Anticancer activity of tetracationic arene ruthenium metalla-cycles

A series of cationic metalla-cycles of the general formulae [(η⁶-<i>p</i>-cym)₄Ru₄(<i>OO</i>∩<i>OO</i>)₂(<i>N</i>∩<i>N</i>)₂]⁴⁺ and [(η⁶-<i>p</i>-cym)₄Ru₄(<i>NO</i>∩<i>NO</i>)₂(<i>N</i>∩<i>N</i>)₂]⁴⁺ has been prepared from the dinuclear arene ruthenium precursors [(η⁶-<i>p</i>-cym)₂Ru₂(<i>OO</i>∩<i>OO</i>)₂Cl₂] (<i>OO</i>∩<i>OO</i> = oxalato, 1,4-benzoquinonato-2,5-diolato, 1,4-naphtoquinonato-5,8-diolato, 9,10-anthraquinonato-1,4-diolato, 5,12-tetraquinonato-6,11-diolato) and [(η⁶-<i>p</i>-cym)₂Ru₂(<i>NO</i>∩<i>NO</i>)₂Cl₂] (<i>NO</i>∩<i>NO</i> = oxamido, oxonico) by reaction with two different bidentate linkers (<i>N</i>∩<i>N</i> = 1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)ethane) in the presence of silver triflate. All complexes were isolated as triflate salts and characterised by NMR, infrared, UV-visible, mass spectrometry and by elemental analysis. The cytotoxicities of the tetranuclear ruthenium complexes have been established using ovarian A2780 and A2780cisR cancer cell lines. All complexes exhibit moderate to excellent activity on both the cisplatin resistant and cisplatin sensitive cells, thus suggesting a mode of action different from cisplatin.