Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The clonal cytotoxic effects and mechanism of action of a new series of 2-amino-4-hydroxyquinazoline folate analogues (5,8-dideazafolates) have been assessed using the human colon tumor cell line HCT-8. Of these compounds only 5-methyl-5,8-dideazafolate was potentially more effective than a compound previously identified, 5,8-dideazaisofolate (H-338, NSC 289517). HCT-8 sublines resistant to methotrexate, 5-fluorodeoxyuridine, and H-338 were either minimally or not cross-resistant to the other agents. The cytotoxicity of H-338 was strongly dependent on the time of exposure; at exposure times shorter than 8 h it was essentially nontoxic. Thymidine alone, as well as leucovorin or folic acid, protected against the cytotoxic effects of H-338. This is consistent with thymidylate synthase (TS) as its only locus of action. Studies with dihydrofolate reductase and TS isolated from HCT-8 cells indicated that these quinazolines were weaker inhibitors of dihydrofolate reductase than was methotrexate, but they were not particularly potent TS inhibitors. However, synthetic poly-gamma-glutamate derivatives of quinazolines showed dramatically increased TS, but not dihydrofolate reductase, inhibition. TS inhibition increased as the polyglutamate chain length increased. Using isolated HCT-8 folylpolyglutamate synthetase, all the parent quinazolines containing L-glutamate were found to be substrates. With H-338, the results indicated that tetraglutamate or longer derivatives could be synthesized intracellularly. These results are consistent with our hypothesis that cytotoxicity by such quinazolines necessarily involves "lethal synthesis" from a prodrug; i.e., the nontoxic parent drug must be converted to polyglutamates before TS inhibition and subsequent cytotoxicity can occur.
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PMID:Mechanism of action of 5,8-dideazaisofolic acid and other quinazoline antifols in human colon carcinoma cells. 366 1

Methotrexate (MTX) was conjugated to an immunoglobulin G1 (IgG1) monoclonal antibody specific for human prostatic acid phosphatase (PAP) by the active ester method. The molar ratio of MTX to IgG was 14. MTX-monoclonal antibody conjugate retained substantially the original PAP-binding inhibition activity of the monoclonal antibody. Both MTX-monoclonal antibody conjugate and an identically prepared MTX-normal mouse IgG conjugate preserved 90% of the original dihydrofolate reductase inhibitory activity of MTX. [3H]MTX conjugated to monoclonal anti-PAP antibody was significantly accumulated more in PAP-producing human prostate tumor LNCaP cells than its normal mouse IgG counterpart. No statistical difference was found between the uptake of [3H]MTX conjugated to monoclonal antibody and that of [3H]MTX conjugated to normal mouse IgG by control PAP nonproducing thyroid tumor cells (TT). The antitumor effect of the conjugate was evaluated in vitro by its inhibition on deoxy[6-3H]uridine incorporation into LNCaP cells. The inhibition by MTX-monoclonal antibody conjugate was significantly higher than that by MTX-normal mouse IgG conjugate at 8 micrograms of drug per ml, although it was significantly less than that by free MTX. However, an in vivo tumor and tissue distribution study of [3H]MTX and its conjugates revealed that, 5 days after i.v. administration, [3H]MTX conjugated to monoclonal antibody was preferentially accumulated in LNCaP prostate tumor. Tumor:blood ratios for [3H]MTX, [3H]MTX-monoclonal antibody conjugate, and [3H]MTX-normal mouse IgG conjugate were 1.47, 5.06, and 1.26, respectively. Preliminary results obtained from a pilot study with a small number of animals demonstrated that multiply injected MTX-monoclonal antibody conjugate retarded the growth of xenografted prostate tumor (LNCaP) as compared with the control groups, including free MTX which showed a shorter period of therapeutic effectiveness. This study suggests that MTX conjugated to monoclonal anti-PAP antibody could be a potential reagent for experimental immunochemotherapy of prostate tumor, should the initial in vivo data be extended and confirmed.
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PMID:Effect of methotrexate-monoclonal anti-prostatic acid phosphatase antibody conjugate on human prostate tumor. 373 Oct 53

A human T-lymphoblast cell line, CCRF-CEM/R1, resistant to methotrexate by virtue of increased dihydrofolate reductase activity, was grown in stepwise increasing concentrations of methotrexate. This additional selection pressure resulted in a cell line, CCRF-CEM/R2, resistant to methotrexate by virtue of both an elevation of dihydrofolate reductase activity and a marked decrease in methotrexate transport. The R1 and R2 cells were approximately 70- and 350-fold more resistant to methotrexate than were the parent cells. The effects of three folate antagonists were studied on these cell lines and also on CCRF-CEM/R3 cells, characterized by impaired methotrexate transport but normal levels of dihydrofolate reductase. The elevated reductase subline CCRF-CEM/R1 was cross-resistant to triazinate [Baker's antifol, NSC 139105; ethanesulfonic acid compounded with alpha-(2-chloro-4-[4,6-diamino-2,2-dimethyl-S-triazine-1-(2H)-yl] phenoxyl)-N,N-dimethyl-m-toluamide (1:1)] and trimetrexate (NSC 249008, JB-11, TMQ; 2,4-diamino-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline), two nonclassical folate antagonists. In contrast, the transport defective subline, CCRF-CEM/R3 was not cross-resistant to these two compounds. In cells resistant to MTX by virtue of both mechanisms, CCRF-CEM/R2, triazinate, and trimetrexate were partially cross-resistant. All three methotrexate-resistant sublines showed minor cross-resistance to isoaminohydroxyquinazoline (IAHQ, NSC 289517; 5,8-dideazaisopteroylglutamate), a folate antagonist inhibitor of thymidylate synthase. These data demonstrate that methotrexate-resistant tumor cells may be effectively inhibited by antifolates with different route of entry into cells or with different enzyme targets.
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PMID:Cytotoxic effects of folate antagonists against methotrexate-resistant human leukemic lymphoblast CCRF-CEM cell lines. 385 84

Sets of 5-(substituted benzyl)-2,4-diaminopyrimidines and 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(3-substituted phenyl)-s-triazines as well as several other antifolates were tested as inhibitors of Escherichia coli dihydrofolate reductase and E. coli cell cultures both sensitive and resistant to methotrexate. From the results quantitative structure-activity relationships (QSAR) were formulated. The triazines were found to inhibit sensitive and resistant cell cultures to the same degree, but the benzylpyrimidines showed marked differences against the two types of cells. Increased hydrophobicity produced benzylpyrimidines more active against the resistant E. coli cell. Metroprine did not discriminate between the two types of cells cultures, but pyrimethamine and 2,4-diamino-6-(2,5-dimethoxybenzyl)-5-methylpyrido[2,3-d]pyrimidin e (BW 301U) did. The results are compared with triazines and benzylpyrimidines acting on Lactobacillus casei and murine tumor cells sensitive and resistant to methotrexate. QSAR is shown to be an effective means for detecting receptor differences.
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PMID:Quantitative structure-activity relationship of antifolate inhibition of bacteria cell cultures resistant and sensitive to methotrexate. 393 85

Detailed cytogenetic and molecular biologic studies have been performed on the human KB tumor cell line and four methotrexate-resistant subclones. Results are presented, demonstrating that the gene encoding the target enzyme dihydrofolate reductase is increasingly amplified in progressively methotrexate-resistant subclones, and that dihydrofolate reductase sequences are localized to a homogeneously staining region on chromosome 10q.
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PMID:Analysis of dihydrofolate reductase gene amplification in a methotrexate-resistant human tumor cell line. 401 14

Radiolabelled Baker's Antifolate (BAF) was administered to 6 patients undergoing surgical resection of intracerebral tumors. Levels of radioactivity in resected tumor and edematous brain adjacent to tumor were generally higher than levels in concurrent plasma samples and were generally comparable to levels in temporalis muscle. Levels in tumor cyst fluid were far lower than concurrent plasma levels and levels in surrounding tumor. Chromatography was performed on tumor from 2 patients and revealed that only a small proportion of the radioactivity represented unchanged BAF. The major metabolite present in tissues was 1 000 times less potent as an inhibitor of dihydrofolate reductase than was BAF. Five patients had cerebrospinal fluid (CSF) sampled following administration of tracer doses of radiolabelled BAF. Radioactivity levels were far lower in CSF than in plasma. Levels of radioactivity in the CSF were also far lower than levels in tumor and brain samples from other patients and were slightly lower than tumor cyst fluid levels. Two patients had CSF collected after they received therapeutic doses of BAF. In these patients, both CSF and plasma were assayed using a dihydrofolate reductase inhibition assay. As with tracer dose studies, CSF concentrations of BAF were substantially lower than were concurrent plasma concentrations. Thus it appears that only very low concentrations of BAF are attainable in human CSF and intracerebral tumor, although a metabolite which is a very weak inhibitor of dihydrofolate reductase attains high concentrations in tumor.
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PMID:Central nervous system pharmacology of Baker's antifolate (NSC139105) in man. 609 40

We studied the conversion of methotrexate to poly-gamma-glutamyl derivatives by cultured human breast cancer cells. After incubation with 2 micro M [3',5',9-3H]methotrexate, MCF-7 cells were washed free of extracellular drug and were boiled to lyse cells and to release drug bound to dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3). The supernatant fraction was chromatographed on Sephadex G-15 to separate parent drug from polyglutamate forms. These cells rapidly and quantitatively converted methotrexate to polyglutamates, such that after 24 hr of incubation, 70 +/- (SEM) 3% of intracellular methotrexate existed as polyglutamates. Examination of that portion of intracellular methotrexate specifically bound to dihydrofolate reductase indicated that, with prolonged incubation, methotrexate polyglutamates become the predominant drug form bound to the enzyme. These studies demonstrate that methotrexate polyglutamates are readily formed in human tumor cells and bind to dihydrofolate reductase. Because these forms of the drug may be selectively retained within the cell, they may be important determinants of the duration of action and, ultimately, the cytotoxicity of methotrexate in human solid tumors.
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PMID:Methotrexate polyglutamate synthesis by cultured human breast cancer cells. 615 58

Ternary complex formation of thymidylate synthase (5,10-methylenetetrahydrofolated:dUMP C-methyltransferase, EC 2.1.1.45), 5-fluorodeoxyuridylate (FdUMP), and poly(gamma-glutamyl) conjugates of pteroate and methotrexate (MTX) has been examined as a basis for the sequence-dependent synergism of the 5-fluorouracil-MTX combination in inhibiting viability of L1210 murine tumor cells. A 1.4-log (25-fold) increase in the inhibition of soft agar colony formation was observed when MTX preceded 5-fluorouracil as compared to the reverse sequence. L1210 cells converted 39% of the total intracellular MTX into MTX poly(gamma-glutamate)s within 4 hr of exposure to 1 microM MTX. MTX and MTX(gamma-glutamate) formed reversible ternary complexes with FdUMP on one site of thymidylate synthase, whereas with 7,8-dihydropteroylpentaglutamate and I-5,10-methylenetetrahydropteroylpentaglutamate stoichiometric binding of FdUMP to two sites on thymidylate synthase was observed. The dissociation constants for FdUMP in the ternary complexes formed in the presence of MTX, MTX(gamma-glutamate), 7,8-dihydropteroylpentaglutamate, and I-5-10-methylenetetrahydropteroylpentaglutamate were estimated to be 370, 27, < 10, and < 10 nM, respectively, by equilibrium dialysis. We propose that the sequence-dependent effect of MTX plus 5-fluorouracil on L1210 cell viability results from MTX and MTX polyglutamate inhibition of dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) and consequently a trapping of intracellular folates as dihydropteroylpolyglutamates, which increase the extent of FdUMP binding to thymidylate synthase.
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PMID:5-fluorouracil-methotrexate synergy: enhancement of 5-fluorodeoxyridylate binding to thymidylate synthase by dihydropteroylpolyglutamates. 616 May 78

Synthesis of poly-gamma-glutamyl metabolites of methotrexate was demonstrated in mouse small intestine, liver, and bone marrow and in L1210 leukemia, Sarcoma 180, and Ehrlich tumor cells after s.c. injections of [3H]methotrexate to tumor-bearing mice. Ion-exchange chromatography of tissue extracts resolved six peaks of radioactivity believed to represent methotrexate and metabolites with up to five additional glutamyl residues. Polyglutamate formation in L1210 cells and small intestine was shown to be independent of dose at least to 400 mg/kg as long as intracellular levels of drug in excess of the dihydrofolate reductase-binding capacity (exchangeable) were maintained. Both the total amount of polyglutamates and the average length of the polyglutamyl chain increased with time as long as exchangeable level of drug was present intracellularly. The results also showed differences in the extent of metabolism of methotrexate polyglutamates among the tissues examined. Although these differences were at times very large, there was no consistent correlation between these differences and other pharmacological parameters or cytotoxicity. Tumor cells appeared to synthesize more polyglutamates than did the normal tissues examined. However, differences in total drug persistence and sensitivity to drug among tumor cells and among normal tissues did not reflect the relative extent of polyglutamate synthesis in each group. It is concluded that the extent of polyglutamate synthesis per se may not be a determinant of drug sensitivity in murine tissues. However, the accumulation of these metabolites may contribute in some way to overall therapeutic response or relative cytotoxicity.
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PMID:Differential synthesis of methotrexate polyglutamates in normal proliferative and neoplastic mouse tissues in vivo. 617 39

The intracellular accumulation of poly-gamma-glutamyl derivatives of methotrexate was evaluated in the presence of vincristine or probenecid (agents which raise the intracellular level of free methotrexate) in Ehrlich ascites tumor cells. The results show that both intracellular methotrexate and its metabolites are increased by these agents and that, in the presence of L-glutamine, polyglutamate derivatives are increased by a higher percentage than is methotrexate. From 1 to 50 microM vincristine increased the levels of polyglutamate derivatives from 25 to over 300%, whereas methotrexate was raised from 25 to 80%. Similarly, 50 to 200 microM probenecid increased methotrexate polyglutamate derivatives from 31 to 88%, whereas methotrexate was raised from 0 to 30%. A determination of the bound fraction of drug indicated that the proportion of dihydrofolate reductase bound with methotrexate polyglutamates increased in the presence of these agents. Efflux studies showed that over 90% of the large pools of intracellular methotrexate polyglutamates produced by these agents was retained for at least 1 hr in the absence of extracellular methotrexate, whereas the majority of intracellular methotrexate exited the cell. These studies (a) indicate that vincristine and probenecid may be potentially useful for selectively increasing methotrexate polyglutamates in tumor cells and (b) introduce another basis for synergism observed between alkaloids and methotrexate.
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PMID:Augmentation of the intracellular levels of polyglutamyl derivatives of methotrexate by vincristine and probenecid in Ehrlich ascites tumor cells. 617 96


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