Evaluation of the pharmacokinetic-pharmacodynamic relationship of praziquantel in the Schistosoma mansoni mouse model

Mechanisms of Arachidonic Acid In Vitro Schistosomicidal Potential

Arachidonic acid (ARA) was shown to possess safe and effective schistosomicidal impact on larval and adult Schistosoma mansoni and Schistosoma hematobium in vitro and in vivo in laboratory rodents and in children residing in low and high endemicity regions. We herein examine mechanisms underlying ARA schistosomicidal potential over two experiments, using in each pool a minimum of 50 adult male, female, or mixed-sex freshly recovered, ex vivo S. mansoni. Worms incubated in fetal calf serum-free medium were exposed to 0 or 10 mM ARA for 1 h at 37 °C and immediately processed for preparation of surface membrane and whole worm body homogenate extracts. Mixed-sex worms were additionally used for evaluating the impact of ARA exposure on the visualization of outer membrane cholesterol, sphingomyelin (SM), and ceramide in immunofluorescence assays. Following assessment of protein content, extracts of intact and ARA-treated worms were examined and compared for SM content, neutral sphingomyelinase activity, reactive oxygen species levels, and caspase 3/7 activity. Arachidonic acid principally led to perturbation of the organization, integrity, and SM content of the outer membrane of male and female worms and additionally impacted female parasites via stimulating neutral sphingomyelinase activity and oxidative stress. Arachidonic powerful action on female worms combined with its previously documented ovocidal activities supports its use as safe and effective therapy against schistosomiasis, provided implementation of the sorely needed and long waited-for chemical synthesis.

Robenidine derivatives as potential antischistosomal drug candidates

Schistosomiasis caused by Schistosoma spp. is a disease that causes a considerable health burden to millions of people worldwide. The limited availability of effective drugs on the market and the increased risk of resistance development due to extensive usage, highlight the urgent need for new antischistosomal drugs. Recent studies have shown that robenidine derivatives, containing an aminoguanidine core, exhibit promising activities against Plasmodium falciparum, motivating further investigation into their efficacy against Schistosoma mansoni, due to their similar habitat and the resulting related cellular mechanisms like the heme detoxification pathway. The conducted phenotypic screening of robenidine and 80 derivatives against newly transformed schistosomula and adult Schistosoma mansoni yielded 11 candidates with low EC50 values for newly transformed schistosomula (1.12-4.63 μM) and adults (2.78-9.47 μM). The structure-activity relationship revealed that electron-withdrawing groups at the phenyl moiety, as well as the presence of methyl groups adjacent to the guanidine moiety, enhanced the activity of derivatives against both stages of Schistosoma mansoni. The two compounds 2,2'-Bis[(3-cyano-4-fluorophenyl)methylene] carbonimidic Dihydrazide Hydrochloride (1) and 2,2'-Bis[(4-difluoromethoxyphenyl) ethylidene] carbonimidic Dihydrazide Hydrochloride (19), were selected for an in vivo study in Schistosoma mansoni-infected mice based on their potency, cytotoxicity, pharmacokinetic-, and physicochemical properties, but failed to reduce the worm burden significantly (worm burden reduction <20%). Thus, robenidine derivatives require further refinements to obtain higher antischistosomal specificity and in vivo activity.

Metabolism of (R)-Praziquantel versus the Activation of a Parasite Transient Receptor Potential Melastatin Ion Channel

Praziquantel (PZQ) is an essential anthelmintic drug recently established to be an activator of a Transient Receptor Potential Melastatin (TRPMPZQ ) ion channel in trematode worms. Bioinformatic, mutagenesis and drug metabolism work indicate that the cyclohexyl ring of PZQ is a key pharmacophore for activation of trematode TRPMPZQ , as well as serving as the primary site of oxidative metabolism which results in PZQ being a short-lived drug. Based on our recent findings, the hydrophobic cleft in schistosome TRPMPZQ defined by three hydrophobic residues surrounding the cyclohexyl ring has little tolerance for polarity. Here we evaluate the in vitro and in vivo activities of PZQ analogues with improved metabolic stability relative to the challenge of maintaining activity on the channel. Finally, an estimation of the respective contribution to the overall activity of both the parent and the main metabolite of PZQ in humans is reported.

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

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

Addressing the oxamniquine in vitro-in vivo paradox to facilitate a new generation of anti-schistosome treatments

The antischistosomal drug oxamniquine, OXA, requires activation by a sulfotransferase within the parasitic worm to enable killing. Examination of the pharmacokinetic/pharmacodynamic (PK/PD) relationship for OXA identified an in vitro-in vivo paradox with the maximal clinical plasma concentrations five-to ten-times lower than the efficacious concentration for in vitro schistosomal killing. The parasite resides in the vasculature between the intestine and the liver, and modeling the PK data to determine portal concentrations fits with in vitro studies and explains the required human dose. In silico models were used to predict murine dosing to recapitulate human conditions for OXA portal concentration and time course. Follow-up PK studies verified in mice that a 50-100 mg/kg oral gavage dose of OXA formulated in acetate buffer recapitulates the 20-40 mg/kg dose common in patients. OXA was rapidly cleared through a combination of metabolism and excretion into bile. OXA absorbance and tissue distribution were similar in wild-type and P-gp efflux transporter knockout mice. The incorporation of in vitro efficacy data and portal concentration was demonstrated for an improved OXA-inspired analog that has been shown to kill S. mansoni, S. haematobium, and S. japonicum, whereas OXA is only effective against S. mansoni. Second-generation OXA analogs should optimize both in vitro killing and physiochemical properties to achieve high portal concentration via rapid oral absorption, facilitated by favorable solubility, permeability, and minimal intestinal metabolism.

In Vitro and In Vivo Antischistosomal Activity Profiling and Pharmacokinetics of Ozonide Carboxylic Acids

Praziquantel, the only drug in clinical use for the treatment and control of schistosomiasis, is inactive against developing infections. Ozonides are synthetic peroxide derivatives inspired by the naturally occurring artemisinin and show particularly promising activity against juvenile schistosomes. We conducted an in-depth characterization of the in vitro and in vivo antischistosomal activity and pharmacokinetics of lead ozonide carboxylic acid OZ418 and four of its active analogs. In vitro, the ozonides featured rapid and consistent activity against schistosomula and adult schistosomes at double-digit micromolar EC50 values. Potency did not vary considerably between Schistosoma spp. The zwitterionic OZ740 and OZ772 were more active in vivo compared to their non-amphoteric carboxylic acids OZ418 and OZ748, despite their much lower systemic plasma exposure (AUC). The most active compound in vivo was ethyl ester OZ780, which was rapidly transformed to its parent zwitterion OZ740 and achieved ED50 values of 35 ± 2.4 and 29 ± 2.4 mg/kg against adult and juvenile Schistosoma mansoni, respectively. Ozonide carboxylic acids represent promising candidates for further optimization and development due to their good efficacy against both life stages together with their broad activity range against all relevant parasite species.

In vivo efficiency of praziquantel treatment of single-sex Schistosoma japonicum aged three months old in mice

Schistosomiasis is a major neglected tropical disease mainly caused by Schistosoma haematobium, S. japonicum and S. mansoni, and results in the greatest disease burden. Mass drug administration (MDA) with praziquantel (PZQ), a single drug only available for the disease, has played a vital role in schistosomiasis control. Therefore, any possibility of selection of the parasites for PZQ resistance or low sensitivity may hamper the 2030's target of global disease elimination. We had experimentally demonstrated the long-term survival and reproductive potential of single-sex (of either sex) S. japonicum infections in definitive hosts mice. What has not yet been adequately addressed is whether the long live single-sex schistosomes remain sensitive to PZQ, and what reproduction potential for those schistosomes surviving treatment may have. We therefore performed experimental mice studies to explore the treatment effectiveness of PZQ (at total doses of 200 or 400 mg/kg, corresponding to the sub-standard or standard treatment doses in humans) for single-sex S. japonicum aged three months old. The results showed that no treatment efficiency was observed on female schistosomes, whereas on male schistosomes only at PZQ 400 mg/kg a significant higher efficiency in reducing worm burdens was observed. Moreover, either schistosome males or females surviving PZQ treatment remained their reproduction potential as normal. The results indicate that long (i.e., three months) live single-sex S. japonicum can easily survive the current treatment strategy, and moreover, any schistosomes, if with PZQ resistance or low sensitivity, could be easily transmitted in nature. Therefore, in order to realize the target for the national and the global schistosomiasis elimination, there is undoubtedly a great need for refining PZQ administration and dosage, looking for alternative therapies, and/or developing vaccines against schistosome.

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.

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

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

Case Report: Moving Tumor-Like Foci Behind Refractory Epilepsy-Cerebral Sparganosis Successfully Treated by Surgery After Failure of Praziquantel Treatment

Cerebral sparganosis is clinically non-specific and easily misdiagnosed, exposing patients to the risk of severe brain damage and neurological dysfunction caused by actively migrating larvae. Diagnostic biomarkers from typical cases can help to establish an early diagnosis and proper treatment. We present a 25-year-old woman who suffered from 9 years of refractory epilepsy and was misdiagnosed with glioma and subjected to surgery. The postoperative pathology confirmed granuloma, and the tumor-like foci reappeared 3 months later. Along with the “tunnel sign” on MRI, cerebral sparganosis was suspected and confirmed by positive serum and cerebrospinal fluid antibodies against Spirometra mansoni. The patient visited us after a failure of four cycles of praziquantel treatment, recurrent seizures and hemiplegia with basal ganglia foci. Craniotomy was not carried out until the larva moved to the superficial lobe on follow-up MRIs, and pathology revealed sparganosis granuloma. The patient became seizure-free and recovered myodynamia but had long-lasting cognitive dysfunction due to severe brain damage. This case indicated the importance of tunnel signs and moving tumor-like foci on MRI as diagnostic clues of cerebral sparganosis. An early diagnosis is vitally important to avoid severe neural dysfunction by the long-living and moving larvae. Surgical removal of the larva is a critical remedy for cases failed by praziquantel treatment.

ABO Blood Groups Do Not Predict Schistosoma mansoni Infection Profiles in Highly Endemic Villages of Uganda

Schistosoma mansoni is a parasite which causes significant public-health issues, with over 240 million people infected globally. In Uganda alone, approximately 11.6 million people are affected. Despite over a decade of mass drug administration in this country, hyper-endemic hotspots persist, and individuals who are repeatedly heavily and rapidly reinfected are observed. Human blood-type antigens are known to play a role in the risk of infection for a variety of diseases, due to cross-reactivity between host antibodies and pathogenic antigens. There have been conflicting results on the effect of blood type on schistosomiasis infection and pathology. Moreover, the effect of blood type as a potential intrinsic host factor on S. mansoni prevalence, intensity, clearance, and reinfection dynamics and on co-infection risk remains unknown. Therefore, the epidemiological link between host blood type and S. mansoni infection dynamics was assessed in three hyper-endemic communities in Uganda. Longitudinal data incorporating repeated pretreatment S. mansoni infection intensities and clearance rates were used to analyse associations between blood groups in school-aged children. Soil-transmitted helminth coinfection status and biometric parameters were incorporated in a generalised linear mixed regression model including age, gender, and body mass index (BMI), which have previously been established as significant factors influencing the prevalence and intensity of schistosomiasis. The analysis revealed no associations between blood type and S. mansoni prevalence, infection intensity, clearance, reinfection, or coinfection. Variations in infection profiles were significantly different between the villages, and egg burden significantly decreased with age. While blood type has proven to be a predictor of several diseases, the data collected in this study indicate that it does not play a significant role in S. mansoni infection burdens in these high-endemicity communities.

In vivo praziquantel efficacy of Schistosoma japonicum over time: A systematic review and meta-analysis

Praziquantel (PZQ), the only choice of chemotherapy for schistosomiasis recommended by World Health Organization (WHO), has been widely used over 40 years. The long-term, and rapid expansion of, PZQ use for disease control across a large populations continues to raise concern regarding the potential for emergence and establishment of drug resistance. Recent research has also proposed that the long survival and low sensitivity of unpaired worms, derived from either incomplete treatment cure rates or single-sex schistosome infections within final hosts, could exacerbate the risk of PZQ resistance (PZQ-R) emerging. With the aim of assessing whether PZQ efficacy amongst S. japonicum may have changed over time in China, we performed a unique systematic review and meta-analyses on datasets which evaluated the efficacy of PZQ via laboratory assays of field S. japonicum isolates on experimental mice over time. Relevant published literatures from four electronic bibliographic databases and lists of article references were searched. Two indexes, d, a measure used in meta-analyses for worm burden difference between two groups, and r, a traditional measure for worm reduction percentage after treatment but without considering sample size were calculated for each study. A total of 25 papers including 127 experimental studies with eligible data on 2230 mice were retrieved. The pooled d (D) was 3.91 (3.56-4.25) and pooled r (R) was 54.52% (52.55%-56.52%). D significantly increased over time, whereas R non-significantly decreased; both estimates were significantly associated with the total drug dose. Such findings suggested no evidence of PZQ-R emergence S. japonicum to date. However, we consider the potential role of parasite origins, PZQ dosage, and single versus mixed gender infections of the results published to date, and the avenues now needed for further research.

Alternatives to Praziquantel for the Prevention and Control of Schistosomiasis

Schistosomiasis, a neglected tropical disease provoked by infection with parasitic blood flukes of the genus Schistosoma, affects almost 240 million people worldwide, and more than 700 million people live in endemic areas. However, 40 years after the approval of praziquantel as an anthelmintic drug, the pipeline is nearly empty, and no other therapeutic alternative has reached the market. In its roadmap to "eliminate Schistosomiasis as a public health problem by 2030", the World Health Organization calls for the development of new therapeutic interventions. A viewpoint on the learnings from praziquantel research as well as shaping the next generation of drugs is shared.

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.

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

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

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

Activities of Quinoxaline, Nitroquinoxaline, and [1,2,4]Triazolo[4,3-a]quinoxaline Analogs of MMV007204 against Schistosoma mansoni

The reliance on one drug, praziquantel, to treat the parasitic disease schistosomiasis in millions of people a year shows the need to further develop a pipeline of new drugs to treat this disease. Recently, an antimalarial quinoxaline derivative (MMV007204) from the Medicines for Malaria Venture (MMV) Malaria Box demonstrated promise against Schistosoma mansoni In this study, 47 synthesized compounds containing quinoxaline moieties were first assayed against the larval stage of this parasite, newly transformed schistosomula (NTS); of these, 16 killed over 70% NTS at 10 µM. Further testing against NTS and adult S. mansoni yielded three compounds with 50% inhibitory concentrations (IC₅₀s) of ≤0.31 µM against adult S. mansoni and selectivity indices of ≥8.9. Administration of these compounds as a single oral dose of 400 mg/kg of body weight to S. mansoni -infected mice yielded only moderate worm burden reduction (WBR) (9.3% to 46.3%). The discrepancy between these compounds' good in vitro activities and their poor in vivo activities indicates that optimization of their pharmacokinetic properties may yield compounds with greater bioavailabilities and better antischistosomiasis activities in vivo.

Use of kinase inhibitors against schistosomes to improve and broaden praziquantel efficacy

Praziquantel (PZQ) is the drug of choice for schistosomiasis. The potential drug resistance necessitates the search for adjunct or alternative therapies to PZQ. Previous functional genomics has shown that RNAi inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII) gene in Schistosoma adult worms significantly improved the effectiveness of PZQ. Here we tested the in vitro efficacy of 15 selective and non-selective CaMK inhibitors against Schistosoma mansoni and showed that PZQ efficacy was improved against refractory juvenile parasites when combined with these CaMK inhibitors. By measuring CaMK activity and the mobility of adult S. mansoni, we identified two non-selective CaMK inhibitors, Staurosporine (STSP) and 1Naphthyl PP1 (1NAPP1), as promising candidates for further study. The impact of STSP and 1NAPP1 was investigated in mice infected with S. mansoni in the presence or absence of a sub-lethal dose of PZQ against 2- and 7-day-old schistosomula and adults. Treatment with STSP/PZQ induced a significant (47-68%) liver egg burden reduction compared with mice treated with PZQ alone. The findings indicate that the combination of STSP and PZQ dosages significantly improved anti-schistosomal activity compared to PZQ alone, demonstrating the potential of selective and non-selective CaMK/kinase inhibitors as a combination therapy with PZQ in treating schistosomiasis.

Systemic and Target-Site Pharmacokinetics of Antiparasitic Agents

About one-sixth of the world's population is affected by a neglected tropical disease as defined by the World Health Organization and Center for Disease Control. Parasitic diseases comprise most of the neglected tropical disease list and they are causing enormous amounts of disability, morbidity, mortality, and healthcare costs worldwide. The burden of disease of the top five parasitic diseases has been estimated to amount to a total 23 million disability-adjusted life-years. Despite the massive health and economic impact, most drugs currently used for the treatment of parasitic diseases have been developed decades ago and insufficient novel drugs are being developed. The current review provides a compilation of the systemic and target-site pharmacokinetics of established antiparasitic drugs. Knowledge of the pharmacokinetic profile of drugs allows for the examination and possibly optimization of existing dosing schemes. Many symptoms of parasitic diseases are caused by parasites residing in different host tissues. Penetration of the antiparasitic drug into these tissues, the target site of infection, is a prerequisite for a successful treatment of the disease. Therefore, for the examination and improvement of established dosing regimens, not only the plasma but also the tissue pharmacokinetics of the drug have to be considered. For the current paper, almost 7000 scientific articles were identified and screened from which 429 were reviewed in detail and 100 were included in this paper. Systemic pharmacokinetics are available for most antiparasitic drugs but in many cases, not for all the relevant patient populations and only for single- or multiple-dose administration. Systemic pharmacokinetic data in patients with organ impairment and target-site pharmacokinetic data for relevant tissues and body fluids are mostly lacking. To improve the treatment of patients with parasitic diseases, research in these areas is urgently needed.

Reassessing therapeutic antibodies for neglected and tropical diseases

In the past two decades there has been a significant expansion in the number of new therapeutic monoclonal antibodies (mAbs) that are approved by regulators. The discovery of these new medicines has been driven primarily by new approaches in inflammatory diseases and oncology, especially in immuno-oncology. Other recent successes have included new antibodies for use in viral diseases, including HIV. The perception of very high costs associated with mAbs has led to the assumption that they play no role in prophylaxis for diseases of poverty. However, improvements in antibody-expression yields and manufacturing processes indicate this is a cost-effective option for providing protection from many types of infection that should be revisited. Recent technology developments also indicate that several months of protection could be achieved with a single dose. Moreover, new methods in B cell sorting now enable the systematic identification of high-quality antibodies from humanized mice, or patients. This Review discusses the potential for passive immunization against schistosomiasis, fungal infections, dengue, and other neglected diseases.

Setting Our Sights on Infectious Diseases

In May 2019, the Wellcome Centre for Anti-Infectives Research (WCAIR) at the University of Dundee, UK, held an international conference with the aim of discussing some key questions around discovering new medicines for infectious diseases and a particular focus on diseases affecting Low and Middle Income Countries. There is an urgent need for new drugs to treat most infectious diseases. We were keen to see if there were lessons that we could learn across different disease areas and between the preclinical and clinical phases with the aim of exploring how we can improve and speed up the drug discovery, translational, and clinical development processes. We started with an introductory session on the current situation and then worked backward from clinical development to combination therapy, pharmacokinetic/pharmacodynamic (PK/PD) studies, drug discovery pathways, and new starting points and targets. This Viewpoint aims to capture some of the learnings.

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.

Enhancement of the therapeutic efficacy of praziquantel in murine Schistosomiasis mansoni using silica nanocarrier

The main objective of this work is preparation of mesoporous silica nanoparticles loaded with praziquantel (PZQ-Si) in order to enhance the therapeutic efficacy of praziquantel (PZQ). Mice were experimentally infected with Schistosoma mansoni and treated 6 weeks post-infection with PZQ in different doses via either oral or intraperitoneal (IP) routes. PZQ in the same doses orally administered to S. mansoni-infected mice was used as a drug control, and infected and non-infected non-treated mice served as positive and negative controls, respectively. PZQ-Si exhibited good physicochemical attributes in terms of small uniform size (105 nm), spherical shape, and PZQ entrapment efficiency (83%). A maximum antischistosomal effect was achieved using orally administered PZQ-Si as reflected by total worm burden, tissue egg count, oogram pattern, and hepatic granuloma count and diameter. The biomarkers related to liver oxidative stress status and immunomodulatory effect (serum TNF-α and IL-10) were significantly improved. Data obtained implied that IP route was less efficacious for the delivery of PZQ-Si. Encapsulation of PZQ permits the reduction of the used therapeutic dose of PZQ. Hepatic DNA fragmentation, measured by comet assay, was significantly improved in infected mice treated with maximum dose of PZQ-Si as compared to positive or PZQ control groups. The results indicate that mesoporous silica NP is a promising safe nanocarrier for PZQ potentiating its antischistosomal, antioxidant, immunomodulatory, and anti-inflammatory action in animal model infected with S. mansoni. From a practical standpoint, PZQ-Si using a lower dose of PZQ could be suggested for effective PZQ antischistosomal mass chemotherapy.

Activity and pharmacokinetics of a praziquantel crystalline polymorph in the Schistosoma mansoni mouse model

Schistosomiasis is a global disease of significant public health relevance. Only one racemic drug, praziquantel, characterized by low bioavailability, low water solubility and extensive first pass metabolism, is currently available. We studied a new praziquantel formulation (polymorph B), which is based on a racemic praziquantel crystalline polymorph (TELCEU01). Its in vitro activity was tested on newly transformed schistosomula (NTS) and adult Schistosoma mansoni. In vivo studies were conducted in mice harboring chronic S. mansoni infections. Pharmacokinetic (PK) profiles of R- and S-praziquantel and R- and S- polymorph B following oral administration with both formulations were generated by sampling mice at 30, 60, 240 min and 24 h post-treatment, followed by LC-MS/MS analysis. PK parameters were calculated using a non-compartmental analysis with a linear trapezoidal model. In vitro, commercial praziquantel and the polymorph B performed similarly on both NTS (IC₅₀ = 2.58 and 2.40 µg/mL at 72 h) and adults (IC₅₀ = 0.05 and 0.07 µg/mL at 72 h). Praziquantel showed higher in vivo efficacy with an ED₅₀ of 58.75 mg/kg compared to an ED₅₀ of 122.61 mg/kg for the polymorph B. The PK profiles of the two drugs exhibited differences: R-praziquantel showed an overall 40% higher area under the plasma drug concentration-time curve (AUC_0→24) (R-praziquantel = 3.42; R-polymorph B = 2.05 h*µg/mL) and an overall 30% lower apparent clearance (Cl/F) (R-praziquantel = 70.68 and R-polymorph B = 97.63 (mg)/(µg/mL)/h). Despite the lack of improved activity and PK properties of polymorph B against S. mansoni, here presented; research on pharmaceutical polymorphism remains a valid and cost-effective option for the development of new praziquantel formulations with enhanced properties such as increased solubility and/or dissolution.

Schistosomicidal and prophylactic activities of phthalimido-thiazoles derivatives on schistosomula and adult worms

Schistosomiasis is a major public health problem worldwide, especially in poor communities. Praziquantel is currently the only drug available to treat schistosomiasis and it shows low efficacy against schistosomula and juveniles stages of Schistosoma mansoni, allowing lower cure rate in areas with high endemicity. There is an urgent need to identify new antischistosomal drugs. Previous works identified phthalimido-thiazoles as privileged structures acting as schistossomicidal agent. In this way, a phthalimido-thiosemicarbazide intermediate and eight phthalimido-thiazoles derivatives were evaluated concerning the in vitro antischistosomal activity compounds in adult phase of Schistosoma mansoni and examined alterations on the tegumental surface. The results revealed that compounds 2f, 2 l and 2 m caused significant mortality in adult worms at concentrations range of 20 μg/mL to 100 μg/mL. These compounds were also selected in view to verify the activity against the schistosomula. Compound 2 m promoted 100% of mortality of larval forms until doses of 2.5 μg/mL within 48 h. In addition, when compound 2 m was administered orally at dose of 200 mg/kg for 5 consecutive days to the infected mouse with adult schistosomes, a reduction in the parasite burden was observed. Furthermore, scanning electron microscopy revealed that compound 2 m kill the parasite by tegumental damage and bubbles generation.

Praziquantel-lipid nanocapsules: an oral nanotherapeutic with potential Schistosoma mansoni tegumental targeting

Purpose

Lipid nanocapsules (LNCs) have shown potential to increase the bioavailability and efficacy of orally administered drugs. However, their intestinal translocation to distal target sites and their implication in pharmacokinetic (PK)–pharmacodynamic (PD) relationships are yet to be elucidated. In this study, the effect of LNCs on the PD activity and pharmacokinetics of praziquantel (PZQ), the mainstay of schistosomiasis chemotherapy, was investigated.

Materials and methods

The composition of LNCs was modified to increase PZQ payload and to enhance membrane permeability. PZQ–LNCs were characterized in vitro for colloidal properties, entrapment efficiency (EE%), and drug release. PD activity of the test formulations was assessed in Schistosoma mansoni-infected mice 7 days post-oral administration of a single 250 mg/kg oral dose. Pharmacokinetics of the test formulations and their stability in simulated gastrointestinal (GI) fluids were investigated to substantiate in vivo data.

Results

PZQ–LNCs exhibited good pharmaceutical attributes in terms of size (46–62 nm), polydispersity index (0.01–0.08), EE% (>95%), and sustained release profiles. Results indicated significant efficacy enhancement by reduction in worm burden, amelioration of liver pathology, and extensive damage to the fluke suckers and tegument. This was partly explained by PK data determined in rats. In addition, oral targeting of the worms was supported by the stability of PZQ–LNCs in simulated GI fluids and scanning electron microscopy (SEM) visualization of nanostructures on the tegument of worms recovered from mesenteric/hepatic veins. Cytotoxicity data indicated tolerability of PZQ–LNCs.

Conclusion

Data obtained provide evidence for the ability of oral LNCs to target distal post-absorption sites, leading to enhanced drug efficacy. From a practical standpoint, PZQ–LNCs could be suggested as a potential tolerable single lower dose oral nanomedicine for more effective PZQ mass chemotherapy.

Screening a repurposing library, the Medicines for Malaria Venture Stasis Box, against Schistosoma mansoni

Background

The development of new treatments against schistosomiasis is imperative but lacks commercial interest. Drug repurposing represents a suitable strategy to identify potential treatments, which have already unblocked several essential steps along the drug development path, hence reducing costs and timelines. Promoting this approach, the Medicines for Malaria Venture (MMV) recently distributed a drug repurposing library of 400 advanced lead candidates (Stasis Box).

Methods

All 400 compounds were initially tested in vitro against the larval stage of Schistosoma mansoni at 10 μM. Hits progressed to screening on adult worms and were further characterised for IC_50, cytotoxicity and selectivity. Ten lead compounds were tested in mice harbouring a chronic S. mansoni infection.

Results

Eleven of the 37 compounds active on the larval stage were also highly active on adult worms in vitro (IC₅₀ = 2.0–7.5 μM). IC₅₀ values on adult S. mansoni decreased substantially in the presence of albumin (7.5–123.5 μM). Toxicity to L6 and MRC cells was moderate. A moderate worm burden reduction of 51.6% was observed for MMV690534, while the other 9 compounds showed low activity. None of the in vivo results were statistically significant (P > 0.05).

Conclusions

Phenotypic screening of advanced lead compounds is a simple and resource-low method to identify novel anthelminthics. None of the promising hits of the Stasis Box identified in vitro against S. mansoni yielded acceptable worm burden reductions in vivo, which might be due to the high plasma protein binding. Since the in vitro hits interfere with different drug targets, they might provide a starting point for target based screening and structure-activity relationship studies.