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Increased Susceptibility of Mouse Cells to Fluorescent Light-induced Chromosome Damage after Long-Term Culture and Malignant Transformation

Department of Pathology, Howard University College of Medicine, Washington, D. C. 20059 [R. P.], and Laboratory of Cellular and Molecular Biology [K. K. S., G. M. J., A. E. B.] and Biometry Branch [R. E. T.], National Cancer Institute, NIH, Bethesda, Maryland 20014

Exposure of mouse cells in culture to fluorescent light has been shown to produce chromatid breaks and exchanges. Hydrogen peroxide formed in the cell during illumination has been implicated as the causative agent. the present results indicate that susceptibility to light-induced chromosome damage increases with time in culture and seems to be associated with or requisite for the spontaneous malignant transformation of mouse cells. All three cell lines followed during long-term culture that either became tumorigenic or showed cytological evidence of neoplastic transformation developed a concomitant increase in susceptibility. In three additional cell lines, susceptibility to light-induced chromatid damage was significantly increased in the spontaneously transformed malignant cells as compared with their nonneoplastic precursors. The increased susceptibility is not simply the result of long-term culture, since three other nonneoplastic cell lines after prolonged culture were significantly less susceptible than their malignant counterparts. Increased susceptibility to light-induced chromatid damage could result from impaired DNA repair or from the loss of defense mechanisms for destroying H₂O₂ or scavenging free radicals.

¹ To whom requests for reprints should be addressed, at in Vitro Carcinogenesis Section, National Cancer Institute, NIH, Building 37, Room 2D02, Bethesda, Md. 20014.

Received 9/21/78. Accepted 12/ 6/78.