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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cancer chemotherapy and pharmacology 30 (1992), S. 370-376 
    ISSN: 1432-0843
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Combination of low doses of de novo pyrimidine biosynthesis inhibitors with 5-fluorouracil (FU) has been proposed to increase the antitumor activity of FU. Brequinar is such an inhibitor that has little clinical antitumor effect when used alone. We determined the clonogenic survival of MGH-U1 cells treated with FU±leucovorin (LV)±brequinar and examined the effects of these treatments on thymidylate synthase (TS). After 24 h exposure, the concentrations resulting in 50% inhibition of cell growth (IC50) for brequinar, FU, and FU+LV (100 μm) were 0.4, 20, and 10 μm, respectively. Both 24 h pretreatment and 48 h continuous treatment with the IC10 (0.1 μm) of brequinar increased the cytotoxicity of FU but did not enhance that of FU+LV. Simultaneous 24 h exposure to 0.1 μm brequinar and FU±LV did not increase the cytotoxicity of FU±LV. Intracellular cytidine triphosphate (CTP) and uridine triphosphate (UTP) pools, free TS binding sites, and levels of free fluorodeoxyuridine monophosphate (FdUMP) and deoxyuridine monophosphate (dUMP) were measured in cells pretreated with 0.1 μm brequinar for 24 h alone or followed by a 2-h exposure to FU (25 μm)±LV (100 μm). In brequinar-treated cells, CTP and UTP pools amounted to 68% and 46% of control values, respectively. The free TS binding sites remaining amounted to 70% of control values in cells treated with FU and 9% of control levels in those treated with FU + brequinar. Free FdUMP levels increased 5-fold in cells pretreated with brequinar as compared with those treated with FU alone. The increased formation of FdUMP was inhibited by simultaneous exposure to 100 μm hypoxanthine and 25 μm FU. Intracellular dUMP levels were not affected by brequinar. We conclude that a low dose of brequinar increases the cytotoxicity of FU but does not enhance that of FU+LV when exposure to brequinar precedes FU treatment. This potentiation appears to be mediated by the increased formation of FdUMP as a consequence of an increase in the cosubstrate phosphoribosyl pyrophosphate (PRPP).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cancer chemotherapy and pharmacology 34 (1994), S. 51-56 
    ISSN: 1432-0843
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Thymidylate synthase (TS) is a critical enzyme in the synthesis of DNA and an important target for cancer chemotherapy. 5-Fluorouracil (5FU) combined with leucovorin (LV) has been used to inhibit TS, and inhibition is dependent on the formation of a ternary complex between a folate cofactor, TS, and 5-fluorodeoxyuridine monophosphate (FdUMP), a metabolite of FU. The folate-based TS inhibitors CB3717, its analogs, and BW1843U89 have been synthesized as specific inhibitors of TS that do not require activation or the presence of a cofactor. We have compared the cytotoxicity of 5FU±LV with that of these folate-based TS inhibitors in human bladder cancer MGH-U1 cells using a colony-forming assay. After a 6-h exposure, FU+LV, CB3717, dCB3717, or C2 methyl dideazafolate analogs demonstrated similar cytotoxic potency that was 0.96 to 2.9 times that of 5FU alone. A 24-h exposure did not increase the potency of 5FU+LV relative to 5FU alone, but there was a marked increase in the cytotoxicity of the dideazafolates as compared with 5FU+LV. Similarly, BW1843U89 was more cytotoxic than 5FU+LV. This was reflected in a 3.2- to 1333-fold decrease in the 50% inhibitory concentration (IC50). Simultaneous exposure to LV and thymidine (TdR) protected MGH-U1 cells from the cytotoxicity of CB3717, its analogs, and BW1843U89. We conclude that (a) the folate-based TS inhibitors are more potent than 5FU+LV after a 24-h exposure, (b) protection by LV and TdR indicates that TS inhibition is the primary site of action, and (c) BW1843U89 is more potent than D1694 in MGH-U1 cells.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cancer chemotherapy and pharmacology 34 (1994), S. 51-56 
    ISSN: 1432-0843
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Thymidylate synthase (TS) is a critical enzyme in the synthesis of DNA and an important target for cancer chemotherapy. 5-Fluorouracil (5FU) combined with leucovorin (LV) has been used to inhibit TS, and inhibition is dependent on the formation of a ternary complex between a folate cofactor, TS, and 5-fluorodeoxyuridine monophosphate (FdUMP), a metabolite of FU. The folate-based TS inhibitors CB3717, its analogs, and BW1843U89 have been synthesized as specific inhibitors of TS that do not require activation or the presence of a cofactor. We have compared the cytotoxicity of 5FU ± LV with that of these folate-based TS inhibitors in human bladder cancer MGH-U1 cells using a colony-forming assay. After a 6-h exposure, FU+LV, CB3717, dCB3717, or C2 methyl dideazafolate analogs demonstrated similar cytotoxic potency that was 0.96 to 2.9 times that of 5FU alone. A 24-h exposure did not increase the potency of 5FU+LV relative to 5FU alone, but there was a marked increase in the cytotoxicity of the dideazafolates as compared with 5FU+LV. Similarly, BW1843U89 was more cytotoxic than 5FU+LV. This was reflected in a 3.2- to 1333-fold decrease in the 50% inhibitory concentration (IC50). Simultaneous exposure to LV and thymidine (TdR) protected MGH-U1 cells from the cytotoxicity of CB3717, its analogs, and BW1843U89. We conclude that (a) the folate-based TS inhibitors are more potent than 5FU+LV after a 24-h exposure, (b) protection by LV and TdR indicates that TS inhibition is the primary site of action, and (c) BW1843U89 is more potent than D1694 in MGH-U1 cells.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Cancer chemotherapy and pharmacology 35 (1994), S. 109-114 
    ISSN: 1432-0843
    Keywords: Key words Thymidylate synthase ; Inhibitors ; Antifolate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The TS-inhibitory effects induced by a 24-h exposure to the folate-based TS inhibitors CB3717, C2-desamino analogs of CB3717 including D1694, and BW1843U89 were quantitated using the MGH-U1 human bladder carcinoma. The effects of D1694 on the time course of TS inhibition and on intracellular deoxyuridine monophosphate (dUMP) accumulation and deoxyuridine (dUrd) production were evaluated. D1694 and BW1843U89 were the most active TS inhibitors with IC50 values of 2.4 and 0.5 nM, respectively. The C2-desamino C2-methyl dideazafolates were 27–292 times more potent than the parent CB3717 as TS inhibitors. A methyl group at the C2 position of CB3717 had the most dramatic effect, whereas a thiazole substitution for a benzyl added a small benefit and N10 substitution had a limited impact on TS-inhibitory potency and clonogenic survival. There was a significant correlation between the IC50 values for TS inhibition and those for cytotoxic potency obtained for these drugs. LV and thymidine protected cells from these folate-based TS inhibitors. Intracellular dUMP levels following 24 h D1694 (IC50) exposure increased 7-fold. Levels of dUrd effluxing into the media increased up to 4.5 μM following a 24-h exposure to D1694 (IC90). We conclude that (a) C2-desamino C2-methyl dideazafolates are potent TS inhibitors, (b) TS inhibition requires prolonged exposure with these folate TS inhibitors, (c) survival is correlated with inhibition of TS for the folate-based TS inhibitors and (d) the biochemical consequences of TS inhibition include increased dUMP and dUrd levels.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Cancer chemotherapy and pharmacology 35 (1994), S. 109-114 
    ISSN: 1432-0843
    Keywords: Thymidylate synthase ; Inhibitors ; Antifolate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The TS-inhibitory effects induced by a 24-h exposure to the folate-based TS inhibitors CB3717, C2-desamino analogs of CB3717 including D1694, and BW1843U89 were quantitated using the MGH-U1 human bladder carcinoma. The effects of D1694 on the time course of TS inhibition and on intracellular deoxyuridine monophosphate (dUMP) accumulation and deoxyuridine (dUrd) production were evaluated. D1694 and BW1843U89 were the most active TS inhibitors with IC50 values of 2.4 and 0.5 nM, respectively. The C2-desamino C2-methyl dideazafolates were 27–292 times more potent than the parent CB3717 as TS inhibitors. A methyl group at the C2 position of CB3717 had the most dramatic effect, whereas a thiazole substitution for a benzyl added a small benefit and N10 substitution had a limited impact on TS-inhibitory potency and clonogenic survival. There was a significant correlation between the IC50 values for TS inhibition and those for cytotoxic potency obtained for these drugs. LV and thymidine protected cells from these folate-based TS inhibitors. Intracellular dUMP levels following 24 h D1694 (IC50) exposure increased 7-fold. Levels of dUrd effluxing into the media increased up to 4.5 μM following a 24-h exposure to D1694 (IC90). We conclude that (a) C2-desamino C2-methyl dideazafolates are potent TS inhibitors, (b) TS inhibition requires prolonged exposure with these folate TS inhibitors, (c) survival is correlated with inhibition of TS for the folate-based TS inhibitors and (d) the biochemical consequences of TS inhibition include increased dUMP and dUrd levels.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-7217
    Keywords: breast cancer ; folinic acid ; 5FU ; metastatic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Standard combination chemotherapy for metastatic breast cancer produces response rates between 30–60% with limited impact on survival. We undertook a phase II trial to determine the activity of 5 fluorouracil (5FU) and folinic acid (FA) in patients with measurable metastatic or recurrent breast cancer who had received no prior chemotherapy. Patients meeting the eligibility criteria received 5FU 370 mg/m2/day and FA 200 mg/m2/day for 5 days repeated every 28 days, toxicity allowing. Response defined by standard criteria was assessed every 8 weeks and toxicity according to WHO criteria was determined on every course. Thirty-three patients were entered on trial. Thirty-two patients were evaluable for response and 33 for toxicity. The dose limiting toxicity was stomatitis with 7/32, 19/32, and 5/32 patients experiencing grade 1, 2, and 3 toxicity. Grades 1 and 2 diarrhea occurred in 17/32 and 11/32 patients respectively. Myelosuppression was not significant. Two complete and 11 partial responses were observed. The overall response rate was 41% (95% CI, 24–58%). Responses were seen in soft tissue and visceral sites. Patients who had received adjuvant chemotherapy more than 6 months prior to receiving 5FU and FA responded also. Six of 29 patients receiving standard combination chemotherapy as second line treatment responded subsequently. We concluded: 1) 5FU and FA is an active combination in the treatment of breast cancer warranting further evaluation in combination with other drugs; 2) the dose-limiting toxicity of stomatitis is tolerable; 3) patients receiving 5FU and FA as first line therapy can respond to conventional combination chemotherapy as second line treatment.
    Type of Medium: Electronic Resource
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