Cyclometalated Palladium(II) N‐Heterocyclic Carbene Complexes: Anticancer Agents for Potent In Vitro Cytotoxicity and In Vivo Tumor Growth Suppression

Palladium(II) complexes are generally reactive toward substitution/reduction, and their biological applications are seldom explored. A new series of palladium(II) N-heterocyclic carbene (NHC) complexes that are stable in the presence of biological thiols are reported. A representative complex, [Pd(C^N^N)(N,N′-nBu2NHC)](CF3SO3) (Pd1 d, HC^N^N=6-phenyl-2,2′-bipyridine, N,N′-nBu2NHC=N,N′-di-n-butylimidazolylidene), displays potent killing activity toward cancer cell lines (IC50=0.09–0.5 μm) but is less cytotoxic toward a normal human fibroblast cell line (CCD-19Lu, IC50=11.8 μm). In vivo anticancer studies revealed that Pd1 d significantly inhibited tumor growth in a nude mice model. Proteomics data and in vitro biochemical assays reveal that Pd1 d exerts anticancer effects, including inhibition of an epidermal growth factor receptor pathway, induction of mitochondrial dysfunction, and antiangiogenic activity to endothelial cells.