IDENTIFYING PROTEIN-PROTEIN INTERACTION INHIBITORS TARGETING APICOMPLEXAN ATG8-ATG3 INTERACTIONS
Miller, Alexia Saehwa
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Malaria is a global health crisis that threatens almost half of the world’s population. The need for novel antimalarials is becoming increasingly urgent as the incidence of resistance rises against the first-line defense, artemisinin. Plasmodium falciparum, the causative agent of the most lethal form of malaria, is a member of the phylum Apicomplexa. This phylum of parasitic protists is responsible for a number of diseases afflicting both human and non-human hosts, resulting in significant health and economic burdens worldwide. Recent work has pointed to the conserved autophagy pathway within these parasites as a potential target for anti-apicomplexan drug development. In this body of work, two approaches are taken to identify novel small molecules targeting the autophagy pathways within Plasmodium, and within other apicomplexans, as well. The first approach involves a Virtual Ligand Screen of the ChemBridgeTM Express Library against the crystal structure of P. falciparum Atg8. Hits are ordered and tested using SPR to detect activity against the plasmodial interaction without targeting the human interaction. The top hit, ALC25, is verified in vitro using SPR dose dependency, thermal shift, and ITC; it is additionally confirmed in vivo against both blood- and liver-stage P. falciparum parasites. ALC25 exhibits modest antimalarial activity, with IC50 values below 20 µM. The second approach expands upon hits identified from the Medicines for Malaria Venture (MMV) Malaria Box. These hits were detected via a medium-throughput Surface Plasmon Resonance (SPR) interaction assay and were subsequently verified in vivo. The small molecule scaffold for these hits is then chemically diversified and tested, again using SPR, against the Atg8-Atg3 interactions from Plasmodium falciparum, Cryptosporidium parvum, Eimeria tenella, and Neospora caninum/T.gondii, with promising results. These compounds, targeting the Atg8 conjugation pathway within P. falciparum, are then used to begin exploring the novel connection between the plasmodial autophagy pathway and the export of P. falciparum Erythrocitic Membrane Protein 1 (PfEMP1), a connection with profound implications for the potential treatment of cerebral malaria.