Anticancer activity of complexes of the third row transition metals, rhenium, osmium, and iridium

The clinical success of the platinum-based chemotherapeutic agents has prompted the investigation of coordination and organometallic complexes of alternative metal centers for use as anticancer agents. Among these alternatives, the third row transition metal neighbors of platinum on the periodic table have only recently been explored for their potential to yield anticancer-active complexes. In this Perspective, we summarize developments within the last six years on the application of rhenium, osmium, and iridium complexes as anticancer drug candidates. This review focuses on studies that discuss the potential mechanisms of action of these complexes. As reflected in this Perspective, complexes of these metal ions induce cancer cell death via a diverse range of mechanisms. Notably, small structural changes can significantly alter the mode of cell death, hindering efforts to elucidate structure-activity relationships. This property may both benefit and hinder the clinical development of these compounds.