The survival curves for cells of two human tumor cell lines, HT29 and MeWo, have been defined using a Dynamic Microscopic Imaging Processing Scanner (DMIPS). There are two major differences between these two cell lines: (a) HT29 is more radioresistant than MeWo (surviving fraction at 2 Gy of 74 and 27%, respectively) and (b) HT29 presents a marked multiphasic survival curve with hypersensitivity at low doses (<0.5 Gy) followed by an increase in radioresistance at higher doses which we have interpreted as "induced radioresistance"; this phenomenon is much less pronounced for the more radiosensitive cell line MeWo. We have now measured in these two cell lines the stable chromosomal aberrations and fragments, with the method of fluorescence in situ hybridization (FISH). We have analyzed chromosome 4, which does not have spontaneous translocations in either of these two cell lines. A dose-effect relationship was studied for radiation doses up to 5 Gy. At all doses, both translocations and breaks are more frequent in the radiosensitive cell line MeWo compared to the radioresistant cell line HT29. The correlation between survival and translocations is different for HT29 and MeWo, thus indicating that another factor(s) may be involved in cell killing in these lines.

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