👤 Dyson PJ.

The new monofunctional Ru(II)-arene complex [(η⁶-arene)Ru(II)(en)Cl]+, where en = 1,2-diaminoethane and the arene is para-terphenyl (complex 1) exhibits promising cytotoxic effects in human tumor cells including those resistant to conventional cisplatin (J. Med. Chem.2008, 51, 5310). The present study is focused on the cellular pharmacology of 1 to elucidate more deeply the mechanisms underlying its antitumor effects. We have identified several cellular mechanisms induced by 1 in human ovarian carcinoma cells, including inhibition of DNA synthesis, overexpression and activation of p53, expression of proapoptotic proteins p21(WAF1) and Bax, G₀/G₁ arrest, and nuclear fragmentation as a result of apoptotic, and, to a much lower extent, also necrotic processes. Thus, 1 inhibits growth of the cancer cells through induction of apoptotic cell death and G₀/G₁ cell cycle arrest. Further investigations have shown that 1 induces apoptosis by regulating the expression of Bcl-2 family proteins. There were significant differences in cellular responses to the treatment with 1 and with conventional cisplatin, particularly in the kinetics and the extent of these responses. In addition, the distinct p53 activation profile of 1 compared with cisplatin provides an explanation for the activity of this ruthenium drug against cisplatin-resistant cells. Hence complex 1 may provide an alternative therapy in patients with acquired cisplatin resistance, particularly with respect to its very low mutagenicity and different mode of action compared to platinum antitumor drugs in clinical use. Show less

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. 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

We have compared the organometallic arene complexes [(eta(6)-biphenyl)M(ethylenediamine)Cl](+) RM175 (M=Ru(II)) and its isostructural osmium(II) analogue AFAP51 (M=Os(II)) for their ability to induce cell detachment resistance from fibronectin, collagen IV and poly-l-lysine, and cell re-adhesion after treatment, their effects on cell migration and cell viability, on matrix metalloproteinases production, and on primary tumour growth of MCa mammary carcinoma, the effect of human serum albumin on their cytotoxicity. There are differences between ruthenium and osmium. The Os complex is up to 6x more potent than RM175 towards highly-invasive breast MDA-MB-231, human breast MCF-7 and human epithelial HBL-100 cancer cells, but whereas RM175 was active against MCa mammary carcinoma in vivo and caused metastasis reduction, AFAP51 was not. Intriguingly the presence of human serum albumin in the growth medium enhanced the cytotoxicity of both compounds. RM175 increased the resistance of MDA-MB-231 cells to detachment from substrates and both compounds inhibited the production of MMP-2. These data confirm the key role of ruthenium itself in anti-metastatic activity. It will be interesting to explore the activity of osmium arene complexes in other tumour models and the possibility of changing the non-arene ligands to tune the anticancer activity of osmium in vivo. 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

We have compared the cancer cell cytotoxicity, cell uptake, and DNA binding properties of the isomeric terphenyl complexes [(eta(6)-arene)Ru(en)Cl](+), where the arene is ortho- (2), meta- (3), or para-terphenyl (1) (o-, m-, or p-terp). Complex 1, the X-ray crystal structure of which confirms that it has the classical "piano-stool" geometry, has a similar potency to cisplatin but is not cross-resistant and has a much higher activity than 2 or 3. The extent of Ru uptake into A2780 or A2780cis cells does not correlate with potency. Complex 1 binds to DNA rapidly and quantitatively, preferentially to guanine residues, and causes significant DNA unwinding. Circular and linear dichroism, competitive binding experiments with ethidium bromide, DNA melting, and surface-enhanced Raman spectroscopic data are consistent with combined intercalative and monofunctional (coordination) binding mode of complex 1. This unusual DNA binding mode may therefore make a major contribution to the high potency of complex 1. Show less

This work is the first in-depth study of osmium binding to DNA and confirms the pharmacological activity of a new class of anticancer metallodrugs. We investigated the interactions between the potential biological target DNA and four osmium(II) arene complexes, of the type [(eta 6-arene)Os(LL)Cl]n+, where arene = biphenyl or p-cymene and LL = ethylenediamine, picolinate, or oxinate in an effort to understand their mechanism of action. Most notably we show that these complexes bind to DNA. DNA adducts of the OsII complexes that exhibit promising cytotoxic effects in ovarian tumor cell lines largely distort its conformation. The data are consistent with DNA binding of the complexes containing biphenyl as the arene ligand that involves combined coordination to guanine residues and noncovalent interactions between the arene ligand and DNA. The results also indicate both a mechanism of action and a detoxification mechanism for OsII arene compounds different from those of cisplatin. Show less

Novel ruthenium(II) organo-metallic compounds are active in ovarian cancer models [Aird RE, Cummings J, Ritchie AA, Muir M, Morris RE, Chen H, et al. In vitro and in vivo activity and cross resistance profiles of novel ruthenium(II) organometallic arene complexes in human ovarian cancer. Br J Cancer 2002;86(10):1652-7]. [(eta6-C6H5C6H5)Ru(en)Cl]+ (as a PF6 salt, where en=ethylenediamine (RM175)) has been evaluated in a 13-cell line panel. Particular sensitivity (approximately 10-fold lower than mean IC50) was noted in breast cancer and non-small cell lung cancer cell lines. In addition, IC50 in the A549 was 2 microM and RM175 (25 mg kg-1, days 1 and 5, i.p.) caused a significant (p=0.004) growth delay in a xenograft model. HC11 [(eta6-tetrahydroanthracene)Ru(en)Cl]PF6 was more potent in the A549 cell line (IC50 0.5 microM). HC11 (25 mg kg-1, days 1, 8 and 15, i.p.) was also active in vivo. Following RM175 25 mg kg-1, days 1 and 5, and 15 mg kg-1, days 1-5, HC11 25 and 40 mg kg-1, day 1, elevated alanine transaminase levels were detected, suggesting hepatotoxicity. No changes were observed in kidney or haematological parameters. In liver sections, multi-focal hepatic necrosis was seen, becoming confluent at high doses of HC11. In vitro studies confirmed that HC11 was more toxic than RM175 to fresh human hepatocytes and equitoxic to mithramycin. Liver toxicity may be related to the arene ligand and modification may reduce the potential for hepatic toxicity, while maintaining the anti-tumour activity seen. Show less

Ruthenium complexes offer the potential of reduced toxicity, a novel mechanism of action, non-cross resistance and a different spectrum of activity compared to platinum containing compounds. Thirteen novel ruthenium(II) organometallic arene complexes have been evaluated for activity (in vitro and in vivo) in models of human ovarian cancer, and cross-resistance profiles established in cisplatin and multi-drug-resistant variants. A broad range of IC50 values was obtained (0.5 to >100 microM) in A2780 parental cells with two compounds (RM175 and HC29) equipotent to carboplatin (6 microM), and the most active compound (HC11) equipotent to cisplatin (0.6 microM). Stable bi-dentate chelating ligands (ethylenediamine), a more hydrophobic arene ligand (tetrahydroanthracene) and a single ligand exchange centre (chloride) were associated with increased activity. None of the six active ruthenium(II) compounds were cross-resistant in the A2780cis cell line, demonstrated to be 10-fold resistant to cisplatin/carboplatin by a mechanism involving, at least in part, silencing of MLH1 protein expression via methylation. Varying degrees of cross-resistance were observed in the P-170 glycoprotein overexpressing multi-drug-resistant cell line 2780AD that could be reversed by co-treatment with verapamil. In vivo activity was established with RM175 in the A2780 xenograft together with non-cross-resistance in the A2780cis xenograft and a lack of activity in the 2780AD xenograft. High activity coupled to non cross-resistance in cisplatin resistant models merit further development of this novel group of anticancer compounds. Show less