Cell cycle responses of heterogeneous human colon adenocarcinoma subpopulations to X-irradiation.

The cell cycle responses of two exponentially growing subpopulations of cells (clones A and D), originally obtained from a human colon adenocarcinoma to X-irradiation, were studied using centrifugal elutriation. Cell suspensions were separated by changing counter-current flow rate while keeping the rotor speed constant (1600 rpm) and the composition of eluted fractions was determined using flow cytometry. The X-ray sensitivity of unseparated clone D cells was somewhat greater than that of clone A cells (e.g. 10% greater at the 10% level of survival). This difference appeared to be due to a greater value of the alpha parameter (one-hit cell killing), using the linear-quadratic equation in which the relative survival S/S0 = exp - (alpha D + beta D2) with dose (D) in Gy. This finding was confirmed in the cell cycle studies where the alpha parameter was always greater for the clone D cells than for the clone A cells. The beta parameter was essentially the same for both cell lines through the cell cycle.