Pyridine Embedded Phenothiazinium Dyes as Lysosome-targeted Photosensitizers for Highly Efficient Photodynamic Antitumor Therapy.

Development of new photosensitizers (PSs) with high photodynamic efficacy and minimal side effects is of great interests 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 ROS (reactive oxygen species) upon light irradiation by almost 40 folds 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 mm3) in 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.