Design and Anticancer Properties of New Water-Soluble Ruthenium-Cyclopentadienyl Complexes

Ruthenium complexes are emerging as one of the most promising classes of complexes for cancer therapy. However, their limited aqueous solubility may be the major limitation to their potential clinical application. In view and to contribute to the progress of this field, eight new water-soluble Ru(II) organometallic complexes of general formula [RuCp(mTPPMS)_n(L)] [CF₃SO₃], where mTPPMS = diphenylphosphane-benzene-3-sulfonate, for n = 2, L is an imidazole-based ligand (imidazole, 1-benzylimidazole, 1-butylimidazole, (1-(3-aminopropyl)imidazole), and (1-(4-methoxyphenyl)imidazole)), and for n = 1, L is a bidentate heteroaromatic ligand (2-benzoylpyridine, (di(2-pyridyl)ketone), and (1,2-(2-pyridyl)benzo-[b]thiophene)) were synthesized and characterized. The new complexes were fully characterized by NMR, FT-IR, UV-vis., ESI-HRMS, and cyclic voltammetry, which confirmed all the proposed molecular structures. The antiproliferative potential of the new Ru(II) complexes was evaluated on MDAMB231 breast adenocarcinoma, A2780 ovarian carcinoma, and HT29 colorectal adenocarcinoma cell lines, showing micromolar (MDAMB231 and HT29) and submicromolar (A2780) IC₅₀ values. The interaction of complex 6 with human serum albumin (HSA) and fatty-acid-free human serum albumin (HSA^faf) was evaluated by fluorescence spectroscopy techniques, and the results revealed that the ruthenium complex strongly quenches the intrinsic fluorescence of albumin in both cases.