An interaction of cisplatin and radiation in two rat yolk sac tumour cell lines with different radiosensitivities in vitro

Abstract. We investigated the interaction of cis platin and radiation in two rat yolk sac tumour cell lines with different radiosensitivities in vitro. The effects were assessed by clonogenic assay. D 0 for the radiosensitivity of the radioresistant variant cell line, NMT-1R was 139 cGy, which was 1. 3 times larger than that for the parent radiosensitive cell line, NMT-1 (D0= 107 cGy). The concentration of cis platin required to reduce colony formation by 50% at 1 h treatment (ID 50 of cis platin) was 0. 25 mug/ml for NMT-1, whereas that for NMT1R was 1.0 mug/ml. Cis platin potentiation of radiation sensitivity was manifested by the decrease in the slope of the radiation dose-response curve. D 0's for NMT-1 and NMT-1R were 83 and 100cGy in combined treatment with ID 50 of cis platin immediately before radiation. The enhancement ratios of cis platin were therefore 1. 30 for NMT-1 and 1. 39 for NMT-1R respectively in D 0. No different enhancement ratio for cis platin was observed in the time course of combi...