title: 5-Ethynyluracil (776C85): inactivation of dihydropyrimidine dehydrogenase in vivo.
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 14CO2 from [2-14C]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 micrograms/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 micrograms/kg, respectively. Rat liver DPD was inactivated completely within 25 min after an oral dose of 500 micrograms/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 degrees 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.
authors.affiliation: Wellcome Research Laboratories, Research Triangle Park, NC 27709.
authors.forename: T
authors.initials: T
authors.lastname: Spector
authors.forename: J A
authors.initials: JA
authors.lastname: Harrington
authors.forename: D J
authors.initials: DJ
authors.lastname: Porter
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D042943:Dihydrouracil Dehydrogenase (NADP); D006801:Humans; D007413:Intestinal Mucosa / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D008297:Male; D051379:Mice; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013154:Spleen / Q000201:enzymology; D014498:Uracil / Q000031:analogs & derivatives* / Q000032:analysis / Q000097:blood / Q000494:pharmacology
chemical_list: C073482:eniluracil; D014498:Uracil; D010088:Oxidoreductases; D042943:Dihydrouracil Dehydrogenase (NADP)