New Platinum(II) Triazole Thiosemicarbazone Complexes: Analysis of Their Reactivity and Potential Antitumoral Action.

The synthesis and characterization of three new platinum complexes, with 3,5-diacetyl-1,2,4-triazole bis(4-N-isopropylthiosemicarbazone) as a ligand, are reported. The specific conditions under which solvent coordination takes place are reported and the X-ray structure of the complex with one solvent molecule of dimethyl sulfoxide is resolved. Analysis of the reactivity of these platinum compounds aids in finding the best solution profile for biological investigations. Then, the interactions of the complexes with biological models, such as calf-thymus DNA, are studied by using UV spectroscopy and tracking the changes in electrophoretic mobility produced in the supercoiled plasmid DNA model. Initial screening of these potential antitumoral compounds indicates possible selective antitumoral action.

Quadruplex DNA-Stabilising Dinuclear Platinum(II) Terpyridine Complexes with Flexible Linkers.

Four dinuclear terpyridineplatinum(II) (Pt-terpy) complexes were investigated for interactions with G-quadruplex DNA (QDNA) and duplex DNA (dsDNA) by synchrotron radiation circular dichroism (SRCD), fluorescent intercalator displacement (FID) assays and fluorescence resonance energy transfer (FRET) melting studies. Additionally, computational docking studies were undertaken to provide insight into potential binding modes for these complexes. The complexes demonstrated the ability to increase the melting temperature of various QDNA motifs by up to 17 °C and maintain this in up to a 600-fold excess of dsDNA. This study demonstrates that dinuclear Pt-terpy complexes stabilise QDNA and have a high degree of selectivity for QDNA over dsDNA.

Assembly of palladium(II) and platinum(II) metallo-rectangles with a guanosine-substituted terpyridine and study of their interactions with quadruplex DNA.

Two novel [2+2] metallo-assemblies based on a guanosine-substituted terpyridine ligand (1) coordinated to palladium(II) (2 a) and platinum(II) (2 b) are reported. These supramolecular assemblies have been fully characterized by NMR spectroscopy, ESI mass spectrometry and elemental analyses. The palladium(II) complex (2 a) has also been characterized by single crystal X-ray diffraction studies confirming that the system is a [2+2] metallo-rectangle in the solid state. The stabilities of these [2+2] assemblies in solution have been confirmed by DOSY studies as well as by variable temperature (1)H NMR spectroscopy. The ability of these dinuclear complexes to interact with quadruplex and duplex DNA was investigated by fluorescent intercalator displacement (FID) assays, fluorescence resonance energy transfer (FRET) melting studies, and electrospray mass spectrometry (ESI-MS). These studies have shown that both these assemblies interact selectively with quadruplex DNA (human telomeric DNA and the G-rich promoter region of c-myc oncogene) over duplex DNA, and are able to induce dimerization of parallel G-quadruplex structures.

Reactivity and biological properties of a series of cytotoxic PtI2(amine)2 complexes, either cis or trans configured.

Six diiodido-diamine platinum(II) complexes, either cis or trans configured, were prepared, differing only in the nature of the amine ligand (isopropylamine, dimethylamine, or methylamine), and their antiproliferative properties were evaluated against a panel of human tumor cell lines. Both series of complexes manifested pronounced cytotoxic effects, with the trans isomers being, generally, more effective than their cis counterparts. Cell cycle analysis revealed different modes of action for these new Pt(II) complexes with respect to cisplatin. The reactivity of these platinum compounds with a number of biomolecules, including cytochrome c, two sulfur containing modified amino acids, 9-ethylguanine, and a single strand oligonucleotide, was analyzed in depth by mass spectrometry and NMR spectroscopy. Interestingly, significant differences in the reactivity of the investigated compounds toward the various model biomolecules were observed: in particular we observed that trans complexes preferentially release their iodide ligands upon biomolecule binding, while the cis isomers may release the amine ligands with retention of iodides. Such differences in reactivity may have important mechanistic implications and a relevant impact on the respective pharmacological profiles.

Tandem cyclization-Michael reaction by combination of metal- and organocatalysis.

The use of a catalytic amount of platinum complexes (1 mol %) was found to be compatible with different organocatalysts (DABCO or the Jørgensen-Hayashi catalyst) that were used in the functionalization of various activated methylenes. By this method, a series of lactones with C-3 quaternary centers and substitution at C-5 were prepared.

Solution behaviour and biomolecular interactions of two cytotoxic trans-platinum(II) complexes bearing aliphatic amine ligands.

A novel trans-platinum(II) complex bearing one dimethylamine (dma) and one methylamine (ma) ligand, namely trans-[PtCl(2)(dma)(ma)], recently synthesised and characterised in our laboratory, displayed relevant antiproliferative properties in vitro, being more active than the parent complex, trans-[PtCl(2)(dma)(ipa)], which has isopropylamine (ipa) in place of methylamine. We have analysed comparatively the solution behaviour of these two complexes under various experimental conditions, and investigated their reactivity with horse heart cytochrome c by mass spectrometry, inductively coupled plasma-optical emission spectroscopy (ICP-OES), 2D [(1)H,(15)N],[(1)H,(13)C] HSQC and [(1)H,(1)H] NOESY NMR. Some important changes that occurred in the [(1)H,(13)C] HSQC NMR spectrum of cytochrome c treated with trans-[PtCl(2)(dma)(ma)] in water, after two days' incubation, most probably arose from direct platinum coordination to the protein side chain; this was proved conclusively by [(1)H,(1)H] NOESY NMR and [(1)H,(15)N] HSQC NMR measurements. Met65 was identified as the primary Pt binding site on cytochrome c. Electrospray mass spectrometry (ESIMS) results provided evidence for extensive platinum-protein adduct formation. A fragment of the [Pt(amine)(amine')] type was established to be primarily responsible for protein metalation. ICP-OES analysis revealed that these trans-platinum(II) complexes bind preferentially to the serum proteins albumin and transferrin rather than to calf thymus DNA. Pt binding to DNA was found to be far lower than in the case of cisplatin. The implications of the results for the mechanism of action of novel cytotoxic trans-platinum complexes are discussed.

Trans platinum complexes design: one novel water soluble oxime derivative that contains aliphatic amines in trans configuration.

In an attempt to design new antitumoral drugs based on transplatin complexes, we determined the experimental conditions for the preparation of trans-[Pt((CH(3))(2)CNOH)((CH(3))(2)CHNH(2))Cl(2)], and solved the crystal structure. The cytotoxicity of the novel complex, the cis counterpart, cisplatin, and a trans complex with aliphatic amines, as well as the capacity of some of these complexes to cause either apoptotic or necrotic cell death, was comparatively examined in NRK-52E rat renal tubular cells and HepG2 human hepatoma cells. The results indicate that the oxime complex with trans geometry, but not the one with cis geometry, causes death by apoptosis, making the complex potentially suitable for therapeutic purposes. However cytotoxicity values are higher in the case of cis geometry than in trans geometry in both tumoral and non-tumoral cell lines.

The second generation of iodido complexes: trans-[PtI2(amine)(amine')] bearing different aliphatic amines.

The antitumoral potential for a series of platinum iodido complexes, all bearing the same aliphatic amines (first iodido complexes generation), was demonstrated in a previous study. Concretely, cis complexes were shown to have a peculiar and different reactivity compared to cisplatin with sulfur donors models and Cyt C. In this work we have synthesized and studied iodido complexes bearing different aliphatic amines in trans configuration (the second generation) to investigate their potential antitumor activity in a panel of cell lines. Their interaction with biological models such as pBR322 and smaller biomolecules (5'-GMP, 9EtG, N-AcMet and N-AcCys) have been studied and compared to cisplatin and to the first iodido series. Their cytotoxicity, on the other hand, turned out to be especially active towards cell lines where cisplatin has no effect.

The preparation and characterization of trans-platinum(IV) complexes with unusually high cytotoxicity.

The physical and biological properties have been determined for three Pt(IV) complexes with trans amine ligands: trans,trans,trans-[PtCl(2)(OH)(2)(dimethylamine)(isopropylamine)] (1(IV)), trans,trans,trans-[PtCl(2)(OH)(2)(dimethylamine)(methylamine)] (2(IV)) and trans,trans,trans-[PtCl(2)(OH)(2)(isopropylamine)(methylamine)] (3(IV)). The crystal structures of 2(IV) and 3(IV) reveal substantial strain resulting from repulsion between the amine ligands and the chlorido and hydroxido ligands. All three complexes have reduction potentials in the range -666 to -770 mV, values usually associated with high resistance to reduction and low cytotoxicity. However, the complexes all demonstrate surprisingly high cytotoxicity with values and trends that closely follow those seen for the Pt(II) congeners of these complexes. These results are consistent with more rapid reduction of the Pt(IV) complexes than would be expected based on the reduction potentials, perhaps associated with the trans arrangement of the chlorido ligands.

New reactions of anticancer-platinum complexes and their intriguing behaviour under various experimental conditions.

The anticancer platinum complexes here described react with organic substrates (such as acids, alkenes, alkynes) and catalyze transformations that can occur in biomolecules which contain unsaturated functions. We have analyzed the role of the platinum complexes in the observed reactions and studied the progress of the detected transformations upon variation of the reaction conditions.

Photoactivation of trans diamine platinum complexes in aqueous solution and effect on reactivity towards nucleotides.

We show that UVA irradiation (365nm) of the Pt(IV) complex trans,trans,trans-[Pt(IV)Cl(2)(OH)(2)(dimethylamine)(isopropylamine)] (1), induces reduction to Pt(II) photoproducts. For the mixed amine Pt(II) complex, trans-[Pt(II)Cl(2)(isopropylamine)(methylamine)] (2), irradiation at 365nm increases the rate and extent of hydrolysis, triggering the formation of diaqua species. Additionally, irradiation increases the extent of reaction of complex 2 with guanosine-5'-monophosphate and affords mainly the bis-adduct, while reactions with adenosine-5'-monophosphate and cytidine-5'-monophosphate give rise only to mono-nucleotide adducts. Density Functional Theory calculations have been used to obtain insights into the electronic structure of complexes 1 and 2, and their photophysical and photochemical properties. UVA-irradiation can contribute to enhanced cytotoxic effects of diamine platinum drugs with trans geometry.

Proteins as possible targets for cytotoxic trans-platinum(II) complexes with aliphatic amine ligands: Further exceptions to the DNA paradigm.

The reactivity of three cytotoxic trans-Pt(II) complexes bearing aliphatic amine ligands, with transferrin and single-stranded oligonucleotides as DNA models, was investigated by ESI-MS and the results obtained are discussed in comparison with cisplatin. Tandem MS studies provided additional information on the preferential Pt binding sites. To determine whether trans-Pt(II) complexes can migrate from a peptide to an oligonucleotide, transfer experiments were also performed using ESI-MS, and competitive binding of the trans-Pt(II) complexes toward a model peptide and different oligonucleotides was also investigated. Significant differences in the reactivity of the trans complexes with respect to cisplatin were observed. In general, adduct formation with the selected peptide is favored for the trans compounds, whereas cisplatin shows a preference for oligonucleotides, especially if adjacent G-G residues are present. The results are discussed in relation to the possible mechanism of action of the trans-Pt(II) complexes.

Cytotoxic Profile and Peculiar Reactivity with Biomolecules of a Novel "Rule-Breaker" Iodidoplatinum(II) Complex.

Novel and surprising biological properties were disclosed for the platinum(II) complex cis-diiodidodiisopropylamineplatinum(II). Remarkably, this new platinum(II) complex manifests pronounced antiproliferative properties in vitro, in some cases superior to those of cisplatin. A peculiar reactivity with the model protein cytochrome c was indeed highlighted based on the loss of amine ligands and retention of iodides.

Influence of amine ligands on the aquation and cytotoxicity of trans-diamine platinum(II) anticancer complexes.

Three (15)N-labelled trans-Pt(ii) amine complexes with isopropylamine ((15)N-ipa), methylamine ((15)N-ma) and dimethylamine ((15)N-dma) have been prepared and characterized. 2D [(1)H,(15)N] HSQC NMR spectroscopy was used to obtain the rate and equilibrium constants for the aquation of trans-[PtCl(2)((15)N-ipa)((15)N-ma)] ((15)N-1), trans-[PtCl(2)((15)N-dma)((15)N-ma)] ((15)N-2) and trans-[PtCl(2)((15)N-dma)((15)N-ipa)] ((15)N-) in 100 mM NaClO(4) solutions at 298 K. New (15)N shift ranges for H(2)N-Pt(II)-N and HN-Pt(II)-N groups are reported. Formation of the diaqua complex was not observed for and accounted for <2% of the species at equilibrium for 1 and 2 . The first aquation step is significantly faster for 2 (k(1) = 14 x 10(-5) s(-1)) than for the two complexes with the bulkier ipa ligand (k(1) = 5.5 x 10(-5) s(-1) (), 6.1 x 10(-5) s(-1) (3)), but 2 is the least aquated of the three complexes at equilibrium. The pK(a) values for the monoaqua adducts of 1-3 are similar (5.98, 5.85 and 5.91, respectively) and 0.4 pH units lower than the related cis complex cis-[PtCl(2)(dma)(2)], indicating a smaller proportion of more reactive aqua species will exist at physiological pH. The pK(a) values for the diaqua adduct of 2 (4.59 and 7.98) are 0.3-0.6 pH units higher than those of 1(4.31 and 7.30) and 3 (4.28 and 7.29), which have very similar values. The speciation profiles of 1-3 , calculated on the basis of the calculated equilibrium and dissociation constants, indicate that <1% hydrolyzed species will exist under physiological conditions in cancer cells. The cytotoxicity of 1-3 (non-(15)N-labelled) was assessed in three cancer lines (SF268, MCF-7 and NCI-H460). The new trans-Pt(ii) diamine complex 2 is more active than 1 and 3 in all cases and is more potent than cisplatin in the MCF-7 adenocarcinoma cell line.