Abstract
A compound containing both CNDP (3-cyano-2,6-dihydroxypyridine), an inhibitor of 5-fluorouracil (5-FU) degradation, and EM-FU (1-ethoxymethyl-5-fluorouracil), a masked form of 5-FU, was synthesized and named BOF-A2 (3-[3-(6-benzoyloxy-3-cyano-2-pyridyloxycarbonyl)benzoyl]-1-ethoxy methyl-5- fluorouracil). The antitumor activity of BOF-A2 was investigated in sarcoma-180-bearing mice and Yoshida sarcoma-bearing rats. The ED50 (the dose for 50% inhibition) values of BOF-A2 were 25 mg/kg against sarcoma-180 and 15 mg/kg against Yoshida sarcoma. In vitro studies showed that BOF-A2 was rapidly degraded to EM-FU and CNDP in homogenates of the liver and small intestine of mice and rats, and in sera of mice, rats and human, and the conversion of EM-FU to 5-FU occurred only in the microsomal fraction of rat liver in the presence of NADPH. After oral administration of BOF-A2 at 15 mg/kg to Yoshida sarcoma-bearing rats, BOF-A2 was hydrolyzed to EM-FU, CNDP and 5-FU, and their maximum concentrations in the blood were 2000 ng/ml, 300 ng/ml and 40 ng/ml, respectively. Moreover when BOF-A2 was given at the same dose to tumor-bearing mice and rats, the 5-FU levels in the tumor tissue increased much more than those in the blood and persisted for more than 8 h, whereas those in the blood decreased more rapidly. This accumulation and maintenance of a high level of 5-FU in the tumor tissue are concluded to be related to the high antitumor activity of BOF-A2.