Trypanocidal drugs: mechanisms, resistance and new targets

Drugs in preclinical and early clinical development for the treatment of Chagas´s disease: the current status

INTRODUCTION

Chagas disease is spreading faster than expected in different countries, and little progress has been reported in the discovery of new drugs to combat Trypanosoma cruzi infection in humans. Recent clinical trials have ended with small hope. The pathophysiology of this neglected disease and the genetic diversity of parasites are exceptionally complex. The only two drugs available to treat patients are far from being safe, and their efficacy in the chronic phase is still unsatisfactory.

AREAS COVERED

This review offers a comprehensive examination and critical review of data reported in the last 10 years, and it is focused on findings of clinical trials and data acquired in vivo in preclinical studies.

EXPERT OPINION

The in vivo investigations classically in mice and dog models are also challenging and time-consuming to attest cure for infection. Poorly standardized protocols, availability of diagnosis methods and disease progression markers, the use of different T. cruzi strains with variable benznidazole sensitivities, and animals in different acute and chronic phases of infection contribute to it. More synchronized efforts between research groups in this field are required to put in evidence new promising substances, drug combinations, repurposing strategies, and new pharmaceutical formulations to impact the therapy.

A panel of phenotypically and genotypically diverse bioluminescent:fluorescent Trypanosoma cruzi strains as a resource for Chagas disease research

Chagas disease is caused by Trypanosoma cruzi, a protozoan parasite that displays considerable genetic diversity. Infections result in a range of pathological outcomes, and different strains can exhibit a wide spectrum of anti-parasitic drug tolerance. The genetic determinants of infectivity, virulence and therapeutic susceptibility remain largely unknown. As experimental tools to address these issues, we have generated a panel of bioluminescent:fluorescent parasite strains that cover the diversity of the T. cruzi species. These reporters allow spatio-temporal infection dynamics in murine models to be monitored in a non-invasive manner by in vivo imaging, provide a capability to detect rare infection foci at single-cell resolution, and represent a valuable resource for investigating virulence and host:parasite interactions at a mechanistic level. Importantly, these parasite reporter strains can also contribute to the Chagas disease drug screening cascade by ensuring that candidate compounds have pan-species in vivo activity prior to being advanced into clinical testing. The parasite strains described in this paper are available on request.

Synthesis of new trypanocidal agents from the hybridisation of metronidazole and eugenol analogues

Nitroimidazole compounds are well-known bioactive substances, and the structural activity relationship has been reported whereby the position of the nitro group within the imidazole ring has a large influence on the activity. This study focuses on synthesising new trypanocidal agents from the hybridisation of metronidazole with different natural phenols (eugenol, dihydroeugenol and guaiacol). Two different coupling methodologies have been explored in order to analyse the influence of the connector on bioactivity: i) classic direct esterification (AD compounds) and ii) "click" chemistry using a triazole connector (AC compounds). The in vitro trypanocidal tests show good results for both AC and AD hybrid compounds against both epimastigote and trypomastigote forms of T. cruzi. In silico studies showed positive data for most of the synthesised compounds and, in general present low toxicological risks. The AC compounds present lower ClogP (lipophilicity) values than those found for the AD series and higher TPSA (topological polar surface area) values, suggesting lower lipophilicity may be related to the presence of the triazole connector. The AD series compounds have higher Drug Score values than the AC series derivatives, suggesting better general properties for a pharmacological action.

PEX1 is essential for glycosome biogenesis and trypanosomatid parasite survival

Trypanosomatid parasites are kinetoplastid protists that compartmentalize glycolytic enzymes in unique peroxisome-related organelles called glycosomes. The heterohexameric AAA-ATPase complex of PEX1-PEX6 is anchored to the peroxisomal membrane and functions in the export of matrix protein import receptor PEX5 from the peroxisomal membrane. Defects in PEX1, PEX6 or their membrane anchor causes dysfunction of peroxisomal matrix protein import cycle. In this study, we functionally characterized a putative Trypanosoma PEX1 orthologue by bioinformatic and experimental approaches and show that it is a true PEX1 orthologue. Using yeast two-hybrid analysis, we demonstrate that TbPEX1 can bind to TbPEX6. Endogenously tagged TbPEX1 localizes to glycosomes in the T. brucei parasites. Depletion of PEX1 gene expression by RNA interference causes lethality to the bloodstream form trypanosomes, due to a partial mislocalization of glycosomal enzymes to the cytosol and ATP depletion. TbPEX1 RNAi leads to a selective proteasomal degradation of both matrix protein import receptors TbPEX5 and TbPEX7. Unlike in yeast, PEX1 depletion did not result in an accumulation of ubiquitinated TbPEX5 in trypanosomes. As PEX1 turned out to be essential for trypanosomatid parasites, it could provide a suitable drug target for parasitic diseases. The results also suggest that these parasites possess a highly efficient quality control mechanism that exports the import receptors from glycosomes to the cytosol in the absence of a functional TbPEX1-TbPEX6 complex.

Parasitic Protozoans: Exploring the Potential of N,N'-Bis[2-(5-bromo-7-azabenzimidazol-1-yl)-2-oxoethyl]ethylene-1,3-Diamine and Its Cyclohexyl-1,2-diamine Analogue as TryR and Pf-DHODH Inhibitors

PURPOSE

Major human parasitic protozoans, such as Plasmodium falciparum and Trypanosoma brucei, cause malaria and trypanosomiasis also known as sleeping sickness. In anti-parasitic drug discovery research, trypanothione reductase (TryR) and P. falciparum dihydroorotate dehydrogenase (Pf-DHODH) enzymes are key drug targets in T. brucei and P. falciparum, respectively. The possibility of co-infection of single host by T. brucei and P. falciparum is because both parasites exist in sub-Saharan Africa and the problem of parasite drug resistance necessitates the discovery of new scaffolds, which are strange to the organisms causing these infectious diseases-new scaffolds may help overcome established resistance mechanisms of the organisms.

METHOD

In this study, N,N'-bis[2-(5-bromo-7-azabenzimidazol-1-yl)-2-oxoethyl]ethylene-1,3-diamine and its cyclohexyl-1,2-diamine analogue were explored for their inhibitory potential against TryR and Pf-DHODH by engaging density functional study, molecular dynamic simulations, drug-likeness, in silico and in vitro studies RESULTS/CONCLUSION: Results obtained indicated excellent binding potential of the ligands to the receptors and good ADMET (adsorption, desorption, metabolism, excretion, and toxicity) properties.

A novel palladium complex with a coumarin-thiosemicarbazone hybrid ligand inhibits Trypanosoma cruzi release from host cells and lowers the parasitemia in vivo

In this work, two analogous coumarin-thio and semicarbazone hybrid compounds were prepared and evaluated as a potential antichagasic agents. Furthermore, palladium and platinum complexes with the thiosemicarbazone derivative as ligand (L1) were obtained in order to establish the effect of metal complexation on the antiparasitic activity. All compounds were fully characterized both in solution and in solid state including the resolution of the crystal structure of the palladium complex by X-ray diffraction methods. Unexpectedly, all experimental and theoretical characterizations in the solid state, demonstrated that the obtained palladium and platinum complexes are structurally different: [PdCl(L1)] and [PtCl2(HL1)]. All the studied compounds lower the proliferation of the amastigote form of Trypanosoma cruzi while some of them also have an effect on the trypomastigote stage. Additionally, the compounds inhibit T. cruzi release from host cells in variable extents. The Pd compound presented a remarkable profile in all the in vitro experiments, and it showed no toxicity for mammalian cells in the assayed concentrations. In this sense, in vivo experiments were performed for this compound using an acute model of Chagas disease. Results showed that the complex significantly lowered the parasite count in the mice blood with no significant toxicity.

Repurposing of rabeprazole as an anti-Trypanosoma cruzi drug that targets cellular triosephosphate isomerase

Trypanosoma cruzi is the causative agent of American trypanosomiasis, which mainly affects populations in Latin America. Benznidazole is used to control the disease, with severe effects in patients receiving this chemotherapy. Previous studies have demonstrated the inhibition of triosephosphate isomerase from T. cruzi, but cellular enzyme inhibition has yet to be established. This study demonstrates that rabeprazole inhibits both cell viability and triosephosphate isomerase activity in T. cruzi epimastigotes. Our results show that rabeprazole has an IC50 of 0.4 µM, which is 14.5 times more effective than benznidazole. Additionally, we observed increased levels of methyl-glyoxal and advanced glycation end products after the inhibition of cellular triosephosphate isomerase by rabeprazole. Finally, we demonstrate that the inactivation mechanisms of rabeprazole on triosephosphate isomerase of T. cruzi can be achieved through the derivatization of three of its four cysteine residues. These results indicate that rabeprazole is a promising candidate against American trypanosomiasis.

Benznidazole treatment leads to DNA damage in Trypanosoma cruzi and the persistence of rare widely dispersed non-replicative amastigotes in mice

Benznidazole is the front-line drug used to treat infections with Trypanosoma cruzi, the causative agent of Chagas disease. However, for reasons that are unknown, treatment failures are common. When we examined parasites that survived benznidazole treatment in mice using highly sensitive in vivo and ex vivo bioluminescence imaging, we found that recrudescence is not due to persistence of parasites in a specific organ or tissue that preferentially protects them from drug activity. Surviving parasites are widely distributed and located in host cells where the vast majority contained only one or two amastigotes. Therefore, infection relapse does not arise from a small number of intact large nests. Rather, persisters are either survivors of intracellular populations where co-located parasites have been killed, or amastigotes in single/low-level infected cells exist in a state where they are less susceptible to benznidazole. To better assess the nature of parasite persisters, we exposed infected mammalian cell monolayers to a benznidazole regimen that reduces the intracellular amastigote population to <1% of the pre-treatment level. Of host cells that remained infected, as with the situation in vivo, the vast majority contained only one or two surviving intracellular amastigotes. Analysis, based on non-incorporation of the thymidine analogue EdU, revealed these surviving parasites to be in a transient non-replicative state. Furthermore, treatment with benznidazole led to widespread parasite DNA damage. When the small number of parasites which survive in mice after non-curative treatment were assessed using EdU labelling, this revealed that these persisters were also initially non-replicative. A possible explanation could be that triggering of the T. cruzi DNA damage response pathway by the activity of benznidazole metabolites results in exit from the cell cycle as parasites attempt DNA repair, and that metabolic changes associated with non-proliferation act to reduce drug susceptibility. Alternatively, a small percentage of the parasite population may pre-exist in this non-replicative state prior to treatment.

From Benznidazole to New Drugs: Nanotechnology Contribution in Chagas Disease

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi. Benznidazole and nifurtimox are the two approved drugs for their treatment, but both drugs present side effects and efficacy problems, especially in the chronic phase of this disease. Therefore, new molecules have been tested with promising results aiming for strategic targeting action against T. cruzi. Several studies involve in vitro screening, but a considerable number of in vivo studies describe drug bioavailability increment, drug stability, toxicity assessment, and mainly the efficacy of new drugs and formulations. In this context, new drug delivery systems, such as nanotechnology systems, have been developed for these purposes. Some nanocarriers are able to interact with the immune system of the vertebrate host, modulating the immune response to the elimination of pathogenic microorganisms. In this overview of nanotechnology-based delivery strategies for established and new antichagasic agents, different strategies, and limitations of a wide class of nanocarriers are explored, as new perspectives in the treatment and monitoring of Chagas disease.

Ferrocene-based nitroheterocyclic sulfonylhydrazones: design, synthesis, characterization and trypanocidal properties

A series of new ferrocenyl nitroheterocyclic sulfonylhydrazones (1a-4a and 1b-2b) were prepared by the reaction between formyl (R = H) or acetyl (R = CH3) nitroheterocyclic precursors [4/5-NO2(C5H2XCOR), where X = O, S)] and ferrocenyl tosyl hydrazine [(η5-C5H5)Fe(η5-C5H4SO2-NH-NH2)]. All compounds were characterized by conventional spectroscopic techniques. In the solid state, the molecular structures of compounds 1a, 2b, and 3a were determined by single-crystal X-ray diffraction. The compounds showed an E-configuration around the C=N moiety. Evaluation of trypanocidal activity, measured in vitro against the Trypanosoma cruzi and Trypanosoma brucei strains, indicated that all organometallic tosyl hydrazones displayed activity against both parasite species with a higher level of potency toward T. brucei than T. cruzi. Moreover, the biological evaluation showed that the 5-nitroheterocyclic derivatives were more efficient trypanocidal agents than their 4-nitroheterocyclic counterparts.

Structure-Guided Design and Synthesis of a Pyridazinone Series of Trypanosoma cruzi Proteasome Inhibitors

There is an urgent need for new treatments for Chagas disease, a parasitic infection which mostly impacts South and Central America. We previously reported on the discovery of GSK3494245/DDD01305143, a preclinical candidate for visceral leishmaniasis which acted through inhibition of the Leishmania proteasome. A related analogue, active against Trypanosoma cruzi, showed suboptimal efficacy in an animal model of Chagas disease, so alternative proteasome inhibitors were investigated. Screening a library of phenotypically active analogues against the T. cruzi proteasome identified an active, selective pyridazinone, the development of which is described herein. We obtained a cryo-EM co-structure of proteasome and a key inhibitor and used this to drive optimization of the compounds. Alongside this, optimization of the absorption, distribution, metabolism, and excretion (ADME) properties afforded a suitable compound for mouse efficacy studies. The outcome of these studies is discussed, alongside future plans to further understand the series and its potential to deliver a new treatment for Chagas disease.

Antiparasitic Activity of Plumbago auriculata Extracts and Its Naphthoquinone Plumbagin against Trypanosoma cruzi

Chagas disease (CD) caused by the protozoan Trypanosoma cruzi affects more than six million people worldwide. Treatment is restricted to benznidazole (Bz) and nifurtimox (Nf) that display low activity in the later chronic stage besides triggering toxic events that result in treatment abandonment. Therefore, new therapeutic options are necessary. In this scenario, natural products emerge as promising alternatives to treat CD. In the family Plumbaginaceae, Plumbago sp. exhibits a broad spectrum of biological and pharmacological activities. Thus, our main objective was to evaluate, in vitro and in silico, the biological effect of crude extracts of root and of aerial parts of P. auriculata, as well as its naphthoquinone Plumbagin (Pb) against T. cruzi. The phenotypic assays revealed potent activity of the root extract against different forms (trypomastigote and intracellular forms) and strains (Y and Tulahuen), with a compound concentration that reduced 50% of the number of the parasite (EC₅₀) values ranging from 1.9 to 3.9 µg/mL. In silico analysis showed that Pb is predicted to have good oral absorption and permeability in Caco2 cells, besides excellent probability of absorption by human intestinal cells, without toxic or mutagenic potential effects, not being predicted as a substrate or inhibitor of P-glycoprotein. Pb was as potent as Bz against intracellular forms and displayed a superior trypanosomicidal effect (about 10-fold) in bloodstream forms (EC₅₀ = 0.8 µM) as compared to the reference drug (8.5 µM). The cellular targets of Pb on T. cruzi were evaluated using electron microscopy assays and the findings on bloodstream trypomastigotes showed several cellular insults related to the autophagic process. Regarding toxicity in mammalian cells, the root extracts and the naphthoquinone present a moderate toxic profile on fibroblasts and cardiac cell lines. Then, aiming to reduce host toxicity, the root extract and Pb were tested in combination with Bz, and the data showed additive profiles with the sum of the fractional inhibitory concentration indexes (ΣFICIs) being 1.45 and 0.87, respectively. Thus, our work reveals the promising antiparasitic activity of Plumbago auriculata crude extracts and its purified naphthoquinone Plumbagin against different forms and strains of Trypanosoma cruzi in vitro.

Oxidative stress, cardiomyocytes senescence and contractile dysfunction in in vitro and in vivo experimental models of Chagas disease

AIMS

The relationship between redox imbalance and cardiovascular senescence in infectious myocarditis is unknown. Thus, the aim of this study was to investigate whether cardiomyocytes parasitism, oxidative stress and contractile dysfunction can be correlated to senescence-associated β-galactosidase (SA-β-Gal) activity in Trypanosoma cruzi-infection in vitro and in vivo.

METHODS

Uninfected, T. cruzi-infected untreated and benznidazole (BZN)-treated H9c2 cardiomyocytes and rats were investigated. Parasitological, prooxidant, antioxidant, microstructural, and senescence-associated markers were quantified in vitro and in vivo.

RESULTS

T. cruzi infection triggered intense cardiomyocytes parasitism in vitro and in vivo, which was accompanied by reactive oxygen species (ROS) upregulation, lipids, proteins and DNA oxidation in cardiomyocytes and cardiac tissue. Oxidative stress was parallel to microstructural cell damage (e.g., increased cardiac toponin I levels) and contractile dysfunction in cardiomyocytes in vitro and in vivo, whose severity accompanied a premature cellular senescence-like phenotype revealed by increased senescence-associated β-galactosidase (SA-β-Gal) activity and DNA oxidation (8-OHdG). Cellular parasitism (e.g., infection rate and parasite load), myocarditis and T. cruzi-induced prooxidant responses were attenuated by early BZN administration to interrupt the progression of T. cruzi infection, protecting against SA-β-gal-based premature cellular senescence, microstructural damage and contractile deterioration in cardiomyocytes from T. cruzi-infected animals.

CONCLUSION

Our findings indicated that cell parasitism, redox imbalance and contractile dysfunction were correlated to SA-β-Gal-based cardiomyocytes premature senescence in acute T. cruzi infection. Therefore, in addition to controlling parasitism, inflammation and oxidative stress; inhibiting cardiomyocytes premature senescence should be further investigated as an additional target of specific Chagas disease therapeutics.

In silico and in vitro assessment of anti-Trypanosoma cruzi efficacy, genotoxicity and pharmacokinetics of pentasubstituted pyrrolic Atorvastatin-aminoquinoline hybrid compounds

Atorvastatin (AVA) is a third-generation statin with several pleiotropic effects, considered the last synthetic pharmaceutical blockbuster. Recently, our group described the effects of AVA on DNA damage prevention and against Trypanosoma cruzi infection. In this study, our aim was to evaluate the efficacy, safety, and in silico pharmacokinetic profile of four hybrids of aminoquinolines with AVA 4a-d against T. cruzi using in vitro and in silico models. These synthetic compounds were designed by hybridization of the pentapyrrolic moiety of AVA with the aminoquinolinic unit of chloroquine or primaquine. Pharmacokinetics (ADME) and toxicity parameters were predicted by SwissADME, admetSAR and LAZAR in silico algorithms. The trypanocidal activity of AVA-quinoline hybrids were evaluated in vitro against amastigotes and trypomastigotes of T. cruzi, from Y (Tc II) and Tulahuen (Tc VI) strains. In vitro cardiocytotoxicity was assessed using primary cultures of mouse embryonic cardiac cells and in vitro hepatocytotoxicity on bidimensional and 3D-cultured HepG2 cells. Genotoxicity was evaluated by Ames test and micronucleus assay. Despite the overall good in silico ADMET profile, all tested compounds were predicted to be hepatotoxic. All hybrid derivatives presented high trypanocidal activity, against both trypomastigote and intracellular forms of T. cruzi, presenting EC₅₀'s lower than 1 µM besides superior selectivity than the reference drug, without evidences of cardiotoxicity in vitro. The compounds 4a and 4b presented a time-dependent toxicity in monolayer culture of HepG2 but no detectable toxic effects in their spheroids, opposing to the in silico prediction. We can conclude that the AVA-aminoquinoline hybrids presented a hit profile as antiparasitic agents in synthetic pharmaceutical innovation platforms.

A functional assay using human whole blood and flow cytometry analysis to evaluate cytotoxicity and immunomodulatory effect of anti-Trypanosoma cruzi drugs

The discovery and development of new drugs for the treatment of Chagas disease is urgent due to the high toxicity and low cure efficacy, mainly during the chronic phase of this disease. Other chemotherapeutic approaches for Chagas disease treatment are being researched and require screening assays suitable for evaluating the effectivity of new biologically active compounds. This study aims to evaluate a functional assay using the internalization of epimastigotes forms of Trypanosoma cruzi by human peripheral blood leukocytes from healthy volunteers and analyses by flow cytometry of cytotoxicity, anti-T. cruzi activity, and immunomodulatory effect of benznidazole, ravuconazole, and posaconazole. The culture supernatant was used to measure cytokines (IL-1-β, IL-6, INF-γ, TNF and IL-10) and chemokines (MCP-1/CCL2, CCL5/RANTES and CXCL8/IL-8). The data showed a reduction in the internalization of T. cruzi epimastigote forms treated with ravuconazole, demonstrating its potential anti-T. cruzi activity. In addition, an increased amount of IL-10 and TNF cytokines was observed in the supernatant of cultures upon the addition of the drug, mainly IL-10 in the presence of benznidazole, ravuconazole and posaconazole, and TNF in the presence of ravuconazole and posaconazole. Moreover, the results revealed a decrease in the MCP-1/CCL2 index in cultures in the presence of benznidazole, ravuconazole, and posaconazole. A decrease in the CCL5/RANTES and CXCL8/IL-8 index in cultures with BZ, when compared to the culture without drugs, was also observed. In conclusion, the innovative functional test proposed in this study may be a valuable tool as a confirmatory test for selecting promising compounds identified in prospecting programs for new drugs for Chagas disease treatment.

Cloning and Characterization of Trypanosoma congolense and T. vivax Nucleoside Transporters Reveal the Potential of P1-Type Carriers for the Discovery of Broad-Spectrum Nucleoside-Based Therapeutics against Animal African Trypanosomiasis

African Animal Trypanosomiasis (AAT), caused predominantly by Trypanosoma brucei brucei, T. vivax and T. congolense, is a fatal livestock disease throughout Sub-Saharan Africa. Treatment options are very limited and threatened by resistance. Tubercidin (7-deazaadenosine) analogs have shown activity against individual parasites but viable chemotherapy must be active against all three species. Divergence in sensitivity to nucleoside antimetabolites could be caused by differences in nucleoside transporters. Having previously characterized the T. brucei nucleoside carriers, we here report the functional expression and characterization of the main adenosine transporters of T. vivax (TvxNT3) and T. congolense (TcoAT1/NT10), in a Leishmania mexicana cell line ('SUPKO') lacking adenosine uptake. Both carriers were similar to the T. brucei P1-type transporters and bind adenosine mostly through interactions with N3, N7 and 3'-OH. Expression of TvxNT3 and TcoAT1 sensitized SUPKO cells to various 7-substituted tubercidins and other nucleoside analogs although tubercidin itself is a poor substrate for P1-type transporters. Individual nucleoside EC₅₀s were similar for T. b. brucei, T. congolense, T. evansi and T. equiperdum but correlated less well with T. vivax. However, multiple nucleosides including 7-halogentubercidines displayed pEC50>7 for all species and, based on transporter and anti-parasite SAR analyses, we conclude that nucleoside chemotherapy for AAT is viable.

Repurposing pentamidine for cancer immunotherapy by targeting the PD1/PD-L1 immune checkpoint

Immunotherapy has emerged as an effective therapeutic approach to several cancer types. The reinvigoration of tumor-infiltrating lymphocyte-mediated immune responses via the blockade of immune checkpoint markers, such as program cell death-1 (PD-1) or its cognate ligand PD-L1, has been the basis for developing clinically effective anticancer therapies. We identified pentamidine, an FDA-approved antimicrobial agent, as a small-molecule antagonist of PD-L1. Pentamidine enhanced T-cell-mediated cytotoxicity against various cancer cells in vitro by increasing the secretion of IFN-γ, TNF-α, perforin, and granzyme B in the culture medium. Pentamidine promoted T-cell activation by blocking the PD-1/PD-L1 interaction. In vivo administration of pentamidine attenuated the tumor growth and prolonged the survival of tumor-bearing mice in PD-L1 humanized murine tumor cell allograft models. Histological analysis of tumor tissues showed an increased number of tumor-infiltrating lymphocytes in tissues derived from pentamidine-treated mice. In summary, our study suggests that pentamidine holds the potential to be repurposed as a novel PD-L1 antagonist that may overcome the limitations of monoclonal antibody therapy and can emerge as a small molecule cancer immunotherapy.

Disruption of multiple copies of the Prostaglandin F2alpha synthase gene affects oxidative stress response and infectivity in Trypanosoma cruzi

Chagas disease, caused by the protozoan Trypanosoma cruzi, is a serious chronic parasitic disease, currently treated with Nifurtimox (NFX) and Benznidazole (BZ). In addition to high toxicity, these drugs have low healing efficacy, especially in the chronic phase of the disease. The existence of drug-resistant T. cruzi strains and the occurrence of cross-resistance between BZ and NFX have also been described. In this context, it is urgent to study the metabolism of these drugs in T. cruzi, to better understand the mechanisms of resistance. Prostaglandin F2α synthase (PGFS) is an enzyme that has been correlated with parasite resistance to BZ, but the mechanism by which resistance occurs is still unclear. Our results show that the genome of the CL Brener clone of T. cruzi, contains five PGFS sequences and three potential pseudogenes. Using CRISPR/Cas9 we generated knockout cell lines in which all PGFS sequences were disrupted, as shown by PCR and western blotting analyses. The PGFS deletion did not alter the growth of the parasites or their susceptibility to BZ and NFX when compared to wild-type (WT) parasites. Interestingly, NTR-1 transcripts were shown to be upregulated in ΔPGFS mutants. Furthermore, the ΔPGFS parasites were 1.6 to 1.7-fold less tolerant to oxidative stress generated by menadione, presented lower levels of lipid bodies than the control parasites during the stationary phase, and were less infective than control parasites.

Comparing in vivo bioluminescence imaging and the Multi-Cruzi immunoassay platform to develop improved Chagas disease diagnostic procedures and biomarkers for monitoring parasitological cure

BACKGROUND

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and is a serious public health problem throughout Latin America. With 6 million people infected, there is a major international effort to develop new drugs. In the chronic phase of the disease, the parasite burden is extremely low, infections are highly focal at a tissue/organ level, and bloodstream parasites are only intermittently detectable. As a result, clinical trials are constrained by difficulties associated with determining parasitological cure. Even highly sensitive PCR methodologies can be unreliable, with a tendency to produce "false-cure" readouts. Improved diagnostic techniques and biomarkers for cure are therefore an important medical need.

METHODOLOGY/PRINCIPAL FINDINGS

Using an experimental mouse model, we have combined a multiplex assay system and highly sensitive bioluminescence imaging to evaluate serological procedures for diagnosis of T. cruzi infections and confirmation of parasitological cure. We identified a set of three antigens that in the context of the multiplex serology system, provide a rapid, reactive and highly accurate read-out of both acute and chronic T. cruzi infection. In addition, we describe specific antibody responses where down-regulation can be correlated with benznidazole-mediated parasite reduction and others where upregulation is associated with persistent infection. One specific antibody (IBAG39) highly correlated with the bioluminescence flux and represents a promising therapy monitoring biomarker in mice.

CONCLUSIONS/SIGNIFICANCE

Robust, high-throughput methodologies for monitoring the efficacy of anti-T. cruzi drug treatment are urgently required. Using our experimental systems, we have identified markers of infection or parasite reduction that merit assessing in a clinical setting for the longitudinal monitoring of drug-treated patients.

Molecular Characterization of Four Mexican Isolates of Trypanosoma cruzi and Their Profile Susceptibility to Nifurtimox

PURPOSE

The objective of this study was to molecularly characterize Mexican isolates of T. cruzi obtained from infected triatomine bugs (the vectors of T. cruzi) and to evaluate their susceptibility to Nifurtimox (NFX).

METHODS

Three isolates obtained from Triatoma dimidiata (collected in the State of Veracruz) and one isolate obtained from Triatoma bassolsae (collected in the State of Puebla) were molecularly characterized and the expression of genes associated with natural resistance to NFX was analyzed by qPCR.

RESULTS

Molecular characterization by PCR showed that isolates Zn3, Zn5, and SRB1 belong to the DTU TcI, while isolate Sum3 belongs to TcIV. The latter was also confirmed by sequencing of mitochondrial genes. Isolate Zn5 was the most sensitive to treatment with NFX (IC50, 6.8 μM), isolates SRB1 and Zn3 were partially resistant (IC50, 12.8 μM and 12.7 μM) and isolate Sum3 showed a high degree of resistance to NFX (IC50, 21.4 µM). We also found an association between decreased NTR1 or OYE gene expression with NFX resistance.

CONCLUSION

Our results also evidenced a high variability in the susceptibility to NFX of these T. cruzi isolates Central and Southeastern Mexico, suggesting the presence of naturally resistant isolates circulating in the country. These results have important implications for defining treatment policies for patients with Chagas disease.

Identification and development of a series of disubstituted piperazines for the treatment of Chagas disease

Approximately 6-7 million people around the world are estimated to be infected with Trypanosoma cruzi, the causative agent of Chagas disease. The current treatments are inadequate and therefore new medical interventions are urgently needed. In this paper we describe the identification of a series of disubstituted piperazines which shows good potency against the target parasite but is hampered by poor metabolic stability. We outline the strategies used to mitigate this issue such as lowering logD, bioisosteric replacements of the metabolically labile piperazine ring and use of plate-based arrays for quick diversity scoping. We discuss the success of these strategies within the context of this series and highlight the challenges faced in phenotypic programs when attempting to improve the pharmacokinetic profile of compounds whilst maintaining potency against the desired target.

Polyamine Metabolism in Leishmania Parasites: A Promising Therapeutic Target

Parasites of the genus Leishmania cause a variety of devastating and often fatal diseases in humans and domestic animals worldwide. The need for new therapeutic strategies is urgent because no vaccine is available, and treatment options are limited due to a lack of specificity and the emergence of drug resistance. Polyamines are metabolites that play a central role in rapidly proliferating cells, and recent studies have highlighted their critical nature in Leishmania. Numerous studies using a variety of inhibitors as well as gene deletion mutants have elucidated the pathway and routes of transport, revealing unique aspects of polyamine metabolism in Leishmania parasites. These studies have also shed light on the significance of polyamines for parasite proliferation, infectivity, and host-parasite interactions. This comprehensive review article focuses on the main polyamine biosynthetic enzymes: ornithine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine synthase, and it emphasizes recent discoveries that advance these enzymes as potential therapeutic targets against Leishmania parasites.

Antitrypanosomal activity of hydromethanol extract of leaves of Cymbopogon citratus and seeds of Lepidium sativum: in-vivo mice model

Background

Trypanosomiasis is one of the neglected tropical diseases of both humans and animals which decreases their productivity and causes death in the worst scenario. Unavailability of vaccines, the low therapeutic index of trypanocidal drugs, and the development of resistance lead to the need for research focused on developing alternative treatment options especially from medicinal plants. The present study was aimed to investigate antitrypanosomal activities of leaves of Cymbopogon citratus and seeds of Lepidium sativum in in-vivo mice model.

Methods

The plant extracts were prepared by maceration using 80% methanol and reconstituted with 10% dimethyl sulfoxide (DMSO) to have the desired concentration. The test doses were adjusted to 100, 200 and 400 mg/kg based on the toxicity profile. The plants extracts were administered to the respective groups of mice after the 12^th day of field isolate T. congolense inoculation for seven consecutive days. The level of parasitemia, bodyweight, packed cell volume (PCV), and differential white blood cell counts were measured.

Results

The in -vivo test results revealed that both plant extracts had dose-dependent antitrypanosomal activity. Both crude extracts showed a significant reduction in parasite load (P < 0.05), increased or prevent the fall of PCV value (P < 0.05), decreased lymphocytosis and increased neutrophil counts (p < 0.05) and improved bodyweight but significant bodyweight increment (P < 0.05) was observed only in C. citratus treated mice compared to the negative and positive controls.

Conclusion

The present study concluded that the crude extracts of leaves of C. citratus and seeds of L. sativum had antitrypanosomal effects. Both plants extracts reduced parasitemia level, prevented anemia and improved bodyweight of treated mice. Comparative results from all tested parameters showed that the best activities were observed with C. citratus treated groups of mice.

Computer-Aided Design and Synthesis of a New Class of PEX14 Inhibitors: Substituted 2,3,4,5-Tetrahydrobenzo[F][1,4]oxazepines as Potential New Trypanocidal Agents

African and American trypanosomiases are estimated to affect several million people across the world, with effective treatments distinctly lacking. New, ideally oral, treatments with higher efficacy against these diseases are desperately needed. Peroxisomal import matrix (PEX) proteins represent a very interesting target for structure- and ligand-based drug design. The PEX5-PEX14 protein-protein interface in particular has been highlighted as a target, with inhibitors shown to disrupt essential cell processes in trypanosomes, leading to cell death. In this work, we present a drug development campaign that utilizes the synergy between structural biology, computer-aided drug design, and medicinal chemistry in the quest to discover and develop new potential compounds to treat trypanosomiasis by targeting the PEX14-PEX5 interaction. Using the structure of the known lead compounds discovered by Dawidowski et al. as the template for a chemically advanced template search (CATS) algorithm, we performed scaffold-hopping to obtain a new class of compounds with trypanocidal activity, based on 2,3,4,5-tetrahydrobenzo[f][1,4]oxazepines chemistry. The initial compounds obtained were taken forward to a first round of hit-to-lead optimization by synthesis of derivatives, which show activities in the range of low- to high-digit micromolar IC₅₀ in the in vitro tests. The NMR measurements confirm binding to PEX14 in solution, while immunofluorescent microscopy indicates disruption of protein import into the glycosomes, indicating that the PEX14-PEX5 protein-protein interface was successfully disrupted. These studies result in development of a novel scaffold for future lead optimization, while ADME testing gives an indication of further areas of improvement in the path from lead molecules toward a new drug active against trypanosomes.

Insight into Recent Drug Discoveries against Trypanosomatids and Plasmodium spp Parasites: New Metal-based Compounds

Scaffolds of metal-based compounds can act as pharmacophore groups in several ligands to treat various diseases, including tropical infectious diseases (TID). In this review article, we investigate the contribution of these moieties to medicinal inorganic chemistry in the last seven years against TID, including American trypanosomiasis (Chagas disease), human African trypanosomiasis (HAT, sleeping sickness), leishmania, and malaria. The most potent metal-based complexes are displayed and highlighted in figures, tables and graphics; according to their pharmacological activities (IC50 > 10µM) against Trypanosomatids and Plasmodium spp parasites. We highlight the current progresses and viewpoints of these metal-based complexes, with a specific focus on drug discovery.

Preclinical Studies in Anti-Trypanosomatidae Drug Development

The trypanosomatid parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania are the causative agents of human African trypanosomiasis, Chagas Disease and Leishmaniasis, respectively. These infections primarily affect poor, rural communities in the developing world, and are responsible for trapping sufferers and their families in a disease/poverty cycle. The development of new chemotherapies is a priority given that existing drug treatments are problematic. In our search for novel anti-trypanosomatid agents, we assess the growth-inhibitory properties of >450 compounds from in-house and/or "Pathogen Box" (PBox) libraries against L. infantum, L. amazonensis, L.braziliensis, T. cruzi and T. brucei and evaluate the toxicities of the most promising agents towards murine macrophages. Screens using the in-house series identified 17 structures with activity against and selective toward Leishmania: Compounds displayed 50% inhibitory concentrations between 0.09 and 25 μM and had selectivity index values >10. For the PBox library, ~20% of chemicals exhibited anti-parasitic properties including five structures whose activity against L. infantum had not been reported before. These five compounds displayed no toxicity towards murine macrophages over the range tested with three being active in an in vivo murine model of the cutaneous disease, with 100% survival of infected animals. Additionally, the oral combination of three of them in the in vivo Chagas disease murine model demonstrated full control of the parasitemia. Interestingly, phenotyping revealed that the reference strain responds differently to the five PBox-derived chemicals relative to parasites isolated from a dog. Together, our data identified one drug candidate that displays activity against Leishmania and other Trypanosomatidae in vitro and in vivo, while exhibiting low toxicity to cultured mammalian cells and low in vivo acute toxicity.

Unraveling the antitrypanosomal mechanism of benznidazole and related 2-nitroimidazoles: From prodrug activation to DNA damage

Nitroheterocycles represent an important class of compound used to treat trypanosomiasis. They often function as prodrugs and can undergo type I nitroreductase (NTR1)-mediated activation before promoting their antiparasitic activities although the nature of these downstream effects has yet to be determined. Here, we show that in an NTR1-dependent process, benznidazole promotes DNA damage in the nuclear genome of Trypanosoma brucei, providing the first direct link between activation of this prodrug and a downstream trypanocidal mechanism. Phenotypic and protein expression studies revealed that components of the trypanosome's homologous recombination (HR) repair pathway (TbMRE11, γH2A, TbRAD51) cooperate to resolve the benznidazole-induced damage, indicating that the prodrug-induced lesions are most likely double stand DNA breaks, while the sequence/recruitment kinetics of these factors parallels that in other eukaryotes HR systems. When extended to other NTR1-activated 2-nitroimidazoles, some were shown to promote DNA damage. Intriguingly, the lesions induced by these required TbMRE11 and TbCSB activities to fix leading us to postulate that TbCSB may operate in systems other than the transcription-coupled nucleotide excision repair pathway. Understanding how existing trypanosomal drugs work will aid future drug design and help unlock novel reactions/pathways that could be exploited as targets for therapeutic intervention.

The Potent Trypanocidal Effect of LQB303, a Novel Redox-Active Phenyl-Tert-Butyl-Nitrone Derivate That Causes Mitochondrial Collapse in Trypanosoma cruzi

Chagas disease, which is caused by Trypanosoma cruzi, establishes lifelong infections in humans and other mammals that lead to severe cardiac and gastrointestinal complications despite the competent immune response of the hosts. Furthermore, it is a neglected disease that affects 8 million people worldwide. The scenario is even more frustrating since the main chemotherapy is based on benznidazole, a drug that presents severe side effects and low efficacy in the chronic phase of the disease. Thus, the search for new therapeutic alternatives is urgent. In the present study, we investigated the activity of a novel phenyl-tert-butyl-nitrone (PBN) derivate, LQB303, against T. cruzi. LQB303 presented trypanocidal effect against intracellular [IC₅₀/48 h = 2.6 μM] and extracellular amastigotes [IC₅₀/24 h = 3.3 μM] in vitro, leading to parasite lysis; however, it does not present any toxicity to host cells. Despite emerging evidence that mitochondrial metabolism is essential for amastigotes to grow inside mammalian cells, the mechanism of redox-active molecules that target T. cruzi mitochondrion is still poorly explored. Therefore, we investigated if LQB303 trypanocidal activity was related to the impairment of the mitochondrial function of amastigotes. The investigation showed there was a significant decrease compared to the baseline oxygen consumption rate (OCR) of LQB303-treated extracellular amastigotes of T. cruzi, as well as reduction of “proton leak” (the depletion of proton motive force by the inhibition of F1Fo ATP synthase) and “ETS” (maximal oxygen consumption after uncoupling) oxygen consumption rates. Interestingly, the residual respiration (“ROX”) enhanced about three times in LQB303-treated amastigotes. The spare respiratory capacity ratio (SRC: cell ability to meet new energy demands) and the ATP-linked OCR were also impaired by LQB303 treatment, correlating the trypanocidal activity of LQB303 with the impairment of mitochondrial redox metabolism of amastigotes. Flow cytometric analysis demonstrated a significant reduction of the ΔΨm of treated amastigotes. LQB303 had no significant influence on the OCR of treated mammalian cells, evidencing its specificity against T. cruzi mitochondrial metabolism. Our results suggest a promising trypanocidal activity of LQB303, associated with parasite bioenergetic inefficiency, with no influence on the host energy metabolism, a fact that may point to an attractive alternative therapy for Chagas disease.

Review on Experimental Treatment Strategies Against Trypanosoma cruzi

Chagas disease is a neglected tropical disease caused by the protozoan Trypanosoma cruzi. Currently, only nitroheterocyclic nifurtimox (NFX) and benznidazole (BNZ) are available for the treatment of Chagas disease, with limitations such as variable efficacy, long treatment regimens and toxicity. Different strategies have been used to discover new active molecules for the treatment of Chagas disease. Target-based and phenotypic screening led to thousands of compounds with anti-T. cruzi activity, notably the nitroheterocyclic compounds, fexinidazole and its metabolites. In addition, drug repurposing, drug combinations, re-dosing regimens and the development of new formulations have been evaluated. The CYP51 antifungal azoles, as posaconazole, ravuconazole and its prodrug fosravuconazole presented promising results in experimental Chagas disease. Drug combinations of nitroheterocyclic and azoles were able to induce cure in murine infection. New treatment schemes using BNZ showed efficacy in the experimental chronic stage, including against dormant forms of T. cruzi. And finally, sesquiterpene lactone formulated in nanocarriers displayed outstanding efficacy against different strains of T. cruzi, susceptible or resistant to BNZ, the reference drug. These pre-clinical results are encouraging and provide interesting evidence to improve the treatment of patients with Chagas disease.

Administration of artinm lectin reduces the severity of the acute phase infection with Trypanosoma cruzi

The acute phase of experimental Trypanosoma cruzi infection is associated with a strong inflammatory reaction, physiological changes, amastigote nests in tissues, and hematological alterations. ArtinM, a lectin extracted from Artocarpus heterophyllus seeds, is a homotetramer exhibiting immunomodulatory properties that promotes Th1 immune responses against intracellular pathogens, including the induction of neutrophil migration and increase in IL‐12 production. This study aimed to evaluate the effects of ArtinM on experimental Chagas disease in mice. We evaluated mouse survival curves, parasitemia, hematological parameters including quantification of inflammatory infiltrates, and amastigote nests in cardiac tissue during infection. The results showed a reduced number of parasites in the blood, an increase in animal survival, improvements in hematological parameters, and decrease in inflammatory infiltrates and amastigote nests in the group treated with ArtinM. Collectively, these data suggest that the administration of ArtinM can lower the number of parasites in peak parasitemia caused by the Colombian strain of T. cruzi and can increase survival of infected mice. The observed reduction in cardiac tissue injury may be due to fewer T. cruzi amastigote nests and lower levels of inflammatory infiltrates. This study highlights the need for further investigation into the use of ArtinM as a potential alternative therapeutic for treating Chagas disease.

Anti-leishmanial and anti-trypanosomal natural products from endophytes

Leishmania spp. and Trypanosoma cruzi are parasites belonging to the Trypanosomatidae family and the causative agents for two very important neglected tropical diseases (NTDs), namely leishmaniasis and trypanosomiasis, respectively. Together, they affect millions of people worldwide and the number of cases is constantly rising; thus, further effort on identifying and developing non-toxic, affordable and effective new drug is urgently needed to overcome this alarming situation. Exploring natural products from fungal and bacterial origin remains hitherto a valuable approach to find new hits and candidates for the development of new drugs against these protozoal human infections. Endophytes, which are microorganisms (fungal and bacterial) inhabiting plant tissues, represent a promising source, as they hold potential to produce a high number of distinct chemical scaffolds. These structurally diverse natural products have previously been successfully tested against a wide range of pathogenic microorganisms. The present review provides an update of endophytic compounds exerting anti-trypanosomal and anti-leishmanial effects and their predicted pharmacokinetic properties.

Benznidazole modulates release of inflammatory mediators by cardiac spheroids infected with Trypanosoma cruzi

Chagas disease (CD) caused by Trypanosoma cruzi remains a serious public health problem in Latin America. The available treatment is limited to two old drugs, benznidazole (Bz) and nifurtimox, which exhibit limited efficacy and trigger side effects, justifying the search for new therapies. Also, more accurate and sensitive experimental protocols for drug discovery programs are necessary to shrink the translational gaps found among pre-clinical and clinical trials. Presently, cardiac spheroids were used to evaluate host cell cytotoxicity and anti-T.cruzi activity of benznidazole, exploring its effect on the release of inflammatory mediators. Bz presented low toxic profile on 3D matrices (LC₅₀ > 200 μM) and high potency in vitro (EC₅₀ = 0.99 μM) evidenced by qPCR analysis of T.cruzi-infected cardiac spheroids. Flow cytometry appraisal of inflammatory mediators released at the cellular supernatant showed increases in IL - 6 and TNF contents (≈190 and ≈ 25-fold) in parasitized spheroids as compared to uninfected cultures. Bz at 10 μM suppressed parasite load (92%) concomitantly decreasing in IL-6 (36%) and TNF (68%). Our findings corroborate the successful use of 3D cardiac matrices for in vitro identification of novel anti-parasitic agents and potential impact in host cell physiology.

Antiproliferative activity of the dibenzylideneacetone derivate (E)-3-ethyl-4-(4-nitrophenyl)but‑3-en-2-one in Trypanosoma cruzi

Chagas disease is one of the most prevalent neglected diseases in the world. The illness is caused by Trypanosoma cruzi, a protozoan parasite with a complex life cycle and three morphologically distinct developmental stages. Nowadays, the only treatment is based on two nitro-derivative drugs, benznidazole and nifurtimox, which cause serious side effects. Since the treatment is limited, the search for new treatment options for patients with Chagas disease is highly necessary. In this study we analyzed the substance A11K3, a dibenzylideneacetone (DBA). DBAs have an acyclic dienone attached to aryl groups in both β-positions and studies have shown that they have biological activity against tumors cells, bacteria, and protozoa such as T. cruzi and Leishmania spp. Here we show that A11K3 is active against all three T. cruzi evolutionary forms: the epimastigote (IC₅₀ = 3.3 ± 0.8), the trypomastigote (EC₅₀ = 24 ± 4.3) and the intracellular amastigote (IC₅₀ = 9.3 ± 0.5 µM). A cytotoxicity assay in LLCMK₂ cells showed a CC₅₀ of 239.2 ± 15.7 µM giving a selectivity index (CC₅₀/IC₅₀) of 72.7 for epimastigotes, 9.9 for trypomastigotes and 25.9 for intracellular amastigotes. Morphological and ultrastructural analysis of the parasites treated with A11K3 by TEM and SEM revealed alterations in the Golgi complex, mitochondria, plasma membrane and cell body, with an increase of autophagic vacuoles and lipid bodies. Biochemical assays of A11K3-treated T. cruzi showed an increase of ROS, plasma membrane ruptures, lipid peroxidation, mitochondrial membrane depolarization with a decrease in ATP and accumulation of autophagic vacuoles. The results lead to the hypothesis that A11K3 causes death of the protozoan through events such as plasma membrane and mitochondrial alterations and autophagy, characteristic of cell collapse.

Benznidazole for the treatment of Chagas disease

INTRODUCTION

Chagas disease affects 6-7 million people, mainly in the Americas, and benznidazole is one of the two therapeutic options available. Trypanocide treatment aims to eliminate the parasite from the body to prevent the establishment or progression of visceral damage, mainly cardiac and/or digestive. Remarkably, it helps interrupt vertical transmission when administered to women of childbearing age.

AREAS COVERED

We discuss the basic and scarce data regarding chemical, pharmacokinetic, and pharmacodynamic structure. We also collect the most important data from previous phase II and III studies, as well as studies currently underway and upcoming. We reflect on the main indications for treatment and its challenges, such as the profile of adverse effects in adults, the pharmaceutical formulations, the search for reliable biomarkers, as well as regulatory aspects and access barriers. Alternative strategies such as shorter regimens, lower doses, and fixed doses are currently being evaluated to improve access and the safety profile of this treatment.

EXPERT OPINION

Benznidazole is likely to continue to be the drug of choice for Chagas disease in the coming years. However, it would probably be with a different treatment scheme.

2-Amino-1,3,4-thiadiazoles as prospective agents in trypanosomiasis and other parasitoses

Parasitic diseases are a serious public health problem affecting hundreds of millions of people worldwide. African trypanosomiasis, American trypanosomiasis, leishmaniasis, malaria and toxoplasmosis are the main parasitic infections caused by protozoan parasites with over one million deaths each year. Due to old medications and drug resistance worldwide, there is an urgent need for new antiparasitic drugs. 1,3,4-Thiadiazoles have been widely studied for medical applications. The chemical, physical and pharmacokinetic properties recommend 1,3,4-thiadiazole ring as a target in drug development. Many scientific papers report the antiparasitic potential of 2-amino-1,3,4-thiadiazoles. This review presents synthetic 2-amino-1,3,4-thiadiazoles exhibiting antitrypanosomal, antimalarial and antitoxoplasmal activities. Although there are insufficient results to state the quality of 2-amino-1,3,4-thiadiazoles as a new class of antiparasitic agents, many reported derivatives can be considered as lead compounds for drug synthesis and a promise for the future treatment of parasitosis and provide a valid strategy for the development of potent antiparasitic drugs.

In Vivo Analysis of Trypanosoma cruzi Persistence Foci at Single-Cell Resolution

Infections with Trypanosoma cruzi are usually lifelong despite generating a strong adaptive immune response. Identifying the sites of parasite persistence is therefore crucial to understanding how T. cruzi avoids immune-mediated destruction. However, this is a major technical challenge, because the parasite burden during chronic infections is extremely low. Here, we describe an integrated approach involving comprehensive tissue processing, ex vivo imaging, and confocal microscopy, which allowed us to visualize infected host cells in murine tissue with exquisite sensitivity. Using bioluminescence-guided tissue sampling, with a detection level of <20 parasites, we showed that in the colon, smooth muscle myocytes in the circular muscle layer are the most common infected host cell type. Typically, during chronic infections, the entire colon of a mouse contains only a few hundred parasites, often concentrated in a small number of cells each containing >200 parasites, which we term mega-nests. In contrast, during the acute stage, when the total parasite burden is considerably higher and many cells are infected, nests containing >50 parasites are rarely found. In C3H/HeN mice, but not BALB/c mice, we identified skeletal muscle as a major site of persistence during the chronic stage, with most parasites being found in large mega-nests within the muscle fibers. Finally, we report that parasites are also frequently found in the skin during chronic murine infections, often in multiple infection foci. In addition to being a site of parasite persistence, this anatomical reservoir could play an important role in insect-mediated transmission and have implications for drug development.IMPORTANCE Trypanosoma cruzi causes Chagas disease, the most important parasitic infection in Latin America. Major pathologies include severe damage to the heart and digestive tract, although symptoms do not usually appear until decades after infection. Research has been hampered by the complex nature of the disease and technical difficulties in locating the extremely low number of parasites. Here, using highly sensitive imaging technology, we reveal the sites of parasite persistence during chronic-stage infections of experimental mice at single-cell resolution. We show that parasites are frequently located in smooth muscle cells in the circular muscle layer of the colon and that skeletal muscle cells and the skin can also be important reservoirs. This information provides a framework for investigating how the parasite is able to survive as a lifelong infection, despite a vigorous immune response. It also informs drug development strategies by identifying tissue sites that must be accessed to achieve a curative outcome.

Of Drugs and Trypanosomatids: New Tools and Knowledge to Reduce Bottlenecks in Drug Discovery

Leishmaniasis (Leishmania species), sleeping sickness (Trypanosoma brucei), and Chagas disease (Trypanosoma cruzi) are devastating and globally spread diseases caused by trypanosomatid parasites. At present, drugs for treating trypanosomatid diseases are far from ideal due to host toxicity, elevated cost, limited access, and increasing rates of drug resistance. Technological advances in parasitology, chemistry, and genomics have unlocked new possibilities for novel drug concepts and compound screening technologies that were previously inaccessible. In this perspective, we discuss current models used in drug-discovery cascades targeting trypanosomatids (from in vitro to in vivo approaches), their use and limitations in a biological context, as well as different examples of recently discovered lead compounds.

Challenges in Chagas Disease Drug Development

The protozoan parasite Trypanosoma cruzi causes Chagas disease, an important public health problem throughout Latin America. Current therapeutic options are characterised by limited efficacy, long treatment regimens and frequent toxic side-effects. Advances in this area have been compromised by gaps in our knowledge of disease pathogenesis, parasite biology and drug activity. Nevertheless, several factors have come together to create a more optimistic scenario. Drug-based research has become more systematic, with increased collaborations between the academic and commercial sectors, often within the framework of not-for-profit consortia. High-throughput screening of compound libraries is being widely applied, and new technical advances are helping to streamline the drug development pipeline. In addition, drug repurposing and optimisation of current treatment regimens, informed by laboratory research, are providing a basis for new clinical trials. Here, we will provide an overview of the current status of Chagas disease drug development, highlight those areas where progress can be expected, and describe how fundamental research is helping to underpin the process.

Structure-guided discovery of selective methionyl-tRNA synthetase inhibitors with potent activity against Trypanosoma brucei

Based on crystal structures of Trypanosoma brucei methionyl-tRNA synthetase (TbMetRS) bound to inhibitors, we designed, synthesized, and evaluated two series of novel TbMetRS inhibitors targeting this parasite enzyme. One series has a 1,3-dihydro-imidazol-2-one containing linker, the other has a rigid fused aromatic ring in the linker. For both series of compounds, potent inhibition of parasite growth was achieved with EC₅₀ < 10 nM and most compounds exhibited low general toxicity to mammalian cells with CC₅₀s > 20 000 nM. Selectivity over human mitochondrial methionyl tRNA synthetase was also evaluated, using a cell-based mitochondrial protein synthesis assay, and selectivity in a range of 20-200-fold was achieved. The inhibitors exhibited poor permeability across the blood brain barrier, necessitating future efforts to optimize the compounds for use in late stage human African trypanosomiasis.

Drug-cured experimental Trypanosoma cruzi infections confer long-lasting and cross-strain protection

BACKGROUND

The long term and complex nature of Chagas disease in humans has restricted studies on vaccine feasibility. Animal models also have limitations due to technical difficulties in monitoring the extremely low parasite burden that is characteristic of chronic stage infections. Advances in imaging technology offer alternative approaches that circumvent these problems. Here, we describe the use of highly sensitive whole body in vivo imaging to assess the efficacy of recombinant viral vector vaccines and benznidazole-cured infections to protect mice from challenge with Trypanosoma cruzi.

METHODOLOGY/PRINCIPAL FINDINGS

Mice were infected with T. cruzi strains modified to express a red-shifted luciferase reporter. Using bioluminescence imaging, we assessed the degree of immunity to re-infection conferred after benznidazole-cure. Those infected for 14 days or more, prior to the onset of benznidazole treatment, were highly protected from challenge with both homologous and heterologous strains. There was a >99% reduction in parasite burden, with parasites frequently undetectable after homologous challenge. This level of protection was considerably greater than that achieved with recombinant vaccines. It was also independent of the route of infection or size of the challenge inoculum, and was long-lasting, with no significant diminution in immunity after almost a year. When the primary infection was benznidazole-treated after 4 days (before completion of the first cycle of intracellular infection), the degree of protection was much reduced, an outcome associated with a minimal T. cruzi-specific IFN-γ+ T cell response.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that a protective Chagas disease vaccine must have the ability to eliminate parasites before they reach organs/tissues, such as the GI tract, where once established, they become largely refractory to the induced immune response.

Assessment of the Cruzain Cysteine Protease Reversible and Irreversible Covalent Inhibition Mechanism

Reversible and irreversible covalent ligands are advanced cysteine protease inhibitors in the drug development pipeline. K777 is an irreversible inhibitor of cruzain, a necessary enzyme for the survival of the Trypanosoma cruzi (T. cruzi) parasite, the causative agent of Chagas disease. Despite their importance, irreversible covalent inhibitors are still often avoided due to the risk of adverse effects. Herein, we replaced the K777 vinyl sulfone group with a nitrile moiety to obtain a reversible covalent inhibitor (Neq0682) of cysteine protease. Then, we used advanced experimental and computational techniques to explore details of the inhibition mechanism of cruzain by reversible and irreversible inhibitors. The isothermal titration calorimetry (ITC) analysis shows that inhibition of cruzain by an irreversible inhibitor is thermodynamically more favorable than by a reversible one. The hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) and Molecular Dynamics (MD) simulations were used to explore the mechanism of the reaction inhibition of cruzain by K777 and Neq0682. The calculated free energy profiles show that the Cys25 nucleophilic attack and His162 proton transfer occur in a single step for a reversible inhibitor and two steps for an irreversible covalent inhibitor. The hybrid QM/MM calculated free energies for the inhibition reaction correspond to -26.7 and -5.9 kcal mol^-1 for K777 and Neq0682 at the MP2/MM level, respectively. These results indicate that the ΔG of the reaction is very negative for the process involving K777, consequently, the covalent adduct cannot revert to a noncovalent protein-ligand complex, and its binding tends to be irreversible. Overall, the present study provides insights into a covalent inhibition mechanism of cysteine proteases.

Computational approaches for drug discovery against trypanosomatid-caused diseases

During three decades, only about 20 new drugs have been developed for malaria, tuberculosis and all neglected tropical diseases (NTDs). This critical situation was reached because NTDs represent only 10% of health research investments; however, they comprise about 90% of the global disease burden. Computational simulations applied in virtual screening (VS) strategies are very efficient tools to identify pharmacologically active compounds or new indications for drugs already administered for other diseases. One of the advantages of this approach is the low time-consuming and low-budget first stage, which filters for testing experimentally a group of candidate compounds with high chances of binding to the target and present trypanocidal activity. In this work, we review the most common VS strategies that have been used for the identification of new drugs with special emphasis on those applied to trypanosomiasis and leishmaniasis. Computational simulations based on the selected protein targets or their ligands are explained, including the method selection criteria, examples of successful VS campaigns applied to NTDs, a list of validated molecular targets for drug development and repositioned drugs for trypanosomatid-caused diseases. Thereby, here we present the state-of-the-art of VS and drug repurposing to conclude pointing out the future perspectives in the field.

Treatment Efficiency of Combination Therapy With Diminazene Aceturate and Quinapyramine Sulfate in a Horse With Dourine

Dourine is a lethal protozoan disease of equids, and it is caused by Trypanosoma equiperdum infection via coitus. To date, treatment strategies against the dourine are not recommended because of the frequent relapses; therefore, the World Organisation for Animal Health recommends the stamping-out policy for the control of dourine. Our previous studies have revealed a number of horses with dourine in Mongolia that is the fifth largest horse-breeding country. It is difficult to apply the stamping-out policy for cases of dourine in Mongolia because of an inadequate livestock guarantee system. Therefore, the development of effective treatment measures is an urgent need. In this study, an 8-year-old stallion was definitely diagnosed with dourine based on clinical signs, molecular analysis, and microscopic examination of trypanosomes. Combination therapy with diminazene aceturate and quinapyramine sulfate was applied. Before the treatment, the characteristic clinical signs of dourine were observed, and trypanosomes were detected in the urogenital tract mucosal swab samples by microscopic examination and polymerase chain reaction (PCR). Moreover, positive serological results were obtained. After the treatment, we observed an improvement in the health of the treated horse and no trypanosome infection in its urogenital tract by microscopic examination and PCR. Moreover, serological tests showed seronegative results. The horse has showed no relapse for at least 2.5 years after the treatment, and its reproductive ability has improved. Our result suggests that trypanosomes did not invade cerebrospinal fluid when we started the therapy. In conclusion, the combination therapy has therapeutic potential against dourine at an early phase.

Mapping benznidazole resistance in trypanosomatids and exploring evolutionary histories of nitroreductases and ABCG transporter protein sequences

The nitro-heterocyclic compound benznidazole (BZ) is the first-line drug for the treatment of Chagas disease, caused by the protozoan Trypanosoma cruzi. However, therapeutic failures are common for reasons that include the influences of parasite and host genetics, the effects of toxicity on adherence to treatment, and difficulties in demonstrating parasitological cure. To obtain information on the origin of the resistance to BZ and eliminate from the scenery the participation of the host, initially we mapped the susceptibility to the drug in thirteen species of seven genera of the family Trypanosomatidae. We verified that all Trypanosoma species are sensitive to low concentrations of the drug (IC₅₀ 2.7 to 25 µM) while Non-Trypanosoma species are highly resistant to these concentrations. The two groups of parasites correspond to the major phylogenetic lineages of trypanosomatids. Next, we searched in the trypanosomatid genome databases homologs of two type-I nitroreductases (NTR-1 and OYE) and an ABC transporter (ABCG1) that have been associated with BZ resistance in T. cruzi. The predicted proteins were characterized regarding domains and used for phylogenetic analyses. Homologous NTR-1 genes were found in all trypanosomatids investigated and the structural characteristics of the enzyme suggest that it may be functional. OYE genes were absent in BZ-sensitive African trypanosomes, which excludes the participation of this enzyme in BZ bio-activation. Two copies of ABCG1 genes were observed in most BZ resistant species, while Trypanosoma species exhibit only one copy per haploid genome. Functional studies are required to verify the involvement of these genes in BZ resistance. In addition, since multiple mechanisms can contribute to BZ susceptibility, our study poses a range of organisms highly resistant to BZ in which these aspects can be investigated. Preliminary studies on BZ uptake indicate marked differences between BZ-sensitive and BZ-resistant species.

Nanocarriers for effective delivery of benznidazole and nifurtimox in the treatment of chagas disease: A review

Neglected tropical diseases (NTDs) constitute a group of infectious diseases prevalent in countries with tropical and subtropical climate that affect the poorest individuals and produce high chronic disability associated with serious problems for the health system and socioeconomic development. Chagas disease or American trypanosomiasis is included on the NTDs list. However, even though this disease affects more than 10 million people, mostly in Latin America, causing the death of over 10,000 people every year, only two drugs are approved for its treatment, benznidazole and nifurtimox. These antiparasitic agents were developed almost half a century ago and present several biopharmaceutical disadvantages such as low aqueous solubility and permeability limiting their bioavailability. In addition, both therapeutic agents are available only as tablets and a liquid pediatric formulation is still lacking. Therefore, novel pharmaceutical strategies to optimize the pharmacotherapy of Chagas disease are urgently required. In this regard, nanotechnological approaches may be a crucial alternative for the delivery of both drugs ensuring an effective pharmacotherapy although the successful bench-to-bedside translation remains a major challenge. The present work reviews in detail the formulation and in-vitro/in-vivo analysis of different nanoformulations of nifurtimox and benznidazole in order to enhance their solubility, dissolution, bioavailability and trypanocidal activity.

An evaluation of benznidazole as a Chagas disease therapeutic

Introduction: As benznidazole is the first-line treatment for patients with Chagas disease, rational chemotherapy strategies are required based on the critical analysis of the evidence on the relevance and applicability of this drug at different disease stages. Areas covered: The authors discuss the current understanding of benznidazole-based chemotherapy for Chagas disease, focusing specifically on epidemiology, pharmacokinetics, mechanism of action, clinical recommendations, cure criteria, and therapeutic efficacy in different phases of the disease. Expert opinion: Benznidazole shows high bioavailability after oral administration. Benznidazole at 5-8 mg/kg/day and 5-10 mg/kg/day for 30-60 days are consistent clinical recommendations for children and adults, respectively. A high correlation between negative parasitological, serological, and polymerase chain reaction (PCR) assays in long-term post-therapeutic follow-up has been consistently used to evaluate therapeutic efficacy. These methods support the evidence that the success of benznidazole-based chemotherapy is closely correlated with the phase of infection in which the treatment is administered. The greater therapeutic efficacy is obtained in acute infections, gradually worsening as the infection becomes chronic. When therapeutic failure is confirmed by any diagnostic assay, benznidazole treatment does not always ensure better long-term prognosis, and Chagas cardiomyopathy may develop as well as in untreated patients.

Metabolomics, lipidomics and proteomics profiling of myoblasts infected with Trypanosoma cruzi after treatment with different drugs against Chagas disease

INTRODUCTION

Chagas disease, the most important parasitic infection in Latin America, is caused by the intracellular protozoan Trypanosoma cruzi. To treat this disease, only two nitroheterocyclic compounds with toxic side effects exist and frequent treatment failures are reported. Hence there is an urgent need to develop new drugs. Recently, metabolomics has become an efficient and cost-effective strategy for dissecting drug mode of action, which has been applied to bacteria as well as parasites, such as different Trypanosome species and forms.

OBJECTIVES

We assessed if the metabolomics approach can be applied to study drug action of the intracellular amastigote form of T. cruzi in a parasite-host cell system.

METHODS

We applied a metabolic fingerprinting approach (DI-MS and NMR) to evaluate metabolic changes induced by six different (candidate) drugs in a parasite-host cell system. In a second part of our study, we analyzed the impact of two drugs on polar metabolites, lipid and proteins to evaluate if affected pathways can be identified.

RESULTS

Metabolic signatures, obtained by the fingerprinting approach, resulted in three different clusters. Two can be explained by already known of mode actions, whereas the three experimental drugs formed a separate cluster. Significant changes induced by drug action were observed in all the three metabolic fractions (polar metabolites, lipids and proteins). We identified a general impact on the TCA cycle, but no specific pathways could be attributed to drug action, which might be caused by a high percentage of common metabolome between a eukaryotic host cell and a eukaryotic parasite. Additionally, ion suppression effects due to differences in abundance between host cells and parasites may have occurred.

CONCLUSION

We validated the metabolic fingerprinting approach to a complex host-cell parasite system. This technique can potentially be applied in the early stage of drug discovery and could help to prioritize early leads or reconfirmed hits for further development.