A high-throughput assay for the identification of malarial transmission-blocking drugs and vaccines

Department of Life Sciences, Imperial College, London SW7 2AZ, UK. Electronic address: .
International journal for parasitology (Impact Factor: 3.87). 09/2012; 42(11). DOI: 10.1016/j.ijpara.2012.08.009
Source: PubMed

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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Available from: Chandra Ramakrishnan, Jul 27, 2014
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    • "To verify if stage V gametocytes are able to continue their differentiation toward male and female gametes, two different assays are available. The P. falciparum exflagellation assay is limited to male gametocytes, and although it has recently been semi-automatized by image acquisition of motile ‘exflagellation’ events, still it is limited by the short time-window of this phenomenon [43]. "
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    ABSTRACT: The Coordination, Rationalization, and Integration of antiMALarial drug Discovery & Development Initiatives (CRIMALDDI) Consortium, funded by the EU Framework Seven Programme, has attempted, through a series of interactive and facilitated workshops, to develop priorities for research to expedite the discovery of new anti-malarials. This paper outlines the recommendations for the development of enabling technologies and the identification of novel targets. Screening systems must be robust, validated, reproducible, and represent human malaria. They also need to be cost-effective. While such systems exist to screen for activity against blood stage Plasmodium falciparum, they are lacking for other Plasmodium spp. and other stages of the parasite’s life cycle. Priority needs to be given to developing high-throughput screens that can identify activity against the liver and sexual stages. This in turn requires other enabling technologies to be developed to allow the study of these stages and to allow for the culture of liver cells and the parasite at all stages of its life cycle. As these enabling technologies become available, they will allow novel drug targets to be studied. Currently anti-malarials are mostly targeting the asexual blood stage of the parasite’s life cycle. There are many other attractive targets that need to be investigated. The liver stages and the sexual stages will become more important as malaria control moves towards malaria elimination. Sexual development is a process offering multiple targets, even though the mechanisms of differentiation are still not fully understood. However, designing a drug whose effect is not curative but would be used in asymptomatic patients is difficult given current safety thresholds. Compounds active against the liver schizont would have a prophylactic effect and Plasmodium vivax elimination requires effectors against the dormant liver hypnozoites. It may be that drugs to be used in elimination campaigns will also need to have utility in the control phase. Compounds with activity against blood stages need to be screened for activity against other stages. Natural products should also be a valuable source of new compounds. They often occupy non-Lipinski chemical space and so may reveal valuable new chemotypes.
    Malaria Journal 11/2013; 12(1):396. DOI:10.1186/1475-2875-12-396 · 3.11 Impact Factor
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    • "Luciferase-expressing mosquito stages could speed up and simplify the transmission blocking vaccine effect as assessment of parasite load could be achieved automatically in a plate reader and thus be more reliably measured. Although a fluorescent Plasmodium berghei parasite line has been created to measure the effect of transmission blocking [9], measurement of luciferase activity is simpler to achieve and ultimately, interventions need to be tested on the human malaria parasite rather than a model rodent malaria parasite. Similarly, a luciferase expressing P. falciparum liver stage parasite could be used to assess interventions that aim at blocking human infection. "
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    ABSTRACT: Plasmodium falciparum is the pathogenic agent of the most lethal of human malarias. Transgenic P. falciparum parasites expressing luciferase have been created to study drug interventions of both asexual and sexual blood stages but luciferase-expressing mosquito stage and liver stage parasites have not been created which has prevented the easy quantification of mosquito stages (e.g. for transmission blocking interventions) and liver stage development (for interventions that prevent infection). To overcome this obstacle, we have created a transgenic P. falciparum NF54 parasite that expresses a GFP-luciferase transgene throughout the life cycle. Luciferase expression is robust and measurable at all life cycle stages, including midgut oocyst, and salivary gland sporozoites as well as liver stages, where in vivo development is easily measurable using humanized mouse infections in conjunction with an in vivo imaging system. This parasite reporter strain will accelerate testing of interventions against mosquito stages and pre-erythrocytic life cycle stages.
    Molecular and Biochemical Parasitology 10/2012; 186(2). DOI:10.1016/j.molbiopara.2012.10.004 · 1.79 Impact Factor
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    Microbial pathogens and strategies for combating them: science, technology and education., 2013 edited by A. Mendez Vilas, 01/2013: chapter Antimalarial drugs resistance in Plasmodium falciparum and the current strategies to overcome them.: pages 269-282; Formatex Research Center., ISBN: ISBN-13 Vol. 1: 978-84-939843-9-7
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