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

Abstract

Summary We report the first demonstration of the biotransformation of the anti-cancer drug 5-fluorouracil (FU) into two new metabolites, a-fluoro-f-hydroxypropionic acid (FHPA) and fluoroacetate (FAC), in the isolated perfused rat liver (IPRL) and in the rat in vivo. IPRL was perfused with solutions of pure FU at two doses, 15 or 45 mg kg-' body weight, and rats were injected i.p. with 180 mg of FU kg-' body weight.Fluorine-19 NMR analysis of perfusates from IPRL and rat urine showed the presence of the normal metabolites of FU and low amounts of FHPA (0.4% or 0.1% of injected FU in perfusates from IPRL treated with 15 or 45 mg of FU kg-' body weight, respectively; 0.08% of the injected FU in rat urine) and FAC (0.1% or 0.03% of injected FU in perfusates from IPRL treated with 15 or 45 mg of FU kg-' body weight, respectively; 0.003% of the injected FU in rat urine). IPRL was also perfused with a solution of a-fluoro-i-alanine (FBAL) hydrochloride at 16.6 mg kg-' body weight dose equivalent to 15 mg of FU kg-' body weight. Low amounts of FHPA (0.2% of injected FBAL) and FAC (0.07%) were detected in perfusates, thus demonstrating that FHPA and FAC arise from FBAL catabolism. As FAC is a well-known cardiotoxic poison, and FHPA is also cardiotoxic at high doses, the cardiotoxicity of FU might stem from at least two sources. The first one, established in previous papers (Lemaire et al, 1992(Lemaire et al, , 1994, is the presence in commercial solutions of FU of degradation products of FU that are metabolized into FHPA and FAC; these are formed over time in the basic medium necessary to dissolve the drug. The second, demonstrated in the present study, is the metabolism of FU itself into the same compounds.Keywords: 5-fluorouracil; a-fluoro-J-alanine; '9F nuclear magnetic resonance; metabolism; fluoroacetate; a-fluoro-o-hydroxypropionic acid; isolated perfused rat liver; rat urine 5-Fluorouracil (FU) is widely used as an anti-tumour agent for treatment of solid tumours. Its chief side-effects are myelosuppression, diarrhoea, vomiting and mucositis. However, over the last decade, the number of reports of cardiotoxicity and neurotoxicity attributed to FU has rapidly increased, probably because of the use of higher doses in continuous perfusion (Moertel et al, 1964;Rezkalla et al, 1989;Moore et al, 1990;Gamelin et al, 1991; De Fomi et al, 1992;Robben et al, 1993;Anand, 1994). The precise biochemical mechanism underlying these two side-effects remains unclear, although several investigators have postulated, but never demonstrated experimentally, that FU might be transformed into fluoroacetate (FAC), a highly cardiotoxic and neurotoxic poison (Koenig and Patel, 1970;Okeda et al, 1990). FAC enters the Krebs cycle and is then transformed into fluorocitrate, which inhibits the enzyme aconitase. Aconitase catalyses the conversion of citrate to isocitrate via the obligatory intermediate cis-aconitate. Inhibition of aconitase leads to a build-up of citrate in animal tissues (in particular heart) and serum, and the heart product...

Mitochondrial Toxin 3-Nitropropionic Acid Induces Cardiac and Neurotoxicity Differentially in Mice

“…Fluoroacetate (1080), a rodenticide and an inhibitor of mitochondrial citric acid cycle enzymes aconitase and SDH, similar to 3NPA, induces damage in the heart and the brain depending on the species studied. 37,92,93 A second cardiac toxin, Doxorubicin (adriamycin) has been shown to redox cycle at complex I producing mitochondrial superoxide, which subsequently damages various complexes of the electron transport chain. 94,95 Thus for its effects on the heart, 3NPA may be another useful compound to study cardiac mitochondrial toxicity and preconditioning.…”

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

“…FHPA did not generate cardiotoxic symptoms at the lowest dose but was highly cardiotoxic on this model at the highest dose (unpublished data). Moreover, FBAL, the precursor of FHPA and FAC (Arellano et al, 1994), accumulated in rats and was retained up to 8 days in various tissues, mainly liver, heart and brain (Zhang et al, 1992(Zhang et al, , 1993. By greatly lowering the metabolization of 5-FU into FBAL, GW776 circumvents the formation of toxic FHPA and FAC (Table 3).…”

“…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 degradation of 5-FU in the basic medium required for its solubilization and are metabolized into FAC and 2-fluoro-3-hydroxypropionic acid (FHPA), another cardiotoxic compound (Lemaire et al, 1992(Lemaire et al, , 1994. Moreover, we were the first to demonstrate experimentally the biotransformation of pure 5-FU into two new catabolites, FAC and FHPA, in the isolated perfused rat liver (IPRL) model and in rats (Arellano et al, 1994). This demonstration was extended to the bioconversion of 5-FU into FHPA in humans (Lemaire et al, 1996).…”

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

“…␣-Fluoro-␤-ureidopropionic acid (FUPA) was prepared by chemical opening of 5-FUH 2 pyrimidine ring in 1 M NaOH (Malet-Martino et al, 1986). 2-Fluoro-3-hydroxypropionic acid (FHPA) was synthesized as described by Arellano et al (1998). All other chemicals were reagent grade and obtained from standard commercial sources.…”