Dimers formed with the mixed-type G-quadruplex binder pyridostatin specifically recognize human telomere G-quadruplex dimers.

By choosing pyridostatin (PDS) with high thermal stabilization towards mixed-type G-quadruplexes as the monomer in dimers, three novel polyether-tethered PDS dimers (1a-c) were first synthesized and their interaction with human telomere G-quadruplex dimers (G2T1) was studied. Through the regulation of the linker length in PDS dimers, the dimer with a medium-length polyether linker (1b) showed higher binding selectivity and thermal stabilization (ΔTm = 29.5 °C) towards antiparallel G2T1 over G-quadruplex monomers (G1). Furthermore, the dimer with the longest-length polyether linker (1c) showed higher binding selectivity and thermal stabilization towards mixed-type G2T1 over mixed-type G1, c-kit 1, c-kit 2, c-myc and ds DNA. This work provides new insights into the development of G2T1 binders, especially mixed-type G2T1 binders, which could be promoted by a polymer formed with a mixed-type G-quadruplex binder. In addition, dimer 1c exhibited stronger telomerase inhibition than dimers 1a and 1b.

A Comparative Study on High Selectivities of Human Telomeric Dimeric G-Quadruplexes by Dimeric G-Quadruplex Binders.

Three new polyether-tethered bisquinolinium dimers (3 a-c) were synthesized, and their binding affinities, selectivities, and thermal stabilization towards dimeric G-quadruplex DNA (G2T1) in human telomeric regions were studied. The bisquinolinium dimer with a medium-length polyether linker (3 b) showed 30-425-fold higher binding affinity and selectivity towards antiparallel G2T1 than towards monomeric quadruplexes, which included human telomeric monomeric G-quadruplexes (G1), c-kit 1, c-kit 2, and c-myc. In addition, compound 3 b induced the formation of quadruplexes and displayed the highest level of thermal stabilization (ΔTm >28.1 °C) among all reported multimeric G-quadruplex binders. Compound 3 b also displayed a higher selectivity towards antiparallel G2T1 than monomer 360 A and bisquinolinium dimers 3 a and c. In contrast with our recent research on the analogous berberine dimer 1 b and dinickel-salphen complex 2 c, polyether linkers and their monomeric G-quadruplex binders in these dimeric G-quadruplex binders play a crucial role in regulating the binding affinities, selectivities, and thermal stabilization towards G2T1. More interestingly, these dimeric G-quadruplex compounds bind through end-stacking with the two adjacent G-quadruplex units in G2T1, and they showed high selectivity towards antiparallel G2T1 rather than mixed-type G2T1. In addition, compound 3 b, which displayed high selectivity towards antiparallel G2T1, showed strong telomerase inhibition and potent anticancer activities against HeLa and MCF-7 cells.

Dinickel-Salphen Complexes as Binders of Human Telomeric Dimeric G-Quadruplexes.

Three new polyether-tethered dinickel-salphen complexes (2 a-c) have been synthesized and fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The binding affinity and selectivity of these complexes and of the parent mono-nickel complex (1) towards dimeric quadruplex DNA have been determined by UV/Vis titrations, fluorescence spectroscopy, CD spectroscopy, and electrophoresis. These studies have shown that the dinickel-salphen complex with the longest polyether linker (2 c) has higher binding affinity and selectivity towards dimeric quadruplexes (over monomeric quadruplexes) than the dinickel-salphen complexes with the shorter polyether linkers (2 a and 2 b). Complex 2 c also has higher selectivity towards human telomeric dimeric quadruplexes with one TTA linker than the monometallic complex 1. Based on the spectroscopic data, a possible binding mode between complex 2 c and the dimeric G-quadruplex DNA under study is proposed.

Specifically targeting mixed-type dimeric G-quadruplexes using berberine dimers.

Three polyether-tethered berberine dimers (1a-c) were studied for their binding affinity, selectivity and thermal stabilization towards human telomeric dimeric quadruplex DNA (G2T1). Compound 1a with the shortest polyether linker showed the highest affinity (Ka > 108 M-1) and 76-508-fold higher selectivity for mixed-type G2T1 over antiparallel G2T1 and three monomeric G-quadruplexes, which are human telomeric monomeric quadruplex G1, c-kit 1 and c-kit 2. Compound 1a induced the formation of quadruplex structures and showed higher thermal stabilization for mixed-type G2T1 than for anti-parallel G2T1, G1 and ds DNA. Spectroscopic studies suggest that compound 1a could bind to mixed-type G2T1 via end-stacking and external binding modes. These results suggest that the polyether linkers in these compounds play an important role in regulating the binding affinity and selectivity towards mixed-type G2T1 and that compound 1a could target mixed-type G2T1 at other genome regions with antiparallel G2T1 and monomeric G-quadruplexes. These results may provide useful guidance for the rational design of selective multimeric G-quadruplex binders and potential anticancer agents.

Highly selective, sensitive and fluorescent sensing of dimeric G-quadruplexes by a dimeric berberine.

This paper describes the highly selective, sensitive and topology-specific fluorescent sensing of dimeric G-quadruplexes by a polyether-tethered dimeric berberine 1. Compound 1 displays high selectivity for dimeric G-quadruplexes over monomeric ones, and can be lit up by dimeric G-quadruplexes, in particular by the one linked with one TTA subunit. In addition, it shows no effect on the topology or thermal stability of the G-quadruplexes.

Synthesis and transmembrane anion/cation symport activity of a rigid bis(choloyl) conjugate functionalized with guanidino groups.

A rigid bis(choloyl) conjugate functionalized with guanidino groups was synthesized and fully characterized on the basis of NMR ((1)H and (13)C) and ESI MS (LR and HR) data. Its transmembrane ionophoric activity across egg-yolk l-α-phosphatidylcholine-based liposomal membranes was investigated by means of chloride ion selective electrode technique and pH discharge assay. The data indicate that under the assay conditions, this conjugate was capable of promoting the transport of anions, presumably via a cation/anion symport process. A Hill analysis reveals that two molecules of this compound are assembled into the transport-active species.

Does lipophilicity affect the effectiveness of a transmembrane anion transporter? Insight from squaramido-functionalized bis(choloyl) conjugates.

Six squaramido-functionalized bis(choloyl) conjugates were synthesized and fully characterized on the basis of NMR ((1)H and (13)C) and ESI MS (LR and HR) data. Their transmembrane anionophoric activity was investigated in detail by means of chloride ion selective electrode technique and pyranine assay. The data indicate that this set of compounds is capable of promoting the transmembrane transport of anions presumably via proton/anion symport and anion exchange processes, and that lipophilicity in terms of clog P from 3.90 to 8.32 affects the apparent ion transport rate in a concentration-dependent fashion. Detailed kinetic analysis on the data obtained from both the chloride efflux and pH discharge experiments reveals that there may exist an optimum clog P range for the intrinsic ion transport rate. However, lipophilicity exhibits little effect on the effectiveness of this set of compounds in terms of either k2/Kdiss or EC50 values.

Synthesis and potent ionophoric activity of a squaramide-linked bis(choloyl) conjugate.

A squaramide-linked bis(choloyl) conjugate was synthesized and fully characterized on the basis of NMR ((1)H and (13)C) and ESI MS (LR and HR) data. Fluorescence and chloride ion selective electrode assays indicate that this compound exhibits potent ionophoric activity across egg-yolk L-α-phosphatidylcholine-based liposomal membranes, presumably via an anion-modulating anion-cation co-transport/symport process. A Hill analysis reveals that three molecules of this compound are assembled into the transport-active species.

Acidic Lysosome-Anchoring Croconium-Based Nanoplatform for Enhanced Triple-Mode Bioimaging and Fe3+-Triggered Tumor Synergistic Therapy.

Metal-modulated croconium dyes with multimodal-imaging and synergistic therapy in the tumor microenvironment have exhibited great potential in tumor theranostics. However, their unideal structure optimization always weakened the efficacy of near-infrared fluorescence-photoacoustic (NIRF/PA) imaging and photothermal therapy (PTT). Here, we screened croconium dye containing two indole groups with better NIRF/PA imaging and PTT in their family, linked to two morpholine rings, and obtained CR-736, as a lysosome-targeting and Fe3+-modulated agent. The established CR-736-Fe3+ nanoplatform was accurately delivered to the breast tumor site, released CR-736 and Fe3+ in the lower acidic lysosome microenvironment, and activated pH-responsive NIRF/PA/magnetic resonance imaging and PTT. Furthermore, ferroptosis generated hydroxyl free radicals and lipid peroxide by consuming GSH and H2O2 by dint of the accumulation of Fe3+ in tumor cells, which resulted in the inhibition of the expression of heat shock proteins and the concomitant recovery of PTT. The synergistic therapy of PTT, ferroptosis, and chemodynamics was further optimized to the maximal extent in tumor lysosome acidic microenvironment and proved both in vitro and a mouse tumor model. This study opens a new avenue in designing excellent and unique croconium-based nanoplatforms, synergizing multiple tumor theranostic methods, and further optimizing the theranostic effects in tumor microenvironment.

Synthesis, crystal structures and DNA-cleaving activities of [Cemp]2[MCl4] (Cemp = N-carbethoxymethyl-1,10-phenanthrolinium, M = Cu(II), Zn(II), Co(II), Ni(II) and Mn(II)).

N-Carbethoxymethyl-1,10-phenanthrolinium bromide (CempBr) and its five ionic metal complexes, [Cemp]2[MCl4] where M = Cu(II) (1), Zn(II) (2), Co(II) (3), Ni(II) (4) and Mn(II) (5) were synthesized and fully characterized. Complexes 1-5 have similar structures, and consist of isolated [Cemp](+) cations and [MCl4](2-) anions in which there are no obvious interactions between the oxygen or nitrogen donor atoms in [Cemp](+) and the metal center in [MCl4](2-). Agarose gel electrophoresis studies on the cleavage of plasmid pBR322 DNA by complexes 1-5 indicated that complex 1 was capable of efficiently cleaving DNA under physiological conditions, most probably via an oxidative mechanism. Kinetic assay of complex 1 afforded the maximal catalytic rate constant kmax of 0.55 h(-1) and Michaelis constant KM of 47.6 µM, respectively, which gives about 1.5×10(7)-fold rate acceleration over uncatalyzed cleavage of supercoiled DNA. Ethidium bromide displacement experiments indicated that complex 1 had a binding affinity of (1.58±1.12)×10(6) M(-1) toward calf-thymus DNA, 20-100-fold higher than those shown by CempBr and complexes 2-5. The high cleaving efficacy of complex 1 is thought to be due to the efficient catalysis of the copper(II)-coordinated center and the efficient binding of the quaternized 1,10-phenanthroline cation to DNA.

Single aromatics sulfonamide substituted dibenzothiazole squaraines for tumor NIR imaging and efficient photodynamic therapy at low drug dose.

On the base of the zwiterionic dibenzothiazole squaraine SQ, five cationic aromatics sulfonamide substituted dibenzothiazole squaraines SQ-D1 âˆ¼ 5 have been designed and synthesized. Through the formation of the cationic compound, a higher rigid structure and the addition of the strong electron-withdrawing group (-CN), an ideal photosensitizer SQ-D2 has been gotten. In all the sulfonaminosquaraines, compound SQ-D2 exhibited the highest ROS generation efficacy and photostability. It also showed the highest photo-cytotoxicity (IC50 = 0.25 ± 0.08 µM), very low dark-cytotoxicity and the excellent cell uptake. In animal study, it not only showed the effective tumor retention and the easy removal from the body, but also exhibited the effective PDT efficacy at low drug dose (0.15 mg/kg) and the good biocompatibility. Furthermore, photosensitizer SQ-D2 as a single component exhibited greater potential than clinically approved photosensitizer m-THPC and some nanomaterials with photosensitizers in PDT therapy towards human breast cancer. This work provides a new perspective to develop the ideal photosensitizer of the squaraine dyes.

Water-solubility croconic acid-bisindole dye with morpholine ring for tumor NIRF/PA imaging and photothermal therapy activated by lysosome pH-response.

A novel croconic acid-bisindole dye CR-630 with a morpholine ring showed good water-solubility and obvious lysosome-targeting. The protonation of the nitrogen atom in the indole and lysosome-targeting of morpholine ring let it exhibit stronger pH-responsive NIR/PA imaging and photothermal effect in the lysosome acidic microenvironment (pH 4.0-5.5) than in the tumor acidic microenvironment. In the animal study, compound CR-630 could NIRF/PA image in the tumor tissues in 1.5-2.0 h, effectively inhibit the growth of the tumor, and even ablate the tumor at the drug dose of 1 mg/kg. It also demonstrated good biosafety. This study gives a new idea to develop water-solubility organic dyes with lysosome targeting, stronger pH-responsive NIRF/PA imaging and PTT for breast cancer.

NIR C-Myc Pu22 G-quadruplex probe as a photosensitizer for bioimaging and antitumor study.

Despite the fact that C-Myc G-quadruplex in the oncogene promoter regions is one of the crucial targets of antitumor drugs, the selectivities and proliferation inhibitions of its probes towards tumor cells remain a big challenge. Until now, no effective C-Myc G-quadruplex probes have been reported as a photosensitizer to increase their antitumor activities. Here, the first NIR C-Myc G-quadruplex probe PDS-SQ has been designed, comprising a G-quadruplex binder PDS and a squaraine dye SQ as a photosensitizer. Conjugate PDS-SQ could selectively NIR image C-Myc Pu22 G-quadruplex in tumor cells, and show stronger antitumor activity in the irradiation by a chemo-photodynamic method than in the dark. The study provides a new way to develop the novel NIR C-Myc G-quadruplex probes with more potent antitumor activities.

Facile synthesis of a dimeric dipyrrole-polyamide and synergetic DNA-cleaving activity of its Cu(II) complex.

Inspired by the potent DNA-cleaving activity of the Cu(II) complex of monopyrrole-polyamide dimer 1 (i.e., 1@Cu(2+)), we designed a new dimeric dipyrrole-polyamide analog 2 with the aim to optimize the catalytic activities of the metal complexes of this type of polypyrrole-polyamides. Compound 2 was prepared in 50% yield from the reaction of 1-methyl-4-[(1-methyl-4-nitro-1H-pyrrole-2-carbonyl)-amino]-1H-pyrrole-2-carboxylic acid with 2,2'-(ethane-1,2-diylbis(oxy))diethanamine, and fully characterized on the basis of NMR ((1)H and (13)C), MS (ESI and HR) and IR. Spectrophotometric titration, ESI-MS and conductivity measurements indicated that compound 2 formed a 1:1 complex with Cu(2+) ion (i.e., 2@Cu(2+)). Agarose gel electrophoresis studies indicated that 2@Cu(2+) was capable of efficiently converting pBR322 DNA into open circular and linear forms under physiological conditions, most probably via an oxidative mechanism. Its overall catalytic activity was estimated to be at least 30-fold higher than that of 1@Cu(2+). The fact that the cleaving activities of these Cu(II) complexes parallel, exactly, their binding affinities, raises the possibility that the cleaving activities of polypyrrole-polyamide derivatives of the type can be regulated by the binding affinities.

Synthesis, characterization and potent DNA-cleaving activity of copper(II)-complexed berberine carboxylate.

9-O-(4-carboxybenzyl)berberine (CBB) 1 was synthesized from the reaction of berberrubine with methyl 4-(bromomethyl)benzoate and subsequent hydrolysis. Its Cu(II) complex 2 was prepared from the reaction with Cu(NO(3))(2)·3H(2)O, and established as [Cu(CBB)(2)](NO(3))(2)·2H(2)O by means of (1)H NMR, UV, IR, elemental analysis and TGA measurements. Agarose gel electrophoresis study on the cleavage of plasmid pBR322 DNA indicated that complex 2 was capable of efficiently cleaving DNA under physiological conditions, most probably via an oxidative mechanistic pathway involving the formation of singlet oxygen as the reactive species. Kinetic assay afforded the maximal first-order rate constant k(max) of 2.41 h(-1) and Michaelis constant K(M) of 2.64 mM, respectively, representing ca. 10(8)-fold acceleration in the cleavage. This catalytic efficacy is attributed to the Cu(II)-assisted formation of dimeric species, in which the two berberine subunits cooperatively bind to DNA, whereas the carboxylate-coordinated Cu(II) moiety functions as the cleavage-active center.

Synergetic DNA-cleaving activities of the metal complexes of a polyether-tethered pyrrole-polyamide dimer.

A simple polyether-tethered pyrrole-polyamide dimer 1 was synthesized in 50% yield from the reaction of 2,2,2-trichloro-1-(1-methyl-4-nitro-1H-pyrrol-2-yl)ethanone with 2,2'-[1,2-ethanediylbis(oxy)]bisethanamine, and fully characterized on the basis of ¹H- and ¹³C-NMR, MS, HR-MS, and IR data. Agarose gel-electrophoresis study of the cleavage of plasmid pBR322 DNA by the complexes of compound 1 with seven metal ions indicated that most of the metal complexes were capable of efficiently cleaving DNA at pH 7.0 and 37°. Among them, the Cu(II) complex exhibited the highest activity, with the maximal catalytic rate constant k(max) and Michaelis constant K(M) being 5.61 h⁻¹ and 7.30 mM, respectively. Spectroscopic, ESI-MS, ethidium-bromide (EB) displacement, and viscosity experiments indicated that compound 1 could form a 1 : 1 complex with Cu(II) ion, and that this complex showed moderate binding affinity toward calf-thymus DNA.

Synthesis, cytotoxicities and DNA-binding affinities of benzofuran-3-ols and their fused analogs.

A series of benzofuropyrazoles 2a-i were synthesized in 10-92% from the reaction of 2-aroylbenzofuran-3-ols 1a-i with hydrazine hydrate, and screened for their antitumor activities toward four human solid tumor cell lines, including gastric carcinoma cells MKN45, hepatocellular carcinoma cells HepG2, breast cancer cells MCF-7, and lung cancer cells A549. The results indicated that both compounds 1a-i and 2a-i displayed moderate antitumor activities. Among them, compound 2e exhibited potent inhibitory activity toward all the four tumor cell lines. In addition, compounds 1e and 2e showed strong DNA-binding affinities, and induced an increase in the viscosity of calf-thymus DNA, suggesting that they might act as an intercalator.

G-quadruplex binder pyridostatin as an effective multi-target ZIKV inhibitor.

At present, there are still no anti-Zika virus (ZIKV) drugs or vaccines approved by FDA with accurate targets and antiviral mechanisms. Considering the RNA G-quadruplex sequences in ZIKV genome, it is very meaningful to develop G-quadruplex binders as potential anti-ZIKV drugs with novel and accurate targets. In this paper, five classical G-quadruplex binders including Ber, Braco 19, NiL, 360A and PDS have been chosen to discuss their interaction with ZIKV RNA G-quadruplexes. PDS shows higher binding affinity and thermal stability than the other G-quadruplex binders. This property is further evidenced in cells by immunofluorescence microscopy. And PDS shows higher anti-ZIKV activity (EC50 = 4.2 ± 0.4 µM) than the other G-quadruplex binders as well as the positive control ribavirin, with a low cytotoxicity. By time-of-addition assay, PDS exerts antiviral activity at the post-entry process of ZIKV replication cycle, thus inhibiting ZIKV mRNA replication and protein expression. Furthermore, PDS combines with ZIKV NS2B-NS3 protease and reduces its catalytic activity. This study suggests that G-quadruplex binder PDS is an effective multi-target ZIKV inhibitor, which provides more guidance to design some novel anti-ZIKV drugs targeting ZIKV RNA G-quadruplexes.

Human telomere double G-quadruplex recognition by berberine-bisquinolinium imaging conjugates in vitro and cells.

Molecular tools of double or multimeric G-quadruplexes have been given higher requirements on detection sensitivity, thermal stabilization and cell imaging to establish functions of these G-quadruplex aggregates and biological mechanisms as anticancer reagents. Here, two smart berberine-bisquinolinium conjugates (Ber-360A and Ber-PDS) by linking the berberine fluorophore ligand and an established G-quadruplex binder (i.e. bisquinolinium scaffold), have been designed and evaluated their activities and mechanisms for G-quadruplex aggregation. Two conjugates, especially Ber-PDS, are two highly selective, sensitive and fluorescent sensors which can distinguish human telomere double G-quadruplexes from other type G-quadruplexes and ds DNA. These two ligands could be the first example to stack two adjacent G-quadruplex units and fluorescently recognize human telomere double G-quadruplexes. Furthermore, conjugate Ber-PDS could enter the nucleoli and target G-quadruplex DNA through microscopy experiments, and also display strong telomerase inhibition and antitumor activities.

A novel square-planar Pt(ii) complex as a monomeric and dimeric G-quadruplex DNA binder.

A novel phenanthroimidazole ethylenediamine Pt(ii) complex with coumarin derivative (1) was synthesized and showed higher affinity, selectivity and thermal stabilization for mixed-type dimeric G-quadruplexes (G2T1) over monomeric G-quadruplexes (G1) and duplex DNA. Complex 1 could bind to G-quadruplexes via end-stacking and external-binding modes.