Screening for potential prophylactics targeting sporozoite motility through the skin

Abstract

BackgroundAnti-malarial compounds have not yet been identified that target the first obligatory step of infection in humans: the migration of Plasmodium sporozoites in the host dermis. This movement is essential to find and invade a blood vessel in order to be passively transported to the liver. Here, an imaging screening pipeline was established to screen for compounds capable of inhibiting extracellular sporozoites.MethodsSporozoites expressing the green fluorescent protein were isolated from infected Anopheles mosquitoes, incubated with compounds from two libraries (MMV Malaria Box and a FDA-approved library) and imaged. Effects on in vitro motility or morphology were scored. In vivo efficacy of a candidate drug was investigated by treating mice ears with a gel prior to infectious mosquito bites. Motility was analysed by in vivo imaging and the progress of infection was monitored by daily blood smears.ResultsSeveral compounds had a pronounced effect on in vitro sporozoite gliding or morphology. Notably, monensin sodium potently affected sporozoite movement while gramicidin S resulted in rounding up of sporozoites. However, pre-treatment of mice with a topical gel containing gramicidin did not reduce sporozoite motility and infection.ConclusionsThis approach shows that it is possible to screen libraries for inhibitors of sporozoite motility and highlighted the paucity of compounds in currently available libraries that inhibit this initial step of a malaria infection. Screening of diverse libraries is suggested to identify more compounds that could serve as leads in developing ‘skin-based’ malaria prophylactics. Further, strategies need to be developed that will allow compounds to effectively penetrate the dermis and thereby prevent exit of sporozoites from the skin.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2469-0) contains supplementary material, which is available to authorized users.

Malaria parasites differentially sense environmental elasticity during transmission

“…Interestingly, we could find sporozoites moving within soft PA hydrogels, which feature narrow pores (30). Their speed inside these hydrogels was similar to the range of speeds observed in vivo in the skin (11,12,37) or natural hydrogels (32). Yet, their trajectories were more regular than in the skin, which might be explained by the heterogenous composition of the skin consisting of different extracellular matrix proteins, fibers and cell types.…”

Regulation of Plasmodium sporozoite motility by formulation components

“…Since SMOOT In vitro allowed for detailed analysis of spz motility at frame level, the tool can be used to further study the action of (novel) motility inhibiting drugs at different concentrations. Potentially, motility analysis with SMOOT In vitro could be performed as an additional assay to previously described high-throughput screening methods [2].…”

“…Infection with malaria is initiated when Plasmodium parasites are injected into the skin by a probing Anopheles mosquito in the highly motile sporozoite (spz) stage [1]. Motility enables spz to exit the skin site, enter the bloodstream and reach and infect the liver, which makes spz motility a target for anti-malarial drugs and vaccines [2]. In addition, the potency of malaria vaccine candidates based on live attenuated spz depends on their potential to migrate in the human host, infect hepatocytes and induce an immune response, which cannot be replicated by dead sporozoites [3].…”

Chemotherapeutic Potential of Monensin as an Anti-microbial Agent

“…Also, monensin could obstruct liver stage infection of Plasmodium berghei at low nanomolar range potency [51]. Likewise, monensin treatment affected sporozoite attachment and motility from freshly isolated salivary glands of mosquitoes [52]. Surprisingly, monensin was able to completely inhibit P. vivax hypnozoites and schizonts suggesting its effectiveness in treating liver stage malaria [53].…”