[Effect of hematoporphyrin derivative (HPD) plus light on DNA repair synthesis and enhancement of HPD photosensitization by vitamin C in mouse hepatoma].

There are only a few reports in the literature on photodynamic effects of HPD on gene expression and the repair of DNA damage. Previously, we suggested that nuclear transcription activity was markedly suppressed by HPD plus light. In this study, we investigated the photodynamic effect or DNA repair synthesis as measured by unscheduled DNA synthesis (UDS) in hepatoma cells. The results indicated that DNA repair capacity was greatly inhibited by HPD plus light. When hepatoma cells were pretreated with HPD of different concentrations and then exposed to the same light dose, significant inhibitions of UDS over control were seen and appeared in a dose-dependent fashion. In addition, while hepatoma cells following the exposure to HPD of the same concentration were irradiated with different time, the UDS was markedly decreased as the duration of irradiation was prolonged. However, no changes were observed when either HPD or light was used alone. The present study also included an experiment to determine whether HPD combined with vitamin C gives an enhanced photosensitization. It was found that vitamin C significantly potentiated the suppressing effect on DNA repair synthesis.