The chemical biology of Cu(II) complexes with imidazole or thiazole containing ligands: Synthesis, crystal structures and comparative biological activity

First iron(II) organometallic compound acting as ABCB1 inhibitor

Five new iron (II) complexes bearing imidazole-based (Imi-R) ligands with the general formula [Fe(η⁵-C₅H₅)(CO)(PPh₃)(Imi-R)][CF₃SO₃] were synthesized and fully characterized by several spectroscopic and analytical techniques. All compounds crystallize in centrosymmetric space groups in a typical "piano stool" distribution. Given the growing importance of finding alternatives to overcome different forms of multidrug resistance, all compounds were tested against cancer cell lines with different ABCB1 efflux pump expression, namely, the doxorubicin-sensitive (Colo205) and doxorubicin-resistant (Colo320) human colon adenocarcinoma cell lines. Compound 3 bearing 1-benzylimidazole was the most active in both cell lines with IC₅₀ values of 1.26 ± 0.11 and 2.21 ± 0.26 μM, respectively, being also slightly selective against the cancer cells (vs. MRC5 normal human embryonic fibroblast cell lines). This compound, together with compound 2 bearing 1H-1,3-benzodiazole, were found to display very potent ABCB1 inhibitory effect. Compound 3 also showed the ability to induce cell apoptosis. Iron cellular accumulation studies by ICP-MS and ICP-OES methods revealed that the compounds' cytotoxicity is not related to the extent of iron accumulation. Yet, it is worth mentioning that, from the compounds tested, 3 was the only one where iron accumulation was greater in the resistant cell line than in the sensitive one, validating the possible role of ABCB1 inhibition in its mechanism of action.

Synthesis and characterization of new thiazole-based Co(II) and Cu(II) complexes; therapeutic function of thiazole towards COVID-19 in comparing to current antivirals in treatment protocol

Two thiazole-based complexes were prepared from Co(II) and Cu(II) ions. The new ligand and its complexes were fully characterized by analytical and spectral techniques. The ligand behaved as a neutral tridentate in its keto-form towards the metals via O(8), O(10) and O(18) atoms. This was suggested based on the lower shift of υ(CH[bond, double bond]O), υ(C[bond, double bond]O)_amide and υ(C-O) vibrations. The electronic transitions in Co(II)-HL and Cu(II)-HL complexes displayed d-d- transitions which belong to ⁴T_1g→⁴A_2g(F) & ⁴T_1g(F)→⁴T_1g (P) and ²Eg →²T₂g, in the two complexes, respectively. ESR spectrum of Cu(II)-HL complex displayed g-factor by the following order; g_//(2.1740)>g_⊥(2.0935)>2.0023, which agrees with octahedral geometry. The geometry optimization was executed by DFT/B3LYP method under valence double zeta polarized basis set (6-31G*), to confirm the structural forms and the mode of bonding. The orientation and the charges of O(8), O(10) and O(18) atoms, support the coordination of the ligand in its keto-form with the metal ions. Pharmacophore profiles were obtained regarding thiazole ligand and other recommended drugs (arbidol, avigan and idoxuridine) that used in treatment protocol of COVID-19 pandemic. Also, query was run in MolPort-library to obtain antiviral analogues, to broaden the search for an effective treatment. Three analogues were obtained for arbidol, avigan and idoxuridine drugs, which have the following numbers; MolPort-047-605-644, MolPort-004-768-508 and MolPort-028-750-709, respectively. Moreover, molecular docking was carried out to obtain all interaction details and rank the efficiency of thiazole compound versus the three antivirals in their interaction with the two COVID-19 proteins. The outcomes suggested the significant antiviral activity of idoxuridine and thiazole (enol-form), which not reach to eliminate the pandemic exactly. While, arbidol and avigan did not have an effective antiviral role, although they still used in COVID-19 treatment protocol.

Development, evaluation and effect of anionic co-ligand on the biological activity of benzothiazole derived copper(II) complexes

Research on development of novel metal based anti-cancer agents continues with its popularity among bioinorganic community. Benzothiazole, an important heterocyclic pharmacophore, was chosen as a valuable and useful scaffold for the synthesis of novel copper(II) complexes. Three new copper(II) complexes obtained from the synthesis of newly synthesized benzothiazole based N-(benzo[d]thiazol-2-ylmethyl)-N-methyl-2-(pyridin-2-yl)ethan-1-amine (btzpy) ligand with CuCl₂ [Cu(btzpy)Cl₂] (1), Cu(NCS)₂ [Cu(btzpy)(NCS)₂] (2), and Cu(NO₃)₂ [Cu(btzpy)(NO₃)(H₂O)]NO₃ (3) were isolated and characterized by physical and spectroscopic measurements, including single-crystal X-ray structures. The interaction of complexes 1 and 3 with calf thymus (CT)-DNA was investigated using ethidium bromide fluorescence quenching assay and weak intercalation with K_SV values of 9.8 × 10² M^-1 and 8.2 × 10² M^-1, respectively was observed. All three complexes have shown DNA cleavage of supercoiled plasmid DNA forming single nicked and double nicked forms in the presence of external reducing agents like 3-mercaptopropionic acid (3-MPA) and ascorbic acid. The water-soluble complexes 1 and 3 also show prominent hydrolytic DNA cleavage. From the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay, it was observed that complex 2 also exhibits good antioxidant properties. The cytotoxicity of complexes 1-3 was tested against the lung cancer cell line (A549) and complex 2 with -NCS moiety shows maximum activity in the micromolar range. A rationale for the observed activity is proposed in light of the other properties of these molecules.

Copper transporter 1 affinity as a delivery strategy to improve the cytotoxic profile of rationally designed copper(II) complexes for cancer treatment

Cisplatin is widely used to treat different types of cancer, but its severe side effects are the major disadvantage of this treatment. Therefore, other metals are currently the subject of research in the rational development of anticancer drugs, such as copper, that has been demonstrated to be promising in this scenario. Here, we evaluated the effects of two novel copper complexes against breast cancer cell lines, and also examined the influence of overexpressing copper transporter 1 (CTR1) on the cytotoxicity of these complexes. Complex (1) [Cu(sdmx^-)₂(phen)] showed low IC₅₀ values, induced intense cell morphological changes and arrested the cell cycle at the sub-G1 phase in cancer cells. Complex (1) was tested in transfected cells overexpressing the CTR1 receptor in order to compare its steric effects with a less bulky ligand and more labile complex (2) [CuCl₂(impy)]. A significant reduction of IC₅₀ value was observed in CTR1 overexpressing cells for complex (2) (32 μM to 20 μM) as compared to (1) (2.78 μM to 3.41 μM), evidencing a possible uptake through copper reduction (Cu⁺² → Cu⁺¹) mediated by CTR1. Thus, considering that CTR1 is a mediator of metallodrugs uptake, the development of strategies that use rational drug design is important in order to improve the therapeutic efficacy through greater specificity and consecutive reduction of side effects. Here we show the example for the case of copper(II) complexes.

Copper-functionalized nanostructured silica-based systems: Study of the antimicrobial applications and ROS generation against gram positive and gram negative bacteria

A series of copper-functionalized SBA-15 (Santa Barbara Amorphous) materials containing the ligands triethoxysilylpropylmaleamic acid (maleamic) or triethoxy-3-(2-imidazolin-1-yl)propylsilane (imidazoline) have been prepared. The nanostructured silica-based systems SBA-maleamic, SBA-imidazoline, SBA-maleamic-Cu and SBA-imidazoline-Cu were characterized by several methods observing that the functionalization took place mainly inside the pores of the mesoporous system. The antimicrobial behaviour of the synthesized materials against Staphylococcus aureus and Escherichia coli was tested observing a very potent activity of the copper-functionalized systems (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values for SBA-maleamic-Cu of ca. 31.25 μg/mL, which correspond with ca. 1.13 μg/mL of Cu). A study of the oxidative stress promoted by the synthesized materials showed that the SBA-maleamic-Cu and the SBA-imidazoline-Cu were able to increase the reactive oxygen species (ROS) production in S. aureus by 427% and 373%, respectively, while this increase was slightly lower in E. coli (387 and 324%, respectively). Furthermore, an electrochemical study was carried out in order to determine if these materials interact with lysine or alanine to validate a potential antimicrobial mechanism based on the inhibition of the synthesis of the peptidoglycan of the bacterial wall. Finally, these studies were also performed to determine the potential interaction of the copper-containing materials with glutathione in order to assess if they are able to perturb the metabolism of this tripeptide.

Structural characterization of two solvates of a luminescent copper(II) bis-(pyridine)-substituted benzimidazole complex

Copper(II) complexes of benzimidazole are known to exhibit biological activity that makes them of inter-est for chemotherapeutic and other pharmaceutical uses. The complex bis-(acetato-κO){5,6-dimethyl-2-(pyridin-2-yl)-1-[(pyridin-2-yl)meth-yl]-1H-benzimidazole-κ2N2,N3}copper(II), has been prepared. The absorption spectrum has features attributed to intra-ligand and ligand-field transitions and the complex exhibits ligand-centered room-temperature luminescence in solution. The aceto-nitrile monosolvate, [Cu(C2H3O2)2(C20H18N4)]·C2H3N (1), and the ethanol hemisolvate, [Cu(C2H3O2)2(C20H18N4)]·0.5C2H6O (2), have been structurally characterized. Compound 2 has two copper(II) complexes in the asymmetric unit. In both 1 and 2, distorted square-planar N2O2 coordination geometries are observed and the Cu-N(Im) bond distance is slightly shorter than the Cu-N(py) bond distance. Inter-molecular π-π inter-actions are found in 1 and 2. A weak C-H⋯π inter-action is observed in 1.