Characterization, modes of interactions with DNA/BSA biomolecules and anti-tumor activity of newly synthesized dinuclear platinum(II) complexes with pyridazine bridging ligand

Platinum-based drugs are widely recognized efficient anti-tumor agents, but faced with multiple undesirable effects. Here, four dinuclear platinum(II) complexes, [{Pt(1,2-pn)Cl}₂(μ-pydz)]Cl₂ (C1), [{Pt(ibn)Cl}₂(μ-pydz)]Cl₂ (C2), [{Pt(1,3-pn)Cl}₂(μ-pydz)]Cl₂ (C3) and [{Pt(1,3-pnd)Cl}₂(μ-pydz)]Cl₂ (C4), were designed (pydz is pyridazine, 1,2-pn is ( ±)-1,2-propylenediamine, ibn is 1,2-diamino-2-methylpropane, 1,3-pn is 1,3-propylenediamine, and 1,3-pnd is 1,3-pentanediamine). Interactions and binding ability of C1–C4 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV–Vis, fluorescence emission spectroscopy and molecular docking. Binding affinities of C1–C4 complexes to the bovine serum albumin (BSA) has been monitored by fluorescence emission spectroscopy. The tested complexes exhibit variable cytotoxicity toward different mouse and human tumor cell lines. C2 shows the most potent cytotoxicity, especially against mouse (4T1) and human (MDA-MD468) breast cancer cells in the dose- and time-dependent manner. C2 induces 4T1 and MDA-MD468 cells apoptosis, further documented by the accumulation of cells at sub-G1 phase of cell cycle and increase of executive caspase 3 and caspase 9 levels in 4T1 cells. C2 exhibits anti-proliferative effect through the reduction of cyclin D3 and cyclin E expression and elevation of inhibitor p27 level. Also, C2 downregulates c-Myc and phosphorylated AKT, oncogenes involved in the control of tumor cell proliferation and death. In order to measure the amount of platinum(II) complexes taken up by the cells, the cellular platinum content were quantified. However, C2 failed to inhibit mouse breast cancer growth in vivo. Chemical modifications of tested platinum(II) complexes might be a valuable approach for the improvement of their anti-tumor activity, especially effects in vivo.

Graphical abstract

Dinuclear platinum(II) complex [{Pt(ibn)Cl}₂(μ-pydz)]Cl₂ shows anti-tumor activity, triggers the apoptosis and reduces the proliferation of mouse breast cancer cells in vitro. However, its inhibitory effect on tumor growth in vivo is absent.