Authors

I Ali³; A Siriwardana²; P Roepe²; A Mete⁴; J Reynisson¹; P Horrocks³;  ¹ Auckland University, New Zealand;  ² Georgetown University, United States;  ³ Keele University;  ⁴ MedSynDesign Ltd

Discussion

Growth inhibition assays of 135 putative ATG8-ATG3 protein-protein inhibitors (PPI) identified compounds SK1.47 and SK1.49 with IC₅₀ of 2.12 and 1.07 µM, respectively. Structure activity relationship data, coupled with molecular docking of interactions with the W and L hydrophobic pockets on the surface of PfATG8, suggest that hydrophobic moieties linked with a spacer chain that contains an amine (to hydrogen bond to Lys48 in PfATG8) are preferred. These compounds are relatively non-toxic against HepG2 cell lines (CC₅₀ > 100µM) and share a fast to moderate rate of kill (between chloroquine and quinine) suggesting a common mode of action. Both compounds inhibited the formation of ATG8 labelled vesicles (autophagosomes) in intraeythrocytic parasites induced into autophagy using starvation conditions. Unlike chloroquine, however, neither compound induces the formation of ATG8 labelled vesicles. Transmission electron microscopy of parasites treated with these compounds both showed swelling of digestive vacuoles and a relative depletion in hemozoin formation. These putative ATG8-ATG3 PPI offer chemical probes of autophagy in P. falciparum and potential discovery leads against a novel target in the parasite.