ENHANCED CELL-KILLING ACTION OF CISPLATIN IN THE PRESENCE OF TERBIUM CHLORIDE

The literature indicates that the interaction of Tb3+ with DNA modifie d by the antitumour drug cis-diaminedichloroplatinum(II) (CDDP) result s in substantial enhancement of the fluorescence of this cation, while no enhancement is observed in the case of DNA modified by irradiation with ionizing radiation. This study investigates the effect of Tb3+ o n the survival of cultured mammalian cells treated with CDDP. HeLa cel ls were treated with a combination of Pt-195m-CDDP and TbCl3, and the relationship between lethal effect and the numbers of Tb and/or Pt ato ms binding to DNA, RNA and proteins was examined. The Tb content in ea ch fraction was determined using instrumental neutron activation analy sis. It was found that the cytotoxic effect of CDDP was greatly enhanc ed by the presence of Tb ions (D-0 of CDDP fell from 8.3 mu M without Tb to 3.2 mu M with 0.75 mM Tb), while no such effect was found in rad iation-induced cell-killing. The number of Tb atoms bound to DNA molec ules in a cell was calculated to be about 4.5.10(7), namely 1 per 1.40 0 nucleotides, under that situation.