c-MYC Promoter G-quadruplex Research Articles

The binding of a c-MYC promoter G-quadruplex to neurotransmitters: An analysis of G-quadruplex stabilization using DNA melting, fluorescence spectroscopy, surface-enhanced Raman scattering and molecular docking

The interactions of several neurotransmitter and neural hormone molecules with the c-MYC G-quadruplex DNA sequence were analyzed using a combination of spectroscopic and computational techniques. The interactions between indole, catecholamine, and amino acid neurotransmitters and DNA sequences could potentially add to the understanding of the role of G-quadruplex structures play in various diseases. Also, the interaction of the DNA sequence derived from the nuclear hypersensitivity element (NHE) III1 region of c-MYC oncogene (Pu22), 5′-TGAGGGTGGGTAGGGTGGGTAA-3′, has added significance in that these molecules may promote or inhibit the formation of G-quadruplex DNA which could lead to the development of promising drugs for anticancer therapy. The results showed that these molecules did not disrupt G-quadruplex formation even in the absence of quadruplex-stabilizing cations. There was also evidence of concentration-dependent binding and high binding affinities based on the Stern-Volmer model, and thermodynamically favorable interactions in the form of hydrogen-bonding and interactions involving the π system of the aromatic neurotransmitters.

Cobalt(ii)–curcumin cysteine conjugate as c-MYC promoter G-quadruplex selective switch-on fluorescence probe

We have synthesized a metal organic framework comprising a cobalt(ii) complex of a curcumin–cysteine conjugate (i.e., Co–CC) as a fluorescent probe for the detection of G-quadruplex DNA sequences.

Binding symmetric porphyrins to the c-MYC promoter Pu24I G-quadruplex: toward more specific ligand recognition by flanking bases

The symmetric cationic porphyrin derivative TPyP4 exhibits higher selectivity toward flanking nucleotides of the c-MYC promoter G-quadruplex Pu24I than TMPyP4.

Significant structural change in human c-Myc promoter G-quadruplex upon peptide binding in potassium.

We selected the G-quadruplex motif located in the nuclease-hypersensitive elements (NHE) III1 region of the c-Myc promoter and for the first time performed its interaction studies with a designed peptide (QW10). Our CD results showed that the peptide bound to the c-Myc G-quadruplex and induced a significant blue shift in the positive peak of 20 nm in KCl alone or with 40wt% PEG200 or 20wt% PEG8000 in comparison to NaCl. Our Native Gel results confirmed that peptide binding destabilized the duplex and stabilized the unimolecular G-quadruplex and not binding to i-motif. UV thermal results confirmed destabilization of bimolecular structure and stabilization of unimolecular G-quadruplex. QW10 showed preferential binding towards c-MYC promoter G4 with binding constant (Kb) values of the order of 0.05 ± 0.2 μM, 0.12 ± 0.1 μM and 0.05 ± 0.3 μM for complexes in K+ alone or 40wt% PEG 200 or 20wt% PEG 8000 respectively. QW10 showed preferential cytotoxicity with IC50 values of 11.10 μM and 6.44 μM after 72 and 96 hours' incubation on Human Breast Carcinoma MDA-MB 231 cells and was found to be non-toxic with Human Embryonic Kidney (HEK-1) cells. Interestingly, we observed reduction of c-Myc gene expression by 2.5 fold due to QW10 binding and stabilizing c-MYC G4. Our study for the first time provides an expanded overview of significant structural change in human c-Myc promoter G-quadruplex upon peptide binding in potassium.

Fluorene/fluorenone carboxamide derivatives as selective light-up fluorophores for c-myc G-quadruplex

The development of fluorescent dyes capable of selective recognition of G-quadruplexes is essential for studying its localization and biological functions. However, considering the G-quadruplex topologies may vary significantly, the synthesis of compounds showing both selectivity and strong fluorescence properties still remains a great challenge. Recently we have developed fluorene/fluorenone derivatives with structure-specific binding towards dsRNA, indicating its potential for structure-selective ligands. Herein, we report the synthesis of novel fluorene/fluorenone derivatives and their selectivity towards various DNA structures, particularly G-quadruplexes, two of which showed strong affinity to the proto-oncogene c-myc promoter G-quadruplex.

Syntheses and Evaluation of New Bisacridine Derivatives for Dual Binding of G-Quadruplex and i-Motif in Regulating Oncogene c-myc Expression.

The c-myc oncogene is an important regulator for cell growth and differentiation, and its aberrant overexpression is closely related to the occurrence and development of various cancers. Thus, the suppression of c-myc transcription and expression has been investigated for cancer treatment. In this study, various new bisacridine derivatives were synthesized and evaluated for their binding with c-myc promoter G-quadruplex and i-motif. We found that a9 could bind to and stabilize both G-quadruplex and i-motif, resulting in the downregulation of c-myc gene transcription. a9 could inhibit cancer cell proliferation and induce SiHa cell apoptosis and cycle arrest. a9 exhibited tumor growth inhibition activity in a SiHa xenograft tumor model, which might be related to its binding with c-myc promoter G-quadruplex and i-motif. Our results suggested that a9 as a dual G-quadruplex/i-motif binder could be effective in both oncogene replication and transcription and become a promising lead compound for further development with improved potency and selectivity.

A small-sized benzothiazole-indolium fluorescent probe: the study of interaction specificity targeting c-MYC promoter G-quadruplex structures and live cell imaging.

A small-sized c-MYC promoter G-quadruplex selective fluorescent BZT-Indolium binding ligand was demonstrated for the first time as a highly target-specific and photostable probe for in vitro staining and live cell imaging and it was found to be able to inhibit the amplification of the c-MYC G-rich sequence (G-quadruplex) and down-regulate oncogene c-MYC expression in human cancer cells (HeLa).

A site-specific self-assembled light-up rotor probe for selective recognition and stabilization of c-MYC G-quadruplex DNA.

Direct and unambiguous evidence of the formation of G-quadruplexes (G4s) in human cells have shown their implication in several key biological events and has emphasized their role as important targets for small-molecule cancer therapeutics. Here, we report on the first example of a self-assembled molecular-rotor G4-binder able to discriminate between an extensive panel of G4 and non-G4 structures and to selectively light-up (up to 64-fold), bind (nanomolar range), and stabilize the c-MYC promoter G4 DNA. In particular, association with the c-MYC G4 triggers the disassembly of its supramolecular state (disaggregation-induced emission, DIE) and induces geometrical restrictions (motion-induced change in emission, MICE) leading to a significant enhancement of its emission yield. Moreover, this optical reporter is able to selectively stabilize the c-MYC G4 and inhibit DNA synthesis. Finally, by using confocal laser-scanning microscopy (CLSM) we show the ability of this compound to localize primarily in the subnuclear G4-rich compartments of cancer cells. This work provides a benchmark for the future design and development of a new generation of smart sequence-selective supramolecular G4-binders that combine outstanding sensing and stability properties, to be utilized in anti-cancer therapy.

New substituted quinoxalines inhibit triple-negative breast cancer by specifically downregulating the c-MYC transcription.

Conventional chemotherapy remains the primary treatment option for triple-negative breast cancer (TNBC). However, the current chemotherapeutic drugs have limited effects on TNBC, and often lead to serious side effects as well as drug resistance. Thus, more effective therapeutic options are sorely needed. As c-MYC oncogene is highly expressed during TNBC pathogenesis, inhibiting c-MYC expression would be an alternative anti-TNBC strategy. In this study, we designed and synthesized a serial of quinoxaline analogs that target c-MYC promoter G-quadruplex (G4), which is believed to be a repressor of c-MYC transcription. Among them, a difluoro-substituted quinoxaline QN-1 was identified as the most promising G4-stabilizing ligand with high selectivity to c-MYC G4 over other G4s, which is distinguished from many other reported ligands. Intracellular studies indicated that QN-1 induced cell cycle arrest and apoptosis, repressed metastasis and inhibited TNBC cell growth, primarily due to the downregulation of c-MYC transcription by a G4-dependent mechanism. Notably, inhibition by QN-1 was significantly greater for c-MYC than other G4-driven genes. Cancer cells with c-MYC overexpression were more sensitive to QN-1, relative to normal cells. Furthermore, QN-1 effectively suppressed tumor growth in a TNBC mouse model. Accordingly, this work provides an alternative strategy for treating TNBC.

Abstract 5207: Functions of nucleolin in its interactions with the MYC promoter G-quadruplex

Abstract DNA G-quadruplexes (G4s) are four-stranded non-canonical secondary structures formed in guanine-rich DNA sequences with functional significance and are found to be specifically enriched in the transcriptional regulatory regions of cancer-related genes. In particular, c-MYC, one of the most commonly deregulated genes in human cancers, has a DNA G4 motif in its proximal promoter which functions as a transcription inhibitor and can be targeted by G-quadruplex-interactive compounds, and is thus considered as an attractive target for cancer therapeutics. Nucleolin is overexpressed in cancer cells and is shown to be an important transcriptional regulator. Nucleolin has been found to specifically bind the c-MYC promoter G-quadruplex and to be involved in the regulation of MYC transcription, however, little is known about how the c-MYC promoter G-quadruplex interacts with and is regulated by nucleolin. By using AcGFP-tagged nucleolin, we observed nucleolin is mainly present in the cell nucleolus and nucleoplasm. We show that the nucleolin protein interacts to the MYC promoter region in vivo using chromatin immunoprecipitation assay coupled with next-generation sequencing analysis (ChIP-seq) in cancer cells. To show the association of nucleolin with G4s in vivo, we treated MCF7 cells with a G4-stabilizing ligand and monitored cellular localization of nucleolin and G4 sites using an immunofluorescent staining assay. Within 24 hr after treatment, we observed a large increase of endogenous G4 structures as well as a rapid cellular translocation of nucleolin from the cell nucleolus to the cell nucleoplasm. Importantly, the nucleolin foci were significantly colocalized with the G4 foci, suggesting the direct interaction of nucleolin and G4s in vivo. In the meantime, both MYC mRNA and protein levels were significantly reduced, indicating the nucleolin/MYC G4 interaction represses MYC transcription. To understand the interactions of nucleolin with the MYC G4 structure, we prepared various nucleolin protein constructs and studied its interactions with the MycG4 structures in vitro using NMR, EMSA, fluorescence, CD, AUC, and UV-crosslinking methods. We found that nucleolin specifically recognizes the c-MYC promoter G-quadruplex and forms a 1:1 complex with MycG4. Importantly, MycG4 maintains its G4 structure in the nucleolin-MycG4 complex. Additionally, CD melting of the MYC G4-nucleolin complex showed that MYC G4 is stabilized by nucleolin by more than 10 Celsius. In a conclusion, our in vitro and in vivo results provide important insights into the nucleolin protein interactions with the MYC promoter G4 structure and the G4-associated biological functions of nucleolin in cancer cells. Citation Format: Guanhui Wu, Luying Chen, Clement Lin, Buket Onel, Danzhou Yang. Functions of nucleolin in its interactions with the MYC promoter G-quadruplex [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5207.

Interactions between a Bioflavonoid and c-MYC Promoter G-Quadruplex DNA: Ensemble and Single-Molecule Investigations.

Small molecules capable of stabilizing the G-quadruplex structure of the nuclease hypersensitivity element III1 (NHE III1) are useful in controlling the overexpression of the c-MYC oncogene. In this study, we have probed the interactions of a 22-mer c-MYC promoter quadruplex-forming sequence (Pu22) with a bioflavonoid 3,4',5,7-tetrahydroxyflavone, commonly known as kaempferol (KF). Ensemble fluorescence resonance energy transfer experiments on labeled Pu22 indicate that KF decreases the affinity of the former toward its complimentary strand, suggesting the stabilization of the quadruplex structure of Pu22. Considering that binding dynamics plays an important role in supramolecular interactions, there is hardly any information on this aspect for quadruplex-flavonoid systems; we have studied the kinetics of KF-Pu22 complexation and decomplexation processes on the single-molecule level by employing fluorescence correlation spectroscopy technique. The binding dynamics is characterized by a fast relaxation time of 10-50 μs. This leads to a high association rate constant ( k+) of ∼109 M-1 s-1, which is close to the pure diffusion controlled limit. However, it is the low dissociation rate constant ( k-) of ∼104 s-1 that is mainly responsible for the stability of the KF-Pu22 complex. Molecular docking study shows that KF binds near the 3'-end of Pu22 by forming several H-bonds with the bases. These findings suggest that KF is a potential binder of the c-MYC promoter quadruplex DNA and can be useful in anticancer therapies.

Abstract 1474: Identifying novel chromatin binding sites of nucleolin protein in cancer cells

Abstract Nucleolin is an important regulator of cell proliferation and has been reported to play a role in c-Myc transcriptional regulation. Elevated expression levels of nucleolin have been shown in a number of malignant cells, but how nucleolin contributes to cancer development and progression remains unknown. Recently, G-quadruplexes (G4s) have been shown in vivo to form in G-rich sequences with biological importance. Nucleolin has been reported to bind to G-quadruplexes for its biological functions. In particular, G4s have been shown to form in the MYC promoter and inhibit MYC transcription; nucleolin was found to display a remarkable binding affinity to the c-Myc promoter G4 over its best-known RNA target. CX-3543, the first-in-class G-quadruplex-targeting small molecule, was shown to induce nucleolin redistribution from the cell nucleolus to the cell nucleoplasm and apoptosis in cancer cells, which was suggested to act through the c-Myc promoter G-quadruplex. Therefore, unbiased analysis of the genomic binding sites of nucleolin in human chromatin is pivotal in understanding nucleolin's biological functions. Using chromatin immunoprecipitation (ChIP) assay, we demonstrated that nucleolin binds to the c-Myc NHE III1 region in vivo. Using an anti-nucleolin antibody, the isolated DNA from the immunoprecipitated DNA-protein complexes from HeLa cells yielded numerous c-Myc promoter sequences that were determined by real-time PCR, suggesting the direct interaction between nucleolin and the c-Myc promoter G4-forming region in vivo. G4-interactive ligands have been shown to facilitate the formation of G4 structures in cells. To elucidate the association of nucleolin with G-quadruplexes in vivo, we monitored cellular localization of nucleolin before and after G4 ligand treatments and observed a rapid cellular translocation of nucleolin from the cell nucleolus to the cell nucleoplasm. Using ChIP coupled with next-generation sequencing analysis (ChIP-seq), we identified several binding sites of nucleolin in human chromatin. The determined chromatin binding sites of nucleolin will provide insights into the biological functions of nucleolin and its relationship with G-quadruplexes in cancer cells. Citation Format: Guanhui Wu, Buket Onel, Danzhou Yang. Identifying novel chromatin binding sites of nucleolin protein in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1474.

Abstract 2662: Indenoisoquinoline topoisomerase I inhibitors target the DNA G-quadruplex formed in the c-Myc promoter and cause MYC downregulation

Abstract The inhibition of DNA topoisomerase I (Top1) has proven to be a successful approach toward the design of anticancer agents. Indenoisoquinoline derivatives have been designed and developed as Top1 inhibitors and can overcome some shortcomings associated with the camptothecin Top1 inhibitors, resulting in three indenoisoquinoline compounds, indotecan (LMP 400), indimitecan (LMP776), and LMP744 entering Phase I clinical trials at the National Cancer Institute. However, some active indenoisoquinolines did not show potent Top1 inhibition, suggesting a separate mechanism of action. c-Myc is one of the most commonly deregulated genes in human cancers; a DNA G-quadruplex (G4) formed in the proximal promoter region of c-Myc has been found to function as a transcriptional silencer and be amenable to small molecule targeting. As indenoisoquinolines share structure similarity to our c-Myc G-quadruplex (MycG4)-interactive compounds, we hypothesized that indenoisoquinolines could stabilize MycG4 and downregulate MYC transcription. Using a fluorescence resonance energy transfer (FRET) assay, we examined the MycG4 stabilization activity of 56 indenoisoquinoline compounds that we previously developed as Top1 inhibitors. Notably, 26 of the 56 compounds decreased the fluorescence intensity by at least 50%, and the 10 most potent compounds reduced fluorescence intensities by over 70%, indicating that these indenoisoquinolines are effective MycG4 stabilizers. The identified compounds were further characterized by fluorescence anisotropy, circular dichroism, and nuclear magnetic resonance for MycG4 interactions, followed by western blot assays for MYC downregulation. Significantly, the compounds with good MycG4 binding activity and affinity exhibited significant dose-dependent reduction of MYC expression, indicating that targeting the c-Myc promoter G-quadruplex is a likely mechanism of action for these active anticancer compounds. Furthermore, some active indenoisoquinolines exhibited both MYC downregulation and Top1 inhibition, suggesting that dual targeting c-Myc G-quadruplex and Top1 may represent a novel mechanism of action for anticancer drug design. Citation Format: Kaibo Wang, Mohamed S. A. Elsayed, Guanhui Wu, Mark Cushman, Danzhou Yang. Indenoisoquinoline topoisomerase I inhibitors target the DNA G-quadruplex formed in the c-Myc promoter and cause MYC downregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2662.

Target guided synthesis using DNA nano-templates for selectively assembling a G-quadruplex binding c-MYC inhibitor

The development of small molecules is essential to modulate the cellular functions of biological targets in living system. Target Guided Synthesis (TGS) approaches have been used for the identification of potent small molecules for biological targets. We herein demonstrate an innovative example of TGS using DNA nano-templates that promote Huisgen cycloaddition from an array of azide and alkyne fragments. A G-quadruplex and a control duplex DNA nano-template have been prepared by assembling the DNA structures on gold-coated magnetic nanoparticles. The DNA nano-templates facilitate the regioselective formation of 1,4-substituted triazole products, which are easily isolated by magnetic decantation. The G-quadruplex nano-template can be easily recovered and reused for five reaction cycles. The major triazole product, generated by the G-quadruplex inhibits c-MYC expression by directly targeting the c-MYC promoter G-quadruplex. This work highlights that the nano-TGS approach may serve as a valuable strategy to generate target-selective ligands for drug discovery.

New Disubstituted Quindoline Derivatives Inhibiting Burkitt's Lymphoma Cell Proliferation by Impeding c-MYC Transcription.

The c-MYC oncogene is overactivated during Burkitt's lymphoma pathogenesis. Targeting c-MYC to inhibit its transcriptional activity has emerged as an effective anticancer strategy. We synthesized four series of disubstituted quindoline derivatives by introducing the second cationic amino side chain and 5-N-methyl group based on a previous study of SYUIQ-5 (1) as c-MYC promoter G-quadruplex ligands. The in vitro evaluations showed that all new compounds exhibited higher stabilities and binding affinities, and most of them had better selectivity (over duplex DNA) for the c-MYC G-quadruplex compared to 1. Moreover, the new ligands prevented NM23-H2, a transcription factor, from effectively binding to the c-MYC G-quadruplex. Further studies showed that the selected ligand, 7a4, down-regulated c-MYC transcription by targeting promoter G-quadruplex and disrupting the NM23-H2/c-MYC interaction in RAJI cells. 7a4 could inhibit Burkitt's lymphoma cell proliferation through cell cycle arrest and apoptosis and suppress tumor growth in a human Burkitt's lymphoma xenograft.

Selective recognition of c-myc promoter G-quadruplex and down-regulation of oncogene c-myc transcription in human cancer cells by 3,8a-disubstituted indolizinone

Indolizinone could selectively recognize c-myc promoter G-quadruplex.

Design, synthesis and biological evaluation of 4-anilinoquinazoline derivatives as new c-myc G-quadruplex ligands

A series of 4-anilinoquinazoline derivatives were designed and synthesized as novel c-myc promoter G-quadruplex binding ligands. Subsequent biophysical and biochemical evaluation demonstrated that the introduction of aniline group at 4-position of quinazoline ring and two side chains with terminal amino group improved their binding affinity and stabilizing ability to G-quadruplex DNA. RT-PCR assay and Western blot showed that compound 7a could down-regulate transcription and expression of c-myc gene in Hela cells, which was consistent with the behavior of an effective G-quadruplex ligand targeting c-myc oncogene. More importantly, RTCA and colony formation assays indicated that 7a obviously inhibited Hela cells proliferation, without influence on normal primary cultured mouse mesangial cells. Flow cytometric assays suggested that 7a induced Hela cells to arrest in G0/G1 phase both in a time-dependent and dose-dependent manner.

In silico identification of novel ligands for G-quadruplex in the c-MYC promoter.

G-quadruplex DNA formed in NHEIII1 region of oncogene promoter inhibits transcription of the genes. In this study, virtual screening combining pharmacophore-based search and structure-based docking screening was conducted to discover ligands binding to G-quadruplex in promoter region of c-MYC. Several hit ligands showed the selective PCR-arresting effects for oligonucleotide containing c-MYC G-quadruplex forming sequence. Among them, three hits selectively inhibited cell proliferation and decreased c-MYC mRNA level in Ramos cells, where NHEIII1 is included in translocated c-MYC gene for overexpression. Promoter assay using two kinds of constructs with wild-type and mutant sequences showed that interaction of these ligands with the G-quadruplex resulted in turning-off of the reporter gene. In conclusion, combined virtual screening methods were successfully used for discovery of selective c-MYC promoter G-quadruplex binders with anticancer activity.

Mechanistic studies on the anticancer activity of 2,4-disubstituted quinazoline derivative

BackgroundAccelerated proliferation of solid tumor and hematologic cancer cells is related to accelerated transcription of ribosomal DNA by the RNA polymerase I to produce elevated level of ribosomal RNA. Therefore, down-regulation of RNA polymerase I transcription in cancer cells is an important anticancer therapeutic strategy. MethodsA variety of methods were used, including cloning, expression and purification of protein, electrophoretic mobility shift assay (EMSA), circular dichroic (CD) spectroscopy, CD-melting, isothermal titration calorimetry (ITC), chromatin immunoprecipitation (Ch-IP), RNA interference, RT-PCR, Western blot, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell assay. ResultsOur results showed that 2,4-disubstituted quinazoline derivative Sysu12d could down-regulate c-myc through stabilization of c-myc promoter G-quadruplex, resulting in down-regulation of nucleolin expression. Sysu12d could also disrupt nucleolin/G-quadruplex complex. Both of the above contributed to the down-regulation of ribosomal RNA synthesis, followed by activation of p53 and then cancer cell apoptosis. ConclusionsThese mechanistic studies set up the basis for further development of Sysu12d as a new type of lead compound for cancer treatment. General significance2,4-Disubstituted quinazoline derivatives may have multi-functional effect for cancer treatment.

Novel Interaction of the Z-DNA Binding Domain of Human ADAR1 with the Oncogenic c-Myc Promoter G-Quadruplex

Both G-quadruplex and Z-DNA can be formed in G-rich and repetitive sequences on genome, and their formation and biological functions are controlled by specific proteins. Z-DNA binding proteins, such as human ADAR1, have a highly conserved Z-DNA binding domain having selective affinity to Z-DNA. Here, our study identifies the Z-DNA binding domain of human ADAR1 (hZαADAR1) as a novel G-quadruplex binding protein that recognizes c-myc promoter G-quadruplex formed in NHEIII1 region and represses the gene expression. An electrophoretic migration shift assay shows the binding of hZαADAR1 to the intramolecular c-myc promoter G-quadruplex-forming DNA oligomer. To corroborate the binding of hZαADAR1 to the G-quadruplex, we conducted CD and NMR chemical shift perturbation analyses. CD results indicate that hZαADAR1 stabilizes the parallel-stranded conformation of the c-myc G-quadruplex. The NMR chemical shift perturbation data reveal that the G-quadruplex binding region in hZαADAR1 was almost identical with the Z-DNA binding region. Finally, promoter assay and Western blot analysis show that hZαADAR1 suppresses the c-myc expression promoted by NHEIII1 region containing the G-quadruplex-forming sequence. This finding suggests a novel function of Z-DNA binding protein as a regulator of G-quadruplex-mediated gene expression.