In vitro and in vivo antitumor studies of potential anticancer agents of platinum(II) complexes of dicyclopentadiene and dithiocarbamates§

Three platinum(II) complexes of dicyclopentadiene (DCP) and dithiocarbamates (DTCs), namely, [Pt(η4-DCP)(Me2DTC)]PF6 (1), [Pt(η4-DCP)(Et2DTC)]PF6 (2), and [Pt(η4-DCP)(Bz2DTC)]PF6 (3) [Me2DTC = dimethyldithiocarbamate, Et2DTC = diethyldithiocarbamate, and Bz2DTC = dibenzyldithiocarbamate] were prepared and characterized by elemental analysis, IR, 1H, and 13C Nuclear Magnetic Resonance spectroscopy. The spectroscopic data indicated the coordination of both DCP and DTC ligands to platinum(II). The solution chemistry of complex 1 revealed that the complexes are stable in both dimethyl sulfoxide (DMSO) and 1:1 mixture of DMSO:H2O. In vitro cytotoxicity of the complexes relative to cisplatin was tested using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, against CHL-1 (human melanoma cancer cells), MDA-MB-231 (breast cancer cells), A549 (lung cancer cells), and B16 (murine melanoma cancer cells). The antiproliferative effect of all three prepared complexes was found to be significantly higher than cisplatin. Furthermore, flow cytometric analysis of complex 1 showed that the complex induced apoptosis, oxidative stress, mitochondrial potential depolarization and cell cycle arrest in a concentration-dependent pattern in the CHL-1 cells. Confirmation of apoptosis via gene expression analysis demonstrated down-regulation of anti-apoptotic genes and up-regulation of pro-apoptotic genes in the CHL-1 cells. Wound-healing assays also lent support to the strong cytotoxicity of the complexes. In vivo studies showed a significant reduction of tumor volume at the end of the experiment. In addition, the drug did not change the weight of the mice. In conclusion, complex 1 inhibited cell proliferation in vitro and reduced tumor growth in vivo.