Praziquantel: mechanisms of anti-schistosomal activity

Topical application of a P2X2/P2X3 purine receptor inhibitor suppresses the bitter taste of medicines and other taste qualities

BACKGROUND AND PURPOSE

Many medications taste intensely bitter. The innate aversion to bitterness affects medical compliance, especially in children. There is a clear need to develop bitter blockers to suppress the bitterness of vital medications. Bitter taste is mediated by TAS2R receptors. Because different pharmaceutical compounds activate distinct sets of TAS2Rs, targeting specific receptors may only suppress bitterness for certain, but not all, bitter-tasting compounds. Alternative strategies are needed to identify universal bitter blockers that will improve the acceptance of every medication. Taste cells in the mouth transmit signals to afferent gustatory nerve fibres through the release of ATP, which activates the gustatory nerve-expressed purine receptors P2X2/P2X3. We hypothesized that blocking gustatory nerve transmission with P2X2/P2X3 inhibitors (e.g. 5-(5-iodo-4-methoxy-2-propan-2-ylphenoxy)pyrimidine-2,4-diamine [AF-353]) would reduce bitterness for all medications and bitter compounds.

EXPERIMENTAL APPROACH

Human sensory taste testing and mouse behavioural analyses were performed to determine if oral application of AF-353 blocks perception of bitter taste and other taste qualities but not non-gustatory oral sensations (e.g. tingle).

KEY RESULTS

Rinsing the mouth with AF-353 in humans or oral swabbing it in mice suppressed the bitter taste and avoidance behaviours of all compounds tested. We further showed that AF-353 suppressed other taste qualities (i.e. salt, sweet, sour and savoury) but had no effects on other oral or nasal sensations (e.g, astringency and oral tingle).

CONCLUSION AND IMPLICATIONS

This is the first time a universal, reversible taste blocker in humans has been reported. Topical application of P2X2/P2X3 inhibitor to suppress bitterness may improve medical compliance.

Can antibody conjugated nanomicelles alter the prospect of antibody targeted therapy against schistosomiasis mansoni?

BACKGROUND

CLA (conjugated linoleic acid)-mediated activation of the schistosome tegument-associated sphingomyelinase and consequent disruption of the outer membrane might allow host antibodies to access the apical membrane antigens. Here, we investigated a novel approach to enhance specific antibody delivery to concealed surface membrane antigens of Schistosoma mansoni utilising antibody-conjugated-CLA nanomicelle technology.

METHODOLOGY/PRINCIPAL FINDINGS

We invented and characterised an amphiphilic CLA-loaded whey protein co-polymer (CLA-W) as an IV injectable protein nanocarrier. Rabbit anti-Schistosoma mansoni infection (anti-SmI) and anti-Schistosoma mansoni alkaline phosphatase specific IgG antibodies were purified from rabbit sera and conjugated to the surface of CLA-W co-polymer to form antibody-conjugated-CLA-W nanomicelles (Ab-CLA-W). We investigated the schistosomicidal effects of CLA-W and Ab-CLA-W in a mouse model of Schistosoma mansoni against early and late stages of infection. Results showed that conjugation of nanomicelles with antibodies, namely anti-SmI, significantly enhanced the micelles' schistosomicidal and anti-pathology activities at both the schistosomula and adult worm stages of the infection resulting in 64.6%-89.9% reductions in worm number; 72.5-94% and 66.4-85.2% reductions in hepatic eggs and granulomas, respectively. Treatment induced overall improvement in liver histopathology, reducing granuloma size and fibrosis and significantly affecting egg viability. Indirect immunofluorescence confirmed CLA-W-mediated antigen exposure on the worm surface. Electron microscopy revealed extensive ultrastructural damage in worm tegument induced by anti-SmI-CLA-W.

CONCLUSION/SIGNIFICANCE

The novel antibody-targeted nano-sized CLA delivery system offers great promise for treatment of Schistosoma mansoni infection and control of its transmission. Our in vivo observations confirm an immune-mediated enhanced effect of the schistosomicidal action of CLA and hints at the prospect of nanotechnology-based immunotherapy, not only for schistosomiasis, but also for other parasitic infections in which chemotherapy has been shown to be immune-dependent. The results propose that the immunodominant reactivity of the anti-SmI serum, Schistosoma mansoni fructose biphosphate aldolase, SmFBPA, merits serious attention as a therapeutic and vaccine candidate.

Assessing risk factors for malaria and schistosomiasis among children in Misungwi, Tanzania, an area of co-endemicity: A mixed methods study

Malaria and schistosomiasis are two major parasitic vector-borne diseases that are a particular threat to young children in Sub-Saharan Africa. In the present study, we investigated factors that are associated with malaria, schistosomiasis, and co-infection among school-aged children, using an explanatory sequential mixed-methods approach. A cross-sectional study was conducted in January 2022 in Misungwi, Tanzania, that sampled 1,122 children aged 5 to 14 years old for malaria and schistosomiasis infection. Mixed-effect logistic regression models were used to assess the association between infection prevalence or seroprevalence, and environmental determinants that create favorable conditions for vectors and parasites and social determinants that relate to disease exposure. Community mapping combined with direct field observations were conducted in August 2022 in three selected villages from the cross-sectional study to understand specific water use behaviors and to identify potential malaria mosquito larval breeding sites and freshwater snail habitat. The prevalence of malaria, seroprevalence of schistosomiasis, and co-infection in this study were 40.4%, 94.3%, and 38.1%, respectively. Individual-level factors emerged as the primary determinants driving the association with infection, with age (every one-year increase in age) and sex (boys vs girls) being statistically and positively associated with malaria, schistosomiasis, and co-infection (P<0.05 for all). Community maps identified many unimproved water sources in all three villages that were used by humans, cattle, or both. We found that children primarily fetched water, and that unprotected wells were dedicated for drinking water whereas ponds were dedicated for other domestic uses and cattle. Although not identified in the community maps, we found hand pumps in all three villages were not in use because of unpleasant taste and high cost. This study improves our understanding of individual, social and environmental factors that are associated with malaria, schistosomiasis, and co-infection, which can inform potential entry points for integrated disease prevention and control.

Small change, big difference: A promising praziquantel derivative designated P96 with broad-spectrum antischistosomal activity for chemotherapy of schistosomiasis japonica

BACKGROUND

Praziquantel (PZQ) has been the first line antischistosomal drug for all species of Schistosoma, and the only available drug for schistosomiasis japonica, without any alternative drugs since the 1980s. However, PZQ cannot prevent reinfection, and cannot cure schistosomiasis thoroughly because of its poor activity against juvenile schistosomes. In addition, reliance on a single drug is extremely dangerous, the development and spread of resistance to PZQ is becoming a great concern. Therefore, development of novel drug candidates for treatment and control of schistosomiasis is urgently needed.

METHODOLOGYS/PRINCIPAL FINDINGS

One of the PZQ derivative christened P96 with the substitution of cyclohexyl by cyclopentyl was synthesized by School of Pharmaceutical Sciences of Shandong University. We investigated the in vitro and in vivo activities of P96 against different developmental stages of S. japonicum. Parasitological studies and scanning electron microscopy were used to study the primary action characteristics of P96 in vitro. Both mouse and rabbit models were employed to evaluate schistosomicidal efficacy of P96 in vivo. Besides calculation of worm reduction rate and egg reduction rate, quantitative real-time PCR was used to evaluate the in vivo antischistosomal activity of P96 at molecular level. In vitro, after 24h exposure, P96 demonstrated the highest activities against both juvenile and adult worm of S. japonicum in comparison to PZQ. The antischistosomal efficacy was concentration-dependent, with P96 at 50μM demonstrating the most evident schistosomicidal effect. Scanning electron microscopy demonstrated that P96 caused more severe damages to schistosomula and adult worm tegument compared to PZQ. In vivo, our results showed that P96 was effective against S. japonicum at all developmental stages. Notably, its efficacy against young stage worms was significantly improved compared to PZQ. Moreover, P96 retained the high activity comparable to PZQ against the adult worm of S. japonicum.

CONCLUSIONS

P96 is a promising drug candidate for chemotherapy of schistosomiasis japonica, which has broad spectrum of action against various developmental stage, potentially addressing the deficiency of PZQ. It might be promoted as a drug candidate for use either alone or in combination with PZQ for the treatment of schistosomiasis.

Praziquantel - 50 Years of Research

Investigations on praziquantel (PZQ) started fifty years ago by a cooperation between Bayer AG and Merck KGaA. Until today PZQ is the drug of choice for schistosomiasis in human medicine and used in many combinations with antinematode drugs in veterinary medicine. The Sm.TRPMPZQ , a Ca2+ -permeable transient receptor potential (TRP) channel, has been discovered as primary target of PZQ during the last decade. Furthermore, there is a short overview of routes of large-scale synthesis of racemic and pure (R)-PZQ. Until now racemic PZQ is used in veterinary and human medicine. In 2012 the Pediatric Praziquantel Consortium started PZQ chemistry and process development of pure (R)-PZQ for human application. It is hoped that (R)-PZQ will become available for pediatric use soon. The knowledge of the binding pocket of PZQ in Sm.TRPMPZQ allows to design synthesis of PZQ-derivatives of the next generation for a target-site directed screening. A similar screening should also be started for Fasciola hepatica TRPMPZQ .

Perspective on Schistosomiasis Drug Discovery: Highlights from a Schistosomiasis Drug Discovery Workshop at Wellcome Collection, London, September 2022

In September 2022, the Drug Discovery Unit at the University of Dundee, UK, organised an international meeting at the Wellcome Collection in London to explore the current clinical situation and challenges associated with treating schistosomiasis. The aim of this meeting was to discuss the need for new treatments in view of the clinical situation and to ascertain what the key requirements would be for any potential new anti-schistosomals. This information will be essential to inform ongoing drug discovery efforts for schistosomiasis. We also discussed the potential drug discovery pathway and associated criteria for progressing compounds to the clinic. To date, praziquantel (PZQ) is the only drug available to treat all species causing schistosomiasis, but it is often unable to completely clear parasites from an infected patient, partially due to its inactivity against juvenile worms. PZQ-mediated mass drug administration campaigns conducted in endemic areas (e.g., sub-Saharan Africa, where schistosomiasis is primarily prevalent) have contributed to reducing the burden of disease but will not eliminate the disease as a public health problem. The potential for Schistosoma to develop resistance towards PZQ, as the sole treatment available, could become a concern. Consequently, new anthelmintic medications are urgently needed, and this Perspective aims to capture some of the learnings from our discussions on the key criteria for new treatments.

Halloysite Nanotubes and Sepiolite for Health Applications

The need for safe, therapeutically effective, and patient-compliant drug delivery systems continuously leads researchers to design novel tools and strategies. Clay minerals are widely used in drug products both as excipients and active agents but, in recent years, there has been a growing interest in research aimed at the development of new organic or inorganic nanocomposites. The attention of the scientific community has been drawn by nanoclays, thanks to their natural origin, worldwide abundance, availability, sustainability, and biocompatibility. In this review, we focused our attention on the studies inherent to the pharmaceutical and biomedical applications of halloysite and sepiolite, and their semi-synthetic or synthetic derivatives, as drug delivery systems. After having described the structure of both materials and their biocompatibility, we delineate the use of the nanoclays to enhance the stability, the controlled release, the bioavailability, and the adsorption properties of drugs. Several types of surface functionalization have been discussed, showing that these materials could be used for the development of an innovative therapeutic approach.

Kinetics of Drug Release from Clay Using Enhanced Sampling Methods

A key step in the development of a new drug, is the design of drug-excipient complexes that lead to optimal drug release kinetics. Computational chemistry and specifically enhanced sampling molecular dynamics methods can play a key role in this context, by minimizing the need for expensive experiments, and reducing cost and time. Here we show that recent advances in enhanced sampling methodologies can be brought to fruition in this area. We demonstrate the potential of these methodologies by simulating the drug release kinetics of the complex praziquantel-montmorillonite in water. Praziquantel finds promising applications in the treatment of schistosomiasis, but its biopharmaceutical profile needs to be improved, and a cheap material such as the montmorillonite clay would be a very convenient excipient. We simulate the drug release both from surface and interlayer space, and find that the diffusion of the praziquantel inside the interlayer space is the process that limits the rate of drug release.

Identification of Inhibitors of the Schistosoma mansoni VKR2 Kinase Domain

Schistosomiasis is a neglected tropical disease caused by parasitic flatworms. Current treatment relies on just one partially effective drug, praziquantel (PZQ). Schistosoma mansoni Venus Kinase Receptors 1 and 2 (SmVKR1 and SmVKR2) are important for parasite growth and egg production, and are potential targets for combating schistosomiasis. VKRs consist of an extracellular Venus Flytrap Module (VFTM) linked via a transmembrane helix to a kinase domain. Here, we initiated a drug discovery effort to inhibit the activity of the SmVKR2 kinase domain (SmVKR2KD) by screening the GSK published kinase inhibitor set 2 (PKIS2). We identified several inhibitors, of which four were able to inhibit its enzymatic activity and induced phenotypic changes in ex vivo S. mansoni. Our crystal structure of the SmVKR2KD displays an active-like state that sheds light on the activation process of VKRs. Our data provide a basis for the further exploration of SmVKR2 as a possible drug target.

Comparing and Quantifying the Efficiency of Cocrystal Screening Methods for Praziquantel

Pharmaceutical cocrystals are highly interesting due to their effect on physicochemical properties and their role in separation technologies, particularly for chiral molecules. Detection of new cocrystals is a challenge, and robust screening methods are required. As numerous techniques exist that differ in their crystallization mechanisms, their efficiencies depend on the coformers investigated. The most important parameters characterizing the methods are the (a) screenable coformer fraction, (b) coformer success rate, (c) ability to give several cocrystals per successful coformer, (d) identification of new stable phases, and (e) experimental convenience. Based on these parameters, we compare and quantify the performance of three methods: liquid-assisted grinding, solvent evaporation, and saturation temperature measurements of mixtures. These methods were used to screen 30 molecules, predicted by a network-based link prediction algorithm (described in Cryst. Growth Des. 2021, 21(6), 3428-3437) as potential coformers for the target molecule praziquantel. The solvent evaporation method presented more drawbacks than advantages, liquid-assisted grinding emerged as the most successful and the quickest, while saturation temperature measurements provided equally good results in a slower route yielding additional solubility information relevant for future screenings, single-crystal growth, and cocrystal production processes. Seventeen cocrystals were found, with 14 showing stability and 12 structures resolved.

Itraconazole, a cytochrome P450 inhibitor, enhanced the efficacy of praziquantel against Schistosoma mansoni infection and alleviated liver injury in mice

Treatment of schistosomiasis is heavily reliant on the single antischistosomal drug praziquantel (PZQ). The use of synergistic drug-drug interactions is one possible solution, which could be used to mitigate PZQ's poor and variable bioavailability. Itraconazole (ITZ), a triazole antifungal agent, is a potent CYP3A inhibitor that can cause significant drug-drug interactions when used with CYP3A substrates. This study investigates the effect of ITZ as adjuvant therapy with PZQ on worm load, egg deposition and maturation, and the consequent histopathology and biochemical abnormalities in the liver during the immature and mature stages of Schistosoma mansoni (S. mansoni) infection. S. mansoni-infected mice were divided into five groups of eight-ten mice each: (I) infected untreated, (II) infected and treated with PZQ 3 weeks PI, (III) infected and treated with both ITZ and PZQ 3 weeks PI, (IV) infected and treated with PZQ 7 weeks PI, and (V) infected and treated with both ITZ and PZQ 7 weeks PI. All mice were killed by rapid decapitation 9 weeks PI. Data revealed that ITZ in combination with PZQ at both immature and mature stages improved the parasitological criteria of cure, and greatly reduced inflammation, granuloma and fibrotic tissue formation, and apoptosis versus PZQ alone. Furthermore, it showed the greatest impact on improving liver injury and oxidative stress markers. Notably, the effect was considerably stronger at the mature stage of S. mansoni infection. These findings support the notion that ITZ increased PZQ's antischistosomal activity by inhibiting CYP450 expression, potentially reducing PZQ metabolism and increasing systemic exposure.

Fifty years of the schistosome tegument: discoveries, controversies, and outstanding questions

The unique multilaminate appearance of the tegument surface of schistosomes was first described in 1973, in one of the earliest volumes of the International Journal for Parasitology. The present review, published almost 50 years later, traces the development of our knowledge of the tegument, starting with those earliest cytological advances, particularly the surface plasma membrane-membranocalyx complex, through an era of protein discovery to the modern age of protein characterization, aided by proteomics. More recently, analysis of single cell transcriptomes of schistosomes is providing insight into the organisation of the cell bodies that support the surface syncytium. Our understanding of the tegument, notably the nature of the proteins present within the plasma membrane and membranocalyx, has provided insights into how the schistosomes interact with their hosts but many aspects of how the tegument functions remain unanswered. Among the unresolved aspects are those concerned with maintenance and renewal of the surface membrane complex, and whether surface proteins and membrane components are recycled. Current controversies arising from investigations about whether the tegument is a source of extracellular vesicles during parasitism, and if it is covered with glycolytic enzymes, are evaluated in the light of cytological and proteomic knowledge of the layer.

Molecular Docking and Dynamics Simulation Revealed Ivermectin as Potential Drug against Schistosoma-Associated Bladder Cancer Targeting Protein Signaling: Computational Drug Repositioning Approach

Urogenital schistosomiasis is caused by Schistosoma haematobium (S. haematobium) infection, which has been linked to the development of bladder cancer. In this study, three repurposing drugs, ivermectin, arteether and praziquantel, were screened to find the potent drug-repurposing candidate against the Schistosoma-associated bladder cancer (SABC) in humans by using computational methods. The biology of most glutathione S-transferases (GSTs) proteins and vascular endothelial growth factor (VEGF) is complex and multifaceted, according to recent evidence, and these proteins actively participate in many tumorigenic processes such as cell proliferation, cell survival and drug resistance. The VEGF and GSTs are now widely acknowledged as an important target for antitumor therapy. Thus, in this present study, ivermectin displayed promising inhibition of bladder cancer cells via targeting VEGF and GSTs signaling. Moreover, molecular docking and molecular dynamics (MD) simulation analysis revealed that ivermectin efficiently targeted the binding pockets of VEGF receptor proteins and possessed stable dynamics behavior at binding sites. Therefore, we proposed here that these compounds must be tested experimentally against VEGF and GST signaling in order to control SABC. Our study lies within the idea of discovering repurposing drugs as inhibitors against the different types of human cancers by targeting essential pathways in order to accelerate the drug development cycle.

Metabolomics reveal alterations in arachidonic acid metabolism in Schistosoma mekongi after exposure to praziquantel

BACKGROUND

Mekong schistosomiasis is a parasitic disease caused by the blood-dwelling fluke Schistosoma mekongi. This disease contributes to human morbidity and mortality in the Mekong region, posing a public health threat to people in the area. Currently, praziquantel (PZQ) is the drug of choice for the treatment of Mekong schistosomiasis. However, the molecular mechanisms of PZQ action remain unclear, and Schistosoma PZQ resistance has been reported occasionally. Through this research, we aimed to use a metabolomic approach to identify the potentially altered metabolic pathways in S. mekongi associated with PZQ treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Adult stage S. mekongi were treated with 0, 20, 40, or 100 μg/mL PZQ in vitro. After an hour of exposure to PZQ, schistosome metabolites were extracted and studied with mass spectrometry. The metabolomic data for the treatment groups were analyzed with the XCMS online platform and compared with data for the no treatment group. After low, medium (IC50), and high doses of PZQ, we found changes in 1,007 metabolites, of which phosphatidylserine and anandamide were the major differential metabolites by multivariate and pairwise analysis. In the pathway analysis, arachidonic acid metabolism was found to be altered following PZQ treatment, indicating that this pathway may be affected by the drug and potentially considered as a novel target for anti-schistosomiasis drug development.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that arachidonic acid metabolism is a possible target in the parasiticidal effects of PZQ against S. mekongi. Identifying potential targets of the effective drug PZQ provides an interesting viewpoint for the discovery and development of new agents that could enhance the prevention and treatment of schistosomiasis.

Whole-genome sequencing of Schistosoma mansoni reveals extensive diversity with limited selection despite mass drug administration

Control and elimination of the parasitic disease schistosomiasis relies on mass administration of praziquantel. Whilst these programmes reduce infection prevalence and intensity, their impact on parasite transmission and evolution is poorly understood. Here we examine the genomic impact of repeated mass drug administration on Schistosoma mansoni populations with documented reduced praziquantel efficacy. We sequenced whole-genomes of 198 S. mansoni larvae from 34 Ugandan children from regions with contrasting praziquantel exposure. Parasites infecting children from Lake Victoria, a transmission hotspot, form a diverse panmictic population. A single round of treatment did not reduce this diversity with no apparent population contraction caused by long-term praziquantel use. We find evidence of positive selection acting on members of gene families previously implicated in praziquantel action, but detect no high frequency functionally impactful variants. As efforts to eliminate schistosomiasis intensify, our study provides a foundation for genomic surveillance of this major human parasite.

Cocrystals of Praziquantel: Discovery by Network-Based Link Prediction

Cocrystallization has been promoted as an attractive early development tool as it can change the physicochemical properties of a target compound and possibly enable the purification of single enantiomers from racemic compounds. In general, the identification of adequate cocrystallization candidates (or coformers) is troublesome and hampers the exploration of the solid-state landscape. For this reason, several computational tools have been introduced over the last two decades. In this study, cocrystals of Praziquantel (PZQ), an anthelmintic drug used to treat schistosomiasis, are predicted with network-based link prediction and experimentally explored. Single crystals of 12 experimental cocrystal indications were grown and subjected to a structural analysis with single-crystal X-ray diffraction. This case study illustrates the power of the link-prediction approach and its ability to suggest a diverse set of new coformer candidates for a target compound when starting from only a limited number of known cocrystals.

Schistosoma mansoni alter transcription of immunomodulatory gene products following in vivo praziquantel exposure

Control of the neglected tropical disease schistosomiasis relies almost entirely on praziquantel (PZQ) monotherapy. How PZQ clears parasite infections remains poorly understood. Many studies have examined the effects of PZQ on worms cultured in vitro, observing outcomes such as muscle contraction. However, conditions worms are exposed to in vivo may vary considerably from in vitro experiments given the short half-life of PZQ and the importance of host immune system engagement for drug efficacy in animal models. Here, we investigated the effects of in vivo PZQ exposure on Schistosoma mansoni. Measurement of pro-apoptotic caspase activation revealed that worm death occurs only after parasites shift from the mesenteric vasculature to the liver, peaking 24 hours after drug treatment. This indicates that PZQ is not directly schistocidal, since PZQ’s half-life is ~2 hours in humans and ~30 minutes in mice, and focuses attention on parasite interactions with the host immune system following the shift of worms to the liver. RNA-Seq of worms harvested from mouse livers following sub-lethal PZQ treatment revealed drug-evoked changes in the expression of putative immunomodulatory and anticoagulant gene products. Several of these gene products localized to the schistosome esophagus and may be secreted into the host circulation. These include several Kunitz-type protease inhibitors, which are also found in the secretomes of other blood feeding animals. These transcriptional changes may reflect mechanisms of parasite immune-evasion in response to chemotherapy, given the role of complement-mediated attack and the host innate/humoral immune response in parasite elimination. One of these isoforms, SmKI-1, has been shown to exhibit immunomodulatory and anti-coagulant properties. These data provide insight into the effect of in vivo PZQ exposure on S. mansoni, and the transcriptional response of parasites to the stress of chemotherapy.

The disease schistosomiasis is caused by parasitic worms that live within the circulatory system. While this disease infects over 200 million people worldwide, treatment relies almost entirely on one drug, praziquantel, whose mechanism is poorly understood. In this study, we analyzed the effects of praziquantel treatment on the gene expression of parasites harvested from mice treated with praziquantel chemotherapy. Despite the rapid action of the drug on worms in vitro, we found that key outcomes in vivo (measurement of cell death and changes in gene expression) occurred relatively late (12+ hours after drug administration). We found that worms increased the expression of immunomodulatory gene products in response to praziquantel, including a Kunitz-type protease inhibitor that localized to the worm esophagus and may be secreted to the external host environment. These are an intriguing class of proteins, because they display anti-coagulant and immunomodulatory properties. Up-regulation of these gene products may reflect a parasite mechanism of immune-evasion in response to chemotherapy. This research provides insight into the mechanism of praziquantel by observing the effect of this drug on worms within the context of the host immune system.

Praziquantel-Clays as Accelerated Release Systems to Enhance the Low Solubility of the Drug

Praziquantel is an antiparasitic drug indicated for the treatment of the schistosomiasis disease. This drug has very low aqueous solubility, requiring high oral doses for its administration which gives rise to side effects, therapeutic noncompliance and the appearance of resistant forms of the parasite. Clay minerals, like sepiolite and montmorillonite, are innocuous, non-toxic, biocompatible and low-cost excipients. Additionally, clays have high adsorbent properties that allow them to encapsulate drugs in nanometric spaces present in the channels in the case of the sepiolite or between the layers in the case of the montmorillonite. The interactions between the drug and clay minerals are studied experimentally with the strategy for preparing interactions products in organic solvents (ethanol, acetonitrile and dichloromethane) so that the interaction will be more effective and will be enhanced the aqueous solubility of praziquantel. The results showed that in the interaction products, the drug interacted with both clay minerals, which produced the loss of the crystallinity of the drug demonstrated by different techniques. This led to a significant increase in the dissolution rate of the praziquantel in all the interaction products in the simulated gastrointestinal tract media, except for the praziquantel–montmorillonite product prepared in dichloromethane that presented a controlled release in acid medium. Moreover, in vitro cytotoxicity and cell cycle studies were performed in the interaction products prepared with ethanol. The interaction product with sepiolite was biocompatible with the HTC116 line cells, and it did not produce alterations in the cell cycle. However, interaction products with montmorillonite did not produce cell death, but they showed affectation and damage of cells in the cell cycle study at the highest concentration tested (20–100 µM). Therefore, the different organic solvents used are adequate for the improvement of the biopharmaceutical profile of praziquantel. Drug–clay interaction products, specifically with sepiolite, showed very promising results in which new accelerated oral release systems of the praziquantel were obtained.

Activation of transient receptor potential channel Sm.(Schistosoma mansoni)TRPMPZQ by PZQ, enhanced Ca++ influx, spastic paralysis, and tegumental disrupture-the deadly cascade in parasitic schistosomes, other trematodes, and cestodes

After almost 50 years of praziquantel (PZQ) research, Park and Marchant (Trends Parasitol 36:182-194, 2020) described the Ca++-permeable transient receptor potential (TRP) channel Sm.TRPMPZQ in Schistosoma mansoni as target of PZQ. Here we describe the deadly cascade in schistosomes which is induced by the (R)-PZQ enantiomer that includes contemporaneous stereoselective activation of Sm.TRPMPZQ-mediated Ca++ influx, disturbed Ca++ homeostasis, Ca++-dependent spastic paralysis, and Ca++- and PZQ-dependent disruption of parasitic teguments. Under normal conditions, there is a reversible balance between bilayer, isotropic, and HII phases in biological membranes (Jouhet 2013). In vitro, we could observe an irreversible but not stereoselective transition to the HII phase in liposomes consisting of phosphatidylethanolamine (PE) and phosphatidylserine (PS), two naturally occurring phospholipids in schistosomes, by the concerted action of Ca++ and PZQ (Harder 2013). HII structures are a prerequisite for induction of fusion processes (Jouhet 2013), which, indeed, become visible as blebs, vacuolation processes, and large balloon-like surface exudates in a large variety of PZQ-sensitive parasitic flukes and cestodes after PZQ treatment. These tegument damages are irreversible. As homologs of Sm.TRPMPZQ are also present in the other trematodes S. japonicum, S. haematobium, or Clonorchis sinensis and cestodes Taenia solium, Echinococcus multilocularis, or Hymenolepis microstoma (Park and Marchant, Trends Parasitol 36:182-194, 2020), it is suggested that a similar deadly cascade will be operating generally in PZQ-sensitive parasites.

Effect of Praziquantel on Schistosoma mekongi Proteome and Phosphoproteome

Schistosoma mekongi causes schistosomiasis in southeast Asia, against which praziquantel (PZQ) is the only treatment option. PZQ resistance has been reported, thus increasing the requirement to understand mechanism of PZQ. Herein, this study aimed to assess differences in proteome and phosphoproteome of S. mekongi after PZQ treatment for elucidating its action. Furthermore, key kinases related to PZQ effects were predicted to identify alternative targets for novel drug development. Proteomes of S. mekongi were profiled after PZQ treatment at half maximal inhibitory concentration and compared with untreated worms. A total of 144 proteins were differentially expressed after treatment. In parallel, immunohistochemistry indicated a reduction of phosphorylation, with 43 phosphoproteins showing reduced phosphorylation, as identified by phosphoproteomic approach. Pathway analysis of mass spectrometric data showed that calcium homeostasis, worm antigen, and oxidative stress pathways were influenced by PZQ treatment. Interestingly, two novel mechanisms related to protein folding and proteolysis through endoplasmic reticulum-associated degradation pathways were indicated as a parasiticidal mechanism of PZQ. According to kinase–substrate predictions with bioinformatic tools, Src kinase was highlighted as the major kinase related to the alteration of phosphorylation by PZQ. Interfering with these pathways or applying Src kinase inhibitors could be alternative approaches for further antischistosomal drug development.

Molecular basis for hycanthone drug action in schistosome parasites

Hycanthone (HYC) is a retired drug formerly used to treat schistosomiasis caused by infection from Schistosoma mansoni and S. haematobium. Resistance to HYC was first observed in S. mansoni laboratory strains and in patients in the 1970s and the use of this drug was subsequently discontinued with the substitution of praziquantel (PZQ) as the single antischistosomal drug in the worldwide formulary. In endemic regions, multiple organizations have partnered with the World Health Organization to deliver PZQ for morbidity control and prevention. While the monotherapy reduces the disease burden, additional drugs are needed to use in combination with PZQ to stay ahead of potential drug resistance. HYC will not be reintroduced into the schistosomiasis drug formulary as a combination drug because it was shown to have adverse properties including mutagenic, teratogenic and carcinogenic activities. Oxamniquine (OXA) was used to treat S. mansoni infection in Brazil during the brief period of HYC use, until the 1990s. Its antischistosomal efficacy has been shown to work through the same mechanism as HYC and it does not possess the undesirable properties linked to HYC. OXA demonstrates cross-resistance in Schistosoma strains with HYC resistance and both are prodrugs requiring metabolic activation in the worm to toxic sulfated forms. The target activating enzyme has been identified as a sulfotransferase enzyme and is currently used as the basis for a structure-guided drug design program. Here, we characterize the sulfotransferases from S. mansoni and S. haematobium in complexes with HYC to compare and contrast with OXA-bound sulfotransferase crystal structures. Although HYC is discontinued for antischistosomal treatment, it can serve as a resource for design of derivative compounds without contraindication.

Proteomic analysis of adult Schistosoma mekongi somatic and excretory-secretory proteins

Schistosoma mekongi is a causative agent of human schistosomiasis. There is limited knowledge of the molecular biology of S. mekongi and very few studies have examined drug targets, vaccine candidates and diagnostic biomarkers for S. mekongi. To explore the biology of S. mekongi, computational as well as experimental approaches were performed on S. mekongi males and females to identify excretory-secretory (ES) proteins and proteins that are differentially expressed between genders. According to bioinformatic prediction, the S. mekongi ES product was approximately 4.7% of total annotated transcriptome sequences. The classical secretory pathway was the main process to secrete proteins. Mass spectrometry-based quantification of male and female adult S. mekongi proteins was performed. We identified 174 and 156 differential expression of proteins in male and female worms, respectively. The dominant male-biased proteins were involved in actin filament-based processes, microtubule-based processes, biosynthetic processes and homeostatic processes. The major female-biased proteins were related to biosynthetic processes, organelle organization and signal transduction. An experimental approach identified 88 proteins in the S. mekongi secretome. The S. mekongi ES proteins mainly contributed to nutrient uptake, essential substance supply and host immune evasion. This research identifies proteins in the S. mekongi secretome and provides information on ES proteins that are differentially expressed between S. mekongi genders. These findings will contribute to S. mekongi drug and vaccine development. In addition, the study enhances our understanding of basic S. mekongi biology.

Schistosomiasis vaccine development: update on human clinical trials

Schistosomiasis causes significant levels of morbidity and mortality in many geographical regions of the world. The disease is caused by infections with parasitic blood flukes known as schistosomes. The control of schistosomiasis over the last several decades has been centered on the mass drug administration (MDA) of praziquantel (PZQ), which is the only drug currently available for treatment. Despite the concerted efforts of MDA programs, the prevalence and transmission of schistosomiasis has remained largely unchecked due to the fact that PZQ is ineffective against juvenile schistosomes, does not prevent re-infection and the emergence of PZQ-resistant parasites. In addition, other measures such as the water, sanitation and hygiene programs and snail intermediate hosts control have had little to no impact. These drawbacks indicate that the current control strategies are severely inadequate at interrupting transmission and therefore, implementation of other control strategies are required. Ideally, an efficient vaccine is what is needed for long term protection thereby eliminating the current efforts of repeated mass drug administration. However, the general consensus in the field is that the integration of a viable vaccine with MDA and other control measures offer the best chance of achieving the goal of schistosomiasis elimination. This review focuses on the present status of schistosomiasis vaccine candidates in different phases of human clinical trials and provide some insight into future vaccine discovery and design.

A concise and unexpected one-pot methodology for the synthesis of pyrazinone-fused pyridones

A post-Ugi/Michael/Retro-Michael reaction, aromatization and 5-exo-dig cyclization cascade reaction was developed and utilized for the synthesis of pyrazinone-fused pyridone derivatives under mild reaction conditions in one-pot.

Development and application of anthelminthic drugs in China

China was once a country plagued by parasitic diseases. At the beginning of the founding of the People's Republic of China, nearly 80% of the population suffered from parasitic diseases because of poverty and poor sanitary conditions. After nearly 70 years of development, China has made remarkable achievements in the prevention and control of parasitic diseases, and the prevalence of parasitic diseases has been greatly reduced. In addition to organizational leadership from the government and various preventive measures, drug treatment and drug research & development are important and irreplaceable links in prevention and control work. Since the 1950s, China has begun to introduce, produce and imitate antiparasitic drugs from abroad, such as santonin, benzimidazole, and praziquantel. Chinese scientists have also contributed to the optimization of production techniques, improvements in drug formulation, the application in the clinic and the mechanisms of actions of generic drugs. At the same time, China has independently developed tribendimidine (TrBD, a broad spectrum anthelminthic), and its anthelminthic spectrum has been comprehensively studied. It is active against almost 20 parasites, is especially superior to benzimidazoles against Necator americanus, and surpasses the effectiveness of praziquantel against Clonorchis sinensis. In the treatment of tapeworm disease, the traditional Chinese medicines pumpkin seeds and betel nuts have good curative effects for taeniasis. Chinese scientists have explored the action modes and clinical administration methods of pumpkin seeds and betel nuts, which is still the main clinical regimen for the disease. This paper reviews the history and progress of the study of anthelmintics in intestinal helminth infections since the founding of the People's Republic of China and aiming to support clinicians and drug researchers in China and other countries.

Investigation of pharmacokinetic interaction between ivermectin and praziquantel after oral administration in healthy dogs

The purpose of this study was to determine the pharmacokinetic interaction between ivermectin (0.4 mg/kg) and praziquantel (10 mg/kg) administered either alone or co-administered to dogs after oral treatment. Twelve healthy cross-bred dogs (weighing 18-21 kg, aged 1-3 years) were allocated randomly into two groups of six dogs (four females, two males) each. In first group, the tablet forms of praziquantel and ivermectin were administered using a crossover design with a 15-day washout period, respectively. Second group received tablet form of ivermectin plus praziquantel. The plasma concentrations of ivermectin and praziquantel were determined by high-performance liquid chromatography using a fluorescence and ultraviolet detector, respectively. The pharmacokinetic parameters of ivermectin following oral alone-administration were as follows: elimination half-life (t_1/2λz ) 110 ± 11.06 hr, area under the plasma concentration-time curve (AUC_0-∞ ) 7,805 ± 1,768 hr^. ng/ml, maximum concentration (C_max ) 137 ± 48.09 ng/ml, and time to reach C_max (T_max ) 14.0 ± 4.90 hr. The pharmacokinetic parameters of praziquantel following oral alone-administration were as follows: t_1/2λz 7.39 ± 3.86 hr, AUC_0-∞ 4,301 ± 1,253 hr^. ng/ml, C_max 897 ± 245 ng/ml, and T_max 5.33 ± 0.82 hr. The pharmacokinetics of ivermectin and praziquantel were not changed, except T_max of praziquantel in the combined group. In conclusion, the combined formulation of ivermectin and praziquantel can be preferred in the treatment and prevention of diseases caused by susceptible parasites in dogs because no pharmacokinetic interaction was determined between them.

The impact of cinnarizine and griseofulvin on juvenile and adult stages of Schistosoma mansoni

Schistosomiasis affects millions globally. There is no vaccine, and treatment depends entirely on praziquantel (PZQ). Field isolates exhibit reduced susceptibility to PZQ, and resistance has been experimentally induced, suggesting that reliance on a single treatment is particularly dangerous. The present study investigated the value of cinnarizine and griseofulvin against Schistosoma mansoni through their in vitro effects on adult worms and oviposition as well as in vivo evaluation in early and late infection, compared to PZQ, in a preliminary experimental model. In vitro, both cinnarizine and griseofulvin showed uncoupling, sluggish worm movement and complete absence of ova at 100 μg/ml. In early infection, cinnarizine showed a significant reduction in the number of porto-mesenteric couples compared to the griseofulvin and control groups, a finding similar to PZQ. Remarkably, cinnarizine significantly exceeded PZQ and griseofulvin in reducing the total worm burden. In late infection, cinnarizine and griseofulvin showed results similar to PZQ by significantly reducing the numbers of hepatic and porto-mesenteric couples and total worm burden compared to controls. Cinnarizine performed better than griseofulvin by reducing hepatic and intestinal ovum counts, and it led to complete disappearance of the first two immature stages. The current work suggests the possibility of using cinnarizine and griseofulvin, mainly in late S. mansoni infection, especially cinnarizine, which showed similar results to PZQ and surpassed it in early infection. Further studies are required to elucidate their exact mechanisms of action and particularly their synergistic effect with PZQ.

TPT sulfonate, a single, oral dose schistosomicidal prodrug: In vivo efficacy, disposition and metabolic profiling

Treatment of schistosomiasis relies precariously on just one drug, praziquantel (PZQ). In the search for alternatives, 15 S-[2-(alkylamino)alkane] thiosulfuric acids were obtained from a previous research program and profiled in mice for efficacy against both mature (>42-day-old) and juvenile (21-day-old) Schistosoma mansoni using a screening dose of 100 mg/kg PO QDx4. One compound, S-[2-(tert-butylamino)-1-phenylethane] thiosulfuric acid (TPT sulfonate), was the most effective by decreasing female and male worm burdens by ≥ 90% and ≥46% (mature), and ≥89% and ≥79% (juvenile), respectively. In contrast, PZQ decreased mature female and male worm burdens by 95% and 94%, respectively, but was ineffective against juvenile stages. Against 7-day-old lung-stage worms, TPT sulfonate was only effective at twice the dose decreasing female and male burdens by 95 and 80%, respectively. Single oral doses at 400 and/or 600 mg/kg across various developmental time-points (1-, 7-, 15-, 21- and/or 42 day-old) were consistent with the QD x4 data; efficacy was strongest once the parasites had completed lung migration, and female and male burdens were decreased by at least 90% and 80%, respectively. In vitro, TPT sulfonate is inactive against the parasite suggesting a pro-drug mechanism of action. In mice, TPT sulfonate is fully absorbed and subject to rapid, non-CYP-mediated, first-pass metabolism that is initiated by desulfation and yields a series of metabolites. The initially-formed free thiol-containing metabolite, termed TP thiol, was chemically synthesized; it dose-dependently decreased S. mansoni and Schistosoma haematobium motility in vitro. Also, when administered as a single 50 mg/kg IP dose, TP thiol decreased 33-day-old S. mansoni female and male burdens by 35% and 44%, with less severe organomegaly. Overall, TPT sulfonate's efficacy profile is competitive with that of PZQ. Also, the characterization of a parasiticidal metabolite facilitates an understanding and improvement of the chemistry, and identification of the mechanism of action and/or target.

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TPT sulfonate provides single dose efficacy that is competitive with the current drug, praziquantel.

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TPT sulfonate must be biotransformed to be active.

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TPT sulfonate is fully absorbed and subject to rapid, non-CYP-mediated, first-pass metabolism.

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One of the key metabolites, TP thiol, is anti-schistosomal in vitro and in vivo.

Conformational polymorphic changes in the crystal structure of the chiral antiparasitic drug praziquantel and interactions with calcium carbonate

Praziquantel is an antiparasitic drug used for decades. Currently, the praziquantel commercial preparation is a racemic mixture, in which only the levo-enantiomer possesses anthelmintic activity. The knowledge of its properties in the solid state and other chemical-physical properties is necessary for improving its efficacy and applications. Drug solid dispersions were prepared with calcium carbonate at 1:5 drug to excipient weight ratio by solvent evaporation method. Then, the modification of the crystal structure of the racemic polymorph of praziquantel in presence of calcium carbonate has been studied by means of several analytical techniques (DSC, TGA, XRD, SEM, FTIR, Raman spectroscopy and chiral liquid chromatography). This study has been completed with atomistic calculations based on empirical interatomic force fields and quantum mechanics methods applied to the crystal structure of praziquantel and of intermolecular interactions. The results evidenced that calcium carbonate provoked a conformational change in the praziquantel molecule yielding the formation of different polymorphs of praziquantel crystal. These alterations were not observed replacing calcium carbonate with colloidal silica as excipient in the solid dispersion.

Pharmacological and immunological effects of praziquantel against Schistosoma japonicum: a scoping review of experimental studies

BACKGROUND

Chemotherapy for schistosomiasis has been around for 100 years. During the past century, great efforts have been made to develop new antischistosomal drugs from antimonials to nonantimonials, and some of these have been used extensively in clinical treatment. With the exception of a few drugs, such as oxamniquine and metrifonate, most of the antischistosomals developed in the pre-praziquantel period have variable limitations with respect to safety and efficacy. Although oxamniquine and metrifonate have been used for schistosomiasis control, they are only effective against Schistosoma mansoni and S. haematobium, respectively. Currently, praziquantel is the only drug used for treatment of all five species of human schistosomes. In this review, the pharmacological and immunological effects of praziquantel against S. japonicum are summarized and discussed.

MAIN TEXT

From the end of the 1970s until the 2000s, scientists have conducted a series of experimental studies on the effects of praziquantel against S. japonicum. These have included examining its unique pharmacological action on schistosomes, the characteristics in susceptibility of the different developmental stages of schistosomes to the drug, the relationship between plasma concentration of the drug and efficacy, the impact of host factors on cidal action of the drug, prevention and early treatment of schistosomal infection, as well as praziquantel-resistant schistosomiasis.

CONCLUSION

The effects of praziquantel against S. japonicum, as elucidated by the experimental studies that are reviewed in this paper, may have some reference significance for the development of new antischistosomals.

Drug Repurposing for Schistosomiasis: Combinations of Drugs or Biomolecules

Schistosomiasis is a major neglected tropical disease. Control of schistosomiasis currently relies on a single drug, praziquantel, and despite its efficacy against the all schistosome species that parasitize humans, it displays some problematic drawbacks and alone is ineffective in counteracting adverse pathologies associated with infection. Moreover, due to the development of the potential emergence of PZQ-resistant strains, the search for additional or alternative antischistosomal drugs have become a public health priority. The current drug discovery for schistosomiasis has been slow and uninspiring. By contrast, repurposing of existing approved drugs may offer a safe, rapid and cost-effective alternative. Combined treatment with PZQ and other drugs with different mode of action, i.e., antimalarials, shows promise results. In addition, a combination of anthelminthic drugs with antioxidant might be advantageous for modulating oxidative processes associated with schistosomiasis. Herein, we review studies dealing with combination therapies that involve PZQ and other anthelminthic drugs and/or antioxidant agents in treatment of schistosomiasis. Whereas PZQ combined with antioxidant agents might or might not interfere with anthelminthic efficacy, combinations may nonetheless ameliorate tissue damage and infection-associated complications. In fact, alone or combine with other drugs, antioxidants might be a valuable adjuvant to reduce morbidity and mortality of schistosomiasis. Therefore, attempting new combinations of anthelmintic drugs with other biomolecules such as antioxidants provides new avenues for discovery of alternatives to PZQ.

Nanotechnology as a potential therapeutic alternative for schistosomiasis

Schistosomiasis is a neglected disease that affects millions of people worldwide, recognized as the most important human helminth infection in terms of morbidity and mortality. The treatment of choice presents low bioavailability and water solubility, in addition to the induction of parasite resistance. In this context, researchers have been conducting studies seeking to develop new drugs to ensure safety, quality, and efficacy against this parasitosis. In this scenario, nanotechnology arises including the drug delivery systems in nanoscale: nanoemulsions, liposomes and nanoparticles. These drug delivery systems have been extensively applied for in vitro and in vivo studies against Schistosoma spp. with promising results. This review pointed out the most relevant development scenarios regarding the treatment of schistosomiasis as well as the application of nanotechnology as a vaccine, highlighting the use of nanotechnology as an alternative therapy for both the repositioning of drugs and the use of new pharmaceutical products, with promising results regarding the aforementioned disease.

Treatment of Schistosoma mansoni with miltefosine in vitro enhances serological recognition of defined worm surface antigens

Background

Miltefosine, an anti-cancer drug that has been successfully repositioned for treatment of Leishmania infections, has recently also shown promising effects against Schistosoma spp targeting all life cycle stages of the parasite. The current study examined the effect of treating Schistosoma mansoni adult worms with miltefosine on exposure of worm surface antigens in vitro.

Methodology/Principal findings

In an indirect immunofluorescence assay, rabbit anti-S.mansoni adult worm homogenate and anti-S. mansoni infection antisera gave strong immunofluorescence of the S. mansoni adult worm surface after treatment with miltefosine, the latter antiserum having previously been shown to synergistically enhance the schistosomicidal activity of praziquantel. Rabbit antibodies that recognised surface antigens exposed on miltefosine-treated worms were recovered by elution off the worm surface in low pH buffer and were used in a western immunoblotting assay to identify antigenic targets in a homogenate extract of adult worms (SmWH). Four proteins reacting with the antibodies in immunoblots were purified and proteomic analysis (MS/MS) combined with specific immunoblotting indicated they were the S. mansoni proteins: fructose-1,6 bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. These antibodies were also found to bind to the surface of 3-hour schistosomula and induce immune agglutination of the parasites, suggesting they may have a role in immune protection.

Conclusion/Significance

This study reveals a novel mode of action of miltefosine as an anti-schistosome agent. The immune-dependent hypothesis we investigated has previously been lent credence with praziquantel (PZQ), whereby treatment unmasks parasite surface antigens not normally exposed to the host during infection. Antigens involved in this molecular mechanism could have potential as intervention targets and antibodies against these antigens may act to increase the drug’s anti-parasite efficacy and be involved in the development of resistance to re-infection.

Schistosomiasis (Bilharzia) is a serious public health problem caused by a parasite of genus Schistosoma. There is an increasing concern about development of parasite resistance to the only drug available for treatment, praziquantel (PZQ). Miltefosine, a repurposed anti-cancer drug for treatment of Leishmania infection, was shown to have activity against Schistosoma in animal models at all the parasite’s life cycle stages. In this work, we examined the potential that miltefosine could act to expose parasite surface antigens that are normally hidden during natural infection as a way to avoid lethal effects of host immunity. We used two immunobinding techniques, immunofluorescence and western immunoblotting, and a protein identification technique, namely mass spectrometry, to identify proteins exposed on the worm surface following incubation with miltefosine. Four S. mansoni proteins were shown to be exposed by miltefosine treatment: fructose-bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. Antibodies specific for these antigens recognised and bound to the surface of early-stage schistosome larvae and antibodies specific for SmFBPA induced clumping of the larvae, suggesting a potential role in early parasite killing and protection against infection. These antibodies may be utilised to increase miltefosine’s anti-parasite efficacy and may be involved in resistance to re-infection.

Praziquantel for Schistosomiasis: Single-Drug Metabolism Revisited, Mode of Action, and Resistance

Schistosomiasis, a major neglected tropical disease, affects more than 250 million people worldwide. Treatment of schistosomiasis has relied on the anthelmintic drug praziquantel (PZQ) for more than a generation. PZQ is the drug of choice for the treatment of schistosomiasis; it is effective against all major forms of schistosomiasis, although it is less active against juvenile than mature parasites. A pyrazino-isoquinoline derivative, PZQ is not considered to be toxic and generally causes few or transient, mild side effects. Increasingly, mass drug administration targeting populations in sub-Saharan Africa where schistosomiasis is endemic has led to the appearance of reduced efficacy of PZQ, which portends the selection of drug-resistant forms of these pathogens. The synthesis of improved derivatives of PZQ is attracting attention, e.g., in the (i) synthesis of drug analogues, (ii) rational design of pharmacophores, and (iii) discovery of new compounds from large-scale screening programs. This article reviews reports from the 1970s to the present on the metabolism and mechanism of action of PZQ and its derivatives against schistosomes.

Molecular modeling and infrared and Raman spectroscopy of the crystal structure of the chiral antiparasitic drug Praziquantel

Anthelmintic praziquantel (PZQ) and its molecular and crystal lattice structures were studied by means of atomistic calculations based on empirical interatomic potentials and quantum mechanical methods (DFT). This chiral drug presents several crystal polymorphs due to the enantiomers (either R or S) or the racemic crystal, and different molecular conformations. The relative configurations of the carbonyl groups in PZQ define these conformations that produce different polymorphs. The polarity of these conformers is quite different and their relative population can vary in media with different polarity. Crystal structures of PZQ were studied by infrared and Raman spectroscopy and their spectroscopical properties were calculated by quantum mechanical methods, assigning many of their bands, and finding a good agreement with experimental data.

Senna leaf extracts induced Ca(+2) homeostasis in a zoonotic tapeworm Hymenolepis diminuta

Context Plants and plant products have been used in traditional medicine as anthelmintic agents in human and veterinary medicine. Three species of Senna plant, S. alata (L), S. alexandrina (M) and S. occidentalis (L.) Link (Fabaceae) have been shown to have a vermicidal/vermifugal effect on a zoonotic tapeworm Hymenolepis diminuta (Rudolphi) (Cyclophyllidean). Objective The present study validates the mode of action of these Senna plants on the parasite. The alcoholic leaf extract was determined to obtain information on the intracellular free calcium concentration level. Materials and methods Hymenolepis diminuta was maintained in Sprague-Dawley rat model for 2 months. Live parasites collected from infected rat intestine were exposed to 40 mg/mL concentration of each plant extracts prepared in phosphate buffer saline at 37 °C, till parasite gets paralyzed. The rate of efflux of calcium from the parasite tissue to the medium and the level of intracellular Ca(2+ )concentration were determined by an atomic absorption spectroscopy. Results This study revealed that exposure of the worms to the plant extract leads to disruption in intracellular calcium homeostasis. A significant increase (44.6% and 25%) of efflux in Ca(2+ )from the tissue to the incubated medium was observed. Senna alata showed high rate of efflux (5.32 mg/g) followed by S. alexandria and S. occidentalis (both 4.6 mg/g) compared with control (3.68 mg/g). Discussion and conclusion These results suggest that leaf extracts caused membrane permeability to Ca(2+ )after vacuolization of the tegument under stress and the extracts may contain compound that can be used as a chemotherapeutic agent.

An artemisinin derivative of praziquantel as an orally active antischistosomal agent

Background

Schistosomiasis is a major health problem in tropical and sub-tropical areas caused by species of trematode belonging to the genus Schistosoma. The treatment and control of this disease has been relying on the use of a single drug praziquantel. However, the drug resistance concern urged the development of new drugs against schistosoma. Here, we report our systematic biological evaluation of DW-3-15, a new lead compound developed based on our conjugation design rationale as an effective anti-schistosomal agent.

Methodology/Principal Findings

The antischistosomal activity of DW-3-15 was systematically evaluated in S. japonicum infected mouse model for its stage-sensitivity and dose response. The results revealed that DW-3-15 exhibited 60–85% worm reduction rate against different development stage of worm. Scanning electron microscopy (SEM) observation indicated that DW-3-15 may damage to the tegument of male schistosomes.

Conclusions/Significance

Our results demonstrated that DW-3-15 showed potent anti-schistosomal activities in vivo. The results strongly support our conjugation design strategy of artemisinin analogs and further development of DW-3-15 as a new lead compound as anti-schistosomal agent.

Tetrasubstituted pyrazinones derived from the reaction of praziquantel with N-bromosuccinimide

When praziquantel was exposed to N-bromosuccinimide in the presence of ethanol, a tricyclic 3-bromo-1-ethoxy pyrazinone was formed. From this and the analogous 1,3-dibromopyrazinone, a small library of 3-alkylamino-1-ethoxy, 1,3-dialkoxy, 3-alkoxy-1-bromo, and 3-alkylamino-1-bromo substituted pyrazinones were synthesized in high yields.

Metabolic profiling of praziquantel enantiomers

Praziquantel (PZQ), prescribed as a racemic mixture, is the most readily available drug to treat schistosomiasis. In the present study, ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOFMS) based metabolomics was employed to decipher the metabolic pathways and enantioselective metabolic differences of PZQ. Many phase I and four new phase II metabolites were found in urine and feces samples of mice 24h after dosing, indicating that the major metabolic reactions encompassed oxidation, dehydrogenation, and glucuronidation. Differences in the formation of all these metabolites were observed between (R)-PZQ and (S)-PZQ. In an in vitro phase I incubation system, the major involvement of CYP3A, CYP2C9, and CYP2C19 in the metabolism of PZQ, and CYP3A, CYP2C9, and CYP2C19 exhibited different catalytic activity toward the PZQ enantiomers. Apparent Km and Vmax differences were observed in the catalytic formation of three mono-oxidized metabolites by CYP2C9 and CYP3A4 further supporting the metabolic differences for PZQ enantiomers. Molecular docking showed that chirality resulted in differences in substrate location and conformation, which likely accounts for the metabolic differences. In conclusion, in silico, in vitro, and in vivo methods revealed the enantioselective metabolic profile of praziquantel.

Design and synthesis of molecular probes for the determination of the target of the anthelmintic drug praziquantel

Schistosomiasis is a highly prevalent neglected tropical disease caused by blood-dwelling helminths of the genus Schistosoma. Praziquantel (PZQ) is the only drug available widely for the treatment of this disease and is administered in racemic form, even though only the (R)-isomer has significant anthelmintic activity. Progress towards the development of a second generation of anthelmintics is hampered by a lack of understanding of the mechanism of action of PZQ. In this Letter, we report an efficient protocol for the small-scale separation of enantiomers of 2 (hydrolyzed PZQ) using supercritical fluid chromatography (SFC). The enantiopure 2 was then used to develop several molecular probes, which can potentially be used to help identify the protein target of PZQ and study its mode of action.

Chemical and genetic validation of the statin drug target to treat the helminth disease, schistosomiasis

The mevalonate pathway is essential in eukaryotes and responsible for a diversity of fundamental synthetic activities. 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) is the rate-limiting enzyme in the pathway and is targeted by the ubiquitous statin drugs to treat hypercholesterolemia. Independent reports have indicated the cidal effects of statins against the flatworm parasite, S. mansoni, and the possibility that SmHMGR is a useful drug target to develop new statin-based anti-schistosome therapies. For six commercially available statins, we demonstrate concentration- and time-dependent killing of immature (somule) and adult S. mansoni in vitro at sub-micromolar and micromolar concentrations, respectively. Cidal activity trends with statin lipophilicity whereby simvastatin and pravastatin are the most and least active, respectively. Worm death is preventable by excess mevalonate, the product of HMGR. Statin activity against somules was quantified both manually and automatically using a new, machine learning-based automated algorithm with congruent results. In addition, to chemical targeting, RNA interference (RNAi) of HMGR also kills somules in vitro and, again, lethality is blocked by excess mevalonate. Further, RNAi of HMGR of somules in vitro subsequently limits parasite survival in a mouse model of infection by up to 80%. Parasite death, either via statins or specific RNAi of HMGR, is associated with activation of apoptotic caspase activity. Together, our genetic and chemical data confirm that S. mansoni HMGR is an essential gene and the relevant target of statin drugs. We discuss our findings in context of a potential drug development program and the desired product profile for a new schistosomiasis drug.

Praziquantel treatment decreases Schistosoma mansoni genetic diversity in experimental infections

BACKGROUND

Schistosomiasis has a considerable impact on public health in many tropical and subtropical areas. In the new world, schistosomiasis is caused by the digenetic trematode Schistosoma mansoni. Chemotherapy is the main measure for controlling schistosomiasis, and the current drug of choice for treatment is praziquantel (PZQ). Although PZQ is efficient and safe, its repetitive large-scale use in endemic areas may lead to the selection of resistant strains. Isolates less susceptible to PZQ have been found in the field and selected for in the laboratory. The impact of selecting strains with a decreased susceptibility phenotype on disease dynamics and parasite population genetics is not fully understood. This study addresses the impact of PZQ pressure on the genetics of a laboratory population by analyzing frequency variations of polymorphic genetic markers.

METHODOLOGY

Infected mice were treated with increasing PZQ doses until the highest dose of 3 × 300 mg/Kg was reached. The effect of PZQ treatment on the parasite population was assessed using five polymorphic microsatellite markers. Parasitological and genetic data were compared with those of the untreated control. After six parasite generations submitted to treatment, it was possible to obtain a S. mansoni population with decreased susceptibility to PZQ. In our experiments we also observed that female worms were more susceptible to PZQ than male worms.

CONCLUSIONS

The selective pressure exerted by PZQ led to decreased genetic variability in S. mansoni and increased endogamy. The understanding of how S. mansoni populations respond to successive drug pressure has important implications on the appearance and maintenance of a PZQ resistance phenotype in endemic regions.

Molecular characterization of voltage-gated calcium channel β-subunits of Clonorchis sinensis

The voltage-gated Ca(2+) channel β-subunit is a member of the membrane-associated guanylate kinase family and modulates kinetic properties of the Ca(2+) channels, such as their voltage-dependent activation and inactivation rates. Two cDNA clones were identified to encode each β-subunit isotype of the voltage-gated Ca(2+) channel of Clonorchis sinensis, CsCavβ1 and CsCavβ2, which consist of 606 and 887 amino acids, respectively. CsCavβ1 was found to be similar to the β-subunit containing two conserved serine residues that constitute the consensus protein kinase C phosphorylation site in the β-interaction domain (BID). CsCavβ2 had cysteine and alanine residues instead of the two serine residues conserved in BID and was homologous to variant β-subunit of Schistosoma mansoni and Schistosoma japonicum. CsCavβ1 and CsCavβ2 were almost equally expressed in the adults and metacercariae, but were more expressed in adult C. sinensis than in metacercariae. Collectively, our findings suggest that substitution of the two serine residues in BID of CsCavβ2 may render C. sinensis sensitive to praziquantel.