Photosensitized formation of 8-hydroxy-2'-deoxyguanosine by a cationic meso-substituted porphyrin.

Abstract

The meso-substituted N-methylpyridyl class of cationic porphyrins are known to have a high affinity for DNA (1). As such, they have been useful tools with which to probe nucleic acid structure and to study a broad range of interactions of cationic ligands with DNA. Activation of this class of porphyrins by visible light produces strand scission in the phosphodiester backbone of DNA at relatively low doses and some metallo-analogs are capable of producing strand scission in the dark. Other substituted porphyrins, hematoporphyrins and methylene blue were found to be less effective under similar conditions. The strand scission activity of cationic porphyrins is not clearly understood, although singlet oxygen has been implicated as a reactive species (1). In this report we have examined the mechanism of photo-induced base damage; specifically, the formation of 8-OHdG. Understanding their role in DNA damage may be useful in screening these compounds as potentially useful agents in photodynamic therapy.