title: The selection of wild-type revertants from methotrexate permeability mutants.
abstract: In a previous report, we described the selection and partial characterization of three distinct classes of methotrexate (Mtx)-resistant Chinese hamster ovary cells (CHO) (1). Class I cells contained a structural alteration in dihydrofolate reductase. Class II cells showed a alteration affecting the permeability of the drug. Class III cells, selected from class I cells, had an increased activity of the altered enzyme. In the work described here, the sensitivity of these lines to the diaminopyrimidines has been investigated. Class I cells are as sensitive, class II cells are 5- to 10-fold more sensitive, and class III cells are 10- to 30-fold more resistant than wild-type cells. The increased sensitivity of the class II cells provided an opportunity to select for revertants of these mutants and such phentotypic wild-type revertant cells have been selected using one diaminopyrimidine, pyrimethamine. Such cells have drug sensitivities and permeability characteristics similar to wild-type cells. A second class has been identified which has wild-type drug sensitivities to the diaminopyrimidines but Mtx class II resistance to Mtx, and drug permeabilities characteristic of Mtx-resistant class II cells.
mesh_terms: D000818:Animals; D002460:Cell Line; D002463:Cell Membrane Permeability; D006224:Cricetinae; D004351:Drug Resistance; D005492:Folic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D008727:Methotrexate / Q000494:pharmacology*; D009154:Mutation; D010641:Phenotype; D011739:Pyrimethamine / Q000494:pharmacology; D012641:Selection, Genetic; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
chemical_list: D005492:Folic Acid; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate; D011739:Pyrimethamine