Interaction of folic acid and some matrix metalloproteinase (MMP) inhibitor folate-γ-hydroxamate derivatives with Zn(II) and human serum albumin

Human serum albumin binding of folic acid and its γ-hydroxamate/ carboxylate derivatives was studied by ultrafiltration and spectrofluorimetry, and it was found that the ligands exhibit a moderate binding (KD ∼ 2-50 μM), and the folate-γ-phenylalanine represents the highest conditional binding constant towards albumin. This feature may have importance in the serum transport processes of these ligands. Interaction of folic acid and its derivatives with Zn(II) was investigated in aqueous solution to obtain the composition and stabilities of the complexes by the means of pH-potentiometry, 1H NMR and electrospray ionization mass spectrometry, together with the characterization of the proton dissociation processes and the hydro-lipophilic properties of the ligands. The formation of mono-ligand complexes was demonstrated in all cases and the contribution of the glutamyl carboxylates to the coordination was excluded. Binding of folic acid and its γ-carboxylate derivatives to Zn(II) via the pteridine moiety is suggested, while the (O,O) coordination fashion of the folate-γ-hydroxamate ligands has importance in their inhibitory activity against Zn(II)-containing matrix metalloproteinases. It was found that the enzyme inhibition of these folate-γ-hydroxamate ligands is mainly tuned by other features, such as the lipophilic character rather than the Zn(II)-chelate stability. © 2010 Elsevier Inc. All rights reserved

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

Solution Equilibrium Studies of Anticancer Ruthenium(II)-η6-p-cymene Complexes of Pyridinecarboxylic Acids

Stoichiometry and stability of antitumor ruthenium(II)-η6-p-cymene complexes of picolinic acid and its 6-methyl and 6-carboxylic acid derivatives were determined by pH-potentiometry, 1H NMR spectroscopy and UV–Vis spectrophotometry in aqueous solution in the presence or absence of coordinating chloride ions. The picolinates form exclusively mono-ligand complexes in which they can coordinate via the bidentate (O,N) mode and a chloride or a water molecule is found at the third binding site of the ruthenium(II)-η6-p-cymene moiety depending on the conditions. [Ru(η6-p-cymene)(L)(H2O/Cl)] species are predominant at physiological pH in all studied cases. Hydrolysis of the aqua complex or the chlorido/hydroxido co-ligand exchange results in the formation of the mixed-hydroxido species [Ru(η6-p-cymene)(L)(OH)] in the basic pH range. There is no indication for the decomposition of the mono-ligand complexes during 24 h in the ruthenium(II)-η6-p-cymene-picolinic acid system between pH 3 and 11; however, a slight dissociation with a low reaction rate was found in the other two systems leading to the appearance of the dinuclear trihydroxido-bridged species [Ru2(η6-p-cymene)2(OH)3]+ and free ligands at pH > 10. The replacement of the chlorido by an aqua ligand in [Ru(η6-p-cymene)(L)Cl] was also monitored and equilibrium constants for the exchange process were determined