Homo- and Hetero-Multinuclear Iridium(III) Complexes with Cytotoxic Activity

Towards the efforts to expand the bioactivity and to reduce toxic and adverse properties of known metal-based drugs, various multinuclear complexes have recently been studied. They have shown enhancement of target specificity and selectivity. Different from small organic compounds and traditional metal-based complexes with anticancer activity, iridium(III) multinuclear or heteronuclear metallodrugs have confirmed potential advantages due to their unique biological and chemical diversities, better activity and different anticancer mechanisms. Ir(III) coordination compounds, similar to most Pt group compounds, are of excessive interest because of their potential cytotoxic activity, effective cellular uptake and tolerance by healthy cells. Although mononuclear Ir(III) complex compounds have been extensively studied as promising candidates for antitumor application, the research on the antineoplastic potential of homo- or hetero-multinuclear iridium(III) complexes is not as abundant; nevertheless, intensive investigations have been conducted in the recent years towards developing complexes that are anticipated to have improved therapeutic potential and biotarget selectivity. Multimetallic iridium(III) frameworks have offered interesting possibilities for designing new antitumor agents by exploiting the action of different metal cations at the same time. This method was very successful in the design of homo- and hetero-multinuclear cyclometalated and half-sandwich organometallic Ir(III) compounds. In the described background, many homonuclear and heteronuclear Ir(III) complexes have been estimated and have exposed promising advantages in cancer therapy. This review intends to summarize newly reported innovative and promising multinuclear Ir(III)-based complexes and to afford a wide-ranging overview of current development and perspectives for the practical impact of these complexes in the tumor therapy field. It is anticipated that this analysis will provide significant direction for the further progress of active homonuclear and heteronuclear iridium-based anticancer agents.