Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:1.5.1.3 (dihydrofolate reductase)
5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Circular-dichroism spectra (200--450 nm) were recorded for Lactobacillus casei MTX/R dihydrofolate reductase and its complexes with substrates, inhibitors and coenzymes. These spectra are compared with those reported by others for dihydrofolate reductase from other sources. The binding of NADP+ or NADPH is associated with the perturbation of one or more aromatic amino acid residues, and there is marked enhancement of the negative c.d. band at 340 nm arising from the dihydronicotinamide chromophore of NADPH. The substrates folate and dihydrofolate give rise to substantial extrinsic c.d. bands on binding, which show a number of specific differences between enzymes from different sources. The binary complexes between the enzyme and the inhibitors methotrexate or trimethoprim also show strong c.d. bands, and these are qualitatively very similar for all dihydrofolate reductases studied so far. The ternary complexes between enzyme, NADPH and trimethoprim or methotrexate are very different from the sum of the spectra of the binary complexes. Trimethoprim leads to the disappearance of the 340 nm c.d. band of bound NADPH, whereas in the methotrexate--NADPH--enzyme ternary complex a "couplet" c.d. spectrum is observed at long wavelengths. Analysis of this latter feature suggests that it arises from a direct interaction between the dihydronicotinamide and pteridine rings in the ternary complex.
...
PMID:Circular-dichroism studies of ligand binding to dihydrofolate reductase from Lactobacillus casei MTX/R. 3 52

A rapid radiometric assay for the folate antagonist MTX, based on the inhibition of chicken liver dihydrofolate reductase activity, has been developed. In the system the inhibition by MTX of the reduction of tritiated FH2 is standardized and used to quantitate this antagonist in plasma of subjects receiving high-dose MTX therapy. The assay permits the detection of plasma MTX levels to 5 X 10(-9)M with a coefficient of variation of 15%. The predominating circulating folate, 5 methyltetrahydrofolate, or the rescue agent leucovorin (5 formyltetrahydrofolate) do not significantly interfere with the assay at concentrations attainable with current rescue programs. Analyses of multiple plasma samples with the present assay show close agreement with the competitive protein-binding assay.
...
PMID:A simple radiometric assay for methotrexate and other folate antagonists. 31 1

The ability of L1210 mouse leukemia cells and of a mutant methotrexate-resistant cell line (L1210/MTX) to synthesize methotrexate polyglutamates was studied. Host DBA/2 mice were treated with methotrexate, after which leukemic cells were harvested from ascitic fluid and levels of methotrexate and metabolites in them were determined by Sephadex G-15 gel chromatography. The level of methotrexate in L1210/MTX cells was 12.5 times greater than that in L1210 cells, reflecting the increased level of dihydrofolate reductase that characterizes this mutant cell line. Synthesis of methotrexate polyglutamates in each cell line required a dose of methotrexate (2.4 mg/kg) 10 times greater than the dose that yielded extensive methotrexate polyglutamate synthesis in rat liver and kidney in previous studies. Total methotrexate polyglutamates synthesized in 4 hr with this dose were the same in each cell line, demonstrating that this metabolism was not affected by differences in the level of dihydrofolate reductase. Methotrexate polyglutamates comprised 47+/-20% of the total methotrexate in L1210 cells. Methotrexate diglutamate was the predominant form. Levels of methotrexate monoglutamate and diglutamate were similar in L1210/MTX cells, whereas methotrexate monoglutamate was the predominant metabolite in host liver, kidney, and small intestine. These differences may reflect differences in substrate preference of pteroylpolyglutamate synthetase in these different tissues. Twenty-four hr after methotrexate administration, total methotrexate in L1210 cells was one-third of that at 4 hr; but the proportion of metabolites was the same, presumably reflecting cell death and division rather than loss of a freely exchangeable portion of intracellular methotrexate present at the earlier time. The affinity of methotrexate polyglutamates for dihydrofolate reductase was found to be similar to that of methotrexate, providing evidence that these metabolites may be as potent antagonists of folate metabolism as is methotrexate itself. Recent studies indicate that inhibition of folate metabolism in cells requires their exposure to high levels of methotrexate in order to achieve intracellular levels of methotrexate greater than needed to bind to dihydrofolate reductase. Such conditions conform to those required for synthesis of methotrexate polyglutamates. Thus, these metabolites may play a specific role in inhibiting folate metabolism, distinct from the antifolate potential that they appear to share with methotrexate.
...
PMID:Synthesis of methotrexate polyglutamates in L1210 murine leukemia cells. 83 65

A variant line (CEM-7A) "overproducing" the reduced folate/MTX carrier system was isolated from human CCRF-CEM leukemia cells grown under selective conditions in medium containing 0.25 nM 5-formyl-THF as the sole folate source. This line exhibits a 95-fold increased Vmax for [3H]-MTX influx as compared to parental cells. The values for [3H]-MTX influx Km, efflux t1/2 and structural specificity for other (anti)folate compounds were unchanged. The amount of carrier protein, estimated by NHS-[3H]-MTX affinity labeling, was approximately 30-fold higher in CEM-7A cells than in parental cells. Influx of [3H]-MTX in CEM-7A cells was found to be down-regulated 6-7-fold after preincubation of cells with adenosine, 5-formyl-THF or 5-methyl-THF, but could be prevented exclusively by inhibitors of dihydrofolate reductase. The underlying mechanism(s) of these effects have not as yet been elucidated. A radioiodinated photoaffinity analog of MTX was used to prove the molecular events in carrier-mediated MTX uptake in parental CCRF-CEM cells, CEM-7A cells, and a line exhibiting a MTX-transport defect (CEM-MTX). Specific labeling of an 80-85 kDa membrane protein was observed in parental cells, but not in CEM/MTX cells. Uptake of photoprobe and levels of the 80-85 kDa membrane protein were significantly increased in CEM-7A cells. Due to extensive glycosylation the MW of the carrier protein in human cells seems to be substantially higher than that of its counterpart in murine L1210 leukemia cells (46-48 kDa). Pulse-labeling experiments at 37 degrees C demonstrated that in CEM-7A cells photoprobe uptake proceeds via a specific pathway. The 80-85 kDa membrane protein is involved in the initial binding and translocation of photoprobe, after which a 38 kDa cytosolic protein is responsible for further intracellular distribution. At this time, the combination of photoaffinity labeling techniques and the availability of variant cell lines overexpressing the reduced folate/MTX carrier protein has provided new insights into the MTX transport process in human leukemia cell lines. In the near future this approach should also allow a further elucidation of the regulatory aspects of carrier function.
...
PMID:Molecular events in the membrane transport of methotrexate in human CCRF-CEM leukemia cell lines. 132 3

Previous findings suggesting that 5,10-dialkyl-substituted derivatives of 5,10-dideazaaminopterin warranted study as potential antifolates prompted synthesis of 10-ethyl-5-methyl-5,10- dideazaaminopterin (12a). The key step in the synthetic route to 12a was Wittig condensation of the tributylphosphorane derived from 6-(bromomethyl)-2,4-diamino-5-methylpyrido[2,3-d]pyrimidine (7a) with methyl 4-propionylbenzoate. Reaction conditions for the Wittig condensation were developed using the tributylphosphorane prepared from 6-(bromomethyl)-2,4-pteridinediamine (7b) as a model. Each of the respective Wittig products 8a and 8b was obtained in 75-80% yield. Hydrogenation of 8a and 8b at their 9,10-double bond afforded 4-amino-4-deoxy-10-ethyl-5-methyl-5,10-dideazapteroic acid methyl ester (9a) and 4-amino-4-deoxy-10-ethyl-10-deazapteroic acid methyl ester (9b). This route to 9b intersects reported synthetic approaches leading to 10-ethyl-10-deazaaminopterin (10-EDAM, edatrexate), an agent now in advanced clinical trials. Thus the Wittig approach affords an alternative synthetic route to 10-EDAM. Remaining steps were ester hydrolysis of 9a,b to give carboxylic acids 10a,b followed by standard peptide coupling with diethyl L-glutamate to produce diethyl esters 11a,b, which on hydrolysis gave 12a and 10-EDAM (12b), respectively. The relative influx of 12a was enhanced about 3.2-fold over MTX, but as an inhibitor of dihydrofolate reductase (DHFR) from L1210 cells and in the inhibition of L1210 cell growth in vitro, this compound was approximately 20-fold less effective than MTX (DHFR inhibition, Ki = 4.82 +/- 0.60 pM for MTX, 100 pM for 12a; cell growth, IC50 = 3.4 +/- 1.0 nM for MTX, 65 +/- 18 nM for 12a).
...
PMID:Synthesis and antifolate evaluation of 10-ethyl-5-methyl-5,10- dideazaaminopterin and an alternative synthesis of 10-ethyl-10- deazaaminopterin (edatrexate). 150 Dec 26

MTX cytotoxicity is not fully explained by its well-known inhibition of dihydrofolate reductase activity which leads to a decrease in the dTMP synthase reaction, since TdR kinase which converts TdR to dTMP could readily circumvent MTX action through this salvage activity. TdR kinase is of particular significance, since in various types of carcinoma cells its activity is orders of magnitude higher than that of dTMP synthase. To throw light on this problem, we tested the hypothesis that the impact of MTX treatment might in fact involve an inhibition or decrease in TdR kinase activity. Injection in rat of MTX (i.p.) decreased TdR kinase activity in a time- and dose-dependent fashion in liver (t1/2 = 46 h; IC50 = 95 mg/kg), bone marrow (t1/2 = 10 h; IC50 = 5 mg/kg) and rapidly growing transplantable hepatoma 3924A (t1/2 = 56 h; IC50 = 5 mg/kg). Injection in rat of cycloheximide (15 mg/kg, i.p.), an inhibitor of protein biosynthesis, rapidly decreased TdR kinase activity in the hepatoma (t1/2 = 3.6 h); activities of other purine and pyrimidine synthetic enzymes, dTMP synthase, IMP dehydrogenase, GMP reductase and GMP synthase, declined at a markedly slower rate (t1/2 = 11, 11.6, 12 and 22 h, respectively). MTX, by curtailing purine and pyrimidine biosynthesis, limits product of TdR kinase which is more sensitive to unopposed protein degradation than other enzymes of nucleic acid biosynthesis. TdR kinase is a newly discovered target of MTX treatment.
...
PMID:Methotrexate decreases thymidine kinase activity. 152 Mar 43

Changes in the mechanisms of folate incorporation were studied in cells treated with low concentrations of methotrexate in order to evaluate their contribution to the development of resistance to antifolate drugs. The uptake of methotrexate via reduced-folate system, the membrane-associated high-affinity folate binding capacity and the activity, levels and affinity for methotrexate of dihydrofolate reductase were measured in L5178 murine leukemic lymphoblasts and in a subline, MTX/R16, 16 times more resistant to methotrexate which was isolated after a short exposure to the antifolate. Various simultaneous changes were characterized in MTX/R16 cells which co-participated in the development of resistance: a decreased affinity of the carrier for methotrexate uptake via the reduced-folate system of entry, the increase of dihydrofolate reductase activity and levels and a two-fold increased expression of a membrane-associated high-affinity folate-binding protein (mFBP). The increase of the mFBP expression, besides ensuring the growth of resistant cells by its contribution to the reduced folate intake, also participates in the methotrexate resistance by the internalization of folate cofactor which would compete with methotrexate hindering the effective inhibition of dihydrofolate reductase by the antifolate.
...
PMID:Simultaneous changes in various mechanisms that mediate the cell incorporation of folate compounds account for low levels of resistance to methotrexate. 153 75

To test the relationship between DMs and drug resistance in newly established AML cell lines, KY821, and its clone KY821A3, the latter had lost DMs during cloning, were cultured in increasing concentrations of MTX. KY821 became resistant against 2 x 10(-4) M MTX, whereas KY821A3 did against 2 x 10(-5) M MTX in a same period. Enhanced enzyme activities of DHFR were correspondent to the increased DMs numbers and DHFR gene amplification in both resistant clones. The amplified DHFR gene was located on DMs by in situ hybridization. These data indicated that the presence of DMs in KY821 would facilitate the acquisition of drug resistance.
...
PMID:A new myeloblastic leukemia cell line with double minute chromosomes. Induction of methotrexate resistance and dihydrofolate reductase gene amplification. 156 Jun 71

High doses of methotrexate with leucovorin rescue are routinely used in the treatment of patients with osteosarcoma; the rationale for this application is controversial. Using human osteosarcoma xenografts growing in mice as a clinically relevant model, we compared the accumulation, intracellular metabolism, and tumor response of methotrexate administered as either high-dose (2400 mg/kg) or low-dose (150 mg/kg) infusions. The high-dose regimen, which included i.v. hydration and leucovorin rescue, resulted in plasma methotrexate levels that approximated those in patients receiving the drug at 12 g/m2. The low-dose infusion produced essentially the same toxicity as the higher dose level, without use of leucovorin. The HxOs33 tumor line was moderately sensitive to the high-dose infusion (55-day delay in tumor volume doubling time), whereas the second line, HxOs2, did not respond. Neither xenograft had a measurable response to low-dose methotrexate. Methotrexate was present in both tumors for up to 72 hr post-infusion, regardless of the dosage regimen. Only shorter-chain polyglutamates (MTXglu2 and MTXglu3) were detected over this period in the high-dose trial, and levels of these derivatives were uniformly higher in the resistant HxOs2 xenograft. Low-dose infusions were associated with formation of longer-chain polyglutamate species, with more abundant production in the HxOs2 line. Methotrexate polyglutamates exceeded baseline [3H]MTX binding of dihydrofolate reductase, as measured in tumor homogenates, at all testing intervals through 72 hr in both tumor lines. Nonetheless, high-dose methotrexate-induced suppression of [14C]formate incorporation into DNA was greater in the drug-sensitive HxOs33 tumor than in HxOs2. These results suggest a therapeutic advantage for high-dose methotrexate regimens in the treatment of human osteosarcoma but show that formation of tumor MTX polyglutamates is not the sole determinant of response to this agent.
...
PMID:Accumulation, intracellular metabolism, and antitumor activity of high- and low-dose methotrexate in human osteosarcoma xenografts. 169 16

2-Carbomethoxy-4-(p-carbomethoxyphenyl)cyclohexanone was prepared in a four-step process and thermally condensed with 2,4,6-triaminopyrimidine to afford methyl 2,4-diamino-4-deoxy-7-hydroxy-5,10-ethano-5,10-dideazapteroate+ ++. Reduction of the 7-oxo function with borane gave the 7,8-dihydro pterin which was subsequently oxidized to the fully aromatic pteroate ester with dicyanodichlorobenzoquinone. Saponification of the benzoate ester, coupling with diethyl glutamate and final ester hydrolysis afforded the title compound. This novel deazaaminopterin analogue was approximately as potent as methotrexate in vitro in terms of DHFR and L1210 cell growth inhibition. There are indications of diastereomeric differences in the enzyme inhibition measurements. A significant transport advantage over MTX for influx into L1210 cells was observed. The compound was active against the E 0771 murine mammary solid tumor, but further investigation with individual diastereomers is required to define the ED50.
...
PMID:Synthesis and antifolate properties of 5,10-ethano-5,10-dideazaaminopterin. 173 49


1 2 3 4 5 6 7 8 9 10 Next >>

---