Organometallic chemistry, biology and medicine: ruthenium arene anticancer complexes

Energetics, conformation, and recognition of DNA duplexes modified by monodentate Ru(II) complexes containing terphenyl arenes

We studied the thermodynamic properties, conformation, and recognition of DNA duplexes site-specifically modified by monofunctional adducts of Ru(II) complexes of the type [Ru(II)(eta(6)-arene)(Cl)(en)](+), in which arene=para-, meta-, or ortho-terphenyl (complexes 1, 2, and 3, respectively) and en=1,2-diaminoethane. It has been shown (J. Med. Chem. 2008, 51, 5310) that 1 exhibits promising cytotoxic effects in human tumor cells, whereas 2 and 3 are much less cytotoxic; concomitantly with the high cytotoxicity of 1, its DNA binding mode involves combined intercalative and monofunctional (coordination) binding modes, whereas less cytotoxic compounds 2 and 3 bind to DNA only through a monofunctional coordination to DNA bases. An analysis of conformational distortions induced in DNA by adducts of 1 and 2 revealed more extensive and stronger distortion and concomitantly greater thermodynamic destabilization of DNA by the adducts of nonintercalating 2. Moreover, affinity of replication protein A to the DNA duplex containing adduct of 1 was pronouncedly lower than to the adduct of 2. On the other hand, another damaged-DNA-binding protein, xeroderma pigmentosum protein A, did not recognize the DNA adduct of 1 or 2. Importantly, the adducts of 1 induced a considerably lower level of repair synthesis than the adducts of 2, which suggests enhanced persistence of the adducts of the more potent and intercalating 1 in comparison with the adducts of the less potent and nonintercalating 2. Also interestingly, the adducts of 1 inhibited DNA polymerization more efficiently than the adducts of 2, and they could also be bypassed by DNA polymerases with greater difficulty. Results of the present work along with those previously published support the view that monodentate Ru(II) arene complexes belong to a class of anticancer agents for which structure-pharmacological relationships might be correlated with their DNA-binding modes.

Discovery of a strongly apoptotic ruthenium complex through combinatorial coordination chemistry

A strategy for combinatorial parallel coordination chemistry is introduced that provides access to libraries of tris-heteroleptic ruthenium complexes in an economical fashion. Using this method, a library of 560 constitutionally unique, monocationic ruthenium complexes was synthesized, followed by a screening for anticancer activity and resulting in the identification of three hits with promising cytotoxic properties in HeLa cancer cells. A subsequent structure-activity relationship led to the discovery of the surprisingly simple anticancer complex [Ru(tBu(2)bpy)(2)(phox)]PF(6) (complex 1), with tBu(2)bpy = 4,4'-di-tert-buty-2,2'-bipyridine and Hphox = 2-(2'-hydroxyphenyl)oxazoline, displaying an LC(50) value in HeLa cells of 1.3 microM and 0.3 microM after incubation for 24 and 72 h, respectively. Complex 1 also shows remarkable antiproliferative and apoptotic properties at submicromolar concentrations in more clinically relevant Burkitt-like lymphoma cells. A reduction of the mitochondrial membrane potential by 1 indicates the involvement of the intrinsic pathway of programmed cell death. Further investigations reveal that 1 requires caspase-3 for the induction of apoptosis but is insensitive to the proapoptotic and antiapoptotic proteins Smac and Bcl-2, respectively.

Studies of the Antiproliferative Activity of Ruthenium (II) Cyclopentadienyl-Derived Complexes with Nitrogen Coordinated Ligands

Four cationic ruthenium(II) complexes with the formula [Ru(eta(5)-C(5)H(5))(PPh(3))(2)](+), with L = 5-phenyl-1H-tetrazole (TzH) 1, imidazole (ImH) 2, benzo[1,2-b;4,3-b'] dithio-phen-2-carbonitrile (Bzt) 3, and [5-(2-thiophen-2-yl)-vinyl]-thiophene-2-carbonitrile] (Tvt) 4 were prepared and characterized in view to evaluate their potentialities as antitumor agents. Studies by Circular Dichroism indicated changes in the secondary structure of ct-DNA. Changes in the tertiary structure of pBR322 plasmid DNA were also observed in gel electrophoresis experiment and the images obtained by atomic force microscopy (AFM) suggest strong interaction with pBR322 plasmid DNA; the observed decreasing of the viscosity with time indicates that the complexes do not intercalate between DNA base pairs. Compounds 1, 2, and 3 showed much higher cytotoxicity than the cisplatin against human leukaemia cancer cells (HL-60 cells).

Antitumor activity of bent metallocenes: electronic structure analysis using DFT computations

The antitumor activities of bent metallocenes [Cp-M-Cp](2+) (M = Ti, V, Nb, Mo) and complexes of them with guanine, adenine, thymine and cytosine nucleotides have been probed using electronic structure calculations. DFT/BP86 calculations have revealed that the bent metallocene-nucleotide interaction strongly depends on the stability of the hydrolyzed form of the bent metallocene dichloride [Cp(2)M](2+) species, and in turn the stability of the [Cp(2)M](2+) species strongly depends on the electronic structure of [Cp(2)M](2+). Detailed electronic structure and Walsh energy analyses have been carried out for the hydrolyzed forms of four [Cp-M-Cp](2+) (M = Ti, V, Nb, Mo) species to find out why the bent structure is unusually stable. Energy changes that occur during the bending process in frontier molecular orbitals as well as the p(π)-d(π) overlap have been invoked to account for the anticipated antitumor activities of these species. The bonding situation and the interactions in bent metallocene-nucleotide adducts were elucidated by fragment analysis. Of the four nucleotides complexed with the four bent metallocenes, adenine and guanine show better binding abilities than the other two nucleotides. Metallocenes of second-row transition metals exhibit better binding with pyrimidine-base nucleotides. In particular, the Lewis acidic bent metallocenes interact strongly with nucleotides. The antitumor activity is directly related to the binding strength of the bent metallocene with nucleotide adducts, and the computed interaction energy values correlate very well with the experimentally observed antitumor activities.

Synthesis and biological applications of ionic triphenyltin(IV) chloride carboxylate complexes with exceptionally high cytotoxicity

The reaction of N-phthaloylglycine (P-GlyH), N-phthaloyl-l-alanine (P-AlaH), and 1,2,4-benzenetricarboxylic 1,2-anhydride (BTCH) with triethylamine led to the formation of the corresponding ammonium salts [NHEt(3)][P-Gly] (1), [NHEt(3)][P-Ala] (2) and [NHEt(3)][BTC] (3) in very high yields. The subsequent reaction of 1-3 with triphenyltin(iv) chloride (1 : 1) yielded the compounds [NHEt(3)][SnPh(3)Cl(P-Gly)] (4), [NHEt(3)][SnPh(3)Cl(P-Ala)] (5), and [NHEt(3)][SnPh(3)Cl(BTC)] (6), respectively. The molecular structure of 4 was determined by X-ray diffraction studies. The cytotoxic activity of the ammonium salts (1-3) and the triphenyltin(iv) chloride derivatives (4-6) were tested against human tumor cell lines from five different histogenic origins: 8505C (anaplastic thyroid cancer), A253 (head and neck cancer), A549 (lung carcinoma), A2780 (ovarian cancer) and DLD-1 (colon cancer). Triphenyltin(iv) chloride derivatives (4-6) show very high activity against these cell lines while the ammonium salts of the corresponding carboxylic acids (1-3) are totally inactive. The most active compound is 4 which is 50 times more active than cisplatin. Compound 4 is found to induce apoptosis via extrinsic pathways on DLD-1 cell lines, probably by accumulation of caspases 2, 3 and 8. Furthermore, compound 4 seems to cause disturbances in G1 and G2/M phases in cell cycle of DLD-1 cell line.

The impact of ion pair association upon the 1H NMR spectra of cationic complexes akin to Grubbs catalysts

A reconsideration of the (1)H NMR spectra of cationic transition metal complexes exhibiting the features of cyclophanes on the basis of Mislow's classification of topic groups arrives at the conclusion that the spectral changes triggered by chiral counterions reflect an intracationic diastereotopication of enantiotopic protons rather than the existence of pairs of long-lived diastereomeric ion pairs.

The ruthenium complex cis-(Dichloro)Tetraammineruthenium(III) chloride presents immune stimulatory activity on human peripheral blood mononuclear cells

Ruthenium compounds in general are well suited for medicinal applications. They have been investigated as immunosuppressants, nitric oxide scavengers, antimicrobial agents, and antimalarials. The aim of this study is to evaluate the immunomodulatory activity of cis-(dichloro)tetraammineruthenium(III) chloride (cis-[RuCl(2)(NH(3))(4)]Cl) on human peripheral blood mononuclear cells (PBMC). The cytotoxic studies performed here revealed that the ruthenium(III) complex presents a cytotoxic activity towards normal human PBMC, only at very high concentration. Results also showed that cis-[RuCl(2)(NH(3))(4)]Cl presents a dual role on PBMC stimulating proliferation and interleukin-2 (IL-2) production at low concentration and inducing cytotoxicity, inability to proliferate, and inhibiting IL-2 production at high concentration. The noncytotoxic activity of cis-[RuCl(2)(NH(3))(4)]Cl at low concentration towards PBMC, which correlates with the small number of annexin V positive cells and also the absence of DNA fragmentation, suggest that this compound does not induce apoptosis on PBMC. For the first time, we show that, at low concentration (10-100 microg L(-1)), the cis-[RuCl(2)(NH(3))(4)]Cl compound induces peripheral blood lymphocytes proliferation and also stimulates them to IL-2 production. These results open a new potential applicability of ruthenium(III) complexes as a possible immune regulatory compound acting as immune suppressor at high concentration and as immune stimulator at low concentration.

Synthesis, Structure, and Selective Cytotoxicity of Organometallic Cp*RuII O-Alkyl-N-phenylcarbamate Sandwich Complexes

Tetraphenylborate salts of the η6-arene Cp*RuII O-alkyl-N-phenyl carbamate organometallic sandwich complexes, [Cp*Ru(PhNHCO2R)]BPh4 for R = Me (1), Et (2), and n-Pr (3), have been prepared by a facile one-pot reaction between ruthenium trichloride, pentamethylcyclopentadiene, and phenylisocyanate in refluxing alcohol solutions, and have been characterized by Fourier-transform IR and NMR spectroscopy, electrospray mass spectrometry, and single-crystal X-ray structure determinations. In vitro cytotoxicity studies show the complexes to be potent growth inhibitors for a range of tumour cell lines, while expressing significantly lower levels of toxicity towards a normal human fibroblast cell line.

Tetranuclear coordination assemblies based on half-sandwich ruthenium(II) complexes: noncovalent binding to DNA and cytotoxicity

The reaction of [(cymene)RuCl(2)](2) with K(2)Hoxonate (H(3)oxonic = 4,6-dihydroxy-2-carboxy-1,3,5-triazine acid) in methanol leads to the formation of the dinuclear half-sandwich ruthenium(II) complex [(cymene)(2)Ru(2)(mu-Hoxonato)Cl(2)] (1a). Removal of the chloride ligands of 1a by treatment with AgCF(3)SO(3) yields [(cymene)(2)Ru(2)(mu-Hoxonato)(CF(3)SO(3))(2)] (1b), which, upon posterior reaction with N,N'-linkers (L = 4,4'-bipyridine (4,4'-bpy), 4,7-phenantroline (4,7-phen)), gives rise to the formation of the tetranuclear open boxes [(cymene)(4)Ru(4)(mu-Hoxonato)(2)(mu-N,N'-L)(2)](CF(3)SO(3))(4) (2a, L = 4,4'-bpy; 2b, L = 4,7-phen). These systems have been characterized by (1)H NMR, UV-vis, and ESI-MS. The single-crystal structures of the dinuclear precursor 1a and of the clathrate 2b 4,7-phen have been determined. The interaction of these systems with cysteine, mononucleotides, and calf-thymus DNA has been studied by means of (1)H NMR, UV-vis, circular dicroism, competitive binding assays, and atomic force microscopy imaging. The results show that the robust tetracationic ruthenium(II) cyclic systems 2a and 2b do not give ligand exchange reactions toward biorelevant ligands. Nevertheless, these systems are able to noncovalently bind to DNA, probably at the surface of the major groove, inducing significant conformational changes in this biomolecule. It is also interesting to note that compounds 2a and 2b, in spite of only giving supramolecular interactions with biomolecules, exhibit antitumor activity, particularly toward the human ovarian cancer cell line A2780cisR, showing acquired resistance to cisplatin, with respective 4.6 and 8.3 microM IC(50) values.

Use of ion mobility mass spectrometry and a collision cross-section algorithm to study an organometallic ruthenium anticancer complex and its adducts with a DNA oligonucleotide

We report the development of an enhanced algorithm for the calculation of collision cross-sections in combination with Travelling-Wave ion mobility mass spectrometry technology and its optimisation and evaluation through the analysis of an organoruthenium anticancer complex [(eta6-biphenyl)Ru(II)(en)Cl]+. Excellent agreement was obtained between the experimentally determined and theoretically determined collision cross-sections of the complex and its major product ion formed via collision-induced dissociation. Collision cross-sections were also experimentally determined for adducts of this ruthenium complex with the single-stranded oligonucleotide hexamer d(CACGTG). Ion mobility tandem mass spectrometry measurements have allowed the binding sites for ruthenium on the oligonucleotide to be determined.