5-Ethynyluracil (GW776): effects on the formation of the toxic catabolites of 5-fluorouracil, fluoroacetate and fluorohydroxypropionic acid in the isolated perfused rat liver model

Br J Cancer. 1997;76(9):1170-80. doi: 10.1038/bjc.1997.529.


We studied the effects of 5-ethynyluracil (GW776), a potent inactivator of dihydropyrimidine dehydrogenase, on the metabolism of 5-fluorouracil (5-FU), in particular with respect to formation of the toxic compounds fluoroacetate (FAC) and 2-fluoro-3-hydroxypropionic acid (FHPA), using fluorine-19 nuclear magnetic resonance and the isolated perfused rat liver model. Livers were perfused with 5-FU alone at a dose of 15 mg kg(-1) body weight or with 5-FU + GW776 at doses of 15 mg 5-FU kg(-1) body weight and 0.5 mg GW776 kg(-1) body weight injected 1 h before 5-FU. All 5-FU was metabolized in experiments with 5-FU alone whereas unmetabolized 5-FU represented 94% of the fluorinated compounds measured in experiments with 5-FU + GW776. GW776 modulated both the catabolic and the anabolic pathways of 5-FU, the most striking effect being on the degradative pathway. The amount of 5-FU catabolites decreased by a factor of 27 in the presence of GW776. The modulator led to a decrease in alpha-fluoro-beta-alanine (FBAL) formation by a factor of approximately 110, while fluoride ion formation decreased by a factor of approximately 10. By strongly lowering the metabolism of 5-FU into FBAL, GW776 circumvented the transformation of FBAL into toxic FAC and FHPA. 5-FU anabolites increased by a factor of approximately 7 in the presence of GW776. The level of free fluoronucleotides and 5-fluorouridine-5'-diphosphate sugars was increased up to fivefold. No incorporation of 5-FU into RNA could be measured in experiments with 5-FU alone whereas, although low (0.1% of 5-FU injected dose), it was detectable in experiments with 5-FU + GW776. These results suggest that GW776 may be useful for attenuating the not very common but serious cardiotoxic and/or neurotoxic side-effects of 5-FU that are probably due to FBAL metabolites.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bile / metabolism
  • Enzyme Inhibitors / pharmacology*
  • Fluoroacetates / metabolism*
  • Fluorouracil / pharmacokinetics*
  • In Vitro Techniques
  • Lactic Acid / analogs & derivatives*
  • Lactic Acid / metabolism
  • Liver / drug effects
  • Liver / metabolism*
  • Magnetic Resonance Spectroscopy
  • Male
  • Rats
  • Rats, Wistar
  • Uracil / analogs & derivatives*
  • Uracil / pharmacology


  • 2-fluoro-3-hydroxypropionic acid
  • Enzyme Inhibitors
  • Fluoroacetates
  • eniluracil
  • Lactic Acid
  • Uracil
  • Fluorouracil