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)

5-Ethynyluracil (5-EU, 776C85) is a mechanism-based irreversible inhibitor of dihydropyrimidine dehydrogenase (EC 1.3.1.2), the rate-determining enzyme in 5-fluorouracil (5-FU) catabolism. In the present study, 5-EU was found to be a potent modulator of 5-FU catabolism in mice and rats. Liver extracts prepared up to 6 hr after a 5-EU dose (2 mg/kg) were > 96% inhibited in their ability to catalyze 5-FU degradation. 5-EU treatment increased the elimination t1/2 and the area under the plasma concentration-time curve of 5-FU. 5-FU oral bioavailability was approximately 100% in rats pretreated with 5-EU. Consequently, 5-EU induced a linear relationship between the area under the plasma concentration-time curve and the oral dose of 5-FU. As expected from the preservation of plasma 5-FU, 5-EU potentiated the antitumor activity and the toxicity of 5-FU in two mouse tumor models (Colon 38 and MOPC-315). However, 5-EU potentiated the antitumor activity to a greater degree and thereby increased the therapeutic index of 5-FU 2- to 4-fold.
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PMID:5-Ethynyluracil (776C85): a potent modulator of the pharmacokinetics and antitumor efficacy of 5-fluorouracil. 824 11

We studied the effects of 5-ethynyluracil (776C85 and 776C), a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase, on the antitumor efficacy and pharmacokinetics of tegafur (FT), a prodrug of 5-fluorouracil (5-FU), in rats with large s.c. colon carcinoma. Rats were dosed p.o. once daily for 7 days with either FT, FT and uracil in a 1:4 molar ratio (UFT), FT 1 h after 776C (776C/FT), or UFT 1 h after 776C (776C/UFT). 776C, which was dosed at 1 mg/kg, had neither intrinsic antitumor activity nor toxicity. The rank order in antitumor efficacy at the maximal tolerated dose of the FT (mg/kg/day) component was 776C/FT (5 mg/kg/day) > or = UFT (80 mg/kg/day) = 776C/UFT (5 mg/kg/day) >> FT (200 mg/kg/day). One-hundred % of rats treated with 776C/FT had complete and sustained tumor regression with no severe toxicity. The area under the plasma 5-FU concentration versus the time curve generated from UFT, FT, and 776C/FT at their maximum tolerated dose was 140, 50, and 27 microM.h, respectively. The area under the concentration in plasma versus time curve did not correlate with the rank order of antitumor efficacy. The vast majority of 5-FU derived from FT (alone) appeared to be rapidly catabolized. Furthermore, plasma exposure of 5-FU derived from UFT was more variable than that from 776C/FT. Each therapy also produced different levels of plasma uracil. Endogenous plasma uracil levels (1-3 microM) were not affected by FT but increased to 100 microM after dosing with 776C. Plasma uracil from UFT was 800 microM 1 h after dosing. These results suggest that moderately elevated uracil (776C/FT) may be beneficial, whereas uracil that is greatly elevated during the first 5 h (UFT) and 5-FU catabolites (FT alone) may interfere with antitumor efficacy. 776C, coadministered with FT, could provide once-a-day oral therapy for cancer patients.
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PMID:5-Ethynyluracil (776C85): effects on the antitumor activity and pharmacokinetics of tegafur, a prodrug of 5-fluorouracil. 852 18

5-Fluorouracil (FU) is metabolized by dihydropyrimidine dehydrogenase (DPD). Patients with suspected or proven DPD deficiency develop more or less severe FU-related side effects including death. In these reported cases, DPD activity in peripheral blood mononuclear cells (PBMC-DPD) was < 100 pmol/min/mg protein. A circadian rhythm in PBMC-DPD activity has been observed, with a peak at 1 a.m. and a trough at 1 p.m. on average. As a corollary, a circadian rhythm was observed in FU plasma concentration, with a peak at 11 a.m. and a trough at 11 p.m. on average. A significant relationship between PBMC-DPD activity and FU clearance was established but the link was weak (r = 0.31). Thus, a FU dose adaptation based on PBMC-DPD is not justified whereas a pharmacokinetically based FU dose adaptation is recommended. Experimental studies have shown that DPD activity in tumor cell lines is related to FU cytotoxicity. Although resistance to FU depends on many factors, recent clinical studies in head and neck cancer patients treated by FU suggest that tumoral DPD activity is a determining factor in predicting FU-responsiveness.
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PMID:Individualizing therapy with 5-fluorouracil related to dihydropyrimidine dehydrogenase: theory and limits. 885 47

We have focused our attention on the development of a novel form of a tegafur-based [FT; a prodrug of 5-fluorouracil (5-FU)] antitumor agent. We have used two biochemical and pharmacological modulators of 5-FU to improve its overall activity. To potentiate the antitumor activity of FT, 5-chloro-2,4-dihydroxypyridine (CDHP) was used as a potent reversible inhibitor of 5-FU degradation. The reduction of gastrointestinal (GI) toxicity, induced in the host by 5-FU, was modulated by potassium oxonate (Oxo), an inhibitor of orotate phosphoribosyltransferase that catalyzes the phosphorylation of 5-FU, a process believed to be responsible for the toxic effects of 5-FU. When CDHP and FT were simultaneously given orally to Yoshida sarcoma-bearing rats in various molar ratios, the antitumor effect of FT was significantly potentiated by the combination consisting of at least a 0.2 versus 1 molar ratio of CDHP to FT, respectively. This augmentation of an antitumor activity was supported by potent and prolonged inhibition of dihydrouracil dehydrogenase activity (5-FU degrading activities) in the liver of tumor-bearing rats after oral CDHP (0.2:0.8 molar ratio) and furthermore by elevation and over 12 h retention of 5-FU levels in the tumors following combined administration of FT and CDHP at a molar ratio of 1:0.4, respectively. Moreover, to reduce the severe GI injury and subsequent loss of body weight, observed in parallel with an increased antitumor efficacy, Oxo was given orally to Yoshida sarcoma-bearing rats and nude rats xenografted with H-81 human gastric carcinoma, during consecutive administration of the FT-CDHP mixture. Combined treatment with Oxo and FT (1:2 molar ratio) supplemented with 0.4 molar CDHP resulted in protection of body weight loss without affecting the high antitumor efficacy of the FT-CDHP mixture. When [2-14C]FT plus CDHP was administered with Oxo, the 14C-labeled fluoronucleotide content was objectively decreased in the GI tract of the tumor-bearing rats but not in the tumor and bone marrow, which supports our initial hypothesis. Based on these promising data, we propose a suitable formulation of a FT-based anticancer drug, called S-1, and consisting of FT, CDHP and Oxo at a 1:0.4:1 molar ratio and showing tumor-selective cytotoxicity of 5-FU.
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PMID:Development of a novel form of an oral 5-fluorouracil derivative (S-1) directed to the potentiation of the tumor selective cytotoxicity of 5-fluorouracil by two biochemical modulators. 886 23

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a new fluoropyrimidine carbamate, which is converted to 5-fluorouracil (5-FUra) selectively in tumors through the intermediate metabolite 5'-deoxy-5-fluorouridine (5'-dFUrd, doxifluridine). 5'-dFUrd is metabolized to 5-FUra by thymidine phosphorylase (dThdPase) located in high levels in various types of solid tumors from patients, whereas 5-FUra generated is catabolized to dihydrofluorouracil by dihydropyrimidine dehydrogenase (DPD). The present study investigated whether the efficacy of capecitabine and its intermediate metabolite 5'-dFUrd correlates with levels of these enzymes in various human cancer xenograft models. Capecitabine and 5'-dFUrd were highly effective and inhibited tumor growth by more than 50% in 18 of 24 xenograft lines (75%) and 15 of 24 xenograft lines (63%), respectively, whereas 5-FUra and a mixture of tegafur and uracil were effective only in 1 of 24 (4.2%) and 5 of 24 (21%), respectively. The efficacy of capecitabine correlated with dThdPase activity. However, capecitabine was effective even in tumors with lower levels of dThdPase if DPD levels were also lower. In contrast, it was not as effective even in tumors with sufficient levels of dThdPase if DPD levels were very high. The efficacy of capecitabine consequently correlated very well with and depended on the ratio of these two enzymes in tumors. These results indicate that capecitabine might exert its efficacy through 5-FUra generated in tumor tissues but not through that generated in normal organs. On the other hand, there was no correlation between the efficacy of a mixture of tegafur and uracil and these enzyme activities in tumors. The efficacy of capecitabine would be optimized by selecting patients who have tumors with a high ratio of dThdPase to DPD activities.
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PMID:Positive correlation between the efficacy of capecitabine and doxifluridine and the ratio of thymidine phosphorylase to dihydropyrimidine dehydrogenase activities in tumors in human cancer xenografts. 948 21

GW776C85 is a new drug that has been shown to be an effective inactivator of dihydropyrimidine dehydrogenase (DPD). Preclinical studies demonstrated that administration of GW776C85 with 5-fluorouracil (5-FU) resulted in several desirable pharmacologic effects. Initial clinical data on 5-FU combined with GW776C85 suggest potentially increased antitumor activity in at least some malignancies with tolerable toxicity, as well as several distinct economic and quality-of-life advantages including the following: (1) The possibility of administering 5-FU as an oral drug due to excellent bioavailability of 5-FU following inactivation of DPD; (2) a cost-effective alternative to continuous or protracted infusion of 5-FU without the need for hospitalization or surgical placement of an intravenous access and availability of an ambulatory pump; and (3) potential for less interpatient variation of 5-FU toxicity (e.g., in host tissues, such as bone marrow and gastrointestinal mucosa cells) due to inactivation of DPD in essentially all patients treated, permitting better 5-FU dosing guidelines. Finally, because tumors may theoretically become resistant to 5-FU by increased levels of DPD, the use of GW776C85 to inactivate DPD may provide a potential means by which tumor resistance can be reversed.
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PMID:Improving 5-FU with a novel dihydropyrimidine dehydrogenase inactivator. 955 84

The cellular and clinical pharmacology of fluoropyrimidines is characterized by marked interpatient variability in tumor response and patient tolerance. Understanding the metabolic pathways followed by 5-fluorouracil (5-FU) has led to new strategies to optimize therapy with these important agents. The "fluoropyrimidine phenotype" of tumor cells can be used to determine whether therapy with these agents is appropriate and, if so, whether one fluoropyrimidine may offer a particular advantage over another. Combining a dihydropyrimidine dehydrogenase inhibitor with 5-FU offers the potential to minimize pharmacokinetic variability and, in that way, to improve oral bioavailability, facilitate dosage adjustment to achieve desired concentrations, and increase the likelihood of tumor response while minimizing the risk of severe toxicity to individual patients.
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PMID:Biochemical and clinical pharmacology of 5-fluorouracil. 983 Jun 19

Over the past several years, the pyrimidine catabolic pathway and, in particular, the first enzymatic step involving dihydropyrimidine dehydrogenase (DPD) have been recognized as being critical in determining the ultimate metabolism and, in turn, the pharmacology of the antimetabolite drug 5-fluorouracil (5-FU). Variability in DPD activity in the normal population accounts for observed differences in the pharmacokinetics and oral bioavailability of 5-FU with an additional smaller percentage (< 5%) of the population having a relatively profound deficiency in DPD activity. Diurnal variation of DPD activity is responsible for the observed variation in 5-FU levels during continuous or protracted 5-FU infusions. Relatively elevated levels of DPD in tumor tissue may also be partially responsible for observed 5-FU tumor resistance. Finally, the pyrimidine catabolic pathway may have a role for at least some of the observed 5-FU clinical toxicities, including cardiotoxicity, hand-foot syndrome, and at least some types of neurotoxicity. In order to reduce DPD variation and potentially some of the 5-FU toxicities, there have been attempts to synthesize new fluoropyrimidine drugs used together with drugs that inhibit DPD activity. In this paper, several new types of DPD inhibitors recently introduced into the clinic will be discussed.
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PMID:The role of dihydropyrimidine dehydrogenase (DPD) modulation in 5-FU pharmacology. 983 Jun 21

Eniluracil is a potent inactivator of dihydropyrimidine dehydrogenase (DPD), which is the first enzyme in the degradative pathway of systemically administered 5-fluorouracil (5-FU). Two completely oral regimens of eniluracil plus 5-FU are being evaluated in clinical trials: (1) a chronic schedule with both agents administered BID in a 10:1 ratio for 28 days of a 5-week course, and (2) a 5-day schedule of eniluracil once daily on days 1 through 7 and 5-FU once daily on days 2 through 6. The clinical development of eniluracil is being pursued in several tumor types, including colorectal cancer, breast cancer, and pancreatic cancer. Response rates achieved in a phase II study of the chronic schedule of oral eniluracil/5-FU in patients with colorectal cancer compare favorably with those obtained in trials of intravenous 5-FU and leucovorin, while results from other trials are awaited. Safety analysis for the 28-day schedule has revealed a low incidence of severe toxicities, particularly as compared with standard 5-FU regimens.
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PMID:Clinical development of eniluracil: current status. 983 Jun 27

S-1 is an oral combined form of 1 M tegafur [a prodrug of 5-fluorouracil (5-FU)], 0.4 M 5-chloro-2,4-dihydroxypyridine (a reversible inhibitor of dihydropyrimidine dehydrogenase) and 1 M potassium oxonate (an inhibitor of orotate phosphoribosyltransferase). S-1 has been shown to exert a potent antitumor effect with low gastrointestinal toxicity in experimental tumor models. We have therefore compared the antitumor effect of oral S-1 with that of continuous infusion of 5-FU in rats bearing transplants of human and murine tumors. Almost complete inhibition of the tumor growth was obtained on 7 day schedules in Yoshida sarcoma-bearing rats by consecutive administration of 30 mg/kg/day of oral S-1 and 40 mg/kg/day infusion of 5-FU. However, a significant difference between the incidence of toxicities of S-1 and 5-FU, including body weight loss and diarrhea, was noted. The rats given the 5-FU infusion had marked weight loss and severe diarrhea, while those given oral S-1 had neither. Although about 50% inhibition of the tumor growth was attained with 15 mg/kg/day of oral S-1 and 30 mg/kg/day infusion of 5-FU in nude rats with xenografted human colon cancer (KM12C), the rate of body weight loss in the 5-FU-treated group was distinctly higher than in the S-1-treated group. The ratio of the 5-fluoronucleotide concentrations in gastrointestinal tissue to that in the tumor was lower in the S-1-treated rats than in the 5-FU-treated rats. In conclusion, the results suggest that oral S-1 might be more effective in the treatment of cancer patients than continuous infusion of 5-FU, from the standpoint of antitumor potency and toxicity.
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PMID:Anticancer activity and toxicity of S-1, an oral combination of tegafur and two biochemical modulators, compared with continuous i.v. infusion of 5-fluorouracil. 984 Jul 29


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