Bromo-pentamethine as mitochondria-targeted photosensitizers for cancer cell apoptosis with high efficiency

Mitochondria play essential roles in cellular energy supply and produce 90% of reactive oxygen species. A mitochondrial targeted photosensitizer is greatly beneficial to improve the photodynamic therapeutic effect via apoptosis. Herein bromo-pentamethine dyes (lambda(abs) > 650 nm) are designed as mitochondria-localized anticancer photosensitizers. Cell experiments demonstrate that Cy-Br localizes in mitochondria with very low cytotoxicity in dark, and induces cancer cells apoptosis under light with IC50 as low as 62 nM, much better than commercial Ce6 (3706 nM). Bromo-group could enhance the quantum yield of reactive oxygen species. The high efficiency might provide a new clue to develop new photosensitizers.