Cytotoxicity and influence on radiation dose response curve of cis-diamminedichloroplantinum II (cis-DDP)

Exponentially growing Chinese hamster ovary (CHO) cells were exposed to varying doses of Cis-diamminedichloroplatinum II (cis DDP) for 1 hour. Cytotoxicity was found to be dose dependent and the dose response curve has shoulder and exponential portions. D0 on the exponential portion of the curve was found to be 2.8 μg/ml. The values of D/sub q/ and the extrapolation number (n) corrected for single cells were found to be 3.1 μg/ml and 12.0 respectively. The influence of exposure to cis DDP on the radiation dose response curve was also studied. The radiation dose response curve of the CHO cells not exposed to cis DDP is characterized by a D0 of 139 rad. The values of D/sub q/ and n corrected for single cells are 105 rad and 4.5 respectively. Exposure to 8 μg/ml of cis DDP for 1 hour decreased D0 to 102 rad when exposure was immediately prior to irradiation and to 106 rad when the exposure was immediately after irradiation. D/sub q/ and n were found to be 140 rad and 18 for pre-radiation exposure and 137 rad and 15 for post-radiation exposure. This influence on the radiation dose response curve was not found to be cis DDP dose dependent since at higher concentration of cis DDP (10 μg/ml, 12 μg/ml, 16 μg/ml) D/sub o/, and n were found to be the same as at 8 μg/ml