In this study, half-sandwich Ru(II) complexes containing acylthiourea
ligands of the general type [Ru(η6-
p-cymene)(PPh3)(S)Cl]PF6 (1m-6m) and [Ru(η6-
p-cymene)(PPh3)(S-O)]PF6 (1b-6b) where S/S-O = N',N'-disubstituted acylthiourea were synthesized and characterized (via elemental analyses, IR spectroscopy, 1H NMR spectroscopy, 13C{1H} NMR spectroscopy, and X-ray diffractometry), and their cytotoxic activity was evaluated. The different coordination modes of the acylthiourea
ligands, monodentately via S (1m-6m) and bidentately via S,O (1b-6b), to
ruthenium were modulated from different synthetic routes. The cytotoxicity of the complexes was evaluated in five human cell lines (DU-145, A549, MDA-MB-231, MRC-5, and MCF-10A) by MTT assay. The IC50 values for
prostate cancer cells (2.89-7.47 μM) indicated that the complexes inhibited cell growth, but that they were less cytotoxic than
cisplatin (2.00 μM). Unlike for
breast cancer cells (IC50 = 0.28-0.74 μM) and
lung cancer cells (IC50 = 0.51-1.83 μM), the complexes were notably more active than the reference drug, and a remarkable selectivity index (SI 4.66-19.34) was observed for
breast cancer cells. Based on both the activity and selectivity, complexes 5b and 6b, as well as their respective analogous complexes in the monodentate coordination 5m and 6m, were chosen for further investigation in the MDA-MB-231 cell line. These complexes not only induced morphology changes but also were able to inhibit colony formation and migration. In addition, the complexes promoted cell cycle arrest at the sub-G1 phase inducing apoptosis. Interaction studies by viscosity measurements, gel electrophoresis, and fluorescence spectroscopy indicated that the complexes interact with the
DNA minor groove and exhibit an HSA binding affinity.