Potent mitochondria-targeting ruthenium^II and iridium^III anticancer complexes containing hybrid N^NH-chelated ligands

A series of half-sandwich ruthenium^II and iridium^III complexes bearing hybrid sp³-N/sp²-N amine-imine bidentate chelating ligands were strategically designed and synthesized. Their structures were fully characterized by ¹H and ¹³C NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction, revealing nonplanar five-membered metallacycles in representative complexes. The complexes exhibited potent cytotoxicity against A549 lung, HeLa cervical, and HepG2 liver cancer cell lines, with IC₅₀ values ranging from 0.88 to 4.98 μM, significantly lower than that of cisplatin. Notably, the amine-imine complexes displayed superior cytotoxicity compared to their α-diimine analogues. Mechanistic studies indicated that DNA binding is not the primary mode of action. Instead, these complexes selectively target mitochondria, induce mitochondrial membrane depolarization, elevate intracellular reactive oxygen species (ROS) levels, and trigger apoptosis. Additionally, they enter A549 cells through an energy-dependent pathway and effectively inhibit cancer cell migration in vitro.