Synthesis, characterization and cytotoxicity studies of methoxy alkyl substituted metallocenes

NHC-Ag(I) and NHC-Au(I) Complexes with N-Boc-Protected α-Amino Acidate Counterions Powerfully Affect the Growth of MDA-MB-231 Cells

N-Heterocyclic carbene (NHC) metal complexes are attracting scientists' interest as an alluring class of metallodrugs. Indeed, the versatile functionalization of NHC ligands makes them optimal scaffolds to be developed in medicinal chemistry. Besides, amino acids are great biological ligands for metals, such as silver and gold, even though their use is still under-investigated. Aiming to shed light on the anticancer properties of this kind of complex, we investigated a series of silver and gold complexes, stabilized by NHC ligands and bearing carboxylate salts of tert-butyloxycarbonyl (Boc)-N-protected glycine and l-phenylalanine as anionic ligands. The most active complexes, AuM1Gly and AuM1Phe, powerfully affect the growth of MDA-MB-231 breast cancer cells, with IC50 values in the low nanomolar range. Further studies demonstrated the blockade of the human topoisomerase I activity and actin polymerization reaction at 0.001 μM. These unique features make these complexes very interesting and worthy to be used for future in vivo studies.

Gold Derivatives Development as Prospective Anticancer Drugs for Breast Cancer Treatment

Commonly used anticancer drugs are cisplatin and other platinum-based drugs. However, the use of these drugs in chemotherapy causes numerous side effects and the onset of frequent drug resistance phenomena. This review summarizes the most recent results on the gold derivatives used for their significant inhibitory effects on the in vitro proliferation of breast cancer cell models and for the consequences deriving from morphological changes in the same cells. In particular, the study discusses the antitumor activity of gold nanoparticles, gold (I) and (III) compounds, gold complexes and carbene-based gold complexes, compared with cisplatin. The results of screening studies of cytotoxicity and antitumor activity for the gold derivatives show that the death of cancer cells can occur intrinsically by apoptosis. Recent research has shown that gold (III) compounds with square planar geometries, such as that of cisplatin, can intercalate the DNA and provide novel anticancer agents. The gold derivatives described can make an important contribution to expanding the knowledge of medicinal bioorganometallic chemistry and broadening the range of anticancer agents available, offering improved characteristics, such as increased activity and/or selectivity, and paving the way for further discoveries and applications.

Antitumor Activity of Pt(II), Ru(III) and Cu(II) Complexes

Metal complexes are currently potential therapeutic compounds. The acquisition of resistance by cancer cells or the effective elimination of cancer-affected cells necessitates a constant search for chemical compounds with specific biological activities. One alternative option is the transition metal complexes having potential as antitumor agents. Here, we present the current knowledge about the application of transition metal complexes bearing nickel(II), cobalt(II), copper(II), ruthenium(III), and ruthenium(IV). The cytotoxic properties of the above complexes causing apoptosis, autophagy, DNA damage, and cell cycle inhibition are described in this review.

Mesoporous SBA-15 modified with titanocene complexes and ionic liquids: interactions with DNA and other molecules of biological interest studied by solid state electrochemical techniques

The immobilization of two titanocene complexes on SBA-15 has been accomplished following post-synthetic procedures. The ionic liquid, 1-methyl-3-[(triethoxysilyl)propyl]imidazolium chloride, has also been incorporated into the titanium containing materials to determine its influence on the interaction with molecules of biological interest. Cyclic voltammetry has been used to study the influence of the ionic liquid on the mechanism of reduction of titanocene derivatives. The interaction of titanocene and titanocene/ionic liquid-containing mesoporous silica SBA-15 materials, with molecules of biological interest associated with important processes of metallodrug action against cancer cells, has been studied. Thus, we have carried out hydrolysis experiments on the materials functionalized with titanocene derivatives in physiological media to determine their stability and the interaction with serum/transport proteins such as transferrin and BSA and with target molecules such as guanosine, single-stranded DNA and double-stranded DNA by means of solid state voltammetry techniques. A qualitative analysis of the data based on peak current and reduction potential value changes of the couple Ti(iv)/Ti(iii) in the presence of biomolecules at physiological pH, has revealed that grafted titanocene complexes show higher affinity for serum/transport proteins than for nucleic acids, indicating that the transport steps to the cells may be easier than the subsequent attack on DNA.

Novel Gold and Silver Carbene Complexes Exert Antitumor Effects Triggering the Reactive Oxygen Species Dependent Intrinsic Apoptotic Pathway

Cisplatin and other platinum-based drugs are well-known valid anticancer drugs. However, during chemotherapy, the presence of numerous side effects and the onset of frequent phenomena of resistance has pushed many research groups to devise new metal-based compounds holding improved anticancer properties and fewer undesired effects. Amongst the variety of synthesized compounds, significant antiproliferative effects have been obtained by employing organometallic compounds, particularly those based on silver and gold. With this in mind, we synthesized four compounds, two silver complexes and two gold complexes, with good inhibitory effects on the in vitro proliferation of breast and ovarian cancer-cell models. The antitumor activity of the most active compound, that is, AuL4, was found to be ninefold higher than that of cisplatin, and this compound induced dramatic morphological changes in HeLa cells. AuL4 induced PARP-1 cleavage, caspases 3/7 and 9 activation, mitochondria disruption, cytochrome c release in cancer-cell cytoplasm, and the intracellular production of reactive oxygen species. Thus, AuL4 treatment caused cancer-cell death by the intrinsic apoptotic pathway, whereas no cytotoxic effects were recorded upon treating non-tumor cell lines. The reported outcomes may be an important contribution to the expanding knowledge of medicinal bio-organometallic chemistry and enlarge the available anticancer toolbox, offering improved features, such as higher activity and/or selectivity, and opening the way to new discoveries and applications.

Synthesis and Antitumor Activity of New Group 3 Metallocene Complexes

The quest for alternative drugs with respect to the well-known cis-platin and its derivatives, which are still used in more than 50% of the treatment regimens for patients suffering from cancer, is highly needed. In this context, organometallic compounds, which are defined as metal complexes containing at least one direct covalent metal-carbon bond, have recently been found to be promising anticancer drug candidates. A series of new metallocene complexes with scandium, yttrium, and neodymium have been prepared and characterized. Some of these compounds show a very interesting anti-proliferative activity in triple negative breast cancer cell line (MDA.MB231) and the non-hormone sensitive prostate cancer cell line (DU145). Moreover, the interaction of some of them with biological membranes, evaluated using liposomes as bio-membrane mimetic model systems, seems to be relevant. The biological activity of these compounds, particularly those based on yttrium, already effective at low concentrations on both cancer cell lines, should be taken into account with regard to new therapeutic approaches in anticancer therapy.

Biopolymeric self-assembled nanoparticles for enhanced antibacterial activity of Ag-based compounds

Microbial infections still remain one of the main issues for human health. The rapid development of resistance towards the most common antimicrobial drugs in bacteria represents today a challenge in the infections management. In the present work we have investigated the antibacterial activity of a group of compounds, namely silver N-heterocyclic carbene complexes, against a broad spectrum of bacteria. For the most promising compound, a biopolymeric nanocarrier has been developed, in order to potentiate the metal complex activity against both Gram +ve and Gram -ve. The polymeric nanovehicle is based on dextran, modified with oleic acid residues, that confer amphiphilic properties to the polysaccharide. We have characterized the obtained biomaterial and studied its ability to self-assemble into nanoparticles in aqueous environment. Next, the transdermal diffusion analyses have been carried out to evaluate the ability of the polymeric particles to penetrate tissues. Thanks to the strategy adopted, we have fabricated an antibacterial system to which K. pneumoniae and E. coli are the most sensitive.

N-heterocyclic carbene complexes of silver and gold as novel tools against breast cancer progression

AIM

Metal carbenic complexes have received considerable attention in both the catalysis and biological fields for their potential applications in cancer and antimicrobial therapies.

RESULTS

A small series of new silver and gold N-heterocyclic carbene complexes has been designed and synthesized. Among the tested complexes, one compound was particularly active in inhibiting anchorage-dependent and -independent breast cancer proliferation, and inducing cell apoptosis via a mitochondria-related process. The antitumor activity was associated to the transcriptional activation of the tumor suppressor gene p53 in an Sp1-dependent manner, as evidenced by biological and docking studies.

CONCLUSION

Our results highlight the importance and the versatility of N-heterocyclic carbene complexes of gold and silver as useful tools against breast cancer progression.

Inhibition of human topoisomerase I and II and anti-proliferative effects on MCF-7 cells by new titanocene complexes

The antitumor activity shown by many platinum complexes has produced a strong interest in research of new organometallic compounds having anticancer action. Among the many metal compounds synthesized and tested, those based on titanium have received considerable attention because of their cytotoxic activity against solid tumors. Particularly, new titanocene compounds containing aromatic groups linked to the Cp (cyclopentadienyl ring, C5H5) have been synthetized, such as the titanocene Y (bis-[(p-methoxybenzyl)cyclopentadienyl]titanium dichloride) that displayed promising medium-high cytotoxic activity on breast cancer cell lines. Other titanocene complexes recently synthesized, obtained by replacing the substituent methoxy-aryl of cyclopentadienes of titanocene Y with ethenyl-methoxide or ethenyl-phenoxide, showed increased cytotoxic activity on breast cancer cell lines being more stable compounds. In this paper, we report that new titanocene complexes holding lipophilic groups, for instance a methyl group on benzyl carbon, exhibit improved antiproliferative effect on breast cancer cell line MCF-7. Similar results have been obtained introducing a 5-methoxy naphthyl group to further stabilize the titanocene complexes. These inhibitory effects on breast cancer cells have been ascribed to human topoisomerase I and II inhibition as demonstrated by specific enzymatic assays.

Anti-cancer applications of titanocene-functionalised nanostructured systems: an insight into cell death mechanisms

A series of alkenyl-substituted titanocene compounds have been supported on the mesoporous silica-based material KIT-6. The corresponding functionalised materials were completely characterised by different techniques (solid-state multinuclear NMR spectroscopy, IR spectroscopy, N2 adsorption-desorption isotherms, X-ray fluorescence and diffraction, SEM and TEM) to observe the incorporation of the titanocene derivatives on the external surface of the material KIT-6. Both the titanocene compounds and the materials were tested in vitro against a wide variety of human cancer and normal cell lines. A very high cytotoxicity of the synthesised titanocene derivatives (IC50 values in the range of those described in the literature for the most active cytotoxic titanocene compounds), with selectivity towards cancer cell lines was observed. The cytotoxic activity of the materials is the highest reported to date for titanocene-functionalised materials. In addition, higher Ti uptake (from 4 to 23% of the initial amount of Ti) of the cells treated with materials was observed with respect to those treated with "free" titanocene derivatives (which gave Ti uptake values from 0.4 to 4.6% of the initial amount of Ti). Additional experiments with the titanocene derivatives and the functionalised materials revealed that changes to the morphological and functional dynamics of apoptosis occurred when the active titanocene species were incorporated into mesoporous materials. In addition, the materials could induce programmed cell death in tumour cell populations by impairing the damaged DNA repair mechanisms and by upregulation of intrinsic and extrinsic apoptotic signalling pathways.

Enhanced in vitro antitumor activity of a titanocene complex encapsulated into polycaprolactone (PCL) electrospun fibers

PURPOSE

The purpose of this work was to achieve detailed biomaterials characterization of a drug delivery system for local cancer treatment based on electrospun titanocene trichloride-loaded resorbable polycaprolactone (PCL) fibers.

METHODS

The PCL fibers were characterized for their structural, morphologic and physical properties. The drug release kinetics of the titanocene complex was investigated at different concentrations, to obtain a set of correlations between structure and tuneable release. After exposing cancer cells directly onto the surface of PCL fibers, the anti-proliferative effects of titanocene-loaded PCL were assessed by: (i) counting viable cells via live/dead staining methods, and (ii) analyzing cell apoptosis.

RESULTS AND CONCLUSIONS

Titanocene concentration influenced fiber diameters reduced for PCL filled with titanocene. X-ray analysis suggested that the titanocene, encapsulated into the PCL fibers, is not allowed to crystallize and exists as amorphous aggregates into the fibers. The titanocene release curves presented two stages unrelated to PCL degradation: an initial burst release followed by a release linear with time, extending for a very long time. All of the titanocene-loaded fibers revealed sustained drug release properties suggesting their potential clinical applicability for the treatment of local cancer diseases.

Synthesis, characterization and cytotoxic activity on breast cancer cells of new half-titanocene derivatives

A series of novel titanocene-complexes has been prepared and evaluated for their growth regulatory effects in MCF7 and SkBr3 breast cancer cells. The capability of some of these compound to elicit relevant repressive effects on cancer cell growth could be taken into account towards novel pharmacological approaches in cancer therapy.

Titanocene / cyclodextrin supramolecular systems: a theoretical approach

Background

Recently, various metallocenes were synthesized and analyzed by biological activity point of view (such as antiproliferative properties): ruthenocenes, cobaltoceniums, titanocenes, zirconocenes, vanadocenes, niobocenes, molibdocenes etc. Two main disadvantages of metallocenes are the poor hydrosolubility and the hydrolytic instability. These problems could be resolved in two ways: synthetically modifying the structure or finding new formulations with enhanced properties. The aqueous solubility of metallocenes with cytostatic activities could be enhanced by molecular encapsulation in cyclodextrins, as well as the hydrolytic instability of these compounds could be reduced.

Results

This study presents a theoretical approach on the nanoencapsulation of a series of titanocenes with cytotoxic activity in α-, β-, and γ-cyclodextrin. The HyperChem 5.11 package was used for building and molecular modelling of titanocene and cyclodextrin structures, as well as for titanocene/cyclodextrin complex optimization. For titanocene/cyclodextrin complex optimization experiments, the titanocene and cyclodextrin structures in minimal energy conformations were set up at various distances and positions between molecules (molecular mechanics functionality, MM+). The best interaction between titanocene structures and cyclodextrins was obtained in the case of β- and γ-cyclodextrin, having the hydrophobic moieties oriented to the secondary face of cyclodextrin. The hydrophobicity of titanocenes (logP) correlate with the titanocene-cyclodextrin interaction parameters, especially with the titanocene-cyclodextrin interaction energy; the compatible geometry and the interaction energy denote that the titanocene/β- and γ-cyclodextrin complex can be achieved. Valuable quantitative structure-activity relationships (QSARs) were also obtained in the titanocene class by using the same logP as the main parameter for the in vitro cytotoxic activity against HeLa, K562, and Fem-x cell lines.

Conclusions

According to our theoretical study, the titanocene/cyclodextrin inclusion compounds can be obtained (high interaction energy; the encapsulation is energetically favourable). Further, the most hydrophobic compounds are better encapsulated in β- and γ-cyclodextrin molecules and are more stable (from energetically point of view) in comparison with α-cyclodextrin case. This study suggests that the titanocene / β- and γ-cyclodextrin complexes (or synthetically modified cyclodextrins with higher water solubility) could be experimentally synthesized and could have enhanced cytotoxic activity and even lower toxicity.