The Role of the Cysteine Fragments of the Nickel Binding Loop in the Activity of the Ni(II)-Containing SOD Enzyme

Detailed equilibrium, spectroscopic, and SOD activity studies are reported on nickel(II) complexes formed with the N-terminally free HHDLPCGVY-NH2 (NiSODHH) and HCDLPHGVY-NH2 (NiSODHC) peptides mimicking the nickel binding loop in NiSOD. In these model peptides, cysteine was incorporated in different positions in order to gain better insight into the role of the cysteine residues in NiSOD. The results are compared with those obtained with the wild-type fragment of NiSOD. The complex formation equilibria of nickel(II) with the two peptides exhibit different features. In the case of NiSODHH, the ligand field of the (NH2,NIm,NIm,S–) donor set is not strong enough to cause spin pairing and an octahedral paramagnetic complex is formed under physiological conditions. In contrast, NiSODHC forms a square-planar diamagnetic complex with (NH2,N–,S–,NIm) donors which exhibits remarkable SOD activity. Our results unambiguously prove that the presence of cysteine in the secondary position of the peptide chain is crucial to establish the square-planar geometry in the reduced form of NiSOD, while the distant cysteine affects the redox properties of the Ni(II)/Ni(III) couple. Compared to the model systems, the Ni(II) complex with the wild-type fragment of NiSOD exhibits superior SOD activity. This confirms that both cysteinyl residues are essential in the efficient degradation of superoxide ion. The enzyme mimetic complexes are also capable of assisting the decomposition of superoxide ion; however, they show considerably smaller catalytic activity due to the absence of one of the cysteine residues

Impact of copper and iron binding properties on the anticancer activity of 8-hydroxyquinoline derived Mannich bases.

The anticancer activity of 8-hydroxyquinolines relies on complex formation with redox active copper and iron ions. Here we employ UV-visible spectrophotometry and EPR spectroscopy to compare proton dissociation and complex formation processes of the reference compound 8-hydroxyquinoline (Q-1) and three related Mannich bases to reveal possible correlations with biological activity. The studied derivatives harbor a CH2-N moiety at position 7 linked to morpholine (Q-2), piperidine (Q-3), and chlorine and fluorobenzylamino (Q-4) substituents. Solid phase structures of Q-3, Q-4·HCl·H2O, [(Cu(HQ-2)2)2]·(CH3OH)2·Cl4·(H2O)2, [Cu(Q-3)2]·Cl2 and [Cu(HQ-4)2(CH3OH)]·ZnCl4·CH3OH were characterized by single-crystal X-ray diffraction analysis. In addition, the redox properties of the copper and iron complexes were studied by cyclic voltammetry, and the direct reaction with physiologically relevant reductants (glutathione and ascorbic acid) was monitored. In vitro cytotoxicity studies conducted with the human uterine sarcoma MES-SA/Dx5 cell line reveal the significant cytotoxicity of Q-2, Q-3, and Q-4 in the sub- to low micromolar range (IC50 values 0.2-3.3 μM). Correlation analysis of the anticancer activity and the metal binding properties of the compound series indicates that, at physiological pH, weaker copper(ii) and iron(iii) binding results in elevated toxicity (e.g.Q4: pCu = 13.0, pFe = 6.8, IC50 = 0.2 μM vs.Q1: pCu = 15.1, pFe = 13.0 IC50 = 2.5 μM). Although the studied 8-hydroxyquinolines preferentially bind copper(ii) over iron(iii), the cyclic voltammetry data revealed that the more cytotoxic ligands preferentially stabilize the lower oxidation state of the metal ions. A linear relationship between the pKa (OH) and IC50 values of the studied 8-hydroxyquinolines was found. In summary, we identify Q-4 as a potent and selective anticancer candidate with significant toxicity in drug resistant cells

Donepezil-based hybrids as multifunctional anti-Alzheimer's disease chelating agents: Effect of positional isomerization

The intricate and multifactorial nature of Alzheimer's disease (AD) requires the development of compounds able to hit different pathophysiological targets, such as cholinergic dysfunction, deposits of amyloid beta (A beta) peptide and metal dyshomeostasis. In order to continue the search for new anti-AD drugs, a design strategy was once more followed based on repositioning donepezil (DNP) drug, by ortho-attaching a benzylpiperidine mimetic of DNP moiety to a hydroxyphenyl-benzimidazole (BIM) chelating unit (compound 1). Herein, compound 1 and a positional isomer 2 are compared in terms of their potential multiple properties: both present good acetylcholinesterase (AChE) inhibition (low mu molar range) and are moderate/good inhibitors of A beta self- and Cu-mediated aggregation, the inhibition process being mainly due to ligand intercalation between the p-sheets of the fibrils; compound 1 has a higher chelating capacity towards Cu2+ and Zn2+ (pCu = 14.3, pZn = 6.4, pH 7.4, C-I/C-M = 10, C-M = 10(-6) M) than 2 (pCu = 10.7, pZn = 6.3), attributed to its ability to establish a tridentate (N,O,O) coordination to the metal ion. Both compounds are eligible as drug candidates for oral administration but compound 1 shows improved neuroprotective role by completely preventing Ali-induced cell toxicity

Anticancer 8-hydroxyquinoline-amino acid hybrids and their half-sandwich Ru and Rh complexes : solution chemistry and interaction with biomolecules

Development of novel chemotherapeutic agents aims to obtain more effective and selective compounds. Platinum(II)-containing chemotherapeutics have been widely used for decades in cancer therapy against solid tumors due to their effectiveness; although, their use is accompanied by drawbacks such the serious side-effects and resistance [1]. To overcome these problems, efforts have been made to find better alternatives such as the complexes of other platinum metals. 8-hydroxyquinolines and their metal complexes are widely investigated due to their anticancer properties [2,3]; however, they often have limited water solubility. In this work two novel water-soluble 8-hydroxyquinoline-D-amino acid hybrids, [(R)-1-((5-chloro-8- hydroxyquinolin-7-yl)methyl)pyrrolidine-2-carboxylic acid (8HQCl-D-Pro) and its homologue 8HQCl-D-hPro (Chart 1), and their [Ru(η6 -p-cymene)(H2O)3] 2+ and [Rh(η5 -C5Me5)(H2O)3] 2+ complexes were developed

Salicylaldehyde thiosemicarbazone copper complexes: impact of hybridization with estrone on cytotoxicity, solution stability and redox activity

An estrone–salicylaldehyde thiosemicarbazone hybrid (estrone–TSC) containing integrated domains was designed and synthesized with excellent yield via the condensation reaction of thiosemicarbazide and 2-formyl-estrone under optimized microwave reaction conditions. A structurally related bicyclic derivative (thn-TSC) starting from 5, 6, 7, 8-tetrahydro-1-naphtol (th-1-n) was also prepared in addition to their copper(II) complexes. The ligands have somewhat higher pKa values determined for the deprotonation of the hydroxyl group by UV-visible spectrophotometric and fluorometric titrations than the reference compound salicylaldehyde thiosemicarbazone (STSC), and are neutral at physiological pH. The novel conjugates are more lipophilic and possess higher membrane permeability than STSC based on the n-octanol/water partitioning and the parallel artificial membrane permeability assays, respectively. The isolated [Cu(estrone–TSCH−2)] and [Cu(thn-TSCH−2)] complexes were characterized by ESI-MS, UV-visible and EPR spectroscopy and a detailed solution study was performed to reveal their stoichiometry, stability and reduction by glutathione. The crystal structure of the ligand thn-TSC and its complex [Cu(thn-TSCH−1)Cl] was studied by single crystal X-ray diffraction method. The complexes are fairly stable at pH 7.4, the observed stability order is STSC < thn-TSC < estrone–TSC, and are able to oxidize glutathione readily. The novel ligands thn-TSC and estrone–TSC were found to be only moderately cytotoxic against several human cancer cell lines ; however rather low IC50 values were measured in the hormone-responsive MCF-7 breast cancer cell lines (thn-TSC: 3.7 μM, estrone–TSC: 6.4 μM). The copper(II) complexes exhibited high cytotoxicity (IC50 < 0.3–2 μM) and were considerably more cytotoxic than the respective ligands. Low level of reactive oxygen species was measured and a weak GSH depletion was observed for the complexes of thn-TSC and estrone–TSC in SUM159 breast cancer cells, thus their mechanism of action might be related to the induction of oxidative stress