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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The antifolate compounds 10-deazaaminopterin (10-dAM) and 10-ethyl-10-deazaaminopterin (10-EdAM) are therapeutically superior to methotrexate in transplanted murine tumor systems and in human tumor xenografts growing in immunodeficient "nude" mice. The increased therapeutic index of these analogs correlates with their selective uptake, retention, and polyglutamation within neoplastic cells. We have developed a fluorescence high-performance liquid chromatographic assay applicable to 10-dAM, 10-EdAM, their polyglutamate anabolites, and their 7-hydroxy (7-OH) and deglutamate catabolites. The assay is based upon the high native fluorescence of pteridine-containing compounds which contain carbon in the 10 position. The assay employs a reverse-phase C-18 column and an ascending acetonitrile gradient in 50 mM phosphate, pH 7.0. The compounds are extracted from plasma and urine with 95 +/- 7% and 98 +/- 2% recoveries, respectively, using C-18 Sep-Paks. The linear range of the assay is, for 10-dAM, 2-100 nM, and for 10-EdAM, 1-100 nM. Polyglutamated metabolites of [3H]10-EdAM isolated from L1210 cells have been separated by HPLC with identification of five derivatives (Glu 1-5) confirmed by enzymatic peak shift using serum conjugase and by quantitative correlation of fluorescence intensity, radioactivity, and titration inhibition of dihydrofolate reductase. The assay has been used successfully in pharmacokinetic analyses of plasma and urine samples from patients receiving 10-dAM and 10-EdAM. In patients who had received 10-EdAM, 7-OH-10-EdAM, and the deglutamate catabolite were also detected. This HPLC fluorescence assay is superior to the dihydrofolate reductase inhibition and binding assays with regard to specificity and precision; moreover, it can provide a means for simultaneous assay of the physiologically important anabolites and catabolites of these new antifolates.
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PMID:Fluorometric high-performance liquid chromatographic analysis of 10-deazaaminopterin, 10-ethyl-10-deazaaminopterin, and known metabolites. 241 7

Evidence indicating that modifications at the 5- and 10-positions of classical folic acid antimetabolites lead to compounds with favorable differential membrane transport in tumor vs. normal proliferative tissue prompted an investigation of 5-alkyl-5-deaza analogues. 2-Amino-4-methyl-3,5-pyridinedicarbonitrile, prepared by hydrogenolysis of its known 6-chloro precursor, was treated with guanidine to give 2,4-diamino-5-methylpyrido[2,3-d]pyrimidine-6-carbonitrile which was converted via the corresponding aldehyde and hydroxymethyl compound to 6-(bromomethyl)-2,4-diamino-5-methylpyrido[2,3-d]pyrimidine. Reductive condensation of the nitrile 8 with diethyl N-(4-amino-benzoyl)-L-glutamate followed by ester hydrolysis gave 5-methyl-5-deazaaminopterin. Treatment of 12 with formaldehyde and Na(CN)BH3 afforded 5-methyl-5-deazamethotrexate, which was also prepared from 15 and dimethyl N-[(4-methylamino)benzoyl]-L-glutamate followed by ester hydrolysis. 5-Methyl-10-ethyl-5-deazaaminopterin was similarly prepared from 15. Biological evaluation of the 5-methyl-5-deaza analogues together with previously reported 5-deazaaminopterin and 5-deazamethotrexate for inhibition of dihydrofolate reductase (DHFR) isolated from L1210 cells and for their effect on cell growth inhibition, transport characteristics, and net accumulation of polyglutamate forms in L1210 cells revealed the analogues to have essentially the same properties as the appropriate parent compound, aminopterin or methotrexate (MTX), except that 20 and 21 were approximately 10 times more growth inhibitory than MTX. In in vivo tests against P388/0 and P388/MTX leukemia in mice, the analogues showed activity comparable to that of MTX, with the more potent 20 producing the same response in the P388/0 test as MTX but at one-fourth the dose; none showed activity against P388/MTX. Hydrolytic deamination of 12 and 20 produced 5-methyl-5-deazafolic acid and 5,10-dimethyl-5-deazafolic acid, respectively. In bacterial studies on the 2-amino-4-oxo analogues, 5-deazafolic acid proved to be a potent inhibitor of Lactobacillus casei DHFR and also the growth of both L. casei ATCC 7469 and Streptococcus faecium ATCC 8043. Its 5-methyl congener 22 is also inhibitory toward L. casei, but its IC50 for growth inhibition is much lower than its IC50 values for inhibition of DHFR or thymidylate synthase from L. casei, suggesting an alternate site of action.
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PMID:Syntheses and antifolate activity of 5-methyl-5-deaza analogues of aminopterin, methotrexate, folic acid, and N10-methylfolic acid. 242 90

The cytogenetic study of colorectal carcinomas is consistent with the following sequence in the tumor evolution: rearrangement of chromosome 17 with loss of 17p and often gain of 17q, loss of chromosome 18, frequent del(5q), frequent del(1p) correlated with the gain of an early replicating X. At least one gene directly involved in nucleotide synthesis, especially in the de novo pathways for thymidine is located on each of these chromosomes or chromosomes segments. A model established on the gene dosage effect, which likely results of these chromosome imbalances, may be proposed: (1) increase of thymidine kinase activity (chromosome 17q) and thus of the salvage pathway of thymidine synthesis (2) decrease of thymidine de novo pathways by decreased of thymidylate synthase (chromosome 18) and of dihydrofolate reductase (chromosome 5q) and thus accumulation of 2'-deoxyuridine-5'-P, which saves 2'-deoxycytidine 5'-P (3) decrease of cytidylate (or uridylate) kinase (chromosome 1p) and thus accumulation of 2-deoxycytidine-5-PP and of uridine-5-P (UMP) decreasing the metabolisation of orotidine-5'-P, precursor of 2-deoxycytidine-5-PP, which (4) saves -D-5-ribosyl-PP (PRPP) or even conversion of orotidine-5'-P in PRPP. The later is the immediate precursor of nucleotides in their major salvage pathways synthesis: PRPP + base----nucleotide + PPi. This reaction which would be much activated needs hypoxanthine phosphorybosyl transferase (HPRT). Its gene is carried by chromosome X which is here duplicated in its active early replicating form.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Induction of increased salvage pathways of nucleotide synthesis by dosage effect due to chromosome imbalances may be fundamental in carcinogenesis: the example of colorectal carcinoma. 242 58

A series of "stretched" methotrexate (MTX) analogues containing up to five 4-aminobutyryl (Gab) spacers between the 4-amino-4-deoxy-N10-methylpteroyl (MeAPA) moiety and the glutamate (Glu) side chain was prepared. Interest in these compounds stemmed from their relationship to MTX gamma-polyglutamates, from which they differ only in lacking "internal" alpha-carboxyl groups. The ability of the MeAPA-Gabn-Glu derivatives to inhibit dihydrofolate reductase (DHFR) and thymidylate synthase (TS) in vitro and to inhibit the growth of tumor cells in culture was evaluated. The IC50 for DHFR inhibition increased progressively from 0.082 to 0.84 microM as the number of Gab spacers was varied from one to five. At the same time the introduction of Gab spacers was found to produce substantial TS inhibition (Ki 0.1-0.4 microM) similar to that reported for MTX polyglutamates. Despite the activity of the MeAPA-Gabn-Glu derivatives as combined inhibitors of TS and DHFR, there was a steep loss of cell growth inhibitory potency as the number of Gab spacers was increased. This most likely reflects low cell uptake and the fact that when n greater than 1 there is almost total abolition of substrate activity for folylpolyglutamate synthetase, which had previously been observed with n = 1.
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PMID:Methotrexate analogues. 29. Effect of gamma-aminobutyric acid spacers between the pteroyl and glutamate moieties on enzyme binding and cell growth inhibition. 242 79

The new folate analog 10-ethyl-10-deaza-aminopterin (10EdAM) was equivalent to methotrexate (MTX) as an inhibitor of dihydrofolate reductase, but was more effectively transported and polyglutamylated in most tumor cells. Also, the transport and polyglutamylation of 10EdAM in tumor cells vis-a-vis normal proliferative tissue is substantially increased compared to MTX, favoring much greater accumulation of 10EdAM as cytotoxic polyglutamates in some of these tumor cells. 10EdAM was superior to MTX against 4 of 6 murine ascites tumors (L1210, S180, Ehrlich and Tapper) and far superior against 4 of 6 solid murine tumors (S180, Tapper, E0771 mammary AC, T241 fibrosarcoma). 10EdAM produced 10% to 30% complete regressions against S180, E0771 and T241 tumors. Both agents showed similar activity against P288 and 1498c leukemias and the Lewis lung tumor, but were inactive against B16 melanoma. Marked superiority of 10EdAM compared to MTX was also shown against the following human tumor xenografts: MX-1 (mammary carcinoma), LX-1 (small cell lung carcinoma) and CX-1 (colon carcinoma). 10EdAM produced 30% to 40% complete regressions against the MX-1 tumor.
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PMID:10-Ethyl-10-deaza-aminopterin: structural design and biochemical, pharmacologic, and antitumor properties. 244 50

Recent studies have clarified the critical role that polyglutamylation plays in methotrexate (MTX) action. Polyglutamate derivatives of MTX bind to dihydrofolate reductase (DHFR) with affinities comparable to the monoglutamate, but their retention in cells results in a sustained block in tetrahydrofolate (FH4) synthesis. One important element in the selectivity of MTX action is the preferential buildup and retention of these polyglutamyl forms in susceptible tumor cells as compared to host cells of the bone marrow or gastrointestinal mucosa. This selectivity in the accumulation of MTX polyglutamyl forms has now been further shown to play an important role in the selectivity of leucovorin rescue and may provide a unique new approach to nucleoside protection as well. This paper reviews the current understanding of the biochemical basis for leucovorin rescue and its selectivity. Important elements in leucovorin rescue are reactivation of DHFR with depression of cellular dihydrofolate (FH2) and provision of folate substrate to circumvent the block in FH4 synthesis. Selectivity of leucovorin rescue may be attributed to direct inhibition by MTX polyglutamyl forms, as well as FH2 polyglutamates that accumulate in their presence, at the levels of thymidylate synthase and transformylation during purine nucleotide biosynthesis. The presence of cellular MTX polyglutamates impairs reactivation of endogenous DHFR activity by leucovorin metabolites, and the resultant maintenance of high cellular levels of cellular FH2 and the polyglutamyl derivations of MTX impair the utilization of added FH4 in susceptible tumor cells. This paper also develops the concept of "early" nucleoside protection in antifolate therapy. In this approach, nucleosides are administered simultaneously with a pulse of MTX to provide early host protection from the cytotoxic effects of modest doses of MTX. Cessation of protection occurs at a time when extracellular and intracellular monoglutamate has fallen to low levels, and the polyglutamyl forms of the drug are present in susceptible tumors but not in host tissues of the gut and bone marrow. Data are presented to demonstrate that increased doses of MTX can be administered in normal and tumor-bearing animal systems as well as in humans by this technique.
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PMID:Biochemical factors in the selectivity of leucovorin rescue: selective inhibition of leucovorin reactivation of dihydrofolate reductase and leucovorin utilization in purine and pyrimidine biosynthesis by methotrexate and dihydrofolate polyglutamates. 244 54

Biochemical alterations associated with acquired resistance of tumor cells to antifolates are diverse and multiple in number. These most often have included both quantitative and qualitative alterations at the level of membrane transport and of the primary intracellular target, dihydrofolate reductase (DHFR). More recent studies suggest determining biochemical alterations at the level of thymidylate synthase activity and 4-aminofolate polyglutamylation. Approaches to the circumvention of acquired antifolate resistance at the level of new drug design are described which incorporate a kinetic analysis of the various biochemical phenotypes and a systematic analysis of their structure-activity relationships. A consideration of the relative frequency of occurrence of individual phenotypes during therapy is also included. This introduces the notion of population genetics in an evaluation of resistance phenomenon and of clinically significant approaches for its circumvention.
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PMID:Determinants of resistance to antifolates: biochemical phenotypes, their frequency of occurrence and circumvention. 244 55

High-dose methotrexate (HDMTX) regimens were initially designed to overcome methotrexate (MTX) resistance due to defective transport of the drug. At high concentrations, enough MTX diffuses into resistant cells to saturate and inhibit the target enzyme, dihydrofolate reductase (DHFR). The high doses of MTX needed to achieve these high drug concentrations must be administered with the reduced folate antidote, leucovorin (LV; 5-formyltetrahydrofolate), to prevent increased toxicity. To increase MTX therapeutic index, LV rescue must be selective, i.e., more effective in normal than in tumor cells. In experimental models, selective rescue can be achieved if strict LV administration guidelines are respected. Since both MTX and LV use the membrane transport system, it was hypothesized that selective rescue occurred because transport-deficient, MTX-resistant tumor cells also transported LV poorly. The unsatisfactory clinical results frequently obtained with HDMTX regimens suggest a need to re-evaluate this underlying rationale, especially in view of recent findings concerning the mechanisms of MTX resistance and LV rescue. Experimentally, cells resistant to MTX because of an increased or altered DHFR, decreased metabolism to polyglutamates, or decreased thymidylate synthase activity are not always significantly more sensitive to higher concentrations of MTX. Furthermore, recent studies on human small cell lung cancer cell lines suggest that decreased MTX polyglutamate metabolism and thymidylate synthase activity might be prevalent MTX-resistant mechanisms in human tumors. Selective LV rescue could also occur through mechanisms other than selective uptake by normal tissues.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Biochemical and pharmacologic rationale for high-dose methotrexate. 244 56

This paper describes studies that further explore the pharmacologic activity of the 7-hydroxy catabolite of methotrexate (7-OH-MTX). A 3-hr exposure of L1210 leukemia cells to 100 microM 7-OH-MTX produced negligible suppression of cell growth despite the build-up of intracellular polyglutamyl congeners to levels 2.7 times greater than the dihydrofolate reductase (DHFR) binding capacity. There was no evidence for direct inhibition of DHFR under these conditions based upon measurements of cellular tetrahydrofolate cofactor and dihydrofolate levels, nor was there suppression of [3H]deoxyuridine incorporation into DNA or [14C]formate incorporation into purines. When the interval of exposure to 100 microM 7-OH-MTX was increased to 6 hr, cell growth was inhibited by 60% and there was mild (approximately 50%) inhibition of purine and thymidylate biosynthesis associated with a small increase in cellular dihydrofolate and a small decline in cellular tetrahydrofolates. Consistent with weak inhibition of DHFR was the absence of significant binding of 7-OH-MTX polyglutamates to DHFR as assessed by gel filtration of cell extracts. Mild direct inhibition of purine biosynthetics by 7-OH-MTX- or MTX-polyglutamyl congeners was demonstrated based upon inhibition of [14C]formate incorporation into purines in cells pretreated with fluorodeoxyuridine so as to prevent tetrahydrofolate cofactor depletion or dihydrofolate polyglutamate build-up. Effects of a 6-hr exposure of cells to 100 microM 7-OH MTX on cell growth were reversed completely by 10 microM leucovorin; effects on cells containing comparable levels of MTX polyglutamyl congeners were unaffected by leucovorin. These studies demonstrate very weak inhibition of L1210 leukemia cell growth and purine, pyrimidine and tetrahydrofolate synthesis by the polyglutamyl congeners of 7-OH-MTX. The data suggest that effects of 7-OH-MTX polyglutamates on folate-requiring enzymes are not likely to play an important role in moderate-dose MTX regimens. However, pharmacologic activity may be expressed in high-dose MTX protocols when high blood levels of 7-OH-MTX are sustained over long intervals to the extent to which polyglutamate congeners accumulate in tumor cells and add to the much more potent inhibitory effects of MTX polyglutamates already present. Pharmacologic activity, however, would be diminished, if not completely reversed, by the concurrent administration of leucovorin.
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PMID:Further studies on the pharmacologic effects of the 7-hydroxy catabolite of methotrexate in the L1210 murine leukemia cell. 246 76

Arsenic is a well-established carcinogen in humans, but there is little evidence for its carcinogenicity in animals and it is inactive as an initiator or tumor promoter in two-stage models of carcinogenicity in mice. Studies with cells in culture have provided some possible mechanisms by which arsenic and arsenical compounds may exert a carcinogenic activity. Sodium arsenite and sodium arsenate were observed to induce morphological transformation of Syrian hamster embryo cells in a dose-dependent manner. The trivalent sodium arsenite was greater than tenfold more potent than the pentavalent sodium arsenate. The compounds also exhibited toxicity; however, transformation was observed at nontoxic as well as toxic doses. At low doses, enhanced colony forming efficiency of the cells was observed. To understand the mechanism of arsenic-induced transformation, the genetic effects of the two arsenicals were examined over the same doses that induced transformation. No arsenic-induced gene mutations were detected at two genetic loci. However, cell transformation and cytogenetic effects, including endoreduplication, chromosome aberrations, and sister chromatid exchanges, were induced by the arsenicals with similar dose responses. These results support a possible role for chromosomal changes in arsenic-induced transformation. The two arsenic salts also induced another form of mutation-gene amplification. Both sodium arsenite and sodium arsenate induced a high frequency of methotrexate-resistant 3T6 cells, which were shown to have amplified copies of the dihydrofolate reductase gene.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanisms of arsenic-induced cell transformation. 248 23


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