Dissimilar effect of organometallic ruthenium complexes on the viability of MDR and non-MDR experimental models

Ruthenium complexes containing triphenylphosphine diamide ligands were prepared, characterized, and tested for their biological activity against various cancer cell lines and the malaria parasite, Plasmodium falciparum. The effect of M (mono-substituted) and B (bis-substituted) complexes on the human cervical carcinoma (HeLa) cell line was investigated using the MTT assay. Five (B2, B3, B5, B6, and B13) of the 24 synthesized ruthenium complexes showed significant effects with IC50 values ranging between 0.3 and 2.3 μM. Evaluation of the potential biomolecular targets of B2 and B13 by fluorescence spectroscopy revealed relevant interactions with BSA and only a weak affinity for ctDNA. Complexes M2, B2, M13 and B13 were selected for further biological characterization. Their effect on the viability of two ovarian cancer cell lines was compared to normal cell lines, denoting their selectivity. Upon treatment of four different drug-resistant gynaecological cancer cell lines, differing in their multidrug-resistant phenotypes, the efficacy of the bis-substituted complexes was shown to be greater than their mono-substituted counterparts. The non-MDR cells are sensitive to all the tested complexes, compared to MDR cells which are less sensitive. Upon investigation of complexes M2, M13, B2, and B13 against sensitive and multidrug-resistant parasite strains of P. falciparum, the bis-substituted complexes were again shown to be the most potent, with submicromolar activity against both strains. Furthermore, the resistance indexes for the complexes were approximately equal to 1, which is at least 5-fold lower than chloroquine diphosphate, suggesting the ability of these complexes to retain their activity in resistant forms of the parasite.

Turn-on fluorescence of ruthenium pyrene complexes in response to bovine serum albumin

Two novel pyrene triphenylphosphine ruthenium conjugates act as fluorescent turn-on beacons for serum albumin, being non-fluorescent in aqueous media but exhibiting strong emission upon binding to BSA. The selective cytotoxicity of the compounds against tumour cells is enhanced upon irradiation by UV-light, paving the way for application in photodynamic therapy under two-photon excitation.

Half-Sandwich Ruthenium Arene Complexes Bearing Clinically Approved Drugs as Ligands: The Importance of Metal-Drug Synergism in Metallodrug Design

A novel strategy in metallodrug discovery today is incorporating clinically approved drugs into metal complexes as coordinating ligands. Using this strategy, various drugs have been repurposed to prepare organometallic complexes to overcome the resistance of drugs and to design promising alternatives to currently available metal-based drugs. Notably, the combination of organoruthenium moiety and clinical drug in a single molecule has been shown, in some instances, to enhance pharmacological activity and reduce toxicity in comparison to the parent drug. Thus, for the past two decades, there has been increasing interest in exploiting metal-drug synergism to develop multifunctional organoruthenium drug candidates. Herein, we summarized the recent reports of rationally designed half-sandwich Ru(arene) complexes containing different FDA-approved drugs. This review also focuses on the mode of coordination of drugs, ligand-exchange kinetics, mechanism of action, and structure-activity relationship of organoruthenated complexes containing drugs. We hope this discussion may serve to shed light on future developments in ruthenium-based metallopharmaceuticals.

Role of the (pseudo)halido ligand in ruthenium(II) p-cymene α-amino acid complexes in speciation, protein reactivity and cytotoxicity

The reactions of the dimeric complexes [RuX₂(η⁶-p-cymene)]₂ (X = Br, I, SCN) with L-proline (ProH) and trans-4-hydroxy-L-proline (HypH), in methanol in the presence of NaOH, afforded [RuX(κ²N,O-Pro)(η⁶-p-cymene)] (X = Br, 1b; I, 1c; SCN, 1d) and [RuX(κ²N,O-Hyp)(η⁶-p-cymene)] (X = Br, 2b; I, 2c; SCN, 2d), respectively. Alternatively, the one-pot, sequential addition of the appropriate α-amino carboxylate and X^- salt to [RuCl₂(η⁶-p-cymene)]₂ led to [RuX(κ²N,O-Pro)(η⁶-p-cymene)] (X = N₃, 1e; NO₂, 1f; CN 1g) and [Ru(N₃)(κ²N,O-Hyp)(η⁶-p-cymene)] (2e). Complexes [Ru(κ³N,O,O'-O₂CCH(NH₂)(R)O)(η⁶-p-cymene)] (R = CH₂, 3h; R = CHMe, 4h; R = CH₂CH₂, 5h) were prepared from the reaction of [RuCl₂(η⁶-p-cymene)]₂ with the appropriate α-amino acid and NaOH in refluxing isopropanol. Treatment of the L-serine (SerH₂) derivative [RuCl(κ²N,O-SerH)(η⁶-p-cymene)] (3a) with 1,3,5-triaza-7-phosphaadamantane (PTA) in water at reflux produced [Ru(κ²N,O-Ser)(κP-PTA)(η⁶-p-cymene)]Cl ([3i]Cl). The products were isolated in good to excellent yields, and were characterized by elemental analysis, IR and multinuclear NMR spectroscopy. The structures of 1f and 2b-e were ascertained by X-ray diffraction studies. The behaviour of the complexes in water and cell culture medium was investigated by multinuclear NMR and UV-Vis spectroscopy, revealing a considerable influence of the monodentate ligand on the aqueous chemistry. Complexes 1d-e, 2d-e, 3h, 4h and [3i]Cl, showing substantial inertness in aqueous media, were assessed for their cytotoxicity towards A2780 and A2780cisR cancer cell lines and the noncancerous HEK 293T cell line. A selection of compounds was also investigated for Ru uptake in A2780 cells and interactions with cytochrome c as a model protein. Combined, these studies provide insights into the previously debated role of the 'leaving' ligand on the biological activity of Ru(II) arene α-amino acid complexes.

Iron Binding in the Ferroxidase Site of Human Mitochondrial Ferritin

Ferritins are nanocage proteins that store iron ions in their central cavity as hydrated ferric oxide biominerals. In mammals, further the L (light) and H (heavy) chains constituting cytoplasmic maxi-ferritins, an additional type of ferritin has been identified, the mitochondrial ferritin (MTF). Human MTF (hMTF) is a functional homopolymeric H-like ferritin performing the ferroxidase activity in its ferroxidase site (FS), in which Fe(II) is oxidized to Fe(III) in the presence of dioxygen. To better investigate its ferroxidase properties, here we performed time-lapse X-ray crystallography analysis of hMTF, providing structural evidence of how iron ions interact with hMTF and of their binding to the FS. Transient iron binding sites, populating the pathway along the cage from the iron entry channel to the catalytic center, were also identified. Furthermore, our kinetic data at variable iron loads indicate that the catalytic iron oxidation reaction occurs via a diferric peroxo intermediate followed by the formation of ferric-oxo species, with significant differences with respect to human H-type ferritin.

Ruthenium(II) Diphosphine Complexes with Mercapto Ligands That Inhibit Topoisomerase IB and Suppress Tumor Growth In Vivo

Ruthenium(II) complexes (Ru1-Ru5), with the general formula [Ru(N-S)(dppe)₂]PF₆, bearing two 1,2-bis(diphenylphosphino)ethane (dppe) ligands and a series of mercapto ligands (N-S), have been developed. The combination of these ligands in the complexes endowed hydrophobic species with high cytotoxic activity against five cancer cell lines. For the A549 (lung) and MDA-MB-231 (breast) cancer cell lines, the IC₅₀ values of the complexes were 288- to 14-fold lower when compared to cisplatin. Furthermore, the complexes were selective for the A549 and MDA-MB-231 cancer cell lines compared to the MRC-5 nontumor cell line. The multitarget character of the complexes was investigated by using calf thymus DNA (CT DNA), human serum albumin, and human topoisomerase IB (hTopIB). The complexes potently inhibited hTopIB. In particular, complex [Ru(dmp)(dppe)₂]PF₆ (Ru3), bearing the 4,6-diamino-2-mercaptopyrimidine (dmp) ligand, effectively inhibited hTopIB by acting on both the cleavage and religation steps of the catalytic cycle of this enzyme. Molecular docking showed that the Ru1-Ru5 complexes have binding affinity by active sites on the hTopI and hTopI-DNA, mainly via π-alkyl and alkyl hydrophobic interactions, as well as through hydrogen bonds. Complex Ru3 displayed significant antitumor activity against murine melanoma in mouse xenograph models, but this complex did not damage DNA, as revealed by Ames and micronucleus tests.

Ruthenium(II) Phosphine/Mercapto Complexes: Their in Vitro Cytotoxicity Evaluation and Actions as Inhibitors of Topoisomerase and Proteasome Acting as Possible Triggers of Cell Death Induction

In this paper, a series of new ruthenium complexes of the general formula [Ru(NS)(dpphpy)(dppb)]PF₆ (Ru1-Ru3), where dpphpy = diphenyl-2-pyridylphosphine, NS ligands = 2-thiazoline-2-thiol (tzdt, Ru1), 2-mercaptopyrimidine (pySm, Ru2), and 4,6-diamino-2-mercaptopyrimidine (damp, Ru3), and dppb = 1,4-bis(diphenylphosphino)butane, were synthesized and characterized by elemental analysis, spectroscopic techniques (IR, UV/visible, and 1D and 2D NMR), and X-ray diffraction. In the characterization, the correlation between the phosphorus atoms and their respective aromatic hydrogen atoms of the compounds in the assignment stands outs, by ¹H-³¹P HMBC experiments. The compounds show anticancer activities against A549 (lung) and MDA-MB-231 (breast) cancer cell lines, higher than the clinical drug cisplatin. All of the complexes are more cytotoxic against the cancer cell lines than against the MRC-5 (lung) and MCF-10A (breast) nontumorigenic human cell lines. For A549 tumor cells, cell cycle analysis upon treatment with Ru2 showed that it inhibits the mitotic phase because arrest was observed in the Sub-G1 phase. Additionally, the compound induces cell death by an apoptotic pathway in a dose-dependent manner, according to annexin V-PE assay. The multitargeted character of the compounds was investigated, and the biomolecules were DNA, topoisomerase IB, and proteasome, as well as the fundamental biomolecule in the pharmacokinetics of drugs, human serum albumin. The experimental results indicate that the complexes do not target DNA in the cells. At low concentrations, the compounds showed the ability to partially inhibit the catalytic activity of topoisomerase IB in the process of relaxation of the DNA plasmid. Among the complexes assayed in cultured cells, complex Ru3 was able to diminish the proteasomal chymotrypsin-like activity to a greater extent.

Glycoconjugated Metal Complexes as Cancer Diagnostic and Therapeutic Agents

The possibility of selectively delivering metal complexes to a defined cohort of cells on the basis of their metabolic features is a highly challenging goal, which may be extremely useful for a series of purposes, including diagnosis and therapy of pathological states, such as cancer. Tumor cells display augmented requests for carbohydrates and, in particular, for glucose in order to sustain their high proliferation rate, which causes an increased glycolytic process (Warburg effect). Since several metal complexes display diagnostic and/or therapeutic properties, their conjugation to carbohydrate portions often induce their preferential accumulation in cancer cells, similarly to what is observed with fluorodeoxyglucose (FDG). In this review we have considered the latest developments of glycoconjugates containing metal complexes in their structures. These compounds are classified as diagnostic or therapeutic agents and are further systematically discussed on the basis of the metal atom they contain. Several diagnostic techniques are possible with these probes, since, depending on the metal species included in their structures, they may be employed in nuclear medicine (PET, SPECT), magnetic resonance imaging, luminescence and phosphorescence. At the same time, the lack of selective cytotoxicity displayed by several metal-based chemotherapeutic agents, may also be solved by the conjugation of these agents to carbohydrate portions. Overall, data so far available reveal the great potential of this chemical class in the early detection and in the cure of severe neoplastic diseases, which still needs to be fully explored in the clinic.

Synthesis, chemical characterization, PARP inhibition, DNA binding and cellular uptake of novel ruthenium(II)-arene complexes bearing benzamide derivatives in human breast cancer cells

Inhibitors of poly(ADP-ribose) polymerase-1 (PARP-1) showed remarkable clinical efficacy in BRCA-mutated tumors. Based on the rational drug design, derivatives of PARP inhibitor 3-aminobenzamide (3-AB), 2-amino-4-methylbenzamide (L1) and 3-amino-N-methylbenzamide (L2), were coordinated to the ruthenium(II) ion, to form potential drugs affecting DNA and inhibiting PARP enzyme. The four conjugated complexes of formula: C1 [(ƞ⁶-toluene)Ru(L1)Cl]PF₆, C2 [(ƞ⁶-p-cymene)Ru(L1)Cl]PF₆, C3 [(ƞ⁶-toluene)Ru(L2)Cl₂] and C4 [(ƞ⁶-p-cymene)Ru(L2)Cl₂], have been synthesized and characterized. Colorimetric 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide (MTT) assay showed the highest antiproliferative activity of C1 in HCC1937, MDA-MB-231, and MCF-7 breast cancer cells. Efficiency of inhibition of PARP-1 enzymatic activity in vitro decreased in order: C2 > C4 > 3-AB>C1 > C3. ICP-MS study of intracellular accumulation and distribution in BRCA1-mutated HCC1937 revealed that C1-C4 entered cells within 24 h. The complex C1 showed the highest intracellular accumulation, nuclear-targeting properties, and exhibited the highest DNA binding (39.2 ± 0.6 pg of Ru per μg of DNA) that resulted in the cell cycle arrest in the S phase.

Synthesis, structure and anti-cancer activity of osmium complexes bearing π-bound arene substituents and phosphane Co-Ligands: A review

While many examples of osmium complexes, as anti-cancer agents, have been reported and some reviews have been devoted to this topic, a particularly interesting and synthetically accessible sub-class of these compounds namely those bearing a π- bound arene and phosphane co-ligand have escaped review. These complexes have made a surprisingly late entry in the literature (2005) in terms of anti-cancer investigations. This is somewhat surprising considering the plethora of analogous complexes that have been reported for the lighter analogue, ruthenium. Herein we review all complexes, neutral and ionic, bearing the "(ƞ⁶-arene)Os(PR₃)" moiety focusing on their synthesis, reactivity, structural features (by X-ray diffraction analysis) as well as anti-cancer biological activity. An attempt is made throughout the article to contrast these to each other and to analogous Ru systems, and a full summary of all existing in vitro biological data is presented.

Effect of N,N Coordination and RuII Halide Bond in Enhancing Selective Toxicity of a Tyramine-Based RuII (p-Cymene) Complex

Ruthenium compounds are promising anticancer candidates owing to their lower side-effects and encouraging activities against resistant tumors. Half-sandwich piano-stool type Ru^II compounds of general formula [(L)Ru^II(η⁶-arene)(X)]⁺ (L = chelating bidentate ligand, X = halide) have exhibited significant therapeutic potential against cisplatin-resistant tumor cell lines. In Ru^II (p-cymene) based complexes, the change of the halide leaving group has led to several interesting features, viz., hydrolytic stability, resistance toward thiols, and alteration in pathways of action. Tyramine is a naturally occurring monoamine which acts as a catecholamine precursor in humans. We synthesized a family of N,N and N,O coordinated Ru^II (p-cymene) complexes, [(L)Ru^II(η⁶-arene)(X)]⁺ (1-4), with tyramine and varied the halide (X = Cl, I) to investigate the difference in reactivity. Our studies showed that complex 2 bearing N,N coordination with an iodido leaving group shows selective in vitro cytotoxicity against the pancreatic cancer cell line MIA PaCa-2 (IC₅₀ ca. 5 μM) but is less toxic to triple-negative breast cancer (MDA-MB-231), hepatocellular carcinoma (Hep G2), and the normal human foreskin fibroblasts (HFF-1). Complex 2 displays stability toward hydrolysis and does not bind with glutathione, as confirmed by ¹H NMR and ESI-HRMS experiments. The inert nature of 2 leads to enhancement of cytotoxicity (IC₅₀ = 5.3 ± 1 μM) upon increasing the cellular treatment time from 48 to 72 h.

The interactions of the ruthenium(II)-cymene complexes with lysozyme and cytochrome c

The reactions of four cymene-capped ruthenium(II) compounds with pro-apoptotic protein, cytochrome c (Cyt), and anti-proliferative protein lysozyme (Ly) in carbonate buffer were investigated by ESI-MS, UV-vis absorption, and CD spectroscopy. The complexes with two chloride ligands (C2 and C3) were more reactive toward proteins than those with only one (C1 and C4), and the complex with S,N-chelating ligand (C4) was less reactive than one with O,N-chelating ligand (C1). Dehalogenated complexes are most likely species, initially coordinating proteins for all tested complexes. During the time, protein adducts vividly exchanged non-arene organic ligand L with CO₃^2- and OH^-, while cymene moiety was retained. In water, only dehalogenated adducts were identified suggesting that in vivo, in the presence of various anions, dynamic ligand exchange could generate different intermediate protein species. Although all complexes reduced Cyt, the reduction was not dependent on their reactivity to protein, implying that initially noncovalent binding to Cyt occurs, causing its reduction, followed by coordination to protein. Cyt reduction was accompanied with rupture of ferro-Met 80 and occupation of this hem coordination site by a histidine His-33/26. Therefore, in Cyt with C2 and C3, less intensive reduction of hem iron leaves more unoccupied target residues for Ru coordination, leading to more efficient formation of covalent adducts, in comparison to C1 and C4. This study contributes to development of new protein-targeted Ru(II) cymene complexes, and to the design of new cancer therapies based on targeted delivery of Ru(II) arene complexes bound on pro-apoptotic/anti-proliferative proteins as vehicles.

Anticancer Potential of Diiron Vinyliminium Complexes

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram-scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC₅₀ values in the low-to-mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non-tumoral human embryonic kidney (HEK-293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron-based anticancer candidates.

Photocytotoxic Pt(iv) complexes as prospective anticancer agents

The use of Pt(iv) complexes as potential anticancer drugs is attractive, because they have higher stability and less side effects than Pt(ii) compounds. Moreover, some Pt(iv) complexes can also be activated with light, opening an avenue to photochemotherapy. Our purpose is to widen the library of photoactivatable Pt(iv)-based prodrugs and here we report on the oxidation of the Pt(ii) compound [PtCl(4'-phenyl-2,2':6',2''-terpyridine)][CF₃SO₃] (1) with PhICl₂ or H₂O₂. The synthetic procedure avoids the formation of multiple species: the treatment with PhICl₂ produces the Pt(iv) complex with axial chlorides, [PtCl₃(4'-phenyl-2,2':6',2''-terpyridine)][CF₃SO₃] (2), while H₂O₂ oxidation and post-synthesis carboxylation produce [Pt(OCOCH₃)₂Cl(4'-phenyl-2,2':6',2''-terpyridine)][CF₃SO₃] (3), bearing acetates in the axial positions. 2 and 3 are stable in physiological-like buffers and in DMSO in the dark, but undergo photoreduction to 1 upon irradiation at 365 nm. Their stability toward reduction is a fundamental parameter to consider: cyclic voltammetry experiments show that the 2 electron reduction Pt(iv) → Pt(ii) occurs at a more negative potential for 3, because of the greater stabilization provided by the acetate axial groups; noteworthily, 3 is stable for hours also in the presence of mM concentration of glutathione. The cytotoxicity of 2 and 3 toward A2780 and A2780cis cell lines reveals that 3 is the least toxic in the dark, but is able to produce cytotoxic effects far higher than cisplatin when irradiated. To shed light on the mechanistic aspects, the interaction with protein and DNA models has been explored through high-resolution mass spectrometry revealing that 2 and 3 behave as prodrugs, but are able to bind to biological targets only after irradiation.

Synthesis and Anticancer Activity of [RuCl2(η6-arene)(aroylthiourea)] Complexes-High Activity against the Human Neuroblastoma (IMR-32) Cancer Cell Line

Eight new organometallic Ru(II)-arene complexes of the type [RuCl₂(η⁶-arene)(η¹-S-aroylthiourea)] (arene = p-cymene or benzene) were synthesized in order to evaluate the effect of the arene moiety and the substituent of the aroylthiourea ligand on the cytotoxicity of the complexes. The ligands (L1 and L2) and complexes (1-8) were characterized using analytical and spectroscopic (UV-visible, infrared, ¹H NMR, ¹³C NMR, and mass) methods. The structure of the ligands (L1 and L2) and complexes (1 and 3-6) was obtained from single-crystal X-ray diffraction studies. The cytotoxicity of the complexes was evaluated against four different cancer cell lines: MCF-7 (breast), COLO 205 (colon), A549 (lung), and IMR-32 (neuroblastoma). All the complexes showed good cytotoxicity and the highest was in the IMR-32 cell line, which articulates the specificity of these complexes toward the IMR-32 cancer cell line. The complexes 5, 7, and 8 exhibited remarkable cytotoxicity in the entire cancer cell lines tested, which was comparable with the standard drug, cisplatin. The anticancer mechanism of the complexes 3 and 7 in IMR-32 cells was evaluated by bright-field microscopy, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), DNA damage, and caspase-3 analyses. The cells treated with the complexes showed upregulated caspase-3 compared to the control, and it was found that ROS and MMP were dose-dependent on analysis. Also, bright-field microscopy and 4',6-diamidino-2-phenylindole (DAPI) staining have correspondingly shown cellular membrane blebbing and DNA damage, which were morphological hallmarks of apoptosis. The study concluded that the complexes promoted the oxidative stress-mediated apoptotic death of the cancer cells through the generation of intracellular ROS, depletion of MMP, and damage of the nuclear material.

The NAMI A - human ferritin system: a biophysical characterization

The reaction of the antimetastatic ruthenium(iii) drug NAMI A with human H-chain ferritin (HuHf) was investigated through a variety of biophysical methods. We observed that the addition of HuHf to NAMI A solutions significantly increases the rate of spontaneous NAMI A hydrolysis suggesting the occurrence of a direct metallodrug-protein interaction. The resulting hydrolyzed Ru species binds the protein mostly forming a relatively tight 1 : 1 ruthenium/ferritin (subunit) adduct that was then separated and characterized. Notably, this adduct shows a characteristic CD spectrum in the visible region, which is diagnostic of the existence of at least one protein bound ruthenium center. The crystal structure of this NAMI A/HuHf adduct was subsequently solved at 1.58 Å resolution; clear evidence is given for the selective binding of a single Ru ion to His105 of each subunit with concomitant release of all other original Ru ligands in agreement with previous observations. We also noted that NAMI A produces a partial inhibition of HuHf ferroxidase activity. The implications of the above results are discussed.

Reactions of Auranofin and Its Pseudohalide Derivatives with Serum Albumin Investigated through ESI-Q-TOF MS

The reactions of auranofin and three pseudohalide derivatives with bovine serum albumin were explored by ESI-Q-TOF mass spectrometry; a detailed molecular description of the resulting adducts is achieved revealing even subtle differences in reactivity within this series of gold(I) complexes. Our study shows that this kind of investigative approach, formerly applied to the interactions of metal-based drugs with small model proteins of MW 10-15 kDa, e.g., cytochrome c and lysozyme, may now be extended with success to far larger proteins such as serum albumin (MW 66 kDa).

α-Diimines as Versatile, Derivatizable Ligands in Ruthenium(II) p-Cymene Anticancer Complexes

α-Diimines are among the most robust and versatile ligands available in synthetic coordination chemistry, possessing finely tunable steric and electronic properties. A series of novel cationic ruthenium(II) p-cymene complexes bearing simple α-diimine ligands, [(η⁶- p-cymene)RuCl{κ² N-(HCNR)₂}]NO₃ (R = Cy, [1]NO₃; R = 4-C₆H₁₀OH, [2]NO₃; R = 4-C₆H₄OH, [3]NO₃), were prepared in near-quantitative yields as their nitrate salts. [2]NO₃ displays high water solubility. The potential of the α-diimine ligand in [3]NO₃ as a carrier of bioactive molecules was investigated via esterification reactions with the hydroxyl groups. Thus, the double-functionalized derivatives [(η⁶- p-cymene)RuCl{κ² N-(HCN(4-C₆H₄OCO-R))₂}]NO₃ (R = aspirinate, [5]NO₃; valproate, [6]NO₃) and also [4]Cl (R = Me) were obtained in good-to-high yields. UV-vis and multinuclear NMR spectroscopy and cyclic voltammetric studies in aqueous solution revealed only minor ruthenium chloride hydrolytic cleavage, biologically accessible reduction potentials, and pH-dependent behavior of [3]NO₃. Density functional theory analysis was performed in order to compare the Ru-Cl bond strength in [1]⁺ with the analogous ethylenediamine complex, showing that the higher stability observed in the former is related to the electron-withdrawing properties of the α-diimine ligand. In vitro cytotoxicity studies were performed against tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK-293) cell lines, with the complexes bearing simple α-diimine ligands ranging from inactive to IC₅₀ values in the low micromolar range. The complexes functionalized with bioactive components, i.e., [5]NO₃ and [6]NO₃, exhibited a marked increase in the cytotoxicity with respect to the precursor [3]NO₃.

Tuning the cytotoxicity of ruthenium(ii) para-cymene complexes by mono-substitution at a triphenylphosphine/phenoxydiphenylphosphine ligand

The cytotoxic activities of novel Ru(ii) arene complexes with variably mono-substituted phosphine ligands have been assessed towards MDA-MB-231 and A2780 cancer cell lines.