Mechanisms of cytotoxicity and antitumor activity of gold(I) phosphine complexes: the possible role of mitochondria

The synthesis, chemical and biological properties of dichlorido(azpy)gold(III) chloride (azpy=2-(phenylazo)pyridine) and the gold-induced conversion of the azpy ligand to the chloride of the novel tricyclic pyrido[2,1-c][1,2,4]benzotriazin-11-ium cation

A new Au(III) coordination compound with the ligand 2-(phenylazo)pyridine has been synthesized and fully characterized by means of elemental analysis, IR, UV-visible, conductivity measurements, NMR, electrospray ionization (ESI-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The chemical stability of the cation in this compound, [Au(azpy)Cl(2)](+) (abbreviated: Au-azpy), was analyzed by means of several physicochemical methods. While stable in the solid state, stability studies performed with the gold compound in solution showed an unexpected and unprecedented reactivity. A cationic organic derivative of 2-(phenylazo)pyridine, (abbreviated: pyrium), was produced from the solution and has been isolated as its chloride salt and characterized by crystal structure determination, elemental analysis, NMR, ESI-MS and conductivity studies in solution. This cyclization reaction is reported for the first time in the case of gold coordination compounds. The Au adduct and the pyrium cation were investigated as potential cytotoxic and anticancer agents, and both show moderate to high cytotoxic properties in cisplatin-sensitive and cisplatin-resistant ovarian carcinoma cell lines, A2780; and cisplatin-sensitive and cisplatin-resistant murine lymphocytic leukemia cell lines, L1210. Significant anticancer activity against the cisplatin resistant cell lines was found for the pyrium salt, ruling out the occurrence of cross resistance phenomena.

Gold(I) chloride adducts of 1,3-bis(di-2-pyridylphosphino)propane: synthesis, structural studies and antitumour activity

The novel water soluble bidentate phosphine ligand 1,3-bis(di-2-pyridylphosphino)propane (d2pypp) has been synthesized by a convenient route involving treatment of 2-pyridyllithium with Cl(2)P(CH(2))(3)PCl(2) and isolation in crystalline form as the hydrochloride salt. The synthesis of the precursor Cl(2)P(CH(2))(3)PCl(2) has been optimized by the use of triphosgene as the chlorinating agent. The 2 : 1 and 1 : 2 AuCl : d2pypp adducts have been synthesized and characterized by NMR spectroscopy and single crystal X-ray studies, and shown to be of the form (AuCl)(2)(mu-d2pypp-P,P') and [Au(d2pypp-P,P')(2)]Cl(.3.75H(2)O), respectively. The latter is more lipophilic than analogous 1 : 2 adducts of gold(I) chloride with the diphosphine ligands 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4, based on measurement of the n-octanol-water partition coefficient (log P = -0.46). A single crystal structure determination of the 1 : 2 Au(I) complex of the 3-pyridyl ethane ligand shows it to be of the form [Au(d3pype-P,P')(2)]Cl.5H(2)O. The in vitro cytotoxic activity of [Au(d2pypp)(2)]Cl was assessed in human normal and cancer breast cells and selective toxicity to the cancer cells found. The significance of these results to the antitumour properties of chelated 1 : 2 Au(I) diphosphine complexes is discussed.

Nickel−Cysteine Binding Supported by Phosphine Chelates

The effect of chelating phosphines was tested on the structure and pH-dependent stability of nickel-cysteine binding. (1,2-Bis(diphenylphosphino)ethane (dppe) and 1,1,1-tris[(diphenylphosphino)methyl]ethane (triphos) were used with three different cysteine derivatives (L-cysteine, Cys; L-cysteine ethyl ester, CysEt; cystamine, CysAm) to prepare complexes of the form (dppe)NiCysR(n+) and (triphos)NiCysR(n+) (n = 0 for Cys; n = 1 for CysEt and CysAm). Similar 31P {1H} NMR spectra for all (dppe)NiCysRn+ confirmed their square-planar P2NiSN coordination spheres. The structure of [(dppe)NiCysAm]PF6 was also confirmed by single-crystal X-ray diffraction methods. The (triphos)NiCysAm+ and (triphos)NiCysEt+ complexes were fluxional at room temperature by 31P NMR. Upon cooling to -80 degrees C, all gave spectra consistent with a P2NiSN coordination sphere with the third phosphorus uncoordinated. Temperature-dependent 31P NMR spectra showed that a trans P-Ni-S pi interaction controlled the scrambling of the coordinated triphos. In aqueous media, (dppe)NiCys was protonated at pH approximately 4-5, leading to possible formation of a nickel-cysteinethiol and eventual cysteine loss at pH < 3. The importance of N-terminus cysteine in such complexes was demonstrated by preparing (dppe)NiCys-bead and trigonal-bipyramidal Tp*NiCys-bead complexes, where Cys-bead represents cysteine anchored to polystyrene synthesis beads and Tp*- = hydrotris(3,5-dimethylpyrazolyl)borate. Importantly, results with these heterogeneous systems demonstrated the selectivity of these nickel centers for cysteine over methionine and serine and most specifically for N-terminus cysteine. The role of Ni-S pi bonding in nickel-cysteine geometries will be discussed, including how these results suggest a mechanism for the movement of electron density from nickel onto the backbone of coordinated cysteine.

Synthesis, structure and cytotoxicity of triphenylphosphinegold(I) sulfanylpropenoates

The reaction of triphenylphosphinegold(I) chloride in ethanol in a 1:1 molar ratio with the 3-(aryl)-2-sulfanylpropenoic acids H(2)xspa [x: p=3-phenyl-, Clp=3-(2-chlorophenyl)-, -o-mp=3-(2-methoxyphenyl)-, -p-mp=3-(4-methoxyphenyl)-, -o-hp=3-(2-hydroxyphenyl)-, -p-hp=3-(4-hydroxyphenyl)-, diBr-o-hp=3-(3,5-dibromo-2-hydroxyphenyl)-, f=3-(2-furyl)-, t=3-(2-thienyl)-, -o-py=3-(2-pyridyl)-; spa=2-sulfanylpropenoato] gave compounds of the type [Au(PPh(3))(Hxspa)], which were isolated and characterized as solids by elemental analysis, IR spectroscopy and FAB mass spectrometry and in solution by (1)H, (13)C and (31)P NMR spectroscopy. The structures of the complexes [Au(PPh(3))(HClpspa)], [Au(PPh(3))(H-o-mpspa)] and [Au(PPh(3))(H-p-mpspa)].2/3C(3)H(6)O were determined by X-ray diffractometry. Hydrogen bonding was found along with Au-S and Au-P bonds in all cases and weak pi-pi stacking was found in the H-p-mpspa derivative. The in vitro antitumour activities against the HeLa-229, A2780 and A2780cis cell lines were determined for all complexes.

A gold(I) phosphine complex selectively induces apoptosis in breast cancer cells: implications for anticancer therapeutics targeted to mitochondria

Bis-chelated gold(I) phosphine complexes have shown great potential as anticancer agents, however, their efficacy has been limited by their high toxicity and lack of selectivity for cancer cells. Here, we have investigated the anticancer activity of a new bis-chelated Au(I) bidentate phosphine complex of the novel water soluble ligand 1,3-bis(di-2-pyridylphosphino)propane (d2pypp). We show that this gold complex [Au(d2pypp)(2)]Cl, at submicromolar concentrations, selectively induces apoptosis in breast cancer cells but not in normal breast cells. Apoptosis was induced via the mitochondrial pathway, which involved mitochondrial membrane potential depolarisation, depletion of the glutathione pool and caspase-3 and caspase-9 activation. The gold lipophilic complex was accumulated in mitochondria of cells, driven by the high mitochondrial membrane potential. To address the molecular basis of the observed selectivity between the two cell lines we investigated the effect of the gold complex on the thioredoxin/thioredoxin reductase system in normal and cancer breast cells. We show that [Au(d2pypp)(2)]Cl inhibits the activities of both thioredoxin and thioredoxin reductase and that this effect is more pronounced in the breast cancer cells. This difference may account for the selective cell death seen in the breast cancer cells but not in the normal cells. Our investigation has led to new insights into the mechanism of action of bis-chelated gold(I) diphosphine complexes and their future development as mitochondria targeted chemotherapeutics.

Non platinum metal complexes as anti-cancer drugs

The development of metal complexes with platinum central atoms such as cisplatin or carboplatin had an enormous impact on current cancer chemotherapy. However, the spectrum of cancers that can be treated with platinum agents is narrow and treatment efficacy suffers from side effects and resistance phenomena. These unresolved problems in platinum-based anti-cancer therapy have stimulated increased research efforts in the search for novel non platinum-containing metal species as cytostatic agents. Preclinical and clinical investigations showed that the development of new metal agents with modes of action different from cisplatin is possible. Thus, complexes with iron, cobalt, or gold central atoms have shown promising results in preclinical studies and compounds with titanium, ruthenium, or gallium central atoms have already been evaluated in phase I and phase II trials. This review covers some relevant examples of preclinical and clinical research on novel non platinum metal complexes.

New platinum(II) complexes containing both an O,O'-chelated acetylacetonate ligand and a sulfur ligand in the platinum coordination sphere induce apoptosis in HeLa cervical carcinoma cells

We report the cytotoxic effects obtained in HeLa cells of three newly synthesized platinum complexes containing both an O,O'-chelated acetylacetonate ligand and a sulfur ligand in the platinum coordination sphere, which show, by (1)H NMR, negligible reactivity with purine bases. These compounds induce cell death with [Pt(O,O'-acac)(gamma-acac)(DMS)] being the most effective (IC(50)=0.98+/-0.056 and 1.82+/-0.023 microM for [Pt(O,O'-acac)(gamma-acac)(DMS)] and cisplatin, respectively). About 50% of cells died after 5h treatment with 100 microM [Pt(O,O'-acac)(gamma-acac)(DMS)] whilst a 16 h incubation was required to get the same results using 100 microM cisplatin. Cellular accumulation measurements, after treatment with equimolar drug concentrations, indicated the major lipophilicity and cellular uptake of the new compounds. While the cytotoxicity of cisplatin was due to both intracellular accumulation and DNA binding, that of [Pt(O,O'-acac)(gamma-acac)(DMS)] was associated with intracellular Pt accumulation only, since it has low reactivity to DNA in intact cells and in vitro. The reaction of the new complexes with guanosine and 5'-GMP was negligible, whereas the L-methionine instantly reacted with the initial Pt complexes. Both cisplatin and [Pt(O,O'-acac)(gamma-acac)(DMS)] induced apoptosis in HeLa cells. [Pt(O,O'-acac)(gamma-acac)(DMS)] provoked the early signs of apoptosis induction (cleavage of PARP and activation of caspases-9, -3 and -7) only 1h after addition of the drug. However, in cisplatin-treated cells, cleavage of PARP was seen after 9h with activation of caspases also proceeding more slowly. In conclusion, these results indicate that the newly synthesized platinum(II) complexes have high and rapid cytotoxic activity in vitro, and suggest that DNA may not be their primary target.

Inhibition of thioredoxin reductase by auranofin induces apoptosis in cisplatin-resistant human ovarian cancer cells

Cisplatin is an effective antitumor agent for the treatment of several carcinomas. However, the development of resistance to cisplatin represents a serious clinical problem. The effects of auranofin, a gold(I) compound clinically used as an antirheumatic agent, on cisplatin-sensitive (2008) and-resistant (C13*) cancer cells were studied. Auranofin is more effective than cisplatin in decreasing cell viability and its action is particularly marked in C13* cells, indicating that no cross-resistance occurs. Furthermore, auranofin is able to permeate C13* cells more efficiently than 2008 cells. Treatment with auranofin determines a consistent release of cytochrome c in both cell lines, while cisplatin is effective only in sensitive cells. Both auranofin and cisplatin induce apoptosis in 2008 cells, while in C13* cells only auranofin is effective. Apoptosis is accompanied by an increased production of hydrogen peroxide that, however, is inhibited by N-acetyl-L-cysteine. In resistant cells, H(2)O(2) production is counteracted by a large overexpression of thioredoxin reductase that constitutes the preferred target of the inhibitory action of auranofin. This specific effect of auranofin might rationalize its ability in overcoming cisplatin resistance in human ovarian cancer cells.

Dicarba-closo-dodecaborane(12) derivatives of phosphonium salts: easy formation of nido-carborane phosphonium zwitterions

The first examples of arylphosphonium salts containing a dicarba-closo-dodecaborane(12) (closo-carborane) are reported; in contrast to the 1,12-carborane derivative, the 1,2- and 1,7-isomers undergo a facile deboronation reaction in polar solvents to afford the corresponding nido-carborane phosphonium zwitterions.

Metals in membranes

In this critical review we discuss recent advances in understanding the modes of interaction of metal ions with membrane proteins, including channels, pumps, transporters, ATP-binding cassette proteins, G-protein coupled receptors, kinases and respiratory enzymes. Such knowledge provides a basis for elucidating the mechanism of action of some classes of metallodrugs, and a stimulus for the further exploration of the coordination chemistry of metal ions in membranes. Such research offers promise for the discovery of new drugs with unusual modes of action. The article will be of interest to bioinorganic chemists, chemical biologists, biochemists, pharmacologists and medicinal chemists. (247 references).

Electronic Structures and Spectroscopic Properties of Mono- and Binuclear d8 Complexes: A Theoretical Exploration on Promising Phosphorescent Materials

The structures of trans-[M(2)(CN)(4)(PH(2)CH(2)PH(2))(2)] (M = Pt (1), Pd (2), and Ni (3)), trans-[Pt(2)X(4)(PH(2)CH(2)PH(2))(2)] (X = Cl (4) and Br (5)), and trans-[M(CN)(2)(PH(3))(2)] (M = Pt (6), Pd (7), and Ni (8)) in the ground state were optimized using the MP2 method. Frequency calculations reveal that the weak metal-metal interaction is essentially attractive for 1, 2, 4, and 5 but not for 3. The TD-DFT calculations associated with the polarized continuum model (PCM) were performed to predict absorption spectra in CH(2)Cl(2) solution. Experimental spectra are well reproduced by our results. With respect to analogous mononuclear d(8) complexes (6-8), a large red shift of the absorption wavelength was calculated for the binuclear d(8) complexes (1-3). Relative to 1 with unsaturated CN- donors, introduction of saturated halogen donors into 4 and 5 changes their electronic structures, especially the HOMO and LUMO. The TD-DFT and subsequent unrestricted MP2 calculations predict that 1 produces the lowest-energy d --> p emission while 2-5 favor the d --> d emissions, agreeing with experimental observations.

DNA dissociation and degradation at gold nanoparticle surfaces

The instability of DNA-functionalized gold nanoparticles (Au-DNA conjugates) upon exposure to high temperatures is characterized using fluorescence spectroscopy, gel electrophoresis and ion-exchange chromatography. Above 70 degrees C, aqueous Au-DNA conjugates decompose within hours due to both desorption of thiol-terminated DNA from the gold nanoparticle surface and chemical degradation of DNA in the presence of colloidal gold. Although the chemical mechanism for DNA degradation was not identified in this study, the gold surface participates directly in the cleavage reaction. These results have important implications for the use of Au-DNA conjugates in biotechnological and clinical applications that require high temperatures, such as polymerase chain reaction (PCR).

A gold(I) complex with a vitamin K3 derivative: characterization and antitumoral activity

Reaction of the vitamin K(3) derivative menadione sodium bisulfite thiosemicarbazone (NaK(3)TSC) with chloro(triethylphosphine)gold(I) afforded the complex [AuPEt(3)(K(3)TSC)]. This compound consists of discrete molecules in which the metal is almost linearly coordinated to P and S. Preliminary in vitro screening showed significant anti-cancer activity, notably against the cisplatin-resistant cell line A2780cis.

Cationic, linear Au(i) N-heterocyclic carbene complexes: synthesis, structure and anti-mitochondrial activity

Six linear, two-coordinate cationic Au(I) N-heterocyclic carbene complexes of the form [(R2Im)2Au]+ (R = Me 1, Me, Et 2, i-Pr 3, n-Bu 4, t-Bu 5 and Cy 6) have been prepared by the reaction of two equivalents of the appropriate dialkylimidazol-2-ylidene (R2Im) with (Me2S)AuCl in dmf. Single crystal structural studies for 1.PF6, 2.PF6), 3.Cl and 4-6.PF6 show that for all six complexes the gold(I) centres have quasi-linear C-Au-C coordination, with quasi-parallel pairs of aromatic imidazole planes, except in 5.PF6 where they are quasi-normal; in the latter, Au-C are 2.038(3), 2.033(3) A, cf. (e.g.) 2.027(2) A. Inter-cation Au...Au are close at 3.487(2), 3.525(2) A in 1PF6 and 2.PF6. The structural studies and low temperature NMR experiments provide no supportive evidence for the presence of pi back-bonding within this series of complexes. The lipophilicities of the six compounds, as estimated from the logarithm of the n-octanol-water partition coefficients (log P), varied across the series within the range -1.09 to 1.73. To investigate their potential as possible anti-mitochondrial anti-tumour agents, five of the compounds have been evaluated for their propensities to induce mitochondrial membrane permeabilization (MMP) in isolated rat liver mitochondria. At concentrations between 1-10 microM compounds 1.Br and 3-6.Cl induced dose-dependent, Ca2+-sensitive mitochondrial swelling at rates that increased with the lipophilicities of the complexes, with the most lipophilic compounds inducing the most rapid onset of swelling. The swelling was completely inhibited by cyclosporin A, the specific inhibitor of the mitochondrial permeability transition pore.

Phosphonioalkylthiosulfate zwitterions—new masked thiol ligands for the formation of cationic functionalised gold nanoparticles

We report the synthesis and structural characterisation of a new family of stable phosphonioalkylthiosulfate zwitterions, R3P+ (CH2)nS2O3- (R = Ph or Bu, n = 3,4,6, 8 or 10) which behave as cationic masked thiolate ligands with applications in the functionalisation of gold nanoparticles, having potential as new diagnostic biorecognition systems. The ligands were prepared by treatment of omega-bromoalkylphosphonium salts with sodium thiosulfate. The crystal and molecular structures of the zwitterions (R = Ph, n = 3) and (R = Bu, n = 3) were determined. A series of phosphonioalkanethiolate-capped gold nanoparticles dispersed in water was prepared by borohydride reduction of potassium tetrachloroaurate in the presence of the zwitterions in a dichloromethane-water system. UV-visible spectroscopy and scanning transmission electron-microscopy indicated that capped nanoparticles of ca. 5 nm diameter were present.

Mechanisms of Cytotoxicity of Selected Organogold(III) Compounds

The effects of a few cytotoxic organogold(III) compounds on ovarian A2780 human cancer cells were investigated in comparison to cisplatin and oxaliplatin. The tested compounds produced significant antiproliferative effects and promoted apoptosis to a greater extent than platinum drugs while causing only modest cell cycle modifications. The mechanistic implications of these findings are discussed: mitochondrial pathways are proposed to be directly involved in the apoptotic process in relation to selective inhibition of thioredoxin reductase.

Synthesis, cytotoxicity, cellular uptake and influence on eicosanoid metabolism of cobalt–alkyne modified fructoses in comparison to auranofin and the cytotoxic COX inhibitor Co-ASS

Propargylhexacarbonyldicobalt complexes with fructopyranose ligands were prepared and investigated for cytotoxicity in the MCF-7 human breast cancer cell line. The antiproliferative effects depended on the presence of isopropylidene protecting groups in the carbohydrate ligand and correlated with the cellular concentration of the complexes. IC(50) values of > 20 microM demonstrated that the fructose derivatives were only moderately active compared to the references auranofin and the aspirin (ASS) derivative [2-acetoxy(2-propynyl)benzoate]hexacarbonyldicobalt (Co-ASS). In continuation of our studies on the mode of action of cobalt-alkyne complexes we studied the influence of the compounds on the formation of 12-HHT (COX-1 product) and 12-HETE (12-LOX product) by human platelets as an indication of the interference in the eicosanoid metabolism, which is discussed as a target system of cytostatics. Co-ASS was an efficient COX-1 inhibitor without LOX inhibitory activity and auranofin inhibited both COX-1 and 12-LOX eicosanoid production. The missing activity of the fructopyranose complexes at the 12-LOX and the only moderate effects at COX-1 indicate that COX/LOX inhibition may be in part responsible for the pharmacological effects of auranofin and Co-ASS but not for those of the fructopyranose complexes.

New structural features in triphenylphosphinesilver(i) sulfanylcarboxylates

We investigated the reactions of 1.5 : 1 : 1 mole ratio mixtures of triphenylphosphine, silver nitrate and 3-(aryl)-2-sulfanylpropenoic acids H(2)xspa in chloroform/water, where in the acid nomenclature, spa = 2-sulfanylpropenoato and x = p, Clp, mp, diBr-o-hp or f with p = 3-phenyl-, Clp = 3-(2-chlorophenyl)-, mp = 3-methoxyphenyl-, diBr-o-hp = 3-(3,5-dibromo-2-hydroxyphenyl)- and f = 3-(2-furyl)-. The compounds [Ag(PPh(3))(Hpspa)](1), [(AgPPh3)2(xspa)][x = Clp (2), o-mp (3), p-mp (4), diBr-o-hp (5) and f (6)] and [Ag(PPh3)3(Hfspa)](7) were isolated and all except 7 were characterized by IR, Raman and FAB mass spectrometry and by 1H, 13C and 31P NMR spectroscopy. Compound 6 was also characterized by (13)C CP/MAS, and compounds 1 and 6 by (109)Ag NMR spectroscopy. The crystal structures of 1, 2, 3, 4.(CH3)2CO, 5, 6.(CH3)2CO and 7 were determined by X-ray diffraction. has a supramolecular structure based on hydrogen bonding between dinuclear units, and all the other complexes adopt discrete structures. 2, 3, 4.(CH3)2CO, 5, and 6.(CH3)2CO are tetranuclear, and 7 mononuclear. The tetranuclear complexes contain the eight-membered coordination ring Ag4S2O2 (2, 3, 4.(CH3)2CO, 6.(CH3)2CO) or the twelve-membered ring Ag4(CO2)2S2 (5).

Gold complexes inhibit mitochondrial thioredoxin reductase: consequences on mitochondrial functions

The effects of gold(I) complexes (auranofin, triethylphosphine gold and aurothiomalate), gold(III) complexes ([Au(2,2'-diethylendiamine)Cl]Cl(2), [(Au(2-(1,1-dimethylbenzyl)-pyridine) (CH(3)COO)(2)], [Au(6-(1,1-dimethylbenzyl)-2,2'-bipyridine)(OH)](PF(6)), [Au(bipy(dmb)-H)(2,6-xylidine)](PF(6))), metal ions (zinc and cadmium acetate) and metal complexes (cisplatin, zinc pyrithione and tributyltin) on mitochondrial thioredoxin reductase and mitochondrial functions have been examined. Both gold(I) and gold(III) complexes are extremely efficient inhibitors of thioredoxin reductase showing IC(50) ranging from 0.020 to 1.42 microM while metal ions and complexes not containing gold are less effective, exhibiting IC(50) going from 11.8 to 76.0 microM. At variance with thioredoxin reductase, auranofin is completely ineffective in inhibiting glutathione peroxidase and glutathione reductase, while gold(III) compounds show some effect on glutathione peroxidase. The mitochondrial respiratory chain is scarcely affected by gold compounds while the other metal complexes and metal ions, in particular zinc ion and zinc pyrithione, show a more marked inhibitory effect that is reflected on a rapid induction of membrane potential decrease that precedes swelling. Therefore, differently from gold compounds, the various metal ions and metal complexes exert their effect on different targets indicating a lower specificity. It is concluded that gold compounds are highly specific inhibitors of mitochondrial thioredoxin reductase and this action influences other functions such as membrane permeability properties. Metal ions and metal complexes markedly inhibit the activity of thioredoxin reductase although to an extent lower than that of gold compounds. They also inhibit mitochondrial respiration, decrease membrane potential and, finally, induce swelling.

Mitochondrial permeability transition induced by dinuclear gold(I)–carbene complexes: potential new antimitochondrial antitumour agents

Seven dinuclear gold(I) complexes of bidentate N-heterocyclic carbene ligands have been evaluated for their ability to induce mitochondrial membrane permeabilisation (MMP) in isolated rat liver mitochondria. Six of the compounds, at concentrations of 10 microM, induced Ca(2+)-sensitive MMP as evidenced by mitochondrial swelling. In the absence of low concentrations of exogenous Ca(2+), the compounds were either inactive or their activity was significantly decreased. The mitochondrial swelling was completely blocked by the addition of cyclosporin A, a well established inhibitor of the mitochondrial permeability transition pore (MPT) that is believed to be responsible for MMP. The rates and levels of uptake of these compounds into mitochondria were estimated by measuring mitochondrial Au levels using inductively coupled plasma optical emission spectroscopy. Significant differences were found in the levels at which the different compounds accumulated in the mitochondria, but these differences did not correlate with the rate at which they induced mitochondrial swelling. These results suggest that the mechanism by which MMP is induced by these lipophilic cationic Au(I)-carbene complexes is not purely a function of the level of compound accumulation. Instead, a more specific mechanism, possibly involving disruption of the function of a particular enzyme, or interaction with a MPT component, appears to be more likely.

[Au2(μ-G)(μ-dmpe)]·(KBr)0.75·2H2O, a cyclic dinuclear gold(I) complex with an N3,N9-bridging coordination mode of guanine and aurophilic interactions: synthesis, X-ray crystal structure and luminescence properties (dmpe=1,2-bis(dimethylphosphino)ethane and G=guaninato dianion)

The digold complex [Au(2)(micro-G)(micro-dmpe)](KBr)(0.75) x 2H(2)O (dmpe=1,2-bis(dimethylphosphino)ethane (1)) has been prepared by nucleophilic attack of the guaninate dianion on the gold(I) atoms of [(AuBr)(2)(micro-dmpe)] and has been characterised by X-ray crystallography and spectroscopic studies. The structure of 1 consists of dinuclear nine-membered ring molecules, K(+) cations, Br(-) anions and water molecules, all of them involved in either weak K....O or hydrogen bonding interactions. Within the cyclic dinuclear molecules, gold(I) atoms are bridged on one side by the diphosphine ligand and on the other side by a doubly deprotonated guaninate anion coordinated through neighbouring N3 and N9 nitrogen atoms, with gold(I)....gold(I) interactions of 3.030(2) A. This is the first X-ray example showing an N3,N9-bridging mode for guanine. There are two types of K(+) cations in the structure, K1 and K2. The former interacts with water molecules to form a unique [K(H(2)O)(3)(micro-H(2)O)(2)K(H(2)O)(3)](2+) dipotassium unit whereas K2 interact with the O6 atom of the guaninate ligands and oxygen atoms of the dipotassium unit leading to a chain running along the c-axis. Each chain is interdigitated with four neighbouring ones to give rise to an intricate network in which Br1, Br2 and [K(H(2)O)(3)(micro-H(2)O)(2)K(H(2)O)(3)](2+) fit snugly into cavities defined by digold molecules. Complex 1 luminescence at room temperature and 77 K in the solid state with excitation maxima at 385 nm and emission maxima at 451.8 and 448.7 nm, respectively. The emission spectrum of a saturated solution of 1 in DMSO (dimethyl sulfoxide) shows the maximum at about 440 nm.

Mitochondrial thioredoxin reductase inhibition by gold(I) compounds and concurrent stimulation of permeability transition and release of cytochrome c

The effects of auranofin, chloro(triethylphosphine)gold(I) (TEPAu), and aurothiomalate on mitochondrial respiration, pyridine nucleotide redox state, membrane permeability properties, and redox enzymes activities were compared. The three gold(I) derivatives, in the submicromolar range, were extremely potent inhibitors of thioredoxin reductase and stimulators of the mitochondrial membrane permeability transition (MPT). Auranofin appeared as the most effective one. In the micromolar range, it inhibited respiratory chain and glutathione peroxidase activity only slightly if not at all. TEPAu and aurothiomalate exhibited effects similar to auranofin, although TEPAu showed a moderate inhibition on respiration. Aurothiomalate inhibited glutathione peroxidase at concentrations where auranofin and TEPAu were without effect. Under nonswelling conditions, the presence of auranofin and aurothiomalate did not alter the redox properties of the mitochondrial pyridine nucleotides indicating that membrane permeability transition occurred independently of the preliminary oxidation of pyridine nucleotides. Under the same experimental conditions, TEPAu showed a moderate stimulation of pyridine nucleotides oxidation. Mitochondrial total thiol groups, in the presence of the gold(I) derivatives, slightly decreased, indicating the occurrence of an oxidative trend. Concomitantly with MPT, gold(I) compounds determined the release of cytochrome c that, however, occurred also in the presence of cyclosporin A and, partially, of EGTA, indicating its independence of MPT. It is concluded that the specific inhibition of thioredoxin reductase by gold(I) compounds may be the determinant of MPT and the release of cytochrome c.

Dinuclear gold(i) complexes of bridging bidentate carbene ligands: synthesis, structure and spectroscopic characterisation

Eight dinuclear Au(i)-carbene complexes have been synthesized from various imidazolium-linked cyclophanes and related acyclic bis(imidazolium) salts, by treatment of the imidazolium salts with [Au(i)(SMe(2))Cl] in the presence of a carboxylate base. Single crystal structural studies showed that the Au(i)-carbene compounds contain dinuclear (AuL)(2) cations in which a pair of gold(i) centres are linked by a pair of bridging dicarbenoid ligands. Interestingly, the structural studies revealed short AuAu contacts of 3.0485(3)[Angstrom] and 3.5425(6)[Angstrom] in two of these complexes. NMR studies showed that the (AuL)(2) cations constructed from the cyclophane-based ligands retain a relatively rigid structure in solution, whilst those of the non-cyclophane ligand systems are fluxional in solution. The electronic absorption and emission spectra of the complexes in solution at room temperature were recorded and the complex with the shortest AuAu contact was found to emit intensely at 400 nm and more weakly at 780 nm upon excitation at 260 nm. The compounds with longer AuAu separations were not emissive under these conditions.

Study of Ruthenium(II) Complexes with Anticancer Drugs as Ligands. Design of Metal-Based Phototherapeutic Agents

The reaction of trans-[RuCl(2)(PPh(3))(3)] (Ph = C(6)H(5)) with 2-thio-1,3-pyrimidine (HTPYM) and 6-thiopurines (TPs) produced mainly crystalline solids that consist of cis,cis,trans-[Ru(PPh(3))(2)(N,S-TPYM)(2)] (1) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-TPs)(2)]X(2) (X = Cl(-), CF(3)SO(3)(-)). In the case of TPs, other coordination isomers have never been isolated and reported. Instead, the mother liquor obtained after filtration of 1 produced red single crystals of trans,cis,cis-[Ru(PPh(3))(2)(N,S-TPYM)(2)].2H(3)O(+).2Cl(-) (2.2H(3)O(+).2Cl(-)). Selected ruthenium(II)-thiobase complexes were studied for their structural, reactivity, spectroscopic, redox, and cytotoxic properties. Single crystals of 1 contain thiopyrimidinato anions chelated to the metal center via N and S. The Ru[bond]N bonds are significantly elongated for 1 [2.122(2) and 2.167(2) A] with respect to 2 [2.063(3) A] because of the trans influence from PPh(3). The coordination pseudo-octahedron for 2 is significantly elongated at the apical sites (PPh(3) ligands). Solutions of cis,cis,trans isomers in air are stable for weeks, whereas those of 2 turn green within 24 h, in agreement with the respective redox potentials. cis,cis,trans- and trans,cis,cis-[Ru(PH(3))(2)(N,S-TPYM)(2)], as optimized through the DFT methods at the Becke3LYP level are in good agreement with experimental geometrical parameters (1 and 2), with cis,cis,trans being more stable than trans,cis,cis by 3.88 kcal. The trend is confirmed by molecular modeling based on semiempirical (ZINDO/1) and molecular mechanics (MM) methods. Cytotoxic activity measurements for cis,cis,trans-[Ru(PPh(3))(N-THZ)(N(7),S -H(2)TP)(2)]Cl(2) (4) (THZ = thiazole, H(2)TP = 6-thiopurine) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-HTPR)2]Cl(2) (5) (HTPR = 6-thiopurine riboside) against ovarian cancer cells A2780/S gave IC(50) values of 17 +/- 1 and 29 +/- 9 microM, respectively. Furthermore, the spectral analysis of HTPYM, TPs, and their Ru(II) complexes in solution shows that intense absorptions occur in the UVA/vis region of light, whereas standard nucleobases absorb in the UVB region.

New metal complexes as potential therapeutics

The many activities of metal ions in biology have stimulated the development of metal-based therapeutics. Cisplatin, as one of the leading metal-based drugs, is widely used in treatment of cancer, being especially effective against genitourinary tumors such as testicular. Significant side effects and drug resistance, however, have limited its clinical applications. Biological carriers conjugated to cisplatin analogs have improved specificity for tumor tissue, thereby reducing side effects and drug resistance. Platinum complexes with distinctively different DNA binding modes from that of cisplatin also exhibit promising pharmacological properties. Ruthenium and gold complexes with antitumor activity have also evolved. Other metal-based chemotherapeutic compounds have been investigated for potential medicinal applications, including superoxide dismutase mimics and metal-based NO donors/scavengers. These compounds have the potential to modulate the biological properties of superoxide anion and nitric oxide.

Antitumor activity of the mixed phosphine gold species chlorotriphenylphosphine-1,3-bis(diphenylphosphino)propanegold(I)

The title compound has been designed for antitumor activity based on structural features of related known antitumor gold agents, that is, gold-monophosphine and gold-diphosphine derivatives. It is a gold complex that contains both types of phosphine ligands, thus suggesting a possible synergistic action. The results of a single crystal X-ray structure determination of this molecule show the metal surrounded by 3 P atoms and one Cl anion in a distorted tetrahedral arrangement. The chloro anion, however, is weakly bound to the metal and so the species shows ionic character. The P NMR study, performed in solution, confirms the structural features observed in the solid and, in addition, indicates partial formation of other known gold(I)-diphosphine antitumor agents. The ionic character and strong Au-P bonds of this novel gold(I) species are similar to those of the most active antitumor gold compounds so far studied. The former feature contributes to solubility in biological fluids, and the latter prevents fast biomolecular attack. In addition, the title compound is less lipophilic, a feature recently correlated to lower liver toxicity. The title compound shows in vitro antitumor activity in the two initial National Cancer Institute protocols against human tumors. In the first screening, a unique dose (0.10 mM) of the title compound reduced cell growth of MCF7 (breast cancer), NCI-H460 (lung cancer), and SF-268 (Central Nervous System cancer-CNS) to 5, 8, and 11%, respectively. In the second protocol a 60-cell line panel was analyzed with the title compound concentration in the 0.1 mM-0.01 microM range. The highest activity was for the breast tumor cell line MCF7 with a LC(50) less than 0.01 microM. LC(50) values in the micromolar range were obtained for 29 cell lines. With the exception of leukemia, these micromolar activities were observed in at least one cell line for each subgroup tumor (non small lung, colon, CNS, melanoma, renal, prostate, breast, and ovarian). The leukemia inactivity was unexpected, as all antitumor gold(I) phosphine compounds in the literature described thus far are active. Melanoma was the most sensitive subgroup screened (five out of seven cell lines).

In vitro and in vivo antitumor properties of tetrakis((trishydroxy- methyl)phosphine)gold(I) chloride

A novel hydrophilic gold compound, tetrakis((trishydroxymethyl)phosphine)gold(I) chloride 1, has been investigated for its antitumor properties. In vitro studies demonstrate that 1 is active against HCT-15, AGS, PC-3, and LNCaP tumor cells. Cell cycle analysis of the HCT-15 cells by flow cytometry revealed elongation of the G1 phase of the cell cycle leading to growth inhibition. Administration of 1 to Balb/C mice inoculated with syngenic meth/A cells demonstrated statistically significant dose-dependent survival time.