¹⁹F NMR monitoring of in vivo tumor metabolism after biochemical modulation of 5‐fluorouracil by the uridine phosphorylase inhibitor 5‐benzylacyclouridine

Abstract

A uridine phosphorylase inhibitor, 5-benzylacyclouridine (BAU), has been utilized as biochemical modulator of 5-fluorouracil (5-FU) anti-tumor activity in a murine tumor model. The effect of BAU on 5-FU metabolism has been evaluated using in vitro and in vivo 19F NMR spectroscopy. The analysis of the NMR data revealed an increased formation and retention of fluorouracil nucleotides and fluorouridine in colon 38 tumors treated with the regimen containing BAU and a reduction in 5-FU catabolites (alpha-fluoro-beta-ureidopropionic acid and alpha-fluoro-beta-alanine). In the normal tissues evaluated, the presence of BAU did not significantly alter the metabolism and presence of fluoropyrimidine species, indicating a more selective effect on tumor tissues. Therapy experiments on C57/BL6 mice bearing colon 38 tumor showed that the administration of 120 mg/kg BAU 30 min before 5-FU at 85 mg/kg, on a weekly basis, resulted in an increased antineoplastic effect compared to the same dose of 5-FU alone. A smaller dose of 5-FU (60 mg/kg) also administered 30 min after 120 mg/kg BAU caused a reduction in tumor growth similar to 5-FU alone. The addition of BAU to 5-FU (85 mg/kg) resulted in a slight increase, although statistically nonsignificant, in host toxicity without causing any toxic death during the chemotherapeutic treatment. 19F NMR spectroscopy is here shown to be a powerful technique to evaluate changes in the metabolism of fluoropyrimidines after the use of biochemical modulator and to allow a correlation between improved therapeutic response with the biochemical effects generated in tissues.

Correlation between 5-fluorouracil metabolism and treatment response in two variants of C26 murine colon carcinoma

“…Our 19 F MRS results show that the more sensitive C26-10 tumour exhibits a significantly higher conversion of 5-FU to fluoronucleotides (cytotoxic anabolites) compared to the insensitive, more rapidly growing C26-B tumour (C max and AUC in Table 1). These results support previous findings that positive therapy response correlates with the concentration of anabolites achieved in tumour tissue, either directly or with the aid of modulators (McSheehy et al, 1989(McSheehy et al, , 1992Koutcher et al, 1991;Sijens and Ng, 1992;Findlay et al, 1993;Tausch-Treml et al, 1996;Holland et al, 1997). The broad anabolite peak observed in Figure 1 represents the complete family of fluoronucleotides (mono-, di-, triphosphates; oxy-and deoxy forms) which cannot be further distinguished with in vivo 19 F MRS.…”

Noninvasive quantitation of cytosine deaminase transgene expression in human tumor xenografts with in vivo magnetic resonance spectroscopy

“…Spectra were acquired as the average of 277 transients (free induction decays) collected in 8,192 data points by using a 25-s pulse width (corresponding to a 90°flip angle at a depth of 2.7 mm), 4.328-ms repetition time, and a 25-kHz spectral width; 20 min were required for each spectrum. The pulse repetition time used was greater than five times the reported T 1 of 5-FU and its metabolites in whole blood (6,23); thus, no saturation of the metabolites of interest was expected. This was empirically verified by varying the repetition time in a single animal after 5-FC injection and comparing the signal intensities from limited number of signal averages.…”

Biochemical modulation of the catabolism and tissue uptake of the anticancer drug 5‐fluorouracil by 5‐bromovinyluracil: Assessment with metabolic 19 F MR imaging

“…Because of the limited sensitivity of the MR approach, a relatively high dose of 200 mg/kg body weight of 5-FU (Fluroblastin; Farmitalia, Freiburg, Germany) was applied. Although this dose lies in the range frequently used in experimental MR examinations (10,11,24,25), it is only slightly below the LD 50 for 5-FU in small rodents (260 mg/kg body weight (10)). Therefore, the animals were killed while they were under anesthesia, immediately after the MR examination has been completed.…”