A novel in vitro bioluminescence rate-of-kill (BRoK) assay to study the pharmacodynamic properties of antimalarial drug action in Plasmodium falciparum

Abstract

Massive screens of chemical libraries for antimalarial activity have identified thousands of compounds that exhibit sub-micromolar potency against the blood stage of the malaria parasite Plasmodium falciparum. Triaging these compounds to establish priorities to take forward for development requires additional information regarding their activity. Key amongst their pharmacodynamics (PD) properties is the rate of kill– with a rapid cytocidal effect specifically identified as a key requirement for a Single Exposure Radical Cure and Prophylaxis (SERCaP) product. Compounds that exert an immediate cytocidal effect rapidly reduce parasite burden to ameliorate the morbidity and mortality of disease. With the overall aim to accelerate drug screening by validating a rapid rate of kill, the validation of a novel, quick (6hr) and potentially scalable bioluminescence rate of kill (BroK) assay is described here that demonstrates a good correlation with in vitro recrudescence-based rate of kill data and available in vivo clinical findings. The BRoK assay was used to screen the Medicine for Malaria Venture Malaria Box to identify compounds with rapid cytocidal activity. Seventeen compounds have an initial rate of kill greater than artemisinins, with a further 39 compounds exhibiting a rate of kill between chloroquine and artemisinins. These compounds represent potential Target Candidate Profile, compounds for a SERCaP product. This work highlights the opportunity for the BRoK assay as a hit discovery tool. In addition, the potential for this assay in lead validation through structure activity relationship studies are highlighted.