and treatment duration used in the initial studies was significantly lower; such results are probably related to suboptimal exposure and/or treatment duration. Combination therapies are a promising perspective but the lack of validated biomarkers of response to etiological treatment and eventual parasitological cures in chronic patients remains a serious challenge.

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.

In vitro activity of the antifungal azoles itraconazole and posaconazole against Leishmania amazonensis

Leishmaniasis, caused by protozoan parasites of the Leishmania genus, is one of the most prevalent neglected tropical diseases. It is endemic in 98 countries, causing considerable morbidity and mortality. Pentavalent antimonials are the first line of treatment for leishmaniasis except in India. In resistant cases, miltefosine, amphotericin B and pentamidine are used. These treatments are unsatisfactory due to toxicity, limited efficacy, high cost and difficult administration. Thus, there is an urgent need to develop drugs that are efficacious, safe, and more accessible to patients. Trypanosomatids, including Leishmania spp. and Trypanosoma cruzi, have an essential requirement for ergosterol and other 24-alkyl sterols, which are absent in mammalian cells. Inhibition of ergosterol biosynthesis is increasingly recognized as a promising target for the development of new chemotherapeutic agents. The aim of this work was to investigate the antiproliferative, physiological and ultrastructural effects against Leishmania amazonensis of itraconazole (ITZ) and posaconazole (POSA), two azole antifungal agents that inhibit sterol C14α-demethylase (CYP51). Antiproliferative studies demonstrated potent activity of POSA and ITZ: for promastigotes, the IC50 values were 2.74 µM and 0.44 µM for POSA and ITZ, respectively, and for intracellular amastigotes, the corresponding values were 1.63 µM and 0.08 µM, for both stages after 72 h of treatment. Physiological studies revealed that both inhibitors induced a collapse of the mitochondrial membrane potential (ΔΨm), which was consistent with ultrastructural alterations in the mitochondrion. Intense mitochondrial swelling, disorganization and rupture of mitochondrial membranes were observed by transmission electron microscopy. In addition, accumulation of lipid bodies, appearance of autophagosome-like structures and alterations in the kinetoplast were also observed. In conclusion, our results indicate that ITZ and POSA are potent inhibitors of L. amazonensis and suggest that these drugs could represent novel therapies for the treatment of leishmaniasis, either alone or in combination with other agents.

Benznidazole and posaconazole in experimental Chagas disease: positive interaction in concomitant and sequential treatments

Background

Current chemotherapy for Chagas disease is unsatisfactory due to its limited efficacy, particularly in the chronic phase, with frequent side effects that can lead to treatment discontinuation. Combined therapy is envisioned as an ideal approach since it may improve treatment efficacy whilst decreasing toxicity and the likelihood of resistance development. We evaluated the efficacy of posaconazole in combination with benznidazole on Trypanosoma cruzi infection in vivo.

Methods and Findings

Benznidazole and posaconazole were administered individually or in combination in an experimental acute murine infection model. Using a rapid treatment protocol for 7 days, the combined treatments were more efficacious in reducing parasitemia levels than the drugs given alone, with the effects most evident in combinations of sub-optimal doses of the drugs. Subsequently, the curative action of these drug combinations was investigated, using the same infection model and 25, 50, 75 or 100 mg/kg/day (mpk) of benznidazole in combination with 5, 10 or 20 mpk of posaconazole, given alone or concomitantly for 20 days. The effects of the combination treatments on parasitological cures were higher than the sum of such effects when the drugs were administered separately at the same doses, indicating synergistic activity. Finally, sequential therapy experiments were carried out with benznidazole or posaconazole over a short interval (10 days), followed by the second drug administered for the same period of time. It was found that the sequence of benznidazole (100 mpk) followed by posaconazole (20 mpk) provided cure rates comparable to those obtained with the full (20 days) treatments with either drug alone, and no cure was observed for the short treatments with drugs given alone.

Conclusions

Our data demonstrate the importance of investigating the potential beneficial effects of combination treatments with marketed compounds, and showed that combinations of benznidazole with posaconazole have a positive interaction in murine models of Chagas disease.

In this study, we investigated the efficacy of posaconazole in combination with benznidazole against Trypanosoma cruzi acute infections in mice, to support the potential clinical evaluation of such combination therapy for Chagas disease. The curative action of benznidazole/posaconazole combinations was explored in an established acute infection model with the Y strain in which benznidazole and posaconazole treatments induced a 70% and 80% cure rate, respectively, when administered alone at optimal doses. When tested in combination, a 80% to 90% cure rate was detected in mice receiving 25, 50 or 75 mpk of benznidazole, plus 5 or 10 mpk of posaconazole, while treatment with the sub-optimal doses of the drugs given alone induced only 0–43% cures, indicating synergistic effects. Finally, sequential short (10 days) treatments with benznidazole (100 mpk) followed by posaconazole (20 mpk) led to an 80% cure rate, comparable with full-length treatments with either drug given alone, while no cures were observed for short treatments with single drugs. Our results demonstrate that it is possible to achieve the same or better therapeutic effect using lower dosages of posaconazole and benznidazole in combination, decreasing treatment costs and potential toxicity.

Effects of amiodarone and posaconazole on the growth and ultrastructure of Trypanosoma cruzi

The antifungal posaconazole (PCZ) is the most advanced candidate for the treatment of Chagas disease, having potent anti-Trypanosoma cruzi activity in vitro and in animal models of the disease as well as an excellent safety profile in humans. Amiodarone (AMD) is the antiarrhythmic drug most frequently used for the symptomatic treatment of chronic Chagas disease patients, but it also has specific anti-T. cruzi activity. When used in combination, these drugs exhibit potent synergistic activity against the parasite. In the present work, electron microscopy was used to analyse the effects of both compounds, acting individually or in combination, against T. cruzi. The 50% inhibitory concentration (IC(50)) against epimastigote and amastigote forms was 25 nM and 1.0 nM for PCZ and 8 μM and 5.6 μM for AMD, respectively. The antiproliferative synergism of the drugs (fractional inhibitory concentration<0.5) was confirmed and the ultrastructural alterations in the parasite induced by them, leading to cell death, were characterised using electron microscopy. These alterations include intense wrinkling of the protozoan surface, swelling of the mitochondrion, shedding of plasma membrane vesicles, the appearance of vesicles in the flagellar pocket, alterations in the kinetoplast, disorganisation of the Golgi complex, accumulation of lipid inclusions in the cytoplasm, and the formation of autophagic vacuoles, the latter confirmed by immunofluorescence microscopy. These findings indicate that the association of PCZ and AMD may constitute an effective anti-T. cruzi therapy with low side effects.

Antiproliferative, Ultrastructural, and Physiological Effects of Amiodarone on Promastigote and Amastigote Forms of Leishmania amazonensis

Amiodarone (AMIO), the most frequently antiarrhythmic drug used for the symptomatic treatment of chronic Chagas' disease patients with cardiac compromise, has recently been shown to have also specific activity against fungi, Trypanosoma cruzi and Leishmania. In this work, we characterized the effects of AMIO on proliferation, mitochondrial physiology, and ultrastructure of Leishmania amazonensis promastigotes and intracellular amastigotes. The IC₅₀ values were 4.21 and 0.46 μM against promastigotes and intracellular amastigotes, respectively, indicating high selectivity for the clinically relevant stage. We also found that treatment with AMIO leads to a collapse of the mitochondrial membrane potential (ΔΨm) and to an increase in the production of reactive oxygen species, in a dose-dependent manner. Fluorescence microscopy of cells labeled with JC-1, a marker for mitochondrial energization, and transmission electron microscopy confirmed severe alterations of the mitochondrion, including intense swelling and modification of its membranes. Other ultrastructural alterations included (1) presence of numerous lipid-storage bodies, (2) presence of large autophagosomes containing part of the cytoplasm and membrane profiles, sometimes in close association with the mitochondrion and endoplasmic reticulum, and (3) alterations in the chromatin condensation and plasma membrane integrity. Taken together, our results indicate that AMIO is a potent inhibitor of L. amazonensis growth, acting through irreversible alterations in the mitochondrial structure and function, which lead to cell death by necrosis, apoptosis and/or autophagy.

Synthetic arylquinuclidine derivatives exhibit antifungal activity against Candida albicans, Candida tropicalis and Candida parapsilopsis

BACKGROUND

Sterol biosynthesis is an essential pathway for fungal survival, and is the biochemical target of many antifungal agents. The antifungal drugs most widely used to treated fungal infections are compounds that inhibit cytochrome P450-dependent C14α-demethylase (CYP51), but other enzymes of this pathway, such as squalene synthase (SQS) which catalyses the first committed step in sterol biosynthesis, could be viable targets. The aim of this study was to evaluate the antifungal activity of SQS inhibitors on Candida albicans, Candida tropicalis and Candida parapsilopsis strains.

METHODS

Ten arylquinuclidines that act as SQS inhibitors were tested as antiproliferative agents against three ATCC strains and 54 clinical isolates of Candida albicans, Candida tropicalis and Candida parapsilopsis. Also, the morphological alterations induced in the yeasts by the experimental compounds were evaluated by fluorescence and transmission electron microscopy.

RESULTS

The most potent arylquinuclidine derivative (3-[1'-{4'-(benzyloxy)-phenyl}]-quinuclidine-2-ene) (WSP1267) had a MIC50 of 2 μg/ml for all species tested and MIC90 varying from 4 μg/ml to 8 μg/ml. Ultrathin sections of C. albicans treated with 1 μg/ml of WSP1267 showed several ultrastructural alterations, including (a) loss of cell wall integrity, (b) detachment of the plasma membrane from the fungal cell wall, (c) accumulation of small vesicles in the periplasmic region, (d) presence of large electron-dense vacuoles and (e) significantly increased cell size and cell wall thickness. In addition, fluorescence microscopy of cells labelled with Nile Red showed an accumulation of lipid droplets in the cytoplasm of treated yeasts. Nuclear staining with DAPI revealed the appearance of uncommon yeast buds without a nucleus or with two nuclei.

CONCLUSION

Taken together, our data demonstrate that arylquinuclidine derivatives could be useful as lead compounds for the rational synthesis of new antifungal drugs.

Amiodarone inhibits Trypanosoma cruzi infection and promotes cardiac cell recovery with gap junction and cytoskeleton reassembly in vitro

We present the results of the first detailed study of the antiproliferative and ultrastructural effects of amiodarone on Trypanosoma cruzi, the causative agent of Chagas' disease. Moreover, we report the effects of this compound on the recovery of F-actin fibrils, connexin43, and contractility in T. cruzi-infected cardiac myocytes. Amiodarone is the most prescribed class III antiarrhythmic agent and is frequently used for the symptomatic treatment of Chagas' disease patients with cardiac compromise. In addition, recent studies identified its antifungal and antiprotozoal activities, which take place through Ca(2+) homeostasis disruption and ergosterol biosynthesis blockade. We tested different concentrations of amiodarone (2.5 to 10 μM) on infected primary cultures of heart muscle cells and observed a dose- and time-dependent effect on growth of the clinically relevant intracellular amastigote form of T. cruzi. Ultrastructural analyses revealed that amiodarone had a profound effect on intracellular amastigotes, including mitochondrial swelling and disorganization of reservosomes and the kinetoplast and a blockade of amastigote-trypomastigote differentiation. Amiodarone showed no toxic effects on host cells, which recovered their F-actin fibrillar organization, connexin43 distribution, and spontaneous contractility concomitant with the drug-induced eradication of the intracellular parasites. Amiodarone is, therefore, a promising compound for the development of new drugs against T. cruzi.

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.

A comparative study of posaconazole and benznidazole in the prevention of heart damage and promotion of trypanocidal immune response in a murine model of Chagas disease

A comparative study was performed between the trypanocidal efficacy of and associated immune response to benznidazole and posaconazole in a murine model of Chagas disease. Both drugs led to 100% survival, suppression of parasitaemia and reduction of specific anti-Trypanosoma cruzi antibodies following chronic infection. All posaconazole-treated animals had negative haemocultures at 54 days post infection, whilst 50% of those treated with benznidazole had positive results. Although both drugs were effective in reducing parasitism and inflammation in the heart, posaconazole-treated animals had plasma enzymatic levels of cardiac lesion that were indistinguishable from those of uninfected mice, whilst for benznidazole the enzyme levels were significantly higher than those of uninfected controls 31 days after the start of treatment. Posaconazole was more effective than benznidazole in controlling spleen enlargement and unspecific splenocyte proliferation in the early acute phase, but allowed higher levels of activation of CD4(+) and CD8(+) T-cells in the late acute phase when the adaptive immune response takes control of the infection. These results support the notion that posaconazole could be superior to benznidazole for the treatment of T. cruzi infection in humans.

Successful treatment with posaconazole of a patient with chronic Chagas disease and systemic lupus erythematosus

American Trypanosomiasis or Chagas disease (CD) is a neglected disease that affects Latin American people worldwide. Two old antiparasitic drugs, benznidazole and nifurtimox, are currently used for specific CD treatment with limited efficacy in chronic infections and frequent side effects. New drugs are needed for patients with chronic CD as well as for immunosuppressed patients, for whom the risk of reactivation is life-threatening. We describe a case of chronic CD and systemic lupus erythematosus (SLE) that required immunosuppression to control the autoimmune process. It was found that benznidazole induced a reduction, but not an elimination, of circulating Trypanosoma cruzi levels, whereas subsequent treatment with posaconazole led to a successful resolution of the infection, despite the maintenance of immunosuppressive therapy.

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.

Growth inhibition and ultrastructural alterations induced by Delta24(25)-sterol methyltransferase inhibitors in Candida spp. isolates, including non-albicans organisms

Background

Although Candida species are commensal microorganisms, they can cause many invasive fungal infections. In addition, antifungal resistance can contribute to failure of treatment.

The purpose of this study was to evaluate the antifungal activity of inhibitors of Δ²⁴⁽²⁵⁾-sterol methyltransferase (24-SMTI), 20-piperidin-2-yl-5α-pregnan-3β-20(R)-diol (AZA), and 24(R,S),25-epiminolanosterol (EIL), against clinical isolates of Candida spp., analysing the ultrastructural changes.

Results

AZA and EIL were found to be potent growth inhibitors of Candida spp. isolates. The median MIC₅₀ was 0.5 μg.ml^-1 for AZA and 2 μg.ml^-1 for EIL, and the MIC₉₀ was 2 μg.ml^-1 for both compounds. All strains used in this study were susceptible to amphotericin B; however, some isolates were fluconazole- and itraconazole-resistant. Most of the azole-resistant isolates were Candida non-albicans (CNA) species, but several of them, such as C. guilliermondii, C. zeylanoides, and C. lipolytica, were susceptible to 24-SMTI, indicating a lack of cross-resistance. Reference strain C. krusei (ATCC 6258, FLC-resistant) was consistently susceptible to AZA, although not to EIL. The fungicidal activity of 24-SMTI was particularly high against CNA isolates. Treatment with sub-inhibitory concentrations of AZA and EIL induced several ultrastructural alterations, including changes in the cell-wall shape and thickness, a pronounced disconnection between the cell wall and cytoplasm with an electron-lucent zone between them, mitochondrial swelling, and the presence of electron-dense vacuoles. Fluorescence microscopy analyses indicated an accumulation of lipid bodies and alterations in the cell cycle of the yeasts. The selectivity of 24-SMTI for fungal cells versus mammalian cells was assessed by the sulforhodamine B viability assay.

Conclusion

Taken together, these results suggest that inhibition of 24-SMT may be a novel approach to control Candida spp. infections, including those caused by azole-resistant strains.

Eliminating Chagas disease: challenges and a roadmap

Millions of people in Central and Southern America are affected by Chagas disease. Richard Reithinger and colleagues explain the difficulties of elimination and suggest a strategy

Altered sterol profile induced in Leishmania amazonensis by a natural dihydroxymethoxylated chalcone

OBJECTIVES

The effects of the antileishmanial chalcone 2',6'-dihydroxy-4'-methoxychalcone (DMC) on Leishmania amazonensis sterol composition and biosynthesis were investigated to obtain information about the mechanism of growth inhibition by DMC on this parasite.

METHODS

The interference of sterol biosynthesis by DMC was studied in drug-treated promastigotes by two different methods. (i) Newly synthesized sterols from parasites grown in the presence of [(3)H]mevalonate were analysed by thin layer chromatography (TLC)/fluorography. (ii) Total sterols extracted from the parasites grown with or without DMC were characterized by gas chromatography coupled to mass spectroscopy (GC/MS).

RESULTS

TLC and GC/MS analyses of sterols extracted from DMC-treated promastigotes revealed the accumulation of early precursors and a reduction in the levels of C-14 demethylated and C-24 alkylated sterols, as well as a reduction in exogenous cholesterol uptake.

CONCLUSIONS

This study demonstrates that the natural chalcone DMC alters the sterol composition of L. amazonensis and suggests that the parasite target is different from other known sterol inhibitors.

The challenges of Chagas Disease-- grim outlook or glimmer of hope

The authors discuss the key challenges that undermine the control of Chagas disease and that must be urgently addressed to ensure long-term, sustainable control.

Sterol methenyl transferase inhibitors alter the ultrastructure and function of the Leishmania amazonensis mitochondrion leading to potent growth inhibition

We describe here the effects of Delta(24(25)) sterol methenyl transferase inhibitors (SMTI) on promastigote and axenic amastigote forms of Leishmania amazonensis. When these cells were exposed to 20-piperidin-2-yl-5alpha-pregnan-3beta-20-diol (22,26-azasterol; AZA), hydrazone-imidazol-2-yl-5alpha-pregnan-3beta-ol (IMI), 20-hydrazone-pyridin-2-yl-5alpha-pregnan-3beta-ol (PYR) or 24(R,S),25-epiiminolanosterol (EIL), a concentration- and time-dependent inhibition of growth was observed, with IC(50) values in the sub-micromolar range. Ultrastructural alterations in treated cells were mainly observed in the mitochondrion, which displayed an intense swelling and a reduction of the electron density of the matrix with remarkable changes in the inner mitochondrial membranes. Mitochondrial transmembrane electric potential (DeltaPsi) was measured using spectrophotometric methods in control and treated promastigotes permeabilized with digitonin. After energization with the substrates for complexes I, II or IV of the respiratory chain, it was possible to detect marked changes of DeltaPsi in promastigotes treated with 1 microM of the SMTI for 48 or 72 h when compared with normal cells, indicating that these compounds led to the loss of the energy-transducing properties of the mitochondrial inner membrane, probably related to the alteration of its lipid composition. The present study confirms these findings, showing that in Leishmania amazonensis the mitochondrial complex appears to be the first organelle affected after treatment with different SMTI.

Quinuclidine derivatives as potential antiparasitics

There is an urgent need for the development of new drugs for the treatment of tropical parasitic diseases such as Chagas' disease and leishmaniasis. One potential drug target in the organisms that cause these diseases is sterol biosynthesis. This paper describes the design and synthesis of quinuclidine derivatives as potential inhibitors of a key enzyme in sterol biosynthesis, squalene synthase (SQS). A number of compounds that were inhibitors of the recombinant Leishmania major SQS at submicromolar concentrations were discovered. Some of these compounds were also selective for the parasite enzyme rather than the homologous human enzyme. The compounds inhibited the growth of and sterol biosynthesis in Leishmania parasites. In addition, we identified other quinuclidine derivatives that inhibit the growth of Trypanosoma brucei (the causative organism of human African trypanosomiasis) and Plasmodium falciparum (a causative agent of malaria), but through an unknown mode(s) of action.

Alterations on the growth and ultrastructure of Leishmania chagasi induced by squalene synthase inhibitors

Leishmaniasis is an important disease in widely dispersed regions of the world. In South America, visceral leishmaniasis (VL) is mainly caused by Leishmania chagasi. The morbidity associated with the infection is high, and death may occur in some untreated patients. Treatment has been based upon pentavalent antimonial drugs for more than half a century and problems, including development of resistance to antimonials and lack of efficacy against VL/HIV co-infections, have emphasized the need for new drugs. Squalene synthase (SQS) is an essential enzyme for the biosynthesis of protozoal sterol molecules. In this work, nineteen synthetic quinuclidines, potentially inhibitors of SQS, were tested against promastigote forms of L. chagasi and the IC50 values of the compounds were determined. The most active compounds had IC50 values of around 30 nM and induced complete growth arrest and cell lysis at sub-micromolar concentrations. We analyzed the morphological structure of the parasites treated with these compounds by transmission electron microscopy of thin sections. Treated parasites showed significant ultrastructural changes, which varied from discrete alterations to total destruction of the cells, depending on the drug concentration and the time of incubation. One important change observed was a typical swelling of the unique and highly branched mitochondrion, where the inner membrane lost its organization. There was an increase in the number of autophagosomal structures. Changes in the organization of the nuclear chromatin and alterations in the flagellar pocket and flagellar membrane were also observed.

Kinetic characterization of squalene synthase from Trypanosoma cruzi: selective inhibition by quinuclidine derivatives

The biosynthesis of sterols is a major route for the development of antitrypanosomals. Squalene synthase (SQS) catalyzes the first step committed to the biosynthesis of sterols within the isoprenoid pathway, and several inhibitors of the enzyme have selective antitrypanosomal activity both in vivo and in vitro. The enzyme from Trypanosoma cruzi is a 404-amino-acid protein with a clearly identifiable membrane-spanning region. In an effort to generate soluble recombinant enzyme, we have expressed in Escherichia coli several truncated versions of T. cruzi SQS with a His tag attached to the amino terminus. Deletions of both the amino- and carboxyl-terminal regions generated active and soluble forms of the enzyme. The highest levels of soluble protein were achieved when 24 and 36 amino acids were eliminated from the amino and carboxyl regions, respectively, yielding a protein of 41.67 kDa. The Michaelis-Menten constants of the purified enzyme for farnesyl diphosphate and NAD (NADPH) were 5.25 and 23.34 microM, respectively, whereas the V(max) was 1,428.56 nmol min(-1)mg(-1). Several quinuclidine derivatives with antiprotozoal activity in vitro were found to be selective inhibitors of recombinant T. cruzi SQS in comparative assays with the human enzyme, with 50% inhibitory concentration values in the nanomolar range. These data suggest that selective inhibition of T. cruzi SQS may be an efficient strategy for the development of new antitrypanosomal agents.

Bisphosphonates as inhibitors of Trypanosoma cruzi hexokinase: kinetic and metabolic studies

Trypanosoma cruzi, the etiologic agent of Chagas disease, has an unusual ATP-dependent hexokinase (TcHK) that is not affected by D-glucose 6-phosphate, but is non-competitively inhibited by inorganic pyrophosphate (PP(i)), suggesting a heterotropic modulator effect. In a previous study we identified a novel family of bisphosphonates, metabolically stable analogs of PP(i), which are potent and selective inhibitors of TcHK as well as the proliferation of the clinically relevant intracellular amastigote form of the parasite in vitro (Hudock, M. P., Sanz-Rodriguez, C. E., Song, Y., Chan, J. M., Zhang, Y., Odeh, S., Kosztowski, T., Leon-Rossell, A., Concepcion, J. L., Yardley, V., Croft, S. L., Urbina, J. A., and Oldfield, E. (2006) J. Med. Chem. 49, 215-223). In this work, we report a detailed kinetic analysis of the effects of three of these bisphosphonates on homogeneous TcHK, as well as on the enzyme in purified intact glycosomes, peroxisome-like organelles that contain most of the glycolytic pathway enzymes in this organism. We also investigated the effects of the same compounds on glucose consumption by intact and digitonin-permeabilized T. cruzi epimastigotes, and on the growth of such cells in liver-infusion tryptose medium. The bisphosphonates investigated were several orders of magnitude more active than PP(i) as non-competitive or mixed inhibitors of TcHK and blocked the use of glucose by the epimastigotes, inducing a metabolic shift toward the use of amino acids as carbon and energy sources. Furthermore, there was a significant correlation between the IC(50) values for TcHK inhibition and those for epimastigote growth inhibition for the 12 most potent compounds of this series. Finally, these bisphosphonates did not affect the sterol composition of the treated cells, indicating that they do not act as inhibitors of farnesyl diphosphate synthase. Taken together, our results suggest that these novel bisphosphonates act primarily as specific inhibitors of TcHK and may represent a novel class of selective anti-T. cruzi agents.

The Anti-Trypanosoma cruzi activity of posaconazole in a murine model of acute Chagas' disease is less dependent on gamma interferon than that of benznidazole

We have investigated the influences of gamma interferon (IFN-gamma) and interleukin-12 (IL-12) on the efficacy of posaconazole (POS) treatment of acute experimental infections with Trypanosoma cruzi; the standard drug, benznidazole (BZ), was used as a positive control. Wild-type (WT) mice infected with T. cruzi and treated with POS or BZ had no parasitemia, 100% survival, and cure rates of 86 to 89%. IFN-gamma-knockout (KO) mice infected with T. cruzi and treated with BZ controlled the infection during treatment but relapsed after the drug pressure ceased and had 0% survival, while those receiving POS better controlled the infection after the end of treatment and had 70% survival (P<0.0001 compared to the results for both untreated and BZ-treated animals). IL-12-KO mice infected and treated with POS or BZ had intermediate results, displaying enhanced parasitemia, decreased survival (77 to 83%), and reduced cure rates (35 to 39%) compared with those of the WT animals. Our results demonstrate that either IFN-gamma or IL-12 deficiency reduces the efficacy of POS or BZ in this experimental model but also indicate that the anti-T. cruzi activity of POS is much less dependent on the activity of IFN-gamma than that of BZ is.

New azasterols against Trypanosoma brucei: role of 24-sterol methyltransferase in inhibitor action

A series of azasterol derivatives, designed as potential inhibitors of the Delta(24)-sterol methyltransferase enzyme (24-SMT), were synthesized and evaluated for their activities against parasitic protozoa. Values in the nanomolar range were obtained for 50% effective dose against the Trypanosoma brucei subsp. rhodesiense bloodstream form cultured in vitro. In order to investigate the mode of action, Trypanosoma brucei subsp. brucei 24-SMT was cloned and overexpressed and compounds were assayed for inhibitory activity. None of the inhibitors tested appeared to be active against the enzyme. Sterol composition analysis showed that only cholestane type sterols are present in membranes of bloodstream forms while ergosterol is a major component of procyclic sterol extracts. Interestingly, Northern blot analysis showed the presence of 24-SMT mRNA in both the procyclic and the bloodstream forms of the parasite, although levels of mRNA were threefold lower in the latter. Likewise, Western blot analysis and activity determinations evidenced the existence of active enzyme in both forms of the parasite. We conclude that the designed compounds act at sites other than 24-SMT in Trypanosoma brucei.

Mechanisms of action of lysophospholipid analogues against trypanosomatid parasites

Lysophospholipid analogues (LPAs) comprise a class of metabolically stable compounds that have been developed as anticancer agents for over two decades, but which have also potent and selective antiparasitic activity, particularly against trypanosomatid parasites such as Leishmania and Trypanosoma cruzi, both in vitro and in vivo. The in vivo activities of LPAs result from direct effects on their target cells and are not dependent on a functional immune system. Because of their chemical nature, LPAs have a potential for interaction with a variety of subcellular structures and biochemical pathways. However, in mammalian cells LPA-induced growth inhibition and programmed cell death is usually associated with a blockade of phosphatidylcholine (PC) biosynthesis at the level of CTP: phosphocholine citidyltransferase, probably through an increase of cellular ceramide levels due to depressed sphingomyelin synthesis. Although in trypanosomatid parasites much less information is available, inhibition of PC biosynthesis by LPA has also been documented but at the level of phosphatidylethanolamine N-methyl-transferase, as well as LPA-induced classical apoptotic phenomena. The higher activity of LPAs as inhibitors of PC biosynthesis in parasites than in mammalian cells, probably due to different biochemical pathways involved in the two types of cells, could explain their selective antiparasitic action in vivo.

Effects of sterol biosynthesis inhibitors on endosymbiont-bearing trypanosomatids

Some protozoa of the Trypanosomatidae family have a close relationship with an endosymbiotic bacterium. As the prokaryote envelope has a controversial origin, a sterol 24-methyltransferase inhibitor (20-piperidin-2-yl-5alpha-pregnan-3beta,20-diol; 22,26-azasterol) was used as a tool to investigate lipid biosynthetic pathways in Crithidia deanei, an endosymbiont-bearing trypanosomatid. Apart from antiproliferative effects, this drug induced ultrastructural alterations, consisting of myelin-like figures in the cytoplasm and endosymbiont envelope vesiculation. Concurrently, a dramatic reduction of 24-alkyl sterols was observed after 22,26-azasterol treatment, both in whole cell homogenates, as well as in isolated mitochondria. These effects were associated with changes of phospholipid composition, in particular a reduction of the phosphatidylcholine content and a concomitant increase in phosphatidylethanolamine levels. Lipid analyses of purified endosymbionts indicated a complete absence of sterols, and their phospholipid composition was different from that of mitochondria or whole protozoa, being similar to eubacteria closely associated with eukaryotes.

Miltefosine: issues to be addressed in the future

Future issues that need to be addressed for miltefosine are efficacy against non-Indian visceral leishmaniasis, efficacy in HIV-coinfected patients, efficacy against the many forms of cutaneous and mucosal disease, effectiveness under clinical practice conditions, generation of drug resistance and the need to provide a second antileishmanial agent to protect against this disastrous event, and the ability to maintain reproductive contraceptive practices under routine clinical conditions.

Cytoskeleton reassembly in cardiomyocytes infected by Trypanosoma cruzi is triggered by treatment with ergosterol biosynthesis inhibitors

We have previously shown that Trypanosoma cruzi-infected cardiomyocytes present alterations in cytoskeletal organisation in vitro. The remarkable change in the host cell cytoskeleton opened up the question of whether treatment of infected cells with antitrypanosomal compounds, such as ergosterol biosynthesis inhibitors (EBIs), allows the reconstruction of myofibrils and the microtubule network, restoring the cell biological function. Therefore, 48-h-old T. cruzi-infected cardiomyocyte cultures were treated with 10 nM ketoconazole or posaconazole and cytoskeletal remodelling of the host cells was analysed by indirect immunofluorescence assay. Both compounds displayed a potent antiparasitic effect and dramatically reduced the infection ratio. After 120 h of treatment, actin polygonal configuration was frequently visualised in the host cell cytoplasm, suggesting the initial stage of actin framework restoration. Rearrangement of myofibrils and the microtubule network was achieved 168 h after the start of drug treatment. Our data demonstrate that the trypanocidal effect of EBIs lead to reconstruction of the cytoskeleton of T. cruzi-infected cardiomyocytes in vitro.

Antiproliferative activities of two novel quinuclidine inhibitors against Toxoplasma gondii tachyzoites in vitro

OBJECTIVES

To study the antiproliferative effects of ER119884 and E5700, two quinuclidine-based inhibitors of squalene synthase (SQS), against Toxoplasma gondii tachyzoites in epithelial cells.

METHODS

The antiproliferative effects of the quinuclidine derivatives, alone or in combination with epiminolanosterol or antifolates, were analysed, resulting in the construction of isobolograms. The ultrastructure of treated tachyzoites was analysed by transmission electron microscopy.

RESULTS

The quinuclidine derivatives demonstrated selective anti-T. gondii activity, arresting parasite growth with IC50 values of 0.66 and 0.23 microM for ER119884 and E5700, respectively, after 24 h of interaction and 0.44 and 0.19 microM after 48 h of interaction. Both compounds induced remarkable alterations in the parasite ultrastructure, such as mitochondrial swelling and the presence of autophagosome-like structures, after 24 h of treatment. Combination of these quinuclidine derivatives with the antifolates sulfadiazine and pyrimethamine produced a synergic effect. When epiminolanosterol was combined with E5700, the effect observed was synergic, whereas the combination with ER119884 produced no interaction.

CONCLUSIONS

E5700 and ER119884 demonstrated selective activity against T. gondii tachyzoites and are a possible alternative to be used in association with the current therapy. The ultrastructural alterations observed suggest a possible interference with lipid metabolism.

Inhibition of Trypanosoma cruzi hexokinase by bisphosphonates

Hexokinase is the first enzyme involved in glycolysis in most organisms, including the etiological agents of Chagas disease (Trypanosoma cruzi) and African sleeping sickness (Trypanosoma brucei). The T. cruzi enzyme is unusual since, unlike the human enzyme, it is inhibited by inorganic diphosphate (PPi). Here, we show that non-hydrolyzable analogues of PPi, bisphosphonates, are potent inhibitors of T. cruzi hexokinase (TcHK). We determined the activity of 42 bisphosphonates against TcHK, and the IC(50) values were used to construct pharmacophore and comparative molecular similarity indices analysis (CoMSIA) models for enzyme inhibition. Both models revealed the importance of electrostatic, hydrophobic, and steric interactions, and the IC(50) values for 17 active compounds were predicted with an average error of 2.4x by using the CoMSIA models. The compound most active against T. cruzi hexokinase was found to have a 2.2 microM IC(50) versus the clinically relevant intracellular amastigote form of T. cruzi, but only a approximately 1-2 mM IC(50) versus Dictyostelium discoideum and a human cell line, indicating selective activity versus T. cruzi.

Amiodarone Has Intrinsic Anti-TrypanosomacruziActivity and Acts Synergistically with Posaconazole†

There is no effective treatment for the prevalent chronic form of Chagas' disease in Latin America. Its causative agent, the protozoan parasite Trypanosoma cruzi, has an essential requirement for ergosterol, and ergosterol biosynthesis inhibitors, such as the antifungal drug posaconazole, have potent trypanocidal activity. The antiarrhythmic compound amiodarone, frequently prescribed for the symptomatic treatment of Chagas' disease patients, has also recently been shown to have antifungal activity. We now show here for the first time that amiodarone has direct activity against T. cruzi, both in vitro and in vivo, and that it acts synergistically with posaconazole. We found that amiodarone, in addition to disrupting the parasites' Ca(2+) homeostasis, also blocks ergosterol biosynthesis, and that posaconazole also affects Ca(2+) homeostasis. These results provide logical explanations for the synergistic activity of amiodarone with azoles against T. cruzi and open up the possibility of novel, combination therapy approaches to the treatment of Chagas' disease using currently approved drugs.

Antiproliferative and ultrastructural effects of BPQ-OH, a specific inhibitor of squalene synthase, on Leishmania amazonensis

Parasites of the Leishmania genus require for the growth and viability the de novo synthesis of specific sterols as such as episterol and 5-dehydroepisterol because cholesterol, which is abundant in their mammalian hosts, does not fulfill the parasite sterol requirements. Squalene synthase catalyzes the first committed step in the sterol biosynthesis and has been studied as a possible target for the treatment of high cholesterol levels in humans. In this work we investigated the antiproliferative and ultrastructural effects induced by 3-(biphenyl-4-yl)-3-hydroxyquinuclidine (BPQ-OH), a specific inhibitor of squalene synthase, on promastigote and amastigote forms of Leishmania amazonensis. BPQ-OH had a potent dose-dependent growth inhibitory effect against promastigotes and amastigotes, with IC(50) values 0.85 and 0.11 microM, respectively. Ultrastructural analysis of the treated parasites revealed several changes in the morphology of promastigote forms. The main ultrastructural change was found in the plasma membrane, which showed signs of disorganization, with the concomitant formation of elaborated structures. We also observed alterations in the mitochondrion-kinetoplast complex such as mitochondrial swelling, rupture of its internal membrane and an abnormal compaction of the kinetoplast. Other alterations included the appearance of multivesicular bodies, myelin-like figures, alterations of the flagellar membrane and presence of parasites with two or more nuclei and kinetoplasts. We conclude that the BPQ-OH was a potent growth inhibitor of L. amazonensis, which led to profound changes of the parasite's ultrastructure and might be a valuable lead compound for the development of novel anti-Leishmania agents.

Chemotherapy of trypanosomiases and leishmaniasis

New formulations, therapeutic switching of the established drugs amphotericin B and paromomycin, and the serendipitous discovery of miltefosine have markedly improved leishmaniasis chemotherapy in the past 21 years. The situation for the two trypanosomiases has been less encouraging. Apart from the introduction of eflornithine for the treatment of late-stage human African trypanosomiasis, with its serious limitations in terms of cost and difficulty of administration, no new drugs have been incorporated into the chemotherapeutic arsenal in the past 25 years, despite important advances in knowledge of the biology of the etiological agents and the pathophysiology of these diseases. In the case of Chagas disease, several classes of compound that target the validated biochemical pathways of the parasite (e.g. inhibitors of sterol biosynthesis and cysteine proteases) are in the pipeline. With the availability of complete genome sequences for all three pathogens, and methods for rapid validation of targets, it is hoped that much-needed amelioration will occur soon. Financial constraints continue to represent a major hurdle to drug development. However, the appearance of not-for-profit product-development partnerships offers a new paradigm for bringing new drugs to patients.

Preparation of transition-state analogues of sterol 24-methyl transferase as potential anti-parasitics

There is an urgent need for new drugs to treat leishmaniasis and Chagas disease. One important drug target in these organisms is sterol biosynthesis. In these organisms the main endogenous sterols are ergosta- and stigmata-like compounds in contrast to the situation in mammals, which have cholesterol as the sole sterol. In this paper we discuss the design, synthesis and evaluation of potential transition state analogues of the enzyme Delta24(25)-methyltransferase (24-SMT). This enzyme is essential for the biosynthesis of ergosterol, but not required for the biosynthesis of cholesterol. A series of compounds were successfully synthesised in which mimics of the S-adenosyl methionine co-factor were attached to the sterol nucleus. Compounds were evaluated against recombinant Leishmania major 24-SMT and the parasites L. donovani and Trypanosoma cruzi in vitro, causative organisms of leishmaniasis and Chagas disease, respectively. Some of the compounds showed inhibition of the recombinant Leishmania major 24-SMT and induced growth inhibition of the parasites. Some compounds also showed anti-parasitic activity against L. donovani and T. cruzi, but no inhibition of the enzyme. In addition, some of the compounds had anti-proliferative activity against the bloodstream forms of Trypanosoma brucei rhodesiense, which causes African trypanosomiasis.

Comparative efficacies of TAK-187, a long-lasting ergosterol biosynthesis inhibitor, and benznidazole in preventing cardiac damage in a murine model of Chagas' disease

We carried out a comparative study of benznidazole and TAK-187, a long-lasting ergosterol biosynthesis inhibitor, with a murine model of Chagas' disease. The results indicated that TAK-187 was more effective than benznidazole in preventing Trypanosoma cruzi-induced cardiac damage in experimental animals.

Anti-proliferative synergy of lysophospholipid analogues and ketoconazole against Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae): cellular and ultrastructural analysis

OBJECTIVES

Investigation of the antiproliferative synergy of the lysophospholipid analogues (LPAs) edelfosine, ilmofosine and miltefosine with the ergosterol biosynthesis inhibitor ketoconazole against Trypanosoma cruzi.

METHODS

The effect of LPAs, ketoconazole and their combination was evaluated against epimastigotes and intracellular amastigotes by the parameter IC50 leading to construction of isobolograms, for determination of a synergic effect. For epimastigotes, ultrastructural damage induced by these treatments was evaluated by transmission and scanning electron microscopy.

RESULTS

Synergy was confirmed against both epimastigotes and amastigotes of the parasite. Edelfosine or ketoconazole alone induced morphological alterations in the plasma membrane and reservosomes of the parasites, while in combination, they also led to severe mitochondrial damage, formation of autophagic structures and multinucleation. Scanning electron microscopy confirmed the effect at the plasma membrane and also revealed alterations in the shape of the parasites.

CONCLUSIONS

Our results describe the synergic anti-proliferative effect of LPAs and ketoconazole against epimastigotes and intracellular amastigotes and suggest that in epimastigotes, plasma membrane, reservosomes and mitochondria are targets of these drugs, possibly by interference with lipid metabolism.

Intermediary metabolism of Trypanosoma cruzi

In this article, Julio Urbino discusses the characteristics o f the intermediary metabolism of Trypanosoma cruzi (the causative agent of Chagas disease), which are responsible for the unusual capacity of this parasite to use carbohydrates or amino acids as carbon and energy sources without drastic changes in its catabolic enzyme levels(1-3). Many, but not all, o f the metabolic capabilities of this organism are shared with Leishmania and the procyclic form o f the African trypanosomes, and the reviewer presents a metabolic model which is also consistent with the information available on these other parasites(2,4).

Antiproliferative synergism of azasterols and antifolates against Toxoplasma gondii

The antiproliferative effects of two azasterols, 22,26-azasterol (20-piperidin-2-yl-5alpha-pregnan-3beta-20(R,S)-diol, AZA) and 24,25(R,S)-epiminolanosterol (EIL), in combination with sulphadiazine (SDZ) and pyrimethamine (PYR) were studied against Toxoplasma gondii tachyzoites growing in cultured mammalian cells. We had previously shown that AZA and EIL, two known inhibitors of Delta24(25)sterol methyl transferase in fungi and protozoa, have a potent and selective anti-T. gondii activity, although no 24-alkyl sterols have been detected in this parasite. We now report that when these sterol analogues were used in combination with the conventional SDZ/PYR treatment, potent synergistic effects were observed, ranging from 10- to 100-fold reductions of the IC50 values in the presence of sub-optimal doses of azasterols. When exposed to these drug combinations, intracellular T. gondii parasites displayed diverse subcellular alterations, including mitochondrial swelling, the arrest of the endodiogeny process with fragmented nuclei and subsequent cell lysis. These results suggest a potential new approach for the treatment of toxoplasmosis, which could significantly lower the required levels of antifolates and thus their adverse side effects.