Copper(II)-Mediated Mitochondria-Targeting in Cancer Cells

Mitochondria are attractive anticancer targets, but selective targeting remains challenging. We report a Cu²⁺-mediated strategy for mitochondria-directed activity based on intracellular metal coordination. Aminoferrocene drugs were functionalized with Cu²⁺-binding ligands to exploit elevated copper levels in cancer cells. Among these, the bipyridine conjugate AFb-L4 displays pronounced Cu²⁺-dependent cytotoxicity, with an IC₅₀ of 29 nM in ovarian carcinoma cells (∼500-fold enhancement upon Cu²⁺ addition). Spectroscopic, magnetic, and mass spectrometric analyses confirm formation of a 1:1 AFb-L4-Cu²⁺ complex without electronic coupling between the Cu²⁺ and ferrocene centers. Intracellular Cu²⁺ coordination converts AFb-L4 into a cationic species that accumulates in mitochondria, inducing loss of membrane potential, mitochondrial remodeling, and mitochondrial ROS generation. Structure-activity relationships show that stabilization of Cu²⁺ is critical, as a sterically hindered isomer with reduced Cu²⁺ binding is largely inactive. These results establish intracellular Cu²⁺ coordination as a trigger for mitochondrial targeting.