Toxoplasma gondii is an obligate intracellular blood and tissue protozoan parasite that infects up to a third of the population worldwide. Several antimalarial drugs, in particular pyrimethamine ( PYR ), have been used for decades to treat toxoplasmosis. Here, the clinical Pf DHFR candidate P218 , and a series of flexible diaminopyrimidine butyrolactone analogues were identified as potent T. gondii dihydrofolate reductase ( Tg DHFR) inhibitors. The most promising butyrolactone analogue, LA4 , displayed an improved Tg DHFR inhibition ( K i 1.71 nM), increased antiparasitic properties in vitro (IC 50 0.44 nM), and a higher cell selectivity compared to PYR ( K i 13.0 nM, IC 50 410 nM) while P218 ( K i 2.19 nM, IC 50 370 nM) presented an improved activity with comparable cell selectivity to PYR . The in vivo results against T. gondii RH strain-infected mice showed that P218 reduced parasitic burden in blood whereas LA4 decreased parasite load in peritoneal fluid and blood with an extended mice survival. These findings position butyrolactone LA4 as a new potential for the treatment of acute toxoplasmosis. • Antimalarial P218 and a butyrolactone series were repurposed as Tg DHFR inhibitors. • All compounds showed nanomolar anti-toxoplasmosis in vitro with high selectivity. • Hydrogen bonds interaction of P218 in Tg DHFR active site is like that of Pf DHFR. • Butyrolactone LA4 reduced parasite load in peritoneal fluid and blood in vivo. • Butyrolactone LA4 displayed an extended mice survival.
Decharuangsilp et al. (2026) studied this question.