Abstract
The effect of combined treatment with X-irradiation and 5-fluorouracil (5-Fu) on the spheroids of rat glioma clone-6 cells was compared with that on exponentially grown monolayer cells. Isobolographic analysis showed the effect of the combined treatment to be supra-additive in both multicellular spheroids and monolayer cells when irradiation followed 24 hours of treatment with 5-Fu.
X-irradiation prior to 5-Fu treatment showed an additive effect. The effect of X-irradiation on spheroids was enhanced after 3 hours of 5-Fu treatment, whereas its effect on monolayer cells was augmented only when prior 5-Fu treatment exceeded 12 hours. Potentiation of the effect of X-irradiation on spheroids by prior treatment with 5-Fu is thought to be due to reoxygenation of previously hypoxic cells and partial synchronization of proliferating cells. These results suggest that when X-irradiation is applied shortly after 5-Fu treatment the effect on solid tumors is selectively enhanced, while the effect on actively proliferating normal tissues is reduced.
