Anticancer Diiron Vinyliminium Complexes: A Structure-Activity Relationship Study

Chitosan/alginate polyelectrolyte complex hydrogels by additive manufacturing for in vitro 3D ovarian cancer modeling

Polyelectrolyte complexes (PECs) are self-assembled systems formed from oppositely charged polymers, used to create hydrogels for cell culture. This work was aimed at additive manufacturing 3D hydrogels made of a PEC between chitosan (Cs) and alginate, as well as their investigation for in vitro 3D ovarian cancer modeling. PEC hydrogels stability in cell culture medium demonstrated their suitability for long-term cell culture applications. Higher in vitro viability of two human ovarian cancer cell lines was detected at different time points on PEC hydrogels than on Cs hydrogels, used as a control. In addition, during the 63-day culture experiment, cells effectively colonized the scaffolds while retaining their aggressive tumor characteristics. A significantly lower sensitivity to cisplatin and eugenol, also when combined, was observed in the developed 3D ovarian cancer models, in comparison to what was achieved in relevant 2D cell cultures. The obtained results demonstrated therefore the suitability of the developed scaffolds for in vitro investigation of tumor modeling.

Aminocarbyne-Alkyne Coupling in Diruthenium Complexes: Exploring the Anticancer Potential of the Resulting Vinyliminium Complexes and Comparison with Diiron Homologues

New diruthenium complexes based on the scaffold Ru2Cp2(CO)2 (Cp = η5-C5H5) and containing a bridging vinyliminium ligand, [2a-d]CF3SO3, were synthesized through regioselective coupling of alkynes with an aminocarbyne precursor (85-90% yields). The reaction involving phenylacetylene proceeded with the formation of a diruthenacyclobutene byproduct, [4]CF3SO3 (10% yield). Complexes [2a-d]+ undergo partial alkyne extrusion in contact with alumina or CDCl3. All products were characterized by elemental analysis, infrared and multinuclear NMR spectroscopy, and single crystal X-ray diffraction in two cases. Complexes [2a-d]+ revealed an outstanding stability in DMEM cell culture medium at 37 °C (<1% degradation over 72 h). These complexes exhibited cytotoxicity in human colon colorectal adenocarcinoma HT-29 cells in the low micromolar range, with lower IC50 values than those obtained with the homologous diiron complexes previously reported. Evaluation of ROS (reactive oxygen species) production and O2 consumption rate (OCR) highlighted the higher potential of Ru2 complexes, compared to the Fe2 counterparts, to impact mitochondrial activity, with the heterometallic Ru2-ferrocenyl complex [2d]+ showing the best performance.

Configurationally regulated half-sandwich iridium(III)-ferrocene heteronuclear metal complexes: Potential anticancer agents

Half-sandwich iridium(III) (IrIII) complexes and ferrocenyl (Fc) derivatives are becoming the research hotspot in the field of anticancer because of their good bioactivity and unique anticancer mechanism different from platinum-based drugs. Then, a series of half-sandwich IrIII-Fc pyridine complexes have been prepared through the structural regulation in this study. The incorporation of half-sandwich IrIII complex with Fc unit successfully improves their anticancer activity, and the optimal performance (IrFc5) is almost 3-fold higher than that of cisplatin against A549 cells, meanwhile, which also shows better anti-proliferative activity against A549/DDP cells. Complexes can aggregate in the intracellular lysosome of A549 cells and induce lysosomal damage, disrupt the cell cycle, increase the level of intracellular reactive oxygen species, and eventually lead to cell apoptosis. Half-sandwich IrIII-Fc heteronuclear metal complexes possess a different anticancer mechanism from cisplatin, which can serve as a potential alternative to platinum-based drugs and show a good application prospect.

N-Indolyl diiron vinyliminium complexes exhibit antiproliferative effects in cancer cells associated with disruption of mitochondrial homeostasis, ROS scavenging, and antioxidant activity

The indole scaffold has been established as a key organic moiety for developing new drugs; on the other hand, a range of diiron bis-cyclopentadienyl complexes have recently emerged for their promising anticancer potential. Here, we report the synthesis of novel diiron complexes with an indole-functionalized vinyliminium ligand (2-5) and an indole-lacking analogue for comparative purposes (6), which were characterized by analytical and spectroscopic techniques. Complexes 2-6 are substantially stable in DMSO‑d6 and DMEM-d solutions at 37 °C (8% average degradation after 48 h) and display a balanced hydrophilic/lipophilic behaviour (LogPow values in the range -0.32 to 0.47), associated with appreciable water solubility. The complexes display selective antiproliferative potency towards several cancer cells in monolayer cultures, mainly in the low micromolar range, with reduced toxicity towards noncancerous epithelial cells. Thus, the cytotoxicity of the complexes is comparable to or better than clinically used metallopharmaceutical cisplatin. Comparing the antiproliferative activity obtained for complexes containing different ligands, we confirmed the importance of the indolyl group in the mechanism of antiproliferative activity of these complexes. Cell-based mechanistic studies suggest that the investigated diiron vinyliminium complexes (DVCs) show cytostatic rather than cytotoxic effects and subsequently induce a population of cells to undergo apoptosis. Furthermore, the molecular mechanism of action involves interactions with mitochondrial DNA and proteins, the reactive oxygen species (ROS)-scavenging properties and antioxidant activity of these complexes in cancer cells. This study highlights the importance of DVCs to their cancer cell activity and reinforces their prospective therapeutic potential as anticancer agents.

Pd(II) and Pt(II) Trinuclear Chelates with Spermidine: Selective Anticancer Activity towards TNBC-Sensitive and -Resistant to Cisplatin

Triple-negative breast cancer (TNBC) is one of the most aggressive forms of breast cancer and constitutes 10-20% of all breast cancer cases. Even though platinum-based drugs such as cisplatin and carboplatin are effective in TNBC patients, their toxicity and development of cancer drug resistance often hamper their clinical use. Hence, novel drug entities with improved tolerability and selectivity profiles, as well as the ability to surpass resistance, are needed. The current study focuses on Pd(II) and Pt(II) trinuclear chelates with spermidine (Pd3Spd2 and Pt3Spd2) for evaluating their antineoplastic activity having been assessed towards (i) cisplatin-resistant TNBC cells (MDA-MB-231/R), (ii) cisplatin-sensitive TNBC cells (MDA-MB-231) and (iii) non-cancerous human breast cells (MCF-12A, to assess the cancer selectivity/selectivity index). Additionally, the complexes' ability to overcome acquired resistance (resistance index) was determined. This study revealed that Pd3Spd2 activity greatly exceeds that displayed by its Pt analog. In addition, Pd3Spd2 evidenced a similar antiproliferative activity in both sensitive and resistant TNBC cells (IC50 values 4.65-8.99 µM and 9.24-13.34 µM, respectively), with a resistance index lower than 2.3. Moreover, this Pd compound showed a promising selectivity index ratio: >6.28 for MDA-MB-231 cells and >4.59 for MDA-MB-231/R cells. Altogether, the data presently gathered reveal Pd3Spd2 as a new, promising metal-based anticancer agent, which should be further explored for the treatment of TNBC and its cisplatin-resistant forms.

Chemical Modification of Auranofin Yields a New Family of Anticancer Drug Candidates: The Gold(I) Phosphite Analogues

A panel of four novel gold(I) complexes, inspired by the clinically established gold drug auranofin (1-Thio-β-D-glucopyranosatotriethylphosphine gold-2,3,4,6-tetraacetate), was prepared and characterized. All these compounds feature the replacement of the triethylphosphine ligand of the parent compound auranofin with a trimethylphosphite ligand. The linear coordination around the gold(I) center is completed by Cl^-, Br^-, I^- or by the thioglucose tetraacetate ligand (SAtg). The in-solution behavior of these gold compounds as well as their interactions with some representative model proteins were comparatively analyzed through ³¹PNMR and ESI-MS measurements. Notably, all panel compounds turned out to be stable in aqueous media, but significant differences with respect to auranofin were disclosed in their interactions with a few leading proteins. In addition, the cytotoxic effects produced by the panel compounds toward A2780, A2780R and SKOV-3 ovarian cancer cells were quantitated and found to be in the low micromolar range, since the IC₅₀ of all compounds was found to be between 1 μM and 10 μM. Notably, these novel gold complexes showed large and similar inhibition capabilities towards the key enzyme thioredoxin reductase, again comparable to those of auranofin. The implications of these results for the discovery of new and effective gold-based anticancer agents are discussed.

The choice of μ-vinyliminium ligand substituents is key to optimize the antiproliferative activity of related diiron complexes

Diiron vinyliminium complexes constitute a large family of organometallics displaying a promising anticancer potential. The complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(R3)C(R4)CN(R1)(R2)}]CF3SO3 (2a-c, 4a-d) were synthesized, assessed for their behavior in aqueous solutions (D2O solubility, Log Pow, stability in D2O/Me2SO-d6 mixture at 37°C over 48 h) and investigated for their antiproliferative activity against A2780 and A2780cisR ovarian cancer cell lines and the nontumoral one Balb/3T3 clone A31. Cytotoxicity data collected for 50 vinyliminium complexes were correlated with the structural properties (i.e. the different R1-R4 substituents) using the partial least squares methodology. A clear positive correlation emerged between the octanol-water partition coefficient and the relative antiproliferative activity on ovarian cancer cell lines, both of which appear as uncorrelated to the cancer cell selectivity. However, the different effects played by the R1-R4 substituents allow tracing guidelines for the development of novel, more effective compounds. Based on these results, three additional complexes (4p-r) were designed, synthesized and biologically investigated, revealing their ability to hamper thioredoxin reductase enzyme and to induce cancer cell production of reactive oxygen species.

Synthesis, chemical characterization, and biological evaluation of a novel auranofin derivative as an anticancer agent

A novel gold(I) complex inspired by the known medicinal inorganic compounds auranofin and thimerosal, namely ethylthiosalicylate(triethylphosphine)gold(I) (AFETT hereafter), was synthesized and characterised and its structure was resolved through X-ray diffraction. The solution behavior of AFETT and its interactions with two biologically relevant proteins (i.e. human serum albumin and haemoglobin) and with a synthetic dodecapeptide reproducing the C-terminal portion of thioredoxin reductase were comparatively analyzed through ³¹P NMR and ESI-MS. Remarkable binding properties toward these biomolecules were disclosed. Moreover, the cytotoxic effects produced by AFETT on two ovarian cancer cell lines (A2780 and A2780 R) and one colorectal cancer cell line (HCT116) were analyzed and found to be strong and nearly superimposable to those of auranofin. Interestingly, for both compounds, the ability to induce downregulation of vimentin expression in A2780 R cells was evidenced. Despite its close similarity to auranofin, AFETT is reported to exhibit some peculiar and distinctive features such as a lower lipophilicity, an increased water solubility and a faster reactivity towards the selected target biomolecules. These differences might confer to AFETT significant pharmaceutical and therapeutic advantages over auranofin itself.

Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

The diiron compounds [Fe₂Cp₂(CO)₂(μ-CO)(μ-CSEt)]CF₃SO₃, [1]CF₃SO₃, K[Fe₂Cp₂(CO)₃(CNCH₂CO₂)], K[2], [Fe₂Cp₂(CO)₂(μ-CO)(μ-CNMe₂)]NO₃, [3]NO₃, [Fe₂Cp₂(CO)₂(PTA){μ-CNMe(Xyl)}]CF₃SO₃, [4]CF₃SO₃, and [Fe₂Cp₂(CO)(μ-CO){μ-η:¹η³-C(4-C₆H₄CO₂H)CHCNMe₂}]CF₃SO₃, [5]CF₃SO₃, containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K[2], [3]NO₃, and [4]CF₃SO₃ were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]CF₃SO₃ were elucidated by ¹H NOESY NMR and single-crystal X-ray diffraction. Cell proliferation studies on human skin cancer (A431) and nontumoral embryonic kidney (HEK293) cells, with and without a 10-min exposure to low-power UV light (350 nm), highlighted the performance of the aminocarbyne [3]NO₃, nicknamed NIRAC (Nitrate-Iron-Aminocarbyne), which is substantially nontoxic in the dark but shows a marked photoinduced cytotoxicity. Spectroscopic (IR, UV-vis, NMR) measurements and the myoglobin assay indicated that the release of one carbon monoxide ligand represents the first step of the photoactivation process of NIRAC, followed by an extensive disassembly of the organometallic scaffold.

Anti-Staphylococcal Activity of the Auranofin Analogue Bearing Acetylcysteine in Place of the Thiosugar: An Experimental and Theoretical Investigation

Auranofin (AF, hereafter) is an orally administered chrysotherapeutic agent approved for the treatment of rheumatoid arthritis that is being repurposed for various indications including bacterial infections. Its likely mode of action involves the impairment of the TrxR system through the binding of the pharmacophoric cation [AuPEt₃]⁺. Accordingly, a reliable strategy to expand the medicinal profile of AF is the replacement of the thiosugar moiety with different ligands. Herein, we aimed to prepare the AF analogue bearing the acetylcysteine ligand (AF-AcCys, hereafter) and characterize its anti-staphylococcal activity. Biological studies revealed that AF-AcCys retains an antibacterial effect superimposable with that of AF against Staphylococcus aureus, whereas it is about 20 times less effective against Staphylococcus epidermidis. Bioinorganic studies confirmed that upon incubation with human serum albumin, AF-AcCys, similarly to AF, induced protein metalation through the [AuPEt₃]⁺ fragment. Additionally, AF-AcCys appeared capable of binding the dodecapeptide Ac-SGGDILQSGCUG-NH₂, corresponding to the tryptic C-terminal fragment (488–499) of hTrxR. To shed light on the pharmacological differences between AF and AF-AcCys, we carried out a comparative experimental stability study and a theoretical estimation of bond dissociation energies, unveiling the higher strength of the Au–S bond in AF-AcCys. From the results, it emerged that the lower lipophilicity of AF-AcCys with respect to AF could be a key feature for its different antibacterial activity. The differences and similarities between AF and AF-AcCys are discussed, alongside the opportunities and consequences that chemical structure modifications imply.

Anti-Staphylococcal Activity of the Auranofin Analogue Bearing Acetylcysteine in Place of the Thiosugar: An Experimental and Theoretical Investigation

Auranofin (AF, hereafter) is an orally administered chrysotherapeutic agent approved for the treatment of rheumatoid arthritis that is being repurposed for various indications including bacterial infections. Its likely mode of action involves the impairment of the TrxR system through the binding of the pharmacophoric cation [AuPEt₃]⁺. Accordingly, a reliable strategy to expand the medicinal profile of AF is the replacement of the thiosugar moiety with different ligands. Herein, we aimed to prepare the AF analogue bearing the acetylcysteine ligand (AF-AcCys, hereafter) and characterize its anti-staphylococcal activity. Biological studies revealed that AF-AcCys retains an antibacterial effect superimposable with that of AF against Staphylococcus aureus, whereas it is about 20 times less effective against Staphylococcus epidermidis. Bioinorganic studies confirmed that upon incubation with human serum albumin, AF-AcCys, similarly to AF, induced protein metalation through the [AuPEt₃]⁺ fragment. Additionally, AF-AcCys appeared capable of binding the dodecapeptide Ac-SGGDILQSGCUG-NH₂, corresponding to the tryptic C-terminal fragment (488-499) of hTrxR. To shed light on the pharmacological differences between AF and AF-AcCys, we carried out a comparative experimental stability study and a theoretical estimation of bond dissociation energies, unveiling the higher strength of the Au-S bond in AF-AcCys. From the results, it emerged that the lower lipophilicity of AF-AcCys with respect to AF could be a key feature for its different antibacterial activity. The differences and similarities between AF and AF-AcCys are discussed, alongside the opportunities and consequences that chemical structure modifications imply.

When ferrocene and diiron organometallics meet: triiron vinyliminium complexes exhibit strong cytotoxicity and cancer cell selectivity

Robust and versatile cationic triiron complexes, obtained from the assembly of ferrocenyl with a di-organoiron structure, display an outstanding cytotoxicity profile, which may be related to redox processes provided by the two metallic components.

N-Heterocyclic Carbene Iron Complexes as Anticancer Agents: In Vitro and In Vivo Biological Studies

Cisplatin and its derivatives are commonly used in chemotherapeutic treatments of cancer, even though they suffer from many toxic side effects. The problems that emerge from the use of these metal compounds led to the search for new complexes capable to overcome the toxic side effects. Here, we report the evaluation of the antiproliferative activity of Fe(II) cyclopentadienyl complexes bearing n-heterocyclic carbene ligands in tumour cells and their in vivo toxicological profile. The in vitro antiproliferative assays demonstrated that complex Fe1 displays the highest cytotoxic activity both in human colorectal carcinoma cells (HCT116) and ovarian carcinoma cells (A2780) with IC₅₀ values in the low micromolar range. The antiproliferative effect of Fe1 was even higher than cisplatin. Interestingly, Fe1 showed low in vivo toxicity, and in vivo analyses of Fe1 and Fe2 compounds using colorectal HCT116 zebrafish xenograft showed that both reduce the proliferation of human HCT116 colorectal cancer cells in vivo.