Metoclopramide enhances the effect of ionizing radiation on xenografted squamous cell carcinoma of the head and neck.

The commonly used drug metoclopramide, a benzamide derivative, has been shown previously in our laboratory to enhance the effect of cisplatin on xenografted squamous cell carcinomas of the head and neck. In the present study, we show that metoclopramide also enhances the effect of ionizing radiation. Two human squamous cell carcinoma lines of the head and neck xenografted to nude mice have been used. Doses of radiation were chosen (5 and 8 Gy single doses) which caused only a slight retardation of tumor growth when administered alone. Tumor response to ionizing radiation was assessed with and without metoclopramide (2.0 mg kg-1), and administered at the time of radiation and 24 and 48 hr after treatment. The effects of these schedules on the tumors were compared using the reduction of the area under the growth curves and specific growth delay. The dose schedule with metoclopramide alone did not induce any significant reduction in the area under the growth curves. The addition of metoclopramide to the radiated groups caused a significant enhancement of the radiation-induced reduction of the area under the growth curves in both of the tumor lines studied.