Sulfadoxine resistance in the human malaria parasite Plasmodium falciparum is determined by mutations in dihydropteroate synthetase and an additional factor associated with folate utilization

Abstract

Sulfadoxine/pyrimethamine (Fansidar) is widely used in Africa for treating chloroquine-resistant falciparum malaria. To clarify how parasite resistance to this combination arises, various lines of Plasmodium falciparum were used to investigate the role of naturally occurring mutations in the target enzyme, dihydropteroate synthetase (DHPS), in the parasite response to sulfadoxine inhibition. An improved drug assay was employed to identify a clear correlation between sulfadoxine-resistance levels and the number of DHPS mutations. Moreover, tight linkage was observed between DHPS mutations and high-level resistance in the 16 progeny of a genetic cross between sulfadoxinesensitive (HB3) and sulfadoxine-resistant (Dd2) parents. However, we also demonstrate a profound influence of exogenous folate on IC 50 values, which, under physiological conditions, may have a major role in determining resistance levels. Importantly, this phenotype does not segregate with dhps genotypes in the cross, but shows complete linkage to the two alleles of the dihydrofolate reductase (dhfr ) gene inherited from the parental lines. However, in unrelated lines, this folate effect correlates less well with DHFR sequence, indicating that the gene responsible may be closely linked to dhfr, rather than dhfr itself. These results have major implications for the acquisition of Fansidar resistance by malaria parasites.

Genomic heterogeneity in the density of noncoding single-nucleotide and microsatellite polymorphisms in Plasmodium falciparum

“…Resistance to all antimalarial drugs arises rapidly and is mediated by mutations in key target (Peterson et al, 1990;Wang et al, 1997) or transport genes (Foote et al, 1990;Fidock et al, 2000). Antigenic variation in key proteins is the basis of immune evasion (Biggs et al, 1991) and may in part explain the lack of sterilizing immunity in humans (Bruce-Chwatt, 1963;Neva, 1977;Marsh, 1992).…”

Antimalarial drug resistance and combination chemotherapy

“…Pyrimethamine, trimethoprim, cycloguanil, and chlorcycloguanil are all competitive inhibitors of plasmodial dihydrofolate reductase (DHFR). The sulphonamides and sulphones inhibit dihydropteroate synthase (DHPS) (Wang et al 1997). Combinations of the two classes therefore provide sequential inhibition of folate biosynthesis, and show marked synergy in antimalarial activity.…”

Shotgun DNA microarrays and stage‐specific gene expression in Plasmodium falciparum malaria

“…Finally, as the complete sexual life cycle of P. falciparum can only be studied in mosquitoes and as yet not in vitro, classical genetics can only be performed with great dif®culty (Walliker et al, 1987). Not surprisingly, only two genetic crosses have been performed with malaria parasites and only a handful of traits have been mapped (Walliker et al, 1987;Vaidya et al, 1995;Wang et al, 1997;Wellems et al, 1999).…”