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.

Development of chiral praziquantel analogues as potential drug candidates with activity to juvenile Schistosoma japonicum.

A series of chiral praziquantel analogues were synthesized and evaluated against Schistosoma japonicum both in vitro and in vivo. All compounds exhibited low to considerable good activity in vivo. Remarkably, worm reduction rate of R-3 was 60.0% at a single oral dose of 200mg/kg against juvenile stage of Schistosoma japonicum. The target compounds displayed in vivo antischistosomal activity against both Schistosoma japonicum and Schistosoma mansoni. Furthermore, all R-isomers displayed stronger antischistosomal activity than S-isomers in vivo, indicating R-isomers were the active enantiomers, while S-isomers were less active ones. This structure activity relationship (SAR) could have important implications in further drug development for schistosomiasis.

Synthesis and SAR studies of praziquantel derivatives with activity against Schistosoma japonicum.

The synthesis and structure-activity relationship (SAR) studies of praziquantel derivatives with activity against adult Schistosoma japonicum are described. Several of them showed better worm killing activity than praziquantel and could serve as leads for further optimization.

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.

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.

Selective Depletion of Chiral 4-Hydroxypraziquantel Metabolites in Three Types of Aquaculture Fish by LC-MS/MS.

The rise of aquaculture has necessitated the use of antibiotics and other agents in these densely populated and often closed environments. An enantioselective depletion study of four chiral 4-hydroxypraziquantel metabolites (4-OH-PZQ) in perch, tilapia, and ricefield-eel muscles was done using a simple, sensitive, and reliable liquid-chromatography-tandem-mass-spectrometry (LC-MS/MS) method. These metabolites result from the uptake of the drug praziquantel (PZQ), which is used in aquaculture. A novel strategy of using a C18 short column in tandem with a chiral hydroxypropyl-ß-cyclodextrin superficially porous particle (CDShell-RSP) column produced the optimal separation for both the enantiomers and diastereoisomers of 4-OH-PZQ. The method was linear over the concentration range of 1-250 µg L-1 ( r2 ≥ 0.99) for R- trans-4-OH-PZQ, S- trans-4-OH-PZQ, R- cis-4-OH-PZQ, and S- cis-4-OH-PZQ. The average recoveries of four analytes at three spiked levels of 1, 10, and 100 µg kg-1 ranged from 84.2 to 93.1%, and the intraday and interday relative standard deviations were less than 7.9%. The limits of quantification of the four 4-OH-PZQ metabolites in perch-, tilapia-, and ricefield-eel-muscle matrices were 1.0 µg kg-1. The method was utilized to monitor the depletion of trans- and cis-4-OH-PZQ enantiomers in perch, tilapia, and ricefield-eel muscle following oral administration (medicine bath for ricefield eel). Species-specific differences in the PZQ metabolism of isomers were observed. In addition, new metabolites of PZQ were observed: 3-hydroxypraziquantel diastereomers.

Praziquantel Resistance in the Zoonotic Cestode Dipylidium caninum.

Dipylidium caninum is a cosmopolitan cestode infecting dogs, cats, and humans. Praziquantel is a highly effective cestocidal drug and resistance in adult cestodes has not been reported. From 2016 to 2018, a population of dogs with cestode infections that could not be eliminated despite multiple treatments with praziquantel or epsiprantel was identified. Cases of D. caninum were clinically resistant to praziquantel and could not be resolved despite increasing the dose, frequency, and duration of treatment. Resistant isolates were identified and characterized by sequencing the 28S, 12S, and voltage-gated calcium channel beta subunit genes. Cases were only resolved following treatment with nitroscanate or a compounded pyrantel/praziquantel/oxantel product. Clinicians should be aware of this alarming development as treatment options for cestodes are limited in both human and veterinary medicine.

In vitro and in vivo activity of R- and S- praziquantel enantiomers and the main human metabolite trans-4-hydroxy-praziquantel against Schistosoma haematobium.

BACKGROUND: Praziquantel (PZQ) is the mainstay of schistosomiasis control and has been successfully used for decades. However, its mechanism of action is not fully understood. While the majority of studies have been conducted on Schistosoma mansoni, it is not known which enantiomer, R- or S-praziquantel (R-/S-PZQ), is responsible for the activity on Schistosoma haematobium. METHODS: In vitro and in vivo studies were conducted to evaluate the activity of R- and S-PZQ, racemic PZQ and the main human metabolite, namely trans-4-OH-PZQ, on S. haematobium. IC50 values on adult S. haematobium were determined in vitro. Dose-response relationship studies were performed in golden Syrian hamsters, harbouring a chronic S. haematobium infection. RESULTS: R-PZQ displayed the highest activity against adult worms in vitro, revealing an IC50 of 0.007 µg/ml at 4 h and 0.01 µg/ml at 72 h. In contrast, S-PZQ was 501× less active (eudysmic ratio at 4 h), with an IC50 of 3.51 and 3.40 µg/ml (4 and 72 h, respectively). Racemic PZQ and trans-4-OH-PZQ resulted in an IC50 of 0.03 µg/ml and 1.47 µg/ml both at 4 and 72 h, respectively. In vivo, R-PZQ was the most potent drug with worm burden reductions (WBRs) of 98.5, 75.6 and 73.3% at 125.0, 62.5 and 31.0 mg/kg, respectively. A single oral dose of 250.0 mg/kg PZQ resulted in a WBR of 99.3%. S-PZQ was highly active in vivo at 250.0 and 500.0 mg/kg with WBRs of 83.0 and 94.1%, respectively. The lowest tested dose of S-PZQ, 125.0 mg/kg, showed moderate activity (WBR of 46.7%). The calculated ED50 for R- and S-PZQ were 24.7 and 127.6 mg/kg, respectively, with a corresponding eudysmic ratio of 5.17. CONCLUSION: Our data support the theory of R-PZQ driving the antischistosomal activity. Interestingly, also S-PZQ proved to possess a significant activity towards S. haematobium, particularly in vivo.

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.

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.

Plasma pharmacokinetics and therapeutic efficacy of praziquantel and 4-hydroxypraziquantel in Schistosoma japonicum-infected rabbits after oral, rectal, and intramuscular administration.

The relationship between plasma level and therapeutic efficacy of praziquantel (PZQ) and its major human oxidative metabolite, 4-hydroxypraziquantel (4-OHPZQ), has been investigated in Schistosoma japonicum-infected rabbits using three different routes of PZQ administration. After intramuscular administration (20 mg/kg), the maximum level of PZQ in rabbit cardiac plasma was 1.6 +/- 1.0 micrograms/ml (mean +/- SD) 30 min after administration. After oral or rectal administration (40 mg/kg), maximum plasma levels were 0.1 +/- 0.2 microgram/ml (oral) and 0.5 +/- 0.4 micrograms/ml (rectal). The corresponding maximum 4-OHPZQ concentrations in cardiac plasma were 4.6 +/- 1.8 micrograms/ml (intramuscular), 1.7 +/- 0.5 micrograms/ml (oral), and 4.1 +/- 1.6 micrograms/ml (rectal) 2 hr after administration of PZQ. After administration of similar doses, maximum levels of PZQ in plasma from the femoral vein were 29.3 +/- 27.5 micrograms/ml (intramuscular), 0.6 +/- 1.0 microgram/ml (oral), and 0.7 +/- 0.6 microgram/ml (rectal). However, 60 min after intramuscular administration, the maximum PZQ concentration in portal venous blood was only 1.0 +/- 0.6 microgram/ml, which is substantially less than corresponding maximum portal vein levels after oral (6.8 +/- 6.5 micrograms/ml) or rectal (3.7 +/- 4.6 micrograms/ml) administration. Therapeutically, in spite of the 4-6-fold lower levels of PZQ in portal venous plasma after intramuscular administration, adult worm reduction rates in infected rabbits using the above doses were 92.2% (intramuscular), 90.1% (rectal), and 72.5% (oral), respectively, four weeks after treatment. Thus, no direct correlation between levels of PZQ in peripheral or portal venous blood and therapeutic efficacy was observed in rabbits infected with S. japonicum.

Human fascioliasis.

Fasciola hepatica, a zoonotic liver fluke, can also cause disease in humans. Common symptoms are epigastric pain, upper abdominal pain and malaise. Fever and arthralgia are common in acute fascioliasis. Eosinophilia is the predominant laboratory finding, especially in patients with the acute form of the disease. Diagnosis and treatment is not easy, as physicians rarely encounter this disease, and effective drugs are not available in many countries. Human fascioliasis may be underestimated. Patients with eosinophilia and abdominal pain should be evaluated for F. hepatica infestation by parasitological, radiological and serological tests.

Isolation and identification of 8-hydroxypraziquantel as a metabolite of the antischistosomal drug praziquantel.

Praziquantel, a broad spectrum anthelmintic drug, is extensively metabolized in the liver, yielding mainly monohydroxylated and dihydroxylated phase-I metabolites. However, the exact chemical structure of most metabolites is still unknown. One of these unidentified phase-I metabolites was isolated from human urine by high performance liquid chromatography using an isocratic separation method. This metabolite was identified as 8-hydroxypraziquantel. For the structure elucidation, electrospray ionization-mass spectrometry, 1H and 13C NMR spectroscopy have been used.

Uptake and effect of praziquantel and the major human oxidative metabolite, 4-hydroxypraziquantel, by Schistosoma japonicum.

After exposure to praziquantel in vitro at a concentration of 1 microgram/ml for 0.5-2 hr, amounts of praziquantel in Schistosoma japonicum varied from 2.1 +/- 1.2 to 3.7 +/- 1.6 ng/male worm and 1.3 +/- 1.2 to 2.2 +/- 1.5 ng/female worm during the time studied. At 30 micrograms/ml, praziquantel amounts were 11-33-fold higher. However, within 2 hr after removal from a medium containing 30 micrograms/ml praziquantel, 95% of the drug was released from the parasites. When S. japonicum worm pairs were incubated in vitro with 1, 10, and 30 micrograms/ml of 4-hydroxypraziquantel, the major human oxidative metabolite of praziquantel, 0.2 +/- 0.2, 3.8 +/- 1.3, and 7.4 +/- 1.3 ng/worm pair, respectively, were found after a 2-hr incubation. 15-30-fold lower than corresponding worm pair amounts of praziquantel. In vivo, when 4- or 5-wk S. japonicum-infected mice were treated orally with praziquantel (300 mg/kg), peak concentrations of praziquantel in plasma determined by high pressure liquid chromatography were 14.7 +/- 1.5 micrograms/ml (4-wk infection) and 16.7 +/- 2.8 micrograms/ml (5-wk infection) 15 min after treatment. Corresponding in vivo worm praziquantel amounts were 1.8 +/- 0.4 ng/male worm and 2.4 +/- 1.1 ng/female worm, respectively, in the 4-wk infection and 4.6 +/- 1.6 ng/male worm and 5.6 +/- 1.2 ng/female worm in the 5-wk infection. Peak plasma concentrations of 4-hydroxypraziquantel were similar but corresponding in vivo worm amounts were 1-20-fold lower, depending on the time after drug administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of epsiprantel against Echinococcus granulosus infections in dogs.

Dogs with 41-day-old experimental infections of Echinococcus granulosus were treated orally with epsiprantel. Single doses of 2.5 mg kg-1, 5.0 mg kg-1 or 7.5 mg kg-1 were effective in removing more than 99 per cent of these parasites, but total clearances of worms only occurred in dogs given the highest dose.

In vitro and in vivo efficacy of epsiprantel against Echinococcus granulosus.

In vitro, epsiprantel at a concentration of 10 micrograms ml-1 caused tegumental damage and death of protoscoleces, juveniles (seven-day-old) and adult (37-day-old) Echinococcus granulosus. Degenerative changes and death occurred more rapidly in the older parasites. Similarly, epsiprantel was more effective against adult (28-day-old) than seven-day-old experimental infections of E granulosus in dogs. Oral doses of 2.5, 5 and 7.5 mg kg-1 were greater than 96 per cent, 99.9 per cent and 99.99 per cent active, respectively, against mature worms, whereas in seven-day-old infections doses of 5, 7.5 and 10 mg kg-1 produced greater than 94 per cent, 90 per cent and 99.8 per cent reduction in worm burdens, respectively. No side effects from treatment were seen.

Synthesis of praziquantel derivatives and their in vitro activity against adult Clonorchis sinensis.

Several praziquantel derivatives have been prepared by the acylation of compound 5, and examined on their biological activity in vitro a against adult Clonorchis sinensis collected from rabbits infected with metacercariae which was isolated from Pseudorasbora parva, a second intermediate host, captured in Nakdong river in Korea.

Dose titration and confirmation tests for determination of cesticidal efficacy of epsiprantel in dogs.

Fifty-five dogs, naturally infected with Taenia sp or Dipylidium caninum or both, were assigned to the following treatment groups for dose titration studies with epsiprantel: nonmedicated control dogs (n = 14), medicated dogs given a dosage of 2.75 mg/kg of body weight (n = 15), medicated dogs given a dosage of 5.5 mg/kg (n = 16), and medicated dogs given a dosage of 8.25 mg/kg (n = 10). Medication was given orally in a tablet formulation. Feces were examined for cestodes passed and the gastrointestinal tract was examined at necropsy for retained cestodes. Efficacy of epsiprantel was 92.9% against Taenia and 44.8% against Dipylidium for a dosage of 2.75 mg/kg, 100% against Taenia and 99.8% against Dipylidium for a dosage of 5.5 mg/kg, and 94.6% against Taenia and 100% against Dipylidium for a dosage of 8.25 mg/kg. For dose confirmation, 36 dogs naturally infected with Taenia sp or D caninum or both were allotted to 2 treatment groups: nonmedicated control dogs (n = 16) and dogs medicated with epsiprantel at a dosage of 5.5 mg/kg (n = 20). Efficacy was 100% for both Taenia sp and D caninum.

Developments in the treatment of gastrointestinal parasites of small animals.

The use of anthelmintics introduced over the past 25 years is discussed. The spectrum of action, efficacy, and toxicity of benzimidazoles, ivermectin, milbemycin, praziquantel, and epsiprantel are considered.

[Determination of the optical purity of praziquanamine by reversed phase HPLC after derivatization with GITC].

The enantiomers of praziquanamine were separated by reversed phase HPLC after derivatization with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylisothiocyanate (GITC). The determination of the optical purity of praziquanamine was successfully achieved. This method was applied to the determination of the optical purity of d- and l-praziquanamines.