Photoenhanced oxidative DNA cleavage with non-heme iron(II) complexes

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

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

Antibacterial Activity of Co(III) Complexes with Diamine Chelate Ligands against a Broad Spectrum of Bacteria with a DNA Interaction Mechanism

Cobalt coordination complexes are very attractive compounds for their therapeutic uses as antiviral, antibacterial, antifungal, antiparasitic, or antitumor agents. Two Co(III) complexes with diamine chelate ligands ([CoCl₂(dap)₂]Cl (1) and [CoCl₂(en)₂]Cl (2)) (where dap = 1,3-diaminopropane, en = ethylenediamine) were synthesized and characterized by elemental analysis, an ATR technique, and a scan method and sequentially tested against Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration results revealed that anaerobic and microaerophilic bacteria were found to be the most sensitive; the serial passages assay presented insignificant increases in bacterial resistance to both compounds after 20 passages. The synergy assay showed a significant reduction in the MIC values of nalidixic acid when combined with Compounds (1) or (2). The assessment of cell damage by the complexes was performed using scanning electron microscopy, transmission electron microscopy, and confocal microscopy, which indicated cell membrane permeability, deformation, and altered cell morphology. DNA interaction studies of the Co(III) complexes with plasmid pBR322 using spectrophotometric titration methods revealed that the interaction between Complex (1) or (2) and DNA suggested an electrostatic and intercalative mode of binding, respectively. Furthermore, the DNA cleavage ability of compounds by agarose gel electrophoresis showed nuclease activity for both complexes. The results suggest that the effect of the tested compounds against bacteria can be complex.

The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications

The iron and manganese complexes that activate oxygen atom play multiple role in technologically relevant reactions as well as in biological transformations, in which exist in different redox states. Among them, high-valent oxo intermediate seems to be the most important one. Iron, and/or manganese-based processes have found application in many areas, starting from catalysis and sustainable technologies, through DNA oxidative cleavage, to new substances useful in chemotherapeutic drugs. This review is not only the latest detailed list of uses of homogeneous N-pentadentate iron and manganese catalysts for syntheses of valuable molecules with huge applications in green technologies, but also a kind of "a cookbook", collecting "recipes" for the discussed complexes, in which the sources necessary to obtain a full characterization of the compounds are presented. Following the catalytic activity of metalloenzymes, and taking into account the ubiquity of iron and manganese salts, which in combination with properly designed ligands may show similarity to natural systems, the discussed complexes can find application as new anti-cancer drugs. Also, owing to ability of oxygen atom to exchange in reaction with H₂O, they can be successfully applied in photodriven reactions of water oxidation, as well as in chemically regenerated fuel cells as a redox catalyst.

Dinuclear metal(ii)-acetato complexes based on bicompartmental 4-chlorophenolate: syntheses, structures, magnetic properties, DNA interactions and phosphodiester hydrolysis

A series of dinuclear metal(ii)-acetato complexes: [Ni2(μ-L(Cl)O)(μ2-OAc)2](PF6)·3H2O (1), [Ni2(μ-L(Cl)O)(μ2-OAc)2](ClO4)·CH3COCH3 (2), [Cu2(μ-L(Cl)O)(μ2-OAc)(ClO4)](ClO4) (3), [Cu2(μ-L(Cl)O)(OAc)2](PF6)·H2O (4), [Zn2(μ-L(Cl)O)(μ2-OAc)2](PF6) (5) and [Mn2(L(Cl)-O)(μ2-OAc)2](ClO4)·H2O (6), where L(Cl)O(-) = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(ii), Zn(ii) and Mn(ii) complexes 1, 2, 5 and 6, whereas with Cu(ii) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1-4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = -0.55 to -9.4 cm(-1)) and ferromagnetic coupling in 3 (J = 15.4 cm(-1)). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1-5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(ii) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(ii) complexes with DNA demonstrated the important impact of the nickel(ii) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5-10.5 at 25 °C. The Michaelis-Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies kcat/KM (kcat = catalytic rate constant, KM = substrate binding constant) decrease in the order: Ni(ii), 1 > Zn(ii), 5 > Cu(ii), 3. A similar trend was also observed with the turnover numbers at pH = 7. The results are discussed in relation to the coordination geometry and nature of the metal center as well as the steric environment imposed by the compartmental phenoxido ligand.

Enhancement in intramolecular interactions and in vitro biological activity of a tripodal tetradentate system upon complexation

Naphthalimide appended metal complexes uniquely exhibited intramolecular interactions, affinity for DNA/proteins and apoptosis mediated anticancer activity.

Efficient hydrolytic cleavage of plasmid DNA by chloro-cobalt(II) complexes based on sterically hindered pyridyl tripod tetraamine ligands: synthesis, crystal structure and DNA cleavage

Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.

Highly efficient synthetic iron-dependent nucleases activate both intrinsic and extrinsic apoptotic death pathways in leukemia cancer cells

The nuclease activity and the cytotoxicity toward human leukemia cancer cells of iron complexes, [Fe(HPClNOL)Cl2]NO3 (1), [Cl(HPClNOL)Fe(μ-O)Fe(HPClNOL)Cl]Cl2·2H2O (2), and [(SO4)(HPClNOL)Fe(μ-O)Fe(HPClNOL)(SO4)]·6H2O (3) (HPClNOL=1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol), were investigated. Each complex was able to promote plasmid DNA cleavage and change the supercoiled form of the plasmid to circular and linear ones. Kinetic data revealed that (1), (2) and (3) increase the rate of DNA hydrolysis about 278, 192 and 339 million-fold, respectively. The activity of the complexes was inhibited by distamycin, indicating that they interact with the minor groove of the DNA. The cytotoxic activity of the complexes toward U937, HL-60, Jukart and THP-1 leukemia cancer cells was studied employing 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), fluorescence and electronic transmission microscopies, flow cytometry and a cytochrome C release assay. Compound (2) has the highest activity toward cancer cells and is the least toxic for normal ones (i.e. peripheral blood mononuclear cells (PBMCs)). In contrast, compound (1) is the least active toward cancer cells but displays the highest toxicity toward normal cells. Transmission electronic microscopy indicates that cell death shows features typical of apoptotic cells, which was confirmed using the annexin V-FITC/PI (fluorescein isothiocyanate/propidium iodide) assay. Furthermore, our data demonstrate that at an early stage during the treatment with complex (2) mitochondria lose their transmembrane potential, resulting in cytochrome C release. A quantification of caspases 3, 9 (intrinsic apoptosis pathway) and caspase 8 (extrinsic apoptosis pathway) indicated that both the intrinsic (via mitochondria) and extrinsic (via death receptors) pathways are involved in the apoptotic stimuli.

DNA cleavage activity of Fe(II)N4Py under photo irradiation in the presence of 1,8-naphthalimide and 9-aminoacridine: unexpected effects of reactive oxygen species scavengers

The DNA cleavage activity of the iron(II) complex of the ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine (N4Py) was investigated in the presence of the chromophores 1,8-naphthalimide (NI) and 9-aminoacridine (AA) under photo irradiation at 355 and 400.8 nm and compared to the activity of the complex without the chromophores. Whereas in most cases no synergistic effect of the added chromophores on DNA cleavage efficiency was observed, it was found that for Fe(II)N4Py, in combination with NI under irradiation at 355 nm, the DNA cleavage activity was increased. Surprisingly, it was found that the addition of reactive oxygen species (ROS) scavengers gave rise to significantly increased DNA cleavage efficiency, which is a highly counterintuitive observation since ROS are needed to achieve DNA cleavage. A hypothesis is put forward to explain, at least partly, these results. It is proposed that the addition of scavengers inhibits quenching of (3)NI*, thus making photo-induced electron transfer between (3)NI* and Fe(III)N4Py more efficient. This results in reduction of Fe(III)N4Py to Fe(II)N4Py, which can then react with ROS giving rise to DNA cleavage. Hence the role of the scavengers is to maintain a close to optimal concentration of ROS. The present study serves as an illustration of the care that needs to be exercised in interpreting the results of experiments using standard ROS scavengers, since especially in complex systems such as presented here they can give rise to unexpected phenomena. In the presence of 1,8-naphthalimide or 9-aminoacridine, ROS scavengers can increase the DNA cleavage efficiency of Fe(II)N4Py complex under photo irradiation.