Benzoindoloquinolines interact with DNA tetraplexes and inhibit telomerase

Telomeric G-rich single-stranded DNA can adopt a G-tetraplex structure which has been shown to inhibit telomerase activity. We have examined benzoindoloquinolines derivatives for their ability to stabilize an intramolecular G-quadruplex. The increase in T(m) value of the G-quadruplex was associated with telomerase inhibition in vitro.     

Amide bond direction modulates G-quadruplex recognition and telomerase inhibition by 2,6 and 2,7 bis-substituted anthracenedione derivatives

G-quadruplex structures of DNA represent a potentially useful target for anticancer drugs. Stabilisation of this arrangement at the ends of chromosomes may inhibit the action of telomerase, an enzyme involved in immortalization of cancer cells. Appropriately substituted amido anthracenediones are effective G-quadruplex stabilizers, but no information is available as yet on the possible modulation of G-quadruplex recognition and telomerase inhibition produced by the direction of the amide bond. To understand the basis of amido anthracenedione selectivity, we have synthesized a number of derivatives bearing the -CO-NH- or -NH-CO- group linked to the planar anthraquinone (AQ) moiety at 2,6 and 2,7 positions. The various isomers were tested in terms of telomerase inhibition, determined by the TRAP assay, G-quadruplex stabilisation measured by the increase in melting temperature of the appropriately folded oligonucleotide using FRET, and conformational and G4 binding properties examined by molecular modelling techniques. In all cases, enzymatic inhibition and G-quadruplex stabilization were directly related, which strongly supports the proposed molecular mechanism of telomerase interference. Interestingly, the AQ-NH-CO- arrangement performs invariantly better than the AQ-CO-NH- arrangement, showing a clear preference among isomeric derivatives. Theoretical calculations suggest that the former amide arrangement is co-planar with the aromatic system, whereas the latter is tilted by about 30 degrees when considering the most stable conformation. A more extended planar surface would allow more efficient stacking interactions with the quadruplex structure, hence more effective telomerase inhibition.     

Selective interaction of ethidium derivatives with quadruplexes: an equilibrium dialysis and electrospray ionization mass spectrometry analysis

The telomeric G-rich single-stranded DNA can adopt in vitro an intramolecular quadruplex structure, which has been shown to directly inhibit telomerase activity. The reactivation of this enzyme in immortalized and most cancer cells suggests that telomerase is a relevant target in oncology, and telomerase inhibitors have been proposed as new potential anticancer agents. In this paper, we have analyzed the selectivity of four ethidium derivatives and ethidium itself toward different G-quadruplex species, with electrospray mass spectrometry and competitive equilibrium dialysis and evaluated their inhibitory properties against telomerase. A selectivity profile may be obtained through electrospray ionization mass spectrometry (ESI-MS), which is in fair agreement with competitive equilibrium dialysis data. It also provides unambiguous data on the number of binding sites per nucleic acid (maximal number of two ethidium derivatives per quadruplex, in agreement with external stacking). Our experiments also demonstrate that one compound (4) is the most active and selective G-quadruplex ligand within this series and the most selective telomerase inhibitor in a modified TRAP-G4 assay.     

Interaction of an acridine dimer with DNA quadruplex structures.

The reactivation of telomerase activity in most cancer cells supports the concept that telomerase is a relevant target in oncology, and telomerase inhibitors have been proposed as new potential anticancer agents. The telomeric G-rich single-stranded DNA can adopt an intramolecular G-quadruplex structure in vitro, which has been shown to inhibit telomerase activity. The C-rich sequence can also adopt a quadruplex (intercalated) structure (i-DNA). Two acridine derivatives were shown to increase the melting temperature of the G- quadruplex and the C-quadruplex at 1 microM dye concentration. The increase in Tm value of the G-quadruplex was associated with telomerase inhibition in vitro. The most active compound, "BisA", showed an IC(50) value of 0.75 microM in a standard TRAP assay.     

Ethidium derivatives bind to G-quartets, inhibit telomerase and act as fluorescent probes for quadruplexes

The telomeric G-rich single-stranded DNA can adopt in vitro an intramolecular quadruplex structure, which has been shown to directly inhibit telomerase activity. The reactivation of this enzyme in immortalized and most cancer cells suggests that telomerase is a relevant target in oncology, and telomerase inhibitors have been proposed as new potential anticancer agents. In this paper, we describe ethidium derivatives that stabilize G-quadruplexes. These molecules were shown to increase the melting temperature of an intramolecular quadruplex structure, as shown by fluorescence and absorbance measurements, and to facilitate the formation of intermolecular quadruplex structures. In addition, these molecules may be used to reveal the formation of multi-stranded DNA structures by standard fluorescence imaging, and therefore become fluorescent probes of quadruplex structures. This recognition was associated with telomerase inhibition in vitro: these derivatives showed a potent anti-telomerase activity, with IC₅₀ values of 18–100 nM in a standard TRAP assay.     

Synthesis and evaluation of cationic phthalocyanine derivatives as potential inhibitors of telomerase

A series of water-soluble cationic phthalocyanine derivatives (1-10) were designed and synthesized to develop novel and potent telomerase inhibitors. These phthalocyanine derivatives as inhibitors of telomerase were investigated via modified telomerase repeat amplification protocol (TRAP) assay. The TRAP assay indicates that these cationic compounds had strong telomerase inhibitory activity (IC(50)<1.65 microM). To determine whether the phthalocyanine derivatives binding to G-quadruplex enhance the block to DNA synthesis, primer extension reactions were carried out in the presence of phthalocyanines. The interaction of the G-quadruplex of telomerase DNA with these molecules was examined by CD melting and PCR stop assay. These cationic phthalocyanine derivatives can stabilize G-quadruplex, which is demonstrated by the increased T(m) values. All these results indicate that the phthalocyanine derivatives might be potential lead compounds for the development of new telomerase inhibitor.     

CST does not evict elongating telomerase but prevents initiation by ssDNA binding

The CST complex (CTC1-STN1-TEN1) has been shown to inhibit telomerase extension of the G-strand of telomeres and facilitate the switch to C-strand synthesis by DNA polymerase alpha-primase (pol α-primase). Recently the structure of human CST was solved by cryo-EM, allowing the design of mutant proteins defective in telomeric ssDNA binding and prompting the reexamination of CST inhibition of telomerase. The previous proposal that human CST inhibits telomerase by sequestration of the DNA primer was tested with a series of DNA-binding mutants of CST and modeled by a competitive binding simulation. The DNA-binding mutants had substantially reduced ability to inhibit telomerase, as predicted from their reduced affinity for telomeric DNA. These results provide strong support for the previous primer sequestration model. We then tested whether addition of CST to an ongoing processive telomerase reaction would terminate DNA extension. Pulse-chase telomerase reactions with addition of either wild-type CST or DNA-binding mutants showed that CST has no detectable ability to terminate ongoing telomerase extension in vitro. The same lack of inhibition was observed with or without pol α-primase bound to CST. These results suggest how the switch from telomerase extension to C-strand synthesis may occur.     

Human telomerase inhibition by substituted acridine derivatives.

A series of 3,6-disubstituted acridine derivatives have been rationally designed as telomerase inhibitors. They have been designed on the basis that inhibition of telomerase occurs by stabilising G-quadruplex structures formed by the folding of telomeric DNA. The most potent inhibitors have IC50 values against telomerase of between 1.3 and 8 microM, comparable to their cytotoxicity in ovarian cancer cell lines.     

Solid phase synthesis of anthraquinone peptides and their evaluation as topoisomerase I inhibitors.

Anthraquinone peptide derivatives have previously been shown to inhibit the enzyme topoisomerase I (topo I), a pharmaceutical target for the prevention of malignant carcinomas. A highly efficient procedure for the attachment of the anthraquinone moiety to the N-terminus of a peptide on a solid support is reported. This methodology provides a convenient method for the synthesis of labelled peptides, with potential applications for chemotherapy, DNA detection and protein purification. As the synthetic strategy utilizes the solid phase, it should also be amenable to the generation of combinatorial libraries. The utility of the method by synthesizing a pool of peptides and assaying for topo I inhibition is demonstrated.     

大黄蒽醌衍生物与环核苷酸磷酸二酯酶、钙调素相互作用的研究

大黄蒽醌衍生物是中药大黄的主要成份。该类衍生物与钙调素(calmo-dulin,CaM)依赖的磷酸二酯酶(PDE)的相互作用表明:它们可作用子钙调素。其中,大黄酸结合CaM并抑制CaM依赖的磷酸二酯酶(CaM-PDE);而大黄素、大黄酚和芦荟大黄素既刺激CaM-PDE的活力,又刺激PDE的基础活力,其作用机制尚待阐明;当有Ca~(2+)或无Ca~(2+)条件下测定时,大黄酸对PDE基础活力均无影响。表明:象其它的CaM拮抗剂一样,大黄酸能抑制钙调素依赖的PDE的活力。     

Design, synthesis, biophysical and biological studies of trisubstituted naphthalimides as G-quadruplex ligands

A series of trisubstituted naphthalimides have been synthesized and evaluated as telomeric G-quadruplex ligands by biophysical methods. Affinity for telomeric G-quadruplex AGGG(TTAGGG)(3) binding was first screened by fluorescence titrations. Subsequently, the interaction of the telomeric G-quadruplex with compounds showing the best affinity has been studied by isothermal titration calorimetry and UV-melting experiments. The two best compounds of the series tightly bind the telomeric quadruplex with a 2:1 drug/DNA stoichiometry. These derivatives have been further evaluated for their ability to inhibit telomerase by a TRAP assay and their pharmacological properties by treating melanoma (M14) and human lung cancer (A549) cell lines with increasing drug concentrations. A dose-dependent inhibition of cell proliferation was observed for all cellular lines during short-term treatment.     

Different roles of p53 in the regulation of DNA damage caused by 1,2-heteroannelated anthraquinones and doxorubicin

The anthracyclin antibiotic agent doxorubicin (DXR) has been widely used as a chemotherapeutic drug for more than 40 years, but its clinical use has been limited by its cardiotoxicity. The mechanism of action of DXR remains uncertain and controversial. A series of 1,2-heteroannelated anthraquinones and anthra[1,2-d]imidazole-6,11-dione compounds were synthesized and their cytotoxicity profiles were analyzed using the National Cancer Institute 60 (NCI 60) platform and human telomerase inhibition assays. In the current study, three of the 1,2-heteroannelated anthraquinones, NSC745795, NSC745885 and NSC745887, were found to differ from each other with respect to their effects on cell cycle regulation, apoptosis, autophagy, senescence and their abilities to induce DNA damage. The differences depended on the presence or absence of a heterocyclic moiety, which suggested that the differences were due, at least in part, to differential effects on specific cellular targets, such as p53. In contrast to DXR, which induced p53 expression, treatment with NSC745885 resulted in the degradation of several proteins, including p53, via proteasome-dependent and -independent pathways in HeLa cells. These results provide insights into the molecular mechanisms governing cell inhibition by 1,2-heteroannelated anthraquinone derivatives and suggest that these mechanisms could serve as the basis for new structure-based drug designs.     

The number and distances of positive charges of polyamine side chains in a series of perylene diimides significantly influence their ability to induce G-quadruplex structures and inhibit human telomerase

We have synthesized eight polyamine perylene diimides to conjugate the efficiency of perylene derivatives in stabilizing G-quadruplex structures and the polyamines' biological activity, due to specific interactions with different DNA domains. Our study was carried out by investigating the ability of these derivatives to induce inter- and intramolecular G-quadruplex structures by polyacrylamide gel electrophoresis (PAGE) and to inhibit telomerase in a modified TRAP assay. The two properties appear to be satisfactorily correlated and they show that the number and distances of positive charges in the side chains dramatically influence both these features. Although our previous studies on perylene derivatives with mono-positively charged side chains indicated that self assembly in aqueous solution leads to a major efficiency, the result observed with the spermine derivative suggests that a too strong aggregation is unfavourable, because it determines a lower solubility of the compounds.     

Natural and synthetic G-quadruplex interactive berberine derivatives

The interaction of the natural alkaloid berberine with various G-quadruplex DNA structures and its ability to inhibit telomerase have been examined and compared with those of a synthetic piperidino derivative and the related compound coralyne. The results show that these molecules have selectivity for G-quadruplex compared to duplex DNA, and that their aromatic moieties play a dominant role in quadruplex binding.     

Targeting telomerase via its key RNA/DNA heteroduplex

Telomerase is a promising "universal" anticancer target. It has been demonstrated that inhibition of telomerase leads to mortalization and death of previously immortal cell lines. We are interested in targeting telomerase by binding to the RNA/DNA duplex that forms during its catalytic cycle. The RNA strand of this duplex is a component of telomerase and acts as a template to direct the synthesis of the single-stranded DNA telomere. We have hypothesized that molecules that bind to this duplex will inhibit the enzyme by either preventing strand dissociation or by sufficiently distorting the substrate, thereby causing a misalignment of key catalytic residues. To test this hypothesis we have examined the activity of telomerase in the presence of a range of intercalating molecules, known for their broad duplex binding properties. Of the nine compounds we examined, four show promising lead activity in the low micromolar range. A kinetic analysis of the telomeric products suggests that these compounds do not act by stabilizing G-quartets, thereby supporting the telomeric RNA/DNA heteroduplex as the site of action. We anticipate using these lead compounds as the basis for combinatorial variation to increase the affinity and specificity for the target telomerase.     

Perylene diimides with different side chains are selective in inducing different G-quadruplex DNA structures and in inhibiting telomerase

Four N,N'-disubstituted perylene diimides, having different side chains, have been studied for their ability in inducing G-quadruplex DNA structures. We found that electrostatic interactions between ligands side chains and DNA grooves play a main role not only in the amount of G-quadruplex formed, but also in selecting its topology. Moreover, such compounds show also a different ability to inhibit telomerase. The correlation of these findings suggests the intriguing possibility that different G-quadruplex structures could differently inhibit the enzyme.     

9-Substituted berberine derivatives as G-quadruplex stabilizing ligands in telomeric DNA

The interaction of berberine and its 9-substituted derivatives with human telomeric DNA d[G(3)(T(2)AG(3))(3)](telo21) has been investigated via CD spectroscopy, fluorescence spectroscopy, PCR-stop assay, competitive dialysis, and telomerase repeat amplification protocol (TRAP) assay. The results indicated that these semisynthesized compounds could induce and stabilize the formation of anti-parallel G-quadruplex of telomeric DNA in the presence or absence of metal cations. Compared with berberine, the 9-substituted derivatives exhibit stronger binding affinity with G-quadruplex and higher inhibitory activity for telomerase. Introduction of a side chain with proper length of methylene and terminal amino group to the 9-position of berberine would significantly strengthen the binding affinity with G-quadruplex, resulting in increasing inhibitory effects on the amplification of telo21 DNA and on the telomerase activity.     

Synthesis,biological evaluation, 3D-QSAR studies of novel aryl-2H-pyrazole derivatives as telomerase inhibitors

A series of novel aryl-2H-pyrazole derivatives bearing 1,4-benzodioxan or 1,3-benzodioxole moiety were designed as potential telomerase inhibitors to enhance the ability of aryl-2H-pyrazole derivatives to inhibit telomerase, a target of anticancer. The telomerase inhibition tests showed that compound 16A displayed the most potent inhibitory activity with IC₅₀ value of 0.9 μM for telomerase. The antiproliferative tests showed that compound 16A exhibited high activity against human gastric cancer cell SGC-7901 and human melanoma cell B16-F10 with IC₅₀ values of 18.07 and 5.34 μM, respectively. Docking simulation showed that compound 16A could bind well with the telomerase active site and act as telomerase inhibitor. 3D-QSAR model was also built to provide more pharmacophore understanding that could be used to design new agents with more potent telomerase inhibitory activity.     

蒽醌衍生物结构及其对小麦白粉病菌生物活性的关系研究

蒽醌衍生物是植物产生的一类次生代谢产物,对植物病原真菌具有明显的活性。为明确蒽醌衍生物结构与其生物活性之间的关系,以小麦白粉病菌为研究对象,测定了蒽醌及16种蒽醌衍生物对该病菌的活性。结果表明,蒽醌衍生物对小麦白粉病菌的活性明显大于葸醌的活性;甲氧基的位置与活性关系密切,6位是决定活性的关键,活性顺序为5、6位〉1、6位〉6位〉8位。