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Thomas Spector - One of the best experts on this subject based on the ideXlab platform.
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BASIC SCIENCE INVESTIGATIONS Blocking Catabolism with Eniluracil Enhances PET Studies of 5-[18F]Fluorouracil
2015Co-Authors: James R. Bading, Thomas Spector, Mian M. Alauddin, John D. Fissekis, Antranik H. Shahinian, Jinhun Joung, Peter S. ContiAbstract:Noninvasive methods for measuring the pharmacokinetics of chemo-therapeutic drugs such as 5-fluorouracil (FU) are needed for individu-alized optimization of treatment regimens. PET imaging of [18F]FU (PET/[18F]FU) is potentially useful in this context, but PET/[18F]FU is severely hampered by low tumor uptake of radiolabel and rapid catabolism of FU in vivo. Pretreatment with eniluracil (5-Ethynyluracil) prevents catabolism of FU. Hypothesizing that suppression of catabo-lism would enhance PET/[18F]FU, we examined the effects of enilura-cil on the short-term pharmacokinetics of the radiotracer. Methods: Anesthetized rats bearing a subcutaneous rat colorectal tumor were given eniluracil or placebo and injected intravenously 1 h later with [18F]FU or [3H]FU. In the 18F studies, dynamic PET image sequences were obtained 0–2 h after injection. Tumors were excised and frozen at 2 h and then analyzed for labeled metabolites by high-performance liquid chromatography. Biodistribution of radiolabel was determine
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Preclinical Development of Eniluracil: Enhancing the Therapeutic Index and Dosing Convenience of 5-Fluorouracil
Investigational New Drugs, 2000Co-Authors: Melanie T. Paff, Stephen T. Davis, David P. Baccanari, Shousong Cao, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:Eniluracil (5-Ethynyluracil, GW 776, 776C85) isbeing developed as a novel modulator of 5-fluorouracil (5-FU) forthe treatment of cancer. Eniluracil is an effective mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD), thefirst enzyme in the catabolic pathway of 5-FU. By temporarilyeliminating this prevalent enzyme, eniluracil providespredictable dosing of 5-FU and enables oral administration of5-FU to replace intravenous bolus and continuously infuseddosing. New DPD is synthesized with a half-life of 2.6 days. Italso eliminates the formation of problematic 5-FU catabolites.Most importantly, in laboratory animals, eniluracil increases thetherapeutic index and absolute efficacy of 5-FU. Accompanyingreports in this journal indicate that eniluracil has promisingclinical potential.
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α-Fluoro-β-alanine: Effects on the antitumor activity and toxicity of 5-fluorouracil
Biochemical pharmacology, 2000Co-Authors: Shousong Cao, David J. T. Porter, Stephen T. Davis, David P. Baccanari, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:We have shown previously that (R)-5-fluoro-5,6-dihydrouracil (FUraH(2)) attenuates the antitumor activity of 5-fluorouracil (FUra) in rats bearing advanced colorectal carcinoma. Presently, we found that alpha-fluoro-beta-alanine (FBAL), the predominant catabolite of FUra that is formed rapidly via FUraH(2), also decreased the antitumor activity and potentiated the toxicity of FUra. In rats treated with Eniluracil (5-Ethynyluracil, GW776), excess FBAL, in a 9:1 ratio to FUra, produced similar effects when administered 1 hr before, simultaneously with, or 2 hr after FUra. FBAL also decreased the antitumor activity of FUra in Eniluracil-treated mice bearing MOPC-315 myeloma at a 9:1 ratio with FUra, but not at a 2:1 ratio. FBAL did not affect the antitumor activity of FUra in mice bearing Colon 38 tumors. We also evaluated the effect of thymidylate synthase (TS) and thymidine kinase (TK) from tumor extracts after FUra +/- Eniluracil +/- FBAL treatment. The activity of TK was similar among the three groups at both 18 and 120 hr. There was also no difference in TS inhibition ( approximately 35%) at 18 hr. However, significantly more TS inhibition was observed in the Eniluracil/FUra group than in the FUra-alone group at 120 hr. FBAL did not alter the effect of Eniluracil/FUra in TS inhibition. Neither FUraH(2) nor FBAL affected the IC(50) of FUra in culture. Thus, the effect of FBAL did not result from direct competition with FUra uptake or immediate anabolism. Either another downstream catabolite that is not formed in cell culture is the active agent, or the effect requires the complexity of a living organism or an established tumor.
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Blocking catabolism with eniluracil enhances PET studies of 5-[18F]fluorouracil pharmacokinetics.
Journal of nuclear medicine : official publication Society of Nuclear Medicine, 2000Co-Authors: James R. Bading, Thomas Spector, Mian M. Alauddin, John D. Fissekis, Antranik H. Shahinian, Jinhun Joung, Peter S. ContiAbstract:Noninvasive methods for measuring the pharmacokinetics of chemotherapeutic drugs such as 5-fluorouracil (FU) are needed for individualized optimization of treatment regimens. PET imaging of [18F]FU (PET/[18F]FU) is potentially useful in this context, but PET/[18F]FU is severely hampered by low tumor uptake of radiolabel and rapid catabolism of FU in vivo. Pretreatment with eniluracil (5-Ethynyluracil) prevents catabolism of FU. Hypothesizing that suppression of catabolism would enhance PET/[18F]FU, we examined the effects of eniluracil on the short-term pharmacokinetics of the radiotracer. Methods: Anesthetized rats bearing a subcutaneous rat colorectal tumor were given eniluracil or placebo and injected intravenously 1 h later with [18F]FU or [3H]FU. In the 18F studies, dynamic PET image sequences were obtained 0–2 h after injection. Tumors were excised and frozen at 2 h and then analyzed for labeled metabolites by high-performance liquid chromatography. Biodistribution of radiolabel was determined by direct tissue assay. Results: Eniluracil improved tumor visualization in PET images. With eniluracil, tumor standardized uptake values ([activity/g]/[injected activity/g body weight]) increased from 0.72 ± 0.06 (mean ± SEM; n = 6) to 1.57 ± 0.20 (n = 12; P
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In vivo effect of 5-Ethynyluracil on 5-fluorouracil metabolism determined by 19F nuclear magnetic resonance spectroscopy
Cancer research, 1999Co-Authors: Earle R. Adams, Thomas Spector, Janine J. Leffert, Daniel J. Craig, Giuseppe PizzornoAbstract:Biochemical modulation of 5-fluorouracil (5-FU) has been used over the past 20 years to improve the therapeutic efficacy of this antineoplastic agent. Recently, modulation of the catabolic pathway of this fluoropy-rimidine has been the focus of extensive preclinical and clinical investigation. Dihydropyrimidine dehydrogenase catalyzes the rate-limiting step in the catabolism of 5-FU and rapidly degrades 60–90% of the drug. An irreversible inactivating inhibitor of this enzyme, 5-Ethynyluracil (EU), markedly improves the antitumor effect of 5-FU in animal models. Early clinical studies have shown a substantial alteration of the systemic disposition of 5-FU with an increase in 5-FU terminal half-life and have also indicated that EU allows safe oral administration of 5-FU by improving the oral bioavailability of the fluoropyrimidine, which is otherwise too erratic and unpredictable for a drug with such a limited therapeutic window. We evaluated the effect of EU on the metabolism of 5-FU in mice bearing colon 38 tumors using 19F nuclear magnetic resonance spectroscopy. Ex vivo measurements of tissue extracts from liver, kidney, and tumor indicated a >95% elimination of α-fluoro-β-ureidopropionic acid and α-fluoro-β-alanine signals in the tissues of mice that received 2 mg/kg of EU before administration of 5-FU. The spectra also showed an increased formation of fluoronucleotides in both normal and tumor tissues, a prolonged presence of 5-FU, and the accumulation of 5-fluorouridine that otherwise is undetectable, particularly in normal tissues. The in vivo NMR experiments on colon 38 tumors confirmed these findings, showing a complete elimination of the α-fluoro-β-ureidopropionic acid and α-fluoro-β-alanine signals in tumors treated with EU and a dramatic formation and accumulation of 5-fluorouridine mono-, di-, and triphosphates and 5-fluorouridine. Thus, by inactivating dihydropyrimidine dehydrogenase, EU prolonged the half-life for 5-FU, almost completely eliminated its catabolism for 4–6 h, which led to an increased accumulation of 5-fluorouridine mono-, di-, and triphosphates in both normal and tumor tissues.
David J. T. Porter - One of the best experts on this subject based on the ideXlab platform.
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α-Fluoro-β-alanine: Effects on the antitumor activity and toxicity of 5-fluorouracil
Biochemical pharmacology, 2000Co-Authors: Shousong Cao, David J. T. Porter, Stephen T. Davis, David P. Baccanari, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:We have shown previously that (R)-5-fluoro-5,6-dihydrouracil (FUraH(2)) attenuates the antitumor activity of 5-fluorouracil (FUra) in rats bearing advanced colorectal carcinoma. Presently, we found that alpha-fluoro-beta-alanine (FBAL), the predominant catabolite of FUra that is formed rapidly via FUraH(2), also decreased the antitumor activity and potentiated the toxicity of FUra. In rats treated with Eniluracil (5-Ethynyluracil, GW776), excess FBAL, in a 9:1 ratio to FUra, produced similar effects when administered 1 hr before, simultaneously with, or 2 hr after FUra. FBAL also decreased the antitumor activity of FUra in Eniluracil-treated mice bearing MOPC-315 myeloma at a 9:1 ratio with FUra, but not at a 2:1 ratio. FBAL did not affect the antitumor activity of FUra in mice bearing Colon 38 tumors. We also evaluated the effect of thymidylate synthase (TS) and thymidine kinase (TK) from tumor extracts after FUra +/- Eniluracil +/- FBAL treatment. The activity of TK was similar among the three groups at both 18 and 120 hr. There was also no difference in TS inhibition ( approximately 35%) at 18 hr. However, significantly more TS inhibition was observed in the Eniluracil/FUra group than in the FUra-alone group at 120 hr. FBAL did not alter the effect of Eniluracil/FUra in TS inhibition. Neither FUraH(2) nor FBAL affected the IC(50) of FUra in culture. Thus, the effect of FBAL did not result from direct competition with FUra uptake or immediate anabolism. Either another downstream catabolite that is not formed in cell culture is the active agent, or the effect requires the complexity of a living organism or an established tumor.
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Reaction of 5-Ethynyluracil with Rat Liver Xanthine Oxidase*
Journal of Biological Chemistry, 1994Co-Authors: David J. T. PorterAbstract:Abstract 5-Ethynyluracil is a time-dependent and tight binding inhibitor of xanthine oxidase. The maximal value of the first-order rate constant for onset of inhibition is 0.01 s-1, and the concentration of 5-Ethynyluracil which gives one-half of this value is 190 microM. Because the t1/2 for formation of active enzyme from inhibited enzyme is greater than 30 h in the absence of NADH, inhibition of xanthine oxidase by 5-Ethynyluracil is functionally irreversible. One equivalent of 5-[2-14C]Ethynyluracil/equivalent of active enzyme is required for complete inhibition. Allopurinol (100 microM), a potent inhibitor of xanthine oxidase, and cyanide (5 mM), an inactivator of the enzyme, do not abolish the binding of 5-[2-14C]Ethynyluracil to the enzyme. Because radiolabel is released from 5-[2-14C]Ethynyluracil-treated enzyme by treatment with 6 M guanidine HCl, a stable covalent bond is not formed between the inhibitor and the enzyme. However, the radiolabel released from inhibited enzyme is not 5-Ethynyluracil. Moreover, NADH restores catalytic activity to the inhibited enzyme and displaces the radiolabel as 5-acetyluracil. Thermal denaturation of 5-Ethynyluracil-inhibited xanthine oxidase results in the release of approximately equal amounts of 5-acetyluracil and a more hydrophilic product. Consequently, the 5-Ethynyluracil-xanthine oxidase complex yields different degradation products of 5-Ethynyluracil under different denaturation conditions. Seven uracil analogues with 5-substituents were tested as time-dependent inhibitors of xanthine oxidase. 5-Ethynyluracil is the only uracil analogue that potently inhibited xanthine oxidase. The reactivity of these uracil derivatives with sulfite was also determined. 5-Ethynyluracil is many fold more susceptible to nonenzymatic nucleophilic addition of sulfite than are the other analogues. Thus, the potency of these uracil analogues as inhibitors of xanthine oxidase is related to the nonenzymatic reactivity of the analogues with sulfite.
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5-Ethynyl-2(1H)-pyrimidinone: Aldehyde oxidase-activation to 5-Ethynyluracil, a mechanism-based inactivator of dihydropyrimidine dehydrogenase
Biochemical pharmacology, 1994Co-Authors: David J. T. Porter, Joan A. Harrington, Merrick R. Almond, Gregory T. Lowen, Thomas P. Zimmerman, Thomas SpectorAbstract:Abstract 5-Ethynyluracil is a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD, EC 1.3.1.2) in vitro (Porter et al., J Biol Chem 267 : 5236–5242, 1992) and in vivo (Spector et al., Biochem Pharmacol , 46 : 2243–2248, 1993. 5-Ethynyl-2(1 H )-pyrimidinone was rapidly oxidized to 5-Ethynyluracil by aldehyde oxidase. The substrate efficiency ( k cat / K m ) was 60-fold greater than that for N -methylnicotinamide. In contrast, xanthine oxidase oxidized 5-ethynyl-2(1 H )-pyrimidinone to 5-Ethynyluracil with a substrate efficiency that was only 0.02% that of xanthine. Because 5-ethynyl-2(1 H )-pyrimidinone did not itself inactivate purified DPD in vitro and aldehyde oxidase is predominately found in liver, we hypothesized that 5-ethynyl-2(1 H )-pyrimidinone could be a liver-specific inactivator of DPD. We found that 5-ethynyl-2(1 H )-pyrimidinone administered orally to rats at 2 μg/kg inactivated DPD in all tissues studied. Although 5-ethynyl-2(1 H )-pyrimidinone produced slightly less inactivation than 5-Ethynyluracil, the two compounds showed fairly similar patterns of inactivation of DPD in these tissues. At doses of 20 μg/kg, however, 5-ethynyl-2-pyrimidinone and 5-Ethynyluracil produced equivalent inactivation of DPD. Thus, 5-ethynyl-2(1 H )-pyrimidinone appeared to be an efficient, but not highly liver-selective prodrug of 5-Ethynyluracil.
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5-Ethynyluracil (776C85): Inactivation of dihydropyrimidine dehydrogenase in vivo
Biochemical pharmacology, 1993Co-Authors: Thomas Spector, Joan A. Harrington, David J. T. PorterAbstract:Abstract 5-Ethynyluracil (776C85), a potent, mechanism-based, irreversible inactivator (Porter et al., J Biol Chem 267 : 5236–5242, 1992) of purified dihydropyrimidine dehydrogenase (DPD, uracil reductase, EC 1.3.1.2), readily inactivated DPD in vivo . DPD was assayed in tissue extracts by measuring the release of 14 CO 2 from [2- 14 C]uracil with an improved method. Specific activities from 0.1 to > 1000 U/mg protein were reproducibly measured. After rats were orally dosed with 20 μg/kg 5-Ethynyluracil, liver, intestinal mucosa, lung, and spleen DPD were inactivated by 83–94%. The dose required to inactivate rat liver, rat brain, and mouse liver DPD by 50% was 1.8, 11, and 8.9 μg/kg, respectively. Rat liver DPD was inactivated completely within 25 min after an oral dose of 500 μg/kg 5-Ethynyluracil. New DPD was synthesized with a half-time of 63 hr. We also developed an assay based on stoichiometric inactivation of DPD by 5-Ethynyluracil to measure 5-Ethynyluracil in plasma samples. Samples containing 5-Ethynyluracil were incubated with rat liver extract for 24 hr at 12° and then assayed for DPD. DPD activity decreased linearly with the concentration of 5-Ethynyluracil (between 0 and 20 nM 5-Ethynyluracil). The assay could detect 5-Ethynyluracil at concentrations as low as 6 nM in human plasma and was not affected by high concentrations of uracil.
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Dihydropyrimidine dehydrogenase : kinetic mechanism for reduction of uracil by NADPH
The Journal of biological chemistry, 1993Co-Authors: David J. T. Porter, T SpectorAbstract:Abstract Steady-state and pre-steady-state kinetic data were used to determine the kinetic mechanism for bovine liver dihydropyrimidine dehydrogenase (DPDase). Steady-state kinetic data suggested a random rapid-equilibrium mechanism with Km values for NADPH and uracil of 0.12 microM and 0.8 microM, respectively, and a kcat of 1.6 s-1 in Tris buffer at pH 8.0 and 37 degrees C. The dissociation constant of DPDase for NADPH at 25 degrees C in the absence of uracil (0.09 microM) was similar to the Km for NADPH. DPDase also catalyzed the exchange of tritium in [4S-3H,4R-1H]NADP3H with solvent protons in the absence of uracil. DPDase inactivated by 5-Ethynyluracil, which covalently modifies the enzyme at the uracil binding site, catalyzed the exchange reaction at the same rate (1 s-1) as native enzyme. Thus, the interaction of NADPH with DPDase was independent of the uracil binding site. Because DPDase catalyzed the exchange of deuterium in [4S-2H,4R-1H]NADP2H with solvent protons with a rate constant of 5.4 s-1, which was significantly larger than that for tritium, the analogous rate constant for exchange of the 4-hydrogen in NADPH must be significantly larger than 5 s-1. Consequently, intermediates on the exchange pathway were kinetically competent to participate in the reduction of uracil by NADPH (kcat = 1.6 s-1). Rate constants for reduction of DPDase by NADPH and 5,6-dihydrouracil were several orders of magnitude greater than kcat. The rate constants for dissociation of E.NADP+ (15 s-1) and for dissociation of E.5,6-dihydrouracil (> 250 s-1) were also greater than kcat. These results supported a random rapid-equilibrium kinetic mechanism and suggested kcat was an internal electron transfer between enzymic prosthetic groups.
Jaroslava Miksovska - One of the best experts on this subject based on the ideXlab platform.
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Fluorescent 5-Pyrimidine and 8-Purine Nucleosides Modified with an N-Unsubstituted 1,2,3-Triazol-4-yl Moiety.
The Journal of organic chemistry, 2019Co-Authors: Zhiwei Wen, Paloma R. Tuttle, A. Hasan Howlader, Anna Vasilyeva, Laura Gonzalez, Antonija Tangar, Ruipeng Lei, Eduardo E. Laverde, Yuan Liu, Jaroslava MiksovskaAbstract:The Cu(I)- or Ag(I)-catalyzed cycloaddition between 8-ethynyladenine or guanine nucleosides and TMSN3 gave 8-(1-H-1,2,3-triazol-4-yl) nucleosides in good yields. On the other hand, reactions of 5-Ethynyluracil or cytosine nucleosides with TMSN3 led to the chemoselective formation of triazoles via Cu(I)-catalyzed cycloaddition or vinyl azides via Ag(I)-catalyzed hydroazidation. These nucleosides with a minimalistic triazolyl modification showed excellent fluorescent properties with 8-(1-H-1,2,3-triazol-4-yl)-2′-deoxyadenosine (8-TrzdA), exhibiting a quantum yield of 44%. The 8-TrzdA 5′-triphosphate was incorporated into duplex DNA containing a one-nucleotide gap by DNA polymerase β.
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Fluorescent 5‑Pyrimidine and 8‑Purine Nucleosides Modified with an N‑Unsubstituted 1,2,3-Triazol-4-yl Moiety
2019Co-Authors: Zhiwei Wen, Paloma R. Tuttle, Anna Vasilyeva, Laura Gonzalez, Antonija Tangar, Ruipeng Lei, Eduardo E. Laverde, Yuan Liu, Hasan A. Howlader, Jaroslava MiksovskaAbstract:The Cu(I)- or Ag(I)-catalyzed cycloaddition between 8-ethynyladenine or guanine nucleosides and TMSN3 gave 8-(1-H-1,2,3-triazol-4-yl) nucleosides in good yields. On the other hand, reactions of 5-Ethynyluracil or cytosine nucleosides with TMSN3 led to the chemoselective formation of triazoles via Cu(I)-catalyzed cycloaddition or vinyl azides via Ag(I)-catalyzed hydroazidation. These nucleosides with a minimalistic triazolyl modification showed excellent fluorescent properties with 8-(1-H-1,2,3-triazol-4-yl)-2′-deoxyadenosine (8-TrzdA), exhibiting a quantum yield of 44%. The 8-TrzdA 5′-triphosphate was incorporated into duplex DNA containing a one-nucleotide gap by DNA polymerase β
David P. Baccanari - One of the best experts on this subject based on the ideXlab platform.
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Preclinical Development of Eniluracil: Enhancing the Therapeutic Index and Dosing Convenience of 5-Fluorouracil
Investigational New Drugs, 2000Co-Authors: Melanie T. Paff, Stephen T. Davis, David P. Baccanari, Shousong Cao, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:Eniluracil (5-Ethynyluracil, GW 776, 776C85) isbeing developed as a novel modulator of 5-fluorouracil (5-FU) forthe treatment of cancer. Eniluracil is an effective mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD), thefirst enzyme in the catabolic pathway of 5-FU. By temporarilyeliminating this prevalent enzyme, eniluracil providespredictable dosing of 5-FU and enables oral administration of5-FU to replace intravenous bolus and continuously infuseddosing. New DPD is synthesized with a half-life of 2.6 days. Italso eliminates the formation of problematic 5-FU catabolites.Most importantly, in laboratory animals, eniluracil increases thetherapeutic index and absolute efficacy of 5-FU. Accompanyingreports in this journal indicate that eniluracil has promisingclinical potential.
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α-Fluoro-β-alanine: Effects on the antitumor activity and toxicity of 5-fluorouracil
Biochemical pharmacology, 2000Co-Authors: Shousong Cao, David J. T. Porter, Stephen T. Davis, David P. Baccanari, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:We have shown previously that (R)-5-fluoro-5,6-dihydrouracil (FUraH(2)) attenuates the antitumor activity of 5-fluorouracil (FUra) in rats bearing advanced colorectal carcinoma. Presently, we found that alpha-fluoro-beta-alanine (FBAL), the predominant catabolite of FUra that is formed rapidly via FUraH(2), also decreased the antitumor activity and potentiated the toxicity of FUra. In rats treated with Eniluracil (5-Ethynyluracil, GW776), excess FBAL, in a 9:1 ratio to FUra, produced similar effects when administered 1 hr before, simultaneously with, or 2 hr after FUra. FBAL also decreased the antitumor activity of FUra in Eniluracil-treated mice bearing MOPC-315 myeloma at a 9:1 ratio with FUra, but not at a 2:1 ratio. FBAL did not affect the antitumor activity of FUra in mice bearing Colon 38 tumors. We also evaluated the effect of thymidylate synthase (TS) and thymidine kinase (TK) from tumor extracts after FUra +/- Eniluracil +/- FBAL treatment. The activity of TK was similar among the three groups at both 18 and 120 hr. There was also no difference in TS inhibition ( approximately 35%) at 18 hr. However, significantly more TS inhibition was observed in the Eniluracil/FUra group than in the FUra-alone group at 120 hr. FBAL did not alter the effect of Eniluracil/FUra in TS inhibition. Neither FUraH(2) nor FBAL affected the IC(50) of FUra in culture. Thus, the effect of FBAL did not result from direct competition with FUra uptake or immediate anabolism. Either another downstream catabolite that is not formed in cell culture is the active agent, or the effect requires the complexity of a living organism or an established tumor.
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dihydropyrimidine dehydrogenase inactivation and 5 fluorouracil pharmacokinetics allometric scaling of animal data pharmacokinetics and toxicodynamics of 5 fluorouracil in humans
Cancer Chemotherapy and Pharmacology, 1996Co-Authors: S P Khor, Stephen T. Davis, David P. Baccanari, H Amyx, Donald J Nelson, Thomas SpectorAbstract:The pharmacokinetics of 5-fluorouracil (5-FU) in different animal species treated with the dihy-dropyrimidine dehydrogenase (DPD) inactivator, 5-Ethynyluracil (776C85) were related through allometric scaling. Estimates of 5-FU dose in combination with 776C85 were determined from pharmacokinetic and toxicodynamic analysis. Method: The pharmacokinetics of 5-FU in the DPD-deficient state were obtained from mice, rats and dogs treated with 776C85 followed by 5-FU. The pharmacokinetics of 5-FU in humans were then estimated using interspecies allometric scaling. Data related to the clinical toxicity for 5-FU were obtained from the literature. The predicted pharmacokinetics of 5-FU and the clinical toxicity data were then used to estimate the appropriate dose of 5-FU in combination with 776C85 in clinical trials. Results: The allometric equation relating total body clearance (CL) of 5-FU to the body weight (B) (CL=0.47B0.74) indicates that clearance increased disproportionately with body weight. In contrast, the apparent volume of distribution (Vc) increased proportionately with body weight (Vc=0.58 B0.99). Based on allometric analysis, the estimated clearance of 5-FU (10.9 l/h) in humans with DPD deficiency was comparable to the observed values in humans lacking DPD activity due to genetic predisposition (10.1 l/h), or treatment with 776C85 (7.0 l/h) or (E)-5-(2-bromovinyl)-2′-deoxyuridine (BVdUrd, 6.6 l/h). The maximum tolerated dose (MTD) of 5-FU in combination with 776C85 was predicted from literature data relating toxicity and plasma 5-FU area under the concentration-time curve (AUC). Based on allometric analysis, the estimated values for the MTD in humans treated with 776C85 and receiving 5-FU as a single i.v. bolus dose, and 5-day and 12-day continuous infusions were about 110, 50 and 30 mg/m2 of 5-FU, respectively. Discussion: The pharmacokinetics of 5-FU in the DPD-deficient state in humans can be predicted from animal data. A much smaller dose of 5-FU is needed in patients treated with 776C85.
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5-Ethynyluracil (776C85): Effects on the Antitumor Activity and Pharmacokinetics of Tegafur, a Prodrug of 5-Fluorouracil
Cancer research, 1995Co-Authors: Shousong Cao, Stephen T. Davis, S. S. Joyner, David P. Baccanari, Youcef M. Rustum, Thomas SpectorAbstract: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) ≥ UFT (80 mg/kg/day) = 776C/UFT (5 mg/kg/day) 3 ≫ 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 µm · 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 µm) were not affected by FT but increased to 100 µm after dosing with 776C. Plasma uracil from UFT was 800 µm 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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5-Ethynyluracil (776C85): protection from 5-fluorouracil-induced neurotoxicity in dogs.
Biochemical pharmacology, 1994Co-Authors: Stephen T. Davis, S. S. Joyner, David P. Baccanari, Thomas SpectorAbstract:Abstract 5-Ethynyluracil (776C85) is a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD), the enzyme that catalyzes the rapid catabolism of 5-fluorouracil (5-FU). Because catabolism is the major route for 5-FU clearance, we studied the effect of 5-Ethynyluracil on the pharmacokinetics and toxicity of continuous i.v. 5-FU infusion in the dog. 5-FU at 40 mg/kg/24 hr resulted in a steady-state plasma 5-FU concentration of 1.3 μM and was fatal with dogs dying from apparent neurotoxicity. 5-Ethynyluracil lowered the total clearance of 5-FU from 9.9 to 0.2 L/hr/kg and enabled 1.6 mg/kg/24 hr 5-FU to achieve a steady-state plasma 5-FU concentration of 2.4 μM with no apparent toxicity. 5-FU at 4 mg/kg/24 hr achieved a steady-state plasma 5-FU concentration of 5.3 μM and produced only mild gastrointestinal disturbances in 5-Ethynyluracil-treated dogs. Thus, a catabolite of 5-FU appears to be responsible for the 5-FU-induced neurotoxicity in dogs.
Stephen T. Davis - One of the best experts on this subject based on the ideXlab platform.
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Preclinical Development of Eniluracil: Enhancing the Therapeutic Index and Dosing Convenience of 5-Fluorouracil
Investigational New Drugs, 2000Co-Authors: Melanie T. Paff, Stephen T. Davis, David P. Baccanari, Shousong Cao, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:Eniluracil (5-Ethynyluracil, GW 776, 776C85) isbeing developed as a novel modulator of 5-fluorouracil (5-FU) forthe treatment of cancer. Eniluracil is an effective mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD), thefirst enzyme in the catabolic pathway of 5-FU. By temporarilyeliminating this prevalent enzyme, eniluracil providespredictable dosing of 5-FU and enables oral administration of5-FU to replace intravenous bolus and continuously infuseddosing. New DPD is synthesized with a half-life of 2.6 days. Italso eliminates the formation of problematic 5-FU catabolites.Most importantly, in laboratory animals, eniluracil increases thetherapeutic index and absolute efficacy of 5-FU. Accompanyingreports in this journal indicate that eniluracil has promisingclinical potential.
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α-Fluoro-β-alanine: Effects on the antitumor activity and toxicity of 5-fluorouracil
Biochemical pharmacology, 2000Co-Authors: Shousong Cao, David J. T. Porter, Stephen T. Davis, David P. Baccanari, Youcef M. Rustum, Robert L. Tansik, Thomas SpectorAbstract:We have shown previously that (R)-5-fluoro-5,6-dihydrouracil (FUraH(2)) attenuates the antitumor activity of 5-fluorouracil (FUra) in rats bearing advanced colorectal carcinoma. Presently, we found that alpha-fluoro-beta-alanine (FBAL), the predominant catabolite of FUra that is formed rapidly via FUraH(2), also decreased the antitumor activity and potentiated the toxicity of FUra. In rats treated with Eniluracil (5-Ethynyluracil, GW776), excess FBAL, in a 9:1 ratio to FUra, produced similar effects when administered 1 hr before, simultaneously with, or 2 hr after FUra. FBAL also decreased the antitumor activity of FUra in Eniluracil-treated mice bearing MOPC-315 myeloma at a 9:1 ratio with FUra, but not at a 2:1 ratio. FBAL did not affect the antitumor activity of FUra in mice bearing Colon 38 tumors. We also evaluated the effect of thymidylate synthase (TS) and thymidine kinase (TK) from tumor extracts after FUra +/- Eniluracil +/- FBAL treatment. The activity of TK was similar among the three groups at both 18 and 120 hr. There was also no difference in TS inhibition ( approximately 35%) at 18 hr. However, significantly more TS inhibition was observed in the Eniluracil/FUra group than in the FUra-alone group at 120 hr. FBAL did not alter the effect of Eniluracil/FUra in TS inhibition. Neither FUraH(2) nor FBAL affected the IC(50) of FUra in culture. Thus, the effect of FBAL did not result from direct competition with FUra uptake or immediate anabolism. Either another downstream catabolite that is not formed in cell culture is the active agent, or the effect requires the complexity of a living organism or an established tumor.
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dihydropyrimidine dehydrogenase inactivation and 5 fluorouracil pharmacokinetics allometric scaling of animal data pharmacokinetics and toxicodynamics of 5 fluorouracil in humans
Cancer Chemotherapy and Pharmacology, 1996Co-Authors: S P Khor, Stephen T. Davis, David P. Baccanari, H Amyx, Donald J Nelson, Thomas SpectorAbstract:The pharmacokinetics of 5-fluorouracil (5-FU) in different animal species treated with the dihy-dropyrimidine dehydrogenase (DPD) inactivator, 5-Ethynyluracil (776C85) were related through allometric scaling. Estimates of 5-FU dose in combination with 776C85 were determined from pharmacokinetic and toxicodynamic analysis. Method: The pharmacokinetics of 5-FU in the DPD-deficient state were obtained from mice, rats and dogs treated with 776C85 followed by 5-FU. The pharmacokinetics of 5-FU in humans were then estimated using interspecies allometric scaling. Data related to the clinical toxicity for 5-FU were obtained from the literature. The predicted pharmacokinetics of 5-FU and the clinical toxicity data were then used to estimate the appropriate dose of 5-FU in combination with 776C85 in clinical trials. Results: The allometric equation relating total body clearance (CL) of 5-FU to the body weight (B) (CL=0.47B0.74) indicates that clearance increased disproportionately with body weight. In contrast, the apparent volume of distribution (Vc) increased proportionately with body weight (Vc=0.58 B0.99). Based on allometric analysis, the estimated clearance of 5-FU (10.9 l/h) in humans with DPD deficiency was comparable to the observed values in humans lacking DPD activity due to genetic predisposition (10.1 l/h), or treatment with 776C85 (7.0 l/h) or (E)-5-(2-bromovinyl)-2′-deoxyuridine (BVdUrd, 6.6 l/h). The maximum tolerated dose (MTD) of 5-FU in combination with 776C85 was predicted from literature data relating toxicity and plasma 5-FU area under the concentration-time curve (AUC). Based on allometric analysis, the estimated values for the MTD in humans treated with 776C85 and receiving 5-FU as a single i.v. bolus dose, and 5-day and 12-day continuous infusions were about 110, 50 and 30 mg/m2 of 5-FU, respectively. Discussion: The pharmacokinetics of 5-FU in the DPD-deficient state in humans can be predicted from animal data. A much smaller dose of 5-FU is needed in patients treated with 776C85.
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5-Ethynyluracil (776C85): Effects on the Antitumor Activity and Pharmacokinetics of Tegafur, a Prodrug of 5-Fluorouracil
Cancer research, 1995Co-Authors: Shousong Cao, Stephen T. Davis, S. S. Joyner, David P. Baccanari, Youcef M. Rustum, Thomas SpectorAbstract: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) ≥ UFT (80 mg/kg/day) = 776C/UFT (5 mg/kg/day) 3 ≫ 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 µm · 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 µm) were not affected by FT but increased to 100 µm after dosing with 776C. Plasma uracil from UFT was 800 µm 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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5-Ethynyluracil (776C85): protection from 5-fluorouracil-induced neurotoxicity in dogs.
Biochemical pharmacology, 1994Co-Authors: Stephen T. Davis, S. S. Joyner, David P. Baccanari, Thomas SpectorAbstract:Abstract 5-Ethynyluracil (776C85) is a potent mechanism-based inactivator of dihydropyrimidine dehydrogenase (DPD), the enzyme that catalyzes the rapid catabolism of 5-fluorouracil (5-FU). Because catabolism is the major route for 5-FU clearance, we studied the effect of 5-Ethynyluracil on the pharmacokinetics and toxicity of continuous i.v. 5-FU infusion in the dog. 5-FU at 40 mg/kg/24 hr resulted in a steady-state plasma 5-FU concentration of 1.3 μM and was fatal with dogs dying from apparent neurotoxicity. 5-Ethynyluracil lowered the total clearance of 5-FU from 9.9 to 0.2 L/hr/kg and enabled 1.6 mg/kg/24 hr 5-FU to achieve a steady-state plasma 5-FU concentration of 2.4 μM with no apparent toxicity. 5-FU at 4 mg/kg/24 hr achieved a steady-state plasma 5-FU concentration of 5.3 μM and produced only mild gastrointestinal disturbances in 5-Ethynyluracil-treated dogs. Thus, a catabolite of 5-FU appears to be responsible for the 5-FU-induced neurotoxicity in dogs.
