Control of Singlet Oxygen Generation Photosensitized by meso-Anthrylporphyrin through Interaction with DNA Kazutaka Hirakawa* 1 , Toru Hirano 2 , Yoshinobu Nishimura 3 , Tatsuo Arai 3 and Yoshio Nosaka 4 1 Department of Basic Engineering (Chemistry), Faculty of Engineering, Shizuoka University, Shizuoka, Japan 2 Photon Medical Research Center, Hamamatsu University School of Medicine, Shizuoka, Japan 3 Department of Chemistry, University of Tsukuba, Ibaraki, Japan 4 Department of Materials Science and Technology, Nagaoka University of Technology, Niigata, Japan Received 14 January 2011, accepted 30 March 2011, DOI: 10.1111/j.1751-1097.2011.00929.x ABSTRACT To control the activity of photosensitized singlet oxygen ( 1 O 2 ) generation, the electron donor-connecting porphyrin, 5-(9¢-anth- ryl)-10,15,20-tris(p-pyridyl)porphyrin (AnTPyP), was designed and synthesized. AnTPyP became water-soluble by the proton- ation of the pyridyl moieties in the presence of 5 mM trifluoro- acetic acid (pH 2.3). The photoexcited state of the porphyrin ring in an AnTPyP molecule was effectively deactivated by intramolecular electron transfer from the anthracene moiety within 0.04 ns in an aqueous solution. The deactivation was suppressed by the interaction with a DNA strand, resulting in the elongation of the lifetime of the porphyrin excited state and the enhancement of the fluorescence intensity. Furthermore, it was confirmed that the interaction enabled the photoexcited AnTPyP to generate 1 O 2 . Selective 1 O 2 generation by forming a complex with DNA should be the initial step to realize the target selective photodynamic therapy. INTRODUCTION As an anticancer agent, DNA is one of the most important target biomacromolecules, and DNA-targeting drugs have been extensively studied (1,2). Photodynamic therapy (PDT) is a promising treatment for cancer and some nonmalignant conditions using a photosensitizer as a drug and visible-light irradiation (3–5). An important mechanism of PDT is the oxidation of biomacromolecules by singlet oxygen ( 1 O 2 ), which is generated through energy transfer from the excited photosensitizer to molecular oxygen. A DNA-selective photo- sensitizer should be developed to improve the treatment effect (6–9). The control of 1 O 2 generation by a specific DNA sequence using photosensitizer ⁄ quencher ⁄ oligonucleotides sys- tems has been studied (6–8). The demonstrated principle is selectively placing the 1 O 2 photosensitizer close to a molecule that can quench the excited state of the photosensitizer by using a positioning system that can then be manipulated to change the distance between photosensitizer and the quencher. Furthermore, the pH regulated 1 O 2 photosensitizer ⁄ quencher ⁄ DNA i-motif system was reported (9). We reported on two photosensitizers, berberine and palm- atine, which can easily bind to DNA through electrostatic interaction and generate 1 O 2 only when the DNA–photosen- sitizer complex is formed (10,11). The interaction changes their redox potentials and suppresses the quenching by intramolec- ular electron transfer, resulting in the elongation of the lifetime of the photoexcited state, making the energy transfer to molecular oxygen possible (11). Generated 1 O 2 effectively oxidizes every guanine residue of DNA (10). Indeed, it has been reported that the guanine residue is the selective target of 1 O 2 (12). The main oxidized product of guanine by 1 O 2 in both isolated and cellular DNA is 8-oxo-7,8-dihydro-2¢-deoxygua- nine (8-oxodGuo) (13,14). In the case of the DNA photodam- age by berberine and palmatine, 8-oxodGuo was detected (10). Berberine and palmatine can act as a DNA-targeting photo- sensitizer, and guanines are specifically oxidized through 1 O 2 generation. However, these photosensitizers cannot absorb long-wavelength light, which is advantageous for PDT. Thus, on the basis of this controlling mechanism of 1 O 2 generation, we designed and synthesized a porphyrinoid photosensitizer, which is important for clinical use because of its high absorptivity for the red region (>600 nm). Relevantly, the control of photosensitized 1 O 2 generation using porphyrinoid molecular systems has been extensively studied (6–9,15–17). The purpose of this study is the development of an electron donor-connecting porphyrin whose electron-accepting ability and activity of the photosensitized 1 O 2 generation can be controlled through interaction with DNA. MATERIALS AND METHODS Materials. As DNA molecules, the synthesized 16-mer oligonucleo- tides (AATT: d(AAAATTTTAAAATTTT) 2 and AGTC: d(AAG CTTTGCAAAGCTT) 2 , Sigma Chemical Co., St. Louis, MO) were used. Trifluoroacetic acid (TFA) and distilled water were purchased from Wako Pure Chemical Industries (Osaka, Japan). Deuterium oxide (D 2 O) was from Across Organics (Morris Plains, NJ). The spectroscopic grade solvents of dichloromethane and water were from Dojin Chemicals Co. (Kumamoto, Japan) and used as received. 5,10,15,20-Tetrakis(4-pyridyl)porphyrin (TPyP) was from Aldrich Chemical Co., Inc. (Milwaukee, WI). 5,10,15,20-Tetrakis(4-sulfophe- nyl)porphyrin (TPPS) was from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). *Corresponding author email: tkhirak@ipc.shizuoka.ac.jp (Kazutaka Hirakawa) Ó 2011 The Authors Photochemistry and Photobiology Ó 2011 The American Society of Photobiology 0031-8655/11 Photochemistry and Photobiology, 2011, 87: 833–839 833