Cyclic Responses of Cultured 9L Cells to Radiation

Abstract

Several responses of cultured 9L rat brain tumor cells to ionizing radiation were investigated as a function of their position in the cell cycle. The mitotic selection procedure for cell cycle analysis was utilized to study the blockade of progression of cells through G/sub 2/ and the resultant division delay. The transition point for this blockade (i.e., the last point in the cell cycle at which cells are blocked, and after which they are refractory to delay) was located approximately at the G/sub 2//M boundary 35 min prior to selection. The duration of division delay was a linear function of the x-ray dose, 33 min of delay/Gy. The survival of cells following exposure to a constant dose of x rays at varous times after incubation of mitotically selected cells demonstrated a definite resistance during the G/sub 1/ phase and slight resistance during the S phase, relative to the level of survival at the G/sub 1//S boundary. As shown with other cell lines there was maximum radiosensitivity during G/sub 2/ and mitosis. Thus the response of 9L rat brain tumor cells in culture to ionizing radiation is similar to that of other cultured mammalian cell lines in regard to induction andmore » duration of division delay, and the sensitivity of M and G/sub 2/ cells to radiation-induced cell lethality. However, the radioresistance exhibited over the remainder of the cell cycle results in a relatively flat age response for radiation-induced lethality. This may in part explain the radiation resistance observed for the 9L gliosarcoma in situ.« less