Science Bite (3 minute oral presentation with PPT in live session and poster) - Students and ECRs only Lorne Infection and Immunity 2023

Identifying the mechanism of action of a novel invasion-blocking compound in Plasmodium falciparum (#55)

Dawson Ling 1 2 , Madeline Dans 3 , Greta Weiss 1 , Zahra Razook 4 5 , Somya Mehra 4 , Alyssa Barry 4 5 , Brendan Crabb AC 1 2 , Hayley Bullen 1 2 , Paul Gilson 1 2
  1. Malaria Virulence and Drug Discovery Group, Burnet Institute, Melbourne, Victoria, Australia
  2. Microbiology & Immunology, The University of Melbourne, Parkville, Victoria, Australia
  3. Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
  4. Infectious Diseases Systems Epidemiology Group, Burnet Institute, Melbourne, Victoria, Australia
  5. School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia

In 2020, Plasmodium falciparum (Pf) accounted for nearly all the 627,000 malaria-associated deaths globally (1). This rise in mortality is partly due to emerging drug resistance against all currently available antimalarials, underpinning the need for new antimalarials with novel mechanisms of action. Parasite invasion of erythrocytes represents an attractive novel drug target as it is responsible for parasite proliferation and symptomatic malaria. By screening the Medicines for Malaria Venture’s (MMV) open-access compound library, the Pathogen Box, we discovered an invasion-specific compound, MMV687794 (2). MMV687794 does not affect the development of ring- and trophozoite-stage parasites but instead specifically inhibits invasion from schizonts, the mature form of the parasite containing the invasive daughter merozoites. Genomic analysis on MMV687794-resistant parasites unveiled mutations in an alpha/beta hydrolase enzyme we have termed ABH-83 that contains a lysophospholipase (LysoPL) motif. To validate ABH-83 as the target of MMV687794, these mutations were engineered into wild-type parasites using CRISPR/Cas9, which recapitulated the drug resistance phenotype. An epitope tag and a GlmS riboswitch were also introduced into these parasites to allow for the detection of ABH-83 within the parasite using epitope-specific antibodies. Furthermore, when activated by the sugar glucosamine, the riboswitch facilitates inducible transcriptional downregulation of ABH-83, consequently reducing ABH-83 expression within one lifecycle and enabling closer examination of the role/s of ABH-83. By conducting a time-course western blot series on the transgenic parasites, the LysoPL ABH-83 is most highly expressed in the schizont stage, concordant with a role in invasion. ABH-83 has also been visualised by microscopy at the surface of rhoptry organelles which secrete important invasion-related proteins during erythrocyte invasion. This data is consistent with previous live-cell microscopy analysis of MMV687794-treated schizonts, which displayed invasion defects exacerbated by increased drug treatment duration. Overall, these results suggest that ABH-83 is involved in rhoptry functioning and/or morphology normally required for efficient merozoite invasion of erythrocytes. Investigations are ongoing to determine how ABH-83-mediated lipid modifications within the rhoptry membrane regulate rhoptry functioning during erythrocyte invasion.

  1. World Health Organization. World Malaria Report 2021. Geneva: World Health Organization; 2021.
  2. Dans MG, Weiss GE, Wilson DW, Sleebs BE, Crabb BS, de Koning-Ward TF, et al. Screening the Medicines for Malaria Venture Pathogen Box for invasion and egress inhibitors of the blood stage of Plasmodium falciparum reveals several inhibitory compounds. bioRxiv. 2020:768648.