Specific Inhibitors of Mitochondrial Deacylase Sirtuin 4 Endowed with Cellular Activity.

Sirtuins are NAD+-dependent protein lysine deacylases implicated in aging-related diseases. Mammalian Sirtuin 4 (Sirt4) is located in mitochondria and a potential therapeutic target for cancer and metabolic diseases, but no potent and selective Sirt4 inhibitors have been reported. Here, we describe the identification of potent Sirt4-specific small-molecule inhibitors. Testing hits from a target-based virtual screen revealed 12 active compounds. A focused screen based on two top compounds, followed by structure-assisted design of derivatives, yielded four first-in-class potent Sirt4 inhibitors. Kinetic analyses indicate compound competition with the acyl peptide substrate, consistent with the docking models and implicating Sirt4's unique acyl binding site. The compounds indeed show preference for Sirt4 over other isoforms, with one of them (69) being highly isoform selective, and they are active in cells. Our results provide first lead compounds and mechanistic insights for optimization toward Sirt4-specific inhibitors useful as experimental tools and potential therapeutics.

Recent advances in epigenetic proteolysis targeting chimeras (Epi-PROTACs).

PROteolysis TArgeting Chimeras (PROTACs) are heterobifunctional molecules that trigger the poly-ubiquitination of the protein of interest (POI) inducing its degradation via the recruitment of the ubiquitin-proteasome system, thus suppressing the POI's intracellular levels and indirectly all its functions. Recently, one of the fields where the protein knockdown induced by PROTACs has demonstrated to serve as a promising biochemical tool and to provide new opportunities for drug discovery is the epigenetics (epi-PROTACs). A full inhibition of the functions of all domains of a specific epigenetic POI (e-POI), rather than just the block of its catalytic/single domain activity, is in fact a new more effective modality to hit an e-POI and, in principle, the complex it belongs to, and potentially to treat the related diseases, first cancer. In this review, we will present the most relevant progresses made, especially in the last two years, in the application of PROTACs technology to the three main classes of e-POIs: "writers", "erasers" and "readers". Emphasis will be devoted to the medicinal chemistry aspects of the epi-PROTACs design, preparation, and optimization and to the comparison with small molecule epi-drugs for both epi-targets functional annotation and potential anticancer therapy purposes.

Sirt4: A Multifaceted Enzyme at the Crossroads of Mitochondrial Metabolism and Cancer.

Sirtuins are NAD+-dependent deacylases that play crucial roles in the regulation of cellular metabolism, and as a result, are implicated in several diseases. The mitochondrial sirtuin Sirt4, for a long time considered as mainly a mono-ADP-ribosyltransferase, recently has shown a robust deacylase activity in addition to the already accepted substrate-dependent lipoamidase and deacetylase properties. Through these and likely other enzymatic and non-enzymatic activities, Sirt4 closely controls various metabolic events, and its dysregulation is linked to various aging-related disorders, including type 2 diabetes, cardiac hypertrophy, non-alcoholic fatty liver disease, obesity, and cancer. For its capability to inhibit glutamine catabolism and for the modulation of genome stability in cancer cells in response to different DNA-damaging conditions, Sirt4 is proposed as either a mitochondrial tumor suppressor or a tumor-promoting protein in a context-dependent manner. In addition to what is already known about the roles of Sirt4 in different biological settings, further studies are certainly still needed in order to validate this enzyme as a new potential target for various aging diseases.

Epigenetic polypharmacology: A new frontier for epi-drug discovery.

Recently, despite the great success achieved by the so-called "magic bullets" in the treatment of different diseases through a marked and specific interaction with the target of interest, the pharmacological research is moving toward the development of "molecular network active compounds," embracing the related polypharmacology approach. This strategy was born to overcome the main limitations of the single target therapy leading to a superior therapeutic effect, a decrease of adverse reactions, and a reduction of potential mechanism(s) of drug resistance caused by robustness and redundancy of biological pathways. It has become clear that multifactorial diseases such as cancer, neurological, and inflammatory disorders, may require more complex therapeutic approaches hitting a certain biological system as a whole. Concerning epigenetics, the goal of the multi-epi-target approach consists in the development of small molecules able to simultaneously and (often) reversibly bind different specific epi-targets. To date, two dual histone deacetylase/kinase inhibitors (CUDC-101 and CUDC-907) are in an advanced stage of clinical trials. In the last years, the growing interest in polypharmacology encouraged the publication of high-quality reviews on combination therapy and hybrid molecules. Hence, to update the state-of-the-art of these therapeutic approaches avoiding redundancy, herein we focused only on multiple medication therapies and multitargeting compounds exploiting epigenetic plus nonepigenetic drugs reported in the literature in 2018. In addition, all the multi-epi-target inhibitors known in literature so far, hitting two or more epigenetic targets, have been included.

Enzymatic and Biological Characterization of Novel Sirtuin Modulators against Cancer.

Sirtuins, a family of nicotinamide adenine dinucleotide (NAD+)-dependent lysine deacetylases, are promising targets for anticancer treatment. Recently, we characterized a novel pan-sirtuin (SIRT) inhibitor, MC2494, displaying antiproliferative effects and able to induce death pathways in several human cancer cell lines and decrease tumor growth in vivo. Based on the chemical scaffold of MC2494, and by applying a structure-activity relationship approach, we developed a small library of derivative compounds and extensively analyzed their enzymatic action at cellular level as well as their ability to induce cell death. We also investigated the effect of MC2494 on regulation of cell cycle progression in different cancer cell lines. Our investigations indicated that chemical substitutions applied to MC2494 scaffold did not confer higher efficacy in terms of biological activity and SIRT1 inhibition, but carbethoxy-containing derivatives showed higher SIRT2 specificity. The carbethoxy derivative of MC2494 and its 2-methyl analog displayed the strongest enzymatic activity. Applied chemical modifications improved the enzymatic selectivity of these SIRT inhibitors. Additionally, the observed activity of MC2494 via cell cycle and apoptotic regulation and inhibition of cell migration supports the potential role of SIRTs as targets in tumorigenesis and makes SIRT-targeting molecules good candidates for novel pharmacological approaches in personalized medicine.

Structure-Reactivity Relationships on Substrates and Inhibitors of the Lysine Deacylase Sirtuin 2 from Schistosoma mansoni (SmSirt2).

The only drug currently available for treatment of the neglected disease Schistosomiasis is Praziquantel, and the possible emergence of resistance makes research on novel therapeutic agents necessary and urgent. To this end, the targeting of Schistosoma mansoni epigenetic enzymes, which regulate the parasitic life cycle, emerged as a promising approach. Due to the strong effects of human sirtuin inhibitors on parasite survival and reproduction, Schistosoma sirtuins were postulated as potential therapeutic targets. In vitro testing of synthetic substrates of S. mansoni sirtuin 2 (SmSirt2) and kinetic experiments on a myristoylated peptide demonstrated lysine long-chain deacylation as an intrinsic SmSirt2 activity in addition to its known deacetylase activity for the first time. Focused in vitro screening of the GSK Kinetobox library and structure-activity relationships of identified hits led to the first SmSirt2 inhibitors with activity in the low micromolar range. Several SmSirt2 inhibitors showed potency against both larval schistosomes (viability) and adult worms (pairing, egg laying) in culture without general toxicity to human cancer cells.

α,γ-Diketocarboxylic Acids and Their Esters Act as Carbonic Anhydrase IX and XII Selective Inhibitors.

Among human carbonic anhydrase (CA) inhibitors, the α,γ-diketocarboxylic acids and esters are still poorly investigated. Here, we report the first compounds of this class (1-6) acting as potent inhibitors at low nanomolar level against the cancer-related human CA IX and XII, and 2-3 magnitude orders selective toward the cytosolic isoforms hCA I and II. At enzymatic level, the α,γ-diketoacids 1-3 were more effective inhibitors compared to the corresponding ethyl esters 4-6. The phenyl- and α-naphthyl-containing compounds (1, 3, 4, and 6) behaved as dual hCA IX/XII inhibitors, while the ß-naphthyl analogues (2 and 5) exhibited hCA IX-selective inhibition. In MG63 and HOS osteosarcoma (OS) cell lines, the ethyl esters 5 and 6 displayed dose-dependent reduction of viability and proliferation after 72 h treatment, with 6 being more potent than 5 likely for its dual hCA IX/XII inhibition.

Epigenetic Metalloenzymes.

Epigenetics controls the expression of genes and is responsible for cellular phenotypes. The fundamental basis of these mechanisms involves in part the post-translational modifications (PTMs) of DNA and proteins, in particular, the nuclear histones. DNA can be methylated or demethylated on cytosine. Histones are marked by several modifications including acetylation and/or methylation, and of particular importance are the covalent modifications of lysine. There exists a balance between addition and removal of these PTMs, leading to three groups of enzymes involved in these processes: the writers adding marks, the erasers removing them, and the readers able to detect these marks and participating in the recruitment of transcription factors. The stimulation or the repression in the expression of genes is thus the result of a subtle equilibrium between all the possibilities coming from the combinations of these PTMs. Indeed, these mechanisms can be deregulated and then participate in the appearance, development and maintenance of various human diseases, including cancers, neurological and metabolic disorders. Some of the key players in epigenetics are metalloenzymes, belonging mostly to the group of erasers: the zinc-dependent histone deacetylases (HDACs), the iron-dependent lysine demethylases of the Jumonji family (JMJ or KDM) and for DNA the iron-dependent ten-eleven-translocation enzymes (TET) responsible for the oxidation of methylcytosine prior to the demethylation of DNA. This review presents these metalloenzymes, their importance in human disease and their inhibitors.

Effect of α-Methoxy Substitution on the Anti-HIV Activity of Dihydropyrimidin-4(3 H)-ones.

Conformational restriction applied to dihydrobenzylpyrimidin-4-(3 H)-ones (DABOs) by the intoduction of a methyl group at the α-benzylic position is known to massively improve the anti-HIV-1 activity of these compounds. Here, we report the effects of methoxy substitution at the α-benzylic position in S-, NH-, and N, N-DABOs carrying 2,6-difluoro, 2-chloro-6-fluoro, or 2,6-dichloro substituted benzyl moieties. The various α-methoxy DABO series (12-14) present different SAR at the dihalo benzyl substitution, with the most potent compounds (12d,e and 13c) showing similar (picomolar/nanomolar) anti-HIV-1 potency as the corresponding α-methyl analogues against wt HIV-1, and 10-100-fold increased potency (up to low nanomolar) against clinically relevant K103N, Y181C, Y188L, IRLL98, and K103N+Y181C HIV-1 mutant strains, highlighting the importance of the α-methoxy substitution to provide highly efficient DABOs as "second generation" NNRTIs. HPLC enantioseparation of three of the most potent derivatives (12d, 13c, and 14c) provided single enantiomers with significant enantioselectivity in HIV-1 inhibition. Computational studies allowed to correlate the best antiviral activity with the ( R) absolute configuration at the α-methoxy stereogenic center.

Novel polyamine-based Histone deacetylases-Lysine demethylase 1 dual binding inhibitors.

Epigenetic modulators Histone deacetylases (HDACs) and Lysine demethylase (LSD1) are validated targets for anticancer therapy. Both HDAC1/2 and LSD1 are found in association with the repressor protein CoREST in a transcriptional co-repressor complex, which is responsible for gene silencing. Combined modulation of both targets results in a synergistic antiproliferative activity. In the present investigation, we report about the design and synthesis of a series of polyamine-based HDACs-LSD1 dual binding inhibitors obtained by coupling Vorinostat and Tranylcypromine. Compound 4 emerged as the most promising of the synthesized series, showing good inhibitory activity towards HDAC1 and LSD1 either in vitro and in cell-based assay (Ki = 42.52 ±â€¯8.94 nM and IC50 = 3.85 µM, respectively). Furthermore, at 70.0 µM compound 4 induced a more pronounced cytotoxic effect than Vorinostat (68.6% vs 56.6% of dead cells) in MCF7 cancer cell line.

Disruptor of telomeric silencing 1-like (DOT1L): disclosing a new class of non-nucleoside inhibitors by means of ligand-based and structure-based approaches.

Chemical inhibition of chromatin-mediated signaling involved proteins is an established strategy to drive expression networks and alter disease progression. Protein methyltransferases are among the most studied proteins in epigenetics and, in particular, disruptor of telomeric silencing 1-like (DOT1L) lysine methyltransferase plays a key role in MLL-rearranged acute leukemia Selective inhibition of DOT1L is an established attractive strategy to breakdown aberrant H3K79 methylation and thus overexpression of leukemia genes, and leukemogenesis. Although numerous DOT1L inhibitors have been several structural data published no pronounced computational efforts have been yet reported. In these studies a first tentative of multi-stage and LB/SB combined approach is reported in order to maximize the use of available data. Using co-crystallized ligand/DOT1L complexes, predictive 3-D QSAR and COMBINE models were built through a python implementation of previously reported methodologies. The models, validated by either modeled or experimental external test sets, proved to have good predictive abilities. The application of these models to an internal library led to the selection of two unreported compounds that were found able to inhibit DOT1L at micromolar level. To the best of our knowledge this is the first report of quantitative LB and SB DOT1L inhibitors models and their application to disclose new potential epigenetic modulators.