Targeting mosquito FREP1 to block malaria transmission with fungal metabolites
Inhibiting Plasmodium development in mosquitoes will block malaria transmission. Fibrinogen-related protein 1 (FREP1) has been demonstrated to be critical for parasite infection in Anopheles gambiae. FREP1 facilitates Plasmodium invasion in mosquitoes through interacting with gametocytes and ookinetes. Therefore, we propose that small molecules disrupting the interaction will prevent parasites from infecting mosquitoes. To test this hypothesis, we developed an ELISA-based method to screen a fungal extract library, and obtained one candidate fungal extract that inhibited about 92% of the interaction between FREP1 and P. falciparum infected cells. The inhibition specificity was confirmed by immunofluorescence assays. Notably, feeding mosquitoes with the candidate fungal extract significantly inhibited P. falciparum infection in midgut without cytotoxicity or inhibition of the development of P. falciparum gametocytes or ookinetes. The candidate fungus was determined to be Aspergillus niger. Moreover, an active pure compound that prevents FREP1 from binding gametocytes and ookinetes was isolated from A. niger extract and was determined to be (+)-orlandin. Importantly, the nontoxic (+)-orlandin significantly reduced the P. falciparum infection intensity in mosquitoes. Therefore, disruption of the interaction between FREP1 and parasites effectively reduces Plasmodium infection in mosquitoes. Targeting FREP1 with small molecules is thus an effective novel approach to block malaria transmission.
