Ruthenium-based compounds are an attractive alternative to clinically used platinum drugs due to several features including a wide range of accessible oxidation states, varied synthetic chemistry and typically lower general toxicities. One series of ruthenium(II)-arene-pta, RAPTA (pta = 1,3,5-triaza-7-phosphatricyclo[] decane) compounds has been found to show particularly high selectivity towards cancer cells in both in vitro and in vivo studies.