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A modified in vitro sulfadoxine susceptibility assay for Plasmodium falciparum suitable for investigating Fansidar resistance

Published online by Cambridge University Press:  01 September 1997

P. WANG ,
P. F. G. SIMS  and
J. E. HYDE
P. WANG
Affiliation:
Department of Biochemistry and Applied Molecular Biology, University of Manchester Institute of Science and Technology (UMIST), Manchester M60 1QD, UK
P. F. G. SIMS
Affiliation:
Department of Biochemistry and Applied Molecular Biology, University of Manchester Institute of Science and Technology (UMIST), Manchester M60 1QD, UK
J. E. HYDE
Affiliation:
Department of Biochemistry and Applied Molecular Biology, University of Manchester Institute of Science and Technology (UMIST), Manchester M60 1QD, UK
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Abstract

The combination of pyrimethamine and sulfadoxine (PSD or Fansidar) represents one of the most important chemo-therapeutic agents currently used to treat falciparum malaria. To investigate the molecular basis of resistance to PSD, reliable in vitro drug assays are required to permit correlation of resistance levels with different genotypes. We describe here protocols that permit accurate evaluation of IC50 values for sulfadoxine (SDX) inhibition of Plasmodium falciparum. Historically, tests for this drug have suffered from poor reproducibility and extreme variability in reported values. We have examined a series of variables, including serum-containing versus serum-free media, erythrocyte source, pre-test growth conditions, test components and post-test processing. We define conditions which better control the levels of the drug antagonists folate and p-aminobenzoate, yielding reproducible differences between lines of P. falciparum with differing alleles of the dihydropteroate synthetase gene, which encodes the target enzyme of SDX. We also use this assay to demonstrate a marked difference in the response of different parasite lines to antagonism of SDX inhibition by exogenous folate. The ability to measure reliable IC50 values for SDX inhibition should greatly facilitate further experiments to explore the molecular basis of Fansidar resistance.

Keywords

Plasmodium falciparummalariasulfadoxineFansidar resistancedihydropteroate synthetasefolate
Type
Research Article
Information
Parasitology , Volume 115 , Issue 3 , September 1997 , pp. 223 - 230
Copyright
1997 Cambridge University Press

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