CULTURED CHINESE-HAMSTER OVARY CELLS LACK A TRANSFERABLE X-RADIATION RESISTANCE FACTOR

We determined if we could transfer X-radiation resistance from CHO AA8 cells to their radiosensitive, mutant V3 cells by several methods. Th ese methods include co-incubating the two cell lines for three days be fore irradiation, adding heavily-irradiated AA8 to V3 cells following irradiation of the latter and then co-incubating these cells for at le ast eight days during the colony-forming assay and lastly, adding cond itioned medium from unirradiated, subconfluent AA8 cells to V3 culture s and incubating for two days before irradiation. None of these proced ures enhanced the clonogenic survival of the V3 cells to a single dose of 4 Gy X-radiation. Adding heavily-irradiated V3, instead of AA8, ce lls did not increase the clonogenic survival of the 4 Gy-irradiated V3 cells either, indicating that there was no autocrine mode of action. Moreover, adding conditioned medium from a related CHO cell line, K1, to its own radiosensitive, mutant 5-11 and incubating for two days bef ore irradiation did not enhance clonogenic survival of the latter to a single dose of 3 Gy X-radiation. We therefore conclude that it is unl ikely that CHO cells have the X-radiation resistance factor that has b een reported in some mouse melanoma cell lines by other investigators.