Determination of the target volume of HeLa cells treated with platinum-195m radiolabeled trans-diaminedichloroplatinum(II): a comparison with cis-diaminedichloroplatinum(II).

HeLa S-3 cells were treated with 195mPt-radiolabeled trans-diaminedichloroplatinum(II) (TDDP) under various conditions, and the relationship between lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentrations for the cells treated with TDDP at 37 degrees C for 1, 2 and 3 h were 163.7, 65.8 and 24.9 microM, respectively. By using identically treated cells, the number of Pt atoms combined with DNA, RNA and protein molecules was determined after the cells were fractionated using the method of Schneider. In this way, the D0 values given as the drug concentration were substituted for the number of Pt atoms combined with each fraction, then the target volumes, expressed as the reciprocals of the D0 values, were calculated for each fraction. The results suggested that DNA and high molecular weight RNAs (except t-RNA), under some limited condition, could be the target molecules for cell killing by TDDP. The target volumes for DNA were 1.31 x 10(3), 3.01 x 10(3) and 6.26 x 10(3) nucleotides for 1, 2 and 3 h treated cells, respectively. Cell killing effects of TDDP were lower than CDDP by a factor of 39.5, 19.0 and 16.5 for 1, 2 and 3 h treatments at 37 degrees C, respectively, when viewed from the stand point of the target volume, while those from the mean lethal dose (D0) were 17.6, 9.8 and 6.7, respectively.