title: Potentially lethal damage repair in human cells.
abstract: Potentially lethal damage repair (PLDR) in human cells was investigated by delayed plating experiments with three malignant tumor cell lines (breast, colon and neuroblastoma) and two normal diploid lines (lung fibroblasts) in exponential and plateau phases. All cell lines demonstrated PLDR which was considerably higher for all the cell lines in plateau phase compared to log phase. At survival levels of 0.01, the two fibroblast lines had recovery ratios of 3.8 and 4.0 for 6 h delayed plating in plateau phase. The malignant lines showed recovery ratios of 5.7 (neuroblastoma), 3.2 (breast carcinoma) and 2.4 (colon carcinoma). The data were fitted to the linear quadratic equation and in addition, a repair factor was developed to compare survival for immediate and delayed plating: S(D) = exp[-gamma (alpha D + beta D2)] where gamma = 1 for immediate plating. Previously published data on human tumor and normal lines were also fitted to this equation. In all instances the three parameter equation (alpha, beta, gamma) allowed a good fit of the survival data for immediate and delayed plating. By using the same alpha, beta for the zero hour and 6 h survival curves, the gamma factor allows a much more useful method of comparing PLDR among different cell lines. The gamma factor for the two lung fibroblast lines were 0.70 and 0.71 while skin fibroblasts also had a 0.71 factor. The six malignant lines ranged from 0.62 to 0.93 with all but the neuroblastoma line having a higher factor (and therefore decreased PLDR capacity) than the normal lines. No correlation between PLDR and in vitro radiosensitivity or clinical radiosensitivity of the tumor type was found.
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D004260:DNA Repair; D006801:Humans