Exploration and Characterization of the Antimalarial Activity of Pyrimidine-2,4-Diamines for which Resistance is Mediated by the ABCI3 Transporter.

The spread of drug-resistant Plasmodium strains is diminishing the effectiveness of current antimalarials, highlighting the importance of discovering new therapeutics with novel targets. A screen of the Jumpstarter library against P. falciparum identified W482 with a pyrimidine-2,4-diamine scaffold. Structure-activity relationships reveal the importance of the pyrimidine core and its endocyclic nitrogen, while alternative amines are tolerated in the 4-position. Bulky and hydrophobic carboxamides or substituted phenyl ureas display the most potent antiplasmodial activity. Resistance selection and whole genome sequencing reveal an amplification of the gene encoding the ABCI3 transporter protein W482-resistant parasites. W482 is found to exhibit greater activity against parasites with reduced expression of ABCI3, confirming that resistance is related to the transporter. W482 arrests asexual parasites at the ring to trophozoite transition stage and exhibits a fast-killing profile with a lag phase of 24 h. Improving the antiparasitic activity alongside metabolic stability and solubility remains a challenge in the future development of the pyrimidine-2,4-diamine class.