Photodynamic DNA strand breaking activities of acridine compounds

Induction of single strand breaks in DNA was assessed by the conversion of supercoiled closed circular plasmid DNA into the open circular form. Euflavine produced single-strand breaks following irradiation but not in the control maintained in the dark. The single strand breaking activity of photoactivated euflavine was found to be dose-dependent. The effective dose convertion 50% (ED50) of the closed circular DNA to the open circular form was 0.53 μM. A comparison of 8 acridine compounds revealed that the ED50 of diaminoacridines such as euflavine, proflavine and acridine yellow or the 3, 6-dimethylamino-derivative (acridine orange) was less than 1 μM while the ED50 values of the other acridines were greater than 80 μM. Euflavine was markedly inhibited by singlet oxygen scavengers such as NaN3, histidine, α-tocopherol or β-carotene and partly inhibited by superoxide dismutase, mannitol or catalase. These results suggest that enflavine induces single strand breaks in DNA mainly by a type II photodynamic mechanism. Photodynamic single strand breaking activities appeared related to their mutagenic activities on yeast.This experimental system described here is useful for the quantitative assessment of the single strand breaking activities of various photosensitizers in vitro and for the determination of active oxygen species involved in those processes.