Chemosensitivity of micrometastases and circulating tumor cells to uracil and tegafur as evaluated using LacZ gene-tagged Lewis lung carcinoma cell.

The chemosensitivity of the sequence of steps responsible for metastasis formation including circulating tumor cells and micrometastases to a 5-fluorouracil derivative (UFT) was examined with a novel micrometastasis model featuring Lewis lung carcinoma cells tagged with the bacterial LacZ gene and hygromycinR gene (hygR). Metastases in the lung could be specifically detected at the single-cell level by X-Gal staining after inoculation of LacZ-transfected tumor cells. Spontaneous metastasis in mice bearing subcutaneous primary tumors was significantly inhibited by UFT at doses of 15-20 mg/kg when it was orally administered from day 14, during the early stage of micrometastasis formation, but not by late administration from day 22. Experimental pulmonary metastasis was also inhibited without significant toxic side effects by oral administration of UFT at a daily dose of 20 mg/kg from day 4, when the tumor cells start new growth in the lung, but not by daily treatment from 8 days after intravenous injection. Oral administration of UFT had no effect on tumor cell arrest in the lung as detected by X-Gal staining. Furthermore, PCR analysis revealed that circulating tumor cells in the peripheral blood of mice bearing primary tumors after subcutaneous injection of hygR-tagged tumor cells were significantly reduced by the oral administration of UFT for 7 days in a dose-dependent manner. These results indicate that circulating tumor cells in the peripheral blood and micrometastases in the initial growth phase in the lungs are sensitive to this chemotherapeutic agent, and suggest that micrometastasis formation can be effectively inhibited by long-term oral administration of anticancer agents with minimal toxic side effects.