Medicinal Applications of Metal Complexes Binding to Biological Macromolecules

Zinc and cadmium complexation of L-methionine: An infrared multiple photon dissociation spectroscopy and theoretical study

Methionine (Met) cationized with Zn2+ , forming Zn (Met-H)+ (ACN) where ACN = acetonitrile, Zn (Met-H)+ , and ZnCl+ (Met), as well as Cd2+ , forming CdCl+ (Met), were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy using light generated from the FELIX free electron laser. A series of low-energy conformers for each complex was found using quantum-chemical calculations in order to identify the structures formed experimentally. For all four complexes, spectral comparison indicated that the main binding motif observed is a charge solvated, tridentate structure where the metal center binds to the backbone amino group nitrogen, backbone carbonyl oxygen (where the carboxylic acid is deprotonated in two of the Zn2+ complexes), and side-chain sulfur. For all species, the predicted ground structures reproduce the experimental spectra well, although low-lying conformers characterized by similar binding motifs may also contribute in each system. The current work provides valuable information regarding the binding interaction between Met and biologically relevant metals. Further, the comparison between the current work and previous analyses involving alkali metal cationized Met as well as cysteine (the other sulfur containing amino acid) cationized with Zn2+ and Cd2+ allows for the elucidation of important metal dependent trends associated with physiologically important metal-sulfur binding.

Transition Metal Ions Promote the Bioavailability of Hydrophobic Therapeutics: Cu and Zn Interactions with RNA Polymerase I Inhibitor CX5461

Low aqueous solubility is a major barrier to the clinical application of otherwise promising drug candidates. We demonstrate that this issue can be resolved in medicinal molecules containing potential ligating groups, through the addition of labile transition-metal ions. Incubation of the chemotherapeutic CX5461 with Cu²⁺ or Zn²⁺ enables solubilization at neutral pH but does not affect intrinsic cytotoxicity. Spectroscopic and computational studies demonstrate that this arises from coordination to the pyrazine functionality of CX5461 and may involve bidentate coordination at physiological pH.

Copper(II) complexes of N3O tripodal ligands appended with pyrene and polyamine groups: Anti-proliferative and nuclease activities

A series of tripodal ligands based on the 2-tert-butyl-4-R-6-phenol was synthesized, where R=aldehyde (HL¹), R=putrescine-pyrene (HL²) and R=putrescine (HL³). A dinucleating ligand wherein a putrescine group connects two tripodal moieties was also prepared (H₂L⁴). The corresponding copper complexes (1, 2, 3, and 4, respectively) were prepared and characterized. We determined the phenol's pKas in the range 2.47-3.93. The DNA binding constants were determined at 6×10⁶, 5.5×10⁵ and 2.7×10⁶ for 2, 3 and 4, respectively. The complexes display a metal-centered reduction wave at E_p^c,red=-0.45 to -0.5V vs. saturated calomel electrode, as well as a ligand-centered oxidation wave above 0.57V at pH7. In the presence of ascorbate they promote an efficient cleavage of DNA, with for example a concentration required to cleave 50% of supercoiled DNA of 1.7μM for 2. The nuclease activity is affected by the nature of the R group: putrescine-pyrene≈bis-ligating>putrescine>aldehyde. The species responsible for strand scission is the hydroxyl radical. The cytotoxicity of the complexes was evaluated on bladder cancer cell lines sensitive or resistant to cis-platin. The IC₅₀ of complexes 2 and 4 span over a short range (1.3-2μM) for the two cell lines. They are lower than those of the other complexes (3.1-9.7μM) and cis-platin. The most active compounds block the cell cycle at the G0/1 phase and promote apoptosis.

Binuclear ruthenium complexes inhibit the fibril formation of human islet amyloid polypeptide

Binuclear ruthenium complexes reverse the aggregation of human islet amyloid polypeptide.

Contrasting cellular uptake pathways for chlorido and iodido iminopyridine ruthenium arene anticancer complexes

The pathways involved in cellular uptake and accumulation of iminopyridine complexes of general formula [Ru(η(6)-p-cymene)(N,N-dimethyl-N'-[(E)-pyridine-2-ylmethylidene]benzene-1,4-diamine)X]PF(6) bearing two different halido ligands X = Cl or I, have been explored. The ratio of passive/active cellular accumulation of Ru in A2780 human ovarian cancer cells is compared and contrasted with cisplatin. Also, saturation of cellular uptake, time-dependence of cellular influx/efflux equilibria, together with endocytotic pathways such as caveolae and facilitated diffusion are investigated and discussed. Temperature dependence studies of Ru accumulation in the A2780 cells show that in contrast to cisplatin (CDDP) and chlorido complex , which are taken up largely through active transport, the iodido complex enters cells via passive transport. The cellular efflux of Ru is slow (ca. 25% retained after 72 h) and is partially inhibited by verapamil, implicating the P-gp protein in the efflux mechanism. Ouabain inhibition experiments suggest that the cellular uptake of these ruthenium complexes relies at least in part on facilitated diffusion, and in particular is dependent on the membrane potential. In addition the finding that depletion of cellular ATP with antimycin A had little effect on cellular Ru accumulation from iodido complex is consistent with passive diffusion. In contrast, ATP depletion caused a major increase in cellular accumulation of ruthenium from chlorido complex .

Synthesis, characterization and interaction of N,N'-dipyridoxyl (1,4-butanediamine) Co(III) salen complex with DNA and HSA

Co(III) salen complex with N,N'-dipyridoxyl (1,4-butanediamine) Schiff-base ligand as tetradentate ligand was synthesized and characterized by the elemental and spectroscopic analysis. The interaction of this complex with calf thymus DNA (ct DNA) has been investigated in vitro using UV absorption, fluorescence spectroscopy, thermal denaturation and gel electrophoresis techniques. The binding constant has been estimated to be 1×10(4)M(-1) using UV absorption. The addition of ct DNA to Co(III) salen solution resulted in a fluorescence quenching. The binding constant and site size binding have been calculated in connection with other experimental observations show that the interactive model between Co(III) salen and ct DNA is an intercalative one. The interaction between plasmid DNA (pTZ57R DNA) and this complex is confirmed by gel electrophoresis studies. Furthermore, the interaction between HSA and Co(III) salen complex was investigated by UV absorption, fluorescence spectroscopy and molecular modeling. The binding constant for the interaction of this complex with HSA were found to be 3.854×10(4)M(-1) using UV absorption, which was in good agreement with the binding constant obtained from fluorescence method (3.866×10(4)M(-1)). The binding distance between HSA and this complex was estimated to be 2.48nm according to Förster theory of non-radioactive energy transfer. Molecular modeling studies suggested that hydrophobic interaction was the predominant intermolecular forces stabilizing Co(III) complex-HSA system.

A SAR study of novel antiproliferative ruthenium and osmium complexes with quinoxalinone ligands in human cancer cell lines

A series of ruthenium(II) arene complexes with 3-(1H-benzimidazol-2-yl)-1H-quinoxalin-2-one, bearing pharmacophoric groups of known protein kinase inhibitors, and related benzoxazole and benzothiazole derivatives have been synthesized. In addition, the corresponding osmium complexes of the unsubstituted ligands have also been prepared. The compounds have been characterized by NMR, UV-vis, and IR spectroscopy, ESI mass spectrometry, elemental analysis, and by X-ray crystallography. Antiproliferative activity in three human cancer cell lines (A549, CH1, SW480) was determined by MTT assays, yielding IC(50) values of 6-60 μM for three unsubstituted metal-free ligands, whereas values for the metal complexes vary in a broad range from 0.3 to 140 μM. Complexation with osmium of quinoxalinone derivatives with benzimidazole or benzothiazole results in a more consistent increase in cytotoxicity than complexation with ruthenium. For selected compounds, the capacity to induce apoptosis was confirmed by fluorescence microscopy and flow-cytometric analysis, whereas cell cycle effects are only moderate.

Studies on the cytotoxic, apoptotic and antitumoral effects of Au(III) and Pt(II) complexes of 1, 10-phenanthroline on V79 379A and A549 cell lines

In the present study, Au(III) and Pt(II) complexes of 1, 10-phenanthroline (phen) were synthesized and used as the test compounds. The structure elucidation of the synthesized compounds was performed by IR, (1)H-NMR and MASS spectroscopic data and the results of elemental analyses. The cytotoxic and apoptotic effects of test compounds were elucidated on V79 379A (Chinese hamster lung fibroblast like) and A549 (human lung carcinoma epithelial like) cell lines. Cytotoxicity was measured with MTT assay and antitumoral effect was determined by colony forming ability methods. In addition, nuclear fragmentation and activation of apoptotic enzyme (caspase-3) and DAPI staining were used to detect the apoptotic effect of the compounds. All the test compounds induced time and concentration-dependent cytotoxic and antitumoral effects. Significant increases in the levels of apoptosis were observed with increasing exposure concentration.

Rhenium(IV) compounds inducing apoptosis in cancer cells

The anticancer properties of a series of mononuclear Re(IV) compounds of formula ReCl(4)L (where L is bpy = 2,2'-bipyridine; bpym = 2,2'-bipyrimidine; dmbpy = 4,4'-dimethyl-2,2'-bipyridine; phen = 1,10-phenanthroline) were investigated for the first time. All compounds displayed potent in vitro antiproliferative activity against selected cancer cells.

Imaging metals in proteins by combining electrophoresis with rapid x-ray fluorescence mapping

Growing evidence points toward a very dynamic role for metals in biology. This suggests that physiological circumstance may mandate metal ion redistribution among ligands. This work addresses a critical need for technology that detects, identifies, and measures the metal-containing components of complex biological matrixes. We describe a direct, user-friendly approach for identifying and quantifying metal-protein adducts in complex samples using native- or SDS-PAGE, blotting, and rapid synchrotron X-ray fluorescence mapping with micro-XANES (X-ray absorption near-edge structure) of entire blots. The identification and quantification of each metal bound to a protein spot has been demonstrated, and the technique has been applied in two exemplary cases. In the first, the speciation of the in vitro binding of exogenous chromium to blood serum proteins was influenced markedly by both the oxidation state of chromium exposed to the serum proteins and the treatment conditions, which is of relevance to the biochemistry of Cr dietary supplements. In the second case, in vivo changes in endogenous metal speciation were examined to probe the influence of oxygen depletion on iron speciation in Shewanella oneidensis.

Recent developments in ruthenium anticancer drugs

Interest in Ru anticancer drugs has been growing rapidly since NAMI-A ((ImH(+))[Ru(III)Cl(4)(Im)(S-dmso)], where Im = imidazole and S-dmso = S-bound dimethylsulfoxide) or KP1019 ((IndH(+))[Ru(III)Cl(4)(Ind)(2)], where Ind = indazole) have successfully completed phase I clinical trials and an array of other Ru complexes have shown promise for future development. Herein, the recent literature is reviewed critically to ascertain likely mechanisms of action of Ru-based anticancer drugs, with the emphasis on their reactions with biological media. The most likely interactions of Ru complexes are with: (i) albumin and transferrin in blood plasma, the former serving as a Ru depot, and the latter possibly providing active transport of Ru into cells; (ii) collagens of the extracellular matrix and actins on the cell surface, which are likely to be involved in the specific anti-metastatic action of Ru complexes; (iii) regulatory enzymes within the cell membrane and/or in the cytoplasm; and (iv) DNA in the cell nucleus. Some types of Ru complexes can also promote the intracellular formation of free radical species, either through irradiation (photodynamic therapy), or through reactions with cellular reductants. The metabolic pathways involve competition among reduction, aquation, and hydrolysis in the extracellular medium; binding to transport proteins, the extracellular matrix, and cell-surface biomolecules; and diffusion into cells; with the extent to which individual drugs participate in various steps along these pathways being crucial factors in determining whether they are mainly anti-metastatic or cytotoxic. This diversity of modes of action of Ru anticancer drugs is also likely to enhance their anticancer activities and to reduce the potential for them to develop tumour resistance. New approaches to metabolic studies, such as X-ray absorption spectroscopy and X-ray fluorescence microscopy, are required to provide further mechanistic insights, which could lead to the rational design of improved Ru anticancer drugs.