Tiziano Marzo

Peculiar features in the crystal structure of the adduct formed between cis-PtI2(NH3)2 and hen egg white lysozyme.

The reactivity of cis-diamminediiodidoplatinum(II), cis-PtI2(NH3)2, the iodo analogue of cisplatin, with hen egg white lysozyme (HEWL) was investigated by electrospray ionization mass spectrometry and X-ray crystallography. Interestingly, the study compound forms a stable 1:1 protein adduct for which the crystal structure was solved at 1.99 Å resolution. In this adduct, the Pt(II) center, upon release of one ammonia ligand, selectively coordinates to the imidazole of His15. Both iodide ligands remain bound to platinum, with this being a highly peculiar and unexpected feature. Notably, two equivalent modes of Pt(II) binding are possible that differ only in the location of I atoms with respect to ND1 of His15. The structure of the adduct was compared with that of HEWL-cisplatin, previously described; differences are stressed and their important mechanistic implications discussed.

Drug repositioning: auranofin as a prospective antimicrobial agent for the treatment of severe staphylococcal infections

Auranofin, (AF), a gold(I) complex in clinical use for the therapy of rheumatoid arthritis, is reported here to produce remarkable bactericidal effects in vitro against Staphylococcus sp. Noticeably, a similar antimicrobial action and potency are also noticed toward a few methicillin-resistant Staphylococcus aureus strains but not toward Escherichia coli. The time and concentration dependencies of the antimicrobial actions of AF have been characterized through recording time kill curves, and a concentration dependent profile highlighted. Overall, the present results point out that auranofin might be quickly and successfully repurposed for the treatment of severe bacterial infections due to resistant Staphylococci.

Unusual Structural Features in the Lysozyme Derivative of the Tetrakis(acetato)chloridodiruthenium(II,III) Complex

The reaction between the paddle-wheel tetrakis(acetato)chloridodiruthenium(II,III) complex, [Ru2(μ-O2CCH3)4Cl] and hen egg-white lysozyme (HEWL) was investigated through ESI-MS and UV/Vis spectroscopy and the formation of a stable metal-protein adduct was unambiguously demonstrated. Remarkably, the diruthenium core is conserved in the adduct while two of the four acetate ligands are released. The crystal structure of this diruthenium-protein derivative was subsequently solved through X-ray diffraction analysis to 2.1 Å resolution. The structural data are in agreement with the solution results. It was found that HEWL binds two diruthenium moieties, at Asp101 and Asp119, respectively, with the concomitant release of two acetate ligands from each diruthenium center.

The X-ray structure of the complex formed in the reaction between oxaliplatin and lysozyme

The X-ray structure of the adduct formed between oxaliplatin and the model protein hen egg white lysozyme is reported here. The structure is compared with those of cisplatin and carboplatin derivatives, previously solved. Relevant changes are highlighted among these crystal structures that are suggestive of significant differences in the reactivity of platinum drugs with this protein; possible biological implications are discussed.

Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs.

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.

Interactions of carboplatin and oxaliplatin with proteins: Insights from X-ray structures and mass spectrometry studies of their ribonuclease A adducts.

Oxaliplatin and carboplatin are two platinum(II) drugs in widespread clinical use for the treatment of various types of cancers; yet, structural information on their interactions with proteins is scarce. Here, the X-ray structures of the adducts formed upon reaction of carboplatin and oxaliplatin with bovine pancreatic ribonuclease (RNase A) are reported and compared with results obtained for the structure of the RNase A-cisplatin adduct derived from isomorphous crystals, under the same experimental conditions. Additional details on the binding mode of these metallodrugs toward RNase A are provided by electrospray ionization mass spectrometry (ESI MS) measurements, thus offering insight on the occurring metal-protein interactions. Notably, while carboplatin and cisplatin mainly bind the side chain of Met29, oxaliplatin also binds the side chains of Asp14, of catalytically important His119 and, to a lesser extent, of His105. On the basis of the available data, a likely mechanism for oxaliplatin hydrolysis and binding to the protein is proposed. These results are potentially useful for a better understanding of the biological chemistry, toxicity and side effects of this important class of antitumor agents.

cis-Pt I2(NH3)2: a reappraisal

The investigation of cis-PtI2(NH3)2, the diiodido analogue of cisplatin (cisPtI2 hereafter), has been unjustly overlooked so far mainly because of old claims of pharmacological inactivity. Some recent - but still fragmentary - findings prompted us to reconsider more systematically the chemical and biological profile of cisPtI2 in comparison with cisplatin. Its solution behaviour, interactions with DNA and cytotoxic properties versus selected cancer cell lines were thus extensively analysed through a variety of biophysical and computational methods. Notably, we found that cisPtI2 is highly cytotoxic in vitro toward a few solid tumour cell lines and that its DNA platination pattern closely reproduces that of cisplatin; cisPtI2 is also shown to completely overcome resistance to cisplatin in a platinum resistant cancer cell line. The differences in the biological actions of these two Pt complexes are most likely related to slight but meaningful differences in their solution behaviour and reactivity. Overall, a very encouraging and unexpected pharmacological profile emerges for cisPtI2 with relevant implications both in terms of mechanistic knowledge and of prospective clinical application. An ab initio DFT study is also included to support the interpretation of the solution behaviour of cisPtI2 under physiological and slightly acidic pH conditions.

Gold(III) complexes with hydroxyquinoline, aminoquinoline and quinoline ligands: Synthesis, cytotoxicity, DNA and protein binding studies.

In this article, we report on the synthesis and the chemical and biological characterization of novel gold(III) complexes based on hydroxyl- or amino-quinoline ligands that are evaluated as prospective anticancer agents. To gain further insight into their reactivity and possible mode of action, their interactions with model proteins and standard nucleic acid molecules were investigated.

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.