👤 Arion VB.

Organometallic Ru(arene)-peptide bioconjugates with potent in vitro anticancer activity are rare. We have prepared a conjugate of a Ru(arene) complex with the neuropeptide [Leu(5)]-enkephalin. [Chlorido(η(6)-p-cymene)(5-oxo-κO-2-{(4-[(N-tyrosinyl-glycinyl-glycinyl-phenylalanyl-leucinyl-NH2)propanamido]-1H-1,2,3-triazol-1-yl)methyl}-4H-pyronato-κO)ruthenium(II)] (8) shows antiproliferative activity in human ovarian carcinoma cells with an IC50 value as low as 13 μM, whereas the peptide or the Ru moiety alone are hardly cytotoxic. The conjugation strategy for linking the Ru(cym) (cym=η(6)-p-cymene) moiety to the peptide involved N-terminal modification of an alkyne-[Leu(5)]-enkephalin with a 2-(azidomethyl)-5-hydroxy-4H-pyran-4-one linker, using Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC), and subsequent metallation with the Ru(cym) moiety. The ruthenium-bioconjugate was characterized by high resolution top-down electrospray ionization mass spectrometry (ESI-MS) with regard to peptide sequence, linker modification and metallation site. Notably, complete sequence coverage was obtained and the Ru(cym) moiety was confirmed to be coordinated to the pyronato linker. The ruthenium-bioconjugate was analyzed with respect to cytotoxicity-determining constituents, and through the bioconjugate models [{2-(azidomethyl)-5-oxo-κO-4H-pyronato-κO}chloride (η(6)-p-cymene)ruthenium(II)] (5) and [chlorido(η(6)-p-cymene){5-oxo-κO-2-([(4-(phenoxymethyl)-1H-1,2,3-triazol-1-yl]methyl)-4H-pyronato-κO}ruthenium(II)] (6) the Ru(cym) fragment with a triazole-carrying pyronato ligand was identified as the minimal unit required to achieve in vitro anticancer activity. Show less

RuII(arene) complexes have been shown to be promising anticancer agents, capable of overcoming major drawbacks of currently used chemotherapeutics. We have synthesized RuII(η6-arene) compounds carrying bioactive flavonol ligands with the aim to obtain multitargeted anticancer agents. To validate this concept, studies on the mode of action of the complexes were conducted which indicated that they form covalent bonds to DNA, have only minor impact on the cell cycle, but inhibit CDK2 and topoisomerase IIα in vitro. The cytotoxic activity was determined in human cancer cell lines, resulting in very low IC50 values as compared to other RuII(arene) complexes and showing a structure-activity relationship dependent on the substitution pattern of the flavonol ligand. Furthermore, the inhibition of cell growth correlates well with the topoisomerase inhibitory activity. Compared to the flavonol ligands, the RuII(η6-p-cymene) complexes are more potent antiproliferative agents, which can be explained by potential multitargeted properties. Show less

In an attempt to combine the ability of indolobenzazepines (paullones) to inhibit cyclin-dependent kinases (Cdks) and that of platinum-group metal ions to interact with proteins and DNA, ruthenium(II) and osmium(II) arene complexes with paullones were prepared, expecting synergies and an increase of solubility of paullones. Complexes with the general formula [M(II)Cl(η(6)-p-cymene)L]Cl, where M=Ru (1, 3) or Os (2, 4), and L=L(1) (1, 2) or L(2) (3, 4), L(1)=N-(9-bromo-7,12-dihydroindolo[3,2-d][1]-benzazepin-6(5H)-yliden-N'-(2-hydroxybenzylidene)azine and L(2)=N-(9-bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6-yl)-N'-[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl-methylene]azinium chloride (L(2)(*)HCl), were now investigated regarding cytotoxicity and accumulation in cancer cells, impact on the cell cycle, capacity of inhibiting DNA synthesis and inducing apoptosis as well as their ability to inhibit Cdk activity. The MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) assay yielded IC(50) values in the nanomolar to low micromolar range. In accordance with cytotoxicity data, the BrdU assay showed that 1 is the most and 4 the least effective of these compounds regarding inhibition of DNA synthesis. Effects on the cell cycle are minor, although concentration-dependent inhibition of Cdk2/cyclin E activity was observed in cell-free experiments. Induction of apoptosis is most pronounced for complex 1, accompanied by a low fraction of necrotic cells, as observed by annexin V-fluorescein isothiocyanate/propidium iodide staining and flow cytometric analysis. Show less

A modified paullone ligand bearing a TEMPO free-radical unit (HL) and its ruthenium(II) and osmium(II)-arene complexes [M(p-cymene)(HL)Cl]Cl·nH(2)O (M = Ru, Os) exhibit high antiproliferative activity in human cancer cell lines. Show less

A series of ruthenium(II) arene complexes with 3-(1H-benzimidazol-2-yl)-1H-quinoxalin-2-one, bearing pharmacophoric groups of known protein kinase inhibitors, and related benzoxazole and benzothiazole derivatives have been synthesized. In addition, the corresponding osmium complexes of the unsubstituted ligands have also been prepared. The compounds have been characterized by NMR, UV-vis, and IR spectroscopy, ESI mass spectrometry, elemental analysis, and by X-ray crystallography. Antiproliferative activity in three human cancer cell lines (A549, CH1, SW480) was determined by MTT assays, yielding IC(50) values of 6-60 μM for three unsubstituted metal-free ligands, whereas values for the metal complexes vary in a broad range from 0.3 to 140 μM. Complexation with osmium of quinoxalinone derivatives with benzimidazole or benzothiazole results in a more consistent increase in cytotoxicity than complexation with ruthenium. For selected compounds, the capacity to induce apoptosis was confirmed by fluorescence microscopy and flow-cytometric analysis, whereas cell cycle effects are only moderate. Show less

Ru(II)(arene) anticancer compounds with maleimide functionality were prepared to allow selective interaction with thiol-containing biomolecules and thereby enforcing the selective delivery of the compounds to the tumour. Show less

Following our strategy of coupling cyclin-dependent kinase (Cdk) inhibitors with organometallic moieties to improve their physicochemical properties and bioavailability, five organoruthenium complexes (1c-5c) of the general formula [RuCl(η(6)-arene)(L)]Cl have been synthesized in which the arene is 4-formylphenoxyacetyl-η(6)-benzylamide and L is a Cdk inhibitor [3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines (L1-L3) and indolo[3,2-d]benzazepines (L4 and L5)]. All of the compounds were characterized by spectroscopic and analytical methods. Upon prolonged standing (2-3 months) at room temperature, the dimethyl sulfoxide (DMSO) solutions of 1c and 2c(-HCl) afforded residues, which after recrystallization from EtOH and EtOH/H(2)O, respectively, were shown by X-ray diffraction to be cis,cis-[Ru(II)Cl(2)(DMSO)(2)(L1)]·H(2)O and mer-[Ru(II)Cl(DMSO)(3)(L2-H)]·H(2)O. Compound 5c, with a coordinated amidine unit, undergoes E/Z isomerization in solution. The antiproliferative activities and effects on the cell cycle of the new compounds were evaluated. Complexes 1c-5c are moderately cytotoxic to cancer cells (CH1, SW480, A549, A2780, and A2780cisR cell lines). Therefore, in order to improve their antiproliferative effects, as well as their drug targeting and delivery to cancer cells, 1c-5c were conjugated to recombinant human serum albumin, potentially exploiting the so-called "enhanced permeability and retention" effect that results in the accumulation of macromolecules in tumors. Notably, a marked increase in cytotoxicity of the albumin conjugates was observed in all cases. Show less

Six organometallic complexes of the general formula [M(II)Cl(η(6)-p-cymene)(L)]Cl, where M = Ru (11a, 12a, 13a) or Os (11b, 12b, 13b) and L = 3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines (L1-L3) have been synthesized. The latter are known as potential cyclin-dependent kinase (Cdk) inhibitors. All compounds have been comprehensively characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, UV-vis spectroscopy, ESI mass spectrometry, and X-ray crystallography (11b and 12b). The multistep synthesis of 3-(1H-benzimidazol-2-yl)-1H-pyrazolo[3,4-b]pyridines (L1-L3), which was reported by other researchers, has been modified by us essentially (e.g., the synthesis of 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylic acid (3) via 5-bromo-3-methyl-1H-pyrazolo[3,4-b]pyridine (2); the synthesis of 1-methoxymethyl-2,3-diaminobenzene (5) by avoiding the use of unstable 2,3-diaminobenzyl alcohol; and the activation of 1H-pyrazolo[3,4-b]pyridine-3-carboxylic acids (1, 3) through the use of an inexpensive coupling reagent, N,N'-carbonyldiimidazole (CDI)). Stabilization of the 7b tautomer of methoxymethyl-substituted L3 by coordination to a metal(II) center, as well as the NMR spectroscopic characterization of two tautomers 7b-L3 and 4b'-L3 in a metal-free state are described. Structure-activity relationships with regard to cytotoxicity and cell cycle effects in human cancer cells, as well as Cdk inhibitory activity, are also reported. Show less

The synthesis, characterization, reactivity and in vitro anticancer activity of a series of Ru(II)-arene complexes with carbohydrate-derived phosphite and biscarboxylato co-ligands are reported. The compounds were characterized by NMR spectroscopy and electrospray ionization (ESI) mass spectrometry, and the molecular structures of oxalato(η(6)-p-cymene)(3,5,6-bicyclophosphite-1,2-O-isopropylidene-α-D-glucofuranoside)ruthenium(II) and oxalato(η(6)-p-cymene)(3,5,6-bicyclophosphite-1,2-O-cyclohexylidene-α-D-glucofuranoside)ruthenium(II) were determined by X-ray diffraction analysis. In contrast to their dichlorido counterparts, the biscarboxylato complexes did not exhibit significant reactivity towards biomolecules, such as cysteine, methionine, ubiquitin or the DNA model 5'-GMP, and resist hydrolysis; no hydrolytic species were detected by (1)H and (31)P{(1)H} NMR spectroscopy over several days. These structural alterations led to a decrease in the tumor-inhibiting potency of the compounds in human cancer cell lines. Show less

The synthesis and in vitro anticancer activity of Os(II)-arene complexes with carbohydrate-derived phosphite co-ligands are reported. The compounds were characterized by standard methods and the molecular structure of dichlorido(eta(6)-p-cymene)(3,5,6-bicyclophosphite-1,2-O-isopropylidene-alpha-D-glucofuranoside)osmium(II) was determined by X-ray diffraction analysis. Complexes with chlorido leaving groups undergo hydrolysis by consecutive formation of aqua compounds, followed by cleavage of a P-O bond of sugar phosphite ligands, as demonstrated by NMR studies. These observations are similar to those of analogous Ru(II)-arene complexes; however the rate of hydrolysis is very slow for osmium compounds. The complexes with oxalato leaving groups resist hydrolysis; no hydrolytic species were detected by (31)P{(1)H} NMR spectroscopy over several days. Within this series of Os compounds, in vitro anticancer activity is highest for the most lipophilic chlorido complex dichlorido(eta(6)-p-cymene)(3,5,6-bicyclophosphite-1,2-O-cyclohexylidene-alpha-D-glucofuranoside)osmium(II). Show less

Organometallic ruthenium-arene compounds bearing a maltol ligand have been shown to be nearly inactive in in vitro anticancer assays, presumably due to the formation of dimeric Ru(II) species in aqueous solutions. In an attempt to stabilize such complexes, [Ru(eta(6)-p-cymene)(XY)Cl] (XY=pyrones or thiopyrones) complexes with different substitution pattern of the (thio)pyrone ligands have been synthesized, their structures characterized spectroscopically, and their aquation behavior investigated as well as their tumor-inhibiting potency. The aquation behavior of pyrone systems with electron-donating substituents and of thiopyrone complexes was found to be significantly different from that of the maltol-type complex reported previously. However, the formation of the dimer can be excluded as the primary reason for the inactivity of the complex because some of the stable compounds are not active in cancer cell lines either. In contrast, studies of their reactivity towards amino acids demonstrate different reactivities of the pyrone and thiopyrone complexes, and the higher stability of the latter probably renders them active against human tumor cells. Show less

Ruthenium(II)-arene complexes of general formulae [(eta(6)-p-cymene)Ru(L(1-3))Cl(2)], where L(1-3) is 3-acetylpyridine (1), 4-acetylpyridine (2) and 2-amino-5-chloropyridine (3), correspondingly, [(eta(6)-p-cymene)Ru(HL(4,5))Cl(2)], where HL(4) and HL(5) are respectively isonicotinic acid (4) and nicotinic acid (5) and [(eta(6)-p-cymene)Ru(HL(6-9))Cl], where H(2)L(6-9) represent 2,3-pyridinedicarboxylic acid (6), 2,4-pyridinedicarboxylic acid (7), 2,5-pyridinedicarboxylic acid (8) and 2,6-pyridinedicarboxylic acid (9), were prepared by the reaction of [(eta(6)-p-cymene)(2)RuCl(2)](2) (10) with the corresponding ligand in 1:2 molar ratio in isopropanol. The complexes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopies. According to these data the molecules adopt the usual "three-leg piano-stool" geometry which is common for this type of complexes. The structures of 1 and 7 were determined by X-ray crystallography. The complexes revealed low antiproliferative activity in six investigated tumor cell lines (HeLa, B16, FemX, MDA-MB-361, MDA-MB-453 and LS-174). The reaction of 6 with 9-methyladenine was studied by (1)H NMR, (1)H, (1)H COSY and (1)H, (1)H NOESY spectroscopy. Show less

The light-protected reaction of [(eta(6)-p-cymene)Ru(II)Cl(2)](2) with 1-(2-hydroxyethyl)piperazine in dry methanol, followed by addition of excess NH(4)PF(6), afforded the complex [(eta(6)-p-cymene)Ru(II)(NH(3))(2)Cl](PF(6)) () in 47% yield. Attempts to use the same protocol for the synthesis of [(eta(6)-p-cymene)Os(II)(NH(3))(2)Cl](PF(6)) led to the isolation of the binuclear triply methoxido-bridged arene-osmium compound [{(eta(6)-p-cymene)Os}(2)(mu-OCH(3))(3)](PF(6)) (). Both compounds were characterised by X-ray crystallography and (1)H NMR spectroscopy, and the ruthenium complex also by spectroscopic techniques (IR and UV-vis spectroscopies). The antiproliferative activity of complex in vitro was studied in A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma) cells and compared to that of [(eta(6)-p-cymene)Ru(II)(en)Cl](PF(6)) (). In contrast to the latter compound, is only modestly cytotoxic in all three cell lines (IC(50): 293-542 muM), probably due to the instability of the diammine ruthenium complex in aqueous solution. Show less

The synthesis and in vitro anticancer activity of dihalogenido(eta6-p-cymene)(3,5,6-bicyclophosphite-alpha-D-glucofuranoside)ruthenium(II) complexes are described. The compounds were characterized by NMR spectroscopy and ESI mass spectrometry, and the molecular structures of dichlorido-, dibromido- and diiodido(eta6-p-cymene)(3,5,6-bicyclophosphite-1,2-O-isopropylidene-alpha-D-glucofuranoside)ruthenium(II) were determined by X-ray diffraction analysis. The complexes were shown to undergo aquation of the first halido ligand in aqueous solution, followed by hydrolysis of a P--O bond of the phosphite ligand, and finally formation of dinuclear species. The hydrolysis mechanism was confirmed by DFT calculations. The aquation of the complexes was markedly suppressed in 100 mM NaCl solution, and notably only very slow hydrolysis of the P--O bond was observed. The complexes showed affinity towards albumin and transferrin and monoadduct formation with 9-ethylguanine. In vitro studies revealed that the 3,5,6-bicyclophosphite-1,2-O-cyclohexylidene-alpha-D-glucofuranoside complex is the most cytotoxic compound in human cancer cell lines (IC50 values from 30 to 300 microM depending on the cell line). Show less

Reactions of (H 2azole) 2[OsCl 6], where Hazole = pyrazole, Hpz, ( 1), indazole, Hind, ( 2), imidazole, Him, ( 3) and benzimidazole, Hbzim, ( 4) with the corresponding azole heterocycle in 1:4 molar ratio in boiling isoamyl alcohol or hexanol-1 afforded novel water-soluble osmium(III) complexes of the type trans-[OsCl 2(Hazole) 4]Cl, where Hazole = Hpz ( 5a), Hind ( 6a), Him ( 7a), and Hbzim ( 9a) in 50-70% ( 5a, 7a, 9a) and 5% ( 6a) yields. The synthesis of 7a was accompanied by a concurrent reaction which led to minor formation (<4%) of cis-[OsCl 2(Him) 4]Cl ( 8). The complexes were characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, ESI mass spectrometry, cyclic voltammetry, and X-ray crystallography. 5a, 7a, and 9a were found to possess remarkable antiproliferative activity in vitro against A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma) cells, which was compared with that of related ruthenium compounds trans-[RuCl 2(Hazole) 4]Cl, where Hazole = Hpz (5b), Hind (6b), Him (7b), and Hbzim (9b). Show less

The osmium(III) complex [(DMSO)2H][trans-OsIIICl4(DMSO)2] (1) has been prepared via stepwise reduction of OsO4 in concentrated HCl using N2H(4).2HCl and SnCl(2).2H2O in DMSO. 1 reacts with a number of azole ligands, namely, indazole (Hind), pyrazole (Hpz), benzimidazole (Hbzim), imidazole (Him), and 1H-1,2,4-triazole (Htrz), in organic solvents, affording novel complexes (H2ind)[OsIIICl4(Hind)(DMSO)] (2), (H2pz)[OsIIICl4(Hpz)(DMSO)] (3), (H2bzim)[OsIIICl4(Hbzim)(DMSO)] (4), (H2im)[OsIIICl4(Him)(DMSO)] (6), and (H2trz)[OsIIICl4(Htrz)(DMSO)] (7), which are close analogues of the antimetastatic complex NAMI-A. Metathesis reaction of 4 with benzyltriphenylphosphonium chloride in methanol led to the formation of (Ph3PCH2Ph)[OsIIICl4(Hbzim)(DMSO)] (5). The complexes were characterized by IR, UV-vis, ESI mass spectrometry, 1H NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. In contrast to NAMI-A, 2-4, 6, and 7 are kinetically stable in aqueous solution and resistant to hydrolysis. Surprisingly, they show reasonable antiproliferative activity in vitro in two human cell lines, HT-29 (colon carcinoma) and SK-BR-3 (mammary carcinoma), when compared with analogous ruthenium compounds. Structure-activity relationships and the potential of the prepared complexes for further development are discussed. Show less

Antineoplastic ruthenium(III) complexes are generally regarded as prodrugs, being activated by reduction. Within a homologous series of ruthenium(III) complexes, cytotoxic potency is therefore expected to increase with increasing ease of reduction. Complexes of the general formula [Ru(III)Cl((6-n))(ind)n](3-n)- (n = 0-4; ind = indazole; counterions = Hind(+) or Cl(-)) and the compound trans-[Ru(II)Cl(2)(ind)(4)] have been prepared and characterized electrochemically. Lever's parametrization method predicts that a higher indazole-to-chloride ratio results in a higher reduction potential, which is confirmed by cyclic voltammetry. In vitro antitumor potencies of these complexes in colon cancer cells (SW480) and ovarian cancer cells (CH1) vary by more than 2 orders of magnitude and increase in the following rank order: [Ru(III)Cl(6)](3-) < [Ru(III)Cl(4)(ind)(2)](-) < [Ru(III)Cl(5)(ind)](2-) << [Ru(III)Cl(3)(ind)(3)] < [Ru(III)Cl(2)(ind)(4)](+) approximately [Ru(II)Cl(2)(ind)(4)]. Thus, the observed differences in potency correlate with reduction potentials largely, though not perfectly, pointing to the influence of additional factors. Differences in the cellular uptake (probably resulting from different lipophilicity) contribute to this correlation but cannot solely account for it. Show less