Enantiomeric ruthenium(II) complexes binding to DNA: binding modes and enantioselectivity

Binding and stabilizating effect of RNA triplex poly(U)⋅poly(A)*poly(U) by enantiomers of ruthenium(II) polypyridyl complex [Ru(bpy)2(dppx)]2

Two chiral ruthenium(II) polypyridyl complexes, Λ-[Ru(bpy)₂(dppx)]²⁺ (bpy = 2,2'-bipyridine, dppx = 7,8-dimethyldipyridophenazine; Λ-1) and Δ-[Ru(bpy)₂(dppx)]²⁺ (Δ-1) have been synthesized and characterized in this work. Interactions of Λ-1 and Δ-1 with the RNA triplex poly(U)⋅poly(A)*poly(U) have been investigated by various biophysical techniques. Spectrophotometric titrations and viscosity measurements suggested that enantiomers Λ-1 and Δ-1 bind with the triplex through intercalation, while the binding strengths of the two enantiomers toward the triplex differed only slightly from each other. Fluorescence titrations showed that although enantiomers Λ-1 and Δ-1 exhibited molecular "light switch" effects toward the triplex, the effect of Δ-1 was more marked. Furthermore, Furthermore, thermal denaturation showed that the two enantiomers have significantly different stabilizing effects on the triplex. The obtained results indicate that the racemic complex [Ru(bpy)₂(dppx)]²⁺ is similar to a non-specific metallointercalator for the triplex investigated in this study, and chiralities of Ru(II) polypyridine complexes have an important influence on the binding and stabilizing effects of enantiomers toward the triplex. Two chiral ruthenium(II) polypyridyl complexes, Λ-[Ru(bpy)₂(dppx)]²⁺ (bpy = 2,2'-bipyridine, dppx = 7,8-dimethyldipyridophenazine; Λ-1) and Δ-[Ru(bpy)₂(dppx)]²⁺ (Δ-1) have been synthesized and characterized in this work. Interactions of Λ-1 and Δ-1 with the RNA triplex poly(U)⋅poly(A)*poly(U) have been investigated by various biophysical techniques. The obtained results indicate that the racemic complex [Ru(bpy)₂(dppx)]²⁺ is similar as a non-specific metallointercalator for the triplex investigated in this study, and chiralities of Ru(II) polypyridine complexes have an important influence on the binding and stabilizing effects of enantiomers toward the triplex.

Interaction of ruthenium(Ⅱ) polypyridyl complexes [Ru(phen)2(L)]2+ (L = PIP, p-HPIP and m-HPIP) with RNA poly(A)•poly(U): each complex unexpectedly exhibiting a destabilizing effect on RNA

To further explore the binding properties of Ru(Ⅱ) polypyridine complexes with RNA, three Ru(Ⅱ) complexes [Ru(phen)₂(PIP)]²⁺ (Ru1), [Ru(phen)₂(p-HPIP)]²⁺ (Ru2), and [Ru(phen)₂(m- HPIP)]²⁺ (Ru3) have been synthesized and characterized in this work. The binding properties of three Ru(Ⅱ) complexes with RNA duplex poly(A)•poly(U) have been investigated by spectral and viscosity experiments. These studies all support that these three Ru(Ⅱ) complexes bind to poly RNA duplex poly(A)•poly(U) by intercalation, and Ru1 without substituents has a stronger binding affinity for poly(A)•poly(U). Interestingly, the thermal melting experiments show that these three Ru(Ⅱ) complexes all destabilize RNA duplex poly(A)•poly(U), and the destabilizing effect can be explained by the conformational changes of duplex structure induced by intercalating agents. To the best of our knowledge, this work report for the first time a small molecule capable of destabilizing an RNA duplex, which reflects that the substitution effect of intercalated ligands has an important influence on the affinity of Ru(Ⅱ) complexes to RNA duplex, and that not all Ru(Ⅱ) complexes show thermal stability effects on an RNA duplex.

Insight into achirality and chirality effects in interactions of an racemic ruthenium(II) polypyridyl complex and its Δ- and Λ-enantiomers with an RNA triplex

RNA triplexes have a variety of potential applications in molecular biology, diagnostics and therapeutics, while low stabilization of the third strand hinders their practical utilities under physiological conditions. In this regard, achieving the third-strand stabilization by binding small molecules is a promising strategy. Chirality is one of the basic properties of nature. To clarify achirality and chirality effects on the binding and stabilizing effects of RNA triplexes by small molecules, we report for the first time the RNA interactions of an racemic ruthenium(II) polypyridyl complex [Ru(bpy)₂(11-CN-dppz)]²⁺ (rac-Ru1) and its two enantiomers Δ/Λ-[Ru(bpy)₂(11-CN-dppz)]²⁺ (Δ/Λ-Ru1) with an RNA triplex poly(U-A*U) (where "-" represents Watson-Crick base pairing, and "*" denotes Hoogsteen base pairing, respectively) in this work. Research shows that although rac-Ru1 and its two enantiomers Δ/Λ-Ru1 bind to the RNA triplex through the same mode of intercalation, the binding affinity for enantiomer Δ-Ru1 is much higher than that for rac-Ru1 and enantiomer Λ-Ru1. However, compared to enantiomer Λ-Ru1, the binding affinity for rac-Ru1 does not show much of an advantage, which is slightly greater than that for the former. Thermal denaturation measurements reveal both rac-Ru1 and Δ-Ru1 to have a preference for stabilizing the third strand rather than the template duplex of the RNA triplex, while Λ-Ru1 stabilizes the RNA triplex without significant selectivity. Besides, the third-strand stabilizing effects by rac-Ru1 and Δ-Ru1 are not markedly different from each other, but more marked than that by Λ-Ru1. This work shows that the binding properties of the racemic Ru(II) polypyridyl complex with the RNA triplex are not simply an average of its two enantiomers, indicating potentially complicated binding events.

Comparative Studies on DNA-Binding Mechanisms between Enantiomers of a Polypyridyl Ruthenium(II) Complex

A pair of ruthenium(II) complex enantiomers, Δ- and Λ-[Ru(bpy)₂MBIP]²⁺ (bpy = 2,2'-bipyridine, MBIP = 2-(3-bromophenyl)imidazo[5,6-f]phenanthroline), were designed, synthesized, and characterized. Comparative studies between the enantiomers on their binding behaviors to calf thymus DNA (CT-DNA) were conducted using UV-visible, fluorescence, and circular dichroism spectroscopies, viscosity measurements, isothermal titration calorimetry, a photocleavage experiment, and molecular simulation. The experimental results indicated that both the enantiomers spontaneously bound to CT-DNA through intercalation stabilized by the van der Waals force or the hydrogen bond and driven by enthalpy and that Δ-[Ru(bpy)₂MBIP]²⁺ intercalated into DNA more deeply than Λ-[Ru(bpy)₂MBIP]²⁺ did and exhibited a better DNA photocleavage ability. Molecular simulation further indicated that Δ-[Ru(bpy)₂MBIP]²⁺ more preferentially intercalated between the base pairs of CT-DNA to the major groove, and Λ-[Ru(bpy)₂MBIP]²⁺ more favorably intercalated to the minor groove. These research findings should be very helpful to the understanding of the stereoselectivity mechanism of DNA-bindings of metal complexes, and be useful for the design of novel metal-complex-based antitumor drugs with higher efficacy and lower toxicity.

Comparative studies on the binding interaction of two chiral Ru(II) polypyridyl complexes with triple- and double-helical forms of RNA

Two chiral Ru(II) polypyridyl complexes, Δ-[Ru(bpy)₂(6-F-dppz)]²⁺ (Δ-1; bpy = 2,2'-bipyridine, 6-F-dppz = 6-fluorodipyrido[3,2-a:2',3'-c]phenazine) and Λ-[Ru(bpy)₂(6-F-dppz)]²⁺ (Λ-1), have been synthesized and characterized as binders for the RNA poly(U)•poly(A)*poly(U) triplex and poly(A)•poly(U) duplex in this work. Analysis of the UV-Vis absorption spectra and fluorescence emission spectra indicates that the binding of intercalating Δ-1 with the triplex and duplex RNA is greater than that of Λ-1, while the binding affinities of the two enantiomers to triplex structure is stronger than that of duplex structure. Fluorescence titrations show that the two enantiomers can act as molecular "light switches" for triple- and double-helical RNA. Thermal denaturation studies revealed that that the two enantiomers are more stable to Watson-Crick base-paired double strand of the triplex than the Hoogsteen base-paired third strand, but their stability and selectivity are different. For Δ-enantiomer, the increase of the thermal stability of the Watson-Crick base-paired duplex (13 °C) is slightly stronger than of the Hoogsteen base-paired strand (10 °C), displaying no obvious selectivity. However, compared to the Hoogsteen base-paired strand (5 °C), the stability of the Λ-enantiomer to the Watson-Crick base-paired duplex (13 °C) is more significant, which has obvious selectivity. The overall increase in viscosity of the RNA-(Λ-1) system and its curve shape are similar to that of the RNA-(Δ-1) system, suggesting that the binding modes of two enantiomers with RNA are intercalation. The obtained results in this work may be useful for understanding the binding differences in chiral Ru(II) polypyridyl complexes toward RNA triplex and duplex.

Biophysical insights into the interaction of two enantiomers of Ru(II) complex [Ru(bpy)2(7-CH3-dppz)]2+ with the RNA poly(U-A⁎U) triplex

To determine the factors affecting the stabilization of RNA triple-stranded structure by chiral Ru(II) polypyridyl complexes, a new pair of enantiomers, ∆-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (∆-1; bpy = 2,2'-bipyridine, 7-CH₃-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) and Λ-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (Λ-1), have been synthesized and characterized in this work. Binding properties of the two enantiomers with the RNA poly(U-A⁎U) triplex (where "-" denotes the Watson - Crick base pairing and "⁎" denotes the Hoogsteen base pairing) have been studied by spectroscopy and hydrodynamics methods. Under the conditions used in this study, changes in absorption spectra of the two enantiomers are not very different from each other when bound to the triplex, although the binding affinity of ∆-1 is higher than that of Λ-1. Fluorescence titrations and viscosity experiments give convincing evidence for a true intercalative binding of enantiomers with the triplex. However, melting experiments indicated that the two enantiomers selectively stabilized the triplex. The enantiomer ∆-1 stabilize the template duplex and third-strand of the triplex, while it's more effective for stabilization of the template duplex. In stark contrast to ∆-1, Λ-1 stabilizes the triplex without any effect on the third-strand stabilization, suggesting this one extremely prefers to stabilize the template duplex rather than third-strand. Besides, the triplex stabilization effect of ∆-1 is more marked in comparison with that of Λ-1. The obtained results suggest that substituent effects and chiralities of Ru(II) polypyridyl complexes play important roles in the triplex stabilization. Complexes Λ/Δ-[Ru(bpy)₂(7-CH₃-dppz)]²⁺ (Λ/Δ-1; bpy = 2,2'-bipyridine, 7-CH₃-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) were prepared as stabilizers for poly(U-A ∗ U) triplex. Results suggest the triplex stabilization depends the chiral structures of Λ/Δ-1, indicating that [Ru(bpy)₂(7-CH₃-dppz)]²⁺ is a non-specific intercalator for poly(U-A ∗ U) investigated in this work.

Synthesis and characterization of chiral Ru(II) polypyridyl complexes and their binding and stabilizing effects toward triple-helical RNA

Two novel chiral Ru(II) complexes, Λ- and Δ-[Ru(bpy)₂(7-CF₃-dppz)]²⁺ (Λ-1 and Δ-1; bpy = 2,2'-bipyridine, 7-CF₃-dppz = 7-trifluoromethyl-dipyrido[3,2-a:2',3'-c]phenazine), were synthesized and characterized in this work. The binding and stabilizing effects of Λ-1 and Δ-1 toward the RNA poly(U)•poly(A)*poly(U) triplex were studied by various biophysical techniques. Absorption spectra and fluorescence quenching indicates that the binding affinity of Δ-1 is slightly higher than that Λ-1. Both enantiomers induce significant positive viscosity changes that are indicative of intercalative binding, whereas changes in the relative viscosities of the triplex are found to be more pronounced with Δ-1. Melting experiments indicate that the triplex stabilization effects of both enantiomers are significantly different from each other. With Λ-1, the stabilization of the Watson-Crick base-paired duplex (the template duplex) of the triplex shows a moderate increase, whereas the stabilization of the Hoogsteen base-paired strand (third-strand) exhibits slight decrease under the same conditions, suggesting Λ-1 prefers to stabilize the template duplex rather than third-strand. In stark contrast to Λ-1, Δ-1 can not only strongly stabilize the template duplex, but also moderately increase the third-strand stabilization, even so, which imply that Δ-1 also prefer to stabilize the template duplex instead of the third-strand. These suggest that the [Ru(bpy)₂(7-CF₃-dppz)]²⁺ is similar as a non-specific metallointercalator the triplex studied in this work. Combined with our recent research, the obtained results further indicate that Δ- enantiomers rather than Λ-ones of Ru(II) polypyridyl complexes usually exhibit stronger binding and stabilizing effects toward the triplex.

Biological activity and photocatalytic properties of a naphthyl-imidazo phenanthroline (HNAIP) ligand and its [Ir(ppy)2(HNAIP)]Cl and [Rh(ppy)2(HNAIP)]Cl complexes

The synthesized 2-(hydroxy-1-naphtyl)imidazo-[4,5-f][1,10]phenanthroline (HNAIP) ligand and its new iridium ([Ir(ppy)₂(HNAIP)]Cl) and rhodium ([Rh(ppy)₂(HNAIP)]Cl) complexes, being ppy = 2-phenylpiridinate, show cytotoxic effects in SW480 (colon adenocarcinoma) and A549 (epithelial lung adenocarcinoma) cells. They all are cytotoxic in the tested cell lines. HNAIP and [Rh(ppy)₂(HNAIP)]⁺ are the most cytotoxic, whereas [Ir(ppy)₂(HNAIP)]⁺ displays negligible cytotoxicity towards A549 cells and moderate activity towards SW480. The interaction of all three compounds with Bovine Serum Albumin (BSA), l-glutathione reduced (GSH), nicotinamide adenine dinucleotide (NADH) and DNA was studied to explain the differences found in terms of cytotoxicity. None of them are able to interact with BSA, thus excluding bioavailability due to plasma protein interaction as the possible differentiating factor in their biological activity. By contrast, small differences have been observed regarding DNA interaction. In addition, taking advantage of the emission properties of these molecules, they have been visualized in the cytoplasmic region of A549 cells. Inductively coupled plasma mass spectrometry (ICP-MS) experiments show, in turn, that the internalization ability follow the sequence [Rh(ppy)₂(HNAIP)]⁺ > [Ir(ppy)₂(HNAIP)]⁺ > cisplatin. Therefore, it seems clear that the cellular uptake by tumour cells is the key factor affecting the different cytotoxicity of the metal complexes and that this cellular uptake is influenced by the hydrophobicity of the studied complexes. On the other hand, preliminary catalytic experiments performed on the photo-oxidation of GSH and some amino acids such as l-methionine (Met), l-cysteine (Cys) and l-tryptophan (Trp) provide evidence for the photocatalytic activity of the Ir(III) complex in this type of reactions.

Binding properties of chiral ruthenium(II) complexes Λ- and Δ-[Ru(bpy)2dppz-11-CO2Me]2+ toward the triplex RNA poly(U)•poly(A)*poly(U)

Two chiral ruthenium(II) complexes containing ligand dppz-CO₂Me (dppz-11-CO₂Me = dipyrido[3,2-a,2',3'-c]phenazine-11-carboxylic acid methyl ester), Δ-[Ru(bpy)₂dppz-11-CO₂Me]²⁺ (bpy = 2,2'-bipyridine; Δ-1) and Λ-[Ru(bpy)₂dppz-11-CO₂Me]²⁺ (Λ-1), were synthesized and characterized. The binding of the two enantiomers with the triplex RNA poly(U)•poly(A)*poly(U) was carried out by various biophysical techniques. Analysis of the absorption and fluorescence features indicates that the binding strengths of the two enantiomers toward the triplex RNA differ only slightly from each other. The total increase in viscosity and shape of the curves for the triplex RNA with Λ-1 is similar to that with Δ-1, suggesting the binding modes of two enantiomers with the triplex RNA are intercalation. Thermal melting measurements indicate that the stabilization effects clearly depended on the concentrations of Λ-1 and Δ-1. However, the third-strand stabilizing effect of Δ-1 dramatically differs from that of Λ-1 when they interact with the chiral environment of the RNA triple at pH = 7.0 and [Na⁺] = 35 mM. Combined with the CD (CD = circular dichroism) variations of the triplex RNA with either Λ-1 or Δ-1, the reason for their different triplex stabilization effects may originate from the two enantiomers through different orientations intercalating into nucleobases of the triplex. In addition, effects of higher ionic strengths on the triplex stabilization in the absence and presence of the two enantiomers have also been studied. The results presented here may be useful for understanding the binding properties of the triplex RNA with small molecule, particularly chiral ruthenium(II) complexes.

The development of ruthenium(ii) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications

Ruthenium(ii) [Ru(ii)] polypyridyl complexes have been the focus of intense investigations since work began exploring their supramolecular interactions with DNA. In recent years, there have been considerable efforts to translate this solution-based research into a biological environment with the intention of developing new classes of probes, luminescent imaging agents, therapeutics and theranostics. In only 10 years the field has expanded with diverse applications for these complexes as imaging agents and promising candidates for therapeutics. In light of these efforts this review exclusively focuses on the developments of these complexes in biological systems, both in cells and in vivo, and hopes to communicate to readers the diversity of applications within which these complexes have found use, as well as new insights gained along the way and challenges that researchers in this field still face.

Binding Differences of Two Homochiral [Ru(bpy)2dppz]2+ Complexes with poly(U)·poly(A)*poly(U) Triplex RNA

The first investigation of chiral ruthenium(II) complexes Δ- and Λ-[Ru(bpy)₂dppz]²⁺ and triplex RNA poly(U)·poly(A)*poly(U) was carried out, which showed that Δ enantiomer displayed significant ability in stabilizing model triplex RNA.

Biological activity and binding properties of [Ru(II)(dcbpy)2Cl2] complex to bovine serum albumin, phospholipase A2 and glutathione

Ruthenium compounds are highly regarded as metallo-drug candidates. Many studies have focused their attention on the interaction between ruthenium complexes with their possible biological targets. The interaction of ruthenium complexes with transport proteins, enzymes and peptides is of great importance for understanding their biodistribution and mechanism of action, therefore, the development of an anti-cancer therapy involving ruthenium complexes has recently shifted from DNA targeting towards protein targeting. With the aim of gaining insight into possible interactions between ruthenium complexes with biologically relevant proteins, we have studied the interaction of cis-dichlorobis(2,2'-bipyridyl-4,4'-dicarboxylic acid)ruthenium(II) complex [Ru(II)(dcbpy)2Cl2], which previously showed good potency in photo-dynamic chemotherapy, with bovine serum albumin (BSA), phospholipase A2 (PLA2) and glutathione (GSH). Binding constants and possible number of binding sites to mentioned proteins and peptide are investigated by ultraviolet-visible spectroscopy and Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI TOF MS). The complex binding affinities were in the following order: PLA2 > BSA > GSH. Moreover, genotoxic profile of the complex, tested on peripheral blood lymphocytes as a model system, was also promising.

Binding Behaviors for Different Types of DNA G-Quadruplexes: Enantiomers of [Ru(bpy)2(L)](2+) (L=dppz, dppz-idzo)

Polymorphic DNA G-quadruplex recognition has attracted great interest in recent years. The strong binding affinity and potential enantioselectivity of chiral [Ru(bpy)2 (L)](2+) (L=dipyrido[3,2-a:2',3'-c]phenazine, dppz-10,11-imidazolone; bpy=2,2'-bipyridine) prompted this investigation as to whether the two enantiomers, Δ and Λ, can show different effects on diverse structures with a range of parallel, antiparallel and mixed parallel/antiparallel G-quadruplexes. These studies provide a striking example of chiral-selective recognition of DNA G-quadruplexes. As for antiparallel (tel-Na(+)) basket G-quadruplex, the Λ enantiomers bind stronger than the Δ enantiomers. Moreover, the behavior reported here for both enantiomers stands in sharp contrast to B-DNA binding. The chiral selectivity toward mixed parallel/antiparallel (tel-K(+)) G-quadruplex of both compounds is weak. Different loop arrangements can change chiral complex selectivity for both antiparallel and mixed parallel/antiparallel G-quadruplex. Whereas both Δ and Λ isomers bind to parallel G-quadruplexes with comparable affinity, no appreciable stereoselective G-quadruplex binding of the isomers was observed. In addition, different binding stoichiometries and binding modes for Δ and Λ enantiomers were confirmed. The results presented here indicate that chiral selective G-quadruplex binding is not only related to G-quadruplex topology, but also to the sequence and the loop constitution.

Anticancer Activities of Mononuclear Ruthenium(II) Coordination Complexes

Ruthenium compounds are highly regarded as potential drug candidates. The compounds offer the potential of reduced toxicity and can be tolerated in vivo. The various oxidation states, different mechanism of action, and the ligand substitution kinetics of ruthenium compounds give them advantages over platinum-based complexes, thereby making them suitable for use in biological applications. Several studies have focused attention on the interaction between active ruthenium complexes and their possible biological targets. In this paper, we review several ruthenium compounds which reportedly possess promising cytotoxic profiles: from the discovery of highly active compounds imidazolium [trans-tetrachloro(dmso)(imidazole)ruthenate(III)] (NAMI-A), indazolium [trans-tetrachlorobis(1H-indazole)ruthenate(III)](KP1019), and sodium trans-[tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) to the recent work based on both inorganic and organometallic ruthenium(II) compounds. Half-sandwich organometallic ruthenium complexes offer the opportunity of derivatization at the arene moiety, while the three remaining coordination sites on the metal centre can be functionalised with various coordination groups of various monoligands. It is clear from the review that these mononuclear ruthenium(II) compounds represent a strongly emerging field of research that will soon culminate into several ruthenium based antitumor agents.

Design and synthesis of enantiomeric (R)- and (S)-copper(II) and diorganotin(IV)-based antitumor agents: their in vitro DNA binding profile, cleavage efficiency and cytotoxicity studies

New chiral reduced Schiff base ligands (R)/(S)-2-(2-hydroxy-1-phenylethylaminomethyl)phenol (L), (R)/(S)-2-(benzylamino)-2-phenylethanol (L') and their Cu(II)/organotin(IV) complexes (1-4) were synthesized and thoroughly characterized. Preliminary in vitro DNA binding studies of (R)- and (S)-enantiomeric pairs of ligands L, L' and complexes 1-4 were carried out employing UV-vis, fluorescence and circular dichroic techniques to evaluate their enantioselective DNA binding potential, thereby to act as antitumor chemotherapeutic drug entities. The observations demonstrated that S-enantiomer of Cu(II) complex, 1 binds more avidly to DNA in comparison to its R-enantiomeric form and organotin(IV) complex 2. This was further established by Kb and Ksv values of ligands L and L' and (S)-/(R)-1-4 complexes, which demonstrated multifold increase in case of S-enantiomer of copper complex 1 in comparison to its R-enantiomeric form. This clearly demonstrates the chiral preference of S-enantiomer over R-enantiomer and its potency to act as a chemotherapeutic agent. Cleavage studies of 1-4 with pBR322 plasmid DNA were carried out, noticeably, S-enantiomer of complex 1 exhibited effective DNA cleavage efficiency in absence of external agents. The cytotoxicity of ligands L and L' and (S)-/(R)-1-4 complexes was examined on a panel of 19 human tumor cell lines of different histological origins by SRB assay. In the both the cases, the S-enantiomer of complex 1 and 3 revealed remarkably good cytotoxic activity (GI50 values <10) against T24 (Urinary Bladder), DU145 (Prostate), U373MG (Astrocytoma) and HCT15, SW620 (Colon) clearly underlining the influence of enantiomeric discrimination. Interestingly, ligands L, L' and rest of the complexes demonstrated moderate cytotoxic activity (GI50 values <40).

Synthesis, characterization, and DNA binding of a novel ligand and its Cu (II) complex

A novel naphthalene-2,3-diamine-2-salicylaldehyde (NS) ligand and its mononuclear copper(II) complex (CuNS) have been synthesized and structurally characterized. The UV–vis absorption and emission spectra of NS showed obvious changes on addition of Cu2+ solution. The interaction of the compounds with calf thymus DNA and G-quadruplex DNA were investigated by spectroscopic methods and thermal melting assay. The nucleolytic cleavage activity of the compounds was investigated on double-stranded circular pBR322 plasmid DNA and G-quadruplex DNA by electrophoretic mobility shift assay. The results show that CuNS has a greater ability to stabilize G-quadruplex DNA over calf-thymus DNA. The cytotoxicity of the compounds toward HpeG2 cancer cells was also studied, and they showed significant potential for antineoplastic effects.

Mitochondria are the primary target in the induction of apoptosis by chiral ruthenium(II) polypyridyl complexes in cancer cells

A series of novel chiral ruthenium(II) polypyridyl complexes (Δ-Ru1, Λ-Ru1, Δ-Ru2, Λ-Ru2, Δ-Ru3, Λ-Ru3) were synthesized and evaluated to determine their antiproliferative activities. Colocalization, inductively coupled plasma mass spectrometry, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay studies showed that these ruthenium(II) complexes accumulated preferentially in the mitochondria and exhibited cytotoxicity against various cancer cells in vitro. The complex Δ-Ru1 is of particular interest because it was found to have half-maximal inhibitory concentrations comparable to those of cisplatin and better activity than cisplatin against a cisplatin-resistant cell line, A549-CP/R. Δ-Ru1 induced alterations in the mitochondrial membrane potential and triggered intrinsic mitochondria-mediated apoptosis in HeLa cells, which involved the regulation of Bcl-2 family members and the activation of caspases. Taken together, these data suggest that Δ-Ru1 may be a novel mitochondria-targeting anticancer agent.

Synthesis and characterization of ruthenium(II)-oligopyridine-peptide conjugates. Interactions of the diasteromeres Δ- and Λ-[Ru(bpy)2(4-COY-4'-Mebpy)]Cl2 (Y=Gly-Lys(1)-Lys(2)CONH2, Lys(1)-Gly-Lys(2)CONH2, Lys(1)-Lys(2)-GlyCONH2) with the oligonucleotide d(5'-CGCGAATTCGCG-3')2

Diastereomeric complexes of the general formulae Λ- and Δ-[Ru(bpy)2(4-COY-4'-Mebpy)]Cl2 where bpy=2,2'-bipyridine and Y=Gly-Lys(1)-Lys(2)CONH2, Lys(1)-Gly-Lys(2)CONH2, Lys(1)-Lys(2)-GlyCONH2, were synthesized and characterized. The ability of these compounds to bind to the oligonucleotide duplex d(5'-CGCGAATTCGCG-3') was studied with NMR techniques. Complex Λ-2, Λ-[Ru(bpy)2(4-COLys(1)-Gly-Lys(2)CONH2),4'-Mebpy)]Cl2 (Mebpy=methyl-2,2'-bipyridine), interacts non-specifically causing changes for both complex and oligonucleotide (1)H NMR signals. Both Λ-1, Λ-[Ru(bpy)2(4-COGly-Lys(1)-Lys(2)CONH2),4'-Mebpy)]Cl2 and Λ-3, Λ-[Ru(bpy)2(4-COLys(1)-Lys(2)-GlyCONH2),4'-Mebpy)]Cl2, were bound to the oligonucleotide through both lysine aliphatic chains, indicating that the side chains of the sequential lysines create a kind of "clamp" to connect the complex with the oligonucleotide. Complex Δ-1, Δ-[Ru(bpy)2(4-COGly-Lys(1)-Lys(2)CONH2),4'-Mebpy)]Cl2, interacts with the oligonucleotide duplex with both lysine side chains in a manner similar to Λ-1. Δ-2, Δ-[Ru(bpy)2(4-COLys(1)-Gly-Lys(2)CONH2),4'-Mebpy)]Cl2, interacts with the oligonucleotide with the bipyridine ligands. In addition, the formation of a hydrogen bond between the Gly-NH and the carbonyl groups of the oligonucleotide bases was detected. A completely different binding mode was observed for Δ-3 Δ-[Ru(bpy)2(4-COLys(1)-Lys(2)-GlyCONH2),4'-Mebpy)]Cl2, which at a ratio of 1:1 ([Ru]/[nucleotide]) opens the oligonucleotide strands. In addition, participation of all three peptidic NH of Δ-3 in hydrogen bonds was observed.

Crystal structure of Δ-[Ru(bpy)₂dppz]²⁺ bound to mismatched DNA reveals side-by-side metalloinsertion and intercalation

DNA mismatches represent a novel target in the development of diagnostics and therapeutics for cancer, because deficiencies in DNA mismatch repair are implicated in cancers, and cells that are repair-deficient show a high frequency of mismatches. Metal complexes with bulky intercalating ligands serve as probes for DNA mismatches. Here, we report the high-resolution (0.92 Å) crystal structure of the ruthenium 'light switch' complex Δ-[Ru(bpy)(2)dppz](2+) (bpy = 2,2'-bipyridine and dppz = dipyridophenazine), which is known to show luminescence on binding to duplex DNA, bound to both mismatched and well-matched sites in the oligonucleotide 5'-(dCGGAAATTACCG)(2)-3' (underline denotes AA mismatches). Two crystallographically independent views reveal that the complex binds mismatches through metalloinsertion, ejecting both mispaired adenosines. Additional ruthenium complexes are intercalated at well-matched sites, creating an array of complexes in the minor groove stabilized by stacking interactions between bpy ligands and extruded adenosines. This structure attests to the generality of metalloinsertion and metallointercalation as DNA binding modes.

Effect of substituent of terpyridines on the DNA-interaction of polypyridyl ruthenium(II) complexes

An octahedral complexes of ruthenium with 2,9-dimethyl-1,10-phenanthroline (dmphen) and substituted terpyridine have been synthesized. The Ru(II) complexes have been characterized by elemental analyses, thermogravimetric analyses, magnetic moment measurements, FT-IR, electronic, (1)H NMR and FAB mass spectra. The binding strength and mode of interaction of the complexes with Herring Sperm DNA has been investigated using absorption titration and viscosity measurement studies. Results suggest that the substituent on terpyridine ligand affects the binding mode and binding ability of the complexes. Effect of time and ionic strength on DNA cleavage ability of complex has also been studied by gel electrophoresis. Results suggest that more than 200 mM concentration of NaCl decreases the cleavage ability of complex.

DENSITY FUNCTIONAL THEORY/TIME-DEPENDENT DENSITY FUNCTIONAL THEORY STUDY ON THE STRUCTURES AND SOLVENT EFFECTS ON THE ELECTRONIC SPECTRA OF Ru(II) POLYPYRIDYL COMPLEXES: [Ru(bpy)2(L)]2+ (L = CNOIP, HPIP, DPPZ, TAPIP)

The structures and solvent dependence of electronic spectra of four Ru ( II ) polypyridyl complexes: [ Ru ( bpy )2 CNOIP ]2+, bpy = 2,2-bipyridine and CNOIP = 2-(2-chloro-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline (Ru-1); [ Ru ( bpy )2 HPIP ]2+, HPIP = 2-(2-hydroxyphenyl) imidazo[4,5-f][1,10]phenanthroline ( Ru -2); [ Ru ( bpy )2 DPPZ ]2+, DPPZ = dipyrido[3,2:a-2′,3′:c]-phenazine ( Ru -3); [ Ru ( bpy )2 TAPIP ]2+, TAPTP = 4,5,9,18-tetraazaphenanthreno-[9,10-b]triphenylene ( Ru -4) have been carried out by density functional theory/time-dependent density functional theory in vacuum and nine solvents are described by the conductor-like polarized continuum model. The calculated results show that the solvent has a strong effect on the electron distribution of molecular orbitals and character of charge transfer. In water, the simulated absorption spectra (λmax) are in accordance with experimental data. The computational results also indicate the electronic spectra of Ru ( II ) polypyridyl complexes: [ Ru ( bpy )2( L )]2+ is very sensitive to the intercalative ligands L = CNOIP, HPIP, DPPZ, TAPIP in the presence of solvent. It was noted that the trend of transition intensity of complexes strongly depends on the polarity of solvents. In the present polar solvents, the transition intensity trend of Ru -4 > Ru -1 > Ru -2 > Ru -3 was obtained, but in the case of nonpolar solvents, the transition intensity trend is Ru -4 > Ru -3 > Ru -1 > Ru -2. Among the four polypyridyl complexes, [ Ru ( bpy )2 TAPIP ]2+( Ru -4) exhibits the strongest oscillator strength in all nine solvents.

Nucleic Acid (Calf Thymus-DNA, Yeast tRNA) Binding and Cytotoxic Properties of a Dinuclear (Ru,Co) Metal Polypyridyl Complex

Based on [L2Ru{DPPZ(11–11′)DPPZ}RuL2]4+ (where L = 1,10-phenanthroline or 2,2′-bipyridyl, DPPZ(11–11′)DPPZ = 11,11′-bi(dipyrido-[3,2-a:2′,3′-c]-phenazinyl)), a heterodinuclear (Ru,Co) metal polypyridyl complex [(phen)2Ru{DPPZ(11–11′)DPPZ}Co(phen)2]5+ (phen = 1,10-phenanthroline) has been designed and synthesized. A comparative study on the interaction of the complex with calf thymus DNA and yeast tRNA was investigated by UV-visible spectroscopy, fluorescence spectroscopy and viscosity measurements, as well as equilibrium dialysis and circular dichroism. The antitumour activities of the complex were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetraazolium bromide method and Giemsa staining experiment. These results indicate that the configuration and structures of nucleic acids have significant effects on the binding behaviours of metal complexes. Furthermore, the complex shows different antitumour activities against selected tumour cell lines, and can cause cell apoptosis.

Oligopyridine-ruthenium(II)-amino acid conjugates: synthesis, characterization, DNA binding properties and interactions with the oligonucleotide duplex d(5'-CGCGCG-3')2

Diastereomeric oligopyridine-ruthenium(II)-amino acid conjugated complexes of the general formulas Lambda- and Delta-[Ru(bpy)(2)(4,4'(CO(2)Y)(2)-bpy)](2+), where Y = L-AlaCONH(2), L-LysCONH(2), L-HisCONH(2), L-TyrCONH(2)), were synthesized and characterized. Their binding properties with ct-DNA and the oligonucleotide duplex d(5'CGCGCG-3')(2), by means of circular dichroism (CD), NMR spectroscopy and DNA thermal denaturation (T(m)) curves were studied. CD and T(m) data indicate that all diastereomeric complexes bind to the DNA major groove, Delta-diastereomers in a similar manner, while Lambda-diastereomers in dependence of the nature of the amino acid. NMR studies of d(5'CGCGCG-3')(2), and the complexes Delta-1, Delta-2, Lambda-1 and Lambda-2 indicate that Delta-1 and Delta-2 were bound having the ancillary bpy ligands towards the DNA groove, while the corresponding Lambda-1 and Lambda-2 were orientated in a similar way, facing the ligand 4,4'(CO(2)Y)(2)bpy towards the DNA major groove. Photoinduced DNA cleavage was observed in all cases studied, which take place through singlet oxygen production. Delta-4 and Lambda-4 show the lower photoinduced cleavage yield, probably because the singlet oxygen ((1)O(2)) oxidizes not only the DNA phosporodiesteric bonds but the tyrosine's phenolic OH bond as well.

Structure-specific binding of [Co(phen)(2)(HPIP)](3+) to a DNA duplex containing sheared G:A mismatch base pairs

The binding of a Co(III) complex to the decanucleotide d(CCGAATGAGG)(2) containing two pairs of G:A mismatches was studied by 2D-NMR, UV absorption, and molecular modeling. NMR investigations indicate that racemic [Co(phen)(2)(HPIP)]Cl(3) [HPIP=2-(2-hydroxyphenyl) imidazo [4,5-f][1,10] phenanthroline] binds the decanucleotide by intercalation: the HPIP ligand selectively inserts between the stacked bases from the minor groove at the terminal regions and from the major groove at the sheared region. Further, molecular modeling revealed that the recognition shows strong enantioselectivity: the Lambda-isomer preferentially intercalates into the T(6)G(7):A(5)A(4) region from the DNA major groove, while Delta-isomer favors the terminal C(1)C(2):G(10)G(9) region and intercalates from the minor groove. Detailed energy analysis suggests that the steric interaction, especially the electrostatic effect, is the primary determinants of the recognition event. Melting experiments indicate that binding stabilizes the DNA duplex and increases the melting temperature by 9.5 degrees C. The intrinsic binding constant of the complex to the mismatched duplex was determined to be 3.5x105M(-1).