RADIATION SENSITIVITY OF MURINE FIBRO-SARCOMA CELLS SEPARATED BY CENTRIFUGAL ELUTRIATION

Murine fibrosarcoma cells from primary asynchronous cultures were separated and partially synchronized on the basis of cell size by centrifugal elutriation. The cell size distribution of each elutriator fraction was determined with a Coulter counter, and cell-cycle parameters were derived from DNA histograms obtained by flow microfluorometry and from autoradiography. The proportion of clonogenic cells from each elutriator fraction surviving 600 rad of γ irradiation under aerobic conditions was determined using a lung colony assay in whole-body irradiated mice. The efficiency of the assay was standardized by adding 10 6 lethally irradiated, unseparated tumor cells to all inocula. The 600-rad surviving fraction was also determined for the original unseparated population (prior to elutriation) and for a reconstituted population composed of proportional aliquots of the elutriated fractions. These latter assays gave similar results, while the surviving fraction of elutriated subpopulations differed by a factor of 3. The age-response curve generated by this method for these fibrosarcoma cells suggests that there is a compartment of radioresistant G 1 cells as well as a relatively sensitive S-cell compartment.