title: Use of bacterial surrogates as a tool to explore antimalarial drug interaction: Synergism between inhibitors of malarial dihydrofolate reductase and dihydropteroate synthase.
abstract: Interaction between antimalarial drugs is important in determining the outcome of chemotherapy using drug combinations. Inhibitors of dihydrofolate reductase (DHFR) such as pyrimethamine and of dihydropteroate synthase (DHPS) such as sulfa drugs are known to have synergistic interactions. However, studies of the synergism are complicated by the fact that the malaria parasite can also salvage exogenous folates, and the salvage may also be affected by the drugs. It is desirable to have a convenient system to study interaction of DHFR and DHPS inhibitors without such complications. Here, we describe the use of Escherichia coli transformed with malarial DHFR and DHPS, while its own corresponding genes have been inactivated by optimal concentration of trimethoprim and genetic knockout, respectively, to study the interaction of the inhibitors. Marked synergistic effects are observed for all combinations of pyrimethamine and sulfa inhibitors in the presence of trimethoprim. At 0.05μM trimethoprim, sum of fractional inhibitory concentrations, ΣFIC of pyrimethamine with sulfadoxine, pyrimethamine with sulfathiazole, pyrimethamine with sulfamethoxazole, and pyrimethamine with dapsone are in the range of 0.24-0.41. These results show synergism between inhibitors of the two enzymes even in the absence of folate transport and uptake. This bacterial surrogate system should be useful as a tool for assessing the interactions of drug combinations between the DHFR and DHPS inhibitors.
authors.affiliation: National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand.
authors.forename: Yuwadee
authors.initials: Y
authors.lastname: Talawanich
authors.affiliation: National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand.
authors.forename: Sumalee
authors.initials: S
authors.lastname: Kamchonwongpaisan
authors.affiliation: Department of Biochemistry, Faculty of Science, Mahidol University, Rama VI Rd., Bangkok 10400, Thailand.
authors.forename: Worachart
authors.initials: W
authors.lastname: Sirawaraporn
authors.affiliation: National Centre for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Road, Khlong Luang, Pathum Thani 12120, Thailand. Electronic address: yongyuth@biotec.or.th.
authors.forename: Yongyuth
authors.initials: Y
authors.lastname: Yuthavong
mesh_terms: D000962:Antimalarials / Q000494:pharmacology*; D003622:Dapsone / Q000494:pharmacology; D004094:Dihydropteroate Synthase / Q000037:antagonists & inhibitors / Q000235:genetics*; D004347:Drug Interactions; D004351:Drug Resistance; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D016778:Malaria, Falciparum / Q000188:drug therapy; D030781:Organisms, Genetically Modified / Q000235:genetics; D010963:Plasmodium falciparum / Q000235:genetics*; D011739:Pyrimethamine / Q000494:pharmacology; D013413:Sulfadoxine / Q000494:pharmacology; D013420:Sulfamethoxazole / Q000494:pharmacology; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*
chemical_list: D000962:Antimalarials; D005493:Folic Acid Antagonists; D013413:Sulfadoxine; D003622:Dapsone; D013762:Tetrahydrofolate Dehydrogenase; D004094:Dihydropteroate Synthase; D013420:Sulfamethoxazole; D011739:Pyrimethamine
keywords: Antimalarial; Bacterial surrogate; Dihydrofolate reductase; Dihydropteroate synthase; Plasmodium falciparum; Synergism