Amino Acids and Peptides as Versatile Ligands in the Synthesis of Antiproliferative Gold Complexes

NHC-Ag(I) and NHC-Au(I) Complexes with N-Boc-Protected α-Amino Acidate Counterions Powerfully Affect the Growth of MDA-MB-231 Cells

N-Heterocyclic carbene (NHC) metal complexes are attracting scientists' interest as an alluring class of metallodrugs. Indeed, the versatile functionalization of NHC ligands makes them optimal scaffolds to be developed in medicinal chemistry. Besides, amino acids are great biological ligands for metals, such as silver and gold, even though their use is still under-investigated. Aiming to shed light on the anticancer properties of this kind of complex, we investigated a series of silver and gold complexes, stabilized by NHC ligands and bearing carboxylate salts of tert-butyloxycarbonyl (Boc)-N-protected glycine and l-phenylalanine as anionic ligands. The most active complexes, AuM1Gly and AuM1Phe, powerfully affect the growth of MDA-MB-231 breast cancer cells, with IC50 values in the low nanomolar range. Further studies demonstrated the blockade of the human topoisomerase I activity and actin polymerization reaction at 0.001 μM. These unique features make these complexes very interesting and worthy to be used for future in vivo studies.

Hydrogen bonds of a water molecule in the second coordination sphere of amino acid metal complexes: Influence of amino acid coordination

The hydrogen bonds of free and coordinated amino acids with water molecule were studied by analyzing data in the crystal structures from the Cambridge Structural Database (CSD) and by quantum chemical calculations. The CSD data indicate bifurcated NH/O hydrogen bonds and O1/HO hydrogen bonds of coordinated oxygen. The O/HO hydrogen bonds of free zwitterions and non-coordinated carbonyl oxygen (O2/HO) in metal complexes form primarily linear, non-bifurcated hydrogen bonds. Calculated M06L-GD3/def2-TZVPP interaction energies for free zwitterions (glycine, cysteine, phenylalanine and, serine) and water molecule are in the range from -5.1 to -9.6 kcal/mol for NH/O and from -6.9 to -7.6 kcal/mol for O/HO interactions. Coordinated amino acids in neutral octahedral cobalt(III) complexes have NH/O interaction energies ca. -7.4 kcal/mol, independent of the amino acid. The singly and doubly charged complexes have stronger NH/O interactions; the strongest has energy of -16.9 kcal/mol. In the case of O1/HO hydrogen bond, the interaction energy decreases upon coordination; interactions are quite weak for neutral complexes (-2.2 to -2.6 kcal/mol). For O2/HO hydrogen bonds, all amino acids except serine show slightly stronger interaction in singly negative complexes (-6.3 to -8.0 kcal/mol), while interactions are weaker for neutral complexes (-2.8 to -4.4 kcal/mol), comparing to zwitterions.

Studying Peptide-Metal Ion Complex Structures by Solution-State NMR

Metal chelation can provide structural stability and form reactive centers in metalloproteins. Approximately one third of known protein structures are metalloproteins, and metal binding, or the lack thereof, is often implicated in disease, making it necessary to be able to study these systems in detail. Peptide-metal complexes are both present in nature and can provide a means to focus on the binding region of a protein and control experimental variables to a high degree. Structural studies of peptide complexes with metal ions by nuclear magnetic resonance (NMR) were surveyed for all the essential metal complexes and many non-essential metal complexes. The various methods used to study each metal ion are presented together with examples of recent research. Many of these metal systems have been individually reviewed and this current overview of NMR studies of metallopeptide complexes aims to provide a basis for inspiration from structural studies and methodology applied in the field.

Selective Anticancer and Antimicrobial Metallodrugs Based on Gold(III) Dithiocarbamate Complexes

New dithiocarbamate cycloaurated complexes have been synthesized and their physicochemical and in vitro antitumor properties have been evaluated. All the performed studies highlighted good transport through the blood and biodistribution, according to the balance between the properties of hydrophilicity/lipophilicity and the binding of moderate strength to the BSA protein. Furthermore, none of the complexes exhibited reduction or decomposition reactions, presenting excellent physiological stability. The in vitro cytotoxic effect was evaluated on human colon cancer cell line Caco-2/TC7, and the complexes showed great antiproliferative activity and excellent selectivity, as much less effect was detected on normal Caco-2/TC7 cells. Most of the complexes exhibit antiproliferative activity that was better than or similar to auranofin, and at least nine times better than that of cisplatin. Its action mechanism is still under discussion since no evidence of cell cycle arrest was found, but an antioxidant role was shown for some of the selective complexes. All complexes were also tested as antimicrobial drugs, exhibiting good activity towards S. aureus and E. coli. bacteria and C. albicans and C. neoformans fungi.

Novel silver glycinate conjugate with 3D polymeric intermolecular self-assembly architecture; an antiproliferative agent which induces apoptosis on human breast cancer cells

The new water soluble silver(I) complex of glycine (GlyH) with formula [Ag₃(Gly)₂NO₃]_n (AGGLY) was synthesized. The compound was characterized by melting point (m.p.), Fourier-transform infrared (FT-IR), Ultraviolet-visible (UV-vis) and Nuclear Magnetic Resonance (¹H-,¹³C NMR) spectroscopic techniques and X-ray crystallography. The in vitro cytotoxic activity of AGGLY against human breast adenocarcinoma cell lines: MCF-7 (hormone depended (HD)) and MDA-MB-231 (hormone independent (HI)) was determined. For comparison other adenocarcinoma cells such as human cervical adenocarcinoma (HeLa) cells and lung adenocarcinoma cells (A549) were also screened. AGGLY inhibits both breast cancer cell lines stronger than cisplatin. On the contrary, AGGLY, exhibits lower toxicity against fetal lung fibroblast (MRC-5) cells than cisplatin. Its genotoxicity against MRC-5 cells was detected from the presence or absence of micronucleus using fluorescence microscopy, while the in vivo genotoxicity was evaluated using Allium cepa model. The MCF-7 cells morphology suggests apoptotic pathway for their death. The apoptotic pathway was confirmed by cell cycle arrest, Acridine Orange/Ethidium Bromide (AO/EB) Staining, and permeabilization of the mitochondrial membrane tests. The molecular mechanism of action was further studied by the binding affinity of AGGLY towards the calf thymus (CT) DNA.