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Biomedical subjects

Mitchell A Avery

Publications and source records attributed to Mitchell A Avery.

At least 19 recordsLinked to original sources
PubMed2006

Ligand-supported homology modeling of the human angiotensin II type 1 (AT(1)) receptor: insights into the molecular determinants of telmisartan binding.

Angiotensin II type 1 (AT(1)) receptor belongs to the super-family of G-protein-coupled receptors, and antagonists of the AT(1) receptor are effectively used in the treatment of hypertension. To understand the molecular interactions of these antagonists, such as losartan and telmisartan, with the AT(1) receptor, a homology model of the human AT(1) (hAT(1)) receptor with all connecting loops was constructed from the 2.6 A resolution crystal structure (PDB i.d., 1L9H) of bovine rhodopsin. The initial model generated by MODELLER was subjected to a stepwise ligand-supported model refinement. This protocol involved initial docking of non-peptide AT(1) antagonists in the putative binding site, followed by several rounds of iterative energy minimizations and molecular dynamics simulations. The final model was validated based on its correlation with several structure-activity relationships and site-directed mutagenesis data. The final model was also found to be in agreement with a previously reported AT(1) antagonist pharmacophore model. Docking studies were performed for a series of non-peptide AT(1) receptor antagonists in the active site of the final hAT(1) receptor model. The docking was able to identify key molecular interactions for all the AT(1) antagonists studied. Reasonable correlation was observed between the interaction energy values and the corresponding binding affinities of these ligands, providing further validation for the model. In addition, an extensive unrestrained molecular dynamics simulation showed that the docking-derived bound pose of telmisartan is energetically stable. Knowledge gained from the present studies can be used in structure-based drug design for developing novel ligands for the AT(1) receptor.

Amino Acid Sequence↗
PubMed2006

Design and synthesis of the first generation of dithiolane thiazolidinedione- and phenylacetic acid-based PPARgamma agonists.

A series of novel derivatives of potent antioxidant vitamin, alpha-lipoic acid, and related analogues were designed, synthesized, and evaluated for their PPARgamma agonist activities. Compounds 9a and the water soluble analogue11e were found to be potent PPARgamma agonists. Compound 9a appeared to have a significant role in improving insulin sensitivity and reducing triglyceride levels in fa/fa rats as well as inhibited proliferation of a variety of normal and neoplastic cultured human cell types. These novel compounds may prove efficacious not only in the treatment of Type 2 diabetes, but also atherosclerosis, prevention of vascular restenosis, and inflammatory skin diseases.

Adipocytes↗
PubMed2006

Bioassay for the identification of natural product-based activators of peroxisome proliferator-activated receptor-gamma (PPARgamma): the marine sponge metabolite psammaplin A activates PPARgamma and induces apoptosis in human breast tumor cells.

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor (NHR) family, are ligand-activated transcription factors. Ligands (agonists) of PPARgamma have been shown to inhibit growth, promote terminal differentiation, and induce apoptosis in human breast tumor cells. A cell-based reporter assay was developed to examine extracts of terrestrial and marine organisms for the ability to activate PPARgamma. Bioassay-guided fractionation and isolation of an active extract from Pseudoceratina rhax yielded the known histone deacetylase (HDAC) inhibitor psammaplin A (1). Compound 1 activates PPARgamma in a MCF-7 cell-based reporter assay and induces apoptosis in human breast tumor cells in vitro. Molecular modeling studies suggest that 1 may interact with binding sites within the PPARgamma ligand-binding pocket. Therefore, in addition to its known effects on HDAC-mediated processes, activation of PPARgamma-regulated gene expression may play a role in the ability of 1 to induce apoptosis.

Animals↗
PubMed2006

Homology modeling of G-protein-coupled receptors and implications in drug design.

G-protein-coupled receptors (GPCRs) are considered therapeutically important due to their involvement in a variety of processes governing several cellular functions, and their tractability as drug targets. A large percentage of drugs on the market, and in development stages, target the super family of the GPCRs. The enormous interest in GPCR drug design is, however, limited by the scarcity of structural information. The only GPCR for which a three dimensional (3D) structure is reported is bovine rhodopsin and it belongs to class A of the GPCR family. As a result, there has been considerable interest in alternative techniques, for example, homology modeling of GPCRs, in order to derive useful three dimensional models of other proteins for use in structure-based drug design. However, homology modeling of GPCRs is not straightforward, and encounters several problems, owing to the availability of a single structural template, as well as the low degree of sequence homology between the template and target sequences. There are several key issues which need to be considered during every stage of GPCR homology modeling, in order to derive reasonable 3D models. Homology modeling of GPCRs has been utilized increasingly in the past few years and has been successful, not only in furthering the understanding of ligand-protein interactions, but also in the identification of new and potent ligands. Thus, with the lessons learned from past experiences and new developments, homology modeling in case of GPCRs can be harnessed for developing more reliable three dimensional models. This, in turn, will provide better tools to use in structure-based drug design leading to the identification of novel and potent GPCR ligands for several therapeutic indications.

Amino Acid Sequence↗
PubMed2006

A new library of C-16 modified artemisinin analogs and evaluation of their anti-parasitic activities.

A library of C-16 modified artemisinin analogs was prepared and their antimalarial as well as antileishmanial activities were evaluated. Synthesis of these compounds involved the conversion of artemisinin to its phenol derivatives 7 and 12, and subsequent parallel derivatization by introducing new chemical groups through ester, carbamate, sulfate, phosphate and isourea linkages. Comparison of in vitro antimalarial activities showed that C9-beta artemisinin analogs (8a-f) are more potent than the corresponding C9-alpha diastereomers (9a-f); however, their antileishmanial activities were in the same range. Many of the 10-deoxoartemisinin analogs studied here showed promising antiparasitic activities. For example, compounds 13a-e are approximately three times more active against drug resistant W2 strain of P. falciparum, compared to artemisinin (IC(50), approximately 0.2 - 0.6 nM; cf. artemisinin = 1.6 nM). Further, a number of compounds in this series were notably leishmanicidal, with activities comparable to or better than pentamidine (e.g., 13g and 13j). Detailed in vivo studies involving these active compounds are underway to identify lead candidates for further development.

Animals↗
PubMed2005

Microbial transformation of artemisinin to 5-hydroxyartemisinin by Eurotium amstelodami and Aspergillus niger.

Transformation of the anti-malarial drug artemisinin by the fungi Eurotium amstelodami and Aspergillus niger were investigated. Cultures were grown in sucrose/malt broth with artemisinin for 14 days and extracted with ethyl acetate. Extracts were characterized by liquid chromatography. Two metabolites from each fungal extract were isolated and identified using mass spectrometry and nuclear magnetic resonance. 5Beta-hydroxyartemisinin and 7beta-hydroxyartemisinin were isolated in 63 and 32% yields, respectively, from the extract of E. amstelodami, and 80 and 19%, respectively, from the extract of A. niger.

Anti-Infective Agents↗
PubMed2005

Antimalarial artemisinin drugs induce cytochrome P450 and MDR1 expression by activation of xenosensors pregnane X receptor and constitutive androstane receptor.

Artemisinin drugs are of utmost importance in the treatment of malaria, because they represent the sole class of therapeutically used antimalarial drugs to which malaria parasites have not yet developed resistance. The major disadvantage of these medicines is the comparatively high recrudescence rate, which has been attributed to the remarkable decrease of artemisinin plasma concentrations during multiple dosing. Autoinduction of CYP2B6-mediated metabolism has been implicated as the underlying mechanism. So far, the molecular mechanism of induction by artemisinin has not been resolved. Because the xenosensors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) have been shown to mediate induction of drug-metabolizing enzymes and drug transporters, we investigated the hypothesis that artemisinin induces cytochrome P450 expression by activating PXR and/or CAR. By combining in vitro transfection methods and quantitative analyses of gene expression in cell lines and primary human hepatocytes, we here show that artemisinin drugs activate human PXR as well as human and mouse CAR and induce the expression of CYP2B6, CYP3A4, and MDR1 in primary human hepatocytes and in the human intestinal cell line LS174T. Furthermore, we demonstrate that artemisinin acts as a ligand of both nuclear receptors, because it modulates the interaction of the receptors with coregulators. In conclusion, activation of PXR and CAR and especially the resulting induction of CYP3A4 and MDR1 demonstrate that artemisinin has a higher risk of potential drug interactions than anticipated previously.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

The epothilones and related analogues-a review of their syntheses and anti-cancer activities.

The macrocylic polyketide class of compounds known as the epothilones has generated substantial interest over the last few years in the areas of chemistry, biology, and medicine due to their interesting structure and, more importantly, their activity against numerous cancer cell lines, including drug-resistant, especially Taxol-resistant, cancer cell lines. To date, numerous total syntheses have been published, hundreds of epothilone analogues have been synthesized, and detailed structure activity relationship studies have been conducted. The purpose of this review is to give a brief summary of the latest advances made concerning the epothilones. Recent total or partial syntheses will be presented along with the syntheses of new epothilone analogues and their corresponding biological data. In addition, we will look at the current state of research into an economically viable method for the biosynthesis of the epothilones and related analogues.

Animals↗
PubMed2004

Total syntheses of epothilones B and d.

A convergent, total synthesis of epothilones B (2) and D (4) is described. The key steps are Normant coupling to establish the desired (Z)-stereochemistry at C12-C13, Wadsworth-Emmons olefination of methyl ketone 28 with the phosphonate ester 8, diastereoselective aldol condensation of aldehyde 5 with the enolate of keto acid derivatives to form the C6-C7 bond, selective deprotection of acid 52, and macrolactonization.

Epothilones↗
PubMed2004

Inhibition of Leishmania major pteridine reductase by 2,4,6-triaminoquinazoline: structure of the NADPH ternary complex.

The structure of Leishmania major pteridine reductase (PTR1) in complex with NADPH and the inhibitor 2,4,6-triaminoquinazoline (TAQ) has been solved in a new crystal form by molecular replacement and refined to 2.6 A resolution. The inhibitor mimics a fragment, the pterin head group, of the archetypal antifolate drug methotrexate (MTX) and exploits similar chemical features to bind in the PTR1 active site. Despite being a much smaller molecule, TAQ displays a similar inhibition constant to that of MTX. PTR1 is a target for the development of improved therapies for infections caused by trypanosomatid parasites and this analysis provides information to assist the structure-based development of novel enzyme inhibitors.

Animals↗
PubMed2004

Alpha-Lipoic acid-based PPARgamma agonists for treating inflammatory skin diseases.

Novel thiazolidinedione derivatives of the potent antioxidant, alpha-lipoic (thioctic, 1,2-dithiolane) acid, were prepared. The prototype N-(2-[4-[2,4-dioxo(1,3-thiazolidin-5-yl)methyl]phenoxy]ethyl)-5-(1,2-dithiolan-3-yl)- N-methylpentanamide (designated BP-1003), and dithioester derivatives thereof were shown to be potent activators of peroxisome proliferator-activated receptor gamma (PPARgamma) (EC(50) range 15-101 nM) and modest activators of PPARalpha (EC(50) 5 microM). Both the relatively hydrophobic dithiolane prototype, BP-1003, and its water-soluble dithioglycinate derivative, BP-1017, were shown to inhibit the proliferation of human keratinocytes and suppress the production of interleukin-2 by human peripheral lymphocytes to a greater extent than the antidiabetic thiazolidinedione, rosiglitazone. Both oral and topical administration of BP-1017 showed significant antiinflammatory effects in the oxazolone-sensitized mouse model of allergic contact dermatitis (ACD). These findings suggest that water-soluble lipoic acid-based thiazolidinediones may be efficacious as oral and topical agents for treating inflammatory skin conditions such as contact dermatitis, atopic dermatitis, and psoriasis.

3T3-L1 Cells↗
PubMed2004

Identification of telmisartan as a unique angiotensin II receptor antagonist with selective PPARgamma-modulating activity.

The metabolic syndrome is a common precursor of cardiovascular disease and type 2 diabetes that is characterized by the clustering of insulin resistance, dyslipidemia, and increased blood pressure. In humans, mutations in the peroxisome proliferator-activated receptor-gamma (PPARgamma) have been reported to cause the full-blown metabolic syndrome, and drugs that activate PPARgamma have proven to be effective agents for the prevention and treatment of insulin resistance and type 2 diabetes. Here we report that telmisartan, a structurally unique angiotensin II receptor antagonist used for the treatment of hypertension, can function as a partial agonist of PPARgamma; influence the expression of PPARgamma target genes involved in carbohydrate and lipid metabolism; and reduce glucose, insulin, and triglyceride levels in rats fed a high-fat, high-carbohydrate diet. None of the other commercially available angiotensin II receptor antagonists appeared to activate PPARgamma when tested at concentrations typically achieved in plasma with conventional oral dosing. In contrast to ordinary antihypertensive and antidiabetic agents, molecules that can simultaneously block the angiotensin II receptor and activate PPARgamma have the potential to treat both hemodynamic and biochemical features of the metabolic syndrome and could provide unique opportunities for the prevention and treatment of diabetes and cardiovascular disease in high-risk populations.

Adipocytes↗
PubMed2004

Diamine derivatives with antiparasitic activities.

There are a lack of effective chemotherapies for many parasitic diseases. Polyamine pathways have been reported as potential targets for the development of new chemotherapies against parasitic diseases. In the present study, different libraries of substituted diamines totalling 78 compounds have been synthesized on solid support and their activities against malaria and leishmania parasites have been determined. Most active compounds demonstrated submicromolar activities against both organisms and their structure-activity relationships are discussed.

Animals↗
PubMed2004

Hydroxylation of 10-deoxoartemisinin by Cunninghamella elegans.

The microbial metabolism of 10-deoxoartemisinin (1), a derivative of the antimalarial drug artemisinin, was investigated. Various strains of fungi were investigated for their ability to transform 1. Of these microorganisms, only Cunninghamella elegans was capable of transforming 1 to 5beta-hydroxy-10-deoxoartemisinin (2), 4alpha-hydroxy-1,10-deoxoartemisinin (3), and 7beta-hydroxy-10-deoxoartemisinin (4). The metabolites 2 and 4 retained an intact peroxide group and are therefore useful scaffolds for synthetic modification in the search for new antimalarial agents.

Antimalarials↗
PubMed2004

Bioactive rearranged and halogenated semisynthetic derivatives of the marine natural product sarcophine.

Cembranoids are natural diterpenes with 14-membered macrocyclic rings. The simplest natural cembranoid, (+)-cembrene, was isolated from pine oleoresin. Sarcophytols A and B are known cembranoids that inhibit tumor promotion. Sarcophine is a related cembranoid isolated from the Red Sea soft coral Sarcophyton glaucum. Sarcophine and its bioconversion products and semisynthetic derivatives are reported to possess cancer chemopreventive activity. Oxymercuration-demercuration of sarcophine using Hg(OAc)2 and NaBH4 afforded four new rearranged and hydroxylated products. Bromination of sarcophine with N-bromosuccinimide (NBS) furnished two new brominated and rearranged products. Reaction with iodine gave the known iso-sarcophinone and (+)-sarcophytoxin B. Structure elucidation was based on a combination of transition state modeling, molecular dynamics, mechanistic considerations, and 2D NMR data. The antiproliferative activity of the new products is also reported.

4-Butyrolactone↗
PubMed2004

Rosiglitazone inhibits proliferation, motility, and matrix metalloproteinase production in keratinocytes.

This study was undertaken to evaluate the effects of thiazolidinediones (TZD) on keratinocyte proliferation, motility, and matrix metalloproteinase (MMP) production. Rosiglitazone (a potent TZD) inhibited both proliferation and motility as well as elaboration of MMP-1 and MMP-9. Inhibition was obtained with keratinocytes in monolayer culture and human skin in organ culture. There were significant concentration-response differences in sensitivity of the three keratinocyte responses to treatment with rosiglitazone. In contrast to keratinocytes, dermal fibroblasts were resistant to the effects of rosiglitazone. Treatment of keratinocytes with rosiglitazone did not suppress epidermal growth factor receptor autophosphorylation, but inhibited signaling through the extracellular regulated kinase mitogen-activated protein kinase pathway without a concomitant effect on pathways that lead to c-jun activation. Pioglitazone, another TZD, also suppressed keratinocyte proliferation, although it was less effective than rosiglitazone. An experimental TZD (BP-1107) inhibited keratinocyte proliferation at a much lower concentration than either rosiglitazone or pioglitazone. Because enhanced keratinocyte motility and increased MMP production as well as increased keratinocyte proliferation are thought to contribute to the phenotype of psoriatic lesional skin, we propose that interference with these keratinocyte responses contributes to the previously reported antipsoriatic activity of TZD.

Adult↗
PubMed2004

An alpha-proteobacterial type malate dehydrogenase may complement LDH function in Plasmodium falciparum. Cloning and biochemical characterization of the enzyme.

Malate dehydrogenase (MDH) may be important in carbohydrate and energy metabolism in malarial parasites. The cDNA corresponding to the MDH gene, identified on chromosome 6 of the Plasmodium falciparum genome, was amplified by RT-PCR, cloned and overexpressed in Escherichia coli. The recombinant Pf MDH was purified to homogeneity and biochemically characterized as an NAD(+)(H)-specific MDH, which catalysed reversible interconversion of malate to oxaloacetate. Pf MDH could not use NADP/NADPH as a cofactor, but used acetylpyridine adenine dinucleoide, an analogue of NAD. The enzyme exhibited strict substrate and cofactor specificity. The highest levels of Pf MDH transcripts were detected in trophozoites while the Pf MDH protein level remained high in trophozoites as well as schizonts. A highly refined model of Pf MDH revealed distinct structural characteristics of substrate and cofactor binding sites and important amino acid residues lining these pockets. The active site amino acid residues involved in substrate binding were conserved in Pf MDH but the N-terminal glycine motif, which is involved in nucleotide binding, was similar to the GXGXXG signature sequence found in Pf LDH and also in alpha-proteobacterial MDHs. Oxamic acid did not inhibit Pf MDH, while gossypol, which interacts at the nucleotide binding site of oxidoreductases and shows antimalarial activity, inhibited Pf MDH also. Treatment of a synchronized culture of P. falciparum trophozoites with gossypol caused induction in expression of Pf MDH, while expression of Pf LDH was reduced and expression of malate:quinone oxidoreductase remained unchanged. Pf MDH may complement Pf LDH function of NAD/NADH coupling in malaria parasites. Thus, dual inhibitors of Pf MDH and Pf LDH may be required to target this pathway and to develop potential new antimalarial drugs.

Amino Acid Sequence↗