CELL KILLING INDUCED BY DECAY OF I-125 DURING THE CELL-CYCLE - COMPARISON OF I-125 ANTIPYRINE WITH I-125 BOVINE SERUM-ALBUMIN

The lethal effects induced by the decay of 125I in synchronized L5178Y cells were studied by suicide experiments. We used 125I-antipyrine, which is freely diffusible in cells, and 125I-bovine serum albumin (BSA), which remains outside the cells. Synchronized cells mixed with either 125I- antipyrine or 125I-BSA were frozen and stored at -196°C for various periods to accumulate 125I decays. A clonogenic assay was used to measure the killing of these stored cells. Cells in G1-S and G2-M phases were more sensitive than those in late S phase for both 125I treatments. The ratio of survival in late S to that in G1-S (late S/G1-S) obtained by the decay of 125I-antipyrine, however, was much smaller than that obtained by the decay of 125I-BSA in the dose range examined. These results suggest that Auger electrons emitted from 125I-antipyrine cause a high-LET-type effect. The reason for the high-LET effect must be the intracellular localization of 125I-antipyrine and its closer contact with DNA.