The isolation and partial characterization of a radiation-sensitive clone of a human bladder carcinoma cell line.

The isolation of radiosensitive mammalian cell mutants has been limited largely to rodent cells. We report here the isolation of a radiosensitive variant (S40b) from 3648 analyzed clones of a mutagenized human bladder carcinoma cell line (MGH-U1). The surviving fraction at 2 Gy was 0.32 for S40b cells compared with 0.72 for MGH-U1 cells. Split-dose recovery experiments done at several doses did not show a difference between S40b and the parental line at any dose. Irradiation at the low dose rate of 2 cGy min-1 did not show a decreased dose-rate sparing at isoeffect in S40b cells. There was no difference between MGH-U1 and S40b cells in the amount of DNA damage present immediately after irradiation, as detected by neutral filter elution. The S40b variant therefore represents a new tool for the examination of the processing of DNA damage in human cells.