Cobalt(II) complexes with thiosemicarbazone as potential antitumor agents: synthesis, crystal structures, DNA interactions, and cytotoxicity

Two cobalt(II) complexes [Co(QCT)(2)]Cl1.5H(2)O (1) (QCT = quinoline-2-carboxaldehyde thiosemicarbazone) and [Co(QCMT)(CH3OH)Cl-2] (2) (QCMT = quinoline-2-carboxaldehyde N-4-methyl-thiosemicarbazone) have been synthesized and structurally characterized. Complex 1 crystallizes in a triclinic system with space group P-1 and complex 2 crystallizes in a monoclinic system with space group P2(1)/n. In both complexes the cobalt(II) center is six coordinated with distorted octahedral geometry. The interactions of two complexes with CT-DNA were investigated by electronic absorption spectra, circular dichroism (CD) spectra and fluorescence spectra. Results suggest that the complexes bind to DNA via groove binding mode, and complex 2 has stronger binding ability than complex 1. The in vitro cytotoxicity has been tested against the human lung adenocarcinoma cell line A-549, cisplatin-resistant cell line A-549/CDDP, and human breast adenocarcinoma cell line MCF-7. Complex 2 is more cytotoxic than complex 1, and both of them show higher cytotoxicity than the parent ligands alone. Compared with cisplatin, the two cobalt(II) complexes are more active against A-549/CDDP and MCF-7 cell lines at most experimental concentrations. Notably, although complex 2 is found to be less effective than cisplatin against the parent cell line A-549, it is much more effective than cisplatin against the resistant cell A-549/CDDP.