Varying the metal to ethacrynic acid ratio in ruthenium(ii)/osmium(ii)-p-cymene conjugates.

Following the identification of a ruthenium(II)-arene complex with an ethacrynic acid-modified imidazole ligand, which inhibits glutathione transferase (GST) and is cytotoxic to chemo-resistant cancer cells, a series of structurally related ruthenium(II)- and osmium(II)-p-cymene compounds have been prepared. In these complexes the ethacrynic acid is linked to the metals via appropriately modified pyridine ligands. The influence of the metal center and the metal:ethacrynic acid ratio on the cytotoxicity of the compounds was evaluated with the derivatives with one metal center and two ethacrynic acid moieties being the most potent against chemo-resistant A2780cisR cells (human ovarian cancer cells with acquired resistance to cisplatin). Moreover, compared to a complex with an ethacrynic acid-modified imidazole ligand (RAIMID-EA, Figure 2), these complexes display a significant degree of cancer cell specificity.

Anticancer Organometallic Osmium(II)-p-cymene Complexes.

Osmium compounds are attracting increasing attention as potential anticancer drugs. In this context, a series of bifunctional organometallic osmium(II)-p-cymene complexes functionalized with alkyl or perfluoroalkyl groups were prepared and screened for their antiproliferative activity. Three compounds from the series display selectivity toward cancer cells, with moderate cytotoxicity observed against human ovarian carcinoma (A2780) cells, whereas no cytotoxicity was observed on non-cancerous human embryonic kidney (HEK-293) cells and human endothelial (ECRF24) cells. Two of these three cancer-cell-selective compounds induce cell death largely via apoptosis and were also found to disrupt vascularization in the chicken embryo chorioallantoic membrane (CAM) model. Based on these promising properties, these compounds have potential clinical applications.

Antiangiogenic and Anticancer Properties of Bifunctional Ruthenium(II)-p-Cymene Complexes: Influence of Pendant Perfluorous Chains.

Two bifunctional ruthenium(II)-p-cymene complexes with perfluorinated side chains, attached via pyridine ligands, have been evaluated in a series of in vitro and in vivo assays. Their effects on human endothelial (ECRF24 and HUVEC) cells, noncancerous human embryonic kidney (HEK-293) cells, and various human tumor cells were investigated. The complex with the shorter chain, 1, inhibits the proliferation of the tumor cell lines and ECRF24, whereas 2 selectively inhibits ECRF24 and HUVEC proliferation. Neither inhibits the migration of ECRF24 cells whereas both compounds inhibit sprout formation in HUVEC cells. Using three preclinical models, i.e., vasculature formation in the chorioallantoic membrane (CAM) of the chicken embryo, human A2780 ovarian carcinoma tumors xenografted on the CAM, and human LS174T colorectal adenocarcinoma tumors grown in athymic mice, the angiostatic and anticancer activities of these two complexes were studied. Overall, 1 inhibited tumor growth predominantly through an anticancer effect whereas 2 inhibited tumor growth predominately via an antiangiogenic mechanism.

Improved angiostatic activity of dasatinib by modulation with hydrophobic chains.

Dasatinib is an orally active nonselective tyrosine kinase inhibitor used to treat certain types of adult leukemia. By inhibiting PDGFR-ß and SFKs in both tumor cells and tumor-associated endothelial cells, dasatinib inhibits tumor growth and angiogenesis. Herein, dasatinib derivatives modified with hydrophobic chains were prepared and evaluated for their in vitro antiproliferative selectivity and their in vivo antiangiogenic activity. For one of the derivatives, modified with a long perfluorinated chain, a significant enhancement in antiangiogenic activity was observed. Combined, these results suggest a possible generic route to modulate the angiostatic activity of drugs.

Modulating the Anticancer Activity of Ruthenium(II)-Arene Complexes.

Following the identification of [Ru(η(6)-p-cymene)Cl2(1H,1H,2H,2H-perfluorodecyl-3-(pyridin-3-yl)propanoate)], a ruthenium(II)-arene complex with a perfluoroalkyl-modified ligand that displays remarkable in vitro cancer cell selectivity, a series of structurally related compounds were designed. In the new derivatives, the p-cymene ring and/or the chloride ligands are substituted by other ligands to modulate the steric bulk or aquation kinetics. The new compounds were evaluated in both in vitro (cytotoxicity and migration assays) and in vivo (chicken chorioallantoic membrane) models and were found to exhibit potent antivascular effects.

In vivo evaluation of small-molecule thermoresponsive anticancer drugs potentiated by hyperthermia.

Hyperthermia used as an adjuvant with chemotherapy is highly promising in the treatment of certain cancers. Currently, the small molecule drugs used in combination with hyperthermia were not designed for this application. Herein, we report the evaluation of a chlorambucil and a ruthenium compound modified with a long fluorous chain, which exhibit thermoresponsive activity in colorectal adenocarcinoma xenografts in athymic mice in combination with mild hyperthermia (42 °C). Intraperitoneal injection of the derivatives followed by local hyperthermia showed a synergistic tumor growth reduction by 79% and 90% for the chlorambucil and ruthenium-based derivatives, respectively, with the latter exhibiting a higher synergy in combination with hyperthermia compared to the monotherapies. Histological analysis shows that both derivatives in combination with hyperthermia significantly decrease the number of proliferating tumor cells.

Synthesis, structure, and antiproliferative activity of ruthenium(II) arene complexes with N,O-chelating pyrazolone-based ß-ketoamine ligands.

Novel ruthenium half-sandwich complexes containing (N,O)-bound pyrazolone-based ß-ketoamine ligands have been prepared, and the solid-state structures of one ligand and five complexes have been determined by single-crystal X-ray diffraction. Some of the complexes display moderate cytotoxicity toward the human ovarian cancer cell lines A2780 and A2780cisR, the latter line having acquired resistance to cisplatin.

Selenoquinones stabilized by ruthenium(II) arene complexes: synthesis, structure, and cytotoxicity.

A new series of monoselenoquinone and diselenoquinone π complexes, [(η(6) -p-cymene)Ru(η(4) -C6 R4 SeE)] (R=H, E=Se (6); R=CH3 , E=Se (7); R=H, E=O (8)), as well as selenolate π complexes [(η(6) -p-cymene)Ru(η(5) -C6 H3 R2 Se)][SbF6 ] (R=H (9); R=CH3 (10)), stabilized by arene ruthenium moieties were prepared in good yields through nucleophilic substitution reactions from dichlorinated-arene and hydroxymonochlorinated-arene ruthenium complexes [(η(6) -p-cymene)Ru(C6 R4 XCl)][SbF6 ]2 (R=H, X=Cl (1); R=CH3 , X=Cl (2); R=H, X=OH (3)) as well as the monochlorinated π complexes [(η(6) -p-cymene)Ru(η(5) -C6 H3 R2 Cl)][SbF6 ]2 (R=H (4); R=CH3 (5)). The X-ray crystallographic structures of two of the compounds, [(η(6) -p-cymene)Ru(η(4) -C6 Me4 Se2 )] (7) and [(η(6) -p-cymene)Ru(η(4) -C6 H4 SeO)] (8), were determined. The structures confirm the identity of the target compounds and ascertain the coordination mode of these unprecedented ruthenium π complexes of selenoquinones. Furthermore, these new compounds display relevant cytotoxic properties towards human ovarian cancer cells.

Discovery of a highly tumor-selective organometallic ruthenium(II)-arene complex.

A ruthenium(II)-arene complex with a perfluoroalkyl-ligand was found to display remarkable selectivity toward cancer cells. IC50 values on several cancer cell lines are in the range of 25-45 µM, and no cytotoxic effect was observed on nontumorigenic (HEK-293) cells at concentrations up to 500 µM (the maximum concentration tested). Consequently, this complex was used as the basis for the development of a number of related derivatives, which were screened in cancerous and noncancerous cell lines. The lead compound was then evaluated in vivo for antiangiogenic activity in the CAM model and in a xenografted ovarian carcinoma tumor (A2780) grown on the CAM. A 90% reduction in the tumor growth was observed.

Ligand substitutions between ruthenium-cymene compounds can control protein versus DNA targeting and anticancer activity.

Ruthenium compounds have become promising alternatives to platinum drugs by displaying specific activities against different cancers and favourable toxicity and clearance properties. Nonetheless, their molecular targeting and mechanism of action are poorly understood. Here we study two prototypical ruthenium-arene agents-the cytotoxic antiprimary tumour compound [(η(6)-p-cymene)Ru(ethylene-diamine)Cl]PF6 and the relatively non-cytotoxic antimetastasis compound [(η(6)-p-cymene)Ru(1,3,5-triaza-7-phosphaadamantane)Cl2]-and discover that the former targets the DNA of chromatin, while the latter preferentially forms adducts on the histone proteins. Using a novel 'atom-to-cell' approach, we establish the basis for the surprisingly site-selective adduct formation behaviour and distinct cellular impact of these two chemically similar anticancer agents, which suggests that the cytotoxic effects arise largely from DNA lesions, whereas the protein adducts may be linked to the other therapeutic activities. Our study shows promise for developing new ruthenium drugs, via ligand-based modulation of DNA versus protein binding and thus cytotoxic potential, to target distinguishing epigenetic features of cancer cells.

Synthesis, characterisation and in vitro anticancer activity of hexanuclear thiolato-bridged arene ruthenium metalla-prisms.

Hexanuclear thiolato-bridged arene ruthenium metalla-prisms of the general formula [(p-cymene)(6)Ru(6)(SR)(6)(tpt)(2) ](6+) (R=CH(2)Ph, CH(2)C(6)H(4)-p-tBu, CH(2)CH(2)Ph; tpt=2,4,6-tris(4-pyridyl)-1,3,5-triazine), obtained from the dinuclear precursors [(p-cymene)(2)Ru(2)(SR)(2)Cl(2)], AgCF(3)SO(3) and tpt, have been isolated and fully characterised as triflate salts. The metalla-prisms are highly cytotoxic against human ovarian cancer cells, especially towards the cisplatin-resistant cell line A2780cisR (IC(50) <0.25 µM).

The influence of RAPTA moieties on the antiproliferative activity of peripheral-functionalised poly(salicylaldiminato) metallodendrimers.

Cationic N,O-chelating dendrimers functionalised on the periphery with RAPTA-like (ruthenium(II)-arene-1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) moieties have been synthesised and characterised using NMR and IR spectroscopy, elemental analysis and MALDI-TOF/HR-ESI mass spectrometry. Metallodendrimers from the first to the fourth-generation containing up to 32 peripheral ruthenium-arene-PTA moieties were obtained. Model mononuclear analogues, [{Ru(η(6)-p-cymene)((C(7)H(5)NO)-κ(2)-N,O)(PTA)}((CH(2))(3))][PF(6)] and [{Ru(η(6)hexamethylbenzene)((C(7)H(5)NO)-κ(2)-N,O)(PTA)}((CH(2))(3))][PF(6)], have been prepared and their structures were determined by single crystal X-ray diffraction analysis. The cytotoxicities of the metallodendrimers and their mononuclear analogues were established on A2780 and A2780cisR human ovarian carcinoma cancer cells and model human embryonic kidney (HEK) cells.

Ruthenium(II) arene PTA (RAPTA) complexes: impact of enantiomerically pure chiral ligands.

Organometallic ruthenium(II) arene complexes containing the PTA ligand ([Ru(η(6)-arene)Cl(2)(PTA)], PTA = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane, termed RAPTA) show pharmacologically relevant anti-tumour properties in vitro. Two new enantiomeric pairs of RAPTA compounds, containing the chiral arene (R)- or (S)-2-phenyl-N-(1-phenylethylene)acetamide and either dichlorido or oxalato ligands were synthesised and fully characterised. The stability of the complexes towards hydrolysis was assessed and the dichlorido complexes were found to be more stable towards hydrolysis than the prototype complex RAPTA-C, ([Ru(η(6)-p-cymene)Cl(2)(PTA)]). The cytotoxicity of the compounds towards human ovarian cancer cells is moderate to good with a degree of selectivity towards the cancer cells over healthy cells. More significantly, for the first time we were able to establish the influence of a bulky, chiral group attached to the arene on the cytotoxicity of this class of compound, with the S-enantiomer being more cytotoxic than the R-enantiomer.

Antiproliferative activity of chelating N,O- and N,N-ruthenium(II) arene functionalised poly(propyleneimine) dendrimer scaffolds.

Chelating neutral (N,O) and cationic (N,N) first- and second-generation ruthenium(II) arene metallodendrimers based on poly(propyleneimine) dendrimer scaffolds were obtained from dinuclear arene ruthenium precursors by reactions with salicylaldimine and iminopyridyl dendritic ligands, respectively. The N,N cationic complexes were isolated as hexafluorophosphate salts and were characterised by NMR and IR spectroscopy, and MALDI-TOF mass spectrometry. Related mononuclear complexes were obtained in a similar manner and their molecular structures have been determined by X-ray diffraction analysis. The cytotoxicities of the mono- and multinuclear complexes were established using A2780 and A2780cisR human ovarian carcinoma cancer cell lines.