Recent developments on other platinum metal complexes as target-specific anticancer therapeutics

Numerous biologically active metal complexes are reported for their unique features and enhanced functions, particularly towards the inhibition of cancer progression. With the availability of multiple targets for different types of cancers, the challenge towards developing drugs with high specificity and selectivity always exists. Though most of these drugs have performed satisfactorily at laboratory levels, but many of them have failed at various levels of clinical trials. The scope of this review includes mono- and multi-nuclear metal complexes of ruthenium(II), rhodium(III), osmium(II) and iridium(III) with various types of ligands with multiple geometries and orientations, including half-sandwich structures, arene complexes, covalently linked homo- or heterometallic species, etc. The discussed complexes are categorized according to the nature of metal, their specific targets and mechanism of actions. The general methods of inhibition included mitochondrial dysfunction, altered membrane potential, subcellular accumulation, etc that leads to apoptosis, DNA damage and cell cycle arrest through their induced cytotoxicity. Further special emphasis is given on photoactive metal complexes and their applications as photodynamic therapeutics. Numerous examples under each category of drugs are discussed in detail.