Anti-toxoplasma activity and DNA-binding of copper(II) and zinc(II) coordination compounds with 5-nitroimidazole-based ligands.

Tetrahedral copper(II) and zinc(II) coordination compounds from 5-nitroimidazole derivatives, viz. 1-(2-chloroethyl)-2-methyl-5-nitroimidazole (cenz) and ornidazole 1-(3-chloro-2-hydroxypropyl)-2-methyl-5-nitroimidazole (onz), were synthesized and spectroscopically characterized. Their molecular structures were determined by X-ray diffraction studies. The complexes [Cu(onz)2X2], [Zn(onz)2X2], [Cu(cenz)2X2] and [Zn(cenz)2X2] (X- = Cl, Br), are stable in solution and exhibit positive LogD7.4 values that are in the range for molecules capable of crossing the cell membrane via passive difussion. Their biological activity against Toxoplasma gondi was investigated, and IC50 and lethal dose (LD50) values were determined. The ornidazole copper(II) compounds showed very good antiparasitic activity in its tachyzoite morphology. The interaction of the coordination compounds with DNA was examined by circular dichroism, fluorescence (using intercalating ethidium bromide and minor groove binding Hoechst 33258) and UV-Vis spectroscopy. The copper(II) compounds interact with the minor groove of the biomolecule, whereas weaker electrostatic interactions take place with the zinc(II) compounds. The spectroscopic data achieved for the two series of complexes (namely with copper(II) and zinc(II) as metal center) agree with the respective DNA-damage features observed by gel electrophoresis.

Cobalt(III)-py2en systems as potential carriers of ß-ketoester-based ligands.

Two cobalt(III) complexes containing different ß-ketoesters, namely [CoIII(L1)(py2en)](ClO4)2·H2O (1) and [CoIII(L2)(py2en)](ClO4)2 (2) (py2en = N,N'-bis(pyridin-2-ylmethyl)ethylenediamine; L1- = methylacetoacetate; L2- = ethyl 4-chloroacetoacetate) have been prepared and investigated as prototypes of bioreductive prodrugs. The presence of ß-ketoester and py2en ligands in 1 and 2, as well as the perchlorate counterions, was supported by IR spectroscopy and CHN elemental analysis. The composition molecular structure of both complexes was confirmed by NMR spectroscopy and ESI mass spectrometry. Structural information was also obtained for 2via X-ray diffraction analysis. The redox properties indicate that 1 and 2 are suitable for reduction under biological conditions. Investigation of DNA-interacting suggest that 1 and 2 bind DNA via electrostatic forces. Both complexes may be employed as possible platforms for the delivery of biologically active compounds, since their reaction with ascorbic acid in PBS at pH 6.2 and 7.4 at 37°C results in the release of the ß-ketoester ligands upon Co(III)/Co(II) reduction.

Cytotoxicity of osmium(II) and cycloosmated half-sandwich complexes from 1-pyrenyl-containing phosphane ligands.

Five metal-arene complexes of formula [MX2(η6-p-cymene)(diR(1-pyrenyl)phosphane)] (M = Os or Ru, X = Cl or I, R = isopropyl or phenyl) and symbolized as MRX2 were synthesized and fully characterized, namely OsiPrCl2, OsiPrI2, OsPhCl2, OsPhI2 and RuPhI2. Furthermore, nine cyclometalated half-sandwich complexes of formula [MX-(η6-p-cymene)(k2C-diR(1-pyrenyl)phosphane)] (M = Os or Ru, X = Cl or I, R = isopropyl or phenyl) or [M(η6-p-cymene)(kS-dmso)(k2C-diR(1-pyrenyl)phosphane)]PF6 (M = Os or Ru, R = isopropyl or phenyl) and symbolized as c-MRX were prepared; hence, c-OsiPrCl, c-OsiPrI, c-OsiPrdmso, c-OsPhCl, c-OsPhI, c-OsPhdmso, c-RuPhCl, c-RuPhI and c-RuPhdmso were obtained and fully characterized. The crystal structures of ten out of the fourteen complexes were solved. All complexes exhibit notable cytotoxic properties against A549 (Lung Adenocarcinoma) human cells, with IC50 values ranging from 48 to 1.42 µM. In addition, complex c-OsiPrdmso shows remarkable toxic behaviours agains other cell lines, namely MCF7 (breast carcinoma), MCF10A (non-tumorigenic epithelial breast) and MDA-MB-435 (melanoma) human cells, as illustrated by IC50 values of 4.36, 4.71 and 2.32 µM, respectively. Finally, it has been found that OsiPrI2 affects the cell cycle of A549 cells, impeding their replication (i.e., the cell cycle is blocked), whereas OsPhI2 (namely with phenyl groups instead of isopropyl ones) does not induce this effect.

Steric hindrance, ligand ejection and associated photocytotoxic properties of ruthenium(II) polypyridyl complexes.

Two ruthenium(II) polypyridyl complexes were prepared with the {Ru(phen)2}2+ moiety and a third sterically non-hindering bidentate ligand, namely 2,2'-dipyridylamine (dpa) and N-benzyl-2,2'-dipyridylamine (Bndpa). Hence, complexes [Ru(phen)2(dpa)](PF6)2 (1) and [Ru(phen)2(Bndpa)](PF6)2 (2) were characterized and their photochemical behaviour in solution (acetonitrile and water) was subsequently investigated. Compounds 1 and 2, which do not exhibit notably distorted octahedral coordination environments, contrarily to the homoleptic "parent" compound [Ru(phen)3](PF6)2, experience two-step photoejection of the dpa and Bndpa ligand upon irradiation (1050-430 nm) for several hours. DNA-binding studies revealed that compounds 1 and 2 affect the biomolecule differently upon irradiation; while 2 solely modifies its electrophoretic mobility, complex 1 is also capable of cleaving it. In vitro cytotoxicity studies with two cancer-cell lines, namely A549 (lung adenocarcinoma) and A375 (melanoma), showed that both 1 and 2 are not toxic in the dark, while only 1 is significantly cytotoxic if irradiated, 2 remaining non-toxic under these conditions. Light irradiation of the complex cation [Ru(phen)2(dpa)]2+ leads to the generation of transient Ru species that is present in the solution medium for several hours, and that is significantly cytotoxic, ultimately producing non-toxic free dpa and [Ru(phen)(OH2)2]2+.

Three to Tango: Inhibitory Effect of Quercetin and Apigenin on Acetylcholinesterase, Amyloid-ß Aggregation and Acetylcholinesterase-Amyloid Interaction.

One of the pathological hallmarks of Alzheimer's disease (AD) is the formation of amyloid-ß plaques. Since acetylcholinesterase (AChE) promotes the formation of such plaques, the inhibition of this enzyme could slow down the progression of amyloid-ß aggregation, hence being complementary to the palliative treatment of cholinergic decline. Antiaggregation assays performed for apigenin and quercetin, which are polyphenolic compounds that exhibit inhibitory properties against the formation of amyloid plaques, reveal distinct inhibitory effects of these compounds on Aß40 aggregation in the presence and absence of AChE. Furthermore, the analysis of the amyloid fibers formed in the presence of these flavonoids suggests that the Aß40 aggregates present different quaternary structures, viz., smaller molecular assemblies are generated. In agreement with a noncompetitive inhibition of AChE, molecular modeling studies indicate that these effects may be due to the binding of apigenin and quercetin at the peripheral binding site of AChE. Since apigenin and quercetin can also reduce the generation of reactive oxygen species, the data achieved suggest that multitarget catechol-type compounds may be used for the simultaneous treatment of various biological hallmarks of AD.

Anti-Amyloid Drug Screening Methods Using Bacterial Inclusion Bodies.

Amyloid aggregation is linked to a number of human disorders that range from non-neurological illnesses such as type 2 diabetes to neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. The formation of insoluble protein aggregates with amyloid conformation inside bacteria, namely, in bacterial inclusion bodies, offers the possibility to use bacteria as simple models to study amyloid aggregation processes and potential effects of both anti-amyloid drugs and/or pro-aggregative compounds. This chapter describes fast, simple, inexpensive, highly reproducible, and tunable in vitro and in cellulo methods that use bacterial inclusion bodies as preliminary screening tools for anti-amyloid drugs.

DNA-interacting properties of two analogous square-planar cis-chlorido complexes: copper versus palladium.

Two square-planar coordination compounds, namely [Cu(CPYA)Cl2] (1) and [Pd(CPYA)Cl2] (2), were prepared from the ligand 4-chloro-N-(pyridin-2-ylmethyl)aniline (CPYA) and two chloride salts, and were fully characterized, including by X-ray diffraction. Spectroscopic, electrophoretic and AFM studies revealed that the two isostructural compounds were interacting differently with DNA. In both cases, the initial interaction involves electrostatic contacts of the CPYA ligand in the minor groove (as suggested by molecular docking), but subsequent strong binding occurs with the palladium(II) complex 2, whereas the binding with the copper complex 1 is weaker and concentration dependent. The strong binding of 2 eventually leads to the cleavage of the double strand and the redox activity of 1 allows to oxidatively cleave the biomolecule.

Piano-Stool Ruthenium(II) Complexes with Delayed Cytotoxic Activity: Origin of the Lag Time.

We have recently reported a series of piano-stool ruthenium(II) complexes of the general formula [RuCl2(η6-arene)(P(1-pyrenyl)R2R3)] showing excellent cytotoxic activities (particularly when R2 = R3 = methyl). In the present study, new members of this family of compounds have been prepared with the objective to investigate the effect of the steric hindrance of a bulky phosphane ligand, namely diisopropyl(1-pyrenyl)phosphane (L), on exchange reactions involving the coordinated halides (X = Cl, I). Two η6-arene rings were used, i.e. η6-methyl benzoate (mba) and η6-p-cymene (p-cym), and four complexes were synthesized, namely [RuCl2(mba)(L)] (1Cl2iPr), [RuI2(mba)(L)] (1I2iPr), [RuCl2(p-cym)(L)] (2Cl2iPr), and [RuI2(p-cym)(L)] (2I2iPr). Unexpectedly, all of the complexes exhibited poor cytotoxic activities after 24 h of incubation with cells, in contrast to the related compounds previously reported. However, it was observed that aged DMSO solutions of 2I2iPr (from 2 to 7 days) exhibited better activities in comparison to freshly prepared solutions and that the activity improved over "aging" time. Thorough studies were therefore performed to uncover the origin of this lag time in the cytotoxicity efficiency. The data achieved clearly demonstrated that compounds 2I2iPr and 2Cl2iPr were undergoing a series of transformation reactions in DMSO (with higher rates for the iodido complex 2I2iPr), ultimately generating cyclometalated species through a mechanism involving DMSO as a coordinated proton abstractor. The cyclometalated complexes detected in solution were subsequently prepared; hence, pure [RuCl(p-cym)(κ2C-diisopropyl(1-pyrenyl)phosphane)] (3CliPr), [RuI(p-cym)(κ2C-diisopropyl(1-pyrenyl)phosphane)] (3IiPr), and [Ru(p-cym)(κS-dmso)(κ2C-diisopropyl(1-pyrenyl)phosphane)]PF6 (3dmsoiPr) were synthesized and fully characterized. Remarkably, 3CliPr, 3IiPr, and 3dmsoiPr are all very efficient cytotoxic agents, exhibiting slightly better activities in comparison to the chlorido noncyclometalated complexes [RuCl2(η6-arene)(P(1-pyrenyl)R2R3)] described in an earlier report. For comparison purposes, the iodido compounds [RuI2(mba)(dimethyl(1-pyrenyl)phosphane)] (1I2Me) and [RuI2(p-cym)(dimethyl(1-pyrenyl)phosphane)] (2I2Me), bearing the less hindered dimethyl(1-pyrenyl)phosphane ligand, have also been prepared. The cytotoxic and chemical behaviors of 1I2Me and 1I2Me were comparable to those of their chlorido counterparts reported previously.

Dual Effect of Prussian Blue Nanoparticles on Aß40 Aggregation: ß-Sheet Fibril Reduction and Copper Dyshomeostasis Regulation.

Alzheimer's disease (AD), affecting almost 50 million individuals worldwide, is currently the first cause of dementia. Despite the tremendous research efforts in the last decade, only four supportive or palliative drugs, namely, acetylcholinesterase (AChE) inhibitors donepezil, galantamine, and rivastigmine and the glutamate NMDA receptor antagonist memantine, are currently available. New therapeutic strategies are becoming prominent, such as the direct inhibition of amyloid formation or the regulation of metal homeostasis. In the present report, the potential use of Prussian blue (PB), a drug that is in the World Health Organization Model List of Essential Medicines, in AD treatment is demonstrated. Both in vitro and in cellulo studies indeed suggest that PB nanoparticles (PBNPs) are capable of reducing the formation of typical amyloid-ß fibers (detected by thioflavin T fluorescence) and restoring the usual amyloid fibrillation pathway via chelation/sequestration of copper, which is found in high concentrations in senile plaques.

Nanochaperone-Based Strategies to Control Protein Aggregation Linked to Conformational Diseases.

The generation of highly organized amyloid fibrils is associated with a wide range of conformational pathologies, including primarily neurodegenerative diseases. Such disorders are characterized by misfolded proteins that lose their normal physiological roles and acquire toxicity. Recent findings suggest that proteostasis network impairment may be one of the causes leading to the accumulation and spread of amyloids. These observations are certainly contributing to a new focus in anti-amyloid drug design, whose efforts are so far being centered on single-target approaches aimed at inhibiting amyloid aggregation. Chaperones, known to maintain proteostasis, hence represent interesting targets for the development of novel therapeutics owing to their potential protective role against protein misfolding diseases. In this minireview, research on nanoparticles that can either emulate or help molecular chaperones in recognizing and/or correcting protein misfolding is discussed. The nascent concept of "nanochaperone" may indeed set future directions towards the development of cost-effective, disease-modifying drugs to treat several currently fatal disorders.

Evaluation of cobalt(III) complexes as potential hypoxia-responsive carriers of esculetin.

Differentiation between hypoxic and normoxic tissues have been exploited for the development of selective chemotherapeutic agents. In this context, cobalt(III)-based coordination compounds have been designed and investigated as prospective hypoxia-responsive drug delivery systems. Three cobalt(III) complexes, namely [CoIII(esc)(py2en)]ClO4·(CH3OH)2 (1) [CoIII(esc)(TPA)]ClO4·3H2O (2) and [CoIII(bipy)2(esc)]ClO4·2.5H2O (3) (py2en = N,N'-bis(pyridin-2-ylmethyl)ethylenediamine, TPA = tris(2-pyridylmethyl)amine, bipy = 2,2'-bipyridine and esc = 6,7-dihydroxycoumarin or esculetin), were prepared and investigated as potential carriers of esculetin. The spectroscopic and electrochemical properties of 1-3 were investigated and compared. Reactions of the complexes with biologically relevant reducing agents, viz. ascorbic acid, cysteine and glutathione, were monitored spectroscopically for 24 h, in pH 6.2 and 7.4 PBS phosphate buffer saline (PBS) solutions at 37 °C, under air, argon and dioxygen atmospheres. Dissociation of esculetin was observed upon Co3+/Co2+ reduction preferably under hypoxic conditions, with more effective conversion rates for 3 > 2 > 1. These results illustrate the importance to modulate the Co3+/Co2+ redox potential through the donor-acceptor properties of the ancillary ligands. Complex 3 is cytotoxic against HCT-116 but not against HT-29 and HEK-293 cells. In addition, DNA-binding studies indicate that interactions of 1 and 3 with the biomolecule are electrostatic.

Thiosemicarbazone Derivatives as Inhibitors of Amyloid-ß Aggregation: Effect of Metal Coordination.

Three thiosemicarbazone derivatives, namely 4-(dimethylamino)benzaldehyde 4,4-dimethylthiosemicarbazone (HL1), 4-(dimethylamino)benzaldehyde thiosemicarbazone (HL2), and 4-(dimethylamino)benzaldehyde 4-methylthiosemicarbazone (HL3), have been synthesized and characterized. The three palladium(II) complexes 1-3 were prepared respectively from HL1, HL2, and HL3. The crystal structures of two coordination compounds, namely Pd(L2)2 (2) and Pd(L3)2 (3), were obtained, which showed the expected square-planar environment for the metal centers. The ligand HL3 and the Pd(II) complexes 1-3, which are stable in buffered solutions containing up to 5% DMSO, exhibit remarkable inhibitory properties against the aggregation of amyloid-ß, reducing the formation of fibrils. HL1, HL3, 2, and 3 display IC50 values (i.e., the concentrations required to reduce Aß fibrillation by 50%) below 1 µM, lower that of the reference compound catechin (IC50 = 2.8 µM). Finally, in cellulo studies with E. coli cells revealed that the palladium(II) compounds are significantly more efficient than the free ligands in inhibiting Aß aggregation inside bacterial inclusion bodies, thus illustrating a beneficial effect of metal coordination.

Time-Dependent Cytotoxic Properties of Terpyridine-Based Copper Complexes.

Five copper complexes supported by terpyridine ligands were prepared and characterized, viz. [Cu3 Cl4 (naphtpy)2 ][CuCl2 ] (1), [Cu2 Cl2 (naphtpy)2 ](ClO4 )2 (2), [CuCl2 (naphtpy)]2 (MeOH)3 (H2 O) (3), [CuCl2 (Cltpy)] (4) and [Cu(Cltpy)2 ](ClO4 )2 (5); (where naphtpy stands for 4'-((naphthalen-2-yl)methoxy)-2,2':6',2''-terpyridine and Cltpy for 4'-chloro-2,2':6',2''-terpyridine). Their ability to interact with DNA was investigated, and their cytotoxic behaviour was examined with three cells lines, namely human ovarian carcinoma cells (A2780), their derived cisplatin-resistant line (A2780cis), and human cervix adenocarcinoma cells (HeLa). All compounds show good cytotoxic properties (especially after 72 h of incubation). Remarkably, two compounds, 4 and 5, are still almost inactive after 24 h (particularly 4), but are highly active after 72 h, with IC50 values in the low-micromolar to sub-micromolar range. Compounds 1 and 2 induce necrosis, whereas late apoptosis is observed with 3-5, 4 exhibiting a behaviour close to that of cisplatin.

Peptidic Scaffolds To Reduce the Interaction of Cu(II) Ions with ß-Amyloid Protein.

Competitive Cu(II)-binding studies have been carried out between five decapeptides (both acyclic and cyclic), namely C-Asp, C-Asn, O-Asp, ODPro-Asp, and O-Asn, and the Aß(1-16) and Aß(1-40) fragments. Conformational constraints in such peptidic scaffolds affect their copper-binding affinity, which can be tuned. In the present study, the ability of these peptides to compete with Aß has been assessed in vitro, with the objective to examine whether such soft chelating agents may be used to lessen the deleterious interaction of Cu(II) with Aß. Fluorescence spectroscopy, electron paramagnetic resonance, and mass spectrometry data show that the more constrained peptide, i.e., cyclic C-Asp, which displays a Cu(II)-binding affinity comparable to that of Aß, is the only potential metal-protein attenuating compound (MPAC) candidate. In vitro aggregation studies with Aß(1-40) reveal that C-Asp can hamper the formation of copper-stabilized oligomeric Aß species, through capturing the metal ion prior to its interaction with monomeric Aß. The present study shows that (cyclic) peptides, preorganized for Cu(II) binding, may be applied for the development of potential copper-Aß attenuating compounds.

Copper, dityrosine cross-links and amyloid-ß aggregation.

Copper is involved in Alzheimer's disease (AD) where it appears to affect the aggregation of amyloid-ß (Aß) and to catalyze the production of reactive oxygen species (ROS). Oxidative stress apparently produces Aß dimers that are covalently linked through two tyrosine residues. Such dityrosine cross-links are considered as potential markers of the disease and seem to be implicated in the pathological disorder. In the present study, pure o,o'-dityrosine (diY) was prepared enzymatically (with horseradish peroxidase; HRP), which was subsequently used to construct calibration lines aimed at quantifying nanomolar amounts of diY in reaction mixtures by fluorescence spectroscopy. Hence, diY concentrations down to 67 nM could be determined, which allowed to find that ca. 3% of dityrosine-bridged dimers of Aß(1-40) were produced after 3 days at 37 °C in the presence of copper and dihydrogen peroxide. These cross-linked dimers in the presence of copper(II) ions completely inhibit the typical aggregation of Aß, since ß sheets could not be detected applying the usual Thioflavin T (ThT) method. Furthermore, the use of a potent Cu(II) chelator, such as the ATCUN tripeptide, L-histidyl-L-alanyl-L-histidine (HAH), efficiently prevented the copper-mediated generation of ROS and the associated dityrosine-bridged Aß dimers, suggesting that such metal chelators may find future applications in the field of anti-AD drug design.

DNA-binding and in vitro cytotoxic activity of platinum(II) complexes of curcumin and caffeine.

Three Pt(II) complexes containing the natural ligands curcumin and caffeine, namely [Pt(curc)(PPh3)2]Cl (1), [PtCl(curc)(DMSO)] (2) (curc = deprotonated curcumin) and trans-[Pt(caffeine)Cl2(DMSO)] (3), were synthesized and fully characterized. The data obtained suggest that, for both 1 and 2, the anion of curcumin is coordinated to the platinum ion via the oxygen atoms of the ß-diketonate moiety. Spectroscopic features reveal that in 2 and 3, a DMSO molecule is S-bonded to the metal centre. For 3, all data indicate a square-planar geometry formed by a 9-N bonded caffeine, two trans chloride anions and a DMSO. The three complexes undergo changes in solution upon incubation for 24 h; 1 and 2 release curcumin while 3 isomerizes from trans to cis configuration. The DNA-binding and cytotoxic properties of 1-3 were evaluated in vitro. Despite their structural similarity, curcuminate-containing 1 and 2 exhibit distinct DNA interactions. While 1 appears to intercalate between nucleobase pairs, inducing the oxidative degradation of the biomolecule, 2 behaves as a groove binder, by means of electrostatic forces. Caffeine-containing 3 exhibits a behaviour that is comparable to that of 2. Complexes 1 and 2 showed moderate to high cytotoxicity and selectivity against several cancer cell lines, while 3 is inactive. Compounds 1 and 2 can be further activated by visible-light irradiation.

Bacterial Inclusion Bodies for Anti-Amyloid Drug Discovery: Current and Future Screening Methods.

Amyloid aggregation is linked to an increasing number of human disorders from nonneurological pathologies such as type-2 diabetes to neurodegenerative ones such as Alzheimer or Parkinson's diseases. Thirty-six human proteins have shown the capacity to aggregate into pathological amyloid structures. To date, it is widely accepted that amyloid folding/aggregation is a universal process present in eukaryotic and prokaryotic cells. In the last decade, several studies have unequivocally demonstrated that bacterial inclusion bodies - insoluble protein aggregates usually formed during heterologous protein overexpression in bacteria - are mainly composed of overexpressed proteins in amyloid conformation. This fact shows that amyloid-prone proteins display a similar aggregation propensity in humans and bacteria, opening the possibility to use bacteria as simple models to study amyloid aggregation process and the potential effect of both anti-amyloid drugs and pro-aggregative compounds. Under these considerations, several in vitro and in cellulo methods, which exploit the amyloid properties of bacterial inclusion bodies, have been proposed in the last few years. Since these new methods are fast, simple, inexpensive, highly reproducible, and tunable, they have aroused great interest as preliminary screening tools in the search for anti-amyloid (beta-blocker) drugs for conformational diseases. The aim of this mini-review is to compile recently developed methods aimed at tracking amyloid aggregation in bacteria, discussing their advantages and limitations, and the future potential applications of inclusion bodies in anti-amyloid drug discovery.

Amyloid Pan-inhibitors: One Family of Compounds To Cope with All Conformational Diseases.

Amyloids are ubiquitous protein aggregates sharing common internal structural features; they are present in all organisms, from prokaryotes to eukaryotes, where they play physiological or pathological roles. Importantly, amyloids, which are generated by aggregation of a range of distinct proteins, could be a key factor in a number of major human disorders, the so-called conformational diseases. Because all amyloids exhibit similar cross-ß motifs, one may envisage that molecules capable of blocking the formation of ß-sheet structures could abolish aggregation of all amyloid proteins, albeit with different efficacies. Herein, two different ß-sheet blockers were tested against a selection of amyloidogenic proteins, encompassing all the major types of amyloid-based disorders. Analysis of their blocking efficiency, using a simple but contrasted cell-based screening procedure, unequivocally confirms that they indeed behave as aggregation pan-inhibitors. The significant inhibitory effects observed for these compounds against all tested amyloidogenic proteins could spur a broader biological evaluation of other known and new amyloid aggregation inhibitors to further determine the potential use of this class of compounds for the universal treatment of conformational diseases.

Highly Cytotoxic Ruthenium(II)-Arene Complexes from Bulky 1-Pyrenylphosphane Ligands.

In the present study, the potential anti-neoplastic properties of a series of ruthenium half-sandwich complexes of formula [Ru(η6-arene)Cl2(PR1R2(1-pyrenyl))] (η6-arene = p-cymene and R1 = R2 = methyl for 1; η6-arene = methylbenzoate and R1 = R2 = methyl for 2; η6-arene = p-cymene and R1 = R2 = phenyl for 3; η6-arene = methylbenzoate and R1 = R2 = phenyl for 4; η6-arene = p-cymene, R1 = methyl and R2 = phenyl for 5; η6-arene = methylbenzoate, R1 = methyl and R2 = phenyl for 6) have been investigated. The six structurally related organoruthenium(II) compounds have been prepared in good yields and fully characterized; the X-ray structures of three of them, i.e., 1, 2, and 4, were determined. Although the piano-stool compounds contain a large polycyclic aromatic moiety, viz. a 1-pyrenyl group, they do not appear to interact with DNA. However, all the piano-stool complexes show significant cytotoxic properties against five human cell lines, namely, lung adenocarcinoma (A549), melanoma (A375), colorectal adenocarcinoma (SW620), breast adenocarcinoma (MCF7), and nontumorigenic epithelial breast (MCF10A), with IC50 values in the micromolar range for most of them. In addition, the most active compound, i.e., 2, induces a remarkable decrease of cell viability, that is in the nanomolar range, against two human neuroblastoma cell lines, namely, SK-N-BE(2) and CHLA-90. Complexes 1-6 are all capable of inducing apoptosis, but with various degrees of magnitude. Whereas 1, 3, 5, and 6 have no effect on the cell cycle of A375 cells, 2 and 4 can arrest it at the G2/M phase; furthermore, 2 (which is the most efficient compound of the series) also stops the cycle at the S phase, behaving as the well-known anticancer agent cisplatin. Finally, 2 is able to inhibit/reduce the cell migration of neuroblastoma SK-N-BE(2) cells.