Matthias Schiedel

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.

Chemically Induced Degradation of Sirtuin 2 (Sirt2) by a Proteolysis Targeting Chimera (PROTAC) Based on Sirtuin Rearranging Ligands (SirReals)

Here we report the development of a proteolysis targeting chimera (PROTAC) based on the combination of the unique features of the sirtuin rearranging ligands (SirReals) as highly potent and isotype-selective Sirt2 inhibitors with thalidomide, a bona fide cereblon ligand. For the first time, we report the formation of a PROTAC by Cu(I)-catalyzed cycloaddition of a thalidomide-derived azide to an alkynylated inhibitor. This thalidomide-derived azide as well as the highly versatile linking strategy can be readily adapted to alkynylated ligands of other targets. In HeLa cells, our SirReal-based PROTAC induced isotype-selective Sirt2 degradation that results in the hyperacetylation of the microtubule network coupled with enhanced process elongation. Thus, our SirReal-based PROTAC is the first example of a probe that is able to chemically induce the degradation of an epigenetic eraser protein.

Chromo-pharmacophores: photochromic diarylmaleimide inhibitors for sirtuins

Controlling the activity of sirtuins is of high biomedical relevance as the enzymes are involved in cancer, neurodegeneration and other diseases. Therefore structural elements of 3,4-bisindoylmaleimides (BIMs), which are known NAD+-dependent histone deacetylase (sirtuin) inhibitors, were merged with photochromic diarylmaleimides to yield photoswitchable enzyme inhibitors. The new inhibitors show excellent photophysical properties, are switchable even in polar solvents, and subtype selective against hSirt2. The inhibitory activity changes up to a factor of 22 for the two photoisomers and physiological properties can therefore be effectively toggled by irradiation with light of different wavelengths. Docking experiments using the enzyme crystal structure explain the observed activity changes based on the steric demand of the thiophene substitution and the rigidity of the molecular structure.

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.

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.

A Continuous, Fluorogenic Sirtuin 2 Deacylase Assay: Substrate Screening and Inhibitor Evaluation

Sirtuins are important regulators of lysine acylation, which is implicated in cellular metabolism and transcriptional control. This makes the sirtuin class of enzymes interesting targets for development of small molecule probes with pharmaceutical potential. To achieve detailed profiling and kinetic insight regarding sirtuin inhibitors, it is important to have access to efficient assays. In this work, we report readily synthesized fluorogenic substrates enabling enzyme-economical evaluation of SIRT2 inhibitors in a continuous assay format as well as evaluation of the properties of SIRT2 as a long chain deacylase enzyme. Novel enzymatic activities of SIRT2 were thus established in vitro, which warrant further investigation, and two known inhibitors, suramin and SirReal2, were profiled against substrates containing ε-N-acyllysine modifications of varying length.

The Current State of NAD(+) -Dependent Histone Deacetylases (Sirtuins) as Novel Therapeutic Targets.

Sirtuins are NAD+‐dependent protein deacylases that cleave off acetyl, as well as other acyl groups, from the ε‐amino group of lysines in histones and other substrate proteins. Seven sirtuin isotypes (Sirt1–7) have been identified in mammalian cells. As sirtuins are involved in the regulation of various physiological processes such as cell survival, cell cycle progression, apoptosis, DNA repair, cell metabolism, and caloric restriction, a dysregulation of their enzymatic activity has been associated with the pathogenesis of neoplastic, metabolic, infectious, and neurodegenerative diseases. Thus, sirtuins are promising targets for pharmaceutical intervention. Growing interest in a modulation of sirtuin activity has prompted the discovery of several small molecules, able to inhibit or activate certain sirtuin isotypes. Herein, we give an update to our previous review on the topic in this journal (Schemies, 2010), focusing on recent developments in sirtuin biology, sirtuin modulators, and their potential as novel therapeutic agents.

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.

Modulation Of Microtubule Acetylation By The Interplay Of TPPP/p25, SIRT2 And New Anticancer Agents With Anti-SIRT2 Potency

The microtubule network exerts multifarious functions controlled by its decoration with various proteins and post-translational modifications. The disordered microtubule associated Tubulin Polymerization Promoting Protein (TPPP/p25) and the NAD+-dependent tubulin deacetylase sirtuin-2 (SIRT2) play key roles in oligodendrocyte differentiation by acting as dominant factors in the organization of myelin proteome. Herein, we show that SIRT2 impedes the TPPP/p25-promoted microtubule assembly independently of NAD+; however, the TPPP/p25-assembled tubulin ultrastructures were resistant against SIRT2 activity. TPPP/p25 counteracts the SIRT2-derived tubulin deacetylation producing enhanced microtubule acetylation. The inhibition of the SIRT2 deacetylase activity by TPPP/p25 is evolved by the assembly of these tubulin binding proteins into a ternary complex, the concentration-dependent formation of which was quantified by experimental-based mathematical modelling. Co-localization of the SIRT2-TPPP/p25 complex on the microtubule network was visualized in HeLa cells by immunofluorescence microscopy using Bimolecular Fluorescence Complementation. We also revealed that a new potent SIRT2 inhibitor (MZ242) and its proteolysis targeting chimera (SH1) acting together with TPPP/p25 provoke microtubule hyperacetylation, which is coupled with process elongation only in the case of the degrader SH1. Both the structural and the functional effects manifesting themselves by this deacetylase proteome could lead to the fine-tuning of the regulation of microtubule dynamics and stability.

Correction to A Continuous, Fluorogenic Sirtuin 2 Deacylase Assay: Substrate Screening and Inhibitor Evaluation.

■ ASSOCIATED CONTENT *S Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jmedchem.6b00239. Michaelis−Menten plot for NAD, synthesis of (Z)-2ene-, (R/S)-3-hydroxy-, and 3-oxo-carboxylic acids, additional experimental procedures, additional compound characterization data, definition of abbreviations used, as well as copies of H NMR and C NMR spectra (PDF)