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

Abstract

Summary 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-' body weight or with 5-FU + GW776 at doses of 15 mg 5-FU kg-' body weight and 0.5 mg GW776 kg-' 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 a-fluoro-3-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.Keywords: 5-fluorouracil; 5-ethynyluracil (GW776); 19F nuclear magnetic resonance; modulation of 5-fluorouracil metabolism; fluoroacetate; 2-fluoro-3-hydroxypropionic acid; isolated perfused rat liver 5-Fluorouracil (5-FU) is one of the most commonly used anticancer agents for treatment of solid tumours. Common clinical adverse reactions include myelosuppression, diarrhoea, vomiting and mucositis. Over the last decade, the number of reports of cardiotoxicity and neurotoxicity attributed to 5-FU has rapidly increased (Anand, 1994;Yeh and Cheng, 1994; and references cited therein). The biochemical mechanism underlying these toxic side-effects remains unclear, although it has been postulated that 5-FU, and more precisely its main catabolite ex-fluoro-p-alanine (FBAL) (Mukherjee and Heidelberger, 1960;Bemadou et al, 1985; Heggie et al, 1987; Hull et al, 1988), might be transformed into fluoroacetate (FAC) (Koenig and Patel, 1970), a highly cardiotoxic and neurotoxic poison (Pattison and Peters, 1966). We demonstrated on the isolated perfused rabbit heart model that commercial solutions of 5-FU contain cardiotoxic impurities, namely fluoromalonic acid semialdehyde (FMASAld) and fluoroacetaldehyde (Facet), that are derived from...

The anti-cancer drug 5-fluorouracil is metabolized by the isolated perfused rat liver and in rats into highly toxic fluoroacetate

“…As FHPA and FAC were not detectable in the non-concentrated perfusates, we determined their concentrations from the spectra of the concentrated perfusates. It should be noted that the amounts of FHPA and FAC were underestimated as demonstrated previously (Arellano et al, 1997). Table 2 shows the results of the IPRL experiments.…”

5-Fluorouracil and dihydropyrimidine dehydrogenase

“…26,27 Because the patterns of toxicity development clearly differ between DIF preparations and non-DIF preprations, 28-31 the possibility cannot be denied that control or inhibition of DPD decreases the degradation products and decreases toxicity. [32][33][34][35] Relation between DPD and sensitivity to 5-FU It is well known that thymidylate synthase (TS), a target enzyme of 5-FU, affects the sensitivity of 5-FU. [36][37][38] It is also reported that DPD determines 5-FU sensitivity.…”

Metabolism of Capecitabine, an Oral Fluorouracil Prodrug:19F NMR Studies in Animal Models and Human Urine

“…A higher cytidine deaminase activity in humans (Ho, 1973) combined with an enhancement of the thymidine phosphorylase level in tumor tissue (Miwa et al, 1998) could account for the high formation of 5-FU and catabolites observed in human urine. It should be pointed out that CAP, as 5-FU (Lemaire et al, 1996;Arellano et al, 1997), leads to the formation of low amounts of two FBAL metabolites, FHPA and FAC, even in humans.…”

“…Male Wistar rats (Iffa Credo, Lyon, France) were used. The IPRL experiments have been described previously (Arellano et al, 1997). CAP was injected into the perfusate after 1 h of liver equilibration, and the experiments were continued for 3 h. At the end of the experiments (n ϭ 5), the perfusate was freeze-dried, stored at Ϫ80°C, and resuspended in H 2 O to a known volume close to 3 ml immediately before 19 F NMR analysis.…”