An in vitro 125IUdR-release assay for measuring the kinetics of cell death

A radionuclide release assay for measuring the in vitro kinetics of cell death has been developed. CHO cells were labelled for 24 h with 3.0 hBq/ml of [125I] iododeoxyuridine (125IUdR) and the fate of the labelled cells and their progeny was monitored at daily intervals by measuring the rate of 125I release. Prelabelling with 125IUdR did not alter the plating efficiency, the doubling time or the selection of mitotic cells. The rate of 125I release from labelled (but otherwise untreated) CHO cells was approximately equal to 4% day. Treatment with a lethal dose of X-rays (30 Gy), heat (46 degrees C, 1 h), cold (-90 degrees C, 1 h) or the antibiotic Geneticin (300 micrograms/ml, continuously) resulted in the release of greater than 99% the 125I activity associated with the cells. Cell death was rapid after heating or freezing, and delayed after treatment with X-rays or Geneticin. The results illustrate the efficacy of the 125I release assay for measuring the kinetics of cell death in mammalian tissue culture cells.