Taste, a new incentive to switch to (R)-praziquantel in schistosomiasis treatment

Worldwide study of the taste of bitter medicines and their modifiers

The bitter taste of medicines hinders patient compliance, but not everyone experiences these difficulties because people worldwide differ in their bitterness perception. To better understand how people from diverse ancestries perceive medicines and taste modifiers, 338 adults, European and recent US and Canada immigrants from Asia, South Asia, and Africa, rated the bitterness intensity of taste solutions on a 100-point generalized visual analog scale and provided a saliva sample for genotyping. The taste solutions were five medicines, tenofovir alafenamide (TAF), moxifloxacin, praziquantel, amodiaquine, and propylthiouracil (PROP), and four other solutions, TAF mixed with sucralose (sweet, reduces bitterness) or 6-methylflavone (tasteless, reduces bitterness), sucralose alone, and sodium chloride alone. Bitterness ratings differed by ancestry for two of the five drugs (amodiaquine and PROP) and for TAF mixed with sucralose. Genetic analysis showed that people with variants in one bitter receptor variant gene (TAS2R38) reported PROP was more bitter than did those with a different variant (p= 7.6e-19) and that people with either an RIMS2 or a THSD4 genotype found sucralose more bitter than did others (p=2.6e-8, p=7.9e-11, resp.). Our findings may help guide the formulation of bad-tasting medicines to meet the needs of those most sensitive to them.

Progress interrogating TRPMPZQ as the target of praziquantel

The drug praziquantel (PZQ) has served as the long-standing drug therapy for treatment of infections caused by parasitic flatworms. These encompass diseases caused by parasitic blood, lung, and liver flukes, as well as various tapeworm infections. Despite a history of clinical usage spanning over 4 decades, the parasite target of PZQ has long resisted identification. However, a flatworm transient receptor potential ion channel from the melastatin subfamily (TRPMPZQ) was recently identified as a target for PZQ action. Here, recent experimental progress interrogating TRPMPZQ is evaluated, encompassing biochemical, pharmacological, genetic, and comparative phylogenetic data that highlight the properties of this ion channel. Various lines of evidence that support TRPMPZQ being the therapeutic target of PZQ are presented, together with additional priorities for further research into the mechanism of action of this important clinical drug.

Praziquantel Fifty Years on: A Comprehensive Overview of Its Solid State

This review discusses the entire progress made on the anthelmintic drug praziquantel, focusing on the solid state and, therefore, on anhydrous crystalline polymorphs, amorphous forms, and multicomponent systems (i.e., hydrates, solvates, and cocrystals). Despite having been extensively studied over the last 50 years, new polymorphs and the greater part of their cocrystals have only been identified in the past decade. Progress in crystal engineering science (e.g., the use of mechanochemistry as a solid form screening tool and more strategic structure-based methods), along with the development of analytical techniques, including Synchrotron X-ray analyses, spectroscopy, and microscopy, have furthered the identification of unknown crystal structures of the drug. Also, computational modeling has significantly contributed to the prediction and design of new cocrystals by considering structural conformations and interactions energy. Whilst the insights on praziquantel polymorphs discussed in the present review will give a significant contribution to controlling their formation during manufacturing and drug formulation, the detailed multicomponent forms will help in designing and implementing future praziquantel-based functional materials. The latter will hopefully overcome praziquantel's numerous drawbacks and exploit its potential in the field of neglected tropical diseases.

Artificial intelligence-guided approach for efficient virtual screening of hits against Schistosoma mansoni

Background: The impact of schistosomiasis, which affects over 230 million people, emphasizes the urgency of developing new antischistosomal drugs. Artificial intelligence is vital in accelerating the drug discovery process. Methodology & results: We developed classification and regression machine learning models to predict the schistosomicidal activity of compounds not experimentally tested. The prioritized compounds were tested on schistosomula and adult stages of Schistosoma mansoni. Four compounds demonstrated significant activity against schistosomula, with 50% effective concentration values ranging from 9.8 to 32.5 μM, while exhibiting no toxicity in animal and human cell lines. Conclusion: These findings represent a significant step forward in the discovery of antischistosomal drugs. Further optimization of these active compounds can pave the way for their progression into preclinical studies.

Development and validation of an LC-MS/MS method for the simultaneous quantification of milbemycin oxime and praziquantel in plasma: application to a pharmacokinetic study in cats

Introduction

Milbemycin oxime (MBO) and praziquantel (PZQ) have a broad spectrum of biological activity and are commonly used to treat the parasitic infection in the veterinary clinic. In this study, a fast and efficient LC-MS/MS method was established and validated for the simultaneous determination of MBO, PZQ, cis-4-hydroxylated-PZQ (C-4-OH-PZQ) and trans-4-hydroxylated-PZQ (T-4-OH-PZQ) and in cat plasma.

Methods

Extraction of analytes and internal standards from cat plasma by acetonitrile protein precipitation, allows rapid processing of large batches of samples. MBO, PZQ, C-4-OH-PZQ, T-4-OH-PZQ, and internal standard (IS) were eluted for 13.5 min on a C18 column with a 0.1% formic acid water/acetonitrile mixture as the mobile phase.

Results

Results showed that the method had good precision, accuracy, recovery, and linearity. The linearity range was 2.5-250 ng/mL for MBO, and 10-1000 ng/mL for PZQ, C-4-OH-PZQ, and T-4-OH-PZQ. The intra-day and inter-day precision CV values of the tested components were within 15%. The extraction recoveries of the four components ranged from 98.09% to 107.46%. The analytes in plasma remained stable for 6 h at room temperature, 26 h in the autosampler (4 °C), after freeze-thaw (-20°C) cycles, and 60 days in a -20°C freezer. Method sensitivity sufficed for assessing pharmacokinetic parameters of MBO, PZQ, C-4-OH-PZQ, and T-4-OH-PZQ in plasma samples with LLOQ of 2.5 ng/mL for MBO and 10 ng/mL for PZQ, C-4-OH-PZQ, and T-4-OH-PZQ.

Conclusion

In this study, a selective and sensitive LC-MS/MS method for the simultaneous quantification of MBO, PZQ, C-4-OH-PZQ, and T-4-OH-PZQ in cat plasma was developed and validated.This method had been successfully applied to evaluate the pharmacokinetics of MBO, PZQ, C-4-OH-PZQ, and T-4-OH-PZQ after a single oral administration of 8 mg MBO and 20 mg PZQ in cats.

Stereoselective Pharmacokinetics and Residue Depletion of Praziquantel and Its Metabolites, 4-Hydroxypraziquantel Enantiomers, in Swine

Praziquantel (PZQ) is administered as a racemic mixture during swine production to treat parasitic diseases. Despite its widespread application, the pharmacokinetics, residue depletion, bioactivity, and toxicity of PZQ enantiomers in swine remain largely unknown. In this study, a systematic investigation of the pharmacokinetics, tissue distribution, and residue depletion of PZQ, its major metabolites (trans- and cis-4-OH-PZQ), and their enantiomers was conducted in swine. The findings indicated that PZQ was absorbed and metabolized rapidly. In swine plasma, the concentrations of S-PZQ, S-trans-4-OH-PZQ, and R-cis-4-OH-PZQ were higher than those of their respective enantiomers. The three analytes exhibited significant tissue distribution and stereoselectivity in 10 swine tissues. Notably, the two enantiomers of PZQ demonstrated comparable tissue concentrations except in the liver and lung. Moreover, the concentrations of S-trans-4-OH-PZQ and R-cis-4-OH-PZQ were higher than those of their respective enantiomers in the 10 tissues. This study has significant implications for the development of rational dosing strategies, reducing drug usage, and minimizing side effects, as well as accurately assessing the risks associated with PZQ administration and, by extension, other chiral drugs. Furthermore, it lays a theoretical foundation for the future use of the active enantiomer, R-PZQ.

Preformulation and Long-Term Stability Studies of an Optimized Palatable Praziquantel Ethanol-Free Solution for Pediatric Delivery

To date, the treatment for cysticercosis and neurocysticercosis consists of a single oral intake of praziquantel (5-10 mg/kg), which since it is only available as tablets, hinders its administration to pediatric patients. Praziquantel is a poorly water-soluble drug which represents a challenge for its formulation in solution, particularly for the pediatric population. Thus, this study aimed to develop a palatable solution for praziquantel using pharmaceutical-accepted co-solvent systems. A design of experiments approach was applied to identify the optimal conditions for achieving a suitable amount of praziquantel in solution using co-solvent mixtures. Thus, praziquantel solubility increased from 0.38 up to 43.50 mg/mL in the optimized system. A taste masking assay in healthy human volunteers confirmed a successful reduction of drug bitterness after the addition of selected flavors and a sweetener. Stability studies were also conducted at different temperatures (4, 25, and 40 °C) for 12 months Even though the presence of the three known impurities of praziquantel was observed, their amounts never exceeded the acceptance criteria of the USP. Thus, this novel approach should be considered a valuable alternative for further preclinical studies considering the high prevalence of this infection worldwide.

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 .

Co-Crystalline Solid Solution Affords a High-Soluble and Fast-Absorbing Form of Praziquantel

Praziquantel (PZQ) is a chiral class-II drug, and it is used as a racemate for the treatment of schistosomiasis. The knowledge of several cocrystals with dicarboxylic acids has prompted the realization of solid solutions of PZQ with both enantiomers of malic acid and tartaric acid. Here, the solid form landscape of such a six-component system has been investigated. In the process, two new cocrystals were structural-characterized and three non-stoichiometric, mixed crystal forms identified and isolated. Thermal and solubility analysis indicates a fourfold solubility advantage for the newly prepared solid solutions over the pure drug. In addition, a pharmacokinetic study was conducted in rats, which involved innovative mini-capsules for the oral administration of the solid samples. The available data indicate that the faster dissolution rate of the solid solutions translates in faster absorption of the drug and helps maintain a constant steady-state concentration.

Drugs for neglected tropical diseases: availability of age-appropriate oral formulations for young children

It is recognised that paediatric indications and age-appropriate formulations are required to ensure that paediatric populations receive appropriate pharmacotherapeutic treatment. The lack of information on dosing, efficacy and safety data (labelling) is a well-recognised problem for all diseases affecting children. For neglected tropical diseases, the fact that they affect to a large extent poor and marginalised populations in low- and middle-income countries means that there is a low economic return on investment into paediatric development activities compared to other diseases [e.g. human immunodeficiency virus (HIV)]. This review provides an introduction to issues affecting the availability and development of paediatric population-relevant data and appropriate formulations of drugs for NTDs. We are summarising why age-appropriate formulations are important to ensure treatment efficacy, safety and effectiveness, outline initiatives to increase the number of paediatric indications/labelling and age-appropriate formulations, provide an overview of publicly available information on the formulations of oral drugs for NTDs relative to age appropriateness and give an introduction to options for age-appropriate formulations. The review completes with 'case studies' of recently developed paediatric formulations for NTDs, complemented by case studies for fixed-dose combinations for HIV infection in children since such formulations have not been developed for NTDs.

Praziquantel: An update on the mechanism of its action against schistosomiasis and new therapeutic perspectives

Praziquantel (PZQ) is the drug of choice for the treatment of all forms of schistosomiasis, although its mechanisms of action are not completely understood. PZQ acts largely on adult worms. This narrative literature review describes what is known about the mechanisms of action of PZQ against schistosomes from in vitro and in vivo studies and highlights the molecular targets in parasites and immune responses induced in definitive hosts by this drug. Moreover, new therapeutic uses of PZQ are discussed. Studies have demonstrated that in addition to impacting voltage-operated Ca2 + channels, PZQ may interact with other schistosome molecules, such as myosin regulatory light chain, glutathione S-transferase, and transient receptor potential channels. Following PZQ administration, increased T regulatory type 1 (Tr1) cell differentiation and decreased inflammation were observed, indicating that PZQ promotes immunoregulatory pathways. Although PZQ is widely used in mass drug administration schemes, the existence of resistant parasites has not been proven; however, it is a concern that should be constantly investigated in human populations. In addition, we discuss studies that evaluate health applications of PZQ (other than helminth infection), such as its effect in cancer therapy and its adjuvant action in vaccines against viruses.

Therapeutic Effect and Immune Changes after Treatment of Hymenolepis nana-Infected BALB/c Mice with Compounds Isolated from Leucaena leucocephala

Simple Summary

This article is mainly about the development of natural medicines against the zoonotic tapeworm (Hymenolepis nana), which is caused by tapeworm eggs in infected mice, through the isolation of the components of jumbay (Leucaena leucocephala). This study allowed for an understanding of the drug therapy through the testing of these isolated components in vitro and in vivo. The authors assessed the survival and motility, and they confirmed that the two components had good effects against tapeworm. One of these components has a promising therapeutic effect in tapeworm-infected mice in the response to egg production, worm numbers, and immune responses. This article highlights the immune-enhancing and therapeutic effects of 13²-hydroxy-(13²-S)-pheophytin a against tapeworms in infected mice.

Abstract

Background/Purpose: Hymenolepis nana is globally distributed. Leucaena leucocephala has been studied as a treatment, including the nematodes and protozoa, but no research results are related to cestodes. Therefore, the aim of this study was to target H. nana. Methods: The natural components of L. leucocephala were isolated and added to H. nana, which was cultured in vitro, to observe changes in the mortality, motility, and morphology. BALB/c male mice infected with H. nana were treated with effective components of L. leucocephala for 10 days, and the changes were recorded. After the mice were sacrificed, the spleen weight was measured, and a primary culture was performed for the subsequent cytokine and chemokine testing. Results: The experiment found that 13²-hydroxy-(13²-S)-pheophytin a and aristophyll-C have clear cestocidal effects in vitro. 13²-hydroxy-(13²-S)-pheophytin a has been shown to be effective at reducing parasite populations and eliciting host immune responses in vivo. IL-2, IL-4, IL-5, IL-6, IL-10, IL-13, IL-17, MCP-1, IFN-γ, TNF-α, MIP-1α, and GM-CSF in 13²-hydroxy-(13²-S)-pheophytin a were significantly increased after stimulation, while IL-1α, IL-1β, IL-3, IL-12p70, and RANTES were unchanged. Conclusions: The investigation shows that components of L. leucocephala have actual cestocidal activity against H. nana.

Improving translational power in antischistosomal drug discovery

Schistosomiasis is a poverty-associated tropical disease caused by blood dwelling trematodes that threaten approximately 10% of the world population. Praziquantel, the sole drug currently available for treatment, is insufficient to eliminate the disease and the clinical drug development pipeline is empty. Here, we review the characteristics of the patent Schistosoma mansoni mouse model used for in vivo antischistosomal drug discovery, highlighting differences in the experimental set-up across research groups and their potential influence on experimental results. We explore the pharmacokinetic/pharmacodynamic relationship of selected drug candidates, showcasing opportunities to improve the drug profile to accelerate the transition from the early drug discovery phase to new clinical candidates.

Pharmacogenetics of Praziquantel Metabolism: Evaluating the Cytochrome P450 Genes of Zimbabwean Patients During a Schistosomiasis Treatment

Schistosomiasis is a parasitic disease infecting over 236 million people annually, with the majority affected residing on the African continent. Control of this disease is reliant on the drug praziquantel (PZQ), with treatment success dependent on an individual reaching PZQ concentrations lethal to schistosomes. Despite the complete reliance on PZQ to treat schistosomiasis in Africa, the characterization of the pharmacogenetics associated with PZQ metabolism in African populations has been sparse. We aimed to characterize genetic variation in the drug-metabolising cytochrome P450 enzymes (CYPs) and determine the association between each variant and the efficacy of PZQ treatment in Zimbabwean patients exposed to Schistosoma haematobium infection. Genomic DNA from blood samples of 114 case-control Zimbabweans infected with schistosomes were sequenced using the CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5 genes as targets. Bioinformatic tools were used to identify and predict functional effects of detected single nucleotide polymorphisms (SNPs). A random forest (RF) model was then used to assess SNPs most predictive of PZQ efficacy, with a misclassification rate of 29%. SNPs were detected across all six genes, with 70 SNPs identified and multiple functional changes to the CYP enzymes predicted. Only four SNPs were significantly associated with PZQ efficacy using χ² tests, with rs951840747 (OR: 3.61, p = 0.01) in the CYP1A2 gene having the highest odds of an individual possessing this SNP clearing infection, and rs6976017 (OR: 2.19, p = 0.045) of CYP3A5 determined to be the most predictive of PZQ efficacy via the RF. Only the rs28371702 (CC) genotype (OR: 2.36, p = 0.024) of CYP2D6 was significantly associated with an unsuccessful PZQ treatment. This study adds to the genomic characterization of the diverse populations in Africa and identifies variants relevant to other pharmacogenetic studies crucial for the development and usage of drugs in these populations.

Unlocking the potential of drug-drug cocrystals - A comprehensive review

Intensive research subjected to the improvement of solubility and bioavailability of certain drugs has popularized the formation of cocrystals, wherein the desired drug is non-ionically bonded to a coformer by means of weak bonds. This paper addresses how crystal engineering of two compatible drug components can enhance the physicochemical and therapeutic properties of either or both of the drugs, resulting in drug-drug cocrystals, with pertinent examples. The paper also discusses the continuous screening processes which are replacing the traditional methods of crystallization due to numerous benefits to the producer as well as the products. Although faced with certain regulatory and scale-up constraints, cocrystals provide immense opportunities to the field of novel drug development.

Development of Praziquantel sulphonamide derivatives as antischistosomal drugs

The almost empty armamentarium to treat schistosomiasis, a neglected parasitic disorder caused by trematode flatworms of the genus Schistosoma, except Praziquantel (PZQ), urged to find new alternatives to fight this infection. Carbonic Anhydrase from Schistosoma mansoni (SmCA) is a possible new target against this nematode. Here, we propose new PZQ derivatives bearing a primary sulphonamide group in order to obtain hybrid drugs. All compounds were evaluated for their inhibition profiles on both humans and Schistosoma CAs, X-ray crystal data of SmCA and hCA II in adduct with some inhibitors were obtained allowing the understanding of the main structural factors responsible of activity. The compounds showed in vitro inhibition of immature and adult S. mansoni, but further optimisation is required for improved activity.

Transformation under pressure: Discovery of a novel crystalline form of anthelmintic drug Praziquantel using high-pressure supercritical carbon dioxide

Supercritical carbon dioxide (CO₂) has been used as a processing technique to control polymorphism of pharmaceuticals. However, there are fewer reports of novel polymorphs being discovered by supercritical CO₂ processing. As supercritical crystallization methods gain attention for potential in pharmaceutical processing, they may become a critical screening tool for discovery of new polymorphs. In this work, a case study is presented for a novel crystalline form of the anthelmintic drug, Praziquantel, found through supercritical CO₂ processing. The novel form of Praziquantel was characterized by chromatography, nuclear magnetic resonance and infrared spectroscopy, X-ray powder diffraction, thermal analysis, and scanning electron microscopy. Furthermore, the novel form exhibited 13-20% improved solubility compared to commercial Form A between pH 1.6 and 7.5 and was physically stable under stressed conditions (40 °C and 75% relative humidity) for 7.5 weeks. Overall, this work showed that supercritical CO₂ processing is a valuable tool to screen for novel, and possibly viable polymorphs of pharmaceutical compounds with improved properties.

Recent trends in praziquantel nanoformulations for helminthiasis treatment

INTRODUCTION

Infections caused by parasitic flatworms impose a considerable worldwide health burden. Recently, World Health Organization launched its roadmap for neglected diseases for the period 2021 to 2030 and oral treatment with praziquantel (PZQ) in tablet form is the main drug therapy for combating these diseases, but its use is limited by many drawbacks, including the high therapeutic dose due to the drug's low solubility and bioavailability. Among the strategies to improve PZQ performance, the use of drug nanocarriers has been cited as an interesting approach to overcome these pharmacological issues.

AREAS COVERED

This review focuses on the various types of nanomaterials (polymeric, lipidic, inorganic nanoparticles, and nanocrystals) which have been recently used to improve PZQ therapy. In addition, recent advances in PZQ nanoformulations, developed to overcome the barriers of the conventional drug are described.

EXPERT OPINION

Considering the poor rate of discovery in the anthelmintic segment observed in recent decades, the effective management of existing drugs has become essential. The application of new strategies based on nanotechnology can extend the useful life of PZQ in new and more effective formulations. Pharmaceutical nanotechnology can solve the pharmacokinetic challenges characteristic of PZQ and improve its solubility and bioavailability.

R-praziquantel integrated population pharmacokinetics in preschool- and school-aged African children infected with Schistosoma mansoni and S. haematobium and Lao adults infected with Opisthorchis viverrini

Racemic praziquantel (PZQ) is the standard treatment for schistosomiasis and liver fluke infections (opisthorchiasis and clonorchiasis). The development of an optimal pediatric formulation and dose selection would benefit from a population pharmacokinetic (popPK) model. A popPK model was developed for R-PZQ, the active enantiomer of PZQ, in 664 subjects, 493 African children (2-15 years) infected with Schistosoma mansoni and S. haematobium, and 171 Lao adults (15-78 years) infected with Opisthorchis viverrini. Racemate tablets were administered as single doses of 20, 40 and 60 mg/kg in children and 30, 40 and 50 mg/kg in 129 adults, and as 3 × 25 mg/kg apart in 42 adults. Samples collected by the dried-blood-spot technique were assayed by LC-MS/MS. A two-compartment disposition model, with allometric scaling and dual first-order and transit absorption, was developed using Phoenix™ software. Inversely parallel functions of age described the apparent oral bioavailability (BA) and clearance maturation in children and ageing in adults. BA decreased slightly in children with dose increase, and by 35% in adults with multiple dosing. Crushing tablets for preschool-aged children increased the first-order absorption rate by 64%. The mean transit absorption time was 70% higher in children. A popPK model for R-PZQ integrated African children over 2 years of age with schistosomiasis and Lao adults with opisthorchiasis, and should be useful to support dose optimization in children. In vitro hepatic and intestinal metabolism data would help refining and validating the model in younger children as well as in target ethnic pediatric and adult groups.

Regression of Schistosoma mansoni associated morbidity among Ugandan preschool children following praziquantel treatment: A randomised trial

Preschool children suffer from morbidity attributable to Schistosoma mansoni. We compared a single and double dose of praziquantel treatment on the regression of S. mansoni associated morbidity in children less than six years in Uganda. We measured the sizes of spleen and liver as well as liver fibrosis before treatment and 8 months after treatment among children who either received one dose (n = 201) or two doses (n = 184) of praziquantel (standard oral dose of 40 mg/kg body weight). Heamoglobin measurements were also taken. Overall, liver enlargement reduced from 52.2% (95% CI (Confidence interval) 45.1, 59.3) to 17.9% (95% CI 12.9, 23.9) with a single dose and from 48.4 (95% CI 40.9, 55.8) to 17.9% (95% CI 12.7, 24.3) with a double dose and there was no significant difference between the changes in proportion of children with enlarged liver between the two treatment groups. The proportion of children with enlarged spleen was not significantly reduced in the group treated with either one or two doses, 47.8% (95% CI 41.7, 54.9) to 45.3% (95% CI 38.3, 52.4) and 48.4% (95% CI 40.9,55.8) to 40.8% 95% CI 33.6, 48.2), respectively. Liver fibrosis detected among children getting single dose (n = 9) or double doses (n = 13) resolved after treatment with praziquantel. The number of children with low heamoglobin significantly reduced from 51.2% (95% CI 44.1, 58.3) to 0.5% (0.2, 0.8) and 61.4% (95% CI 53.9,68.5) to 1.1% (95% CI 0.1, 3.9) after single and double dose treatment, respectively. These results suggest that there is no evidence of a difference in effect between one dose of praziquantel and two doses in reversing morbidity attributable to S. mansoni among children less than six years of age.

Efficacy and Safety of New Orodispersible Tablet Formulations of Praziquantel (Racemate and L-Praziquantel) in Schistosoma mansoni-Infected Preschool-Age Children and Infants: A Randomized Dose-Finding Phase 2 Study

Introduction

Two novel formulations of praziquantel (PZQ) and Levo-(L-)PZQ (arpraziquantel) have been developed for the treatment of schistosomiasis in preschool-age children and infants.

Methods

This open-label, dose-finding Phase 2 study assessed the efficacy and safety of PZQ formulations in children and infants infected with Schisostoma mansoni in Côte d’Ivoire. In Part 1, 420 children aged 2.1–6.9 years (weight 10.0–29.9 kg) were enrolled and randomized to one of 7 treatment arms (n=60 per arm): commercially available racemate (rac)-PZQ at 3x20 mg/kg or 40 mg/kg (treatment arms 1 and 2); rac-PZQ orodispersible tablet (ODT) at 40 mg/kg or 60 mg/kg (treatment arms 3 and 4); or L-PZQ ODT at 30 mg/kg, 45 mg/kg, or 60 mg/kg (treatment arms 5, 6, and 7). The optimal formulation and dose identified (L-PZQ ODT 50 mg/kg) was used in Part 2, which enrolled 24 infants aged 6–24 months (weight 7.5–14.8 kg). Infants were treated in an age-staggered approach: age 13–24 months (treatment arm 8, n=20) and age 6–12 months (treatment arm 9, n=4). The primary endpoint was clinical cure rate (CR) demonstrated by the Kato–Katz method 14–21 days post-treatment. Secondary endpoints included CR by point-of-care circulating cathodic antigen, egg reduction rate (ERR), and adverse events (AEs).

Results

In Part 1, CRs ≥70% were achieved in all treatment arms and were highest with L-PZQ ODT 60 mg/kg (89.7%), rac-PZQ 3x20 mg/kg (89.5%), and L-PZQ ODT 45 mg/kg (86.0%). In Part 2, CRs were >90%. All treatment arms had ERRs >95%. Treatment-related AEs were reported by 71 participants (16.0%) and were similar across treatment arms; most were mild and transient. The most common treatment-emergent AEs were laboratory abnormalities. No deaths or discontinuation due to treatment-emergent AEs were reported and no new safety concerns were identified.

Conclusion

New rac-PZQ and L-PZQ ODT formulations used as single-dose therapy against S. mansoni demonstrated acceptable overall efficacy and safety in preschool-age children and infants, warranting further studies in this population.

Clinical Trial Registration

ClinicalTrials.gov, identifier NCT02806232; Pan African Clinical Trials Registry, identifier PACTR201604001493593.

Mechanochemical Synthesis and Physicochemical Characterization of Previously Unreported Praziquantel Solvates with 2-Pyrrolidone and Acetic Acid

Two new solvates of the widely used anthelminthic Praziquantel (PZQ) were obtained through mechanochemical screening with different liquid additives. Specifically, 2-pyrrolidone and acetic acid gave solvates with 1:1 stoichiometry (PZQ-AA and PZQ-2P, respectively). A wide-ranging characterization of the new solid forms was carried out by means of powder X-ray diffraction, differential scanning calorimetry, FT-IR, solid-state NMR and biopharmaceutical analyses (solubility and intrinsic dissolution studies). Besides, the crystal structures of the two new solvates were solved from their Synchrotron-PXRD pattern: the solvates are isostructural, with equivalent triclinic packing. In both structures acetic acid and 2-pyrrolidone showed a strong interaction with the PZQ molecule via hydrogen bond. Even though previous studies have shown that PZQ is conformationally flexible, the same syn conformation as the PZQ Form A of the C=O groups of the piperazinone-cyclohexylcarbonyl segment is involved in these two new solid forms. In terms of biopharmaceutical properties, PZQ-AA and PZQ-2P exhibited water solubility and intrinsic dissolution rate much greater than those of anhydrous Form A.

Drug Discovery and Target Identification against Schistosomiasis: a Reality Check on Progress and Future Prospects

Schistosomiasis ranks among the most important infectious diseases, with over 200 million people currently being infected and > 280,000 deaths reported annually. Chemotherapeutic treatment has relied on one drug, praziquantel, for four decades, while other drugs, such as oxamniquine and metrifonate, are no longer preferred for clinical use due to their narrow spectrum of activity - these are only active against S. mansoni and S. haematobium, respectively. Despite being cheap, safe, and effective against all schistosome species, praziquantel is ineffective against immature worms, which may lead to reinfections and treatment failure in endemic areas; a situation that necessitates repeated administration besides other limitations. Therefore, novel drugs are urgently needed to overcome this situation. In this paper, an up to date review of drug targets identified and validated against schistosomiasis while also encompassing promising clinical and preclinical candidate drugs is presented. While there are considerable efforts aimed at identifying and validating drug targets, the pipeline for new antischistosomals is dry. Moreover, the majority of compounds evaluated preclinically are not really advanced because most of them were evaluated in very small preclinical species such as mice alone. Overall, it appears that although a lot of research is going on at discovery phases, unfortunately, it does not translate to advanced preclinical and clinical evaluation.

Effect of Pharmacogenetics Variations on Praziquantel Plasma Concentrations and Schistosomiasis Treatment Outcomes Among Infected School-Aged Children in Tanzania

Studies on pharmacogenetics of praziquantel (PZQ) and its relevance on plasma drug concentrations and schistosomiasis treatment outcomes are lacking. We investigated the effect of pharmacogenetics variations of PZQ on plasma drug levels and schistosomiasis treatment outcomes among infected Tanzanian school-aged children. A total of 340 Schistosoma mansoni infected children were enrolled and treated with single-dose PZQ. Stool samples analysis was done by thick smear Kato-Katz technique, and treatment efficacy was assessed at 3-weeks post-treatment. Safety was assessed within 4 h after PZQ intake. Plasma samples were collected at 4 h post-dose, and PZQ and trans-4-OH-PZQ concentrations were quantified using UPLCMS/MS. Genotyping for CYP3A4*1B, CYP3A5 (*3, *6, *7), CYP2C19 (*2, *3, *17), and CYP2C9 (*2, *3) were done by Real-Time PCR. The median age (range) of the study participants was 12 years (7-17). There was a significant association of CYP2C19 genotypes with PZQ concentrations and its metabolic ratio (trans-4-OH-PZQ/PZQ). PZQ concentration was significantly higher among CYP2C19 (*2, *3) carriers than CYP2C19 *1/*1 and CYP2C19 *17 carriers (ultra-rapid metabolizers) (p = 0.04). The metabolic ratio was significantly higher among CYP2C19*17 carriers than CYP2C19 (*2, *3) carriers (p = 0.01). No significant effect of CYP3A4, CYP3A5, CYP2C19, and CYP2C9 genotypes on treatment efficacy or adverse events were observed. Baseline infection intensity and CYP3A5 genotype were significant predictors of treatment associated-adverse events. In conclusion, CYP2C19 genotype significantly affects plasma PZQ concentration and its metabolic ratio. For the first time, we report the importance of pharmacogenetic variation for the treatment of schistosomiasis, a neglected tropical disease.

Optimal single sampling time-point for monitoring of praziquantel exposure in children

Praziquantel pharmacokinetics studies in schistosomiasis infected children are scarce partly due to the challenges/complexity of intensive blood sampling in the target population. This study was aimed to investigate the optimal single sampling time-point for monitoring praziquantel exposure. This was intensive pharmacokinetic study conducted among 32 Schistosoma mansoni infected children treated with an oral standard single-dose 40 mg/kg praziquantel. Plasma samples were collected at 0, 1, 2, 4, 6 and 8 h post-praziquantel administration. Quantification of praziquantel and its enantiomers (R- and S-praziquantel) concentrations was done by Liquid chromatography-tandem mass spectrometer (LC-MS/MS). The correlation between area under the plasma concentration-time curve from 0 to 8 h (AUC₈) and plasma concentrations at each specific sampling time-point was determined by Pearson's correlation coefficient (r²). The median age (range) of the study population was 12.5 years (10-17). The study participants were 17 males and 15 females. Both total praziquantel and its enantiomers (R- and S-praziquantel) displayed a wide inter-individual pharmacokinetic variability. Regression analysis indicated that, plasma concentrations collected at 4 h post-dose had a significantly highest correlation with the AUC₈ for both total praziquantel (r² = 0.81, p < 0.001) and S-praziquantel (r² = 0.84, p < 0.001) than any other sampling time-point; while for R-praziquantel, plasma concentrations collected at 6 h sampling time-point had a significantly highest correlation with the AUC₈ (r² = 0.79, p < 0.001) than any other sampling time-point. Four hours sampling time-point post-praziquantel administration is ideal optimal single sampling time-point for therapeutic monitoring of total praziquantel exposure while 6 h sampling time-point is suitable for monitoring of a pharmacologically active R-praziquantel enantiomer.

Direct Powder Extrusion 3D Printing of Praziquantel to Overcome Neglected Disease Formulation Challenges in Paediatric Populations

For the last 40 years, praziquantel has been the standard treatment for schistosomiasis, a neglected parasitic disease affecting more than 250 million people worldwide. However, there is no suitable paediatric formulation on the market, leading to off-label use and the splitting of commercial tablets for adults. In this study, we use a recently available technology, direct powder extrusion (DPE) three-dimensional printing (3DP), to prepare paediatric Printlets™ (3D printed tablets) of amorphous solid dispersions of praziquantel with Kollidon^® VA 64 and surfactants (Span™ 20 or Kolliphor^® SLS). Printlets were successfully printed from both pellets and powders obtained from extrudates by hot melt extrusion (HME). In vitro dissolution studies showed a greater than four-fold increase in praziquantel release, due to the formation of amorphous solid dispersions. In vitro palatability data indicated that the printlets were in the range of praziquantel tolerability, highlighting the taste masking capabilities of this technology without the need for additional taste masking excipients. This work has demonstrated the possibility of 3D printing tablets using pellets or powder forms obtained by HME, avoiding the use of filaments in fused deposition modelling 3DP. Moreover, the main formulation hurdles of praziquantel, such as low drug solubility, inadequate taste, and high and variable dose requirements, can be overcome using this technology.

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.

Comparative palatability of orally disintegrating tablets (ODTs) of Praziquantel (L-PZQ and Rac-PZQ) versus current PZQ tablet in African children: A randomized, single-blind, crossover study

BACKGROUND

Praziquantel (PZQ) is currently the only recommended drug for infection and disease caused by the schistosome species that infects humans; however, the current tablet formulation is not suitable for pre-school age children mainly due to its bitterness and the large tablet size. We assessed the palatability of two new orally disintegrating tablet (ODT) formulations of PZQ.

METHODOLOGY

This randomized, single-blind, crossover, swill-and-spit palatability study (NCT02315352) was carried out at a single school in Tanzania in children aged 6-11 years old, with or without schistosomiasis infection as this was not part of the assessment. Children were stratified according to age group (6-8 years or 9-11 years) and gender, then randomized to receive each formulation in a pre-specified sequence. Over 2 days, the children assessed the palatability of Levo-Praziquantel (L-PZQ) ODT 150 mg and Racemate Praziquantel (Rac-PZQ) ODT 150 mg disintegrated in the mouth without water on the first day, and L-PZQ and Rac-PZQ dispersed in water and the currently available PZQ 600 mg formulation (PZQ-Cesol) crushed and dispersed in water on the second day. The palatability of each formulation was rated using a 100 mm visual analogue scale (VAS) incorporating a 5-point hedonic scale, immediately after spitting out the test product (VASt = 0 primary outcome) and after 2-5 minutes (VASt = 2-5).

PRINCIPAL FINDINGS

In total, 48 children took part in the assessment. Overall, there was no reported difference in the VASt = 0 between the two ODT formulations (p = 0.106) without water. Higher VASt = 0 and VASt = 2-5 scores were reported for L-PZQ ODT compared with Rac-PZQ ODT in older children (p = 0.046 and p = 0.026, respectively). The VASt = 0 and VASt = 2-5 were higher for both ODT formulations compared with the standard formulation (p<0.001 for both time points). No serious adverse events were reported.

CONCLUSIONS/SIGNIFICANCE

The new paediatric-friendly formulations dispersed in water were both found to be more palatable than the existing standard formulation of PZQ. There may be gender and age effects on the assessment of palatability. Further research is needed for assessing efficacy and tolerability of the newly ODTs Praziquantel drug in younger children.

TRIAL REGISTRATION

The trial was registered on ClinicalTrials.gov (NCT02315352) and in the Pan African Clinical Trials Registry (PACTR201412000959159).

Schistosomiasis Drug Discovery in the Era of Automation and Artificial Intelligence

Schistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma and affects over 200 million people worldwide. The control and treatment of this neglected tropical disease is based on a single drug, praziquantel, which raises concerns about the development of drug resistance. This, and the lack of efficacy of praziquantel against juvenile worms, highlights the urgency for new antischistosomal therapies. In this review we focus on innovative approaches to the identification of antischistosomal drug candidates, including the use of automated assays, fragment-based screening, computer-aided and artificial intelligence-based computational methods. We highlight the current developments that may contribute to optimizing research outputs and lead to more effective drugs for this highly prevalent disease, in a more cost-effective drug discovery endeavor.

Congeners Derived from Microtubule-Active Phenylpyrimidines Produce a Potent and Long-Lasting Paralysis of Schistosoma mansoni In Vitro

Schistosomiasis is a parasitic disease that affects approximately 200 million people in developing countries. Current treatment relies on just one partially effective drug, and new drugs are needed. Tubulin and microtubules (MTs) are essential constituents of the cytoskeleton in all eukaryotic cells and considered potential drug targets to treat parasitic infections. The α- and β-tubulin of Schistosoma mansoni have ∼96% and ∼91% sequence identity to their respective human tubulins, suggesting that compounds which bind mammalian tubulin may interfere with MT-mediated functions in the parasite. To explore the potential of different classes of tubulin-binding molecules as antischistosomal leads, we completed a series of in vitro whole-organism screens of a target-based compound library against S. mansoni adults and somules (postinfective larvae), and identified multiple biologically active compounds, among which phenylpyrimidines were the most promising. Further structure-activity relationship studies of these hits identified a series of thiophen-2-yl-pyrimidine congeners, which induce a potent and long-lasting paralysis of the parasite. Moreover, compared to the originating compounds, which showed cytotoxicity values in the low nanomolar range, these new derivatives were 1-4 orders of magnitude less cytotoxic and exhibited weak or undetectable activity against mammalian MTs in a cell-based assay of MT stabilization. Given their selective antischistosomal activity and relatively simple drug-like structures, these molecules hold promise as candidates for the development of new treatments for schistosomiasis.

Effect of Dihydroartemisinin-Piperaquine on the Pharmacokinetics of Praziquantel for Treatment of Schistosoma mansoni Infection

Praziquantel (PZQ) and dihydroartemisinin-piperaquine (DHP) combination recently showed superior effectiveness than PZQ alone to treat intestinal schistosomiasis. In this follow-up study, we investigated the effect of DHP co-administration on the pharmacokinetics of PZQ and its enantiomers among 64 Schistosoma mansoni infected children treated with PZQ alone (n = 32) or PZQ + DHP combination (n = 32). Plasma samples collected at 0, 1, 2, 4, 6, and 8 h post-dose were quantified using UPLCMS/MS. The geometric mean (GM) of AUCs for total PZQ, R-PZQ and S-PZQ were significantly higher among children who received PZQ + DHP than PZQ alone. The geometric mean ratio (GMR) and (90% CI) of AUC_0–∞ for PZQ + DHP to PZQ for total PZQ, R-PZQ, and S-PZQ were 2.18 (1.27, 3.76), 3.98 (2.27, 7.0) and 1.86 (1.06, 3.28), respectively. The GMR and (90% CI) of AUC_0–8 for total PZQ, R-PZQ, and S-PZQ were 1.73 (1.12, 2.69), 2.94 (1.75, 4.92), and 1.50 (0.97, 2.31), respectively. The GM of C_max for total PZQ, R-PZQ and S-PZQ were significantly higher among those who received PZQ + DHP than PZQ alone. The GMR (90% CI) of C_max of PZQ + DHP to PZQ for total PZQ, R-PZQ, and S-PZQ were 1.75 (1.15, 2.65), 3.08 (1.91, 4.96), and 1.50 (1.0, 2.25%), respectively. The 90% CI of the GMRs for both AUCs and C_max for total PZQ, R-PZQ, and S-PZQ were outside the acceptable 0.80–1.25 range, indicating that the two treatment arms were not bioequivalent. DHP co-administration significantly increases systemic PZQ exposure, and this may contribute to increased effectiveness of PZQ + DHP combination therapy than PZQ alone to treat schistosomiasis.

Different Inductive Effects of Praziquantel Racemate and its Enantiomers on the Enzyme CYP3A4 Mediated by Pregnane X Receptor and its Variants

BACKGROUND

Praziquantel (PZQ), which possesses an asymmetric center, is classified as a pyrazinoisoquinoline and has been the mainstay in the treatment of schistosomiasis since 1980. PZQ undergoes a pronounced first-pass metabolism in the liver through the CYP450 system which could be mediated by nuclear receptors.

OBJECTIVE

The purpose of this study was to investigate the possible different induction effects of CYP3A4 by PZQ racemate and enantiomers via the pregnane X receptor (PXR) and the effect of PXR polymorphism on the induction potency of PZQs.

METHODS

The dual-luciferase reporter gene systems constructed in HepG2 cells were used to measure the abilities of PZQs to induce CYP3A4 expression mediated by PXR. The mRNA and protein levels of CYP3A4 were evaluated by polymerase chain reaction (PCR) and western blotting, respectively.

RESULTS

In HepG2 cells transfected with PXRwt, PXR158, PXR163, PXR370 or PXR403 expression plasmids, PZQ racemate and its enantiomers up-regulated the luciferase activity in a concentration-dependent manner, while reaching saturation after transfected with PXR379 expression plasmids. The mRNA and protein expression of CYP3A4 was effectively activated in PXR-transfected HepG2 cells. The induction ability of CYP3A4 mediated by PXR activation by PZQ racemate and its enantiomers were statistically different between the same PXR group and different PXR groups.

CONCLUSION

The enantioselective induction effects of PZQs on CYP3A4 were related to the enantioselective activations of PXR by PZQs and were influenced by the PXR gene polymorphism. These findings provide a basis for further understanding the enantiomeric metabolism and the variable efficacy of PZQs.

Target animal safety evaluation of a novel topical combination of esafoxolaner, eprinomectin and praziquantel for cats

The safety profile of NexGard® Combo, a novel topical product for cats combining esafoxolaner, eprinomectin and praziquantel, for the treatment and prevention of internal and external parasites, was evaluated in kittens, in two margin-of-safety studies (Studies #1 and #2), and in an oral tolerance study (Study #3). In the margin of safety studies, kittens were dosed several times topically with multiples of the maximum exposure dose (1×): in Study #1, 3× and 5× doses four times at 2-week intervals; in Study #2, 1×, 3× and 5× doses six times at 4-week intervals. In Study #3, kittens were dosed orally once with a 1× dose. Furthermore, in Study #1, another group of kittens was dosed topically twice at a 4-week interval with a formulation of esafoxolaner as the sole active ingredient dosed at 23×. Physical examinations and clinical pathology analyses were performed throughout the studies, followed by necropsy and detailed histopathological evaluation in Studies #1 and #2. No significant treatment related effects were observed in the three studies, except for one occurrence of reversible neurological signs attributed to eprinomectin in one cat after the third 5× dose in Study #2, with clinical signs observed nine hours after dosing, pronounced for a few hours, significantly improved the next day, and absent 2 days after dosing. In conclusion, NexGard® Combo was demonstrated safe in kittens following repeated topical administrations and following oral ingestion, and very high topical doses of esafoxolaner were well tolerated.

Drug metabolism and pharmacokinetics of praziquantel: A review of variable drug exposure during schistosomiasis treatment in human hosts and experimental models

Schistosomiasis control is heavily reliant on the drug praziquantel (PZQ), which is used as preventive chemotherapy as part of national helminth control strategies. Given the heavy reliance on PZQ for mass drug administration, there has been considerable research on the potential of parasites developing resistance to the drug, resulting in decreased drug efficacy. However, there have been comparatively fewer studies of other factors that can potentially alter PZQ efficacy. Here, we investigate whether host PZQ metabolism contributes towards variable cure rates. We evaluate factors that can influence the metabolism of PZQ and the resultant effect on the efficacy of PZQ treatment to determine factors that potentially influence an individual's response to the drug. The literature search was directed at published studies from three online databases: Web of Science, PubMed, and EMBASE. The search terms for the review comprised of ([praziquantel OR PZQ] AND [schistosom* OR bilharzia] AND [pharmaco*]) and included studies evaluating PZQ metabolism. Publications were categorised into pharmacokinetics, drug-drug interactions, pharmacogenetics, and metabolite analysis. Forty publications describing human and experimental studies fitted the inclusion criteria and were subjected to data extraction and analysis. The analyses showed that variable exposure to PZQ was associated with alterations in the liver's capacity to metabolise PZQ and observed drug-drug interactions. Other factors influencing the efficacy of PZQ were brand, formulation, and co-administered food. Although some work has been performed on metabolite identification, there was minimal information on PZQ's metabolic pathway, and no pharmacogenetics studies were identified. The study indicated that in both human and experimental studies alterations in the liver's capacity to metabolise PZQ as well as drug-drug interactions affected systemic levels of PZQ that could result in variable cure rates. The study confirmed previous findings of higher antischistosomal activity of (R)-PZQ enantiomer when administered alone compared to the racemate at the same dose as well as improved efficacy when the drug is administered with food. The study also highlighted the need for more comprehensive studies of the PZQ metabolic pathway and PZQ pharmacogenetic studies in humans.

Schistosome TRP channels: An appraisal

Ion channels underlie electrical excitability in cells and are essential for a variety of functions, most notably neuromuscular and sensory activity. They are also validated targets for a preponderance of approved anthelmintic compounds. Transient receptor potential (TRP) channels constitute an ion channel superfamily whose members play important roles in sensory signaling, regulation of ion homeostasis, organellar trafficking, and other key cellular and organismal activities. Unlike most other ion channels, TRP channels are often polymodal, gated by a variety of mechanisms. Furthermore, TRP channels fall into several classes or subtypes based on sequence and structure. Until recently, there had been very little investigation of the properties and functions of TRP channels from parasitic helminths, including schistosomes, but that situation has changed in the past few years. Indeed, it is now clear that at least some schistosome TRP channels exhibit unusual pharmacological properties, and, intriguingly, both a mammalian and a schistosome TRP channel are activated by praziquantel, the current antischistosomal drug of choice. With the latest release of the Schistosoma mansoni genome database, several changes in predicted TRP channel sequences appeared, some of which were significant. This review updates and reassesses the TRP channel repertoire in S. mansoni, examines recent findings regarding these potential therapeutic targets, and provides guideposts for some of the physiological functions that may be mediated by these channels in schistosomes.

Structural basis for the function and inhibition of dihydroorotate dehydrogenase from Schistosoma mansoni

Schistosomiasis is a serious public health problem, prevalent in tropical and subtropical areas, especially in poor communities without access to safe drinking water and adequate sanitation. Transmission has been reported in 78 countries, and its control depends on a single drug, praziquantel, which has been used over the past 30 years. Our work is focused on exploiting target-based drug discovery strategies to develop new therapeutics to treat schistosomiasis. In particular, we are interested in evaluating the enzyme dihydroorotate dehydrogenase (DHODH) as a drug target. DHODH is a flavoenzyme that catalyzes the stereospecific oxidation of (S)-dihydroorotate (DHO) to orotate during the fourth and only redox step of the de novo pyrimidine nucleotide biosynthetic pathway. Previously, we identified atovaquone, used in the treatment of malaria, and its analogues, as potent and selective inhibitors against Schistosoma mansoni DHODH (SmDHODH). In the present article, we report the first crystal structure of SmDHODH in complex with the atovaquone analogue inhibitor 2-((4-fluorophenyl)amino)-3-hydroxynaphthalene-1,4-dione (QLA). We discuss three major findings: (a) the open conformation of the active site loop and the unveiling of a novel transient druggable pocket for class 2 DHODHs; (b) the presence of a protuberant domain, only present in Schistosoma spp DHODHs, that was found to control and modulate the dynamics of the inhibitor binding site; (c) a detailed description of an unexpected binding mode for the atovaquone analogue to SmDHODH. Our findings contribute to the understanding of the catalytic mechanism performed by class 2 DHODHs and provide the molecular basis for structure-guided design of SmDHODH inhibitors. DATABASE: The structural data are available in Protein Data Bank (PDB) database under the accession code number 6UY4.

Preparation and characterization of a new solid form of praziquantel, an essential anthelmintic drug. Praziquantel racemic monohydrate

Praziquantel (PZQ) is a highly effective low-cost anthelmintic agent used as the first-choice treatment against schistosomiasis. The low solubility of the active is a major drawback for pharmaceutical formulation. A valid approach of the pharmaceutical industry for the improvement of the pharmacotechnical features of the active principles (such as solubility, processability, stability, among others), is the preparation of new solid forms, such as salts, polymorph, and pseudo-polymorph. Herein we report the preparation and characterization of a new solid form PZQ. The PZQ monohydrate (PZQ-MH) was prepared by a solventless procedure from the commercial racemate and the product was characterized at the solid-state employing optical digital microscopy, thermal methods (melting point, differential scanning calorimetry and thermogravimetric analysis), as well as and mid-infrared and near infrared spectroscopies. The chemical structure and content of water were full assessed by ¹H nuclear magnetic resonance (NMR) in solution. The amount of water in PZQ-was also determined by different approaches, including thermogravimetric analysis and the loss on drying test. Solid-state ¹³C NMR (ssNMR) and X-ray powder diffraction (XRPD) completed the structural characterization of the new monohydrate. PZQ-MH showed a crystalline behavior during XRPD experiments and showed relevant differences in spectroscopic, calorimetric, ssNMR and XRPD signals when it was compared with the known crystal (Form A) and amorphous forms of PZQ. The determination of the intrinsic dissolution rate (IDR) of PZQ-MH was carried out as a functional characterization, observing that the new form had slightly higher IDR than Form A.

Mechanochemical Formation of Racemic Praziquantel Hemihydrate with Improved Biopharmaceutical Properties

Praziquantel (PZQ) is the first-line drug used against schistosomiasis, one of the most common parasitic diseases in the world. A series of crystalline structures including two new polymorphs of the pure drug and a series of cocrystals of PZQ have been discovered and deposited in the Cambridge Structural Database (CSD). This work adds to the list of multicomponent forms of PZQ a relevant example of a racemic hemihydrate (PZQ-HH), obtainable from commercial PZQ (polymorphic Form A) through mechanochemistry. Noteworthy, the formation of the new hemihydrate strongly depends on the initial polymorphic form of PZQ and on the experimental conditions used. The new PZQ-HH has been fully characterized by means of HPLC, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Hot-Stage Microscopy (SEM), Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), FT-IR, polarimetry, solid-state NMR (SS-NMR), solubility and intrinsic dissolution rate (IDR), and in vitro tests on Schistosoma mansoni adults. The crystal structure was solved from the powder X-ray diffraction pattern and validated by periodic-DFT calculations. The new bioactive hemihydrate was physically stable for three months and showed peculiar biopharmaceutical features including enhanced solubility and a double intrinsic dissolution rate in water in comparison to the commercially available PZQ Form A.

Insights into Praziquantel Metabolism and Potential Enantiomeric Cytochrome P450-Mediated Drug-Drug Interaction

The active enantiomer R-Praziquantel (PZQ) shows a clinically lower relative exposure when administered enantiomerically pure compared with a racemic form. We investigated the hypothesis that enantiomer-enantiomer interactions on cytochrome P450 (P450) enzymes could explain this observation and aimed to further deepen the understanding of PZQ metabolism. First, in an in vitro metabolite profiling study, the formation of multiple metabolites per P450, together with an observed interconversion of cis-4'-OH-PZQ to trans-4'-OH-PZQ in human hepatocytes, pointed out the inadequacy of measuring metabolite formation in kinetic studies. Thus, a substrate depletion approach to study PZQ enantiomeric interactions was applied. Second, an abundant CYP3A4 metabolite found in previous studies was structurally characterized. Third, substrate depletion methodologies were applied to determine P450 enzyme kinetics of PZQ and to further estimate enantiomer-enantiomer inhibitory parameters. A competitive inhibition between PZQ enantiomers for CYP2C9, 2C19, 3A4, and 3A5 was revealed. Analyses considering the clearance of only one or both enantiomers provided comparable enantiomer-enantiomer inhibition estimates. To conclude, this paper provides new insights into PZQ metabolic profile to enable a better understanding of enantioselective pharmacokinetics using substrate depletion-based methods. SIGNIFICANCE STATEMENT: In this study, enantiomer-enantiomer interactions of praziquantel on cytochrome P450 metabolizing enzymes are investigated via substrate depletion measurement using modeling methods. Together with new insights into the praziquantel metabolism, this work provides a novel data set to understand its pharmacokinetics.

Praziquantel: An Enigmatic, Yet Effective, Drug

Praziquantel is a remarkably effective drug for the treatment of schistosomiasis. It has few side effects, some of which have been attributed to its inactive enantiomer. Few, if any, verified cases of drug resistance have been reported in a clinical setting. The preponderance of scientific evidence suggests that the drug works by dysregulating calcium homeostasis in the worm. Voltage-gated calcium channels have been proposed as the main pharmacological target of praziquantel, although no direct evidence of interaction with this protein is available. Here, the biochemical pharmacology of praziquantel is briefly reviewed and a hypothesis for its mechanism proposed. This hypothesis suggests that the drug works, in part, by disrupting an interaction between a voltage-gated calcium channel (SmCav1B) and an accessory protein, SmTAL1.

Exploring mechanochemical parameters using a DoE approach: Crystal structure solution from synchrotron XRPD and characterization of a new praziquantel polymorph

A rotated Doehlert matrix was utilized to explore the experimental design space around the milling parameters of Praziquantel (PZQ) polymorph B formation in terms of frequency and milling time. Three experimental responses were evaluated on the resulting ground samples: two quantitative responses, i.e. median particle size by Laser Light scattering (LLS) and drug recovery by HPLC, and one qualitative dependent variable, i.e. the obtained PZQ crystalline form, characterized through X-Ray Powder Diffraction (XRPD) and confirmed by Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA). Temperature inside the jars was kept under constant control during the milling process by using temperature sensor equipped jars (thermojars), thus allowing evaluation of the obtained solid states at each experimental point, considering the specific temperature of the process. This explorative analysis led to the finding of a novel PZQ polymorph, named "Form C", produced without degradation, then fully characterized, including by means of Synchrotron XRPD, Polarimetric, FT-IR, SS-NMR, ESEM and saturation solubility. Crystal structure was solved from XRPD data and its geometry was optimized by DFT calculations (CASTEP). Finally, Form C and Form A activity against adult schistosoma mansoni were compared through in vitro testing, and Form C's physical stability checked. The new polymorph, crystallizing in space group I2/c, physically stable for approximately 2 months, showed a m.p. of 106.84 °C and displayed excellent biopharmaceutical properties (water solubility of 382.69±9.26 mg/l), while preserving excellent activity levels against adult schistosoma mansoni.

The Journey to Discovering a Flatworm Target of Praziquantel: A Long TRP

Infections caused by parasitic flatworms impose a considerable worldwide health burden. One of the most impactful is schistosomiasis, a disease caused by parasitic blood flukes. Treatment of schistosomiasis has relied on a single drug - praziquantel (PZQ) - for decades. The utility of PZQ as an essential medication is, however, intertwined with a stark gap in our knowledge as to how this drug works. No flatworm target has been identified that readily explains how PZQ paralyzes and damages schistosomes. Recently, a schistosome ion channel was discovered that is activated by PZQ and displays characteristics which mirror key features of PZQ action on schistosomes. Here, the journey to discovery of this target, properties of this ion channel, and remaining questions are reviewed.

Use of praziquantel to control platyhelminth parasites of fish

Fish are common definitive and intermediate hosts for a variety of parasitic flatworms. In unstressed wild populations, parasitic infections often go unnoticed and are perceived to represent a lesser threat to fish health. In contrast, platyhelminth parasitism of captive fish often results in decreased weight gain and increased mortality which often necessitates chemotherapeutic treatment. The presence of platyhelminth parasites in fish tissues is not only unappealing but in some cases also represents a threat to human health. In veterinary medicine, one of the most commonly used agents with anti-flatworm activity is praziquantel; yet, no praziquantel products are labeled for use in fish in the United States. Veterinarians may use praziquantel preparations approved for other vertebrate species under the Animal Medicinal Drug Use Clarification Act (AMDUCA). However, such extra-label use should be informed by scientific evidence including efficacy and tissue residue studies. Herein, we review studies testing the efficacy of praziquantel for treatment of platyhelminthes along with an assessment of routes of administration, pharmacokinetics, and toxicity information.