Enhanced malignant transformation is accompanied by increased survival recovery after ionizing radiation in Chinese hamster embryo fibroblasts

D. A. Boothman

Research output: Contribution to journalArticle

15 Scopus citations


Transformed Chinese hamster embryo fibroblasts (CHEF), which gradually increase in tumor-forming ability in nude mice, were isolated from normal diploid CHEF/18 cells. Transformed CHEF cells (i.e. T30-4 > 21-2M3 > 21-2 > normal CHEF/18) showed gradual increases in potentially lethal damage (PLD) survival recovery. β-Lapachone and camptothecin, modulators of topoisomerase I (Topo I) activity, not only prevented survival recovery in normal as well as in tumor cells, but enhanced unscheduled DNA synthesis. These seemingly conflicting results are due to the fact that Topo I activity can be modulated by inhibitors to convert single-stranded DNA lesions into double-stranded breaks. Increases in unscheduled DNA synthesis may result from a continual supply of free ends, on which DNA repair processes may act. Altering Topo I activity with modulators appears to increase X-ray lethality via a DNA lesion modification suicide pathway. Cells down-regulate Topo I immediately after ionizing radiation to prevent Topo I-mediated lesion modification and to enhance survival recovery.

Original languageEnglish (US)
JournalRadiation Research
Issue number1 SUPPL.
Publication statusPublished - 1994


ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Biophysics
  • Radiology Nuclear Medicine and imaging
  • Radiation

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