Dinuclear Ru^II(bipy)₂ Derivatives: Structural, Biological, and in Vivo Zebrafish Toxicity Evaluation

Ruthenium-based drugs exhibit interesting properties as potential anticancer pharmaceuticals. We herein present the synthesis and characterization of a new family of ruthenium complexes with formulas [{Ru(bipy)₂}₂(μ-L)][CF₃SO₃]₄ (L = bptz, 1a) and [{Ru(bipy)₂}₂(μ-L)][CF₃SO₃]₂ (L = arphos, 2a; dppb, 3a; dppf, 4a), which were synthesized from the Ru(II) precursor compound cis-Ru(bipy)₂Cl₂. The complexes were characterized by elemental analysis, mass spectrometry, ¹H and ³¹P{¹H} NMR, IR spectroscopy, and conductivity measurements. The molecular structures for three Ru(II) compounds were determined by single-crystal X-ray diffraction. The newly developed compounds interact with CT-DNA by intercalation, in particular, 2a, 3a, and 4a, which also seemed to induce some extent of DNA degradation. This effect seemed to be related with the formation of reactive oxygen species. The cytotoxic activity was evaluated against A2780, MCF7, and MDAMB231 human tumor cells. Compounds 2a and 4a were the most cytotoxic with activity compared to cisplatin (∼2 μM, 72 h) in the A2780 cisplatin sensitive cells. All the compounds induced A2780 cell death by apoptosis, however, to a lesser extent for compounds 4a and 2a. For these compounds, the mechanism of cell death in addition to apoptosis seemed to involve autophagy. In vivo toxicity was evaluated using the zebrafish embryo model. LC₅₀ estimates varied from 5.397 (3a) to 39.404 (1a) mg/L. Considering the in vivo toxicity in zebrafish embryos and the in vitro cytotoxicity in cancer cells, compound 1a seems to be the safest having no effect on dechirionation and presenting a good antiproliferative activity against ovarian carcinoma cells.