Molecular epidemiology of malaria in Yaounde, Cameroon. I. Analysis of point mutations in the dihydrofolate reductase–thymidylate synthase gene of Plasmodium falciparum. Am J Trop Med Hyg 58

Abstract. Pyrimethamine and cycloguanil, the major human metabolite of proguanil, are inhibitors of dihydrofolate reductase that play a key role in the treatment and prevention of chloroquine-resistant Plasmodium falciparum infec-tions in sub-Saharan Africa. Resistance to these antifolate drugs has emerged in some areas of Africa. Earlier mo-lecular studies have demonstrated that point mutations at key positions of the dihydrofolate reductase–thymidylate synthase gene are strongly associated with antifolate resistance. However, whether the same or distinct mutations are involved in the development of resistance to both pyrimethamine and cycloguanil has not been well established in naturally occurring P. falciparum isolates. In this study, the in vitro responses to both antifolate drugs were measured in 42 Cameroonian isolates and compared with the complete sequence of the dihydrofolate reductase domain of the gene (from 34 of 42 isolates) to analyze the genotype that may distinguish between pyrimethamine and cycloguanil resistance. The wild-type profile (n 11 isolates) was associated with low 50 % inhibitory concentrations (IC50s) ranging from 0.32 to 21.4 nanamole for pyrimethamine and 0.60–6.40 nM for cycloguanil. Mutant isolates had at least one amino acid substitution, Asn-108. Only three mutant codons were observed among the antifolate-resistan