Pt(II) complexes with (N,N') or (C,N,E)(-) (E=N,S) ligands: cytotoxic studies, effect on DNA tertiary structure and structure-activity relationships.

The cytotoxic activity of two series of platinum(II) complexes containing the polyfunctional imines R(1)-CHN-R(2) [R(1)=phenyl or ferrocenyl unit and R(2)=(CH2)n-CH2-NMe2 where n=1 or 2) (1 and 2) or C6H4-2-SMe (3)] acting as a bidentate (N,N') (4-7) or terdentate [C(phenyl or ferrocenyl),N,N'](-) (8-10) or [C(ferrocenyl),N,S](-) ligand (11) in front of A549 lung, MDA-MB231 breast and HCT116 colon human adenocarcinoma cell lines is reported. The results reveal that most of the platinum(II) complexes are active against the three assayed lines and compounds 6, 7 and the platinacycles 10 and 11 exhibit a remarkable antiproliferative activity, even greater than cisplatin itself, in the cisplatin resistant HCT116 human cancer cell line. Electrophoretic DNA migration studies showed that most of them modify the DNA tertiary structure in a similar way as the reference cisplatin. Solution studies of a selection of the most relevant complexes have also been performed in order to test: (a) their stability in the aqueous biological medium and/or the formation of biologically active species and (b) their proclivity to react with 9-methylguanine (9-MeG), as a model nucleobase. Computational studies at DFT level have also been performed in order to explain the different solution behaviour of the complexes and their proclivity to react with the nucleobase.