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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of the inhibition of dihydrofolate reductase by methotrexate on the cellular folates involved in de novo purine and thymidylate biosynthesis has been measured in H35 hepatoma cells grown in 4 microM folic acid or 20 nM folinic acid. The major cellular folate species in cells from medium with folate or folinate is 10-formyltetrahydrofolate (approximately 5 microM), with lesser amounts of 5,10-methylenetetrahydrofolate and tetrahydrofolate. Cultures were exposed to a pulse dose of methotrexate, resulting in the accumulation of nearly exclusively methotrexate polyglutamates (predominantly Glu3, Glu4, and Glu5), or a continuous exposure to the poorly glutamylated analog threo-4-fluoromethotrexate, resulting in 93% intracellular monoglutamate. At 4 hr and 18 hr after exposure to either compound there was extensive depletion of the reduced folate coenzymes, which generally corresponded to the extent of inhibition of glycine and deoxyuridine incorporation. This was accompanied by an increase of the cellular dihydrofolate and 10-formyldihydrofolate. In the H35 cells the effect of methotrexate polyglutamates on the reduced folate coenzyme pools was restricted to dividing cultures, because the reduced folate coenzymes were not depleted in confluent cultures. The results demonstrate that the methotrexate and methotrexate polyglutamates that initially accumulate within dividing H35 cells readily inhibit dihydrofolate reductase but are not adequate to inhibit thymidylate synthase and prevent the depletion of reduced folate coenzymes. Thus, inhibition of de novo glycine and deoxyuridine incorporation into DNA as a result of dihydrofolate reductase inhibitors appears to be closely related to a reduction in the intracellular concentration of 10-formyltetrahydrofolate and 5,10-methylenetetrahydrofolate, the respective folate coenzymes for de novo purine and thymidylate synthesis.
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PMID:Depletion of 5,10-methylenetetrahydrofolate and 10-formyltetrahydrofolate by methotrexate in cultured hepatoma cells. 143 54

Reduced derivatives of 10-formylfolate have been evaluated as inhibitors of mammalian thymidylate synthase (EC 2.1.1.45) from H35 hepatoma cells. With 5,10-methylenetetrahydrofolylheptaglutamate as the substrate, 10-formyltetrahydrofolylmonoglutamate is a competitive inhibitor with a Ki of 2.4 microM, which is reduced to 0.1 microM for the heptaglutamate derivative. 10-Formyldihydrofolylmono- and -heptaglutamate are approximately threefold less inhibitory than the tetrahydro analog. The concentrations of 10-formyltetrahydrofolate and 10-formyldihydrofolate were measured in dividing hepatoma cells by a novel enzymatic assay and were found to be 5 microM and undetectable, respectively. These results suggest that the concentration of 10-formyltetrahydrofolate within the dividing cells has the potential to severely inhibit or modulate thymidylate biosynthesis.
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PMID:Inhibition of mammalian thymidylate synthase by 10-formyltetrahydropteroylpolyglutamate. 198 99