Chemical matter is needed to target the divergent biology associated with the different life cycle stages of Plasmodium. Here, we report the parallel de novo screening of the Medicines for Malaria Venture (MMV) Pandemic Response Box against Plasmodium asexual and liver stage parasites, stage IV/V gametocytes, gametes, oocysts and as endectocides. Unique chemotypes were identified with both multistage activity or stage-specific activity, including structurally diverse gametocyte-targeted compounds with potent transmission-blocking activity, such as the JmjC inhibitor ML324 and the antitubercular clinical candidate SQ109. Mechanistic investigations prove that ML324 prevents histone demethylation, resulting in aberrant gene expression and death in gametocytes. Moreover, the selection of parasites resistant to SQ109 implicates the druggable V-type H+-ATPase for the reduced sensitivity. Our data therefore provides an expansive dataset of compounds that could be redirected for antimalarial development and also point towards proteins that can be targeted in multiple parasite life cycle stages.

A novel diazaspiro [3.4]octane series was identified from a Plasmodium falciparum whole-cell high-throughput screening campaign. Hits displayed activity against multiple stages of the parasite lifecycle, which together with a novel sp 3 -rich scaffold provided an attractive starting point for a hit-to-lead medicinal chemistry optimization and biological profiling program. Structure−activity-relationship studies led to the identification of compounds that showed low nanomolar asexual blood-stage activity (<50 nM) together with strong gametocyte sterilizing properties that translated to transmission-blocking activity in the standard membrane feeding assay. Mechanistic studies through resistance selection with one of the analogues followed by wholegenome sequencing implicated the P. falciparum cyclic amine resistance locus in the mode of resistance.

BackgroundInsecticide use via indoor residual spraying (IRS) or treated nets is the primary method for controlling malaria vector populations. The incidence of insecticide resistance in vector populations is burgeoning globally making resistance management key to the design of effective malaria control and elimination strategies. Vector populations can be assessed for insecticide resistance using a binary (susceptible or resistant) classification based on the use of the standard WHO insecticide susceptibility assay for adult anopheline mosquitoes. However, the recent scaling up of vector control activities has necessitated a revision of the WHO bioassay protocol to include the production of information that not only diagnoses resistance but also gives information on the intensity of expression of resistance phenotypes detected. This revised protocol is expected to inform on the range of resistance phenotypes in a target vector population using discriminating/diagnostic insecticide concentrations (DC) as well as their potential operational significance using 5× DC and 10× DC assays. The aim of this project was to use the revised protocol to assess the intensity of pyrethroid resistance in a range of insecticide resistant Anopheles strains with known resistance mechanisms and for which there is evidence of operational significance in the field setting from which these colonies were derived.MethodsDiagnostic concentration (DC) bioassays followed by 5× DC and 10× DC assays using the pyrethroid insecticides permethrin and deltamethrin were conducted according to the standard WHO bioassay method against pyrethroid resistant laboratory strains of Anopheles funestus, An. arabiensis and An. gambiae.ResultsLow to moderate resistance intensities were recorded for the An. arabiensis and An. gambiae strains while moderate to high intensities were recorded for the An. funestus strains.ConclusionsIt is evident that resistance intensity assays can add predictive value to the decision making process in vector control settings, although more so in an IRS setting and especially when bench-marked against resistance phenotypes of known operational significance.