Insights into the in vitro Anticancer Effects of Diruthenium-1

The in vitro anticancer activity of the dinuclear trithiolato-bridged arene ruthenium complex diruthenium-1 (DiRu-1) was evaluated against a panel of human cancer cell lines used as in vitro models for hepatocellular carcinoma (HepG2 cells), estrogen-responsive breast adenocarcinoma (MCF-7 cells), and triple-negative breast adenocarcinoma (MDA-MB-231 cells). DiRu-1 is highly cytotoxic to these cell lines, demonstrating half-maximal inhibitory concentrations (IC₅₀ ) in the low-nanomolar range (77±1.4 to 268.2±4.4 nm). The main molecular mechanisms responsible for the high cytotoxicity of DiRu-1 against the most responsive MCF-7 cell line (IC₅₀ =77±1.4 nm) were investigated on the basis of the capacity of DiRu-1 to induce oxidative stress, apoptosis, and DNA damage, and to inhibit the cell cycle and proliferation. The results show that DiRu-1 triggers caspase-dependent apoptosis in MCF-7 cells on both the intrinsic and extrinsic pathways. Moreover, the Ru complex also causes necrosis, mitotic catastrophe, and autophagy. DiRu-1 increases the intracellular levels of reactive oxygen species (ROS), which play a significant role in its cytotoxicity and pro-apoptotic activity. An important mechanism of the anticancer activity of DiRu-1 appears to be the induction of DNA lesions, mainly due to apoptotic DNA fragmentation and cell-cycle arrest at the G₂ /M checkpoint. These changes are correlated with the concentration of DiRu-1, the duration of the cell treatment, and the post-treatment time.