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Special Issue "G-Quadruplex Ligands and Cancer"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Medicinal Chemistry".

Deadline for manuscript submissions: closed (15 March 2019)

Special Issue Editor

Guest Editor
Prof. Danzhou Yang

Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, Purdue Center for Cancer Research, 201 S. University St., West Lafayette, IN 47907, USA
Website | E-Mail
Interests: DNA structures and functions; G-quadruplexes; anticancer drugs; NMR; ligand interactions

Special Issue Information

Dear Colleagues,

G-quadruplexes are four-stranded nucleic acid secondary structures, which form in guanine-rich DNA and RNA sequences. Once a laboratory curiosity, these non-canonical structures are now known to form readily under physiological conditions in regions of biological significance, such as human telomeres, oncogene promoter regions, replication initiation sites, and 5’ and 3’-untranslated (UTR) regions. Many G-quadruplex forming sequences are found to be associated with cancer, thus, these non-canonical nucleic acid structures are considered to be attractive molecular targets for cancer therapeutics with novel mechanisms of action. In recent years, G-quadruplexes have received elevated research interest, and G-quadruplex interactive ligands have been identified to exhibit antiproliferative and chemosensitizing effects against tumor models both in vitro and in vivo. Notably, quarfloxin, a G-quadruplex-interactive fluoroquinoline derivative, reached phase II clinical trials for the treatment of carcinoid/neuroendocrine tumors. While significant advances have been made towards targeting G-quadruplex structures, many questions and challenges on the subject remain to be addressed. This Special Issue aims to provide opportunity to share new findings and recent advances on G-quadruplex targeted small-molecules toward the development of new anticancer drugs.

Prof. Danzhou Yang
Guest Editor

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Keywords

  • G-quadruplexes nucleic acid secondary structures
  • molecular targets for cancer therapeutics
  • G-quadruplex-targeted ligands
  • anticancer and chemosensitizing effects

Published Papers (18 papers)

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Research

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Open AccessArticle Binding of BRACO19 to a Telomeric G-Quadruplex DNA Probed by All-Atom Molecular Dynamics Simulations with Explicit Solvent
Molecules 2019, 24(6), 1010; https://doi.org/10.3390/molecules24061010
Received: 5 January 2019 / Revised: 1 March 2019 / Accepted: 9 March 2019 / Published: 13 March 2019
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Abstract
Although BRACO19 is a potent G-quadruplex binder, its potential for clinical usage is hindered by its low selectivity towards DNA G-quadruplex over duplex. High-resolution structures of BRACO19 in complex with neither single-stranded telomeric DNA G-quadruplexes nor B-DNA duplex are available. In this study, [...] Read more.
Although BRACO19 is a potent G-quadruplex binder, its potential for clinical usage is hindered by its low selectivity towards DNA G-quadruplex over duplex. High-resolution structures of BRACO19 in complex with neither single-stranded telomeric DNA G-quadruplexes nor B-DNA duplex are available. In this study, the binding pathway of BRACO19 was probed by 27.5 µs molecular dynamics binding simulations with a free ligand (BRACO19) to a DNA duplex and three different topological folds of the human telomeric DNA G-quadruplex (parallel, anti-parallel and hybrid). The most stable binding modes were identified as end stacking and groove binding for the DNA G-quadruplexes and duplex, respectively. Among the three G-quadruplex topologies, the MM-GBSA binding energy analysis suggested that BRACO19′s binding to the parallel scaffold was most energetically favorable. The two lines of conflicting evidence plus our binding energy data suggest conformation-selection mechanism: the relative population shift of three scaffolds upon BRACO19 binding (i.e., an increase of population of parallel scaffold, a decrease of populations of antiparallel and/or hybrid scaffold). This hypothesis appears to be consistent with the fact that BRACO19 was specifically designed based on the structural requirements of the parallel scaffold and has since proven effective against a variety of cancer cell lines as well as toward a number of scaffolds. In addition, this binding mode is only slightly more favorable than BRACO19s binding to the duplex, explaining the low binding selectivity of BRACO19 to G-quadruplexes over duplex DNA. Our detailed analysis suggests that BRACO19′s groove binding mode may not be stable enough to maintain a prolonged binding event and that the groove binding mode may function as an intermediate state preceding a more energetically favorable end stacking pose; base flipping played an important role in enhancing binding interactions, an integral feature of an induced fit binding mechanism. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Practical Microwave Synthesis of Carbazole Aldehydes for the Development of DNA-Binding Ligands
Molecules 2019, 24(5), 965; https://doi.org/10.3390/molecules24050965
Received: 13 January 2019 / Revised: 25 February 2019 / Accepted: 6 March 2019 / Published: 9 March 2019
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Abstract
Microwave formylation of carbazole derivatives was investigated and 3-monoaldehydes were obtained in high yield. A potential DNA-binding ligand, 3-[(3-ethyl)-2-vinylbenzothiazolium]-9-N-ethyl carbazole iodide, was synthesized and characterized including spectral properties (UV-Vis absorption and fluorescence spectra). The binding selectivity and affinity of three carbazole [...] Read more.
Microwave formylation of carbazole derivatives was investigated and 3-monoaldehydes were obtained in high yield. A potential DNA-binding ligand, 3-[(3-ethyl)-2-vinylbenzothiazolium]-9-N-ethyl carbazole iodide, was synthesized and characterized including spectral properties (UV-Vis absorption and fluorescence spectra). The binding selectivity and affinity of three carbazole ligands for double-stranded and G-quadruplex DNA structures were studied using a competitive dialysis method in sodium- and potassium-containing buffer solutions. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Investigating the Effect of Mono- and Dimeric 360A G-Quadruplex Ligands on Telomere Stability by Single Telomere Length Analysis (STELA)
Molecules 2019, 24(3), 577; https://doi.org/10.3390/molecules24030577
Received: 30 November 2018 / Revised: 14 January 2019 / Accepted: 31 January 2019 / Published: 6 February 2019
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Abstract
Telomeres are nucleoprotein structures that cap and protect the natural ends of chromosomes. Telomeric DNA G-rich strands can form G-quadruplex (or G4) structures. Ligands that bind to and stabilize G4 structures can lead to telomere dysfunctions by displacing shelterin proteins and/or by interfering [...] Read more.
Telomeres are nucleoprotein structures that cap and protect the natural ends of chromosomes. Telomeric DNA G-rich strands can form G-quadruplex (or G4) structures. Ligands that bind to and stabilize G4 structures can lead to telomere dysfunctions by displacing shelterin proteins and/or by interfering with the replication of telomeres. We previously reported that two pyridine dicarboxamide G4 ligands, 360A and its dimeric analogue (360A)2A, were able to displace in vitro hRPA (a single-stranded DNA-binding protein of the replication machinery) from telomeric DNA by stabilizing the G4 structures. In this paper, we perform for the first time single telomere length analysis (STELA) to investigate the effect of G4 ligands on telomere length and stability. We used the unique ability of STELA to reveal the full spectrum of telomere lengths at a chromosome terminus in cancer cells treated with 360A and (360A)2A. Upon treatment with these ligands, we readily detected an increase of ultrashort telomeres, whose lengths are significantly shorter than the mean telomere length, and that could not have been detected by other methods. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Selectivity of Terpyridine Platinum Anticancer Drugs for G-quadruplex DNA
Molecules 2019, 24(3), 404; https://doi.org/10.3390/molecules24030404
Received: 14 December 2018 / Revised: 18 January 2019 / Accepted: 22 January 2019 / Published: 23 January 2019
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Abstract
Guanine-rich DNA can form four-stranded structures called G-quadruplexes (G4s) that can regulate many biological processes. Metal complexes have shown high affinity and selectivity toward the quadruplex structure. Here, we report the comparison of a panel of platinum (II) complexes for quadruplex DNA selective [...] Read more.
Guanine-rich DNA can form four-stranded structures called G-quadruplexes (G4s) that can regulate many biological processes. Metal complexes have shown high affinity and selectivity toward the quadruplex structure. Here, we report the comparison of a panel of platinum (II) complexes for quadruplex DNA selective recognition by exploring the aromatic core around terpyridine derivatives. Their affinity and selectivity towards G4 structures of various topologies have been evaluated by FRET-melting (Fluorescence Resonance Energy Transfert-melting) and Fluorescent Intercalator Displacement (FID) assays, the latter performed by using three different fluorescent probes (Thiazole Orange (TO), TO-PRO-3, and PhenDV). Their ability to bind covalently to the c-myc G4 structure in vitro and their cytotoxicity potential in two ovarian cancerous cell lines were established. Our results show that the aromatic surface of the metallic ligands governs, in vitro, their affinity, their selectivity for the G4 over the duplex structures, and platination efficiency. However, the structural modifications do not allow significant discrimination among the different G4 topologies. Moreover, all compounds were tested on ovarian cancer cell lines and normal cell lines and were all able to overcome cisplatin resistance highlighting their interest as new anticancer drugs. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Synthesis and Telomeric G-Quadruplex-Stabilizing Ability of Macrocyclic Hexaoxazoles Bearing Three Side Chains
Molecules 2019, 24(2), 263; https://doi.org/10.3390/molecules24020263
Received: 13 December 2018 / Revised: 4 January 2019 / Accepted: 10 January 2019 / Published: 11 January 2019
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Abstract
G-quadruplexes (G4s), which are structures formed in guanine-rich regions of DNA, are involved in a variety of significant biological functions, and therefore “sequence-dependent” selective G4-stabilizing agents are required as tools to investigate and modulate these functions. Here, we describe the synthesis of a [...] Read more.
G-quadruplexes (G4s), which are structures formed in guanine-rich regions of DNA, are involved in a variety of significant biological functions, and therefore “sequence-dependent” selective G4-stabilizing agents are required as tools to investigate and modulate these functions. Here, we describe the synthesis of a new series of macrocyclic hexaoxazole-type G4 ligand (6OTD) bearing three side chains. One of these ligands, 5b, stabilizes telomeric G4 preferentially over the G4-forming DNA sequences of c-kit and K-ras, due to the interaction of its piperazinylalkyl side chain with the groove of telomeric G4. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Binding of Small Molecules to G-quadruplex DNA in Cells Revealed by Fluorescence Lifetime Imaging Microscopy of o-BMVC Foci
Received: 15 November 2018 / Revised: 12 December 2018 / Accepted: 19 December 2018 / Published: 21 December 2018
Cited by 1 | PDF Full-text (4585 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
G-quadruplex (G4) structures have recently received increasing attention as a potential target for cancer research. We used time-gated fluorescence lifetime imaging microscopy (FLIM) with a G4 fluorescent probe, 3,6-bis(1-methyl-2-vinylpyridinium) carbazole diiodide (o-BMVC), to measure the number of o-BMVC foci, which [...] Read more.
G-quadruplex (G4) structures have recently received increasing attention as a potential target for cancer research. We used time-gated fluorescence lifetime imaging microscopy (FLIM) with a G4 fluorescent probe, 3,6-bis(1-methyl-2-vinylpyridinium) carbazole diiodide (o-BMVC), to measure the number of o-BMVC foci, which may represent G4 foci, in cells as a common signature to distinguish cancer cells from normal cells. Here, the decrease in the number of o-BMVC foci in the pretreatment of cancer cells with TMPyP4, BRACO-19 and BMVC4 suggested that they directly bind to G4s in cells. In contrast, the increase in the number of o-BMVC foci in the pretreatment of cells with PDS and Hoechst 33258 (H33258) suggested that they do not inhabit the binding site of o-BMVC to G4s in cells. After the H33258 was removed, the gradual decrease of H33258-induced G4 foci may be due to DNA repair. The purpose of this work is to introduce o-BMVC foci as an indicator not only to verify the direct binding of potential G4 ligands to G4 structures but also to examine the possible effect of some DNA binding ligands on DNA integrity by monitoring the number of G4 foci in cells. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Design and Properties of Ligand-Conjugated Guanine Oligonucleotides for Recovery of Mutated G-Quadruplexes
Molecules 2018, 23(12), 3228; https://doi.org/10.3390/molecules23123228
Received: 14 November 2018 / Revised: 27 November 2018 / Accepted: 5 December 2018 / Published: 6 December 2018
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Abstract
The formation of a guanine quadruplex DNA structure (G4) is known to repress the expression of certain cancer-related genes. Consequently, a mutated G4 sequence can affect quadruplex formation and induce cancer progression. In this study, we developed an oligonucleotide derivative consisting of a [...] Read more.
The formation of a guanine quadruplex DNA structure (G4) is known to repress the expression of certain cancer-related genes. Consequently, a mutated G4 sequence can affect quadruplex formation and induce cancer progression. In this study, we developed an oligonucleotide derivative consisting of a ligand-containing guanine tract that replaces the mutated G4 guanine tract at the promoter of the vascular endothelial growth factor (VEGF) gene. A ligand moiety consisting of three types of polyaromatic hydrocarbons, pyrene, anthracene, and perylene, was attached to either the 3′ or 5′ end of the guanine tract. Each of the ligand-conjugated guanine tracts, with the exception of anthracene derivatives, combined with other intact guanine tracts to form an intermolecular G4 on the mutated VEGF promoter. This intermolecular G4, exhibiting parallel topology and high thermal stability, enabled VEGF G4 formation to be recovered from the mutated sequence. Stability of the intramolecular G4 increased with the size of the conjugated ligand. However, suppression of intermolecular G4 replication was uniquely dependent on whether the ligand was attached to the 3′ or 5′ end of the guanine tract. These results indicate that binding to either the top or bottom guanine quartet affects unfolding kinetics due to polarization in DNA polymerase processivity. Our findings provide a novel strategy for recovering G4 formation in case of damage, and fine-tuning processes such as replication and transcription. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Binding Study of the Fluorescent Carbazole Derivative with Human Telomeric G-Quadruplexes
Molecules 2018, 23(12), 3154; https://doi.org/10.3390/molecules23123154
Received: 4 November 2018 / Revised: 28 November 2018 / Accepted: 29 November 2018 / Published: 30 November 2018
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Abstract
The carbazole ligand 3 was synthesized, characterized and its binding interactions with human telomeric (22HT) G-quadruplex DNA in Na+ and K+-containing buffer were investigated by ultraviolet-visible (UV-Vis) spectrophotometry, fluorescence, circular dichroism (CD) spectroscopy, and DNA melting. The results showed that [...] Read more.
The carbazole ligand 3 was synthesized, characterized and its binding interactions with human telomeric (22HT) G-quadruplex DNA in Na+ and K+-containing buffer were investigated by ultraviolet-visible (UV-Vis) spectrophotometry, fluorescence, circular dichroism (CD) spectroscopy, and DNA melting. The results showed that the studied carbazole ligand interacted and stabilized the intramolecular G-quadruplexes formed by the telomeric sequence in the presence of sodium and potassium ions. In the UV-Vis titration experiments a two-step complex formation between ligand and G-quadruplex was observed. Very low fluorescence intensity of the carbazole derivative in Tris HCl buffer in the presence of the NaCl or KCl increased significantly after addition of the 22HT G4 DNA. Binding stoichiometry of the ligand/G-quadruplex was investigated with absorbance-based Job plots. Carbazole ligand binds 22HT with about 2:1 stoichiometry in the presence of sodium and potassium ions. The binding mode appeared to be end-stacking with comparable binding constants of ~105 M−1 as determined from UV-Vis and fluorescence titrations data. The carbazole ligand is able to induce formation of G4 structure of 22HT in the absence of salt, which was proved by CD spectroscopy and melting studies. The derivative of carbazole 3 shows significantly higher cytotoxicity against breast cancer cells then for non-tumorigenic breast epithelial cells. The cytotoxic activity of ligand seems to be not associated with telomerase inhibition. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessFeature PaperArticle Molecular Recognition of Parallel G-quadruplex [d-(TTGGGGT)]4 Containing Tetrahymena Telomeric DNA Sequence by Anticancer Drug Daunomycin: NMR-Based Structure and Thermal Stability
Molecules 2018, 23(9), 2266; https://doi.org/10.3390/molecules23092266
Received: 10 August 2018 / Revised: 27 August 2018 / Accepted: 4 September 2018 / Published: 5 September 2018
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Abstract
The anticancer drug daunomycin exerts its influence by multiple strategies of action to interfere with gene functioning. Besides inhibiting DNA/RNA synthesis and topoisomerase-II, it affects the functional pathway of telomere maintenance by the telomerase enzyme. We present evidence of the binding of daunomycin [...] Read more.
The anticancer drug daunomycin exerts its influence by multiple strategies of action to interfere with gene functioning. Besides inhibiting DNA/RNA synthesis and topoisomerase-II, it affects the functional pathway of telomere maintenance by the telomerase enzyme. We present evidence of the binding of daunomycin to parallel-stranded tetramolecular [d-(TTGGGGT)]4 guanine (G)-quadruplex DNA comprising telomeric DNA from Tetrahymena thermophilia by surface plasmon resonance and Diffusion Ordered SpectroscopY (DOSY). Circular Dichroism (CD) spectra show the disruption of daunomycin dimers, suggesting the end-stacking and groove-binding of the daunomycin monomer. Proton and phosphorus-31 Nuclear Magnetic Resonance (NMR) spectroscopy show a sequence-specific interaction and a clear proof of absence of intercalation of the daunomycin chromophore between base quartets or stacking between G-quadruplexes. Restrained molecular dynamics simulations using observed short interproton distance contacts depict interaction at the molecular level. The interactions involving ring A and daunosamine protons, the stacking of an aromatic ring of daunomycin with a terminal G6 quartet by displacing the T7 base, and external groove-binding close to the T1–T2 bases lead to the thermal stabilization of 15 °C, which is likely to inhibit the association of telomerase with telomeres. The findings have implications in the structure-based designing of anthracycline drugs as potent telomerase inhibitors. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle HnRNPA1 Specifically Recognizes the Base of Nucleotide at the Loop of RNA G-Quadruplex
Molecules 2018, 23(1), 237; https://doi.org/10.3390/molecules23010237
Received: 13 December 2017 / Revised: 5 January 2018 / Accepted: 16 January 2018 / Published: 22 January 2018
Cited by 2 | PDF Full-text (910 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Human telomere RNA performs various cellular functions, such as telomere length regulation, heterochromatin formation, and end protection. We recently demonstrated that the loops in the RNA G-quadruplex are important in the interaction of telomere RNA with heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1). Here, we [...] Read more.
Human telomere RNA performs various cellular functions, such as telomere length regulation, heterochromatin formation, and end protection. We recently demonstrated that the loops in the RNA G-quadruplex are important in the interaction of telomere RNA with heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1). Here, we report on a detailed analysis of hnRNPA1 binding to telomere RNA G-quadruplexes with a group of loop variants using an electrophoretic mobility shift assay (EMSA) and circular dichroism (CD) spectroscopy. We found that the hnRNPA1 binds to RNA G-quadruplexes with the 2’-O-methyl and DNA loops, but fails to bind with the abasic RNA and DNA loops. These results suggested that hnRNPA1 binds to the loop of the RNA G-quadruplex by recognizing the base of the loop’s nucleotides. The observation provides the first evidence that the base of the loop’s nucleotides is a key factor for hnRNPA1 specifically recognizing the RNA G-quadruplex. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Design, Synthesis and Biological Evaluation of New Substituted Diquinolinyl-Pyridine Ligands as Anticancer Agents by Targeting G-Quadruplex
Received: 8 December 2017 / Revised: 20 December 2017 / Accepted: 29 December 2017 / Published: 30 December 2017
Cited by 3 | PDF Full-text (2846 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
G-quadruplexes (G4) are stacked non-canonical nucleic acid structures found in specific G-rich DNA or RNA sequences in the human genome. G4 structures are liable for various biological functions; transcription, translation, cell aging as well as diseases such as cancer. These structures are therefore [...] Read more.
G-quadruplexes (G4) are stacked non-canonical nucleic acid structures found in specific G-rich DNA or RNA sequences in the human genome. G4 structures are liable for various biological functions; transcription, translation, cell aging as well as diseases such as cancer. These structures are therefore considered as important targets for the development of anticancer agents. Small organic heterocyclic molecules are well known to target and stabilize G4 structures. In this article, we have designed and synthesized 2,6-di-(4-carbamoyl-2-quinolyl)pyridine derivatives and their ability to stabilize G4-structures have been determined through the FRET melting assay. It has been established that these ligands are selective for G4 over duplexes and show a preference for the parallel conformation. Next, telomerase inhibition ability has been assessed using three cell lines (K562, MyLa and MV-4-11) and telomerase activity is no longer detected at 0.1 μM concentration for the most potent ligand 1c. The most promising G4 ligands were also tested for antiproliferative activity against the two human myeloid leukaemia cell lines, HL60 and K562. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessArticle Investigation of ‘Head-to-Tail’-Connected Oligoaryl N,O-Ligands as Recognition Motifs for Cancer-Relevant G-Quadruplexes
Molecules 2017, 22(12), 2160; https://doi.org/10.3390/molecules22122160
Received: 27 October 2017 / Revised: 22 November 2017 / Accepted: 2 December 2017 / Published: 6 December 2017
Cited by 3 | PDF Full-text (2287 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Oligomeric compounds, constituted of consecutive N,O-heteroaromatic rings, introduce useful and tunable properties as alternative ligands for biomolecular recognition. In this study, we have explored a synthetic scheme relying on Van Leusen oxazole formation, in conjunction with C–H activation of the [...] Read more.
Oligomeric compounds, constituted of consecutive N,O-heteroaromatic rings, introduce useful and tunable properties as alternative ligands for biomolecular recognition. In this study, we have explored a synthetic scheme relying on Van Leusen oxazole formation, in conjunction with C–H activation of the formed oxazoles and their subsequent C–C cross-coupling to 2-bromopyridines in order to assemble a library of variable-length, ‘head-to-tail’-connected, pyridyl-oxazole ligands. Through investigation of the interaction of the three longer ligands (5-mer, 6-mer, 7-mer) with cancer-relevant G-quadruplex structures (human telomeric/22AG and c-Myc oncogene promoter/Myc2345-Pu22), the asymmetric pyridyl-oxazole motif has been demonstrated to be a prominent recognition element for G-quadruplexes. Fluorescence titrations reveal excellent binding affinities of the 7-mer and 6-mer for a Na+-induced antiparallel 22AG G-quadruplex (KD = 0.6 × 10−7 M−1 and 0.8 × 10−7 M−1, respectively), and satisfactory (albeit lower) affinities for the 22AG/K+ and Myc2345-Pu22/K+ G-quadruplexes. All ligands tested exhibit substantial selectivity for G-quadruplex versus duplex (ds26) DNA, as evidenced by competitive Förster resonance energy transfer (FRET) melting assays. Additionally, the 7-mer and 6-mer are capable of promoting a sharp morphology transition of 22AG/K+ G-quadruplex. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Review

Jump to: Research

Open AccessReview Small Molecule Fluorescent Probes for G- Quadruplex Visualization as Potential Cancer Theranostic Agents
Molecules 2019, 24(4), 752; https://doi.org/10.3390/molecules24040752
Received: 15 November 2018 / Revised: 10 January 2019 / Accepted: 22 January 2019 / Published: 19 February 2019
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Abstract
G-quadruplexes have gained prominence over the past two decades for their role in gene regulation, control of anti-tumour activity and ageing. The physiological relevance and significance of these non-canonical structures in the context of cancer has been reviewed several times. Putative roles of [...] Read more.
G-quadruplexes have gained prominence over the past two decades for their role in gene regulation, control of anti-tumour activity and ageing. The physiological relevance and significance of these non-canonical structures in the context of cancer has been reviewed several times. Putative roles of G-quadruplexes in cancer prognosis and pathogenesis have spurred the search for small molecule ligands that are capable of binding and modulating the effect of such structures. On a related theme, small molecule fluorescent probes have emerged that are capable of selective recognition of G-quadruplex structures. These have opened up the possibility of direct visualization and tracking of such structures. In this review we outline recent developments on G-quadruplex specific small molecule fluorescent probes for visualizing G-quadruplexes. The molecules represent a variety of structural scaffolds, mechanism of quadruplex-recognition and fluorescence signal transduction. Quadruplex selectivity and in vivo imaging potential of these molecules places them uniquely as quadruplex-theranostic agents in the predominantly cancer therapeutic context of quadruplex-selective ligands. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessFeature PaperReview Promise of G-Quadruplex Structure Binding Ligands as Epigenetic Modifiers with Anti-Cancer Effects
Molecules 2019, 24(3), 582; https://doi.org/10.3390/molecules24030582
Received: 27 November 2018 / Revised: 31 January 2019 / Accepted: 1 February 2019 / Published: 6 February 2019
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Abstract
Evidences from more than three decades of work support the function of non-duplex DNA structures called G-quadruplex (G4) in important processes like transcription and replication. In addition, G4 structures have been studied in connection with DNA base modifications and chromatin/nucleosome arrangements. Recent work, [...] Read more.
Evidences from more than three decades of work support the function of non-duplex DNA structures called G-quadruplex (G4) in important processes like transcription and replication. In addition, G4 structures have been studied in connection with DNA base modifications and chromatin/nucleosome arrangements. Recent work, interestingly, shows promise of G4 structures, through interaction with G4 structure-interacting proteins, in epigenetics—in both DNA and histone modification. Epigenetic changes are found to be intricately associated with initiation as well as progression of cancer. Multiple oncogenes have been reported to harbor the G4 structure at regulatory regions. In this context, G4 structure-binding ligands attain significance as molecules with potential to modify the epigenetic state of chromatin. Here, using examples from recent studies we discuss the emerging role of G4 structures in epigenetic modifications and, therefore, the promise of G4 structure-binding ligands in epigenetic therapy. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessReview Recent Progress of Targeted G-Quadruplex-Preferred Ligands Toward Cancer Therapy
Molecules 2019, 24(3), 429; https://doi.org/10.3390/molecules24030429
Received: 3 December 2018 / Revised: 22 January 2019 / Accepted: 23 January 2019 / Published: 24 January 2019
Cited by 1 | PDF Full-text (4440 KB) | HTML Full-text | XML Full-text
Abstract
A G-quadruplex (G4) is a well-known nucleic acid secondary structure comprising guanine-rich sequences, and has profound implications for various pharmacological and biological events, including cancers. Therefore, ligands interacting with G4s have attracted great attention as potential anticancer therapies or in molecular probe applications. [...] Read more.
A G-quadruplex (G4) is a well-known nucleic acid secondary structure comprising guanine-rich sequences, and has profound implications for various pharmacological and biological events, including cancers. Therefore, ligands interacting with G4s have attracted great attention as potential anticancer therapies or in molecular probe applications. To date, a large variety of DNA/RNA G4 ligands have been developed by a number of laboratories. As protein-targeting drugs face similar situations, G-quadruplex-interacting drugs displayed low selectivity to the targeted G-quadruplex structure. This low selectivity could cause unexpected effects that are usually reasons to halt the drug development process. In this review, we address the recent research on synthetic G4 DNA-interacting ligands that allow targeting of selected G4s as an approach toward the discovery of highly effective anticancer drugs. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessFeature PaperReview Naphthalene Diimides as Multimodal G-Quadruplex-Selective Ligands
Molecules 2019, 24(3), 426; https://doi.org/10.3390/molecules24030426
Received: 5 December 2018 / Revised: 11 January 2019 / Accepted: 22 January 2019 / Published: 24 January 2019
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Abstract
G-quadruplexes are four-stranded nucleic acids structures that can form in guanine-rich sequences. Following the observation that G-quadruplexes are particularly abundant in genomic regions related to cancer, such as telomeres and oncogenes promoters, several G-quadruplex-binding molecules have been developed for therapeutic purposes. Among them, [...] Read more.
G-quadruplexes are four-stranded nucleic acids structures that can form in guanine-rich sequences. Following the observation that G-quadruplexes are particularly abundant in genomic regions related to cancer, such as telomeres and oncogenes promoters, several G-quadruplex-binding molecules have been developed for therapeutic purposes. Among them, naphthalene diimide derivatives have reported versatility, consistent selectivity and high affinity toward the G-quadruplex structures. In this review, we present the chemical features, synthesis and peculiar optoelectronic properties (absorption, emission, redox) that make naphtalene diimides so versatile for biomedical applications. We present the latest developments on naphthalene diimides as G-quadruplex ligands, focusing on their ability to bind G-quadruplexes at telomeres and oncogene promoters with consequent anticancer activity. Their different binding modes (reversible versus irreversible/covalent) towards G-quadruplexes and their additional use as antimicrobial agents are also presented and discussed. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessReview Developing Novel G-Quadruplex Ligands: From Interaction with Nucleic Acids to Interfering with Nucleic Acid–Protein Interaction
Molecules 2019, 24(3), 396; https://doi.org/10.3390/molecules24030396
Received: 28 November 2018 / Revised: 10 January 2019 / Accepted: 22 January 2019 / Published: 22 January 2019
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Abstract
G-quadruplex is a special secondary structure of nucleic acids in guanine-rich sequences of genome. G-quadruplexes have been proved to be involved in the regulation of replication, DNA damage repair, and transcription and translation of oncogenes or other cancer-related genes. Therefore, targeting G-quadruplexes has [...] Read more.
G-quadruplex is a special secondary structure of nucleic acids in guanine-rich sequences of genome. G-quadruplexes have been proved to be involved in the regulation of replication, DNA damage repair, and transcription and translation of oncogenes or other cancer-related genes. Therefore, targeting G-quadruplexes has become a novel promising anti-tumor strategy. Different kinds of small molecules targeting the G-quadruplexes have been designed, synthesized, and identified as potential anti-tumor agents, including molecules directly bind to the G-quadruplex and molecules interfering with the binding between the G-quadruplex structures and related binding proteins. This review will explore the feasibility of G-quadruplex ligands acting as anti-tumor drugs, from basis to application. Meanwhile, since helicase is the most well-defined G-quadruplex-related protein, the most extensive research on the relationship between helicase and G-quadruplexes, and its meaning in drug design, is emphasized. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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Open AccessReview Natural Alkaloids and Heterocycles as G-Quadruplex Ligands and Potential Anticancer Agents
Molecules 2018, 23(2), 493; https://doi.org/10.3390/molecules23020493
Received: 30 December 2017 / Revised: 4 February 2018 / Accepted: 20 February 2018 / Published: 23 February 2018
Cited by 4 | PDF Full-text (1793 KB) | HTML Full-text | XML Full-text
Abstract
G-quadruplexes are four-stranded nucleic acid secondary structures that are formed in guanine-rich sequences. G-quadruplexes are widely distributed in functional regions of the human genome and transcriptome, such as human telomeres, oncogene promoter regions, replication initiation sites, and untranslated regions. Many G-quadruplex-forming sequences are [...] Read more.
G-quadruplexes are four-stranded nucleic acid secondary structures that are formed in guanine-rich sequences. G-quadruplexes are widely distributed in functional regions of the human genome and transcriptome, such as human telomeres, oncogene promoter regions, replication initiation sites, and untranslated regions. Many G-quadruplex-forming sequences are found to be associated with cancer, and thus, these non-canonical nucleic acid structures are considered to be attractive molecular targets for cancer therapeutics with novel mechanisms of action. In this mini review, we summarize recent advances made by our lab in the study of G-quadruplex-targeted natural alkaloids and their derivatives toward the development of potential anticancer agents. Full article
(This article belongs to the Special Issue G-Quadruplex Ligands and Cancer)
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