Quinazoline-quinoline bisubstrate inhibitors target eukaryotic translation initiation factor 3 in Plasmodium falciparum

Malaria drug resistance is hampering the fight against the deadliest parasitic disease affecting over 200 million people worldwide. We recently developed quinoline-quinazoline-based inhibitors (as compound 70) as promising new antimalarials. Here we aimed to investigate their mechanism of action by using Thermal Proteome Profiling (TPP). The eukaryotic translation initiation factor 3 (EIF3i) subunit I was identified as the main target of the inhibitor in P. falciparum. This protein is not a known drug target in malaria parasites. P. falciparum parasite lines were generated expressing either a HA tag or an inducible knockdown of the PfEIF3i gene to further characterize the target protein. PfEIF3i was stabilized in presence of the compound 70 in a cellular thermal shift-western blot assay, confirming that PfEIF3i is a target of quinoline-quinazoline-based inhibitors. In addition, PfEIF3i-inducible knock-down blocks intra-erythrocytic development in the trophozoite stage indicating that it has a vital function. We show that PfEIF3i is mostly expressed in late intraerythrocytic stages and localizes in the cytoplasm. Previous mass spectrometry reports show that EIF3i is expressed in all parasite life cycle stages. Hence, quinoline-quinazoline-based inhibitors allowed to identify PfEIF3i as a valuable target for the design of new antimalarial drugs active all along the life cycle of the parasite.