Phthalocyanines for G-quadruplex aptamers binding

Role of Secondary Structure and Time-Dependent Binding on Disruption of Phthalocyanine Aggregates by Guanine-Rich Nucleic Acids

Phthalocyanines are versatile photodynamic therapy agents whose biological activity depends on their aggregation state, which is expected to be influenced by binding to biomolecules. Here, guanine-rich nucleic acid binding of a water-soluble cationic, regiopure C4h zinc phthalocyanine bearing four triethylene glycol methyl ether and four N-methyl-4-pyridinium substituents (1) is reported. In contrast to double-stranded DNA, guanine systems GpG, (GG)10, poly(G) and quadruplex DNA are shown to effectively disrupt phthalocyanine aggregates in buffered solution. This process is accompanied by evolution of the Q-band absorbance and enhanced emission. Increasing the sequence length from GpG to (GG)10 increases the binding and confirms the importance of multiple binding interactions. Enhanced binding in the presence of KCl suggests the importance of nucleobase hydrogen-bonded mosaics in phthalocyanine binding. Notably, the (GT)10 sequence is even more effective than quadruplex and pure guanine systems at disrupting the aggregates of 1. Significant time-dependent binding of 1 with poly(G) reveals biexponential binding over minutes and hours, which is linked to local conformations of poly(G) that accommodate monomers of 1 over time. The study highlights the ability of biomacromolecules to disrupt phthalocyanines aggregates over time, which is an important consideration when rationalizing photoactivity of photosensitizers in-vivo.

Enhanced targeted liposomal delivery of imiquimod via aptamer functionalization for head and neck cancer therapy

The incidence of head and neck cancers, particularly those associated with Human Papillomavirus (HPV) infections, has been steadily increasing. Conventional therapies exhibit limitations and drawbacks, prompting the exploration of new strategies over the years, with nanomedicine approaches, especially liposomes gaining relevance. Additionally, the functionalization of liposomes with aptamers enables selective delivery to target cells. For instance, AT11 can serve as a targeting moiety for cancer cells due to its high affinity for nucleolin, a protein overexpressed on the cancer cell's surface. In this study, liposomes functionalized with AT11 are proposed as drug delivery systems for imiquimod (IQ), aiming to maximize its potential as an anticancer agent for HPV-related cancers. To this end, firstly liposomes were produced through the ethanol injection method, functionalized with AT11-TEG-Cholesteryl, and characterized using dynamic light scattering. The obtained liposomes presented suitable properties for cancer therapy (with sizes from 120 to 140 nm and low polydispersity PDI < 0.16) and were further evaluated in terms of potential anticancer effects. AT11 IQ-associated liposomes allowed a selective delivery of IQ towards a tongue cancer cell line (UPCI-SCC-154) relative to the non-malignant cell line (Het1A). Specifically, they induced a selective reduction of the cell viability (∼52 % versus ∼113 %; p < 0.0001), proliferation (∼68 % versus ∼102 %; p<0.0001) and increased cell death (∼7-fold increase; p < 0.0001)). Additionally, they decreased the migration (from ∼24 % to ∼8 %; p < 0.0001) and invasion (to 11 %; p = 0.0047) capacities of the cancer cells. In summary, the produced liposomes represent a promising approach to enhance the anticancer potential of IQ in head and neck cancer, particularly in tongue cancer.

Light-Promoted Lysosomal Escape of a Phthalocyanine and Antisense Oligonucleotide-Complexed G-Quadruplex for Dual Photodynamic and Antisense Therapy

Combination therapy has been proven as an effective strategy for cancer treatment. To this end, we report herein a self-assembled nucleic acid-based complex for dual photodynamic and antisense therapy. It contains a nucleolin-targeting As1411-based G-quadruplex platform, a partially hybridized antisense oligonucleotide 4625, which can inhibit the antiapoptotic protein B cell lymphoma-xL inducing apoptotic cell death, and a zinc(II) phthalocyanine (ZnPc)-based photosensitizer held by noncovalent interactions. Through a series of in vitro experiments, we have demonstrated that this DNA complex can be internalized selectively to nucleolin-overexpressed MCF-7 and A549 cells through receptor-mediated endocytosis and is localized in the lysosomes. Upon light irradiation, the photosensitization of ZnPc triggers the formation of reactive oxygen species for cell killing and promotes the lysosomal escape of 4625 for antisense therapy. The combined therapeutic effect can eliminate the cancer cells effectively with a half maximal inhibitory concentration of ca. 0.5 μM.

Complexed Photosensitizer of Hypericin with G-Quadruplex: Structure-Dependent Behavior

Despite the increased interest of visible-light-absorbing compound Hypericin (Hyp) in photodiagnosis, photocatalysis, and photodynamic therapy (PDT) applications, a major obstacle still exists; i.e., the photoactivity is diminished due to the facile aggregation of Hyp in aqueous environment that induces excited-state quenching. Herein, we explore the excited-state property of Hyp bound to the DNA G-quadruplex by combining multiple steady-state and time-resolved spectroscopy. We find that the aggregation-induced quenching effect can be successfully prevented by appropriate G-quadruplex binders that disperse Hyp into monomer. The binding of Hyp/G-quadruplex is selective, however, exhibiting a preferential binding toward parallel G-quadruplexes (c-kit2, C14B1, STAT3, S50, and PS2.M), over antiparallel or hybrid G-quadruplex (Tel22, TBA). The excited-state property of Hyp is highly related to the binding behavior, showing a consistent trend that the better the Hyp/G-quadruplex binding, the longer the triplet 3Hyp* lifetime and the higher the efficiency to produce 1O2. For Hyp/c-kit2, the major binding mode is 5'-end stacking, which offers protection from collisional quenching reactions and ensures a stable photocycle of 3Hyp*-O2 energy transfer forming 1O2, leading to the highest 1O2 quantum yield (0.67) with superior photostability. These findings open possibilities of developing Hyp/G-quadruplex complex as a biocompatible photosensitizer for PDT applications, etc.

G-Quadruplexes in the Regulation of Viral Gene Expressions and Their Impacts on Controlling Infection

G-quadruplexes (G4s) are noncanonical nucleic acid structures that play significant roles in regulating various biological processes, including replication, transcription, translation, and recombination. Recent studies have identified G4s in the genomes of several viruses, such as herpes viruses, hepatitis viruses, and human coronaviruses. These structures are implicated in regulating viral transcription, replication, and virion production, influencing viral infectivity and pathogenesis. G4-stabilizing ligands, like TMPyP4, PhenDC3, and BRACO19, show potential antiviral properties by targeting and stabilizing G4 structures, inhibiting essential viral life-cycle processes. This review delves into the existing literature on G4's involvement in viral regulation, emphasizing specific G4-stabilizing ligands. While progress has been made in understanding how these ligands regulate viruses, further research is needed to elucidate the mechanisms through which G4s impact viral processes. More research is necessary to develop G4-stabilizing ligands as novel antiviral agents. The increasing body of literature underscores the importance of G4s in viral biology and the development of innovative therapeutic strategies against viral infections. Despite some ligands' known regulatory effects on viruses, a deeper comprehension of the multifaceted impact of G4s on viral processes is essential. This review advocates for intensified research to unravel the intricate relationship between G4s and viral processes, paving the way for novel antiviral treatments.

G-quadruplex ligands as therapeutic agents against cancer, neurological disorders and viral infections

G-quadruplexes (G4s) within the human genome have undergone extensive molecular investigation, with a strong focus on telomeres, gene promoters and repetitive regulatory sequences. G4s play central roles in regulating essential biological processes, including telomere maintenance, replication, transcription and translation. Targeting these molecular processes with G4-binding ligands holds substantial therapeutic potential in anticancer treatments and has also shown promise in treating neurological, skeletal and muscular disorders. The presence of G4s in bacterial and viral genomes also suggests that G4-binding ligands could be a critical tool in fighting infections. This review provides an overview of the progress and applications of G4-binding ligands, their proposed mechanisms of action, challenges faced and prospects for their utilization in anticancer treatments, neurological disorders and antiviral activities.

Development and application of metallo-phthalocyanines as potent G-quadruplex DNA binders and photosensitizers

Metallo-phthalocyanines (MPc) are common photosensitizers with ideal photophysical and photochemical properties. Also, these molecules have shown to interact with non-canonical nucleic acid structures, such as G-quadruplexes, and modulate oncogenic expression in cancer cells. Herein, we report the synthesis and characterisation of two metallo-phthalocyanines containing either zinc (ZnPc) or nickel (NiPc) in the central aromatic core and four alkyl ammonium lateral chains. The interaction of both molecules with G-quadruplex DNA was assessed by UV-Vis, fluorescence and FRET melting experiments. Both molecules bind strongly to G-quadruplexes and stabilise these structures, being NiPc the most notable G-quadruplex stabiliser. In addition, the photosensitizing ability of both metal complexes was explored by the evaluation of the singlet oxygen generation and their photoactivation in cells. Only ZnPc showed a high singlet oxygen generation either by direct observation or by indirect evaluation using a DPBF dye. The cellular evaluation showed mainly cytoplasmic localization of ZnPc and a decrease of the IC₅₀ values of the cell viability of ZnPc upon light activation of two orders of magnitude. Two metallo-phthalocyanines containing zinc and nickel within the aromatic core have been investigated as G-quadruplex stabilizers and photosensitizers. NiPc shows a high G4 binding but negligible photosensitizing ability while ZnPc exhibits a moderate binding to G-quadruplex together with a high potency to generate singlet oxygen and photocytotoxicity. The interaction with G4s and capacity to be photosensitized is associated with the geometry adopted by the central metal core of the phthalocyanine scaffold.

Probing the Efficiency of 13-Pyridylalkyl Berberine Derivatives to Human Telomeric G-Quadruplexes Binding: Spectroscopic, Solid State and In Silico Analysis

The interaction between the series of berberine derivatives 1-5 (NAX071, NAX120, NAX075, NAX077 and NAX079) and human telomeric G-quadruplexes (G4), which are able to inhibit the Telomerase enzyme's activity in malignant cells, was investigated. The derivatives bear a pyridine moiety connected by a hydrocarbon linker of varying length (n = 1-5, with n number of aliphatic carbon atoms) to the C13 position of the parent berberine. As for the G4s, both bimolecular 5'-TAGGGTTAGGGT-3' (Tel12) and monomolecular 5'-TAGGGTTAGGGTTAGGGTTAGGG-3' (Tel23) DNA oligonucleotides were considered. Spectrophotometric titrations, melting tests, X-ray diffraction solid state analysis and in silico molecular dynamics (MD) simulations were used to describe the different systems. The results were compared in search of structure-activity relationships. The analysis pointed out the formation of 1:1 complexes between Tel12 and all ligands, whereas both 1:1 and 2:1 ligand/G4 stoichiometries were found for the adduct formed by NAX071 (n = 1). Tel12, with tetrads free from the hindrance by the loop, showed a higher affinity. The details of the different binding geometries were discussed, highlighting the importance of H-bonds given by the berberine benzodioxole group and a correlation between the strength of binding and the hydrocarbon linker length. Theoretical (MD) and experimental (X-ray) structural studies evidence the possibility for the berberine core to interact with one or both G4 strands, depending on the constraints given by the linker length, thus affecting the G4 stabilization effect.

Exploring the Relationship between G-Quadruplex Nucleic Acids and Plants: From Plant G-Quadruplex Function to Phytochemical G4 Ligands with Pharmaceutic Potential

G-quadruplex (G4) oligonucleotides are higher-order DNA and RNA secondary structures of enormous relevance due to their implication in several biological processes and pathological states in different organisms. Strategies aiming at modulating human G4 structures and their interrelated functions are first-line approaches in modern research aiming at finding new potential anticancer treatments or G4-based aptamers for various biomedical and biotechnological applications. Plants offer a cornucopia of phytocompounds that, in many cases, are effective in binding and modulating the thermal stability of G4s and, on the other hand, contain almost unexplored G4 motifs in their genome that could inspire new biotechnological strategies. Herein, we describe some G4 structures found in plants, summarizing the existing knowledge of their functions and biological role. Moreover, we review some of the most promising G4 ligands isolated from vegetal sources and report on the known relationships between such phytochemicals and G4-mediated biological processes that make them potential leads in the pharmaceutical sector.

G-Quadruplex Aptamer-Ligand Characterization

In this work we explore the structure of a G-rich DNA aptamer termed AT11-L2 (TGGTGGTGGTTGTTGTTGGTGGTGGTGGT; derivative of AT11) by evaluating the formation and stability of G-quadruplex (G4) conformation under different experimental conditions such as KCl concentration, temperature, and upon binding with a variety of G4 ligands (360A, BRACO-19, PDS, PhenDC3, TMPyP4). We also determined whether nucleolin (NCL) can be a target of AT11-L2 G4. Firstly, we assessed by circular dichroism, UV and NMR spectroscopies the formation of G4 by AT11-L2. We observed that, for KCl concentrations of 65 mM or less, AT11-L2 adopts hybrid or multiple topologies. In contrast, a parallel topology predominates for buffer containing 100 mM of KCl. The T_m of AT11-L2 in 100 mM of KCl is 38.9 °C, proving the weak stability of this sequence. We also found that upon titration with two molar equivalents of 360A, BRACO-19 and PhenDC3, the G4 is strongly stabilized and its topology is maintained, while the addition of 3.5 molar equivalents of TMPyP4 promotes the disruption of G4. The K_D values between AT11-L2 G4, ligands and NCL were obtained by fluorescence titrations and are in the range of µM for ligand complexes and nM when adding NCL. In silico studies suggest that four ligands bind to the AT11-L2 G4 structure by stacking interactions, while the RBD1,2 domains of NCL interact preferentially with the thymines of AT11-L2 G4. Finally, AT11-L2 G4 co-localized with NCL in NCL-positive tongue squamous cell carcinoma cell line.

Interfacial assembly of zinc(II) phthalocyanines on graphene oxide (GO): Stable "turn-off-on" nanoplatforms to detect G-quadruplexes (G4)

HYPOTHESIS

The aggregation of phthalocyanines (Pcs) enfeebles their suitability as G-quadruplex (G4) ligands over time. It is hypothesized that the interfacial assembly of Pcs on graphene oxide (GO) influences intermolecular interactions, thereby affecting their physicochemical properties and inducing stabilization of Pcs in solution. Hence, the stacking of Pcs on GO could be tuned to create nanosystems with the ability to detect G4 for longer periods through a slow release of Pcs.

EXPERIMENTS

Four cationic structurally-related zinc(II) phthalocyanines (ZnPc) were non-covalently assembled on GO by ultrasonic exfoliation. A comprehensive characterization of ZnPcs@GO was carried out by spectroscopic techniques and electron microscopy to understand the organization of ZnPcs on GO. The fluorescence of ZnPcs@GO was studied in the presence of G4 (T₂G₅T)₄ and duplex ds26 through spectrofluorimetric titrations and monitored along time.

FINDINGS

GO induced a re-organization of the ZnPcs mostly to J-aggregates and quenched their original fluorescence up to 98 % ("turn-off"). In general, ZnPcs@GO recovered their fluorescence ("turn-on") after the titrations and showed affinity to G4 (K_D up to 1.92 μM). This is the first report that highlights the contribution of GO interfaces to assemble ZnPcs and allow their slow and controlled release to detect G4 over longer periods.

Development of quantum dot-phthalocyanine integrated G-quadruplex /double-stranded DNA biosensor

In the present study, the phthalocyanine (Pc) integrated mercaptopropionic acid capped quantum dot (mpa@QD) biosensor has been developed for the quantitative determination of G-quadruplex and double-stranded DNA. The working principle of the developed biosensor platform is based on the quenching of the emission signal of the mpa@QD in the presence of Pc (closed position) and the recovery of the fluorescence signal in the presence of DNA (open position). The parameters affecting biosensor performance, such as Pc type and concentration, were optimized. Since the developed biosensor aimed to determine G-quadruplex and double-stranded DNA in biological samples, the effect of common ions (such as Na⁺, Mg²⁺) and serum albumin found in many biological matrices on the biosensor performance were examined. The effect of common ions on biosensor signal was negligible, except Zn²⁺. The analytical properties of the biosensor, such as linear range, calibration sensitivity, relative standard deviation %, the limit of detection, and quantification, were determined. The limit of detection and quantification values were found 0.055 μM and 0.18 μM for AS1411, 0.061 μM and 0.20 μM for Tel21, 0.038 μM and 0.13 μM for Tel45 and 0.091 μM and 0.30 μM for ctDNA. Several different synthetic samples were prepared. The spiked synthetic samples such as mammalian cell medium were used to evaluate the analytical performance of Pc-mpa@QD. All synthetic samples were prepared with polyethylene glycol, which resembles biological samples' crowded environment.

Thiopyridinium phthalocyanine for improved photodynamic efficiency against pathogenic fungi

The emergence of opportunistic pathogens and the selection of resistant strains have created a grim scenario for conventional antimicrobials. Consequently, there is an ongoing search for alternative techniques to control these microorganisms. One such technique is antimicrobial photodynamic therapy (aPDT), which combines photosensitizers, light, and molecular oxygen to produce reactive oxygen species and kill the target pathogen. Here, the in vitro susceptibilities of three fungal pathogens, namely Candida albicans, Aspergillus nidulans, and Colletotrichum abscissum to aPDT with zinc(II) phthalocyanine (ZnPc) derivative complexes were investigated. Three ZnPc bearing thiopyridinium substituents were synthesized and characterized by several spectroscopic techniques. The Q-band showed sensitivity to the substituent with high absorptivity coefficient in the 680-720 nm region. Derivatization and position of the rings with thiopyridinium units led to high antifungal efficiency of the cationic phthalocyanines, which could be correlated with singlet oxygen quantum yield, subcellular localization, and cellular uptake. The minimum inhibitory concentrations (MIC) of the investigated ZnPc-R complexes against the studied microorganisms were 2.5 μM (C. albicans) and 5 μM (A. nidulans and C. abscissum). One ZnPc derivative achieved complete photokilling of C. albicans and, furthermore, yielded low MIC values when used against the tolerant plant-pathogen C. abscissum. Our results show that chemical modification is an important step in producing better photosensitizers for aPDT against fungal pathogens.

Stabilization of a DNA aptamer by ligand binding

G-rich aptamers such as AS1411 are small oligonucleotides that present several benefits comparatively to monoclonal antibodies, since they are easier to manufacture and store, have small size and do not stimulate an immune response. We analyzed AT11-B1, a modified sequence of AT11 (itself a modified version of AS1411), in which one thymine was removed from the bulge region. We studied G-quadruplex (G4) formation/stabilization using PhenDC3, PDS, BRACO-19, TMPyP4 and 360A ligands by different biophysical techniques, namely circular dichroism (CD), Förster resonance energy transfer (FRET-melting) and nuclear magnetic resonance (NMR). The CD spectra showed that AT11-B1 adopts a predominant G4 of parallel topology when the buffer contains KCl or when ligands are added. PhenDC3 induced a ΔT_m of 30 °C or more of the G4 structure as shown by CD- and FRET-melting experiments. The ligands demonstrate high affinity for AT11-B1 G4 and the NMR studies revealed that the AT11-B1 G4 involves four G-tetrad layers. The in silico studies suggest that all ligands bind AT11-B1 G4, namely, by stacking interactions, except PDS that may bind to the loop/groove interface. In addition, molecular dynamics simulations revealed that nucleolin (NCL) interacts with the AT11-B1 G4 structure through the RNA binding domain (RBD) 2 and the 12-residue linker between RBD1,2. Moreover, AT11-B1 G4 was internalized into a NCL-positive tongue squamous cell carcinoma cell line. In a nutshell, this study may help the identification of the ligands scaffolds to bind and stabilize AT11-B1, improving the targeting towards NCL that is overexpressed in cancer cells.

An Energy-Storing DNA-Based Nanocomplex for Laser-Free Photodynamic Therapy

Photodynamic therapy (PDT) is a therapeutic strategy that is dependent on external light irradiation that faces a major challenge in cancer treatment due to the poor tissue-penetration depths of light irradiation. Herein, a DNA nanocomplex that integrates persistent-luminescence nanoparticles (PLNPs) is developed, which realizes tumor-site glutathione-activated PDT for breast cancer without exogenous laser excitation. The scaffold of the nanocomplex is AS1411-aptamer-encoded ultralong single-stranded DNA chain with two functions: i) providing sufficient intercalation sites for the photosensitizer, and ii) recognizing nucleolin that specifically overexpresses on the surface of cancer cells. The PLNPs in the nanocomplex are energy-charged to act as a self-illuminant and coated with a shell of MnO₂ for blocking energy degradation. In response to the overexpressed glutathione in cancer cells, the MnO₂ shell decomposes to provide Mn²⁺ to catalytically produce O₂ , which is essential to PDT. Meanwhile, PLNPs are released and act as a self-illuminant to activate the photosensitizer to convert O₂ into cytotoxic ¹ O₂ . Significant tumor inhibition effects are demonstrated in breast tumor xenograft models without exogenous laser excitation. It is envisioned that a laser-excitation-free PDT strategy enabled by the PLNP-DNA nanocomplex promotes the development of PDT and provides a new local therapeutic approach.

The Surprisingly Positive Effect of Zinc-Phthalocyanines With High Photodynamic Therapy Efficacy of Melanoma Cancer

Phthalocyanine (Pc) dyes are photoactive molecules that can absorb and emit light in the visible spectrum, especially in the red region of the spectrum, with great potential for biological scopes. For this target, it is important to guarantee a high Pc solubility, and the use of suitable pyridinium units on their structure can be a good strategy to use effective photosensitizers (PSs) for photodynamic therapy (PDT) against cancer cells. Zn(II) phthalocyanines (ZnPcs) conjugated with thiopyridinium units (1–3) were evaluated as PS drugs against B16F10 melanoma cells, and their photophysical, photochemical, and in vitro photobiological properties were determined. The photodynamic efficiency of the tetra- and octa-cationic ZnPcs 1–3 was studied and compared at 1, 2, 5, 10, and 20 µM. The different number of charge units, and the presence/absence of a-F atoms on the Pc structure, contributes for their PDT efficacy. The 3-(4′,5′-dimethylthiazol-2′-yl)-2,5-diphenyl tetrazolium bromide (MTT) assays on B16F10 melanoma cells show a moderate to high capacity to be photoinactivated by ZnPcs 1–3 (ZnPc 1 > ZnPc 2 > ZnPc 3). The best PDT conditions were found at a Pc concentration of 20 μM, under red light (λ = 660 ± 20 nm) at an irradiance of 4.5 mW/cm² for 667 s (light dose of 3 J/cm²). In these conditions, it is noteworthy that the cationic ZnPc 1 shows a promising photoinactivation ratio, reaching the detection limit of the MTT method. Moreover, these results are comparable to the better ones in the literature.

Progress in cancer drug delivery based on AS1411 oriented nanomaterials

Targeted cancer therapy has become one of the most important medical methods because of the spreading and metastatic nature of cancer. Based on the introduction of AS1411 and its four-chain structure, this paper reviews the research progress in cancer detection and drug delivery systems by modifying AS1411 aptamers based on graphene, mesoporous silica, silver and gold. The application of AS1411 in cancer treatment and drug delivery and the use of AS1411 as a targeting agent for the detection of cancer markers such as nucleoli were summarized from three aspects of active targeting, passive targeting and targeted nucleic acid apharmers. Although AS1411 has been withdrawn from clinical trials, the research surrounding its structural optimization is still very popular. Further progress has been made in the modification of nanoparticles loaded with TCM extracts by AS1411.

Combined spectroscopic and theoretical analysis of the binding of a water-soluble perylene diimide to DNA/RNA polynucleotides and G-quadruplexes

We present here a combined spectroscopic and theoretical analysis of the binding of N,N'-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dichloride (PZPERY) to different biosubstrates. Absorbance titrations and circular dichroism experiments, melting studies and isothermal calorimetry (ITC) titrations reveal a picture where the binding to natural double-stranded DNA is very different from that to double and triple-stranded RNAs (poly(A)∙poly(U) and poly(U)∙poly(A)⁎poly(U)). As confirmed also by the structural and energetic details clarified by density functional theory (DFT) calculations, intercalation occurs for DNA, with a process driven by the combination of aggregates disruption and monomers intercalation. Oppositely, for RNAs, no intercalation but groove binding with the formation of supramolecular aggregates is observed. Among all the tested biosubstrates, the affinity of PZPERY towards DNA G-quadruplexes (G4) is the greatest one with a preference for human telomeric G4s. Focusing on hybrid G4 forms, either sitting-atop ("tetrad-parallel") or lateral ("groove-parallel") binding modes were considered in the discussion of the experimental results and molecular dynamics (MD) simulations. Both turned out to be possible concurrently, in agreement also with the experimental binding stoichiometries higher than 2:1.

The Interactions of H2TMPyP, Analogues and Its Metal Complexes with DNA G-Quadruplexes-An Overview

The evidence that telomerase is overexpressed in almost 90% of human cancers justifies the proposal of this enzyme as a potential target for anticancer drug design. The inhibition of telomerase by quadruplex stabilizing ligands is being considered a useful approach in anticancer drug design proposals. Several aromatic ligands, including porphyrins, were exploited for telomerase inhibition by adduct formation with G-Quadruplex (GQ). 5,10,15,20-Tetrakis(N-methyl-4-pyridinium)porphyrin (H₂TMPyP) is one of the most studied porphyrins in this field, and although reported as presenting high affinity to GQ, its poor selectivity for GQ over duplex structures is recognized. To increase the desired selectivity, porphyrin modifications either at the peripheral positions or at the inner core through the coordination with different metals have been handled. Herein, studies involving the interactions of TMPyP and analogs with different DNA sequences able to form GQ and duplex structures using different experimental conditions and approaches are reviewed. Some considerations concerning the structural diversity and recognition modes of G-quadruplexes will be presented first to facilitate the comprehension of the studies reviewed. Additionally, considering the diversity of experimental conditions reported, we decided to complement this review with a screening where the behavior of H₂TMPyP and of some of the reviewed metal complexes were evaluated under the same experimental conditions and using the same DNA sequences. In this comparison under unified conditions, we also evaluated, for the first time, the behavior of the Ag^II complex of H₂TMPyP. In general, all derivatives showed good affinity for GQ DNA structures with binding constants in the range of 10⁶–10⁷ M⁻¹ and ligand-GQ stoichiometric ratios of 3:1 and 4:1. A promising pattern of selectivity was also identified for the new Ag^II derivative.

G-Quadruplex-Based Drug Delivery Systems for Cancer Therapy

G-quadruplexes (G4s) are a class of nucleic acids (DNA and RNA) with single-stranded G-rich sequences. Owing to the selectivity of some G4s, they are emerging as targeting agents to overtake side effects of several potential anticancer drugs, and delivery systems of small molecules to malignant cells, through their high affinity or complementarity to specific targets. Moreover, different systems are being used to improve their potential, such as gold nano-particles or liposomes. Thus, the present review provides relevant data about the different studies with G4s as drug delivery systems and the challenges that must be overcome in the future research.

Synthesis and molecular docking studies of Zn(II)phthalocyanines containing anthraquinone moieties as selective ligands for G-quadruplex structures

New zinc(II) phthalocyanines (p-ZnPc and np-ZnPc) containing peripheral and non-peripheral positioned four anthraquinone moieties were synthesized by cyclotetramerization of 4-((2-(2-((8-Chloro-9,10-dioxo-9,10-dihydroanthracen-1-yl) amino) ethoxy) ethyl) thio) phthalonitrile and 3-((2-(2-((8-Chloro-9,10-dioxo-9,10-dihydroanthracen-1-yl) amino) ethoxy) ethyl) thio) phthalonitrile. All compounds were characterized by using a combination of analytical and spectroscopic techniques such as 1H, [Formula: see text]C NMR, FT-IR, UV-vis and MS spectral data. Also, molecular docking studies were performed using different G-quadruplex and double stranded nucleic acid fragments as possible interaction sites to predict the binding ability of the newly synthesized compounds.

Biological studies of an ICG-tagged aptamer as drug delivery system for malignant melanoma

Malignant melanoma accounts for about 1% of all skin malignant tumors and represents the most aggressive and lethal form of skin cancer. Clinically, there exist different therapeutic options for melanoma treatment, such as surgery, chemotherapy, radiotherapy, photodynamic therapy and immunotherapy. However, serious adverse effects usually arise, and survival rates are still low because a high number of patients present relapses within 6-9 months after therapy. AS1411 is a G-quadruplex (G4) aptamer capable of tumor-specific recognition, since it binds to nucleolin, a multi-functional protein expressed in many different types of cancer cells. In this work, we present a novel drug delivery system composed of AS1411 and indocyanine green (ICG) to track its accumulation in tumoral cells in a melanoma mouse model. Using a simple supramolecular strategy, we conjugated the complex AS1411-ICG with C₈ ligand, an acridine orange derivative with potential anticancer ligand. Then, we performed in vitro cytotoxicity experiments using the B16 mouse melanoma cell line, and in vivo experiments using a B16 mouse melanoma model to study biodistribution and histological changes. The circular dichroism (CD) data suggest that C₈ does not affect the parallel G4 topology of AS1411-ICG, whereas it increases its thermal stability. Incubation of B16 melanoma cells with the AS1411-ICG complex associated with C₈ increases the cytotoxicity compared with AS1411-ICG alone. From the in vivo studies, we conclude that both AS1411-ICG and AS1411-ICG-C₈ presented the potential to accumulate preferentially in tumor tissues. Moreover, these compounds seem to be efficiently removed from the mice's bodies through kidney clearance. In summary, these results suggest that these complexes derived from AS1411 aptamer could act as a delivery system of ligands with antitumoral activity for in vivo melanoma therapy.