Tumor uptake of radiolabeled pyrimidine bases and pyrimidine nucleosides in animal models—I. 6-[ 3H]-5-fluorouracil

The differential tissue distribution and urinary excretion of small intravenous doses (4 μg kg −1) of 6-[ 3H]-5-fluorouracil have been studied in two strains of mice bearing transplantable tumors. The subcutaneous Lewis Lung carcinoma and the solid Ehrlich Ascites carcinoma both retained less than 1.5% of the dose, and for all tissues assayed the tumor: blood ratios for radioactivity were 11:1 or less. Approximately 75% of the injected dose was excreted during the first 12 h. Urinary excretion was resolved using a two-compartmental model. The half-life of the fast component was just over 1 h while that for the slow component was in excess of 10 days.