Impact of Biphenyl Benzhydrazone-Incorporated Arene Ru(II) Complexes on Cytotoxicity and the Cancer Cell Death Mechanism

Abstract

The biological efficacy of arene ruthenium complexes is currently of great interest due to the significance of arene moieties, chelates, and metal centers in defining and controlling their anticancer activity. The synthesis of six new arene ruthenium(II) complexes containing biphenyl benzhydrazone ligands of general composition [(η6-benzene)Ru(L)Cl] (1–3) and [(η6-p-cymene)Ru(L)Cl] (4–6, L = biphenyl benzhydrazones), and their antiproliferative properties are described in this study. The complexes have been successfully synthesized and thoroughly characterized by elemental analysis and spectral methods such as Fourier transform infrared (FT-IR), UV–vis, NMR, and high-resolution mass spectrometry (HR-MS) techniques. The coordination of azomethine nitrogen and imidolate oxygen of the hydrazone ligand to the ruthenium metal and the presence of a pseudo-octahedral geometry around the ruthenium ion were confirmed by the single-crystal X-ray diffraction (XRD) technique. Further, in vitro cytotoxicity of all of the complexes was evaluated against cancerous A549 (lung cancer), MDA-MB-231 (breast cancer), and HEPG2 (liver cancer) and noncancerous HEK-293 (human kidney) cells and was found to be good with low IC50 values compared to the standard drug cisplatin. In particular, complex 5 exhibits potential cytotoxicity against all of the cancer cells among the synthesized complexes, and this may be attributed to the hydrophobic nature of the p-cymene moiety as well as the substituent effect of the ligand. In addition, staining studies such as AO–EB and Hoechst 33342 ascertain that the complex induces the apoptosis mechanism in cancer cells. Furthermore, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) confirm apoptosis in cancer cells via the mitochondrial pathway. Additionally, the quantification of apoptosis and ROS have been established by flow cytometry and the plate reader assay, respectively. It is worth noting that the present ruthenium complexes have significant cytotoxicity, raising the prospect of promoting potential ruthenium-based anticancer drugs over platinum drugs.