Mechanism of action of glycyrrhizin against Plasmodium falciparum

Extracts of the plant Glycyrrhiza glabra (licorice) are used in traditional medicine to treat malaria. The main active components are the saponin glycyrrhizin (GLR) and its active metabolite glycyrrhetinic acid (GA) which both display activities against Plasmodium falciparum. We have identified three main mechanisms at the origin of their anti-plasmodial activity: (i) drug-induced disorganisation of membrane lipid rafts, (ii) blockade of the alarmin protein HMGB1 and (iii) potential inhibition of the detoxifying enzyme glyoxalase 1 (GLO-1) considered as an important drug target for malaria. Our analysis shed light on the mechanism of action of GLR against P. falciparum.</div

Copolymer Hydrogels of Acrylic Acid and a Nonionic Surfmer: pH-Induced Switching of Transparency and Volume and Improved Mechanical Stability

Copolymer hydrogels were prepared from an aqueous micellar solution of the nonionic surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)40undecyl-α-methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using γ-irradiation. The hydrogels were transparent if the polymerization was carried out at pH ≥ 4, whereas turbid gels were obtained if the polymerization was carried out at lower pH. Exposure of the turbid gels to an aqueous solution of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepared at pH 4 became turbid, if exposed to an aqueous solution of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amount of surfmer copolymerized in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, especially if the gels were prepared at pH 4. The mechanical stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mechanical stability of the hydrogels. The increase originates from copolymerized micellar aggregates acting as additional, stable cross-linking units in the gel. The true stress at break of copolymer hydrogels prepared at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymerized PEO-R-MA-40 are discussed

Binding of Daunomycin to Diaminopurine- and/or Inosine-Substituted DNA^†^,^‡

The binding of the anticancer drug daunomycin to double-helical DNA has been investigated by DNase I footprinting and fluorescence titration, using a series of polymerase chain reaction (PCR) synthesized DNA fragments that contained systematic base substitutions to alter the disposition of functional groups within the minor groove. The 160 bp tyrT DNA fragment constituted the starting material. Fragments in which (i) inosine was substituted for guanosine, (ii) diaminopurine was substituted for adenine, and (iii) both inosine and diaminopurine were substituted for guanosine and adenine, respectively, were studied. These fragments permit the role of the 2-amino group in the minor groove to be systematically explored. The results of DNase I footprinting experiments confirmed that daunomycin binds preferentially to 5‘(A/T)GC and 5‘(A/T)CG triplets in the normal fragment. Substitution of inosine for guanosine, with the concomitant loss of the N-2 in the minor groove, weakened binding affinity but did not dramatically alter the sequence preference associated with daunomycin binding. Complete reversal of the location of the N-2 group by the double substitution, however, completely altered the sequence preference of daunomycin and shifted its binding from the canonical triplets to ones with a 5‘IDD motif. These results have critically tested and confirmed the proposed key roles of the daunosamine moiety and the 9-OH group of daunomycin in dictating binding to preferred sites. In a parallel study, both macroscopic and microscopic binding to the normal tyrT fragment were investigated, experiments made possible by using PCR to prepare large quantities of the long, defined DNA sequence. The results of these experiments underscored the complexity of the interaction of the drug with the DNA lattice and revealed unequivocal heterogeneity in its affinity for different binding sites. A class of high-affinity sites, most probably corresponding to the 5‘(A/T)GC and 5‘(A/T)CG triplets, was identified and characterized in macroscopic binding isotherms

Confinement Effects on Chain and Glass Dynamics in Immiscible Polymer Blends

Confinement Effects on Chain and Glass Dynamics in Immiscible Polymer Blend

Further Insight into the DNA Recognition Mechanism of Trabectedin from the Differential Affinity of Its Demethylated Analogue Ecteinascidin ET729 for the Triplet DNA Binding Site CGA

Trabectedin and its N12-demethylated analogue ET729 bind covalently to the central guanine of selected DNA triplets. Although both drugs equally target several sites, including AGA, we show that covalent modification of CGA is only achieved by ET729. By means of molecular dynamics simulations of the precovalent complexes, we explain in atomic detail how such a simple structural modification brings about this notable change in the DNA-binding selectivity profiles of these two drugs

Oxidation of Cu^II to Cu^III, Free Radical Production, and DNA Cleavage by Hydroxy-salen−Copper Complexes. Isomeric Effects Studied by ESR and Electrochemistry

A series of copper complexes of bis(hydroxysalicylidene)ethylenediamine (hydroxy-salens) have been synthesized. The hydroxy group in the ortho, meta, or para position on each salicylidene unit was added to reinforce the stability of the copper complex and to create a hydroquinone system cooperating with the copper redox system to facilitate the spontaneous formation of oxidizing CuIII species. Cyclic voltammetry and ESR spectroscopy in combination with electrochemistry and spin trapping experiments have been used to characterize the structure and the redox state of the hydroxy-salen−copper complexes and to evidence the production of oxygen-based free radicals. A complete set of magnetic values were determined. In addition, we studied the capacity of complexes 3a,b,c to cleave DNA in the absence of activating agents. The meta isomer 3b does not generate oxygen radicals, and as a result it cannot cleave DNA. In sharp contrast, the para isomer 3c and to a lower extent the ortho isomer 3a exhibit nuclease activities in relation to their capacities to produce oxygen radicals. Electrochemistry provides unequivocal evidence for the formation of CuIII species with compounds 3a and 3c, but not with 3b. The nuclease activity correlates well with the ability of the hydroxy-salens to form the oxidizing CuIII species. The redox properties and therefore the DNA cleaving activities of the complexes depend crucially on the position of the OH groups which contribute significantly to stabilize the square planar copper complexes. The present work supports the hypothesis that a hydroquinone system can cooperate with a redox metal system to trigger DNA cleavage. The design of metallo(hydroxy-salens) provides an original route for the development of self-activated chemical nucleases

4-Hydroxymethyl-3-aminoacridine Derivatives as a New Family of Anticancer Agents

3-Amino- and 3-alkylamino-4-hydroxymethylacridines bearing various substituents on the C ring have been prepared by regioselective electrophilic aromatic substitution of the corresponding 3-aminoacridines and ring opening of the dihydrooxazinoacridine key intermediates. Most of the new compounds show potent cytotoxic activities against murine L1210 (leukemia), human A549 (lung), and HT29 (colon) cancer cell lines. The most cytotoxic molecules, 1 and 13, are active at nanomolar concentrations. As predicted for acridine derivatives, the new compounds intercalate in DNA, but interestingly they do not interfere with topoisomerase I and II activities. The mode of action remains uncertain because intracellular distribution indicated very different behaviors for 1 and 13. Compound 13 is uniformly distributed in the cell both in the cytoplasm and in the nucleus, whereas compound 1 is essentially localized in cytoplasmic granules

Thermoresponsive Copolymer Hydrogels on the Basis of <i>N</i>-Isopropylacrylamide and a Non-Ionic Surfactant Monomer: Swelling Behavior, Transparency and Rheological Properties

Copolymer hydrogels were prepared upon γ-ray-induced polymerization of aqueous micellar solutions containing N-isopropylacrylamide (NiPAAm) and the surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)40undecyl-α-methacrylate (PEO-R-MA-40). Stable, transparent, and thermosensitive hydrogels were obtained in a one-step process. Dose versus conversion measurements showed a complete conversion of comonomer solutions to hydrogels. The size of the surfmer micelles prior and subsequent to polymerization was studied using SAXS measurements. Presence of NiPAAm in the aqueous phase did not influence the size of the PEO-R-MA-40 micelles. During the polymerization process the particle diameter decreased from 7.0 to 5.6 nm probably due to cross-linking in the shell of the micelles. The thermosensitive behavior of the copolymer gels was investigated. The lower critical solution temperature (LCST) of the surfmer-containing gels was higher than for pure poly-NiPAAm (P-NiPAAm) gels, the increase being a direct function of the surfmer concentration. For hydrogels containing small amounts of surfmer, the shrinking at temperatures above the LCST was increased, and the swelling behavior at temperatures below the LCST was slightly increased. The mechanical stability of the copolymer hydrogels was studied using elongational deformation measurements. Presence of surfmer increased the mechanical stability of the hydrogels, the true stress at break being clearly higher for the copolymer gels compared with pure P-NiPAAm gels. A hydrogel containing only 1% (w/w) of surfmer can be elongated up to a true stress being nearly twice as large as for the pure P-NiPAAm gel. This can be explained by the presence of copolymerized micellar aggregates acting as new, stable cross-linking units. A structure model correlating the mechanical properties with a possible network structure is presented

DNA Sequence Dependent Monomer−Dimer Binding Modulation of Asymmetric Benzimidazole Derivatives

A number of studies indicate that DNA sequences such as AATT and TTAA have significantly different physical and interaction properties. To probe these interaction differences in detail and determine the influence of charge, we have synthesized three bisbenzimidazole derivatives, a diamidine, DB185, and monoamidines, DB183 and DB210, that are related to the well-known minor groove agent, Hoechst 33258. Footprinting studies with several natural and designed DNA fragments indicate that the synthetic compounds bind at AT sequences in the minor groove and interact more weakly at sites with TpA steps relative to sites without such steps. Circular dichroism spectroscopy also indicates that the compounds bind in the DNA minor groove. Surprisingly, Tm studies as a function of ratio indicate that the monoamidines bind to TTAA sequences as dimers, whereas the diamidine binds as a monomer. Biosensor-surface plasmon resonance (SPR) studies allowed us to quantitate the interaction differences in more detail. SPR results clearly show that the monoamidine compounds bind to the TTAA sequence in a cooperative 2:1 complex but bind as monomers to AATT. The dication binds to both sequences in monomer complexes but the binding to AATT is significantly stronger than binding to TTAA. Molecular dynamics simulations indicate that the AATT sequence has a narrow time-average minor groove width that is a very good receptor site for the bisbenzimidazole compounds. The groove in TTAA sequences is wider and the width must be reduced to form a favorable monomer complex. The monocations thus form cooperative dimers that stack in an antiparallel orientation and closely fit the structure of the TTAA minor groove. The amidine groups in the dimer are oriented in the 5‘ direction of the strand to which they are closest. Charge repulsion in the dication apparently keeps it from forming the dimer. It instead reduces the TTAA groove width, in an induced fit process, sufficiently to form a minor groove complex. The dimer-binding mode of DB183 and DB210 is a new DNA recognition motif and offers novel design concepts for selective targeting of DNA sequences with a wider minor groove, including those with TpA steps

Effects of Compound Structure on Carbazole Dication−DNA Complexes: Tests of the Minor-Groove Complex Models

Carbazole dications have shown excellent activity against opportunistic infections, but they are quite different in structure from previously studied unfused aromatic cations that function by targeting the DNA minor groove. In a previous report [Tanious, F. A., Ding, D., Patrick, D. A., Tidwell, R. R., and Wilson, W. D. (1997) Biochemistry 36, 15315−15325] we showed that, despite their fused ring structure, the carbazoles also bind in A/T sequences of the DNA minor groove and we proposed models for the carbazole−DNA complexes with the carbazole nitrogen facing out of the groove for 3,6 substituted compounds but into the groove in 2,7 carbazoles. To test and refine the models, carbazole-N-methyl substituted derivatives have been synthesized in both the 3,6 and 2,7 series as well as a new 2,6 substituted NH derivative that is intermediate in structure. Footprinting results indicate a broad AT specificity of carbazole binding and a pattern in agreement with a minor groove complex. Surface plasmon resonance biosensor analysis of carbazole binding to an oligomer with an AATT central sequence indicated that the 2,7 NH compound has the largest binding constant. Both the 3,6 NH and NMe compounds bind with similar equilibrium constants that are less than for the 2,7 NH compound. The 2,7 NMe compound has the lowest binding constant of all the carbazoles. Spectroscopic results are also similar for the two 3,6 derivatives but are quite different for the 2,7 NH and NMe carbazole dications. Structural analysis of carbazole complexes with an AATT sequence by 2D NMR methods also supported a minor groove complex of the carbazoles in orientations in agreement with the previously proposed models. From these results, it is clear that the fused ring carbazoles can bind strongly in the DNA minor groove with a broad A/T specificity and that the 2,7 and 3,6 substituted carbazoles bind to the minor groove in opposite orientations