Synthesis, characterization, and biological activity of Co(II) and Zn(II) complexes of imidazoles-based azo-functionalized Schiff bases

•New imidazoles-based azo-functionalized Schiff bases (HL1‒HL3) were successfully prepared.•The Co(II)/Zn(II) complexes of HL1‒HL3 were successfully synthesized.•New compounds were structurally and thermally characterized using various techniques.•New compounds can greatly increase the apoptosis of MCF-7 cells.•CoL3 was the most potent anticancer agent and exhibited high DNA Topo-II inhibitory activity. A new series of azo-functionalized Schiff base ligands containing different imidazole derivatives (HL1‒HL3) and their Co(II)/Zn(II) complexes were successfully prepared. The molecular structures of the new ligands and their metal complexes have been deduced using microanalytical and spectral techniques. The thermal stability study revealed that the Co(II)/Zn(II) complexes are more stable than their corresponding ligands. The results of in vitro cytotoxicity test revealed that all compounds have the capacity to inhibit the growth of breast carcinoma (MCF-7) cells with a structure-dependent performance. Among all, complex CoL3, (IC50 = 0.90±0.05 µg/mL) was the most potent and selective (SI = 90.56) anti-breast cancer agent. Flow-cytometric study revealed that CoL3 dramatically enhanced the proportion of MCF-7 cells in the sub G1 phase while decreasing the proportion of cells in the S phase. In addition, CoL3 showed better inhibitory activity on DNA topoisomerase-II.