Interaction of a Cationic Porphyrin and Its Metal Derivatives with G-Quadruplex DNA

Quercetin Exhibits Preferential Binding Interaction by Selectively Targeting HRAS1 I-Motif DNA-Forming Promoter Sequences

I-Motif (iM) DNA structures represent among the most significant noncanonical nucleic acid configurations. iM-forming DNA sequences are found in an array of vital genomic locations and are particularly frequent in the promoter islands of various oncogenes. Thus, iM DNA is a crucial candidate for anticancer medicines; therefore, binding interactions between iM DNA and small molecular ligands, such as flavonoids, are critically important. Extensive sets of spectroscopic strategies and thermodynamic analysis were utilized in the present investigation to find out the favorable interaction of quercetin (Que), a dietary flavonoid that has various health-promoting characteristics, including anticancer properties, with noncanonical iM DNA structure. Spectroscopic studies and thermal analysis revealed that Que interacts preferentially with HRAS1 iM DNA compared with VEGF, BCL2 iM, and duplex DNA. Que, therefore, emerged as a suitable natural-product-oriented antagonist for targeting HRAS1 iM DNA. The innovative spectroscopic as well as mechanical features of Que and its specific affinity for HRAS1 iM may be useful for therapeutic applications and provide crucial insights for the design of compounds with remarkable medicinal properties.

opp-Dibenzoporphyrin Pyridinium Derivatives as Potential G-Quadruplex DNA Ligands

Since the occurrence of tumours is closely associated with the telomerase function and oncogene expression, the structure of such enzymes and genes are being recognized as targets for new anticancer drugs. The efficacy of several ligands in telomerase inhibition and in the regulation of genes expression, by an effective stabilisation of G-quadruplexes (G4) DNA structures, is being considered as a promising strategy in cancer therapies. When evaluating the potential of a ligand for telomerase inhibition, the selectivity towards quadruplex versus duplex DNA is a fundamental attribute due to the large amount of double-stranded DNA in the cellular nucleus. This study reports the evaluated efficacy of three tetracationic opp-dibenzoporphyrins, a free base, and the corresponding zinc(II) and nickel(II) complexes, to stabilise G4 structures, namely the telomeric DNA sequence (AG3(T2AG3)3). In order to evaluate the selectivity of these ligands towards G4 structures, their interaction towards DNA calf thymus, as a double-strand DNA sequence, were also studied. The data obtained by using different spectroscopic techniques, such as ultraviolet-visible, fluorescence, and circular dichroism, suggested good affinity of the free-base porphyrin and of its zinc(II) complex for the considered DNA structures, both showing a pattern of selectivity for the telomeric G4 structure. A pattern of aggregation in aqueous solution was detected for both Zn(II) and Ni(II) metallo dibenzoporphyrins and the ability of DNA sequences to induce ligand disaggregation was observed.

Targeting the RNA G-Quadruplex and Protein Interactome for Antiviral Therapy

In recent years, G-quadruplexes (G4s), types of noncanonical four-stranded nucleic acid structures, have been identified in many viruses that threaten human health, such as HIV and Epstein-Barr virus. In this context, G4 ligands were designed to target the G4 structures, among which some have shown promising antiviral effects. In this Perspective, we first summarize the diversified roles of RNA G4s in different viruses. Next, we introduce small-molecule ligands developed as G4 modulators and highlight their applications in antiviral studies. In addition to G4s, we comprehensively review the medical intervention of G4-interacting proteins from both the virus (N protein, viral-encoded helicases, severe acute respiratory syndrome-unique domain, and Epstein-Barr nuclear antigen 1) and the host (heterogeneous nuclear ribonucleoproteins, RNA helicases, zinc-finger cellular nucelic acid-binding protein, and nucleolin) by inhibitors as an alternative way to disturb the normal functions of G4s. Finally, we discuss the challenges and opportunities in G4-based antiviral therapy.

Porphyrin induced structural destabilization of a parallel DNA G-quadruplex in human MRP1 gene promoter

Porphyrins are among the first ligands that have been tested for their quadruplex binding and stabilization potential. We report the differential interaction of the positional cationic porphyrin isomers TMPyP3 and TMPyP4 with a parallel G-quadruplex (GQ) formed by 33-mer (TP) regulatory sequence present in the promoter region of the human multidrug resistance protein 1 (MRP1) transporter gene. This GQ element encompasses the three evolutionary conserved SP1 transcription factor binding sites. Taking into account that SP1 binds to a non-canonical GQ motif with higher affinity than to a canonical duplex DNA consensus motif, it is suggestive that GQ distortion by cationic porphyrin will have important implications in the regulation of MRP1 expression. Herein, we employed biophysical analysis using circular dichroism, visible absorption, UV-thermal melting and steady-state fluorescence spectroscopy, reporting destabilization of MRP1 GQ by cationic porphyrins. Results suggest that TMPyP4 and TMPyP3 interact with GQ with a binding affinity of 10⁶ to 10⁷  M^-1 . Thermodynamic analysis indicated a significant decrease in melting temperature of GQ (ΔTm of 15.5°C-23.5°C), in the presence of 2 times excess of porphyrins. This study provides the biophysical evidence indicating the destabilisation of a parallel DNA G-quadruplex by cationic porphyrins.

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.

Porphyrin Binding and Irradiation Promote G-Quadruplex DNA Dimeric Structure

Nucleic acid sequences rich in guanines can organize into noncanonical DNA G-quadruplexes (G4s) of variable size. The design of small molecules stabilizing the structure of G4s is a rapidly growing area for the development of novel anticancer therapeutic strategies and bottom-up nanotechnologies. Among a multitude of binders, porphyrins are very attractive due to their light activation that can make them valuable conformational regulators of G4s. Here, a structure-based strategy, integrating complementary probes, is employed to study the interaction between TMPyP4 porphyrin and a 22-base human telomeric sequence (Tel22) before and after irradiation with blue light. Porphyrin binding is discovered to promote Tel22 dimerization, while light irradiation of the Tel22-TMPyP4 complex controls dimer fraction. Such a change in quaternary structure is found to be strictly correlated with modifications at the secondary structure level, thus providing an unprecedented link between the degree of dimerization and the underlying conformational changes in G4s.

Interactions of porphyrins with DNA: A review focusing recent advances in chemical modifications on porphyrins as artificial nucleases

The advance of porphyrins as artificial nucleases along the years have developed a class of compounds having potential therapeutic applications. Being an extrovert of chemistry, a variety of chemical modifications have been done on porphyrin macrocycle in order to improve the spectroscopic properties and to adapt as artificial receptors that can recognize molecules. The last twenty years has witnessed broad research in the arena of porphyrin- DNA interactions and their evolution from simple to more complex entities. In this review, we summarize the recent advances in the porphyrin-based structural modifications, with a specific emphasis on various effects of porphyrin on DNA cleavage potency. We particularly detailed the nuclease activity of cationic and anionic porphyrins, porphyrin dimers and conjugates as well as heme proteins till the third generation porphyrins as artificial nucleases.

KRAS Promoter G-Quadruplexes from Sequences of Different Length: A Physicochemical Study

DNA G-quadruplexes (G4s) form in relevant genomic regions and intervene in several biological processes, including the modulation of oncogenes expression, and are potential anticancer drug targets. The human KRAS proto-oncogene promoter region contains guanine-rich sequences able to fold into G4 structures. Here, by using circular dichroism and differential scanning calorimetry as complementary physicochemical methodologies, we compared the thermodynamic stability of the G4s formed by a shorter and a longer version of the KRAS promoter sequence, namely 5′-AGGGCGGTGTGGGAATAGGGAA-3′ (KRAS 22RT) and 5′-AGGGCGGTGTGGGAAGAGGGAAGAGGGGGAGG-3′ (KRAS 32R). Our results show that the unfolding mechanism of KRAS 32R is more complex than that of KRAS 22RT. The different thermodynamic stability is discussed based on the recently determined NMR structures. The binding properties of TMPyP4 and BRACO-19, two well-known G4-targeting anticancer compounds, to the KRAS G4s were also investigated. The present physicochemical study aims to help in choosing the best G4 target for potential anticancer drugs.

The significance of the metal cation in guanine-quartet – metalloporphyrin complexes

The distinct positions of the divalent metal ions with respect to the porphyrin ring are responsible for different interaction energies between metalloporphyrins and the guanine quartet.

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.

Macrocyclic NHC complexes of group 10 elements with enlarged aromaticity for biological studies

Two sets of macrocyclic, bio-inspired, non-heme ligands are utilized for the synthesis of NiII, PdII and PtII complexes. The ligands consist of a 16-atom macrocycle, formed by four methylene bridged NHC moieties, with imidazole or benzimidazole as building blocks. The complexes exhibit a square planar coordination geometry and are characterized by NMR, ESI-MS, elemental analysis, SC-XRD and UV/Vis. For complexes incorporating benzimidazole, an evaluation of luminescence properties is performed, and is found that phosphorescence is present for the PdII derivative and there is fluorescence for the PtII derivative. Stability studies in cell culture medium are performed for subsequent MTT assays. Here, the NiII complexes show low to no activity, and PdII and PtII complexes exhibit remarkable low IC50 values in cisplatin resistant A2780cisR cells.

Duplex-tetraplex equilibria in guanine- and cytosine-rich DNA

Noncanonical four-stranded DNA structures, including G-quadruplexes and i-motifs, have been discovered in the cell and are implicated in a variety of genomic regulatory functions. The tendency of a specific guanine- and cytosine-rich region of genomic DNA to adopt a four-stranded conformation depends on its ability to overcome the constraints of duplex base-pairing by undergoing consecutive duplex-to-coil and coil-to-tetraplex transitions. The latter ability is determined by the balance between the free energies of participating ordered and disordered structures. In this review, we present an overview of the literature on the stability of G-quadruplex and i-motif structures and discuss the extent of duplex-tetraplex competition as a function of the sequence context of the DNA and environmental conditions including temperature, pH, salt, molecular crowding, and the presence of G-quadruplex-binding ligands. We outline how the results of in vitro studies can be expanded to understanding duplex-tetraplex equilibria in vivo.

Dual-binding conjugates of diaromatic guanidines and porphyrins for recognition of G-quadruplexes

The first conceptualised class of dual-binding guanine quadruplex binders has been designed, synthesised and biophysically studied. These compounds combine diaromatic guanidinium systems and neutral tetra-phenylporphyrins (classical binding moiety for guanine quadruplexes) by means of a semi-rigid linker. An extensive screening of a variety of guanine quadruplex structures and double stranded DNA via UV-vis, FRET and CD experiments revealed the preference of the conjugates towards guanine quadruplexes. Additionally, docking studies indicate the potential dual mode of binding.

Targeting the KRAS oncogene: Synthesis, physicochemical and biological evaluation of novel G-Quadruplex DNA binders

The oncogene KRAS is involved in the pathogenesis of many tumors such as pancreatic, lung and colorectal cancers, thereby representing a relevant target for the treatment of these diseases. The KRAS P1 promoter contains a nuclease hypersensitive, guanine-rich sequence able to fold into a G-quadruplex motif (G4). The stabilization of this G4 structure by small molecules is emerging as a feasible approach to downregulate KRAS expression. Here, a set of novel stabilizing molecules was identified through a virtual screening campaign on the NMR structure of the 22-mer KRAS G4. The most promising hits were then submitted to structure-activity relationships studies which allowed improving their binding affinity and selectivity over double helix DNA and different G4 topologies. The best derivative (19) underwent fluorescence titration experiments and further computational studies to disclose its binding mechanism to KRAS G4. Finally, biological assays showed that this compound is capable to reduce the viability of colorectal cancer cells in which mutated KRAS acts as a driver oncogene. Thus, 19 might represent the prototype of a new class of drugs for the treatment of tumors that, expressing mutated forms of KRAS, are refractory to current therapeutic regimens.

Surface plasmon resonance study of the interaction of N-methyl mesoporphyrin IX with G-quadruplex DNA

Surface plasmon resonance (SPR) was used to investigate the interaction between N-methyl mesoporphyrin IX (NMM) and different G-quadruplex (G4) topologies. The study was associated with circular dichroism analysis (CD) to assess the topology of the G4s when they interacted with NMM. We demonstrate the high selectivity of NMM for the parallel G4 structure with a dissociation constant at least ten times lower than those of other G4 topologies. We also confirm the ability of NMM to shift the G4 conformation from both the hybrid and antiparallel topologies toward the parallel structure.

Photodynamic Therapy for ras-Driven Cancers: Targeting G-Quadruplex RNA Structures with Bifunctional Alkyl-Modified Porphyrins

Designing small molecules able to break down G4 structures in mRNA (RG4s) offers an interesting approach to cancer therapy. Here, we have studied cationic porphyrins (CPs) bearing an alkyl chain up to 12 carbons, as they bind to RG4s while generating reactive oxygen species upon photoirradiation. Fluorescence-activated cell sorting (FACS) and confocal microscopy showed that the designed alkyl CPs strongly penetrate cell membranes, binding to KRAS and NRAS mRNAs under low-abundance cell conditions. In Panc-1 cells, alkyl CPs at nanomolar concentrations promote a dramatic downregulation of KRAS and NRAS expression, but only if photoactivated. Alkyl CPs also reduce the metabolic activity of pancreatic cancer cells and the growth of a Panc-1 xenograft in SCID mice. Propidium iodide/annexin assays and caspase 3, caspase 7, and PARP-1 analyses show that these compounds activate apoptosis. All these data demonstrate that the designed alkyl CPs are efficient photosensitizers for the photodynamic therapy of ras-driven cancers.

Selective binding of a bioactive porphyrin-based photosensitizer to the G-quadruplex from the KRAS oncogene promoter

BACKGROUND

The G-quadruplex-forming sequence within the KRAS proto-oncogene P1 promoter is a promising target for anticancer therapy. Porphyrin derivatives are among the most rewarding G-quadruplex binders. They can also behave as photosensitizers.

METHODS

Three water-soluble, positively charged porphyrin-like compounds were synthesized and tested for their interaction with the KRAS G-quadruplex by circular dichroism, fluorescence, and molecular docking calculations. For a comparison of ligands binding affinity and selectivity, TMPyP4 was taken as a reference.

RESULTS

One out of the three tested compounds proved biological activity and selectivity for G-quadruplex over duplex DNA. It also showed to discriminate between different G-quadruplex topologies, with a preference for the parallel over antiparallel conformation. Molecular docking studies suggested a preferential binding to the 3'-end of the KRAS G-quadruplex driven through π-π stacking interactions. Biological assays also revealed a good photodynamic-induced cytotoxicity on HeLa cells.

CONCLUSIONS

The reported results show that these porphyrin-like compounds could actually give the basis for the development of G-quadruplex ligands with effective photodynamic-induced cytotoxicity on cancer cells.

GENERAL SIGNIFICANCE

The possibility of obtaining photosensitizers with improved physico-chemical features and able to selectively target G-quadruplexes is a very interesting perspective to develop new therapeutic agents.

Cationic porphyrins as destabilizer of a G-quadruplex located at the promoter of human MYH7 β gene

G-quadruplex (GQ) architecture is adopted by guanine rich sequences, present throughout the eukaryotic genome including promoter locations and telomeric ends. The in vivo presence indicates their involvement and role in various biological processes. Various small ligands have been developed to interact and stabilize/destabilize G-quadruplex structures. Cationic porphyrins are among the most studied ligands, reported to bind and stabilize G-quadruplexes. Herein, we report the recognition and destabilization of a parallel G-quadruplex by porphyrins (TMPyP3 and TMPyP4). This G-quadruplex forming 23-nt G-rich sequence is in the promoter region of Human Myosin Heavy Chain β gene (MYH7β). Presence of various putative regulatory sequence elements (TATA Box, CCAAT, SP-1) located in the vicinity of this quadruplex motif, highlight its regulatory implications. Biophysical methods as Circular Dichroism Spectroscopy, UV-Absorption Spectroscopy, UV-Thermal Denaturation and Fluorescence Spectroscopy (steady as well as Time Resolved) have been used for studying the interaction and binding parameters. It is proposed that porphyrins have a destabilizing effect on the G-quadruplexes with parallel topology and a stronger binding specifically via intercalation mode is needed to cause destabilization. The study deals with better understanding and insights of DNA-Drug interactions in biological systems.Communicated by Ramaswamy H. Sarma.

Multicharged Phthalocyanines as Selective Ligands for G-Quadruplex DNA Structures

The stabilization of G-Quadruplex DNA structures by ligands is a promising strategy for telomerase inhibition in cancer therapy since this enzyme is responsible for the unlimited proliferation of cancer cells. To assess the potential of a compound as a telomerase inhibitor, selectivity for quadruplex over duplex DNA is a fundamental attribute, as the drug must be able to recognize quadruplex DNA in the presence of a large amount of duplex DNA, in the cellular nucleus. By using different spectroscopic techniques, such as ultraviolet-visible, fluorescence and circular dichroism, this work evaluates the potential of a series of multicharged phthalocyanines, bearing four or eight positive charges, as G-Quadruplex stabilizing ligands. This work led us to conclude that the existence of a balance between the number and position of the positive charges in the phthalocyanine structure is a fundamental attribute for its selectivity for G-Quadruplex structures over duplex DNA structures. Two of the studied phthalocyanines, one with four peripheral positive charges (ZnPc1) and the other with less exposed eight positive charges (ZnPc4) showed high selectivity and affinity for G-Quadruplex over duplex DNA structures and were able to accumulate in the nucleus of UM-UC-3 bladder cancer cells.

Interactions Between Spermine-Derivatized Tentacle Porphyrins and The Human Telomeric DNA G-Quadruplex

G-rich DNA sequences have the potential to fold into non-canonical G-Quadruplex (GQ) structures implicated in aging and human diseases, notably cancers. Because stabilization of GQs at telomeres and oncogene promoters may prevent cancer, there is an interest in developing small molecules that selectively target GQs. Herein, we investigate the interactions of meso-tetrakis-(4-carboxysperminephenyl)porphyrin (TCPPSpm4) and its Zn(II) derivative (ZnTCPPSpm4) with human telomeric DNA (Tel22) via UV-Vis, circular dichroism (CD), and fluorescence spectroscopies, resonance light scattering (RLS), and fluorescence resonance energy transfer (FRET) assays. UV-Vis titrations reveal binding constants of 4.7 × 10⁶ and 1.4 × 10⁷ M⁻¹ and binding stoichiometry of 2–4:1 and 10–12:1 for TCPPSpm4 and ZnTCPPSpm4, respectively. High stoichiometry is supported by the Job plot data, CD titrations, and RLS data. FRET melting indicates that TCPPSpm4 stabilizes Tel22 by 36 ± 2 °C at 7.5 eq., and that ZnTCPPSpm4 stabilizes Tel22 by 33 ± 2 °C at ~20 eq.; at least 8 eq. of ZnTCPPSpm4 are required to achieve significant stabilization of Tel22, in agreement with its high binding stoichiometry. FRET competition studies show that both porphyrins are mildly selective for human telomeric GQ vs duplex DNA. Spectroscopic studies, combined, point to end-stacking and porphyrin self-association as major binding modes. This work advances our understanding of ligand interactions with GQ DNA.

Interactions of tetracationic porphyrins with DNA and their effects on DNA cleavage

The interaction of tetracationic porphyrins with DNA was studied using UV-Vis absorption, fluorescence spectroscopy and viscometry, and the particle sizes were determined. Аs cationic porphyrins, two isomer porphyrins, 3,3',3″,3‴-(5,10,15,20-Porphyrintetrayl)tetrakis(1-methylpyridinium) (TMPyP3) and 4,4',4″,4‴-(5,10,15,20-Porphyrintetrayl)tetrakis(1-methylpyridinium) (TMPyP4), were studied. They differ in the position of NCH₃⁺ group in phenyl ring of the porphyrins and hence, in degree of freedom of rotation of the phenyl rings about the central macrocycle. It was found that intercalated complexes are formed at DNA/porphyrin molar ratios (R) of 2.2 and 3.9 for TMPyP3 и TMPyP4, respectively. Decreasing R up to 0.4 and 0.8 for TMPyP3 и TMPyP4, respectively, leads mainly to formation of outside complexes due to π-π stacking between the porphyrin chromophores interacting electrostatically with phosphate framework of DNA. Each type of the obtained complexes was characterized using Scatchard approach. It was ascertained that the affinity of TMPyP4 to DNA is stronger than TMPyP3, meanwhile the wedge effect of the latter is higher. The differences between the porphyrin isomers become more evident at irradiation of their complexes with DNA. It was established that irradiation of the intercalated complexes results in DNA fragmentation. In the case of TMPyP4, DNA fragments of different size are formed. The irradiation of the outside DNA/porphyrin complexes leads to cleavage of DNA (TMPyP3 and TMPyP4) and partial destruction of the complex due to photolysis of the porphyrin (TMPyP3).

In Vitro Photodynamic Activity of N-Methylated and N-Oxidised Tripyridyl Porphyrins with Long Alkyl Chains and Their Inhibitory Activity in Sphingolipid Metabolism

A series of N-methylated and N-oxidised tripyridyl porphyrins were synthesised, characterised, and their PDT activity was studied with six cell lines. All the tested porphyrins with a long alkyl chain, except one, were more efficient for PDT than an N-methylated hydrophilic porphyrin and N-oxidised porphyrin without the long alkyl chain. Generally, N-methylated tripyridyl porphyrins were more active than those N-oxidised, but IC₅₀ values for phototoxicity of two N-oxides, named TOPyP3-C₁₇ H₃₃ O and TOPyP3-C₁₇ H₃₅ , were still in the nanomolar concentration range for most of the tested cell lines. However, TOPyP3-C₁₇ H₃₅ did not show phototoxicity on human foreskin fibroblast cells. Two methylated amphiphilic porphyrins, named TMPyP3-C₁₇ H₃₃ and TMPyP4-C₁₇ H_35, showed significant dark toxicity, whereas none of the oxidopyridyl porphyrins were toxic without light activation. The selected photosensitisers were shown to be apoptosis inducers, and had inhibitory effects on the clonogenic growth of HCT116 and HeLa cells. All three N-methylated amphiphilic porphyrins significantly reduced the migratory potential of HCT116 cells. Porphyrins TMPyP3-C₁₇ H₃₅ and TOPyP3-C₁₇ H₃₅ reduced the activity of acid ceramidase, whereas TOPyP3-C₁₇ H₃₃ O had a significant inhibitory effect on sphingosine kinase 1 activity in HeLa cells. Compounds with this dual activity were shown to be the most promising photosensitisers, with potential to treat invasive cancers.

Far-red fluorescent probes for canonical and non-canonical nucleic acid structures: current progress and future implications

Our review presents the recent progress on far-red fluorescent probes of canonical and non-canonical nucleic acid (NA) structures, critically discusses the design principles, applications, limitations and outline the future prospects of developing newer probes with target-specificity for different NA structures.

DNA interactions of non-chelating tinidazole-based coordination compounds and their structural, redox and cytotoxic properties

DNA interactions of novel tinidazole Cu^II complexes.

Interaction between G-Quadruplex and Zinc Cationic Porphyrin: The Role of the Axial Water

The interaction of ligands with G-quadruplexes has attracted considerable attention due to its importance in molecular recognition and anticancer drugs design. Here, we utilize triplet excited state as a sensitive reporter to study the binding interaction of zinc cationic porphyrin (ZnTMPyP4) with three G-quadruplexes, AG3(T2AG3)3, (G4T4G4)2, and (TG4T)4. By monitoring the triplet decay dynamics of ZnTMPyP4 with transient absorption spectroscopy, the coexisted binding modes via π-π stacking of porphyrin macrocycle and the G-quartets are allowed to be identified quantitatively, which involve intercalation (25% and 36%) versus end-stacking (75% and 64%) for AG3(T2AG3)3 and (G4T4G4)2, and end-stacking (23%) versus partial intercalation (77%) for (TG4T)4. It is shown that the steric hindrance of the axial water decreases greatly the percentage of intercalation. Further, a rapid assessment of binding stoichiometry is fulfilled by measuring the triplet decay dynamics under various [G-quadruplex]/[ZnTMPyP4] ratios. The binding stoichiometric ratios of G-quadruplex/ZnTMPyP4 are 1:2 for AG3(T2AG3)3, 1:1 for (G4T4G4)2, and 1:2 for (TG4T)4, which agree well with results obtained by the conventional method of continuous variation analysis. These results reveal a clear scenario of G-quadruplex/ZnTMPyP4 interaction and provide mechanistic insights for the application of anticancer drug designs using G-quadruplex as target.