Copper Complexes with 1,10-Phenanthroline Derivatives: Underlying Factors Affecting Their Cytotoxicity

Enhanced selectivity towards melanoma cells with zinc(II)-Schiff bases containing imidazole derivatives

Zinc(II)-complexes with the general formula [Zn(L)2] containing 8-hydroxyquinoline Schiff bases functionalized with 1-(3-aminopropyl)imidazole or 1-(3-aminopropyl)-2-methyl-1H-imidazole on 2-position and their respective ligands (HL1 or HL2) were synthesized and characterized by NMR, UV-Vis, FTIR and CD spectroscopies as well as ESI-MS spectrometry. Single crystals of HL2 and [Zn(L1)2]n were analysed by SC-XRD. [Zn(L1)2]n shows a 1D polymeric chain structure of alternating Zn(II) cations and bridging Schiff base ligands, in contrast to previously reported monomeric structures of analogous complexes. DFT calculations were performed to rationalize the polymeric X-ray structure of Zn(L1)2. Results showed that the ligands can bind as bi- or tridentate to Zn(II) and there is the possibility of a dynamic behavior for the complexes in solution. Both ligands and complexes present limited stability in aqueous media, however, in the presence of bovine serum albumin the complexes are stable. Molecular docking simulations and circular dichroism spectroscopic studies suggest binding to this protein in close proximity to the Trp213 residue. Biological studies on a panel of cancer cells revealed that the Zn(II)-complexes have a lower impact on cell viability than cisplatin, except for triple-negative breast cancer cells in which they were comparable. Notwithstanding, they display much higher selectivity towards cancer cells vs. normal cells, than cisplatin. They induce the generation of ROS and DNA double-strand breaks, primarily through apoptosis as the mode of cell death. Overall, the novel Zn(II)-complexes demonstrate improved induction of apoptosis and higher selectivity, particularly for melanoma cells, compared to previously reported analogues, making them promising candidates for clinical application.

Neutral rhenium(I) tricarbonyl complexes with sulfur-donor ligands: anti-proliferative activity and cellular localization

Rhenium(I) tricarbonyl complexes are widely studied for their cell imaging properties and anti-cancer and anti-microbial activities, but the complexes with S-donor ligands remain relatively unexplored. A series of six fac-[Re(NN)(CO)3(SR)] complexes, where (NN) is 2,2'-bipyridyl (bipy) or 1,10-phenanthroline (phen), and RSH is a series of thiocarboxylic acid methyl esters, have been synthesized and characterized. Cellular uptake and anti-proliferative activities of these complexes in human breast cancer cell lines (MDA-MB-231 and MCF-7) were generally lower than those of the previously described fac-[Re(NN)(CO)3(OH2)]+ complexes; however, one of the complexes, fac-[Re(CO)3(phen)(SC(Ph)CH2C(O)OMe)] (3b), was active (IC50 ∼ 10 μM at 72 h treatment) in thiol-depleted MDA-MB-231 cells. Moreover, unlike fac-[Re(CO)3(phen)(OH2)]+, this complex did not lose activity in the presence of extracellular glutathione. Taken together these properties show promise for further development of 3b and its analogues as potential anti-cancer drugs for co-treatment with thiol-depleting agents. Conversely, the stable and non-toxic complex, fac-[Re(bipy)(CO)3(SC(Me)C(O)OMe)] (1a), predominantly localized in the lysosomes of MDA-MB-231 cells, as shown by live cell confocal microscopy (λex = 405 nm, λem = 470-570 nm). It is strongly localized in a subset of lysosomes (25 μM Re, 4 h treatment), as shown by co-localization with a Lysotracker dye. Longer treatment times with 1a (25 μM Re for 48 h) resulted in partial migration of the probe into the mitochondria, as shown by co-localization with a Mitotracker dye. These properties make complex 1a an attractive target for further development as an organelle probe for multimodal imaging, including phosphorescence, carbonyl tag for vibrational spectroscopy, and Re tag for X-ray fluorescence microscopy.

Encapsulation of copper phenanthroline within horse spleen apoferritin: characterisation, cytotoxic activity and ability to retain temozolomide

Protein capsules are promising drug delivery vehicles for cancer research therapies. Apoferritin (AFt) is a self-assembling 12 nm diameter hollow nanocage with many desirable features for drug delivery, however, control of drug retention inside the protein cage remains challenging. Here we report the encapsulation of copper(ii)-1,10-phenanthroline (Cu(phen)) within the horse spleen AFt (HSAFt) nanocage, by diffusion of the metal through the pores between the protein subunits. Transmission electron microscopy revealed the formation of organised copper adducts inside HSAFt, without affecting protein integrity. These structures proved stable during storage (>4 months at -20 °C). Exposure to physiologically relevant conditions (37 °C) showed some selectivity in cargo release after 24 h at pH 5.5, relevant to the internalisation of AFt within the endosome (60% release), compared to pH 7.4, relevant to the bloodstream (40% release). Co-encapsulation of temozolomide, a prodrug used to treat glioblastoma multiforme, and Cu(phen) enabled entrapment of an average of 339 TMZ molecules per cage. In vitro results from MTT and clonogenic assays identified cytotoxic activity of the Cu(phen), HSAFt-Cu(phen) and HSAFt-Cu(phen)-TMZ adducts against colorectal cancer cells (HCT-116) and glioblastoma cells (U373V, U373M). However, the presence of the metal also contributed to more potent activity toward healthy MRC5 fibroblasts, a result that requires further investigation to assess the clinical viability of this system.

Synthesis, characterization, and cancer cell-selective cytotoxicity of mixed-ligand cobalt(III) complexes of 8-hydroxyquinolines and phenanthroline bases

Transition metal complexes exhibiting selective toxicity towards a broad range of cancer types are highly desirable as potential anticancer agents. Herein, we report the synthesis, characterization, and cytotoxicity studies of six new mixed-ligand cobalt(III) complexes of general formula [Co(B)2(L)](ClO4)2 (1-6), where B is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), and L is the monoanion of 8-hydroxyquinoline (HQ in 1, 3, 5) and 5-chloro-7-iodo-8-hydroxyquinoline (CQ in 2, 4, 6). The X-ray single crystal structures of complexes 1 and 2 as PF6- salts revealed a distorted octahedral CoN5O coordination environment. Complexes demonstrated good stability in an aqueous buffer medium and in the presence of ascorbic acid as a reductant. Cytotoxicity studies using a panel of nine cancer cell lines showed that complex 6, with the dppz and CQ ligands, was significantly toxic against most cancer cell types, yielding IC50 values in the range of 2 to 14 μM. Complexes 1, 3, and 5, containing the HQ ligand, displayed lower toxicity compared to their CQ counterparts. The phenanthroline complexes demonstrated marginal toxicity towards the tested cell lines, while the dpq complexes exhibited moderate toxicity. Interestingly, all complexes demonstrated negligible toxicity towards normal HEK-293 kidney cells (IC50 > 100 μM). The observed cytotoxicity of the complexes correlated well with their lipophilicities (dppz > dpq > phen). The cytotoxicity of complex 6 was comparable to that of the clinical drug cisplatin under similar conditions. Notably, neither the HQ nor the CQ ligands alone demonstrated noticeable toxicity against any of the tested cell lines. The Annexin-V-FITC and DCFDA assays revealed that the cell death mechanism induced by the complexes involved apoptosis, which could be attributed to the metal-assisted generation of reactive oxygen species. Overall, the dppz complex 6, with its remarkable cytotoxicity against a broad range of cancer cells and negligible toxicity toward normal cells, holds significant potential for cancer chemotherapeutic applications.

Dinuclear copper(II) complexes with a bridging bis(chalcone) ligand reveal considerable in vitro cytotoxicity on human cancer cells and enhanced selectivity

A bis(chalcone) molecule (H2L) was synthesized via Aldol's condensation from terephthalaldehyde and 2'-hydroxyacetophenone and it was used as bridging ligand for the preparation of five dinuclear copper(II) complexes of the composition [Cu(NN)(μ-L)Cu(NN)](NO3)2⋅nH2O (n = 0-2) (1-5), where NN stands for a bidentate N-donor ligand such as phen (1,10-phenanthroline, 1), bpy (2,2'-bipyridine, 2), mebpy (5,5'-dimethyl-2,2'-dipyridine, 3), bphen (bathophenanthroline, 4) and nphen (5-nitro-1,10-phenanthroline, 5). The compounds were characterized by different suitable techniques to confirm their purity, composition, and structure. Moreover, the products were evaluated for their in vitro cytotoxicity on a panel of human cancer cell lines: ovarian (A2780), ovarian resistant to cisplatin (A2780R), prostate (PC3), osteosarcoma (HOS), breast (MCF7) and lung (A549), and normal fibroblasts (MRC-5), showing significant cytotoxicity in most cases, with IC50 ≈ 0.35-7.8 μM. Additionally, the time-dependent cytotoxicity and cellular uptake of copper, together with flow cytometric studies concerning cell-cycle arrest, induction of cell death and autophagy and induction of intracellular ROS/superoxide production in A2780 cells, were also performed. The results of biological testing on A2780 cells pointed out a possible mechanism of action characterized by the G2/M cell cycle arrest and induction of apoptosis by triggering the intrinsic signalling pathway associated with the damage of mitochondrial structure and depletion of mitochondrial membrane potential. SYNOPSIS: Dinuclear Cu(II) complexes bearing a bridging bis(chalcone) ligand revealed high in vitro cytotoxicity, initiated A2780 cell arrest at G2/M phase and efficiently triggered intrinsic pathway of apoptosis.

New copper(II) and oxidovanadium(IV) complexes with a vitamin B6 Schiff base: mechanism of action and synergy studies on 2D and 3D human osteosarcoma cell models

We report the synthesis, characterization and anticancer activity of a new Schiff base (H2L) derived from the condensation of pyridoxamine with pyridoxal and its novel copper(II) and oxidovanadium(IV) complexes: [Cu(HL)Cl] (1), [Cu(LH2)(phen)]Cl2 (2), [Cu(LH2)(amphen)]Cl2 (3), [VIVO(HL)Cl] (4), and [VIVO(LH2)(phen)]Cl2 (5), where phen is 1,10-phenanthroline and amphen is its 5-amino derivative. All compounds were characterized by analytical and spectroscopic techniques, namely FTIR, UV-vis and EPR spectroscopy. Their stability in aqueous media was evaluated, revealing that the presence of the phen co-ligand significantly increases the stability. The ternary Cu(II) complexes (2 and 3) impaired cell viability of osteosarcoma cells (MG-63) (IC50 values of 3.6 ± 0.6 and 7 ± 1.9 μM for 2 and 3), while 1 and the VIVO complexes did not show relevant anticancer activity. Complexes 2 and 3 are also more active than cisplatin (CDDP). Synergistic studies between 2 and sorafenib showed significant synergism on MG-63 cells for the following combinations: 2 (2.0 μM) + sorafenib (10.0 μM) and 2 (2.5 μM) + sorafenib (12.5 μM), whilst the combination of 2 and CDDP did not show synergy. Complex 2 interacts with DNA, inducing significant genotoxic effects on MG-63 cells from 1.0 to 2.5 μM and it increases the ROS levels 880% over basal. Moreover, 2 induces apoptosis at 1.0 and 2.0 μM, while its combination with sorafenib induces apoptosis and necrosis. Finally, compound 2 reduces the cell viability of MG-63 spheroids showing an IC50 value 7-fold lower than that of CDDP (8.5 ± 0.4 μM vs. 65 ± 6 μM). The combination of 2 and sorafenib also showed synergism on spheroids, suggesting that the combination of these drugs improves the anticancer effect against bone cancer cells.

A review on metal complexes and its anti-cancer activities: Recent updates from in vivo studies

Research into cancer therapeutics has uncovered various potential medications based on metal-containing scaffolds after the discovery and clinical applications of cisplatin as an anti-cancer agent. This has resulted in many metallodrugs that can be put into medical applications. These metallodrugs have a wider variety of functions and mechanisms of action than pure organic molecules. Although platinum-based medicines are very efficient anti-cancer agents, they are often accompanied by significant side effects and toxicity and are limited by resistance. Some of the most studied and developed alternatives to platinum-based anti-cancer medications include metallodrugs based on ruthenium, gold, copper, iridium, and osmium, which showed effectiveness against many cancer cell lines. These metal-based medicines represent an exciting new category of potential cancer treatments and sparked a renewed interest in the search for effective anti-cancer therapies. Despite the widespread development of metal complexes touted as powerful and promising in vitro anti-cancer therapeutics, only a small percentage of these compounds have shown their worth in vivo models. Metallodrugs, which are more effective and less toxic than platinum-based drugs and can treat drug-resistant cancer cells, are the focus of this review. Here, we highlighted some of the most recently developed Pt, Ru, Au, Cu, Ir, and Os complexes that have shown significant in vivo antitumor properties between 2017 and 2023.

Structural and solution speciation studies on selected [Cu(NN)(OO)] complexes and an investigation of their biomimetic activity, ROS generation and their cytotoxicity in normoxic, hypoxic and anoxic environments in MCF-7 breast cancer-derived cells

Reactive oxygen species(ROS) generation with subsequent DNA damage is one of the principle mechanisms of action assigned to copper-based anticancer complexes. The efficacy of this type of chemotherapeutic may be reduced in the low oxygen environment of tumours. In this study the cytotoxicity of three complexes, [Cu(dips)(phen)] (1), [Cu(ph)(phen)]·2H2O (2) and [Cu(ph)(bpy)]·H2O (3) (disp: 3,5-diisopropylsalicylate, phen: 1,10- phenanthroline, ph: phthalate, bpy: 2,2'-bipyridyl) were assessed for anticancer activity in the breast-cancer derived MCF-7 line under normoxic, hypoxic and anoxic conditions. In an immortalised keratinocyte HaCaT cell line, the cytotoxicity of complexes 2 and 3 was significantly reduced under both normoxic and hypoxic conditions, whilst the cytotoxicity of complex 1 was increased under hypoxic conditions. The ability of the complexes to generate ROS in the MCF-7 cell line was evaluated as was their ability to act as superoxide dismutase(SOD) and catalase mimics using a yeast cell assay. ROS generation was significant for complexes 2 and 3, less so for complex 1 though all three complexes had SOD mimetic ability. Given the ternary nature of the complexes, solution speciation studies were undertaken but were only successful for complex 3, due to solubility issues with the other two complexes. The concentration distribution of various species, formed in aqueous solution, was evaluated as a function of pH and confirmed that complex 3 is the dominant species at physiological pH in the mM concentration range. However, as its concentration diminishes, it experiences a progressive dissociation, leading to the formation of binary complexes of bpy alongside unbound phthalate.

Synthesis, characterisation, and solution behaviour of Ag(I) bis(phenanthroline-oxazine) complexes and the evaluation of their biological activity against the pathogenic yeast Candida albicans

Three Ag(I) bis(phenanthroline-oxazine) complexes with varying lipophilicity were synthesised and characterised. The solution stoichiometry of 1:2 Ag(I):ligand was determined for each complex by the continuous variation Job's plot method using NMR spectroscopy. NMR studies were also carried out to investigate the fluxional behaviour of the Ag(I) complexes in solution. The biological activity of the silver(I) complexes and the corresponding ligands towards a clinical strain of Candida albicans MEN was studied using broth microdilution assays. Testing showed the choice of media and the duration of incubation were key determinants of the inhibitory behaviour towards Candida albicans, however, the difference between freshly prepared and pre-prepared solutions was insignificant in minimal media. The activity of the metal-free ligands correlated with the length of the alkyl chain. In minimal media, the methyl ester phenanthroline-oxazine ligand was effective only at 60 μM, limiting growth to 67% of the control, while a 60 μM dose of the propyl ester analogue limited fungal growth at < 20% of the control. MIC50 and MIC80 values for the propyl and hexyl ester analogues were calculated to be 45 and 59 µM (propyl), and 18 and 45 µM (hexyl). Moreover, in a study of activity as a function of time it was observed that the hexyl ester ligand maintained its activity for longer than the methyl and propyl analogues; after 48 h a 60 μM dose held fungal growth at 24% of that of the control. Complexation to Ag(I) was much more effective in enhancing biological activity of the ligands than was increasing the ester chain length. Significantly no difference in activity between the three silver(I) complexes was observed under the experimental conditions. All three complexes were substantially more active than their parent ligands against Candida albicans and AgClO4 and the three silver(I) bis(phen-oxazine) complexes have MIC80 values of < 15 μM. The ability of the silver(I) complexes to hold fungal growth at about 20% of the control even after 48 h incubation at low dosages (15 μM) showcases their superiority over the simple silver(I) perchlorate salt, which ceased to be effective at dosages below 60 μM at the extended time point.

Impact of human serum albumin on CuII and ZnII complexation by ATSM (diacetyl-bis(N4-methylthiosemicarbazone)) and a water soluble analogue

The chelator diacetyl-bis(N4-methylthiosemicarbazone) (ATSM) and its complexes with CuII and ZnII are becoming increasingly investigated for medical applications such as PET imaging for anti-tumour therapy and the treatment of amyotrophic lateral sclerosis. However, the solubility in water of both the ligand and the complexes presents certain limitations for in vitro studies. Moreover, the stability of the CuII and ZnII complexes and their metal exchange reaction against the potential biological competitor human serum albumin (HSA) has not been studied in depth. In this work it was observed that the ATSM with an added carboxylic group into the structure increases its solubility in aqueous solutions without altering the coordination mode and the conjugated system of the ligand. The poorly water-soluble CuII- and ZnII-ATSM complexes were prevented from precipitating due to the binding to HSA. Both HSA and ATSM show a similar thermodynamic affinity for ZnII. Finally, the CuII-competition experiments with EDTA and the water-soluble ATSM ligands yielded an apparent log Kd at pH 7.4 of about -19. When ATSM was added to CuII- and ZnII-loaded HSA, withdrawing of ZnII was kinetically favoured, but this metal is slowly substituted by the CuII afterwards taken from HSA so that this protein could be considered as a source of CuII for ATSM.

Synthesis, Structural Characterization, Cytotoxicity, and Protein/DNA Binding Properties of Pyridoxylidene-Aminoguanidine-Metal (Fe, Co, Zn, Cu) Complexes

Pyridoxylidene-aminoguanidine (PLAG) and its transition metal complexes are biologically active compounds with interesting properties. In this contribution, three new metal-PLAG complexes, Zn(PLAG)(SO4)(H2O)].∙H2O (Zn-PLAG), [Co(PLAG)2]SO4∙2H2O (Co-PLAG), and [Fe(PLAG)2]SO4∙2H2O) (Fe-PLAG), were synthetized and characterized by the X-ray crystallography. The intermolecular interactions governing the stability of crystal structure were compared to those of Cu(PLAG)(NCS)2 (Cu-PLAG) within Hirshfeld surface analysis. The structures were optimized at B3LYP/6-31+G(d,p)(H,C,N,O,S)/LanL2DZ (Fe,Co,Zn,Cu), and stability was assessed through Natural Bond Orbital Theory and Quantum Theory of Atoms in Molecules. Special emphasis was put on investigating the ligand's stability and reactivity. The binding of these compounds to Bovine and Human serum albumin was investigated by spectrofluorometric titration. The importance of complex geometry and various ligands for protein binding was shown. These results were complemented by the molecular docking study to elucidate the most important interactions. The thermodynamic parameters of the binding process were determined. The binding to DNA, as one of the main pathways in the cell death cycle, was analyzed by molecular docking. The cytotoxicity was determined towards HCT116, A375, MCF-7, and A2780 cell lines. The most active compound was Cu-PLAG due to the presence of PLAG and two thiocyanate ligands.

Anti-Migratory and Cytotoxic Activities of [Ga(8-hydroxyquinolinato)3 ]: Roles of Endogenous Cu(II) and Drug-Induced Phenotypic Changes

As shown by IncuCyte Zoom imaging proliferation assays, invasive triple-negative human breast MDA-MB-231 cancer cells treated with sub-toxic doses (5.0-20 μM, 72 h) of [GaQ3 ] (Q=8-hydroxyquinolinato) caused profound morphological changes and inhibition of cell migration, which were likely due to terminal cell differentiation or similar phenotypical change. This is the first demonstration of potential use of a metal complex in differentiation anti-cancer therapy. Additionally, a trace amount of Cu(II) (0.20 μM) added to the medium dramatically increased [GaQ3 ] cytotoxicity (IC50 ~2 μM, 72 h) due to its partial dissociation and the action of the HQ ligand as a Cu(II) ionophore, as shown with electrospray mass spectrometry and fluorescence spectroscopy assays in the medium. Hence, cytotoxicity of [GaQ3 ] is strongly linked to ligand binding of essential metal ions in the medium, for example, Cu(II). Appropriate delivery mechanisms of such complexes and their ligands could enable a powerful new triple therapeutic approach for cancer chemotherapy, including cytotoxicity against primary tumour, arrest of metastases, and activation of innate and adaptive immune responses.

Interaction of Vanadium Complexes with Proteins: Revisiting the Reported Structures in the Protein Data Bank (PDB) since 2015

The structural determination and characterization of molecules, namely proteins and enzymes, is crucial to gaining a better understanding of their role in different chemical and biological processes. The continuous technical developments in the experimental and computational resources of X-ray diffraction (XRD) and, more recently, cryogenic Electron Microscopy (cryo-EM) led to an enormous growth in the number of structures deposited in the Protein Data Bank (PDB). Bioinorganic chemistry arose as a relevant discipline in biology and therapeutics, with a massive number of studies reporting the effects of metal complexes on biological systems, with vanadium complexes being one of the relevant systems addressed. In this review, we focus on the interactions of vanadium compounds (VCs) with proteins. Several types of binding are established between VCs and proteins/enzymes. Considering that the V-species that bind may differ from those initially added, the mentioned structural techniques are pivotal to clarifying the nature and variety of interactions of VCs with proteins and to proposing the mechanisms involved either in enzymatic inhibition or catalysis. As such, we provide an account of the available structural information of VCs bound to proteins obtained by both XRD and/or cryo-EM, mainly exploring the more recent structures, particularly those containing organic-based vanadium complexes.

Cu(II) and Zn(II) Complexes of New 8-Hydroxyquinoline Schiff Bases: Investigating Their Structure, Solution Speciation, and Anticancer Potential

We report the synthesis and characterization of three novel Schiff bases (L1-L3) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with amines containing morpholine or piperidine moieties. These were reacted with CuCl₂ and ZnCl₂ yielding six new coordination compounds, with the general formula ML₂, where M = Cu(II) or Zn(II) and L = L1-L3, which were all characterized by analytical, spectroscopic (Fourier transform infrared (FTIR), UV-visible absorption, nuclear magnetic resonance (NMR), or electron paramagnetic resonance (EPR)), and mass spectrometric techniques, as well as by single-crystal X-ray diffraction. In the solid state, two Cu(II) complexes, with L1 and L2, are obtained as dinuclear compounds, with relatively short Cu-Cu distances (3.146 and 3.171 Å for Cu₂(L1)₄ and Cu₂(L2)₄, respectively). The free ligands show moderate lipophilicity, while their complexes are more lipophilic. The pK_a values of L1-L3 and formation constants of the complex (for ML and ML₂) species were determined by spectrophotometric titrations, with the Cu(II) complexes showing higher stability than the Zn(II) complexes. EPR indicated the presence of several species in solution as pH varied and binding modes were proposed. The binding of the complexes to bovine serum albumin (BSA) was evaluated by fluorescence and circular dichroism (CD) spectroscopies. All complexes bind BSA, and as demonstrated by CD, the process takes several hours to reach equilibrium. The antiproliferative activity was evaluated in malignant melanoma cells (A375) and in noncancerous keratinocytes (HaCaT). All complexes display significant cytotoxicity (IC₅₀ < 10 μM) but modest selectivity. The complexes show higher activity than the free ligands, the Cu(II) complexes being more active than the Zn(II) complexes, and approximately twice more cytotoxic than cisplatin. A Guava ViaCount assay corroborated the antiproliferative activity.

A Series of Non-Oxido VIV Complexes of Dibasic ONS Donor Ligands: Solution Stability, Chemical Transformations, Protein Interactions, and Antiproliferative Activity

A series of mononuclear non-oxido vanadium(IV) complexes, [V^IV(L^1-4)₂] (1-4), featuring tridentate bi-negative ONS chelating S-alkyl/aryl-substituted dithiocarbazate ligands H₂L^1-4, are reported. All the synthesized non-oxido V^IV compounds are characterized by elemental analysis, spectroscopy (IR, UV-vis, and EPR), ESI-MS, as well as electrochemical techniques (cyclic voltammetry). Single-crystal X-ray diffraction studies of 1-3 reveal that the mononuclear non-oxido V^IV complexes show distorted octahedral (1 and 2) or trigonal prismatic (3) arrangement around the non-oxido V^IV center. EPR and DFT data indicate the coexistence of mer and fac isomers in solution, and ESI-MS results suggest a partial oxidation of [V^IV(L^1-4)₂] to [V^V(L^1-4)₂]⁺ and [V^VO₂(L^1-4)]^-; therefore, all these three complexes are plausible active species. Complexes 1-4 interact with bovine serum albumin (BSA) with a moderate binding affinity, and docking calculations reveal non-covalent interactions with different regions of BSA, particularly with Tyr, Lys, Arg, and Thr residues. In vitro cytotoxic activity of all complexes is assayed against the HT-29 (colon cancer) and HeLa (cervical cancer) cells and compared with the NIH-3T3 (mouse embryonic fibroblast) normal cell line by MTT assay and DAPI staining. The results suggest that complexes 1-4 are cytotoxic in nature and induce cell death in the cancer cell lines by apoptosis and that a mixture of V^IV, V^V, and V^VO₂ species could be responsible for the biological activity.

Cytotoxicity and Antibacterial Potentials of Mixed Ligand Cu(II) and Zn(II) Complexes: A Combined Experimental and Computational Study

[Cu(C₁₅H₉O₄)(C₁₂H₈N₂)O₂C₂H₃]·3H₂O (1) and [Zn(C₁₅H₉O₄)(C₁₂H₈N₂)]O₂C₂H₃ (2) have been synthesized and characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, mass spectrometry, thermogravimetric analysis/differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and molar conductance, and supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Square pyramidal and tetrahedral geometries are proposed for Cu(II) and Zn(II) complexes, respectively, and the XRD patterns showed the polycrystalline nature of the complexes. Furthermore, in vitro cytotoxic activity of the complexes was evaluated against the human breast cancer cell line (MCF-7). A Cu(II) centered complex with an IC₅₀ value of 4.09 μM was more effective than the Zn(II) centered complex and positive control, cisplatin, which displayed IC₅₀ values of 75.78 and 18.62 μM, respectively. In addition, the newly synthesized complexes experienced the innate antioxidant nature of the metal centers for scavenging the DPPH free radical (up to 81% at 400 ppm). The biological significance of the metal complexes was inferred from the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy band gap, which was found to be 2.784 and 3.333 eV, respectively for 1 and 2, compared to the ligands, 1,10-phenathroline (4.755 eV) and chrysin (4.403 eV). Moreover, the molecular docking simulations against estrogen receptor alpha (ERα; PDB: 5GS4) were strongly associated with the in vitro biological activity results (E _B and K _i are -8.35 kcal/mol and 0.76 μM for 1, -7.52 kcal/mol and 3.07 μM for 2, and -6.32 kcal/mol and 23.42 μM for cisplatin). However, more research on in vivo cytotoxicity is suggested to confirm the promising cytotoxicity results.

Thermodynamics-based rules of thumb to evaluate the interaction of chelators and kinetically-labile metal ions in blood serum and plasma

Metal ions play a very important role in nature and their homeostasis is crucial. A lot of metal-related chemical research activities are ongoing that concern metal-based drugs or tools, such as chelation therapy, metal- and metabolite sensors, metallo-drugs and prodrugs, PET and MRI imaging agents, etc. In most of these cases, the applied chelator/ligand (L) or metal-ligand complex (M-L) has at least to pass the blood plasma to reach the target. Hence it is exposed to several metal-binding proteins (mainly serum albumin and transferrin) and to all essential metal ions (zinc, copper, iron, etc.). This holds also for studies in cultured cells when fetal calf serum is used in the medium. There is a risk that the applied compound (L or M-L) in the serum is transformed into a different entity, due to trans-metallation and/or ligand exchange reactions. This depends on the thermodynamics and kinetics. For kinetically-labile complexes, the complex stability with all the ligands and all metal ions present in serum is decisive in evaluating the thermodynamic driving force towards a certain fate of the chelator or metal-ligand complex. To consider that, an integrative view is needed on the stability constants, by taking into account all the metal ions present and all the main proteins to which they are bound, as well as the non-occupied metal binding site in proteins. Only then, a realistic estimation of the complex stability, and hence its potential fate, can be done. This perspective aims to provide a simple approach to estimate the thermodynamic stability of labile metal-ligand complexes in a blood plasma/serum environment. It gives a guideline to obtain an estimation of the plasma and serum complex stability and metal selectivity starting from the chemical stability constants of metal-ligand complexes. Although of high importance, it does not focus on the more complex kinetic aspects of metal-transfer reactions. The perspective should help for a better design of such compounds, to perform test tube assays which are relevant to the conditions in the plasma/serum and to be aware of the importance of ternary complexes, kinetics and competition experiments.

Organic-inorganic hybrid salt and mixed ligand Cr(III) complexes containing the natural flavonoid chrysin: Synthesis, characterization, computational, and biological studies

Organic-inorganic hybrid salt and mixed ligand Cr(III) complexes (Cr1 and Cr2) containing the natural flavonoid chrysin were synthesized. The metal complexes were characterized using UV-Vis, Fourier-transform infrared, MS, SEM-EDX, XRD, and molar conductance measurements. Based on experimental and DFT/TD-DFT calculations, octahedral geometries for the synthesized complexes were suggested. The powder XRD analysis confirms that the synthesized complexes were polycrystalline, with orthorhombic and monoclinic crystal systems having average crystallite sizes of 21.453 and 19.600 nm, percent crystallinities of 51% and 31.37%, and dislocation densities of 2.324 × 10^-3 and 2.603 × 10^-3 nm^-2 for Cr1 and Cr2, respectively. The complexes were subjected to cytotoxicity, antibacterial, and antioxidant studies. The in vitro biological studies were supported with quantum chemical and molecular docking computational studies. Cr1 showed significant cytotoxicity to the MCF-7 cell line, with an IC₅₀ value of 8.08 μM compared to 30.85 μM for Cr2 and 18.62 μM for cisplatin. Cr2 showed better antibacterial activity than Cr1. The higher E _HOMO (-5.959 eV) and dipole moment (10.838 Debye) values of Cr2 obtained from the quantum chemical calculations support the observed in vitro antibacterial activities. The overall results indicated that Cr1 is a promising cytotoxic drug candidate.

Cytotoxic mixed-ligand complexes of Cu(II): A combined experimental and computational study

Herein, we report the synthesis of mixed-ligand Cu(II) complexes of metformin and ciprofloxacin drugs together with 1,10-phenanthroline as a co-ligand. The synthesized complexes were characterized using different spectroscopic and spectrometric techniques. In vitro cytotoxic activity against human breast adenocarcinoma cancer cell line (MCF-7) as well as antibacterial activity against two gram-negative and two gram-positive bacterial strains were also investigated. The analyses of the experimental results were supported using quantum chemical calculations and molecular docking studies against estrogen receptor alpha (ERα; PDB: 5GS4). The cytotoxicity of the [Cu(II) (metformin) (1,10-phenanthroline)] complex (1), with IC₅₀ of 4.29 µM, and the [Cu(II) (ciprofloxacin) (1,10-phenanthroline)] complex (2), with IC₅₀ of 7.58 µM, were found to be more effective than the referenced drug, cisplatin which has IC₅₀ of 18.62 µM against MCF-7 cell line. The molecular docking analysis is also in good agreement with the experimental results, with binding affinities of –7.35, –8.76 and –6.32 kcal/mol, respectively, for complexes 1, 2 and cisplatin against ERα. Moreover, complex 2 showed significant antibacterial activity against E. coli (inhibition diameter zone, IDZ, = 17.3 mm), P. aeruginosa (IDZ = 17.08 mm), and S. pyogen (IDZ = 17.33 mm), at 25 μg/ml compared to ciprofloxacin (IDZ = 20.0, 20.3, and 21.3 mm), respectively. Our BOILED-egg model indicated that the synthesized metal complexes have potentially minimal neurotoxicity than that of cisplatin.

Liposomal Formulations of a New Zinc(II) Complex Exhibiting High Therapeutic Potential in a Murine Colon Cancer Model

Colorectal cancer is the second leading cause of cancer-related mortality. Many current therapies rely on chemotherapeutic agents with poor specificity for tumor cells. The clinical success of cisplatin has prompted the research and design of a huge number of metal-based complexes as potential chemotherapeutic agents. In this study, two zinc(II) complexes, [ZnL2] and [ZnL(AcO)], where AcO is acetate and L is an organic compound combining 8-hydroxyquinoline and a benzothiazole moiety, were developed and characterized. Analytical and spectroscopic studies, namely, NMR, FTIR, and UV-Vis allowed us to establish the complexes’ structures, demonstrating the ligand-binding versatility: tetradentate in [ZnL(AcO)] and bidentate in [ZnL2]. Complexes were screened in vitro using murine and human colon cancer cells cultured in 2D and 3D settings. In 2D cells, the IC50 values were <22 µM, while in 3D settings, much higher concentrations were required. [ZnL(AcO)] displayed more suitable antiproliferative properties than [ZnL2] and was chosen for further studies. Moreover, based on the weak selectivity of the zinc-based complex towards cancer cell lines in comparison to the non-tumorigenic cell line, its incorporation in long-blood-circulating liposomes was performed, aiming to improve its targetability. The resultant optimized liposomal nanoformulation presented an I.E. of 76% with a mean size under 130 nm and a neutral surface charge and released the metal complex in a pH-dependent manner. The antiproliferative properties of [ZnL(AcO)] were maintained after liposomal incorporation. Preliminary safety assays were carried out through hemolytic activity that never surpassed 2% for the free and liposomal forms of [ZnL(AcO)]. Finally, in a syngeneic murine colon cancer mouse model, while free [ZnL(AcO)] was not able to impair tumor progression, the respective liposomal nanoformulation was able to reduce the relative tumor volume in the same manner as the positive control 5-fluorouracil but, most importantly, using a dosage that was 3-fold lower. Overall, our results show that liposomes were able to solve the solubility issues of the new metal-based complex and target it to tumor sites.

New iron(III) anti-cancer aminobisphenolate/phenanthroline complexes: Enhancing their therapeutic potential using nanoliposomes

Malignant melanoma is an aggressive and deadly form of skin cancer and novel and improved therapeutic options are needed. A promising strategy involves the use of metallodrugs combined with liposomes for targeted delivery to cancer cells. In this work, a family of iron(III) complexes was synthesized bearing a trianionic aminobisphenolate ligand (L) and phenanthroline-type co-ligands (NN). Four ternary iron complexes of general formula [Fe(L)(NN)] were obtained: [Fe(L)(amphen)] (1), [Fe(L)(phen)] (2), [Fe(L)(Clphen)] (3), and [Fe(L)(Mephen)] (4), as well as a fifth complex [Fe(L)(NEt₃)(H₂O)] (5) without the bidentate co-ligand. All complexes were characterized by analytic and spectroscopic techniques and demonstrated to be stable in aqueous environment. Complexes 1 and 2 were able to bind DNA and presented high cytotoxic activity towards human cancer cells. Complex 1 (IronC) was selected for incorporation into different liposomal formulations, which were fully characterized and screened against murine melanoma cells. The IronC liposomal formulation with the highest incorporation efficiency (∼95%) and a low IC₅₀ value (7.1 ± 0.7 μM) was selected for in vivo evaluation. In a syngeneic murine melanoma model the liposomal formulation of IronC yielded the highest impairment on tumour progression when compared with the control, temozolomide, and with the iron complex in free form.

Tetramethyl-phenanthroline copper complexes in the development of drugs to treat cancer: synthesis, characterization and cytotoxicity studies of a series of copper(II)-L-dipeptide-3,4,7,8-tetramethyl-phenanthroline complexes

New compounds to fight cancer are needed due to cancer high incidence and lack of curative treatments for several classes of this disease. Metal-based coordination compounds offer a variety of molecules that can turn into drugs. Among them, coordination copper complexes are emerging as an attractive class of compounds for cancer treatment. A series of [Cu(L-dipeptide)(tmp)] (tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) complexes were synthesized and characterized in the solid state, including the determination of the crystalline structure of [Cu(Gly-Gly)(tmp)]·3.5 H₂O and [Cu₂Cl₄(tmp)₂]. The complexes were studied in solution, where the major species are also ternary ones. The lipophilicity of the complexes was determined and the binding to the DNA was evaluated, suggesting that it occurs in the DNA's major groove. The cytotoxicity of the complexes was evaluated on different cancer cell lines: human metastatic breast adenocarcinoma MDA-MB-231 (triple negative, ATCC: HTB-26), MCF-7 (ATCC: HTB-22), SK-BR-3 (ATCC: HTB-30), human lung epithelial carcinoma A549 (ATCC: CCL-185), cisplatin resistant-human ovarian carcinoma A2780cis (SIGMA) and nontumoral cell lines: MRC-5 (lung; ATCC: CCL-171) and MCF-10A (breast, ATCC: CRL-10317). [Cu(L-dipeptide)(tmp)] complexes are highly cytotoxic as compared to [Cu(L-dipeptide)(phenanthroline)] and cisplatin. Therefore, [Cu(L-dipeptide)(tmp)] complexes are promising candidates to have their in vivo activity further studied toward new treatments for triple negative breast cancer and other aggressive tumors for which there is no curative pharmacological treatment to the date.

Hybrid Catalysts from Copper Biosorbing Bacterial Strains and Their Recycling for Catalytic Application in the Asymmetric Addition Reaction of B2(pin)2 on α,β-Unsaturated Chalcones

The recycling of heavy metal contaminants from wastewater as a source of valuable products perfectly fits with the principles of a Circular Economy system in view of restoring pollutants back into the system endowed with new social and economic benefits. Heavy metals are often present in such a low concentration that it makes the removal efficiency difficult to realize through the conventional physicochemical methods with high selectivity. Biosorption, conversely, by EPSs (extracellular polymeric substances) produced by several bacterial cells’ strains, is gaining a great deal of attention as an economic, efficient and sustainable depolluting process of wastewater from metal cations such as copper. Metal coordination to EPS components was thus deeply investigated by 1H NMR titration experiments. The 1,10–Phenanthroline–copper complex was exploited for quantifying the ability of different strains to sequester copper by a practical UV-Vis spectrophotometric method. The obtained data distinguished Serratia plymuthica strain SC5II as the bacterial strain displaying copper-adsorbing properties higher than any other, with Stenotrophomonas sp. strain 13a resulting in the worst one. Different analytical techniques, i.e., Dynamic Light Scattering (DLS), FT-IR analysis and SEM spectroscopy were thus employed to rationalize these results. Finally, the obtained copper chelates were successfully employed as hybrid catalysts in the asymmetric boron addition to α,β-unsaturated chalcones for the synthesis of valuable pharmaceutical intermediates, thus placing waste management in a new circular perspective.

Advantageous Reactivity of Unstable Metal Complexes: Potential Applications of Metal-Based Anticancer Drugs for Intratumoral Injections

Injections of highly cytotoxic or immunomodulating drugs directly into the inoperable tumor is a procedure that is increasingly applied in the clinic and uses established Pt-based drugs. It is advantageous for less stable anticancer metal complexes that fail administration by the standard intravenous route. Such hydrophobic metal-containing complexes are rapidly taken up into cancer cells and cause cell death, while the release of their relatively non-toxic decomposition products into the blood has low systemic toxicity and, in some cases, may even be beneficial. This concept was recently proposed for V(V) complexes with hydrophobic organic ligands, but it can potentially be applied to other metal complexes, such as Ti(IV), Ga(III) and Ru(III) complexes, some of which were previously unsuccessful in human clinical trials when administered via intravenous injections. The potential beneficial effects include antidiabetic, neuroprotective and tissue-regenerating activities for V(V/IV); antimicrobial activities for Ga(III); and antimetastatic and potentially immunogenic activities for Ru(III). Utilizing organic ligands with limited stability under biological conditions, such as Schiff bases, further enhances the tuning of the reactivities of the metal complexes under the conditions of intratumoral injections. However, nanocarrier formulations are likely to be required for the delivery of unstable metal complexes into the tumor.

Synthesis and characterisation of phenanthroline-oxazine ligands and their Ag(I), Mn(II) and Cu(II) complexes and their evaluation as antibacterial agents

A series of phenanthroline-oxazine ligands were formed by a cyclisation reaction between L-tyrosine amino acid esters and 1,10-phenanthroline-5,6-dione (phendione). The methyl derivative of the phenanthroline-oxazine ligand 1 was complexed with Ag(I), Mn(II) and Cu(II) to form [Ag(1)₂]ClO₄, [Mn(1)₃](ClO₄)₂ and [Cu(1)₃](ClO₄)₂. The activity of these metal complexes was tested against the bacteria Escherichia coli and Staphylococcus aureus. Each of the metal complexes was more active than 1 against S. aureus and the Mn(II) and Cu(II) complexes also showed greater activity than 1 towards E. coli. The effect of increasing the length of the alkyl moiety on the phenanthroline-oxazine ligands and their corresponding tris homoleptic Cu(II) complexes was investigated. In all cases both the ligands and their complexes were more active against Gram-positive S. aureus than against Gram-negative E. coli. Differences in the lipophilicity of the ligands and their corresponding Cu(II) complexes did alter the antibacterial activity, with the hexyl and octyl derivatives and their complexes showing the greatest activity and comparing well with clinically used antibiotics. The most active Cu(II) complexes and their respective ligands were also active against Methicillin-resistant S. aureus (MRSA). In vivo toxicity studies, conducted using the Galleria mellonella model, showed that all of the compounds were well tolerated by the insect larvae.

Mixed-ligand complexes of copper(ii) with thienoyltrifluoroacetonate and nitrogen containing ligands: synthesis, structures, antimicrobial activity, cytotoxicity, Hirshfeld surface analysis and DFT studies

Mixed-ligand complexes of copper(ii) with thienoyltrifluoroacetonate (TTA-H), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), and tetramethylethylenediamine (tmen), associated with counter ions such as Cl⁻, and NO₃⁻ have been synthesized and characterized by molar conductance measurements, elemental analysis, mass spectrometry, IR and UV-Vis spectroscopy, antimicrobial activity, cytotoxicity assay studies, and single-crystal X-ray diffraction. The UV-Vis spectra and crystal structures are consistent with the adoption of square pyramidal geometry for all of the complexes except [Cu(TTA)tmen]NO₃ and [Cu(TTA)₂tmen] which have square planar and octahedral geometries, respectively. Conductance measurements of the mixed-ligand complexes indicated that they were all non-electrolytes, with the ligands and anions being coordinated to Cu except [Cu(TTA)tmen]NO₃ which is a 1 : 1 electrolyte. All of the complexes were moderately active on all the fungi tested (Candida albicans, Aspergillus niger, Penicillium notatum, Rhizopus stolonifer) except [Cu(TTA)bipyCl] which showed increased activity in Candida albicans and Aspergillus niger. All of the compounds tested showed LC₅₀ values greater than 100 with [Cu(TTA)(phen)NO₃] being the least toxic of the compounds. Molecular geometries of the complexes were optimized at the PBE1PBE/def2SVP and PBE1PBE/6-311g(d,p) level of theory and the results were compared with the single-crystal X-ray diffraction data. Electronic properties such as HOMO, LUMO, HOMO–LUMO gaps and global reactivity descriptors are reported at the PBE1PBE/6-311g(d,p) level of theory. Hirshfeld surface analysis was carried out to investigate the cooperative non-covalent supramolecular interactions within the various complexes.

Mixed-ligand complexes of copper(ii) with thienoyltrifluoroacetonate, 2,2′-bipyridine, 1,10-phenanthroline, and tetramethylethylenediamine, associated with counter ions such as Cl⁻ and NO₃ have been synthesized and characterized.

Mössbauer effect using 57Fe-ferrabisdicarbollide ([o-57FESAN]-): a glance into the potential of a low-dose approach for glioblastoma radiotherapy

Although a variety of cancers is initially susceptible to chemotherapy, they eventually develop multi-drug resistance. To overcome this situation, more effective and selective treatments are necessary by using anti-tumour agents...

Experimental and Theoretical DFT Study of Cu(I)/N,N-Disubstituted-N'-acylthioureato Anticancer Complexes: Actin Cytoskeleton and Induction of Death by Apoptosis in Triple-Negative Breast Tumor Cells

Six complexes with the general formula [Cu(acylthioureato)(PPh₃)₂] were synthesized and characterized using spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), mass spectrometry, elemental analysis, and X-ray diffraction. Interpretation of the in vitro cytotoxicity data of Cu(I) complexes took into account their stability in cell culture medium. DFT calculations showed that NMR properties, such as the shielding of carbon atoms, are affected by relativistic effects, supported by the ZORA Hamiltonian in the theoretical calculations. Additionally, the calculation of the energies of the frontier molecular orbitals predicted that the structural changes of the acylthiourea ligands did not cause marked changes in the reactivity descriptors. All complexes were cytotoxic to the evaluated tumor cell lines [MDA-MB-231 (triple-negative breast cancer, TNBC), MCF-7 (breast cancer), and A549 (lung cancer)]. In the MDA-MB-231 cell line, complex 1 significantly altered the cytoskeleton of the cells, reducing the density and promoting the condensation of F-actin filaments. In addition, the compound caused an increase in the percentage of cells in the fragmented DNA region (sub-G0) and induced cell death via the apoptotic pathway starting at the IC₅₀ concentration. Taken together, the results show that complex 1 has cytotoxic and apoptotic effects on TNBC cells, which is a cell line originating from an aggressive, difficult-to-treat breast cancer.

Copper(II) and oxidovanadium(IV) complexes of chromone Schiff bases as potential anticancer agents

We report the synthesis, characterization and biological screening of new chromone Schiff bases derived from the condensation of three 6-substituted-3-formyl-chromones with pyridoxal (HL^1-3) and its Cu(II) complexes [Cu(L^1-3)Cl], 1-3. For the 6-methyl derivative, HL², the V^IVO-complex [VO(L²)Cl] (5), as well as ternary Cu and V^IVO complexes with 1,10-phenanthroline (phen), [Cu(L²)(phen)Cl] (4) and [VO(L²)(phen)Cl] (6), were also prepared and evaluated. Their stability in aqueous medium and radical scavenging activity toward DPPH are screened, with [Cu(L²)(phen)Cl] (4) showing hydrolytic stability and [VO(L²)(phen)Cl] (6) high radical scavenging activity. Spectroscopic studies establish bovine serum albumin (BSA), a model for HSA, as a potential reversible carrier of [Cu(L²)(phen)Cl] in blood with K_BC ≈ 10⁵ M^-1. The cytotoxic activity of a group of compounds is evaluated against a panel of human cancer cell lines of different origin (ovary, cervix, brain and breast) and compared to normal cells. Our results indicate that Cu complexes are more cytotoxic than the ligands but not selective towards cancer cells. The most potent complexes (4 and 6) are further evaluated for their apoptotic potential, induction of reactive oxygen species (ROS) and genotoxicity. Both complexes efficiently triggered cell death through apoptosis as evaluated by DNA morphology and TUNEL assay, increased ROS formation as determined by DCFDA (2',7'-dichlorodihydrofluorescein diacetate) analysis, and induced genotoxic damage as visualized via COMET assay in all cancer cells under study. Therefore, 4 and 6 may be potential precursor anticancer molecules, yet they need to be targeted toward cancer cells.

Structure elucidation, in vitro binding studies and ROS-dependent anti-cancer activity of Cu(II) and Zn(II) phthaloylglycinate(phen) complexes against MDA-MB-231 cells

New mononuclear Cu(II) and Zn(II)-based complexes 1 [Cu(L)2(diimine)HOCH3] and 2 [Zn(L)2(diimine)] have been synthesized as anti-cancer chemotherapeutics targeted to tRNA. The structure elucidation of complexes 1 and 2 was carried out by spectroscopic and single X-ray diffraction studies. In vitro interaction studies of complexes 1 and 2 with ct-DNA/tRNA were performed by employing various biophysical techniques to evaluate and predict their interaction behavior and preferential selectivity at biomolecular therapeutic targets. The corroborative results of the interaction studies demonstrated that complexes 1 and 2 exhibited avid binding propensity via intercalative mode of binding toward ct-DNA/tRNA. Electrophoretic assay revealed that the complexes 1 and 2 were able to promote single- and double-strand cleavage of the plasmid DNA at low micromolar concentrations under physiological conditions in the absence of an additional oxidizing or reducing agent. RNA hydrolysis studies revealed that the complexes 1 and 2 could promote tRNA cleavage in a concentration and time-dependent manner. The cytotoxic potential of complexes 1 and 2 was evaluated against the MDA-MB-231 cell line, which showed that the complexes were able to inhibit the cell growth in a dose-dependent manner. The intracellular ROS production and mitochondrial superoxide anion assay revealed that the complexes 1 and 2 induce a dose-dependent activity, suggesting the involvement of ROS-mediated mitochondrial apoptotic pathway leading to cell death.

In vitro activity of N-phenyl-1,10-phenanthroline-2-amines against tachyzoites and bradyzoites of Toxoplasma gondii

Toxoplasma gondiiis an apicomplexan parasite, the causative agent of toxoplasmosis, a common disease in the world. Toxoplasmosis could be severe, especially in immunocompromised patients. The current therapy is limited, where pyrimethamine and sulfadiazine are the best choices despite being associated with side effects and ineffective against the bradyzoites, the parasitic form present during the chronic phase of the infection. Thus, new therapies against both tachyzoites and bradyzoites from T. gondii are urgent. Herein, we present the anti-T. gondii effect of 1,10-phenanthroline and its N-phenyl-1,10-phenanthroline-2-amine derivatives. The chemical modification of 1,10-phenanthroline tonew derivatives improved the anti-T. gondiiactivity 3.4 fold. The most active derivative presented ED₅₀in the nanomolar range, the smallest value found was for Ph8, 0.1 µM for 96 h of treatment. The host cell viability was maintained after the treatment with the compounds, which were found to be highly selective presenting large selectivity indexes. Treatment with derivatives for 96 h was able to eliminate the T. gondii infection irreversibly. The ultrastructural alterations caused after the treatment with the most effective derivative (Ph8) included signs of cell death, specifically revealed by the Tunel assay for detection of DNA fragmentation. The Phen derivatives were also able to control the growth of the in vitro-derived bradyzoite forms of T. gondii EGS strain, causing its lysis and death. These findings promote the 1,10-phenanthroline derivatives as potential lead compounds for the development of a treatment for acute and chronic phases of toxoplasmosis.

Copper(II) Complexes Containing Natural Flavonoid Pomiferin Show Considerable In Vitro Cytotoxicity and Anti-inflammatory Effects

A series of new heteroleptic copper(II) complexes of the composition [Cu(L)(bpy)]NO₃·2MeOH (1), [Cu(L)(dimebpy)]NO₃·2H₂O (2), [Cu(L)(phen)]NO₃·2MeOH (3), [Cu(L)(bphen)]NO₃·MeOH (4), [Cu(L)(dppz)]NO₃·MeOH (5) was prepared, where HL = 3-(3,4-dihydroxyphenyl)-5-hydroxy-8,8-dimethyl-6-(3-methylbut-2-ene-1-yl)-4H,8H-benzo[1,2-b:3,4-b′]dipyran-4-one, (pomiferin) and bpy = 2,2′-bipyridine, dimebpy = 4,4′-dimethyl-2,2′-bipyridine, phen = 1,10-phenanthroline, bphen = 4,7-diphenyl-1,10-phenanthroline, and dppz = dipyrido[3,2-a:2′,3′-c]phenazine. The complexes were characterized using elemental analysis, infrared and UV/Vis spectroscopies, mass spectrometry, thermal analysis and conductivity measurements. The in vitro cytotoxicity, screened against eight human cancer cell lines (breast adenocarcinoma (MCF-7), osteosarcoma (HOS), lung adenocarcinoma (A549), prostate adenocarcinoma (PC-3), ovarian carcinoma (A2780), cisplatin-resistant ovarian carcinoma (A2780R), colorectal adenocarcinoma (Caco-2) and monocytic leukemia (THP-1), revealed the complexes as effective antiproliferative agents, with the IC₅₀ values of 2.2–13.0 μM for the best performing complexes 3 and 5. All the complexes 1–5 showed the best activity against the A2780R cells (IC₅₀ = 2.2–6.6 μM), and moreover, the complexes demonstrated relatively low toxicity on healthy human hepatocytes, with IC₅₀ > 100 μM. The complexes were evaluated by the Annexin V/propidium iodide apoptosis assay, induction of cell cycle modifications in A2780 cells, production of reactive oxygen species (ROS), perturbation of mitochondrial membrane potential, inhibition of apoptosis and inflammation-related signaling pathways (NF-κB/AP-1 activity, NF-κB translocation, TNF-α secretion), and tested for nuclease mimicking activity. The obtained results revealed the corresponding complexes to be effective antiproliferative and anti-inflammatory agents.

Biological activities of polypyridyl-type ligands: implications for bioinorganic chemistry and light-activated metal complexes

Polypyridyl coordinating ligands are common in metal complexes used in medicinal inorganic chemistry. These ligands possess intrinsic cytotoxicity, but detailed data on this phenomenon are sparse, and cytotoxicity values vary widely and are often irreproducible. To provide new insights into the biological effects of bipyridyl-type ligands and structurally related metal-binding systems, reports of free ligand cytotoxicity were reviewed. The cytotoxicity of 25 derivatives of 2,2'-bipyridine and 1,10-phenanthroline demonstrates that there is no correlation between IC₅₀ values and ligand properties such as pKa, log D, polarizability volume, and electron density, as indicated by NMR shifts. As a result of these observations, as well as the various reported mechanisms of action of polypyridyl ligands, we offer the hypothesis that biological effects are governed by the availability of and affinity for specific metal ions within the experimental model.

Therapeutic potential of a copper complex loaded in pH-sensitive long circulating liposomes for colon cancer management

Colorectal carcinoma is a complex malignancy and current therapies are hampered by systemic toxicity and tumor resistance to treatment. In the field of cancer therapy, copper (Cu) compounds hold great promise, with some reaching clinical trials. However, the anticancer potential of Cu complexes has not yet been fully disclosed due to speciation in biological systems, leading to inactivation and/or potential side effects. This is the case of the widely studied Cu(II) complexes featuring phenanthroline ligands, with potent antiproliferative effects in vitro, but often failing in vivo. Aiming to overcome these limitations and maximize its anticancer effects in vivo, the Cu(II) complex (Cu(1,10-phenanthroline)Cl₂) (Cuphen), displaying IC₅₀ values <6 μM against different tumor cell lines, was loaded in long circulating liposomes with pH-sensitive properties (F1, DMPC:CHEMS:DSPE-PEG; F2, DOPE:CHEMS:DMPC:DSPE-PEG). This enabled a pH-dependent Cuphen release, with F1 and F2 releasing 36/78% and 47/94% of Cuphen at pH 6/4.5, respectively. The so formed nanoformulations preserved Cuphen effects towards cancer cell lines, with F2 presenting IC₅₀ of 2.7 μM and 4.9 μM towards colon cancer CT-26 and HCT-116 cells, respectively. Additional in vitro studies confirmed that Cuphen antiproliferative activity towards colon cancer cells does not rely on cell cycle effect. Furthermore, in these cells, Cuphen reduced glycerol permeation and impaired cell migration. At 24 h incubation, wound closure was reduced by Cuphen, with migration values of 29% vs 54% (control) and 45% (1,10-phenanthroline) in CT-26 cells, and 33% vs ~44% (control and 1,10-phenanthroline) in HCT-116 cells. These effects were probably due to inhibition of aquaglyceroporins, membrane water and glycerol channels that are often abnormally expressed in tumors. In a syngeneic murine colon cancer model, F2 significantly reduced tumor progression, compared to the control group and to mice treated with free Cuphen or with the ligand, 1,10-phenanthroline, without eliciting toxic side effects. F2 led to a tumor volume reduction of ca. 50%. This was confirmed by RTV analysis, where F2 reached a value of 1.3 vs 4.4 (Control), 5.8 (Phen) and 3.8 (free Cuphen). These results clearly demonstrated the important role of the Cu(II) for the observed biological activity that was maximized following the association to a lipid-based nanosystem. Overall, this study represents a step forward in the development of pH-sensitive nanotherapeutic strategies of metallodrugs for colon cancer management.

Aqueous chemistry of the smallest rare earth: Comprehensive characterization of radioactive and non-radioactive scandium complexes for biological applications

The aqueous chemistry of scandium(III) is of emerging interest for biological applications, specifically in nuclear medicine, as radioactive isotopes of scandium are becoming more readily accessible. In contrast to other rare earths, Sc³⁺ has no d or f electrons, limiting characterization of corresponding coordination complexes to spectroscopic techniques that do not rely on the characteristic electronic transitions of f-elements or transition metal ions. Herein, we provide a comprehensive overview on characterization techniques suitable to elucidate the solution behavior of small and macromolecular complexes of the smallest rare earth.

Forty Years after the Discovery of Its Nucleolytic Activity: [Cu(phen)2 ]2+ Shows Unattended DNA Cleavage Activity upon Fluorination

[Cu(phen)₂]²⁺ (phen=1,10‐phenanthroline) is the first and still one of the most efficient artificial nucleases. In general, when the phen ligand is modified, the nucleolytic activity of its Cu^II complex is significantly reduced. This is most likely due to higher steric bulk of such ligands and thus lower affinity to DNA. Cu^II complexes with phen ligands having fluorinated substituents (F, CF₃, SF₅, SCF₃) surprisingly showed excellent DNA cleavage activity—in contrast to the unsubstituted [Cu(phen)₂]²⁺—in the absence of the otherwise required classical, bioabundant external reducing agents like thiols or ascorbate. This nucleolytic activity correlates well with the half‐wave potentials E_1/2 of the complexes. Cancer cell studies show cytotoxic effects of all complexes with fluorinated ligands in the low μm range, whereas they were less toxic towards healthy cells (fibroblasts).

Therapeutic potential of vanadium complexes with 1,10-phenanthroline ligands, quo vadis? Fate of complexes in cell media and cancer cells

V^IVO-complexes formulated as [V^IVO(OSO₃)(phen)₂] (1) (phen = 1,10-phenanthroline), [V^IVO(OSO₃)(Me₂phen)₂] (2) (Me₂phen = 4,7-dimethyl-1,10-phenanthroline) and [V^IVO(OSO₃)(amphen)₂] (3) (amphen = 5-amino-1,10-phenanthroline) were prepared and stability in cell incubation media evaluated. Their cytotoxicity was determined against the A2780 (ovarian), MCF7 (breast) and PC3 (prostate) human cancer cells at different incubation times. While at 3 and 24 h the cytotoxicity differs for complexes and corresponding free ligands, at 72 h incubation all compounds are equally active presenting low IC₅₀ values. Upon incubation of A2780 cells with 1-3, cellular distribution of vanadium in cytosol, membranes, nucleus and cytoskeleton, indicate that the uptake of V is low, particularly for 1, and that the uptake pattern depends on the ligand. Nuclear microscopic techniques are used for imaging and elemental quantification in whole PC3 cells incubated with 1. Once complexes are added to cell culture media, they decompose, and with time most V^IV oxidizes to V^V-species. Modeling of speciation when [V^IVO(OSO₃)(phen)₂] (1) is added to cell media is presented. At lower concentrations of 1, V^IVO- and phen-containing species are mainly bound to bovine serum albumin, while at higher concentrations [V^IVO(phen)_n]²⁺-complexes become relevant, being predicted that the species taken up and mechanisms of action operating depend on the total concentration of complex. This study emphasizes that for these V^IVO-systems, and probably for many others involving oxidovanadium or other labile metal complexes, it is not possible to identify active species or propose mechanisms of cytotoxic action without evaluating speciation occurring in cell media.

Water-mediated reduction of [Cu(dmp)2(CH3CN)]2+: implications of the structure of a classical complex on its activity as an anticancer drug

[Cu(dmp)₂(CH₃CN)]²⁺ can be reduced in acetonitrile containing water due to steric constraints of the ligands. Hydroxyl radicals are produced from water oxidation. We take advantage of this reaction to evaluate the anticancer activity of the complex.

Influence of anchoring moieties on new benzimidazole-based Schiff base copper(II) complexes towards estrogen dependent breast cancer cells

Two new benzimidazole Schiff base copper(ii) compounds [Cu(5-CH2PPh3-2-salmethylben)(NO3)(H2O)][BF4]·2/3(H2O)·1/3(MeOH) (1) and [Cu(5-CH2NEt3-2-salmethylben)(Cl)][BF4] (2) were synthesised by mixing 2-(1-methyl-1H-benzo[d]imidazol-2-yl)aniline, (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride or N,N-diethyl-N-(3-formyl-4-hydroxybenzyl)ethanaminium chloride and Cu(NO3)2·3H2O or CuCl2·2H2O in the presence of tetrafluoroborate in a binary mixture of MeOH : H2O under refluxing conditions. The structures of the compounds were established by elemental analysis, FT-IR, ESI-MS analytical techniques and, for 1, by single-crystal X-ray diffraction analysis. Absorption and fluorescence spectroscopic methods were performed to evaluate the calf thymus DNA interactions with the compounds. The calculated binding constants (Kb) of 3.14 × 105 M-1 for 1 and 3.20 × 105 M-1 for 2 were established. The intercalative DNA binding mode was also verified by molecular docking studies. Both compounds demonstrated a notable in vitro cytotoxic effect against human A-549 (lung carcinoma), MCF-7 (breast cancer) and HeLa (cervical cancer) cancer cell lines. A substantial repressive effect on the proliferation of MCF-7 cells (breast cancer cells) was observed for compound 1. The mechanism of action for the effective antiproliferative activity of 1 has additionally been confirmed by means of various biological studies such as morphological assessment through AO/EB, detection of apoptotic induction via Hoechst/PI dual staining, flow cytometry for detection of cell cycle arrest, quantitative analysis of apoptotic cells, DNA degradation, generation of reactive oxygen species (ROS) and by apoptotic induction through mitochondrial staining.

PBT2 acts through a different mechanism of action than other 8-hydroxyquinolines: an X-ray fluorescence imaging study

8-Hydroxyquinolines (8HQs) comprise a family of metal-binding compounds that have been used or tested for use in numerous medicinal applications, including as treatments for bacterial infection, Alzheimer's disease, and cancer. Two key 8HQs, CQ (5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (2-(dimethylamino)methyl-5,7-dichloro-8-hydroxyquinoline), have drawn considerable interest and have been the focus of many studies investigating their in vivo properties. These drugs have been described as copper and zinc ionophores because they do not cause metal depletion, as would be expected for a chelation mechanism, but rather cellular accumulation of these ions. In studies of their anti-cancer properties, CQ has been proposed to elicit toxic intracellular copper accumulation and to trigger apoptotic cancer cell death through several possible pathways. In this study we used synchrotron X-ray fluorescence imaging, in combination with biochemical assays and light microscopy, to investigate 8HQ-induced alterations to metal ion homeostasis, as well as cytotoxicity and cell death. We used the bromine fluorescence from a bromine labelled CQ congener (5,7-dibromo-8-hydroxyquinoline; B2Q) to trace the intracellular localization of B2Q following treatment and found that B2Q crosses the cell membrane. We also found that 8HQ co-treatment with Cu(ii) results in significantly increased intracellular copper and significant cytotoxicity compared with 8HQ treatments alone. PBT2 was found to be more cytotoxic, but a weaker Cu(ii) ionophore than other 8HQs. Moreover, treatment of cells with copper in the presence of CQ or B2Q resulted in copper accumulation in the nuclei, while PBT2-guided copper was distributed near to the cell membrane. These results suggest that PBT2 may be acting through a different mechanism than that of other 8HQs to cause the observed cytotoxicity.