Development of new photosensitizers (PSs) with high photodynamic efficacy and minimal side effects is of great interest in photodynamic therapy (PDT). In this work, we reported several pyridine-embedded phenothiazinium (pyridophenothiazinium) dyes, which could be conveniently synthesized in a few short steps and acted as highly efficient and potent PSs to selectively localize to lysosomes and photosensitively kill cancer cells. Among them, compound 5, which possessed the ability of promoting intracellular reactive oxygen species (ROS) upon light irradiation by almost 40-fold higher than that of methylene blue (MB, a general phenothiazinium-based PS), exhibited a remarkable phototherapeutic index (PI = 53.8) against HT29 cancer cells, leading to eradication of large solid tumors (∼300 mm 3 ) in a xenograft mouse model without apparent side effects. These results suggest that the pyridophenothiazinium dyes developed herein, especially compound 5, may serve as promising lysosome-targeted PSs for efficient photodynamic antitumor therapy.
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Photodynamic Therapy (PDT), as a clinically approved modality for the treatment of various disordered diseases including cancer, has received great advances in recent years. By preferentially accumulating non-toxic Photosensitizers (PSs) in the pathological area, and in situ generation of cytotoxic reactive oxygen species (ROS) under local irradiation by a light source with appropriate wavelength, PDT works in a dual-selective manner. Over the past decades, numerous studies and reviews on PDT mainly focused on activable PSs and the newly emerging PSs in PDT. However, to the best of our knowledge, there are few articles on the systematic introduction of light sources and limited reports about targeted strategies in PDT. This review comprehensively summarizes various light sources applied in PDT together with typical enhanced targeting strategies, and outlines their advantages and disadvantages, respectively. The clinical applications and future perspectives in light sources are also partly presented and discussed.
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