A high-throughput assay for the identification of malarial transmission-blocking drugs and vaccines
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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ABSTRACT: Current antimalarials are under continuous threat due to the relentless development of drug resistance by malaria parasites. We previously reported promising in vitro parasite killing activity with the histone methyltransferase inhibitor BIX-01294 and its analogue TM2-115. Here we further characterize these diaminoquinazolines for in vitro and in vivo efficacy and pharmacokinetic properties to prioritize and direct compound development. BIX-01294 and TM2-115 displayed potent in vitro activity with IC50 values <50 nM against drug sensitive laboratory strains and multi-drug resistant field isolates including artemisinin refractory P. falciparum isolates. Activity against ex vivo clinical isolates of both P. falciparum and P. vivax were similar with potencies of 300-400 nM. Sexual stage gametocyte inhibition occurs at micromolar levels, however, mature gametocyte progression to gamete formation is inhibited at sub-micromolar concentrations. Parasite reduction ratio analysis confirms a fast asexual stage rate of killing. Both compounds examined displayed oral efficacy in in vivo mouse models of P. berghei and P. falciparum infection. The discovery of a rapid and broad-acting antimalarial compound class targeting blood stage infection, including transmission stage parasites, and effective against multiple malaria species reveals the diaminoquinazoline scaffold to be a very promising lead for development into greatly needed novel therapies to control malaria. Copyright © 2014, American Society for Microbiology. All Rights Reserved.Antimicrobial Agents and Chemotherapy 11/2014; 59(2). DOI:10.1128/AAC.04419-14 · 4.45 Impact Factor
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ABSTRACT: Indirect clinical measures assessing anti-malarial drug transmission-blocking activity in falciparum malaria include measurement of the duration of gametocytaemia, the rate of gametocyte clearance or the area under the gametocytaemia-time curve (AUC). These may provide useful comparative information, but they underestimate dose-response relationships for transmission-blocking activity. Following 8-aminoquinoline administration P. falciparum gametocytes are sterilized within hours, whereas clearance from blood takes days. Gametocytaemia AUC and clearance times are determined predominantly by the more numerous female gametocytes, which are generally less drug sensitive than the minority male gametocytes, whereas transmission-blocking activity and thus infectivity is determined by the more sensitive male forms. In choosing doses of transmission-blocking drugs there is no substitute yet for mosquito-feeding studies.Malaria Journal 12/2014; 13(1):483. DOI:10.1186/1475-2875-13-483 · 3.49 Impact Factor
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ABSTRACT: To achieve malarial elimination we must employ interventions that reduce the exposure of human populations to infectious mosquitoes. To this end, numerous anti-malarial drugs are under assessment in a variety of transmission-blocking assays which fail to measure the single crucial criteria of a successful intervention; namely impact on case incidence within a vertebrate population (reduction in Ro/effect size). Consequently, any reduction in new infections due to drug treatment (and how this may be influenced by differing transmission settings) is not currently examined, limiting the translation of any findings. We describe the use of a laboratory population model to assess how individual anti-malarial drugs can impact the number of secondary P.berghei infections over a cycle of transmission. We examine the impact of multiple clinical and pre-clinical drugs on both insect and vertebrate populations at multiple transmission settings. Both primaquine (>6mg/kg) and NITD609 (8.1mg/kg) have significant impact across multiple transmission settings, but artemether/lumefantrine (57/11.8mg/kg), OZ439 (6.5mg/kg) and primaquine (<1.25mg/kg) demonstrated potent efficacy only at lower transmission settings. While directly demonstrating the impact of drug treatment on anti-malarial drug treatment on vertebrate populations, we additionally calculate effect size for each treatment, allowing for head-to-head comparison of the potential impact of individual drugs within epidemiologically relevant settings, supporting their usage within elimination campaigns.Antimicrobial Agents and Chemotherapy 11/2014; 59(1). DOI:10.1128/AAC.03942-14 · 4.45 Impact Factor