[Irradiation of solid Walker carcino-sarcomas after synchronisation with hydroxyurea (author's transl)]

Sprague-Dawley rats with solid Walker carcino-sarcomas were synchronized with hydroxyurea (HU; 6 x 50 mg and 1 x 300 mg HU/kg body weight) and then irradiated at different time points (60Co). The synchronized tumors showed a significant delay of growth when irradiation was applied in the late G1 phase, at the transition G1/S and in the early S phase. The remaining phases of the cell cycle, especially the S phase showed the same sensitivity as the non-synchronized controls. Improvement of therapy by irradiation after HU application was largely due to the synchronization of tumor cells. Only the increased therapeutic effect of irradiation shortly after application of HU can be explained also by combination of both HU and irradiation.