Novel mitochondrial-targeted thiadiazolo[3,4-g]quinoxaline dyes as efficient photosensitizers for ultra-low dose operable photodynamic therapy

Two novel thiadiazolo[3,4-g]quinoxaline (TQ) photosensitizers (PSs), TQs-3 and TQs-4, were designed and synthesized. Both of them presented ultra-high singlet oxygen quantum yields under red light irradiation. By carrying out in vitro photodynamic therapy (PDT) experiments using TQs-4 loaded nanoparticles (TQs-4 NPs) to treat three kinds of tumor cell lines: 4T1, HeLa and MCF-7 cells, it was demonstrated that TQs-4 NPs had outstanding PDT efficacies. An ultra-low dose of TQs-4 (0.14 μg mL−1) can realize the death of more than 90% HeLa cells (635 nm, 60 mW cm−2, 10 min), which indicated that TQs-4 show promising potential as a novel PS for PDT applications.