Redox-active metal complexes of sterically hindered phenolic ligands: Antibacterial activity and reduction of cytochrome c. Part IV. Silver(I) complexes with hydrazone and thiosemicarbazone derivatives of 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde

Metal Complexes as Promising Agents for Biomedical Applications

Background::

In this review article, a brief overview of novel metallotherapeutic agents (with an emphasis on the complexes of essential biometals) promising for medical application is presented. We have also focused on the recent work carried out by our research team, specifically the development of redox-active antimicrobial complexes of sterically hindered diphenols with some essential biometals (copper, zinc, nickel).

Results::

The complexes of essential metals (manganese, iron, cobalt, nickel, copper, zinc) described in the review show diverse in vitro biological activities, ranging from antimicrobial and antiinflammatory to antiproliferative and enzyme inhibitory. It is necessary to emphasize that the type of organic ligands in these metal complexes seems to be responsible for their pharmacological activities. In the last decades, there has been a significant interest in synthesis and biological evaluation of metal complexes with redox-active ligands. A substantial step in the development of these redox-active agents is the study of their physicochemical and biological properties, including investigations in vitro of model enzyme systems, which can provide evidence on a plausible mechanism underlying the pharmacological activity. When considering the peculiarities of the pharmacological activity of the sterically hindered diphenol derivatives and their nickel(II), copper(II) and zinc(II) complexes synthesized, we took into account the following: (i) all these compounds are potential antioxidants and (ii) their antimicrobial activity possibly results from their ability to affect the electron-transport chain.

Conclusion::

We obtained novel data demonstrating that the level of antibacterial and antifungal activity in the series of the above-mentioned metal-based antimicrobials depends not only on the nature of the phenolic ligands and complexing metal ions, but also on the lipophilicity and reducing ability of the ligands and metal complexes, specifically regarding the potential biotargets of their antimicrobial action – ferricytochrome c and the superoxide anion radical. The combination of antibacterial, antifungal and antioxidant activity allows one to consider these compounds as promising substances for developing therapeutic agents with a broad spectrum of activities.

Silver(I) metallodrugs of thiosemicarbazones and naproxen: biocompatibility, in vitro anti-proliferative activity and in silico interaction studies with EGFR, VEGFR2 and LOX receptors

Four new heteroleptic silver(I) complexes with the general formula [Ag(L1-4)(nap)] (1-4), where L1-4 =  2-(1-(4-substitutedphenyl)ethylidene)hydrazinecarbothioamide and nap = naproxen, have been synthesized and characterized. The geometric parameters determined from density functional theory and UV-Vis studies indicate distorted tetrahedral geometry around silver(I) ion. Fourier transform infrared (FT IR) spectra evidenced asymmetric bidentate coordination mode of carboxyl oxygen atoms of naproxen with silver(I) ion. The complexes are stable for 72 h and biocompatibility was analysed towards normal human dermal fibroblast cells, which showed non-toxic nature up to 100 ng/ml. In vitro anti-proliferative activity of the complexes by MTT assay was tested against three human cancerous cell lines and one non-tumorigenic human breast epithelial cell line (MCF-10a) in which the complex 4 exhibited enhanced activity. The morphological changes observed by acridine orange/ethidium bromide and Hoechst 33258 staining method reveal apoptosis-inducing ability of the complexes. The molecular docking studies suggest hydrogen bonding, hydrophobic and π-pair interactions with the active site of epidermal growth factor receptor, vascular endothelial growth factor receptor 2 and lipoxygenase receptors.

Synthesis of Ag(I) camphor sulphonylimine complexes and assessment of their cytotoxic properties against cisplatin-resistant A2780cisR and A2780 cell lines

Camphorsulphonylimine complexes [Ag(NO₃)(^IL)₂] (^IL=C₁₂H₁₉N₃SO₂, 1) and [(AgNO₃)₂(^IIL)] (^IIL=C₂₂H₂₃N₃SO₂, 2) were synthesized and characterized by elemental analysis, spectroscopy (IR, NMR) and cyclic voltammetry. [Ag(NO₃)(^IL)₂] crystalizes in the monoclinic C2 space group with a triangular geometry assuming a chalice-type shape. The anti-proliferative properties of the new complexes 1 and 2 and those of the previously reported [Ag(NO₃)(^IIIL)] (^IIIL=C₁₆H₁₈N₃SO₂, 3) were assessed against the human ovarian cancer cells (cisplatin-sensitive A2780, cisplatin-resistant A2780cisR) and the non-tumoral human HEK 293 cell line, using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The NR (3-amino-7-dimethylamino-2-methylphenazine hydrochloride) assay was alternatively used to assess the cytotoxicity on the A2780 cells. Results from the MTT assay (48h exposure) show that the complexes display IC₅₀ values lower (by at least one order of magnitude) than cisplatin, while the cytotoxicity of AgNO₃ is of the same order of cisplatin. The camphorsulphonylimine ligands display irrelevant (^IL, ^IIIL) or no cytotoxicity (^IIL). The highest cytotoxicity (lower IC₅₀) was found for [(AgNO₃)₂(^IIL)]. The binding ability of the complexes to calf thymus-deoxyribonucleic acid (CT-DNA) was studied by fluorescence. Constants (K_sv, K_a) and the number (n) of binding centres to DNA were calculated showing that DNA intercalation possibly occurs in the cases of complexes 2 and 3, while a more complicated process operates for 1. As expected from the cytotoxicity, [(AgNO₃)₂(^IIL)] displays the highest binding affinity (K_a=1.61×105 M^-1). No binding to DNA was detected for AgNO₃ or ^IIL under the experimental conditions used. The binding trend to CT-DNA found by fluorescence was corroborated by cyclic voltammetry.