Metal thiosemicarbazonates as dual mR2 RNR and colchicine-site tubulin inhibitors: from biochemical inhibition to mitotic arrest in MCF-7 breast cancer cells.

Cancer cells exploit multiple proliferation pathways, making single-target therapies vulnerable to resistance. Here, a thiosemicarbazone-based strategy is introduced for striking two validated oncotargets, the R2 subunit of ribonucleotide reductase (RNR) and the colchicine site of tubulin, with one agent. Guided by molecular docking, quinoline-8-carboxaldehyde N4-(3,4,5-trimethoxyphenyl)thiosemicarbazone (HL) and its metal complexes [Cu II (L)(Cl 2 CHCOO)] (1), [Cu II (L)Cl] (2), [Pd II (L)Cl] (3), and [Fe III (L)2]Cl (4) were synthesized and characterized by spectroscopic, spectrometric, electrochemical, and crystallographic techniques. Complexes 1, 2, and 4 effectively quench the R2 tyrosyl radical and inhibit tubulin polymerization in cell-free assays, yet only coordination to Cu(ii) translates this activity into sub- to low-micromolar cytotoxicity toward MCF-7 breast cancer cells, while the parent Schiff base and its Pd(ii) and Fe(iii) complexes remain largely inactive (HL and 3) or show somewhat reduced activity (4). Strikingly, cell cycle profiling at a single treatment time point shows that this activity manifests predominantly as mitotic accumulation mirroring the microtubule poison nocodazole, with no detectable S-phase signature. A time-dependent analysis would be required to determine whether an earlier or transient S-phase perturbation precedes this mitotic phenotype; therefore, the present data do not establish the proposed temporal relationship between RNR inhibition and mitotic arrest. These findings establish Cu(ii) thiosemicarbazonates as a dual-target chemotype, while the relative contribution and temporal sequence of the two cellular activities remain to be resolved.