Multiple DNA binding modes of anthracene-9-carbonyl-N1-spermine

Asymmetric Monomethine Cyanine Dyes with Hydrophobic Functionalities for Fluorescent Intercalator Displacement Assay

A new green procedure has been applied for the synthesis and purification of asymmetric monomethine cyanine dyes. The photophysical properties of the newly synthesized compounds have been examined by combined application of spectroscopic and theoretical methods. The structural characteristics of the molecules and dimer formation were characterized by quantum chemical computation and juxtaposed to the aggregachromism in UV/Vis spectra. The applicability of the dyes as fluorogenic nucleic acid probes has been proven by fluorescence titration, and their binding constants have been calculated. The mode of ligand-dsDNA/RNA interaction was rationalized by means of CD spectroscopy, molecular docking analysis, and fluorescent intercalator displacement experiments.

Predicted Negative Ion Photoelectron Spectra of 1-, 2-, and 9-Cyanoanthracene Radical Anions and Computed Thermochemical Values of the Three Cyanoanthracene Isomers

In this work, the negative ion photoelectron spectra of 1-, 2-, and 9-cyanoanthracene (anthracenecarbonitrile, ACN) radical anions, obtained via the calculation of Franck-Condon (FC) factors based on a harmonic oscillator model, are reported. The FC calculations utilize harmonic vibrational frequencies and normal mode vectors derived from density functional theory using the B3LYP/6-311++G (2d,2p) basis set. The removal of an electron from the doublet anion allows for the computation of the negative ion photoelectron spectra that represents the neutral ground singlet state (S_o) and the lowest triplet state (T₁) in each of the three ACN molecules. The respective adiabatic electron affinity (EA) values for the S_o state in 1-, 2-, and 9-ACN isomers are calculated to be 1.353, 1.360, and 1.423 eV. The calculated EA of the 9-cyanoanthracene singlet isomer is in close agreement with the previously reported experimental value of 1.27 ± 0.1 eV. Calculations show that the T₁ states in 1-, 2-, and 9-ACN are located 1.656, 1.663, and 1.599 eV above the S_o state. The calculated T₁ negative ion spectra exhibit intense vibrational origins and weak FC activity beyond the origins, indicating little change in geometry following electron detachment from the doublet anionic state. Upon deprotonation, the EA values of the radical isomers increase by ∼400-700 meV, resulting in neutral deprotonated radicals with EAs between 1.740 and 2.220 eV. The calculated site-specific gas-phase acidity values of ACN isomers indicate that ACN molecules are more acidic than benzonitrile.

Integrative Multiomics Analysis of the Heat Stress Response of Enterococcus faecium

A continuous heat-adaptation test was conducted for one Enterococcus faecium (E. faecium) strain wild-type (WT) RS047 to obtain a high-temperature-resistant strain. After domestication, the strain was screened with a significantly higher ability of heat resistance. which is named RS047-wl. Then a multi-omics analysis of transcriptomics and metabolomics was used to analyze the mechanism of the heat resistance of the mutant. A total of 98 differentially expressed genes (DEGs) and 115 differential metabolites covering multiple metabolic processes were detected in the mutant, which indicated that the tolerance of heat resistance was regulated by multiple mechanisms. The changes in AgrB, AgrC, and AgrA gene expressions were involved in quorum-sensing (QS) system pathways, which regulate biofilm formation. Second, highly soluble osmotic substances such as putrescine, spermidine, glycine betaine (GB), and trehalose-6P were accumulated for the membrane transport system. Third, organic acids metabolism and purine metabolism were down-regulated. The findings can provide target genes for subsequent genetic modification of E. faecium, and provide indications for screening heat-resistant bacteria, so as to improve the heat-resistant ability of E. faecium for production.

Interactions of mono spermine porphyrin derivative with DNAs

In this work, we have characterized the interactions of monospermine porphyrin derivative with calf thymus DNA (ct-DNA) and poly (dG-dC)₂ in both B and Z conformation. By several spectroscopic techniques (UV-vis, electronic circular dichroism and resonance light scattering), the binding modes of monospermine porphyrin derivative with different DNA sequences have been elucidated. In the presence of ct-DNA, the porphyrin binds along the external double helix as well as in the presence of B conformation of poly (dG-dC)₂ . Whilst when the Z form of the poly (dG-dC)₂ is induced, a slight intercalation of the porphyrin between the basis has been detected.

Synthetic Cannabinoid Receptor Agonists Detection Using Fluorescence Spectral Fingerprinting

Synthetic cannabinoid receptor agonists (SCRAs), termed “Spice” or “K2”, are molecules that emulate the effects of the active ingredient of marijuana, and they have gained enormous popularity over the past decade. SCRAs are Schedule 1 drugs that are highly prevalent in the U.K. prison system and among homeless populations. SCRAs are highly potent and addictive. With no way to determine the dose/amount at the point-of care, they pose severe health risks to users, including psychosis, stroke, epileptic seizures, and they can kill. SCRAs are chemically diverse, with over a hundred compounds used as recreational drugs. The chemical diversity of SCRA structures presents a challenge in developing detection modalities. Typically, GC-MS is used for chemical identification; however, this cannot be in place in most settings where detection is critical, e.g., in hospital Emergency Departments, in custody suites/prisons, or among homeless communities. Ideally, real time, point-of-care identification of SCRAs is desirable to direct the care pathway of overdoses and provide information for informed consent. Herein, we show that fluorescence spectral fingerprinting can be used to identify the likely presence of SCRAs, as well as provide more specific information on structural class and concentration (∼1 μg mL^–1). We demonstrate that that fluorescence spectral fingerprints, combined with numerical modeling, can detect both parent and combusted material, and such fingerprinting is also practical for detecting them in oral fluids. Our proof-of-concept study suggests that, with development, the approach could be useful in a range of capacities, notably in harm reduction for users of Spice/K2.

Interactions of 4,4'-diaminoazobenzene derivatives with telomeric G-quadruplex DNA

The development of small molecules to stabilize the G-quadruplex structure has garnered significant attention for anticancer drug discovery. Herein, we report the synthesis of several 4,4'-diaminoazobenzene derivatives containing different substituent groups and their ability to bind and stabilize telomeric G-quadruplex DNA. Circular dichroism (CD) spectroscopy was performed to characterize the quadruplex topologies, measure stabilization effects, and evaluate their capabilities for conformational photoregulation. 4,4'-Diaminoazobenzene derivatives were found to moderately stabilize quadruplex structures but not affect conformational photoregulation. This work further develops the design and general understanding of the stabilization effects of small molecules with telomeric G-quadruplex DNA.

Rationalisation of a mechanism for sensing single point variants in target DNA using anthracene-tagged base discriminating probes

The fluorescence sensing mechanism for identifying single base changes in target DNA strands has been established through detailed biophysical measurements.

Schiff base derived from thiosemicarbazone and anthracene showed high potential in overcoming multidrug resistance in vitro with low drug resistance index

Multidrug resistance (MDR) is a huge obstacle in cancer chemotherapeutics. Overcoming MDR is a great challenge for anticancer drug discovery. Here, DNA binding and cytotoxicity of Schiff base L1 and L2 were explored to assess their efficiency in fighting cancer and overcoming the MDR. L1 and L2 could treat extremely chemoresistant MCF-7/ADR cell as drug-sensitive cell, with drug resistance index (DRI) <2.13, showing high potential in overcoming the MDR. The apoptotic ratio induced by L1 and L2 was low for both MCF-7 and MCF-7/ADR cells. L1 and L2 induced an impairment of cell cycle progression of MCF-7 and MCF-7/ADR cell lines and suppressed cell growth by perturbing progress through the G0/G1 phase, with L2 causing more profound effect, which might account for lower drug resistance after L2 treatment. The molecular docking revealed weak interaction between L1/L2 and P-glycoprotein (P-gp), the most important drug efflux pump and intracellular Rhodamine 123 accumulation indicated that the activity of P-gp was not inhibited by L1 and L2. Combined with the cellular uptake results, it implied that L1 and L2 could bypass P-gp efflux to exert anticancer activity.

Effective control of the intrinsic DNA morphology by photosensitive polyamines

Changes occurring in the intrinsic B-DNA morphology upon binding to molecular photoswitches.

Anthracene-terpyridine metal complexes as new G-quadruplex DNA binders

The formation of quadruple-stranded DNA induced by planar metal complexes has particular interest in the development of novel anticancer drugs. This is especially relevant for the inhibition of telomerase, which plays an essential role in cancer cell immortalization and is overexpressed in ca. 85-90% of cancer cells. Moreover, G-quadruplexes also exist in other locations in the human genome, namely oncogene promoter regions, and it has been hypothesized that they play a regulatory role in gene transcription. Herein we report a series of new anthracene-containing terpyridine ligands and the corresponding Cu(II) and Pt(II) complexes, with different linkers between the anthracenyl moiety and the terpyridine chelating unit. The interaction of these ligands and metal complexes with different topologies of DNA was studied by several biophysical techniques. The Pt(II) and Cu(II) complexes tested showed affinity for quadruplex-forming sequences with a good selectivity over duplex DNA. Importantly, the free ligands do not have significant affinity for any of the DNA sequences used, which shows that the presence of the metal is essential for high affinity (and selectivity). This effect is more evident in the case of the Pt(II) complexes. Moreover, the presence of a longer linker between the chelating terpyridine unit and the anthracene moiety enhances the interaction with G-quadruplex-forming sequences. We further evaluated the ability of the Cu(II) complexes to interact with, and stabilize G-quadruplex containing regions in oncogene promoters via a polymerase stop assay. These studies indicated that the metal complexes are able to induce G-quadruplex formation and stop polymerase activity.

Homo- and Heterobimetallic Ruthenium(II) and Osmium(II) Complexes Based on a Pyrene-Biimidazolate Spacer as Efficient DNA-Binding Probes in the Near-Infrared Domain

We report in this work a new family of homo- and heterobimetallic complexes of the type [(bpy)2M(Py-Biimz)M'(II)(bpy)2](2+) (M = M' = Ru(II) or Os(II); M = Ru(II) and M' = Os(II)) derived from a pyrenyl-biimidazole-based bridge, 2-imidazolylpyreno[4,5-d]imidazole (Py-BiimzH2). The homobimetallic Ru(II) and Os(II) complexes were found to crystallize in monoclinic form with space group P21/n. All the complexes exhibit strong absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. For osmium-containing complexes (2 and 3) both the absorption and emission band stretched up to the NIR region and thus afford more biofriendly conditions for probable applications in infrared imaging and phototherapeutic studies. Detailed luminescence studies indicate that the emission originates from the respective (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes and is only slightly affected by the pyrene moiety. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations in the positive potential window and several reduction processes in the negative potential window. An efficient intramolecular electronic energy transfer is found to occur from the Ru center to the Os-based component in the heterometallic dyad. The binding studies of the complexes with DNA were thoroughly studied through different spectroscopic techniques such as UV-vis absorption, steady-state and time-resolved emission, circular dichroism, and relative DNA binding study using ethidium bromide. The intercalative mode of binding was suggested to be operative in all cases. Finally, computational studies employing DFT and TD-DFT were also carried out to interpret the experimentally observed absorption and emission bands of the complexes.

Naphthalene Imide Conjugates: Formation of Supramolecular Assemblies, and the Encapsulation and Release of Dyes through DNA-Mediated Disassembly

We report the synthesis of two new amphiphilic conjugates 1 and 2 based on naphthalene di- and monoimide chromophores and the investigation of their photophysical, self-assembly and DNA-binding properties. These conjugates showed aqueous good solubility and exhibited strong interactions with DNA and polynucleotides such as poly(dG⋅dC)-poly(dG⋅dC) and poly(dA⋅dT)-poly(dA⋅dT). The interaction of these conjugates with DNA was evaluated by photo- and biophysical techniques. These studies revealed that the conjugates interact with DNA through intercalation with association constants in the order of 5-8×10(4)  M(-1) . Of these two conjugates, bolaamphiphile 1 exhibited a supramolecular assembly that formed vesicles with an approximate diameter of 220 nm in the aqueous medium at a critical aggregation concentration of 0.4 mM, which was confirmed by SEM and TEM. These vesicular structures showed a strong affinity for hydrophobic molecules such as Nile red through encapsulation. Uniquely, when exposed to DNA the vesicles disassembled, and therefore this transformation could be utilised for the encapsulation and release of hydrophobic molecules by employing DNA as a stimulus.

Anthracene-polyamine conjugates inhibit in vitro proliferation of intraerythrocytic Plasmodium falciparum parasites

Anthracene-polyamine conjugates inhibit the in vitro proliferation of the intraerythrocytic human malaria parasite Plasmodium falciparum, with 50% inhibitory concentrations (IC50s) in the nM to μM range. The compounds are taken up into the intraerythrocytic parasite, where they arrest the parasite cell cycle. Both the anthracene and polyamine components of the conjugates play a role in their antiplasmodial effect.

Modulation of DNA binding by reversible metal-controlled molecular reorganizations of scorpiand-like ligands

DNA interaction with scorpiand azamacrocycles has been achieved through modulation of their binding affinities. Studies performed with different experimental techniques provided evidence that pH or metal-driven molecular reorganizations of these ligands regulate their ability to interact with calf thymus DNA (ctDNA) through an intercalative mode. Interestingly enough, metal-driven molecular reorganizations serve to increase or decrease the biological activities of these compounds significantly.

Interactions between the etoposide derivative F14512 and human type II topoisomerases: implications for the C4 spermine moiety in promoting enzyme-mediated DNA cleavage

F14512 is a novel etoposide derivative that contains a spermine in place of the C4 glycosidic moiety. The drug was designed to exploit the polyamine transport system that is upregulated in some cancers. However, a preliminary study suggests that it is also a more efficacious topoisomerase II poison than etoposide [Barret et al. (2008) Cancer Res. 68, 9845-9853]. Therefore, we undertook a more complete study of the actions of F14512 against human type II topoisomerases. As determined by saturation transfer difference (1)H NMR spectroscopy, contacts between F14512 and human topoisomerase IIα in the binary enzyme-drug complex are similar to those of etoposide. Although the spermine of F14512 does not interact with the enzyme, it converts the drug to a DNA binder [Barret et al. (2008)]. Consequently, the influence of the C4 spermine on drug activity was assessed. F14512 is a highly active topoisomerase II poison and stimulates DNA cleavage mediated by human topoisomerase IIα or topoisomerase IIβ. The drug is more potent and efficacious than etoposide or TOP-53, an etoposide derivative that contains a C4 aminoalkyl group that strengthens drug-enzyme binding. Unlike the other drugs, F14512 maintains robust activity in the absence of ATP. The enhanced activity of F14512 correlates with a tighter binding and an increased stability of the ternary topoisomerase II-drug-DNA complex. The spermine-drug core linkage is critical for these attributes. These findings demonstrate the utility of a C4 DNA binding group and provide a rational basis for the development of novel and more active etoposide-based topoisomerase II poisons.

Tricarbonyl M(I) (M = Re, (99m)Tc) complexes bearing acridine fluorophores: synthesis, characterization, DNA interaction studies and nuclear targeting

New pyrazolyl-diamine ligands with acridine derivatives at the 4-position of the pyrazolyl ring were synthesized and characterized (L1 and L2). Coordination towards the fac-[M(CO)(3)](+) (M = Re, (99m)Tc) led to complexes fac-[M(CO)(3)(kappa(3)-L)] (L = L1: M = Re1, Tc1; L = L2: M = Re2, Tc2). The interaction of the novel pyrazolyl-diamine ligands (L1 and L2) and rhenium(i) complexes (Re1 and Re2) with calf thymus DNA (CT-DNA) was investigated by a variety of techniques, namely UV-visible, fluorescence spectroscopy and circular and linear dichroism. Compounds L1 and Re1 have moderate affinity to CT-DNA and bind to DNA by intercalation, while L2 and Re2 have a poor affinity for CT-DNA. Moreover, LD measurements showed that L1 and Re1 act as perfect intercalators. By confocal fluorescence microscopy we found that L1 and Re1 internalize and localize in the nucleus of B16F1 murine melanoma cells. The congener Tc1 complex also targets the cell nucleus exhibiting a time-dependent cellular uptake and a fast and high nuclear internalization (67.2% of activity after 30 min). Plasmid DNA studies have shown that Tc1 converts supercoiled (sc) puc19 DNA to the open circular (oc) form.

Circular dichroism to determine binding mode and affinity of ligand-DNA interactions

Circular dichroism (CD) is a useful technique for an assessment of DNA-binding mode, being a more accessible, low-resolution complement to NMR and X-ray diffraction methods. Ligand-DNA interactions can be studied by virtue of the interpretation of induced ligand CD signals resulting from the coupling of electric transition moments of the ligand and DNA bases within the asymmetric DNA environment. This protocol outlines methods to determine the binding mode and affinity of ligand-DNA interactions and takes approximately 7.5 h.

DNA binding properties and evaluation of cytotoxic activity of 9,10-bis-N-substituted (aminomethyl)anthracenes

The results of DNA binding properties for four selected N-substituted 9,10-bis(aminomethyl)anthracenes are presented. DNA binding affinities were studied using UV-vis and fluorescence spectrophotometric titrations, CD spectroscopy, denaturation transition temperature (Tm) measurements and AM1 quantum chemical calculations. The results obtained indicate that the anthracene products intercalate into the stacked base pairs of DNA with binding constants, K, in the range 1.3-10.9 x 10(5)M(-1) and the binding site size in DNA-base pairs, n, extending over the range 2.4-4.6. Tm values increased in the presence of the anthryl probes, thereby reflecting an increased stability of the calf-thymus (CT) DNA double helix and rendering agreement with the spectrometric titration results. The synthesized compounds were tested against L1210 and HeLa tumor cell lines wherein the HeLa cells appeared to be more sensitive than the L1210 cells. 9,10-Bis{[2-(piperazin-1-yl)ethyl]aminomethyl}anthracene exhibited the highest activity of the tested compounds. Our findings were compared with those of a control drug bisantrene.

Construction of polyamine-modified uridine and adenosine derivatives--evaluation of DNA binding capacity and cytotoxicity in vitro

We here report the synthesis of the two polyamine-based nucleoside derivatives 5-{[bis-(3-aminopropyl)amino]acetamido-1-propynyl}uridine and 2-{[bis-(3-aminopropyl)amino]-acetamido-1-propynyl}adenosine. The various polyamine derivatives have been used in thermal melting analysis using DNA from herring testes, and in cellular studies using four different cell lines. The compounds were all found to be non-toxic, thus holding good promise for future use as siRNA building blocks.

Spectroscopic identification of binding modes of anthracene probes and DNA sequence recognition

The binding properties of two anthracene derivatives with calf thymus DNA (CT DNA), poly(dA-dT), and poly(dG) x poly(dC) are reported. One contained bulky, cyclic cationic substituents at the 9 and 10 positions, and the other carried acylic, branched, cationic substituents. Binding of the probes to the DNA was examined by calorimetry, spectroscopy and helix melting studies. The cyclic derivative indicated exothermic binding, strong hypochromism, bathochromism, positive induced circular dichroism (CD, 300-400 nm), significant unwinding of the helix, large increases in the helix melting temperature, strong but negative linear dichroism (LD, 300-400 nm) and considerable stabilization of the helix. In contrast, the acyclic analog indicated thermoneutral binding, smaller hypochromism, no bathochromism, very weak induced CD, and no change in the helix melting temperature with any of the DNA polymers. A sharp distinction between the binding properties of the two probes is indicated, and both have intrinsic binding constants of approximately 10(6) M(-1) for the three polymers. However, when the ionic strength of the medium was lowered (10 mM NaCl), the absorption as well as CD spectral changes associated with the binding of the acyclic derivative corresponded with those of the cyclic derivative. The acyclic derivative showed large preference (10-fold) for poly(dG) x poly(dC) over poly(dA-dT), whereas the cyclic analog showed no preference. The characteristic spectroscopic signatures of the two distinct binding modes of these probes will be helpful in deciphering the interaction of other anthracene derivatives with DNA.

Polyamine conjugates of meso-tritolylporphyrin and protoporphyrin IX: Potential agents for photodynamic therapy of cancers

An efficient five-step synthesis method was developed to obtain tritolylporphyrin and protoporphyrin IX polyamine conjugates. These compounds were composed of either one polyamine unit (spermidine or spermine) covalently tethered to monocarboxyphenyl tritolylporphyrin or two molecules of polyamines borne by protoporphyrin IX. In each compound, an aliphatic spacer arm is linked to the N(4) polyamine position. Photocytotoxicity of these new compounds was evaluated against K562 human chronic myelogenous leukemia cells and compared to Photofrin II; protoporphyrin IX polyamine conjugates exhibited much stronger photocytocicity than Photofrin II and were shown to readily induce necrosis in treated cells.

Detection of a single DNA base-pair mismatch using an anthracene-tagged fluorescent probe

A novel anthracene-tagged oligonucleotide can discriminate between a fully-matched DNA target sequence and one with a single mismatching base-pair through a remarkable difference in fluorescence emission intensity upon duplex formation.

Effect of Polyamine Homologation on the Transport and Biological Properties of Heterocyclic Amidines

Five sets of heterocyclic derivatives of various sizes and complexities coupled by an amidine function to putrescine, spermidine, or spermine were prepared. They were essentially tested to determine the influence of the polyamine chain on their cellular transport. To comment on affinity and on selective transport via the polyamine transport system (PTS), K(i) values for polyamine uptake were determined in L1210 cells, and the cytotoxicity and accumulation of the conjugates were determined in CHO and polyamine transport-deficient mutant CHO-MG cells, as well as in L1210 and alpha-difluoromethylornithine- (DFMO-) treated L1210 cells. Unlike spermine, putrescine and spermidine were clearly identified as selective motifs that enable cellular entry via the PTS. However, this property was clearly limited by the size of substituents: these polyamines were able to ferry a dihydroquinoline system via the PTS but did not impart any selectivity to bulkier substituents.

N1-substituent effects in the selective delivery of polyamine conjugates into cells containing active polyamine transporters

Several N(1)-arylalkylpolyamines containing various aromatic ring systems were synthesized as their respective HCl salts. The N(1)-substituents evaluated ranged in size from N(1)-benzyl, N(1)-naphthalen-1-ylmethyl, N(1)-2-(naphthalen-1-yl)ethyl, N(1)-3-(naphthalen-1-yl)propyl, N(1)-anthracen-9-ylmethyl, N(1)-2-(anthracen-9-yl)ethyl, N(1)-3-(anthracen-9-yl)propyl, and pyren-1-ylmethyl. The polyamine architecture was also altered and ranged from diamine to triamine and tetraamine systems. Biological activities in L1210 (murine leukemia), Chinese hamster ovary (CHO), and CHO's polyamine transport-deficient mutant (CHO-MG) cell lines were investigated via IC(50) cytotoxicity determinations. K(i) values for spermidine uptake were also determined in L1210 cells. The size of the N(1)-arylalkyl substituent as well as the polyamine sequence used had direct bearing on the observed cytotoxicity profiles. N(1)-Tethers longer than ethylene showed dramatic loss of selectivity for the polyamine transporter (PAT) as shown in a CHO/CHO-MG cytotoxicity screen. In summary, there are clear limits to the size of N(1)-substituents, which can be accommodated by the polyamine transporter. A direct correlation was observed between polyamine-conjugate uptake and cytotoxicity. In this regard, a cytotoxicity model was proposed, which describes a hydrophobic pocket of set dimensions adjacent to the putative PAT polyamine-binding site.

Syntheses and copper(ii)-dependent DNA photocleavage by acridine and anthracene 1,10-phenanthroline conjugate systems

We report the syntheses and characterization of a series of compounds based on 1,10-phenanthroline covalently tethered, at the 2 and 9 positions, to either two benzene, naphthalene, acridine or anthracene chromophores. The acridine and anthracene derivatives are shown to efficiently cleave pUC19 plasmid DNA upon irradiation with ultraviolet light (pH = 7.0, 22 degrees C, 350 nm). Furthermore, photocleavage levels are markedly increased by the addition of Cu2+ to the DNA photolysis reactions. Interestingly, when the concentrations of the anthracene compounds are lowered from 35 microM to 0.25 microM, the reverse trend is observed. DNA photocleavage is markedly reduced in the presence of copper(II).

Defining the Molecular Requirements for the Selective Delivery of Polyamine Conjugates into Cells Containing Active Polyamine Transporters

Several N(1)-substituted polyamines containing various spacer units between nitrogen centers were synthesized as their respective HCl salts. The N(1)-substituents included benzyl, naphthalen-1-ylmethyl, anthracen-9-ylmethyl, and pyren-1-ylmethyl. The polyamine spacer units ranged from generic (4,4-triamine, 4,3-triamine, and diaminooctane) spacers to more exotic [2-(ethoxy)ethanoxy-containing diamine, hydroxylated 4,3-triamine, and cyclohexylene-containing triamine] spacers. Two control compounds were also evaluated: N-(anthracen-9-ylmethyl)-butylamine and N-(anthracen-9-ylmethyl)-butanediamine. Biological activities in L1210 (murine leukemia), alpha-difluoromethylornithine (DFMO)-treated L1210, and Chinese hamster ovary (CHO) and its polyamine transport-deficient mutant (CHO-MG) cell lines were investigated via IC(50) cytotoxicity determinations. K(i) values for spermidine uptake were also determined in L1210 cells. Of the series studied, the N(1)-benzyl-4,4-triamine system 6 had significantly higher IC(50) values (lower cytotoxicity) in the L1210, CHO, and CHO-MG cell lines. A cellular debenzylation process was observed in L1210 cells with 6 and generated "free" homospermidine. The size of the N(1)-arylmethyl substituent had direct bearing on the observed cytotoxicity in CHO-MG cells. The N(1)-naphthalenylmethyl, N(1)-anthracenylmethyl, and N(1)-pyrenylmethyl 4,4-triamines had similar toxicity (IC(50)s: approximately 0.5 microM) in CHO cells, which have an active polyamine transporter (PAT). However, this series had IC(50) values of >100 microM, 66.7 microM, and 15.5 microM, respectively, in CHO-MG cells, which are PAT-deficient. The observed lower cytotoxicity in the PAT-deficient CHO-MG cell line supported the premise that the conjugates use PAT for cellular entry. In general, moderate affinities for the polyamine transporter were observed for the N-arylmethyl 4,4-triamine series with their L1210 K(i) values all near 3 microM. In summary, the 4,4-triamine motif was shown to facilitate entry of polyamine conjugates into cells containing active polyamine transporters.

Synthesis and biological evaluation of N1-(anthracen-9-ylmethyl)triamines as molecular recognition elements for the polyamine transporter

An efficient modular synthesis of N(1)-substituted triamines containing different tether lengths between nitrogen centers was developed. A series of N(1)-(9-anthracenylmethyl)triamines were evaluated for biological activity in L1210 (murine leukemia), alpha-difluoromethylornithine (DFMO)-treated L1210, Chinese hamster ovary (CHO), and CHO-MG cell lines. All triamines 8 had increased potency in DFMO-treated L1210 cells. The 4,4- and 5,4-triamine systems had the highest affinity for the polyamine transporter (PAT) with L1210 K(i) values of 1.8 and 1.7 microM, respectively. This trend was also reflected in the CHO studies. Surprisingly, the respective 4,4- and 5,4-triamine systems had 150-fold and 38-fold higher cytotoxicity in CHO cells containing active polyamine transporters. Initial microscopy studies revealed the rapid formation of vesicular structures within A375 melanoma cells treated with the N(1)-(9-anthracenylmethyl)homospermidine (4,4-triamine) conjugate. In summary, the 4,4- and 5,4-triamines were identified as selective vector motifs to ferry anthracene into cells via the PAT.

Molecular requirements for targeting the polyamine transport system. Synthesis and biological evaluation of polyamine-anthracene conjugates

A series of nine N(1)-(9-anthracenylmethyl)tetraamines (e.g., Ant-4,4,4-tetraamine) were synthesized and evaluated for cytotoxicity in L1210, alpha-difluoromethylornithine (DFMO)-treated L1210, Chinese hamster ovary (CHO), and CHO-MG cell lines. Surprisingly, the 3,3,4- and 3,4,3-tetraamine motifs had the same or decreased cytotoxicity in DFMO-treated L1210 cells, whereas the rest of the tetraamine systems were usually more cytotoxic and gave lower IC(50) values in this treated cell line. The most sensitive derivatives to DFMO treatment were the Ant-4,4,3- and Ant-4,4,4-tetraamine analogues, which were 7 and 5 times more cytotoxic in DFMO-treated L1210 cells, respectively. K(i) values for each of the anthracenylmethyl(Ant)-polyamine conjugates were determined in L1210 cells and revealed that these systems are high-affinity ligands for the polyamine transporter (PAT). Mixed results were observed in the CHO and CHO-MG assays. The 4,4,4- and 5,4,4-tetraamine motifs were 3 times more toxic to CHO cells with active polyamine transporters. For example, the Ant-4,4,4-tetraamine conjugate displayed IC(50) values of 11 microM in CHO cells and 33 microM in CHO-MG cells, a PAT-deficient cell line. This suggested that these derivatives used the PAT in part to access cells. However, most of the other tetraamine derivatives had similar potencies in both the CHO and CHO-MG cell lines. In terms of vector design, higher affinity for the PAT (lower K(i) values) did not translate into higher potency for the tetraamine conjugate. In contrast, the related triamine systems, which had micromolar K(i) values in L1210 cells, were more efficacious and selective. In one case, the 4,4-triamine motif imparted 150-fold higher potency in CHO cells than the CHO-MG mutant. A deconvolution microscopy study in A375 melanoma cells revealed a rapid internalization of the Ant-4,4-triamine as fluorescent vesicles, whereas the Ant-4,4,4-tetraamine remained mostly at the cell surface. These findings help define the key characteristics required for selective delivery of polyamine-drug conjugates into cell types with active polyamine transporters.

Bisimidazoacridones: 2. Steady-state and Time-resolved Fluorescence Studies of Their Diverse Interactions with DNA¶§

Several bisimidazoacridones (BIA) are potent, selective antineoplastic agents, whereas others have potent anti-human immunodeficiency virus activity. BIA are bifunctional agents that consist of two imidazoacridone (IA) chromophores held together by various linkers. Interaction of BIA with DNA has been postulated to be required for their biological activity. Fluorescence data on free and bound BIA suggest that the binding of BIA and similar drugs to DNA is driven by a transfer of hydrophobic molecules from aqueous media to the more amphiphilic DNA environment. Binding to DNA was sensitive to sequence and depended on the length and rigidity of the linker. Time-resolved fluorescence measurements showed that BIA adopt an extended conformation upon binding and that all of the molecules are tightly associated with DNA. Gel-shift and melting assays indicated that one of the aromatic residues of BIA is intercalated, whereas the other, together with a linker, resides in a groove, probably the minor groove. A continuum of structures may be possible where intercalation and classical minor groove binding are limiting structures. In general, the hypothesis for the mechanism of action of BIA wherein the unintercalated residue, accessible for additional interactions, captures a critical protein involved in repair or transcription, is consistent with this model.

Effect of spermine conjugation on the cytotoxicity and cellular transport of acridine

Polyamines are believed to be potent vectors for the selective delivery of chemotherapeutic agents into cancer cells. In this paper, we report the effect of spermine conjugation on the cytotoxic and transport properties of acridine. Six derivatives, composed of a spermine chain attached at its N(1) position to an acridine via an aliphatic chain, were synthesized. The aliphatic linker, comprised of 3-5 methylene units, was connected to the position-9 of the heterocycle through either an amide (amidoacridines 8-10) or an amine (aminoacridines 11-13) linkage. Independently of their architecture, all ligands showed a high affinity for DNA binding but a limited DNA sequence selectivity. In a whole cell assay with L1210 and Chinese hamster ovary (CHO) cells, the aminoacridines (IC(50) values around 2 microM) were more potent than the amidoacridines (IC(50) values between 20 and 40 microM). This was related to a less efficient transport for the latter. As determined from competitive uptake studies with [(14)C]spermidine, all conjugates had a high affinity for the polyamine transport system (PTS). However, on the basis of competitive studies with an excess of spermidine and on the differential effect on cell growth and accumulation in CHO and in the mutant PTS deficient CHO-MG cells, the accumulation of the conjugates through the PTS was found to be poor but still more efficient for the aminoacridines. alpha-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, which induces an up-regulation of the activity of the PTS, enhanced accumulation of all acridine conjugates through the PTS and had a synergistic effect on the potency of the acridine conjugates to inhibit cell growth. Despite their high affinity for the PTS, the low amount of derivatives transiting through the PTS is likely to be related to their ability to repress rapidly and efficiently the activity of the PTS and, consequently, to inhibit their own uptake via this system.

Synthesis and antitumour activity of new dendritic polyamines-(imide-DNA-intercalator) conjugates: potent Lck inhibitors

A series of dendritic polyamines-(imide-DNA-intercalators) conjugates with different connectivity in their basic chain were synthesised and evaluated as antitumour compounds. Although their antiproliferative activity against HT-29 was not significant, conjugates 13 and 16 showed a promising profile as inhibitors of Lck.

Effects of polyamines on the thermal stability and formation kinetics of DNA duplexes with abnormal structure

The effects of ions (i.e. Na+, Mg2+ and polyamines including spermidine and spermine) on the stability of various DNA oligonucleotides in solution were studied. These synthetic DNA molecules contained sequences that mimic various cellular DNA structures, such as duplexes, bulged loops, hairpins and/or mismatched base pairs. Melting temperature curves obtained from the ultraviolet spectroscopic experiments indicated that the effectiveness of the stabilization of cations on the duplex formation follows the order of spermine > spermidine > Mg2+ > Na+ > Tris-HCl buffer alone at pH 7.3. Circular dichroism spectra showed that salts and polyamines did not change the secondary structures of those DNA molecules under study. Surface plasmon resonance (SPR) observations suggested that the rates of duplex formation are independent of the kind of cations used or the structure of the duplexes. However, the rate constants of DNA duplex dissociation decrease in the same order when those cations are involved. The enhancement of the duplex stability by polyamines, especially spermine, can compensate for the instability caused by abnormal structures (e.g. bulged loops, hairpins or mismatches). The effects can be so great as to make the abnormal DNAs as stable as the perfect duplex, both kinetically and thermodynamically. Our results may suggest that the interconversion of various DNA structures can be accomplished readily in the presence of polyamine. This may be relevant in understanding the role of DNA polymorphism in cells.

Influence of polyamine architecture on the transport and topoisomerase II inhibitory properties of polyamine DNA-intercalator conjugates

An efficient five-step synthetic method was developed to access a series of spermine derivatives containing appended acridine, anthracene, and 7-chloroquinoline motifs. The derivatives were composed of a spermine fragment covalently tethered at its N4 and N9 positions to an aromatic nucleus via an aliphatic chain (e.g., 8: acridine -[C4 aliphatic tether]-spermine-[C4 aliphatic tether]-acridine). The distance separating the spermine and aromatic nuclei was altered via different tethers composed of four or five methylene units. These bis ligands (8, 9, 12, and 13) were shown to inhibit human DNA topoisomerase II (topo II) activity at 5 microM. Enzymatic activity was assessed as the ability to unknot (decatenate) and cleave kinetoplast DNA (kDNA). Polyamine conjugation did not disrupt the ability of the acridine-spermine conjugates 8 and 9 to inhibit topo II activity as compared with the 9-aminoacridine and 9-(N-butyl)aminoacridine controls (at 5 microM). The parent polyamines, spermine (5 microM) and spermidine (10 microM), had little effect on topo II activity. In general, the bis-substituted spermine derivatives (8, 9, 12, and 13) were more efficient topo II inhibitors at 5 microM than their monosubstituted spermidine counterparts (22-25) at 10 microM. Within the bisintercalator spermine series, insertion of an additional methylene unit (i.e., C5 tethers) increased potency 2-fold (8, bis-C4-acridine, 47 h IC(50) = 40 microM; 9, bis-C5-acridine, IC(50) = 17 microM). Comparison of the bis- and monoacridine spermine motifs (8 and 17) revealed a 4-fold increase in potency for the latter architecture (94 h IC(50) for 8, 74 microM; for 17, 17 microM). In general the bisintercalators (8, 9, 12, and 13) behaved as cytostatic agents, while the monosubstituted acridine and anthracene derivatives (22-25) were cytotoxic. Anthracene-containing conjugates were generally more toxic than their acridine counterparts in an L1210 (murine leukemia) cell assay. Of the conjugates tested the (monointercalator)-spermine motif (e.g., 17) had the highest affinity for the L1210 polyamine transporter as revealed by spermidine protection experiments.

Synthesis and characterization of polyamine-based biomimetic catalysts as artificial ribonuclease

Several polyamine derivatives (I-V) conjugated with or without an intercalative moiety were prepared as ribonuclease mimics. Although no DNA-cleaving activity was observed for all compounds tested, mimics I, III, and V bearing an intercalative moiety along with the primary amine and/or imidazole moieties exhibited potent RNA-cleaving activity at near physiological pH. The RNA-cleaving reactions of the compounds show characteristic bell-shaped pH dependency, and the optimal pH values for III and V were well correlated to the pKa values of their active sites, primary amine, and imidazole moieties.

The effect of polyamine homologation on the transport and cytotoxicity properties of polyamine-(DNA-intercalator) conjugates

An efficient five-step synthetic method was developed to access a homologous series of spermidine-acridine and spermidine-anthracene conjugates. The derivatives were comprised of a spermidine fragment covalently tethered at its N4 position to either an acridine or anthracene nucleus via an aliphatic chain (e.g., spermidine-[aliphatic tether]-acridine). The distance separating the spermidine and aromatic nucleus was altered by using different tethers comprised of four or five methylene units, respectively. These ligands (2-5) were shown to inhibit human DNA topoisomerase-II (TOPO-II) activity at 10 microM. Enzymatic activity was assessed as the ability to unknot (decatenate) and cleave kinetoplast DNA (kDNA). Polyamine conjugation did not disrupt the ability of the acridine-spermidine conjugates 2 and 3 to inhibit TOPO-II activity as compared with the 9-aminoacridine and 9-(N-butyl)aminoacridine controls (at 10 microM). In general, the acridine derivatives (2 and 3) showed higher TOPO-II inhibitory activity than their anthracene counterparts (4 and 5). However, this trend was reversed in a whole cell assay with L1210 (murine leukemia) cells, wherein the anthracene analogues were more potent than their acridine counterparts. In this regard the qualitative enzyme-based assay did not predict the trends in the corresponding IC(50) values. Within either series insertion of an additional methylene unit did not significantly alter activity. While the appended spermidine unit did not disrupt TOPO II inhibition by the tethered DNA intercalator, it did provide an alternative mode of entry into the cell as demonstrated by spermidine protection assays. These results were compared with a spermine-intercalator analogue. Of all the conjugates tested the N(4)-(4-(9-aminoacridinyl)butyl)spermine hexahydrochloride (conjugate 16)resulted in the highest degree of L1210 cell rescue upon cotreatment of the cells with exogenous spermidine. It was concluded that the monoalkylated spermine motif present in 16 holds promise as a better vector than its N4 monoalkylated spermidine counterpart.