A novel benzodioxole-containing inhibitor of Toxoplasma gondii growth alters the parasite cell cycle.

Toxoplasma gondii is an obligate intracellular parasite that can cause disease in the developing fetus and in immunocompromised humans. Infections can last for the life of the individual, and to date there are no drugs that eliminate the chronic cyst stages that are characteristic of this parasite. In an effort to identify new chemical scaffolds that could form the basis for new therapeutics, we carried out a chemoinformatic screen for compounds that had the potential to interact with members of a superfamily of parasite-secreted kinases and assayed them for growth inhibition in vitro. Of 17 candidate compounds, we identified one with potent antiparasitic activity. The compound has a 50% inhibitory concentration (IC(50)) of ~2 nM, and structure-function analyses implicate the benzodioxole moiety in its action. The compound does not appear to be cytotoxic to host cells. Using microarray analyses of both parasites and host cells treated with the compound, we found that the levels of very few host cell transcripts are altered by the compound, while a large number of parasite transcripts have a different abundance after compound treatment. Gene ontology analyses of parasite transcripts with a different abundance revealed an enrichment of cell cycle-related genes, suggesting that the compound alters progression of the parasite through the cell cycle. Assaying the nuclear content of treated parasites demonstrated that compound treatment significantly increased the percentage of parasites in the S/M phase of the cell cycle compared to controls. This compound and its analogs represent a novel scaffold with antiparasitic activity.