Soon after this study, the metallopharmaceutical approach was clearly validated by the identification of a ruthenium(II) complex as a nanomolar inhibitor of glycogen synthase kinase 3 (GSK-3) [19]. The rutheniu- m(II) complex, which contained a pyridocarbazole ligand (PC, Figure 2), was stable in aqueous media, demon- strated good selectivity over other kinases, and was actu- ally more potent than staurosporine against GSK-3. The metal and additional ancillary ligands were proven to be essential for good activity as the pyridocarbazole ligand alone was a poor inhibitor of GSK-3. The crystal structure of a protected precursor to the ruthenium(II)–pyridocar- bazole complex was determined and used to show the structural similarity to staurosporine and predict the mode of binding in the GSK-3 active site.