The effect of combined treatment with a platinum complex and ionizing radiation on chinese hamster ovary cells in vitro.

Cis-dichlorobis(cyclopentylamine)platinum II (DBCP) belongs to the group of platinum complexes which have recently been reported to have anti-tumour activity. Its cytotoxic activity in CHO cells is not cell-age-dependent, but enhancement of the effect of ionizing radiation is both dose-and cell cycle phase-dependent. In asynchronous cell populations DBCP acts as a dose-modifying factor for ionizing radiation. Doses of DBCP reducing survival of CHO cells to 26% and 4% applied 1 h before irradiation reduce the Do value of radiation dose-survival curves by factors of 1-34 and 1-59 respectively. In synchronized CHO populations enhancement by DBCP of the effect of radiation is most pronounced in G1 and in late S while it is reduced in mid-S. Possible mechanisms of DBCP-radiation interaction are discussed.