In Vitro Drug Efficacy Testing Against Trypanosoma brucei.

The recent endorsement of fexinidazole by the European Medicines Agency for the treatment of human African trypanosomiasis has demonstrated the high predictive value of cell-based assays for parasite chemotherapy. Here we describe three in vitro drug susceptibility tests with Trypanosoma brucei that have served as the basis for the identification of fexinidazole as a promising lead: (1) a standard assay with end-point measurement to determine drug efficacy; (2) a wash-out assay to test for reversibility and speed of drug action; (3) isothermal microcalorimetry for real-time measurement of onset of drug action and time to kill. Together, these assays allow to estimate pharmacodynamic parameters in vitro and to devise appropriate treatment regimens for subsequent in vivo experiments.