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Comparison of Mutagenicity and Induction of Sister Chromatid Exchange in Chinese Hamster Cells Exposed to Hematoporphyrin Derivative Photoradiation, Ionizing Radiation, or Ultraviolet Radiation¹

Clayton Center for Ocular Oncology [C. J. G., N. R., W. F. B.] and Divisions of Ophthalmology [C. J. G.] and Hematology Oncology [C. J. G., A. B., W. F. B.], Childrens Hospital of Los Angeles, Los Angeles, California 90027

Cell culture studies have been performed to compare the mutagenic potential and the induction of sister chromatid exchanges for hematoporphyrin derivative photoradiation, ionizing radiation, and UV radiation. The mutation frequency in Chinese hamster ovary cells at the hypoxanthine-guanine phosphoribosyltransferase locus was measured using resistance to 6-thioguanine. Phenotypic expression time prior to mutation selection was also examined. Treatment with either X-rays or UV was effective in producing mutants resistant to 6-thioguanine, but treatment with hematoporphyrin derivative photoradiation (at comparable toxicity levels) did not induce any mutagenic activity above background levels. The hematoporphyrin derivative incubation and photosensitization conditions used in this study did induce sister chromatid exchanges at frequencies comparable to those induced by X-rays but at lower frequencies than for UV treatments.

¹ This investigation was performed in conjunction with the Clayton Foundation for Research and was supported in part by USPHS Grant CA 31230 awarded by the National Cancer Institute, Department of Health and Human Services, and by American Cancer Society Research Grant IN-21-T to the LAC-USC Comprehensive Cancer Center.

² To whom requests for reprints should be addressed, at Clayton Center for Ocular Oncology, Childrens Hospital of Los Angeles, 4650 Sunset Boulevard, Los Angeles, Calif. 90027.

Received 6/11/82. Accepted 2/25/83.