In vitro and in vivo studies of the trypanocidal properties of WRR-483 against Trypanosoma cruzi

Targeting Cysteine Proteases and their Inhibitors to Combat Trypanosomiasis

BACKGROUND

Trypanosomiasis, caused by protozoan parasites of the Trypanosoma genus, remains a significant health burden in several regions of the world. Cysteine proteases play a crucial role in the pathogenesis of Trypanosoma parasites and have emerged as potential therapeutic targets for the development of novel antiparasitic drugs.

INTRODUCTION

This review article aims to provide a comprehensive overview of the role of cysteine proteases in trypanosomiasis and their potential as therapeutic targets. We discuss the biological significance of cysteine proteases in Trypanosoma parasites and their involvement in essential processes, such as host immune evasion, cell invasion, and nutrient acquisition.

METHODS

A comprehensive literature search was conducted to identify relevant studies and research articles on the role of cysteine proteases and their inhibitors in trypanosomiasis. The selected studies were critically analyzed to extract key findings and provide a comprehensive overview of the topic.

RESULTS

Cysteine proteases, such as cruzipain, TbCatB and TbCatL, have been identified as promising therapeutic targets due to their essential roles in Trypanosoma pathogenesis. Several small molecule inhibitors and peptidomimetics have been developed to target these proteases and have shown promising activity in preclinical studies.

CONCLUSION

Targeting cysteine proteases and their inhibitors holds great potential for the development of novel antiparasitic drugs against trypanosomiasis. The identification of potent and selective cysteine protease inhibitors could significantly contribute to the combat against trypanosomiasis and improve the prospects for the treatment of this neglected tropical disease.

Targeting SmCB1: Perspectives and Insights to Design Antischistosomal Drugs

Neglected tropical diseases (NTDs) are prevalent in tropical and subtropical countries, and schistosomiasis is among the most relevant diseases worldwide. In addition, one of the two biggest problems in developing drugs against this disease is related to drug resistance, which promotes the demand to develop new drug candidates for this purpose. Thus, one of the drug targets most explored, Schistosoma mansoni Cathepsin B1 (SmCB1 or Sm31), provides new opportunities in drug development due to its essential functions for the parasite's survival. In this way, here, the latest developments in drug design studies targeting SmCB1 were approached, focusing on the most promising analogs of nitrile, vinyl sulphones, and peptidomimetics. Thus, it was shown that despite being a disease known since ancient times, it remains prevalent throughout the world, with high mortality rates. The therapeutic arsenal of antischistosomal drugs (ASD) consists only of praziquantel, which is widely used for this purpose and has several advantages, such as efficacy and safety. However, it has limitations, such as the impossibility of acting on the immature worm and exploring new targets to overcome these limitations. SmCB1 shows its potential as a cysteine protease with a catalytic triad consisting of Cys100, His270, and Asn290. Thus, design studies of new inhibitors focus on their catalytic mechanism for designing new analogs. In fact, nitrile and sulfonamide analogs show the most significant potential in drug development, showing that these chemical groups can be better exploited in drug discovery against schistosomiasis. We hope this manuscript guides the authors in searching for promising new antischistosomal drugs.

Structure-based design, optimization of lead, synthesis, and biological evaluation of compounds active against Trypanosoma cruzi

Chagas' disease affects approximately eight million people throughout the world, especially the poorest individuals. The protozoan that causes this disease-Trypanosoma cruzi-has the enzyme cruzipain, which is the main therapeutic target. As no available medications have satisfactory effectiveness and safety, it is of fundamental importance to design and synthesize novel analogues that are more active and selective. In the present study, molecular docking and the in silico prediction of ADMET properties were used as strategies to optimize the trypanocidal activity of the pyrimidine compound ZN3F based on interactions with the target site in cruzipain. From the computational results, eight 4-amino-5-carbonitrile-pyrimidine analogues were proposed, synthesized (5a-f and 7g-h) and, tested in vitro on the trypomastigote form of the Tulahuen strain of T. cruzi. The in silico study showed that the designed analogues bond favorably to important amino acid residues of the active site in cruzipain. An in vitro evaluation of cytotoxicity was performed on L929 mammal cell lines. All derivatives inhibited the Tulahuen strain of T. cruzi and also exhibited lower toxicity to L929 cells. The 5e product, in particular, proved to be a potent, selective (IC50  = 2.79 ± 0.00 μM, selectivity index = 31.3) inhibitor of T. cruzi. The present results indicated the effectiveness of drugs based on the structure of the receptor, revealing the potential trypanocidal of pyrimidines. This study also provides information on molecular aspects for the inhibition of cruzipain.

Structure-based discovery of novel cruzain inhibitors with distinct trypanocidal activity profiles

Over 110 years after the first formal description of Chagas disease, the trypanocidal drugs thus far available have limited efficacy and several side effects. This encourages the search for novel treatments that inhibit T. cruzi targets. One of the most studied anti-T. cruzi targets is the cysteine protease cruzain; it is associated with metacyclogenesis, replication, and invasion of the host cells. We used computational techniques to identify novel molecular scaffolds that act as cruzain inhibitors. First, with a docking-based virtual screening, we identified compound 8, a competitive cruzain inhibitor with a K_i of 4.6 μM. Then, aided by molecular dynamics simulations, cheminformatics, and docking, we identified the analog compound 22 with a K_i of 27 μM. Surprisingly, despite sharing the same isoquinoline scaffold, compound 8 presented higher trypanocidal activity against the epimastigote forms, while compound 22, against the trypomastigotes and amastigotes. Taken together, compounds 8 and 22 represent a promising scaffold for further development of trypanocidal compounds as drug candidates for treating Chagas disease.

Design, synthesis and biological evaluation of novel thiosemicarbazones as cruzipain inhibitors

Based on the activity of 23 TSCs on CZ taken from the literature, we have developed a QSAR model for predicting the activity of TSCs. New TSCs were designed and then tested against CZP, resulting in inhibitors with IC₅₀ values in the nanomolar range. The modelling of the corresponding TSC-CZ complexes by molecular docking and QM/QM ONIOM refinement indicates a binding mode compatible with what was expected for active TSCs, according to a geometry-based theoretical model previously developed by our research group. Kinetic experiments on CZP suggest that the new TSCs act by a mechanism that involves the formation of a reversible covalent adduct with slow association and dissociation kinetics. These results demonstrate the strong inhibitory effect of the new TSCs and the benefit of the combined use of QSAR and molecular modelling techniques in the design of new and potent CZ/CZP inhibitors.

Screening the Pathogen Box to Discover and Characterize New Cruzain and TbrCatL Inhibitors

Chagas disease and Human African Trypanosomiasis, caused by Trypanosoma cruzi and T. brucei, respectively, pose relevant health challenges throughout the world, placing 65 to 70 million people at risk each. Given the limited efficacy and severe side effects associated with current chemotherapy, new drugs are urgently needed for both diseases. Here, we report the screening of the Pathogen Box collection against cruzain and TbrCatL, validated targets for Chagas disease and Human African Trypanosomiasis, respectively. Enzymatic assays were applied to screen 400 compounds, validate hits, determine IC₅₀ values and, when possible, mechanisms of inhibition. In this case, 12 initial hits were obtained and ten were prioritized for follow-up. IC₅₀ values were obtained for six of them (hit rate = 1.5%) and ranged from 0.46 ± 0.03 to 27 ± 3 µM. MMV687246 was found to be a mixed inhibitor of cruzain (K_i = 57 ± 6 µM) while MMV688179 was found to be a competitive inhibitor of cruzain with a nanomolar potency (K_i = 165 ± 63 nM). A putative binding mode for MMV688179 was obtained by docking. The six hits discovered against cruzain and TbrCatL are of great interest for further optimization by the medicinal chemistry community.

Novel Selective and Low-Toxic Inhibitor of LmCPB2.8ΔCTE (CPB) One Important Cysteine Protease for Leishmania Virulence

Leishmaniasis is a highly prevalent, yet neglected disease caused by protozoan parasites of the genus Leishmania. In the search for newer, safer, and more effective antileishmanial compounds, we herein present a study of the mode of action in addition to a detailed structural and biological characterization of LQOF-G6 [N-benzoyl-N'-benzyl-N″-(4-tertbutylphenyl)guanidine]. X-ray crystallography and extensive NMR experiments revealed that LQOF-G6 nearly exclusively adopts the Z conformation stabilized by an intramolecular hydrogen bond. The investigated guanidine showed selective inhibitory activity on Leishmania major cysteine protease LmCPB2.8ΔCTE (CPB) with ~73% inhibition and an IC50-CPB of 6.0 µM. This compound did not show any activity against the mammalian homologues cathepsin L and B. LQOF-G6 has been found to be nontoxic toward both organs and several cell lines, and no signs of hepatotoxicity or nephrotoxicity were observed from the analysis of biochemical clinical plasma markers in the treated mice. Docking simulations and experimental NMR measurements showed a clear contribution of the conformational parameters to the strength of the binding in the active site of the enzyme, and thus fit the differences in the inhibition values of LQOF-G6 compared to the other guanidines. Furthermore, the resulting data render LQOF-G6 suitable for further development as an antileishmanial drug.

Two Tags in One Probe: Combining Fluorescence- and Biotin-based Detection of the Trypanosomal Cysteine Protease Rhodesain

Rhodesain is the major cysteine protease of the protozoan parasite Trypanosoma brucei and a therapeutic target for sleeping sickness, a fatal neglected tropical disease. We designed, synthesized and characterized a bimodal activity-based probe that binds to and inactivates rhodesain. This probe exhibited an irreversible mode of action and extraordinary potency for the target protease with a k_inac /K_i value of 37,000 M^-1 s^-1 . Two reporter tags, a fluorescent coumarin moiety and a biotin affinity label, were incorporated into the probe and enabled highly sensitive detection of rhodesain in a complex proteome by in-gel fluorescence and on-blot chemiluminescence. Furthermore, the probe was employed for microseparation and quantification of rhodesain and for inhibitor screening using a competition assay. The developed bimodal rhodesain probe represents a new proteomic tool for studying Trypanosoma pathobiochemistry and antitrypanosomal drug discovery.

Immunomodulation for the Treatment of Chronic Chagas Disease Cardiomyopathy: A New Approach to an Old Enemy

Chagas disease is a parasitic infection caused by the intracellular protozoan Trypanosoma cruzi. Chronic Chagas cardiomyopathy (CCC) is the most severe manifestation of the disease, developed by approximately 20-40% of patients and characterized by occurrence of arrhythmias, heart failure and death. Despite having more than 100 years of discovery, Chagas disease remains without an effective treatment, especially for patients with CCC. Since the pathogenesis of CCC depends on a parasite-driven systemic inflammatory profile that leads to cardiac tissue damage, the use of immunomodulators has become a rational alternative for the treatment of CCC. In this context, different classes of drugs, cell therapies with dendritic cells or stem cells and gene therapy have shown potential to modulate systemic inflammation and myocarditis in CCC models. Based on that, the present review provides an overview of current reports regarding the use of immunomodulatory agents in treatment of CCC, bringing the challenges and future directions in this field.

Cysteine proteases as potential targets for anti-trypanosomatid drug discovery

Leishmaniasis and trypanosomiasis are endemic neglected disease in South America and Africa and considered a significant public health problem, mainly in poor communities. The limitations of the current available therapeutic options, including the lack of specificity, relatively high toxicity, and the drug resistance acquiring, drive the constant search for new targets and therapeutic options. Advances in knowledge of parasite biology have revealed essential enzymes involved in the replication, survival, and pathogenicity of Leishmania and Trypanosoma species. In this scenario, cysteine proteases have drawn the attention of researchers and they are being proposed as promising targets for drug discovery of antiprotozoal drugs. In this systematic review, we will provide an update on drug discovery strategies targeting the cysteine proteases as potential targets for chemotherapy against protozoal neglected diseases.

The gene repertoire of the main cysteine protease of Trypanosoma cruzi, cruzipain, reveals four sub-types with distinct active sites

Cruzipains are the main papain-like cysteine proteases of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease. Encoded by a multigenic family, previous studies have estimated the presence of dozens of copies spread over multiple chromosomes in different parasite strains. Here, we describe the complete gene repertoire of cruzipain in three parasite strains, their genomic organization, and expression pattern throughout the parasite life cycle. Furthermore, we have analyzed primary sequence variations among distinct family members as well as structural differences between the main groups of cruzipains. Based on phylogenetic inferences and residue positions crucial for enzyme function and specificity, we propose the classification of cruzipains into two families (I and II), whose genes are distributed in two or three separate clusters in the parasite genome, according with the strain. Family I comprises nearly identical copies to the previously characterized cruzipain 1/cruzain, whereas Family II encompasses three structurally distinct sub-types, named cruzipain 2, cruzipain 3, and cruzipain 4. RNA-seq data derived from the CL Brener strain indicates that Family I genes are mainly expressed by epimastigotes, whereas trypomastigotes mainly express Family II genes. Significant differences in the active sites among the enzyme sub-types were also identified, which may play a role in their substrate selectivity and impact their inhibition by small molecules.

Structure-Based Optimization of Quinazolines as Cruzain and TbrCATL Inhibitors

The cysteine proteases, cruzain and TbrCATL (rhodesain), are therapeutic targets for Chagas disease and Human African Trypanosomiasis, respectively. Among the known inhibitors for these proteases, we have described N⁴-benzyl-N²-phenylquinazoline-2,4-diamine (compound 7 in the original publication, 1a in this study), as a competitive cruzain inhibitor (K_i = 1.4 μM). Here, we describe the synthesis and biological evaluation of 22 analogs of 1a, containing modifications in the quinazoline core, and in the substituents in positions 2 and 4 of this ring. The analogs demonstrate low micromolar inhibition of the target proteases and cidal activity against Trypanosoma cruzi with up to two log selectivity indices in counterscreens with myoblasts. Fourteen compounds were active against Trypanosoma brucei at low to mid micromolar concentrations. During the optimization of 1a, structure-based design and prediction of physicochemical properties were employed to maintain potency against the enzymes while removing colloidal aggregator characteristics observed for some molecules in this series.

Self-Masked Aldehyde Inhibitors: A Novel Strategy for Inhibiting Cysteine Proteases

Cysteine proteases comprise an important class of drug targets, especially for infectious diseases such as Chagas disease (cruzain) and COVID-19 (3CL protease, cathepsin L). Peptide aldehydes have proven to be potent inhibitors for all of these proteases. However, the intrinsic, high electrophilicity of the aldehyde group is associated with safety concerns and metabolic instability, limiting the use of aldehyde inhibitors as drugs. We have developed a novel class of self-masked aldehyde inhibitors (SMAIs) for cruzain, the major cysteine protease of the causative agent of Chagas disease-Trypanosoma cruzi. These SMAIs exerted potent, reversible inhibition of cruzain (Ki* = 18-350 nM) while apparently protecting the free aldehyde in cell-based assays. We synthesized prodrugs of the SMAIs that could potentially improve their pharmacokinetic properties. We also elucidated the kinetic and chemical mechanism of SMAIs and applied this strategy to the design of anti-SARS-CoV-2 inhibitors.

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.

Synthesis of new N,S-acetal analogs derived from juglone with cytotoxic activity against Trypanossoma cruzi

A series of 11 new N,S-acetal juglone derivatives were synthesized and evaluated against T. cruzi epimastigote forms. These compounds were obtained in good to moderate yields using a microwave irradiation protocol. Among all compounds, two N,S-acetal analogs, showed significant trypanocidal activity. Notably, one compound 11g exhibited selectivity index 10-fold higher than the reference drug benznidazole for epimastigote. The compound 11h was more effective for amastigote forms. Both prototypes exhibited S.I. higher than the benznidazole description. Thus, both compounds proving to be useful candidate molecules to further studies in infected animals.

Recent discovery and development of inhibitors targeting coronaviruses

Human coronaviruses (CoVs) are enveloped viruses with a positive-sense single-stranded RNA genome. Currently, six human CoVs have been reported including human coronavirus 229E (HCoV-229E), OC43 (HCoV-OC43), NL63 (HCoV-NL63), HKU1 (HCoV-HKU1), severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV), and MiddleEast respiratory syndrome (MERS) coronavirus (MERS-CoV). They cause moderate to severe respiratory and intestinal infections in humans. In this review, we focus on recent advances in the research and development of small-molecule anti-human coronavirus therapies targeting different stages of the CoV life cycle.

Peptidomimetic Vinyl Heterocyclic Inhibitors of Cruzain Effect Antitrypanosomal Activity

Cruzain, an essential cysteine protease of the parasitic protozoan, Trypanosoma cruzi, is an important drug target for Chagas disease. We describe here a new series of reversible but time-dependent inhibitors of cruzain, composed of a dipeptide scaffold appended to vinyl heterocycles meant to provide replacements for the irreversible reactive "warheads" of vinyl sulfone inactivators of cruzain. Peptidomimetic vinyl heterocyclic inhibitors (PVHIs) containing Cbz-Phe-Phe/homoPhe scaffolds with vinyl-2-pyrimidine, vinyl-2-pyridine, and vinyl-2-(N-methyl)-pyridine groups conferred reversible, time-dependent inhibition of cruzain (K_i* = 0.1-0.4 μM). These cruzain inhibitors exhibited moderate to excellent selectivity versus human cathepsins B, L, and S and showed no apparent toxicity to human cells but were effective in cell cultures of Trypanosoma brucei brucei (EC₅₀ = 1-15 μM) and eliminated T. cruzi in infected murine cardiomyoblasts (EC₅₀ = 5-8 μM). PVHIs represent a new class of cruzain inhibitors that could progress to viable candidate compounds to treat Chagas disease and human sleeping sickness.

Structure-based Approaches Targeting Parasite Cysteine Proteases

Cysteine proteases are essential hydrolytic enzymes present in the majority of organisms, including viruses and unicellular parasites. Despite the high sequence identity displayed among these proteins, specific structural features across different species grant distinct functions to these biomolecules, frequently related to pathological conditions. Consequently, their relevance as promising targets for potential specific inhibitors has been highlighted and occasionally validated in recent decades. In this review, we discuss the recent outcomes of structure-based campaigns aiming the discovery of new inhibitor prototypes against cruzain and falcipain, as alternative therapeutic tools for Chagas disease and malaria treatments, respectively. Computational and synthetic approaches have been combined on hit optimization strategies and are also discussed herein. These rationales are extended to additional tropical infectious and neglected pathologies, such as schistosomiasis, leishmaniasis and babesiosis, and also to Alzheimer's Disease, a widespread neurodegenerative disease poorly managed by currently available drugs and recently linked to particular physiopathological roles of human cysteine proteases.

Cruzain structures: apocruzain and cruzain bound to S-methyl thiomethanesulfonate and implications for drug design

Chagas disease, which is caused by Trypanosoma cruzi, affects more than six million people worldwide. Cruzain is the major cysteine protease involved in the survival of this parasite. Here, the expression, purification and crystallization of this enzyme are reported. The cruzain crystals diffracted to 1.2 Å resolution, yielding two novel cruzain structures: apocruzain and cruzain bound to the reversible covalent inhibitor S-methyl thiomethanesulfonate. Mass-spectrometric experiments confirmed the presence of a methylthiol group attached to the catalytic cysteine. Comparison of these structures with previously published structures indicates the rigidity of the cruzain structure. These results provide further structural information about the enzyme and may help in new in silico studies to identify or optimize novel prototypes of cruzain inhibitors.

Dipeptidyl nitrile derivatives have cytostatic effects against Leishmania spp. promastigotes

Cysteine proteases are involved in critical cell processes to the protozoa from Leishmania genus, and their inhibition is a therapeutic alternative to treat the disease. In this work, derivatives of dipeptidyl nitriles acting as reversible covalent inhibitors of cysteine proteases were studied as cytostatic agents. The proteolytic activity inside the living and lysed parasite cells was quantified using a selective substrate for cysteine proteases (Z-FR-MCA) from Leishmania amazonensis and L. infantum. The overall proteolytic activity of intact cells and even cell extracts was only marginally affected at high concentrations, with the observation of cytostatic activity and cell cycle arrest of promastigotes. However, the cytotoxic effects were only observed for infected J774 macrophages, which impaired further analysis of the amastigote infection. Therefore, the proteolytic inhibition in intact L. amazonensis and L. infantum promastigotes had no relationship to the cytostatic activity, which emphasizes that these dipeptidyl nitriles act through another mechanism of action.

Cysteine proteases in protozoan parasites

Cysteine proteases (CPs) play key roles in the pathogenesis of protozoan parasites, including cell/tissue penetration, hydrolysis of host or parasite proteins, autophagy, and evasion or modulation of the host immune response, making them attractive chemotherapeutic and vaccine targets. This review highlights current knowledge on clan CA cysteine proteases, the best-characterized group of cysteine proteases, from 7 protozoan organisms causing human diseases with significant impact: Entamoeba histolytica, Leishmania species (sp.), Trypanosoma brucei, T. cruzi, Cryptosporidium sp., Plasmodium sp., and Toxoplasma gondii. Clan CA proteases from three organisms (T. brucei, T. cruzi, and Plasmodium sp.) are well characterized as druggable targets based on in vitro and in vivo models. A number of candidate inhibitors are under development. CPs from these organisms and from other protozoan parasites should be further characterized to improve our understanding of their biological functions and identify novel targets for chemotherapy.

Investigation of the binding mode of a novel cruzain inhibitor by docking, molecular dynamics, ab initio and MM/PBSA calculations

Chagas disease remains a major health problem in South America, and throughout the world. The two drugs clinically available for its treatment have limited efficacy and cause serious adverse effects. Cruzain is an established therapeutic target of Trypanosoma cruzi, the protozoan that causes Chagas disease. Our group recently identified a competitive cruzain inhibitor (compound 1) with an IC₅₀ = 15 µM that is also more synthetically accessible than the previously reported lead, compound 2. Prior studies, however, did not propose a binding mode for compound 1, hindering understanding of the structure-activity relationship and optimization. Here, the cruzain binding mode of compound 1 was investigated using docking, molecular dynamics (MD) simulations with ab initio derived parameters, ab initio calculations, and MM/PBSA. Two ligand protonation states and four binding poses were evaluated. A careful ligand parameterization method was employed to derive more physically meaningful parameters than those obtained by automated tools. The poses of unprotonated 1 were unstable in MD, showing large conformational changes and diffusing away from the binding site, whereas the protonated form showed higher stability and interaction with negatively charged residues Asp161 and Cys25. MM/PBSA also suggested that these two residues contribute favorably to binding of compound 1. By combining results from MD, ab initio calculations, and MM/PBSA, a binding mode of 1 is proposed. The results also provide insights for further optimization of 1, an interesting lead compound for the development of new cruzain inhibitors.

Experimental and Clinical Treatment of Chagas Disease: A Review

Chagas disease (CD) is caused by the protozoan parasite Trypanosoma cruzi that infects a broad range of triatomines and mammalian species, including man. It afflicts 8 million people in Latin America, and its incidence is increasing in nonendemic countries owing to rising international immigration and nonvectorial transmission routes such as blood donation. Since the 1960s, the only drugs available for the clinical treatment of this infection have been benznidazole (BZ) and nifurtimox (NFX). Treatment with these trypanocidal drugs is recommended in both the acute and chronic phases of CD. These drugs have low cure rates mainly during the chronic phase, in addition both drugs present side effects that may result in the interruption of the treatment. Thus, more efficient and better-tolerated new drugs or pharmaceutical formulations containing BZ or NFX are urgently needed. Here, we review the drugs currently used for CD chemotherapy, ongoing clinical assays, and most-promising new experimental drugs. In addition, the mechanism of action of the commercially available drugs, NFX and BZ, the biodistribution of the latter, and the potential for novel formulations of BZ based on nanotechnology are discussed. Taken together, the literature emphasizes the urgent need for new therapies for acute and chronic CD.

Frontline Science: Multiple cathepsins promote inflammasome-independent, particle-induced cell death during NLRP3-dependent IL-1β activation

Sterile particles cause several chronic, inflammatory diseases, characterized by repeating cycles of particle phagocytosis and inflammatory cell death. Recent studies have proposed that these processes are driven by the NLRP3 inflammasome, a platform activated by phagocytosed particles, which controls both caspase-1-dependent cell death (pyroptosis) and mature IL-1β secretion. After phagocytosis, particles can disrupt lysosomes, and inhibitor studies have suggested that the resulting release of a lysosomal protease-cathepsin B-into the cytosol somehow activates NLRP3. However, using primary murine macrophages, we found that particle-induced cell death occurs independent of NLRP3/caspase-1 and depends instead on multiple, redundant cathepsins. In contrast, nigericin, a soluble activator of NLRP3 inflammasomes, induced cell death that was dependent on the NLRP3. Interestingly, nigericin-induced cell death depended partly on a single cathepsin, cathepsin X. By inhibiting or silencing multiple cathepsins in macrophages, several key proinflammatory events induced by sterile particles are blocked, including cell death, pro-IL-1β production, and IL-1β secretion. These data suggest that cathepsins might be potential therapeutic targets in particulate-mediated inflammatory disease. In support of this concept, we find that a broad-spectrum cathepsin inhibitor can suppress particle-induced IL-1-dependent peritonitis.

In vitro effects of cysteine protease inhibitors on Trichomonas foetus-induced cytopathic changes in porcine intestinal epithelial cells

OBJECTIVE To investigate the effects of specific cysteine protease (CP) inhibitors on cytopathic changes to porcine intestinal epithelial cells induced by Tritrichomonas foetus isolated from naturally infected cats. SAMPLE T foetus isolates from 4 naturally infected cats and nontransformed porcine intestinal epithelial cells. PROCEDURES T foetus isolates were treated with or without 0.1 to 1.0mM of the CP inhibitors antipain, cystatin, leupeptin, and chymostatin and the vinyl sulfone inhibitors WRR-483 and K11777. In-gel gelatin zymography was performed to evaluate the effects of these inhibitors on CP activity of T foetus isolates. Each treated or untreated isolate was also cocultured with monolayers of porcine intestinal epithelial cells for 24 hours, and cytopathic effects of T foetus were evaluated by light microscopy and crystal violet spectrophotometry. RESULTS Results of in-gel gelatin zymography suggested an ability of WRR-483, K11777, and cystatin to target specific zones of CP activity of the T foetus isolates. These inhibitors had no effect on T foetus growth, and the cytopathic changes to the intestinal epithelium induced by all 4 T foetus isolates were significantly inhibited. CONCLUSIONS AND CLINICAL RELEVANCE This study revealed that certain protease inhibitors were capable of inhibiting regions of CP activity (which has been suggested to cause intestinal cell damage in cats) in T foetus organisms and of ameliorating T foetus-induced cytopathic changes to porcine intestinal epithelium in vitro. Although additional research is needed, these inhibitors might be useful in the treatment of cats with trichomonosis.

The Potential of Secondary Metabolites from Plants as Drugs or Leads against Protozoan Neglected Diseases-Part III: In-Silico Molecular Docking Investigations

Malaria, leishmaniasis, Chagas disease, and human African trypanosomiasis continue to cause considerable suffering and death in developing countries. Current treatment options for these parasitic protozoal diseases generally have severe side effects, may be ineffective or unavailable, and resistance is emerging. There is a constant need to discover new chemotherapeutic agents for these parasitic infections, and natural products continue to serve as a potential source. This review presents molecular docking studies of potential phytochemicals that target key protein targets in Leishmania spp., Trypanosoma spp., and Plasmodium spp.

Coronaviruses - drug discovery and therapeutic options

In humans, infections with the human coronavirus (HCoV) strains HCoV-229E, HCoV-OC43, HCoV-NL63 and HCoV-HKU1 usually result in mild, self-limiting upper respiratory tract infections, such as the common cold. By contrast, the CoVs responsible for severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), which were discovered in Hong Kong, China, in 2003, and in Saudi Arabia in 2012, respectively, have received global attention over the past 12 years owing to their ability to cause community and health-care-associated outbreaks of severe infections in human populations. These two viruses pose major challenges to clinical management because there are no specific antiviral drugs available. In this Review, we summarize the epidemiology, virology, clinical features and current treatment strategies of SARS and MERS, and discuss the discovery and development of new virus-based and host-based therapeutic options for CoV infections.

Novel drug discovery for Chagas disease

INTRODUCTION

Chagas disease is a chronic infection associated with long-term morbidity. Increased funding and advocacy for drug discovery for neglected diseases have prompted the introduction of several important technological advances, and Chagas disease is among the neglected conditions that has mostly benefited from technological developments. A number of screening campaigns, and the development of new and improved in vitro and in vivo assays, has led to advances in the field of drug discovery.

AREAS COVERED

This review highlights the major advances in Chagas disease drug screening, and how these are being used not only to discover novel chemical entities and drug candidates, but also increase our knowledge about the disease and the parasite. Different methodologies used for compound screening and prioritization are discussed, as well as novel techniques for the investigation of these targets. The molecular mechanism of action is also discussed.

EXPERT OPINION

Technological advances have been executed with scientific rigour for the development of new in vitro cell-based assays and in vivo animal models, to bring about novel and better drugs for Chagas disease, as well as to increase our understanding of what are the necessary properties for a compound to be successful in the clinic. The gained knowledge, combined with new exciting approaches toward target deconvolution, will help identifying new targets for Chagas disease chemotherapy in the future.

Coronaviruses - drug discovery and therapeutic options

Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) are examples of emerging zoonotic coronavirus infections capable of person-to-person transmission that result in large-scale epidemics with substantial effects on patient health and socioeconomic factors. Unlike patients with mild illnesses that are caused by other human-pathogenic coronaviruses, patients with SARS or MERS coronavirus infections may develop severe acute respiratory disease with multi-organ failure. The case–fatality rates of SARS and MERS are approximately 10% and 35%, respectively.

Both SARS and MERS pose major clinical management challenges because there is no specific antiviral treatment that has been proven to be effective in randomized clinical trials for either infection. Substantial efforts are underway to discover new therapeutic agents for coronavirus infections.

Virus-based therapies include monoclonal antibodies and antiviral peptides that target the viral spike glycoprotein, viral enzyme inhibitors, viral nucleic acid synthesis inhibitors and inhibitors of other viral structural and accessory proteins.

Host-based therapies include agents that potentiate the interferon response or affect either host signalling pathways involved in viral replication or host factors utilized by coronaviruses for viral replication.

The major challenges in the clinical development of novel anti-coronavirus drugs include the limited number of suitable animal models for the evaluation of potential treatments for SARS and MERS, the current absence of new SARS cases, the limited number of MERS cases — which are also predominantly geographically confined to the Middle East — as well as the lack of industrial incentives to develop antivirals for mild infections caused by other, less pathogenic coronaviruses.

The continuing threat of MERS-CoV to global health 3 years after its discovery presents a golden opportunity to tackle current obstacles in the development of new anti-coronavirus drugs. A well-organized, multidisciplinary, international collaborative network consisting of clinicians, virologists and drug developers, coupled to political commitment, should be formed to carry out clinical trials using anti-coronavirus drugs that have already been shown to be safe and effective in vitro and/or in animal models, particularly lopinavir–ritonavir, interferon beta-1b and monoclonal antibodies and antiviral peptides targeting the viral spike glycoprotein.

Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), which are caused by coronaviruses, have attracted substantial attention owing to their high mortality rates and potential to cause epidemics. Yuen and colleagues discuss progress with treatment options for these syndromes, including virus- and host-targeted drugs, and the challenges that need to be overcome in their further development.

In humans, infections with the human coronavirus (HCoV) strains HCoV-229E, HCoV-OC43, HCoV-NL63 and HCoV-HKU1 usually result in mild, self-limiting upper respiratory tract infections, such as the common cold. By contrast, the CoVs responsible for severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), which were discovered in Hong Kong, China, in 2003, and in Saudi Arabia in 2012, respectively, have received global attention over the past 12 years owing to their ability to cause community and health-care-associated outbreaks of severe infections in human populations. These two viruses pose major challenges to clinical management because there are no specific antiviral drugs available. In this Review, we summarize the epidemiology, virology, clinical features and current treatment strategies of SARS and MERS, and discuss the discovery and development of new virus-based and host-based therapeutic options for CoV infections.

Total Synthesis of K777: Successful Application of Transition-Metal-Catalyzed Alkyne Hydrothiolation toward the Modular Synthesis of a Potent Cysteine Protease Inhibitor

We report the total synthesis of K777 and a series of analogues via alkyne hydrothiolation catalyzed by Wilkinson's complex (ClRh(PPh3)3). The alkyne hydrothiolation reactions proceeded with excellent regio- and diastereoselectivity to generate the desired E-linear vinyl sulfides in high yield. The use of Ellman's auxiliary generates the requisite propargyl amines in excellent enantiomeric excess (ee) and obviates the use of L-homophenylalanine, an expensive unnatural amino acid. The vinyl sulfone derivatives exhibit a large difference in rate toward Michael addition. Kinetic data are consistent with rate-limiting nucleophilic attack to generate the carbanion intermediate.

Synthesis and Evaluation of Oxyguanidine Analogues of the Cysteine Protease Inhibitor WRR-483 against Cruzain

A series of oxyguanidine analogues of the cysteine protease inhibitor WRR-483 were synthesized and evaluated against cruzain, the major cysteine protease of the protozoan parasite Trypanosoma cruzi. Kinetic analyses of these analogues indicated that they have comparable potency to previously prepared vinyl sulfone cruzain inhibitors. Co-crystal structures of the oxyguanidine analogues WRR-666 (4) and WRR-669 (7) bound to cruzain demonstrated different binding interactions with the cysteine protease, depending on the aryl moiety of the P1' inhibitor subunit. Specifically, these data demonstrate that WRR-669 is bound noncovalently in the crystal structure. This represents a rare example of noncovalent inhibition of a cysteine protease by a vinyl sulfone inhibitor.

Multiple Cathepsins Promote Pro-IL-1β Synthesis and NLRP3-Mediated IL-1β Activation

Sterile particles induce robust inflammatory responses that underlie the pathogenesis of diseases like silicosis, gout, and atherosclerosis. A key cytokine mediating this response is IL-1β. The generation of bioactive IL-1β by sterile particles is mediated by the NOD-like receptor containing a pyrin domain 3 (NLRP3) inflammasome, although exactly how this occurs is incompletely resolved. Prior studies have found that the cathepsin B inhibitor, Ca074Me, suppresses this response, supporting a model whereby ingested particles disrupt lysosomes and release cathepsin B into the cytosol, somehow activating NLRP3. However, reports that cathepsin B-deficient macrophages have no defect in particle-induced IL-1β generation have questioned cathepsin B's involvement. In this study, we examine the hypothesis that multiple redundant cathepsins (not just cathepsin B) mediate this process by evaluating IL-1β generation in murine macrophages, singly or multiply deficient in cathepsins B, L, C, S and X. Using an activity-based probe, we measure specific cathepsin activity in living cells, documenting compensatory changes in cathepsin-deficient cells, and Ca074Me's dose-dependent cathepsin inhibition profile is analyzed in parallel with its suppression of particle-induced IL-1β secretion. Also, we evaluate endogenous cathepsin inhibitors cystatins C and B. Surprisingly, we find that multiple redundant cathepsins, inhibited by Ca074Me and cystatins, promote pro-IL-1β synthesis, and to our knowledge, we provide the first evidence that cathepsin X plays a nonredundant role in nonparticulate NLRP3 activation. Finally, we find cathepsin inhibitors selectively block particle-induced NLRP3 activation, independently of suppressing pro-IL-1β synthesis. Altogether, we demonstrate that both small molecule and endogenous cathepsin inhibitors suppress particle-induced IL-1β secretion, implicating roles for multiple cathepsins in both pro-IL-1β synthesis and NLRP3 activation.

Molecular Design, Synthesis and Trypanocidal Activity of Dipeptidyl Nitriles as Cruzain Inhibitors

A series of compounds based on the dipeptidyl nitrile scaffold were synthesized and assayed for their inhibitory activity against the T. cruzi cysteine protease cruzain. Structure activity relationships (SARs) were established using three, eleven and twelve variations respectively at the P1, P2 and P3 positions. A K_i value of 16 nM was observed for the most potent of these inhibitors which reflects a degree of non-additivity in the SAR. An X-ray crystal structure was determined for the ligand-protein complex for the structural prototype for the series. Twenty three inhibitors were also evaluated for their anti-trypanosomal effects and an EC₅₀ value of 28 μM was observed for the most potent of these. Although there remains scope for further optimization, the knowledge gained from this study is also transferable to the design of cruzain inhibitors based on warheads other than nitrile as well as alternative scaffolds.

Chagas disease is a parasitic infection with high morbidity and mortality that is endemic in much of Latin America where it remains a serious public health problem. With increased migration, Chagas disease represents an emerging worldwide challenge and there is an urgent, unmet need for safe and effective medication. The available drugs to treat Chagas disease may be effective in the acute phase of the disease, but efficacy in the chronic phase remains controversial. They can cause serious side effects that lead sufferers to abandon treatment. Using a hypothesis-driven approach to molecular design and drawing on cysteine protease cruzain structural information, we have mapped structure-activity relationships for a dipeptidyl nitrile scaffold and demonstrated that compounds are competitive inhibitors, bind reversibly and bear trypanocidal activity. The binding mode revealed by the crystal structure of the protein-ligand complex for one of the inhibitors shows that binding involves the formation of a covalent bond between the catalytic cysteine and the nitrile carbon. As such, we believe that our study represents a valuable step in the search for new drugs for the treatment of a neglected disease that continues to affect the lives of millions of people.

Accurate macromolecular crystallographic refinement: incorporation of the linear scaling, semiempirical quantum-mechanics program DivCon into the PHENIX refinement package

Macromolecular crystallographic refinement relies on sometimes dubious stereochemical restraints and rudimentary energy functionals to ensure the correct geometry of the model of the macromolecule and any covalently bound ligand(s). The ligand stereochemical restraint file (CIF) requires a priori understanding of the ligand geometry within the active site, and creation of the CIF is often an error-prone process owing to the great variety of potential ligand chemistry and structure. Stereochemical restraints have been replaced with more robust functionals through the integration of the linear-scaling, semiempirical quantum-mechanics (SE-QM) program DivCon with the PHENIX X-ray refinement engine. The PHENIX/DivCon package has been thoroughly validated on a population of 50 protein-ligand Protein Data Bank (PDB) structures with a range of resolutions and chemistry. The PDB structures used for the validation were originally refined utilizing various refinement packages and were published within the past five years. PHENIX/DivCon does not utilize CIF(s), link restraints and other parameters for refinement and hence it does not make as many a priori assumptions about the model. Across the entire population, the method results in reasonable ligand geometries and low ligand strains, even when the original refinement exhibited difficulties, indicating that PHENIX/DivCon is applicable to both single-structure and high-throughput crystallography.

Synthesis, biological evaluation, and structure-activity relationships of potent noncovalent and nonpeptidic cruzain inhibitors as anti-Trypanosoma cruzi agents

The development of cruzain inhibitors has been driven by the urgent need to develop novel and more effective drugs for the treatment of Chagas' disease. Herein, we report the lead optimization of a class of noncovalent cruzain inhibitors, starting from an inhibitor previously cocrystallized with the enzyme (K(i) = 0.8 μM). With the goal of achieving a better understanding of the structure-activity relationships, we have synthesized and evaluated a series of over 40 analogues, leading to the development of a very promising competitive inhibitor (8r, IC50 = 200 nM, K(i) = 82 nM). Investigation of the in vitro trypanocidal activity and preliminary cytotoxicity revealed the potential of the most potent cruzain inhibitors in guiding further medicinal chemistry efforts to develop drug candidates for Chagas' disease.

Further insights into biological evaluation of new anti-Trypanosoma cruzi 5-nitroindazoles

Twelve molecules from a series of 35 new 5-nitroindazole derivatives, selected from a successful primary screening on Trypanosoma cruzi epimastigotes, have been evaluated against intracellular amastigotes according to the previous results of their trypanocidal activity and unspecific cytotoxicity. 2-Benzyl-1-propyl (22), 2-benzyl-1-isopropyl (23), and 2-benzyl-1-butyl (24) 5-nitroindazolin-3-ones have inhibited the growth of amastigotes similarly to the reference drugs benznidazole and nifurtimox, inducing complete growth inhibition at concentrations lower than 8 μM (IC₅₀ < 5 μM) and accomplishing great selectivity indexes on the intracellular form of the parasite (SI > 30). Further in vivo assays were developed only for two of the most active molecules (22 and 24), reaching significant reductions in parasitemia levels (52 % and 77%, respectively) after their oral administration to infected mice. In addition, none of the mice in experimental and benznidazole groups died, unlike in the control group which is only treated with the vehicle. The trypanocidal properties found in some of the 5-nitroindazole derivatives assayed in the present work represent an interesting contribution to the urgent need for searching new antichagasic drugs.

Quantum mechanics-based scoring rationalizes the irreversible inactivation of parasitic Schistosoma mansoni cysteine peptidase by vinyl sulfone inhibitors

The quantum mechanics (QM)-based scoring function that we previously developed for the description of noncovalent binding in protein-ligand complexes has been modified and extended to treat covalent binding of inhibitory ligands. The enhancements are (i) the description of the covalent bond breakage and formation using hybrid QM/semiempirical QM (QM/SQM) restrained optimizations and (ii) the addition of the new ΔG(cov)' term to the noncovalent score, describing the "free" energy difference between the covalent and noncovalent complexes. This enhanced QM-based scoring function is applied to a series of 20 vinyl sulfone-based inhibitory compounds inactivating the cysteine peptidase cathepsin B1 of the Schistosoma mansoni parasite (SmCB1). The available X-ray structure of the SmCB1 in complex with a potent vinyl sulfone inhibitor K11017 is used as a template to build the other covalently bound complexes and to model the derived noncovalent complexes. We present the correlation of the covalent score and its constituents with the experimental binding data. Four outliers are identified. They contain bulky R1' substituents structurally divergent from the template, which might induce larger protein rearrangements than could be accurately modeled. In summary, we propose a new computational approach and an optimal protocol for the rapid evaluation and prospective design of covalent inhibitors with a conserved binding mode.

Non-peptidic cruzain inhibitors with trypanocidal activity discovered by virtual screening and in vitro assay

A multi-step cascade strategy using integrated ligand- and target-based virtual screening methods was developed to select a small number of compounds from the ZINC database to be evaluated for trypanocidal activity. Winnowing the database to 23 selected compounds, 12 non-covalent binding cruzain inhibitors with affinity values (K_i) in the low micromolar range (3–60 µM) acting through a competitive inhibition mechanism were identified. This mechanism has been confirmed by determining the binding mode of the cruzain inhibitor Nequimed176 through X-ray crystallographic studies. Cruzain, a validated therapeutic target for new chemotherapy for Chagas disease, also shares high similarity with the mammalian homolog cathepsin L. Because increased activity of cathepsin L is related to invasive properties and has been linked to metastatic cancer cells, cruzain inhibitors from the same library were assayed against it. Affinity values were in a similar range (4–80 µM), yielding poor selectivity towards cruzain but raising the possibility of investigating such inhibitors for their effect on cell proliferation. In order to select the most promising enzyme inhibitors retaining trypanocidal activity for structure-activity relationship (SAR) studies, the most potent cruzain inhibitors were assayed against T. cruzi-infected cells. Two compounds were found to have trypanocidal activity. Using compound Nequimed42 as precursor, an SAR was established in which the 2-acetamidothiophene-3-carboxamide group was identified as essential for enzyme and parasite inhibition activities. The IC₅₀ value for compound Nequimed42 acting against the trypomastigote form of the Tulahuen lacZ strain was found to be 10.6±0.1 µM, tenfold lower than that obtained for benznidazole, which was taken as positive control. In addition, by employing the strategy of molecular simplification, a smaller compound derived from Nequimed42 with a ligand efficiency (LE) of 0.33 kcal mol⁻¹ atom⁻¹ (compound Nequimed176) is highlighted as a novel non-peptidic, non-covalent cruzain inhibitor as a trypanocidal agent candidate for optimization.

Chagas disease (American trypanosomiasis) is a parasitic infection that kills millions of mostly poverty-stricken people in Latin America. In recent years it has also spread to nonendemic countries – the United States, Canada, Europe, Australia and Japan – as a result of immigration. The only available drugs for its treatment were introduced more than forty years ago, have low efficacy, and cause various severe side effects. This dire public health situation has prompted us to search for new small molecules to act as drug candidates to treat Chagas disease. The T. cruzi enzyme cruzain, a key biological catalyst used by the protozoan to digest host proteins, is a validated drug target for Chagas disease. By combining in silico molecular design, X-ray crystallography and biological screening, we found a new class of non-covalent small molecules that inhibit cruzain in low micromolar concentrations.

The natural compounds piperovatine and piperlonguminine induce autophagic cell death on Trypanosoma cruzi

The currently available treatments for Chagas disease show limited therapeutic potential and are associated with serious side effects. Our group has been attempting to find alternative drugs isolated from natural products as a potential source of pharmacological agents against Trypanosoma cruzi. Here, we demonstrate the antitrypanosomal activity of the amides piperovatine and piperlonguminine isolated from Piper ovatum against epimastigotes and intracellular amastigotes. We also investigated the mechanisms of action of these compounds on extracellular amastigote and epimastigote forms of T. cruzi. These amides showed low toxicity to LLCMK(2) mammalian cells. By using transmission and scanning electron microscopy, we observed that the compounds caused severe alterations in T. cruzi. These alterations were mainly located in plasma membrane and mitochondria. Furthermore, the study of treated parasites labeled with Rh123, PI and MDC corroborate with our TEM data. These mitochondrial dysfunctions induced by the amides might trigger biochemical alterations that lead to cell death. Altogether, our data evidence a possible autophagic process.

Organocatalytic, enantioselective synthesis of VNI: a robust therapeutic development platform for Chagas, a neglected tropical disease

VNI is a potent inhibitor of CYP51 and was recently shown to achieve a parasitological cure of mice infected with T. cruzi in both acute and chronic stages of infection. T. cruzi is the causative parasite of Chagas disease, a neglected tropical disease. The first enantioselective chemical synthesis of VNI (at a materials cost of less than $0.10/mg) is described. Furthermore, the key enantioselective step is performed at the 10 g scale.

A static-cidal assay for Trypanosoma brucei to aid hit prioritisation for progression into drug discovery programmes

Human African Trypanosomiasis is a vector-borne disease of sub-Saharan Africa that causes significant morbidity and mortality. Current therapies have many drawbacks, and there is an urgent need for new, better medicines. Ideally such new treatments should be fast-acting cidal agents that cure the disease in as few doses as possible. Screening assays used for hit-discovery campaigns often do not distinguish cytocidal from cytostatic compounds and further detailed follow-up experiments are required. Such studies usually do not have the throughput required to test the large numbers of hits produced in a primary high-throughput screen. Here, we present a 384-well assay that is compatible with high-throughput screening and provides an initial indication of the cidal nature of a compound. The assay produces growth curves at ten compound concentrations by assessing trypanosome counts at 4, 24 and 48 hours after compound addition. A reduction in trypanosome counts over time is used as a marker for cidal activity. The lowest concentration at which cell killing is seen is a quantitative measure for the cidal activity of the compound. We show that the assay can identify compounds that have trypanostatic activity rather than cidal activity, and importantly, that results from primary high-throughput assays can overestimate the potency of compounds significantly. This is due to biphasic growth inhibition, which remains hidden at low starting cell densities and is revealed in our static-cidal assay. The assay presented here provides an important tool to follow-up hits from high-throughput screening campaigns and avoid progression of compounds that have poor prospects due to lack of cidal activity or overestimated potency.

Molecular characterization and expression analysis of ubiquitin-activating enzyme E1 gene in Citrus reticulata

Ubiquitin-activating enzyme E1 (UBE1) catalyzes the first step in the ubiquitination reaction, which targets a protein for degradation via a proteasome pathway. UBE1 plays an important role in metabolic processes. In this study, full-length cDNA and DNA sequences of UBE1 gene, designated CrUBE1, were obtained from 'Wuzishatangju' (self-incompatible, SI) and 'Shatangju' (self-compatible, SC) mandarins. 5 amino acids and 8 bases were different in cDNA and DNA sequences of CrUBE1 between 'Wuzishatangju' and 'Shatangju', respectively. Southern blot analysis showed that there existed only one copy of the CrUBE1 gene in genome of 'Wuzishatangju' and 'Shatangju'. The temporal and spatial expression characteristics of the CrUBE1 gene were investigated using semi-quantitative RT-PCR (SqPCR) and quantitative real-time PCR (qPCR). The expression level of the CrUBE1 gene in anthers of 'Shatangju' was approximately 10-fold higher than in anthers of 'Wuzishatangju'. The highest expression level of CrUBE1 was detected in pistils at 7days after self-pollination of 'Wuzishatangju', which was approximately 5-fold higher than at 0 h. To obtain CrUBE1 protein, the full-length cDNA of CrUBE1 genes from 'Wuzishatangju' and 'Shatangju' were successfully expressed in Pichia pastoris. Pollen germination frequency of 'Wuzishatangju' was significantly inhibited with increasing of CrUBE1 protein concentrations from 'Wuzishatangju'.

Antiparasitical chemotherapy in Chagas' disease cardiomyopathy: current evidence

Chronic chagasic cardiomyopathy affects 20% of Chagas' disease patients. At present, Chagas' disease chemotherapy uses nitrofurans, benznidazole (Rochagan®, Rodanil®, Roche) or nifurtimox (Lampit®, Bayer). Treatment during acute and recent chronic phases in childhood effects 71.5% and 57.6%, respectively, of parasitological cure. However, in clinical trials during the late chronic phase, only 5.9% of parasitological cure were achieved. This review focuses on the benefit from aetiological treatment to avoid, stop or revert myocarditis. Divergent data gathered from clinical practice are not convincing to support prescription of aetiological treatment as routine for indeterminate and cardiac chronic patients.