Biomedical subjects

John A Beutler

Publications and source records attributed to John A Beutler.

12 recordsLinked to original sources

PubMed2006

High-content fluorescence-based screening for epigenetic modulators.

Epigenetic processes have gained a great amount of attention in recent years, particularly due to the influence they exert on gene transcription. Several human diseases, including cancer, have been linked to aberrant epigenetic pathways. Consequently, the cellular enzymes that mediate epigenetic events, including histone deacetylases and DNA methyltransferases, have become prime molecular targets for therapeutic intervention. The effective and specific chemical inhibition of these activities is a top priority in cancer research and appears to have therapeutic potential. This chapter describes the development of mammalian cell-based fluorescent assays to screen for epigenetic modulators using an innovative combination of approaches. Detailed protocols for the use of the assays in drug screens, as well as for the initial characterization of hits, are provided. Furthermore, options for evaluating the mechanism of action of these compounds are presented and principles to govern the choice of hit compounds for the development of leads are discussed.

Animals↗

PubMed2005

Inhibition of transcription factor NF-kappaB signaling proteins IKKbeta and p65 through specific cysteine residues by epoxyquinone A monomer: correlation with its anti-cancer cell growth activity.

Transcription factor NF-kappaB is constitutively active in many human chronic inflammatory diseases and cancers. Epoxyquinone A monomer (EqM), a synthetic derivative of the natural product epoxyquinol A, has previously been shown to be a potent inhibitor of tumor necrosis factor-alpha (TNF-alpha)-induced activation of NF-kappaB, but the mechanism by which EqM inhibits NF-kappaB activation was not known. In this report, we show that EqM blocks activation of NF-kappaB by inhibiting two molecular targets: IkappaB kinase IKKbeta and NF-kappaB subunit p65. EqM inhibits TNF-alpha-induced IkappaBalpha phosphorylation and degradation by targeting IKKbeta, and an alanine substitution for Cys179 in the activation loop of IKKbeta makes it resistant to EqM-mediated inhibition. EqM also directly inhibits DNA binding by p65, but not p50; moreover, replacement of Cys38 in p65 with Ser abolishes EqM-mediated inhibition of DNA binding. Pretreatment of cells with reducing agent dithiothreitol dose-dependently reduces EqM-mediated inhibition of NF-kappaB, further suggesting that EqM directly modifies the thiol group of Cys residues in protein targets. Modifications of the exocyclic alkene of EqM substantially reduce EqM's ability to inhibit NF-kappaB activation. In the human SUDHL-4 lymphoma cell line, EqM inhibits both proliferation and NF-kappaB DNA binding, and activates caspase-3 activity. EqM also effectively inhibits the growth of human leukemia, kidney, and colon cancer cell lines in the NCI's tumor cell panel. Among six colon cancer cell lines, those with low amounts of constitutive NF-kappaB DNA-binding activity are generally more sensitive to growth inhibition by EqM. Taken together, these results suggest that EqM inhibits growth and induces cell death in tumor cells through a mechanism that involves inhibition of NF-kappaB activity at multiple steps in the signaling pathway.

Animals↗

PubMed2005

Synthesis and structure-activity studies of schweinfurthin B analogs: Evidence for the importance of a D-ring hydrogen bond donor in expression of differential cytotoxicity.

The synthesis and biological evaluation of several enantioenriched schweinfurthin B analogs were undertaken to develop structure-activity relationships and guide design of probes for their putative molecular target. The desired stilbenes contain a common left-half hexahydroxanthene ring system and an aromatic right-half with varied substituents. The synthesis involves penultimate Horner-Wadsworth-Emmons coupling of one of several right-half phosphonates with the aldehyde comprising the left-half of 3-deoxyschweinfurthin B. Preparation of the requisite phosphonates, and the respective stilbenes, as well as the cytotoxicity profiles of these new compounds in the National Cancer Institute's 60 cell-line anticancer screen is described. Several of these analogs displayed cytotoxicity patterns well-correlated with the natural product and differences in activity of approximately 10(3) across the various cell lines. Together, these assay results indicate the importance of at least one free phenol group on the aromatic D-ring of this system for differential cytotoxicity.

Cell Line, Tumor↗

PubMed2005

Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones.

High-throughput screening of a National Cancer Institute library of pure natural products identified the hydroxylated tropolone derivatives beta-thujaplicinol (2,7-dihydroxy-4-1(methylethyl)-2,4,6-cycloheptatrien-1-one) and manicol (1,2,3,4-tetrahydro-5-7-dihydroxy-9-methyl-2-(1-methylethenyl)-6H-benzocyclohepten-6-one) as potent and selective inhibitors of the ribonuclease H (RNase H) activity of human immunodeficiency virus-type 1 reverse transcriptase (HIV-1 RT). beta-Thujaplicinol inhibited HIV-1 RNase H in vitro with an IC50 of 0.2 microM, while the IC50 for Escherichia coli and human RNases H was 50 microM and 5.7 microM, respectively. In contrast, the related tropolone analog beta-thujaplicin (2-hydroxy-4-(methylethyl)-2,4,6-cycloheptatrien-1-one), which lacks the 7-OH group of the heptatriene ring, was inactive, while manicol, which possesses a 7-OH group, inhibited HIV-1 and E.coli RNases H with IC50 = 1.5 microM and 40 microM, respectively. Such a result highlights the importance of the 2,7-dihydroxy function of these tropolone analogs, possibly through a role in metal chelation at the RNase H active site. Inhibition of HIV-2 RT-associated RNase H indirectly indicates that these compounds do not occupy the nonnucleoside inhibitor-binding pocket in the vicinity of the DNA polymerase domain. Both beta-thujaplicinol and manicol failed to inhibit DNA-dependent DNA polymerase activity of HIV-1 RT at a concentration of 50 microM, suggesting that they are specific for the C-terminal RNase H domain, while surface plasmon resonance studies indicated that the inhibition was not due to intercalation of the analog into the nucleic acid substrate. Finally, we have demonstrated synergy between beta-thujaplicinol and calanolide A, a nonnucleoside inhibitor of HIV-1 RT, raising the possibility that both enzymatic activities of HIV-1 RT can be simultaneously targeted.

Anti-HIV Agents↗

PubMed2005

Synthesis of nonracemic 3-deoxyschweinfurthin B.

Synthesis of nonracemic 3-deoxyschweinfurthin B has been accomplished through a synthetic sequence including a key cascade cyclization of an epoxy olefin. The intermediate epoxide could be prepared as a single enantiomer through an AD-mix-alpha (or AD-mix-beta) oxidation, and the stereochemistry of the epoxide has been shown to control formation of the two additional stereogenic centers created through the cyclization. Synthetic 3-deoxyschweinfurthin B was found to have potent differential activity in the National Cancer Institute's 60 cell line anticancer assay. This represents the first synthesis of the tetracyclic schweinfurthin skeleton, validating our overall synthetic strategy and providing the first schweinfurthin analogue with activity slightly greater than those of the natural products.

Antineoplastic Agents↗

PubMed2004

A capillary electrophoretic assay for ribonuclease H activity.

A capillary electrophoretic assay was developed to measure the ribonuclease (RNase) H activity of human immunodeficiency virus (HIV) type 1 reverse transcriptase. Cleavage of a fluorescein-labeled RNA-DNA heteroduplex was monitored by capillary electrophoresis. This new assay was used as a secondary assay to confirm hits from a high-throughput screening program. Since autofluorescent compounds in samples migrated differently from both substrate and product in most cases, the assay was extremely robust for assaying enzymatic inhibition of such samples, in contrast to a simple well-based approach. The assay was broadly applicable to other RNases H, specifically those from human, Escherichia coli, and HIV-2, although product profiles varied for each enzyme.

Base Sequence↗

PubMed2004

Isolation and characterization of anti-HIV peptides from Dorstenia contrajerva and Treculia obovoidea.

Using a high throughput screen based on the interaction of the HIV-1 gp41 ectodomain with the virucidal protein cyanovirin-N (CV-N), we isolated two new peptides which inhibited the binding of CV-N to gp41 and which subsequently showed anti-HIV activity in a whole cell assay. A 5-kDa (contrajervin) and 10 kDa (treculavirin) peptide were isolated from Dorstenia contrajerva and Treculia obovoidea, respectively. Treculavirin was composed of two subunits, each containing 50 amino acid residues, which are covalently linked by at least one disulfide bond between the subunits. Both peptides were shown to bind to gp41 and gp120 and to inhibit the cytopathic effects of HIV-1(RF) infection in a human T-lymphoblastoid cell line (CEM-SS).

Acetylglucosamine↗

PubMed2003

A fluorescence-based high-throughput screening assay for inhibitors of human immunodeficiency virus-1 reverse transcriptase-associated ribonuclease H activity.

A fluorescence resonance energy transfer assay readily applicable to 96-well and 384-well microplate formats with robotic operation was developed to enable high-throughput screening for inhibitors of human immunodeficiency virus-1 (HIV-1) reverse transcriptase (RT)-associated RNase H activity, an underexplored target for antiretroviral development. The assay substrate is an 18-nucleotide 3'-fluorescein-labeled RNA annealed to a complementary 18-nucleotide 5'-Dabcyl-modified DNA. The intact duplex has an extremely low background fluorescent signal and provides up to 50-fold fluorescent signal enhancement following hydrolysis. The size and sequence of the duplex are such that HIV-1 RT-RNase H cuts the RNA strand close to the 3' end. The fluorescein-labeled ribonucleotide fragment readily dissociates from the complementary DNA at room temperature with immediate generation of a fluorescent signal. This assay is rapid, inexpensive, and robust, providing Z' factors of 0.8 and coefficients of variation of about 5%. The assay can be carried out both in real-time (continuous) and in "quench" modes; the latter requires only two addition steps with no washing and is thus suitable for robotic operation. Several chemical libraries totaling more than 106,000 compounds were screened with this assay in approximately 1 month.

Base Sequence↗

PubMed2003

Tannic acid is an inhibitor of CXCL12 (SDF-1alpha)/CXCR4 with antiangiogenic activity.

PURPOSE: Increasing evidence suggests that interaction between the chemoattractant CXCL12/stromal cell-derived factor-1alpha and its receptor CXCR4 plays a pivotal role in the metastasis of various tumors. Our previous studies showed that multi-component Chinese herbal medicines inhibited the effects of CXCL12/CXCR4. As a result of sequential chromatographic fractionation of one herbal medicine ingredient, Lianqiao (fruit of Forsythia suspensa), we observed that tannins were, at least in part, responsible for this activity. The aim of this study was to assess the anti-CXCL12/CXCR4 activity of a commercial tannic acid and evaluate its potential to inhibit tumor cell migration and angiogenesis in vitro. EXPERIMENTAL DESIGN: The inhibitory effect of tannic acid on CXCL12/CXCR4 was measured by chemotaxis assay, ligand binding assay, and fluorescence-activated cell sorter analysis. The antiangiogenic effect of tannic acid was assessed by in vitro endothelial cell tube formation. RESULTS: Tannic acid, at nontoxic concentrations, specifically inhibited CXCL12-induced human monocyte migration (IC(50), 7.5 micro g/ml) but did not inhibit CCL2-, CCL3-, CCL5-, formylmethionylleucylphenylalanine (fMLP)-, or C5a-induced migration. The compound markedly blocked CXCL12 binding to THP-1 cells (IC(50), 0.36 micro g/ml). Tannic acid also inhibited CXCL12-induced, but not epidermal growth factor-induced, migration of MDA 231 breast tumor cells. Additionally, 0.5 micro g/ml of tannic acid selectively inhibited CXCL12-mediated, but not basic fibroblast growth factor- or endothelial cell growth supplement-mediated, bovine aorta endothelial cell capillary tube formation. CONCLUSION: These studies indicate that tannic acid is a novel selective CXCL12/CXCR4 antagonist and consequently may provide a mechanistic basis for the reported antitumor and anti-inflammatory properties of tannic acid.

Angiogenesis Inhibitors↗

PubMed2003

Novel marine and microbial natural product inhibitors of vacuolar ATPase.

Vacuolar-ATPase (V-ATPase) has been proposed as a drug target in osteoporosis due to its involvement in bone resorption, and as a target in cancer due to potential involvement in tumor invasion and metastasis. The classical selective inhibitors of V-ATPase are microbial macrolides of the bafilomycin and concanamycin class. These inhibitors have proven to be too toxic for therapeutic use, however recent structure-activity studies on bafilomycins, and the isolation of novel macrolide structures from marine sources, have provided new avenues for development of potentially less toxic V-ATPase inhibitors. The novel salicylihalamide and lobatamide series of compounds were predicted to share a common mechanism of action based on the patterns of cytotoxicity produced in the NCI 60-cell cancer screen. They have subsequently been shown to selectively interact with mammalian V-ATPases, but not with fungal V-ATPases. With the recent achievement of total syntheses of salicylihalamide, lobatamide, and related compounds, the elaboration of congeners with specificity for particular enzyme isoforms may provide drug candidates which are less toxic. This review summarizes recent advances in V-ATPase inhibition and the prospects for further progress.

Animals↗

PubMed2002

New dimeric macrolide glycosides from the marine sponge Myriastra clavosa.

Clavosolides A-D (1-4), dimeric macrolides incorporating cyclopropyl, tetrahydropyranyl, and glycosidic ring systems, were isolated from the cytotoxic extract of a Philippines collection of the marine sponge Myriastra clavosa. The structures of the clavosolides, which occurred as only trace metabolites, were elucidated through extensive NMR spectroscopic analyses. Clavosolides A (1) and B (2) were recently reported metabolites from M. clavosa, while the unsymmetrical dimers clavosolides C (3) and D (4) had new structures.

Animals↗

PubMed2002

High throughput screening for cyanovirin-N mimetics binding to HIV-1 gp41.

The human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein gp41 is an important mediator of viral entry into host cells. Previous studies showed that the virucidal protein cyanovirin-N (CV-N) bound to both gp120 and gp41, and that this binding was associated with its antiviral activity. We constructed an HTS assay based on the interaction of europium-labeled CV-N with recombinant glycosylated gp41 ectodomain to support identification of small-molecule mimetics of CV-N that might be developed as antiviral drug leads. Primary screening of over 107,000 natural product extracts in the assay yielded 347 confirmed hits. Secondary assays eliminated extracts that bound directly to labeled CV-N or for which the simple sugars mannose and N-acetylglucosamine blocked the interaction with gp41 (lectin activity). Extracts were further prioritized based on anti-HIV activity and other biological, biochemical, and chemical criteria. The distribution of source organism taxonomy of active extracts was analyzed, as was the cross-correlation of activity between the CV-N-gp41 binding competition assay and the previously reported CV-N-gp120 binding competition assay. A limited set of extracts was selected for bioassay-guided fractionation.

Acetylglucosamine↗