Characterization of Plasmodium Atg3-Atg8 Interaction Inhibitors Identifies Novel Alternative Mechanisms of Action in Toxoplasma gondii

• Published in: Antimicrobial agents and chemotherapy 2018-02, Vol.62 (2)
• Main Authors: Varberg, Joseph M, LaFavers, Kaice A, Arrizabalaga, Gustavo, Sullivan, Jr, William J
• Format: Article
• Language: English
• Subjects: Antiprotozoal Agents; Autophagy-Related Proteins; Experimental Therapeutics; Plasmodium falciparum; Protein Isoforms; Protozoan Proteins; Small Molecule Libraries; Toxoplasma
• ISSN: 0066-4804; 1098-6596
• DOI: 10.1128/AAC.01489-17

Protozoan parasites, including the apicomplexan pathogens (which causes malaria) and (which causes toxoplasmosis), infect millions of people worldwide and represent major human disease burdens. Despite their prevalence, therapeutic strategies to treat infections caused by these parasites remain limited and are threatened by the emergence of drug resistance, highlighting the need for the identification of novel drug targets. Recently, homologues of the core autophagy proteins, including Atg8 and Atg3, were identified in many protozoan parasites. Importantly, components of the Atg8 conjugation system that facilitate the lipidation of Atg8 are required for both canonical and parasite-specific functions and are essential for parasite viability. Structural characterization of the Atg3-Atg8 (PfAtg3-Atg8) interaction has led to the identification of compounds that block this interaction. Additionally, many of these compounds inhibit growth , demonstrating the viability of this pathway as a drug target. Given the essential role of the Atg8 lipidation pathway in , we sought to determine whether three PfAtg3-Atg8 interaction inhibitors identified in the Medicines for Malaria Venture Malaria Box exerted a similar inhibitory effect in While all three inhibitors blocked replication at submicromolar concentrations, they did not inhibit Atg8 (TgAtg8) lipidation. Rather, high concentrations of two of these compounds induced TgAtg8 lipidation and fragmentation of the parasite mitochondrion, similar to the effects seen following starvation and monensin-induced autophagy. Additionally, we report that one of the PfAtg3-Atg8 interaction inhibitors induces egress and provide evidence that this is mediated by an increase in intracellular calcium in response to drug treatment.