Screening and evaluation of inhibitors of Plasmodium falciparum merozoite egress and invasion using cytometry.

Drug discovery programs heavily rely on assays adequately monitoring the activity of the drug on the -parasite stage targeted. So far, assays used to screen molecules active against Plasmodium falciparum parasites have mostly been based on measuring growth inhibition of asexual blood stages. We have developed a robust protocol allowing for monitoring parasite egress at the late schizont stage and subsequent erythrocyte invasion. This cytometry-based methodology uses nucleic acid labelling by the dye YOYO-1 and synchronized in vitro culture of P.falciparum exposed to inhibitors during the late phase of the intraerythrocytic cycle and the reinvasion process. This cytometry-based method is quick, accurate and allows for distinguishing egress from reinvasion on thousands of events. The throughput is also increased, as the assay can be scaled up for medium throughput screening for compounds that inhibit either the egress of merozoites or their entry into host erythrocytes.