Cationic corrole derivatives: a new family of G-quadruplex inducing and stabilizing ligands

Decoding the prospective of metal complexes in anti-cancer therapeutics by targeting of G-quadruplex DNA

The use of metallodrugs in cancer therapy received widespread interest after the successful application of cisplatin and its analogous compounds as chemotherapeutic medications. Despite the development of various metallodrugs in past years, platinum-based chemotherapeutic agents are the only clinically approved metallodrugs that primarily interact with genomic DNA and trigger severe dose-limiting adverse side effects in cancer patients. As a consequence, the advancement of new risk-free metallodrugs has become a topmost concern in cancer research to minimize toxicity and improve therapeutic outcomes. G-quadruplex (G4) DNA structures have recently come to light as an attractive drug target in cancer therapy because of their gene regulation ability and role in maintaining genomic stability. Their presence in telomere and promoter region of oncogenes has the potential to induce apoptosis in cancer cells through the inhibition of telomerase activity and gene expression. Therefore, the development of new G4 DNA targeting small molecular entities including metal complexes came out as a viable approach for uprooting cancer disease. Beyond organic small molecules, innumerable metal complexes have been developed in past years to target G4 DNA structures in the context of cancer therapy. This review primarily aims to highlight these metal complexes through a comprehensive discussion about their structural properties, their binding interactions with G4 DNA, their cancer cell growth inhibition mechanisms, and their efficacy in both cellular and in vivo systems, to decode their potential as anti-cancer drugs. Additionally, the potential of these metal complexes in the field of bio-imaging and photodynamic therapy is also explored.

Hallmarks of anticancer and antimicrobial activities of corroles

Corroles provide a remarkable opportunity for the development of cancer theranostic agents among other porphyrinoids. While most transition metal corrole complexes are only therapeutic, post-transition metallocorroles also find their applications in bioimaging. Moreover, corroles exhibit excellent photo-physicochemical properties, which can be harnessed for antitumor and antimicrobial interventions. Nevertheless, these intriguing, yet distinct properties of corroles, have not attained sufficient momentum in cancer research. The current review provides a comprehensive summary of various cancer-relevant features of corroles ranging from their structural and photophysical properties, chelation, protein/corrole interactions, to DNA intercalation. Another aspect of the paper deals with the studies of corroles conducted in vitro and in vivo with an emphasis on medical imaging (optical and magnetic resonance), photo/sonodynamic therapies, and photodynamic inactivation. Special attention is also given to a most recent finding that shows the development of pH-responsive phosphorus corrole as a potent antitumor drug for organelle selective antitumor cytotoxicity in preclinical studies. Another biomedical application of corroles is also highlighted, signifying the application of water-soluble and completely lipophilic corroles in the photodynamic inactivation of microorganisms. We strongly believe that future studies will offer a greater possibility of utilizing advanced corroles for selective tumor targeting and antitumor cytotoxicity. In the line with future developments, an ideal pipeline is envisioned on grounds of cancer targeting nanoparticle systems upon decoration with tumor-specific ligands. Hence, we envision that a bright future lies ahead of corrole anticancer research and therapeutics.

Structure-based discovery of Licoflavone B and Ginkgetin targeting c-Myc G-quadruplex to suppress c-Myc transcription and myeloma growth

G-quadruplex (G4), present in the c-Myc promoter, has emerged as an attractive cancer-specific molecular target for drug development. So, the discovery of small molecules to stabilize c-Myc-G4 to inhibit transcription of c-Myc protein is of great significance. Herein, a combined molecular docking-based virtual screening strategy, molecular dynamics (MD) simulation, and molecular mechanics/generalized Born surface area (MM/GBSA) free energy calculation was conducted on the existing L6000 Natural Compound Library. Four natural compounds, including Licoflavone B, Demethyleneberberine, Ginkgetin, and Mulberroside C, were predicted to have preferable binding affinities to c-Myc G4 and then selected for commercial purchase and experimental evaluation. Compounds Licoflavone B and Ginkgetin can significantly inhibit myeloma cell proliferation, with IC₅₀ values <8 μM against the RPMI-8226 cell line. Moreover, our data demonstrated that the two compounds could simultaneously downregulate c-Myc transcription and expression. Collectively, compounds Licoflavone B and Ginkgetin might be regarded as new candidates for the development of the more potent c-Myc-G4 stabilizers in the future.

Identification of Trovafloxacin, Ozanimod, and Ozenoxacin as potent c-Myc G-quadruplex stabilizers to suppress c-Myc transcription and myeloma growth

c-Myc is a major oncogene that is estimated to result in almost all human cancers and the c-Myc downregulation has become an attractive strategy for cancer treatment. For it is hard to design compounds that can directly interact with the c-Myc protein, the DNA G-quadruplex (G4) was discovered in its promoter region which was referred to as a potential drug target for controlling c-Myc expression. In this study, a combined strategy of molecular docking-based virtual screening, molecular dynamics (MD) simulation, and molecular mechanics/generalized Born surface area (MM/GBSA) free energy calculation was conducted on the existing FDA-Approved Drugs Library, eight compounds were selected for further experimental assay. Among them, five compounds exhibited dose-dependently anticancer activities against RPMI-8226 cells with IC50 values less than 18.4 μM. Further experiments showed that Trovafloxacin, Ozanimod, and Ozenoxacin decreased c-Myc mRNA level obviously and downregulated c-Myc expression significantly. In summary, compounds Trovafloxacin, Ozanimod, and Ozenoxacin might be regarded as new c-Myc G4 stabilizers for the treatment of c-Myc related cancers in the future.

Corroles at work: a small macrocycle for great applications

Corrole chemistry has witnessed an impressive boost in studies in the last 20 years, thanks to the possibility of preparing corrole derivatives by simple synthetic procedures. The investigation of a large number of corroles has highlighted some peculiar characteristics of these macrocycles, having features different from those of the parent porphyrins. With this progress in the elucidation of corrole properties, attention has been focused on the potential for the exploitation of corrole derivatives in different important application fields. In some areas, the potential of corroles has been studied in certain detail, for example, the use of corrole metal complexes as electrocatalysts for energy conversion. In some other areas, the field is still in its infancy, such as in the exploitation of corroles in solar cells. Herein, we report an overview of the different applications of corroles, focusing on the studies reported in the last five years.

Recent Update on Targeting c-MYC G-Quadruplexes by Small Molecules for Anticancer Therapeutics

Guanine-rich DNA sequences have the propensity to adopt four-stranded tetrahelical G-quadruplex (G4) structures that are overrepresented in gene promoters. The structural polymorphism and physicochemical properties of these non-Watson-Crick G4 structures make them important targets for drug development. The guanine-rich nuclease hypersensitivity element III₁ present in the upstream of P1 promoter of c-MYC oncogene has the ability to form an intramolecular parallel G4 structure. The G4 structure that forms transiently in the c-MYC promoter functions as a transcriptional repressor element. The c-MYC oncogene is overexpressed in a wide variety of cancers and plays a key role in cancer progression. Till now, a large number of compounds that are capable of interacting and stabilizing thec-MYC G4 have been reported. In this review, we summarize various c-MYC G4 specific molecules and discuss their effects on c-MYC gene expression in vitro and in vivo.

Porphyrinoid Drug Conjugates

Drawing inspiration from nature today remains a time-honored means of discovering the therapies of tomorrow. Porphyrins, the so-called "pigments of life" have played a key role in this effort due to their diverse and unique properties. They have seen use in a number of medically relevant applications, including the development of so-called drug conjugates wherein functionalization with other entities is used to improve efficacy while minimizing dose limiting side effects. In this Perspective, we highlight opportunities associated with newer, completely synthetic analogs of porphyrins, commonly referred to as porphyrinoids, as the basis for preparing drug conjugates. Many of the resulting systems show improved medicinal or site-localizing properties. As befits a Perspective of this type, our efforts to develop cancer-targeting, platinum-containing conjugates based on texaphyrins (a class of so-called "expanded porphyrins") will receive particular emphasis; however, the promise inherent in this readily generalizable approach will also be illustrated briefly using two other common porphyrin analogs, namely the corroles (a "contracted porphyrin") and porphycene (an "isomeric porphyrin").

Investigation of G-quadruplex formation in the FGFR2 promoter region and its transcriptional regulation by liensinine

BACKGROUND

Fibroblast growth factor receptor 2 (FGFR2) is overexpressed in breast cancer tissues and cells, and has been shown to be a susceptibility factor for breast cancer. In this study, we found that the G-rich sequences in the FGFR2 promoter region can form G-quadruplexes, which could be the target and inhibitor of the FGFR2 gene.

METHODS

Initially, the formation of G-quadruplexes was confirmed by ESI-MS and CD, and DMS footprinting experiments gave the folding pattern of the G-quadruplexes. After luciferase reporter assays revealed that the G-quadruplex could inhibit the activity of the FGFR2 promoter, MS and SPR showed binding affinity and selectivity of the ligand. Then cell culture experiments and ChIP assay showed the bioactivity of the ligand.

RESULTS

We found that three G-rich sequences (S1-S3) in the FGFR2 promoter region can form G-quadruplex structures. And a natural alkaloid, liensinine, was found to bind to the S1 G-quadruplex with relative high affinity and selectivity. Cell culture experiments showed that liensinine inhibits FGFR2 activity at both the transcriptional and translational levels. Moreover, chromatin immunoprecipitation assay (ChIP) results showed that liensinine blocks the binding of E2F1 at the transcription factor binding site (TFBS) in the S1 sequence, which is the mechanism through which liensinine inhibits the FGFR2 gene.

CONCLUSIONS

A natural alkaloid was discovered to selectively bind to the S1 G-quadruplex with relative high affinity, and therefore inhibited FGFR2 transcription and translation.

GENERAL SIGNIFICANCE

Our discovery offers a useful strategy to inhibit FGFR2 transcription, i.e., targeting the G-quadruplex with a natural alkaloid.

Synthesis of Corroles and Their Heteroanalogs

Corroles have come a long way from being a curiosity to being a mainstream research topic. They are now regularly synthesized in numerous research laboratories worldwide with diverse specific aims in mind. In this review we present a comprehensive description of corroles' synthesis, developed both before and after 1999. To aid the investigator in developing synthetic strategies, some of the sections culminate in tables containing comparisons of various methodologies leading to meso-substituted corroles. The remaining challenges are delineated. In the second part of this review, we also describe the syntheses of isocorroles and heteroanalogs of corroles such as triazacorroles (corrolazines), 10-heterocorroles, 21-heterocorroles, 22-heterocorroles, N-confused corroles, as well as norcorroles. The review is complemented with a short outlook.

Fighting Cancer with Corroles

Corroles are exceptionally promising platforms for the development of agents for simultaneous cancer-targeting imaging and therapy. Depending on the element chelated by the corrole, these theranostic agents may be tuned primarily for diagnostic or therapeutic function. Versatile synthetic methodologies allow for the preparation of amphipolar derivatives, which form stable noncovalent conjugates with targeting biomolecules. These conjugates can be engineered for imaging and targeting as well as therapeutic function within one theranostic assembly. In this review, we begin with a brief outline of corrole chemistry that has been uniquely useful in designing corrole-based anticancer agents. Then we turn attention to the early literature regarding corrole anticancer activity, which commenced one year after the first scalable synthesis was reported (1999-2000). In 2001, a major advance was made with the introduction of negatively charged corroles, as these molecules, being amphipolar, form stable conjugates with many proteins. More recently, both cellular uptake and intracellular trafficking of metallocorroles have been documented in experimental investigations employing advanced optical spectroscopic as well as magnetic resonance imaging techniques. Key results from work on both cellular and animal models are reviewed, with emphasis on those that have shed new light on the mechanisms associated with anticancer activity. In closing, we predict a very bright future for corrole anticancer research, as it is experiencing exponential growth, taking full advantage of recently developed imaging and therapeutic modalities.

Exploration of binding affinity and selectivity of brucine with G-quadruplex in the c-myb proto-oncogene by electrospray ionization mass spectrometry

RATIONALE

The c-myb gene is a potential therapeutic target for human tumors and leukemias. Active ingredients from natural products may be used as drugs in chemotherapy for human cancers. Here, electrospray ionization mass spectrometry (ESI-MS) was used to probe the formation and recognition of the G-quadruplex structure from the G-rich sequence that is found in the c-myb gene promoter, 5'-GGGCTGGGCTGGGCGGGG-3'. The aim of our study is to evaluate a potential binder for the c-myb gene from natural products, and thereby to modulate c-myb gene expression.

METHODS

ESI-MS, as an effective method, was utilized not only to characterize the formation of the G-quadruplex in the c-myb oncogene, but also as a tool to probe the binding characteristics of alkaloid molecules with the target G-quadruplex DNA.

RESULTS

ESI-MS results with the support of circular dichroism (CD) spectra demonstrated the formation of an intramolecular parallel-stranded G-quadruplex in the c-myb oncogene promoter. A screening of six alkaloid molecules showed that brucine (P1) had a strong binding affinity to the c-myb G-quadruplex DNA. It is notable that P1 can bind selectively to the c-myb G-quadruplex with respect to duplex DNAs, as well as to G-quadruplexes in other types of gene sequences. According to ESI-MS results, in which the stability was tested by capillary heating and collision-induced dissociation, the binding of P1 could thermally stabilize the c-myb G-quadruplex DNA.

CONCLUSIONS

In this work, brucine (P1), an alkaloid molecule, has been found to bind to the intramolecular parallel G-quadruplex in the c-myb oncogene promoter with high affinity and selectivity, and could thermally stabilize the c-myb G-quadruplex DNA, indicating that the binding of P1 has the potential to modulate c-myb gene expression. Copyright © 2015 John Wiley & Sons, Ltd.

A Nitroxide-Tagged Platinum(II) Complex Enables the Identification of DNA G-Quadruplex Binding Mode

We reported a novel strategy for investigating small molecule binding to G-quadruplexes (GQs). A newly synthesized dinuclear platinum(II) complex (Pt₂L) containing a nitroxide radical was shown to selectively bind a GQ-forming sequence derived from human telomere (hTel). Using the nitroxide moiety as a spin label, electron paramagnetic resonance (EPR) spectroscopy was carried out to investigate binding between Pt₂L and hTel GQ. Measurements indicated that two molecules of Pt₂L bind with one molecule of hTel GQ. The inter-spin distance measured between the two bound Pt₂L, together with molecular docking analyses, revealed that Pt₂L predominately binds to the neighboring narrow and wide grooves of the G-tetrads as hTel adopts the antiparallel conformation. The design and synthesis of nitroxide tagged GQ binders, and the use of spin-labeling/EPR to investigate their interactions with GQs, will aid the development of small molecules for manipulating GQs involved in crucial biological processes.

Photoinduced Electron Transfer between Anionic Corrole and DNA

The interaction between a water-soluble anionic Ga(III) corrole [Ga(tpfc)(SO3Na)2] and calf thymus DNA (ct-DNA) has been investigated by using femtosecond transient absorption spectroscopy. A significant broadening from 570 to 585 nm of positive absorption band of the blend of Ga(tpfc)(SO3Na)2 and ct-DNA (Ga(tpfc)(SO3Na)2-ctDNA) has been observed from 0.15 to 0.50 ps after photoexcitation of Ga(tpfc)(SO3Na)2 into the Soret band. The control experiment has been performed on the model DNA ([poly(dG-dC)]2) rich in guanine bases, which exhibits a similar spectral broadening, whereas it is absent for [poly(dA-dT)]2 without guanine bases. The molecular orbital calculation shows that HOMO of Ga(tpfc)(SO3Na)2 is lower than that of guanine bases. The results of the electrochemical experiment show the reversible electron transfer (ET) between Ga(tpfc)(SO3Na)2 and guanine bases of ct-DNA is thermodynamically favorable. The dynamical analysis of the transient absorption spectra reveals that an ultrafast forward ET from the guanine bases to Ga(tpfc)(SO3Na)2 occurs within the pulse duration (156 fs), leading to the formation of an intermediate state. The following back ET to the ground state of Ga(tpfc)(SO3Na)2 may be accomplished in 520 fs.

DNA Binding, Photonuclease Activity and Human Serum Albumin Interaction of a Water-Soluble Freebase Carboxyl Corrole

The DNA binding property of 5,10,15-Tris(4-carboxyphenyl) corrole (TCPC) was studied by UV-Visible, fluorescence and circular dichroism (CD) spectroscopic methods. TCPC can bind to ct-DNA via an outside binding mode with the binding constant of K_b = 1.05 × 10⁵ M⁻¹. TCPC also displayed good photonuclease activity, which involves singlet oxygen species (¹O₂). The binding constant between TCPC and human serum albumin (HSA) is K_A = 2.24 × 10⁵ M⁻¹ with a simulated binding distance of 2.06 nm. The fluorescence quenching of HSA by TCPC followed a static quenching process. Site marker competitive displacement experiments indicated that warfarin site I is the main binding site. The secondary structure of HSA was changed upon interaction with TCPC, which was confirmed by UV-Visible and CD spectroscopy.

Recent developments in out-of-plane metallocorrole chemistry across the periodic table

This article presents a brief review of recent developments in metallocorrole chemistry, with a focus on species with significant displacement of the metal from the N4 plane of the corrole ring. Comparisons based on X-ray crystallographic data are made between a range of early and/or heavy transition metal, lanthanide, actinide, and main group metallocorrole species.

Stabilization of G-quadruplex DNA, inhibition of telomerase activity, and tumor cell apoptosis by organoplatinum(II) complexes with oxoisoaporphine

Two G-quadruplex ligands [Pt(L(a))(DMSO)Cl] (Pt1) and [Pt(L(b))(DMSO)Cl] (Pt2) have been synthesized and fully characterized. The two complexes are more selective for SK-OV-3/DDP tumor cells versus normal cells (HL-7702). It was found that both Pt1 and Pt2 could be a telomerase inhibitor targeting G-quadruplex DNA. This is the first report demonstrating that telomeric, c-myc, and bcl-2 G-quadruplexes and caspase-3/9 preferred to bind with Pt2 rather than Pt1, which also can induce senescence and apoptosis. The different biological behavior of Pt1 and Pt2 may correlate with the presence of a 6-hydroxyl group in L(b). Importantly, Pt1 and Pt2 exhibited higher safety in vivo and more effective inhibitory effects on tumor growth in the HCT-8 and NCI-H460 xenograft mouse model, compared with cisplatin. Taken together, these mechanistic insights indicate that both Pt1 and Pt2 display low toxicity and could be novel anticancer drug candidates.

Advances in the molecular design of potential anticancer agents via targeting of human telomeric DNA

Telomerase is an attractive drug target to develop new generation drugs against cancer.

V-shaped dinuclear Pt(II) complexes: selective interaction with human telomeric G-quadruplex and significant inhibition towards telomerase

A quaternized trigeminal ligand, 4-[4,6-di(4-pyridyl)-1,3,5-(2-triazinyl)]-1-methylpyridine-1-ium hexafluorophosphate (dptmp·PF6), and two derivative V-shaped dinuclear Pt(II) complexes, {[Pt(dien)]₂(dptmp)}(PF₆)₅ (1) and {[Pt(dpa)]₂(dptmp)}(PF₆)₅ (2), were synthesized, characterized and applied to a series of biochemical studies. FRET and SPR analyses showed these compounds, especially Pt(II) complexes, bound more strongly to human telomeric (hTel) G-quadruplex than to promoters (such as c-myc and bcl2) or to the duplex DNA. PCR-stop assays revealed that the Pt(II) complexes could bind to and stabilize G-quadruplex far more effectively than corresponding ligand. CD analyses further indicated the three compounds likely stabilized the formation of mixed-type parallel/antiparallel G-quadruplex structures. Their efficacy as telomerase inhibitors and potential anticancer drugs was explored via TRAP. The IC₅₀ value was determined to be 0.113 ± 0.019 μM for 1, indicating that it is one of the strongest known telomerase inhibitors. These results confirm that both V-shaped dinuclear Pt(II) complexes act as selective G-quadruplex binders and significant telomerase inhibitors.

Interaction of tricationic corroles with single/double helix of homopolymeric nucleic acids and DNA

In this manuscript a multitechnique approach is proposed to characterize the interaction between new tri-N-methylpyridyl corrole (TMPC) and its germanium(IV) derivative (GeTMPC), with single- and double-stranded nucleic acid homopolymers and calf thymus DNA. The specificity of each spectroscopic technique has been exploited to analyze the different aspects of corrole binding. Noteworthy, this approach allows us to distinguish between H aggregation of TMPC in the presence of polyriboadenilic acid (poly(rA)) and J aggregates in the presence of polyribocytidinic acid (poly(rC)) as well as to identify the formation of GeTMPC dimers in the presence of single-stranded poly(rA) and pseudointercalation with single-stranded poly(rC).

Promoting the formation and stabilization of human telomeric G-quadruplex DNA, inhibition of telomerase and cytotoxicity by phenanthroline derivatives

Four new di-substituted phenanthroline-based compounds a-d have been designed and prepared, and they have been shown to induce the formation of anti-parallel structure of human telomeric G-quadruplex DNA by CD spectra. FRET assay indicates that the melting temperature increases (ΔT(m) values) of G-quadruplex in buffer (pH 7.4) containing 100 mM NaCl are 31.6, 34.6, 17.8 and 32.6 °C for the compounds (1.0 μM) a, b, c and d, respectively. Competitive FRET assay shows that the four compounds exhibit a high G-quadruplex DNA selectivity over duplex DNA. Three of the compounds are the potent telomerase inhibitors and HeLa cell proliferation inhibitors.

Aminoglycoside binding to Oxytricha nova telomeric DNA

Telomeric DNA sequences have been at the center stage of drug design for cancer treatment in recent years. The ability of these DNA structures to form four-stranded nucleic acid structures, called G-quadruplexes, has been perceived as target for inhibiting telomerase activity vital for the longevity of cancer cells. Being highly diverse in structural forms, these G-quadruplexes are subjects of detailed studies of ligand-DNA interactions of different classes, which will pave the way for logical design of more potent ligands in future. The binding of aminoglycosides was investigated with Oxytricha nova quadruplex forming DNA sequence (GGGGTTTTGGGG)(2). Isothermal titration calorimetry (ITC) determined ligand to quadruplex binding ratio shows 1:1 neomycin:quadruplex binding with association constants (K(a)) ∼ 10(5) M(-1) while paromomycin was found to have a 2-fold weaker affinity than neomycin. The CD titration experiments with neomycin resulted in minimal changes in the CD signal. FID assays, performed to determine the minimum concentration required to displace half of the fluorescent probe bound, showed neomycin as the best of the all aminoglycosides studied for quadruplex binding. Initial NMR footprint suggests that ligand-DNA interactions occur in the wide groove of the quadruplex. Computational docking studies also indicate that aminoglycosides bind in the wide groove of the quadruplex.

"One ring to bind them all"-part I: the efficiency of the macrocyclic scaffold for g-quadruplex DNA recognition

Macrocyclic scaffolds are particularly attractive for designing selective G-quadruplex ligands essentially because, on one hand, they show a poor affinity for the “standard” B-DNA conformation and, on the other hand, they fit nicely with the external G-quartets of quadruplexes. Stimulated by the pioneering studies on the cationic porphyrin TMPyP4 and the natural product telomestatin, follow-up studies have developed, rapidly leading to a large diversity of macrocyclic structures with remarkable-quadruplex binding properties and biological activities. In this review we summarize the current state of the art in detailing the three main categories of quadruplex-binding macrocycles described so far (telomestatin-like polyheteroarenes, porphyrins and derivatives, polyammonium cyclophanes), and in addressing both synthetic issues and biological aspects.

Small-molecule selectively recognizes human telomeric G-quadruplex DNA and regulates its conformational switch

Structural complexity is an inherent feature of the human telomeric sequence, and it presents a major challenge for developing ligands of pharmaceutical interest. Recent studies have pointed out that the induction of a quadruplex or change of a quadruplex conformation on binding may be the most powerful method to exert the desired biological effect. In this study, we demonstrate a quadruplex ligand that binds selectively to different forms of the human telomeric G-quadruplex structure and regulates its conformational switch. The results show that not only can oxazine750 selectively induce parallel quadruplex formation from a random coil telomeric oligonucleotide in the absence of added cations, it also can easily surpass the energy barrier between two structures and change the G-quadruplex conformation in Na(+) or K(+) solution. The combination of its unique properties, including the size and shape of the G-quadruplex and the small molecule, is proposed as the predominant force for regulating the special structural formation and transitions. These results may stimulate the design of new quadruplex binders that would be capable of discriminating different G-quadruplex structures as well as controlling biological phenomena, functional molecules, and nanomaterials.

Verification of specific G-quadruplex structure by using a novel cyanine dye supramolecular assembly: II. The binding characterization with specific intramolecular G-quadruplex and the recognizing mechanism

The supramolecular assembly of a novel cyanine dye, 3,3′-di(3-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethyl-thiacarbocyanine triethylammonium salt (ETC) was designed to verify specific intramolecular G-quadruplexes from duplex and single-strand DNAs. Spectral results have shown that ETC presented two major distinct signatures with specific intramolecular G-quadruplexes in vitro: (i) dramatic changes in the absorption spectra (including disappearance of absorption peak around 660 nm and appearance of independent new peak around 584 nm); (ii) ∼70 times enhancement of fluorescence signal at 600 nm. Furthermore, based on ¹H-nuclear magnetic resonance and circular dichroism results, the preferring binding of ETC to specific intramolecular G-quadruplexes probably result from end-stacking, and the loop structure nearby also plays an important role.