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Association among DNA/Chromosome Break Rejoining Rates, Chromatin Structure Alterations, and Radiation Sensitivity in Human Cell Lines¹

Department of Radiation and Cellular Oncology, University of Chicago, Chicago, Illinois 60637 [J. L. S.], and Division of Biological and Medical Research, Argonne National Laboratory, Argonne, Illinois 60439-4833, and Department of Immunology, Birmingham University, Birmingham, B15 2TJ, United Kingdom [A. T. M. V.]

The basis for radioresistance and radiosensitivity in human tumor cell lines is unknown. In a previous study, radiosensitivity in human tumor cell lines was found to be a function of the rate of DNA double-strand break rejoining. Radioresistant cell lines rejoined DNA double-strand breaks at a faster rate than more sensitive cell lines. In this study, we have expanded on that work and analyzed the rate of chromosome break rejoining, as well as the type and frequency of chromosome aberrations induced in three relatively radioresistant (D₀ > 2.0 Gy) human squamous cell carcinoma cell lines and three relatively radiosensitive (D₀ < Gy) squamous cell carcinoma cell lines. Radioresistant cells were found to rejoin chromosome breaks faster than more sensitive cells. The faster rate of rejoining was associated with a reduced frequency of misrepair events (chromosome exchange-type aberrations) and greater survival. There were qualitative differences between these two groups of cell lines in their ability to bind ethidium bromide as nucleoids, suggesting that the basis for altered break rejoining rates might be related to chromatin structure.

¹ This work was supported by grants from the National Cancer Institute (CA 42596 and CA 37435), the Department of Energy (W-31-109-ENG-38), and the Cancer Research Foundation.

² Recipient of a Junior Faculty Research Award from the American Cancer Society. To whom requests for reprints should be addressed, at Department of Radiation and Cellular Oncology, University of Chicago, 5841 S. Maryland Ave., Box 442, Chicago, IL 60637.

³ On sabbatical from the University of Birmingham during the course of these studies.

Received 1/17/89. Revised 4/17/89. Revised 5/26/89. Accepted 6/15/89.