THE ROLE OF DNA-DAMAGE AND INHIBITION OF POLY(ADP-RIBOSYL)ATION IN LOSS OF CLONOGENICITY OF MURINE L929 FIBROBLASTS, CAUSED BY PHOTODYNAMICALLY INDUCED OXIDATIVE STRESS

Reactive oxygen species are used to eradicate malignant cells in photo dynamic therapy as well as in other cancer therapies. Despite many eff orts, the pathways leading to cellular damage and cell killing due to the action of these species are poorly understood In previous studies with hematoporphyrin derivative-sensitized L929 murine fibroblasts, th e only parameter for which a relation with photodynamically induced re productive cell death could not be excluded was inhibition of DNA exci sion repair. The present results show that loss of clonogenicity of th ese cells in fact is related to a series of effects, including the dev elopment of slight, irreperable DNA damage, a virtually complete inhib ition of poly(ADP-ribosyl)ation activation, a transient elevation of t he intracellular calcium concentration and, after a tag time of about 8 h, DNA fragmentation caused by endonuclease activity. This conclusio n is supported by the observation that photodynamic treatment inhibite d the repair of X-ray-induced DNA strand breaks and suppressed X-ray- and methyl methanesulfonate-induced enhancement of poly(ADP-ribosyl)at ion. Our experimental results further suggest that in this: cell line the photodynamically induced inhibition of enhanced poly(ADP-ribosyl)a tion could web be involved in inhibition of repair of DNA strand break s and in activation of endonuclease activity.