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.

Natural Perylenequinone Compounds as Potent Inhibitors of Schistosoma mansoni Glutathione S-Transferase

The existing treatment strategy for Schistosomiasis centers on praziquantel, a single drug, but its effectiveness is limited due to resistance and lack of preventive benefits. Thus, there is an urgent need for novel antischistosomal agents. Schistosoma glutathione S-transferase (GST) is an essential parasite enzyme, with a high potential for targeted drug discovery. In this study, we conducted a screening of compounds possessing antihelminth properties, focusing on their interaction with the Schistosoma mansoni glutathione S-transferase (SmGST) protein. We demonstrated the unique nature of SmGST in comparison to human GST. Evolutionary analysis indicated its close relationship with other parasitic worms, setting it apart from free-living worms such as C. elegans. Through an assessment of binding pockets and subsequent protein-ligand docking, we identified Scutiaquinone A and Scutiaquinone B, both naturally derived Perylenequinones, as robust binders to SmGST. These compounds have exhibited effectiveness against similar parasites and offer promising potential as antischistosomal agents.

Anti-schistosomal activities of quinoxaline-containing compounds: From hit identification to lead optimisation

Schistosomiasis is a neglected disease of poverty that is caused by infection with blood fluke species contained within the genus Schistosoma. For the last 40 years, control of schistosomiasis in endemic regions has predominantly been facilitated by administration of a single drug, praziquantel. Due to limitations in this mono-chemotherapeutic approach for sustaining schistosomiasis control into the future, alternative anti-schistosomal compounds are increasingly being sought by the drug discovery community. Herein, we describe a multi-pronged, integrated strategy that led to the identification and further exploration of the quinoxaline core as a promising anti-schistosomal scaffold.

Firstly, phenotypic screening of commercially available small molecules resulted in the identification of a moderately active hit compound against Schistosoma mansoni (1, EC₅₀ = 4.59 μM on schistosomula). Secondary exploration of the chemical space around compound 1 led to the identification of a quinoxaline-core containing, non-genotoxic lead (compound 22). Compound 22 demonstrated substantially improved activities on both intra-mammalian (EC₅₀ = 0.44 μM, 0.20 μM and 84.7 nM, on schistosomula, juvenile and adult worms, respectively) and intra-molluscan (sporocyst) S. mansoni lifecycle stages. Further medicinal chemistry optimisation of compound 22, resulting in the generation of 20 additional analogues, improved our understanding of the structure-activity relationship and resulted in considerable improvements in both anti-schistosome potency and selectivity (e.g. compound 30; EC₅₀ = 2.59 nM on adult worms; selectivity index compared to the HepG2 cell line = 348). Some derivatives of compound 22 (e.g. 31 and 33) also demonstrated significant activity against the two other medically important species, Schistosoma haematobium and Schistosoma japonicum. Further optimisation of this class of anti-schistosomal is ongoing and could lead to the development of an urgently needed alternative to praziquantel for assisting in schistosomiasis elimination strategies.

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Lead compound 22 was identified with EC₅₀ of 0.44 µM and 84.7 nM for schistosomula and adult worms.

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20 analogues of the lead compound 22 were synthesised.

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Compounds 25, 30 and 32 showed the best selectivity profile.

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Compounds 31 and 33 are the most active on three medically important schistosome species.

Discovery of novel antischistosomal scaffolds from the open access Pandemic Response Box

BACKGROUND

Treatment and control of schistosomiasis rely on a single drug, praziquantel. New orally active antischistosomals featuring novel molecular scaffolds are urgently needed to prevent the emergence of resistance.

METHODS

We screened 400 drug-like compounds contained in the open-access Pandemic Response Box (PRB) against newly transformed schistosomula (NTS) at a concentration of 10 µM scoring death, changes in motility, and morphological alterations. Compounds displaying an activity ≥66% at 72 h underwent testing against adult Schistosoma mansoni in vitro. Fast-acting (≥66% at 24 h), nontoxic drugs focusing on late-stage and approved drugs were investigated in the patent S. mansoni mouse model.

RESULTS

We identified 26 hits active against NTS, of which 17 elicited ≥66% activity against adult S. mansoni following 24 h of drug exposure. The highest activity against adult S. mansoni was observed with MMV1581558 (EC₅₀ value of 0.18 ± 0.01 µM) and nitazoxanide (0.47 ± 0.07 µM). Of the five compounds tested in vivo, MMV1581558 and the approved drug ozanimod reduced average worm burden versus controls by 42 % and 36 %, respectively, after a single oral dose of 200 mg/kg bodyweight in mice harboring a chronic S. mansoni infection.

CONCLUSION

MMV1581558 discovered from screening the PRB represents a novel antischistosomal scaffold with high in vitro antischistosomal activity amenable to chemical modification for drug development.

The discovery of a novel series of compounds with single-dose efficacy against juvenile and adult Schistosoma species

Treatment and control of schistosomiasis depends on a single drug, praziquantel, but this is not ideal for several reasons including lack of potency against the juvenile stage of the parasite, dose size, and risk of resistance. We have optimised the properties of a series of compounds we discovered through high throughput screening and have designed candidates for clinical development. The best compounds demonstrate clearance of both juvenile and adult S. mansoni worms in a mouse model of infection from a single oral dose of < 10 mg/kg. Several compounds in the series are predicted to treat schistosomiasis in humans across a range of species with a single oral dose of less than 5 mg/kg.

Unveiling the Potential of Purinergic Signaling in Schistosomiasis Treatment

Schistosomiasis is a neglected tropical disease. It is related to long-lasting granulomatous fibrosis and inflammation of target organs, and current sub-optimal pharmacological treatment creates global public health concerns. Intravascular worms and eggs release antigens and extracellular vesicles that target host endothelial cells, modulate the immune system, and stimulate the release of damageassociated molecular patterns (DAMPs). ATP, one of the most studied DAMPs, triggers a cascade of autocrine and paracrine actions through purinergic P2X and P2Y receptors, which are shaped by ectonucleotidases (CD39). Both P2 receptor families, and in particular P2Y₁, P2Y₂, P2Y₁₂, and P2X7 receptors, have been attracting increasing interest in several inflammatory diseases and drug development. Current data obtained from the murine model unveiled a CD39-ADP-P2Y₁/P2Y₁₂ receptors signaling pathway linked to the liver and mesenteric exacerbations of schistosomal inflammation. Therefore, we proposed that members of this purinergic signaling could be putative pharmacological targets to reduce schistosomal morbidity.

Characterization of class II fumarase from Schistosoma mansoni provides the molecular basis for selective inhibition

Schistosomiasis is a neglected tropical disease that affects more than 250 million people worldwide. The only drug available for its treatment undergoes first-pass hepatic metabolism and is not capable of preventing reinfection, which makes the search of new therapies urgently needed. Due to the essential role of fumarases in metabolism, these enzymes represent potential targets for developing novel schistosomiasis treatments. Here, we evaluate the expression profiles for class I and class II fumarases from Schistosoma mansoni (SmFH_I and SmFH_II, respectively), and report the complete characterization of SmFH_II. The first SmFH_II structure in complex with L-malate was determined at 1.85 Å resolution. The significant thermoshift observed for SmFH_II in the presence of identified ligands makes the differential scanning fluorimetry an adequate technique for ligand screening. A complete kinetic characterization of SmFH_II was performed, and comparison with the human fumarase (HsFH) revealed differences regarding the turnover number (k_cat). Structural characterization allowed us to identify differences between SmFH_II and HsFH that could be explored to design new selective inhibitors. This work represents the very first step towards validate the fumarases as drug targets to treat schistosomiasis. Our results provide the structural basis to rational search for selective ligands.

Identification of 6-(piperazin-1-yl)-1,3,5-triazine as a chemical scaffold with broad anti-schistosomal activities

Background: Schistosomiasis, caused by infection with blood fluke schistosomes, is a neglected tropical disease of considerable importance in resource-poor communities throughout the developing world. In the absence of an immunoprophylactic vaccine and due to over-reliance on a single chemotherapy (praziquantel), schistosomiasis control is at risk should drug insensitive schistosomes develop. In this context, application of in silico virtual screening on validated schistosome targets has proven successful in the identification of novel small molecules with anti-schistosomal activity.   Methods: Focusing on the Schistosoma mansoni histone methylation machinery, we herein have used RNA interference (RNAi), ELISA-mediated detection of H3K4 methylation, homology modelling and in silico virtual screening to identify a small collection of small molecules for anti-schistosomal testing. A combination of low to high-throughput whole organism assays were subsequently used to assess these compounds' activities on miracidia to sporocyst transformation, schistosomula phenotype/motility metrics and adult worm motility/oviposition readouts. Results: RNAi-mediated knockdown of smp_138030/smmll-1 (encoding a histone methyltransferase, HMT) in adult worms (~60%) reduced parasite motility and egg production. Moreover, in silico docking of compounds into Smp_138030/SmMLL-1's homology model highlighted competitive substrate pocket inhibitors, some of which demonstrated significant activity on miracidia, schistosomula and adult worm lifecycle stages together with variable effects on HepG2 cells. Particularly, the effect of compounds containing a 6-(piperazin-1-yl)-1,3,5-triazine core on adult schistosomes recapitulated the results of the smp_138030/smmll-1 RNAi screens. Conclusions: The biological data and the structure-activity relationship presented in this study define the 6-(piperazin-1-yl)-1,3,5-triazine core as a promising starting point in ongoing efforts to develop new urgently needed schistosomicides.

Molecular Context of ADP-ribosylation in Schistosomes for Drug Discovery and Vaccine Development

Schistosome infection is regarded as one of the most important and neglected tropical diseases associated with poor sanitation. Like other living organisms, schistosomes employ multiple biological processes, of which some are regulated by a post-translational modification called Adenosine Diphosphate-ribosylation (ADP-ribosylation), catalyzed by ADP-ribosyltransferases. ADP-ribosylation is the addition of ADP-ribose moieties from Nicotinamide Adenine Dinucleotide (NAD+) to various targets, which include proteins and nucleotides. It is crucial in biological processes such as DNA repair, apoptosis, carbohydrate metabolism and catabolism. In the absence of a vaccine against schistosomiasis, this becomes a promising pathway in the identification of drug targets against various forms of this infection. The tegument of the worm is an encouraging immunogenic target for anti-schistosomal vaccine development. Vaccinology, molecular modeling and target-based drug discovery strategies have been used for years in drug discovery and for vaccine development. In this paper, we outline ADP-ribosylation and other different approaches to drug discovery and vaccine development against schistosomiasis.

Identification of 6-(piperazin-1-yl)-1,3,5-triazine as a chemical scaffold with broad anti-schistosomal activities

Background: Schistosomiasis, caused by infection with blood fluke schistosomes, is a neglected tropical disease of considerable importance in resource-poor communities throughout the developing world. In the absence of an immunoprophylactic vaccine and due to over-reliance on a single chemotherapy (praziquantel), schistosomiasis control is at risk should drug insensitive schistosomes develop. In this context, application of in silico virtual screening on validated schistosome targets has proven successful in the identification of novel small molecules with anti-schistosomal activity.   Methods: Focusing on the Schistosoma mansoni histone methylation machinery, we herein have used RNA interference (RNAi), ELISA-mediated detection of H3K4 methylation, homology modelling and in silico virtual screening to identify a small collection of small molecules for anti-schistosomal testing. A combination of low to high-throughput whole organism assays were subsequently used to assess these compounds' activities on miracidia to sporocyst transformation, schistosomula phenotype/motility metrics and adult worm motility/oviposition readouts. Results: RNAi-mediated knockdown of smp_138030/smmll-1 (encoding a histone methyltransferase, HMT) in adult worms (~60%) reduced parasite motility and egg production. Moreover, in silico docking of compounds into Smp_138030/SmMLL-1's homology model highlighted competitive substrate pocket inhibitors, some of which demonstrated significant activity on miracidia, schistosomula and adult worm lifecycle stages together with variable effects on HepG2 cells. Particularly, the effect of compounds containing a 6-(piperazin-1-yl)-1,3,5-triazine core on adult schistosomes recapitulated the results of the smp_138030/smmll-1 RNAi screens. Conclusions: The biological data and the structure-activity relationship presented in this study define the 6-(piperazin-1-yl)-1,3,5-triazine core as a promising starting point in ongoing efforts to develop new urgently needed schistosomicides.

Deciphering the enzymatic target of a new family of antischistosomal agents bearing a quinazoline scaffold using complementary computational tools

A previous phenotypic screening campaign led to the identification of a quinazoline derivative with promising in vitro activity against Schistosoma mansoni. Follow-up studies of the antischistosomal potential of this candidate are presented here. The in vivo studies in a S. mansoni mouse model show a significant reduction of total worms and a complete disappearance of immature eggs when administered concomitantly with praziquantel in comparison with the administration of praziquantel alone. This fact is of utmost importance because eggs are responsible for the pathology and transmission of the disease. Subsequently, the chemical optimisation of the structure in order to improve the metabolic stability of the parent compound was carried out leading to derivatives with improved drug-like properties. Additionally, the putative target of this new class of antischistosomal compounds was envisaged by using computational tools and the binding mode to the target enzyme, aldose reductase, was proposed.

Interaction of Selected Terpenoids From Dalbergia sissoo With Catalytic Domain of Matrix Metalloproteinase-1: An In Silico Assessment of Their Anti-wrinkling Potential

Matrix metalloproteinase-1 (MMP-1) is a predominant collagenase enzyme that cleaves collagen fibers, contributing to skin wrinkling. Matrix metalloproteinase-1 inhibitors of herbal origin may provide an earnest probability to offer a novel curative approach against MMP-1-mediated collagenolysis, prompted by ultraviolet (UV)-induced overexpression of MMP-1. In this in silico study, we have explored the MMP-1 inhibitory potential of selected terpenoids from Dalbergia sissoo extracts. Two triterpenoids (lupeol and betulin), 1 diterpenoid (phytol), and 1 ester derivative of lupeol (lupeol acetate) were studied along with a reference inhibitor (doxycycline) using molecular docking approach. Non covalent interaction between the target ligands was found. Lupeol was found interacting with amino acid (AA) residues in the catalytic domain of MMP-1 with 3 hydrogen bonds (H-bond) formation, phytol with 1 and doxycycline with 2 H-bonds, whereas betulin and lupeol acetate were not able to form any H-bond with the AA residues in the catalytic site of the target protein. However, hydrophobic interaction between these ligands and protein was evident with select residues. The binding affinity of lupeol was highest (binding free energy, ΔG = −8.24 kcal/mol), which was greater than reference drug, doxycycline (ΔG = −8.05 kcal/mol). Lupeol acetate and phytol displayed a ΔG value of −7.12 and −7.06 kcal/mol, respectively, whereas betulin holds less binding affinity for the target receptor (ΔG = −4.66 kcal/mol). In silico pharmacokinetic studies demonstrated drug-like properties of the ligand compounds. This study shows that hydroxyl groups present in the ligands play a substantial role in establishing protein ligand interaction via hydrogen bonding.

Discovery of novel Schistosoma mansoni PDE4A inhibitors as potential agents against schistosomiasis

Aim: Due to the urgent need for effective drugs to treat schistosomiasis that act through a known molecular mechanism of action, we focused on a target-based approach with the aim to discover inhibitors of a cyclic nucleotide phosphodiesterase from Schistosoma mansoni (SmPDE4A). Materials & methods: To discover new inhibitors of SmPDE4A homology models of the enzyme structure were constructed based on known human and protozoan homologs. The best two models were selected for subsequent virtual screening of our in-house chemical library. Results & conclusion: A total of 25 library compounds were selected for experimental confirmation as SmPDE4A inhibitors and after dose-response experiments, three top hits were identified. The results presented validate the virtual screening approach to identify new inhibitors for clinically relevant phosphodiesterases.

Could we expect new praziquantel derivatives? A meta pharmacometrics/pharmacoinformatics analysis of all antischistosomal praziquantel derivatives found in the literature

Praziquantel (PZQ) is the first line drug for the treatment of human Schistosoma spp. worm infections. However, it suffers from low activity towards immature stages of the worm, and its prolonged use induces resistance/tolerance. During the last 40 years, 263 PZQ analogues have been synthesized and tested against Schistosoma spp. worms, but less than 10% of them showed significant activity. Here, we propose a rationalization of the chemical space of the PZQ derivatives by a ligand-based approach. First, we constructed an in-house database with all PZQ derivatives available in the literature. This analysis shows a high heterogeneity in the data. Fortunately, all studies include PZQ as a reference, permitting the classification of compounds into three classes according to their activities. Models involving ligand-based pharmacophore and logistic regression were performed. Five physicochemical parameters were identified as the best to explain the biological activity. In the end, we proposed new PZQ derivatives with modifications at positions 1 and 7, we analysed them with our models, and we observed that they can be more active than the previously synthesized derivatives. The main goal of this work was to conduct the most valuable meta-pharmacometrics/pharmacoinformatics analysis with all Praziquantel medicinal chemistry data available in the literature.

The natural compound 7-epiclusianone inhibits superoxide dismutase activity in Schistosoma mansoni

Schistosomiasis - caused by trematodes from the genus Schistosoma - affects more than 200 million people worldwide. Growing resistance to therapy with praziquantel (PZQ) has encouraged the search for novel treatments against this neglected disease. The compound 7-epiclusianone (7-epi) - isolated from 'bacupari' (the fruit of the Gracinia brasiliensis tree) - has promising activity against Schistosoma mansoni in vitro, damaging the parasite's tegument. However, the target and mechanism of action of 7-epi have not been identified. Here, we examined the possibility that 7-epi harms the tegument by inhibiting parasite superoxide dismutase (SOD), which protects the tegument from damage by reactive oxygen species produced by host immune cells. Molecular docking analysis in silico suggested strong interactions between 7-epi and S. mansoni cytosolic superoxide dismutase (SmCtSOD) at allosteric cavities. Schistosoma mansoni couples were cultivated ex vivo with 12.44-198.96 μm 7-epi for 24 h, and then parasite extracts were tested for lipid peroxidation (as a surrogate for oxidative stress), and SOD activity and expression. Lipid peroxidation levels increased after incubation with concentrations ≥99.48 μm 7-epi, and this compound reduced SOD activity at concentrations ≥24.87 μm. However, contact with 7-epi did not alter SOD expression, by quantitative real-time polymerase chain reaction (qRT-PCR). Our results show that the inhibition of SmCtSOD is partly responsible for the tegument detachment observed after incubation with 7-epi, but is not the only cause of the antiparasitic action of this compound in vitro.

Controlling schistosomiasis with praziquantel: How much longer without a viable alternative?

The current approach of morbidity control of schistosomiasis, a helminth disease of poverty with considerable public health and socioeconomic impact, is based on preventive chemotherapy with praziquantel. There is a pressing need for new drugs against this disease whose control entirely depends on this single drug that has been widely used over the past 40 years. We argue that a broader anthelminthic approach supplementing praziquantel with new antischistosomals targeting different parasite development stages would not only increase efficacy but also reduce the risk for drug resistance. Repositioning drugs already approved for other diseases provides a shortcut to clinical trials, as it is expected that such drugs rapidly pass the regulatory authorities. The antischistosomal properties of antimalarial drugs (e.g., semisynthetic artemisinins, synthetic trioxolanes, trioxaquines and mefloquine) and of drugs being developed or registered for other purposes (e.g., moxidectin and miltefosin), administered alone or in combination with praziquantel, have been tested in the laboratory and clinical trials. Another avenue to follow is the continued search for new antischistosomal properties in plants. Here, we summarise recent progress made in schistosomiasis chemotherapy, placing particular emphasis on repositioning of existing drugs against schistosomiasis.

Purinergic signaling in schistosomal infection

Human schistosomiasis is a chronic inflammatory disease caused by blood fluke worms belonging to the genus Schistosoma. Health metrics indicate that the disease is related to an elevated number of years lost-to-disability and years lost-to-life. Schistosomiasis is an intravascular disease that is related to a Th1 and Th2 immune response polarization, and the degree of polarization affects the outcome of the disease. The purinergic system is composed of adenosine and nucleotides acting as key messenger molecules. Moreover, nucleotide-transforming enzymes and cell-surface purinergic receptors are obligatory partners of this purinergic signaling. In mammalian cells, purinergic signaling modulates innate immune responses and inflammation among other functions; conversely purinergic signaling may also be modulated by inflammatory mediators. Moreover, schistosomes also express some enzymes of the purinergic system, and it is possible that worms modulate host purinergic signaling. Current data obtained in murine models of schistosomiasis support the notion that the host purinergic system is altered by the disease. The dysfunction of adenosine receptors, metabotropic P2Y and ionotropic P2X₇ receptors, and NTPDases likely contributes to disease morbidity.

Quinazolinone azolyl ethanols: potential lead antimicrobial agents with dual action modes targeting methicillin-resistant Staphylococcus aureus DNA

Aim: Due to bacterial drug resistance, a new series of quinazolinone azolyl ethanols were synthesized and evaluated. Results: In vitro antibacterial assay showed that triazolyl ethanol quinazolinone 3a was the most active compound, especially against methicillin-resistant Staphylococcus aureus (MRSA) with minimal inhibitory concentration value of 8 µg/ml, which was superior to chloromycin and comparable to norfloxacin. Molecular docking study displayed that compound 3a could interact with MRSA DNA by the formation of hydrogen bonds. Further interactions of quinazolinone 3a with MRSA DNA suggested that it could intercalate into MRSA DNA to form 3a–DNA complex. DNA cleavage properties of 3a–Cu2+ and 3a–Zn2+ complexes were confirmed by agarose gel electrophoresis experiments. Conclusion: Compound 3a should be a potential lead antibacterial molecule with dual action modes.

Discovery of Novel Antischistosomal Agents by Molecular Modeling Approaches

Schistosomiasis, a chronic neglected tropical disease caused by Schistosoma worms, is reported in nearly 80 countries. Although the disease affects approximately 260 million people, the treatment relies exclusively on praziquantel, a drug discovered in the mid-1970s that lacks efficacy against the larval stages of the parasite. In addition, the dependence on a single treatment has raised concerns about drug resistance, and reduced susceptibility has already been found in laboratory and field isolates. Therefore, novel therapies for schistosomiasis are needed, and several approaches have been used to that end. One of these strategies, molecular modeling, has been increasingly integrated with experimental techniques, resulting in the discovery of novel antischistosomal agents.

Discovery of New Anti-Schistosomal Hits by Integration of QSAR-Based Virtual Screening and High Content Screening

Schistosomiasis is a debilitating neglected tropical disease, caused by flatworms of Schistosoma genus. The treatment relies on a single drug, praziquantel (PZQ), making the discovery of new compounds extremely urgent. In this work, we integrated QSAR-based virtual screening (VS) of Schistosoma mansoni thioredoxin glutathione reductase (SmTGR) inhibitors and high content screening (HCS) aiming to discover new antischistosomal agents. Initially, binary QSAR models for inhibition of SmTGR were developed and validated using the Organization for Economic Co-operation and Development (OECD) guidance. Using these models, we prioritized 29 compounds for further testing in two HCS platforms based on image analysis of assay plates. Among them, 2-[2-(3-methyl-4-nitro-5-isoxazolyl)vinyl]pyridine and 2-(benzylsulfonyl)-1,3-benzothiazole, two compounds representing new chemical scaffolds have activity against schistosomula and adult worms at low micromolar concentrations and therefore represent promising antischistosomal hits for further hit-to-lead optimization.

Modern approaches to accelerate discovery of new antischistosomal drugs

INTRODUCTION

The almost exclusive use of only praziquantel for the treatment of schistosomiasis has raised concerns about the possible emergence of drug-resistant schistosomes. Consequently, there is an urgent need for new antischistosomal drugs. The identification of leads and the generation of high quality data are crucial steps in the early stages of schistosome drug discovery projects.

AREAS COVERED

Herein, the authors focus on the current developments in antischistosomal lead discovery, specifically referring to the use of automated in vitro target-based and whole-organism screens and virtual screening of chemical databases. They highlight the strengths and pitfalls of each of the above-mentioned approaches, and suggest possible roadmaps towards the integration of several strategies, which may contribute for optimizing research outputs and led to more successful and cost-effective drug discovery endeavors.

EXPERT OPINION

Increasing partnerships and access to funding for drug discovery have strengthened the battle against schistosomiasis in recent years. However, the authors believe this battle also includes innovative strategies to overcome scientific challenges. In this context, significant advances of in vitro screening as well as computer-aided drug discovery have contributed to increase the success rate and reduce the costs of drug discovery campaigns. Although some of these approaches were already used in current antischistosomal lead discovery pipelines, the integration of these strategies in a solid workflow should allow the production of new treatments for schistosomiasis in the near future.

High Throughput Screening Identifies Novel Lead Compounds with Activity against Larval, Juvenile and Adult Schistosoma mansoni

An estimated 600 million people are affected by the helminth disease schistosomiasis caused by parasites of the genus Schistosoma. There is currently only one drug recommended for treating schistosomiasis, praziquantel (PZQ), which is effective against adult worms but not against the juvenile stage. In an attempt to identify improved drugs for treating the disease, we have carried out high throughput screening of a number of small molecule libraries with the aim of identifying lead compounds with balanced activity against all life stages of Schistosoma. A total of almost 300,000 compounds were screened using a high throughput assay based on motility of worm larvae and image analysis of assay plates. Hits were screened against juvenile and adult worms to identify broadly active compounds and against a mammalian cell line to assess cytotoxicity. A number of compounds were identified as promising leads for further chemical optimization.

Schistosomiasis is a parasitic infection that affects an estimated 600 million people in developing countries. Treatment is currently dependent on a single drug which is only active against the adult form of the disease. Treatment of infected patients eliminates adult worms but leaves any juveniles to survive and develop, thus continuing the infection. A drug acting equally against adult and juvenile worms is likely to be more effective at eliminating the disease. We have identified quality chemical leads with balanced activity against all life stages of the parasite and with a good window over cytotoxicity, which could form the basis of an exciting new drug discovery project.