Discovery of the catechol structural moiety as a Stat3 SH2 domain inhibitor by virtual screening

The Stat3 SH2 domain is essential for its activation, and development of a potent SH2 inhibitor will be therapeutically valuable in treating cancers with constant Stat3 activation. We report here the identification of the catechol (1,2-dihydroxybenzene) structural moiety by virtual screening as a Stat3 SH2 inhibitor. The catechol compound docked to the Stat3 SH2 domain in computer modeling forms hydrogen bonds with the conserved pTyr-interacting amino acids. In the biochemical assay, a catechol-containing compound, but not the hydroxyl group-acetalized analogue, was able to inhibit Stat3 DNA-binding activity. Furthermore, the catechol compound was demonstrated to compete with pTyr peptides in binding to the Stat3 SH2 domain, suggesting that the catechol moiety is a pTyr bioisostere and may potentially be used for designing cell-permeable SH2 inhibitors. In our preliminary effort, we also demonstrated that the potency of catechol compound as Stat3 SH2 inhibitors could be improved by modifying the non-catechol part of the compound structure.     

l-Type amino acid transporter 1 activity of 1,2,3-triazolyl analogs of l-histidine and l-tryptophan

A series of 1,2,3-triazole analogs of the amino acids l-histidine and l-tryptophan were modeled, synthesized and tested for l-type amino acid transporter 1 (LAT1; SLC7A5) activity to guide the design of amino acid-drug conjugates (prodrugs). These triazoles were conveniently prepared by the highly convergent Huisgen 1,3-dipolar cycloaddition (Click Chemistry). Despite comparable predicted binding modes, triazoles generally demonstrated reduced cell uptake and LAT1 binding potency relative to their natural amino acid counterparts. The structure-activity relationship (SAR) data for these triazoles has important ramifications for treating cancer and brain disorders using amino acid prodrugs or LAT1 inhibitors.     

Docking,molecular dynamics,binding energy-MM-PBSA studies of naphthofuran derivatives to identify potential dual inhibitors against BACE-1 and GSK-3β

BACE-1 and GSK-3β both are potential therapeutic drug targets for Alzheimer’s disease. Recently, both these targets received attention for designing dual inhibitors. Till now only two scaffolds (triazinone and curcumin) derivatives have been reported as BACE-1 and GSK-3β dual inhibitors. In our previous work, we have reported first in class dual inhibitor for BACE-1 and GSK-3β. In this study, we have explored other naphthofuran derivatives for their potential to inhibit BACE-1 and GSK-3β through docking, molecular dynamics, binding energy (MM-PBSA). These computational methods were performed to estimate the binding affinity of naphthofuran derivatives towards the BACE-1 and GSK-3β. In the docking results, two derivatives (NS7 and NS9) showed better binding affinity as compared to previously reported inhibitors. Hydrogen bond occupancy of NS7 and NS9 generated from MD trajectories showed good interaction with the flap residues Gln73, Thr72 of BACE-1 and Arg141, Thr138 residues of GSK-3β. MM-PBSA and energy decomposition per residue revealed different components of binding energy and relative importance of amino acid involved in binding. The results showed that the binding of inhibitors was majorly governed by the hydrophobic interactions and suggesting that hydrophobic interactions might be the key to design dual inhibitors for BACE1-1 and GSK-3β. Distance between important pair of amino acid residues indicated that BACE-1 and GSK-3β adopt closed conformation and become inactive after ligand binding. The results suggested that naphthofuran derivatives might act as dual inhibitor against BACE-1 and GSK-3β.     

Use of natural molecules as anti-angiogenic inhibitors for vascular endothelial growth factor receptor

Angiogenesis refers to the formation of new blood vessels, controlled by certain chemicals, which on stimulation repairs damaged cells or form new ones. Other chemicals, called angiogenesis inhibitors, signal the process to stop, having only mild side effects and are non toxic to most healthy cells. In our study, attempt was made to find potent anti-angiogenic inhibitor (pazopanib was considered as a reference drug) for vascular endothelial growth factor receptor (VEGFR-1/FLT-1), which served as a molecular target, using natural agents targeting biological processes important in cancer. Hundreds of natural molecules were initially screened based on lipinski''s rule of five and the satisfying ones were taken for receptor-ligand interaction study using docking tools like HEX and quantum. Around fifteen molecules were taken as lead molecule and their binding pocket on VEGF was analyzed using SwissPDBviewer and Q-site finder. The investigational drug pazopanib was found to be interacting with leucine 32 and glutamine 30 in terms of hydrogen bond with the distance of 1.86 and 2.49 A0 respectively. Ames test for the molecules was predicted for probability of mutagenicity on molecular systems such as blood, cardiovascular system, gastrointestinal system; kidney, liver and lung were considered for further screening of the molecules. The natural molecules curcumin, epigallocatechin gallate (EGCG), barrigtozenol and finasteride were showing reliable interaction with VEGFR and their pharmacokinetics parameters were comparatively good than the pazopanib. The dietary product curcumin and EGCG can be cancer chemopreventive agents and the natural molecules barringtozenol and finasteride can be effective inhibitors for VEGFR.     

Docking and SAR studies of salacinol derivatives as α-glucosidase inhibitors

Salacinol is a potent α-glucosidase inhibitor isolated from Salacia reticulata, and a good lead compound for an antidiabetic drug. It is essential to clarify the binding state of salacinol to α-glucosidase for efficient optimization study using structure-based drug design. Redocking simulations of two inhibitors, acarbose and casuarine whose complex structures are known, were performed to assure the appropriate docking pose prediction. The simulation reproduced both experimental binding states with accuracy. Then, using the same simulation protocol, the binding mode of salacinol and its derivatives has been predicted. Salacinol bound to the protein with a similar binding mode as casuarine, and the predicted structures could explain most of the structure–activity relationships of salacinol derivatives.     

Molecular modifications on carboxylic acid derivatives as potent histone deacetylase inhibitors: Activity and docking studies

In the light of known HDAC inhibitors, 33 carboxylic acid derivatives were tested to understand the structural requirements for HDAC inhibition activity. Several modifications were applied to develop the structure–activity relationships of carboxylic acid HDAC inhibitors. HDAC inhibition activities were investigated in vitro by using HeLa nuclear extract in a fluorimetric assay. Molecular docking was also carried out for the human HDAC8 enzyme in order to predict inhibition activity and the 3D poses of inhibitor–enzyme complexes. Of these compounds, caffeic acid derivatives such as chlorogenic acid and curcumin were found to be highly potent compared to sodium butyrate, which is a well-known HDAC inhibitor.     

Interactions of thrombin with benzamidine-based inhibitors.

Trypsin and trypsin-like enzymes cleave C-terminal bonds of the basic amino acids Arg and Lys. Inhibitors of these enzymes have been found not only among Arg and Lys derivatives but also with structurally related benzamidines. Especially cyclic amides of 4-amidinophenylalanine were found to be inhibitors of thrombin. The most potent selective thrombin inhibitor of these type is N alpha-(beta-naphthylsulfonylglycyl)-4-amidinophenylalanine piperidine. From the X-ray crystal structures of thrombin and trypsin-inhibitor complexes the thrombin complexes formed with inhibitors derived from amidinophenylalanine have been modeled. These models allow valuable predictions to design inhibitors of improved selection and binding properties. Most recently, also the X-ray crystal structures of complexes of inhibitors with bovine thrombin have been solved.     

Synthesis and biological evaluation of curcumin derivatives modified with α-amino boronic acid as proteasome inhibitors

Curcumin is a well-known pharmacophore and some of its derivatives are shown to target 20S proteasome recently. In this report, we designed and synthesized two series of curcumin derivatives modified with different α-amino boronic acids as potent proteasome inhibitors. The synthesized compounds were evaluated for their cytotoxic activities against HCT116 cells, and the results showed that all of them exhibited excellent cell growth inhibitory activity comparing with curcumin, with the IC₅₀ values varying from 0.17?μM to 1.63?μM. Compound II-2F with free boronic acid was assayed for its proteasome inhibitory activity and the results indicated that II-2F exhibited more potent inhibitory activity against ChT-L with high subunit selectivity than any other reported curcumin derivatives.     

Inhibition of glycogen synthase kinase by curcumin: Investigation by simulated molecular docking and subsequent in vitro/in vivo evaluation

Curcumin was investigated as an inhibitor of glycogen synthase kinase-3beta (GSK-3beta) in an attempt to explain some of its interesting multiple pharmacological effects, such as its anti-diabetic, anti-inflammatory, anti-cancer, anti-malarial and anti-alzheimer's properties. The investigation included simulated docking experiments to fit curcumin within the binding pocket of GSK-3beta followed by experimental in vitro and in vivo validations. Curcumin was found to optimally fit within the binding pocket of GSK-3beta via several attractive interactions with key amino acids. Experimentally, curcumin was found to potently inhibit GSK-3beta (IC50 = 66.3 nM). Furthermore, our in vivo experiments illustrated that curcumin significantly increases liver glycogen in fasting Balb/c mice. Our findings strongly suggest that the diverse pharmacological activities of curcumin are at least partially mediated by inhibition of GSK-3beta.     

Novel tricyclic aminoacetyl and sulfonamide inhibitors of Ras farnesyl protein transferase

Novel tricyclic FPT inhibitors with submicromolar FPT activity are described. Greatly enhanced FPT activity is realized with phthaloyl derivatized amino compound 2k, which showed FPT inhibitory activity of IC₅₀ = 0.66 μM. Sulfonamides 5g and 50 were also found to be potent FPT inhibitor. SAR resulting from a variety of tricyclic amino acids and sulfonamide derivatives is discussed.     

SER-1, a Caenorhabditis elegans 5-HT2-like receptor, and a multi-PDZ domain containing protein (MPZ-1) interact in vulval muscle to facilitate serotonin-stimulated egg-laying

Serotonin (5-HT) stimulation of egg-laying in Caenorhabditis elegans is abolished in ser-1 (ok345) animals and is rescued by ser-1 expression in vulval muscle. A PDZ binding motif (ETFL) at the SER-1 C-terminus is not essential for rescue, but facilitates SER-1 signaling. SER-1 binds specifically to PDZ domain 10 of the multi-PDZ domain protein, MPZ-1, based on GST pulldown and co-immunoprecipitation. mpz-1 is expressed in about 60 neurons and body wall and vulval muscles. In neurons, GFP-tagged MPZ-1 is punctate and colocalizes with the synaptic marker, synaptobrevin. The expression patterns of ser-1 and mpz-1 overlap in 3 pairs of neurons and vulval muscle. In addition, MPZ-1 also interacts with other GPCRs with acidic amino acids in the -3 position of their PDZ binding motifs. mpz-1 RNAi reduces 5-HT stimulated egg-laying in wild type animals and in ser-1 mutants rescued by muscle expression of SER-1. In contrast, mpz-1 RNAi has no effect on 5-HT stimulated egg-laying in ser-1 mutants rescued by expression of a truncated SER-1 that lacks the C-terminal PDZ binding motif. The overexpression of MPZ-1 PDZ domain 10 also inhibits 5-HT stimulated egg-laying. These studies suggest that the SER-1/MPZ-1 interaction facilitates SER-1 mediated signaling.     

GABA-Mimetic Activity and Effects on Diazepam Binding of Aminosulphonic Acids Structurally Related to Piperidine-4-Sulphonic Acid

The relationship between structure, in vivo activity, and in vitro activity of some analogues of the gamma-aminobutyric acid (GABA) agonist piperidine-4-sulphonic acid (P4S) was studied. The syntheses of 1,2,3,6-tetrahydropyridine-4-sulphonic acid (DH-P4S) and (RS)-pyrrolidin-3-yl-methanesulphonamide (PMSA-amide) are described. Like P4S, its unsaturated analogue DH-P4S and the five-ring isomer (RS)-pyrrolidin-3-yl-methanesulphonic acid (PMSA) were bicuculline methochloride (BMC)-sensitive inhibitors of the firing of neurones in the cat spinal cord. Whereas isonipecotic acid was less potent than its unsaturated analogue isoguvacine as a GABA-mimetic and as an inhibitor of GABA binding, the opposite relative potencies of P4S and DH-P4S were observed, P4S being proportionally more potent than DH-P4S. In contrast with P4S and DH-P4S, PMSA, which is an analogue of the potent GABA uptake inhibitor and BMC-sensitive GABA-mimetic homo-beta-proline, was a relatively weak inhibitor of GABA uptake in vitro. PMSA-amide was more than two orders of magnitude weaker than PMSA as an inhibitor of GABA binding and did not significantly affect GABA uptake in vitro. The effects of 3-aminopropanesulphonic acid (3-APS), PMSA, P4S, and DH-P4S on the binding of [3H]diazepam in vitro at 30 degrees C, in the presence or absence of chloride ions, were studied and compared with those of the structurally related amino acids GABA, homo-beta-proline, isonipecotic acid, and isoguvacine. Under these conditions the aminosulphonic acids were weaker than the respective amino acids in enhancing [3H]diazepam binding, the difference being more pronounced in the absence of chloride.     

New Caspase-1 inhibitor by scaffold hopping into bio-inspired 3D-fragment space

Virtual fragmentation of a library of 12,000 compounds inspired by natural products led to a dataset of 153,000 fragments that was used as a source to identify effective P2-P3 scaffold replacement solutions for peptidic Caspase-1 inhibitors. Our strategy led to the identification of an original 2-azabicyclo-octane scaffold (2-ABO) that was further elaborated into the potent Caspase-1 inhibitor CD10847 (IC₅₀?=?17?nM). The crystal structure of Caspase-1 in complex with CD10847 was obtained, and its binding mode was shown to be similar to the one predicted by docking and in good agreement with other known inhibitors.     

Inhibition of glycogen synthase kinase by curcumin: Investigation by simulated molecular docking and subsequent in vitro/in vivo evaluation

Curcumin was investigated as an inhibitor of glycogen synthase kinase-3β (GSK-3β) in an attempt to explain some of its interesting multiple pharmacological effects, such as its anti-diabetic, anti-inflammatory, anti-cancer, anti-malarial and anti-alzheimer's properties. The investigation included simulated docking experiments to fit curcumin within the binding pocket of GSK-3β followed by experimental in vitro and in vivo validations. Curcumin was found to optimally fit within the binding pocket of GSK-3β via several attractive interactions with key amino acids. Experimentally, curcumin was found to potently inhibit GSK-3β (IC50 = 66.3 nM). Furthermore, our in vivo experiments illustrated that curcumin significantly increases liver glycogen in fasting Balb/c mice. Our findings strongly suggest that the diverse pharmacological activities of curcumin are at least partially mediated by inhibition of GSK-3β.     

Indenoindolone derivatives as topoisomerase II–inhibiting anticancer agents

Based on known heterocyclic topoisomerase II inhibitors and anticancer agents, various indenoindolone derivatives were predicted as potential topoisomerase II–inhibiting anticancer agents. They are hydrazones, (thio)semicarbazones, and oximes of indenoindolones, and indenoindolols. These derivatives with suitable substitutions exhibited potent specific inhibition of human DNA TopoIIα while not showing inhibition of topoisomerase I and DNA intercalation, despite the fact that parent indenoindolones are known poor/moderate inhibitors of topoisomerase II. The potent topoisomerase II inhibitor indenoindolone derivatives exhibited good anticancer activities compared to etoposide and 5-fluorouracil, and relatively low toxicity to normal cells. These derivatizations of indenoindolones were found to result in enhancement of anticancer activities.     

Curcumin binds in silico to anti-cancer drug target enzyme MMP-3 (human stromelysin-1) with affinity comparable to two known inhibitors of the enzyme

In silico interaction of curcumin with the enzyme MMP-3 (human stromelysin-1) was studied by molecular docking using AutoDock 4.2 as the docking software application. AutoDock 4.2 software serves as a valid and acceptable docking application to study the interactions of small compounds with proteins. Interactions of curcumin with MMP-3 were compared to those of two known inhibitors of the enzyme, PBSA and MPPT. The calculated free energy of binding (ΔG binding) shows that curcumin binds with affinity comparable to or better than the two known inhibitors. Binding interactions of curcumin with active site residues of the enzyme are also predicted. Curcumin appears to bind in an extendended conformation making extensive VDW contacts in the active site of the enzyme. Hydrogen bonding and pi-pi interactions with key active site residues is also observed. Thus, curcumin can be considered as a good lead compound in the development of new inhibitors of MMP-3 which is a potential target of anticancer drugs. The results of these studies can serve as a starting point for further computational and experimental studies.     

Inhibition of rat liver iodothyronine deiodinase. Interaction of aurones with the iodothyronine ligand-binding site

We report that aurone derivatives of plant extracts produce potent, dose-dependent, and ultimately complete inhibition of three different metabolic monodeiodination pathways catalyzed by rat liver microsomal type I iodothyronine deiodinase. These data show that (3'),4',4,6-(tetra)trihydroxyaurones are the most potent naturally occurring plant-derived inhibitors of this deiodinase enzyme (IC50 V 0.5 microM). Lineweaver-Burk analysis using both L-thyroxine (T4) and 3',5',3-triiodothyronine as substrates suggests a cofactor competitive mechanism of inhibition for 4',4,6-trihydroxyaurone which also can displace 125I-L-T4 from binding to thyroxine-binding prealbumin with a potency comparable to its inhibition of T4-5'-deiodinase. Among type I deiodinase inhibitors, cofactor competition has been observed only for propylthiourea. Computer graphic modeling studies were also carried out to explore aurone conformations and to compare them with those of the thyroid hormones. This analysis shows that the aurones can adopt either a planar or an antiskewed conformation, such as observed for 3',5',3-triiodothyronine, the most potent natural deiodinase substrate inhibitor. The thyroxine-binding prealbumin complex was used to model the deiodinase ligand binding site because of the similarity observed between inhibitor binding affinity and enzyme inhibition characteristics. These studies show that the aurones which adopt an antiskewed conformation can interact favorably in the prealbumin binding site. This model of the deiodinase active site can be used to design other deiodinase inhibitors.