The potent Toxoplasma gondii growth inhibitor QQ-437 does not bind to its predicted target, parasite adaptin3𝛽, in yeast three-hybrid assays

Abstract

New drugs are needed to treat infections with Toxoplasma gondii, a ubiquitous protozoan parasite that can cause miscarriage, blindness, and life-threatening encephalitis in its human hosts. A novel N-benzoyl-2-hydroxybenzamide named QQ-437 was recently shown to be a potent inhibitor of T. gondii growth in vitro (EC50 = 16nM), and to reduce parasite load in a mouse model of infection. Intriguingly, mutations in the parasite protein TgAP3𝛽, which is thought to play an important role in intracellular protein trafficking, confer resistance to QQ-437. In this report, we use yeast three-hybrid analysis to test the hypothesis that QQ-437 inhibits parasite growth via a direct effect on TgAP3𝛽. We see no evidence for the ability of QQ-437 to bind directly to TgAP3𝛽, suggesting that the mutation in TgAP3𝛽 that confers resistance does so through an indirect mechanism. Further studies are needed to identify the direct molecular target(s) of this promising class of compounds.