A distal regulatory region of a class I human histone deacetylase.

Histone deacetylases (HDACs) are key enzymes in epigenetics and important drug targets in cancer biology. Whilst it has been established that HDACs regulate many cellular processes, far less is known about the regulation of these enzymes themselves. Here, we show that HDAC8 is allosterically regulated by shifts in populations between exchanging states. An inactive state is identified, which is stabilised by a range of mutations and resembles a sparsely-populated state in equilibrium with active HDAC8. Computational models show that the inactive and active states differ by small changes in a regulatory region that extends up to 28 Å from the active site. The regulatory allosteric region identified here in HDAC8 corresponds to regions in other class I HDACs known to bind regulators, thus suggesting a general mechanism. The presented results pave the way for the development of allosteric HDAC inhibitors and regulators to improve the therapy for several disease states.

Potent non-hydroxamate inhibitors of histone deacetylase-8: Role and scope of an isoindolin-2-yl linker with an α-amino amide as the zinc-binding unit.

A series of potent inhibitors of histone deacetylase-8 (HDAC8) is described that contains an α-amino amide zinc-binding unit and a substituted isoindolinyl capping group. The presence of a 2,4-dichlorophenyl unit located in the acetate-release cavity was shown to confer a gain of approx. 4.3 kJ mol-1 in binding energy compared to a phenyl group, and the isoindoline linker has approx. 5.8 kJ mol-1 greater binding energy than the corresponding tetrahydroisoquinoline ring system. In a series of 5-substituted isoindolin-2-yl inhibitors, a 5-acetylamino derivative was found to be more potent than the 5-unsubstituted lead HDAC8 inhibitor (increase in binding energy of 2.0 kJ mol-1, ascribed to additional binding interactions within the Nε-acetyl-l-lysine binding tunnel in HDAC8, including hydrogen bonding to Asp101. Tolerance of a 5-substituent (capping group) on the isoindoline ring has been demonstrated, and which in some cases confers improved enzyme inhibition, the HDAC8 substrate-binding region providing a platform for additional interactions.

Monocyclic Quinone Structure-Activity Patterns: Synthesis of Catalytic Inhibitors of Topoisomerase II with Potent Antiproliferative Activity.

The monocyclic 1,4-benzoquinone, HU-331, the direct oxidation product of cannabidiol, inhibits the catalytic activity of topoisomerase II but without inducing DNA strand breaks or generating free radicals, and unlike many fused-ring quinones exhibits minimal cardiotoxicity. Thus, monocyclic quinones have potential as anticancer agents, and investigation of the structural origins of their biological activity is warranted. New syntheses of cannabidiol and (±)-HU-331 are here reported. Integrated synthetic protocols afforded a wide range of polysubstituted resorcinol derivatives; many of the corresponding novel 2-hydroxy-1,4-benzoquinone derivatives are potent inhibitors of the catalytic activity of topoisomerase II, some more so than HU-331, whose monoterpene unit replaced by a 3-cycloalkyl unit conferred increased antiproliferative properties in cell lines with IC50 values extending below 1 mM, and greater stability in solution than HU-331. The principal pharmacophore of quinones related to HU-331 was identified. Selected monocyclic quinones show potential for the development of new anticancer agents.

Targeting TAO Kinases Using a New Inhibitor Compound Delays Mitosis and Induces Mitotic Cell Death in Centrosome Amplified Breast Cancer Cells.

Thousand-and-one amino acid kinases (TAOK) 1 and 2 are activated catalytically during mitosis and can contribute to mitotic cell rounding and spindle positioning. Here, we characterize a compound that inhibits TAOK1 and TAOK2 activity with IC50 values of 11 to 15 nmol/L, is ATP-competitive, and targets these kinases selectively. TAOK inhibition or depletion in centrosome-amplified SKBR3 or BT549 breast cancer cell models increases the mitotic population, the percentages of mitotic cells displaying amplified centrosomes and multipolar spindles, induces cell death, and inhibits cell growth. In contrast, nontumorigenic and dividing bipolar MCF-10A breast cells appear less dependent on TAOK activity and can complete mitosis and proliferate in the presence of the TAOK inhibitor. We demonstrate that TAOK1 and TAOK2 localize to the cytoplasm and centrosomes respectively during mitosis. Live cell imaging shows that the TAOK inhibitor prolongs the duration of mitosis in SKBR3 cells, increases mitotic cell death, and reduces the percentages of cells exiting mitosis, whereas MCF-10A cells continue to divide and proliferate. Over 80% of breast cancer tissues display supernumerary centrosomes, and tumor cells frequently cluster extra centrosomes to avoid multipolar mitoses and associated cell death. Consequently, drugs that stimulate centrosome declustering and induce multipolarity are likely to target dividing centrosome-amplified cancer cells preferentially, while sparing normal bipolar cells. Our results demonstrate that TAOK inhibition can enhance centrosome declustering and mitotic catastrophe in cancer cells, and these proteins may therefore offer novel therapeutic targets suitable for drug inhibition and the potential treatment of breast cancers, where supernumerary centrosomes occur. Mol Cancer Ther; 16(11); 2410-21. ©2017 AACR.

Pteridine-2,4-diamine derivatives as radical scavengers and inhibitors of lipoxygenase that can possess anti-inflammatory properties.

BACKGROUND: Reactive oxygen species are associated with inflammation implicated in cancer, atherosclerosis and autoimmune diseases. The complex nature of inflammation and of oxidative stress suggests that dual-target agents may be effective in combating diseases involving reactive oxygen species. RESULTS: A novel series of N-substituted 2,4-diaminopteridines has been synthesized and evaluated as antioxidants in several assays. Many exhibited potent lipid antioxidant properties, and some are inhibitors of soybean lipoxygenase, IC50 values extending down to 100 nM for both targets. Several pteridine derivatives showed efficacy at 0.01 mmol/kg with little tissue damage in a rat model of colitis. 2-(4-methylpiperazin-1-yl)-N-(thiophen-2-ylmethyl)pteridin-4-amine (18f) at 0.01 mmol/kg exhibited potent anti-inflammatory activity (reduction by 41%). CONCLUSION: The 2,4-diaminopteridine core represents a new scaffold for lipoxygenase inhibition as well as sustaining anti-inflammatory properties.

Potent and Selective Inhibitors of Histone Deacetylase-3 Containing Chiral Oxazoline Capping Groups and a N-(2-Aminophenyl)-benzamide Binding Unit.

A novel series of potent chiral inhibitors of histone deacetylase (HDAC) is described that contains an oxazoline capping group and a N-(2-aminophenyl)-benzamide unit. Among several new inhibitors of this type exhibiting Class I selectivity and potent inhibition of HDAC3-NCoR2, in vitro assays for the inhibition of HDAC1, HDAC2, and HDAC3-NCoR2 by N-(2-aminophenyl)-benzamide 15k gave respective IC50 values of 80, 110, and 6 nM. Weak inhibition of all other HDAC isoforms (HDAC4, 5, 6, 7, and 9: IC50 > 100 000 nM; HDAC8: IC50 = 25 000 nM; HDAC10: IC50 > 4000 nM; HDAC11: IC50 > 2000 nM) confirmed the Class I selectivity of 15k. 2-Aminoimidazolinyl, 2-thioimidazolinyl, and 2-aminooxazolinyl units were shown to be effective replacements for the pyrimidine ring present in many other 2-(aminophenyl)-benzamides previously reported, but the 2-aminooxazolinyl unit was the most potent in inhibiting HDAC3-NCoR2. Many of the new HDAC inhibitors showed higher solubilities and lower binding to human serum albumin than that of Mocetinostat. Increases in histone H3K9 acetylation in the human cell lines U937 and PC-3 was observed for all three oxazolinyl inhibitors evaluated; those HDAC inhibitors also lowered cyclin E expression in U937 cells but not in PC-3 cells, indicating underlying differences in the mechanisms of action of the inhibitors on those two cell lines.

Discovery of potent, isoform-selective inhibitors of histone deacetylase containing chiral heterocyclic capping groups and a N-(2-aminophenyl)benzamide binding unit.

The synthesis of a novel series of potent chiral inhibitors of histone deacetylase (HDAC) is described that contain a heterocyclic capping group and a N-(2-aminophenyl)benzamide unit that binds in the active site. In vitro assays for the inhibition of HDAC1, HDAC2, HDAC3-NCoR1, and HDAC8 by the N-(2-aminophenyl)benzamide 24a gave respective IC50 values of 930, 85, 12, and 4100 nM, exhibiting class I selectivity and potent inhibition of HDAC3-NCoR1. Both imidazolinone and thiazoline rings are shown to be effective replacements for the pyrimidine ring present in many other 2-(aminophenyl)benzamides previously reported, an example of each ring system at 1 µM causing an increase in histone H3K9 acetylation in the human cell lines Jurkat and HeLa and an increase in cell death consistent with induction of apoptosis. Inhibition of the growth of MCF-7, A549, DU145, and HCT116 cell lines by 24a was observed, with respective IC50 values of 5.4, 5.8, 6.4, and 2.2 mM.

Multicomponent and sequential organocatalytic reactions: diversity with atom-economy and enantiocontrol.

Reactions in which several components are combined in sequence, and without isolation of intermediates, are greatly sought because of the inherent molecular diversity, efficiency, and atom-economy. However, organocatalytic reactions, employing an organic catalyst to assemble products of high enantiomeric excess (a single optical isomer), are also cutting-edge methodology. This tutorial review covers the overlap of these two areas, outling the structural diversity and stereocontrol arising from one-pot combinations of at least three components, powerful approaches with great potential that minimise formation of by-products and operating costs.

New and unusual scaffolds in medicinal chemistry.

Contemporary medicinal chemistry faces diverse challenges from several directions, including the need for both potency and specificity of any therapeutic agent; the increasingly demanding requirements of low toxicity shown across all patients treated; and the need for novelty in intellectual property, given the extensive use of benzenoid and heteroaromatic ring systems in numerous patents. Increasingly, such challenges are being met by a shift to new and/or unusual ring systems (scaffolds) that lie outside the field of (hetero)aromatic systems. This critical review surveys a necessarily limited selection of currently atypical scaffolds, chiefly drawn from the literature of the last three years, that have found application in medicinal chemistry, some being present in agents with therapeutic potential while others are found in agents already in clinical use (163 references).

Histone deacetylase inhibitors: design, structure-activity relationships and therapeutic implications for cancer.

Histone deacetylases (HDACs) remove acetyl groups from the tails of lysine residues of histone protein in nuclear chromatin and also from acetylated sites in non-histone proteins. HDACs and histone acetyltransferases (HATs) are major influences on the level of cellular protein acetylation, and an imbalance in acetylation levels, particularly under-acetylated (hypoacetylated) histone protein has been associated with precancerous or malignant states. Consequently, small molecule inhibitors of HDACs have been synthesised and some now form a newly emerging class of anti-cancer agents that can regulate transcription and inhibit proliferation of cancer cells by inducing cell cycle arrest, differentiation and/or apoptosis, among other major biological phenomena. The different mechanism(s) of action of HDAC inhibitors compared to conventional anti-neoplastic agents provides a possibility that HDAC inhibitors may be effective for refractory cancers. Accordingly, a number of programs for the development of HDAC inhibitors as anti-cancer drugs have been initiated. This review highlights recent developments in the design, synthesis and biological properties of HDAC inhibitors in the context of potential cancer therapy.

Effects of a selection of histone deacetylase inhibitors on mast cell activation and airway and colonic smooth muscle contraction.

Studies of histone deacetylase (HDAC) inhibitors, novel anticancer drugs, in models of autoimmune diseases, asthma, and inflammatory bowel disease suggest that HDAC inhibitors may also have useful anti-inflammatory effects. Accordingly, in vitro studies relevant to asthma and inflammatory bowel disease were conducted using a selection of HDAC inhibitors: suberoylanilide hydroxamic acid (SAHA, Vorinostat), and a related branched hydroxamic acid, diamide (1), MGCD0103 and two short chain fatty acid derivatives: sodium butyrate (of use in inflammatory bowel disease) and sodium valproate. The ability of those HDAC inhibitors to modulate antigen- or agonist-induced contraction of isolated guinea pig tracheal rings and colon, agonist-induced contraction of rat colon, and histamine release from rat peritoneal mast cells was examined. Pre-incubation (up to 6 h) with 10-40 microM of SAHA, diamide (1), or MGCD0103 caused significant inhibition of the antigen-induced contraction of sensitised guinea pig tracheal rings as well as inhibition of the contraction induced by histamine, 5-hydroxytryptamine and carbachol (G-protein coupled receptor agonists), while sodium butyrate (1 mM) and sodium valproate (100 microM) were weak inhibitors. Contraction of tracheal rings by sodium fluoride (NaF, a non-selective G-protein activator), KCl and a peroxyl radical generator was blocked by MGCD0103. Additionally, MGCD0103 significantly inhibited antigen-induced histamine release from IgE antibody-sensitised rat peritoneal mast cells, and NaF-induced histamine release, as well as inhibiting NaF-induced colon contraction. Those various effects appear to involve modulation of cell signaling, probably involving G-protein coupled pathways, and further support the development of HDAC inhibitors as anti-inflammatory agents.

Thiostrepton selectively targets breast cancer cells through inhibition of forkhead box M1 expression.

Elevated expression or activity of the transcription factor forkhead box M1 (FOXM1) is associated with the development and progression of many malignancies, including breast cancer. In this study, we show that the thiazole antibiotic thiostrepton selectively induces cell cycle arrest and cell death in breast cancer cells through down-regulating FOXM1 expression. Crucially, our data show that thiostrepton treatment reduced FOXM1 expression in a time- and dose-dependent manner, independent of de novo protein synthesis and predominantly at transcriptional and gene promoter levels. Our results indicate that thiostrepton can induce cell death through caspase-dependent intrinsic and extrinsic apoptotic pathways as well as through caspase-independent death mechanisms, as observed in MCF-7 cells, which are deficient of caspase-3 and caspase-7. Cell cycle analysis showed that thiostrepton induced cell cycle arrest at G(1) and S phases and cell death, concomitant with FOXM1 repression in breast cancer cells. Furthermore, thiostrepton also shows efficacy in repressing breast cancer cell migration, metastasis, and transformation, which are all downstream functional attributes of FOXM1. We also show that overexpression of a constitutively active FOXM1 mutant, DeltaN-FOXM1, can abrogate the antiproliferative effects of thiostrepton. Interestingly, thiostrepton has no affect on FOXM1 expression and proliferation of the untransformed MCF-10A breast epithelial cells. Collectively, our data show that FOXM1 is one of the primary cellular targets of thiostrepton in breast cancer cells and that thiostrepton may represent a novel lead compound for targeted therapy of breast cancer with minimal toxicity against noncancer cells.

A catalytic asymmetric protocol for the enantioselective synthesis of 3(2H)-furanones.

3(2H)-Furanones can be prepared by a catalytic asymmetric protocol from enynones, which, if electron-rich, require only one reagent and involve two reactions in a single operation--a domino process.

Structure-activity relationships of aryloxyalkanoic acid hydroxyamides as potent inhibitors of histone deacetylase.

Syntheses of aryloxyalkanoic acid hydroxyamides are described, all of which are potent inhibitors of histone deacetylase, some being more potent in vitro than trichostatin A (IC(50)=3 nM). Variation of the substituents on the benzene ring as well as fusion of a second ring have marked effects on potency, in vitro IC(50) values down to 1 nM being obtained.

Synthesis of the penta-oxazole core of telomestatin in a convergent approach to poly-oxazole macrocycles.

A protocol for the construction of poly-oxazoles with consecutive 2,4'-linkages is described, and has afforded an efficient route to a penta-oxazole which demarcates a route to telomestatin and related macrocyclic poly-oxazole systems.

Aromatic sulfide inhibitors of histone deacetylase based on arylsulfinyl-2,4-hexadienoic acid hydroxyamides.

The synthesis of a novel series of potent inhibitors of histone deacetylases is described, based on arylsulfinyl-2,4-hexadienoic acid hydroxyamides and their derivatives. In vitro IC(50) values down to 40 nM were obtained, and several compounds showed inhibition of CEM (human leukemic) cell viability with IC(50) of approximately 1.5 microM, comparable to or better than that of suberoylanilide hydroxamic acid, an inhibitor of histone deacetylase currently in clinical trials.

Enantioselective syntheses of trans-3,4-difluoropyrrolidines and investigation of their applications in catalytic asymmetric synthesis.

[reaction: see text] Asymmetric syntheses of enantiopure trans-3,4-difluoropyrrolidines have been prepared by the introduction of fluorine at both centers in a single operation; asymmetric epoxidations and additions to benzaldehyde were conducted using catalysts whose chirality depends on organofluorine asymmetry.

Stereodefined and polyunsaturated inhibitors of histone deacetylase based on (2E,4E)-5-arylpenta-2,4-dienoic acid hydroxyamides.

Syntheses of (2E,4E)-5-arylpenta-2,4-dienoic acid hydroxyamides are described, some of which are potent inhibitors of histone deacetylase, a double bond conferring more than a 10-fold increase in potency compared with the triple bond analogue oxamflatin. Variation of substituents on the aromatic ring has a marked effect on potency, in vitro IC(50) values down to 50 nM being obtained.