New approach for the preparation of efficient DNA cleaving agents: ditopic copper-platinum complexes based on 3-Clip-Phen and cisplatin

Unveiling the promising anticancer effect of copper-based compounds: a comprehensive review

Copper is a necessary micronutrient for maintaining the well-being of the human body. The biological activity of organic ligands, especially their anticancer activity, is often enhanced when they coordinate with copper(I) and (II) ions. Copper and its compounds are capable of inducing tumor cell death through various mechanisms of action, including activation of apoptosis signaling pathways by reactive oxygen species (ROS), inhibition of angiogenesis, induction of cuproptosis, and paraptosis. Some of the copper complexes are currently being evaluated in clinical trials for their ability to map tumor hypoxia in various cancers, including locally advanced rectal cancer and bulky tumors. Several studies have shown that copper nanoparticles can be used as effective agents in chemodynamic therapy, phototherapy, hyperthermia, and immunotherapy. Despite the promising anticancer activity of copper-based compounds, their use in clinical trials is subject to certain limitations. Elevated copper concentrations may promote tumor growth, angiogenesis, and metastasis by affecting cellular processes.

Platinum-containing heterometallic complexes in cancer therapy: advances and perspectives

Platinum-based anticancer drugs are among the most widely used antineoplastics in clinical settings. Their therapeutic applications and outcomes are, however, greatly hampered by drug resistance, systemic toxicity, and the lack...

A heterotrinuclear bioinspired coordination complex capable of binding to DNA and emulation of nuclease activity

The investigation of compounds capable of strongly and selectively interacting with DNA comprises a field of research in constant development. In this work, we demonstrate that a trinuclear coordination complex based on a dinuclear Fe(III)Zn(II) core designed for biomimicry of the hydrolytic enzyme kidney bean purple acid phosphatase, containing an additional pendant arm coordinating a Pd(II) ion, has the ability to interact with DNA and to promote its hydrolytic cleavage. These results were found through analysis of plasmid DNA interaction and cleavage by the trinuclear complex 1 and its derivatives 2 and 3, in addition to the analysis of alteration in the DNA structure in the presence of the complexes through circular dichroism and DNA footprinting techniques. The suggested covalent interaction of the palladium-containing complex with DNA was analysed using an electrophoretic mobility assay, circular dichroism, high resolution gel separation techniques and kinetic analysis. This is a new and promising metal complex targeted to nucleic acids and acting in two separate ways: strong DNA interaction and hydrolytic cleavage.

Synergy of DNA intercalation and catalytic activity of a copper complex towards improved polymerase inhibition and cancer cell cytotoxicity

Improving the binding of metal complexes to DNA to boost cancer cell cytotoxicity requires fine tuning of their structural and chemical properties. Copper has been used as a metal center in compounds containing intercalating ligands due to its ability to catalytically generate reactive oxygen species (ROS), such as hydroxyl radicals (OH˙). We envision the synergy of DNA binding and ROS generation in proximity to target DNA as a powerful chemotherapy treatment. Here, we explore the use of [Cu(2CP-Bz-SMe)]2+ (2CP-Bz-SMe = 1,3-bis(1,10-phenanthrolin-2-yloxy)-N-(4-(methylthio)benzylidene)propan-2-amine) for this purpose by characterizing its cytotoxicity, DNA binding, and ability to affect DNA replication through the polymerase chain reaction - PCR and nuclease assays. We determined the binding (Kb) and Stern-Volmer constants (KSV) for complex-DNA association of 5.8 ± 0.14 × 104 and 1.64 (±0.08), respectively, through absorption titration and competitive fluorescence experiments. These values were superior to those of other Cu-complex intercalators. We hypothesize that the distorted trigonal bipyramidal geometry of [Cu(2CP-Bz-SMe)]2+ allows the phenanthroline fragments to be better accommodated into the DNA double helix. Moreover, the aromaticity of these fragments increases the local hydrophobicity thus increasing the affinity for the hydrophobic domains of DNA. Nuclease assays in the presence of common reducing agents ascorbic acid, nicotinamide adenine dinucleotide, and glutathione showed the effective degradation of DNA due to the in situ generation of OH˙. The [Cu(2CP-Bz-SMe)]2+ complex showed cytotoxicity against the following human cancer cells lines A549, MCF-7, MDA-MB-231 and MG-63 with half maximal inhibitory concentration (IC50) values of 4.62 ± 0.48, 5.20 ± 0.76, 5.70 ± 0.42 and 2.88 ± 0.66 μM, respectively. These low values of IC50, which are promising if compared to that of cisplatin, are ascribed to the synergistic effect of ROS generation with the intercalation ability into the DNA minor grooves and blocking DNA replication. This study introduces new principles for synergizing the chemical and structural properties of intercalation compounds for improved drug-DNA interactions targeting cancer.

Anticancer Compounds Based on Isatin-Derivatives: Strategies to Ameliorate Selectivity and Efficiency

In this review we compare and discuss results of compounds already reported as anticancer agents based on isatin-derivatives, metalated as well as non-metallated. Isatin compounds can be obtained from plants, marine animals, and is also found in human fluids as a metabolite of amino acids. Its derivatives include imines, hydrazones, thiosemicarbazones, among others, already focused on numerous anticancer studies. Some of them have entered in pre-clinical and clinical tests as antiangiogenic compounds or inhibitors of crucial proteins. As free ligands or coordinated to metal ions, such isatin derivatives showed promising antiproliferative properties against different cancer cells, targeting different biomolecules or organelles. Binding to metal ions usually improves its biological properties, indicating a modulation by the metal and by the ligand in a synergistic process. They also reveal diverse mechanisms of action, being able of binding DNA, generating reactive species that cause oxidative damage, and inhibiting selected proteins. Strategies used to improve the efficiency and selectivity of these compounds comprise structural modification of the ligands, metalation with different ions, syntheses of mononuclear and dinuclear species, and use of inserted or anchored compounds in selected drug delivery systems.

Efficient self-assembly of heterometallic triangular necklace with strong antibacterial activity

Sophisticated mechanically interlocked molecules (MIMs) with interesting structures, properties and applications have attracted great interest in the field of supramolecular chemistry. We herein report a highly efficient self-assembly of heterometallic triangular necklace 1 containing Cu and Pt metals with strong antibacterial activity. Single-crystal X-ray analysis shows that the finely arranged triangular necklace 1 has two racemic enantiomers in its solid state with intriguing packing motif. The superior antibacterial activity of necklace 1 against both standard and clinically drug-resistant pathogens implies that the presence of Cu(I) center and platinum(II) significantly enhance the bacterium-binding/damaging activity, which is mainly attributed to the highly positively charged nature, the possible synergistic effect of heterometals in the necklace, and the improved stability in culture media. This work clearly discloses the structure-property relationships that the existence of two different metal centers not only facilitates successful construction of heterometallic triangular necklace but also endows it with superior nuclease properties and antibacterial activities.

Precise assembly of heterometallic complexes is a challenge. Here, the authors design a heterometallic triangular necklace through a highly efficient threading-and-ring-closing approach driven by metal-ligand coordination, which shows strong bacterium-binding and cell wall/plasma membrane-disrupting capacity for killing bacterial cells.

Heterobinuclear copper(II)‑platinum(II) complexes with oxindolimine ligands: Interactions with DNA, and inhibition of kinase and alkaline phosphatase proteins

Two mononuclear copper(II) compounds, [Cu(isad)(H₂O)Cl]Cl 1 and [Cu(isah)(H₂O)Cl]Cl 2, and its corresponding heterobinuclear species containing also platinum(II), [CuCl(isad)Pt(NH₃)Cl₂] 3 and [CuCl(isah)Pt(NH₃)Cl₂] 4 (where isad and isah are oxindolimine ligands, (E)-3-(2-(3-aminopropylamino)ethylimino)indolin-2-one, and (E)-3-(3-amino-2-hydroxypropylimino)indolin-2-one, respectively), have been previously synthesized and characterized by different spectroscopic techniques in our laboratory. Cytotoxicity assays performed with B16F10 murine cancer cells, and MES-SA human uterine sarcoma cells, showed IC₅₀ values lower or in the same order of cisplatin. Herein, in order to better elucidate their probable modes of action, possible interaction and damage to DNA, as well as their effect on the activity of crucial proteins were verified. Both mononuclear complexes and the binuclear compound 4 displayed a significant cleavage activity toward plasmid DNA, while compound 3 tends to protect DNA from oxidative damage, avoiding degradation. Complementary experiments indicated a significant inhibition activity toward cyclin-dependent kinase (CDK1/cyclinB) activity in the phosphorylation of histone H1, and only moderate inhibition concerning alkaline phosphatase. Results also revealed that the reactivity is reliant on the ligand structure and on the nature of the metal present, in a synergistic effect. Simulation studies complemented and supported our results, indicating different bindings of the binuclear compounds to DNA. Therefore, the verified cytotoxicity of these complexes comprises multiple modes of action, including modification of DNA conformation, scission of DNA strands by reactive oxygen species, and inhibition of selected proteins that are crucial to the cellular cycle.

Synthesis of copper and zinc 2-(pyridin-2-yl)imidazo[1,2-a]pyridine complexes and their potential anticancer activity

A small library of novel copper and zinc imidazo[1,2-a]pyridine complexes have been synthesized. Their structures were confirmed by X-ray diffraction crystallography and a selection of these compounds was tested against five cancer cell lines originating from breast cancer (MCF-7 and MDA-MB-231), leukemia (K562 and HL-60) and colorectal cancer (HT-29). The imidazo[1,2-a]pyridines and their zinc complexes showed poor anticancer activity, while the copper complexes were active against the cancer cell lines with IC₅₀ values comparable to and lower than camptothecin. For example, copper 6-bromo-N-cyclohexyl-2-(pyridin-2-yl)imidazo[1,2-a]pyridin-3-amine acetate 21 had an IC₅₀ value lower than 1 μM against the HT-29 cells. Fluorescence microscopy with acridine orange, Hoechst 33342 and ethidium bromide, used in a preliminary investigation to evaluate morphological changes showed that copper 6-bromo-N-cyclohexyl-2-(pyridin-2-yl)imidazo[1,2-a]pyridin-3-amine acetate 21 caused both apoptosis, necrosis and paraptosis in the MCF-7 and HL-60 cells. A select group of copper N-cyclohexyl-2-(pyridin-2-yl)imidazo[1,2-a]pyridin-3-amines (26, 27, 29 and 31) induced apoptosis, paraptosis and deformed nuclei in MCF-7 cells.

Design, syntheses, characterization, and cytotoxicity studies of novel heterobinuclear oxindolimine copper(II)-platinum(II) complexes

Herein, the design and syntheses of two new mononuclear oxindolimine-copper(II) (1 and 2) and corresponding heterobinuclear oxindolimine Cu(II)Pt(II) complexes (3 and 4), are described. All the isolated complexes were characterized by spectroscopic techniques (UV/Vis, IR, EPR), in addition to elemental analysis and mass spectrometry. Cyclic voltammetry (CV) measurements showed that in all cases, one-electron quasi-reversible waves were observed, and ascribed to the formation of corresponding copper(I) complexes. Additionally, waves related to oxindolimine ligand reduction was verified, and confirmed using analogous oxindolimine-Zn(II) complexes. The Pt(IV/II) reduction, and corresponding oxidation, for complexes 3 and 4 occurred at very close values to those observed for cisplatin. By complementary fluorescence studies, it was shown that glutathione (GSH) cannot reduce any of these complexes, under the experimental conditions (room temperature, phosphate buffer 50mM, pH7.4), using an excess of 20-fold [GSH]. All these complexes showed characteristic EPR spectral profile, with parameters values g_ǁ>g_⊥ suggesting an axially distorted environment around the copper(II) center. Interactions with calf thymus-DNA, monitored by circular dichroism (CD), indicated different effects modulated by the ligands. Finally, the cytotoxicity of each complex was tested toward different tumor cells, in comparison to cisplatin, and low values of IC₅₀ in the range 0.6 to 4.0μM were obtained, after 24 or 48h incubation at 37°C. The obtained results indicate that such complexes can be promising alternative antitumor agents.

Characterization of antiproliferative potential and biological targets of a copper compound containing 4'-phenyl terpyridine

Several copper complexes have been assessed as anti-tumor agents against cancer cells. In this work, a copper compound [Cu(H2O){OS(CH3)2}L](NO3)2 incorporating the ligand 4'-phenyl-terpyridine antiproliferative activity against human colorectal, hepatocellular carcinomas and breast adenocarcinoma cell lines was determined, demonstrating high cytotoxicity. The compound is able to induce apoptosis and a slight delay in cancer cell cycle progression, probably by its interaction with DNA and induction of double-strand pDNA cleavage, which is enhanced by oxidative mechanisms. Moreover, proteomic studies indicate that the compound induces alterations in proteins involved in cytoskeleton maintenance, cell cycle progression and apoptosis, corroborating its antiproliferative potential.

Interaction of methotrexate, an anticancer agent, with copper(II) ions: coordination pattern, DNA-cleaving properties and cytotoxic studies

The acid-base properties and the Cu(II) binding processes of methotrexate (MTX) were characterized by selected spectroscopic techniques and potentiometric measurements. The pH titration data showed that MTX behaves as a triprotic ligand. The deprotonation constants were determined for α-COOH and γ-COOH groups and (N1)H⁺ from the pteridine ring. Taking all the obtained results into consideration, a coordination pattern was proposed. The DNA-cleaving activity and reactive oxygen species (ROS) generation were investigated for both MTX and the Cu(II)-MTX system. The complex displayed a promising nuclease activity toward plasmid DNA in the presence of hydrogen peroxide. Interestingly, the induction of ROS, such as hydroxyl radicals, superoxide anions or singlet oxygen, was excluded and a different mechanism of DNA degradation was proposed. As MTX is now commonly used in anticancer therapy i.e. against lung cancer, basic cell-based studies were carried out to establish if its Cu(II) complex exhibits higher cytotoxic properties than the ligand alone. Activities of both compounds were also tested against colon carcinoma. Moreover, the determined values of IC₅₀ were confronted with the cytotoxic activity of cisplatin.

Selective chemical modification of DNA with alkoxy- and benzyloxyamines

DNA is modified selectively at cytosine with benzyloxyamine and -derivatives carrying handles for click reactions.

A multifunctional molecular entity CuII–SnIV heterobimetallic complex as a potential cancer chemotherapeutic agent: DNA binding/cleavage, SOD mimetic, topoisomerase Iα inhibitory and in vitro cytotoxic activities

New chiral l-valine-derived Schiff base complexes with the bioactive heterocyclic ligand scaffold pyrazole (Hpz) were designed and synthesized with a view to find their potential as anticancer chemotherapeutic drug candidates.

A tri-copper(II) complex displaying DNA-cleaving properties and antiproliferative activity against cancer cells

A new disubstituted terpyridine ligand and the corresponding tri-copper(II) complex have been prepared and characterised. The binding affinity and binding mode of this tri-copper complex (as well as the previously reported mono- and di-copper analogues) towards duplex DNA were determined by using UV/Vis spectroscopic titrations and fluorescent indicator displacement (FID) assays. These studies showed the three complexes to bind moderately (in the order of 10(4)  M(-1)) to duplex DNA (ct-DNA and a 26-mer sequence). Furthermore, the number of copper centres and the nature of the substituents were found to play a significant role in defining the binding mode (intercalative or groove binding). The nuclease potential of the three complexes was investigated by using circular plasmid DNA as a substrate and analysing the products by agarose-gel electrophoresis. The cleaving activity was found to be dependent on the number of copper centres present (cleaving potency was in the order: tri-copper>di-copper>mono-copper). Interestingly, the tri-copper complex was able to cleave DNA without the need of external co-reductants. As this complex displayed the most promising nuclease properties, cell-based studies were carried out to establish if there was a direct link between DNA cleavage and cellular toxicity. The tri-copper complex displayed high cytotoxicity against four cancer cell lines. Of particular interest was that it displayed high cytotoxicity against the cisplatin-resistant MOLT-4 leukaemia cell line. Cellular uptake studies showed that the tri-copper complex was able to enter the cell and more importantly localise in the nucleus. Immunoblotting analysis (used to monitor changes in protein levels related to the DNA damage response pathway) and DNA-flow cytometric studies suggested that this tri-copper(II) complex is able to induce cellular DNA damage.

Nuclease activity via self-activation and anticancer activity of a mononuclear copper(II) complex: novel role of the tertiary butyl group in the ligand frame

The copper complex [Cu((t)BuPhimp)(Cl)] (1) derived from tridentate ligand (t)BuPhimpH having N(2)O donors was synthesized, and its molecular structure was determined. A phenoxyl radical complex was generated in solution at room temperature using Ce(IV). The nuclease and anticancer activities of 1 were investigated. The roles of the tert-butyl group and singlet oxygen in the DNA cleavage activity were also discussed.

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.

Carbohydrate-conjugate heterobimetallic complexes: synthesis, DNA binding studies, artificial nuclease activity and in vitro cytotoxicity

New carbohydrate-conjugated heterobimetallic complexes [C(32)H(62)N(10)O(8)NiSn(2)Cl(4)]Cl(2)(1) and [C(32)H(62)N(10)O(8)CuSn(2)Cl(4)]Cl(2) (2) were synthesized and characterized by spectroscopic (IR, (1)H, (13)C, and (119)Sn NMR, EPR, UV-vis, ESI-MS) and analytical methods. The interaction studies of 2 with CT DNA were studied by using various biophysical techniques, which showed high binding affinity of 2 toward CT DNA. The extent of interaction was further confirmed by the interaction of 2 with the nucleotides viz.; 5'-AMP, 5'-CMP, 5'-GMP, and 5'-TMP, by absorption titration. (1)H, (31)P, (119)Sn NMR spectroscopy further validated the interaction mode of 2 with 5'-GMP. The electrophoresis pattern observed for 2 with supercoiled pBR322 DNA, exhibited significantly good nuclease activity following oxidative pathway. The preferential selectivity of 2 toward the major groove was observed on interaction of 2 with pBR322 DNA, in the presence of standard groove binders viz.; DAPI and methyl green. Additionally, in vitro antitumor activity of 2 was evaluated on a panel of human cancer cell lines, exhibiting remarkable cytotoxicity activity against Colo205 (colon) and MCF7 (breast) cell lines with GI(50) values <10 μg/mL.

Copper curcuminoids containing anthracene groups: fluorescent molecules with cytotoxic activity

The coordination chemistry of the new curcuminoid ligand, 1,7-(di-9-anthracene-1,6-heptadiene-3,5-dione), abbreviated 9Accm has been studied, resulting in two new copper-9Accm compounds. Compound 1, [Cu(phen)Cl(9Accm)], was synthesized by reacting 9Accm with [Cu(phen)Cl(2)] in a 1:1 ratio (M:L) and compound 2, [Cu(9Accm)(2)], was prepared from Cu(OAc)(2) and 9Accm (1:2). UV-vis, electron paramagnetic resonance (EPR), and superconducting quantum interference device (SQUID) measurements were some of the techniques employed to portray these species; studies on single crystals of free 9Accm, [Cu(phen)Cl(9Accm)] and [Cu(9Accm)(2)(py)] provided detailed structural information about compounds 1 and 2·py, being the first two copper-curcuminoids crystallographically described. In addition the antitumor activity of the new compounds was studied and compared with free 9Accm for a number of human tumor cells. To provide more insight on the mode of action of these compounds under biological conditions, additional experiments were accomplished, including studies on the nature of their interactions with calf thymus DNA by UV-vis titration and Circular Dichroism. These experiments together with DNA-binding studies indicate electrostatic interactions between some of these species and the double helix, pointing out the weak nature of the interaction of the compounds with CT-DNA. The intrinsic fluorescence of the free ligand and both copper compounds provided valuable information over the cellular process and therefore, fluorescence microscopy studies were performed using a human osteosarcoma cell line. Studies in vitro using this technique suggest that the action of these molecules seems to occur outside the nuclei.

Copper in diseases and treatments, and copper-based anticancer strategies

Copper is found in all living organisms and is a crucial trace element in redox chemistry, growth and development. It is important for the function of several enzymes and proteins involved in energy metabolism, respiration, and DNA synthesis, notably cytochrome oxidase, superoxide dismutase, ascorbate oxidase, and tyrosinase. The major functions of copper-biological molecules involve oxidation-reduction reactions in which they react directly with molecular oxygen to produce free radicals. Therefore, copper requires tightly regulated homeostatic mechanisms to ensure adequate supplies without any toxic effects. Overload or deficiency of copper is associated, respectively, with Wilson disease (WD) and Menkes disease (MD), which are of genetic origin. Researches on Menkes and Wilson disorders have provided useful insights in the field of copper homeostasis and in particular into the understanding of intracellular trafficking and distribution of copper at molecular levels. Therapies based on metal supplementation with copper histidine or removal of copper excess by means of specific copper chelators are currently effective in treating MD and WD, respectively. Copper chelation therapy is now attracting much attention for the investigation and treatment of various neurodegenerative disorders such as Alzheimer, Parkinson and CreutzfeldtJakob. An excess of copper appears to be an essential co-factor for angiogenesis. Moreover, elevated levels of copper have been found in many types of human cancers, including prostate, breast, colon, lung, and brain. On these basis, the employment of copper chelators has been reported to be of therapeutic value in the treatment of several types of cancers as anti-angiogenic molecules. More recently, mixtures of copper chelators with copper salts have been found to act as efficient proteasome inhibitors and apoptosis inducers, specifically in cancer cells. Moreover, following the worldwide success of platinum(II) compounds in cancer chemotherapy, several families of individual copper complexes have been studied as potential antitumor agents. These investigations, revealing the occurrence of mechanisms of action quite different from platinum drugs, head toward the development of new anticancer metallodrugs with improved specificity and decreased toxic side effects.