Direct ¹⁹f NMR spectroscopic observation of 5‐fluorouracil metabolism in the isolated perfused mouse liver model

Abstract

A direct analysis of 5-fluorouracil (FUra) metabolism in the isolated perfused mouse liver was carried out using 19F NMR spectroscopy. In livers treated with low (30 mg/kg body weight (b.w.] or high (180 mg/kg b.w.) doses of FUra, with (180 mg/kg b.w.) or without thymidine (dThd), FUra was rapidly catabolized to alpha-fluoro-beta-ureidopropionic acid (FUPA) and alpha-fluoro-beta-alanine (FBAL), the latter usually becoming by far the major catabolite. The first catabolite of FUra, 5,6-dihydro-5-fluorouracil (5FUH2), was never detected both in the liver and in perchloric acid (PCA) extracts. In the latter, it was generally split into three signals, the major one being attributed to 5-fluorouridine-5'-monophosphate. Moreover, when the liver was treated with high doses of FUra and dThd, a signal for fluoronucleoside was observed in the liver, in PCA extracts and in perfusate where it was attributed to 5-fluoro-2'-deoxyuridine (FdUrd). The injection of concurrent dThd with the high dose of FUra led to a marked reduction of catabolism due to competitive inhibition of dihydrouracil dehydrogenase. Moreover, a significant formation of FdUrd was noticed whereas 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) was not detected. dThd therefore inhibits the conversion of FdUrd to FdUMP.

Prediction of 5-fluorouracil cytotoxicity towards the Walker carcinosarcoma using peak integrals of fluoronucleotides measured by MRS in vivo

“…Yet in the extracts there was no correlation between FBal concentrations and the concentrations of FNuct or 5FU. It is possible the FBal we observe owes its source to the rapid 5FU catabolism that occurs in rat liver (Cabanac et al, 1988) and it may be extracellular. So, neither FBal peaks in vivo, nor FBal concentrations in vitro, are related to 5FU cytotoxicity.…”

“…FUTP and FdUMP have different chemical shifts in vitro (0.1-0.2 p.p.m. resolution) (Keniry et al, 1986;Cabanac et al, 1988), but these and the other fluoronucleotides are indistinguishable by MRS in vivo, having similar pH-dependent chemical shifts of 4.5-5 p.p.m. downfield from 5FU.…”

“…FNuct has been observed in mouse liver in vivo by MRS (Hull et al, 1987;Prior et al, 1987;Cabanac et al, 1988). More intense signals were detected in mouse tumours (Stevens et al, 1984;Hull et al, 1986;Koutcher et al, 1987) Correspondence: P.M.J.…”

Fluorine-19 or phosphorus-31 NMR spectroscopy: A suitable analytical technique for quantitative in vitro metabolic studies of fluorinated or phosphorylated drugs

“…During the last 15 years, several attempts have been done to assign individual FNUCs and FNUCt signals in tissue extracts. Since the range of δ for these species at a given pH is small (0.04 ppm for the two nucleosides FUrd and FdUrd [65], and 0.3-0.6 ppm for all the FNUCt [66][67][68]), unambiguous a priori assignments are difficult. Using authentic references, Cabanac et al [65] find that FdUrd resonates 0.04 ppm upfield than FUrd at 25 • C and pH 5-6 in PCA extracts of liver.…”

Perfused Cells, Tissues and Organs by Magnetic Resonance Spectroscopy

“…76 Many drugs contain fluorine and this technique has been used to examine 5-fluorouracil metabolism in perfused mouse liver. 77 …”