Copper(II) Complexes with 2,2':6',2″-Terpyridine Derivatives Displaying Dimeric Dichloro-μ-Bridged Crystal Structure: Biological Activities from 2D and 3D Tumor Spheroids to In Vivo Models

Eight 2,2':6',2″-terpyridines, substituted at the 4'-position with aromatic groups featuring variations in π-conjugation, ring size, heteroatoms, and methoxy groups, were employed to enhance the antiproliferative potential of [Cu2Cl2(R-terpy)2](PF6)2. Assessing the cytotoxicity in A2780 (ovarian carcinoma), HCT116 (colorectal carcinoma), and HCT116DoxR (colorectal carcinoma resistant to doxorubicin) and normal primary fibroblasts revealed that Cu(II) complexes with 4-quinolinyl, 4-methoxy-1-naphthyl, 2-furanyl, and 2-pyridynyl substituents showed superior therapeutic potential in HCT116DoxR cells with significantly reduced cytotoxicity in normal fibroblasts (42-129× lower). Besides their cytotoxicity, the Cu(II) complexes are able to increase intracellular ROS and interfere with cell cycle progression, leading to cell death by apoptosis and autophagy. Importantly, they demonstrated antimetastatic and antiangiogenic properties without in vivo toxicity. In accordance with their nuclear accumulation, the Cu(II) complexes are able to cleave pDNA and interact with bovine serum albumin, which is a good indication of their ability for internalization and transport toward tumor cells.

Antitumor activity of synthetic three copper(II) complexes with terpyridine ligands

Three new synthetic terpyridine copper(II) complexes were characterized. The copper(II) complexes induced apoptosis of three cancer cell lines and arrested T-24 cell cycle in G1 phase. The complexes were accumulated in mitochondria of T-24 cells and caused significant reduction of the mitochondrial membrane potential. The complexes increased both intracellular ROS and Ca²⁺ levels and activated the caspase-3/9 expression. The apoptosis was further confirmed by Western Blotting analysis. Bcl-2 was down-regulated and Bax was upregulated after treatment with complexes 1-3. The in vivo studies showed that complexes 1-3 obviously inhibited the growth of tumor without significant toxicity to other organs.

Synthesis of a Zirconium Complex of an N,O-type p-tert-Butylcalix[4]arene and Its Application in Some Multicomponent Reactions

The synthesis and characterization of a new octahedral Zr(IV) complex of oxygen-depleted N,O-type calixarene ligand comprising two distal-functionalized pyrazole rings have been reported. The cone shape and structure of the prepared complex were confirmed univocally by single-crystal X-ray diffraction and NMR studies. The Zr metal lies at 2.091 Å from the plane of the calixarene ring. This complex has been utilized as an efficient catalyst for the synthesis of Biginelli adducts, bis(indolyl)methanes, and coumarins. This complex (Cl₂Zr-calixarene) showed superior activity for these multicomponent reactions in comparison to the corresponding Ti(IV) and Zn(II) analogues. Ferrocene-appended bis(indolyl)methane, prepared using this catalyst, was also evaluated for its anticancer activity against the A-172 cell line.

Phototherapeutic anticancer strategies with first-row transition metal complexes: a critical review

Photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) are therapeutic techniques based on a photosensitizer (PS) and light. These techniques allow the spatial and temporal control of the activation of drugs with light. Transition metal complexes are attractive compounds as photoactivatable prodrugs since their excited states can be appropriately designed by subtle modifications of the ligands, the metal centre, or the oxidation state. However, most metal-based PSs contain heavy metals such as Ru, Os, Ir, Pt or Au, which are expensive and non-earth-abundant, contrary to first-row transition metals. In this context, the exploration of the photochemical properties of complexes based on first-row transition metals appears to be extremely promising. This did encourage several groups to develop promising PSs based on these metals. This review presents up-to-date state-of-the-art information on first-row-transition metal complexes, from titanium to zinc in regard to their application as PSs for phototherapeutic applications.

Terpyridines as promising antitumor agents: an overview of their discovery and development

INTRODUCTION

The fused aromatic system of terpyridines makes them good, innocent ligands for various metals. The resulting complexes have been extensively studied for both their biological activity and physico-chemical properties. However, although free ligands also have an interesting biological activity, their share in recent research is considerably limited.

AREAS COVERED

This review covers the literature on the anticancer activity of terpyridines with special attention being paid to their use as free ligands. Whenever possible, the mechanism of action has been discussed, thereby providing evidence of the substantial differences between sole ligands or less stable complexes and those that have heavier elements.

EXPERT OPINION

The existing literature indicates that there is a specific attitude for investigating terpyridines and their transition metal complexes. While the latter have been well explored and recognized in the scientific community, the free terpyridines are considered to be useful solely due to their complexing ability. At the same time, terpyridines could have similar or even higher anticancer potency than their complexes. Moreover, a mechanistic analysis of the stability and intracellular activity would provide information that would be useful for designing new drugs.

Copper(ii) and zinc(ii) complexes of mono- and bis-1,2,3-triazole-substituted heterocyclic ligands

Chelating 1,4-disubstituted mono- (8a-8d) and bis-1,2,3-triazole-based (9a-11a) ligands were prepared by regioselective copper(i)-catalysed 1,3-dipolar cycloaddition of terminal alkynes with aromatic azides, together with bioconjugate 13a synthesized by amide coupling of l-phenylalanine methyl ester to 11a. Cu(ii) and Zn(ii) complexes were prepared and single crystal structures were determined for complexes 8aCu, 8dCu, 9cCu and 10cCu, as well as the free ligands 10a and 10c. The in situ prepared Zn(ii) complexes were studied by NMR spectroscopy, while the stoichiometry of the Cu(ii) complexes in solution was determined by UV-Vis titrations and confirmed by the electronic structure DFT calculations at the (SMD)/M05-2X/6-31+G(d)/LanL2DZ+ECP level of theory.

A long-lived cuprous bis-phenanthroline complex for the photodynamic therapy of cancer

An earth-abundant cuprous bis-phenanthroline photosensitizer showed potential use in the photodynamic therapy of cancer.

Crystal structures and third-order optical properties of three manganese(II) complexes constructed from N-heterocyclic and polycarboxylate ligands

Three new manganese(II) complexes, {[Mn(PTP)]2[Mn(PTP)(H2O)]}(BTA)2·2H2O (1), [Mn(PTP)(ODA)]2 (2), and [Mn(FTP)(ODA)]2·H2O (3), were synthesized by the reactions of manganese acetate and polycarboxylic acid in the presence of N-heterocyclic ligands (where PTP=4′-phenyl-2,2′:6′,2″-terpyridine, H3BTA=benzene-1,3,5-tricarboxylic acid, H2ODA=4,4′-oxydibenzoic acid, FTP=4′-(furan-2-yl)-2,2′:6′,2″-terpyridine). In complex 1, each BTA ligand serves as a μ 3-bridge to link three Mn(II) centers, whereas each Mn(II) center is coordinated by two BTA ligands. This connection mode results in a grid sheet. Complexes 2 and 3 have very similar molecular structures with Mn(II) centers connected by ODA ligands to result in ring-like arrays. We investigated the third-order nonlinear optical (NLO) properties of the three complexes by single beam Z-scan techniques. Complexes 1–3 exhibit strong third-order NLO reverse saturable absorption with NLO absorptive indices β=1.32×10−6, 3.01×10−6, and 9.42×10−6 m W−1, respectively. In addition, complex 1 shows all excellent self-focusing effect with an NLO refractive index of γ=1.25×10−12 m2 W−1. The third-order NLO susceptibility χ (3) of the three complexes were calculated as 47.55×10−8, 4.85×10−8, and 15.16×10−8 esu, respectively.

Novel mitochondria targeted copper(ii) complexes of ferrocenyl terpyridine and anticancer active 8-hydroxyquinolines showing remarkable cytotoxicity, DNA and protein binding affinity

Mixed-ligand ferrocenyl copper(ii) complexes target the mitochondria of cancer cells showing remarkable cytotoxicity against HeLa and MCF-7 cancer cells while being much less toxic to MCF-10A normal cells.

Enhanced third-order nonlinear optical properties determined in thin films using the Z-scan technique: bis(μ-4,4′-oxydibenzoato)bis[(4′-phenyl-2,2′:6′,2′′-terpyridine)cobalt(II)]

π-Conjugated organic materials exhibit high and tunable nonlinear optical (NLO) properties, and fast response times. 4′-Phenyl-2,2′:6′,2′′-terpyridine (PTP) is an important N-heterocyclic ligand involving π-conjugated systems, however, studies concerning the third-order NLO properties of terpyridine transition metal complexes are limited. The title binuclear terpyridine CoIIcomplex, bis(μ-4,4′-oxydibenzoato)-κ3O,O′:O′′;κ3O′′:O,O′-bis[(4′-phenyl-2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)cobalt(II)], [Co2(C14H8O5)2(C21H15N3)2], (1), has been synthesized under hydrothermal conditions. In the crystal structure, each CoIIcation is surrounded by three N atoms of a PTP ligand and three O atoms, two from a bidentate and one from a symmetry-related monodentate 4,4′-oxydibenzoate (ODA2−) ligand, completing a distorted octahedral coordination geometry. Neighbouring [Co(PTP)]2+units are bridged by ODA2−ligands to form a ring-like structure. The third-order nonlinear optical (NLO) properties of (1) and PTP were determined in thin films using the Z-scan technique. The title compound shows a strong third-order NLO saturable absorption (SA), while PTP exhibits a third-order NLO reverse saturable absorption (RSA). The absorptive coefficient β of (1) is −37.3 × 10−7 m W−1, which is larger than that (8.96 × 10−7 m W−1) of PTP. The third-order NLO susceptibility χ(3)values are calculated as 6.01 × 10−8 e.s.u. for (1) and 1.44 × 10−8 e.s.u. for PTP.

New Bio-Based Cu(II) Complexes and Study of their Anti-Cancer Activities

Two new Cu(II) complexes with Picolinic acid and Tryptophan [Cu(II)(DPTR)(H2O)2](1:1) (1) and [Cu(II)(DPTR)(Phen)] (1:1:1) (2) were synthesized, characterized and studied their DNA binding, cleavage, docking and anti-cancer properties. The molecular modeling studies were carried out with energy minimized structures of metal complexes. CT-DNA binding studies revealed that the complexes bind through an intercalative mode and show good binding propensity. The docking study also confirms the intercalative mode of binding. The hydrolytic DNA cleavage activity of these complexes has been studied using gel electrophoresis. Complex 2 shows better efficiency than 1. Cell viability experiments indicated that the ligand, complexes show significant dose dependent cytotoxicity in selected cell lines. Graphical Abstract Two new Cu(II) complexes with Picolinic acid and Tryptophan, [Cu(II)(DPTR)(H2O)2](1:1) (1) and [Cu(II)(DPTR)(Phen)] (1:1:1) (2) were synthesized, characterized and studied their DNA binding, cleavage, docking and anti-cancer properties.

Biological Evaluation of Ferrocenyl Olefins: Cancer Cell Growth Inhibition, ROS Production, and Apoptosis Activity

The antiproliferative effects of various ferrocenyl olefins were evaluated against the cell lines MCF-7 (human breast cancer cells), DLD-1 (human colon adenocarcinoma cells), HUVEC (human umbilical vein endothelial cells), and A549 (human lung carcinoma cells), using the MTT test. IC50 values were determined. Compounds 8, 9, 11, and 12 with high antiproliferative activity were tested for their reactive oxygen species (ROS) production, and cell cycle analysis was performed on A549 cells. The results show that these compounds might perform their antiproliferative activity through inducing ROS generation, apoptosis induction, and cell cycle arrest.

Two dpa-based zinc(ii) complexes as potential anticancer agents: nuclease activity, cytotoxicity and apoptosis studies

Two new mononuclear Zn(ii)-PhMe-dpa complexes have been synthesized and the apoptosis-inducing activity of1was assessed by Hoechst 33342 staining, Annexin V binding and cell cycle experiments.

Synthesis and characterization of ML and ML2 metal complexes with amino acid substituted bis(2-picolyl)amine ligands

Metal complexes with ML or ML2 stoichiometry have been isolated in the reaction of Zn(NO3)2, ZnBr2 or M(NO3)2/NaBF4, M = Zn(ii), Co(ii) or Ni(ii), with either amino acid or amine substituted tridentate nitrogen ligands based on bis(2-picolyl)amine (bpa) or bis(2-quinaldyl)amine (bqa). The stoichiometry (M : L = 1 : 1 or 1 : 2) and stereochemistry (mer, trans-fac or cis-fac) of the products have been studied by NMR and IR spectroscopy, X-ray single crystal analysis and quantum-chemical calculations with an implicit SMD solvation model.

Synthesis, structure and photophysical properties of a highly luminescent terpyridine-diphenylacetylene hybrid fluorophore and its metal complexes

A new fluorescent terpyridyl-diphenylacetylene hybrid fluorophore 4'-[4-{(4-methoxyphenyl)ethynyl}phenyl]-2,2':6',2''-terpyridine, L, was synthesized via Sonogashira cross-coupling of 4'-(4-bromophenyl)-2,2':6',2''-terpyridine and 4-ethynylanisole in the presence of Pd(PPh3)4/CuI as a catalyst. The solid state structure of L shows a trans arrangement of pyridine nitrogen atoms along the interannular bond in the terpyridine domain. Five transition metal complexes of L, {[FeL2](CF3SO3)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3), [RuL2](PF6)2 (4), and PtMe3IL (5)}, have also been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. The X-ray crystal structures of complexes 1-3 show a distorted octahedral MN6 arrangement with tridentate coordination of the two terpyridine ligands, whereas in complex 5 the ligand L binds in a bidentate fashion. The ligand L displays bright blue emission in the solid state and in both non-polar and polar organic media. The fluorescence quantum yield of L is exceptionally high for a monoterpyridine ligand of its kind, which can be rationalized with density functional theory calculations. The electronic structure of L shows that the fluorescence involves intramolecular charge transfer from the diphenylacetylene moiety to the terpyridine group, and it is not affected by the usual non-radiative relaxation processes such as pyridine rotation. The Fe(II), Ru(II) and Pt(IV) complexes of L were found to be non-emissive, whereas both Zn(II) and Cd(II) complexes displayed significant green emission attributed to intra-ligand charge transfer states. These results were supported by the observed red-shift of the emission maxima of complexes 2 and 3 with increasing the solvent polarity.

Redox induced colour changes between red-violet and blue in hetero-metal complexes of the type [CoII(4′-ferrocenyl-2,2′;6′2′′-terpyridine)2]X2 (X = counter anion)

Cobalt complexes incorporating ferrocene–terpyridine ligands show a reversible color change in response to redox reactions involving the cobalt centers.

Metallomics insights into the programmed cell death induced by metal-based anticancer compounds

Since the discovery of cisplatin more than 40 years ago, enormous research efforts have been dedicated to developing metal-based anticancer agents and to elucidating the mechanisms involved in the action of these compounds. Abnormal metabolism and the evasion of apoptosis are important hallmarks of malignant transformation, and the induction of apoptotic cell death has been considered to be a main pathway by which cytotoxic metal complexes combat cancer. However, many cancers have cellular defects involving the apoptotic machinery, which results in an acquired resistance to apoptotic cell death and therefore reduced chemotherapeutic effectiveness. Over the past decade, it has been revealed that a growing number of cell death pathways induced by metal complexes are not dependent on apoptosis. Metal complexes specifically triggering these alternative cell death pathways have been identified and explored as novel cancer treatment options. In this review, we discuss recent examples of metallomics studies on the different types of cell death induced by metal-based anticancer drugs, especially on the three major forms of programmed cell death (PCD) in mammalian cells: apoptosis, autophagy and regulated necrosis, also called necroptosis.

5-Ferrocenyl-2,2′-bipyridine ligands: synthesis, palladium(ii) and copper(i) complexes, optical and electrochemical properties

Two 5-ferrocenyl-2,2′-bipyridine ligands were synthesised using the palladium(0) catalysed Suzuki–Miyaura cross-coupling reaction. Palladium(ii) and copper(i) complexes of these ligands were synthesised and the optical and electrochemical properties of the complexes were compared to those of the “free” ligands.

Integrated and passive 1,2,3-triazolyl groups in fluorescent indicators for zinc(II) ions: thermodynamic and kinetic evaluations

In addition to being a covalent linker in molecular conjugation chemistry, the function of a 1,2,3-triazolyl moiety resulting from the copper(I)-catalyzed azide-alkyne cycloaddition reaction as a ligand for metal ions is receiving considerable attention. In this work, we characterize the thermodynamic and kinetic effects of incorporating a 1,2,3-triazolyl group in a multidentate ligand scaffold on metal coordination in the context of fluorescent zinc(II) indicator development. Ligands L14, BrL14, and FL14 (1,4-isomers) contain the 1,4-disubstituted-1,2,3-triazolyl group that is capable of binding with zinc(II) in conjunction with a di(2-picolylamino) (DPA) moiety within a multidentate ligand scaffold. Therefore, the 1,2,3-triazolyl in the 1,4-isomers is "integrated" in chelation. The 1,5-isomers L15, BrL15, and FL15 contain 1,2,3-triazolyls that are excluded from participating in zinc(II) coordination. These 1,2,3-triazolyls are "passive linkers". Zinc(II) complexes of 2:1 (ligand/metal) stoichiometry are identified in solution using (1)H NMR spectroscopy and isothermal titration calorimetry (ITC) and, in one case, characterized in the solid state. The 1:1 ligand/zinc(II) affinity ratio of L14 over L15, which is attributed to the affinity enhancement of a 1,2,3-triazolyl group to zinc(II) over that of the solvent acetonitrile, is quantified at 18 (-1.7 kcal/mol at 298 K) using an ITC experiment. Fluorescent ligands FL14 and FL15 are evaluated for their potential in zinc(II) sensing applications under pH neutral aqueous conditions. The 1,4-isomer FL14 binds zinc(II) both stronger and faster than the 1,5-isomer FL15. Visualization of free zinc(II) ion distribution in live HeLa cells is achieved using both FL14 and FL15. The superiority of FL14 in staining endogenous zinc(II) ions in live rat hippocampal slices is evident. In summation, this work is a fundamental study of 1,2,3-triazole coordination chemistry, with a demonstration of its utility in developing fluorescent indicators.

Photocytotoxicity of copper(II) complexes of curcumin and N-ferrocenylmethyl-L-amino acids

Copper(II) complexes [Cu(Fc-aa)(cur)] (1-3) of curcumin (Hcur) and N-ferrocenylmethyl-L-amino acids (Fc-aa), viz., ferrocenylmethyl-L-tyrosine (Fc-TyrH), ferrocenylmethyl-L-tryptophan (Fc-TrpH) and ferrocenylmethyl-L-methionine (Fc-MetH), were prepared and characterized. The DNA photocleavage activity, photocytotoxicity and cellular localization in HeLa and MCF-7 cancer cells of these complexes were studied. Acetylacetonate (acac) complexes [Cu(Fc-aa)(acac)] (4-6) were prepared and used as controls. The chemical nuclease inactive complexes showed efficient pUC19 DNA cleavage activity in visible light. Complexes 1-3 showed high photocytotoxicity with low dark toxicity thus giving remarkable photodynamic effect. FACScan analysis showed apoptosis of the cancer cells. Fluorescence microscopic studies revealed primarily cytosolic localization of the complexes.