Au2phen and Auoxo6, Two Dinuclear Oxo-Bridged Gold(III) Compounds, Induce Apoptotic Signaling in Human Ovarian A2780 Cancer Cells

Some remarks on the biological application of gold(III) complexes

Gold(III) complexes are widely studied as antitumor agents and show good results. The interaction with biologically active thiols (thiomalate, cysteine, glutathione (GSH) and human serum albumin) of a number of gold(III) complexes with N-containing polydentate ligands in aqueous solution with pH 7.4 and 0.2 M NaCl was studied. Complexes with 1,10-phenanthroline and 2,2'-bipyridyl, Au(phen)(OH)2+ and Au(bipy)(OH)2+, react fast with an excess of any of these thiols and in less than a few seconds transform into gold(I) bis-thiolate complexes. For complexes with deprotonated ethylenediamine and diethylenetriamine, Au(en)(en-H)2+ and Au(dien-H)(Cl,OH)+, at a significant excess of GSH, a relatively long-lived gold(III) complex AuIII(GSH)iLj is formed. At t = 37 °C, it transforms into the gold(I) bis-thiolate complex Au(GSH)2 by 90% in 4 h. However, for other thiols, the rate of decomposition of similar complexes is about 10 times higher. Some other complexes were also considered. In all cases, a fairly fast reduction of gold(III) to gold(I) occurs with the formation of the gold(I) bis-thiolates.

Recent development of gold(I) and gold(III) complexes as therapeutic agents for cancer diseases

Metal complexes have demonstrated significant antitumor activities and platinum complexes are well established in the clinical application of cancer chemotherapy. However, the platinum-based treatment of different types of cancers is massively hampered by severe side effects and resistance development. Consequently, the development of novel metal-based drugs with different mechanism of action and pharmaceutical profile attracts modern medicinal chemists to design and synthesize novel metal-based agents. Among non-platinum anticancer drugs, gold complexes have gained considerable attention due to their significant antiproliferative potency and efficacy. In most situations, the gold complexes exhibit anticancer activities by targeting thioredoxin reductase (TrxR) or other thiol-rich proteins and enzymes and trigger cell death via reactive oxygen species (ROS). Interestingly, gold complexes were recently reported to elicit biochemical hallmarks of immunogenic cell death (ICD) as an ICD inducer. In this review, the recent progress of gold(I) and gold(III) complexes is comprehensively summarized, and their activities and mechanism of action are documented.

The effects of two gold-N-heterocyclic carbene (NHC) complexes in ovarian cancer cells: a redox proteomic study

PURPOSE

Ovarian cancer is the fifth leading cause of cancer-related deaths in women. Standard treatment consists of tumor debulking surgery followed by platinum and paclitaxel chemotherapy; yet, despite the initial response, about 70-75% of patients develop resistance to chemotherapy. Gold compounds represent a family of very promising anticancer drugs. Among them, we previously investigated the cytotoxic and pro-apoptotic properties of Au(NHC) and Au(NHC)2PF6, i.e., a monocarbene gold(I) complex and the corresponding bis(carbene) complex. Gold compounds are known to alter the redox state of cells interacting with free cysteine and selenocysteine residues of several proteins. Herein, a redox proteomic study has been carried out to elucidate the mechanisms of cytotoxicity in A2780 human ovarian cancer cells.

METHODS

A biotinylated iodoacetamide labeling method coupled with mass spectrometry was used to identify oxidation-sensitive protein cysteines.

RESULTS

Gold carbene complexes cause extensive oxidation of several cellular proteins; many affected proteins belong to two major functional classes: carbohydrate metabolism, and cytoskeleton organization/cell adhesion. Among the affected proteins, Glyceraldehyde-3-phosphate dehydrogenase inhibition was proved by enzymatic assays and by ESI-MS studies. We also found that Au(NHC)2PF6 inhibits mitochondrial respiration impairing complex I function. Concerning the oxidized cytoskeletal proteins, gold binding to the free cysteines of actin was demonstrated by ESI-MS analysis. Notably, both gold compounds affected cell migration and invasion.

CONCLUSIONS

In this study, we deepened the mode of action of Au(NHC) and Au(NHC)2PF6, identifying common cellular targets but confirming their different influence on the mitochondrial function.

Effects of trans-(±)-kusunokinin on chemosensitive and chemoresistant ovarian cancer cells

Ovarian cancer ranks eighth in cancer incidence and mortality among women worldwide. Cisplatin-based chemotherapy is commonly used for patients with ovarian cancer. However, the clinical efficacy of cisplatin is limited due to the occurrence of adverse side effects and development of cancer chemoresistance during treatment. Trans-(±)-kusunokinin has been previously reported to inhibit cell proliferation and induce cell apoptosis in various cancer cell types, including breast, colon and cholangiocarcinoma. However, the potential effects of (±)-kusunokinin on ovarian cancer remains unknown. In the present study, chemosensitive ovarian cancer cell line A2780 and chemoresistant ovarian cancer cell lines A2780cis, SKOV-3 and OVCAR-3 were treated with trans-(±)-kusunokinin to investigate its potential effects. MTT, colony formation, apoptosis and multi-caspase assays were used to determine cytotoxicity, the ability of single cells to form colonies, induction of apoptosis and multi-caspase activity, respectively. Moreover, western blot analysis was performed to determine the proteins level of topoisomerase II, cyclin D1, CDK1, Bax and p53-upregulated modulator of apoptosis (PUMA). The results demonstrated that trans-(±)-kusunokinin exhibited the strongest cytotoxicity against A2780cis cells with an IC50 value of 3.4 µM whilst also reducing the colony formation of A2780 and A2780cis cells. Trans-(±)-kusunokinin also induced the cells to undergo apoptosis and increased multi-caspase activity in A2780 and A2780cis cells. This compound significantly downregulated topoisomerase II, cyclin D1 and CDK1 expression, but upregulated Bax and PUMA expression in both A2780 and A2780cis cells. In conclusion, trans-(±)-kusunokinin suppressed ovarian cancer cells through the inhibition of colony formation, cell proliferation and the induction of apoptosis. This pure compound could be a potential targeted therapy for ovarian cancer treatment in the future. However, studies in an animal model and clinical trial need to be performed to support the efficacy and safety of this new treatment.

In Vitro Anti-SARS-CoV-2 Activity of Selected Metal Compounds and Potential Molecular Basis for Their Actions Based on Computational Study

Metal-based drugs represent a rich source of chemical substances of potential interest for the treatment of COVID-19. To this end, we have developed a small but representative panel of nine metal compounds, including both synthesized and commercially available complexes, suitable for medical application and tested them in vitro against the SARS-CoV-2 virus. The screening revealed that three compounds from the panel, i.e., the organogold(III) compound Aubipyc, the ruthenium(III) complex KP1019, and antimony trichloride (SbCl₃), are endowed with notable antiviral properties and an acceptable cytotoxicity profile. These initial findings prompted us to perform a computational study to unveil the likely molecular basis of their antiviral actions. Calculations evidenced that the metalation of nucleophile sites in SARS-CoV-2 proteins or nucleobase strands, induced by Aubipyc, SbCl₃, and KP1019, is likely to occur. Remarkably, we found that only the deprotonated forms of Cys and Sec residues can react favorably with these metallodrugs. The mechanistic implications of these findings are discussed.