Novel peptide-based copper(II) complexes for total hydrolytic cleavage of DNA

Stable Cu(II) complexes with histamine- and histidine-containing dipeptides histidylserine and histidylphenylalanine have been developed. Their interaction in solution has been investigated, and the stability of their complexes was determined. The nature of binding in these complexes has been explained with the help of potentiometric pH titrations and 1H-NMR spectroscopy. The geometry of these complexes has been established by electronic spectra. The DNA-binding and -cleavage abilities of these Cu(II) complexes have been probed by the absorption, thermal denaturation, fluorescence, and electrophoresis experiments. The results suggest that these peptide-based Cu(II) complexes effectively bind and efficiently cleave DNA under mild biological conditions. Since Cu(II) complexes are known to play an important role in phosphodiester bond cleavages, these results assume importance.     

ESR an optical absorption studies on the copper(II) interaction with small peptides containing aromatic amino acids.

The interaction of Cu(II) with di- and tripeptides each containing phenylalanine, tryptophan or histidine in the amino acid chain has been investigated by means of electron spin resonance (ESR) and optical absorption spectroscopy. Cu(II) complexes of dipeptides and tripeptides exhibit different magnetic and optical parameters. Dipeptide complexes have larger gparallel-values and smaller A parallel values than tripeptide complexes. When compared to dipeptide complexes, the d-d band of the central metal ion is blue shifted for tripeptide complexes. There are no significant difference in the behavior of Cu(II) peptide complexes containing phenylalanine or tryptophan. Complexes of histidine containing peptides, however, show modified spectra caused by the participation of the imidazole nitrogen in the coordination to Cu(II). The imidazole nitrogen seems to coordinate in-plane with other coordinating atoms or in an axial position depending on the kind of peptide.     

Subcellular localization of a fluorescent derivative of CuII(atsm) offers insight into the neuroprotective action of CuII(atsm)

Copper complexes of bis(thiosemicarbazone) (Cu(II)(btsc)s) have been studied as potential anti-cancer agents and hypoxia imaging agents. More recently, Cu(II)(btsc)s have been identified as possessing potent neuroprotective properties in cell and animal models of neurodegenerative disease. Despite their broad range of pharmacological activity little is known about how cells traffic Cu(II)(btsc)s and how this relates to potential anti-cancer or neuroprotective outcomes. One method of investigating sub-cellular localization of metal complexes is through confocal fluorescence imaging of the compounds in cells. Previously we harnessed the fluorescence of a pyrene group attached to diacetyl-bis(N4-methylthiosemicarbazonato)copper(ii)) (Cu(II)(atsm)), (Cu(II)L(1)). We demonstrated that Cu(II)L(1) was partially localized to lysosomes in HeLa cancer epithelial cells. Here we extend these studies to map the sub-cellular localization of Cu(II)L(1) in M17 neuroblastoma cells. Treatment of M17 or HeLa cells led to rapid association of the Cu-complex into distinct punctate structures that partially co-localized with lysosomes as assessed by co-localization with Lysotracker and acridine orange. No localization to early or late endosomes, the nucleus or mitochondria was observed. We also found evidence for a limited association of Cu(II)L(1) with autophagic structures, however, this did not account for the majority of the punctate localization of Cu(II)L(1). In addition, Cu(II)L(1) revealed partial localization with ER Tracker and was found to inhibit ER stress induced by tunicamycin. This is the first report to comprehensively characterize the sub-cellular localization of a Cu(II)(atsm) derivative in cells of a neuronal origin and the partial association with lysosome/autophagic structures and the ER may have a potential role in neuroprotection.     

The complex formation of copper(II) with GHL and related peptides

The formation constants for complexes of Cu(II) with GHL and a series of related dipeptides were determined by means of potentiometric titration and ESR spectroscopy in aqueous solution. The complex formation of the related peptides AH, LH, HL, GL and VL is compared to that of GHL. The somewhat higher affinity of GHL to Cu(II) as compared to AH and LH seems to be a poor explanation for the biological functions of GHL. A dimeric Cu(II)HL complex is detected, which displays an ESR spectrum at room temperature. The ESR spectra of the different complexes and the influences of structures on the spectra are discussed.     

Copper chelating anti-inflammatory agents; N1-(2-aminoethyl)-N2-(pyridin-2-ylmethyl)-ethane-1,2-diamine and N-(2-(2-aminoethylamino)ethyl)picolinamide: an in vitro and in vivo study

An in vitro and in vivo study of some copper chelating anti-inflammatory agents for alleviation of inflammation associated with rheumatoid arthritis (RA) has been conducted. Two copper chelating agents, N(1)-(2-aminoethyl)-N(2)-(pyridin-2-ylmethyl)ethane-1,2-diamine ([555-N]) and N-(2-(2-aminoethylamino)ethyl)picolinamide ([H(555)-N]) have been synthesized as their hydrochloride salt; their protonation constants and formation constants with Cu(II), Zn(II) and Ca(II) determined by glass electrode potentiometry at 298K and an ionic strength of 0.15M. Cu(II) formed stable complexes at physiological pH while the in vivo competitors, Zn(II) and Ca(II) formed weak complexes with both chelating agents. Both [555-N] and [H(555)-N] showed better selectivity for Cu(II) than for Zn(II) and Ca(II). Electronic spectra for species formed at physiological pH suggest a square planar geometry. Speciation calculations using a blood plasma model predicted that these copper chelating agents are able to mobilize Cu(II) in vivo, while bio-distribution studies of their (64)Cu(II)-labelled complexes at physiological pH showed tissue accumulation and retention indicating an encouraging biological half life.     

The interaction of metal ions with nucleic acids. Ternary complexes of copper(II) with peptides and nucleosides

Difference electronic absorption and electron paramagnetic resonance spectroscopy were used to monitor the formation of the ternary complexes of Cu(II) ions with nucleosides and dipeptides containing Gly, Leu and Trp residues. Stability constants of these mixed-ligand complexes of Cu(II)-peptides with nucleosides were found to decrease in the following order: 6-ketopurines greater than 6-aminopurine greater than pyrimidines. Interpretation of the EPR data indicated that the covalent nature of the copper-ligand bond also decreases in the same order. The EPR findings suggest that nucleosides are bonded in the equatorial position of the Cu(II)-peptide complexes, however, in the case of pyrimidine nucleosides weak axial bonding also seems to occur.     

Synthesis and characterization of three new Cu(II)-dipeptide complexes

Three new copper(II) complexes of stoichiometry [Cu(L-dipeptide)].nH(2)O, containing as ligands the dipeptides L-alanine-L-isoleucine, L-alanine-L-threonine and L-alanine-L-tyrosine were prepared. They were characterized by single crystal X-ray diffractometry, and electronic and infrared spectroscopy. In all cases, the Cu(II) cation has essentially the same elongated square pyramidal coordination, being equatorially cis coordinated by a N(2)O(2) arrangement of ligand atoms and axially by a carbonyl oxygen atom. The compounds show rather similar polymeric structures which resemble those recently reported for the [Cu(ala-val)] and [Cu(ala-phe)] complexes. The electronic and infrared spectra are briefly discussed on the basis of the structural peculiarities of the complexes. Superoxide dismutase (SOD)-like activity was also tested for the compounds.     

Enhancement of cytotoxicity of bleomycin by dithiocarbamates: formation of bis(dithiocarbamato) cu(II).

Properties of the reactions of dithiocarbamates and their Cu(II) or Fe(III) complexes with Ehrlich cells were determined and related to their effects on the inhibition of cell proliferation caused by bleomycin and Cu bleomycin. In complete culture medium containing Eagle's minimal essential medium plus Earles salts and 2.5% fetal calf serum, dimethyl- and diethyldithiocarbamates and their copper complexes inhibit cell proliferation and cause cell death. The copper complexes are more effective agents. Ferric tris-diethyldithiocarbamate is also a cytotoxic species. In contrast, when cells are exposed to dimethyldithiocarbamate or its copper complex in Ringer's buffer under metal-restricted condition, washed, and then placed in complete medium, the copper complex is much more active in inhibiting cell growth. The difference is magnified when dihydroxyethyldithiocarbamate and N-methylglucamine dithiocarbamate and their copper complexes are compared in complete media. Incubation of bleomycin or copper bleomycin with Ehrlich cells in Ringer's buffer with or without dimethyldithiocarbamate or bis-dimethyldithiocarbamato Cu(II) leads to no enhancement of cytotoxicity from combinations of agents, except when the two copper complexes are present. Diethyl- or dimethyldithiocarbamate readily extracts copper from Cu(II)bleomycin and iron from Fe(III)bleomycin when ethylacetate is present to remove the tris-dithiocarbamato Fe(III) complex from aqueous solution. When bis-dimethyldithiocarbamato Cu(II) is incubated with Ehrlich cells, copper is released from the complex and bound to high molecular weight and metallothionein fractions. A reductive mode of dissociation of the copper complexes in cells is supported by ESR experiments. Reactions of diethyl- and dimethyldithiocarbamato Cu(II) with thiol compounds demonstrates one possible mechanism of reduction of these complexes.     

Hydrolysis of DNA by a Dipeptides Containing Histidine

Three ligands which contain histidine and conjugated by a flexible linker, have been characterized and evaluated as DNA cleavage agents. The cleavage activity of metal complexes were evaluated by monitoring the conversion of supercoiled plasmid DNA (pUC19) (Form I) to nicked circular DNA (Form II) by agarose gel electrophoresis. The results showed that the cleavage activity of Cu(II) complexes was enhanced compared with histidine. Specially, at a high reaction concentration (0.2 mM), Cu(II) complexes can cleave the plasmid DNA with some selectivity.     

The effect of histidine on the structure and antitumor activity of metal-5-halouracil complexes

The ternary complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) ions with 5-halouracils, viz., 5-fluorouracil (5FU), 5-chlorouracil (5ClU), and 5-bromouracil (5BrU), and the biologically important ligand L-histidine (HISD) have been synthesized and characterized by elemental analysis, conductance measurements, infrared spectra, electronic spectra, and magnetic moment (room temperature) measurements. On the basis of these studies, the structures of the complexes have been proposed. All these ternary complexes were screened for their antitumor activity against Dalton's lymphoma in C3H/He mice. It was found that only Mn(II)-5BrU-HISD, Co(II)-5BrU-HISD, Cu(II)-5ClU-HISD, Cu(II)-5BrU-HISD, Zn(II)-5FU-HISD, and Zn(II)-5BrU-HISD complexes have significant antitumor activity with T/C greater than 125% (where T and C represent mean lifespan of treated mice and control mice respectively). The Mn(II)-5FU-HISD, Co(II)-5FU-HISD, Co(II)-5ClU-HISD, Ni(II)-5ClU-HISD, Ni(II)-5BrU-HISD, and Zn(II)-5ClU-HISD complexes are also effective antitumor agents, with T/C greater than 115%. The complexes that showed effective antitumor action in vivo were also found to inhibit 3H-thymidine incorporation (DNA replication) in Dalton's lymphoma cells in vitro.     

Antibacterial dimeric copper(II) complexes with chromone-derived compounds

A new series of six chromone-derived compounds and their Cu(II) complexes have been synthesized and characterized by their physical, spectral and analytical data. The ligands and their Cu(II) complexes were screened for their in vitro antibacterial activity against four Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri) and two Gram-positive (Bacillus subtilis, Staphylococcus aureus) bacterial strains by agar-well diffusion method. The ligands were found to exhibit either no or low-to-moderate activities against one or more bacterial species whereas, the Cu(II) complexes exhibited moderate-to-high activity. The ligands which were inactive before complexation became active upon complexation with the Cu(II) metal ion and less active became more active.     

Copper complexes as therapeutic agents

The importance of transition metals in biological processes has been well established. Copper (Cu) is a transition metal that can exist in oxidised and reduced states. This allows it to participate in redox and catalytic chemistry, making it a suitable cofactor for a diverse range of enzymes and molecules. Cu deficiency or toxicity is implicated in a variety of pathological conditions; therefore inorganic complexes of Cu have been investigated for their therapeutic and diagnostic potential. These Cu complexes have been shown to be effective in cancer treatment due to their cytotoxic action on tumour cells. Alternatively, Cu complexes can also modulate Cu homeostasis in the brain, resulting in protective effects in several models of neurodegeneration. In other diseases such as coronary heart disease and skin disease, the success of Cu complexes as potential therapeutics will most likely be due to their ability to increase SOD activity, leading to relief of oxidative stress. This review seeks to provide a broad insight into some of the diverse actions of Cu complexes and demonstrate the strong future for these compounds as potential therapeutic agents.     

ESR and optical absorption studies on the copper(II) interaction with small peptides containing aromatic amino acids

The interaction of Cu(II) with di- and tripeptides each containing phenylalanine, tryptophan or histidine in the amino acid chain has been investigated by means of electron spin resonance (ESR) and optical absorption spectroscopy. Cu(II) complexes of dipeptides and tripeptides exhibit different magnetic and optical parameters. Dipeptide complexes have larger g -values and smaller {A –values than tripeptide complexes. When compared to dipeptide complexes, the d-d band of the central metal ion is blue shifted for tripeptide complexes. There are no significant differences in the behavior of Cu(II) peptide complexes containing phenylalanine or tryptophan. Complexes of histidine containing peptides, however, show modified spectra caused by the participation of the imidazole nitrogen in the coordination to Cu(II). The imidazole nitrogen seems to coordinate in-plane with other coordinating atoms or in an axial position depending on the kind of peptide.Part of the Ph.D. thesis of L.S., D-26Dedicated to Prof. Dr. H. Glubrecht on the occasion of his 60th birthday     

Metal complexes of carboxamidrazone analogs as antitubercular agents. 1. Synthesis,X-ray crystal-structures,spectroscopic properties and antimycobacterial activity against Mycobacterium tuberculosis H(37)Rv

N¹-Benzylidene-pyridine carboxamidrazones and their metal conjugates have emerged as a new class of potential antimycobacterial agents. Nine such carboxamidrazone analogs (L₁–L₉) along with their Cu(II) (MC₁–MC₉) and Fe(III) (MC₁₀–MC₁₈) complexes were synthesized. Single crystal X-ray structures of copper complexes MC₁ and MC₅ were determined which suggest slightly distorted square planer geometries for copper complexes and octahedral geometries for ferric compounds. All compounds were evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H₃₇Rv. The results show 32–64-fold enhancement in antitubercular activity upon copper complexation.     

Cytotoxic effect, differentiation, inhibition of growth and theoretical calculations of an N,N-donor ligands and its platinum(II), palladium(II) and copper(II) complexes

The new pyrazole ligand 5-(2-hydroxyphenyl)-3-methyl-1-(2-pyridylo)-1H-pyrazole-4-carboxylic acid methyl ester (2) and the corresponding Pt(II), Pd(II) and Cu(II) complexes 3-5 have been synthesized as potential anticancer compounds, and characterized using IR, and (1)H NMR as well as mass spectrometry. The 3-D structures of the Cu(II) complexes were determined by quantum mechanic calculation DFT methodology (density functional theory). The cytotoxicity assay of the ligand and complexes has been performed on leukemia cell lines. In general, the complexes showed lower cytotoxicity than cisplatin, and the Pt(II) and Cu(II) complexes were found to be more efficient in the induction of leukemia cell death than the Pd(II) complex. Our investigations indicate that the antiproliferating activity of the Pt(II) and Cu(II) complexes was partly due to the modulation of cellular differentiation.     

Copper(II) and manganese(III) complexes of N'-[(2-hydroxy phenyl) carbonothioyl] pyridine-2-carbohydrazide: novel therapeutic agents for cancer

c-Src is a non-receptor tyrosine kinase which plays a significant role in the growth mediated signaling pathway impacting cellular proliferation, differentiation, mobility, survival and transformation. Myristoylation of pp60(c-src) leads to its membrane association and activation, a process catalyzed by N-myristoyltransferase (NMT). We have shown earlier increased NMT activity in the early stages of colon cancer. A novel sulfur nitrogen donor ligand and its Cu(II) and Mn(III) complexes have been prepared and characterized using various physicochemical analyses. These Cu(II) and Mn(III) complexes showed cytotoxicity against the colon cancer cell line HT29. The IC(50) for Cu(II) and Mn(III) complexes were 12.2 and 16.1 microM, respectively. HT29 cells treated with Cu(II) and Mn(III) complexes induced apoptosis and inhibited endogenous NMT activity. Furthermore, they induced higher levels of hsc70 and inhibited the expression of c-Src. Inhibition of endogenous NMT activity by metal complexes was demonstrated for the first time. This study also suggested that NMT activity is crucial for cell survival and demonstrated that cessation in activity results in apoptosis. These metal complexes may prove to be novel therapeutic agents for cancer targeting NMT.     

Metal based drugs: design,synthesis and in-vitro antimicrobial screening of Co(II), Ni(II), Cu(II) and Zn(II) complexes with some new carboxamide derived compounds: crystal structures of N-[ethyl(propan-2-yl)carbamothioyl]thiophene-2-carboxamide and its copper(II) complex

A new series of compounds derived from thiophene-2-carboxamide were synthesized and characterized by IR, ¹H-NMR and ¹³C-NMR, mass spectrometry and elemental analysis. These compounds were further used to prepare their Co(II), Ni(II), Cu(II) and Zn(II) metal complexes. All metal(II) complexes were air and moisture stable. Physical, spectral and analytical data have shown the Ni(II) and Cu(II) complexes to exhibit distorted square-planar and Co(II) and Zn(II) complexes tetrahedral geometries. The ligand (L¹) and its Cu(II) complex were characterized by the single-crystal X-ray diffraction method. All the ligands and their metal(II) complexes were screened for their in-vitro antimicrobial activity. The antibacterial and antifungal bioactivity data showed that the metal(II) complexes were found to be more potent than the parent ligands against one or more bacterial and fungal strains.     

Antifungal potential of binary and mixed-ligand complexes of N,2'-diphenyl acetohydroxamic acid.

Chelating potential of N,2'-DPAHA with 3d metal ions such as Cu(II), Ni(II), Zn(II), and Cd(II) in the presence of Gly and Phen has been investigated. These experiments were designed to study the role of the stability of mixed-ligand complexes in the modulation of its fungicidal potential. The mixed-ligand complexes were found to be more stable than binary complexes. Enhanced stability of mixed-ligand complexes of Ni(II), Co(II), Zn(II), and Cd(II) is presumably due to pi-bonding effects. In the stabilization of the Cu(II) mixed-ligand complex system, the Jahn-Tellar effect may play a vital role, in addition to pi-bonding effects. Fungicidal activity of N,2'-DPAHA and its binary complexes with Cu(II), Ni(II), and Co(II) was examined against Fusarium oxysporum using the inhibition zone technique. Binary complexes of Zn(II) and Cd(II) with N,2'-DPAHA and mixed-ligand complexes M(II)-Gly or Phen-N,2'-DPAHA, where M(II) = Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) were screened against Alternaria alternata by slide germination technique. All mixed-ligand complexes exhibited fungicidal activity but did not improve significantly compared to binary complexes. Synergistic action of primary and secondary ligands has increased the stability of the mixed-ligand complex compared to the binary complex (1:1) of the secondary ligand (N,2'-DPAHA), and the fungicidal potential of the mixed-ligand complex involving N,2'-DPAHA as secondary ligand was not increased.     

Antiproliferative effects of metal complexes of new isatin hydrazones against HCT116, MCF7 and HELA tumour cell lines

New hydrazone ligands (HL) derived from 5-substituted isatins and 1-(4-(2-methoxybenzyl)-6-arylpyridazin-3-yl)hydrazines and its complexes with Co(II) and Cu(II) were synthesized. The new hydrazones and their complexes were characterized by means of elemental, spectral analyses and magnetic studies. Primary cytotoxicity evaluation of HL 5a and the new complexes showed that these complexes could act as anticancer agents since they reduced the growth of samples of human tumour cell lines (HCT116((Colon)), MCF7((Breast)) and HELA((Cervix))) to ≤18.5 μg/mL for the new complexes.