Bidentate Ligands on Osmium(VI) Nitrido Complexes Control Intracellular Targeting and Cell Death Pathways

The cellular response evoked by antiproliferating osmium­(VI) nitrido compounds of general formula OsN­(N^N)­Cl3 (N^N = 2,2′-bipyridine 1, 1,10-phenanthroline 2, 3,4,7,8-tetramethyl-1,10-phenanthroline 3, or 4,7-diphenyl-1,10-phenanthroline 4) can be tuned by subtle ligand modifications. Complex 2 induces DNA damage, resulting in activation of the p53 pathway, cell cycle arrest at the G2/M phase, and caspase-dependent apoptotic cell death. In contrast, 4 evokes endoplasmic reticulum (ER) stress leading to the upregulation of proteins of the unfolded protein response pathway, increase in ER size, and p53-independent apoptotic cell death. To the best of our knowledge, 4 is the first osmium compound to induce ER stress in cancer cells.