Radiation Response of Synchronized 9L Rat Brain Tumor Cells Separated by Centrifugal Elutriation

Survival curves of 9L rat brain tumor cells separated by centrifugal elutriation in early G/sub 1/ (greater than or equal to 97%), mid-S (greater than or equal to 80%), and mid-G/sub 2/ (greater than or equal to 70%) have been measured after 0 to 1800 rad of /sup 137/Cs ..gamma.. rays. The D/sub 0/, D/sub q/, and n values calculated from the cell survival curves at early G/sub 1/, mis-S, and mid-G/sub 2/ were not significantly different (P > 0.1). Identical results were found with three different elutriation-irradiation procedures: (1) elutriating, irradiating, and plating for colony formation; (2) irradiating, elutriating, and plating for colony formation; (3) elutriating to obtain G/sub 1/ cells, allowing them to progress, then irradiating in S or G/sub 2/ and plating for colony formation. After doses of 600 and 900 rad given to every fraction separated by centrifugal elutriation from an asynchronous population of 9L cells, a very small but significant increase in resistance ( approx. 1.4) was found in late G/sub 1/ cells. The survival curve obtained with these resistant cells after elutriation showed a significant (P < 0.05) increase in the value of D/sub 0/. The absence of any substantial change in radiosensitivity throughoutmore » the cell cycle makes it unlikely that the BCNU-radiation interaction previously observed for 9L cells was caused by presynchronizing the cells into a radiation-sensitive phase of the cell cycle.« less