Experimental chemotherapy for Chagas disease: 15 years of research contributions from in vivo and in vitro studies

C57BL/6 α-1,3-Galactosyltransferase Knockout Mouse as an Animal Model for Experimental Chagas Disease

The leading animal model of experimental Chagas disease, the mouse, plays a significant role in studies for vaccine development, diagnosis, and human therapies. Humans, along with Old World primates, alone among mammals, cannot make the terminal carbohydrate linkage of the α-Gal trisaccharide. It has been established that the anti-α-Gal immune response is likely to be a critical factor for protection against Trypanosoma cruzi (T. cruzi) infection in humans. However, the mice customarily employed for the study of T. cruzi infection naturally express the α-Gal epitope and therefore do not produce anti-α-Gal antibodies. Here, we used the C57BL/6 α-1,3-galactosyltransferase knockout (α-GalT-KO) mouse, which does not express the α-Gal epitope as a model for experimental Chagas disease. We found the anti-α-Gal IgG antibody response to an increase in α-GalT-KO mice infected with Arequipa and Colombiana strains of T. cruzi, leading to fewer parasite nests, lower parasitemia, and an increase of INF-γ, TNF-α, and IL-12 cytokines in the heart of α-GalT-KO mice compared with α-GalT-WT mice on days 60 and 120 postinfection. We therefore agree that the C57BL/6 α-GalT-KO mouse represents a useful model for initial testing of therapeutic and immunological approaches against different strains of T. cruzi.

Therapeutic Interventions for Countering Leishmaniasis and Chagas's Disease: From Traditional Sources to Nanotechnological Systems

The incidence of neglected diseases in tropical countries, such as Leishmaniasis and Chagas's disease, is attributed to a set of biological and ecological factors associated with the socioeconomic context of developing countries and with a significant burden to health care systems. Both Leishmaniasis and Chagas's disease are caused by different protozoa and develop diverse symptoms, which depend on the specific species infecting man. Currently available drugs to treat these disorders have limited therapeutic outcomes, frequently due to microorganisms' drug resistance. In recent years, significant efforts have been made towards the development of innovative drug delivery systems aiming to improve bioavailability and pharmacokinetic profiles of classical drug therapy. This paper discusses the key facts of Leishmaniasis and Chagas's disease, the currently available pharmacological therapies and the new drug delivery systems for conventional drugs.

American trypanosomiasis, or Chagas disease, in Panama: a chronological synopsis of ecological and epidemiological research

American trypanosomiasis, or Chagas disease, is a growing public health problem in Panama, and further forest degradation due to human population growth is expected to worsen the situation. Most people infected with the parasite Trypanosoma cruzi are silently ill, and their life expectancy is severely compromised, which contributes to further deterioration of living conditions in endemic regions. Here, we review the outcomes of nearly 100 years of ecological and epidemiological investigation about Chagas disease in Panama, in an attempt to highlight progress, identify needs, and re-orient future efforts. Rhodnius pallescens and Triatoma dimidiata are both primary vectors of T. cruzi in Panama, but R. pallescens seems more efficient in human-altered forest ecosystems due to a greater degree of association with Attalea butyracea. In contrast, T. dimidiata transmits T. cruzi efficiently under more sylvatic conditions (e.g. settlements inside old-growth or secondary forest patches), where its populations reach considerable numbers irrespective of the absence of A. butyracea. A trend of increasing forest degradation, suburbanization, and development of tourism in Panama favoring the establishment of A. butyracea and other palm tree species (Acrocomia sp.) suggests that a colonist species like R. pallescens will continue to play a more prominent role in the transmission of T. cruzi than a forest specialist like T. dimidiata. However, studies about the taxonomic status and ecology of these vectors are still needed in Panama to address their transmission potential fully. The implementation of an active surveillance system and education programs could greatly minimize the risk of Chagas disease transmission in Panama, preventing fatal infections in children from endemic areas.

Phenotypic evaluation and in silico ADMET properties of novel arylimidamides in acute mouse models of Trypanosoma cruzi infection

Arylimidamides (AIAs), previously termed as reversed amidines, present a broad spectrum of activity against intracellular microorganisms. In the present study, three novel AIAs were evaluated in a mouse model of Trypanosoma cruzi infection, which is the causative agent of Chagas disease. The bis-AIAs DB1957, DB1959 and DB1890 were chosen based on a previous screening of their scaffolds that revealed a very promising trypanocidal effect at nanomolar range against both the bloodstream trypomastigotes (BTs) and the intracellular forms of the parasite. This study focused on both mesylate salts DB1957 and DB1959 besides the hydrochloride salt DB1890. Our current data validate the high activity of these bis-AIA scaffolds that exhibited EC₅₀ (drug concentration that reduces 50% of the number of the treated parasites) values ranging from 14 to 78 nM and 190 to 1,090 nM against bloodstream and intracellular forms, respectively, also presenting reasonable selectivity indexes and no mutagenicity profile predicted by in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET). Acute toxicity studies using murine models revealed that these AIAs presented only mild toxic effects such as reversible abdominal contractions and ruffled fur. Efficacy assays performed with Swiss mice infected with the Y strain revealed that the administration of DB1957 for 5 consecutive days, with the first dose given at parasitemia onset, reduced the number of BTs at the peak, ranging between 21 and 31% of decrease. DB1957 was able to provide 100% of animal survival, while untreated animals showed 70% of mortality rates. DB1959 and DB1890B did not reduce circulating parasitism but yielded >80% of survival rates.

Cardioprotective actions of curcumin on the pathogenic NFAT/COX-2/prostaglandin E2 pathway induced during Trypanosoma cruzi infection

BACKGROUND

Diverse cardiovascular signaling routes have been considered critical for Chagas cardiomyopathy caused by the protozoan parasite Trypanosoma cruzi. Along this line, T. cruzi infection and endothelin-1 (ET-1) have been shown to cooperatively activate the Ca²⁺/NFAT cascade in cardiomyocytes, leading to cyclooxygenase type 2 (COX-2) induction and increased release of prostanoids and prohypertrophic peptides.

PURPOSE

To determine whether the well-known cardioprotective and anti-inflammatory effects of curcumin (Cur) could be helpful to interfere with this key machinery for pathogenesis of Chagas myocarditis.

STUDY DESIGN

Cur treatment was evaluated through in vivo studies using a murine model of acute T. cruzi infection and in vitro experiments using ET-1-stimulated and parasite-infected mouse cardiomyocytes.

METHODS

Cur-treated and untreated infected mice were followed-up to estimate survival postinfection and heart tissues from both groups were analyzed for inflammatory infiltration by histopathology, whereas parasite load, induction of arachidonic acid pathway and natriuretic peptide expression were determined by real-time PCR. Molecular analysis of Cur myocardial targets included intracellular calcium measurement, NFAT and COX-2 induction in transfected cells, and assessment of NFAT, COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) levels by immunoblotting, prostaglandin E₂ (PGE₂) by ELISA, b-type natriuretic peptide (BNP) by real-time PCR, and PGE₂/EP4 receptor/BNP interaction by transwell experiments.

RESULTS

Cur treatment of acute Chagas mice enhanced survival and proved to hinder relevant inflammatory processes in the heart, including leukocyte recruitment, activation of the eicosanoid pathway and BNP overexpression, without modifying parasite burden in the organ. Cur was capable of blocking Ca²⁺-dependent NFATc1 transcriptional activity, COX-2 and mPGES-1 induction, and subsequent PGE₂ production in ET-1-stimulated and parasite-infected cardiomyocytes. Furthermore, the decline of cardiomyocyte-derived prostaglandin levels achieved upon Cur treatment impaired effective PGE₂/EP4 receptor interaction, resulting in attenuated expression of BNP, a strong indicator of cardiac pathogenesis in Chagas disease, in both infected and uninfected cells.

CONCLUSION

Our current study shows a putative mechanism of action of Cur involving inhibition of the Ca²⁺/NFAT-dependent, pathogenic COX-2/mPGES-1/PGE₂ pathway in T. cruzi-infected myocytes, underlying cardioprotection achieved in Cur-treated infected mice. With a view to the limited therapeutic possibilities available, Cur represents a promising approach for the treatment of Chagas heart disease.

Preventing the transmission of American trypanosomiasis and its spread into non-endemic countries

American trypanosomiasis, commonly known as Chagas disease, is caused by the flagellate protozoan parasite Trypanosoma cruzi. An estimated eight million people infected with T. cruzi currently reside in the endemic regions of Latin America. However, as the disease has now been imported into many non-endemic countries outside of Latin America, it has become a global health issue. We reviewed the transmission patterns and current status of disease spread pertaining to American trypanosomiasis at the global level, as well as recent advances in research. Based on an analysis of the gaps in American trypanosomiasis control, we put forward future research priorities that must be implemented to stop the global spread of the disease.

Chagas Disease Drug Discovery

American trypanosomiasis, or Chagas disease, is the result of infection by the Trypanosoma cruzi parasite. Endemic in Latin America where it is the major cause of death from cardiomyopathy, the impact of the disease is reaching global proportions through migrating populations. New drugs that are safe, efficacious, low cost, and adapted to the field are critically needed. Over the past five years, there has been increased interest in the disease and a surge in activities within various organizations. However, recent clinical trials with azoles, specifically posaconazole and the ravuconazole prodrug E1224, were disappointing, with treatment failure in Chagas patients reaching 70% to 90%, as opposed to 6% to 30% failure for benznidazole-treated patients. The lack of translation from in vitro and in vivo models to the clinic observed for the azoles raises several questions. There is a scientific requirement to review and challenge whether we are indeed using the right tools and decision-making processes to progress compounds forward for the treatment of this disease. New developments in the Chagas field, including new technologies and tools now available, will be discussed, and a redesign of the current screening strategy during the discovery process is proposed.

The in vitro activity of fatty diamines and amino alcohols against mixed amastigote and trypomastigote Trypanosoma cruzi forms

Four diamines and three amino alcohols derived from 1-decanol, 1-dodecanol and 1,2-dodecanediol were evaluated in an in vitro assay against a mixture of trypomastigote and intracellular amastigote forms of Trypanosoma cruzi. Two of these compounds (6 and 7) showed better activity against both proliferative stages of T. cruzi than the positive control benznidazole, three were of similar potency (1, 2 and 5) and two were less active (3 and 4).

In vitro and in vivo studies of the biological activity of novel arylimidamides against Trypanosoma cruzi

Fifteen novel arylimidamides (AIAs) (6 bis-amidino and 9 mono-amidino analogues) were assayed against Trypanosoma cruzi in vitro and in vivo. All the bis-AIAs were more effective than the mono-AIAs, and two analogues, DB1967 and DB1989, were further evaluated in vivo. Although both of them reduced parasitemia, protection against mortality was not achieved. Our results show that the number of amidino-terminal units affects the efficacy of arylimidamides against T. cruzi.

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

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

Trypanocidal activity of guaianolide obtained from Tanacetum parthenium (L.) Schultz-Bip. and its combinational effect with benznidazole

In the present study, we evaluated the in vitro antiprotozoal activity of a guaianolide (11,13-dehydrocompressanolide) isolated from Tanacetum parthenium against Trypanosoma cruzi and investigated the possible combinational effect of guaianolide and benznidazole. The isolated compound was shown to be effective against T. cruzi, with IC₅₀ values of 18.1±0.8 and 66.6±1.3 μM against the multiplicative epimastigote and amastigote forms, respectively. The best results were obtained against trypomastigotes, with an EC₅₀ of 5.7±0.7 μM. The guaianolide presented no toxicity in LLCMK₂ cells (CC₅₀ of 93.5 μM) and was 16.4-fold more selective for trypomastigotes. The study of the combinational effect of benznidazole and guaianolide revealed the presence of a synergistic effect against the epimastigote form and marginal additive effect against the trypomastigote form. Striking morphological changes were observed in epimastigotes treated with guaianolide, such as thinning and stretching of the cell body and flagellum and changes in the format of the cell body with apparent leakage of the cytoplasmic content in trypomastigote forms. The ultrastructural analysis of epimastigotes revealed the presence of membranes that involved organelles and formation of myelin-like figures. Flow cytometry revealed a cell volume reduction and decrease in mitochondrial membrane potential. However, no major changes in cell membrane integrity were found in the epimastigote form treated with guaianolide.

CYP51 structures and structure-based development of novel, pathogen-specific inhibitory scaffolds

CYP51 (sterol 14α-demethylase) is a cytochrome P450 enzyme essential for sterol biosynthesis and the primary target for clinical and agricultural antifungal azoles. The azoles that are currently in clinical use for systemic fungal infections represent modifications of two basic scaffolds, ketoconazole and fluconazole, all of them being selected based on their antiparasitic activity in cellular experiments. By studying direct inhibition of CYP51 activity across phylogeny including human pathogens Trypanosoma brucei, Trypanosoma cruzi and Leishmania infantum, we identified three novel protozoa-specific inhibitory scaffolds, their inhibitory potency correlating well with antiprotozoan activity. VNI scaffold (carboxamide containing β-phenyl-imidazoles) is the most promising among them: killing T. cruzi amastigotes at low nanomolar concentration, it is also easy to synthesize and nontoxic. Oral administration of VNI (up to 400 mg/kg) neither leads to mortality nor reveals significant side effects up to 48 h post treatment using an experimental mouse model of acute toxicity. Trypanosomatidae CYP51 crystal structures determined in the ligand-free state and complexed with several azole inhibitors as well as a substrate analog revealed high rigidity of the CYP51 substrate binding cavity, which must be essential for the enzyme strict substrate specificity and functional conservation. Explaining profound potency of the VNI inhibitory scaffold, the structures also outline guidelines for its further development. First steps of the VNI scaffold optimization have been undertaken; the results presented here support the notion that CYP51 structure-based rational design of more efficient, pathogen-specific inhibitors represents a highly promising direction.

Novel 3-nitro-1H-1,2,4-triazole-based amides and sulfonamides as potential antitrypanosomal agents

A series of novel 3-nitro-1H-1,2,4-triazole-based (and in some cases 2-nitro-1H-imidazole-based) amides and sulfonamides were characterized for their in vitro antitrypanosomal and antileishmanial activities as well as mammalian toxicity. Out of 36 compounds tested, 29 (mostly 3-nitro-1H-1,2,4-triazoles) displayed significant activity against Trypanosoma cruzi intracellular amastigotes (IC(50) ranging from 28 nM to 3.72 μM) without concomitant toxicity to L6 host cells (selectivity 66-2782). Twenty-three of these active compounds were more potent (up to 58-fold) than the reference drug benznidazole, tested in parallel. In addition, nine nitrotriazoles which were moderately active (0.5 μM ≤ IC(50) < 6.0 μM) against Trypanosoma brucei rhodesiense trypomastigotes were 5-31-fold more active against bloodstream-form Trypanosoma brucei brucei trypomastigotes engineered to overexpress reduced nicotinamide adenine dinucleotide dependent nitroreductase. Finally, three nitrotriazoles displayed a moderate activity against the axenic form of Leishmania donovani . Therefore, 3-nitro-1H-1,2,4-triazole-based amides and sulfonamides are potent antitrypanosomal agents.

Experimental chemotherapy and approaches to drug discovery for Trypanosoma cruzi infection

In the 100 years since the discovery of Chagas disease, only two drugs have been developed and introduced into clinical practice, and these drugs were introduced over 40 years ago. The tools of drug discovery have improved dramatically in the interim; however, this has not translated into new drugs for Chagas disease. This has been largely because the main practitioners of drug discovery are pharmaceutical companies who are not financially motivated to invest in Chagas disease and other "orphan" diseases. As a result, it has largely been up to academic groups to bring drug candidates through the discovery pipeline and to clinical trials. The difficulty with drug discovery in academia has been the challenge of bringing together the diverse expertise in biology, chemistry, and pharmacology in concerted efforts towards a common goal of developing therapeutics. Funding is often inadequate, but lack of coordination amongst academic investigators with different expertise has also contributed to the slow progress. The purpose of this chapter is to provide an overview of approaches that can be accomplished in academic settings for preclinical drug discovery for Chagas disease. The chapter addresses methods of drug screening against Trypanosoma cruzi cultures and in animal models and includes general topics on compound selection, testing for drug-like properties (including oral bioavailability), investigating the pharmacokinetics and toxicity of compounds, and finally providing parameters to help with triaging compounds.

The efficacy of novel arylimidamides against Trypanosoma cruzi in vitro

The present study aimed to determine the in vitro biological efficacy and selectivity of 7 novel AIAs upon bloodstream trypomastigotes and intracellular amastigotes of Trypanosoma cruzi. The biological activity of these aromatic compounds was assayed for 48 and 24 h against intracellular parasites and bloodstream forms of T. cruzi (Y strain), respectively. Additional assays were also performed to determine their potential use in blood banks by treating the bloodstream parasites with the compounds diluted in mouse blood for 24 h at 4°C. Toxicity against mammalian cells was evaluated using primary cultures of cardiac cells incubated for 24 and 48 h with the AIAs and then cellular death rates were determined by MTT colorimetric assays. Our data demonstrated the outstanding trypanocidal effect of AIAs against T. cruzi, especially DB1853, DB1862, DB1867 and DB1868, giving IC50 values ranging between 16 and 70 nanomolar against both parasite forms. All AIAs presented superior efficacy to benznidazole and some, such as DB1868, also demonstrated promising activity as a candidate agent for blood prophylaxis. The excellent anti-trypanosomal efficacy of these novel AIAs against T. cruzi stimulates further in vivo studies and justifies the screening of new analogues with the goal of establishing a useful alternative therapy for Chagas disease.

Combined treatment of heterocyclic analogues and benznidazole upon Trypanosoma cruzi in vivo

Chagas disease caused by Trypanosoma cruzi is an important cause of mortality and morbidity in Latin America but no vaccines or safe chemotherapeutic agents are available. Combined therapy is envisioned as an ideal approach since it may enhance efficacy by acting upon different cellular targets, may reduce toxicity and minimize the risk of drug resistance. Therefore, we investigated the activity of benznidazole (Bz) in combination with the diamidine prodrug DB289 and in combination with the arylimidamide DB766 upon T. cruzi infection in vivo. The oral treatment of T.cruzi-infected mice with DB289 and Benznidazole (Bz) alone reduced the number of circulating parasites compared with untreated mice by about 70% and 90%, respectively. However, the combination of these two compounds decreased the parasitemia by 99% and protected against animal mortality by 100%, but without providing a parasitological cure. When Bz (p.o) was combined with DB766 (via ip route), at least a 99.5% decrease in parasitemia levels was observed. DB766+Bz also provided 100% protection against mice mortality while Bz alone provided about 87% protection. This combined therapy also reduced the tissular lesions induced by T. cruzi infection: Bz alone reduced GPT and CK plasma levels by about 12% and 78% compared to untreated mice group, the combination of Bz with DB766 resulted in a reduction of GPT and CK plasma levels of 56% and 91%. Cure assessment through hemocultive and PCR approaches showed that Bz did not provide a parasitological cure, however, DB766 alone or associated with Bz cured ≥13% of surviving animals.

In vitro efficacy of dicationic compounds and mefloquine enantiomers against Echinococcus multilocularis metacestodes

The current chemotherapy of alveolar echinococcosis (AE) is based on benzimidazoles such as albendazole and has been shown to be parasitostatic rather than parasiticidal, requiring lifelong duration. Thus, new and more efficient treatment options are urgently needed. By employing a recently validated assay based on the release of functional phosphoglucose isomerase (PGI) from dying parasites, the activities of 26 dicationic compounds and of the (+)- and (-)-erythro-enantiomers of mefloquine were investigated. Initial screening of compounds was performed at 40 μM, and those compounds exhibiting considerable antiparasitic activities were also assessed at lower concentrations. Of the dicationic drugs, DB1127 (a diguanidino compound) with activities comparable to nitazoxanide was further studied. The activity of DB1127 was dose dependent and led to severe structural alterations, as visualized by electron microscopy. The (+)- and (-)-erythro-enantiomers of mefloquine showed similar dose-dependent effects, although higher concentrations of these compounds than of DB1127 were required for metacestode damage. In conclusion, of the drugs investigated here, the diguanidino compound DB1127 represents the most promising compound for further study in appropriate in vivo models for Echinococcus multilocularis infection.

Experimental Chemotherapy for Chagas Disease: A Morphological, Biochemical, and Proteomic Overview of Potential Trypanosoma cruzi Targets of Amidines Derivatives and Naphthoquinones

Chagas disease (CD), caused by Trypanosoma cruzi, affects approximately eight million individuals in Latin America and is emerging in nonendemic areas due to the globalisation of immigration and nonvectorial transmission routes. Although CD represents an important public health problem, resulting in high morbidity and considerable mortality rates, few investments have been allocated towards developing novel anti-T. cruzi agents. The available therapy for CD is based on two nitro derivatives (benznidazole (Bz) and nifurtimox (Nf)) developed more than four decades ago. Both are far from ideal due to substantial secondary side effects, limited efficacy against different parasite isolates, long-term therapy, and their well-known poor activity in the late chronic phase. These drawbacks justify the urgent need to identify better drugs to treat chagasic patients. Although several classes of natural and synthetic compounds have been reported to act in vitro and in vivo on T. cruzi, since the introduction of Bz and Nf, only a few drugs, such as allopurinol and a few sterol inhibitors, have moved to clinical trials. This reflects, at least in part, the absence of well-established universal protocols to screen and compare drug activity. In addition, a large number of in vitro studies have been conducted using only epimastigotes and trypomastigotes instead of evaluating compounds' activities against intracellular amastigotes, which are the reproductive forms in the vertebrate host and are thus an important determinant in the selection and identification of effective compounds for further in vivo analysis. In addition, due to pharmacokinetics and absorption, distribution, metabolism, and excretion characteristics, several compounds that were promising in vitro have not been as effective as Nf or Bz in animal models of T. cruzi infection. In the last two decades, our team has collaborated with different medicinal chemistry groups to develop preclinical studies for CD and investigate the in vitro and in vivo efficacy, toxicity, selectivity, and parasite targets of different classes of natural and synthetic compounds. Some of these results will be briefly presented, focusing primarily on diamidines and related compounds and naphthoquinone derivatives that showed the most promising efficacy against T. cruzi.

Screening of Potential anti-Trypanosoma cruzi Candidates: In Vitro and In Vivo Studies

Chagas disease (CD), caused by the intracellular protozoan Trypanosoma cruzi, is a parasitic illness endemic in Latin America. In the centennial after CD discovery by Carlos Chagas (1909), although it still represents an important public health problem in these affected areas, the existing chemotherapy, based on benznidazole and nifurtimox (both introduced more than four decades ago), is far from being considered ideal due to substantial toxicity, variable effect on different parasite stocks and well-known poor activity on the chronic phase. CD is considered one of the major "neglected" diseases of the world, as commercial incentives are very limited to guarantee investments for developing and discovering novel drugs. In this context, our group has been pursuing, over the last years, the efficacy, selectivity, toxicity, cellular targets and mechanisms of action of new potential anti-T. cruzi candidates screened from an in-house compound library of different research groups in the area of medicinal chemistry. A brief review regarding these studies will be discussed, mainly related to the effect on T. cruzi of (i) diamidines and related compounds, (ii) natural naphthoquinone derivatives, and (iii) megazol derivatives.

In vitro and in vivo efficacies of mefloquine-based treatment against alveolar echinococcosis

Alveolar echinococcosis (AE) is caused by the metacestode stage of the fox tapeworm Echinococcus multilocularis and causes severe disease in the human liver, and occasionally in other organs, that is fatal when treatment is unsuccessful. The present chemotherapy against AE is based on mebendazole and albendazole. Albendazole treatment has been found to be ineffective in some instances, is parasitostatic rather than parasiticidal, and usually involves the lifelong uptake of large doses of drugs. Thus, new treatment options are urgently needed. In this study we investigated the in vitro and in vivo efficacy of mefloquine against E. multilocularis metacestodes. Treatment using mefloquine (20 μM) against in vitro cultures of metacestodes resulted in rapid and complete detachment of large parts of the germinal layer from the inner surface of the laminated layer within a few hours. The in vitro activity of mefloquine was dependent on the dosage. In vitro culture of metacestodes in the presence of 24 μM mefloquine for a period of 10 days was parasiticidal, as determined by murine bioassays, while treatment with 12 μM was not. Oral application of mefloquine (25 mg/kg of body weight administered twice a week for a period of 8 weeks) in E. multilocularis-infected mice was ineffective in achieving any reduction of parasite weight, whereas treatment with albendazole (200 mg/kg/day) was highly effective. However, when the same mefloquine dosage was applied intraperitoneally, the reduction in parasite weight was similar to the reduction seen with oral albendazole application. Combined application of both drugs did not increase the treatment efficacy. In conclusion, mefloquine represents an interesting drug candidate for the treatment of AE, and these results should be followed up in appropriate in vivo studies.

The biological in vitro effect and selectivity of aromatic dicationic compounds on Trypanosoma cruzi

Trypanosoma cruzi is a parasite that causes Chagas disease, which affects millions of individuals in endemic areas of Latin America. One hundred years after the discovery of Chagas disease, it is still considered a neglected illness because the available drugs are unsatisfactory. Aromatic compounds represent an important class of DNA minor groove-binding ligands that exhibit potent antimicrobial activity. This study focused on the in vitro activity of 10 aromatic dicationic compounds against bloodstream trypomastigotes and intracellular forms of T. cruzi. Our data demonstrated that these compounds display trypanocidal effects against both forms of the parasite and that seven out of the 10 compounds presented higher anti-parasitic activity against intracellular parasites compared with the bloodstream forms. Additional assays to determine the potential toxicity to mammalian cells showed that the majority of the dicationic compounds did not considerably decrease cellular viability. Fluorescent microscopy analysis demonstrated that although all compounds were localised to a greater extent within the kinetoplast than the nucleus, no correlation could be found between compound activity and kDNA accumulation. The present results stimulate further investigations of this class of compounds for the rational design of new chemotherapeutic agents for Chagas disease.

In vitro and in vivo experimental models for drug screening and development for Chagas disease

Chagas disease, a neglected illness, affects nearly 12-14 million people in endemic areas of Latin America. Although the occurrence of acute cases sharply has declined due to Southern Cone Initiative efforts to control vector transmission, there still remain serious challenges, including the maintenance of sustainable public policies for Chagas disease control and the urgent need for better drugs to treat chagasic patients. Since the introduction of benznidazole and nifurtimox approximately 40 years ago, many natural and synthetic compounds have been assayed against Trypanosoma cruzi, yet only a few compounds have advanced to clinical trials. This reflects, at least in part, the lack of consensus regarding appropriate in vitro and in vivo screening protocols as well as the lack of biomarkers for treating parasitaemia. The development of more effective drugs requires (i) the identification and validation of parasite targets, (ii) compounds to be screened against the targets or the whole parasite and (iii) a panel of minimum standardised procedures to advance leading compounds to clinical trials. This third aim was the topic of the workshop entitled Experimental Models in Drug Screening and Development for Chagas Disease, held in Rio de Janeiro, Brazil, on the 25th and 26th of November 2008 by the Fiocruz Program for Research and Technological Development on Chagas Disease and Drugs for Neglected Diseases Initiative. During the meeting, the minimum steps, requirements and decision gates for the determination of the efficacy of novel drugs for T. cruzi control were evaluated by interdisciplinary experts and an in vitro and in vivo flowchart was designed to serve as a general and standardised protocol for screening potential drugs for the treatment of Chagas disease.

Arylimidamide DB766, a potential chemotherapeutic candidate for Chagas' disease treatment

Chagas' disease, a neglected tropical illness for which current therapy is unsatisfactory, is caused by the intracellular parasite Trypanosoma cruzi. The goal of this work is to investigate the in vitro and in vivo effects of the arylimidamide (AIA) DB766 against T. cruzi. This arylimidamide exhibits strong trypanocidal activity and excellent selectivity for bloodstream trypomastigotes and intracellular amastigotes (Y strain), giving IC(50)s (drug concentrations that reduce 50% of the number of the treated parasites) of 60 and 25 nM, respectively. DB766 also exerts striking effects upon different parasite stocks, including those naturally resistant to benznidazole, and displays higher activity in vitro than the reference drugs. By fluorescent and transmission electron microscopy analyses, we found that this AIA localizes in DNA-enriched compartments and induces considerable damage to the mitochondria. DB766 effectively reduces the parasite load in the blood and cardiac tissue and presents efficacy similar to that of benznidazole in mouse models of T. cruzi infection employing the Y and Colombian strains, using oral and intraperitoneal doses of up to 100 mg/kg/day that were given after the establishment of parasite infection. This AIA ameliorates electrocardiographic alterations, reduces hepatic and heart lesions induced by the infection, and provides 90 to 100% protection against mortality, which is similar to that provided by benznidazole. Our data clearly show the trypanocidal efficacy of DB766, suggesting that this AIA may represent a new lead compound candidate to Chagas' disease treatment.

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.