Anticancer cyclometalated complexes of platinum group metals and gold

A direct access to heterobimetallic complexes by roll-over cyclometallation

Complexes of the type [Cp*Ir(N,N')Cl]⁺ (N,N' = 2-(2-dialkylaminopyrimidin-4-yl)pyrimidine) can undergo roll-over cyclometallation leading to a novel N,N'-donor site. Following this strategy heterobimetallic complexes including iridium(iii) and a Group X metal centre in the oxidation state +II were achieved.

Synthesis and structures of a pincer-type rhodium(iii) complex: reactivity toward biomolecules

A novel rhodium(iii) complex [Rh^III(H₂L^tBu)Cl₃] (1) (H₂L^tBu = 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine) containing a pincer type, tridentate nitrogen-donor chelate system was synthesized. Single crystal X-ray structure analysis revealed that 1 crystallizes in the orthorhombic space group Pbcn with a = 20.7982(6), b = 10.8952(4), c = 10.9832(4) Å, V = 2488.80(15) ų, and eight molecules in the unit cell. The rhodium center in the complex [Rh^III(H₂L^tBu)Cl₃] (1) is coordinated in a slightly distorted octahedral geometry by the tridentate N,N,N-donor and three chloro ligands, adopting a mer arrangement with an essentially planar ligand skeleton. Due to the tridentate coordination of the N,N,N-donor, the central nitrogen atom N1 is located closer to the Rh^III center. The reactivity of the synthesized complex toward small biomolecules (l-methionine (l-Met), guanosine-5'-monophosphate (5'-GMP), l-histidine (l-His) and glutathione (GSH)) and to a series of duplex DNAs and RNA was investigated. The order of reactivity of the studied small biomolecules is: 5'-GMP > GSH > l-Met > l-His. Duplex RNA reacts faster with the [Rh^III(H₂L^tBu)Cl₃] complex than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. In addition, a higher reactivity is achieved with a DNA duplex with a centrally located GG-sequence than with a 22GTG duplex DNA, in which the GG-sequence is separated by a T base. Furthermore, the interaction of this metal complex 1 with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) was examined by absorption (UV-Vis) and emission spectral studies (EthBr displacement studies). Overall, the studied complex exhibited good DNA and BSA interaction ability.

Benzothiazole-Based Cycloplatinated Chromophores: Synthetic, Optical, and Biological Studies

Cycloplatinated complexes based on 2-(4-substituted)benzothiazole ligands of type [Pt(R-PBT-κC,N)Cl(L)] (PBT=2-phenylbenzothiazole; R=Br (1), Me₂ N (2); L=dimethyl sulfoxide (DMSO; a), 1,3,5- triaza-7-phosphaadamantane (PTA; b), triphenylphosphine 3,3',3''-trisulfonate (TPPTS; c)) and [Pt(Br-PBT-κC)Cl(PTA)₂ ] (3) are presented. On the basis of the photophysical data and time-dependent (TD)-DFT calculations (1 a and 2 a), the low-lying transitions (absorption and emission) were associated with ligand-center (LC) charge transfer, with minor metal-to-ligand charge transfer (MLCT), and intraligand charge transfer (ILCT) [Me₂ N-PBT→PBT] excited states, respectively. Simultaneous fluorescence/phosphorescence bands were found in fluid solutions (and also in the solid state for 2 a), which become dominated by triplet emission bands in rigid media at 77 K. The effect of the concentration on emissive behavior of 2 a, b indicated the occurrence of aggregation-induced luminescence properties related to the occurrence of metal-metal and π⋅⋅⋅π interactions, which are more enhanced in 2 a because of the less bulky DMSO ligand. The behavior of 2 a toward para-toluenesulfonic acid (PTSA) in aerated acetonitrile and to hydrogen chloride gas in the solid state has been evaluated, thus showing a clear reversible change between the ¹ ILCT and ³ LC/³ MLCT states due to protonation of the NMe₂ group (theoretical calculations on 2 a-H⁺ ). Solid 2 a undergoes a surprising oxidation of the Pt^II center to Pt^IV with concomitant deoxygenation of DMSO, under prolonged reaction with hydrogen chloride gas to afford the Pt^IV /dimethyl sulfide complex (mer-[Pt(Me₂ N-PBT-κC,N)Cl₃ (SMe₂ )]; mer-4), which evolves in solution to fac-4, as confirmed by X-ray studies. Cytotoxic activity studies on A549 and HeLa cell lines indicated cytotoxic activity of 1 b and 2 a, b. In addition, fluorescent cell microscopy revealed cytoplasmic staining, more visible in perinuclear areas. Inhibition of tubulin polymerization by 1 b in both cells is presented as a preliminary mechanism of its cytotoxic action.

Geometry matters: inverse cytotoxic relationship for cis/trans-Ru(ii) polypyridyl complexes from cis/trans-[PtCl2(NH3)2]

Two thermally activated ruthenium(ii) polypyridyl complexes, cis-Ru(bpy)2Cl2 and trans-Ru(qpy)Cl2 were investigated to determine the impact of the geometric arrangement of the exchangable ligands on the potential of the compounds to act as chemotherapeutics. In contrast to the geometry requirements for cisplatin, trans-Ru(qpy)Cl2 was 7.1-9.5× more cytotoxic than cis-Ru(bpy)2Cl2. This discovery could open up a new area of metal-based chemotherapeutic research.

Cycloplatinated(ii) complexes bearing 1,1′-bis(diphenylphosphino)ferrocene ligand: biological evaluation and molecular docking studies

Cycloplatinated(ii) complexes containing dppf ligand were prepared. These complexes exhibited high cytotoxicity and apoptosis-inducing activities to human cancer cell lines.

Synthesis, characterisation, crystal structures and biological studies of palladium(ii) complexes containing 5-(2-hydroxy-3-methoxy-phenyl)-2,4-dihydro[1,2,4]triazole-3-thione derivatives

New structurally different palladium(ii) complexes have been synthesized and characterized and evaluated for their cytotoxic nature against human breast cancer cell line (MCF 7) which showed significant activity.

Electronic effects on reactivity and anticancer activity by half-sandwich N,N-chelated iridium(iii) complexes

This work demonstrated how the chemical reactivity and anticancer activity as well as the selectivity of these half-sandwich N,N-chelated iridium(iii) complexes can be controlled and fine-tuned by the modification of the ligand electronic perturbations.

Spectroscopy, electrochemistry and antiproliferative properties of Au(iii), Pt(ii) and Cu(ii) complexes bearing modified 2,2′:6′,2′′-terpyridine ligands

Impact of the metal centre and the substituent incorporated into a terpy framework.

Palladium iminophosphorane complexes: the pre-cursors to the missing link in triphenylphosphane chalcogenide metallacycles

A dinuclear iminophosphorane palladacycle produces the missing link in the triphenylphosphane chalcogenide series of metallacycles.

Preparation and characterization of terdentate [C,N,N] acetophenone and acetylpyridine hydrazone platinacycles: a DFT insight into the reaction mechanism

The reaction of N-ortho-chlorophenyl-substituted acetylpyridine hydrazones (a and d) with K₂[PtCl₄] (n-butanol/water, 100 °C) gave mononuclear complexes 1a and 1d with the ligands as [N,N] bidentate. In contrast, the reaction of N-phenyl or N-meta-chlorophenyl hydrazones (b and c, respectively) under analogous reaction conditions gave the cycloplatinated species 2b and 2c with the ligand as [C,N,N] terdentate. The treatment of the mononuclear complexes 1a and 1d with NaOAc (n-butanol, 100 °C) gave the corresponding cycloplatinated complexes 2a and 2d. Acetophenone hydrazone platinacycle 2e was prepared in a similar fashion and its reaction with tertiary mono- and triphosphines gave mono- or trinuclear species depending on the reaction conditions. The X-ray crystal structures of some of these complexes showed interesting π-π slipped stacking interactions between metallacyclic rings which, according to NCI analyses, showed an aromatic character. With an aim to rationalize the different reactivities shown by acetylpyridine hydrazones and the precise role of the acetate anion, the energy profiles for the three main steps of cycloplatination (iminoplatinum complex formation, chelation and cyclometallation) have been determined by using the DFT (M06) methods. Calculations indicate that the cycloplatination of 1b proceeds via electrophilic substitution, involving the direct replacement of the chloride anion at the Pt(ii) centre with the N-phenyl moiety as the rate-determining step, to give an agostic intermediate 5b+ that, subsequently, leads to the elimination of a proton as hydrogen chloride. When present as an "external" base, acetate enters the coordination sphere around the Pt(ii) centre and facilitates hydrazone N-H deprotonation and electrophilic C-H activation through a dissociative route, leading to a Wheland-type σ-complex intermediate 9ac.

Synthesis and crystal structure of [Pd{C6H4(CH2NHCH2Ph)-2-κ2C,N}(μ-I)]2

The binuclear title complex, di-μ-iodido-bis(-{2-[(benzylamino-κN)meth-yl]phenyl-κC1}palladium(II)), [Pd2I2(C14H14N)2], was prepared by reaction of [Pd{C6H4(CH2NHCH2Ph)-2}(μ-OAc)]2 with NaI. It crystallizes with one discrete mol-ecule in the asymmetric unit. The mol-ecule presents an iodide-bridged dimeric structure with a cisoid arrangement with respect to the C,N-cyclo-palladated ligands. Both PdII atoms have a slightly distorted square-planar coordination environment. Weak inter-molecular contacts of the type C-H⋯Pd seem to have a significant influence on the arrangement of the mol-ecules along the b axis in the crystal.

Flexible ligated ruthenium(II) self-assemblies sensitizes glioma tumor initiating cells in vitro

The tumorigenic potentials of residual cancer stem-like cells within tumors represent limitations of current cancer therapies. Here, the authors describe the effects of synthesized flexible, ligated, supramolecular self-assembled chair type tetranuclear ruthenium (II) metallacycles (2–5) on glioblastoma and glioma stem like cells. These self-assemblies were observed to be selectively toxic to glioma cells and CD133-positive glioma stem like cells population. Of the self-assembled compounds tested, metallacycle 4 more efficiently induced glioma stem like cells death within a brain cancer cell population and simultaneously inhibited the formation of free-floating gliospheres by reducing the sphere size. Detailed cell death studies revealed that treatment with metallacycle 4 reduced mitochondrial membrane potentials (an indicator of apoptosis) of glioma stem like cells. These results shows the elimination of cancer stem-like cells using an appropriate ligand binding adaptor offers a potential means of developing metal-based compounds for the treatment of chemo-resistant tumors.

New Acridine Thiourea Gold(I) Anticancer Agents: Targeting the Nucleus and Inhibiting Vasculogenic Mimicry

Two new 1-acridin-9-yl-3-methylthiourea Au(I) DNA intercalators [Au(ACRTU)₂]Cl (2) and [Au(ACRTU) (PPh₃)]PF₆ (3) have been prepared. Both complexes were highly active in the human ovarian carcinoma cisplatin-sensitive A2780 cell line, exhibiting IC₅₀ values in the submicromolar range. Compounds 2 and 3 are also cytotoxic toward different phenotypes of breast cancer cell lines MDA-MB-231 (triple negative), SK-BR-3 (HER2+, ERα-, and ERβ-), and MCF-7 (ER+). Both complexes induce apoptosis through activation of caspase-3 in vitro. While inhibition of some proteins (thiol-containing enzymes) seems to be the main mechanism of action for cytotoxic gold complexes, 2 and 3 present a DNA-dependent mechanism of action. They locate in the cell nucleus according to confocal microscopy and transmission electronic microscopy. The binding to DNA resulted to be via intercalation as shown by spectroscopic methods and viscometry, exhibiting a dose-dependent response on topoisomerase I mediated DNA unwinding. In addition, 2 and 3 exhibit potent antiangiogenic effects and are also able to inhibit vasculogenic mimicry of highly invasive MDA-MB-231 cells.

Somatostatin receptor-targeted organometallic iridium(iii) complexes as novel theranostic agents

A novel somatostatin receptor-targeted anticancer agent based on the conjugation of a highly cytotoxic and luminescent cyclometalated iridium(iii) complex to tumor-targeting vectors based on octreotide peptide has been described, and its potential for targeted theranostic applications has been demonstrated.

Cytotoxicity of Pyrazine-Based Cyclometalated (C^Npz^C)Au(III) Carbene Complexes: Impact of the Nature of the Ancillary Ligand on the Biological Properties

The synthesis of a series of cyclometalated gold(III) complexes supported by pyrazine-based (C^N^C)-type pincer ligands is reported, including the crystal structure of a cationic example. The compounds provide a new platform for the study of antiproliferative properties of gold(III) complexes. Seven complexes were tested: the neutral series (C^N^pz^C)AuX [X = Cl (1), 6-thioguanine (4), C≡CPh (5), SPh (6)] and an ionic series that included the N-methyl complex [(C^N^pzMe^C)AuCl]BF₄ (7) and the N-heterocyclic carbene complexes [(C^N^pz^C)AuL]⁺ with L = 1,3-dimethylbenzimidazol-2-ylidene (2) or 1,3,7,9-tetramethylxanthin-8-ylidene (3). Tests against human leukemia cells identified 1, 2, 3, and 4 as particularly promising, whereas protecting the noncoordinated N atom on the pyrazine ring by methylation (as in 7) reduced the cytotoxicity. Complex 2 proved to be the most effective of the entire series against the HL60 leukemia, MCF-7 breast cancer, and A549 lung cancer cell lines, with IC₅₀ values down to submicromolar levels, associated with a lower toxicity toward healthy human lung fibroblast cells. The benzimidazolylidene complex 2 accumulated more effectively in human lung cancer cells than its caffeine-based analogue 3 and the gold(III) chloride 1. Compound 2 proved to be unaffected by glutathione under physiological conditions for periods of up to 6 days and stabilizes the DNA G-quadruplex and i-motif structures; the latter is the first such report for gold compounds. We also show the first evidence of inhibition of MDM2–p53 protein–protein interactions by a gold-based compound and identified the binding mode of the compound with MDM2 using saturation transfer difference NMR spectroscopy combined with docking calculations.

We synthesized three new (C^N^pz^C)Au(III) complexes and screened them along with four other complexes as potential anticancer agents against leukemia cells. We tested the cellular uptake, the interaction with G4 and i-motif DNA structures, and the interaction with MDM2 protein. We highlight the very different biological behaviors of the compounds due to the different ancillary ligands.

Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO₂L^1-7] (1-7) derived from various tetradentate diamino bis(phenolato) "salan" ligands, N,N'-dimethyl-N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H₂L¹); X=Me, YCl, Z=H (H₂L²); X=ⁱPr, Y=Cl, Z=Me (H₂L³)} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=^tBu, Z=H (H₂L⁴); X=Y=Me, Z=H (H₂L⁵); X=ⁱPr, YCl, Z=Me (H₂L⁶); X=Y=Br, Z=H (H₂L⁷)} containing O-N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV-vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O₂N₂ donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC₅₀ values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC₅₀ values of 6 are 2.62 and 10.74μM and that of 7 is 11.79 and 30.48μM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.

Designing new iridium(iii) arene complexes of naphthoquinone derivatives as anticancer agents: a structure-activity relationship study

A series of iridium(iii) arene complexes of naphthoquinone derivatives of the formula [IrIII(η6-L1)(L2)(3,5-(NO2)2pcyd)](PF6) (L1 = p-methylphenyl)ethynylferrocene; L2 = Lap: lapachol, 1, Plum: plumbagin, 2, Law: lawsone, 3, and Jug: juglone, 4; 3,5-(NO2)2pcyd = 3,5-dinitrophenylcyanamide) have been synthesized and investigated for their suitability as potential anticancer drugs. The DNA-binding interactions of the complexes with calf thymus DNA have been studied by absorption, emission, and viscosity measurements. Their cytotoxicity against the cancer cell lines including colon adenocarcinoma (HT-29), liver hepatocellular carcinoma (HepG-2), breast (MCF-7), colon carcinoma (HCT-8), and ovary (A2780) is reported. Remarkably, almost all complexes exhibit significant cytotoxic effects towards HepG-2, MCF-7, and HCT-8 cancer cell lines and complex 1 emerged as the most cytotoxic derivative in comparison with other complexes. The complexes 1-4 increase the production of reactive oxygen species (ROS) in MCF-7 cells. The new compounds also inhibit the enzyme thioredoxin reductase activity at nanomolar concentrations. Furthermore, the complexes induce major levels of cancer cell death by apoptosis that is in correlation with activity in cytotoxicity studies.

Gas-phase reactivity of Cp* group IX metal complexes bearing aromatic N,N′-chelating ligands

Compounds of the type [(η⁵-Cp*)M(Cl)(N,N′)]⁺ bearing N,N′-coordinating ligands show different modes of HCl cleavage depending on the nature of the N,N′-chelate ligand and the metal center.

Structurally different mono-, bi- and trinuclear Pd(ii) complexes and their DNA/protein interaction, DNA cleavage, and anti-oxidant, anti-microbial and cytotoxic studies

A series of new structurally different Pd(ii) complexes was obtained by the reactions between K₂[PdCl₄], 3-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazone [H₂L1–H₂L4] and bis(diphenylphosphino)ethane [dppe].

Cytotoxic gold(iii) complexes incorporating a 2,2′:6′,2′′-terpyridine ligand framework – the impact of the substituent in the 4′-position of a terpy ring

The possibility of tuning the cytotoxic activity of Au(iii) complexes by structural modifications of a terpy ligand has been examined.

(C^Npz^C)AuIII complexes of acyclic carbene ligands: synthesis and anticancer properties

Synthesis of amino ester conjugated (C^N^pz^C)Au acyclic carbene complexes with low micromolar cytotoxicity on human cancer cells.

The anticancer effect related to disturbances in redox balance on Caco-2 cells caused by an alkynyl gold(I) complex

The alkynyl gold(I) derivative [Au(C≡CPh)(PTA)] (PTA=1,3,5-triaza-7-phosphaadamantane) induces apoptosis in colorectal carcinoma tumour cells (Caco-2) without affecting to normal enterocytes. [Au(C≡CPh)(PTA)] is a slight lipophilic drug, stable in PBS (Phosphate Buffered Saline) and able to bind BSA (Bovin Serum Albumin) by hydrophobic interactions. Once inside the cell, [Au(C≡CPh)(PTA)] targets seleno proteins such as Thioredoxin Reductase 1, increasing ROS (Reactive Oxygen Species) levels, reducing cell viability and proliferation and inducing mitochondrial apoptotic pathway, pro-apoptotic and anti-apoptotic protein imbalance, loss of mitochondrial membrane potential, cytochrome c release and activation of caspases 9 and 3. Moreover, unlike other metal-based drugs such as cisplatin, [Au(C≡CPh)(PTA)] does not target nucleic acid, reducing the risk of side mutation in the DNA. In consequence, our results predict a promising future for [Au(C≡CPh)(PTA)] as a chemotherapeutic agent for colorectal carcinoma.