Cinnarizine and flunarizine improve the tumour radiosensitisation induced by erythrocyte transfusion in anaemic mice

The ability of the calcium antagonists, cinnarizine and flunarizine, to enhance the radiosensitisation produced by the administration of an erythrocyte transfusion to anaemic, RIF-1 or SCCVII/St tumour bearing mice was determined. Erythrocyte transfusion alone increased radiation cell killing 10-fold in the RIF-1 tumour when given 0-4 h before X-rays. In contrast, the SCCVII/St showed only a 4-fold increase in sensitivity, apparent when erythrocytes were given 2-6 h before irradiation. The administration of 50 mg kg-1 cinnarizine or flunarizine to anaemic mice followed by erythrocyte transfusion 0 h before X-rays produced the same level of cell survival for both tumours, a 20-fold increase in cell killing for cinnarizine, and a 30-40-fold effect for flunarizine, even though at this time interval, the erythrocyte transfusion alone did not sensitise the SCCVII/St tumour to X-rays. Further investigations indicated, however, that the erythrocyte transfusion was necessary to achieve the sensitisation with the calcium antagonists, since giving flunarizine to anaemic mice alone only achieved a 4-fold increase in radiation cell killing. In addition, flunarizine given with erythrocyte transfusion 4 h before X-rays, in SCCVII/St, the optimal time for radiosensitisation in this tumour, did not further increase the level of cell killing achieved by flunarizine plus erythrocyte transfusion 0 h before X-rays.