Malaria Parasite Research Laboratory

Head: Dr Danny Wilson

Plasmodium falciparum malaria is a mosquito borne parasite that causes the majority of the ≈600,000 malaria related deaths that occur each year, mainly of children under the age of 5 in Africa. Although Australia has been ‘malaria free' since the 1980's, our nearest neighbours (Indonesia, East Timor, Papua New Guinea) still have some of the highest malaria incidence and mortality rates in Asia. Malaria has a critical bottleneck in its lifecycle, namely, the invasion of oxygen carrying red blood cells (RBCs) by the small merozoite form that initiates the disease causing cycle of replication inside these host cells. Host-cell invasion by malaria is an ideal drug target because (i) extracellular parasites are directly exposed to antimalarials in the bloodstream, (ii) many proteins required for invasion are not shared with host cells, and (iii) failure to invade immediately ends the parasite lifecycle, thereby preventing disease. My research is focussed on developing new antimalarial drugs against this essential step in disease progression. I apply a breakthrough P. falciparum merozoite purification method (#Boyle MJ, #Wilson DW et al., PNAS, 2010, #joint primary authors) that is superior to alternatives for studying malaria parasite invasion biology, opening up new opportunities to study this previously intractable lifecycle stage (Figure 1).

Figure 1

Figure 1: Highly reproducible purification of viable P. falciparum daughter merozoites (examples blue arrow) from mature schizonts (examples green arrow) and assessment of newly invaded ring stage parasites that have established an infection of a new human red blood cell (red arrow) by microscopy (Boyle and Wilson et al. PNAS. 2010).

The invasion inhibitory activity of drugs is assessed using a highly reproducible flow cytometry based approach (Wilson et al. Antimicrobial Agents Chemotherapy, 2013; Figure 2 A & B). Using this approach I have screened traditional antimalarial therapies, protease inhibitors, kinase inhibitors, a range of antibiotics and identified several compounds and there analogues that rapidly inhibit merozoite invasion. The mechanisms by which these compounds inhibit invasion is the subject of ongoing research. To understand how compounds inhibit the essential process of merozoite invasion I apply mutation analysis of gene targets, live filming (in collaboration with Dr. Paul Gilson, The Burnet Institute Melbourne), phenotypic screens of related Apicomplexan parasites (in collaboration with Dr. Dean Goodman and Professor Geoff McFadden, The University of Melbourne), modifications and screens of analogues (in collaboration Dr. Brad Sleebs, WEHI Melbourne and Prof. James Beeson, The Burnet Institute Melbourne) and fluorescence microscopy (Figure 2C, in collaboration with Dr. Jake Baum, Imperial College London & WEHI Melbourne). By applying these state of the art methods I aim to develop invasion inhibitory antimalarials as viable alternative or partner drugs in a climate of increasing drug resistance to current frontline treatments.

Figure 2

Flow cytometry assessment of invasion inhibitory compounds clearly identifies newly invaded rings (population in box) in the non-inhibitory control (Figure 2A) but not in after treatment with an invasion inhibitory compound (Figure 2B, Wilson et al. AAC. 2013). Using state of the art fluorescence microscopy techniques (Figure 2C; example from Riglar and Richards et al. Cell Host & Microbe. 2011; merozoite invading a red blood cell indicated by white arrow) and live filming it is possible to examine the stage of merozoite invasion that is inhibited by an inhibitor, such as a drug, using purified merozoites (Boyle and Wilson et al. PNAS. 2010).