Activity of OZ78 analogues against Fasciola hepatica and Echinostoma caproni

New benzimidazole derivative compounds with in vitro fasciolicidal properties

BACKGROUND

Control of the zoonotic food-borne parasite Fasciola hepatica remains a major challenge in humans and livestock. It is estimated that annual economic losses due to fasciolosis can reach US$3.2 billion in agriculture and livestock. Moreover, the wide distribution of drug-resistant parasite populations and the absence of a vaccine threaten sustainable control, reinforcing the need for novel flukicides.

METHODS

The present work analyses the flukicidal activity of a total of 70 benzimidazole derivatives on different stages of F. hepatica. With the aim to select the most potent ones, and screenings were first performed on eggs at decreasing concentrations ranging from 50 to 5 µM and then on adult worms at 10 µM. Only the most effective compounds were also evaluated using a resistant isolate of the parasite.

RESULTS

After the first screenings at 50 and 10 µM, four hit compounds (BZD31, BZD46, BZD56, and BZD59) were selected and progressed to the next assays. At 5 µM, all hit compounds showed ovicidal activities higher than 71% on the susceptible isolate, but only BZD31 remained considerably active (53%) when they were tested on an albendazol-resistant isolate, even with values superior to the reference drug, albendazole sulfoxide. On the other hand, BZD59 displayed a high motility inhibition when tested on adult worms from an albendazole-resistant isolate after 72 h of incubation.

CONCLUSIONS

BZD31 and BZD59 compounds could be promising candidates for the development of fasciolicidal compounds or as starting point for the new synthesis of structure-related compounds.

In Vitro Activities of Dithiocarbamate Derivatives against Echinococcus multilocularis Metacestode Vesicles

The metacestode stage of the fox tapeworm Echinococcus multilocularis causes the severe zoonotic disease alveolar echinococcosis. New treatment options are urgently needed. Disulfiram and dithiocarbamates were previously shown to exhibit activity against the trematode Schistosoma mansoni. As both parasites belong to the platyhelminths, here we investigated whether these compounds were also active against E. multilocularis metacestode vesicles in vitro. We used an in vitro drug-screening cascade for the identification of novel compounds against E. multilocularis metacestode vesicles with disulfiram and 51 dithiocarbamates. Five compounds showed activity against E. multilocularis metacestode vesicles after five days of drug incubation in a damage marker release assay. Structure-activity relationship analyses revealed that a S-2-hydroxy-5-nitro benzyl moiety was necessary for anti-echinococcal activity, as derivatives without this group had no effect on E. multilocularis metacestode vesicles. The five active compounds were further tested for potential cytotoxicity in mammalian cells. For two compounds with low toxicity (Schl-32.315 and Schl-33.652), IC50 values in metacestode vesicles and IC50 values in germinal layer cells were calculated. The compounds were not highly active on isolated GL cells with IC50 values of 27.0 ± 4.2 µM for Schl-32.315 and 24.7 ± 11.5 µM for Schl-33.652, respectively. Against metacestode vesicles, Schl-32.315 was not very active either with an IC50 value of 41.6 ± 3.2 µM, while Schl-33.652 showed a low IC50 of 4.3 ± 1 µM and should be further investigated in the future for its activity against alveolar echinococcosis.

Whole-organism phenotypic screening methods used in early-phase anthelmintic drug discovery

Diseases caused by parasitic helminths (worms) represent a major global health burden in both humans and animals. As vaccines against helminths have yet to achieve a prominent role in worm control, anthelmintics are the primary tool to limit production losses and disease due to helminth infections in both human and veterinary medicine. However, the excessive and often uncontrolled use of these drugs has led to widespread anthelmintic resistance in these worms - particularly of animals - to almost all commercially available anthelmintics, severely compromising control. Thus, there is a major demand for the discovery and development of new classes of anthelmintics. A key component of the discovery process is screening libraries of compounds for anthelmintic activity. Given the need for, and major interest by the pharmaceutical industry in, novel anthelmintics, we considered it both timely and appropriate to re-examine screening methods used for anthelmintic discovery. Thus, we reviewed current literature (1977-2021) on whole-worm phenotypic screening assays developed and used in academic laboratories, with a particular focus on those employed to discover nematocides. This review reveals that at least 50 distinct phenotypic assays with low-, medium- or high-throughput capacity were developed over this period, with more recently developed methods being quantitative, semi-automated and higher throughput. The main features assessed or measured in these assays include worm motility, growth/development, morphological changes, viability/lethality, pharyngeal pumping, egg hatching, larval migration, CO₂- or ATP-production and/or enzyme activity. Recent progress in assay development has led to the routine application of practical, cost-effective, medium- to high-throughput whole-worm screening assays in academic or public-private partnership (PPP) contexts, and major potential for novel high-content, high-throughput platforms in the near future. Complementing this progress are major advances in the molecular data sciences, computational biology and informatics, which are likely to further enable and accelerate anthelmintic drug discovery and development.

Drug resistance in liver flukes

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.

Drug discovery technologies: Caenorhabditis elegans as a model for anthelmintic therapeutics

Helminthiasis is one of the gravest problems worldwide. There is a growing concern on less available anthelmintics and the emergence of resistance creating a major threat to human and livestock health resources. Novel and broad-spectrum anthelmintics are urgently needed. The free-living nematode Caenorhabditis elegans could address this issue through automated high-throughput technologies for the screening of large chemical libraries. This review discusses the strong advantages and limitations for using C elegans as a screening method for anthelmintic drug discovery. C elegans is the best model available for the validation of novel effective drugs in treating most, if not all, helminth infections, and for the elucidation the mode of action of anthelmintic candidates. This review also focuses on available technologies in the discovery of anthelmintics published over the last 15 years with particular attention to high-throughput technologies over conventional screens. On the other hand, this review highlights how combinatorial and nanomedicine strategies could prolong the use of anthelmintics and control resistance problems.

Exogenous Iron Increases Fasciocidal Activity and Hepatocellular Toxicity of the Synthetic Endoperoxides OZ78 and MT04

The synthetic peroxides OZ78 and MT04 recently emerged as fasciocidal drug candidates. However, the effect of iron on fasciocidal activity and hepatocellular toxicity of these compounds is unknown. We investigated the in vitro fasciocidal activity and hepatocellular toxicity of OZ78 and MT04 in absence and presence of Fe(II)chloride and hemin, and conducted a toxicological study in mice. Studies were performed in comparison with the antimalarial artesunate (AS), a semisynthetic peroxide. Fasciocidal effects of OZ78 and MT04 were confirmed and enhanced by Fe²⁺ or hemin. In HepG2 cells, AS reduced cellular ATP and impaired membrane integrity concentration-dependently. In comparison, OZ78 or MT04 were not toxic at 100 µM and reduced the cellular ATP by 13% and 19%, respectively, but were not membrane-toxic at 500 µM. The addition of Fe²⁺ or hemin increased the toxicity of OZ78 and MT04 significantly. AS inhibited complex I, II, and IV of the mitochondrial electron transport chain, and MT04 impaired complex I and II, whereas OZ78 was not toxic. All three compounds increased cellular reactive oxygen species (ROS) concentration-dependently, with a further increase by Fe²⁺ or hemin. Mice treated orally with up to 800 mg OZ78, or MT04 showed no relevant hepatotoxicity. In conclusion, we confirmed fasciocidal activity of OZ78 and MT04, which was increased by Fe²⁺ or hemin. OZ78 and MT04 were toxic to HepG2 cells, which was explained by mitochondrial damage associated with ROS generation in the presence of iron. No relevant hepatotoxicity was observed in mice in vivo, possibly due to limited exposure and/or high antioxidative hepatic capacity.

Chemiluminescence in the reaction of 1,2,4,5-tetraoxanes with ferrous ions in the presence of xanthene dyes: fundamentals and perspectives of analytical applications

The reaction of biologically active bridged 1,2,4,5-tetraoxanes and diperoxide of trifluoroacetone with Fe²⁺ ions in the presence of xanthenes, methylene blue and methylene green is accompanied by bright chemiluminescence.

Ultrastructural changes to the tegumental system and gastrodermal cells of adult Fasciola hepatica following treatment in vivo with a commercial preparation of myrrh (Mirazid)

An in vivo study in the laboratory rat model has been carried out to monitor changes to the tegument and gut of adult Fasciola hepatica following treatment with myrrh ('Mirazid'). Rats infected with the triclabendazole-resistant Dutch isolate were dosed orally with Mirazid at a concentration of 250 mg/kg and flukes recovered 2, 3 and 7 days post-treatment (pt). The flukes were processed for examination by scanning and transmission electron microscopy. A variety of changes to the external surface were observed, culminating in the sloughing of the tegumental syncytium. Internal changes to the syncytium and tegumental cell bodies were more severe and were evident from 2 days pt onwards. Swelling of the basal infolds (leading to flooding of the surface layer) and a decline in secretory body production were the major changes seen. The gastrodermal cells were less severely affected than the tegument, pointing to a trans-tegumental route of uptake for Mirazid by the fluke. Some loss of muscle fibres in the main somatic muscle layers was observed, which may be correlated with the decline in movement of flukes seen at recovery.

In vitro ovicidal activity of Peganum harmala seeds extract on the eggs of Fasciola hepatica

Peganum harmala seeds extract has been previously reported to have antimicrobial and other medicinal properties. The aim of this study was to evaluate the ovicidal activity of the methanolic extract of P. harmala seeds against the eggs of F. hepatica. The phenolic compounds of the methanolic extract of P. harmala seeds were identified by HPLC analysis. Catechin, rutin, p-Coumaric acid, chloregenic acid and hesperetin were found to be the major phenolic compounds. F. hepatica eggs were collected from the gall bladder of naturally infected sheep. The eggs were exposed to two concentrations of P. harmala seeds extract (1 and 3 mg/mL) for 24 and 48 h. To investigate the effect of the P. harmala seeds extract on the miracidial formation, the treated eggs were incubated at 28 °C for 14 days. The results indicated that F. hepatica eggs were susceptible to the methanolic extract of P. harmala seeds. Following 24 h exposure of the eggs to P. harmala seeds extract with concentrations of 1 and 3 mg/mL, the miracidial formation reduced to 5 and 2.2 % respectively (compared with 60 % for the control group). Following 48 h of exposure of the eggs to P. harmala seeds extract with 1 mg/mL concentration, the miracidial formation reduced to 0.5 %. In this exposure time, no miracidial formation was observed in the eggs exposed to P. harmala seeds extract with concentration of 3 mg/mL. Therefore, the results of this study indicated that P. harmala seeds extract has high ovicidal activity against the eggs of F. hepatica. Accordingly, this extract may have the potential flukicidal activity against the immature and mature F. hepatica.

Disruption of spermatogenesis in the liver fluke, Fasciola hepatica by two artemisinin derivatives, artemether and artesunate

An in vivo study in the laboratory rat model has been carried out to monitor changes to the spermatogenic cells in the testis tubules of adult Fasciola hepatica following treatment with the artemisinins, artemether and artesunate. Rats infected with the triclabendazole (TCBZ)-resistant Sligo isolate were dosed orally with artemether at a concentration of 200 mg/kg and flukes recovered at 24, 48 and 72 h post treatment (pt). Rats infected with the TCBZ-resistant Oberon isolate were dosed orally with artesunate at a concentration of 200 mg/kg and flukes recovered 24, 48, 72 and 96 h pt. The flukes were processed for histological and transmission electron microscope (TEM) examination. Changes to the spermatogenic cells were evident at 24 h pt with artemether. The spermatogonial and spermatocyte cells contained abnormal mitochondria, there were fewer spermatids and spermatozoa in the tubules than normal, and a number of cells showed signs of apoptosis. There was a further decline in cell numbers at 48 h pt and the organization of the spermatocyte and spermatid rosettes was atypical. Sperm formation had become abnormal and those spermatozoa present possessed only a single axoneme. By 72 h pt, the testis tubules were vacuolated and filled with abnormal cells and cell debris. Only spermatogonial cells could be identified and there was widespread evidence of apoptosis in the cells. Distinct cellular changes following artesunate treatment did not become apparent until 48 h pt. The changes seen were similar to those described for artemether, but were generally less severe at matching time-periods. The fine structural changes occurring in the spermatogenic cells were compared to those observed in other cell types and fluke tissues and the overall information was collated to identify the cellular targets for artemisinin action and to establish the time-line for drug action.

A comparative study on the impact of two artemisinin derivatives, artemether and artesunate, on the female reproductive system of Fasciola hepatica

An in vivo study in the laboratory rat model has been carried out to monitor changes to the female reproductive system in adult Fasciola hepatica following treatment with the artemisinins, artemether and artesunate. Rats infected with the triclabendazole (TCBZ)-resistant Sligo isolate were dosed orally with artemether at a concentration of 200mg/kg and flukes recovered at 24, 48 and 72 h post-treatment (pt). Rats infected with the TCBZ-resistant Oberon isolate were dosed orally with artesunate at a concentration of 200mg/kg and flukes recovered 24, 48, 72 and 96 h pt. The flukes were processed for histological and transmission electron microscope (TEM) examination of the uterus, Mehlis' gland, ovary and vitellaria. After treatment with artemether, egg production had become abnormal by 72 h pt, with free vitelline cells and masses of shell protein material within the uterus; spermatozoa were absent. The Mehlis' gland and ovary retained a normal morphology over the 3-day period. A change in the cell population in the vitelline follicles was seen at 48 h pt, with a decline in the number of immature cells. This became more marked by 72 h and the follicles became progressively vacuolated over the 3-day period. At the TEM level, there were changes in the immature vitelline cells at 24h pt, as evidenced by a decrease in shell protein production and the presence of lipid droplets and abnormal mitochondria. Spaces in the follicles separated the cells from each other. The changes became progressively more severe with time, so that, by 72 h pt, the follicles were very disrupted, containing cells in the advanced stages of apoptotic breakdown. In extreme cases, the follicles were scarcely recognisable and had become filled with cellular debris. Fine structural changes to the vitelline cells induced by artesunate treatment were similar to those described for artemether, but generally occurred more quickly and were greater; this was particularly true of the swelling of the ger cisternae. Overall, the results have shown that artemisinin treatment has a severe impact on egg production by TCBZ-resistant flukes, an effect that is mediated by disruption of the vitelline cells.

The diterpenoid 7-keto-sempervirol, derived from Lycium chinense, displays anthelmintic activity against both Schistosoma mansoni and Fasciola hepatica

Background

Two platyhelminths of biomedical and commercial significance are Schistosoma mansoni (blood fluke) and Fasciola hepatica (liver fluke). These related trematodes are responsible for the chronic neglected tropical diseases schistosomiasis and fascioliasis, respectively. As no vaccine is currently available for anti-flukicidal immunoprophylaxis, current treatment is mediated by mono-chemical chemotherapy in the form of mass drug administration (MDA) (praziquantel for schistosomiasis) or drenching (triclabendazole for fascioliasis) programmes. This overreliance on single chemotherapeutic classes has dramatically limited the number of novel chemical entities entering anthelmintic drug discovery pipelines, raising significant concerns for the future of sustainable blood and liver fluke control.

Methodology/ Principle Findings

Here we demonstrate that 7-keto-sempervirol, a diterpenoid isolated from Lycium chinense, has dual anthelmintic activity against related S. mansoni and F. hepatica trematodes. Using a microtiter plate-based helminth fluorescent bioassay (HFB), this activity is specific (Therapeutic index = 4.2, when compared to HepG2 cell lines) and moderately potent (LD₅₀ = 19.1 μM) against S. mansoni schistosomula cultured in vitro. This anti-schistosomula effect translates into activity against both adult male and female schistosomes cultured in vitro where 7-keto-sempervirol negatively affects motility/behaviour, surface architecture (inducing tegumental holes, tubercle swelling and spine loss/shortening), oviposition rates and egg morphology. As assessed by the HFB and microscopic phenotypic scoring matrices, 7-keto-sempervirol also effectively kills in vitro cultured F. hepatica newly excysted juveniles (NEJs, LD₅₀ = 17.7 μM). Scanning electron microscopy (SEM) evaluation of adult F. hepatica liver flukes co-cultured in vitro with 7-keto-sempervirol additionally demonstrates phenotypic abnormalities including breaches in tegumental integrity and spine loss.

Conclusions/ Significance

7-keto-sempervirol negatively affects the viability and phenotype of two related pathogenic trematodes responsible for significant human and animal infectious diseases. This plant-derived, natural product is also active against both larval and adult developmental forms. As such, the data collectively indicate that 7-keto-sempervirol is an important starting point for anthelmintic drug development. Medicinal chemistry optimisation of more potent 7-keto-sempervirol analogues could lead to the identification of novel chemical entities useful for future combinatorial or replacement anthelmintic control.

Schistosomiasis and fascioliasis are caused by two related trematodes found within the phylum Platyhelminthes (flatworms), and are classified as neglected diseases of poverty due to their effects on people living in the most underprivileged areas of the world. With no vaccine currently near development, and the existing strategy for global control based on the over-reliance on single-class chemotherapies, there is an urgent requirement for the identification of next generation anthelmintics. Here we demonstrate that 7-keto-sempervirol, a natural product derived from Lycium chinense, displays dual anthelmintic activity towards both Schistosoma mansoni (causative agent of schistosomiasis) and Fasciola hepatica (causative agent of fascioliasis). Utilising objective and phenotypic matrices, we show this activity to be selective (compared to a human cell line) and moderately potent against S. mansoni and F. hepatica larvae. This anti-larval effect translates into additional activity against both S. mansoni and F. hepatica adults where 7-keto-sempervirol induces phenotypic abnormalities including tegumental damage, motility disruption and oviposition inhibition. Due to 7-keto-sempervirol’s anthelmintic activity against multiple life stages of two parasitic trematodes, we contend that this starting chemical scaffold could be used to develop more effective compounds useful in controlling important parasites of biomedical and commercial relevance.

History of echinostomes (Trematoda)

Echinostomatidae (Trematoda) is the largest family within the class Trematoda. Members of this family have been studied for many years in relation to their utility as basic research models in biodiversity and systematics and also as experimental models in parasitology since they offer many advantages. Echinostomes have contributed significantly to numerous developments in many areas studied by parasitologists and experimental biologists. In this review, we examine the history of the echinostomebased studies from the beginnings to the present. For this purpose, we have divided the history of echinostomes into four periods (i.e. 18(th) and 19(th) centuries, first half of the 20(th) century, second half of the 20(th) century and the late 20(th) and 21(th) century) according to the types of studies performed in each of them. Moreover, we also briefly review the history of echinostome infections in humans.

Automated imaging and other developments in whole-organism anthelmintic screening

Helminth infections still represent a huge public health problem throughout the developing world and in the absence of vaccines control is based on periodic mass drug administration. Poor efficacy of some anthelmintics and concerns about emergence of drug resistance has highlighted the need for new drug discovery. Most current anthelmintics were discovered through in vivo screening of selected compounds in animal models but recent approaches have shifted towards screening for activity against adult or larval stages in vitro. Larvae are normally available in greater numbers than adults, can often be produced in vitro and are small enough for microplate assays. However, the manual visualization of drug effects in vitro is subjective, laborious and slow. This can be overcome by application of automated readouts including high-content imaging. Incorporated into robotically controlled HTS platforms such methods allow the very large compound collections being made available by the pharmaceutical industry or academic organizations to be screened against helminths for the first time, invigorating the drug discovery pipeline. Here, we review the status of whole-organism screens based on in vitro activity against living worms and highlight the recent progress towards automated image-based readouts.

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

The present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents.

Efficacy and pharmacokinetics of OZ78 and MT04 against a natural infection with Fasciola hepatica in sheep

Fasciolosis is a parasitosis caused by the food-borne trematode Fasciola spp. of major veterinary significance. Triclabendazole is the first line treatment in humans and animals but cases of resistance are spreading worldwide. The synthetic peroxides OZ78 and MT04 are lead compounds for the treatment of fasciolosis. In the present study we investigated the efficacy and drug disposition following a single intramuscular dose of 100 mg/kg OZ78 and MT04 in sheep harbouring a natural Fasciola hepatica infection. A liquid chromatography and tandem mass spectrometry (LC-MS/MS) method was developed and validated to quantify plasma and bile concentrations of both compounds. Plasma samples were analysed with an accuracy for OZ78 and MT04 from 91 to 115% and a precision lower than 8.9%. Bile samples displayed an accuracy between 92 and 101% and a precision up to 12.7%. Bile samples were collected at 0 and 6h post-administration. Plasma mean peak concentration was 11.1 μg/ml at 1.5 h for OZ78 and 4.8 μg/ml at 4.2 h for MT04. Mean AUC of OZ78 and MT04 was 6698 and 3567 μg min/ml, respectively. Bile concentration at 6h post-treatment was 1.0 μg/ml for OZ78 and 1.4 μg/ml for MT04. Treatment with OZ78 showed no effect on egg burden and adult worm counts in vivo, whereas MT04 displayed a significant egg count reduction of 98.5% and a worm burden reduction of 92%. In conclusion, our study reveals an excellent activity of MT04 against F. hepatica in naturally infected sheep and a first insight into its PK behaviour.

Comparison of novel and existing tools for studying drug sensitivity against the hookworm Ancylostoma ceylanicum in vitro

The motility assay is the current gold standard for evaluating drug effects on hookworm larvae and adults, however, among other drawbacks the assay is time consuming, and prone to individual subjectivity. We evaluated six alternative in vitro assays, namely the feeding inhibition assay, the colourimetric AlamarBlue®, MTT formazan and acid phosphatase activity assays, as well as isothermal calorimetry and the xCELLigence System using Ancylostoma ceylanicum third-stage larvae, stimulated third-stage larvae and adults. The performances of the assays were compared to the motility assay using three standard drugs: albendazole, levamisole and ivermectin (100-1 μg/ml). None of the assays investigated offered an advantage over the motility assay, because they were all inapplicable to third-stage larvae, which were presumably metabolically and physically too inactive. Among all assays tested the xCELLigence System performed best on adult worms as the test was accurate, simple, required a minimal number of worms and offered the possibility for conducting a medium-throughput screening.

Isothermal microcalorimetry to study the activity of triclabendazole and its metabolites on juvenile and adult Fasciola hepatica

Isothermal microcalorimetry (IMC) is an analytical tool that continuously measures the heat flow generated by chemical, physical or biological processes. We have demonstrated that IMC is a useful tool to analyze drug effects on helminths, including adult Fasciola hepatica. Here, we used IMC to examine the activity of triclabendazole and its metabolites triclabendazole sulphone and triclabendazole sulphoxide on juvenile and adult F. hepatica. Worms (one adult or 2-3 juveniles) were placed in 4 or 20 ml glass ampoules containing RPMI 1640 and the test compound (25-100 μg/ml) and the heat flow and motility of worms was examined with TAM48 and TAMIII isothermal microcalorimetry instruments. IMC was found to be precisely document drug effects on juvenile F. hepatica and confirmed the pronounced effect of the benzimidazole derivatives on the motor activity of F. hepatica. Juvenile F. hepatica incubated with 100 μg/ml triclabendazole, triclabendazole sulphone and triclabendazole sulphoxide showed no movements 8.3, 35 and 6h post-incubation (all p<0.001). The metabolic heat of triclabendazole sulphoxide treated worms (100 μg/ml) was reduced by 50% and 76% 24 and 120 h post-incubation, respectively. Limitations of calorimetric measurements were observed using adult F. hepatica as only three worms could be measured simultaneously and also control worms showed a considerable decrease in heat flow. Adult F. hepatica exposed to triclabendazole, triclabendazole sulphone and triclabendazole sulphoxide showed no movements after 31 (p=0.009), 49 (p>0.05) and 88 (p>0.05)h. In conclusion, IMC is useful to document drug effects on juvenile F. hepatica and since rapid technological developments in this field are occurring IMC might also hold promise to study adult F. hepatica in the near future.

Identification of antischistosomal leads by evaluating bridged 1,2,4,5-tetraoxanes, alphaperoxides, and tricyclic monoperoxides

Although antischistosomal properties of peroxides were studied in recent years, systematic structure-activity relationships have not been conducted. We evaluated the antischistosomal potential of 64 peroxides belonging to bridged 1,2,4,5-tetraoxanes, alphaperoxides, and tricyclic monoperoxides. Thirty-nine compounds presented IC₅₀ values <15 μM on newly transformed schistosomula. Active drugs featured phenyl-, adamantane-, or alkyl residues at the methylene bridge. Lower susceptibility was documented on adult schistosomes, with most hit compounds being tricyclic monoperoxides (IC₅₀: 7.7-13.4 μM). A bridged 1,2,4,5-tetraoxane characterized by an adamantane residue showed the highest activity (IC₅₀: 0.3 μM) on adult Schistosoma mansoni . Studies with hemin and heme supplemented medium indicated that antischistosomal activation of peroxides is not necessarily triggered by iron porphyrins. Two compounds (tricyclic monoperoxide; bridged 1,2,4,5-tetraoxane) revealed high worm burden reductions in the chronic (WBR: 75.4-82.8%) but only moderate activity in the juvenile (WBR: 18.9-43.1%) S. mansoni mouse model. Our results might serve as starting point for the preparation and evaluation of related derivatives.

Pharmacokinetics of the fasciocidal drug candidates MT04 and OZ78 in uninfected rats and in vitro pharmacodynamic studies

OZ78 and MT04 are promising drug candidates against fascioliasis (fasciolosis). We determined basic pharmacokinetic (PK) parameters of OZ78 and MT04 in uninfected rats. Rats were treated with single oral doses of 50 mg/kg OZ78 or MT04. Blood samples were withdrawn at selected time points post treatment and the plasma concentrations were quantified by a validated liquid chromatography/mass spectrometry (LC/MS) method. The LC/MS method for MT04 and OZ78, initially developed for sheep plasma analysis, was adapted for rat plasma. In vitro pharmacodynamic studies with Fasciola hepatica incubated in solutions of either test agent complemented our work. The adapted and validated method was precise and accurate to measure OZ78 and MT04 in rat plasma. Accuracies for MT04 ranged from 87.9% to 104.7% with precisions not exceeding 14.3%. Precisions for OZ78 were lower than 9.8% and accuracies were between 88.4% and 105.3%. Following oral administration, maximum plasma concentrations (C max) of MT04 and OZ78 were 49.8 and 70.1 μg/ml after 2.7 h and 1.6 h, respectively (p > 0.05). The estimated area under the plasma time curves (AUCs) were comparable for MT04 and OZ78. Mean elimination half-lives (t1/2) of MT04 and OZ78 covered a range from 1 to 7 h. In vitro studies demonstrated that the fasciocidal activity of MT04 and OZ78 was dependent on the incubation-time, with exposure of flukes for 24 h to the drugs not being sufficient to kill the worms. In conclusion, differences in PK parameters of MT04 and OZ78 were observed in rats. However, further studies (e.g. in infected rats) are necessary to characterize these drugs in greater detail.

The activity of dispiro peroxides against Fasciola hepatica

Dispiro 1,2,4-trioxanes and 1,2,4,5-tetraoxanes had superior efficacy against Fasciola hepatica than the corresponding ozonides (1,2,4-trioxolanes). For highest efficacy, spiroadamantane and carboxymethyl substructures were required. Three compounds completely cured F. hepatica-infected mice at single oral doses of 50mg/kg and two were partially curative at single doses of 25mg/kg.

Exploration of novel in vitro assays to study drugs against Trichuris spp

Though trichuriasis is a significant public health problem, few effective drugs are available underscoring the need for new drug therapies. For the evaluation of trichuricidal activity of test compounds in vitro an accurate, reliable, sensitive, fast and cheap drug sensitivity assay is essential. The aim of the present investigation was to evaluate the performance of different in vitro drug sensitivity assays in comparison to the standard motility assay. Trichuris muris L4 larvae or adult worms were isolated from the intestinal tract from infected female C57BL/10 mice and incubated in the presence of ivermectin, levamisole and nitazoxanide (200, 100 and 50 μg/ml) for 72 h. The health status of the worms was either evaluated microscopically using a motility scale from 0 to 3 (motility assay), by examination of absorbance or emission in response to metabolic activity (MTT (Thiazolyl Blue Tetrazolium Bromide) and Alamar Blue assay), through analysis of absorbance of an enzyme-substrate reaction (acid phosphatase activity assay), by measuring the noise amplitudes (isothermal microcalorimetry and xCELLigence System) or the heat flow (isothermal microcalorimetry) of T. muris. The Alamar Blue assay, xCELLigence and microcalorimetry compared favorably to the standard motility assay. These three assays precisely determined the trichuricidal activity of the three test drugs. The acid phosphatase and the MTT assays showed a poorer performance than the motility assay. In conclusion, the colorimetric Alamar Blue in vitro assay is a good alternative to the motility assay to study drug effects against T. muris L4 and adults, since it is easy to perform, precise and of low cost.