Changes in sensitivity to radiation and ICRF 159 during the life of monolayer cultures of EMT6 tumour line.

The response of EMT6 mouse tumour cells to ICRF 159, both with and without X-radiation, has been measured during the life of monolayer cultures. The cytotoxic effect of ICRF 159 was found to be proliferation-dependent. Flow cytofluorimetry studies of cell cycle distribution showed that ICRF 159 prevented cell division while allowing DNA synthesis to continue. This anti-mitotic action and the cytotoxic effect of the drug were found to be closely related. Increased sensitivity to X-radiation was observed in cultures pretreated for 24 h with 200 microgram/ml ICRF 159 In exponential and early plateau cultures this was seen as a reduced shoulder of the survival curve. In late plateau cultures there was no apparent reduction of the shoulder, but an increase in slope.