Enhanced cell-killing effect of potassium hexachloroplatinum(IV) solution irradiated by Co-60 gamma-rays under the presence of NH4Cl

The enhancement of cell-killing effect induced by Co-60 gamma-rays on the a queous solutions of potassium hexachloroplatinum(IV) (K2PtCl6) irradiated i n the presence of various concentrations of NH4Cl was examined. HeLa S-3 ce lls were treated with the irradiated solutions for 60 minutes at 37 degrees C, and cell survival was measured by colony forming efficiency. The mean l ethal concentration (D-0) for the cells treated with non-irradiated K2PtCl6 solution(1 mg/ml) was 34.5 mu l/ml. However, it decreased. namely the cell -killing effect of the solution increased with increasing radiation dose up to 2.64.10(4) Gy in the case of 0.1 M NH4Cl solution tin this condition, t he D-0 decreased to 9.6 mu l/ml). No or only a slight enhancement was obser ved in the case of K2PtCl6 solutions irradiated in the presence of NaCl (NH 4)(2)HPO4, ammonium acetate or glycine. Observations using high performance liquid chromatography (HPLC) of irradiated K2PtCl6 solutions revealed the formation of cis- and/or trans-diaminedichloroplatinum (IV) (DDPs(IV)). How ever, the observed cell-killing action of the solution was too high to be e xplained by the amount of both the DDPs(IV) formed by gamma-rays.