Research progress in the treatment of schistosomiasis with traditional Chinese medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Schistosomiasis, caused by infection with organisms of the Schistoma genus, is a parasitic and infectious disease that poses a significant risk to human health. Schistosomiasis has been a widespread issue in China for at least 2000 years. Traditional Chinese medicine (TCM) has a rich history of treating this disease, and the significant theoretical and practical knowledge attained therein may be useful in modern practice.

AIM OF THE STUDY

To comprehensively review TCM for the treatment of schistosomiasis, summarize the molecular basis, mechanism of action, active ingredients and formulas of TCM, and clarify the value of TCM for expanding drug options for the clinical treatment of schistosomiasis.

MATERIALS AND METHODS

In PubMed, Web of Science, ScienceDirect, Google Scholar and CNKI databases, "Schistosomiasis", "Schistosoma mansoni", "Schistosoma japonicum", "Liver fibrosis" and "Granuloma" were used as the key words. Information related to in vivo animal studies and clinical studies of TCM for the treatment of schistosomiasis in the past 25 years was retrieved, and the inclusion criteria focused on medicinal plants that had a history of use in China.

RESULTS

In this study, we collected and organized a large amount of literature on the treatment of schistosomiasis by TCM. TCM exerts therapeutic effects through antischistosomal and immunomodulatory effects, suppresses HSC activation and proliferation, reduces ECM deposition, and inhibits oxidative stress and other activities. The treatment of schistosomiasis by TCM has a unique advantage, especially for the treatment of schistosomal liver fibrosis, and the treatment of schistosomiasis with TCM in combination with praziquantel is superior to monotherapy.

CONCLUSION

Schistosomiasis remains a global public health problem, and TCM has made significant progress in the prevention and treatment of schistosomiasis and is a potential source of drugs for the treatment of schistosomiasis. However, research on drug screening and the mechanism of action of TCM for the treatment of schistosomiasis is lacking, and further studies and research are needed.

GNN-DDAS: Drug discovery for identifying anti-schistosome small molecules based on graph neural network

Schistosomiasis is a tropical disease that poses a significant risk to hundreds of millions of people, yet often goes unnoticed. While praziquantel, a widely used anti-schistosome drug, has a low cost and a high cure rate, it has several drawbacks. These include ineffectiveness against schistosome larvae, reduced efficacy in young children, and emerging drug resistance. Discovering new and active anti-schistosome small molecules is therefore critical, but this process presents the challenge of low accuracy in computer-aided methods. To address this issue, we proposed GNN-DDAS, a novel deep learning framework based on graph neural networks (GNN), designed for drug discovery to identify active anti-schistosome (DDAS) small molecules. Initially, a multi-layer perceptron was used to derive sequence features from various representations of small molecule SMILES. Next, GNN was employed to extract structural features from molecular graphs. Finally, the extracted sequence and structural features were then concatenated and fed into a fully connected network to predict active anti-schistosome small molecules. Experimental results showed that GNN-DDAS exhibited superior performance compared to the benchmark methods on both benchmark and real-world application datasets. Additionally, the use of GNNExplainer model allowed us to analyze the key substructure features of small molecules, providing insight into the effectiveness of GNN-DDAS. Overall, GNN-DDAS provided a promising solution for discovering new and active anti-schistosome small molecules.

Stem cell-derived exosomes as a potential therapy for schistosomal hepatic fibrosis in experimental animals

Schistosomiasis is a neglected tropical disease. Egg-induced granuloma formation and tissue fibrosis are the main causes of the high morbidity and mortality of schistosomiasis. Mesenchymal stem cells (MSCs)-derived exosomes play an important role with a superior safety profile than MSCs in the treatment of liver fibrosis. Therefore, the aim of this study was to investigate the potential therapeutic effect of MSCs-derived exosomes on schistosomal hepatic fibrosis. Exosomes were isolated from bone marrow MSCs and characterized. A total of 85 mice were divided into four groups: group I (control group), group II (PZQ group) infected and treated with PZQ, group III (EXO group) infected and treated with MSCs-derived exosomes and group IV (PZQ+EXO group) infected and treated with both PZQ and MSCs-derived exosomes. Assessment of treatment efficacy was evaluated by histopathological and immunohistochemical examination of liver sections by proliferating cell nuclear antigen (PCNA) and nuclear factor-κB (NF-κB). The results showed significant reduction of the number and diameter of hepatic granulomas, hepatic fibrosis, upregulation of PCNA expression and reduction of NF-κB expression in EXO and PZQ+EXO groups as compared to other groups at all durations post infection. Additionally, more improvement was observed in PZQ+EXO group. In conclusion, MSCs-derived exosomes are a promising agent for the treatment of schistosomal hepatic fibrosis, and their combination with PZQ shows a synergistic action including antifibrotic and anti-inflammatory effects. However, further studies are required to establish their functional components and their mechanisms of action.

Enabling targeted mass drug administration for schistosomiasis in north-western Tanzania: Exploring the use of geostatistical modeling to inform planning at sub-district level

INTRODUCTION

Schistosomiasis is a parasitic disease in Tanzania affecting over 50% of the population. Current control strategies involve mass drug administration (MDA) campaigns at the district level, which have led to problems of over- and under-treatment in different areas. WHO guidelines have called for more targeted MDA to circumvent these problems, however a scarcity of prevalence data inhibits decision makers from prioritizing sub-district areas for MDA. This study demonstrated how geostatistics can be used to inform planning for targeted MDA.

METHODS

Geostatistical sub-district (ward-level) prevalence estimates were generated through combining a zero-inflated poisson model and kriging approach (regression kriging). To make predictions, the model used prevalence survey data collected in 2021 of 17,400 school children in six regions of Tanzania, along with several open source ecological and socio-demographic variables with known associations with schistosomiasis.

RESULTS

The model results show that regression kriging can be used to effectively predict the ward level parasite prevalence of the two species of Schistosoma endemic to the study area. Kriging was found to further improve the regression model fit, with an adjusted R-squared value of 0.51 and 0.32 for intestinal and urogenital schistosomiasis, respectively. Targeted treatment based on model predictions would represent a shift in treatment away from 193 wards estimated to be over-treated to 149 wards that would have been omitted from the district level MDA.

CONCLUSIONS

Geostatistical models can help to support NTD program efficiency and reduce disease transmission by facilitating WHO recommended targeted MDA treatment through provision of prevalence estimates where data is scarce.

Artificial intelligence-guided approach for efficient virtual screening of hits against Schistosoma mansoni

Background: The impact of schistosomiasis, which affects over 230 million people, emphasizes the urgency of developing new antischistosomal drugs. Artificial intelligence is vital in accelerating the drug discovery process. Methodology & results: We developed classification and regression machine learning models to predict the schistosomicidal activity of compounds not experimentally tested. The prioritized compounds were tested on schistosomula and adult stages of Schistosoma mansoni. Four compounds demonstrated significant activity against schistosomula, with 50% effective concentration values ranging from 9.8 to 32.5 μM, while exhibiting no toxicity in animal and human cell lines. Conclusion: These findings represent a significant step forward in the discovery of antischistosomal drugs. Further optimization of these active compounds can pave the way for their progression into preclinical studies.

Therapeutic Potential of Natural Products in the Treatment of Schistosomiasis

It is estimated that 250 million people worldwide are affected by schistosomiasis. Disease transmission is related to the poor sanitation and hygiene habits that affect residents of impoverished regions in tropical and subtropical countries. The main species responsible for causing disease in humans are Schistosoma Mansoni, S. japonicum, and S. haematobium, each with different geographic distributions. Praziquantel is the drug predominantly used to treat this disease, which offers low effectiveness against immature and juvenile parasite forms. In addition, reports of drug resistance prompt the development of novel therapeutic approaches. Natural products represent an important source of new compounds, especially those obtained from plant sources. This review compiles data from several in vitro and in vivo studies evaluating various compounds and essential oils derived from plants with cercaricidal and molluscicidal activities against both juvenile and adult forms of the parasite. Finally, this review provides an important discussion on recent advances in molecular and computational tools deemed fundamental for more rapid and effective screening of new compounds, allowing for the optimization of time and resources.

Identification and characterisation of the tegument-expressed aldehyde dehydrogenase SmALDH_312 of Schistosoma mansoni, a target of disulfiram

Schistosomiasis is an infectious disease caused by blood flukes of the genus Schistosoma and affects approximately 200 million people worldwide. Since Praziquantel (PZQ) is the only drug for schistosomiasis, alternatives are needed. By a biochemical approach, we identified a tegumentally expressed aldehyde dehydrogenase (ALDH) of S. mansoni, SmALDH_312. Molecular analyses of adult parasites showed Smaldh_312 transcripts in both genders and different tissues. Physiological and cell-biological experiments exhibited detrimental effects of the drug disulfiram (DSF), a known ALDH inhibitor, on larval and adult schistosomes in vitro. DSF also reduced stem-cell proliferation and caused severe tegument damage in treated worms. In silico-modelling of SmALDH_312 and docking analyses predicted DSF binding, which we finally confirmed by enzyme assays with recombinant SmALDH_312. Furthermore, we identified compounds of the Medicine for Malaria Venture (MMV) pathogen box inhibiting SmALDH_312 activity. Our findings represent a promising starting point for further development towards new drugs for schistosomiasis.

A self-purifying microfluidic system for identifying drugs acting against adult schistosomes

The discovery of novel antihelmintic molecules to combat the development and spread of schistosomiasis, a disease caused by several Schistosoma flatworm species, mobilizes significant research efforts worldwide. With a limited number of biochemical assays for measuring the viability of adult worms, the antischistosomicidal activity of molecules is usually evaluated by a microscopic observation of worm mobility and/or integrity upon drug exposure. Even if these phenotypical assays enable multiple parameters analysis, they are often conducted during several days and need to be associated with image-based analysis to minimized subjectivity. We describe here a self-purifying microfluidic system enabling the selection of healthy adult worms and the identification of molecules acting instantly on the parasite. The worms are assayed in a dynamic environment that eliminates unhealthy worms that cannot attach firmly to the chip walls prior to being exposed to the drug. The detachment of the worms is also used as second step readout for identifying active compounds. We have validated this new fluidic screening approach using the two major antihelmintic drugs, praziquantel and artemisinin. The reported dynamic system is simple to produce and to parallelize. Importantly, it enables a quick and sensitive detection of antischistosomal compounds in no more than one hour.

Drug Repurposing and De Novo Drug Discovery of Protein Kinase Inhibitors as New Drugs against Schistosomiasis

Schistosomiasis is a neglected tropical disease affecting more than 200 million people worldwide. Chemotherapy relies on one single drug, praziquantel, which is safe but ineffective at killing larval stages of this parasite. Furthermore, concerns have been expressed about the rise in resistance against this drug. In the absence of an antischistosomal vaccine, it is, therefore, necessary to develop new drugs against the different species of schistosomes. Protein kinases are important molecules involved in key cellular processes such as signaling, growth, and differentiation. The kinome of schistosomes has been studied and the suitability of schistosomal protein kinases as targets demonstrated by RNA interference studies. Although protein kinase inhibitors are mostly used in cancer therapy, e.g., for the treatment of chronic myeloid leukemia or melanoma, they are now being increasingly explored for the treatment of non-oncological conditions, including schistosomiasis. Here, we discuss the various approaches including screening of natural and synthetic compounds, de novo drug development, and drug repurposing in the context of the search for protein kinase inhibitors against schistosomiasis. We discuss the status quo of the development of kinase inhibitors against schistosomal serine/threonine kinases such as polo-like kinases (PLKs) and mitogen-activated protein kinases (MAP kinases), as well as protein tyrosine kinases (PTKs).

Synthesis, structure-activity relationships, cocrystallization and cellular characterization of novel smHDAC8 inhibitors for the treatment of schistosomiasis

Schistosomiasis is a major neglected parasitic disease that affects more than 265 million people worldwide and for which the control strategy consists of mass treatment with the only available drug, praziquantel. In this study, we chemically optimized our previously reported benzhydroxamate-based inhibitors of Schistosoma mansoni histone deacetylase 8 (smHDAC8). Crystallographic analysis provided insights into the inhibition mode of smHDAC8 activity by the highly potent inhibitor 5o. Structure-based optimization of the novel inhibitors was carried out using the available crystal structures as well as docking studies on smHDAC8. The compounds were evaluated in screens for inhibitory activity against schistosome and human HDACs (hHDAC). The in vitro and docking results were used for detailed structure activity relationships. The synthesized compounds were further investigated for their lethality against the schistosome larval stage using a fluorescence-based assay. The most promising inhibitor 5o showed significant dose-dependent killing of the schistosome larvae and markedly impaired egg laying of adult worm pairs maintained in culture.

Synthesis and antischistosomal activity of linker- and thiophene-modified biaryl alkyl carboxylic acid derivatives

Schistosomiasis is a neglected tropical disease caused by blood flukes of the genus Schistosoma and causes severe morbidity in infected patients. In 2018, 290.8 million people required treatment, and 200,000 deaths are reported per year. Treatment of this disease depends on a single drug, praziquantel (PZQ). However, in the past few years, reduced sensitivity of the parasites toward PZQ has been reported. Therefore, there is an urgent need for new drugs against this disease. In the past few years, we have focused on a new substance class called biaryl alkyl carboxylic acid derivatives, which showed promising antischistosomal activity in vitro. Structure-activity relationship (SAR) studies of the carboxylic acid moiety led to three promising carboxylic amides (morpholine, thiomorpholine, and methyl sulfonyl piperazine) with an antischistosomal activity down to 10 µM (morpholine derivative) and no cytotoxicity up to 100 µM. Here, we show our continued work on this substance class. We investigated, in extended SAR studies, whether modification of the linker and the thiophene ring could improve the antischistosomal activity. We found that the exchange of the alkyl linker by a pentadienyl or benzyl linker was tolerated and led to similar antischistosomal effects, whereas the exchange of the thiophene ring was not tolerated. Our data suggest that the thiophene ring is important for the antischistosomal activity of this compound class.

In vitro, in vivo, and ADME evaluation of SF5-containing N,N'-diarylureas as antischistosomal agents

In recent years, N,N'-diarylureas have emerged as a promising chemotype for the treatment of schistosomiasis, a disease that poses a considerable health burden to millions of people worldwide. Here, we report a novel series of N,N'-diarylureas featuring the scarcely explored pentafluorosulfanyl group. Low IC₅₀ values for Schistosoma mansoni newly transformed schistosomula (0.6 - 7.7 μM) and adult worms (0.1 - 1.6 μM) were observed. Four selected compounds, highly active in presence of albumin (>70% at 10 μM), endowed with decent cytotoxicity profile (SI against L6 cells >8.5) and good microsomal hepatic stability (>62.5% of drug remaining after 60 min), were tested in S. mansoni infected mice. Despite the promising in vitro worm killing potency, none of them showed significant activity in vivo. Pharmacokinetic data showed a slow absorption, with maximal drug concentrations reached after 24 h of exposure. Finally, no direct correlation between drug exposure and in vivo activity was found. Thus, further investigations are needed to better understand the underlying mechanisms of SF₅-containing N,N'-diarylureas.

Licochalcone A-loaded solid lipid nanoparticles improve antischistosomal activity in vitro and in vivo

Aim: To isolate licochalcone A (LicoA) from licorice, prepare LicoA-loaded solid lipid nanoparticles (L-SLNs) and evaluate the L-SLNs in vitro and in vivo against Schistosoma mansoni. Materials & methods: LicoA was obtained by chromatographic fractionation and encapsulated in SLNs by a modified high shear homogenization method. Results: L-SLNs showed high encapsulation efficiency, with satisfactory particle size, polydispersity index and Zeta potential. Transmission electron microscopy revealed that L-SLNs were rounded and homogenously distributed. Toxicity studies revealed that SLNs decreased the hemolytic and cytotoxic properties of LicoA. Treatment with L-SLNs showed in vivo efficacy against S. mansoni. Conclusion: L-SLNs are efficient in reducing worm burden and SLNs may be a promising delivery system for LicoA to treat S. mansoni infections.

Schistosomiasis Drug Discovery in the Era of Automation and Artificial Intelligence

Schistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma and affects over 200 million people worldwide. The control and treatment of this neglected tropical disease is based on a single drug, praziquantel, which raises concerns about the development of drug resistance. This, and the lack of efficacy of praziquantel against juvenile worms, highlights the urgency for new antischistosomal therapies. In this review we focus on innovative approaches to the identification of antischistosomal drug candidates, including the use of automated assays, fragment-based screening, computer-aided and artificial intelligence-based computational methods. We highlight the current developments that may contribute to optimizing research outputs and lead to more effective drugs for this highly prevalent disease, in a more cost-effective drug discovery endeavor.

Expanding the Activity Profile of Pyrido[1,2-a]benzimidazoles: Synthesis and Evaluation of Novel N1-1-Phenylethanamine Derivatives against Schistosoma mansoni

Praziquantel is the only widely available drug to treat schistosomiasis. With very few candidates currently in the drug development pipeline, there is an urgent need to discover and develop novel antischistosomal drugs. In this regard, the pyrido[1,2-a]benzimidazole (PBI) scaffold has emerged as a promising chemotype in hit-to-lead efforts. Here, we report a novel series of antischistosomal PBIs with potent in vitro activity (IC₅₀ values of 0.08-1.43 μM) against Schistosoma mansoni newly transformed schistosomula and adult worms. Moreover, the current PBIs demonstrated good hepatic microsomal stability (>70% of drug remaining after 30 min) and were nontoxic to the Chinese hamster ovarian and human liver HepG2 cells, though toxicity (selectivity index, SI < 10) against the rat L6 myoblast cell line was observed. The compounds showed a small therapeutic window but were efficacious in vivo, exhibiting moderate to high worm burden reductions of 35.8-89.6% in S. mansoni-infected mice.

Diarylureas: Repositioning from Antitumor to Antimicrobials or Multi-Target Agents against New Pandemics

Antimicrobials have allowed medical advancements over several decades. However, the continuous emergence of antimicrobial resistance restricts efficacy in treating infectious diseases. In this context, the drug repositioning of already known biological active compounds to antimicrobials could represent a useful strategy. In 2002 and 2003, the SARS-CoV pandemic immobilized the Far East regions. However, the drug discovery attempts to study the virus have stopped after the crisis declined. Today’s COVID-19 pandemic could probably have been avoided if those efforts against SARS-CoV had continued. Recently, a new coronavirus variant was identified in the UK. Because of this, the search for safe and potent antimicrobials and antivirals is urgent. Apart from antiviral treatment for severe cases of COVID-19, many patients with mild disease without pneumonia or moderate disease with pneumonia have received different classes of antibiotics. Diarylureas are tyrosine kinase inhibitors well known in the art as anticancer agents, which might be useful tools for a reposition as antimicrobials. The first to come onto the market as anticancer was sorafenib, followed by some other active molecules. For this interesting class of organic compounds antimicrobial, antiviral, antithrombotic, antimalarial, and anti-inflammatory properties have been reported in the literature. These numerous properties make these compounds interesting for a new possible pandemic considering that, as well as for other viral infections also for CoVID-19, a multitarget therapeutic strategy could be favorable. This review is meant to be an overview on diarylureas, focusing on their biological activities, not dwelling on the already known antitumor activity. Quite a lot of papers present in the literature underline and highlight the importance of these molecules as versatile scaffolds for the development of new and promising antimicrobials and multitarget agents against new pandemic events.

Antischistosomal properties of aurone derivatives against juvenile and adult worms of Schistosoma mansoni

Schistosomiasis is a neglected disease caused by helminth flatworms of the genus Schistosoma, affecting over 240 million people in more than 70 countries. The treatment relies on a single drug, praziquantel, making urgent the discovery of new compounds. Aurones are a natural type of flavonoids that display interesting pharmacological activities, particularly as chemotherapeutic agents against parasites. In pursuit of treatment alternatives, the present work conducted an in vitro and in vivo antischistosomal investigation with aurone derivatives against Schistosoma mansoni. After preparation of aurone derivatives and their in vitro evaluation on adult schistosomes, the three most active aurones were evaluated in cytotoxicity and haemolytic assays, as well as in confocal laser-scanning microscope studies, showing tegumental damage in parasites in a concentration-dependent manner with no haemolytic or cytotoxic potential toward mammalian cells. In a mouse model of schistosomiasis, at a single oral dose of 400 mg/kg, the selected aurones showed worm burden reductions of 35% to 65.0% and egg reductions of 25% to 70.0%. The most active thiophenyl aurone derivative 18, unlike PZQ, had efficacy in mice harboring juvenile S. mansoni, also showing significant inhibition of oviposition by parasites, giving support for the antiparasitic potential of aurones as lead compounds for novel antischistosomal drugs.

Sedum sarmentosum Total Flavonoids Alleviate Schistosomiasis-Induced Liver Fibrosis by Altering TGF-β1 and Smad7 Expression

Objectives

Schistosomiasis is a parasitic disease that affects over 142 million people worldwide. The main causes of death of schistosomiasis include liver granuloma and secondary hepatic cirrhosis resulting from severe fibrosis. Despite intensive research, controlling liver fibrosis associated with schistosomiasis remains challenging. Sedum sarmentosum total flavonoid (SSTF) is a promising agent to reduce liver fibrosis with an unknown mechanism. Thus, the objectives of this study are to validate its effect on the liver fibrosis caused by schistosomiasis and to explore the underlying molecular mechanism.

Methods

Sixty male Sprague-Dawley rats were randomly divided into six groups: one group of normal control and five groups of liver fibrosis induced by schistosomiasis japonica with or without SSTF or colchicine treatment, the latter serving as the positive control. Liver tissues from each animal were harvested to observe the degree and grade of hepatic fibrosis. We also measured the expression of transforming growth factor-beta 1 (TGF-β1) and Smad7 using RT-qPCR, Western blot, and immunohistochemistry.

Results

Compared with the untreated model group, groups treated with SSTF at all three tested doses had significantly reduced hepatic fibrosis (P < 0.05). Each dose of SSTF also significantly reduced TGF-β1 protein expression and mRNA levels in the liver tissues (P < 0.05). In contrast, the middle and high doses of SSTF significantly increased Smad7 protein expression and mRNA levels (P < 0.05). Immunohistochemistry showed that each dose of SSTF reduced TGF-β1 protein expression (P < 0.05).

Conclusion

Our results demonstrated that SSTF alleviated schistosomiasis japonica-induced hepatic fibrosis by inhibiting the TGF-β1/Smad7 pathway.

Comparative genomics and transcriptomics of 4 Paragonimus species provide insights into lung fluke parasitism and pathogenesis

BACKGROUND

Paragonimus spp. (lung flukes) are among the most injurious foodborne helminths, infecting ∼23 million people and subjecting ∼292 million to infection risk. Paragonimiasis is acquired from infected undercooked crustaceans and primarily affects the lungs but often causes lesions elsewhere including the brain. The disease is easily mistaken for tuberculosis owing to similar pulmonary symptoms, and accordingly, diagnostics are in demand.

RESULTS

We assembled, annotated, and compared draft genomes of 4 prevalent and distinct Paragonimus species: Paragonimus miyazakii, Paragonimus westermani, Paragonimus kellicotti, and Paragonimus heterotremus. Genomes ranged from 697 to 923 Mb, included 12,072-12,853 genes, and were 71.6-90.1% complete according to BUSCO. Orthologous group analysis spanning 21 species (lung, liver, and blood flukes, additional platyhelminths, and hosts) provided insights into lung fluke biology. We identified 256 lung fluke-specific and conserved orthologous groups with consistent transcriptional adult-stage Paragonimus expression profiles and enriched for iron acquisition, immune modulation, and other parasite functions. Previously identified Paragonimus diagnostic antigens were matched to genes, providing an opportunity to optimize and ensure pan-Paragonimus reactivity for diagnostic assays.

CONCLUSIONS

This report provides advances in molecular understanding of Paragonimus and underpins future studies into the biology, evolution, and pathogenesis of Paragonimus and related foodborne flukes. We anticipate that these novel genomic and transcriptomic resources will be invaluable for future lung fluke research.

Identification of annotated bioactive molecules that impair motility of the blood fluke Schistosoma mansoni

Neglected tropical diseases are of growing worldwide concern and schistosomiasis, caused by parasitic flatworms, continues to be a major threat with more than 200 million people requiring preventive treatment. As praziquantel (PZQ) remains the treatment of choice, an urgent need for alternative treatments motivates research to identify new lead compounds that would complement PZQ by filling the therapeutic gaps associated with this treatment. Because impairing parasite neurotransmission remains a core strategy for control of parasitic helminths, we screened a library of 708 compounds with validated biological activity in humans on the blood fluke Schistosoma mansoni, measuring their effect on the motility on schistosomulae and adult worms. The primary phenotypic screen performed on schistosomulae identified 70 compounds that induced changes in viability and/or motility. Screening different concentrations and incubation times identified molecules with fast onset of activity on both life stages at low concentration (1 μM). To complement this study, similar assays were performed with chemical analogs of the cholinomimetic drug arecoline and the calcilytic molecule NPS-2143, two compounds that rapidly inhibited schistosome motility; 17 arecoline and 302 NPS-2143 analogs were tested to enlarge the pool of schistosomicidal molecules. Finally, validated hit compounds were tested on three functionally-validated neuroregulatory S. mansoni G-protein coupled receptors (GPCRs): Sm5HTR (serotonin-sensitive), SmGPR2 (histamine) and SmD2 (dopamine), revealing NPS-2143 and analogs as potent inhibitors of dopamine/epinine responses on both human and S. mansoni GPCRs. This study highlights the potential for repurposing known human therapeutic agents for potential schistosomicidal effects and expands the list of hits for further progression.

In-vitro safety and off-target profile of the anti-parasitic arylmethylaminosteroid 1o

Parasite-mediated diseases like malaria and schistosomiasis are growing health problems worldwide and novel drug candidates are urgently needed. In this study, the in-vitro safety profile of steroid compound 1o (sc1o), effective against the parasites Plasmodium falciparum and Schistosoma mansoni with an IC₅₀ value of 5 nM, was characterized. We assessed viability/proliferation, apoptosis and cell cycle tests to determine the cytotoxic profile of sc1o in cancer cells. The mutagenic potential was determined with the AMES test. To identify off-target effects we investigated whether sc1o interacts with safety-relevant molecules such as cytochrome P450 (CYP) enzymes, phosphodiesterases (PDE), histone deacteylases (HDAC) and human ether-a-go-go related gene (hERG). Furthermore, to predict the potential bioavailability of sc1o, its effect on Caco-2 cell barrier integrity, by measurement of the transepithelial electrical resistance (TEER), was determined. Sc1o at 25 µM reduced cell viability, probably through cell-cycle arrest, but did not induce apoptosis in cancer cells. No adverse off-target effects nor mutagenic potential of sc1o were observed. Furthermore, sc1o did not disturb the integrity of the cell barrier, but exhibited low membrane permeability, apparently due to cell adherence. In conclusion, sc1o up to 10 µM showed a good in-vitro safety profile.

Chemotherapy for human schistosomiasis: how far have we come? What's new? Where do we go from here?

Globally, schistosomiasis threatens more than 700 million lives, mostly children, in poor localities of tropical and sub-tropical areas with morbidity due to acute and chronic pathological manifestations of the disease. After a century since the first antimonial-based drugs were introduced to treat the disease, anti-schistosomiasis drug development is again at a bottleneck with only one drug, praziquantel, available for treatment purposes. This review focuses on promising chemotypes as potential starting points in a drug discovery effort to meet the urgent need for new schistosomicides.

Screening and Phenotypical Characterization of Schistosoma mansoni Histone Deacetylase 8 (SmHDAC8) Inhibitors as Multistage Antischistosomal Agents

Schistosomiasis (also known as bilharzia) is a neglected tropical disease caused by platyhelminths of the genus Schistosoma. The disease is endemic in tropical and subtropical areas of the world where water is infested by the intermediate parasite host, the snail. More than 800 million people live in endemic areas and more than 200 million are infected and require treatment. Praziquantel (PZQ) is the drug of choice for schistosomiasis treatment and transmission control being safe and very effective against adult worms of all the clinically relevant Schistosoma species. Unfortunately, it is ineffective on immature, juvenile worms; therefore, it does not prevent reinfection. Moreover, the risk of development and spread of drug resistance because of the widespread use of a single drug in such a large population represents a serious threat. Therefore, research aimed at identifying novel drugs to be used alone or in combination with PZQ are needed. Schistosoma mansoni histone deacetylase 8 (SmHDAC8) is a class I zinc-dependent HDAC, which is abundantly expressed in all stages of its life cycle, thus representing an interesting target for drug discovery. Through virtual screening and phenotypical characterization of selected hits, we discovered two main chemical classes of compounds characterized by the presence of a hydroxamate-based metal binding group coupled to a spiroindoline or a tricyclic thieno[3,2-b]indole core as capping groups. Some of the compounds of both classes were deeply investigated and showed to impair viability of larval, juvenile, and adult schistosomes, to impact egg production in vitro and/or to induce morphological alterations of the adult schistosome reproductive systems. Noteworthy, all of them inhibit the recombinant form of SmHDAC8 enzyme in vitro. Overall, we identified very interesting scaffolds, paving the way to the development of effective antischistosomal agents.

Development of Biarylalkyl Carboxylic Acid Amides with Improved Anti-schistosomal Activity

The parasitic disease schistosomiasis is the cause of more than 200 000 human deaths per year. Although the disease is treatable, there is one major shortcoming: praziquantel has been the only drug used to combat these parasites since 1977. The risk of the emergence of resistant schistosomes is known to be increasing, as a reduced sensitivity of these parasites toward praziquantel has been observed. We developed a new class of substances, which are derived from inhibitors of human aldose reductase, and which showed promising activity against Schistosoma mansoni couples in vitro. Further optimisation of the compounds led to an increase in anti-schistosomal activity with observed phenotypes such as reduced egg production, vitality, and motility as well as tegumental damage and gut dilatation. Here, we performed structure-activity relationship studies on the carboxylic acid moiety of biarylalkyl carboxylic acids. Out of 82 carboxylic acid amides, we identified 10 compounds that are active against S. mansoni at 25 μm. The best five compounds showed an anti-schistosomal activity up to 10 μm and induced severe phenotypes. Cytotoxicity tests in human cell lines showed that two derivatives had no cytotoxicity at 50 or 100 μm. These compounds are promising candidates for further optimisation toward the new anti-schistosomal agents.

A phase 1 study of the safety, reactogenicity, and immunogenicity of a Schistosoma mansoni vaccine with or without glucopyranosyl lipid A aqueous formulation (GLA-AF) in healthy adults from a non-endemic area

BACKGROUND

Schistosomiasis caused by Schistosoma mansoni (Sm) is a chronic, debilitating and potentially deadly neglected tropical disease. The licensure of a vaccine to prevent schistosomiasis would represent a major breakthrough in public health.

METHODS

The safety and immunogenicity of a candidate Sm vaccine were assessed in this phase I, double-blind, dose-escalation trial. Seventy-two healthy Sm-naïve 18-50 year olds were randomized to receive 3 doses ∼ 8 weeks apart of saline placebo, or 10 µg, 30 µg, or 100 µg of recombinant Sm-Tetraspanin-2 vaccine formulated on aluminum hydroxide adjuvant (Sm-TSP-2/Al) with or without 5 µg of glucopyranosyl lipid A aqueous formulation (GLA-AF). Clinical and serologic responses were assessed for 1 year after dose 3.

RESULTS

Vaccines were safe and well-tolerated. The most common reactions were injection site tenderness and pain, and headache and fatigue. Tenderness and pain were more frequent in groups receiving vaccine with GLA-AF than placebo (p = 0.0036 and p = 0.0014, respectively). Injection site reactions among those given Sm-TSP-2/Al with GLA-AF lasted 1.22 and 1.33 days longer than those receiving Sm-TSP-2/Al without GLA-AF or placebo (p < 0.001 for both). Dose- and adjuvant-related increases in serum IgG against Sm-TSP-2 were observed. Peak IgG levels occurred 14 days after dose 3. Seroresponse frequencies were low among recipients of Sm-TSP-2/Al without GLA-AF, but higher among subjects receiving 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF. More seroresponses were observed among those given 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF compared to placebo (p = 0.023 and p < 0.001, respectively). Seroresponse frequencies were 0%, 30%, 50%, and 89%, respectively, among those given placebo, or 10 µg, 30 µg or 100 µg of Sm-TSP-2/Al with GLA-AF, suggesting a dose-response relationship for Sm-TSP-2/Al with GLA-AF (p = 0.0001).

CONCLUSIONS

Sm-TSP-2/Al with or without GLA-AF was safe and well tolerated in a Sm-naïve population. A vaccine like the one under development may represent our best hope to eliminating this neglected tropical disease.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Cyanobacterial peptides as a tour de force in the chemical space of antiparasitic agents

Parasites are scarcely addressed target for antimicrobial peptides despite their big impact in health and global economy. The notion of antimicrobial peptides is frequently associated to the innate immune defense of vertebrates and invertebrate vectors, as the ultimate recipients of the parasite infection. These antiparasite peptides are produced by ribosomal synthesis, with few post-translational modifications, and their diversity come mostly from their amino acid sequence. For many of them permeabilization of the cell membrane of the targeted pathogen is crucial for their microbicidal mechanism. In contrast, cyanobacterial peptides are produced either by ribosomal or non-ribosomal biosynthesis. Quite often, they undergo heavy modifications, such as the inclusion of non-proteinogenic amino acids, lipid acylation, cyclation, N^α-methylation, or heterocyclic rings. Furthermore, the few targets identified for cyanobacterial peptides in parasites are intracellular. Some cyanobacterial antiparasite peptides are active at picomolar concentrations, whereas those from higher eukaryotes usually work in the micromolar range. In all, cyanobacterial peptides are an appealing target to develop new antiparasite therapies and a challenge in the invention of new synthetic methods for peptides. This review aims to provide an updated appraisal of antiparasite cyanobacterial peptides and to establish a side-by -side comparison with those antiparasite peptides from higher eukaryotes.

A novel cell-free method to culture Schistosoma mansoni from cercariae to juvenile worm stages for in vitro drug testing

Background

The arsenal in anthelminthic treatment against schistosomiasis is limited and relies almost exclusively on a single drug, praziquantel (PZQ). Thus, resistance to PZQ could constitute a major threat. Even though PZQ is potent in killing adult worms, its activity against earlier stages is limited. Current in vitro drug screening strategies depend on newly transformed schistosomula (NTS) for initial hit identification, thereby limiting sensitivity to new compounds predominantly active in later developmental stages. Therefore, the aim of this study was to establish a highly standardized, straightforward and reliable culture method to generate and maintain advanced larval stages in vitro. We present here how this method can be a valuable tool to test drug efficacy at each intermediate larval stage, reducing the reliance on animal use (3Rs).

Methodology/Principal findings

Cercariae were mechanically transformed into skin-stage (SkS) schistosomula and successfully cultured for up to four weeks with no loss in viability in a commercially available medium. Under these serum- and cell-free conditions, development halted at the lung-stage (LuS). However, the addition of human serum (HSe) propelled further development into liver stage (LiS) worms within eight weeks. Skin and lung stages, as well as LiS, were submitted to 96-well drug screening assays using known anti-schistosomal compounds such as PZQ, oxamniquine (OXM), mefloquine (MFQ) and artemether (ART). Our findings showed stage-dependent differences in larval susceptibility to these compounds.

Conclusion

With this robust and highly standardized in vitro assay, important developmental stages of S. mansoni up to LiS worms can be generated and maintained over prolonged periods of time. The phenotype of LiS worms, when exposed to reference drugs, was comparable to most previously published works for ex vivo harvested adult worms. Therefore, this in vitro assay can help reduce reliance on animal experiments in search for new anti-schistosomal drugs.

Schistosomiasis remains a major health threat, predominantly in developing countries. Even though there has been some progress in search of new drugs, praziquantel remains the only available drug. Probably the most important advance in the search for new drugs was in vitro transformation of cercariae and their subsequent culture. However, hit identification in compound screenings is exclusively tested in skin stage parasites and is only confirmed for more mature worms in a subsequent step. This is in part due to the lack of an easy culture system for advance-stage parasites. We present here a reliable and highly standardized way to generate LiS worms in vitro in a cell-free culture system. The inclusion of in vitro drug tests on advanced-stage parasites in initial hit identification will help to identify compounds that might otherwise be overlooked. Furthermore, the ability to continuously observe the parasite’s development in vitro will provide an important platform for a better understanding of its maturation in the human host. Taken together, this opens up new avenues to investigate the influence of specific cell types or host proteins on the development of Schistosoma mansoni and provides an additional tool to reduce animal use in future drug discovery efforts (3Rs).