A gold(I) phosphine complex containing a naphthalimide ligand functions as a TrxR inhibiting antiproliferative agent and angiogenesis inhibitor

Use of zebrafish in chemical biology and drug discovery

The zebrafish (Danio rerio) is a small, tropical, freshwater fish that has emerged as a powerful vertebrate model organism for studying genetics and development. Its small size, transparency, cost-effectiveness, close genome homology to humans compared with invertebrates, and capacity for genetic manipulation are all valuable attributes for an excellent animal model. There are additional advantages for using zebrafish specifically in drug discovery, including ease of exposure to chemicals in water. In effect, zebrafish can bridge a gap between in vitro and mammalian work, reducing the use of larger animals and attrition rates. In the drug-discovery process, zebrafish can be used at many stages, including target identification and validation, identification of lead compounds, studying structure-activity relationships and drug safety profiling. In this review, we highlight the potential for the zebrafish model to make the drug-discovery process simpler, more effective and cost-efficient.

Gold(I) N-heterocyclic carbene complexes with naphthalimide ligands as combined thioredoxin reductase inhibitors and DNA intercalators

Organometallic conjugates consisting of a gold(I) N-heterocyclic carbene (NHC) moiety and a naphthalimide were prepared and investigated as cytotoxic agents that interact with both DNA and the disulfide reductase enzyme thioredoxin reductase (TrxR). The complexes were potent DNA intercalators related to their naphthalimide partial structure, inhibited TrxR as a consequence of the incorporation of the gold(I) moiety, and triggered efficient cytotoxic effects in MCF-7 breast and HT-29 colon adenocarcinoma cells. Strong effects on tumor cell metabolism were noted for the most cytotoxic complex, chlorido[1-(3'-(4''-ethylthio-1'',8''-naphthalimid-N''-yl))-propyl-3-methyl-imidazol-2-ylidene]gold(I) (4 d). In conclusion, the conjugation of naphthalimides with gold(I) NHC moieties provided a useful strategy for the design of bioorganometallic anticancer agents with multiple modes of action.

Fluorescent silver(I) and gold(I)-N-heterocyclic carbene complexes with cytotoxic properties: mechanistic insights

Silver(I) and gold(I)-N-heterocyclic carbene (NHC) complexes bearing a fluorescent anthracenyl ligand were examined for cytotoxicity in normal and tumor cells. The silver(I) complex exhibits greater cytotoxicity in tumor cells compared with normal cells. Notably, in cell extracts, this complex determines a more pronounced inhibition of thioredoxin reductase (TrxR), but it is ineffective towards glutathione reductase (GR). Both gold and silver complexes lead to oxidation of the thioredoxin system, the silver(I) derivative being particularly effective. In addition, the dimerization of peroxiredoxin 3 (Prx3) was also observed, demonstrating the ability of these compounds to reach the mitochondrial target. The fluorescence microscopy visualization of the subcellular distribution of the complexes shows a larger diffusion of these molecules in tumor cells with respect to normal cells.

Novel fluorescent 1,8-naphthalimide derivatives containing thiophene and pyrazole moieties: synthesis by direct C-H arylation and evaluation of photophysical and electrochemical properties

A series of novel 1,8-naphthalimide derivatives containing thiophene and pyrazole moities were synthesized by direct Pd-catalyzed C-H arylation and then characterized by (1)H NMR, (13)C NMR, MALDI-HRMS, and elementary analysis. The photophysical and electrochemical properties of the derivatives were also investigated. All compounds have green emission both in diluted CH2Cl2 solution and solid film. The cyclic voltammetry (CV) measurements showed that the target compounds had a lowest unoccupied molecular orbital (LUMO) range from -3.49 eV to -3.29 eV and a highest occupied molecular orbital (HOMO) range from -6.04 eV to -5.81 eV. Quantum chemical calculations were performed to obtain the optimized ground-state geometry as well as the spatial distributions of the HOMO, LUMO levels of the compounds.

Apoptotic events induced by maleimides on human acute leukemia cell lines

Cyclic imides are known for their antitumor activity, especially the naphthalimide derivatives, such as Mitonafide and Amonafide. Recently, we have demonstrated the cytotoxic effect of a series of naphthalimide derivatives against B16F10 melanoma cells. On the basis of this fact, we have developed a study starting from the synthesis of different cyclic imides and the evaluation of their cytotoxic properties on human acute leukemia cells (K562 and Jurkat). Initially, a screening test was conducted to select the compound with the best cytotoxic effect, using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. After this selection, structural modifications were performed in the most active compound to obtain five more derivatives. All compounds presented a good cytotoxic effect. The results of cell cycle analysis, fluorescence microscopy, and Annexin V-FITC assay confirmed that the cells observed in the sub-G0/G1 phase were undergoing apoptosis. From this set of results, cyclic imides 8, 10, and 12 were selected for the evaluation of the mechanisms involved in the apoptotic process. The results demonstrate the involvement of the intrinsic pathway of apoptosis, evidenced by the reduction in mitochondrial potential, an increase in the level of AIF protein expression, a decreased level of expression of anti-apoptotic Bcl-2 protein, and an increased level of expression of pro-apoptotic protein Bax in both K562 and Jurkat cells treated with cyclic imides (8, 10, and 12). Furthermore, cyclic imides 8 and 10 caused an increase in the level of Fas expression in Jurkat cells, indicating the additional involvement of the extrinsic apoptosis pathway. The compounds (8, 10, and 12) also caused a decreased level of expression of anti-apoptotic protein survivin. The biological effects observed with these cyclic imide derivatives in this study suggest promising applications against acute leukemia.

Effect of 2-chloro-substitution of adenine moiety in mixed-ligand gold(I) triphenylphosphine complexes on anti-inflammatory activity: the discrepancy between the in vivo and in vitro models

A series of gold(I) triphenylphosphine (PPh₃) complexes (1–9) involving 2-chloro-N6-(substituted-benzyl)adenine derivatives as N-donor ligands was synthesized and thoroughly characterized by relevant methods, including electrospray-ionization (ESI) mass spectrometry and multinuclear NMR spectroscopy. The anti-inflammatory and antiedematous effects of three representatives 1, 5 and 9 were evaluated by means of in vitro model based on the expression of pro- and anti-inflammatory cytokines and influence of the complexes on selected forms of matrix metalloproteinases secreted by LPS-activated THP-1 monocytes and in vivo model evaluating the antiedematous effect of the complexes in the carrageenan-induced rat hind-paw edema model. In addition to the pharmacological observations, the affected hind paws were post mortem subjected to histological and immunohistochemical evaluations. The results of both in vivo and ex vivo methods revealed low antiedematous and anti-inflammatory effects of the complexes, even though the in vitro model identified them as promising anti-inflammatory acting compounds. The reason for this discrepancy lies probably in low stability of the studied complexes in biological environment, as demonstrated by the solution interaction studies with sulfur-containing biomolecules (cysteine and reduced glutathione) using the ESI mass spectrometry.

Some new [(thione)2Au(diamine)]Cl3 complexes: synthesis, spectroscopic characterization, computational and in vitro cytotoxic studies

Recent advances in oncology are focused on developing new complexes of gold(III) with various ligands that show augmented anti-proliferative potential and reduced toxicity as compared to cis-platin. In this study, new Au(III) complexes of the type [(thione)2Au(diamine)]Cl3 are reported, where thione=1,3-imidazolidine-2-thione (Imt), 1,3-Diazinane-2-thione (Diaz) and diamine=1,2-diaminoethane (en), 1,3-diaminopropane (pn) or 1,4-diaminobutane (bn). The solid state IR as well as (13)C and (15)N NMR data indicate that Au(III) center is bonded via sulfur of thiocarbonyl SC site of the thiones and also chelated by the diamines from the trans side of coordinated thiones. Spectroscopic data are evaluated by comparisons with calculated data from the built and optimized structure by GAUSSIAN 09 at the RB3LYP level with LanL2DZ bases set. These new Au(III) complexes based on mixed thione and diamine ligands are very similar to the square planar structure of tetracoordinate [Au(en)2]Cl3complex. In this study, cytotoxicity data for these gold(III) complexes against C6 glioma cell lines are also reported, and the results indicate some complexes have cytotoxicity comparable to cis-platin.

Film/contact loading method improves the encapsulated amount of triazene anticancer compounds in polymeric micelles

The development of organic solvent-free methods for the encapsulation of hydrophobic molecules is necessary for advances in micelle-mediated drug delivery. In this study we investigated the film/contact approach in which the use of organic solvents is limited to the preparation of a dry film before encapsulation. Unloaded micelles of five structurally related block copolymers were placed in contact with thin homogeneous films of two hydrophobic triazene anticancer compounds (1-(4-amidophenyl)-3-(4-acetylphenyl)triazene (1) and corresponding triazenido complex with triphenylphosphanegold(I) fragment (2)). The micelle surface becomes saturated with the drug, which eventually penetrates as a front into the core. Because the drug interacts with both the shell and the core microenvironments of micelle during the process, the maximum loading capacities were very sensitive to block copolymer micelle composition, ranging from 2.2 to 20.4% (wt./wt. of polymer). We conclude that micelles with poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) cores are the best option for the encapsulation of triazene compounds because i) they are prepared in absence of organic phase; ii) the drug concentration in the particles is high enough for a therapeutic effect and iii) the responsiveness properties of PDPA is appropriate for practical applications in pH-triggered drug release systems.

Dual anticancer activity in a single compound: visible-light-induced apoptosis by an antiangiogenic iridium complex

A metal complex is identified in which the metal fulfills two independent functions: as a structural scaffold for the specific molecular recognition of protein kinases resulting in antiangiogenic properties, together with a visible-light-induced photoreactivity triggering apopotosis in cancer cells.

Small molecule inhibitors of mammalian thioredoxin reductase

Mammalian thioredoxin reductases (TrxRs) are a family of NADPH-dependent flavoproteins with a penultimate selenocysteine residue at the carboxy-terminus. Besides their native substrate thioredoxins (Trx), the enzymes show a broad substrate specificity, at least partially, because of the C-terminal redox-active site that is easily accessible in the reduced form. TrxRs are ubiquitous in all kinds of cells and have a critical role in regulating intracellular redox signaling. In recent years, a wealth of evidence has revealed that overactivation/dysfunction of TrxRs is closely related to various diseases, especially in tumor development, and thus the past decades have witnessed an expanding interest in finding TrxRs inhibitors, which might be promising agents for cancer chemotherapy. Herein we reviewed the small molecule inhibitors of mammalian TrxRs, with an emphasis on those that have potential anticancer activity. This review includes the nonpatent references up to 2010 that deal with mammalian TrxR inhibitors.

Comparative in vitro evaluation of N-heterocyclic carbene gold(I) complexes of the benzimidazolylidene type

Gold(I) complexes with a 1,3-diethylbenzimidazol-2-ylidene N-heterocyclic carbene (NHC) ligand of the type NHC-Au-L (L=-Cl, -NHC, or -PPh3) were comparatively evaluated as thioredoxin reductase (TrxR) inhibitors and antimitochondrial anticancer agents. Different effects were noted in various biochemical assays (e.g., inhibition of TrxR, cellular and mitochondrial uptake, or effects on mitochondrial membrane potential), and this was related to properties of the complexes such as bond dissociation energies and overall charge. Remarkable antiproliferative effects, a strong induction of apoptosis, and enhancement of reactive oxygen species (ROS) formation as well as other effects on tumor cell metabolism confirmed the promising potential of the complexes as novel anticancer chemotherapeutics.

Iminophosphorane-organogold(III) complexes induce cell death through mitochondrial ROS production

Gold compounds are being investigated as potential antitumor drugs. Some gold(III) derivatives have been shown to induce cell death in solid tumors but their mechanism of action differs from that of cisplatin, since most of these compounds do not bind to DNA. We have explored cellular events triggered by three different iminophosphorane-organogold(III) compounds in leukemia cells (a neutral compound with two chloride ligands [Au{κ(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}Cl(2)] 1, and two cationic compounds with either a dithiocarbamate ligand [Au{κ(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}(S(2)CN-Me(2))]PF(6)2, or a water-soluble phosphine and a chloride ligand [Au{κ(2)-C,N-C(6)H(4)(PPh(2)=N(C(6)H(5))-2}(P{Cp(m-C(6)H(4)-SO(3)Na)(2)}(3)) Cl]PF(6)3). All three compounds showed higher toxicity against leukemia cells when compared to normal T-lymphocytes. Compounds 1 and 2 induced both necrosis and apoptosis, while 3 was mainly apoptotic. Necrotic cell death induced by 1 and 2 was Bax/Bak- and caspase-independent, while apoptosis induced by 3 was Bax/Bak-dependent. Reactive oxygen species (ROS) production at the mitochondrial level was a critical step in the antitumor effect of these compounds.

Recent Advances in Mapping the Sub-cellular Distribution of Metal-Based Anticancer Drugs

There are increasing reports of novel metal-based chemotherapeutics that have either improved cancer cell selectivity, or alternative mechanisms of action, to existing anticancer drugs, and techniques are required for determining their sub-cellular molecular targets. Imaging methods offer many distinct advantages over destructive fractionation techniques, including the preservation of useful morphological information; however, mapping the intracellular distribution of metal ions inside tumour cells still remains challenging. Recent advances in three modes of imaging are discussed in this review, with a particular focus on the application to metal-based cancer chemotherapy – fluorescence microscopy, electron microscopy (including energy-filtered transmission electron microscopy (EFTEM)), and a new technique, Nano-scale secondary ion mass spectrometry (NanoSIMS).

Copper, gold and silver compounds as potential new anti-tumor metallodrugs

Although platinum-based drugs such as cisplatin are powerful anticancer agents, they have undesirable side effects and are effective against only a few kinds of cancers. There is, therefore, a need for new drugs with an improved spectrum of efficacy and lower toxicity. Complexes of copper, gold and silver (coinage metals) are potential candidates to fullfill this need. The development of anticancer drugs based on these metals is currently a very active field. Considerable effort has also been put into elucidating the mechanisms of action of these complexes and optimizing their bioactivity through structural modification. In this review, we highlight recent developments in the design of coinage metal complexes with anti-tumor activity and discuss the emerging importance of quantitative structure–activity relationship methods in the study of anticancer metal complexes. Future work in this field, including likely coinage metal complexes that will attract attention, are proposed.