Induction of Dna‐protein Cross‐links in Chinese Hamster Cells by the Photodynamic Action of Chloroaluminum Phthalocyanine and Visible Light

Chloroaluminum phthalocyanine (CAPC) is an efficient photosensitizer for the inactivation of Chinese hamster V79 cells. In order to investigate possible molecular mechanisms in the photo‐dynamic action of CAPC and visible light, the induction and repair rate of two classes of DNA lesions have been determined, i.e. DNA single‐strand breaks and DNA‐protein cross‐links. In cells pretreated with 1 μ.M CAPC, a fluence of 12 kJ/m 2 of red light (>600 nm) kills approximately 50% of the cells and induces 3 to 3.5 Gy‐equivalents of single‐strand breaks. The repair of these breaks was slower than the repair of single‐strand breaks induced by m̀‐irradiation. The photodynamic action of CAPC also induces a large number of DNA‐protein cross‐links which, in contrast to m̀‐radiation‐induced DNA‐protein cross‐links, do not appear to be repaired during 4 h of post‐treatment incubation in fresh medium. These studies suggest that DNA may be an important target for the cytotoxicity of CAPC + red light.