DNA SINGLE-STRAND BREAKS AND SISTER CHROMATID EXCHANGES INDUCED BY TREATMENT WITH HEMATOPORPHYRIN AND LIGHT OR BY X-RAYS IN HUMAN NHIK-3025 CELLS

Abstract

Alkali-labile sites resulting in single-strand breaks in DNA and sister chromatid exchanges are produced when human [carcinoma] cells (NHIK 3025) in vitro are exposed to sublethal doses of light in the presence of hematoporphyrin. The irradiation doses required to reduce the survival from 1 to 0.1 for 220-kV X-rays and treatment with 10-4 M hematoporphyrin in phosphate-buffered saline and 380 nm light were 6.2 grays and 230 J/m2, respectively. X-rays induce about 5 times more sister chromatid exchanges and about 80% more DNA single-strand breaks than exposure to hematoporphyrin plus light when the 2 treatment modalities are compared on the same level of survival. In both cases, the single-strand breaks are practically completely repaired within 15 min. [The usefulness of photochemotherapy in treating human cancer is discussed.].