In vitro pharmacodynamics of the antimalarial drug cabamiquine
ABSTRACT Detailing the mode-of-action of novel antimalarial drugs is important to predict and optimize their treatment efficacy. To complement standardized in vivo studies, an in vitro pharmacodynamic characterization of the Plasmodium elongation factor 2 inhibitor cabamiquine has been undertaken on Plasmodium falciparum-infected red blood cells. Parasite growth arrest and killing kinetics were assessed using a MitoTracker assay, two genetically engineered luminescent parasite lines expressing firefly luciferase or NanoLuc (BRRoK assays), standard growth inhibition assays, and long-term live cell imaging. The results confirm that cabamiquine is a potent and fast-acting inhibitor of parasite protein translation, inducing complete arrest of the translational machinery within 6 h of drug exposure. Rate-of-kill assays showed a >100-fold difference in potency between the block on translation (luciferase-based BRRoK IC50 = 0.9 nM) and overall parasite killing (6 h-treatment, ring-stage standard growth inhibition assay IC50 > 100 nM), highlighting that translational arrest occurs well before parasite death. Prolonged inhibition of protein synthesis drives parasite exhaustion, followed by irreversible cell death within 48 h, preceding the parasite clearance observed in patients. These in vitro findings help contextualize why the clinically observed lag in parasite clearance may be temporally distinct from symptomatic improvement, including fever resolution. Here, cabamiquine presents itself as a fast-acting, slow clearing antimalarial drug.