Synthesis, structural characterization, computational studies, and anticancer evaluation of novel rufloxacin Schiff base metal complexes with involvement of Mcl-1 modulation in breast cancer cells.

[BACKGROUND AND OBJECTIVE] Breast cancer remains a leading cause of cancer-related mortality among women worldwide, emphasizing the urgent need for the development of novel and effective metal-based chemotherapeutics. This study aimed to synthesize and characterize a new Schiff base ligand derived from rufloxacin and to evaluate the anticancer potential of its metal complexes against triple-negative breast cancer (TNBC) cells, focusing on Mcl-1 protein suppression as a mechanistic target.

[METHODS] A novel Schiff base ligand, N,N-phenylene(bis(9-fluoro-2,3-dihydro-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzothiazine-6-carboxylic acid)) dihydrochloride (H₂Ruf-o-phdn·2HCl), was synthesized via the condensation of rufloxacin hydrochloride with o-phenylenediamine in ethanol. The ligand was complexed with zinc(II), yttrium(III), zirconium(IV), and lanthanum(III) salts in an alkaline medium at a 1:2:1 molar ratio to yield the corresponding coordination complexes. The products were characterized using elemental analysis, molar conductivity, magnetic susceptibility, FT-IR, ¹H NMR, UV-vis. spectroscopy, mass spectrometry, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The cytotoxic activity of the ligand and its complexes was assessed against the MDA-MB-231 (TNBC) cell line. Western blotting was employed to determine Mcl-1 expression, and molecular dynamics (MD) simulations with MM-PBSA calculations were conducted to elucidate binding stability and energetics.

[RESULTS] Spectroscopic data confirmed that the ligand coordinates in a tetradentate fashion through nitrogen and oxygen donor atoms, forming octahedral complexes around the metal centers. XRD patterns indicated crystalline nature, while TGA revealed stepwise decomposition involving coordinated water, anions, and organic moieties. Cytotoxicity assays demonstrated that metal complexation enhanced the antiproliferative activity relative to the free ligand. The ZrO(IV)-complex exhibited the highest potency (IC₅₀ ≈ 9 μM), accompanied by significant downregulation of the antiapoptotic Mcl-1 protein and clear evidence of apoptosis induction. MD simulations and MM-PBSA free-energy analyses confirmed a stable and energetically favorable ZrO(IV)-Mcl-1 interaction (ΔG_bind ≈ -12.9 kcal·mol⁻¹), primarily stabilized by a persistent hydrogen-bond network involving Arg263.

[CONCLUSION] The findings suggest that the ZrO(IV)-rufloxacin Schiff base complex exhibits strong antiproliferative activity against TNBC cells through Mcl-1 inhibition and apoptosis induction. This complex represents a promising therapeutic candidate targeting Mcl-1-mediated chemoresistance in aggressive breast cancer subtypes.