title: Effects of 5-methyltetrahydrofolate on the activity of fluoropyrimidines against human leukemia (CCRF-CEM) cells.
abstract: The growth inhibitory effects of 5-fluorouracil (FUra) or 5-fluoro-2'-deoxyuridine (FdUrd) combined with 5-methyltetrahydrofolate (5-CH3-H4PteGlu) were determined, as a function of time, dose, and sequence of exposure, on human T-lymphoblast leukemia cells, CCRF-CEM. Synergistic inhibitory effects on cell growth were obtained when exponentially growing CCRF-CEM cells were exposed to 5-CH3-H4PteGlu (1-100 microM) for 4 hr and to FUra (250 microM) or FdUrd (0.5 microM) during the last 2 hr. Synergism was dependent on 5-CH3-H4PteGlu dose (100 greater than 10 greater than 1 microM) and did not occur at 0.1 microM. No clear dependence of synergism on sequence was observed with FUra and 5-CH3-H4PteGlu combinations (5-CH3-H4PteGlu----FUra,5-CH3-H4PteGlu + FUra, or FUra----5-CH3-H4PteGlu). With 5-CH3-H4PteGlu and FdUrd combinations, synergism was dependent on sequence of exposure (5-CH3-H4PteGlu + FdUrd, 5-CH3-H4PteGlu----FdUrd were synergistic, but FdUrd----5-CH3-H4PteGlu was not). Thymidine (0.1 microM), added after drug treatment, substantially rescued CCRF-CEM cells from 5-CH3-H4PteGlu----FUra cytotoxicity. L-methionine (1500 mg/l) completely protected CCRF-CEM cells from enhanced cytotoxicity of the combination, 5-CH3-H4PteGlu-FdUrd. The results are consistent with the hypothesis that the mechanism by which 5-CH3-H4PteGlu potentiates fluoropyrimidine cytotoxicity is the enhancement of complex formation between thymidylate synthase and 5-fluorodeoxyuridylate, as a consequence of an increase of intracellular levels of 5,10-methylenetetrahydrofolate generated from 5-CH3-H4PteGlu. Also, enhanced stability of the complex in the presence of high levels of this folate coenzyme may contribute to the synergism observed. These data provide a rationale basis for further trials of folate coenzymes and fluoropyrimidine combinations in the clinic.
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology / Q000627:therapeutic use*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005467:Floxuridine / Q000008:administration & dosage*; D005472:Fluorouracil / Q000008:administration & dosage*; D006801:Humans; D007945:Leukemia, Lymphoid / Q000188:drug therapy* / Q000473:pathology; D008715:Methionine / Q000494:pharmacology; D013763:Tetrahydrofolates / Q000008:administration & dosage*; D013936:Thymidine / Q000494:pharmacology
chemical_list: D013763:Tetrahydrofolates; D005467:Floxuridine; D008715:Methionine; C005984:5-methyltetrahydrofolate; D005472:Fluorouracil; D013936:Thymidine