A Supramolecular Approach For Modulated Photoprotection, Lysosomal Delivery, And Photodynamic Activity Of A Photosensitizer

Prompted by a knowledge of the photoprotective mechanism operating in photosystem supercomplexes and bacterial antenna complexes by pigment binding proteins, we have appealed to a boxlike synthetic receptor (ExBox center dot 4Cl) that binds a photosensitizer, 5,15-diphenylporphyrin (DPP), to provide photoprotection by regulating light energy. The hydrophilic ExBox(4+) renders DPP soluble in water and modulates the phototoxicity of DPP by trapping it in its cavity and releasing it when required. While trapping removes access to the DPP triplet state, a pH-dependent release of diprotonated DPP (DPPH22+) restores the triplet deactivation pathway, thereby activating its ability to generate reactive oxygen species. We have employed the ExBox(4+)-bound DPP complex (ExBox(4+)superset of DDPP) for the safe delivery of DPP into the lysosomes of cancer cells, imaging the cells by utilizing the fluorescence of the released DPPH22+ and regulating photodynamic therapy to kill cancer cells with high efficiency.