Effects of a combined Bleomycin/radiotherapy on the increase of cell numbers in Ehrlich ascitic carcinoma

The effects of separate and combined application of the cytostatic Bleomycin and X-radiation on the multiplication of the Ehrlich ascitic tumour cells in vivo and on the survival time of tumourous mice was examined by applying automatic, electronic cell counting. If this cytostatic is administered alone up to 100 mg/kg the growth curve of the EAT-cells shows, after a 24 hours' delay, hardly any difference to that of untreated tumour cells. The separate administration of such Bleomycin doses and the separate X-radiation of the EAT cells with doses of up to 1000 rad had no significant influence on the survival time of tumourous mice. The combined application of Bleomycin and X-radiation elongates the 50%-survival time of the tumourous mice. If the X-radiation takes place 12 hours after the Bleomycin treatment the animals survive longer than is the case with simultaneous treatment. Although no dose effect curves could be set up the results obtained let assume a synergistic effect of Bleomycin and irradiation which is especially significant if the radiation is carried out 12 hours after a Bleomycin treatment. The reasons of this are assumed to lie in the increased radiation sensitivity of the tumour cells caused by the bleomycin-induced partial synchronisation of the EAT cells. (orig.)