Ferrocene-Conjugated Copper(II) Complexes of l-Methionine and Phenanthroline Bases: Synthesis, Structure, and Photocytotoxic Activity

Silver complexes with substituted terpyridines as promising anticancer metallodrugs and their crystal structure, photoluminescence, and DNA interactions

Six silver hexafluoroantimonate complexes (1-6) with 4'-(4'-substituted-phenyl)-2,2':6',2''-terpyridine compounds bearing hydrogen (L1), methyl (L2), methylsulfonyl (L3), chloro (L4), bromo (L5) and iodo (L6) were prepared and characterized by 1H NMR, 13C NMR, IR, elemental analysis and single crystal X-ray diffraction. All the compounds exhibit interesting photoluminescence properties in the solid state and solution. In vitro data demonstrate that all of them show higher antiproliferative activities than cisplatin against three human carcinoma cell lines, A549, Eca-109 and MCF-7. Compound 3 exhibits the lowest IC50 value (2.298 μM) against A549 cell lines, which is 2.963 μM for 4 against Eca-109 and 1.830 μM for 1 against MCF-7. For silver halogen-substituted terpyridine compounds, their anticancer activities decrease following the sequence of -Cl, -Br, and -I substituents. The comparison results show that their anticancer activity is significantly higher than that of their free ligands. The DNA interaction was studied by fluorescence titration, circular dichroism spectroscopy and molecular modeling methods. Spectrophotometric results reveal that the compounds have strong affinity binding with DNA as intercalators and molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The DNA binding ability of the complexes has been correlated with their anticancer activities, which could potentially provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

DNA Interaction, DNA Photocleavage, Photocytotoxicity In Vitro, and Molecular Docking of Naphthyl-Appended Ruthenium Complexes

With the development of metal-based drugs, Ru(II) compounds present potential applications of PDT (photodynamic therapy) and anticancer reagents. We herein synthesized two naphthyl-appended ruthenium complexes by the combination of the ligand with naphthyl and bipyridyl. The DNA affinities, photocleavage abilities, and photocytotoxicity were studied by various spectral methods, viscosity measurement, theoretical computation method, gel electrophoresis, and MTT method. Two complexes exhibited strong interaction with calf thymus DNA by intercalation. Production of singlet oxygen (¹O₂) led to obvious DNA photocleavage activities of two complexes under 365 nm light. Furthermore, two complexes displayed obvious photocytotoxicity and low dark cytotoxicity towards Hela, A549, and A375 cells.

Co(II) complexes of curcumin and a ferrocene-based curcuminoid: a study on photo-induced antitumor activity

Co(II) complexes having a ferrocene-based curcuminoid (Fc-curH) ligand viz. [Co(L)₂(Fc-cur)]ClO₄ (1, 2), where L is phenanthroline base, namely, 1,10-phenanthroline (phen in 1) and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 2) have been synthesized, characterized and evaluated as photochemotherapeutic agents in vitro. The corresponding Co(II) complexes of the naturally occurring polyphenol curcumin (curH), namely, [Co(L)₂(cur)]ClO₄ (3, 4), where L is phen (in 3) and dppz (in 4) were synthesized and their photo-induced anticancer activities compared with their ferrocene containing counterparts 1 and 2. The Co(II) acetylacetonato complex viz. [Co(phen)₂(acac)]ClO₄ (5) was structurally characterized through X-ray crystallography and used as control for cellular experiments. The Co(II) complexes having ferrocene-based curcuminoid are remarkably stable at physiological condition with higher lipophilicity compared to their curcumin analogues. The complexes display significant binding propensity to calf thymus (ct) DNA and human serum albumin (HSA). The complexes 1-4 display remarkable visible light induced cytotoxicity with the ferrocenyl analogues showing more phototoxic index (PI). The Co(II) curcumin complexes localize in the nucleus and mitochondria of A549 cells. The primary cell death mechanism is believed to be apoptotic in nature induced by light assisted generation of reactive oxygen species (ROS).Graphic abstract.

Dual sensing of methionine and aspartic acid in aqueous medium by a quinoline-based fluorescent probe

A quinoline-based Schiff base sensor, 6-methyl-2-oxo-1,2-dihydro-quinoline-3-carboxaldehyde-4(N)-phenylsemicarbazone (6MPS), has been developed for selective sensing of methionine and aspartic acid in aqueous medium through "on-off-on" type selective detection of copper ion. Fluorescence imaging of 6MPS, 6MPSC, 6MPSCN, 6MPSC-met, 6MPSCN-met, 6MPSC-asp and 6MPSCN-asp has been successfully demonstrated, in which the sensing probes 6MPSC-met, 6MPSCN-met, 6MPSC-asp and 6MPSCN-asp displayed bright green fluorescence in both in vitro and in vivo live cells.

Copper chloride complexes with substituted 4'-phenyl-terpyridine ligands: synthesis, characterization, antiproliferative activities and DNA interactions

Eleven copper chloride coordination compounds (1-11) with 4'-(4'-substituted-phenyl)-2,2':6',2''-terpyridine ligands bearing hydrogen (L¹), cyano (L²), p-hydroxyl (L³), m-hydroxyl (L⁴), o-hydroxyl (L⁵), methoxyl (L⁶), iodo (L⁷), bromo (L⁸), chloro (L⁹), fluoro (L¹⁰) or methylsulfonyl (L¹¹) were prepared and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Antiproliferative activities against tumor cells were investigated and DNA interactions were studied by circular dichroism spectroscopy and molecular modeling methods. In vitro data demonstrate that all the compounds exhibit higher antiproliferative activities as compared to cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 6 with methoxyl shows the best anti-proliferation activity. Spectrophotometric results reveal the strong affinity of the compounds for binding with DNA as intercalators and induce DNA conformational transitions. The results of molecular docking studies show that the compounds interact with DNA through π-π stacking, van der Waals forces, hydrophobic interactions and hydrogen bonds. The binding energies between compound 11 and three macromolecules, including DNA duplex, oligonucleotide and DNA-Topo I complex, are the lowest. The binding stability of compounds containing hydroxyl, methoxy and methylsulfonyl groups with biological macromolecules mainly relies on the hydrogen bonds. The ability of a compound to form hydrogen bonds can promote its binding to biological targets, thereby exhibiting high antiproliferative activity.

A novel biocompatible formate bridged 1D-Cu(ii) coordination polymer induces apoptosis selectively in human lung adenocarcinoma (A549) cells

Copper compounds are promising candidates for next-generation metal anticancer drugs. Therefore, we synthesized and characterized a formate bridged 1D coordination polymer [Cu(L)(HCOO)₂]_n, (L = 2-methoxy-6-methyl-3-((quinolin-8-ylimino)methyl)chroman-4-ol), PCU1, wherein the Cu(ii) center adopts a square pyramidal coordination environment with adjacent CuCu distances of 5.28 Å. Primarily, in vitro DNA interaction studies revealed a metallopolymer which possesses high DNA binding propensity and cleaves DNA via the oxidative pathway. We further analysed its potential on cancerous cells MCF-7, HeLa, A549, and two non-tumorigenic cells HEK293 and HBE. The selective cytotoxicity potential of PCU1 against A549 cells driven us to examine the mechanistic pathways comprehensively by carrying out various assays viz, cell cycle arrest, Annexin V-FTIC/PI assay, autophagy, intercellular localization, mitochondrial membrane potential 'MMP', antiproliferative assay, and gene expression of TGF-β and MMP-2.

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

The role of a weakly coordinating thioether group in ligation controlled molecular self-assemblies and their inter-conversions in Ni(ii) complexes of l-methionine derived ligand

A series of Ni(ii) complexes of an amino acid derived ligand (Salmet) has been synthesized, and characterized by various techniques including X-ray crystallography. Alkali ions K⁺/Na⁺ direct the conversion of monomers to multi-nuclear complexes.

Photocytotoxic copper(II) complexes of N-salicylyl-l-tryptophan and phenanthroline bases

Four ternary copper(II) complexes of N-salicylyl-l-Tryptophan (Sal-TrpH) and phenanthroline bases of general formula [Cu(Sal-Trp)(L)], where L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3) and 2-(anthracen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip, 4), were synthesized and fully characterized. The complexes were evaluated for their affinity for biomolecules and photocytotoxic activities. Single crystal X-ray diffraction studies of complex 1 revealed that it has a square pyramidal CuN₃O₂ core with the phenolate oxygen of salicylaldehyde occupying the axial coordination site in the solid state. Complexes 1-4 displayed the Cu(II)-Cu(I) redox couples at ~-0.3 V vs. Ag/AgCl reference electrode in DMF-0.1 M [Buⁿ₄N](ClO₄). A Cu(II)-based weak d-d band ~650 nm and a moderately strong ligand to metal charge transfer band at ~430 nm were observed in DMF-Tris-HCl buffer (pH 7.2) (1:4 v/v). The complexes are efficient binders to calf thymus DNA and model proteins such as bovine serum albumin and lysozyme. They cleave supercoiled plasmid DNA efficiently when exposed to 446 and 660 nm laser radiation. They are cytotoxic to HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells showing significant enhancement of cytotoxicity upon photo-excitation with low energy visible light. The complexes are found to kill cancer cells through generation of reactive oxygen species (ROS) as confirmed by DCFDA (2',7'-dichlorofluorescin diacetate) assay. The apoptotic cell death induced by complex 4 was confirmed by Annexin V-Fluorescein isothiocyanate-Propidium iodide assay. Confocal microscopic images using 4 showed its primary cytosolic localization in the HeLa and MCF-7 cells.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(iii) complex of terpyridine and curcumin in cancer cells

A mixed-ligand neodymium(iii) complex of ferrocene appended terpyridine and curcumin targets the mitochondria and shows remarkable visible-light induced cytotoxicity in HeLa and MCF-7 cancer cells while being much less toxic in dark and to MCF-10A normal cells.

Heteroleptic Cu(ii)–polypyridyl complexes as photonucleases

Four new copper(ii)–polypyridyl complexes having tail groups with increasing aromaticity, hydrophobicity and planarity are synthesized. These complexes are found to be avid DNA binders and show efficient nuclease activity under either chemical stimulus or UV-A light irradiation.

Theoretical studies on binding modes of copper-based nucleases with DNA

In the present work, molecular simulations were performed for the purpose of predicting the binding modes of four types of copper nucleases (a total 33 compounds) with DNA. Our docking results accurately predicted the groove binding and electrostatic interaction for some copper nucleases with B-DNA. The intercalation modes were also reproduced by "gap DNA". The obtained results demonstrated that the ligand size, length, functional groups and chelate ring size bound to the copper center could influence the binding affinities of copper nucleases. The binding affinities obtained from the docking calculations herein also replicated results found using MM-PBSA approach. The predicted DNA binding modes of copper nucleases with DNA will ultimately help us to better understand the interaction of copper compounds with DNA.

DNA binding, photoactivated DNA cleavage and cytotoxic activity of Cu(II) and Co(II) based Schiff-base azo photosensitizers

A new class of Cu(II) and Co(II) complexes of azo-containing Schiff base of the type [Cu(L1)2] and [Co(L1)2], where L1=4-[(E)-{2-hydroxy-3-[(E)-(4-bromophenyl)diazenyl]benzylidene}amino]benzoic acid have been synthesized and characterized. Extension of conjugation and the presence of free carboxylic acid group of the ligand L1 increased the wavelength of the complexes from visible region to the near IR region (620-850 nm). The Cu(II) and Co(II) complexes interacted with CT-DNA via intercalative mode with the respective Kb value of 3.2×10(4) M(-1) and 2.9×10(4) M(-1) and acted as proficient photocleavers of SC pUC19 DNA in UV-A light, forming (1)O2 as the reactive oxygen species with the quantum yield of 0.38 and 0.36, respectively. Furthermore, the Cu(II) and Co(II) complexes showed photocytotoxicity toward two selected tumor cell lines MCF-7 and A549 by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) method, and the Cu(II) complex exhibits higher photocytotoxicity than Co(II) complex against each of the selected cell lines, this result is identical with their DNA binding ability order.

Photocytotoxic oxovanadium(IV) complexes of ferrocenyl-terpyridine and acetylacetonate derivatives

Oxovanadium(IV) complexes [VO(Fc-tpy)(acac)](ClO4) (1), [VO(Fc-tpy)(nap-acac)](ClO4) (2), [VO(Fc-tpy)(py-acac)](ClO4) (3) and [VO(Ph-tpy)(py-acac)](ClO4) (4) of 4'-ferrocenyl-2,2':6',2"-terpyridine (Fc-tpy) and 4'-phenyl-2,2':6',2"-terpyridine (Ph-tpy) having monoanionic acetylacetonate (acac), naphthylacetylacetonate (nap-acac) or pyrenylacetylacetonate (py-acac) ligand were prepared, characterized and their photocytotoxicity in visible light studied. The ferrocenyl complexes 1-3 showed an intense charge transfer band near 585 nm in DMF and displayed Fc(+)/Fc and V(IV)/V(III) redox couples near 0.66 V and -0.95 V vs. SCE in DMF-0.1 M TBAP. The complexes as avid binders to calf thymus DNA showed significant photocleavage of plasmid DNA in green light (568 nm) forming OH radicals. The complexes that are photocytotoxic in HeLa and MCF-7 cancer cells in visible light (400-700 nm) with low dark toxicity remain nontoxic in normal fibroblast 3T3 cells. ICP-MS and fluorescence microscopic studies show significant cellular uptake of the complexes. Photo-irradiation of the complexes causes apoptotic cell death by ROS as evidenced from the DCFDA assay.

Synthesis, DNA interaction and anticancer activity of copper(II) complexes with 4'-phenyl-2,2':6',2″-terpyridine derivatives

Three novel copper(II) complexes CuL(1)Cl2 (1) (L(1)=4'-(3-methoxyphenyl)-2,2':6'- 2″-terpyridine), CuL(2)Cl2 (2) (L(2)=4'-(4-methoxyphenyl)-2,2':6'-2″-terpyridine) and CuL(3)Cl2 (3) (L(3)=4'-(3,5-dimethoxyphenyl)-2,2':6'-2″-terpyridine) have been synthesized and characterized. Absorption spectral titration experiments, ethidium bromide displacement assays, and cyclic voltammetric experiments were carried out and the results suggested that these complexes bound to DNA through an intercalative mode. Moreover, these complexes were found to cleave pBR322 DNA efficiently in the presence of glutathione (GSH), and exhibited good anticancer activity against HeLa, Hep-G2 and BEL-7402 cell lines. Nuclear chromatin cleavage was also observed by acridine orange/ethidium bromide (AO/EB) staining assays and comet assays. These results demonstrated that these three Cu(II) complexes caused DNA damage and induced the apoptosis of HeLa cells. Mechanistic investigations revealed the participation of reactive oxygen species which can be trapped by reactive oxygen species (ROS) radical scavengers and ROS sensors.

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.