Structural characterization, ROS-inductive and proteasome inhibitory properties of ternary and binary copper(II) complexes of N2- and N2O2-ligands

Dinuclear and mononuclear metal(II) polypyridyl complexes against drug-sensitive and drug-resistant Plasmodium falciparum and their mode of action

BACKGROUND

Malaria remains one of the most virulent and deadliest parasitic disease in the world, particularly in Africa and Southeast Asia. Widespread occurrence of artemisinin-resistant Plasmodium falciparum strains from the Greater Mekong Subregion is alarming. This hinders the national economies, as well as being a major drawback in the effective control and elimination of malaria worldwide. Clearly, an effective anti-malarial drug is urgently needed.

METHODS

The dinuclear and mononuclear copper(II) and zinc(II) complexes were synthesized in ethanolic solution and characterized by various physical measurements (FTIR, CHN elemental analysis, solubility, ESI-MS, UV-Visible, conductivity and magnetic moment, and NMR). X-ray crystal structure of the dicopper(II) complex was determined. The in vitro haemolytic activities of these metal complexes were evaluated spectroscopically on B+ blood while the anti-malarial potency was performed in vitro on blood stage drug-sensitive Plasmodium falciparum 3D7 (Pf3D7) and artemisinin-resistant Plasmodium falciparum IPC5202 (Pf5202) with fluorescence dye. Mode of action of metal complexes were conducted to determine the formation of reactive oxygen species using PNDA and DCFH-DA dyes, JC-1 depolarization of mitochondrial membrane potential, malarial 20S proteasome inhibition with parasite lysate, and morphological studies using Giemsa and Hoechst stains.

RESULTS

Copper(II) complexes showed anti-malarial potency against both Pf3D7 and Pf5202 in sub-micromolar to micromolar range. The zinc(II) complexes were effective against Pf3D7 with excellent therapeutic index but encountered total resistance against Pf5202. Among the four, the dinuclear copper(II) complex was the most potent against both strains. The zinc(II) complexes caused no haemolysis of RBC while copper(II) complexes induced increased haemolysis with increasing concentration. Further mechanistic studies of both copper(II) complexes on both Pf3D7 and Pf5202 strains showed induction of ROS, 20S malarial proteasome inhibition, loss of mitochondrial membrane potential and morphological features indicative of apoptosis.

CONCLUSION

The dinuclear [Cu(phen)-4,4'-bipy-Cu(phen)](NO₃)₄ is highly potent and can overcome the total drug-resistance of Pf5202 towards chloroquine and artemisinin. The other three copper(II) and zinc(II) complexes were only effective towards the drug-sensitive Pf3D7, with the latter causing no haemolysis of RBC. Their mode of action involves multiple targets.

Macrocycle-Induced Modulation of Internuclear Interactions in Homobimetallic Complexes

A synthetic route has been developed for a series of 3d homobimetallic complexes of Mn, Fe, Co, Ni, and Cu using three different pyridyldiimine and pyridyldialdimine macrocyclic ligands with ring sizes of 18, 20, and 22 atoms. Crystallographic analyses indicate that while the distances between the metals can be modulated by the size of the macrocycle pocket, the flexibility in the alkyl linkers used to construct the macrocycles enables the ligand to adjust the orientation of the PD(A)I fragments in response to the geometry of the [M₂(μ-Cl)₂]²⁺ core, particularly with respect to Jahn-Teller distortions. Analyses by UV-vis spectroscopy and SQUID magnetometry revealed deviations in the properties [M₂(μ-Cl)₂]²⁺-containing complexes bound by standard mononucleating ligands, highlighting the ability of macrocycles to use ring size to control the magnetic interactions of pseudo-octahedral, high-spin metal centers.

Evaluation of the binding of four anti-tumor Casiopeínas® to human serum albumin

The metal complexes designated by Casiopeínas® are mixed-ligand Cu^II-compounds some of them having promising antineoplastic properties. We report studies of binding of Cu(glycinato)(4,7-dimethyl-1,10-phenanthroline) (Cas-II-Gly (1)), Cu(acetylacetonato)(4,7-dimethyl-1,10-phenanthroline) (Cas-III-Ea (2)), Cu(glycinato)(4,4'-dimethyl-2,2'-bipyridine) (Cas-IV-Gly (3)) and Cu(acetylacetonato)(4,4'-dimethyl-2,2'-bipyridine) (Cas-III-ia (4)) to human serum albumin (HSA) by circular dichroism (CD), Electron paramagnetic resonance (EPR) and fluorescence spectroscopy. The results indicate that HSA may bind up to three molecules of the tested Casiopeínas. This is confirmed by inductively coupled plasma - atomic absorption spectroscopy measurements of samples of HSA-Casiopeínas after passing by adequate size-exclusion columns. The binding of Cas-II-Gly to HSA was also confirmed by MALDI-TOF mass spectrometric experiments. In the physiological range of concentrations the Casiopeínas form 1:1 adducts with HSA, with conditional binding constants of ca. 1×10⁹ (1), 4×10⁷ (2), 1×10⁶ (3) and 2×10⁵ (4), values determined from the CD spectra measured, and the fluorescence emission spectra indicates that the binding takes place close to the Trp214 residue. Overall, the data confirm that these Casiopeínas may bind to HSA and may be transported in blood serum by this protein; this might allow some selective tumor targeting, particularly in the case of Cas-II-Gly. In this work we also discuss aspects associated to the reliability of the frequently used methodologies to determine binding constants based on the measurement of fluorescence emission spectra of solutions containing low concentrations of proteins such as HSA and BSA, by titrations with solutions of metal complexes.

Biophysical and biological studies of some polymer grafted metallo-intercalators

Two water-soluble polymer-copper(II) complexes, [Cu(ip)₂(BPEI)](ClO₄)₂·H₂O (Complex 1) and [Cu(dppz)₂BPEI](ClO₄)₂·H₂O (Complex 2) with different degree of coordination have been synthesized and characterized. The interaction between the prepared complexes and CTDNA has been assessed by various physico-chemical methods The spectroscopic and the cyclic voltammetry studies have revealed that both the complexes interact with CTDNA through intercalation binding mode. Among the two complexes, Complex 2 has higher binding affinity with CTDNA. The antiproliferative activity of the complexes has been examined on human breast cancer cells, MDAMB231, adopting various techniques. The results indicate that both the polymer-copper(II) complexes are effective against the breast cancer cell line and the order of the activity is consistent with the DNA-binding ability.