Rhodium(III) and iridium(III) complexes as anticancer agents

Until recently, Rh(III) and particularly Ir(III) complexes were generally considered as being unlikely candidates for anticancer agents owing to the typical kinetic inertness of their transition metal centres. Systematic studies on the cellular impact of a range of octahedral Rh(III) complexes containing polypyridyl and other aromatic chelates have now, however, demonstrated that high cytotoxicity in cancer cells and in certain cases promising relative tolerance by healthy cells can be achieved by judicious selection of the remaining ligands. Current knowledge on the biological properties of Rh(III) and Ir(III) compounds is reviewed in this article, with particular emphasis being placed on design strategies and on their solution behaviour, DNA binding preferences, structure–activity relationships and apoptosis induction in both adhesive and non-adhesive cells.