Structurally Simple Osmium(II) Polypyridyl Complexes as Photosensitizers for Photodynamic Therapy in the Near Infrared

Five osmium(II) polypyridyl complexes of the general formula [Os(4,7-diphenyl-1,10-phenanthroline)(2)L](2+) were synthesized as photosensitizers for photodynamic therapy by varying the nature of the ligand L. Thanks to the pronounced p-extended structure of the ligands and the heavy atom effect provided by the osmium center, these complexes exhibit a high absorption in the near-infrared (NIR) region (up to 740 nm), unlike related ruthenium complexes. This led to a promising phototoxicity in vitro against cancer cells cultured as 2D cell layers but also in multicellular tumor spheroids upon irradiation at 740 nm. The complex [Os(4,7-diphenyl-1,10-phenanthroline)2(2,2'-bipyridine)](2+) was found to be the most efficient against various cancer cell lines, with high phototoxicity indexes. Experiments on CT26 tumor-bearing BALB/c mice also indicate that the OsII complexes could significantly reduce tumor growth following 740 nm laser irradiation. The high phototoxicity in the biological window of this structurally simple complex makes it a promising photosensitizer for cancer treatment.

Automated summary

Five osmium(II) polypyridyl complexes with different ligands were synthesized as photosensitizers for photodynamic therapy. These complexes exhibited high absorption in the near-infrared region and showed promising phototoxicity against cancer cells in vitro and in multicellular tumor spheroids upon irradiation at 740 nm. The complex with 2,2'-bipyridine ligand showed the highest phototoxicity against various cancer cell lines. Experiments on tumor-bearing mice also demonstrated significant tumor growth reduction with laser irradiation at 740 nm. This structurally simple complex has great potential as a photosensitizer for cancer treatment.