Synthesis, Characterization, and Biological Evaluation of Novel [M(η 6 -arene) 2 ] + (M = Re, 99m Tc) Hosted Terpyridines and Copper Complexes Thereof.

We report the synthesis, characterization, and in vitro biological activities of [Re(η 6 -arene) 2 ] + -terpyridine conjugates and their Cu II complexes. The terpyridine (terpy) chelators were attached to the [Re(η 6 -arene) 2 ] + scaffold via secondary amine linkers allowing for heteroleptic mono- and homoleptic bis-terpyridine-substituted chelators. Complexation with CuCl 2 afforded the respective square pyramidal [Cu(terpy)Cl 2 ] complexes hosted on the [Re(η 6 -arene) 2 ] + scaffold. The chelator conjugates and their respective complexes were found to be remarkably cytotoxic against malignant HT29 and A549 human cancer cell lines in vitro with IC 50 values in the low micromolar range. Mitochondrial respiration disruption was identified as a possible mode of action of these novel drug candidates. Crucially, the [Re(η 6 -arene) 2 ] + hosts delivered water solubility of the otherwise insoluble [Cu(terpy)Cl 2 ] motif. Importantly, the homoleptic [ 99m Tc(η 6 -arene) 2 ] + -terpyridine conjugate is available in a single step, which enables the presented system to be used as a theranostic approach to modern medicinal inorganic chemistry.