Lara Massai

Chemistry and Biology of Two Novel Gold(I) Carbene Complexes as Prospective Anticancer Agents

Two novel gold carbene compounds, namely, chlorido (1-butyl-3-methyl-imidazole-2-ylidene) gold(I) (1) and bis(1-butyl-3-methyl-imidazole-2-ylidene) gold(I) (2), were prepared and characterized as prospective anticancer drug candidates. These compounds consist of a gold(I) center linearly coordinated either to one N-heterocyclic carbene (NHC) and one chloride ligand (1) or to two identical NHC ligands (2). Crystal structures were solved for both compounds, the resulting structural data being in good agreement with expectations. We wondered whether the presence of two tight carbene ligands in 2 might lead to biological properties distinct from those of the monocarbene complex 1. Notably, in spite of their appreciable structural differences, these two compounds manifested similarly potent cytotoxic actions in vitro when challenged against A2780 human ovarian carcinoma cells. In addition, both were able to overcome resistance to cisplatin in the A2780R line. Solution studies revealed that these gold carbene complexes are highly stable in aqueous buffers at physiological pH. Their reactivity with proteins was explored: no adduct formation was detected even upon a long incubation with the model proteins cytochrome c and lysozyme; in contrast, both compounds were able to metalate, to a large extent, the copper chaperone Atox-1, bearing a characteristic CXXC motif. The precise nature of the resulting gold-Atox-1 adducts was elucidated through ESI-MS analysis. On the basis of these findings, it is proposed that the investigated gold(I) carbene compounds are promising antiproliferative agents warranting a wider pharmacological evaluation. Most likely these gold compounds produce their potent biological effects through selective metalation and impairment of a few crucial cellular proteins.

The mode of action of anticancer gold-based drugs: a structural perspective

The interactions between a few representative gold-based drugs and hen egg white lysozyme were studied by X-ray crystallography. High resolution crystal structures solved for three metallodrug-protein adducts provide valuable insight into the molecular mechanism of these promising metal compounds and the inherent protein metalation processes.

Determinants for Tight and Selective Binding of a Medicinal Dicarbene Gold(I) Complex to a Telomeric DNA G-Quadruplex: a Joint ESI MS and XRD Investigation.

The dicarbene gold(I) complex [Au(9-methylcaffein-8-ylidene)2 ]BF4 is an exceptional organometallic compound of profound interest as a prospective anticancer agent. This gold(I) complex was previously reported to be highly cytotoxic toward various cancer cell lines in vitro and behaves as a selective G-quadruplex stabilizer. Interactions of the gold complex with various telomeric DNA models have been analyzed by a combined ESI MS and X-ray diffraction (XRD) approach. ESI MS measurements confirmed formation of stable adducts between the intact gold(I) complex and Tel 23 DNA sequence. The crystal structure of the adduct formed between [Au(9-methylcaffein-8-ylidene)2 ](+) and Tel 23 DNA G-quadruplex was solved. Tel 23 maintains a characteristic propeller conformation while binding three gold(I) dicarbene moieties at two distinct sites. Stacking interactions appear to drive noncovalent binding of the gold(I) complex. The structural basis for tight gold(I) complex/G-quadruplex recognition and its selectivity are described.

Size dependent biological profiles of PEGylated gold nanorods

The perspective of introducing plasmonic particles for applications in biomedical optics is receiving much interest. However, their translation into clinical practices is delayed by various factors, which include a poor definition of their biological interactions. Here, we describe the preparation and the biological profiles of gold nanorods belonging to five different size classes with average effective radii between ∼5 and 20 nm and coated with polyethylene glycol (PEG). All these particles exhibit decent stability in the presence of representative proteins, low cytotoxicity and satisfactory compatibility with intravenous administration, in terms of their interference with blood tissue. However, the suspension begins to become unstable after a few days of exposure to blood proteins. Moreover, the cytotoxicity is a little worse for smaller particles, probably because their purification is more critical, while undesirable interactions with the mononuclear phagocyte system are minimal in the intermediate size range. Overall, these findings hold implications of practical relevance and suggest that PEGylated gold nanorods may be a versatile platform for a variety of biomedical applications.

Interaction of anticancer Ru(III) complexes with single stranded and duplex DNA model systems

The interaction of the anticancer Ru(iii) complex AziRu - in comparison with its analogue NAMI-A, currently in advanced clinical trials as an antimetastatic agent - with DNA model systems, both single stranded and duplex oligonucleotides, was investigated using a combined approach, including absorption UV-vis spectroscopy, circular dichroism (CD) and electrospray mass spectrometry (ESI-MS) techniques. UV-vis absorption spectra of the Ru complexes were recorded at different times in a pseudo-physiological solution, to monitor the ligand exchange processes in the absence and in the presence of the examined oligonucleotides. CD experiments provided information on the overall conformational changes of the DNA model systems induced by these metal complexes. UV- and CD-monitored thermal denaturation studies were performed to analyse the effects of AziRu and NAMI-A on the stability of the duplex structures. ESI-MS experiments, carried out on the oligonucleotide/metal complex mixtures under investigation, allowed us to detect the formation of stable adducts between the guanine-containing oligomers and the ruthenium complexes. These data unambiguously demonstrate that both AziRu and NAMI-A can interact with the DNA model systems. Although very similar in their structures, the two metal compounds manifest a markedly different reactivity with the examined sequences, respectively, with either a naked Ru(3+) ion or a Ru(Im)(3+) (Im = imidazole) fragment being incorporated into the oligonucleotide structure via stable linkages.

Proteomic analysis of A2780/S ovarian cancer cell response to the cytotoxic organogold(III) compound Aubipyc

UNLABELLED Aubipyc is an organogold(III) compound endowed with encouraging anti-proliferative properties in vitro that is being evaluated pre-clinically as a prospective anticancer agent. A classical proteomic approach is exploited here to elucidate the mechanisms of its biological actions in A2780 human ovarian cancer cells. Based on 2-D gel electrophoresis separation and subsequent mass spectrometry identification, a considerable number of differentially expressed proteins were highlighted in A2780 cancer cells treated with Aubipyc. Bioinformatic analysis of the groups of up-regulated and down-regulated proteins pointed out that Aubipyc primarily perturbs mitochondrial processes and the glycolytic pathway. Notably, some major alterations in the glycolytic pathway were validated through Western blot and metabolic investigations. BIOLOGICAL SIGNIFICANCE This is the first proteomic analysis regarding Aubipyc cytotoxicity in A2780/S ovarian cancer cell line. Aubipyc is a promising gold(III) compound which manifests an appreciable cytotoxicity toward the cell line A2780, being able to overcome resistance to platinum. The proteomic study revealed for Aubipyc different cellular alterations with respect to cisplatin as well as to other gold compound such as auranofin. Remarkably, the bioinformatic analysis of proteomic data pointed out that Aubipyc treatment affected, directly or indirectly, several glycolytic enzymes. These data suggest a new mechanism of action for this gold drug and might have an impact on the use of gold-based drug in cancer treatment.

Synthesis, spectroscopic and DFT structural characterization of two novel ruthenium(III) oxicam complexes. In vivo evaluation of anti-inflammatory and gastric damaging activities

The reactions of ruthenium(III) chloride trihydrate with piroxicam (H2PIR) and tenoxicam (H2TEN), two widely used non-steroidal anti-inflammatory drugs, afforded [Ru(III)Cl2(H2PIR)(HPIR)],·1, and [Ru(III)Cl2(H2TEN)(HTEN)],·2. Both compounds were obtained as pure green solids through purification via flash column chromatography. Characterizations were accomplished through UV-vis and IR spectroscopy, potentiometry and HPLC. Quantum mechanics and density functional computational methods were applied to investigate their respective molecular structures. The experimental and computational results are in agreement with a pseudo-octahedral coordination where the two chlorido ligands are in trans positions (apical) and the two trans-N,O chelating oxicam ligands occupy the equatorial sites. Both compounds revealed an acceptable solubility and stability profile upon dissolution in a standard buffer at physiological pH. Nonetheless, the addition of biologically occurring reducing agents caused spectral changes. The two complexes manifested a poor reactivity with the model proteins cytochrome c and lysozyme: no evidence for adduct formation was indeed obtained based on a standard ESI MS analysis; in contrast, some significant reactivity with serum albumin was proved spectrophotometrically. Remarkably, both study compounds revealed pronounced anti-edema effects in vivo suggesting that the pharmacological actions of the ligands are mostly retained; in addition, they were less irritating than piroxicam on the gastric mucosa when the coordination compounds and free oxicam were administered at the same overall molar concentration of the ligand. Overall, the present results point out that ruthenium coordination may represent an effective strategy to improve the pharmacological properties of oxicam drugs reducing their undesired side effects.

Structural evidences for a secondary gold binding site in the hydrophobic box of Lysozyme.

A new crystal structure is reported here for the adduct formed in the reaction between NH4 [Au(Sac)2], AuSac2, a cytotoxic homoleptic gold(I) complex with the saccharinate ligand, and the model protein hen egg white lysozyme. To produce this adduct, AuSac2 breaks down and releases both saccharinate ligands. The resulting Au(I) ions bind the protein to ND1 and NE2 atoms of His15 but also to SD atom of the zero-solvent accessible Met105 side chain, which is located in the protein hydrophobic box. The unexpected existence of this secondary gold(I) binding site is confirmed by spectroscopic and spectrometric measurements in solution.Graphical Abstract

IgG and IgM antibodies to the refolded MOG1–125 extracellular domain in humans

Antibodies to MOG in serum have a dubious prognostic value in multiple sclerosis. The MOG recombinant protein conformational properties relevant to the antigenic activity are unknown. We employed a solid-phase ELISA based on a product (rMOG(ED)(His)(6)) expressed in E. coli after subcloning the cDNA of the extracellular domain of rat MOG, performing a refolding procedure on column and affinity purification. The far-UV Circular Dichroism (CD) spectra of rMOG(ED)(His)(6) showed a β-sheet, a characteristic feature of the Ig-fold. However, in MS sera and controls we failed to detected IgM or IgG antibodies.

Elucidating the reactivity of Pt(II) complexes with (O,S) bidentate ligands towards DNA model systems.

In the search for novel platinum-based anticancer therapeutic agents, we have recently established a structural motif of (O,S) bidentate ligands bound to a Pt(II) metal center which is effective against various cancer cell lines. Aiming at further enhancing the cytotoxicity of metal-based drugs, the identification of potential biological targets and elucidation of the mode of action of selected lead compounds is of utmost importance. Here we report our studies on the DNA interaction of three representative Pt(II) complexes of the investigated series, using various model systems and analytical techniques. In detail, CD spectroscopy as well as ESI-MS and MS(2) techniques were applied to gain an overall picture of the binding properties of this class of (O,S) bidentate Pt(II) compounds with defined oligonucleotide sequences in single strand, duplex or G-quadruplex form, as well as with the nucleobase 9-methylguanine. On the whole, it was demonstrated that the tested compounds interact with DNA and produce conformational changes of different extents depending on the sequence and structure of the examined oligonucleotide. Guanine was established as the preferential target within the DNA sequence, but in the absence or unavailability of guanines, alternative binding sites can be addressed. The implications of these results are thoroughly discussed.