Amino acids in the dihydrofolate reductase-thymidylate synthase gene of Plasmodium falciparum involved in cycloguanil resistance differ from those involved in pyrimethamine resistance

Abstract

Cycloguanil, the active metabolite of the antimalarial drug proguanil, is an inhibitor of dihydrofolate reductase as is another antimalarial, pyrimethamine. Its use has been limited by the rapid development of resistance by parasites around the world. We have determined the cycloguanil- and pyrimethamine-sensitivity status of 10 isolates of Plasmodium falciparum and have sequenced in all these isolates the dihydrofolate reductase (DHFR; 5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) portion of the DHFR-thymidylate synthase (TS; 5,10-methylenetetrahydrofolate: dUMP C-methyltransferase, EC 2.1.1.45) gene. Instead of the known serine-to-asparagine change at position 108 that is imp..