title: Characterization of de novo folate synthesis in Pneumocystis carinii and Toxoplasma gondii: potential for screening therapeutic agents.
abstract: Drug therapy studies imply that Pneumocystis carinii and Toxoplasma gondii possess the enzymes necessary for de novo folate synthesis. To verify this, incorporation of [3H]paraaminobenzoic acid [( 3H]PABA) into reduced folates by P. carinii and T. gondii was investigated. Both organisms synthesized tritiated reduced folates. In P. carinii, 10-formyltetrahydrofolate and tetrahydrofolate, and in T. gondii, 5-formyltetrahydrofolate were the major synthesized folates. P. carinii remained metabolically active in vitro for only a few days. Because current systems for screening antipneumocystis agents are cumbersome, the utility of this assay system for screening therapeutic agents was investigated. Sulfonamides and pentamidine efficiently inhibited de novo folate synthesis in P. carinii. Inhibitors of dihydrofolate reductase such as trimethoprim and trimetrexate were poor inhibitors for P. carinii but efficient inhibitors for T. gondii. This study demonstrates the first unambiguous evidence of metabolic activity in P. carinii, and provides a potential assay for efficiently screening antipneumocystis drugs in vitro.
authors.affiliation: Critical Care Medicine Department, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: J A
authors.initials: JA
authors.lastname: Kovacs
authors.forename: C J
authors.initials: CJ
authors.lastname: Allegra
authors.forename: J
authors.initials: J
authors.lastname: Beaver
authors.forename: D
authors.initials: D
authors.lastname: Boarman
authors.forename: M
authors.initials: M
authors.lastname: Lewis
authors.forename: J E
authors.initials: JE
authors.lastname: Parrillo
authors.forename: B
authors.initials: B
authors.lastname: Chabner
authors.forename: H
authors.initials: H
authors.lastname: Masur
mesh_terms: D010129:4-Aminobenzoic Acid / Q000378:metabolism; D000818:Animals; D004338:Drug Combinations / Q000494:pharmacology; D004353:Drug Evaluation, Preclinical; D005492:Folic Acid / Q000096:biosynthesis*; D011010:Pneumocystis / Q000187:drug effects / Q000378:metabolism*; D011799:Quinazolines / Q000494:pharmacology; D051381:Rats; D013420:Sulfamethoxazole / Q000494:pharmacology; D014122:Toxoplasma / Q000187:drug effects / Q000378:metabolism*; D014295:Trimethoprim / Q000494:pharmacology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D016597:Trimetrexate
chemical_list: D004338:Drug Combinations; D011799:Quinazolines; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D005492:Folic Acid; D014295:Trimethoprim; D013420:Sulfamethoxazole; D010129:4-Aminobenzoic Acid; D016597:Trimetrexate