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.

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.

Metal Coordination and Biological Screening of a Schiff Base Derived from 8-Hydroxyquinoline and Benzothiazole

Designing new metallodrugs for anticancer therapy is a driving force in the scientific community. Aiming to contribute to this field, we hereby report the development of a Schiff base (H2L) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with 2-hydrazinobenzothiazole and its complexation with transition metal ions. All compounds were characterised by analytical and spectroscopic techniques, which disclosed their structure: [Cu(HL)Cl], [Cu(HL)2], [Ni(HL)(acetate)], [Ni(HL)2], [Ru(HL)Cl(DMSO)], [VO(HL)2] and [Fe(HL)2Cl(H2O)]. Different binding modes were proposed, showing the ligand’s coordination versatility. The ligand proton dissociation constants were determined, and the tested compounds showed high lipophilicity and light sensitivity. The stability of all complexes in aqueous media and their ability to bind to albumin were screened. Based on an antiproliferative in vitro screening, [Ni(HL)(acetate)] and [Ru(HL)Cl(DMSO)] were selected for further studies aiming to investigate their mechanisms of action and therapeutic potential towards colon cancer. The complexes displayed IC50 < 21 μM towards murine (CT-26) and human (HCT-116) colon cancer cell lines. Importantly, both complexes exhibited superior antiproliferative properties compared to the clinically approved 5-fluorouracil. [Ni(HL)(acetate)] induced cell cycle arrest in S phase in CT-26 cells. For [Ru(HL)Cl(DMSO)] this effect was observed in both colon cancer cell lines. Additionally, both compounds significantly inhibited cell migration particularly in the human colon cancer cell line, HCT-116. Overall, the therapeutic potential of both metal complexes was demonstrated.

New ternary Fe(III)-8-hydroxyquinoline-reduced Schiff base complexes as selective anticancer drug candidates

Due to the growing prevalence of cancer diseases, new therapeutic options are urgently needed, and drugs based on metal ions other than platinum are alternatives with exciting possibilities. We report the synthesis, characterization and biological effect of mixed-ligand Fe(III)-aminophenolate complexes derived from salicylaldehyde and L-tryptophan with quinoline derivatives as co-ligands, namely 8-hydroxyquinoline (8HQ), [Fe(L)(8HQ)(H₂O)] (1) and its 5-cloro derivative (Cl8HQ), [Fe(L)(Cl8HQ)(H₂O)] (2). The complex bearing the aminophenolate and lacking the quinoline co-ligand, [Fe(L)(Cl)(H₂O)₂] (3), was prepared for comparison. The analytical and spectroscopic characterization revealed that 1 and 2 are octahedral Fe(III) complexes with the aminophenolate acting as a dianionic tridentate ligand and 8HQ co-ligands as bidentate chelates. Spectroscopic techniques and molecular docking studies were used to evaluate the ability of these complexes to bind bovine serum albumin (BSA) and calf thymus DNA. Complex 2 [Fe(L)(Cl8HQ)(H₂O)] was the one showing higher affinity for both biomolecules. Cell viability was assessed in breast, colorectal and bone human cancer cell lines. 1 and 2 were found to be more active than cisplatin in all cell lines tested. A non-tumoral fibroblast line (L929, mouse non-tumoral fibroblasts) was used to evaluate selectivity. The results evidence that 2 shows much higher selectivity than 1 in all cell lines tested, but particularly in bone cancer cells in which selectivity index (SI) values are 8.0 and 18.8 for 1 and 2, respectively.

Binding of VIV O2+ , VIV OL, VIV OL2 and VV O2 L Moieties to Proteins: X-ray/Theoretical Characterization and Biological Implications

Vanadium compounds have frequently been proposed as therapeutics, but their application has been hampered by the lack of information on the different V-containing species that may form and how these interact with blood and cell proteins, and with enzymes. Herein, we report several resolved crystal structures of lysozyme with bound V^IV O²⁺ and V^IV OL²⁺ , where L=2,2'-bipyridine or 1,10-phenanthroline (phen), and of trypsin with V^IV O(picolinato)₂ and V^V O₂ (phen)⁺ moieties. Computational studies complete the refinement and shed light on the relevant role of hydrophobic interactions, hydrogen bonds, and microsolvation in stabilizating the structure. Noteworthy is that the trypsin-V^V O₂ (phen) and trypsin-V^IV O(OH)(phen) adducts correspond to similar energies, thus suggesting a possible interconversion under physiological/biological conditions. The obtained data support the relevance of hydrolysis of V^IV and V^V complexes in the several types of binding established with proteins and the formation of different adducts that might contribute to their pharmacological action, and significantly widen our knowledge of vanadium-protein interactions.

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.

New phosphotetradecavanadate hybrids: crystal structure, DFT analysis, stability and binding interactions with bio-macromolecules

Two novel bicapped Keggin polyoxidovanadates with organic cations, (C₆H₈N)₅[H₄PV₁₄O₄₂]·5H₂O (1) and (C₆H₁₄N₄)₂(NH₄)[H₄PV₁₄O₄₂]·11H₂O (2), (PV₁₄O₄₂^6- = PV14, C₆H₇N = 3-picoline and C₆H₁₂N₄ = methenamine) were synthesized. These compounds were isolated and characterized in the solid state and in solution by elemental analysis, powder X-ray diffraction, FTIR, UV-vis, ⁵¹V, ³¹P, ¹³C and ¹H NMR, and fluorescence spectroscopy. Further confirmation of the PV14 structures was obtained by single-crystal X-ray diffraction studies of 1 and 2. The Hirshfeld surface analysis was performed to confirm that within the intermolecular interactions occurring in the two crystals, the O⋯H/H⋯O, O⋯O and H⋯H interactions dominate. The protonation and one-electron reduction of the PV14 moiety were also analysed by means of DFT calculations; besides confirming the protonation sites and correctly predicting the pK_a values, the DFT results also indicate that molecular reduction is energetically more favourable in protonated PV14 anions. Upon the addition of PV14 anions to bovine serum albumin (BSA) up to a ratio of 1 : 1, the fluorescence decreased by 45% for both 1 and 2, indicating that the interaction of vanadium-containing species with this protein takes place; log(K_SV) values of ca. 5.5 were obtained in both systems. Upon the addition of 1 or 2 to solutions of calf-thymus DNA (ctDNA), changes were observed in the UV-vis absorption and circular dichroism spectra. The significance of the changes observed is discussed considering the several V-containing species that form in the solution.

Cu(ii) and V(iv)O complexes with tri- or tetradentate ligands based on (2-hydroxybenzyl)-l-alanines reveal promising anticancer therapeutic potential

New Cu^II- and V^IVO amino acid complexes show antiproliferative activity mediated by apoptosis and genomic damage.

Antimicrobial and antitumor activity of S-methyl dithiocarbazate Schiff base zinc(II) complexes

Schiff bases (SB) obtained from S-methyl dithiocarbazate and aromatic aldehydes: salicylaldehyde (H₂L¹), o-vanillin (H₂L²), pyridoxal (H₂L³) and 2,6-diformyl-4-methylphenol (H₃L⁴), and their corresponding Zn(II)-complexes (1-4), are synthesized. All compounds are characterized by elemental analyses, infrared, UV-Vis, nuclear magnetic resonance spectroscopy and mass spectrometry. The structures of H₂L² and [Zn₂(L¹)₂(H₂O)(DMF)] (1a) (DMF = dimethylformamide) are solved by single crystal X-ray diffraction. The SB coordinates the metal center through the O_phenolate, N_imine and S_thiolate atoms. The radical scavenging activity is tested using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, with all ligand precursors showing IC₅₀ values ~40 μM. Cytotoxicity studies with several tumor cell lines (PC-3, MCF-7 and Caco-2) as well as a non-tumoral cell line (NHDF) are reported. Interestingly, 1 has relevant and selective antiproliferative effect against Caco-2 cells (IC₅₀ = 9.1 μM). Their antimicrobial activity is evaluated in five bacterial strains (Klebsiella pneumoniae, Acinetobacter baumannii, Listeria monocytogenes, Pseudomonas aeruginosa and Staphylococcus aureus) and two yeast strains (Candida albicans and Candida tropicalis) with some compounds showing bacteriostatic and fungicidal activity. The minimal inhibitory concentration (MIC₉₀) of H_nL against Mycobacterium tuberculosis is also reported, with H₂L² and H₃L⁴ showing very high activity (MIC₉₀ < 0.6 μg/mL). The ability of the compounds to bind bovine serum albumin (BSA) and DNA is evaluated for H₃L⁴ and [Zn₂(L⁴)(CH₃COO)] (4), both showing high binding constants to BSA (ca. 10⁶ M^-1) and ability to bind DNA. Overall, the reported compounds show relevant antitumor and antimicrobial properties, our data indicating they may be promising compounds in several fields of medicinal chemistry.

New VIV, VIVO, VVO, and VVO2 Systems: Exploring their Interconversion in Solution, Protein Interactions, and Cytotoxicity

The synthesis and characterization of one oxidoethoxidovanadium(V) [V^VO(L¹)(OEt)] (1) and two nonoxidovanadium(IV) complexes, [V^IV(L^2-3)₂] (2 and 3), with aroylhydrazone ligands incorporating naphthalene moieties, are reported. The synthesized oxido and nonoxido vanadium complexes are characterized by various physicochemical techniques, and their molecular structures are solved by single crystal X-ray diffraction (SC-XRD). This revealed that in 1 the geometry around the vanadium atom corresponds to a distorted square pyramid, with a O₄N coordination sphere, whereas that of the two nonoxido V^IV complexes 2 and 3 corresponds to a distorted trigonal prismatic arrangement with a O₄N₂ coordination sphere around each "bare" vanadium center. In aqueous solution, the V^VO moiety of 1 undergoes a change to V^VO₂ species_, yielding [V^VO₂(L¹)]^- (1'), while the nonoxido V^IV-compounds 2 and 3 are partly converted into their corresponding V^IVO complexes, [V^IVO(L^2-3)(H₂O)] (2' and 3'). Interaction of these V^VO₂, V^IVO, and V^IV systems with two model proteins, ubiquitin (Ub) and lysozyme (Lyz), is investigated through docking approaches, which suggest the potential binding sites: the interaction is covalent for species 2' and 3', with the binding to Glu16, Glu18, and Asp21 for Ub, and His15 for Lyz, and it is noncovalent for species 1', 2, and 3, with the surface residues of the proteins. The ligand precursors and complexes are also evaluated for their in vitro antiproliferative activity against ovarian (A2780) and prostate (PC3) human cancer cells and in normal fibroblasts (V79) to check the selectivity of the compounds for cancer cells.

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

The interpretation of in vitro cytotoxicity data of Cu(II)-1,10-phenanthroline (phen) complexes normally does not take into account the speciation that complexes undergo in cell incubation media and its implications in cellular uptake and mechanisms of action. We synthesize and test the activity of several distinct Cu(II)-phen compounds; up to 24 h of incubation, the cytotoxic activity differs for the Cu complexes and the corresponding free ligands, but for longer incubation times (e.g., 72 h), all compounds display similar activity. Combining the use of several spectroscopic, spectrometric, and electrochemical techniques, the speciation of Cu-phen compounds in cell incubation media is evaluated, indicating that the originally added complex almost totally decomposed and that Cu(II) and phen are mainly bound to bovine serum albumin. Several methods are used to disclose relationships between structure, activity, speciation in incubation media, cellular uptake, distribution of Cu in cells, and cytotoxicity. Contrary to what is reported in most studies, we conclude that interaction with cell components and cell death involves the separate action of Cu ions and phen molecules, not [Cu(phen)_n] species. This conclusion should similarly apply to many other Cu-ligand systems reported to date.

Unusual chemistry of Cu(ii) salan complexes: synthesis, characterization and superoxide dismutase activity

Cu(ii)-salan complexes: structural and spectral characterization, solvent assisted ring cleavage and correlation of superoxide dismutase activity with cyclic voltammetry data and steric effects.

Trinuclear vanadium(iv) and vanadium(v) complexes derived from 2,4,6-triacetylphloroglucinol and study of their peroxidase mimicking activity

Solid state and solution studies of trinuclear V^IVO- and V^VO₂-complexes and their peroxidase mimicking activity, through oxidation of dopamine to aminochrome, are reported.

Experimental data on novel Fe(III)-complexes containing phenanthroline derivatives for their anticancer properties

This dataset is related to the research article entitled "May iron(III) complexes containing phenanthroline derivatives as ligands be prospective anticancer agents?" [1]. It includes the characterization by UV-Vis absorption spectroscopy and magnetic techniques of a group of mixed ligand Fe(III) complexes bearing a tripodal aminophenolate ligand L^2-, H₂L = N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N-(2-pyridylmethyl)amine, and different aromatic bases (NN = 2,2'-bipyridine [Fe(L)(bipy)]PF₆ (1), 1,10-phenanthroline [Fe(L)(phen)]PF₆ (2), or a phenanthroline derivative co-ligand: [Fe(L)(amphen)]NO₃ (3), [Fe(L)(amphen)]PF₆ (3a), [Fe(L)(Clphen)]PF₆ (4), [Fe(L)(epoxyphen)]PF₆ (5) (where amphen = 1,10-phenanthroline-5-amine, epoxyphen = 5,6-epoxy-5,6-dihydro-1,10-phenanthroline, Clphen = 5-chloro-1,10-phenanthroline), as well as [Fe(L)(EtOH)]NO₃ (6), [Fe(phen)Cl₃] (7) and [Fe(amphen)Cl₃] (8). Data on their hydrolytic stability in physiological buffers is shown, as well as on their interaction with calf thymus DNA by spectroscopic tools. Additionally, the anticancer efficacy and the cellular death mechanisms activated in response to these drugs in HeLa, H1299 and MDA-MB-231 cells are provided.

Exploring the cytotoxic activity of new phenanthroline salicylaldimine Zn(II) complexes

Zinc(II) complexes bearing N-salicylideneglycinate (Sal-Gly) and 1,10-phenanthroline (phen) or phenanthroline derivatives [NN = 5-chloro-1,10-phenanthroline, 5-amine-1,10-phenanthroline (amphen), 4,7-diphenyl-1,10-phenanthroline (Bphen) and 5,6-epoxy-5,6-dihydro-1,10-phenanthroline] are synthesized. Complexes formulated as [Zn(NN)₂(H₂O)₂]²⁺(NN = phen and amphen), are also prepared. The cytotoxicity of the compounds is evaluated towards a panel of human cancer cells: ovarian (A2780), breast (MCF7) and cervical (HeLa), as well as non-tumoral V79 fibroblasts. All compounds display higher cytotoxicity than cisplatin (IC₅₀ = 22.5 ± 5.0 μM) towards ovarian cells, showing IC₅₀values in the low micromolar range. Overall, all compounds show higher selectivity for the A2780 cells than for the non-tumoral cells and higher selectivity indexes (IC₅₀(V79)/IC₅₀(A2780) than cisplatin. [Zn(Sal-Gly)(NN)(H₂O)] complexes induce caspase-dependent apoptosis in A2780 cells, except [Zn(Sal-Gly)(Bphen)(H₂O)], one of the most cytotoxic of the series. The cellular uptake in the ovarian cells analyzed by Inductively Coupled Plasma mass spectrometry indicates different Zn distribution profiles. Transmission electronic microscopy shows mitochondria alterations and apoptotic features consistent with caspase activation; cells incubated with [Zn(Sal-Gly)(amphen)(H₂O)] present additional nuclear membrane alterations in agreement with significant association with the nucleus. The increase of reactive oxygen species and lipid peroxidation forms could be related to apoptosis induction. [Zn(NN)₂(H₂O)₂]²⁺complexes have high ability to bind DNA through intercalation/groove binding, and circular dichroism data suggests that the main type of species that interact with DNA is [Zn(NN)]²⁺. Studies varying the % of fetal bovine serum (1-15%) in cell media show that albumin binding decreases the complex activity, indicating that distinct speciation of Zn- and phen-containing species in cell media may affect the cytotoxicity.

New heterobimetallic ferrocenyl derivatives are promising antitrypanosomal agents

In the search for a more effective chemotherapy for the treatment of Chagas' disease and human African trypanosomiasis, caused by Trypanosoma cruzi and Trypanosoma brucei parasites, respectively, the use of organometallic compounds may be a promising strategy. In this work, eight new heterobimetallic compounds are described including four 5-nitrofuryl containing thiosemicarbazones as bioactive ligands (HL1-HL4) and dppf = 1,1'-bis(diphenylphosphino) ferrocene as an organometallic co-ligand. Complexes of the formula [M^II(L)(dppf)](PF₆) with M = Pd or Pt were synthesized and fully characterized in the solid state and in solution, including the determination of the molecular structure of four of them by single crystal X-ray diffraction methods. Most compounds showed activity in the low micromolar or submicromolar range against both parasites, with the platinum compounds being more active than the palladium analogues. Activity was significantly increased by generation of the M-dppf compounds (3-24 fold increase with respect to free ligands HL for T. cruzi and up to 99 fold increase with respect to HL for T. brucei). The inclusion of the organometallic co-ligand also led to lower toxicity in mammalian cells and higher selectivity towards both parasites when compared to the free HL compounds. The complexes interact with DNA and affect the redox metabolism of the parasites. Furthermore, the most active and selective compound of the new series showed no in vivo toxicity in zebrafish embryos.

Naphthoylhydrazones: coordination to metal ions and biological screening

V^IVO, Cu^II and Zn^II complexes from three new naphthoylhydrazones were screened towards their ability to bind albumin and their cytotoxicity.

New thiosemicarbazide and dithiocarbazate based oxidovanadium(iv) and dioxidovanadium(v) complexes. Reactivity and catalytic potential

The new thiosemicarbazide and dithiocarbazate based vanadium complexes show remarkable catalytic potential for oxidation of alcohols and simple arenes.

Lanthanide complexes with phenanthroline-based ligands: insights into cell death mechanisms obtained by microscopy techniques

The biological properties of four lanthanide complexes with phenanthroline derivatives in ovarian cancer cells.

New ternary iron(iii) aminobisphenolate hydroxyquinoline complexes as potential therapeutic agents

Fe(iii)-Aminobisphenolate hydroxyquinoline complexes are active anticancer drug candidates in the low micromolar range, displaying apoptosis as the mode of cell death.

Photophysical properties and biological evaluation of a Zinc(II)-5-methyl-1H-pyrazole Schiff base complex

A new ZnL₂ complex containing two molecules of a tridentate Schiff base derived from 5-methyl-1H-pyrazole (HL) is synthesized and characterized. The photophysical properties of HL and ZnL₂ are disclosed and supported by CAMB3LYP DFT/TDDFT calculations. It is shown that there is keto-tautomer stabilization upon excitation with an energetically accessible triplet state in HL, not present in ZnL₂, this explaining the differences found in the emissions of the compounds. The intrinsic fluorescence of ZnL₂ is used as probe for a detailed study of its binding to human serum albumin. The protein-complex association is thermodynamically favourable and it is shown by fluorescence quenching and time-resolved analysis that the fluorescence quenching involves a mixed mechanism with prevalence of static quenching, which corroborates adduct formation at site I, close to the Trp214 residue. The ability of ZnL₂ to bind DNA was also evaluated, as well as its cytotoxic activity against MCF7 (breast), PC3 (prostate) cancer cells and hamster V79 fibroblasts. ZnL₂ is a moderate DNA intercalator (K_app = 3.9 × 10⁴ M^-1) and depicts a quite low IC₅₀ value at 48 h against MCF7 cells (IC₅₀ = 530 nM), but much higher for PC3 and V79 cells. The relevance of a more careful speciation evaluation of ZnL₂ and other potential metal-based drugs in incubation media used in in vitro tests is highlighted.

Synthesis, structure, solution behavior, reactivity and biological evaluation of oxidovanadium(iv/v) thiosemicarbazone complexes

The synthesis and characterization of an oxidovanadium(iv) [VIVO(L)(acac)] (1) and of two dioxidovanadium(v) [VVO2(L')] (2) and [VVO2(L)] (2a) complexes of the Schiff base formed from the reaction of 4-(p-fluorophenyl) thiosemicarbazone with pyridine-2-aldehyde (HL) are described. The oxidovanadium(iv) species [VIVO(L)(acac)] (1) was synthesized by the reaction of VIVO(acac)2 with the thiosemicarbazone HL in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same product i.e. the dioxidovanadium(v) complex [VVO2(L)] (2a); however, upon recrystallization of 1 in DMSO a distinct compound [VVO2(L')] (2) was formed, wherein the original ligand L- is transformed to a rearranged one, L'-. In the presence of DMSO the ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen (aldimine) and transformed to the corresponding VVO2-species through in situ reaction. The synthesized HL and the metal complexes were characterized by elemental analysis, IR, UV-Vis, NMR and EPR spectroscopy. The molecular structure of [VVO2(L')] (2) was determined by single crystal X-ray crystallography. The methylation of various other ligands and complexes prepared from different vanadium precursors under similar reaction conditions was also attempted and it was confirmed that the imine methylation observed is both ligand and metal precursor specific. Complexes 1 and 2 show in vitro insulin-like activity against insulin responsive L6 myoblast cells, higher than VIVO(acac)2, with complex 1 being more potent. In addition, the in vitro cytotoxicity studies of HL, and of complexes 1 and 2 against the MCF-7 and Vero cell lines were also done. The ligand is not cytotoxic and complex 2 is significantly more cytotoxic than 1. DAPI staining experiments indicate that an increase in the time of incubation and an increase of concentration of the complexes lead to the increase in cell death.

Binding of vanadium to human serum transferrin - voltammetric and spectrometric studies

Previous studies generally agree that in the blood serum vanadium is transported mainly by human serum transferrin (hTF). In this work through the combined use of electrochemical techniques, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry and small-angle X-ray scattering (SAXS) data it is confirmed that both V^IV and V^V bind to apo-hTF and holo-hTF. The electrochemical behavior of solutions containing vanadate(V) solutions at pH=7.0, analyzed by using two different voltammetric techniques, with different time windows, at a mercury electrode, Differential Pulse Polarography (DPP) and Cyclic Voltammetry (CV), is consistent with a stepwise reduction of V^V→V^IV and V^IV→V^II. Globally the voltammetric data are consistent with the formation of 2:1 complexes in the case of the system V^V-apo-hTF and both 1:1 and 2:1 complexes in the case of V^V-holo-hTF; the corresponding conditional formation constants were estimated. MALDI-TOF mass spectrometric data carried out with samples of V^IVOSO₄ and apo-hTF and of NH₄V^VO₃ with both apo-hTF and holo-hTF with V:hTF ratios of 3:1 are consistent with the binding of vanadium to the proteins. Additionally the SAXS data suggest that both V^IVOSO₄ and NaV^VO₃ can effectively interact with human apo-transferrin, but for holo-hTF no clear evidence was obtained supporting the existence or the absence of protein-ligand interactions. This latter data suggest that the conformation of holo-hTF does not change in the presence of either V^IVOSO₄ or NH₄V^VO₃. Therefore, it is anticipated that V^IV or V^V bound to holo-hTF may be efficiently up-taken by the cells through receptor-mediated endocytosis of hTF.

Cytotoxic activity and structural features of Ru(II)/phosphine/amino acid complexes

Thirteen new ruthenium amino acid complexes were synthesized and characterized. They were obtained by the reaction of α-amino acids (AA) with [RuCl₂(P-P)(N-N)], where P-P=1,4-bis(diphenylphosphino)butane (dppb) or 1,3-bis(diphenylphosphino)propane (dppp) and N-N=4,4'-dimethyl-2,2'-bipyridine (4'-Mebipy), 5,5'-dimethyl-2,2'-bipyridine (5'-Mebipy) or 4,4'-Methoxy-2-2'-bipyridine (4'-MeObipy). This afforded a family of complexes formulated as [Ru(AA-H)(P-P)(N-N)]PF₆, where AA=glycine (Gly), L-alanine (Ala), L-valine (Val), L-tyrosine (Tyr), L-tryptophan (Trp), L-histidine (His) and L-methionine (Met). All compounds were characterized by elemental analysis, spectroscopic and electrochemical techniques. The [Ru(AA-H)(P-P)(N-N)]PF₆ complexes are octahedral (the AA-H ligand binding involves N-amine and O-carboxylate), diamagnetic (low-spin d⁶, S=0) and present bands due to electronic transitions in the visible region. ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectra of the complexes indicate the presence of C₂ symmetry, and the identification of diastereoisomers. In vitro cytotoxicity assays of the compounds and cisplatin were carried out using MDA-MB-231 (human breast) tumor cell line and a non-tumor breast cell line (MCF-10A). Most complexes present promising results with IC₅₀ values comparable with the reference drug cisplatin and high selectivity indexes were found for the complexes containing L-Trp. The binding of two Ru-precursors of the type [RuCl₂(dppb)(NN)] (N-N=4'-MeObipy or 4'-Mebipy) to the blood transporter protein human serum albumin (HSA) was evaluated by fluorescence and circular dichroism spectroscopy. Both complexes bind HSA, probably in the hydrophobic pocket near Trp214, and the Ru-complex containing 4'-MeObipy shows higher affinity for HSA than the 4'-Mebipy one.

Binding of Oxovanadium(IV) Complexes to Blood Serum Albumins

In this work the binding of V^IVO²⁺ and V^IVO-complexes to serum albumins {human serum albumin (HSA), bovine serum albumin (BSA) and porcine serum albumin (PSA)} are studied using circular dichroism (CD), electron paramagnetic resonance (EPR) and visible absorption spectroscopy. The results confirm previous findings that V^IVO²⁺ occupies at least two types of binding sites on albumin: ‘the strong vanadium binding site’ (designated by VBS1) and ‘the weak vanadium binding sites’ (designated by VBS2). VBS1 binds 1 mol equivalent of V^IVO²⁺. On the other hand VBS2 correspond to binding of several mol equivalents of V^IVO, and studies done with PSA in the presence of excess Zn^II ions indicate that VSB2 corresponds to two distinct types of sites. The hyperfine coupling constant A_z for V^IVO²⁺ binding at VBS2 on HSA and BSA are all very similar (~168 × 10-4 cm^-1) but differ slightly on PSA (~166 × 10-4 cm^-1) due to differences in the binding sets. When (V^IVO)-HSA systems are titrated with maltol ternary species of (maltol)_m(V^IVO)_mHSA and (maltol)_2m(V^IVO)_mHSA stoichiometry form which are clearly distinguishable from the binary (V^IVO)-HSA system by the type and intensity of the CD spectra recorded. Changes are also observable in the intensity of the X-band EPR spectra, but not much in the hyperfine coupling constants A_z, which are all in the range 166-167 × 10-4 cm^-1. The results further demonstrate that the presence of maltol may enhance the binding of VIVO to albumin.

Evaluation of the binding of four anti-tumor Casiopeínas® to human serum albumin

The metal complexes designated by Casiopeínas® are mixed-ligand Cu^II-compounds some of them having promising antineoplastic properties. We report studies of binding of Cu(glycinato)(4,7-dimethyl-1,10-phenanthroline) (Cas-II-Gly (1)), Cu(acetylacetonato)(4,7-dimethyl-1,10-phenanthroline) (Cas-III-Ea (2)), Cu(glycinato)(4,4'-dimethyl-2,2'-bipyridine) (Cas-IV-Gly (3)) and Cu(acetylacetonato)(4,4'-dimethyl-2,2'-bipyridine) (Cas-III-ia (4)) to human serum albumin (HSA) by circular dichroism (CD), Electron paramagnetic resonance (EPR) and fluorescence spectroscopy. The results indicate that HSA may bind up to three molecules of the tested Casiopeínas. This is confirmed by inductively coupled plasma - atomic absorption spectroscopy measurements of samples of HSA-Casiopeínas after passing by adequate size-exclusion columns. The binding of Cas-II-Gly to HSA was also confirmed by MALDI-TOF mass spectrometric experiments. In the physiological range of concentrations the Casiopeínas form 1:1 adducts with HSA, with conditional binding constants of ca. 1×10⁹ (1), 4×10⁷ (2), 1×10⁶ (3) and 2×10⁵ (4), values determined from the CD spectra measured, and the fluorescence emission spectra indicates that the binding takes place close to the Trp214 residue. Overall, the data confirm that these Casiopeínas may bind to HSA and may be transported in blood serum by this protein; this might allow some selective tumor targeting, particularly in the case of Cas-II-Gly. In this work we also discuss aspects associated to the reliability of the frequently used methodologies to determine binding constants based on the measurement of fluorescence emission spectra of solutions containing low concentrations of proteins such as HSA and BSA, by titrations with solutions of metal complexes.

Interaction of [VIV O(acac)2 ] with Human Serum Transferrin and Albumin

[VO(acac)₂ ] is a remarkable vanadium compound and has potential as a therapeutic drug. It is important to clarify how it is transported in blood, but the reports addressing its binding to serum proteins have been contradictory. We use several spectroscopic and mass spectrometric techniques (ESI and MALDI-TOF), small-angle X-ray scattering and size exclusion chromatography (SEC) to characterize solutions containing [VO(acac)₂ ] and either human serum apotransferrin (apoHTF) or albumin (HSA). DFT and modeling protein calculations are carried out to disclose the type of binding to apoHTF. The measured circular dichroism spectra, SEC and MALDI-TOF data clearly prove that at least two VO-acac moieties may bind to apoHTF, most probably forming [V^IV O(acac)(apoHTF)] complexes with residues of the HTF binding sites. No indication of binding of [VO(acac)₂ ] to HSA is obtained. We conclude that V^IV O-acac species may be transported in blood by transferrin. At very low complex concentrations speciation calculations suggest that [(VO)(apoHTF)] species form.

Validation data supporting the characterization of novel copper complexes as anticancer agents

Three copper(II) complexes, Cu(Sal-Gly)(phen), Cu(Sal-Gly)pheamine, Cu(Sal-Gly)phepoxy were synthesized and characterized for their anticancer properties and mechanism of action (Acilan et al., in press) [1]. Here, we provide supporting data on colon cancer cell lines complementing our previous findings in cervix cells. This paper also contains a data table for the fold changes and p-values of all genes analyzed in this study via a custom RT-qPCR array. All compounds induced DNA damage (based on 8-oxo-guanidine, ɣH2AX staining in cells) and apoptosis (based on elevated DNA condensation/fragmentation, Annexin V staining, caspase 3/7 activity and mitochondrial membrane depolarization) in HCT-116 colon cancer cells. The increase in oxidative stress was also further confirmed in these cells. Further interpretation of the data presented here can be found in the article entitled “Synthesis, biological characterization and evaluation of molecular mechanisms of novel copper complexes as anticancer agents” (Acilan et al., in press) [1].

Evaluation of cellular uptake, cytotoxicity and cellular ultrastructural effects of heteroleptic oxidovanadium(IV) complexes of salicylaldimines and polypyridyl ligands

Searching for prospective vanadium-based drugs for cancer treatment, a new series of structurally related [V^IVO(L-2H)(NN)] compounds (1-8) was developed. They include a double deprotonated salicylaldimine Schiff base ligand (L-2H) and different NN-polypyridyl co-ligands having DNA intercalating capacity. Compounds were characterized in solid state and in solution. EPR spectroscopy suggests that the NN ligands act as bidentate and bind through both nitrogen donor atoms in an axial-equatorial mode. The cytotoxicity was evaluated in human tumoral cells (ovarian A2780, breast MCF7, prostate PC3). The cytotoxic activity was dependent on type of cell and incubation time. At 24h PC3 cells presented low sensitivity, but at 72h all complexes showed high cytotoxic activity in all cells. Human kidney HEK293 and ovarian cisplatin resistant A2780cisR cells were also included to evaluate selectivity towards cancer cells and potency to overcome cisplatin resistance, respectively. Most complexes showed no detectable interaction with plasmid DNA, except 2 and 7 which depicted low ability to induce single strand breaks in supercoiled DNA. Based on the overall cytotoxic profile, complexes with 2,2´-bipyridine and 1,10-phenanthroline ligands (1 and 2) were selected for further studies, which consisted on cellular distribution and ultrastructural analyses. In the A2780 cells both depicted different distribution profiles; the former accumulates mostly at the membrane and the latter in the cytoskeleton. Morphology of treated cells showed nuclear atypia and membrane alterations, more severe for 1. Complexes induce different cell death pathways, predominantly necrosis for 1 and apoptosis for 2. Complexes alternative mode of cell death motivates the possibility for further developments.

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

A camphor-derived sulfonimine with a conjugated carbonyl group, oxoimine 1 (O₂SNC₁₀H₁₃O), reacts with amino acids (glycine, L-alanine, L-phenylalanine, L-leucine) to form a compound O₂SNC₁₀H₁₃NC₁₀H₁₄NSO₂ (2) which was characterized by spectroscopic means (MS and NMR) and supported by DFT calculations. The product, a single diastereoisomer, contains two oxoimine units connected by a –N= bridge, and thus has a structural analogy to the colored product Ruhemann´s purple obtained by the ninhydrin reaction with amino acids. A plausible reaction mechanism that involves zwitterions, a Strecker degradation of an intermediate imine and water-catalyzed tautomerizations was developed by means of DFT calculations on potential transition states.

Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior

A series of mononuclear non-oxido vanadium(IV) [V(IV)(L(1-4))2] (1-4), oxidoethoxido vanadium(V) [V(V)O(L(1-4))(OEt)] (5-8), and dinuclear μ-oxidodioxidodivanadium(V) [V(V)2O3(L(1))2] (9) complexes with tridentate aroylazine ligands are reported [H2L(1) = 2-furoylazine of 2-hydroxy-1-acetonaphthone, H2L(2) = 2-thiophenoylazine of 2-hydroxy-1-acetonaphthone, H2L(3) = 1-naphthoylazine of 2-hydroxy-1-acetonaphthone, H2L(4) = 3-hydroxy-2-naphthoylazine of 2-hydroxy-1-acetonaphthone]. The complexes are characterized by elemental analysis, by various spectroscopic techniques, and by single-crystal X-ray diffraction (for 2, 3, 5, 6, 8, and 9). The non-oxido V(IV) complexes (1-4) are quite stable in open air as well as in solution, and DFT calculations allow predicting EPR and UV-vis spectra and the electronic structure. The solution behavior of the [V(V)O(L(1-4))(OEt)] compounds (5-8) is studied confirming the formation of at least two different types of V(V) species in solution, monomeric corresponding to 5-8, and μ-oxidodioxidodivanadium [V(V)2O3(L(1-4))2] compounds. The μ-oxidodioxidodivanadium compound [V(V)2O3(L(1))2] (9), generated from the corresponding mononuclear complex [V(V)O(L(1))(OEt)] (5), is characterized in solution and in the solid state. The single-crystal X-ray diffraction analyses of the non-oxido vanadium(IV) compounds (2 and 3) show a N2O4 binding set and a trigonal prismatic geometry, and those of the V(V)O complexes 5, 6, and 8 and the μ-oxidodioxidodivanadium(V) (9) reveal that the metal center is in a distorted square pyramidal geometry with O4N binding sets. For the μ-oxidodioxidodivanadium species in equilibrium with 5-8 in CH2Cl2, no mixed-valence complexes are detected by chronocoulometric and EPR studies. However, upon progressive transfer of two electrons, two distinct monomeric V(IV)O species are detected and characterized by EPR spectroscopy and DFT calculations.

The effect of phosphate on the nuclease activity of vanadium compounds

The nuclease activity of VO(acac)2 (1, acac = acetylacetone) and its derivatives VO(hd)2 (2, hd = 3,5-heptanedione), VO(Cl-acac)2 (3, Cl-acac = 3-chloro-2,4-pentanedione), VO(Et-acac)2 (4, Et-acac = 3-ethyl-2,4-pentanedione) and VO(Me-acac)2 (5, Me-acac = 3-methyl-2,4-pentanedione), is studied by agarose gel electrophoresis, UV-visible spectroscopy, cyclic and square wave voltammetry and (51)V NMR. The mechanism is shown to be oxidative and associated with the formation of reactive oxygen species (ROS). Hydrolytic cleavage of the phosphodiester bond is also promoted by 1, but at much slower rate which cannot compete with the oxidative mechanism. The generation of ROS is much higher in the presence of phosphate buffer when compared with organic buffers and this was attributed to the formation of a mixed-ligand complex containing phosphate, (V(IV)O)(V(V)O)(acac)2(HnPO4(n-3)), presenting a quasi-reversible voltammetric behavior. The formation of this species was further observed by Electrospray Ionization Mass Spectrometry (ESI-MS). Phosphate being an essential species in most biological media, the importance of the formation of mixed-ligand species in other vanadium systems is emphasized.

Expanding the family of heteroleptic oxidovanadium(IV) compounds with salicylaldehyde semicarbazones and polypyridyl ligands showing anti-Trypanosoma cruzi activity

Searching for prospective vanadium-based drugs for the treatment of Chagas disease, a new series of heteroleptic [V(IV)O(L-2H)(NN)] compounds was developed by including the lipophilic 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) NN ligand and seven tridentate salicylaldehyde semicarbazone derivatives (L1-L7). The compounds were characterized in the solid state and in solution. EPR spectroscopy suggests that the NN ligand is bidentate bound through both nitrogen donor atoms in an axial-equatorial mode. The EPR and (51)V-NMR spectra of aerated solutions at room temperature indicate that the compounds are stable to hydrolysis and that no significant oxidation of V(IV) to V(V) takes place at least in 24h. The complexes are more active in vitro against Trypanosoma cruzi, the parasite responsible for Chagas disease, than the reference drug Nifurtimox and most of them are more active than previously reported [V(IV)O(L-2H)(NN)] complexes of other NN co-ligands. Selectivity towards the parasite was analyzed using J-774 murine macrophages as mammalian cell model. Due to both, high activity and high selectivity, L2, L4, L5 and L7 complexes could be considered new hits for further drug development. Lipophilicity probably plays a relevant role in the bioactivity of the new compounds. The [V(IV)O(L-2H)(NN)] compounds were designed aiming DNA as potential molecular target. Therefore, the novel L1-L7 tmp complexes were screened by computational modeling, comparing their DNA-binding features with those of previously reported [V(IV)O(L-2H)(NN)] compounds with different NN co-ligands. Whereas all the complexes interact well with DNA, with binding modes and strength tuned in different extents by the NN and semicarbazone co-ligands, molecular docking suggests that the observed anti-T. cruzi activity cannot be explained upon DNA intercalation as the sole mechanism of action.

Vanadium(IV) and copper(II) complexes of salicylaldimines and aromatic heterocycles: Cytotoxicity, DNA binding and DNA cleavage properties

Five copper(II) complexes, [Cu(sal-Gly)(bipy)](1), [Cu(sal-Gly)(phen)] (2), [Cu(sal-l-Ala)(phen)] (3), [Cu(sal-D-Ala)(phen)] (4), [Cu(sal-l-Phe)(phen)] (5) and five oxidovanadium(IV) complexes, [V(IV)O(sal-Gly)(bipy)] (6), [V(IV)O(sal-Gly)(phen)] (7), [V(IV)O(sal-l-Phe)(H2O)] (8), [V(IV)O(sal-l-Phe)(bipy)] (9), [V(IV)O(sal-l-Phe)(phen)] (10) (sal=salicylaldehyde, bipy=2,2'-bipyridine, phen=1,10-phenanthroline) were synthesized and characterized, and their interaction with DNA was evaluated by different techniques: gel electrophoresis, fluorescence, UV-visible and circular dichroism spectroscopy. The complexes interact with calf-thymus DNA and efficiently cleave plasmid DNA in the absence (only 2 and 5) and/or presence of additives. The cleavage ability is concentration-dependent as well as metal and ligand-dependent. Moreover, DNA binding experiments show that the phen-containing Cu(II) and V(IV)O compounds display stronger DNA interaction ability than the corresponding bipy analogues. The complexes present cytotoxic activity against human ovarian (A2780) and breast (MCF7) carcinoma cells. Cell-growth inhibition (IC50) of compounds 1, 2 and 5 in human promyelocytic leukemia (HL60) and human cervical cancer (HeLa) cells were also determined. The copper complexes show much higher cytotoxic activity than the corresponding vanadium complexes and the reference drug cisplatin (except for the sal-Gly complexes); namely, the phenanthroline copper complexes 2-5 are ca. 10-fold more cytotoxic than cisplatin and more cytotoxic than their bipyridine analogues.