Gold(III) to Ruthenium(III) Metal Exchange in Dithiocarbamato Complexes Tunes Their Biological Mode of Action for Cytotoxicity in Cancer Cells

Abstract

Malignant tumors have affected the human being since the pharaoh period, but in the last century the incidence of this disease has increased due to a large number of risk factors, including deleterious lifestyle habits (i.e., smoking) and the higher longevity. Many efforts have been spent in the last decades on achieving an early stage diagnosis of cancer, and more effective cures, leading to a decline in age-standardized cancer mortality rates. In the last years, our research groups have developed new metal-based complexes, with the aim to obtain a better selectivity for cancer cells and less side effects than the clinically established reference drug cisplatin. This work is focused on four novel Au(III) and Ru(III) complexes that share the piperidine dithiocarbamato (pipe-DTC) as the ligand, in a different molar ratio. The compounds [AuCl₂(pipeDTC)], [Au(pipeDTC)₂]Cl, [Ru(pipeDTC)₃] and β-[Ru₂(pipeDTC)₅] have been synthesized and fully characterized by several chemical analyses. We have then investigated their biological properties in two different cell lines, namely, AGS (gastric adenocarcinoma) and HCT116 (colon carcinomas), showing significant differences among the four compounds. First, the two gold-based compounds and β-[Ru₂(pipeDTC)₅] display IC₅₀ in the µM range, significantly lower than cisplatin. Second, we showed that [AuCl₂(pipeDTC)] and β-[Ru₂(pipeDTC)₅]Cl drive different molecular mechanisms. The first was able to induce the protein level of the DNA damage response factor p53 and the autophagy protein p62, in contrast to the second that induced the ATF4 protein level, but repressed p62 expression. This study highlights that the biological activity of different complexes bringing the same organic ligand depends on the electronic and structural properties of the metal, which are able to fine tune the biological properties, giving us precious information that can help to design more selective anticancer drugs.

Keywords: ER stress; autophagy; chemotherapy; dithiocarbamates; drug mechanism of action; gastric cancer; metal complexes; p53.

Figure 1

Chemical structures of the ligand K pipeDTC and the gold and ruthenium piperidine dithiocarbamato derivatives. The compounds’ names and their abbreviations are reported here.

Figure 2

(a) IC₅₀ values of the 3D-cultured HCT116 cell line. The average of IC₅₀ (red line) was calculated from three independent experiments; Cells were cultured for 7 days and then treated for 7 days. (b) The 3D spheroids after treatment with different concentrations (0 µM (NT)–10 µM) of [Ru₂(pipeDTC)₅]Cl.

Figure 3

Electrophoretic mobility of pJoJo plasmid DNA in presence of the different DTC derivatives and cisplatin. The plasmid was incubated with the complexes for 24 h at room temperature. For the gold and ruthenium compounds the following concentrations were realized: column 1–4: 15 μM, 30 μM, 45 μM, 60 μM, respectively. For cisplatin: column 1–4: 1 μM, 5 μM, 10 μM, 15 μM, respectively.

Figure 4

Expression of cleaved caspase-3, p53 and p62. Cisplatin was used as positive control (IC₅₀). IC₂₅, IC₅₀ and IC₇₅ were utilized to treat the cells. This image is representative of three independent experiments. The expression of proteins in AGS cells for [Au(pipeDTC)₂]Cl and in HCT116 cells for [Ru₂(pipeDTC)₃] is reported.

Figure 5

Expression of the autophagy biomarker p62 in HCT116 cells with and without co-treatment with pifithrin-α over 48 h. Cisplatin was used as positive control (IC₅₀). This image is representative of three independent experiments.

Figure 6

Expression of the ER stress biomarker ATF4 after treatment with Ru 2:5 in HCT116 cell lines. Cisplatin was used as positive control (IC₅₀). This image is representative of three independent experiments.