title: Resistance to antifolates in Plasmodium falciparum monitored by sequence analysis of dihydropteroate synthetase and dihydrofolate reductase alleles in a large number of field samples of diverse origins.
abstract: Resistance of Plasmodium falciparum to antifolate chemotherapy is a significant problem where combinations such as Fansidar (pyrimethamine-sulfadoxine; PYR-SDX) are used in the treatment of chloroquine-resistant malaria. Antifolate resistance has been associated with variant sequences of dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS), the targets of PYR and SDX respectively. However, while the nature and distribution of mutations in the dhfr gene are well established, this is not yet the case for dhps. We have thus examined by DNA sequence analysis 141 field samples from several geographical regions with differing Fansidar usage (West and East Africa, the Middle East and Viet Nam) to establish a database of the frequency and repertoire of dhps mutations, which were found in 60% of the samples. We have also simultaneously determined from all samples their dhfr sequences, to better understand the relationship of both types of mutation to Fansidar resistance. Whilst the distribution of mutations was quite different across the regions surveyed, it broadly mirrored our understanding of relative Fansidar usage. In samples taken from individual patients before and after drug treatment, we found an association between the more highly mutated forms of dhps and/or dhfr and parasites that were not cleared by antifolate therapy. We also report a novel mutation in a Pakistani sample at position 16 of DHFR (A16S) that is combined with the familiar C59R mutation, but is wild-type at position 108. This is the first observation in a field sample of a mutant dhfr allele where the 108 codon is unchanged.
authors.affiliation: Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, UK.
authors.forename: P
authors.initials: P
authors.lastname: Wang
authors.forename: C S
authors.initials: CS
authors.lastname: Lee
authors.forename: R
authors.initials: R
authors.lastname: Bayoumi
authors.forename: A
authors.initials: A
authors.lastname: Djimde
authors.forename: O
authors.initials: O
authors.lastname: Doumbo
authors.forename: G
authors.initials: G
authors.lastname: Swedberg
authors.forename: L D
authors.initials: LD
authors.lastname: Dao
authors.forename: H
authors.initials: H
authors.lastname: Mshinda
authors.forename: M
authors.initials: M
authors.lastname: Tanner
authors.forename: W M
authors.initials: WM
authors.lastname: Watkins
authors.forename: P F
authors.initials: PF
authors.lastname: Sims
authors.forename: J E
authors.initials: JE
authors.lastname: Hyde
mesh_terms: D000349:Africa; D000483:Alleles; D000818:Animals; D000962:Antimalarials / Q000627:therapeutic use*; D004252:DNA Mutational Analysis; D004094:Dihydropteroate Synthase / Q000235:genetics*; D004338:Drug Combinations; D004351:Drug Resistance / Q000235:genetics; D005493:Folic Acid Antagonists / Q000627:therapeutic use*; D017125:Genes, Protozoan / Q000235:genetics; D006801:Humans; D016778:Malaria, Falciparum / Q000188:drug therapy; D008877:Middle East; D010963:Plasmodium falciparum / Q000201:enzymology / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics; D011739:Pyrimethamine / Q000627:therapeutic use; D013413:Sulfadoxine / Q000627:therapeutic use; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D014744:Vietnam
chemical_list: D000962:Antimalarials; D004338:Drug Combinations; D005493:Folic Acid Antagonists; C001205:fanasil, pyrimethamine drug combination; D013413:Sulfadoxine; D013762:Tetrahydrofolate Dehydrogenase; D004094:Dihydropteroate Synthase; D011739:Pyrimethamine