Nature-Inspired Gallinamides Are Potent Antischistosomal Agents: Inhibition of the Cathepsin B1 Protease Target and Binding Mode Analysis.

Schistosomiasis, caused by a parasitic blood fluke of the genus Schistosoma, is a global health problem for which new chemotherapeutic options are needed. We explored the scaffold of gallinamide A, a natural peptidic metabolite of marine cyanobacteria that has previously been shown to inhibit cathepsin L-type proteases. We screened a library of 19 synthetic gallinamide A analogs and identified nanomolar inhibitors of the cathepsin B-type protease SmCB1, which is a drug target for the treatment of schistosomiasis mansoni. Against cultured S. mansoni schistosomula and adult worms, many of the gallinamides generated a range of deleterious phenotypic responses. Imaging with a fluorescent-activity-based probe derived from gallinamide A demonstrated that SmCB1 is the primary target for gallinamides in the parasite. Furthermore, we solved the high-resolution crystal structures of SmCB1 in complex with gallinamide A and its two analogs and describe the acrylamide covalent warhead and binding mode in the active site. Quantum chemical calculations evaluated the contribution of individual positions in the peptidomimetic scaffold to the inhibition of the target and demonstrated the importance of the P1' and P2 positions. Our study introduces gallinamides as a powerful chemotype that can be exploited for the development of novel antischistosomal chemotherapeutics.

In Silico Comparison of Bioactive Compounds Characterized from Azadirachta indica with an FDA-Approved Drug against Schistosomal Agents: New Insight into Schistosomiasis Treatment.

The burden of human schistosomiasis, a known but neglected tropical disease in Sub-Saharan Africa, has been worrisome in recent years. It is becoming increasingly difficult to tackle schistosomiasis with praziquantel, a drug known to be effective against all Schistosoma species, due to reports of reduced efficacy and resistance. Therefore, this study seeks to investigate the antischistosomal potential of phytochemicals from Azadirachta indica against proteins that have been implicated as druggable targets for the treatment of schistosomiasis using computational techniques. In this study, sixty-three (63) previously isolated and characterized phytochemicals from A. indica were identified from the literature and retrieved from the PubChem database. In silico screening was conducted to assess the inhibitory potential of these phytochemicals against three receptors (Schistosoma mansoni Thioredoxin glutathione reductase, dihydroorotate dehydrogenase, and Arginase) that may serve as therapeutic targets for schistosomiasis treatment. Molecular docking, ADMET prediction, ligand interaction, MMGBSA, and molecular dynamics simulation of the hit compounds were conducted using the Schrodinger molecular drug discovery suite. The results show that Andrographolide possesses a satisfactory pharmacokinetic profile, does not violate the Lipinski rule of five, binds with favourable affinity with the receptors, and interacts with key amino acids at the active site. Importantly, its interaction with dihydroorotate dehydrogenase, an enzyme responsible for the catalysis of the de novo pyrimidine nucleotide biosynthetic pathway rate-limiting step, shows a glide score and MMGBSA of -10.19 and -45.75 Kcal/mol, respectively. In addition, the MD simulation shows its stability at the active site of the receptor. Overall, this study revealed that Andrographolide from Azadirachta indica could serve as a potential lead compound for the development of an anti-schistosomal drug.

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.

In vitro and in vivo evaluation of cnicin from blessed thistle (Centaurea benedicta) and its inclusion complexes with cyclodextrins against Schistosoma mansoni.

Schistosomiasis, caused by a blood fluke of the genus Schistosoma, afflicts over 230 million people worldwide. Treatment of the disease relies on just one drug, praziquantel. Cnicin (Cn) is the sesquiterpene lactone found in blessed thistle (Centaurea benedicta) that showed antiparasitic activities but has not been evaluated against Schistosoma. However, cnicin has poor water solubility, which may limit its antiparasitic activities. To overcome these restrictions, inclusion complexes with cyclodextrins may be used. In this work, we evaluated the in vitro and in vivo antischistosomal activities of cnicin and its complexes with ß-cyclodextrin (ßCD) and 2-hydroxypropyl-ß-cyclodextrin (HPßCD) against Schistosoma mansoni. Cnicin were isolated from C. benedicta by chromatographic fractionation. Complexes formed by cnicin and ßCD (Cn/ßCD), as well as by cnicin and HPßCD (Cn/HPßCD), were prepared by coprecipitation and characterized. In vitro schistosomicidal assays were used to evaluate the effects of cnicin and its complexes on adult schistosomes, while the in vivo antischistosomal assays were evaluated by oral and intraperitoneal routes. Results showed that cnicin caused mortality and tegumental alterations in adult schistosomes in vitro, also showing in vivo efficacy after intraperitoneal administration. The oral treatment with cnicin or Cn/ßCD showed no significant worm reductions in a mouse model of schistosomiasis. In contrast, Cn/HPßCD complex, when orally or intraperitoneally administered to S. mansoni-infected mice, decreased the total worm load, and markedly reduced the number of eggs, showing high in vivo antischistosomal effectiveness. Permeability studies, using Nile red, indicated that HPßCD complex may reach the tegument of adult schistosomes in vivo. These results demonstrated the antischistosomal potential of cnicin in preparations with HPßCD.

In vivo studies of the effect of PPQ-6, a quinoline-based agent against Schistosoma mansoni in mice.

Schistosomiasis is still a public health problem. Praziquantel is the only drug available for treatment of all forms of human schistosomiasis. Although praziquantel is an effective drug against all species of human schistosomes, concerns about resistance have been raised, especially in endemic areas. A hybrid compound containing several pharmacophore within a single molecule is a promising strategy. Here, we described the anti-schistosomal effect of 4-(2-Chloroquinolin-3-yl)-2-oxo-6-(p-tolyl)-1,2-dihydropyridine-3-carbonitrile (PPQ-6), a hybrid drug based on quinoline and pyridine. PPQ-6 was given as two regimens (20 or 40 mg/kg). In both regimens, PPQ-6 significantly reduced liver and spleen indices, nitric oxide production, tissue egg load, hepatic granuloma size and count, immature eggs and total worm burden especially females. Our findings suggested that PPQ-6 is a promising anti-schistosomal agent; however more research is needed to elucidate its mechanism of action and report its activity on juvenile schistosomes and other species of human schistosomes.

In vitro and in vivo activities of DW-3-15, a commercial praziquantel derivative, against Schistosoma japonicum.

BACKGROUND: Schistosomiasis is a debilitating neglected tropical disease that affects approximately 190 million people around the world. Praziquantel (PZQ) is the only drug available for use against all Schistosoma species. Although PZQ has a high efficacy, recognized concerns have prompted the development of new, alternative drugs for repeated use in endemic areas where PZQ efficacy against strains of Schistosoma is reduced. A hybrid drug containing different pharmacophores within a single molecule is a promising strategy. Our earlier in vivo studies showed the significant antiparasitic activity of a praziquantel derivative, DW-3-15, against Schistosoma japonicum. In the present study, DW-3-15 was synthesized in large amounts by a pharmaceutical company and its schistosomicidal efficacy and stability were further confirmed. Parameters such as parasite viability, pairing and oviposition were evaluated in vitro. An in vivo study was conducted to assess the effect of commercial DW-3-15 on worm burden, egg production and diameter of granulomas. Additionally, to gain insight into the mechanism of action for DW-3-15, morphological changes in the tegument of S. japonicum were also examined. RESULTS: The in vitro study showed the antiparasitic activity of DW-3-15 against S. japonicum, with significant reductions in viability of adult and juvenile worms, worm pairings and egg output. Compared to PZQ, DW-3-15 induced similar ultrastructural changes and evident destruction of the tegument surface in male worms. In vivo, the oral administration of DW-3-15 at a dose of 400 mg/kg per day for five consecutive days in mice significantly reduced the total worm burden and number of eggs in the liver. Histological analysis of the livers showed a marked reduction in the average diameter of the egg granuloma. CONCLUSIONS: Our findings suggest that DW-3-15, a PZQ derivative with the prospect of commercial production, can be developed as a potential promising schistosomicide.

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.

Niosomes for enhanced activity of praziquantel against Schistosoma mansoni: in vivo and in vitro evaluation.

Praziquantel (PZQ) is recommended by the WHO as the first line in treatment of schistosomiasis. Unfortunately, it exhibits low oral bioavailability which can compromise its efficacy. Nanostructures showed promising potential to overcome this problem. Accordingly, the aim of this study was to investigate the effect of niosomal encapsulation of PZQ on its activity on Schistosoma mansoni in vitro and in vivo. PZQ was encapsulated in niosomal formulation comprising span 60, cholesterol with peceol being included as absorption enhancer. The in vitro work determined the schistosomicidal activity and morphological changes after incubation with drug solution or PZQ-niosomes. The in vivo study utilized infected mice which received PZQ orally as solution or as niosomes. The activity was assessed by monitoring egg and worm count in addition to histopathological and immunohistochemical studies. The in vitro studies revealed that niosomes alone caused a 30% death of adult parasites and caused completely coiled body, destruction, and peeling of tubercles and spines, with flattening and effacement of gynecophoric canal, blebbing with niosomes vesicles attached to it. Niosomes containing PZQ at a concentration of 0.001 µg/ml increased the death from 30 to 50% with the corresponding PZQ solution causing only 10% death. The in vivo study reflected of niosome-PZQ over PZQ solution as indicated from significant reduction of adult worm count, hepatic and intestinal egg depositions, hepatic granuloma size, and numbers, with marked reduction of vascular endothelial growth factor expression. The study introduced niosomes as promising carriers for enhanced activity of PZQ.

Antischistosomal Properties of Hederacolchiside A1 Isolated from Pulsatilla chinensis.

Background: Schistosomiasis is a major neglected disease for which the current control strategy involves mass treatment with praziquantel, the only available drug. Hence, there is an urgent need to develop new antischistosomal compounds. Methods: The antischistosomal activity of hederacolchiside A1 (HSA) were determined by total or female worm burden reductions in mice harboring Schistosoma japonicum or S. mansoni. Pathology parameters were detected on HSA against 1-day-old S. japonicum-harboring mice. Moreover, we confirmed the antischistosomal effect of HSA on newly transformed schistosomula (NTS) of S. japonicum in vitro. Results: HSA, a natural product isolated from Pulsatilla chinensis (Bunge) Regel, was initially corroborated to possess promising antischistosomal properties. We demonstrated that HSA had high activity against S. japonicum and S. mansoni less in 11 days old parasites harbored in mice. The antischistosomal effect was even more than the currently used drugs, praziquantel, and artesunate. Furthermore, HSA could ameliorate the pathology parameters in mice harboring 1-day-old juvenile S. japonicum. We also confirmed that HSA-mediated antischistosomal activity is partly due to the morphological changes in the tegument system when NTS are exposed to HSA. Conclusions: HSA may have great potential to be an antischistosomal agent for further research.

Chemical Composition, Antibacterial, Schistosomicidal, and Cytotoxic Activities of the Essential Oil of Dysphania ambrosioides (L.) Mosyakin & Clemants (Chenopodiaceae).

We have investigated the chemical composition and the antibacterial activity of the essential oil of Dysphania ambrosioides (L.) Mosyakin & Clemants (Chenopodiaceae) (DA-EO) against a representative panel of cariogenic bacteria. We have also assessed the in vitro schistosomicidal effects of DA-EO on Schistosoma mansoni and its cytotoxicity to GM07492-A cells in vitro. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS) revealed that the monoterpenes cis-piperitone oxide (35.2%), p-cymene (14.5%), isoascaridole (14.1%), and α-terpinene (11.6%) were identified by as the major constituents of DA-EO. DA-EO displayed weak activity against Streptococcus sobrinus and Enterococcus faecalis (minimum inhibitory concentration (MIC) = 1000 µg/ml). On the other hand, DA-EO at 25 and 12.5 µg/ml presented remarkable schistosomicidal action in vitro and killed 100% of adult worm pairs within 24 and 72 h, respectively. The LC50 values of DA-EO were 6.50 ± 0.38, 3.66 ± 1.06, and 3.65 ± 0.76 µg/ml at 24, 48, and 72 h, respectively. However, DA-EO at concentrations higher than 312.5 µg/ml significantly reduced the viability of GM07492-A cells (IC50  = 207.1 ± 4.4 µg/ml). The selectivity index showed that DA-EO was 31.8 times more toxic to the adult S. mansoni worms than GM07492-A cells. Taken together, these results demonstrate the promising schistosomicidal potential of the essential oil of Dysphania ambrosioides.

Antischistosomal activity of hederacochiside C against Schistosoma japonicum harbored in experimentally infected animals.

The present study was undertaken to investigate whether hederacochiside C (HSC) possesses antischistosomal effects and anti-inflammatory response activities in Schistosoma japonicum-infected mice. Different concentrations of HSC were administrated to the mice infected by schistosomula or adult worm by intravenous injection twice a day for five consecutive days. The total worm burden, female worm burden, and the egg burden in liver of mice treated with 400 mg/kg HSC were fewer than those in non-treated ones. Murine immune responses following HSC treatment were investigated using enzyme-linked immunosorbent assays (ELISA). Our results indicated that 200 mg/kg HSC could reduce the expression of IgG, tumor necrosis factor (TNF)-α, interleukin (IL)-4 and IL-17 in comparison to infected group, exhibiting best immunomodulatory effects. In addition, scanning electron microscopical examination revealed that male worms treated with HSC lost their normal surface architecture since its surface showed extensive swelling, erosion, and peeling in tegumental regions. Remarkable amelioration was noticed in histopathological investigations, and 200 mg/kg HSC treatment could reduce the size of granulomatous inflammatory infiltrations in the liver which was reflected in nearly normalization of liver architecture. These results suggested that HSC had potential antischistosomal activity and provided a basis for subsequent experimental.

Revisiting the SAR of the Antischistosomal Aryl Hydantoin (Ro 13-3978).

The aryl hydantoin 1 (Ro 13-3978) was identified in the early 1980s as a promising antischistosomal lead compound. However, this series of aryl hydantoins produced antiandrogenic side effects in the host, a not unexpected outcome given their close structural similarity to the antiandrogenic drug nilutamide. Building on the known SAR of this compound series, we now describe a number of analogs of 1 designed to maximize structural diversity guided by incorporation of substructures and functional groups known to diminish ligand-androgen receptor interactions. These analogs had calculated polar surface area (PSA), measured LogD7.4, aqueous kinetic solubility, and estimated plasma protein binding values in ranges predictive of good ADME profiles. The principal SAR insight was that the hydantoin core of 1 is required for high antischistosomal activity. We identified several compounds with high antischistosomal efficacy that were less antiandrogenic than 1. These data provide direction for the ongoing optimization of antischistosomal hydantoins.

Copaifera duckei Oleoresin and Its Main Nonvolatile Terpenes: In Vitro Schistosomicidal Properties.

In this article, the in vitro schistosomicidal effects of three Brazilian Copaifera oleoresins (C. duckei, C. langsdorffii, and C. reticulata) are reported. From these botanical sources, the oleoresin of C. duckei (OCd) demonstrated to be the most promising, displaying LC50 values of 75.8, 50.6, and 47.2 µg/ml at 24, 48, and 72 h of incubation, respectively, against adult worms of Schistosoma mansoni, with a selectivity index of 10.26. Therefore, the major compounds from OCd were isolated, and the diterpene, (-)-polyalthic acid (PA), showed to be active (LC50 values of 41.7, 36.2, and 33.4 µg/ml, respectively, at 24, 48, and 72 h of incubation). Moreover, OCd and PA affected the production and development of eggs, and OCd modified the functionality of the tegument of S. mansoni. Possible synergistic and/or additive effects of this balsam were also verified when a mixture of the two of its main compounds (PA and ent-labd-8(17)-en-15,18-dioic acid) in the specific proportion of 3:1 (w/w) was tested. The obtained results indicate that PA should be considered for further investigations against S. mansoni, such as, synergistic (combination with praziquantel (PZQ)) and in vivo studies. It also shows that diterpenes are an important class of natural compounds for the investigation of agents capable of fighting the parasite responsible for human schistosomiasis.

Structure-Bioactivity Relationship for Benzimidazole Thiophene Inhibitors of Polo-Like Kinase 1 (PLK1), a Potential Drug Target in Schistosoma mansoni.

BACKGROUND: Schistosoma flatworm parasites cause schistosomiasis, a chronic and debilitating disease of poverty in developing countries. Praziquantel is employed for treatment and disease control. However, its efficacy spectrum is incomplete (less active or inactive against immature stages of the parasite) and there is a concern of drug resistance. Thus, there is a need to identify new drugs and drug targets. METHODOLOGY/PRINCIPAL FINDINGS: We show that RNA interference (RNAi) of the Schistosoma mansoni ortholog of human polo-like kinase (huPLK)1 elicits a deleterious phenotypic alteration in post-infective larvae (schistosomula or somules). Phenotypic screening and analysis of schistosomula and adult S. mansoni with small molecule inhibitors of huPLK1 identified a number of potent anti-schistosomals. Among these was a GlaxoSmithKline (GSK) benzimidazole thiophene inhibitor that has completed Phase I clinical trials for treatment of solid tumor malignancies. We then obtained GSKs Published Kinase Inhibitor Sets (PKIS) 1 and 2, and phenotypically screened an expanded series of 38 benzimidazole thiophene PLK1 inhibitors. Computational analysis of controls and PLK1 inhibitor-treated populations of somules demonstrated a distinctive phenotype distribution. Using principal component analysis (PCA), the phenotypes exhibited by these populations were mapped, visualized and analyzed through projection to a low-dimensional space. The phenotype distribution was found to have a distinct shape and topology, which could be elicited using cluster analysis. A structure-activity relationship (SAR) was identified for the benzimidazole thiophenes that held for both somules and adult parasites. The most potent inhibitors produced marked phenotypic alterations at 1-2 µM within 1 h. Among these were compounds previously characterized as potent inhibitors of huPLK1 in cell assays. CONCLUSIONS/SIGNIFICANCE: The reverse genetic and chemical SAR data support a continued investigation of SmPLK1 as a possible drug target and/or the prosecution of the benzimidazole thiophene chemotype as a source of novel anti-schistosomals.

Antischistosomal and Cytotoxic Effects of the Essential Oil of Tetradenia riparia (Lamiaceae).

This paper reports on the antischistosomal and cytotoxic effects of the essential oil obtained from Tetradenia riparia leaves (TR-EO). At concentrations of 50 and 100 µg/mL, TR-EO killed all the worms after 120 and 24 h of incubation, respectively. At a concentration equal to or higher than 50 µg/mL, this oil also separated the coupled pairs and decreased the adult worm motor activity after incubation periods higher than 72 h. In addition, at 120 h of incubation, TR-EO slightly decreased the number of eggs produced by Schistosoma mansoni adult worms and significantly reduced the percentage of developed eggs, in a dose-dependent manner. XTT-colorimetric assays showed that the tested TR-EO concentrations were not considerably cytotoxic to V79 cells (IC50 = 253.5 µg/mL). The effects of TR-EO on egg development were noteworthy; therefore, this essential oil deserves further investigation to identify the chemical constituents that elicit activity against S. mansoni.

Schistosomicidal activity and docking of Schistosoma mansoni ATPDase 1 with licoflavone B isolated from Glycyrrhiza inflata (Fabaceae).

Schistosomiasis is one of the world's major public health problems, and its treatment is widely dependent on praziquantel (PZQ), the only available drug. Schistosoma mansoni ATP diphosphohydrolases are ecto-enzymes localized on the external tegumental surface of S. mansoni and considered an important target for action of new drugs. In this work, the in vitro schistosomicidal activity of the crude extract of Glycyrrhiza inflata roots (GI) and its isolated compounds echinatin, licoflavone A and licoflavone B were evaluated against S. mansoni adult worms. Results showed that GI (200 µg/mL) was active against adult schistosomes, causing 100% mortality after 24 h of incubation. Chromatographic fractionation of GI led to isolation of echinatin, licoflavone A and licoflavone B. Licoflavone B (25-100 µM) caused 100% mortality, tegumental alterations, and reduction of oviposition and motor activity of all adult worms, without affecting mammalian Vero cells. Confocal laser scanning microscopy showed tegumental morphological alterations and changes on the numbers of tubercles of S. mansoni worms in a dose-dependent manner after incubation with licoflavone B. Licoflavone B also showed high S. mansoni ATPase (IC50 of 23.78 µM) and ADPase (IC50 of 31.50 µM) inhibitory activities. Docking studies predicted different interactions between licoflavone B and S. mansoni ATPDase 1, corroborating with the in vitro inhibitory activity. This report demonstrated the first evidence for the schistosomicidal activity of licoflavone B and suggests that its mechanism of action involve the inhibition of S. mansoni ATP diphosphohydrolases.

Synthesis and evaluation of 1,4-naphthoquinone ether derivatives as SmTGR inhibitors and new anti-schistosomal drugs.

Investigations regarding the chemistry and mechanism of action of 2-methyl-1,4-naphthoquinone (or menadione) derivatives revealed 3-phenoxymethyl menadiones as a novel anti-schistosomal chemical series. These newly synthesized compounds (1-7) and their difluoromethylmenadione counterparts (8, 9) were found to be potent and specific inhibitors of Schistosoma mansoni thioredoxin-glutathione reductase (SmTGR), which has been identified as a potential target for anti-schistosomal drugs. The compounds were also tested in enzymic assays using both human flavoenzymes, i.e. glutathione reductase (hGR) and selenium-dependent human thioredoxin reductase (hTrxR), to evaluate the specificity of the inhibition. Structure-activity relationships as well as physico- and electro-chemical studies showed a high potential for the 3-phenoxymethyl menadiones to inhibit SmTGR selectively compared to hGR and hTrxR enzymes, in particular those bearing an α-fluorophenol methyl ether moiety, which improves anti-schistosomal action. Furthermore, the (substituted phenoxy)methyl menadione derivative (7) displayed time-dependent SmTGR inactivation, correlating with unproductive NADPH-dependent redox cycling of SmTGR, and potent anti-schistosomal action in worms cultured ex vivo. In contrast, the difluoromethylmenadione analog 9, which inactivates SmTGR through an irreversible non-consuming NADPH-dependent process, has little killing effect in worms cultured ex vivo. Despite ex vivo activity, none of the compounds tested was active in vivo, suggesting that the limited bioavailability may compromise compound activity. Therefore, future studies will be directed toward improving pharmacokinetic properties and bioavailability.

Design, synthesis and biological evaluation of praziquantel and endoperoxide conjugates as antischistosomal agents.

BACKGROUND: The widespread use of praziquantel for the treatment of schistosomiasis has led to concerns over the potential development of drug resistance. Therefore, the discovery of novel antischistosomal agents is imperative. In this study, a series of praziquantel and endoperoxide conjugates were synthesized and evaluated as potential antischistosomal agents. RESULTS: Some compounds exhibited high efficacy against both adult and juvenile Schistosoma, in in vitro studies. Structure-activity relationship (SAR) analysis revealed that compounds with amide bond linker and cyclopentyl adjacent to the 1,2,4,5-tetraxane pharmacophore displayed the highest efficacy. Overall, compounds showed consistent activity against Schistosoma japonicum and Schistosoma mansoni. In vivo study resulted in moderate but statistically significant activity. CONCLUSION: Important preliminary results were obtained from thorough activity evaluation of praziquantel-endoperoxide conjugates. Further pharmacokinetic property investigation is necessary to improve in vivo efficacy.

Natural products with antischistosomal activity.

In recent years, natural product groups have been gaining prominence as possible sources of new drugs for schistosomiasis. This review attempts to update the antischistosomal natural compounds, or natural product-derived compounds, from the mid-1980s. Some of the main metabolites obtained from plants (e.g., terpenes, alkaloids, phenolic compounds and peptides) with in vitro and/or in vivo antischistosomal properties are discussed. Less thoroughly, due to scarcity of data in the literature, molecules from animals (e.g., peptides) are also described. Special mention of the anthelmintic activity against different parasitic stages of schistosomes is made; the mechanism of action of most of the metabolites is discussed, and a number of bioassay procedures are listed.

Toward organometallic antischistosomal drug candidates.

In the recent years, there has been a growing interest in the use of novel approaches for the treatment of parasitic diseases such as schistosomiasis. Among the different approaches used, organometallic compounds were found to offer unique opportunities in the design of antiparasitic drug candidates. A ferrocenyl derivative, namely ferroquine, has even entered clinical trials as a novel antimalarial. In this short review, we report on the studies describing the use of organometallic compounds against schistosomiasis.