Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Folic acid binding protein (FABP) has been measured in the supernatant of leukocytes of 12 patients affected with chronic granulocytic leukaemia (CGL). The folate binding capacity ranged from 1.37 to 697.52 pg/mg protein, showing a considerable heterogeneity. When the supernatant was preincubated with methotrexate (MTX), the inhibition of folic acid binding was complete in some cases whereas in others it was negligible: these findings have been confirmed by studying the 3H-MTX binding capacity by the same supernatants. In this case the range of bound 3H-HTX varied from 0.00 to 927 pg/mg protein. The presence of a binder in the cytoplasm of leukocytes might represent a new step in the regulation of endogenous folate metabolism. The MTX, widely used as an antifolate drug, may also be bound by FABP of CGL leukocytes, although in different amounts from case to case: this finding suggests a new point of interference of MTX in the folate metabolism. It has also been demonstrated that FABP, which is present in serum, may reduce the uptake of folate by leukocytes opening a new field of investigation on the megaloblastic transformation.
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PMID:Folic acid binding protein in chronic granulocytic leukaemia: the effect of methotrexate. 10 54

Folic acid analogues containing an additional nitrogen atom between the phenyl ring and the carbonyl group of the side chain were synthesized. None of the compounds showed significant inhibitory activity against human lymphoblastic leukemia cells (CCRF-CEM) in culture or against Lactobacillus casei (ATCC 7469) growth. Against L1210 leukemia in mice, the aza homologue of folic acid, 4, and the aspartic acid analogue, 14, showed no increase in life span over control animals. These compounds were more toxic in vivo than the corresponding methotrexate analogues. Compound 4 supported the growth of Streptococcus faecium (ATCC 8043), and its tetrahydro derivative supported the growth of Pediococcus cerevisiae (ATCC 8081). These results strongly suggest that 4 can substitute for folate derivatives as cofactors for serine transhydroxymethylase, thymidylate synthetase, and dihydrofolate reductase.
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PMID:Synthesis of aza homologues of folic acid. 10 17

A direct ligand-banding radioassay for methotrexate (MTX) has been developed using dihydrofolate reductase, contained in the lysate of L1210 leukemia cells, as the binding determinant. The procedure is a two-phase reaction system where standard MTX concentrations or the sample being assayed in incubated with the reagent lysate in the first phase, and [3H]MTX is then added in the second phase to titrate the remaining unoccupied binding sites on the enzyme. This method eliminates the need for measuring the residual catalytic activity of the enzyme. The sensitivity of the radioassay is limited only by the specific activity of the [3H]MTX and how approximates 10 pg of the drug. Folic acid, methyltetrahydrofolate, formyltetrahydrofolate, and dehydrofolate in concentrations that are physiological do not interfere in the radioassay. Both mercaptoethanol and reduced nicotinamide andnine dinucleotide phosphate increase the binding capacity of the lysate for MTX; but the reduced nucleotide also increases the affinity of the enzyme for the inhibitor. MTX added to serum can be assayed without extraction if the concentration is greater than 500 pg/ml and recovery of the drug added to serum is about 92%. MTX has been assayed in serum, spinal fluid, and urine of patients who were treated with this drug. It has also been assayed in the lysates of L1210 cells from C57BL X DBA/2 F1 mice treated with MTX. The procedure is simple, rapid, and accurate and should permit better correlation of the therapeutic and toxic effects of MTX with blood concentrations over long-term treatment periods.
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PMID:A direct ligand-binding radioassay for the measurement of methotrexate in tissues and biological fluids. 80 20

The effect of reduced and oxidized folates on the development of methotrexate (MTX) resistance has been examined in human leukemia cell line K562 (K562/S). K562/S cells were made resistant to MTX by soft-agar cloning either in RPMI-1640 medium (K562/MTX-PGA) or in folic-acid-free RPMI-1640 medium containing 10 nM leucovorin (K562/MTX-LV). The optimal concentrations of leucovorin for the growth of K562/S, K562/MTX-PGA and K562/MTX-LV cells were 1 nM, 5 nM and 10 nM respectively. K562/MTX-PGA cells were 24-fold resistant to MTX as noted by impaired MTX transport. In contrast, K562/MTX-LV cells were 26-fold resistant to MTX as noted by gene amplification of dihydrofolate reductase. Furthermore cross-resistance to cytosine arabinoside was only demonstrated in K562/MTX-PGA, while the K562/MTX-LV cells showed no significant cross-resistance to cytosine arabinoside. These results suggest that the type and level of folates used during the development of MTX resistance may play a role in the mechanism for MTX resistance. Leukemia cells that are grown in leucovorin might serve as a model for acquired MTX resistance in vivo.
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PMID:The role of folates in the development of methotrexate resistance in human leukemia cell line K562. 142 25

The pathway for de novo biosynthesis of purine nucleotides contains two one-carbon transfer reactions catalyzed by glycinamide ribotide (GAR) and 5-aminoimidazole-4-carboxamide ribotide (AICAR) transformylases in which N10-formyltetrahydrofolate is the one-carbon donor. We have found that the antifolates methotrexate (MTX) and piritrexim (PTX) completely block the de novo purine pathway in mouse L1210 leukemia cells growing in culture but with only minor accumulations of GAR and AICAR to less than 5% of the polyphosphate derivatives of N-formylglycinamide ribotide (FGAR) which accumulate when the pathway is blocked completely by azaserine. This azaserine-induced accumulation of FGAR polyphosphates is completely abolished by MTX, indicating that inhibition of the pathway is at or before GAR transformylase (reaction 3; Lyons, S. D., and Christopherson, R. I. (1991) Biochem. Int. 24, 187-197). Three h after the addition of MTX (0.1 microM), cellular 5-phosphoribosyl-1-pyrophosphate has accumulated 3.4-fold while 6-methyl-mercaptopurine riboside (25 microM) induces a 6.3-fold accumulation. These data suggest that amido phosphoribosyltransferase catalyzing reaction 1 of the pathway is the primary site of inhibition. In support of this conclusion, we have found that dihydrofolate-Glu5, which accumulates in MTX-treated cells, is a noncompetitive inhibitor of amido phosphoribosyltransferase with a dissociation constant of 3.41 +/- 0.08 microM for interaction with the enzyme-glutamine complex in vitro. Folate-Glu5, MTX-Glu5, PTX, dihydrotriazine benzenesulfonyl fluoride, and AICAR also inhibit amido phosphoribosyltransferase.
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PMID:Antifolates induce inhibition of amido phosphoribosyltransferase in leukemia cells. 159 45

Folylpolyglutamyl synthetase (FPGS), partially purified from murine L1210 leukemia and Sarcoma 180 cells and the proliferative fraction of luminal epithelium from mouse small intestine (the site of limiting toxicity to folate analogues), was examined for its ability to utilize various 4-aminofolates as substrates. For tumor-derived FPGS, aminopterin was the most preferred substrate overall, exhibiting the lowest value for apparent Km and highest Vmax. The other analogues and folic acid exhibited nearly 2-fold lower Vmax. Folic acid exhibited a 3-fold higher Km than aminopterin. Alkylation of aminopterin (methotrexate) or carbon for nitrogen substitution (10-deazaaminopterin) at N-10 increased Km 3- to 6-fold, while alkylation at C10 (10-ethyl-10-deazaaminopterin) restored Km to near equivalency with aminopterin. For FPGS derived from proliferative intestinal epithelium, aminopterin was also the preferred substrate, but the value for Vmax (derived with crude cell-free extract) was 6-fold lower than for tumor cell FPGS. Values for Vmax (derived with partially purified FPGS) for the other 4-aminofolate analogues and folic acid were similar (methotrexate) or 2-fold (10-ethyl-10-deazaaminopterin) and 5-fold (folic acid) lower than for aminopterin. The value for Km derived with aminopterin was similar to that derived for either tumor cell FPGS. The value for folic acid was 2-fold higher, and alkylation of aminopterin (methotrexate) or carbon to nitrogen substitution (10-deazaaminopterin) at N-10 with (10-ethyl-10-deazaaminopterin) or without alkylation markedly increased Km (27-, 90-, and greater than 100-fold, respectively, for methotrexate, 10-ethyl-10-deazaaminopterin, and 10-deazaaminopterin). In other studies, it was found that the diglutamate of aminopterin (aminopterin +G1) was a relatively poor substrate for FPGS derived from all three sources compared with methotrexate diglutamate, both in respect to values for Km and Vmax that were measured in each case. Findings with FPGS derived from L1210 cells were confirmed by high-pressure liquid chromatography analysis of product formation during the reaction with the parent compounds. The significance of the results presented here to the question of relative toxicity and therapeutic activity of these analogues is discussed.
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PMID:Differing specificities for 4-aminofolate analogues of folylpolyglutamyl synthetase from tumors and proliferative intestinal epithelium of the mouse with significance for selective antitumor action. 236 41

Folate analogs that inhibit dihydrofolate reductase result in only partial interconversion of tetrahydrofolate cofactors to dihydrofolate with preservation of the major portion of reduced cellular folate cofactors in L1210 leukemia cells. One possible explanation for this phenomenon is that low levels of dihydrofolate polyglutamates that accumulate in the presence of antifolates block thymidylate synthase to prevent depletion of reduced folate pools. This paper correlates biochemical analyses of rapid interconversions of radiolabeled folates and changes in purine and pyrimidine biosynthesis in L1210 murine leukemia cells exposed to antifolates with network thermodynamic computer modeling to assess this hypothesis. When cells are exposed to 1 microM trimetrexate there is an almost instantaneous inhibition of [3H] deoxyuridine or [14C]formate incorporation into nucleotides which is maximal within 5 min. This is associated with a rapid rise in cellular dihydrofolate (t1/2 approximately 1.5 min), which reaches a steady state that represents only 27.9% of the total folate pool. Pretreatment of cells with fluorodeoxyuridine, to inhibit thymidylate synthase by about 95% followed by trimetrexate only slows the rate of folate interconversion (t1/2 approximately 25 min) but not the final dihydrofolate level achieved. This is consistent with computer simulations which predict that direct inhibition of thymidylate synthase by 97, 98, and 99% should increase the half-time of dihydrofolate rise after trimetrexate to 40, 60, and 124 min, respectively, but the final level achieved is always the same as in cells with normal thymidylate synthase activity. The data reflect the high degree of catalytic activity of thymidylate synthase relative to tetrahydrofolate cofactor pools in the cells and the enormous extent of inhibition of this enzyme that is necessary to slow the rate of folate interconversions after addition of antifolates. The model predicts, and the data demonstrate, that virtually any residual thymidylate synthase activity will permit the interconversion of all tetrahydrofolate cofactors available for oxidation to dihydrofolate when dihydrofolate reductase activity is abolished, but the rate of interconversion will be slowed. Additional simulations indicate that the time course of cessation of tetrahydrofolate-dependent purine and pyrimidine biosynthesis after antifolates in these cells can be accounted for solely on the basis of tetrahydrofolate cofactor depletion alone. These data exclude the possibility that direct inhibition of thymidylate synthase by dihydrofolate polyglutamates, or any other intracellular folates that accumulate in cells after antifolates, can account for the rapid but partial interconversion of reduced folate cofactors to dihydrofolate.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Folate-pool interconversions and inhibition of biosynthetic processes after exposure of L1210 leukemia cells to antifolates. Experimental and network thermodynamic analyses of the role of dihydrofolate polyglutamylates in antifolate action in cells. 252 54

Cyclopentenone prostaglandins (PGs) such as prostaglandin A1 (PGA1) and prostaglandin J2 (PGJ2) significantly increased the life span of Ehrlich ascites tumor-bearing mice. In order to obtain PG derivatives which have more potent antitumor activity than PGA1 and PGJ2, we synthesized a number of alkylidenecyclopentenone PGs and studied the antitumor activity of these compounds in vitro and in vivo. delta 7-PGA1, 12-epi-delta 7-PGA1, and delta 12,14-PGJ2 showed 50% inhibitory concentrations of 0.3 microgram/ml against the growth of L1210 culture cells. These compounds are several times more cytotoxic than parent compounds. From a structure-activity relationship analysis, we concluded that, as for PGA derivatives: (a) a double bond in C7-8 potentiates the cytotoxicity; (b) a 15-hydroxy group is not essential for cytotoxicity; (c) the stereochemistry of R2 chain is not essential, while 12-epi derivatives also have full activity; (d) a double bond in C12-13 seems to be essential for full activity, and for PGJ derivatives a double bond in C12-13 and C14-15 potentiates the cytotoxicity. These compounds showed marked antitumor activity against Ehrlich ascites tumor in vivo. At doses of 20-30 mg/kg/day three or five consecutive i.p. treatments with these compounds resulted in a 66 to 111% increase in life span with long-term survivors. A single i.p. injection with 12-epi-delta 7-PGA1 (100 mg/kg) resulted in 73% increase in life span with 33% of long-term survivors, indicating an activity comparable to that of cyclophosphamide (200 mg/kg). However, delta 7-PGA1 and 12-epi-delta 7-PGA1 were marginally effective against P388 leukemia. Treatment with delta 7-PGA1 (10 mg/kg/day i.p.) and 12-epi-delta 7-PGA1 (20 mg/kg/day i.p.) on Days 1-9 resulted in 25.8 and 29.6% increases in life span, respectively. delta 7-PGA1 and delta 12-PGJ2 derivatives may be a potential new class of antitumor agents.
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PMID:Antitumor activity of delta 7-prostaglandin A1 and delta 12-prostaglandin J2 in vitro and in vivo. 370 85

The cytostatic activity of 5-fluorouracil (5-FU) can be modified by the addition of reduced folates, as well as antifolates. This is indicative of the complex involvement of folate metabolism in the effects of 5-FU. In the BN rat leukemia model, 5-FU treatment was combined with the inactivation of cobalamin (vitamin B12) by nitrous oxide (N2O). Exposure to nitrous oxide causes severe disturbance of folate metabolism through the inhibition of the cobalamin-dependent enzyme methionine synthetase, and leads to loss of folates from the cell. With regard to the effects on growth of leukemia, the addition of nitrous oxide did not antagonize 5-FU. On the contrary, therapeutic effects were enhanced by combined treatment, as was evident from a further reduction of leukemic infiltration in spleen and liver, from a decrease or even disappearance of leukemic cells in the peripheral blood, and from extended survival of rats. These findings were in accordance with metabolic studies in isolated leukemic cells of treated rats, in which combined treatment caused further impairment of thymidylate and DNA synthesis. Pretreatment with nitrous oxide, for a period of 3 days, was more effective than treatment after the administration of 5-FU. Folate levels, in plasma and intracellular, were reduced after combined treatment. It is concluded that in this leukemia, unlike observations in some models of solid tumors, the activity of 5-FU is enhanced with a depletion of folates. This effect is probably comparable to the combination of methotrexate pretreatment with 5-FU, and might be important to applications of 5-FU in combination chemotherapy of hematological neoplasms.
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PMID:Effects of 5-fluorouracil treatment of rat leukemia with concomitant inactivation of cobalamin. 375 54

Folate (pteroylglutamate) and methotrexate rapid (seconds) uptake by the trophoblast was investigated from either the maternal or fetal circulations of the isolated dually-perfused guinea-pig placenta. Tissue uptake was measured by using a single-circulation paired-tracer (3H-test and 14C-extracellular marker) technique. [3H]Folate uptakes were 80 and 52% (mean) in perfusates without unlabelled folate, on maternal and fetal sides, respectively. There was negligible 3H-tracer backflux into the circulation up to 6 min probably due to metabolic sequestration. [3H]Methotrexate uptakes were about 85 and 22% on maternal and fetal sides, respectively; however these uptakes were followed by rapid and complete backflux of the label. Specific transplacental transfer of [3H]folate or [3H]methotrexate in either direction was not detectable within 5-6 min. At the brush-border side (maternal) uptake of [3H]folate was highly inhibited by 100 nM unlabelled folate or its reduced form, methyltetrahydrofolate (the main form in plasma); however, equimolar methotrexate (an antifolate chemotherapeutic agent) failed to produce any inhibition of folate uptake. Our findings demonstrate that on both sides of the placenta a high-affinity transport system exists for trophoblast uptake of folate compounds. For methotrexate, either a separate transport system may exist or methotrexate may have a very low affinity for the folate system. These results are distinct from the findings reported in mouse L1210 leukemia cells.
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PMID:Transport of folates at maternal and fetal sides of the placenta: lack of inhibition by methotrexate. 407 42


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