G-quadruplex DNA Binding Research Articles

DNA-Targeted Complexes of Tc and Re for Biomedical Applications.

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

NMR characterization of the structure of the intrinsically disordered region of human origin recognition complex subunit 1, hORC1, and of its interaction with G-quadruplex DNAs

Human origin recognition complex (hORC) binds to the DNA replication origin and then initiates DNA replication. However, hORC does not exhibit DNA sequence-specificity and how hORC recognizes the replication origin on genomic DNA remains elusive. Previously, we found that hORC recognizes G-quadruplex structures potentially formed near the replication origin. Then, we showed that hORC subunit 1 (hORC1) preferentially binds to G-quadruplex DNAs using a hORC1 construct comprising residues 413 to 511 (hORC1413−511). Here, we investigate the structural characteristics of hORC1413−511 in its free and complex forms with G-quadruplex DNAs. Circular dichroism and nuclear magnetic resonance (NMR) spectroscopic studies indicated that hORC1413−511 is disordered except for a short α-helical region in both the free and complex forms. NMR chemical shift perturbation (CSP) analysis suggested that basic residues, arginines and lysines, and polar residues, serines and threonines, are involved in the G-quadruplex DNA binding. Then, this was confirmed by mutation analysis. Interestingly, CSP analysis indicated that hORC1413−511 binds to both parallel- and (3 + 1)-type G-quadruplex DNAs using the same residues, and thereby in the same manner. Our study suggests that hORC1 uses its intrinsically disordered G-quadruplex binding region to recognize parallel-type and (3 + 1)-type G-quadruplex structures at replication origin.

Selective, Disruptive Luminescent Ru(II) Polypyridyl Probes of G-Quadruplex.

Sensors capable of transducing G-quadruplex DNA binding are important both in solution and for imaging and interrogation in cellulo. Ru(II)-based light switches incorporating dipyridylphenazine (dppz) ligands are effective probes for recognition and imaging of DNA and its polymorphs including G-quadruplex, although selectivity is a limitation. While the majority of Ru(II)-based light switches reported to date, stabilize the quadruplex, imaging/theranostic probes that can disrupt G4s are of potentially enormous value in study and therapy for a range of disease states. We report here, on a Ru(II) complex (Ru-PDC3) that assembles the light switch capability of a Ru(II) dipyridylphenazine complex with the well-known G4-selective ligand Phen-DC3, into a single structure. The complex shows the anticipated light switch effect and strong affinity for G4 structures. Affinity depended on the G4 topology and sequence, but across all structures bar one, it was roughly an order of magnitude greater than for duplex or single-stranded DNA. Moreover, photophysical and Raman spectral data showed clear discrimination between duplex DNA and G4-bound structures offering the prospect of discrimination in imaging as well as in solution. Crucially, unlike the constituent components of the probe, Ru-PDC3 is a powerful G4 disrupter. From circular dichroism (CD), a reduction of ellipticity of the G4 between 70 and 95% was observed depending on topology and in many cases was accompanied by an induced CD signal for the metal complex. The extent of change in ellipticity is amongst the largest reported for small-molecule ligand G4 binding. While a promising G4 probe, without modification, the complex is fully water-soluble and readily permeable to live cells.

G-quadruplex DNA binding properties of novel nickel Schiff base complexes with four pendant groups.

Three new nickel Schiff base complexes were prepared using a two-step procedure that involves initial selective dialkylation of 2,4,6-trihydroxybenzaldehyde, followed by reaction with 1,2-phenylenediamine and nickel(II) acetate. Each of the complexes possessed the same Schiff base core but differed in the identity of the four pendant groups. All complexes were characterised by microanalysis, NMR spectroscopy and ESI mass spectrometry. In addition, two of the complexes were also characterised in the solid state using X-ray crystallography, which confirmed the presence of a square planar geometry around the metal ion. The DNA binding properties of the three nickel complexes with double stranded DNA and a range of G-quadruplex DNA structures were explored using ESI mass spectrometry, CD spectroscopy, UV melting curves, Fluorescence Resonance Energy Transfer (FRET) assays, Fluorescent Indicator Displacement (FID) assays and molecular docking studies. These techniques confirmed the ability of the three nickel complexes to bind to most of the DNA molecules examined, as well as stabilise the latter in several instances. In addition, the results of these investigations provided evidence that pendant groups with morpholine rings generally reduced DNA binding behaviour, whilst pendants featuring piperidine ring systems attached to the Schiff base core by three and not two methylene linkers often showed the greatest extent of binding or DNA stabilisation.

Anticancer Activity, Reduction Mechanism and G-Quadruplex DNA Binding of a Redox-Activated Platinum(IV)-Salphen Complex.

Aiming at reducing the unselective cytotoxicity of Pt(II) chemotherapeutics, a great deal of effort has been concentrated into the design of metal-containing drugs with different anticancer mechanisms of action. Inert Pt(IV) prodrugs have been proposed to be a valid alternative as they are activated by reduction directly into the cell releasing active Pt(II) species. On the other hand, a promising strategy for designing metallodrugs is to explore new potential biological targets rather than canonical B-DNA. G-quadruplex nucleic acid, obtained by self-assembly of guanine-rich nucleic acid sequences, has recently been considered an attractive target for anticancer drug design. Therefore, compounds capable of binding and stabilizing this type of DNA structure would be greatly beneficial in anticancer therapy. Here, computational analysis reports the mechanism of action of a recently synthesized Pt(IV)-salphen complex conjugating the inertness of Pt(IV) prodrugs with the ability to bind G-quadruplexes of the corresponding Pt(II) complex. The reduction mechanism of the Pt(IV) complex with a biological reducing agent was investigated in depth by means of DFT, whereas classical MD simulations were carried out to shed light into the binding mechanism of the released Pt(II) complex. The results show that the Pt(IV) prodrug may be reduced by both inner- and outer-sphere mechanisms, and the active Pt(II) complex, as a function of its protonation state, stabilizes the G-quadruplex DNA prevalently, either establishing π-stacking interactions with the terminal G-tetrad or through electrostatic interactions along with H-bonds formation.

Arene Ru(II) Complexes with Difluorinated Ligands Act as Potential Inducers of S-Phase Arrest via the Stabilization of c-myc G-Quadruplex DNA.

Here, a series of half-sandwich arene Ru(II) complexes with difluorinated ligands [Ru(η6-arene)(L)Cl] (L1 = 2-(2,3-difluorophenyl)imidazole[4,5f][1,10]-phenanthroline; L2 = 2-(2,4-difluorophenyl)imidazole[4,5f][1,10]-phenanthroline; arene = benzene, toluene, and p-cymene) were synthesized and characterized. Molecular docking analysis showed that these complexes bind to c-myc G-quadruplex DNA through either groove binding or π–π stacking, and the relative difluorinated site in the main ligand plays a role in regulating the binding mode. The binding behavior of these complexes with c-myc G-quadruplex DNA was evaluated using ultraviolet–visible spectroscopy, fluorescence intercalator displacement assay, fluorescence resonance energy transfer melting assay, and polymerase chain reaction. The comprehensive analysis indicated that complex 1 exhibited a better affinity and stability in relation to c-myc G-quadruplex DNA with a DC50 of 6.6 μM and ΔTm values of 13.09 °C, than other molecules. Further activity evaluation results displayed that this class of complexes can also inhibit the growth of various tumor cells, especially complexes 3 and 6, which exhibited a better inhibitory effect against human U87 glioblastoma cells (51.61 and 23.75 μM) than other complexes, even superior to cisplatin (32.59 μM). Owing to a befitting lipophilicity associated with the high intake of drugs by tumor cells, complexes 3 and 6 had favorable lipid-water partition coefficients of −0.6615 and −0.8077, respectively. Moreover, it was found that complex 6 suppressed the proliferation of U87 cells mainly through an induced obvious S phase arrest and slight apoptosis, which may have resulted from the stabilization of c-myc G-quadruplex DNA to block the transcription and expression of c-myc. In brief, these types of arene Ru(II) complexes with difluorinated ligands can be developed as potential inducers of S-phase arrest and apoptosis through the binding and stabilization of c-myc G-quadruplex DNA, and could be used in clinical applications in the future.

Carbazole-based fluorescent probes for G-quadruplex DNA targeting with superior selectivity and low cytotoxicity

G-quadruplex DNA plays a very important role in clinical diagnosis and fluorescence analysis has attracted extensive attention. A class of carbazole-based fluorescent probes for the detection of G-quadruplex DNA was established in this work. In this system, the installation of an oligo(ethylene glycol) chain on the scaffold will improve the water-solubility and biocompatibility. The presence of styrene-like different side groups could tune the selectivity toward G-quadruplex DNA binding. Results revealed that the substitution pattern and position gave a great influence on the ability for the discrimination of the G-quadruplex from other DNA structures. Especially, probe E1 bound to G-quadruplex DNA with superior selectivity, which exhibiting almost no fluorescence response in the presence of non-G-quadruplex DNA structures. Comprehensive analyses revealed that E1 could bind both ends of the G-quadruplex, resulting in a significant increase of fluorescence emission intensity. Cellular uptake assay suggested that E1 could pass through membrane and enter living cells with low cytotoxicity.

Synthesis, G-Quadruplex DNA binding and cytotoxic properties of naphthalimide substituted styryl dyes

G-Quadruplex DNAs, formed by G-rich DNA sequences in human genes, are promising targets for design of cancer drugs. In this study, two naphthalimide substituted styryl dyes with different sizes of aromatic groups were synthesized. The spectral analysis showed that the dye X-2 with a large aromatic group formed aggregates in buffer solution displaying very weak fluorescence intensity, and disaggregated in the presence of G-Quadruplex DNAs with large intensity enhancements (up to ~1800 fold). Moreover, X-2 displayed good selectivity to G-Quadruplex DNAs. In contrast, dye X-3 with the smaller aromatic group had much lower fluorescence enhancements and poor selectivity to G-Quadruplex DNAs, suggesting that the suitably sized aromatic ring was essential for the interaction with G-Quadruplex. Further binding studies suggested that X-2 mainly bound on G-quartet surface through end-stacking mode. Cytotoxicity assay showed that both of the two dyes showed good anti-proliferative activities against the cancer cell lines and less cytotoxicity in non-malignant cell lines, which were better than a standard drug 5-fluorouracil. In addition, living cell imaging was also studied and demonstrated the potential applications of the new dye X-2 in bioassays and cell imaging.

Computational Structure-Activity Relationship (SAR) of Berberine Analogs in Double-Stranded and G-Quadruplex DNA Binding Reveals Both Position and Target Dependence

Berberine, a natural product alkaloid, and its analogs have a wide range of medicinal properties, including antibacterial and anticancer effects. Previous studies showed that berberine and its analogs intercalate into DNA, thereby inhibiting DNA replication. Berberine has also been studied as a photosensitizer and was shown to generate reactive singlet oxygen in situ, and this has applications in photodynamic therapy. Various groups have synthesized berberine analogs that have comparable or improved biological activity; however, an exhaustive structure-activity relationship of the free energy of binding of berberine analogs with substitution at C-8, C-12, and C-13 to DNA have not been previously reported. High throughput virtual screening (HTVS) allows for efficient analysis of compound libraries to identify lead compounds as possible pharmaceutical agents. Here, we employed HTVS towards a library of alkyl or aryl berberine analogs on C-8, C-12, and C-13 to probe binding to double-stranded and G-quadruplex DNA. Predicted free energies of binding to double-stranded DNA and G-quadruplex DNA were generated via molecular docking. The excited state electronic structure calculations were conducted via time-dependent density functional theory to probe the potential photosensitizing activity of each compound, and the potential G-quadruplex stabilizing abilities of key berberine analogs were probed through molecular dynamics simulations on a 4.0 nanosecond timescale. We determined that the nature of the substituent, the position of the substituent, and the nucleic acid target affect the free energy of binding of berberine analogs to DNA and G-quadruplex DNA, however berberine analogs did not result in net stabilization of G-quadruplex DNA.

One-step synthesis of methylene-bridged bis-carbazole and evaluation of its antitumor activity and G-quadruplex DNA binding property

Most reported carbazolyl G-quadruplex DNA (G4-DNA) ligands possess a rigid structure rather than a flexible one. The conformationally flexible ligands are paid much less attention. In this study, we report a novel class of non-rigid methylene-bridged biscarbazolyl ligand and their G4-DNA binding properties. Moreover, the antitumor activities of all these oligomers have been evaluated. The results show that this family of oligomers could be facilely synthesized via solely one step. Among them, compound 2, the bis-carbazole derivative, displays the best antitumor activity and IC50 values against HT-29, HepG2, A375 and MCF-7 cells are 0.69, 5.09, 3.15 and 3.8 μ mol/L, respectively. Although conformationally flexible, 2 is still capable of binding to as well as stabilizing G4-DNA via π-π stacking interaction. Moreover, 2 selectively binds to G4-DNA over duplex DNA. The current study enriches the category of carbazolyl G4-DNA ligands and paves the way for the search of more efficient G4-DNA ligands and antitumor leads.

G-quadruplex and duplex DNA binding studies of novel Ruthenium(II) complexes containing ascididemin ligands

In this paper, three new Ruthenium(II) polypyridyl complexes containing ascididemin (ASC) as main ligand have been synthesized and characterized. Their interactions with different G-quadruplex (Htelo, c-myc and c-kit) (Htelo: human telomeric DNA, c-myc: cellular-myelocytomatosis viral oncogene, c-kit: oncogene c-kit promoter sequences) and duplex (ds26) DNA sequences were comparatively studied with the free ligand ASC by a series of spectroscopic techniques including UV–vis (ultraviolet-visible) spectroscopy, FID (fluorescent intercalator displacement) assay, and FRET (fluorescence resonance energy transfer) melting assay. Molecular docking studies were also performed to support the binding mode of the compounds with G-quadruplex DNA. Results indicated that [Ru(bpy)2ASC]·(PF6)2 (1), [Ru(phen)2ASC]·(PF6)2 (2), [Ru(tatp)2ASC]·(PF6)2 (3) (bpy = 2,2′‑bipyridine, phen = 1,10‑phenanthroline, tatp = 1,4,8,9‑tetra‑aza‑triphenylene) and ASC can effectively bind G-quadruplex and duplex DNA and stabilization ability lies in the order 3 > 2 > 1 > ASC. Complex 3 was determined to be the most promising candidate for further in vitro studies and potential anticancer drug.

A hydroxyquinoline-appended ruthenium(II)-polypyridyl complex that induces and stabilizes G-quadruplex DNA

A polypyridyl ruthenium(II) complex with hydroxyquinoline-derived ligand has been synthesized and characterized. The ability to act as telomeric quadruplex inducer and stabilizer, and quadruplex-binding properties of the complex have been evaluated by absorption and emission analyses, fluorescent intercalator displacement (FID) titrations, circular dichroism (CD) spectroscopy, polymerase chain reaction (PCR) stop assay, color reaction studies, fluorescence resonance energy transfer (FRET) melting assay, Job plot, and molecular modeling. Observations revealed that the complex could well induce and stabilize the formation of antiparallel G-quadruplex of telomeric DNA in the presence or absence of metal cations, and showed superior G-quadruplex selectivity over duplex DNA with remarkable ΔTm value of 18.0 °C even at 50-fold excessive supplies of calf thymus (ct) DNA. The complex exhibited high interaction affinity of 2.56 × 106 M−1 with G-quadruplex DNA and evident luminescence enhancements of 3.1 and 4.2 times for quadruplex binding in Na+ and K+ buffer, respectively. In addition, the 1:1 [quadruplex]/[complex] binding mode ratio was determined. The results suggest that the complex can be developed as potential anticancer reagent through binding and stabilization of G-quadruplex DNA.

Plant nucleoside diphosphate kinase 1: A housekeeping enzyme with moonlighting activity

ABSTRACTNucleoside diphosphate kinase (NDPK) catalyzes the interconversion of nucleoside diphosphates and triphosphates using ATP as phosphate donor. This housekeeping enzyme is present in several subcellular compartments. The main isoform (NDPK1) is located in the cytosol and is highly expressed in meristems and provascular tissues. The manipulation of NDPK1 levels in transgenic potato roots demonstrates that this enzyme plays a key role in the transfer of energy between the cytosolic adenine and uridine nucleotide pools and in the distribution of carbon between starch and cellulose. Modulation of the expression of NDPK1 also alters the homeostasis of root respiration, glycolytic flux, reactive oxygen species production and growth. Herein, we propose a model summarizing the effects of the manipulation of NDPK1 levels on root metabolism. The model also accounts for G-quadruplex DNA binding, a moonlighting activity recently attributed to NDPK1, which possibly contributes to the metabolic phenotype of transgenic roots.

Insights into the structural and mechanistic basis of multifunctional S. cerevisiae Pif1p helicase.

The Saccharomyces cerevisiae Pif1 protein (ScPif1p) is the prototypical member of the Pif1 family of DNA helicases. ScPif1p is involved in the maintenance of mitochondrial, ribosomal and telomeric DNA and suppresses genome instability at G-quadruplex motifs. Here, we report the crystal structures of a truncated ScPif1p (ScPif1p237−780) in complex with different ssDNAs. Our results have revealed that a yeast-specific insertion domain protruding from the 2B domain folds as a bundle bearing an α-helix, α16. The α16 helix regulates the helicase activities of ScPif1p through interactions with the previously identified loop3. Furthermore, a biologically relevant dimeric structure has been identified, which can be further specifically stabilized by G-quadruplex DNA. Basing on structural analyses and mutational studies with DNA binding and unwinding assays, a potential G-quadruplex DNA binding site in ScPif1p monomers is suggested. Our results also show that ScPif1p uses the Q-motif to preferentially hydrolyze ATP, and a G-rich tract is preferentially recognized by more residues, consistent with previous biochemical observations. These findings provide a structural and mechanistic basis for understanding the multifunctional ScPif1p.

The interaction of Schiff Base complexes of nickel(II) and zinc(II) with duplex and G-quadruplex DNA

The duplex and G-quadruplex DNA-binding of six nickel(II) and zinc(II) complexes of three salphen-like ligands (salphen=N,N′-bis-salicylidene-1,2-phenylenediaminato) was investigated by UV–visible absorption and circular dichroism spectroscopy. The results obtained, in particular the values of the DNA-binding constants, Kb, point out that the nickel(II) complexes show a higher affinity toward both duplex and G-quadruplex DNA, compared to the analogous zinc(II) complexes. Interestingly, the zinc(II) complexes possess high selectivity toward G-quadruplex DNA, being negligible their binding with duplex DNA. Molecular dynamics (MD) simulations provided atomistic models for the interpretation of the binding of the zinc(II) complexes with G-quadruplex DNA, allowing a structural comparison of the three salphen-like ligands, due to the presence of different substituents (H, F, CF3) on the position 4 of the phenyl ring on the N,N′ bridge.

Microwave-assisted synthesis of ruthenium(II) complexes with alkynes as potential inhibitor by selectively recognizing c-myc G-quadruplex DNA

Herein, two polypyridyl ruthenium(II) complexes with alkynes, [Ru(bpy)2L](ClO4)2 (L=p-TEPIP (1) and p-BEPIP (2); bpy=2,2′-bipyridine; p-TEPIP=2-(4-trimethylsilylpropargyl)-1H-imidazo[4,5f][1,10]phenanthroline; p-BEPIP=2-(4-phenyacetylenephenyl)-1H-imidazo[4,5f][1,10]phenanthroline) have been successfully achieved in yields of 32%–89% by a Sonogashira coupling reaction under microwave irradiation. We studied these complexes as potential stabilizers of c-myc G-quadruplex DNA. Observations revealed that both complexes could selectively bind to and stabilize c-myc G-quadruplex DNA with a constant of approximately 1.61±0.78 and 9.47±4.20×103M−1, respectively, as determined from ITC (isothermal ttitration calorimetry) experiments, FRET (fluorescence resonance energy ttransfer) assay and competitive FRET assay. Moreover, the melting point (Tm) of the c-myc G-quadruplex DNA increased in the presence of 1 and 2 ([Ru]=0.2μM) by approximately 9 and 19.9°C, respectively. It is noteworthy that the conformation of the c-myc G-quadruplex DNA appeared to change when titrated with 1 and 2, which was accompanied by a negative-induced CD (circular dichroism) signal that appeared at a wavelength of 295nm. Furthermore, the conformational change in c-myc G-quadruplex DNA induced by 1 and 2have also been confirmed by TEM (transmission electron microscopy) and AFM (atomic force microscopy). Consequently, the replication of c-myc DNA was blocked by 1 and 2, and especially by 2, as verified by PCR (polymerase chain reaction) -stop assay and Western-blot assay. Thus, these ruthenium(II) complexes can be developed as potential inhibitors in chemotherapy through their binding and stabilization of c-myc G-quadruplex DNA.

Cyclic ferrocenylnaphthalene diimide derivative as a new class of G-quadruplex DNA binding ligand

To identify an effective ligand that binds to a G-quadruplex structure but not a double-stranded DNA (dsDNA), a set of biophysical and biochemical experiments were carried out using newly synthesized cyclic ferrocenylnaphthalene diimide (cFNDI, 1) or the non-cyclic derivative (2) with various structures of G-quadruplex DNAs and dsDNA. Compound 1 bound strongly to G-quadruplexes DNAs (106M−1 order) with diminished binding to dsDNA (104M−1 order) in 100mM AcOH-AcOK buffer (pH 5.5) containing 100mM KCl. Interestingly, 1 showed an approximately 50-fold higher selectivity to mixed hybrid-type telomeric G-quadruplex DNA (K=3.4×106M−1 and a 2:1 stoichiometry) than dsDNA (K=7.5×104M−1) did. Furthermore, 1 showed higher thermal stability to G-quadruplex DNAs than it did to dsDNA with a preference for c-kit and c-myc G-quadruplex DNAs over telomeric and thrombin binding aptamers. Additionally, 1 exhibited telomerase inhibitory activity with a half-maximal inhibitory concentration (IC50) of 0.4μM. Compound 2 showed a preference for G-quadruplex; however, the binding affinity magnitude and preference were improved in 1 because the former had a cyclic structure.

Synthesis of New Benzimidazole and Benzothiazole Disulfide Metal Complexes as G-quadruplex Binding Ligands.

Compounds that can bind and stabilize non-canonical DNA structures are named quadruplex and are of interest in anticancer drug design due to their selective inhibitions of telomerase and consequent effects on cell proliferation. In this study, we report novel Co/Cu [II] complex compounds as G-quadruplex DNA binding ligands. The results from the preliminary assay indicated that the introduction of a positively charged 6-membered tail to the aromatic terminal group of benzimidazole significantly enhanced the binding affinity with the quadruplex and exhibited anti-telomerase activity. These derivatives showed significant selectivities for the telomeric quadruplex over duplex nucleic acids. The stabilization of non-canonical forms estimated with the FRET DNA technology using different sequences, such as F21T, c-kit1 and c-kit2, in cancer cell lines were assessed. Three members of this family showed to be very selective in stabilizing one particular G-quadruplex.

New pyridinium-based fluorescent dyes: A comparison of symmetry and side-group effects on G-Quadruplex DNA binding selectivity and application in live cell imaging

A series of C1-, C2-and C3-symmetric pyridinium conjugates with different styrene-like side groups were synthesized and were utilized as G-quadruplex selective fluorescent probes. The new compounds were well-characterized. Their selectivity, sensitivity, and stability towards G-quadruplex were studied by fluorescence titration, native PAGE experiments, FRET and circular dichroism (CD) analyses. These new compounds investigated in the fluorescence assays were preferentially bound with G-quadruplex DNA compared with other type of nucleic acids and it is fascinating to realize the effects of molecular symmetry and associated side groups showing unexpectedly great influence on the fluorescent signal enhancement for the discrimination of G-quadruplexes DNA from other nucleic acids. This may correlate with the pocket symmetry and shape of the G-quadruplex DNA inherently. Among the compounds, a C2-symmetric dye (2,6-bis-((E)-2-(1H-indol-3-yl)-vinyl)-1-methylpyridin-1-ium iodide) with indolyl-groups substituted was screened out from the series giving the best selectivity and sensitivity towards G-quadruplexes DNA, particularly telo21, due to its high equilibrium binding constant (K=2.17×105M−1). In addition, the limit of detection (LOD) of the dye to determine telo21 DNA in bioassays was found as low as 33nM. The results of the study give insight and certain crucial factors, such as molecular symmetry and the associated side groups, on developing of effective fluorescent dyes for G-quadruplex DNA applications including G-quadruplex structure stabilization, biosensing and clinical applications. The compound was also demonstrated as a very selective G-quadruplex fluorescent agent for living cell staining and imaging.

Photophysical, G-quadruplex DNA binding and cytotoxic properties of terpyridine complexes with a naphthalimide ligand

The complex3inhibits A549 cells selectively over non-cancerous NIH3T3 cells, which may correlate with its selective G-quadruplex binding and nuclear location.