New Tin (IV) and Organotin (IV) Complexes with a Hybrid Thiosemicarbazone/Hydrazone Ligand: Synthesis, Crystal Structure, and Antiproliferative Activity

Nowadays, the search for new chemotherapeutic agents with low toxicity and high selectivity is a major concern. In this paper, we report the synthesis and characterization of a hybrid thiosemicarbazone/hydrazone ligand in its neutral form (L¹H₂) and as the chloride salt ([L¹H₃]Cl)-, three diorganotin (IV) complexes, and one complex with Sn (IV). The compounds have been fully characterized by IR, mass spectra, ¹H, ¹³C, and ¹¹⁹Sn NMR, ¹¹⁹Sn CP/MAS NMR, and by single crystal X-ray diffraction. The organotin compounds have the empirical formula [SnR₂L¹] (R = Me, Bu, and Ph), but in the solid state, they are polymeric species with seven coordination number due to weak coordination of the pyridine nitrogen, whereas in solution, the polymeric structure is lost to afford hexacoordinate monomeric species. Reaction with SnI₄ yields complex [Sn (L¹)₂]·EtOH, with the metal in a distorted dodecahedral arrangement. We have evaluated the antiproliferative activity of the two forms of the ligands and the four coordination compounds against MDA-MB-231, HeLa, PC3, and HepG2 cancer cell lines, and WI-38 normal cell line, and all the compounds present higher activity than cisplatin, used as the standard control. To investigate the mode of action, we have selected the most active complex, containing phenyl substituents, and used the triple negative breast cancer cell line MDA-MB-231. The results show that the complex induces apoptotic cell death promoted by generation of reactive oxygen species and by disruption of mitochondrial membrane potential.