5-methyltetrahydrofolate and Breast-Neoplasms

Folates found in natural foods are thought to protect against cancer. However, folic acid (FA), a synthetic form of folate used in supplements and fortified foods, may increase breast cancer risk if present in unmetabolized form (UMFA) in the circulation. This study examined the associations of serum UMFA and 5-methyltetrahydrofolate (5-mTHF), the predominant form of circulating folate, with breast cancer risk.. We conducted a nested case-control study in a prospective cohort. In total, 553 cases of invasive breast cancer, diagnosed before mandatory FA fortification of grain in the US in 1998, were individually-matched to 1059 controls. Serum UMFA and 5-mTHF were measured using liquid chromatography-tandem mass spectrometry in stored serum samples, and 5-mTHF was corrected for storage degradation.. Circulating UMFA was not associated with breast cancer risk. These results apply to countries without mandatory FA food fortification. Studies are needed in countries with mandatory fortification, where levels of UMFA are much higher than in our study.

Topics: Breast Neoplasms; Case-Control Studies; Female; Folic Acid; Humans; Prospective Studies; Tetrahydrofolates

A high adherence to the Mediterranean diet (MD) was previously associated with a decreased risk of breast cancer (BC) among Greek-Cypriot women. Additionally, particular polymorphisms were shown to modulate this MD-BC association. Herein, we aimed to investigate the effect of polymorphisms-MD interactions on the levels of specific metabolites that could be related to dietary adherence or enzymatic activity, which is itself modulated by polymorphisms.. Greek-Cypriot women who were BC controls and had the lowest or the highest MD adherence (vegetables, fruit, legumes, fish) as assessed by principal component analysis (n = 564) were included. Participants were previously genotyped for nine polymorphisms of the one-carbon metabolism, oxidative stress, and xenobiotic metabolism. The serum levels of 14 metabolites that are key players in the aforementioned pathways were measured by UPLC-MS/MS. ANCOVA was used to assess polymorphism-MD interactions on metabolites' levels within a multivariate linear regression model. Statistically significant interactions between GSTM1 (where GST is glutathione S-transferase) deletion polymorphism and MD on flavin mononucleotide and on 5-methyltetrahydrofolate (5-MTHF) concentrations were observed. The MTHFR rs1801133 interacted significantly with MD on 5-MTHF concentration.. Serum levels of flavin mononucleotide and 5-MTHF were shown to be influenced by interactions between GSTM1 deletion or MTHFR (rs1801133) polymorphisms and a dietary pattern, characteristic of MD.

Topics: Adult; Aged; Breast Neoplasms; Diet, Mediterranean; Fabaceae; Female; Fruit; Genotype; Glutathione Transferase; Greece; Humans; Metabolomics; Middle Aged; Oxidative Stress; Polymorphism, Genetic; Tetrahydrofolates; Vegetables

Intracellular metabolism of methotrexate (MTX) to MTX-polyglutamates (MTXPG) is one determinant of cytotoxicity. Steady-state accumulation of MTXPG seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them. Overexpression of GGH would be expected to decrease intracellular MTXPG, thereby increasing efflux of MTX and decreasing cytotoxicity. Increased expression of GGH has been shown to be associated with resistance to MTX in human sarcoma cell lines and a rat hepatoma cell line. To clarify the specific role of GGH in determining MTX sensitivity, we investigated the phenotype produced by forced GGH overexpression in two cell types. Furthermore, because MTX and folic acid share metabolic pathways, we measured the effects of GGH overexpression on folic acid metabolism. The full-length cDNA for GGH, subcloned into a constitutive expression vector, was transfected into a human fibrosarcoma (HT-1080) and a human breast carcinoma (MCF-7) cell line. Compared with the clones containing an empty vector, the GGH-overexpressing cells express 15- to 30-fold more GGH mRNA, more GGH protein, and 15- to 90-fold more GGH enzyme activity. GGH overexpression altered MTX accumulation and metabolism to long-chain polyglutamates. In contrast to expectations, however, GGH overexpression did not confer resistance to short MTX exposures in either cell line. Changes in MTX metabolism were found to be balanced by alterations in accumulation and metabolism of folic acid. The ratio of MTX:folate accumulation may be a better predictor of MTX cytotoxicity than the accumulation of either alone. We conclude that, at least for these two cell lines, GGH overexpression alone is insufficient to produce clinical resistance to MTX.

Topics: Antimetabolites, Antineoplastic; Breast Neoplasms; Drug Resistance, Neoplasm; Fibrosarcoma; Folic Acid; gamma-Glutamyl Hydrolase; Humans; Methotrexate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tetrahydrofolates; Transfection; Tumor Cells, Cultured

This report describes the intracellular metabolism of 5-methyltetrahydrofolate (5-methyl-H4PteGlu) and 5-formyltetrahydrofolate (5-formyl-H4PteGlu) to the various folate forms and their respective polyglutamated states in the MCF-7 human breast-cancer cell line. The intracellular folate distribution observed in MCF-7 cells treated with 5-methyl-H4PteGlu was similar to that seen in cells treated with 5-formyl-H4PteGlu. In cells exposed to 5-formyl-H4PteGlu for 24 h, the folate pool consisted of 103 +/- 10 pmol/mg 10-formyl-H4PteGlu, 120 +/- 18 pmol/mg H4PteGlu, and 71 +/- 18 pmol/mg 5-methyl-H4PteGlu versus 88 +/- 5, 54 +/- 20 and 87 +/- 10 pmol/mg, respectively, for cells exposed to 5-methyl-H4PteGlu. Only the difference seen in H4PteGlu levels between cells exposed to either 5-methyl-H4PteGlu or 5-formyl-H4PteGlu reached statistical significance (P < 0.05). In the absence of vitamin B12, exposure to 5-methyl-H4PteGlu resulted in 154 +/- 17 pmol/mg 5-methyl-H4PteGlu along with only 8 +/- 5 pmol/mg 10-formyl-H4PteGlu and 4 +/- 2 pmol/mg H4PteGlu, thus demonstrating the marked dependence on vitamin B12 for the metabolism of 5-methyl-H4PteGlu to the other intracellular folates. 5-10-Methylene- H4PteGlu (2 +/- 1.3 pmol/mg) was detected only in cells exposed to 5-formyl-H4PteGlu for 24 h, not in cells treated with 5-methyl-H4PteGlu. The profile of polyglutamates detected in cells treated with either 5-formyl-H4PteGlu or 5-methyl-H4PteGlu for 24 h was not significantly different, although cells treated with 5-methyl-H4PteGlu tended to have less conversion to the higher polyglutamates (Glu3-Glu5) as compared with those treated with 5-formyl-H4PteGlu. In 5-methyl-H4PteGlu-treated cells grown in the absence of vitamin B12, the pentaglutamate was the only polyglutamate form detected, accounting for only 11% of the total folate pool. Since there does not appear to be a greater formation of the optimal reduced-folate forms necessary to achieve enhanced thymidylate synthase (TS) inhibition through ternary-complex formation in cells exposed to 5-methyl-H4PteGlu versus 5-formyl-H4PteGlu, these studies suggest that the use of 5-methyl-H4PteGlu would not be advantageous over that of 5-formyl-H4PteGlu in combination regimens with the fluoropyrimidines.

Topics: Breast Neoplasms; Humans; Leucovorin; Polyglutamic Acid; Tetrahydrofolates; Tumor Cells, Cultured

Topics: Biological Transport; Breast Neoplasms; Carrier Proteins; Cell Division; Cell Line; Cell Survival; Clone Cells; Female; Folate Receptors, GPI-Anchored; Humans; Kinetics; Methotrexate; Receptors, Cell Surface; Tetrahydrofolates; Tumor Cells, Cultured; Up-Regulation

DL-N5-Methyltetrahydrohomofolate (MTHHF; NSC-139490; N- [(4-[(2-(2-amino-3,4,5,6,7,8-hexahydro-4-oxo-5-methyl-6- pteridinyl)ethyl) amino) benzoyl)] -L-glutamate), a new folate antagonist of relatively low toxicity, is active against experimental tumor systems resistant to methotrexate and consequently now in clinical trial. We investigated its clinical pharmacokinetics in six patients; four of them received by rapid i.v. infusion tracer doses of [N5-methyl-14C]MTHHF ranging from 13 to 16 mg/sq m, and 2 received 150 mg/sq m; the total radioactivity dose was 100 to 200 mu Ci/patient. MTHHF was assayed by radiochemical and chromatographic techniques. The elimination of MTHHF from the plasma followed a triexponential pattern, with a harmonic mean initial half-life of 20.1 min, an intermediary half-life of 4.5 hr, and a terminal half-life of 74.6 hr. The apparent volume of distribution was 1.6 liters/kg, suggesting rapid and extensive tissue binding. This, together with the low total clearance of 0.2 ml/kg/min, contributed to the long half-life of this agent. Although 68% of the administered dose was excreted in the urine on the first day, only an additional 1% was excreted on the ensuing 3 days. In the two patients who received the higher dose, very little MTHHF was found in the cerebrospinal fluid. In concentrations ranging from 25 to 500 micrograms/ml, the drug was about 50% bound to plasma protein. MTHHF was not metabolized in humans as also reported in animals. These results suggest that MTHHF is excreted in the bile to certain extent. Moreover, since it tends to localize and persist in the body, to forestall cumulative toxicity, frequent administration of this agent should be undertaken only with caution.

Topics: Breast Neoplasms; Carbon Radioisotopes; Female; Hodgkin Disease; Humans; Kinetics; Lymphoma; Tetrahydrofolates