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

Using chemical shift–selective 19F magnetic resonance (MR) imaging, we investigated the biomodulating action of 5‐bromovinyluracil (BVU) on the degradation of the anticancer drug 5‐fluorouracil (5‐FU) to its major catabolite α‐fluoro‐β‐alanine (FBAL) and the tissue uptake of 5‐FU in ACI rats with transplanted Morris hepatoma. Rats in the control group (n = 7) received 200 mg/kg body weight of 5‐FU intravenously, whereas the rats in the BVU group (n = 7) additionally received 30 mg/kg body weight of BVU intraperitoneally about 45 min before 5‐FU injection. In each animal examination, three selective 19F MR images were acquired sequentially after 5‐FU administration with an acquisition time of 32 min each: an early 5‐FU image (dominant Fourier line, 8 min p.i.) that characterized the early uptake of the drug into the various tissues, an FBAL image (dominant Fourier line, 56 min p.i.) that reflected the catabolism of the drug, and a late 5‐FU image (dominant Fourier line, 78 min p.i.) that assessed the retention (“trapping”) of unmetabolized 5‐FU and its MR‐visible anabolites. Pretreatment with BVU resulted in a highly statistical significant decrease (P < 0.001) of the FBAL signal in the liver. The marked effect of BVU on 5‐FU degradation, however, improved neither the early uptake nor the retention of 5‐FU in skeletal muscle and tumor tissue (P > 0.7). Moreover, our results indicate that 5‐FU tumor uptake is not only dependent on the plasma concentration of unmetabolized 5‐FU but is also determined by tumor‐specific factors, these showing considerable variations between individual neoplasms. Magn Reson Med 42:936–943, 1999. © 1999 Wiley‐Liss, Inc.