Targeting Antioxidant Pathways with Ferrocenylated N-Heterocyclic Carbene Supported Gold(I) Complexes in A549 Lung Cancer Cells

Cationic and Neutral N-Heterocyclic Carbene Gold(I) Complexes: Cytotoxicity, NCI-60 Screening, Cellular Uptake, Inhibition of Mammalian Thioredoxin Reductase, and Reactive Oxygen Species Formation

A structurally diverse library of 14 gold(I) cationic bis(NHC) and neutral mono(NHC) complexes (NHC: N-heterocyclic carbene) was synthesized and characterized in this work. Four of them were new cationic gold(I) complexes containing functionalized NHCs, and their X-ray crystal structures are presented herein. All of the complexes were investigated for their anticancer activities in four cancer cell lines, including a cisplatin-resistant variant, and a noncancerous cell line. Seven of the cationic gold(I) complexes were found to display high and specific cytotoxic activities toward cancer cells. Two of them were even able to overcome cisplatin resistance. Two highly potent cationic complexes (11 and 15) were also submitted to the NCI-60 cancer panel for further cytotoxicity evaluation. Complex 15 showed a surprisingly high potency toward leukemia among the nine examined cancer subtypes, particularly toward the CCRF-CEM leukemia cell line with a concentration for 50 % inhibition of growth down to 79.4 nm. In addition, cationic complex 13, which demonstrated a remarkable cytotoxicity against hepatocellular carcinoma, was selected to obtain insight into the mechanistic aspects in HepG2 cells. Cellular uptake measurements were indicative of good bioavailability. By various biochemical assays, this complex was found to effectively inhibit thioredoxin reductase and its cytotoxicity toward HepG2 cells was found to be reactive oxygen species dependent.

Anti-tumour active gold(i), palladium(ii) and ruthenium(ii) complexes with thio- and selenoureato ligands: a comparative study

We report the results of a comparative study of the biological activity of a series of gold(i), palladium(ii) and ruthenium(ii) complexes containing deprotonated thio- and selenoureato ligands. A library of compounds was prepared and characterised by spectroscopic methods and the solid-state structures of several derivatives were determined by single crystal X-ray diffraction. The in vitro activity of these compounds was evaluated in mammary and ovarian carcinoma, acute lymphatic and acute and chronic myeloid leukemia cell lines. At lower concentrations Ru- and Pd-containing compounds displayed stronger anti-cancer effects than the gold compounds. In all cases, the selenium derivatives proved to be more active than the corresponding sulfur compounds.

Synthesis and biological evaluation of ferrocene-based cannabinoid receptor 2 ligands

Ferrocene analogs of known fatty acid amide hydrolase inhibitors and CB2 ligands have been synthesized and characterized spectroscopically and crystallographically. The resulting bio-organometallic isoxazoles were assayed for their effects on CB1 and CB2 receptors as well as on fatty acid amide hydrolase. None had any fatty acid amide hydrolase activity but compound 3, 5-(2-(pentyloxy)phenyl)-N-ferrocenylisoxazole-3-carboxamide, was found to be a potent CB2 ligand (Ki = 32.5 nM).

New insights in Au-NHCs complexes as anticancer agents

Within the research field of antitumor metal-based agents alternative to platinum drugs, gold(I/III) coordination complexes have always been in the forefront due mainly to the familiarity of medicinal chemists with gold compounds, whose application in medicine goes back in the ancient times, and to the rich chemistry shown by this metal. In the last decade, N-heterocyclic carbene ligands (NHC), a class of ligands that largely resembles the chemical properties of phosphines, became of interest for gold(I) medicinal applications, and since then, the research on NHC-gold(I/III) coordination complexes as potential antiproliferative agents boosted dramatically. Different classes of gold(I/III)-NHC complexes often showed an outstanding in vitro antiproliferative activity, however up to now very few in vivo data have been reported to corroborate the in vitro results. This review summarizes all achievements in the field of gold (I/III) complexes comprising NHC ligands proposed as potential antiproliferative agents in the period 2004-2016, and critically analyses biological data (mainly IC₅₀ values) in relation to the chemical structures of Au compounds. The state of art of the in vivo studies so far described is also reported.

Isoelectronic Pt(ii)– and Au(iii)–N-heterocyclic carbene complexes: a structural and biological comparison

To differentiate the intrinsic biological activities displayed by Pt vs. Au reagents, a series of square planar carbene complexes were compared.

Screening of ferrocenyl–phosphines identifies a gold-coordinated derivative as a novel anticancer agent for hematological malignancies

The development of new organometallic compounds as anticancer agents is currently an active area of research. Here, we report the design, synthesis and characterization of a panel of 10 new ferrocenyl–phosphine derivatives (FD1–FD10) and the analysis of their anti-proliferative activities in hematolymphoid cells representing non-Hodgkin cutaneous T-cell lymphoma (CTCL). The gold-coordinated ferrocenyl–phosphine complex FD10 exhibited a significant and dose-dependent cytotoxicity in 4 different CTCL cell lines – HuT78, HH, MJ and MyLa. FD10 concentrations causing 50% cell growth inhibition (IC₅₀) of HuT78, HH, MJ and MyLa cells at 24 h were recorded to be 5.55 ± 0.20, 7.80 ± 0.09, 3.16 ± 0.10 and 6.46 ± 0.24 μM respectively. Further mechanistic studies showed that FD10 induced apoptosis in CTCL cells by an intrinsic pathway mediated via the activation of caspase-3 and poly(ADP-ribose)polymerase. It suppressed the expression and activity of STAT3 oncoprotein in CTCL cells. FD10 caused robust G0/G1 phase cell cycle arrest and reduced the expression levels of Akt S473 phosphorylation and c-Myc, both are key cell cycle regulator proteins. Taken together, this study highlights anticancer properties of the ferrocenyl–phosphine gold organometallic complex FD10 and suggests that further development of this novel class of molecule may contribute to new drug discovery for certain hematolymphoid malignancies.

Development of organometallic compounds as novel anticancer agents.

Dual targeting of the cancer antioxidant network with 1,4-naphthoquinone fused Gold(i) N-heterocyclic carbene complexes

To achieve a systems-based approach to targeting the antioxidant pathway, 1,4-naphthoquinone annulated N-heterocyclic carbene (NHC) [bis(1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i)] [silver(i) dichloride] (1), [bis(1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i)] chloride (2), and 1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i) chloride (3)) were designed, synthesized, and tested for biological activity in a series of human cancer cell lines. The solution phase of complexes 1-3 were assigned using several spectroscopy techniques, including NMR spectroscopic analysis. Complexes 1 and 3 were further characterized by single crystal X-ray diffraction analysis. Electrochemical and spectroelectrochemical studies revealed that quinone reductions are reversible and that the electrochemically generated semiquinone and quinone dianions are stable under these conditions. Complex 1, containing two NHC-quinone moieties (to accentuate exogenous ROS via redox cycling) centered around a Au(i) center (to inactivate thioredoxin reductase (TrxR) irreversibly), was found to inhibit cancer cell proliferation to a much greater extent than the individual components (i.e., Au(i)-NHC alone or naphthoquinone alone). Treatment of A549 lung cancer cells with 1 produced a 27-fold increase in exogenous reactive oxygen species (ROS) which was found to localize to the mitochondria. The inhibition of TrxR, an essential mediator of ROS homeostasis, was achieved in the same cell line at low administrated concentrations of 1. TrxR inhibition by 1 was similar to that of auranofin, a gold(i) containing complex known to inhibit TrxR irreversibly. Complex 1 was found to induce cell death via an apoptotic mechanism as confirmed by annexin-V staining. Complex 1 was demonstrated to be efficacious in zebrafish bearing A549 xenografts. These results provide support for the suggestion that a dual targeting approach that involves reducing ROS tolerance while concurrently increasing ROS production can perturb antioxidant homeostasis, enhance cancer cell death in vitro, and reduce tumor burden in vivo, as inferred from preliminary zebra fish model studies.

Biscarbene gold(i) complexes: structure-activity-relationships regarding antibacterial effects, cytotoxicity, TrxR inhibition and cellular bioavailability

A series of gold(i) complexes with two N-heterocyclic carbene ligands (biscarbene gold complexes) were prepared and evaluated for their effects against cancer cells and pathogenic bacteria. Proliferation inhibition was observed in cancer cells and in Gram-positive bacteria, whereas Gram-negative bacteria were less sensitive towards the compounds. The protein binding and cellular uptake were quantified and the combined results indicated a strong correlation between cellular bioavailability and antiproliferative effects. The biscarbene gold complexes inhibited bacterial and mammalian TrxRs with low to moderate potency. However, based on the obtained structure-activity-relationships and the high cellular accumulation levels, TrxR inhibition can be considered as a relevant contributor to the cellular pharmacology of biscarbene gold(i) complexes.

Ferrocene–cinchona hybrids with triazolyl-chalcone linkers act as pro-oxidants and sensitize human cancer cell lines to paclitaxel

Epimeric ferrocene–quinidine hybrids with triazolyl-chalcone linkers act as pro-oxidative agents and autophagy modulators in paclitaxel resistant cancer cells.

First Crystal Structure for a Gold Carbene-Protein Adduct

The X-ray structure of the adduct formed in the reaction between the gold N-heterocyclic carbene compound Au(NHC)Cl (with NHC = 1-butyl-3-methyl-imidazole-2-ylidene) and the model protein thaumatin is reported here. The structure reveals binding of Au(NHC)(+) fragments to distinct protein sites. Notably, binding of the gold compound occurs at lysine side chains and at the N-terminal tail; the metal binds the protein after releasing Cl(-) ligand, but retaining NHC fragment.

Anticancer metal drugs and immunogenic cell death

Conventional chemotherapeutics, but also innovative precision anticancer compounds, are commonly perceived to target primarily the cancer cell compartment. However, recently it was discovered that some of these compounds can also exert immunomodulatory activities which might be exploited to synergistically enhance their anticancer effects. One specific phenomenon of the interplay between chemotherapy and the anticancer immune response is the so-called "immunogenic cell death" (ICD). ICD was discovered based on a vaccination effect exerted by cancer cells dying from pretreatment with certain chemotherapeutics, termed ICD inducers, in syngeneic transplantation mouse models. Interestingly, only a minority of drugs is able to trigger ICD without a clear-cut relation to chemical structures or their primary modes-of-action. Nevertheless, generation of reactive oxygen species (ROS) and induction of endoplasmic reticulum (ER) stress are clearly linked to ICD. With regard to metal drugs, oxaliplatin but not cisplatin is considered a bona fide ICD inducer. Taken into account that several experimental metal compounds are efficient ROS and ER stress mediators, presence of potent ICD inducers within the plethora of novel metal complexes seems feasible and has occasionally been reported. In the light of recent successes in cancer immunotherapy, here we review existing literature regarding anticancer metal drugs and ICD induction. We recommend a more profound investigation of the immunogenic features of experimental anticancer metal drugs.

Metal complexes with di(N-heterocyclic carbene) ligands bearing a rigid ortho-, meta or para-phenylene bridge

Ag(i) complexes with diNHC ligands are efficient transmetalating agents towards transition metals.