THE RELATIONSHIP BETWEEN CELL-KILLING EFFECT AND NUMBER OF LANTHANIDEATOMS BOUND TO DNA-MOLECULES IN CULTURED HELA-CELLS TREATED WITH RARE-EARTH ELEMENTS

HeLa S-3 cells were treated with several cue earth elements, Ce, La, a nd Sm, at 37 degrees C for 1 hour and the relationship between the let hal effects of these elements and the number of the atoms bound to DNA , RNA, and proteins was examined. Among the 3 elements, only Ce gave a n exponential dose-survival relationship from which the value of mean lethal concentration (D-0) Was determined to be 6.75 mM. By using iden tically treated cells, the number of Ce atoms combined with DNA, RNA a nd protein molecules in HeLa cells were determined after fractionation of the cells using neutron activation analysis. In this way, the D-0 value given as the Ce concentration was replaced by the number of Ce a toms combined with each fraction, then the target volumes, viz., cell killing efficiency, expressed as the reciprocal of D-0 value was calcu lated for each fraction. The results suggested that DNA and RNA could stoichiometrically be the primary target molecule for cell killing by Ce.