Photosensitized Generation of Singlet Oxygen (¹O₂) from Pyropheophorbide a Specifically Bound to All Parallel-Stranded G-Quadruplex DNAs

Pyropheophorbide a (Pyro-a),a chlorophyll metabolite, is a potential photosensitizer for photodynamictherapy (PDT), but little is known about its interaction with thetarget molecules for PDT, e.g., nucleic acids. Elucidation of theinteraction between photosensitizers and nucleic acids will help usunderstand the initial process of PDT at the molecular level and henceto develop photosensitizing agents. We found that pyro-a forms a 1:1 complex with an all parallel-stranded G-quadruplex DNAand that pyro-a in the complex exhibits a quantumyield for singlet oxygen generation, with excitation at 664 nm, higherby a factor of similar to 10 than that of pyro-a inan aqueous solution. These findings provided novel insights into moleculardesign of pyro-a-based photosensitizers to enhancetheir PDT efficacy.