Toward the development of effective metal-based coordination drugs for the treatment of cisplatin-resistant cancers, we report four new ruthenium(II) coordination compounds, namely, [RuCl2(yc1)2(DMSO)2] (QY1), [RuCl2(yc2)2(DMSO)2] (QY2), [RuCl2(yc3)2(DMSO)2] (QY3), and [RuCl2(yc4)2(DMSO)2]·1.25H2O (QY4), which contain 3-pyridin-2-yl-chromen-2-one (yc1), 8-methyl-3-pyridin-2-yl-chromen-2-one (yc2), 7-methoxy-3-pyridin-2-yl-chromen-2-one (yc3), and 2-pyridin-2-yl-benzo[f]chromen-3-one (yc4) ligands, respectively. Complex QY4 possessing a more extended planar yc4 ligand showed the highest cytotoxicity against cisplatin-resistant A549/DDP lung cancer cells (R9LC), yielding a remarkably low micromolar IC50 value of 5.02 ± 0.14 μM and low toxicity against embryonic kidney HEK293 (e293) normal cells under equal conditions (IC50 = 88.04 ± 1.03 μM). Notably, QY4 exhibited higher cytotoxicity than QY1–QY3, yc1–yc4, and cisplatin. QY4 and QY1, especially QY4, induced R9LC apoptosis via mitochondrial dysfunction, which involved mitochondrial membrane potential (MP) damage, ROS/Ca2+ activation, and apoptosis protein up-regulation. Thus, these coumarin ruthenium(II) coordination compounds are promising mitochondria-targeting anticancer agents.
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