This research presents the design, synthesis, structural characterization, and evaluation of the anticancer activities of three new pyrimidylanthrahydrazone cobalt(II) complexes: 1) 9-MPMAH-Co, 2) 9-FPMAH-Co, and 3) 9-PMAH-Co. Single-crystal X-ray diffraction analysis confirmed that all three complexes adopt a hexacoordinate mononuclear geometry. However, differences in their coordination modes were observed due to variations in the ligand substituents (-CH3, -F, -H). Spectroscopic DNA interaction studies indicated that all three cobalt complexes exhibit varying levels of DNA intercalation. Topoisomerase I inhibition assays revealed that 9-PMAH-Co demonstrates significant enzyme inhibition at a low concentration of 1 μM. In vitro antiproliferative assays confirmed that 9-PMAH-Co exhibits potent cytotoxic activity against SK-OV-3 and HeLa-229 cancer cell lines, with IC₅₀ values of 4.99 ± 0.18 μM and 8.09 ± 1.13 μM, respectively, while showing reduced toxicity toward normal liver cells (HL-7702) compared to cisplatin. Further investigation through cell cycle analysis indicated that 9-PMAH-Co induces G2/M phase arrest in SK-OV-3 cells, with a population increase to 91.37 % (Δ = 76.59 %). Studies on the structural-activity relationship suggest that the synergistic interactions between the ligand substituents and the cobalt center play a crucial role in modulating biological activity, highlighting 9-PMAH-Co as a promising lead compound for the development of targeted anticancer agents.
