Trans-DDP, a less toxic isomer of cisplatin, was examined for its radiosensitizing activity at high and low doses of ionizing radiation. Cells were exposed to the drug to produce low toxicity before exposure to X rays. A sensitive assay using the DMIPS Cell Analyzer was employed to measure cell survival response in low dose region (0-4 Gy) and conventional assay was used for high doses (4-25 Gy). The results show that trans-DDP is a much more effective radiosensitizer at low doses than at high doses, whether or not cytotoxicity was pronounced. This is in contrast to any other sensitizer studied to date, including oxygen, misonidazole, SR-2508 and Ro-03-8799, regardless of prior incubation and/or cytotoxicity.
