Identification of Bichalcones as Sirtuin Inhibitors by Virtual Screening and In Vitro Testing.

Sirtuins are nicotinamide adenine dinucleotide (NAD⁺)-dependent class III histone deacetylases, which have been linked to the pathogenesis of numerous diseases, including HIV, metabolic disorders, neurodegeneration and cancer. Docking of the virtual pan-African natural products library (p-ANAPL), followed by in vitro testing, resulted in the identification of two inhibitors of sirtuin 1, 2 and 3 (sirt1-3). Two bichalcones, known as rhuschalcone IV (8) and an analogue of rhuschalcone I (9), previously isolated from the medicinal plant Rhus pyroides, were shown to be active in the in vitro assay. The rhuschalcone I analogue (9) showed the best activity against sirt1, with an IC50 value of 40.8 µM. Based on the docking experiments, suggestions for improving the biological activities of the newly identified hit compounds have been provided.

Structure-Based Development of an Affinity Probe for Sirtuin†2.

Sirtuins are NAD(+)-dependent protein deacylases that cleave off acetyl groups, as well as other acyl groups, from the ɛ-amino group of lysines in histones and other substrate proteins. Dysregulation of human Sirt2 activity has been associated with the pathogenesis of cancer, inflammation, and neurodegeneration, thus making Sirt2 a promising target for pharmaceutical intervention. Here, based on a crystal structure of Sirt2 in complex with an optimized sirtuin rearranging ligand (SirReal) that shows improved potency, water solubility, and cellular efficacy, we present the development of the first Sirt2-selective affinity probe. A slow dissociation of the probe/enzyme complex offers new applications for SirReals, such as biophysical characterization, fragment-based screening, and affinity pull-down assays. This possibility makes the SirReal probe an important tool for studying sirtuin biology.

Molecular modeling of potential anticancer agents from African medicinal plants.

Naturally occurring anticancer compounds represent about half of the chemotherapeutic drugs which have been put in the market against cancer until date. Computer-based or in silico virtual screening methods are often used in lead/hit discovery protocols. In this study, the "drug-likeness" of ~400 compounds from African medicinal plants that have shown in vitro and/or in vivo anticancer, cytotoxic, and antiproliferative activities has been explored. To verify potential binding to anticancer drug targets, the interactions between the compounds and 14 selected targets have been analyzed by in silico modeling. Docking and binding affinity calculations were carried out, in comparison with known anticancer agents comprising ~1,500 published naturally occurring plant-based compounds from around the world. The results reveal that African medicinal plants could represent a good starting point for the discovery of anticancer drugs. The small data set generated (named AfroCancer) has been made available for research groups working on virtual screening.

2-[6-(4-Chloro-phen-yl)imidazo[2,1-b][1,3]thia-zol-2-yl]-N'-[(E)-4-meth-oxy-benzyl-idene]acetohydrazide.

In the imidazo[2,1-b][1,3]thia-zole group of the title compound, C(21)H(17)ClN(4)O(2)S, the dihedral angle between the thia-zole and imidazole rings is 1.9 (2)°. The mean plane of this group makes dihedral angles of 5.5 (2) and 39.9 (2)° with the benzene rings of the chloro-phenyl and meth-oxy-phenyl groups, respectively. The dihedral angle between these two benzene rings is 34.4 (2)°. In the crystal, mol-ecules are connected to each other by inter-molecular N-H⋯O hydrogen bonds along the b axis, generating a C(4) chain. Weak C-H⋯π inter-actions also occur.

Computational Drug Repurposing: Current Trends.

Biomedical discovery has been reshaped upon the exploding digitization of data which can be retrieved from a number of sources, ranging from clinical pharmacology to cheminformatics-driven databases. Now, supercomputing platforms and publicly available resources such as biological, physicochemical, and clinical data, can all be integrated to construct a detailed map of signaling pathways and drug mechanisms of action in relation to drug candidates. Recent advancements in computer-aided data mining have facilitated analyses of 'big data' approaches and the discovery of new indications for pre-existing drugs has been accelerated. Linking gene-phenotype associations to predict novel drug-disease signatures or incorporating molecular structure information of drugs and protein targets with other kinds of data derived from systems biology provide great potential to accelerate drug discovery and improve the success of drug repurposing attempts. In this review, we highlight commonly used computational drug repurposing strategies, including bioinformatics and cheminformatics tools, to integrate large-scale data emerging from the systems biology, and consider both the challenges and opportunities of using this approach. Moreover, we provide successful examples and case studies that combined various in silico drug-repurposing strategies to predict potential novel uses for known therapeutics.

Increased Potency and Selectivity for Group III Metabotropic Glutamate Receptor Agonists Binding at Dual sites.

A group III metabotropic glutamate (mGlu) receptor agonist (PCEP) was identified by virtual HTS. This orthosteric ligand is composed by an l-AP4-derived fragment that mimics glutamate and a chain that binds into a neighboring pocket, offering possibilities to improve affinity and selectivity. Herein we describe a series of derivatives where the distal chain is replaced by an aromatic or heteroaromatic group. Potent agonists were identified, including some with a mGlu4 subtype preference, e.g., 17m (LSP1-2111) and 16g (LSP4-2022). Molecular modeling suggests that aromatic functional groups may bind at either one of the two chloride regulatory sites. These agonists may thus be considered as particular bitopic/dualsteric ligands. 17m was shown to reduce GABAergic synaptic transmission at striatopallidal synapses. We now demonstrate its inhibitory effect at glutamatergic parallel fiber-Purkinje cell synapses in the cerebellar cortex. Although these ligands have physicochemical properties that are markedly different from typical CNS drugs, they hold significant therapeutic potential.

Antibacterial, Antitubercular and Antiviral Activity Evaluations of Some Arylidenehydrazide Derivatives Bearing Imidazo[2,1-b]thiazole Moiety.

OBJECTIVES: The aim of this study was to determine the probable antibacterial, antitubercular, and antiviral activities of some N2 -arylidene-(6-(4-chlorophenyl)imidazo[2,1-b]thiazol-3-yl) acetic acid hydrazides (3a-j). Further structural optimization of the identified lead structures can lead us to new more active potential antibacterial, antitubercular, and antiviral agents. MATERIALS AND METHODS: Antibacterial activities of the title compounds against Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922. These molecules were also evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv (ATCC 27294) using the BACTEC 460 radiometric system and BACTEC 12B medium. Moreover, all the compounds (3a-j) were also evaluated against some DNA and RNA viruses in Madin-Darby Canine Kidney, Crandell-Rees Feline Kidney (CRFK), Vero, human embryonic lung (HEL) and HeLa cells. RESULTS: Among the tested compounds, 3i displayed the highest efficacy against S. aureus and E. coli. Compound 3j, 5-nitro-2-furfurylidene derivative showed the highest antituberculosis activity (IC50: 6.16 µg/mL and IC90: 14.390 µg/mL). Compound 3i showed the most potent antiviral activity against feline corona virus in CRFK cell cultures (antiviral EC50: 7.5 µM and SI>13). Furthermore, compounds 3c and 3g displayed activity against herpes simplex virus-1 and vaccinia virus in HEL cell cultures (antiviral EC50 values of 9; 16 and 20; 14 µM, respectively). CONCLUSION: On the basis of aforementioned results, it can be conluded that imidazo[2,1-b]thiazole derivatives bearing hydrazone moieties serve as promising chemical probes to design therapeutic agents with antibacterial, antitubercular, and antiviral properties.

Pharmacophore modeling and in silico toxicity assessment of potential anticancer agents from African medicinal plants.

Molecular modeling has been employed in the search for lead compounds of chemotherapy to fight cancer. In this study, pharmacophore models have been generated and validated for use in virtual screening protocols for eight known anticancer drug targets, including tyrosine kinase, protein kinase B ß, cyclin-dependent kinase, protein farnesyltransferase, human protein kinase, glycogen synthase kinase, and indoleamine 2,3-dioxygenase 1. Pharmacophore models were validated through receiver operating characteristic and Güner-Henry scoring methods, indicating that several of the models generated could be useful for the identification of potential anticancer agents from natural product databases. The validated pharmacophore models were used as three-dimensional search queries for virtual screening of the newly developed AfroCancer database (~400 compounds from African medicinal plants), along with the Naturally Occurring Plant-based Anticancer Compound-Activity-Target dataset (comprising ~1,500 published naturally occurring plant-based compounds from around the world). Additionally, an in silico assessment of toxicity of the two datasets was carried out by the use of 88 toxicity end points predicted by the Lhasa's expert knowledge-based system (Derek), showing that only an insignificant proportion of the promising anticancer agents would be likely showing high toxicity profiles. A diversity study of the two datasets, carried out using the analysis of principal components from the most important physicochemical properties often used to access drug-likeness of compound datasets, showed that the two datasets do not occupy the same chemical space.

Aminothiazoles as Potent and Selective Sirt2 Inhibitors: A Structure-Activity Relationship Study.

Sirtuins are NAD(+)-dependent protein deacylases that cleave off acetyl but also other acyl groups from the ε-amino group of lysines in histones and other substrate proteins. Dysregulation of human Sirt2 (hSirt2) activity has been associated with the pathogenesis of cancer, inflammation, and neurodegeneration, which makes the modulation of hSirt2 activity a promising strategy for pharmaceutical intervention. The sirtuin rearranging ligands (SirReals) have recently been discovered by us as highly potent and isotype-selective hSirt2 inhibitors. Here, we present a well-defined structure-activity relationship study, which rationalizes the unique features of the SirReals and probes the limits of modifications on this scaffold regarding inhibitor potency. Moreover, we present a crystal structure of hSirt2 in complex with an optimized SirReal derivative that exhibits an improved in vitro activity. Lastly, we show cellular hyperacetylation of the hSirt2 targeted tubulin caused by our improved lead structure.

Docking and binding free energy calculations of sirtuin inhibitors.

Sirtuins form a unique and highly conserved class of NAD(+)-dependent lysine deacylases. Among these the human subtypes Sirt1-3 has been implicated in the pathogenesis of numerous diseases such as cancer, metabolic syndromes, viral diseases and neurological disorders. Most of the sirtuin inhibitors that have been identified so far show limited potency and/or isoform selectivity. Here, we introduce a promising method to generate protein-inhibitor complexes of human Sirt1, Sirt2 and Sirt3 by means of ligand docking and molecular dynamics simulations. This method highly reduces the complexity of such applications and can be applied to other protein targets beside sirtuins. To the best of our knowledge, we present the first binding free energy method developed by using a validated data set of sirtuin inhibitors, where both a fair number of compounds (33 thieno[3,2-d]pyrimidine-6-carboxamide derivatives) was developed and tested in the same laboratory and also crystal structures in complex with the enzyme have been reported. A significant correlation between binding free energies derived from MM-GBSA calculations and in vitro data was found for all three sirtuin subtypes. The developed MM-GBSA protocol is computationally inexpensive and can be applied as a post-docking filter in virtual screening to find novel Sirt1-3 inhibitors as well as to prioritize compounds with similar chemical structures for further biological characterization.

Fluorescence-based screening assays for the NAD⁺-dependent histone deacetylase smSirt2 from Schistosoma mansoni.

Sirtuins are NAD(+)-dependent histone deacetylases (HDACs) that cleave off acetyl but also other acyl groups from the ϵ-amino group of lysines in histones and other substrate proteins. Five sirtuin isoforms are encoded in the genome of the parasitic pathogen Schistosoma mansoni. During its life cycle, S. mansoni undergoes drastic changes in phenotype that are associated with epigenetic modifications. Previous work showed strong effects of hSirt2 inhibitors on both worm life span and reproduction. Thus, we postulate smSirt2 as a new antiparasite target. We report both the optimization of a homogeneous fluorescence-based assay and the development of a new heterogeneous fluorescence-based assay to determine smSirt2 activity. The homogeneous assay uses a coumarin-labeled acetyl lysine derivative, and the heterogeneous version is using a biotinylated and fluorescence-labeled oligopeptide. Magnetic streptavidin-coated beads allow higher substrate loading per well than streptavidin-coated microtiter plates and make it possible to screen for inhibitors of either smSirt2 or its human isoform (hSirt2) for selectivity studies. We also present hits from a pilot screen with inhibitors showing an IC50 lower than 50 µM. Binding of the hits to their targets is rationalized by docking studies using a homology model of smSirt2.

Selective Sirt2 inhibition by ligand-induced rearrangement of the active site.

Sirtuins are a highly conserved class of NAD(+)-dependent lysine deacylases. The human isotype Sirt2 has been implicated in the pathogenesis of cancer, inflammation and neurodegeneration, which makes the modulation of Sirt2 activity a promising strategy for pharmaceutical intervention. A rational basis for the development of optimized Sirt2 inhibitors is lacking so far. Here we present high-resolution structures of human Sirt2 in complex with highly selective drug-like inhibitors that show a unique inhibitory mechanism. Potency and the unprecedented Sirt2 selectivity are based on a ligand-induced structural rearrangement of the active site unveiling a yet-unexploited binding pocket. Application of the most potent Sirtuin-rearranging ligand, termed SirReal2, leads to tubulin hyperacetylation in HeLa cells and induces destabilization of the checkpoint protein BubR1, consistent with Sirt2 inhibition in vivo. Our structural insights into this unique mechanism of selective sirtuin inhibition provide the basis for further inhibitor development and selective tools for sirtuin biology.