Mutagenesis: Evaluating Targets of an Experimental Treatment of Toxoplasma gondii

Project Description: Toxoplasma gondii (T. gondii) is an intracellular parasite capable of infecting nearly all mammals, including humans1. Worldwide, it is estimated that T. gondii infects up to half of the world’s population, making it one of the most prevalent infection in humans2. The infectious process, termed toxoplasmosis, can be devastating in congenitally infected infants; in these patients, infection can lead to toxoplasmic encephalitis or lifelong disabilites3. The parasite is spread to humans, including expectant mothers, via the ingestion of oocysts present in the fecal matter of felines (the primary host of Toxoplasma gondii) or through the consumption of undercooked meat from infected animals4. The few drugs that are clinically available in the United States are not able to treat infected mothers in the first trimester of pregnancy due to its teratogenic and other toxic effects5. Regardless of when the treatment is taken, it is often ineffective at clearing congenital infection, thus the infant is born with an active case of toxoplasmosis6. These infants are then treated with a regimen of pyrimethamine and sulfadiazine, a poorly tolerated combination therapy that has significant side effects7. In order to address these shortcomings in current toxoplasmosis treatment, work in our laboratory has evaluated several compounds selected in a screen of more than 300,000 compounds tested against T. gondii for their efficacy against the parasites8. This proposal aims to move these novel anti-Toxoplasma compounds through the identification of the parasite’s mechanism of resistance against one of these promising drug-like compounds, codenamed KG3. Understanding this mechanism is significant because it can provide insight into how the parasite can mutate to become resistant to the compound. If mutation is easily achieved, it would suggest that natural mutation may occur with insufficient treatment regimens or modalities (i.e. multidrug cocktails). Previous work in our lab generated resistant Toxoplasma gondii parasite strains for pyrimethamine (as a control) and KG3. We propose to identify a putative mechanism of resistance for compound KG3 from these recently generated resistant clones.