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Raisch T, Raunser S. The modes of action of ion-channel-targeting neurotoxic insecticides: lessons from structural biology. Nat Struct Mol Biol 2023; 30:1411-1427. [PMID: 37845413 DOI: 10.1038/s41594-023-01113-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 08/31/2023] [Indexed: 10/18/2023]
Abstract
Insecticides are indispensable tools for plant protection in modern agriculture. Despite having highly heterogeneous structures, many neurotoxic insecticides use similar principles to inhibit or deregulate neuronal ion channels. Insecticides targeting pentameric ligand-gated channels are structural mimetics of neurotransmitters or manipulate and deregulate the proteins. Those binding to (pseudo-)tetrameric voltage-gated(-like) channels, on the other hand, are natural or synthetic compounds that directly block the ion-conducting pore or prevent conformational changes in the transmembrane domain necessary for opening and closing the pore. The use of a limited number of inhibition mechanisms can be problematic when resistances arise and become more widespread. Therefore, there is a rising interest in the development of insecticides with novel mechanisms that evade resistance and are pest-insect-specific. During the last decade, most known insecticide targets, many with bound compounds, have been structurally characterized, bringing the rational design of novel classes of agrochemicals within closer reach than ever before.
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Affiliation(s)
- Tobias Raisch
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
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2
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Pfarr KM, Krome AK, Al-Obaidi I, Batchelor H, Vaillant M, Hoerauf A, Opoku NO, Kuesel AC. The pipeline for drugs for control and elimination of neglected tropical diseases: 1. Anti-infective drugs for regulatory registration. Parasit Vectors 2023; 16:82. [PMID: 36859332 PMCID: PMC9979492 DOI: 10.1186/s13071-022-05581-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Accepted: 11/05/2022] [Indexed: 03/03/2023] Open
Abstract
The World Health Organization 'Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021-2030' outlines the targets for control and elimination of neglected tropical diseases (NTDs). New drugs are needed to achieve some of them. We are providing an overview of the pipeline for new anti-infective drugs for regulatory registration and steps to effective use for NTD control and elimination. Considering drugs approved for an NTD by at least one stringent regulatory authority: fexinidazole, included in WHO guidelines for Trypanosoma brucei gambiense African trypanosomiasis, is in development for Chagas disease. Moxidectin, registered in 2018 for treatment of individuals ≥ 12 years old with onchocerciasis, is undergoing studies to extend the indication to 4-11-year-old children and obtain additional data to inform WHO and endemic countries' decisions on moxidectin inclusion in guidelines and policies. Moxidectin is also being evaluated for other NTDs. Considering drugs in at least Phase 2 clinical development, a submission is being prepared for registration of acoziborole as an oral treatment for first and second stage T.b. gambiense African trypanosomiasis. Bedaquiline, registered for tuberculosis, is being evaluated for multibacillary leprosy. Phase 2 studies of emodepside and flubentylosin in O. volvulus-infected individuals are ongoing; studies for Trichuris trichuria and hookworm are planned. A trial of fosravuconazole in Madurella mycetomatis-infected patients is ongoing. JNJ-64281802 is undergoing Phase 2 trials for reducing dengue viral load. Studies are ongoing or planned to evaluate oxantel pamoate for onchocerciasis and soil-transmitted helminths, including Trichuris, and oxfendazole for onchocerciasis, Fasciola hepatica, Taenia solium cysticercosis, Echinococcus granulosus and soil-transmitted helminths, including Trichuris. Additional steps from first registration to effective use for NTD control and elimination include country registrations, possibly additional studies to inform WHO guidelines and country policies, and implementation research to address barriers to effective use of new drugs. Relative to the number of people suffering from NTDs, the pipeline is small. Close collaboration and exchange of experience among all stakeholders developing drugs for NTDs may increase the probability that the current pipeline will translate into new drugs effectively implemented in affected countries.
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Affiliation(s)
- Kenneth M. Pfarr
- grid.15090.3d0000 0000 8786 803XInstitute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany ,grid.452463.2German Center for Infection Research, Partner Site Bonn-Cologne, Bonn, Germany
| | - Anna K. Krome
- grid.10388.320000 0001 2240 3300Department of Pharmaceutical Technology and Biopharmaceutics, University of Bonn, Bonn, Germany
| | - Issraa Al-Obaidi
- grid.11984.350000000121138138Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Hannah Batchelor
- grid.11984.350000000121138138Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Michel Vaillant
- grid.451012.30000 0004 0621 531XCompetence Center for Methodology and Statistics, Luxembourg Institute of Health, Strassen, Grand Duchy of Luxembourg
| | - Achim Hoerauf
- grid.15090.3d0000 0000 8786 803XInstitute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany ,grid.452463.2German Center for Infection Research, Partner Site Bonn-Cologne, Bonn, Germany
| | - Nicholas O. Opoku
- grid.449729.50000 0004 7707 5975Department of Epidemiology and Biostatistics School of Public Health, University of Health and Allied Sciences, Hohoe, Ghana
| | - Annette C. Kuesel
- UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (WHO/TDR), World Health Organization, Geneva, Switzerland
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Tagboto S, Orish V. Drug development for onchocerciasis-the past, the present and the future. FRONTIERS IN TROPICAL DISEASES 2022. [DOI: 10.3389/fitd.2022.953061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Onchocerciasis affects predominantly rural communities in Africa, and with small foci in South America and the Yemen. The disease is a major cause of blindness and other significant morbidity and mortality. Control programs have achieved a major impact on the incidence and prevalence of onchocerciasis by interrupting transmission with vector control programs, and treatment with mass drug administration using the microfilaricide ivermectin. Over the last few decades, several microfilaricides have been developed. This initially included diethylcarbamazine, which had significant side effects and is no longer used as such. Ivermectin which is a safe and highly effective microfilaricide and moxidectin which is a longer acting microfilaricide are presently recognized therapies. Suramin was the first effective macrofilaricide but was prohibitively toxic. Certain antibiotics including doxycycline can help eliminate adult worms by targeting its endosymbiont bacteria, Wolbachia pipientis. However, the dosing regimens may make this difficult to use as part of a mass disease control program in endemic areas. It is now widely recognized that treatments that are able to kill or permanently sterilize adult filarial worms should help achieve the elimination of this disease. We summarize in detail the historic drug development in onchocerciasis, including prospective future candidate drugs.
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Choudhary S, Kashyap SS, Martin RJ, Robertson AP. Advances in our understanding of nematode ion channels as potential anthelmintic targets. Int J Parasitol Drugs Drug Resist 2022; 18:52-86. [PMID: 35149380 PMCID: PMC8841521 DOI: 10.1016/j.ijpddr.2021.12.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 12/14/2021] [Accepted: 12/15/2021] [Indexed: 12/15/2022]
Abstract
Ion channels are specialized multimeric proteins that underlie cell excitability. These channels integrate with a variety of neuromuscular and biological functions. In nematodes, the physiological behaviors including locomotion, navigation, feeding and reproduction, are regulated by these protein entities. Majority of the antinematodal chemotherapeutics target the ion channels to disrupt essential biological functions. Here, we have summarized current advances in our understanding of nematode ion channel pharmacology. We review cys-loop ligand gated ion channels (LGICs), including nicotinic acetylcholine receptors (nAChRs), acetylcholine-chloride gated ion channels (ACCs), glutamate-gated chloride channels (GluCls), and GABA (γ-aminobutyric acid) receptors, and other ionotropic receptors (transient receptor potential (TRP) channels and potassium ion channels). We have provided an update on the pharmacological properties of these channels from various nematodes. This article catalogs the differences in ion channel composition and resulting pharmacology in the phylum Nematoda. This diversity in ion channel subunit repertoire and pharmacology emphasizes the importance of pursuing species-specific drug target research. In this review, we have provided an overview of recent advances in techniques and functional assays available for screening ion channel properties and their application.
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Affiliation(s)
- Shivani Choudhary
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Sudhanva S Kashyap
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Richard J Martin
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Alan P Robertson
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA.
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Assmus F, Hoglund RM, Monnot F, Specht S, Scandale I, Tarning J. Drug development for the treatment of onchocerciasis: Population pharmacokinetic and adverse events modeling of emodepside. PLoS Negl Trop Dis 2022; 16:e0010219. [PMID: 35271567 PMCID: PMC8912909 DOI: 10.1371/journal.pntd.0010219] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 02/01/2022] [Indexed: 12/17/2022] Open
Abstract
Background To accelerate the progress towards onchocerciasis elimination, a macrofilaricidal drug that kills the adult parasite is urgently needed. Emodepside has shown macrofilaricidal activity against a variety of nematodes and is currently under clinical development for the treatment of onchocerciasis. The aims of this study were i) to characterize the population pharmacokinetic properties of emodepside, ii) to link its exposure to adverse events in healthy volunteers, and iii) to propose an optimized dosing regimen for a planned phase II study in onchocerciasis patients. Methodology / Principal findings Plasma concentration-time profiles and adverse event data were obtained from 142 subjects enrolled in three phase I studies, including a single-dose, and a multiple-dose, dose-escalation study as well as a relative bioavailability study. Nonlinear mixed-effects modeling was used to evaluate the population pharmacokinetic properties of emodepside. Logistic regression modeling was used to link exposure to drug-related treatment-emergent adverse events (TEAEs). Emodepside pharmacokinetics were well described by a transit-absorption model, followed by a 3-compartment disposition model. Body weight was included as an allometric function and both food and formulation had a significant impact on absorption rate and relative bioavailability. All drug-related TEAEs were transient, and mild or moderate in severity. An increase in peak plasma concentration was associated with an increase in the odds of experiencing a drug-related TEAE of interest. Conclusions/Significance Pharmacokinetic modeling and simulation was used to derive an optimized, body weight-based dosing regimen, which allows for achievement of extended emodepside exposures above target concentrations while maintaining acceptable tolerability margins. Onchocerciasis (‘River Blindness’), is a worm infection common in sub-Saharan Africa. More than 20 million people are suffering from the disease which can lead to disfiguring skin disease, visual impairment and permanent blindness. The currently recommended treatment is ivermectin, which kills the juvenile worms and reduces the severity of the symptoms, but fails to kill the adult worm. As a consequence, the treatment needs to be repeated for 10–15 years (life span of the adult worm), imposing a large burden on patients and communities. Hence, there is an urgent need for a new, safe and short-course drug that kills the adult worm and offers a rapid cure. Emodepside is a promising drug candidate which has recently been administered to healthy volunteers for the first time. In this study, we characterized the relationship between dose, systemic exposure in human and the probability of experiencing an adverse event. Modeling and simulation were used to propose a short-course dosing regimen which balances risks and benefits in order to achieve efficacy while maintaining safety. Our results support the further clinical development of emodepside thus contributing to onchocerciasis elimination efforts.
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Affiliation(s)
- Frauke Assmus
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Richard M. Hoglund
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | | | - Sabine Specht
- Drugs for Neglected Disease initiative, Geneva, Switzerland
| | - Ivan Scandale
- Drugs for Neglected Disease initiative, Geneva, Switzerland
| | - Joel Tarning
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
- * E-mail:
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The Current Directions of Searching for Antiparasitic Drugs. Molecules 2022; 27:molecules27051534. [PMID: 35268635 PMCID: PMC8912034 DOI: 10.3390/molecules27051534] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Revised: 02/18/2022] [Accepted: 02/22/2022] [Indexed: 12/02/2022] Open
Abstract
Parasitic diseases are still a huge problem for mankind. They are becoming the main cause of chronic diseases in the world. Migration of the population, pollution of the natural environment, and climate changes cause the rapid spread of diseases. Additionally, a growing resistance of parasites to drugs is observed. Many research groups are looking for effective antiparasitic drugs with low side effects. In this work, we present the current trends in the search for antiparasitic drugs. We report known drugs used in other disease entities with proven antiparasitic activity and research on new chemical structures that may be potential drugs in parasitic diseases. The described investigations of antiparasitic compounds can be helpful for further drug development.
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Small molecule modulation of the Drosophila Slo channel elucidated by cryo-EM. Nat Commun 2021; 12:7164. [PMID: 34887422 PMCID: PMC8660915 DOI: 10.1038/s41467-021-27435-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 11/18/2021] [Indexed: 12/16/2022] Open
Abstract
Slowpoke (Slo) potassium channels display extraordinarily high conductance, are synergistically activated by a positive transmembrane potential and high intracellular Ca2+ concentrations and are important targets for insecticides and antiparasitic drugs. However, it is unknown how these compounds modulate ion translocation and whether there are insect-specific binding pockets. Here, we report structures of Drosophila Slo in the Ca2+-bound and Ca2+-free form and in complex with the fungal neurotoxin verruculogen and the anthelmintic drug emodepside. Whereas the architecture and gating mechanism of Slo channels are conserved, potential insect-specific binding pockets exist. Verruculogen inhibits K+ transport by blocking the Ca2+-induced activation signal and precludes K+ from entering the selectivity filter. Emodepside decreases the conductance by suboptimal K+ coordination and uncouples ion gating from Ca2+ and voltage sensing. Our results expand the mechanistic understanding of Slo regulation and lay the foundation for the rational design of regulators of Slo and other voltage-gated ion channels. Slowpoke (Slo) channels are voltage-gated potassium channels that are activated by high intracellular Ca2+ concentrations, and they are targets for insecticides and antiparasitic drugs. Here, the authors present the cryo-EM structures of the Drosophila melanogaster Slo channel in the Ca2+-bound and Ca2+-free conformations, as well as in complex with the fungal neurotoxin verruculogen and the anthelmintic drug emodepside and discuss the mechanisms by which they affect the activity of Slo.
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Krücken J, Holden-Dye L, Keiser J, Prichard RK, Townson S, Makepeace BL, Hübner MP, Hahnel SR, Scandale I, Harder A, Kulke D. Development of emodepside as a possible adulticidal treatment for human onchocerciasis-The fruit of a successful industrial-academic collaboration. PLoS Pathog 2021; 17:e1009682. [PMID: 34293063 PMCID: PMC8297762 DOI: 10.1371/journal.ppat.1009682] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Current mass drug administration (MDA) programs for the treatment of human river blindness (onchocerciasis) caused by the filarial worm Onchocerca volvulus rely on ivermectin, an anthelmintic originally developed for animal health. These treatments are primarily directed against migrating microfilariae and also suppress fecundity for several months, but fail to eliminate adult O. volvulus. Therefore, elimination programs need time frames of decades, well exceeding the life span of adult worms. The situation is worsened by decreased ivermectin efficacy after long-term therapy. To improve treatment options against onchocerciasis, a drug development candidate should ideally kill or irreversibly sterilize adult worms. Emodepside is a broad-spectrum anthelmintic used for the treatment of parasitic nematodes in cats and dogs (Profender and Procox). Our current knowledge of the pharmacology of emodepside is the result of more than 2 decades of intensive collaborative research between academia and the pharmaceutical industry. Emodepside has a novel mode of action with a broad spectrum of activity, including against extraintestinal nematode stages such as migrating larvae or macrofilariae. Therefore, emodepside is considered to be among the most promising candidates for evaluation as an adulticide treatment against onchocerciasis. Consequently, in 2014, Bayer and the Drugs for Neglected Diseases initiative (DNDi) started a collaboration to develop emodepside for the treatment of patients suffering from the disease. Macrofilaricidal activity has been demonstrated in various models, including Onchocerca ochengi in cattle, the parasite most closely related to O. volvulus. Emodepside has now successfully passed Phase I clinical trials, and a Phase II study is planned. This Bayer–DNDi partnership is an outstanding example of “One World Health,” in which experience gained in veterinary science and drug development is translated to human health and leads to improved tools to combat neglected tropical diseases (NTDs) and shorten development pathways and timelines in an otherwise neglected area. Onchocerca volvulus is the causative agent of human river blindness, and current elimination programs rely on the use of ivermectin to kill microfilariae. Since no adulticidal drug is available and adult worms have a life span of up to 15 years, elimination programs need to be sustained over several decades. Emodepside is an anthelmintic that is licensed as a dewormer for cats and dogs. Due to its ability to eliminate nematodes located in various extraintestinal host tissues, including migrating larvae and adult filarial worms, it is considered to be an excellent candidate for the treatment of onchocerciasis. Intense collaboration between academia and the pharmaceutical industry has led to a deep understanding of the novel mode of action of the drug and of its parasite target spectrum. Phase I clinical trials with emodepside have demonstrated its safety and adulticide activity against the closely related cattle parasite Onchocerca ochengi. Currently, Phase II clinical trials are planned to confirm that emodepside, developed initially to improve animal health, has also the potential to improve human health by tackling a very important neglected tropical disease (NTD).
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Affiliation(s)
- Jürgen Krücken
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
| | - Lindy Holden-Dye
- School of Biological Sciences, Institute for Life Sciences, University of Southampton, Southampton, United Kingdom
| | - Jennifer Keiser
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Roger K. Prichard
- Institute of Parasitology, McGill University, Sainte Anne-de-Bellevue, Quebec, Canada
| | - Simon Townson
- The Griffin Institute, Northwick Park and St. Mark’s Hospital, Harrow, United Kingdom
| | - Benjamin L. Makepeace
- Institute of Infection, Veterinary & Ecological Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Marc P. Hübner
- Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany
- German Center for Infection Research (DZIF), partner site Bonn-Cologne, Bonn, Germany
| | - Steffen R. Hahnel
- Elanco Animal Health, Research & Exploratory Development, Monheim, Germany
| | - Ivan Scandale
- Drugs for Neglected Disease initiative, Geneva, Switzerland
| | | | - Daniel Kulke
- Department of Biomedical Sciences, Iowa State University, Ames, Iowa, United States of America
- * E-mail:
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Wen JY, Zhang J, Chen S, Chen Y, Zhang Y, Ma ZY, Zhang F, Xie WM, Fan YF, Duan JS, Chen ZW. Endothelium-derived hydrogen sulfide acts as a hyperpolarizing factor and exerts neuroprotective effects via activation of large-conductance Ca 2+ -activated K + channels. Br J Pharmacol 2021; 178:4155-4175. [PMID: 34216027 DOI: 10.1111/bph.15607] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 06/15/2021] [Accepted: 06/18/2021] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND AND PURPOSE Endothelium-derived hyperpolarizing factor (EDHF) has been suggested as a therapeutic target for vascular protection against ischaemic brain injury. However, the molecular entity of EDHF and its action on neurons remains unclear. This study was undertaken to demonstrate whether the hydrogen sulfide (H2 S) acts as EDHF and exerts neuroprotective effect via large-conductance Ca2+ -activated K+ (BKCa /KCa 1.1) channels. EXPERIMENTAL APPROACH The whole-cell patch-clamp technology was used to record the changes of BKCa currents in rat neurons induced by EDHF. The cerebral ischaemia/reperfusion model of mice and oxygen-glucose deprivation/reoxygenation (OGD/R) model of neurons were used to explore the neuroprotection of EDHF by activating BKCa channels in these neurons. KEY RESULTS Increases of BKCa currents and membrane hyperpolarization in hippocampal neurons induced by EDHF could be markedly inhibited by BKCa channel inhibitor iberiotoxin or endothelial H2 S synthase inhibitor propargylglycine. The H2 S donor, NaHS-induced BKCa current and membrane hyperpolarization in neurons were also inhibited by iberiotoxin, suggesting that H2 S acts as EDHF and activates the neuronal BKCa channels. Besides, we found that the protective effect of endothelium-derived H2 S against mice cerebral ischaemia/reperfusion injury was disrupted by iberiotoxin. Importantly, the inhibitory effect of NaHS or BKCa channel opener on OGD/R-induced neuron injury and the increment of intracellular Ca2+ level could be inhibited by iberiotoxin but enhanced by co-application with L-type but not T-type calcium channel inhibitor. CONCLUSION AND IMPLICATIONS Endothelium-derived H2 S acts as EDHF and exerts neuroprotective effects via activating the BKCa channels and then inhibiting the T-type calcium channels in hippocampal neurons.
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Affiliation(s)
- Ji-Yue Wen
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Jie Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Shuo Chen
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Ye Chen
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Yang Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Zi-Yao Ma
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Fang Zhang
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Wei-Ming Xie
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Yi-Fei Fan
- Department of Physiology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
| | - Jing-Si Duan
- Department of Cardiovascular Surgery, The First Affiliated Hospital of Anhui Medical University, Hefei, China
| | - Zhi-Wu Chen
- Department of Pharmacology, School of Basic Medical Sciences, Anhui Medical University, Hefei, China
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10
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Emodepside targets SLO-1 channels of Onchocerca ochengi and induces broad anthelmintic effects in a bovine model of onchocerciasis. PLoS Pathog 2021; 17:e1009601. [PMID: 34077488 PMCID: PMC8202924 DOI: 10.1371/journal.ppat.1009601] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 06/14/2021] [Accepted: 05/01/2021] [Indexed: 12/14/2022] Open
Abstract
Onchocerciasis (river blindness), caused by the filarial worm Onchocerca volvulus, is a neglected tropical disease mostly affecting sub-Saharan Africa and is responsible for >1.3 million years lived with disability. Current control relies almost entirely on ivermectin, which suppresses symptoms caused by the first-stage larvae (microfilariae) but does not kill the long-lived adults. Here, we evaluated emodepside, a semi-synthetic cyclooctadepsipeptide registered for deworming applications in companion animals, for activity against adult filariae (i.e., as a macrofilaricide). We demonstrate the equivalence of emodepside activity on SLO-1 potassium channels in Onchocerca volvulus and Onchocerca ochengi, its sister species from cattle. Evaluation of emodepside in cattle as single or 7-day treatments at two doses (0.15 and 0.75 mg/kg) revealed rapid activity against microfilariae, prolonged suppression of female worm fecundity, and macrofilaricidal effects by 18 months post treatment. The drug was well tolerated, causing only transiently increased blood glucose. Female adult worms were mostly paralyzed; however, some retained metabolic activity even in the multiple high-dose group. These data support ongoing clinical development of emodepside to treat river blindness.
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11
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Verma S, Kulke D, McCall JW, Martin RJ, Robertson AP. Recording drug responses from adult Dirofilaria immitis pharyngeal and somatic muscle cells. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2020; 15:1-8. [PMID: 33348209 PMCID: PMC7753077 DOI: 10.1016/j.ijpddr.2020.12.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 12/09/2020] [Accepted: 12/11/2020] [Indexed: 12/13/2022]
Abstract
Despite being considered one of the most pathogenic helminth infections of companion animals, members of macrocyclic lactone class are the only drugs available for the prevention of heartworm disease caused by Dirofilaria immitis. Alarmingly, heartworm prevention is at risk; several studies confirm the existence of macrocyclic lactone resistance in D. immitis populations across the United States. To safeguard the long term prevention and control of this disease, the identification and development of novel anthelmintics is urgently needed. To identify novel, resistance-breaking drugs, it is highly desirable to: Unfortunately, none of the three above statements can be answered sufficiently for D. immitis and most of our hypotheses derive from surrogate species and/or in vitro studies. Therefore, the present study aims to improve our fundamental understanding of the neuromuscular system of the canine heartworm by establishing new methods allowing the investigation of body wall and pharyngeal muscle responses and their modulation by anthelmintics. We found that the pharynx of adult D. immitis responds to both ivermectin and moxidectin with EC50s in the low micromolar range. We also demonstrate that the somatic muscle cells have robust responses to 30 μM acetylcholine, levamisole, pyrantel and nicotine. This is important preliminary data, demonstrating the feasibility of electrophysiological studies in this important parasite.
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Affiliation(s)
- S Verma
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA, 50011, USA
| | - D Kulke
- Drug Discovery and External Innovation, Bayer Animal Health GmbH, 51373, Leverkusen, Germany.
| | | | - R J Martin
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA, 50011, USA
| | - A P Robertson
- Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, Ames, IA, 50011, USA
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Jimenez Castro PD, Mansour A, Charles S, Hostetler J, Settje T, Kulke D, Kaplan RM. Efficacy evaluation of anthelmintic products against an infection with the canine hookworm (Ancylostoma caninum) isolate Worthy 4.1F3P in dogs. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2020; 13:22-27. [PMID: 32403053 PMCID: PMC7214830 DOI: 10.1016/j.ijpddr.2020.04.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 04/15/2020] [Accepted: 04/16/2020] [Indexed: 12/20/2022]
Abstract
Ancylostoma caninum is the most prevalent intestinal nematode of dogs, and has a zoonotic potential. Multiple-drug resistance (MDR) has been confirmed in a number of A. caninum isolates, including isolate Worthy 4.1F3P, against all anthelmintic drug classes approved for hookworm treatment in dogs in the United States (US). The cyclooctadepsipeptide emodepside is not registered to use in dogs in the US, but in a number of other countries/regions. The objective of this study was to evaluate the efficacy of emodepside + praziquantel, as well as three commercial products that are commonly used in the US for treatment of hookworms, against a suspected (subsequently confirmed) MDR A. caninum isolate Worthy 4.1F3P. 40 dogs infected on study day (SD) 0 with 300 third-stage larvae, were randomly allocated to one of five treatment groups with eight dogs each: pyrantel pamoate (Nemex®-2), fenbendazole (Panacur® C), milbemycin oxime (Interceptor®), emodepside + praziquantel tablets and non-treated control. Fecal egg counts (FEC) were performed on SDs 19, 20, 22, 27, 31 and 34. All treatments were administered as per label requirements on SD 24 to dogs in Groups 1 through 4. Two additional treatments were administered on SDs 25 and 26 to dogs in Group 2 as per label requirements. Dogs were necropsied on SD 34 and the digestive tract was removed/processed for worm recovery and enumeration. The geometric mean (GM) worm counts for the control group was 97.4, and for the pyrantel pamoate, fenbendazole, milbemycin oxime, and emodepside + praziquantel groups were 74.8, 72.0, 88.9, and 0.4, respectively. These yielded efficacies of 23.2%, 26.1%, and 8.8%, and 99.6%, respectively. These data support previous findings of the MDR status of Worthy 4.1F3P as treatments with pyrantel pamoate, fenbendazole and milbemycin oxime lacked efficacy. In sharp contrast, Worthy 4.1F3P was highly susceptible to treatment with emodepside + praziquantel.
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Affiliation(s)
- Pablo D Jimenez Castro
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, 30602, USA; Grupo de Parasitología Veterinaria, Universidad Nacional de Colombia, Colombia.
| | | | - Samuel Charles
- Bayer US LLC, Animal Health, Research and Development, Shawnee, KS, USA
| | - Joe Hostetler
- Bayer US LLC, Animal Health, Research and Development, Shawnee, KS, USA
| | - Terry Settje
- Bayer US LLC, Animal Health, Research and Development, Shawnee, KS, USA
| | - Daniel Kulke
- Bayer Animal Health GmbH, Drug Discovery & External Innovation, Leverkusen, Germany
| | - Ray M Kaplan
- Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, 30602, USA
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Abstract
Neglected parasitic helminth diseases such as onchocerciasis and lymphatic filariasis affect an estimated 145 million people worldwide, creating a serious health burden in endemic areas such as sub-Saharan Africa and India. Although these diseases are not usually lethal, these filarial nematodes, transmitted by blood-feeding insect vectors, cause severe debilitation and cause chronic disability to infected individuals. The adult worms can reproduce from 5 to up to 14 years, releasing millions of microfilariae, juvenile worms, over an infected individual's lifetime. The current treatments for controlling human filarial infections is focused on killing microfilariae, the earliest larval stage. Currently, there is an unmet medical need for treatments consisting of a macrofilaricidal regimen, one that targets the adult stage of the parasite, to increase the rate of elimination, allow for safe use in coendemic regions of Onchocerca volvulus and Loa loa, and to provide a rapid method to resolve reinfections. Herein, recent approaches for targeting human filarial diseases are discussed, including direct acting agents to target parasitic nematodes and antibacterial approaches to target the endosymbiotic bacteria, Wolbachia.
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Affiliation(s)
- Natalie A. Hawryluk
- Bristol-Myers Squibb, Global Health, 10300 Campus Point Drive, San Diego, California 92121, United States
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14
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Andrade CH, Neves BJ, Melo-Filho CC, Rodrigues J, Silva DC, Braga RC, Cravo PVL. In Silico Chemogenomics Drug Repositioning Strategies for Neglected Tropical Diseases. Curr Med Chem 2019. [DOI: 10.2174/0929867325666180309114824] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Only ~1% of all drug candidates against Neglected Tropical Diseases (NTDs)
have reached clinical trials in the last decades, underscoring the need for new, safe and effective
treatments. In such context, drug repositioning, which allows finding novel indications
for approved drugs whose pharmacokinetic and safety profiles are already known,
emerging as a promising strategy for tackling NTDs. Chemogenomics is a direct descendent
of the typical drug discovery process that involves the systematic screening of chemical
compounds against drug targets in high-throughput screening (HTS) efforts, for the identification
of lead compounds. However, different to the one-drug-one-target paradigm, chemogenomics
attempts to identify all potential ligands for all possible targets and diseases. In
this review, we summarize current methodological development efforts in drug repositioning
that use state-of-the-art computational ligand- and structure-based chemogenomics approaches.
Furthermore, we highlighted the recent progress in computational drug repositioning
for some NTDs, based on curation and modeling of genomic, biological, and chemical data.
Additionally, we also present in-house and other successful examples and suggest possible solutions
to existing pitfalls.
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Affiliation(s)
- Carolina Horta Andrade
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Bruno Junior Neves
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Cleber Camilo Melo-Filho
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Juliana Rodrigues
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Diego Cabral Silva
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Rodolpho Campos Braga
- LabMol - Laboratory for Molecular Modeling and Drug Design, Faculty of Pharmacy, Federal University of Goias, Goiania, GO, 74605-170, Brazil
| | - Pedro Vitor Lemos Cravo
- Laboratory of Cheminformatics, Centro Universitario de Anapolis (UniEVANGELICA), Anapolis, GO, 75083-515, Brazil
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15
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Gaens D, Leithäuser C, Hamann M, Geyer J. Adverse Drug Reactions After Administration of Emodepside/Praziquantel (Profender®) in an MDR1-Mutant Australian Shepherd Dog: Case Report. Front Vet Sci 2019; 6:296. [PMID: 31555677 PMCID: PMC6743036 DOI: 10.3389/fvets.2019.00296] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 08/19/2019] [Indexed: 11/22/2022] Open
Abstract
A 3-year-old male Australian Shepherd was presented with signs of neurological toxicity following the administration of Profender® at the recommended dosage. Unfortunately, the owner had received the product from a veterinarian without any further instructions on fasting as recommended by the manufacturer, so the dog was fed prior to Profender® administration. Neurological toxicity included generalized tremor, agitation and panting, and required hospitalization of the dog. All neurological signs resolved after symptomatic treatment within 24 h and the dog was discharged without the need for further medication. MDR1 genotyping revealed a homozygous mutation of the MDR1 gene, which is normally important to prevent brain penetration of emodepside by an efflux-based transport mechanism at the blood brain barrier. This case indicates that Profender® can lead to serious, but transient neurological toxicity in dogs with homozygous MDR1 mutation even at therapeutic dosage, in particular when fasting recommendations are disregarded. Therefore, the case report highlights both the importance of MDR1 genotyping in predisposed dog breeds as well as strict compliance with fasting recommendations around the time of Profender® administration.
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Affiliation(s)
- Daniela Gaens
- Faculty of Veterinary Medicine, Institute of Pharmacology and Toxicology, Justus Liebig University Giessen, Giessen, Germany
| | - Carola Leithäuser
- Animal Clinic Norderstedt, Evidensia Tierärztliche Klinik Für Kleintiere, Norderstedt, Germany
| | - Melanie Hamann
- Faculty of Veterinary Medicine, Institute of Pharmacology and Toxicology, Justus Liebig University Giessen, Giessen, Germany
| | - Joachim Geyer
- Faculty of Veterinary Medicine, Institute of Pharmacology and Toxicology, Justus Liebig University Giessen, Giessen, Germany
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Karpstein T, Pasche V, Häberli C, Scandale I, Neodo A, Keiser J. Evaluation of emodepside in laboratory models of human intestinal nematode and schistosome infections. Parasit Vectors 2019; 12:226. [PMID: 31088525 PMCID: PMC6515646 DOI: 10.1186/s13071-019-3476-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 04/30/2019] [Indexed: 12/22/2022] Open
Abstract
Background Helminthiases are very prevalent worldwide, yet their treatment and control rely on a handful of drugs. Emodepside, a marketed broad-spectrum veterinary anthelminthic with a unique mechanism of action, undergoing development for onchocerciasis is an interesting anthelmintic drug candidate. We tested the in vitro and in vivo activity of emodepside on nematode species that serve as models for human soil-transmitted helminth infection as well as on schistosomes. Methods In vitro viability assays were performed over a time course of 72 hours for Trichuris muris, Necator americanus, Ancylostoma ceylanicum, Heligmosomoides polygyrus, Strongyloides ratti, Schistosoma mansoni and Schistosoma haematobium. The drug effect was determined by the survival rate for the larvae and by phenotypical scores for the adult worms. Additionally, mice infected with T. muris and hamsters harboring hookworm infection (N. americanus or A. ceylanicum) were administered orally with emodepside at doses ranging from 1.25 to 75 mg/kg. Expelled worms in the feces were counted until 3 days post-drug intake and worms residing in the intestines were collected and counted after dissection. Results After 24 hours, emodepside was very active in vitro against both larval and adult stages of the nematodes T. muris, A. ceylanicum, N. americanus, H. polygyrus and S. ratti (IC50 < 4 µM). The good in vitro activity was confirmed in vivo. Hamsters infected with the hookworms were cured when administered orally with 2.5 mg/kg of the drug. Emodepside was also highly active in vivo against T. muris (ED50 = 1.2 mg/kg). Emodepside was moderately active on schistosomula in vitro (IC50 < 8 µM) 24 h post-drug incubation and its activity on adult S. mansoni and S. haematobium was low (IC50: 30–50 µM). Conclusions Emodepside is highly active against a broad range of nematode species both in vitro and in vivo. The development of emodepside for treating soil-transmitted helminth infections should be pursued. Electronic supplementary material The online version of this article (10.1186/s13071-019-3476-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Tanja Karpstein
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Valérian Pasche
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Cécile Häberli
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Ivan Scandale
- Drugs for Neglected Disease initiative, Chemin Louis-Dunant 15, 1202, Geneva, Switzerland
| | - Anna Neodo
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.,University of Basel, Basel, Switzerland
| | - Jennifer Keiser
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland. .,University of Basel, Basel, Switzerland.
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17
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Murdoch ME. Onchodermatitis: Where Are We Now? Trop Med Infect Dis 2018; 3:E94. [PMID: 30274490 PMCID: PMC6160948 DOI: 10.3390/tropicalmed3030094] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 08/27/2018] [Accepted: 08/28/2018] [Indexed: 02/07/2023] Open
Abstract
Onchocerciasis causes debilitating pruritus and rashes as well as visual impairment and blindness. Prior to control measures, eye disease was particularly prominent in savanna areas of sub-Saharan Africa whilst skin disease was more common across rainforest regions of tropical Africa. Mass drug distribution with ivermectin is changing the global scene of onchocerciasis. There has been successful progressive elimination in Central and Southern American countries and the World Health Organization has set a target for elimination in Africa of 2025. This literature review was conducted to examine progress regarding onchocercal skin disease. PubMed searches were performed using keywords 'onchocerciasis', 'onchodermatitis' and 'onchocercal skin disease' over the past eight years. Articles in English, or with an English abstract, were assessed for relevance, including any pertinent references within the articles. Recent progress in awareness of, understanding and treatment of onchocercal skin disease is reviewed with particular emphasis on publications within the past five years. The global burden of onchodermatitis is progressively reducing and is no longer seen in children in many formerly endemic foci.
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Affiliation(s)
- Michele E Murdoch
- Department of Dermatology, West Herts Hospitals NHS Trust, Vicarage Road, Watford, Hertfordshire WD18 0HB, UK.
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18
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The interactions of anthelmintic drugs with nicotinic receptors in parasitic nematodes. Emerg Top Life Sci 2017; 1:667-673. [PMID: 33525839 DOI: 10.1042/etls20170096] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 11/09/2017] [Accepted: 11/13/2017] [Indexed: 02/01/2023]
Abstract
Parasitic nematodes express a large number of distinct nicotinic acetylcholine receptors and these in turn are the targets of many classes of anthelmintic drug. This complexity poses many challenges to the field, including sorting the exact subunit composition of each of the receptor subtypes and how much they vary between species. It is clear that the model organism Caenorhabditis elegans does not recapitulate the complexity of nicotinic pharmacology of many parasite species and data using this system may be misleading when applied to them. The number of different receptors may allow nematodes some plasticity which they can exploit to evolve resistance to a specific cholinergic drug; however, this may mean that combinations of cholinergic agents may be effective at sustainably controlling them. Resistance may involve the expression of truncated receptor subunits that affect the expression levels of the receptors via mechanisms that remain to be deciphered.
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19
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Abongwa M, Martin RJ, Robertson AP. A BRIEF REVIEW ON THE MODE OF ACTION OF ANTINEMATODAL DRUGS. ACTA VET-BEOGRAD 2017; 67:137-152. [PMID: 29416226 DOI: 10.1515/acve-2017-0013] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Anthelmintics are some of the most widely used drugs in veterinary medicine. Here we review the mechanism of action of these compounds on nematode parasites. Included are the older classes of compounds; the benzimidazoles, cholinergic agonists and macrocyclic lactones. We also consider newer anthelmintics, including emodepside, derquantel and tribendimidine. In the absence of vaccines for most parasite species, control of nematode parasites will continue to rely on anthelmintic drugs. As a consequence, vigilance in detecting drug resistance in parasite populations is required. Since resistance development appears almost inevitable, there is a continued and pressing need to fully understand the mode of action of these compounds. It is also necessary to identify new drug targets and drugs for the continued effective control of nematode parasites.
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Affiliation(s)
- Melanie Abongwa
- Department of Biomedical Sciences, College of Veterinary Medicine , Iowa State University , Ames , IA 50011 , United States of America
| | - Richard J. Martin
- Department of Biomedical Sciences, College of Veterinary Medicine , Iowa State University , Ames , IA 50011 , United States of America
| | - Alan P. Robertson
- Department of Biomedical Sciences, College of Veterinary Medicine , Iowa State University , Ames , IA 50011 , United States of America
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20
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Kuesel AC. Research for new drugs for elimination of onchocerciasis in Africa. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2016; 6:272-286. [PMID: 27693536 PMCID: PMC5196484 DOI: 10.1016/j.ijpddr.2016.04.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2016] [Accepted: 04/20/2016] [Indexed: 01/12/2023]
Abstract
Onchocerciasis is a parasitic, vector borne disease caused by the filarial nematode Onchocerca volvulus. More than 99% of the population at risk of infection live in Africa. Onchocerciasis control was initiated in West Africa in 1974 with vector control, later complemented by ivermectin mass drug administration and in the other African endemic countries in 1995 with annual community directed treatment with ivermectin (CDTI.) This has significantly reduced infection prevalence. Together with proof-of-concept for onchocerciasis elimination with annual CDTI from foci in Senegal and Mali, this has resulted in targeting onchocerciasis elimination in selected African countries by 2020 and in 80% of African countries by 2025. The challenges for meeting these targets include the number of endemic countries where conflict has delayed or interrupted control programmes, cross-border foci, potential emergence of parasite strains with low susceptibility to ivermectin and co-endemicity of loiasis, another parasitic vector borne disease, which slows down or prohibits CDTI implementation. Some of these challenges could be addressed with new drugs or drug combinations with a higher effect on Onchocerca volvulus than ivermectin. This paper reviews the path from discovery of new compounds to their qualification for large scale use and the support regulatory authorities provide for development of drugs for neglected tropical diseases. The status of research for new drugs or treatment regimens for onchocerciasis along the path to regulatory approval and qualification for large scale use is reviewed. This research includes new regimens and combinations of ivermectin and albendazole, antibiotics targeting the O. volvulus endosymbiont Wolbachia, flubendazole, moxidectin and emodepside and discovery of new compounds.
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Affiliation(s)
- Annette C Kuesel
- UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, 20 Avenue Appia, 1211 Geneva, Switzerland.
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21
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Harder A. The Biochemistry of Haemonchus contortus and Other Parasitic Nematodes. ADVANCES IN PARASITOLOGY 2016; 93:69-94. [PMID: 27238003 DOI: 10.1016/bs.apar.2016.02.010] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Different life cycle stages of Haemonchus contortus adapt to different ecosystems. This adaptation is accompanied by alterations in gene transcription and expression associated with the energy, amino acid, nitrogen, lipid and/or nucleic acid metabolism of the respective stages. For example, the aerobic metabolism of larvae depends on an efficient citric acid cycle, whereas the anaerobic metabolism of adults requires glycolysis, resulting in the production of volatile fatty acids, such as acetic acid and propionic acid. There are only few anthelmintics targeting nematode energy metabolism. In addition, H. contortus has reduced pathways for amino acid metabolism, polyamine metabolism and nitrogen excretion pathways. Moreover, nucleic acid metabolism comprising purine and pyrimidine salvage pathways as well as lipid metabolism are reduced. In addition, nematodes possess a particular composition of their cuticle. Energy production of adult worms is mainly linked to egg production and complex regulation of the neuromuscular system in both females and males. In this context, microtubules consisting of α- and β-tubulin heterodimers play a crucial role in the presynaptic vesicle transport. Due to the significant distinction of its quarternary structure in nematodes in comparison to other organisms, β-tubulin was identified as a major target for benzimidazoles used for anthelmintic treatment. Concerning the function of the neuromuscular system, acetylcholine, a ligand of the nicotinic acetylcholine receptor (nAChR), is the major excitatory neurotransmitter in H. contortus. In contrast, glutamate-gated chloride channels, calcium- and voltage-dependent potassium channels as well as γ-aminobutyric acid (GABA)A and its receptors act as inhibitory neurotransmitters and thus opponents to nAChR. For example, the calcium- and voltage-dependent potassium channel SLO-1 is an important target of emodepside, which is involved in the sensitive regulation of activatory and inhibitory receptors of the nervous system. Most of the modern anthelmintics target these different neuromuscular receptors. The mechanisms of resistance to anthelmintics, either specific or non-specific, are associated with changes in the molecular targets of the drugs, changes in metabolism of the drug (inactivation, removal or prevention of its activation) and/or increased efflux systems. The biochemical and molecular analyses of key developmental, metabolic and structural process of H. contortus still require substantial efforts. The nAChR, glutamate-gated chloride channel and calcium- and voltage-dependent potassium channel SLO-1 have long been known as being essential for nematode survival. Therefore, future research should be intensified to fully resolve the three-dimensional structures of these receptors, as has already been started for glutamate-gated chloride channel. With this knowledge, it should be possible to design new anthelmintics, which possess improved binding capacities to corresponding receptors.
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Affiliation(s)
- A Harder
- WE Biology, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
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