MOLECULAR MECHANISM OF DRUG PHOTOSENSITIZATION .7. PHOTOCLEAVAGE OF DNA SENSITIZED BY SUPROFEN

Ultraviolet-A irradiation of a suprofen (2-[4-(2-thenoyl)phenyl]propio nic acid) (SPF) buffered solution (pH 7.4) in the presence of supercoi led pBR322 DNA leads to single strand breaks with the formation of an open circular form and subsequent linearization of the plasmid. On the basis of agarose gel electrophoresis data of samples irradiated in an air-saturated solution or in an oxygen-modified atmosphere, and the e ffects of sodium azide, D2O, mannitol, copper(II), superoxide dismutas e, 2-H-propanol, deferoxamine and surfactants, we suggest a photosensi tization mechanism involving singlet oxygen and free radicals. The hig her rate of photocleavage in nitrogen compared to that in an air-satur ated solution and the results obtained from oxygen consumption measure ments support the hypothesis that both the type I and type II photosen sitization mechanisms are operative and that oxygen quenches the excit ed state of the irradiated drug. The photosensitization model applied was in agreement with that previously applied to cell membrane SPF pho toinduced damage. Interaction of the drug with DNA, studied through ci rcular dichroism and fluorescence anisotropy, probably occurs through a surface binding mode. The experimental techniques used for assessing the photodamaging activity of this drug may be useful for screening o f phototoxic compounds in the environment and for determining the acti ve species involved.