Characterization of Plasmodium knowlesi dihydrofolate reductase-thymidylate synthase and sensitivity to antifolates.

Malaria caused by an infection of Plasmodium knowlesi can result in high parasitemia and deaths. Therefore, effective and prompt treatment is necessary to reduce morbidity and mortality. The study aims to characterize P. knowlesi dihydrofolate reductase-thymidylate synthase enzyme (PkDHFR-TS) and its sensitivity to antifolates. The putative Pkdhfr gene was PCR amplified from field isolates collected from the Southern Thailand. Molecular analysis showed 11 polymorphisms in the dhfr domain of the bifunctional dhfr-ts gene. Of these, 1 polymorphism was a non-synonymous substitution (R34L) that had previously been reported but not associated with antifolate resistance. The recombinant PkDHFR-TS enzyme was found to be sensitive to standard antifolates-pyrimethamine and cycloguanil-as well as P218, a registered candidate drug currently first in human clinical trial. Results suggest that antifolates class of compounds should be effective against P. knowlesi infection.