A series of four homoleptic Cu(I) bis-phenanthroline complexes were synthesized, characterized and tested for their potential use in photodynamic therapy (PDT). It was found that the sterically-locked Cu(dsbtmp)2+ where [dsbtmp = 2,9-(disec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline], which possessed the longest triplet metal-to-ligand charge transfer excited state lifetime, exhibited significant improvement of cytotoxicity upon exposure to light versus dark on melanocytes and A549 cell lines. Fluorescence imaging of this compound revealed its localization to the nuclei of cancer cells and comet assay experiments showed significant DNA damage as potential mechanism of cell death. The photocytotoxicity was associated with the formation of reactive oxygen species (ROS), a known intermediate in PDT. To the best of our knowledge, this compound represents the first example of Cu(I) phenanthroline as a potential drug in PDT. Our results pave the way for the investigation of a new class of earth-abundant complexes for photochemotherapy applications.

Photodynamic therapy of cancer using a long-lived Cu(I) bis-phenanthroline sensitizer

255th National Meeting (2018)

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