The biological activity of Zeise's salt and its derivatives.

With the aim to design new biologically active bioinorganic drugs of aspirin, whose mode of action is based on the inhibition of the cyclooxygenase(COX) enzymes, derivatives of Zeise's salt were synthesized in this structure-activity relationship study. Surprisingly, not only these Zeise-aspirin compounds but also Zeise's salt itself showed high inhibitory potency against COX enzymes in in vitro assays. In contrast, potassium tetrachloroplatinate and cisplatin did not influence the enzyme activity at equimolar concentrations. It was demonstrated by LC-ESI tandem-mass spectrometry that Zeise's salt platinates the essential amino acids Tyr385 (active site of the enzyme) and Ser516 (will be acetylated by aspirin) of COX-1, thereby strongly impairing the function of the enzyme. This finding demonstrates for the first time that Zeise's salt is pharmacologically active and is a potent enzyme inhibitor.

Synthesis, characterization, and in vitro antiproliferative activity of [salophene]platinum(II) complexes.

A series of methoxy- and fluorine-substituted [salophene]platinum(II) complexes (salophene=N,N'-bis(salicylidene)-1,2-phenylenediamine) were synthesized and characterized by (1) H NMR spectroscopy and mass spectrometry. The structure was confirmed on the example of [5-OCH3 -salophene]platinum(II) (4-Pt) by crystal structure analysis. The cytotoxicity of all complexes against MCF-7 cells showed strong dependence on the kind of substituent and its position on the salicylidene moiety, whereas 1-Pt (H), 3-Pt (4-OCH3 ), and 6-Pt (3-F) exhibited high antiproliferative effects (IC50 <2 µM). Drug lipophilicity and cellular accumulation were analyzed in an attempt to explain the differences in antitumor potency. To gain insight into their mode of action, DNA interaction studies were performed, in which compounds such as 1-Pt acted as non-DNA-binding platinum anticancer drugs, as neither intercalation nor DNA covalent binding were detected.

Gold(I) N-heterocyclic carbene complexes with naphthalimide ligands as combined thioredoxin reductase inhibitors and DNA intercalators.

Organometallic conjugates consisting of a gold(I) N-heterocyclic carbene (NHC) moiety and a naphthalimide were prepared and investigated as cytotoxic agents that interact with both DNA and the disulfide reductase enzyme thioredoxin reductase (TrxR). The complexes were potent DNA intercalators related to their naphthalimide partial structure, inhibited TrxR as a consequence of the incorporation of the gold(I) moiety, and triggered efficient cytotoxic effects in MCF-7 breast and HT-29 colon adenocarcinoma cells. Strong effects on tumor cell metabolism were noted for the most cytotoxic complex, chlorido[1-(3'-(4''-ethylthio-1'',8''-naphthalimid-N''-yl))-propyl-3-methyl-imidazol-2-ylidene]gold(I) (4 d). In conclusion, the conjugation of naphthalimides with gold(I) NHC moieties provided a useful strategy for the design of bioorganometallic anticancer agents with multiple modes of action.

Evaluation of arene ruthenium(II) N-heterocyclic carbene complexes as organometallics interacting with thiol and selenol containing biomolecules.

Metal complexes with N-heterocyclic carbene (NHC) ligands have been widely used in catalytic chemistry and are now increasingly considered for the development of new chemical tools and metal based drugs. Ruthenium complexes of the type (p-cymene)(NHC)RuCl(2) interacted with biologically relevant thiols and selenols, which resulted in the inhibition of enzymes such as thioredoxin reductase or cathepsin B. Pronounced antiproliferative effects could be obtained provided that an appropriate cellular uptake was achieved. Inhibition of tumor cell growth was accompanied by a perturbation of metabolic parameters such as cellular respiration.

Cytotoxicity and cellular impact of dinuclear organoiridium DNA intercalators and nucleases with long rigid bridging ligands.

The DNA binding modes and cleavage properties of novel dinuclear Ir(III) polypyridyl (pp) complexes [{(η(5)-C(5)Me(5))Ir(pp)}(2)(µ-B)](CF(3)SO(3))(4) depend on the lengths of their rigid bridging dipyridinyl ligands B. Mono-intercalation and strong DNA cleavage properties were observed for the dipyrido[2,3-a:2',3'-c]phenazine (dppz) complexes 1 (B = 4-[(E)-2-(4-pyridinyl)ethenyl]pyridine) and 3 (B = 4-(2-pyridin-4-ylethynyl)pyridine), whose intracationic Ir···Ir' distances are about 13.1 and 13.3 Å, respectively. In contrast, UV/Vis and CD spectra were in accordance with a stable intertwined bis-intercalation mode for pairs of cations of 5 (B = 1,4-di(2-pyridin-4-ylethynyl)benzene), whose much longer Ir···Ir' distance of 20.6 Å allows a stack of five aromatic chromophores to be sandwiched between its effectively parallel dppz ligands. Whereas both 1 and 3 cleaved DNA in the dark, complex 5 exhibited only photoinduced nuclease activity. A significantly higher antiproliferative activity towards MCF-7 breast carcinoma cells was observed for the nucleases 1 and 3, whose IC(50) values of 0.61 and 0.49 were much lower than that of 2.2 µM for bis-intercalator 5. Values of 3.8 µM, only slightly higher than that of 5, were recorded for the 5,6-dimethylphenanthroline complexes 4 and 6, whose bridging ligands are identical to those of 3 and 5, respectively. Marked antileukemic activity (IC(50) = 6-7 µM) associated with increased levels of reactive oxygen species and apoptosis induction was recorded for both 3 and 5 towards Jurkat cells at concentrations of 5 µM and above. Online studies with a sensor chip system indicated that 5 µM solutions of these complexes invoke a rapid and massive reduction in MCF-7 cell respiration.

Cellular impact and selectivity of half-sandwich organorhodium(III) anticancer complexes and their organoiridium(III) and trichloridorhodium(III) counterparts.

Half-sandwich organorhodium(III) complexes and their trichloridorhodium(III) counterparts are potent anticancer agents that enhance the formation of reactive oxygen species and invoke a strong induction of apoptosis in leukemia cells. The antiproliferative activity towards human MCF-7 and HT-29 adenocarcinoma cells of novel nonintercalating complexes containing the 5-substituted phenanthroline ligands 5,6-dimethylphenanthroline, 5-chlorophenanthroline, and 5-nitrophenanthroline (phen*) increases dramatically in the order [(η(5)-C(5)Me(5))IrCl(phen*)](CF(3)SO(3)) < [(η(5)-C(5)Me(5))RhCl(phen*)](CF(3)SO(3)) < mer-[RhCl(3)(DMSO)(phen*)] (DMSO is dimethyl sulfoxide). Improved activity was also achieved by attaching a cell-penetrating peptide to the dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligand of an organorhodium(III) complex. Whereas 5-substitution led to significant improvements in the activity of the organoiridium(III) and trichloridorhodium(III) compounds in comparison with the parent phenanthroline complex, the IC(50) values of their organorhodium(III) counterparts remained effectively invariable. The high activities of the trichloridorhodium(III) complexes (IC(50) = 0.06-0.13 µM) were accompanied by pronounced selectivity towards human cancer cells in comparison with immortalized HEK-293 cells. In contrast, [(η(5)-C(5)Me(5))RhCl(5,6-Me(2)phen)](CF(3)SO(3)) (phen is phenanthroline) was markedly more active towards BJAB lymphoma cells than ex vivo healthy leukocytes and caused an immediate decrease in cellular adhesion possibly associated with interactions with membrane proteins. Its dppz analogue invoked an initial increase in glycolysis to compensate for reduced respiration before inducing a delayed onset of cell death. Strong antimitochondrial activity with respiration impairment and release of cytochrome c was established for both complexes.

Synthesis and cellular impact of diene-ruthenium(II) complexes: a new class of organoruthenium anticancer agents.

The cytostatic properties and cellular effects of novel diene-ruthenium(II) complexes of the types OC-6-13-[RuCl(2)(pp)(cod)] 1-5 (pp=2,2'-bipyridyl (bpy), phen=1,10-phenanthroline (phen), 5,6-dimethylphenanthroline (5,6-Me2phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), ethylenediamine (en)) and OC-6-24-[RuCl{(Me(2)N)(2)CS}(pp)(cod)](CF(3)SO(3)) 6-8 (pp=phen, 5,6-Me(2)phen, dpq) have been studied for the human cancer cell lines MCF-7 and HT-29 and for Jurkat leukemia cells. CD spectra indicate that 7 causes a massive distortion of the CT DNA B double helix toward the A form. Whereas the neutral complexes 1, 2 and 5 exhibit only modest antiproliferative activity toward MCF-7 and HT-29 cells, the monocationic complexes are significantly more active, in particular the DNA-distorting complex 7 with its IC(50) values of 0.73 and 0.42 µM, respectively. As established by online monitoring with a cell-based sensor chip, this potent 5,6-Me(2)phen complex invokes dose-dependent decreases in MCF-7 cellular respiration and extracellular acidification rates and causes a time-delayed decrease in the impedance of the cell layers, that can be ascribed to cell death. Treatment of Jurkat cells with 7 leads to high concentrations of reactive oxygen species and the induction of apoptosis. The pronounced dose-dependent inhibition of oxygen consumption by isolated mice mitochondria indicates the involvement of an intrinsic mitochondrial pathway in the programmed cell death process.

Comparative in vitro evaluation of N-heterocyclic carbene gold(I) complexes of the benzimidazolylidene type.

Gold(I) complexes with a 1,3-diethylbenzimidazol-2-ylidene N-heterocyclic carbene (NHC) ligand of the type NHC-Au-L (L=-Cl, -NHC, or -PPh3) were comparatively evaluated as thioredoxin reductase (TrxR) inhibitors and antimitochondrial anticancer agents. Different effects were noted in various biochemical assays (e.g., inhibition of TrxR, cellular and mitochondrial uptake, or effects on mitochondrial membrane potential), and this was related to properties of the complexes such as bond dissociation energies and overall charge. Remarkable antiproliferative effects, a strong induction of apoptosis, and enhancement of reactive oxygen species (ROS) formation as well as other effects on tumor cell metabolism confirmed the promising potential of the complexes as novel anticancer chemotherapeutics.

Cell response of Escherichia coli to cisplatin-induced stress.

Cisplatin is undoubtedly one of the most common and successful anticancer drugs worldwide. Though its DNA-based mechanism of action is well established, the contribution of the proteome to this process remains unclear. The possible impact of particular Escherichia coli proteins on the cytostatic activity of cisplatin was the subject of this study. Our main focus was not only the "bottom-up" identification of novel cisplatin protein targets through LC/LC-MS/MS analysis, but also a label-free quantification of their regulation profile by spectral-counting. The regulation of two proteins, aconitate hydratase 2 and 60 kDa chaperonin 1, could be linked to a platinated amino acid in the protein sequence, whereas in the cases of 30S ribosomal protein S1 and enolase, it could be shown that cisplatin fragments are coordinated to an essential site for the functionality of the protein. Nucleoside triphosphate pyrophosphohydrolase (MazG) regulates the programmed cell death and was found to be platinated on the protein surface, which probably correlates with the established mode of action. A possible new chapter in the understanding of cisplatin's mechanism of action and its severe side effects is opened, since evidence is provided that platinated proteins are not only involved in cellular stress response but also in energy metabolism through glycolysis and catabolic processes, in gene regulatory mechanisms and protein synthesis.

Highly cytotoxic substitutionally inert rhodium(III) tris(chelate) complexes: DNA binding modes and biological impact on human cancer cells.

The antiproliferative properties and cellular impact of novel substitutionally inert rhodium(III) complexes of the types [Rh{(CH3)2 NCS2}2(pp)]Cl 3-5 (pp=5,6-Me2phen, dpq, dppz) and OC-6-23-[Rh(2-S-py)2(pp)]Cl 6 and 7 (2-S-py=pyridine-2-thiolate; pp=dpq, dppz) have been investigated for the adherent human cancer cell lines MCF-7 and HT-29 and for non-adherent Jurkat cells. Whereas CD and viscosity measurements indicate that the polypyridyl ligands of 4 and 5 intercalate into CT DNA, this is not the case for the analogous pyridine-2-thiolate complexes 6 and 7. Complexes 3-7 all exhibit a high antiproliferative activity towards MCF-7 and HT-29 cells, with IC(50) values in the range 0.055-0.285 µM. As established by online monitoring with a cell-based sensor chip, the highly cytostatic complex 6 (IC(50)=0.059 and 0.078 µM) invokes an immediate concentration-dependent reduction of MCF-7 cell respiration and a time-delayed decrease in cellular impedance, which can be ascribed to the induction of cell death. Annexin V/PI assays demonstrated that 6 also has a pronounced antiproliferative activity towards Jurkat cells and that it invokes extensive apoptosis and high concentrations of reactive oxygen species in these leukemia cells. The observation of a dose-dependent inhibition of the oxygen consumption of isolated mice mitochondria indicates the involvement of an intrinsic mitochondrial pathway in this process.

Self-assembly of novel molecular complexes of 1,10-phenanthroline and 5-amino-1,10-phenanthroline and evaluation of their in vitro antitumour activity.

Novel molecular complexes of 1,10-phenanthroline (phen) and 5-amino-1,10-phenanthroline (5-NH2-phen) [(5-NH2-phen)2(phen) (H2O)3 (1), (phen)2(imidazole) (H+) (BF4-) (2), (phen)2(benzimidazole) (H+) (BF4-) (3), (5-NH2-phen)4(H2O)3 (4), and (phen)3 (indole) (H+) (BF4-) (5)] were synthesized via self-assembly processes and their in vitro anticancer activity was investigated. The structures of the compounds were confirmed by UV, FTIR, CIMS(CH4) and elemental analysis. The crystal structure of 2 was determined by X-ray diffraction. Cytotoxicity of the substances was measured using the cultivated human tumour cell lines HepG2, HEp-2, and 8-MB-GA. The tested substances showed different activity depending on the cell line and amount used. Substances 2 and 3 were not toxic to the non-tumour cells (Lep-3), but significantly toxic to all tumour ones. This is not the case with compounds 4 and 5, which are non-toxic towards carcinogenic cell lines, but even stimulate both HepG2 and HEp-2.

Cellular selectivity and biological impact of cytotoxic rhodium(III) and iridium(III) complexes containing methyl-substituted phenanthroline ligands.

The antiproliferative properties and biological impact of octahedral iridium(III) complexes of the type fac-[IrCl3 (DMSO)(pp)] containing pp=phenanthroline (1) and its 4- and 5-methyl (2, 3) and 4,7- and 5,6-dimethyl derivatives (4, 5) were investigated for both adherent and non-adherent cells. A series of similar rhodium(III) complexes were studied for comparison purposes. The antiproliferative activity toward MCF-7 cancer cells increases eightfold from IC50=4.6 for 1 to IC50=0.60 µM for 5, and an even more pronounced 18-fold improvement was established for the analogous rhodium complexes 6 and 8, the respective IC50 values for which are 1.1 and 0.06 µM. Annexin V/propidium iodide assays demonstrated that the 5,6-dimethylphenanthroline complexes 5 and 8 both cause significant inhibition of Jurkat leukemia cell proliferation and invoke extensive apoptosis but negligible necrosis. The percentages of Jurkat cells exhibiting high levels of reactive oxygen species correlate with the percentages of cells undergoing apoptosis. The antiproliferative activity of 5 and 8 is strongly selective toward MCF-7 and HT-29 cancer cells over normal HFF-1 and immortalized HEK-293 cells. Complex 5 also exhibits high selectivity toward BJAB lymphoma cells relative to healthy leukocytes. Both 5 and 8 invoke permanent decreases in the adhesion and respiration of MCF-7 cells.

Carbaboranes as pharmacophores: similarities and differences between aspirin and asborin.

In medicinal chemistry carbaboranes have been used almost exclusively as boron carriers for boron neutron capture therapy (BNCT). Recent developments extended the carrier approach and use carbaboranes as scaffolds for radiodiagnostic or therapeutic agents. Most recent studies, however, focus on carbaboranes as modern hydrophobic pharmacophores. This research employs preferably meta- and para-carbaborane, because these isomers are extremely hydrophobic and very stable. In this paper we therefore investigated the pharmacophoric behavior of the ortho isomer as putative phenyl mimetic by comparing aspirin to asborin, its ortho-carbaborane analogue. Special emphasis is placed on the impact of the cluster properties on the pharmacological profile. Subjects under study are the mode of cyclooxygenase (COX) inhibition, stability, and toxicity. The straightforward syntheses of the corresponding nido compounds as well as their contribution to the pharmacology of the closo precursors will be highlighted. Finally, proof will be given that the ortho-carbaborane core of asborin merits the designation "pharmacophore" by definition and is a multifunctional group rather than just a hydrophobic, bulky spectator.

Antileukemic activity and cellular effects of rhodium(III) crown thiaether complexes.

The cytostatic properties of novel rhodium(III) thiacrown ether complexes [RhCl(LL)([9]aneS(3))](n+) with either aromatic κ(2)N ligands (n = 2) or anionic chelate ligands (n = 1) have been investigated for the human cancer cell lines HT-29 and MCF-7 and for immortalized HEK-293 cells. Taken together with literature IC(50) values for analogous complexes with polypyridyl ligands or 1,4-dithiane, the in vitro assays indicate that dicationic complexes with soft κ(2)N (imino) or κ(2)S (thiaether) ligands exhibit significantly higher antiproliferative effects than those with hard κ(2)N (amino) ligands. Dicationic complexes are more active than monocationic complexes with similar ligands. Pronounced apoptosis-inducing properties towards Jurkat cells were established for complexes with LL = bpm, dpq, and 1,4-dithiane. The order of activity (bpm > 1,4-dithiane > dpq > bpy) contrasts to that observed for adhesive cancer cells (bpm > bpy, 1,4-dithiane > dpq). Necrosis is insignificant in all cases. The percentage of Jurkat cells exhibiting apoptosis after 24 or 48 h incubation periods is directly correlated to the percentage of cells exhibiting high levels of reactive oxygen species. As established by online monitoring with a sensor chip system, treatment of MCF-7 cells with the bpm and 1,4-dithiane complexes leads to a significant and permanent concentration-dependent decrease in oxygen consumption and cellular adhesion.

Benzimidazol-2-ylidene gold(I) complexes are thioredoxin reductase inhibitors with multiple antitumor properties.

Gold(I) complexes such as auranofin have been used for decades to treat symptoms of rheumatoid arthritis and have also demonstrated a considerable potential as new anticancer drugs. The enzyme thioredoxin reductase (TrxR) is considered as the most relevant molecular target for these species. The here investigated gold(I) complexes with benzimidazole derived N-heterocyclic carbene (NHC) ligands represent a promising class of gold coordination compounds with a good stability against the thiol glutathione. TrxR was selectively inhibited by in comparison to the closely related enzyme glutathione reductase, and all complexes triggered significant antiproliferative effects in cultured tumor cells. More detailed studies on a selected complex revealed a distinct pharmacodynamic profile including the high increase of reactive oxygen species formation, apoptosis induction, strong effects on cellular metabolism (related to cell surface properties, respiration, and glycolysis), inhibition of mitochondrial respiration and activity against resistant cell lines.

Cell-selective, apoptosis-inducing rhodium(III) crown thiaether complexes.

Half-sandwich rhodium(III) polypyridyl (pp) complexes with the metal atom capped by the facial crown thiaether 1,4,7-trithiacyclononane [9]aneS(3) represent a promising class of apoptosis-inducing potent cytostatic agents. The necrotic damage caused by the complexes is negligible. In vitro cytotoxicity assays with the human cancer cell lines MCF-7 and HT-29 and immortalized HEK-293 cells indicate that the dicationic kappa(2)N(imino) complexes [([9]aneS(3))RhCl(pp)](2+) are much more active than monocationic complexes [([9]aneS(3))RhCl(2)(L)](+) (L=imidazole, CH(3)CN). Whereas the kappa(2)N(amino) complex [([9]aneS(3))RhCl(piperazine)](2+) is inactive, replacing piperazine with the structurally analogous kappa(2)S (thiaether) ligand 1,4-dithiane restores cytotoxicity as evidenced by IC(50) values in the range 8.1-11.6 microM. Spectroscopic (CD, UV/Vis, NOESY) and viscosity measurements indicate that the active dppz complex 8 (IC(50) values: 4.7-8.9 microM) exhibits strong intercalative binding towards DNA whereas the even more potent bipyrimidine complex 9 (IC(50) values: 0.6-1.9 microM) causes no alteration of the duplex B conformation. Weaker intercalative binding is observed for the dpq complex 7. A comparative annexin V-propidium iodide binding assay with lymphoma (BJAB) cells and healthy leukocytes demonstrates that the cytotoxic activity of complex 8 and particularly complex 9 is highly selective towards the malignant cells.

Crystal structure and spectroscopic elucidation of 3-phenylpyridinium hydrogensquarate.

The novel 3-phenylpyridinium hydrogensquarate (1) has been synthesized and its structure and properties are elucidated spectroscopically, thermally and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-spectroscopy, TGA, DSC, DTA and ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectrum. 3-Phenylpyridinium hydrogensquarate, crystallizes in the space group P-1 and the ions in the unit cell are joined into layers by intermolecular NH...O=C((Sq)) bonds with bond lengths of 2.625 and 2.626 A, respectively. Hydrogentartarates form dimers by strong O=COH...OCO interactions (2.499 A).

First solid state alkaline-earth complexes of monensic acid A (MonH): crystal structure of [M(Mon)2(H (2)O)2] (M = Mg, Ca), spectral properties and cytotoxicity against aerobic Gram-positive bacteria.

Alkaline-earth metal complexes of the monoanionic form of the polyether ionophore monensin A were isolated for the first time in solid state and were structurally characterized using various spectroscopic methods (IR, NMR, FAB-MS). The stoichiometric reaction of monensic acid (MonH) with M(2+) (M = Mg, Ca) in the presence of an organic base leads to the formation of mononuclear complexes of composition [M(Mon)(2)(H(2)O)(2)]. The structures of magnesium (1) and calcium (2) monensin complexes in the solid state were established by single crystal X-ray crystallography. The complexes crystallize as [Mg(Mon)(2)(H(2)O)(2)]x5MeCN (1) and [Ca(Mon)(2)(H(2)O)(2)]xH(2)Ox5MeCN (2) in the monoclinic P21 space group. The alkaline-earth metal ion is placed in a distorted octahedral environment, defined by two monensin anions acting as bidentate ligands in the equatorial plane of the complex as well as by two water molecules occupying the axial positions of the inner coordination sphere. The bactericidal activity of 1 and 2 was evaluated against aerobic Gram-positive microorganisms applying the double layer agar hole diffusion method.

Dinuclear organoiridium(III) mono- and bis-intercalators with rigid bridging ligands: synthesis, cytotoxicity and DNA binding.

The DNA binding and in vitro cytotoxicity of the dinuclear Ir(III) polypyridyl complexes [{(eta(5)-C(5)Me(5))Ir(dppz)}(2)(mu-pyz)](CF(3)SO(3))(4)1 and [{(eta(5)-C(5)Me(5))Ir(pp)}(2)(mu-4,4'-bpy)](CF(3)SO(3))(4)2-4 (pp=dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), dipyrido[2,3-a:2',3'-c]phenazine (dppz), benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (dppn)) with the rigid bridging ligands pyrazine (pyz) or 4,4'-bipyridine (4,4'-bpy) have been studied. Stable intercalative binding into CT DNA (calf thymus DNA) is indicated for the dppz complexes 1 and 3 by induced negative CD bands at about 300nm and large viscosity increases, with the individual measurements being in accordance with intrastrand bis-intercalation for 3 and mono-intercalation for 1. The observed interruption of specific interresidue NOE cross peaks from the relevant nucleobase H6/H8 protons to the sugar H2'/H2'' protons of the preceding nucleotide is in accordance with bis-intercalation of complex 3 between the C3G18 and G4C17 base pairs and the T5A16 and A6T15 base pairs of the decanucleotide d(5'-CGCGTAGGCC-3'). Complexes 1 and 3 exhibit a greatly improved uptake by HT-29 (colon carcinoma) cells and significantly improved in vitro IC(50) values of 1.8+/-0.1 and 3.8+/-0.1microM towards this cell line in comparison to the mononuclear complex [(eta(5)-C(5)Me(5))IrCl(dppz)](CF(3)SO(3)) (IC(50)=7.4+/-0.9microM).