Ruthenium(II)/diphosphine/naphthoquinone complexes: synthesis, characterization, anticancer activity and molecular...

Breast cancer (BC) is one of the most challenging types of cancer in women. Triple-negative breast cancer (TNBC) is an aggressive and rapidly progressive subtype that lacks targeted therapies, relying primarily on chemotherapy. Given the limited treatment options for TNBC, novel therapeutic strategies are needed to address this disease. In this context, here we report the synthesis and characterization of four ruthenium(II) complexes containing naphthoquinone derivatives as ligands: [Ru(NQ1)(bipy)(dppen)]PF₆ (Ru1), [Ru(NQ2)(bipy)(dppen)]PF₆ (Ru2), [Ru(NQ1)(bipy)(DPEphos)]PF₆ (Ru3), and [Ru(NQ2)(bipy)(DPEphos)]PF₆ (Ru4), where bipy = 2,2'-bipyridine, dppen = 1,2-bis(diphenylphosphino)ethylene, DPEphos = bis[(2-diphenylphosphino)phenyl]ether, and NQ1 and NQ2 = deprotonated lawsone and lapachol, respectively. Mass spectrometry and elemental analyses were used to confirm the purity of the complexes. In vitro assays showed that Ru1-Ru4 were cytotoxic against MDA-MB-231 and MCF-7 (breast cancer cell lines) and A549 (lung cell line). The compounds exhibited lower IC₅₀ values than cisplatin, used as a control. Ru4 was the most promising compound, with the highest selectivity index for the triple-negative breast cancer cell line (SI = 25.5). Furthermore, this complex inhibited colony formation, induced apoptosis, and affected the cell cycle in these cancer cells. Western blot analysis showed increased cleaved caspase-3 expression, corroborating the apoptotic mechanism observed by flow cytometry. Furthermore, cell uptake studies showed that ruthenium was found at the intracellular level after treatment with the MDA-MB-231 cell line. DNA-binding studies revealed an interaction between Ru1-Ru4 and Ct-DNA via the minor groove pocket, as confirmed by molecular docking. Overall, our results suggest [Ru(NQ2)(bipy)(DPEphos)]PF₆ (Ru4) to be a promising cytotoxic agent against breast cancer.