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Oxygen Dependence of Two‐photon Activation of Zinc and Copper Phthalocyanine Tetrasulfonate in Jurkat Cells
Author(s) -
Mir Youssef,
Van Lier Johan E.,
Paquette Benoit,
Houde Daniel
Publication year - 2008
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2008.00311.x
Subject(s) - jurkat cells , photosensitizer , photodynamic therapy , singlet oxygen , phototoxicity , chemistry , zinc , photochemistry , excited state , phthalocyanine , two photon excitation microscopy , oxygen , biophysics , fluorescence , immunology , in vitro , biology , biochemistry , t cell , optics , physics , immune system , organic chemistry , nuclear physics
Photodynamic therapy (PDT), the use of light‐activated drugs, is a promising treatment of cancer as well as several nonmalignant conditions. However, the efficacy of one‐photon (1‐γ) PDT is limited by hypoxia, which can prevent the production of the cytotoxic singlet oxygen ( 1 O 2 ) species, leading to tumor resistance to PDT. To solve this problem, we propose an irradiation protocol based on a simultaneous, two‐photon (2‐γ) excitation of the photosensitizer (Ps). Excitation of the Ps triplet state leads to an upper excited triplet state T n with distinct photochemical properties, which could inflict biologic damage independent of the presence of molecular oxygen. To determine the potential of a 2‐γ excitation process, Jurkat cells were incubated with zinc or copper phthalocyanine tetrasulfonate (ZnPcS 4 or CuPcS 4 ). ZnPcS 4 is a potent 1 O 2 generator in 1‐γ PDT, while CuPcS 4 is inactive under these conditions. Jurkat cells incubated with either ZnPcS 4 or CuPcS 4 were exposed to a 670 nm continuous laser (1‐γ PDT), 532 nm pulsed‐laser light (2‐γ PDT), or a combination of 532 and 670 nm (2‐γ PDT). The efficacy of ZnPcS 4 to photoinactivate the Jurkat cells decreased as the concentration of oxygen decreased for both the 1‐γ and 2‐γ protocols. In the case of CuPcS 4 , cell phototoxicity was measured only following 2‐γ irradiation, and its efficacy also decreased at a lower oxygen concentration. Our results suggest that for CuPcS 4 the T n excited state can be populated after 2‐γ irradiation at 532 nm or the combination of 532 and 670 nm light. Dependency of phototoxicity upon aerobic conditions for both 1‐γ and 2‐γ PDT suggests that reactive oxygen species play an important role in 1‐γ and 2‐γ PDT.