Metal N-heterocyclic carbene complexes as potential metallodrugs in antitumor therapy

Metal complexes, which exhibit alterable oxidation states, coordination numbers, and capacity to coordinate with different ligands, have provided a versatile platform for designing novel theranostic agents. By optimizing ligands, the curative effect of metal ions can be improved by the suitable stability and spatial configuration to act with the therapeutic target. In the past several decades, N-heterocyclic carbene (NHC) ligands with strong σ donation have become of great interest for transition metal (Au, Ag, Pt, etc.) medicinal applications. The research on metal–NHC (M−NHC) complexes as potential antitumor metallodrugs has been boosted dramatically since the seminal research by Berners-Price et al. in 2004. This review provides the latest advances in NHC-based metallodrugs from 2017 to the present. The antitumor properties, possible mode of action, and structure–activity relationships for NHC metallodrugs are summarized. We hope this comprehensive review will be of great benefit to researchers designing novel M−NHC antitumor drugs and developing metallodrugs for successful clinical application.