A series of half-sandwich iridium(III) benzimidazole-appended imidazolium-based N-heterocyclic carbene (NHC) antitumor complexes [(η5 -Cpx )Ir(C^N)Cl]Cl, where Cpx is pentamethylcyclopentadienyl (Cp*) or its biphenyl derivative (Cpxbiph ) and C^N is a NHC chelating ligand, were successfully synthesized and characterized. The IrIII complexes showed potential antitumor activity against A549 cells, at most three times more potent than cis-platin under the same conditions. Complexes could bind to BSA by a static quenching mode, catalyzing the change of NADH to NAD+ and inducing the production of reactive oxygen species (maximum turnover number, 9.8), which play an important role in regulating cell apoptosis. Confocal microscopy showed that the complexes could specifically target lysosomes in cells with a Pearson's co-localization coefficient 0.76 and 0.72 after 1 h and 6 h, respectively, followed an energy-dependent cellular uptake mechanism and damaged the integrity of lysosomes. At the same time, complexes caused a marked loss of mitochondrial membrane potential.
Keywords: N-heterocyclic carbenes; antitumor; half-sandwich iridium complexes; lysosomes; reactive oxygen species.
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