Abstract
Toxoplasma gondii is a widespread apicomplexan parasite that can cause severe disease in its human hosts. The ability of T. gondii and other apicomplexan parasites to invade into, egress from, and move between cells of infected hosts is critical to parasite virulence and disease progression. An unusual and highly conserved parasite myosin motor (TgMyoA) plays a central role in T. gondii motility. The goal of this work was to test whether pharmacological inhibition of TgMyoA can ameliorate disease in an animal model of infection. To this end, we sought to identify small molecule inhibitors of TgMyoA by screening a collection of 50,000 structurally diverse small molecules for inhibitors of the recombinant motor’s actin-activated ATPase activity. The top hit to emerge from the screen, KNX-002, inhibited TgMyoA with little to no effect on any of the vertebrate myosins tested. KNX-002 was also active against parasites, inhibiting parasite motility and growth in culture in a dose-dependent manner. We used chemical mutagenesis, selection in KNX-002, and targeted sequencing to identify a mutation in TgMyoA (T130A) that renders the motor less sensitive to compound. Compared to wild-type parasites, parasites expressing the T130A mutation showed reduced sensitivity to KNX-002 in motility and growth assays, confirming TgMyoA as a biologically relevant target of KNX-002. Finally, KNX-002 was shown to decrease the susceptibility of mice to infection with wild-type parasites, but not parasites expressing the resistance-conferring TgMyoA T130A mutation. These data demonstrate the specificity of KNX-002 for TgMyoA, both in vitro and in vivo, and validate TgMyoA as a druggable target for toxoplasmosis. Since TgMyoA is essential for virulence, conserved in apicomplexan parasites, and distinctly different from the myosins found in humans, pharmacological inhibition of MyoA offers a promising new approach to treating the devastating diseases caused by T. gondii and other apicomplexan parasites.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
New data added showing that KNX-002 decreases the susceptibility of mice to infection with wild-type parasites, but not parasites expressing the TgMyoA T130A mutation (Figure 9, Suppl. Figure 9C). Title and text modified accordingly. Bruno Martorelli di Genova added as an additional author. Author COI statement added.