Anticancer activity and DNA binding of a bifunctional Ru(II) arene aqua-complex with the 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine ligand.
The synthesis and full characterization of the new aqua-complex [(?(6)-p-cymene)Ru(OH2)(?(2)-N,N-2-pydaT)](BF4)2, (BF4)2, and the nucleobase derivative [(?(6)-p-cymene)Ru(9-MeG)(?(2)-N,N-2-pydaT)](BF4)2, (PF6)2, where 2-pydaT = 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine and 9-MeG = 9-methylguanine, are reported here. The crystal structures of both (PF6)2 and the chloro complex [(?(6)-p-cymene)RuCl(?(2)-N,N-2-pydaT)](PF6), (PF6), have been elucidated by X-ray diffraction. The former provided relevant information regarding the interaction of the metallic fragment [(?(6)-p-cymene)Ru(?(2)-N,N-2-pydaT)](2+) and a simple model of DNA. NMR and kinetic absorbance studies have proven that the aqua-complex (BF4)2 binds to the N7 site of guanine in nucleobases, nucleotides, or DNA. A stable bifunctional interaction (covalent and partially intercalated) between the [(?(6)-p-cymene)Ru(?(2)-N,N-2-pydaT)](2+) fragment and CT-DNA has been corroborated by kinetic, circular dichroism, viscometry, and thermal denaturation experiments. The reaction mechanism entails the very fast formation of the Ru-O-(PO3) linkage prior to the fast intercalation of the 2-pydaT fragment. Then, a Ru-N7-(G) covalent bond is formed at the expense of the Ru-O-(PO3) bond, yielding a bifunctional complex. The dissociation rate of the intercalated fragment is slow, and this confers additional interest to (BF4)2 in view of the likely correlation between slow dissociation and biological activity, on the assumption that DNA is the only biotarget. Furthermore, (BF4)2 displays notable pH-dependent cytotoxic activity in human ovarian carcinoma cells (A2780, IC50 = 11.0 ?M at pH = 7.4; IC50 = 6.58 ?M at pH = 6.5). What is more, complex (BF4)2 is not cross-resistant with cisplatin, exhibiting a resistance factor, RF(A2780cis), of 0.28, and it shows moderate selectivity toward the cancer cell lines, in particular, A2780cis (IC50 = 3.0 5 ± 0.08 ?M), relative to human lung fibroblast cells (MRC-5; IC50 = 24 ?M), the model for healthy cells.