Multistage Inhibition of the Myosin XIV-Based Invasion Motor in the Malaria Parasite and Related Pathogens

Abstract

Myosins have become attractive targets for a directed small molecule-based modulation of their physiological function. A number of chemical inhibitors and activators have been reported and proven valuable tools for studying myosin function in healthy and diseased cells, and served as lead candidates towards new therapeutic treatments. Given the large number of myosin classes and isoforms directly linked to human pathologies, the current set of myosin modulators has proven specific for particular myosins, whereas the majority of classes remains inaccessible. Here we show the first small molecule inhibitors of apicomplexan class XIV myosins, developed using structure-based de novo design and thermodynamics-driven optimization. Apicomplexan class XIV myosins play critical roles in infectious diseases, such as toxoplasmosis, coccidiosis, and malaria, with mortality rates of up to half million deaths every year. In particular, myosin A is a key component of the parasitic invasion motor, responsible for parasite motility and host cell invasion. Our compounds display low cytotoxicity and inhibit myosin ATPase and motor function in the submicromolar range. Crystallographic data confirm binding to an allosteric site in myosin. In blood stage malaria growth-inhibition assays, the compounds significantly reduce intracellular parasite growth and the degree of parasitic infection with comparable potencies both, against drug-sensitive parasite strains and multidrug-resistant strains. Functional assays of multiple life-cycle stages revealed a direct effect of the compounds on the myosin XIV-based invasion machinery and associated processes, including invasion of red blood cells and motility of blood and liver stage parasites. The present study confirms an essential role of Pf myosin A for parasite infection and opens new perspectives for a targeted modulation of specific myosin classes and associated diseases.