Combination of reduced folates with methotrexate or 5-fluorouracil: Comparison between 5-formyltetrahydrofolate (folinic acid) and 5-methyltetrahydrofolate in vitro activities

• Published in: Biochemical pharmacology Vol. 46; no. 10; pp. 1767 - 1774
• Main Authors: Etienne, Marie-Christine, Fischel, Jean-Louis, Formento, Patricia, Schneider, Maurice, Guillot, Thierry, Bardon, Mia, Milano, Gérard
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 17.11.1993; Elsevier Science
• Subjects: Antineoplastic agents; Antineoplastic Agents - pharmacology; Biological and medical sciences; Cell Division - drug effects; Drug Stability; Drug Synergism; Fluorouracil - pharmacology; General aspects; Humans; Leucovorin - administration & dosage; Leucovorin - pharmacology; Medical sciences; Methotrexate - pharmacology; Oxidation-Reduction; Pharmacology. Drug treatments; Stereoisomerism; Tetrahydrofolates - pharmacology; Tumor Cells, Cultured - drug effects; MTX; PBS; DMEM; CF; 5FU; 5MTHF; FA; MTT; 5-FdUMP; AUC; Antineoplastic agent; Antifolate; Human; Cell culture; Cell line; Mechanism of action; In vitro; Tumor cell
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/0006-2952(93)90581-G

Folinic acid ( dlFA) is increasingly used in clinical oncology. The active isomer lFA is intensively metabolized into l 5-methyltetrahydrofolate ( l 5 MTHF), the relative proportions of lFA, d FA and l 5 MTHF in blood varying considerably between oral and i.v. FA administration. The purpose of the study was to compare the in vitro activities of pure l FA and pure l 5MTHF at equivalent drug exposure [area under curve (AUC)], taking into account their respective chemical stability in the culture medium. The in vitro growth inhibition [3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) test] was evaluated on five human tumor cell lines after methotrexate (MTX)-folate or 5-fluorouracil (5FU)-folate exposures. Not only were the activities of l FA and l 5MTHF compared, but also clinically relevant mixtures of lFA + d FA + l 5MTHF corresponding to the proportions found at steady state during oral (PO mixture, 4, 39 and 57%, respectively) and i.v. administrations (i.v. mixture, 7, 81 and 12%, respectively). Measurement of folates demonstrated the marked lability of l 5MTHF (65.8% loss over 5 days in the culture medium) as compared to l FA (2.6% loss). Whatever the pharmacological model tested (MTX-folate or 5FU-folate), comparison of the folate effects at equivalent drug exposure taking into account their relative stability showed that l 5MTHF was never more potent than l FA. Moreover, a higher efficiency of l FA was demonstrated for the cell line most sensitive to 5FU; in this case, as expected, the i.v. mixture was more potent than the PO mixture. This study shows that depending on the tumor, l FA can be more potent than its main circulating metabolite l 5MTHF. Along with the limited capacity of oral absorption, the choice between oral and i.v. route for FA administration in patients should take into consideration the different pharmacological activities between l FA and l 5MTHF which suggest that the oral route is potentially detrimental to the optimal activity of the 5FU-FA combination as compared to i.v. administration.