levoleucovorin and purine

To determine if folinic acid supplementation during methotrexate (MTX) therapy for rheumatoid arthritis (RA) reduces both urinary 5-aminoimidazole-4-carboxamide (AICA) and urinary adenosine excretion more than does folic acid supplementation. AICA and adenosine are markers for MTX interference with purine metabolism.. Forty patients with RA who received MTX for 6 weeks were randomized to receive either daily folic acid or folinic acid supplements during an additional week of MTX therapy. Colorimetric and radioimmunocompetition assays were used to measure 24-hour urinary AICA and adenosine excretion levels, respectively.. At the end of 6 weeks, 24-hour urinary levels of AICA, but not adenosine, were elevated as compared with baseline levels (i.e., prior to MTX therapy). Folinic acid, but not folic acid, supplementation normalized urinary AICA levels during MTX therapy. Relatively high urinary levels of AICA were correlated with reduced disease activity. No similar correlations were seen with urinary adenosine levels.. The blockade of purine nucleotide biosynthesis by MTX at the AICA ribonucleotide transformylase-catalyzed step may be related to the efficacy of MTX, and this blockade is effectively relieved by folinic acid, but not by folic acid, supplementation.

Topics: Adenosine; Aminoimidazole Carboxamide; Arthritis, Rheumatoid; Erythrocytes; Female; Folic Acid; Homocysteine; Humans; Leucovorin; Male; Methotrexate; Middle Aged; Purines; Pyridoxine; Ribonucleotides; Treatment Outcome; Vitamin B 12

Pemetrexed is a novel antifolate with polyglutamate derivatives that are potent inhibitors of thymidylate synthase (TS) and to a lesser extent glycinamide ribonucleotide formyltransferase (GARFT). Conditions that might modulate relative suppression of these sites were assessed by the pattern of hypoxanthine and thymidine protection. When grown with 25 nmol/L racemic 5-formyltetrahydrofolate, thymidine alone fully protected wild-type HeLa cells to at least 1 micromol/L pemetrexed, but protection of a reduced folate carrier (RFC)-null subline required both thymidine and hypoxanthine above a concentration of 30 nmol/L pemetrexed. As medium 5-formyltetrahydrofolate was decreased, protection by thymidine alone decreased, and was further diminished when HeLa cells were grown in dialyzed serum. There was little protection by thymidine of RFC-null HeLa cells under the latter conditions. Thymidine alone was not protective, and hypoxanthine alone produced only a small (2-fold) increase in IC(50), in a HeLa-derived line 8-fold resistant to pemetrexed due to a modest increase in TS. Finally, in MCF-7 breast cancer cells there was greater protection with thymidine alone than in HeLa cells when cells were grown in medium containing a low concentration of 5-formyltetrahydrofolate. These observations indicate that as intracellular folates decrease in HeLa cells, due to decreased extracellular reduced folate, or loss of RFC function, pemetrexed inhibition of GARFT increases. These data support the concept that the contribution to pemetrexed activity by inhibition of GARFT, particularly at low folate levels, is a contributing factor to drug activity but relative inhibition of TS and GARFT may vary among human tumors and cell lines.

Topics: Animals; Blotting, Western; Cattle; Cell Division; Cell Line, Tumor; Culture Media; Dose-Response Relationship, Drug; Folic Acid; Folic Acid Antagonists; Glutamates; Guanine; HeLa Cells; Humans; Hypoxanthine; Leucovorin; Membrane Transport Proteins; Pemetrexed; Purines; Reduced Folate Carrier Protein; Serum; Thymidylate Synthase; Thymine

Topics: Folic Acid; Formates; Inosine Monophosphate; Leucovorin; Nucleotides; Purines