1
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Delves M, Lafuente-Monasterio MJ, Upton L, Ruecker A, Leroy D, Gamo FJ, Sinden R. Fueling Open Innovation for Malaria Transmission-Blocking Drugs: Hundreds of Molecules Targeting Early Parasite Mosquito Stages. Front Microbiol 2019; 10:2134. [PMID: 31572339 PMCID: PMC6753678 DOI: 10.3389/fmicb.2019.02134] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 08/30/2019] [Indexed: 11/13/2022] Open
Abstract
Background Despite recent successes at controlling malaria, progress has stalled with an estimated 219 million cases and 435,000 deaths in 2017 alone. Combined with emerging resistance to front line antimalarial therapies in Southeast Asia, there is an urgent need for new treatment options and novel approaches to halt the spread of malaria. Plasmodium, the parasite responsible for malaria propagates through mosquito transmission. This imposes an acute bottleneck on the parasite population and transmission-blocking interventions exploiting this vulnerability are recognized as vital for malaria elimination. Methods 13,533 small molecules with known activity against Plasmodium falciparum asexual parasites were screened for additional transmission-blocking activity in an ex vivo Plasmodium berghei ookinete development assay. Active molecules were then counterscreened in dose response against HepG2 cells to determine their activity/cytotoxicity window and selected non-toxic representative molecules were fully profiled in a range of transmission and mosquito infection assays. Furthermore, the entire dataset was compared to other published screens of the same molecules against P. falciparum gametocytes and female gametogenesis. Results 437 molecules inhibited P. berghei ookinete formation with an IC50 < 10 μM. of which 273 showed >10-fold parasite selectivity compared to activity against HepG2 cells. Active molecules grouped into 49 chemical clusters of three or more molecules, with 25 doublets and 94 singletons. Six molecules representing six major chemical scaffolds confirmed their transmission-blocking activity against P. falciparum male and female gametocytes and inhibited P. berghei oocyst formation in the standard membrane feeding assay at 1 μM. When screening data in the P. berghei development ookinete assay was compared to published screens of the same library in assays against P. falciparum gametocytes and female gametogenesis, it was established that each assay identified distinct, but partially overlapping subsets of transmission-blocking molecules. However, selected molecules unique to each assay show transmission-blocking activity in mosquito transmission assays. Conclusion The P. berghei ookinete development assay is an excellent high throughput assay for efficiently identifying antimalarial molecules targeting early mosquito stage parasite development. Currently no high throughput transmission-blocking assay is capable of identifying all transmission-blocking molecules.
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Affiliation(s)
- Michael Delves
- Department of Infection Biology, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom.,Department of Life Sciences, Imperial College London, London, United Kingdom
| | | | - Leanna Upton
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Andrea Ruecker
- Department of Life Sciences, Imperial College London, London, United Kingdom.,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
| | - Didier Leroy
- Medicines for Malaria Venture, Geneva, Switzerland
| | | | - Robert Sinden
- Department of Life Sciences, Imperial College London, London, United Kingdom
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2
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Colmenarejo G, Lozano S, González-Cortés C, Calvo D, Sanchez-Garcia J, Matilla JLP, Leroy D, Rodrigues J. Predicting transmission blocking potential of anti-malarial compounds in the Mosquito Feeding Assay using Plasmodium falciparum Male Gamete Inhibition Assay. Sci Rep 2018; 8:7764. [PMID: 29773818 PMCID: PMC5958111 DOI: 10.1038/s41598-018-26125-w] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 05/04/2018] [Indexed: 02/01/2023] Open
Abstract
Plasmodium falciparum Standard Membrane Feeding Assay (PfSMFA) is the current gold standard mosquito based confirmatory transmission blocking (TrB) assay for human malaria. However, owing to its complexity only selected gametocytocidal molecules are progressed into SMFA. Predictive tools for evaluation of TrB behavior of compounds in SMFA would be extremely beneficial, but lack of substantially large data sets from many mosquito feeds preempts the ability to perform correlations between outcomes from in vitro assays and SMFA. Here, a total of 44 different anti-malarial compounds were screened for inhibitory effect on male gamete formation in exflagellation inhibition assay (EIA) and the same drug-treated parasites were fed to mosquitoes in SMFA. Regression analysis was performed between outcomes of the two assays and regression models were applied to a randomly selected validation set of four compounds indicating no overfitting and good predictive power. In addition, the pIC50 for 11 different compounds obtained in the EIA was also correlated with pIC50’s in SMFA. Resulting regression models provided pIC50 predictions in SMFA with reasonably good accuracy thereby demonstrating the use of a simple in vitro assay to predict TrB of molecules in a complex mosquito based assay.
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Affiliation(s)
- Gonzalo Colmenarejo
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain.,Biostatistics and Bioinformatics Unit, IMDEA Food Institute, CEI UAM+CSIC, Ctra Cantoblanco 8, 28049, Madrid, Spain
| | - Sonia Lozano
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain
| | - Carolina González-Cortés
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain.,Complejo Asistencial Universitario de León. Altos de Nava s/n, 24071, León, Spain
| | - David Calvo
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain
| | - Juliana Sanchez-Garcia
- In vivo Science & Delivery (IVSD), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain
| | - Jesús-Luís Presa Matilla
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain
| | - Didier Leroy
- Medicines for Malaria Venture, Route de Pré-Bois 20, 1215, Geneva 15, Switzerland
| | - Janneth Rodrigues
- Diseases of the Developing World (DDW), GlaxoSmithKline, Severo Ochoa 2, Tres Cantos, 28760, Madrid, Spain.
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3
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Bioluminescence Method for In Vitro Screening of Plasmodium Transmission-Blocking Compounds. Antimicrob Agents Chemother 2017; 61:AAC.02699-16. [PMID: 28348156 PMCID: PMC5444155 DOI: 10.1128/aac.02699-16] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 03/23/2017] [Indexed: 12/12/2022] Open
Abstract
The sporogonic stage of the life cycle of Plasmodium spp., the causative agents of malaria, occurs inside the parasite's mosquito vector, where a process of fertilization, meiosis, and mitotic divisions culminates in the generation of large numbers of mammalian-infective sporozoites. Efforts to cultivate Plasmodium mosquito stages in vitro have proved challenging and yielded only moderate success. Here, we describe a methodology that simplifies the in vitro screening of much-needed transmission-blocking (TB) compounds employing a bioluminescence-based method to monitor the in vitro development of sporogonic stages of the rodent malaria parasite Plasmodium berghei. Our proof-of-principle assessment of the in vitro TB activity of several commonly used antimalarial compounds identified cycloheximide, thiostrepton, and atovaquone as the most active compounds against the parasite's sporogonic stages. The TB activity of these compounds was further confirmed by in vivo studies that validated our newly developed in vitro approach to TB compound screening.
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4
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Carvalho TG, Morahan B, John von Freyend S, Boeuf P, Grau G, Garcia-Bustos J, Doerig C. The ins and outs of phosphosignalling in Plasmodium: Parasite regulation and host cell manipulation. Mol Biochem Parasitol 2016; 208:2-15. [PMID: 27211241 DOI: 10.1016/j.molbiopara.2016.05.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 05/16/2016] [Indexed: 12/15/2022]
Abstract
Signal transduction and kinomics have been rapidly expanding areas of investigation within the malaria research field. Here, we provide an overview of phosphosignalling pathways that operate in all stages of the Plasmodium life cycle. We review signalling pathways in the parasite itself, in the cells it invades, and in other cells of the vertebrate host with which it interacts. We also discuss the potential of these pathways as novel targets for antimalarial intervention.
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Affiliation(s)
- Teresa Gil Carvalho
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Victoria 3800, Australia
| | - Belinda Morahan
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Victoria 3800, Australia
| | - Simona John von Freyend
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Victoria 3800, Australia
| | - Philippe Boeuf
- Burnet Institute, Melbourne, Victoria 3004, Australia; The University of Melbourne, Department of Medicine, Melbourne, Victoria 3010, Australia; Victorian Infectious Diseases Service, Royal Melbourne Hospital, Melbourne, Victoria 3010, Australia
| | - Georges Grau
- Vascular Immunology Unit, Department of Pathology, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia
| | - Jose Garcia-Bustos
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Victoria 3800, Australia
| | - Christian Doerig
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Microbiology, Monash University, Victoria 3800, Australia.
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5
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A male and female gametocyte functional viability assay to identify biologically relevant malaria transmission-blocking drugs. Antimicrob Agents Chemother 2014; 58:7292-302. [PMID: 25267664 DOI: 10.1128/aac.03666-14] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Malaria elimination will require interventions that prevent parasite transmission from the human host to the mosquito. Experimentally, this is usually determined by the expensive and laborious Plasmodium falciparum standard membrane feeding assay (PfSMFA), which has limited utility for high-throughput drug screening. In response, we developed the P. falciparum dual gamete formation assay (PfDGFA), which faithfully simulates the initial stages of the PfSMFA in vitro. It utilizes a dual readout that individually and simultaneously reports on the functional viability of male and female mature stage V gametocytes. To validate, we screen the Medicines for Malaria Venture (MMV) Malaria Box library with the PfDGFA. Unique to this assay, we find compounds that target male gametocytes only and also compounds with reversible and irreversible activity. Most importantly, we show that compound activity in the PfDGFA accurately predicts activity in PfSMFAs, which validates and supports its adoption into the transmission-stage screening pipeline.
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6
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Morahan B, Garcia-Bustos J. Kinase signalling in Plasmodium sexual stages and interventions to stop malaria transmission. Mol Biochem Parasitol 2014; 193:23-32. [PMID: 24509402 DOI: 10.1016/j.molbiopara.2014.01.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 01/22/2014] [Accepted: 01/28/2014] [Indexed: 12/26/2022]
Abstract
The symptoms of malaria, one of the infectious diseases with the highest mortality and morbidity world-wide, are caused by asexual parasites replicating inside red blood cells. Disease transmission, however, is effected by non-replicating cells which have differentiated into male or female gametocytes. These are the forms infectious to mosquito vectors and the insects are the only hosts where parasite sexual reproduction can take place. Malaria is thus a complex infection in which pharmacological treatment of symptoms may still allow transmission for long periods, while pharmacological blockage of infectivity may not cure symptoms. The process of parasite sexual differentiation and development is still being revealed but it is clear that kinase-mediated signalling mechanisms play a significant role. This review attempts to summarise our limited current knowledge on the signalling mechanisms involved in the transition from asexual replication to sexual differentiation and reproduction, with a brief mention to the effects of current treatments on the sexual stages and to some of the difficulties inherent in developing pharmacological interventions to curtail disease transmission.
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Affiliation(s)
- Belinda Morahan
- Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
| | - Jose Garcia-Bustos
- Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
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7
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Chemical signatures and new drug targets for gametocytocidal drug development. Sci Rep 2014; 4:3743. [PMID: 24434750 PMCID: PMC3894558 DOI: 10.1038/srep03743] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Accepted: 12/20/2013] [Indexed: 01/14/2023] Open
Abstract
Control of parasite transmission is critical for the eradication of malaria. However, most antimalarial drugs are not active against P. falciparum gametocytes, responsible for the spread of malaria. Consequently, patients can remain infectious for weeks after the clearance of asexual parasites and clinical symptoms. Here we report the identification of 27 potent gametocytocidal compounds (IC50 < 1 μM) from screening 5,215 known drugs and compounds. All these compounds were active against three strains of gametocytes with different drug sensitivities and geographical origins, 3D7, HB3 and Dd2. Cheminformatic analysis revealed chemical signatures for P. falciparum sexual and asexual stages indicative of druggability and suggesting potential targets. Torin 2, a top lead compound (IC50 = 8 nM against gametocytes in vitro), completely blocked oocyst formation in a mouse model of transmission. These results provide critical new leads and potential targets to expand the repertoire of malaria transmission-blocking reagents.
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8
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Male and Female Plasmodium falciparum Mature Gametocytes Show Different Responses to Antimalarial Drugs. Antimicrob Agents Chemother 2013; 57:3268-74. [DOI: 10.1128/aac.00325-13] [Citation(s) in RCA: 149] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
ABSTRACT
It is the mature gametocytes of
Plasmodium
that are solely responsible for parasite transmission from the mammalian host to the mosquito. They are therefore a logical target for transmission-blocking antimalarial interventions, which aim to break the cycle of reinfection and reduce the prevalence of malaria cases. Gametocytes, however, are not a homogeneous cell population. They are sexually dimorphic, and both males and females are required for parasite transmission. Using two bioassays, we explored the effects of 20 antimalarials on the functional viability of both male and female mature gametocytes of
Plasmodium falciparum
. We show that mature male gametocytes (as reported by their ability to produce male gametes, i.e., to exflagellate) are sensitive to antifolates, some endoperoxides, methylene blue, and thiostrepton, with submicromolar 50% inhibitory concentrations (IC
50
s), whereas female gametocytes (as reported by their ability to activate and form gametes expressing the marker Pfs25) are much less sensitive to antimalarial intervention, with only methylene blue and thiostrepton showing any significant activity. These findings show firstly that the antimalarial responses of male and female gametocytes differ and secondly that the mature male gametocyte should be considered a more vulnerable target than the female gametocyte for transmission-blocking drugs. Given the female-biased sex ratio of
Plasmodium falciparum
(∼3 to 5 females:1 male), current gametocyte assays without a sex-specific readout are unlikely to identify male-targeted compounds and prioritize them for further development. Both assays reported here are being scaled up to at least medium throughput and will permit identification of key transmission-blocking molecules that have been overlooked by other screening campaigns.
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9
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Biamonte MA, Wanner J, Le Roch KG. Recent advances in malaria drug discovery. Bioorg Med Chem Lett 2013; 23:2829-43. [PMID: 23587422 PMCID: PMC3762334 DOI: 10.1016/j.bmcl.2013.03.067] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 03/11/2013] [Accepted: 03/20/2013] [Indexed: 01/18/2023]
Abstract
This digest covers some of the most relevant progress in malaria drug discovery published between 2010 and 2012. There is an urgent need to develop new antimalarial drugs. Such drugs can target the blood stage of the disease to alleviate the symptoms, the liver stage to prevent relapses, and the transmission stage to protect other humans. The pipeline for the blood stage is becoming robust, but this should not be a source of complacency, as the current therapies set a high standard. Drug discovery efforts directed towards the liver and transmission stages are in their infancy but are receiving increasing attention as targeting these stages could be instrumental in eradicating malaria.
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Affiliation(s)
- Marco A Biamonte
- Drug Discovery for Tropical Diseases, Suite 230, San Diego, CA 92121, USA.
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10
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Plasmodium cell biology should inform strategies used in the development of antimalarial transmission-blocking drugs. Future Med Chem 2013; 4:2251-63. [PMID: 23234549 DOI: 10.4155/fmc.12.182] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Malaria is a disease with a devastating impact affecting 216 million people each year and causing 655,000 deaths, most of which are children under 5 years old. Recent appreciation that malaria eradication will require novel interventions to target the parasite during transmission from the human host to the mosquito has lead to an exciting surge in activity to develop transmission-blocking drugs and the high-throughput assays to screen for them. This article presents an overview of transmission-stage cell biology and discusses its impact on assay development to provide a context for researchers to evaluate the relative merits/drawbacks of both screening data obtained from current assays and considerations for future assay design. The most recent knowledge of the transmission-blocking properties of current antimalarial classes is also summarized and, underdeveloped targets for transmission-stage drug discovery are highlighted.
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11
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A high-throughput assay for the identification of malarial transmission-blocking drugs and vaccines. Int J Parasitol 2012; 42:999-1006. [PMID: 23023046 DOI: 10.1016/j.ijpara.2012.08.009] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 07/16/2012] [Accepted: 08/21/2012] [Indexed: 11/21/2022]
Abstract
Following the cessation of the global malaria eradication initiative in the 1970s, the prime objective of malarial intervention has been to reduce morbidity and mortality. This motivated the development of high throughput assays to determine the impact of interventions on asexual bloodstage parasites. In response to the new eradication agenda, interrupting parasite transmission from the human to the mosquito has been recognised as an important and additional target for intervention. Current assays for Plasmodium mosquito stage development are very low throughput and resource intensive, and are therefore inappropriate for high throughput screening. Using an ookinete-specific GFP reporter strain of the rodent parasite Plasmodium berghei, it has been possible to develop and validate a high biological complexity, high throughput bioassay that can rapidly, reproducibly and accurately evaluate the effect of transmission-blocking drugs or vaccines on the ability of host-derived gametocytes to undergo the essential onward steps of gamete formation, fertilisation and ookinete maturation. This assay may greatly accelerate the development of malaria transmission-blocking interventions.
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12
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Delves M, Plouffe D, Scheurer C, Meister S, Wittlin S, Winzeler EA, Sinden RE, Leroy D. The activities of current antimalarial drugs on the life cycle stages of Plasmodium: a comparative study with human and rodent parasites. PLoS Med 2012; 9:e1001169. [PMID: 22363211 PMCID: PMC3283556 DOI: 10.1371/journal.pmed.1001169] [Citation(s) in RCA: 253] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 12/28/2011] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Malaria remains a disease of devastating global impact, killing more than 800,000 people every year-the vast majority being children under the age of 5. While effective therapies are available, if malaria is to be eradicated a broader range of small molecule therapeutics that are able to target the liver and the transmissible sexual stages are required. These new medicines are needed both to meet the challenge of malaria eradication and to circumvent resistance. METHODS AND FINDINGS Little is known about the wider stage-specific activities of current antimalarials that were primarily designed to alleviate symptoms of malaria in the blood stage. To overcome this critical gap, we developed assays to measure activity of antimalarials against all life stages of malaria parasites, using a diverse set of human and nonhuman parasite species, including male gamete production (exflagellation) in Plasmodium falciparum, ookinete development in P. berghei, oocyst development in P. berghei and P. falciparum, and the liver stage of P. yoelii. We then compared 50 current and experimental antimalarials in these assays. We show that endoperoxides such as OZ439, a stable synthetic molecule currently in clinical phase IIa trials, are strong inhibitors of gametocyte maturation/gamete formation and impact sporogony; lumefantrine impairs development in the vector; and NPC-1161B, a new 8-aminoquinoline, inhibits sporogony. CONCLUSIONS These data enable objective comparisons of the strengths and weaknesses of each chemical class at targeting each stage of the lifecycle. Noting that the activities of many compounds lie within achievable blood concentrations, these results offer an invaluable guide to decisions regarding which drugs to combine in the next-generation of antimalarial drugs. This study might reveal the potential of life-cycle-wide analyses of drugs for other pathogens with complex life cycles.
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Affiliation(s)
- Michael Delves
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - David Plouffe
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
| | - Christian Scheurer
- Swiss Tropical & Public Health Institute Swiss TPH, Basel, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Stephan Meister
- The Scripps Research Institute, La Jolla, California, United States of America
| | - Sergio Wittlin
- Swiss Tropical & Public Health Institute Swiss TPH, Basel, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Elizabeth A. Winzeler
- Genomics Institute of the Novartis Research Foundation, San Diego, California, United States of America
- The Scripps Research Institute, La Jolla, California, United States of America
| | - Robert E. Sinden
- Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Didier Leroy
- Medicines for Malaria Venture, Geneva, Switzerland
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Sinden RE, Talman A, Marques SR, Wass MN, Sternberg MJE. The flagellum in malarial parasites. Curr Opin Microbiol 2010; 13:491-500. [PMID: 20566299 DOI: 10.1016/j.mib.2010.05.016] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 05/26/2010] [Accepted: 05/27/2010] [Indexed: 12/19/2022]
Abstract
The malarial parasites assemble flagella exclusively during the formation of the male gamete in the midgut of the female mosquito vector. The observation of gamete formation ex vivo reported by Laveran (Laveran MA: De la nature parasitaire des accidents de l'impaludisme. Comptes Rendues De La Societe de Biologie. Paris 1881, 93:627-630) was seminal to the discovery of the parasite itself. Following ingestion of malaria-infected blood by the mosquito, microgamete formation from the terminally arrested gametocytes is exceptionally rapid, completing three mitotic divisions in just a few minutes, and is precisely regulated. This review attempts to draw together the diverse original observations with subsequent electron microscopic studies, and recent work on the signalling pathways regulating sexual development, together with transcriptomic and proteomic studies that are paving the way to new understandings of the molecular mechanisms involved and the potential they offer for effective interventions to block the transmission of the parasites in natural communities.
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Affiliation(s)
- R E Sinden
- The Malaria Centre, The Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
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14
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Delves MJ, Sinden RE. A semi-automated method for counting fluorescent malaria oocysts increases the throughput of transmission blocking studies. Malar J 2010; 9:35. [PMID: 20113492 PMCID: PMC2824803 DOI: 10.1186/1475-2875-9-35] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Accepted: 01/29/2010] [Indexed: 11/30/2022] Open
Abstract
Background Malaria transmission is now recognized as a key target for intervention. Evaluation of the Plasmodium oocyst burden in the midguts of Anopheles spp. is important for many of assays investigating transmission. However, current assays are very time-consuming, manually demanding and patently subject to observer-observer variation. Methods This report presents the development of a method to rapidly, accurately and consistently determine oocyst burdens on mosquito midguts using GFP-expressing Plasmodium berghei and a custom-written macro for ImageJ. The counting macro was optimized and found to be fit-for-purpose by performing gametocyte membrane feeds with parasite infected blood. Dissected midguts were counted both manually and using the automated macro, then compared. The optimized settings for the macro were then validated by using it to determine the transmission blocking efficacies of two anti-malarial compounds - dehydroepiandrosterone sulphate and lumefantrine, in comparison to manually determined analysis of the same experiment. Results Concurrence of manual and macro counts was very high (R2 = 0.973) and reproducible. Estimated transmission blocking efficacies between manual and automated analysis were highly concordant, indicating that dehydroepiandrosterone sulphate has little or no transmission blocking potential, whilst lumefantrine strongly inhibits sporogony. Conclusion Recognizing a potential five-fold increase in throughput, the resulting reduction in personnel costs, and the absence of inter-operator/laboratory variation possible with this approach, this counting macro may be a benefit to the malaria community.
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Affiliation(s)
- Michael J Delves
- Division of Cell and Molecular Biology, Imperial College London, London, UK.
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15
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Lang-Unnasch N, Murphy AD. Metabolic changes of the malaria parasite during the transition from the human to the mosquito host. Annu Rev Microbiol 1999; 52:561-90. [PMID: 9891808 DOI: 10.1146/annurev.micro.52.1.561] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Plasmodium falciparum is an obligate human parasite that is the causative agent of the most lethal form of human malaria. Transmission of P. falciparum to a new human host requires a mosquito vector within which sexual replication occurs. P. falciparum replicates as an intracellular parasite in man and as an extracellular parasite in the mosquito, and it undergoes multiple developmental changes in both hosts. Changes in the environment and the activities of parasites in these various life-cycle stages are likely to be reflected in changes in the metabolic needs and capabilities of the parasite. Most of our knowledge of the metabolic capabilities of P. falciparum is derived from studies of the asexual erythrocytic cycle of the parasite, the portion of the parasite life cycle found in infected humans that is responsible for malarial symptoms. Efforts to control transmission and to understand the sometimes unique biology of this parasite have led to information about the metabolic capabilities of sexual and/or sporogonic stages of these parasites. This review focuses on comparing and contrasting the carbohydrate, nucleic acid, and protein synthetic capabilities of asexual erythrocytic stages and sexual stages of P. falciparum.
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Affiliation(s)
- N Lang-Unnasch
- Department of Medicine, University of Alabama at Birmingham 35294-2170, USA.
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16
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Abstract
The Steering Committee on Drugs for Malaria (CHEMAL) of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR) has identified tubulin as a potential drug target, but one that is not yet ;validated'. Several inhibitors of tubulins, the principal proteins of microtubules, are potent inhibitors of the development and multiplication of malarial parasites in culture and in vivo. However, most of these compounds are also inhibitors of mammalian cell proliferation. Here, Angus Bell reviews the structure and properties of microtubules, their roles in Plasmodium cells, and the effects of various microtubule inhibitors on the parasite. He argues that microtubule inhibitors are not equally toxic to all proliferating cells but, by virtue of differential tubulin binding, show selective toxicity that might allow their use as antimalarial drugs.
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Affiliation(s)
- A Bell
- Department of Microbiology, Moyne Institute, Trinity College, Dublin 2, Ireland
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Sinden RE, Butcher GA, Billker O, Fleck SL. Regulation of infectivity of Plasmodium to the mosquito vector. ADVANCES IN PARASITOLOGY 1996; 38:53-117. [PMID: 8701799 DOI: 10.1016/s0065-308x(08)60033-0] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- R E Sinden
- Department of Biology, Imperial College of Science, Technology and Medicine, South Kensington, London, UK
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Fries HC, Lamers MB, van Deursen J, Ponnudurai T, Meuwissen JH. Biosynthesis of the 25-kDa protein in the macrogametes/zygotes of Plasmodium falciparum. Exp Parasitol 1990; 71:229-35. [PMID: 2197114 DOI: 10.1016/0014-4894(90)90025-8] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Synthesis of the 25-kDa protein in the early midgut stages of Plasmodium falciparum was studied, using metabolic inhibitors (colchicine and actinomycin D) and pulse-labeling experiments. Experiments with colchicine showed that, immediately after induction of macrogametogenesis, 25-kDa protein synthesis occurs in both fertilized and nonfertilized macrogametes. The amount of 25-kDa protein synthesized increased slowly during time. Experiments with actinomycin D revealed that the slow increase of synthesis may be dependent on de novo messenger RNA synthesis.
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Affiliation(s)
- H C Fries
- Institute of Medical Parasitology, University of Nijmegen, The Netherlands
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Janse CJ, Ponnudurai T, Lensen AH, Meuwissen JH, Ramesar J, Van der Ploeg M, Overdulve JP. DNA synthesis in gametocytes of Plasmodium falciparum. Parasitology 1988; 96 ( Pt 1):1-7. [PMID: 3283664 DOI: 10.1017/s0031182000081609] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The DNA content of Plasmodium falciparum gametocytes during intra-erythrocytic development and during gametogenesis was established by cytophotometric methods. Intraerythrocytic micro- and macrogametocytes (Stage I-Stage VB) contain about twice the amount of DNA of haploid sporozoites and ringstages, indicating that DNA is synthesized during transformation of ringforms into Stage I gametocytes. Microgametocytes, after activation at pH 8, rapidly duplicate their genome several times, while the DNA content of macrogametocytes remains constant during gametogenesis.
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Affiliation(s)
- C J Janse
- Department of Tropical Veterinary Medicine and Protozoology, University of Utrecht, The Netherlands
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Dearsly AL, Nicholas J, Sinden RE. Sexual development in Plasmodium berghei: the use of mitomycin C to separate infective gametocytes in vivo and ookinetes in vitro. Int J Parasitol 1987; 17:1307-12. [PMID: 3123410 DOI: 10.1016/0020-7519(87)90096-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Janse CJ, van der Klooster PF, van der Kaay HJ, van der Ploeg M, Overdulve JP. Mitomycin-C is an unreliable inhibitor for study of DNA synthesis in Plasmodium. Mol Biochem Parasitol 1986; 21:33-6. [PMID: 3095638 DOI: 10.1016/0166-6851(86)90076-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Cytophotometric studies on DNA synthesis during asexual and sexual development of Plasmodium berghei contradicted earlier conclusions on DNA synthesis in Plasmodium which were largely based on experiments in which mitomycin-C had been used as a DNA replication inhibitor. Therefore, the effect of mitomycin on intra erythrocytic asexual development and on microgametogenesis, fertilization and zygote/ookinete development of P. berghei was studied in vitro. All DNA-synthesizing stages (schizonts, exflagellating microgametocytes and zygotes) and also DNA synthesis itself in all such stages, are totally unaffected by mitomycin concentrations 10 times higher than that which inhibits normal development of the non-DNA-synthesizing rings and trophozoites. The results are explained by the mode of action of mitomycin.
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Janse CJ, van der Klooster PF, van der Kaay HJ, van der Ploeg M, Overdulve JP. DNA synthesis in Plasmodium berghei during asexual and sexual development. Mol Biochem Parasitol 1986; 20:173-82. [PMID: 3092048 DOI: 10.1016/0166-6851(86)90029-0] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
DNA contents of individual stages of Plasmodium berghei were measured by direct microfluorometry after Feulgen-pararosaniline (SO2) staining. Sporozoites, intra-erythrocytic ringforms and trophozoites (until at least 15 h after invasion) are haploid and non-synthesizing DNA. DNA is synthesized just before and during schizogony, which takes 4-6 h. Genome duplication and segregation are alternating events throughout this process. Mature micro- and macrogametocytes have DNA contents between the haploid and diploid value; most, if not all of the DNA in excess of the haploid value is synthesized during the last 5-10 h of maturation. During gametogenesis microgametocytes within 8-10 min synthesize DNA steadily and at a very high rate to more than the octoploid value while the DNA content of macrogametocytes remains constant. Fertilization in vitro takes place within 1 h after gamete formation. Within 2 h and coinciding with the onset of meiosis the zygote then synthesizes DNA up to almost the tetraploid value, after which synthesis stops during ookinete development. All the above mentioned processes of DNA synthesis are reversibly inhibited by aphidicolin (C50 from 3-13 microM). From the rate of DNA synthesis during microgametogenesis we calculated a minimum of 1300 origins of replication in the haploid genome of P. berghei.
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Janse CJ, Van der Klooster PF, Van der Kaay HJ, Van der Ploeg M, Overdulve JP. Rapid repeated DNA replication during microgametogenesis and DNA synthesis in young zygotes of Plasmodium berghei. Trans R Soc Trop Med Hyg 1986; 80:154-7. [PMID: 3088783 DOI: 10.1016/0035-9203(86)90219-1] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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Sinden RE, Hartley RH, King NJ. Gametogenesis in Plasmodium; the inhibitory effects of anticytoskeletal agents. Int J Parasitol 1985; 15:211-7. [PMID: 4039709 DOI: 10.1016/0020-7519(85)90089-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Abstract
This review examines the sexual development of Plasmodium spp. particularly relating the ultrastructural organization of their cells to the limited, though rapidly expanding, body of metabolic and biochemical studies. Thus it is hoped the article may provide a useful background of information for those undertaking studies on the sexual parasites with the objective of developing methods for the immunological and chemotherapeutic control of malaria transmission. These objectives, however, should not dominate our clear recognition that the three phases of sexual development, gametocytogenesis, gametogenesis and fertilization contain within them examples of control and assembly of organelles without peer amongst eukaryotic cells.
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Abstract
Plasmodium falciparum was grown in vitro in blood taken from naturally infected Gambian patients, and the development of the cultured sexual parasites was studied by light and electron microscopy. The young (Stage II and III) female gametocytes undergo a single cryptomitotic nuclear division. This division immediately follows the S phase which Sinden & Smalley (1979) have demonstrated in the Stage I and II gametocytes of both sexes. The male gametocytes, by contrast, do not undergo mitosis during their maturation period in the erythrocyte and thus remain polyploid. Hence the cell cycles of the male and female gametocytes differ significantly. The ultrastructural basis of the characteristic changes in shape of the developing gametocyte are shown to be due to the assembly and subsequent loss of components of the subpellicular membranous and microtubular cytoskeleton. Stage I-III gametocytes synthesize numerous ribosomes and endoplasmic reticulum. This correlates with the active synthesis of RNA and protein in these young parasites (Sinden & Smalley, 1979). The marked reduction in macromolecular synthesis in the mature parasites is paralleled by a reduction in cytoplasmic ribosome density in the male gametocyte only. In the female, however, this reduction in activity is correlated with the appearance of a nucleolus. These changes suggest that different mechanisms are being used to control RNA synthesis in the two sexes of gametocyte.
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Golenser J, Casuto D, Pollack Y. Plasmodium falciparum: in vitro induction of resistance to aminopterin. Exp Parasitol 1981; 52:371-7. [PMID: 6172284 DOI: 10.1016/0014-4894(81)90095-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Abstract
Reproducible growth of gametocytes of Plasmodium falciparum in vitro was obtained from ring-stages taken directly from naturally infected patients and from the same material following storage in liquid nitrogen. Progressive sexual differentiation in vitro was examined for a finite period of 9 days in microcultures and was, for convenience, divided into 5 stages using established morphological criteria (Hawking, Wilson & Gammage, 1971). This microculture system was adapted as a bioassay for various anti-metabolites. Drug activity was measured by observing the inhibition of the established pattern of sequential development in experimental as compared to control cultures. Inhibitors used were directed against DNA, RNA and protein metabolism and microtubule assembly. As a result of these studies it is proposed that the sexual cell-cycle of P. falciparum is characterized by 4 phases. (1) A G1 period which lasts only a few hours. (2) The S phase, where DNA synthesis occurs, occupies the remainder of the first 2 days of development - both G1 and S are confined to stage I and II gametocytes. (3) G2, which is subdivided into 2 sections: G2A, characterized by stage II and III gametocytes, in which significant RNA and protein synthesis continue to occur; and G2B, where there is a progressive increase in transcription control resulting in the depression of both RNA and protein synthesis. Nonetheless, continued morphological differentiation occurs in the latter section transforming the parasites to stage IV and the morphologically and functionally mature stage V. The final M phase is marked by the brief and exposive events of gametogenesis, during which further protein synthesis occurs de novo. The proposed cell-cycle is examined as a model for studies on the activity of gametocytocidal compounds.
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Smalley ME. Plasmodium falciparum gametocytes: The effect of chloroquine on their development. Trans R Soc Trop Med Hyg 1977; 71:526-9. [PMID: 343314 DOI: 10.1016/0035-9203(77)90149-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Asexual erythrocytic parasites of Plasmodium falciparum are killed by chloroquine, whilst mature gametocytes are not. The gametocytes of P. falciparum take 10 days to develop to maturity and their sensitivity to chloroquine during this time was studied in vitro to investigate when the switch from susceptibility to insusceptibility occurred and to compare the responses of asexual and immature sexual parasites to the drug. 45 to 50% of asexual parasites and immature gametocytes less than one day old survived in 0.1n. mols of chloroquine per ml but 0.3n. mols of drug per ml was lethal to both. Chloroquine at 1.0n mols per ml was lethal to developing gametocytes during their first six days of growth probably due, at least in part, to the drug disorganizing the parasite's digestion of host erythrocyte haemoglobin. The drug clumped the pigment of developing gametocytes. Only immature gametocytes in the final stage of development (stage 4) survive in high chloroquine concentrations.
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