Oral Administration of BOF‐A2 to Rats with Lung Transplanted Tumors Results in Increased 5‐Fluorouracil Levels

A new tumor model was developed in which solid Yoshida sarcoma tissue injected intravenously developed into tumors in the lungs of about 30% (13/42) of the inoculated rats. Histological examination revealed that alveoli were occupied with tumor cells and the tumors were similar to those obtained by subcutaneous inoculation. Using this model, the concentrations of 5‐fluorouracil (5‐FU) in tumor tissue 12 h after oral administration of 3‐[3‐(6‐benzoyloxy‐3‐cyano‐2‐pyridyloxycarbonyl)‐benzoyl]‐1‐ethoxymethyl‐5‐fluorouracil (BOF‐A2, 36 μmol/kg) or a combination of tegafur and uracil in a molar ratio 1 to 4 (UFT, 50 μmol/kg) were found to be 129.8 ng/g and 19.2 ng/g, respectively. Thus, compared to treatment with UFT, BOF‐A2 resulted in higher levels of 5‐FU in lung tumor tissues. Increased concentrations of 5‐FU should have a superior anti‐tumor effect and so BOF‐A2 merits clinical trial in the treatment of patients with lung cancer.