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      A high throughput screen for next-generation leads targeting malaria parasite transmission

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          Abstract

          Spread of parasite resistance to artemisinin threatens current frontline antimalarial therapies, highlighting the need for new drugs with alternative modes of action. Since only 0.2–1% of asexual parasites differentiate into sexual, transmission-competent forms, targeting this natural bottleneck provides a tangible route to interrupt disease transmission and mitigate resistance selection. Here we present a high-throughput screen of gametogenesis against a ~70,000 compound diversity library, identifying seventeen drug-like molecules that target transmission. Hit molecules possess varied activity profiles including male-specific, dual acting male–female and dual-asexual-sexual, with one promising N-((4-hydroxychroman-4-yl)methyl)-sulphonamide scaffold found to have sub-micromolar activity in vitro and in vivo efficacy. Development of leads with modes of action focussed on the sexual stages of malaria parasite development provide a previously unexplored base from which future therapeutics can be developed, capable of preventing parasite transmission through the population.

          Abstract

          Sexual forms of malaria parasites are responsible for transmission to the mosquito. Anti-malarial drug resistance remains a serious problem and requires advent of new drug therapies. Here, the authors present a high-throughput screen of potential antimalarial compounds, identifying seventeen drug-like molecules specifically targeting transmission.

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          Most cited references35

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          Regulation of sexual development of Plasmodium by translational repression.

          G Mair (2006)
          Translational repression of messenger RNAs (mRNAs) plays an important role in sexual differentiation and gametogenesis in multicellular eukaryotes. Translational repression and mRNA turnover were shown to influence stage-specific gene expression in the protozoan Plasmodium. The DDX6-class RNA helicase, DOZI (development of zygote inhibited), is found in a complex with mRNA species in cytoplasmic bodies of female, blood-stage gametocytes. These translationally repressed complexes are normally stored for translation after fertilization. Genetic disruption of pbdozi inhibits the formation of the ribonucleoprotein complexes, and instead, at least 370 transcripts are diverted to a degradation pathway.
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            Chemical genetics of Plasmodium falciparum

            Malaria caused by Plasmodium falciparum is a catastrophic disease worldwide (880,000 deaths yearly). Vaccine development has proved difficult and resistance has emerged for most antimalarials. In order to discover new antimalarial chemotypes, we have employed a phenotypic forward chemical genetic approach to assay 309,474 chemicals. Here we disclose structures and biological activity of the entire library, many of which exhibited potent in vitro activity against drug resistant strains, and detailed profiling of 172 representative candidates. A reverse chemical genetic study identified 19 new inhibitors of 4 validated drug targets and 15 novel binders among 61 malarial proteins. Phylochemogenetic profiling in multiple organisms revealed similarities between Toxoplasma gondii and mammalian cell lines and dissimilarities between P. falciparum and related protozoans. One exemplar compound displayed efficacy in a murine model. Overall, our findings provide the scientific community with new starting points for malaria drug discovery.
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              Revisiting the circulation time of Plasmodium falciparum gametocytes: molecular detection methods to estimate the duration of gametocyte carriage and the effect of gametocytocidal drugs

              Background There is renewed acknowledgement that targeting gametocytes is essential for malaria control and elimination efforts. Simple mathematical models were fitted to data from clinical trials in order to determine the mean gametocyte circulation time and duration of gametocyte carriage in treated malaria patients. Methods Data were used from clinical trials from East Africa. The first trial compared non-artemisinin combination therapy (non-ACT: sulphadoxine-pyrimethamine (SP) plus amodiaquine) and artemisinin-based combination therapy (ACT: SP plus artesunate (AS) or artemether-lumefantrine). The second trial compared ACT (SP+AS) with ACT in combination with a single dose of primaquine (ACT-PQ: SP+AS+PQ). Mature gametocytes were quantified in peripheral blood samples by nucleic acid sequence based amplification. A simple deterministic compartmental model was fitted to gametocyte densities to estimate the circulation time per gametocyte; a similar model was fitted to gametocyte prevalences to estimate the duration of gametocyte carriage after efficacious treatment. Results The mean circulation time of gametocytes was 4.6-6.5 days. After non-ACT treatment, patients were estimated to carry gametocytes for an average of 55 days (95% CI 28.7 - 107.7). ACT reduced the duration of gametocyte carriage fourfold to 13.4 days (95% CI 10.2-17.5). Addition of PQ to ACT resulted in a further fourfold reduction of the duration of gametocyte carriage. Conclusions These findings confirm previous estimates of the circulation time of gametocytes, but indicate a much longer duration of (low density) gametocyte carriage after apparently successful clearance of asexual parasites. ACT shortened the period of gametocyte carriage considerably, and had the most pronounced effect on mature gametocytes when combined with PQ.
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                Author and article information

                Contributors
                francisco-javier.b.gamo@gsk.com
                jake.baum@imperial.ac.uk
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                18 September 2018
                18 September 2018
                2018
                : 9
                : 3805
                Affiliations
                [1 ]ISNI 0000 0001 2113 8111, GRID grid.7445.2, Department of Life Sciences, , Imperial College London, Sir Alexander Fleming Building, ; Exhibition Road, South Kensington, London SW7 2AZ UK
                [2 ]ISNI 0000 0004 1768 1287, GRID grid.419327.a, Diseases of the Developing World (DDW), GlaxoSmithKline, ; 28760 Tres Cantos, Madrid Spain
                [3 ]ISNI 0000 0001 2107 4242, GRID grid.266100.3, School of Medicine, , University of California San Diego, ; 9500 Gilman Drive 0760, La Jolla, CA 92093 USA
                [4 ]ISNI 0000 0001 2113 8111, GRID grid.7445.2, Department of Chemistry, , Imperial College London, ; Exhibition Road, South Kensington, London SW7 2AZ UK
                Author information
                http://orcid.org/0000-0003-3804-9670
                http://orcid.org/0000-0002-2101-6939
                http://orcid.org/0000-0001-7082-6201
                http://orcid.org/0000-0002-1767-7072
                Article
                5777
                10.1038/s41467-018-05777-2
                6143625
                30228275
                5d64a378-cbf2-4f71-91d0-f0f949bc1c8e
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 24 May 2018
                : 26 July 2018
                Funding
                Funded by: FundRef https://doi.org/10.13039/100000865, Bill and Melinda Gates Foundation;
                Award ID: OPP1043501
                Award Recipient :
                Funded by: FundRef https://doi.org/10.13039/100004440, Wellcome Trust;
                Award ID: 100993/Z/13/Z
                Award Recipient :
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