A mouse infection model and long-term lymphatic endothelium co-culture system to evaluate drugs against adult Brugia malayi

The development of new drugs targeting adult-stage lymphatic filarial nematodes is hindered by the lack of a robust long-term in vitro culture model. Testing potential direct-acting and anti-Wolbachia therapeutic candidates against adult lymphatic filariae in vitro requires their propagation via chronic infection of gerbils. We evaluated Brugia malayi parasite burden data from male Mongolian gerbils compared with two immune-deficient mouse strains highly susceptible to B. malayi: CB.17 Severe-Combined Immmuno-Deficient (SCID) and interleukin-4 receptor alpha, interleukin-5 double knockout (IL-4Rα-/-IL-5-/-) mice. Adult worms generated in IL-4Rα-/-IL-5-/- mice were tested with different feeder cells (human embryonic kidney cells, human adult dermal lymphatic endothelial cells and human THP-1 monocyte differentiated macrophages) and comparative cell-free conditions to optimise and validate a long-term in vitro culture system. Cultured parasites were compared against those isolated from mice using motility scoring, metabolic viability assay (MTT), ex vivo microfilariae release assay and Wolbachia content by qPCR. A selected culture system was validated as a drug screen using reference anti-Wolbachia (doxycycline, ABBV-4083 / flubentylosin) or direct-acting compounds (flubendazole, suramin). BALB/c IL-4Rα-/-IL-5-/- or CB.17 SCID mice were superior to Mongolian gerbils in generating adult worms and supporting in vivo persistence for periods of up to 52 weeks. Adult females retrieved from BALB/c IL-4Rα-/-IL-5-/- mice could be cultured for up to 21 days in the presence of a lymphatic endothelial cell co-culture system with comparable motility, metabolic activity and Wolbachia titres to those maintained in vivo. Drug studies confirmed significant Wolbachia depletions or direct macrofilaricidal activities could be discerned when female B. malayi were cultured for 14 days. We therefore demonstrate a novel methodology to generate adult B. malayi in vivo and accurately evaluate drug efficacy ex vivo which may be adopted for drug screening with the dual benefit of reducing overall animal use and improving anti-filarial drug development.

Development and validation of an LC-MS/MS method for the quantification of the anthelmintic drug moxidectin in a volumetric absorptive microsample, blood, and plasma: Application to a pharmacokinetic study of adults infected with Strongyloides stercoralis in Laos

Moxidectin is a promising candidate for addition to the lean repertoire of drugs against neglected tropical diseases (NTD) including strongyloidiasis. Pharmacokinetic (PK) and -dynamic studies are required to support its clinical development. Microsampling approaches enable PK studies in the challenging environments where NTDs are most prevalent, due to simplified collection and processing. We developed a liquid chromatography tandem mass spectrometry method for the sensitive quantification of moxidectin in human blood obtained by capillary sampling with the microsampling device Mitra® compared to blood and plasma obtained by venous sampling. Sample preparation consisted of protein precipitation, evaporation and reconstitution and also included phospholipid filtration for blood and plasma. Moxidectin was detected by multiple reaction monitoring (640.4 → 528.5 m/z) using a Luna C8(2) (30 × 2.0 mm, 3 µm particle size, 100 Å) analytical column with a gradient program of 6 min duration. Validation was performed with respect to accuracy, precision, sensitivity, selectivity, linearity, stability, recovery, and haematocrit influence with a limit of quantification of 0.5 and 2.5 ng/mL, for venous and capillary blood respectively. Moxidectin was stable up to 2 months at storage condition (blood and plasma: -20 °C, microsamples: room temperature), 3 cycles of temperature shift, for at least 4 h on the bench-top and 24 h in the autosampler (4 °C). Deviations of inter- and intra-assay accuracy and precision were smaller than 12.6% and recoveries were in the range of 80.7-111.2%. The method was applied to samples obtained from nine Strongyloides stercoralis-infected adults from northern Laos. A good agreement in the time-concentration profiles of moxidectin and a high consistency in PK parameters was found between the different matrixes and sampling strategies: e.g. identical time to reach maximal concentration of 4.0 h and a similar maximal concentration of 83.9-88.5 ng/mL of moxidectin. The simple and practical capillary procedure using Mitra® microsampling has been demonstrated to be suitable for PK studies of moxidectin and will pave the way for future PK studies.

An Integrated Approach to Identify New Anti-Filarial Leads to Treat River Blindness, a Neglected Tropical Disease

Filarial worms cause multiple debilitating diseases in millions of people worldwide, including river blindness. Currently available drugs reduce transmission by killing larvae (microfilariae), but there are no effective cures targeting the adult parasites (macrofilaricides) which survive and reproduce in the host for very long periods. To identify effective macrofilaricides, we carried out phenotypic screening of a library of 2121 approved drugs for clinical use against adult Brugia pahangi and prioritized the hits for further studies by integrating those results with a computational prioritization of drugs and associated targets. This resulted in the identification of 18 hits with anti-macrofilaricidal activity, of which two classes, azoles and aspartic protease inhibitors, were further expanded upon. Follow up screening against Onchocerca spp. (adult Onchocerca ochengi and pre-adult O. volvulus) confirmed activity for 13 drugs (the majority having IC50 < 10 μM), and a counter screen of a subset against L. loa microfilariae showed the potential to identify selective drugs that prevent adverse events when co-infected individuals are treated. Stage specific activity was also observed. Many of these drugs are amenable to structural optimization, and also have known canonical targets, making them promising candidates for further optimization that can lead to identifying and characterizing novel anti-macrofilarial drugs.

Moxidectin: an oral treatment for human onchocerciasis

INTRODUCTION

Moxidectin is a milbemycin endectocide recently approved for the treatment of human onchocerciasis. Onchocerciasis, earmarked for elimination of transmission, is a filarial infection endemic in Africa, Yemen, and the Amazonian focus straddling Venezuela and Brazil. Concerns over whether the predominant treatment strategy (yearly mass drug administration (MDA) of ivermectin) is sufficient to achieve elimination in all endemic foci have refocussed attention upon alternative treatments. Moxidectin's stronger and longer microfilarial suppression compared to ivermectin in both phase II and III clinical trials indicates its potential as a novel powerful drug for onchocerciasis elimination.

AREAS COVERED

This work summarizes the chemistry and pharmacology of moxidectin, reviews the phase II and III clinical trials evidence on tolerability, safety, and efficacy of moxidectin versus ivermectin, and discusses the implications of moxidectin's current regulatory status.

EXPERT OPINION

Moxidectin's superior clinical performance has the potential to substantially reduce times to elimination compared to ivermectin. If donated, moxidectin could mitigate the additional programmatic costs of biannual ivermectin distribution because, unlike other alternatives, it can use the existing community-directed treatment infrastructure. A pediatric indication (for children <12 years) and determination of its usefulness in onchocerciasis-loiasis co-endemic areas will greatly help fulfill the potential of moxidectin for the treatment and elimination of onchocerciasis.

Economic evaluations of lymphatic filariasis interventions: a systematic review and research needs

In 2000, the World Health Organization established the Global Programme to Eliminate Lymphatic Filariasis (GPELF), with the goal of eliminating the disease as a public health problem by 2020. Since the start of the programme, a cumulative total of 6.2 billion treatments have been delivered to affected populations - with more than 556 million people treated in 2015 alone. In this paper, we perform a rigorous systematic review of the economic evaluations of lymphatic filariasis interventions have been conducted. We demonstrate that the standard interventions to control lymphatic filariasis are consistently found to be highly cost-effective. This finding has important implications for advocacy groups and potential funders. However, there are several important inconsistencies and research gaps that need to be addressed as we move forward towards the 2020 elimination goals. One of the most important identified research gaps was a lack of evaluation of new interventions specifically targeting areas co-endemic with onchocerciasis and Loa loa - which could become a major barrier to achieving elimination.

Effect of Moxidectin on Bed Bug Feeding, Development, Fecundity, and Survivorship

The common bed bug, Cimex lectularius L. (Hemiptera: Cimicidae), is a blood-feeding ectoparasite which experienced world-wide resurgence during recent decades. The control of bed bugs is often challenging, due to their cryptic nature and resistance to commonly used insecticides. In this study, we evaluated the effect of the antiparasitic drug moxidectin on bed bug survival, reproduction, and development. The LC50 (lethal concentration to kill half the members of a tested population) of moxidectin against bed bug male adults, female adults, and large nymphs were 52.7 (95% CI (confidence interval): 39.5-70.8), 29.3 (95% CI: 20.7-40.5), and 29.1 ng/mL (95% CI: 23.3-35.3), respectively. Moxidectin (≥ 25 ng/mL) reduced egg laying of bed bug females, but showed no significant effect on egg hatching. One time feeding on rabbit blood containing 20 and 40 ng/mL moxidectin showed no negative effects in bed bug feeding and blood meal ingestion, but significantly reduced digestion rates and nymph molting rates. Although moxidectin at concentrations of 20 and 40 ng/mL only caused moderate mortality in bed bugs, it significantly interrupted digestion, development, and oviposition of survived bed bugs for at least one week after feeding. Moxidectin is a promising supplement of the existing bed bug control materials if its use on humans can be approved in the future.

Efficacy and Safety of Moxidectin, Synriam, Synriam-Praziquantel versus Praziquantel against Schistosoma haematobium and S. mansoni Infections: A Randomized, Exploratory Phase 2 Trial

Background

Schistosomiasis affects millions of people, yet treatment options are limited. The antimalarial Synriam (piperaquine 150 mg/arterolane 750 mg) and the anthelminthic moxidectin revealed promising antischistosomal properties in preclinical or clinical studies.

Methodology

We conducted two single-blind, randomized exploratory Phase 2 trials in Schistosoma mansoni and S. haematobium-infected adolescents in northern and central Côte d’Ivoire. Our primary endpoints were cure rates (CRs) and egg reduction rates (ERRs) based on geometric mean and safety. Each subject was asked to provide two stool samples (S. mansoni trial) for Kato-Katz analysis or three urine samples (S. haematobium trial) for urine filtration and one finger prick for malaria screening at baseline and follow-up. Participants were randomly assigned to either moxidectin, Synriam, Synriam plus praziquantel or praziquantel.

Principal Findings

128 adolescents (age: 12–17 years) were included in each study. Against S. haematobium moxidectin and Synriam revealed low efficacy. On the other hand, Synriam plus praziquantel and praziquantel yielded CRs of 60.0% and 38.5% and ERRs of 96.0% and 93.5%, respectively. CRs observed in the treatment of S. mansoni were 13.0%, 6.7%, 27.0%, and 27.6% for moxidectin, Synriam, Synriam plus praziquantel and praziquantel, respectively. ERRs ranged from 64.9% (Synriam) to 87.5% (praziquantel).

Conclusion/Significance

Synriam and moxidectin show low efficacy against S. haematobium, hence an ancillary benefit is not expected when these drugs are used for treating onchocerciasis and malaria in co-endemic settings. Further studies are needed to corroborate our findings that moxidectin and Synriam show moderate ERRs against S. mansoni.

Schistosomiasis is a parasitic infection that affects millions of people all over the world and it is due to schistosomes, helminths (worms) that infect the intestine and the urinary bladder. Treatment options are limited, with praziquantel being the only used drug. The antimalarial Synriam and the anthelminthic moxidectin revealed good action against this worm in previous studies. We conducted two studies in Schistosoma mansoni and S. haematobium-infected adolescents in Côte d’Ivoire. Subjects positive for the infection were allocated by chance to the four groups of treatment (moxidectin, Synriam, Synriam plus praziquantel or praziquantel); participants did not know which drug they took. Our aim was to calculate how many participants were negative after the treatment and how did the intensity of infection change before and after treatment. Each subject provided stools and urines for examination. 128 adolescents were included in each study. Moxidectin and Synriam did not work well against S. haematobium. Against S. mansoni, only a small part of the participants were negative after treatment in all treatment groups, but the intensity of infections were reduced. Further studies are needed to better understand this result.