Cyclic tetrapeptides bearing a sulfhydryl group potently inhibit histone deacetylases

New inhibitors of histone deacetylase (HDAC) containing a sulfhydryl group were designed on the basis of the corresponding hydroxamic acid (CHAP31) and FK228. Their disulfide dimers and hybrids exhibited potent HDAC inhibitory activity in vivo with potential as anticancer prodrugs. [structure: see text]     

Improved total synthesis of the potent HDAC inhibitor FK228 (FR-901228)

A scaleable synthesis of the potent histone deacetylase (HDAC) inhibitor FK228 is described. A reliable strategy for preparing the key beta-hydroxy mercapto heptenoic acid partner was accomplished in nine steps and 13% overall yield. A Noyori asymmetric hydrogen-transfer reaction established the hydroxyl stereochemistry in >99:1 er via the reduction of a propargylic ketone.     

Phenolic Rubber Foam Plastics Possessing Elasticity

This article is devoted to FK-20, FK-40, FK-60, FK-60T, and FK-20-A-20 heat-resistant elastic phenolic rubber foam plastics. A number of physicomechanical and performance properties are compared.     

Macrolactamization versus macrolactonization: total synthesis of FK228, the depsipeptide histone deacetylase inhibitor

The cyclic depsipeptide FK228 is the only natural product histone deacetylase (HDAC) inhibitor that has advanced to clinical trials as an anticancer agent. While currently obtained by fermentation, total synthesis is an attractive alternative that will facilitate the preparation of unnatural analogues. The previous total syntheses of FK228 featured macrocylization by ester bond formation from a seco-hydroxy acid. Such routes are operationally jeopardized by the steric hindrance of the carboxylic acid and the sensitivity of the allylic alcohol toward elimination. We report a strategically different approach whereby the ester bond is formed intermolecularly at an early stage and macrocyclization is efficiently achieved by amide bond formation.     

Total synthesis of spiruchostatin B aided by an automated synthesizer

The total synthesis of a natural product HDAC inhibitor, spiruchostatin B, was successfully achieved. A 5-step synthesis that included an asymmetric aldol reaction was carried out in an automated synthesizer to provide an (E)-(S)-3-hydroxy-7-thio-4-heptenoic acid segment that is the crucial structure of cysteine-containing, depsipeptidic natural products such as spiruchostatins, FK228, FR901375, and largazole for their inhibitory activity against HDACs.     

Identification of thiols and glutathione conjugates of depsipeptide FK228 (FR901228), a novel histone protein deacetylase inhibitor,in the blood

Four glutathione (GSH) conjugates and two thiols were detected when depsipeptide FK228, formerly FR901228, a naturally occurring potent histone deacetylase (HDAC) inhibitor, was incubated in rat or human plasma in the presence of GSH. Their structures were elucidated by the high-performance liquid chromatography/electrospray ionization multi-stage mass spectrometry (HPLC/ESI-MS(n)) technique, and in some cases confirmed by accurate mass measurement. These products were also detected in rat and human blood homogenates following their incubation with FK228, but were not detected in GSH solution alone. A possible scheme for its formation is proposed. One of the thiols has recently been found to be more active as a histone deacetylase inhibitor than the parent compound.     

Application of stereocontrolled aldol coupling to synthesis of segments of immunosuppressants FK-506 and rapamycin

The sector comprising C24-C34 of FK-506 containing five of the stereogenic centers in this macrolide was synthesized from (−)-quinic acid. Aldol coupling of the C24-C34 unit with a methyl ketone representing C20-C23 of FK-506 proceeded with complete Felkin stereoselectivity to afford the C20-C34 portion of the immunosuppressant. A chelate transition state invoking coordination of a lithium enolate with a trityl ether is proposed to explain this stereoselectivity. The strategy adopted for construction of the C26-C34 moiety of FK-506 was extended to the C34-C42 subunit of rapamycin. A Mukaiyama asymmetric anti-aldol coupling was used to set in place the vicinal diol functionality at C27,28 in the C26-C33 segment of this macrolide.     

Total Synthesis of the Bicyclic Depsipeptide HDAC Inhibitors Spiruchostatins A and B, 5′′‐epi‐Spiruchostatin B,FK228 (FR901228) and Preliminary Evaluation of Their Biological Activity

The bicyclic depsipeptide histone deacetylase (HDAC) inhibitors spiruchostatins A and B, 5′′‐epi‐spiruchostatin B and FK228 were efficiently synthesized in a convergent and unified manner. The synthetic method involved the following crucial steps: i) a Julia–Kocienski olefination of a 1,3‐propanediol‐derived sulfone and a L ‐ or D ‐malic acid‐derived aldehyde to access the most synthetically challenging unit, (3S or 3R,4E)‐3‐hydroxy‐7‐mercaptohept‐4‐enoic acid, present in a D ‐alanine‐ or D ‐valine‐containing segment; ii) a condensation of a D ‐valine‐D ‐cysteine‐ or D ‐allo‐isoleucine‐D ‐cysteine‐containing segment with a D ‐alanine‐ or D ‐valine‐containing segment to directly assemble the corresponding seco‐acids; and iii) a macrocyclization of a seco‐acid using the Shiina method or the Mitsunobu method to construct the requisite 15‐ or 16‐membered macrolactone. The present synthesis has established the C5′′ stereochemistry of spiruchostatin B. In addition, HDAC inhibitory assay and the cell‐growth inhibition analysis of the synthesized depsipeptides determined the order of their potency and revealed some novel aspects of structure–activity relationships. It was also found that unnatural 5′′‐epi‐spiruchostatin B shows extremely high selectivity (ca. 1600‐fold) for class I HDAC1 (IC₅₀=2.4 nM ) over class II HDAC6 (IC₅₀=3900 nM ) with potent cell‐growth‐inhibitory activity at nanomolar levels of IC₅₀ values.     

Total synthesis of spiruchostatin A, a potent histone deacetylase inhibitor

The total synthesis of spiruchostatin A was accomplished, unambiguously confirming its structure. Key steps included the use of the Nagao thiazolidinethione auxiliary for a diastereoselective acetate aldol reaction and as an activated acylating agent for amide formation, and macrolactonization by the Yamaguchi protocol. Spiruchostatin A is shown to have biological activity similar to that of FK228, a potent histone deacetylase (HDAC) inhibitor in clinical trials. The spiruchostatin A analogue, epimeric at the beta-hydroxy acid, is inactive, highlighting the importance of stereochemistry at this position for interactions with HDACs.     

Treatment of the Wastewater of Finishing-and-Dyeing Production Using Polyelectrolyte Flocculants Based on Nitron Fiber Scrap

The performance of FK-1 and FK-3 cationic polyelectrolytes and of new AMF-2 amphoteric polyelectrolyte in treatment of the wastewater of finishing-and-dyeing production was studied as influenced by the concentrations of flocculant and coagulant.     

Limited proteolysis of human histone deacetylase 1

Background  

Histone deacetylase (HDAC) proteins are associated with cell proliferation, differentiation, apoptosis, and cancer. Specifically, HDAC1 is linked with cell growth, a hallmark of cancer formation. HDAC1 is a phosphoprotein and phosphorylation at S421 and S423 promotes HDAC1 enzymatic activity and protein association. While single and double point mutants of HDAC1 at S421 and S423 appear functionally similar, the evidence suggests that HDAC1 is phosphorylated simultaneously at both S421 and S423 in vivo. Additional experiments are necessary to probe the role of double phosphorylation of HDAC1 at S421 and S423.     

Identification of novel HDAC8 selective inhibitors through ligand and structure based studies: Exploiting the acetate release channel differences among class I isoforms

Histone deacetylases (HDACs) are key regulators of gene expression and have emerged as crucial therapeutic targets for cancer. Among the HDACs, inhibition of HDAC8 enzyme has been reported to be a novel strategy in the treatment of female-specific cancers. Most of the HDAC inhibitors discovered so far inhibit multiple HDAC isoforms causing toxicities in the clinic thus limiting their potential. Therefore, the discovery of isoform-selective HDAC8 inhibitors is highly desirable. In the present study, a combination of ligand and structure based drug design tools were utilized to build a statistically significant pharmacophore based 3D QSAR model with statistical parameters R²: 0.9964, and Q²: 0.7154, from a series of 31 known HDAC8 inhibitors. Top 1000 hits obtained from Virtual screening of Phase database were subjected to docking studies against HDAC8. Top 100 hits obtained were redocked into HDAC Class I (HDAC 1,2,3) and Class II isoforms (HDAC 4, 6) and rescored with XP Glide Score. Based on fitness score, XP glide score and interacting amino acid residues, five HDAC8 inhibitors (1–5) were selected for in vitro studies. The HDAC8 activity assay followed by enzyme kinetics clearly indicated Compounds 1, 2 and 3 to be potent HDAC8 selective inhibitors with IC₅₀ of 126 pM, 112 nM, and 442 nM respectively. These compounds were cytotoxic to HeLa cells where HDAC8 is overexpressed but not to normal cells, HEK293. Also, they were able to induce apoptosis by modulating Bax/Bcl2, cleavage of PARP and release of Cytochrome C. Molecular Dynamics simulations observed most favorable interaction patterns and presented a rationale for the activities of the identified compounds. Selectivity against HDAC8 was due to exploitation of the architectural difference in the acetate release channel among class I HDAC isoforms.     

Ring-closing metathesis protocol for a diastereocontrolled preparation of the C28–C34 segment of FK-506

A new synthesis of the C₂₈–C₃₄ segment of FK-506 has been developed using a chiral building block having a 6,8-dioxabicyclo[3.2.1]octane framework by employing a ring-closing metathesis reaction as the key step.     

Switching the Switch: Ligand Induced Disulfide Formation in HDAC8

Human histone deacetylase 8 is a well-recognized target for T-cell lymphoma and particularly childhood neuroblastoma. PD-404,182 was shown to be a selective covalent inhibitor of HDAC8 that forms mixed disulfides with several cysteine residues and is also able to transform thiol groups to thiocyanates. Moreover, HDAC8 was shown to be regulated by a redox switch based on the reversible formation of a disulfide bond between cysteines Cys₁₀₂ and Cys₁₅₃. This study on the distinct effects of PD-404,182 on HDAC8 reveals that this compound induces the dose-dependent formation of intramolecular disulfide bridges. Therefore, the inhibition mechanism of HDAC8 by PD-404,182 involves both, covalent modification of thiols as well as ligand mediated disulfide formation. Moreover, this study provides a deep molecular insight into the regulation mechanism of HDAC8 involving several cysteines with graduated capability to form reversible disulfide bridges.     

Identification of Histone deacetylase (HDAC)‐Associated Proteins with DNA‐Programmed Affinity Labeling

Histone deacetylase (HDAC) is a major class of deacetylation enzymes. Many HDACs exist in large protein complexes in cells and their functions strongly depend on the complex composition. The identification of HDAC‐associated proteins is highly important in understanding their molecular mechanisms. Although affinity probes have been developed to study HDACs, they were mostly targeting the direct binder HDAC, while other proteins in the complex remain underexplored. We report a DNA‐based affinity labeling method capable of presenting different probe configurations without the need for preparing multiple probes. Using one binding probe, 9 probe configurations were created to profile HDAC complexes. Notably, this method identified indirect HDAC binders that may be inaccessible to traditional affinity probes, and it also revealed new biological implications for HDAC‐associated proteins. This study provided a simple and broadly applicable method for characterizing protein‐protein interactions.     

同源模建和分子对接研究HDAC1/HDAC8的选择性

组蛋白去乙酰化酶(HDACs)是近年来治疗肿瘤的重要靶标之一.由于HDACs包含多种亚型,且各亚型的生理功能存在一定的差异,其选择性抑制剂的开发已成为当前的研发热点.我们通过同源模建的HDAC1结构,与已有的HDAC8晶体结构的活性位点进行比较分析,探讨了对两者选择性有重要影响的残基,为基于受体的选择性抑制剂研究提供重要信息.同时选择了52个HDAC抑制剂,分别建立了HDAC1、HDAC8的活性值与对接打分值的线性回归模型.所建的HDAC1和HDAC8的线性构效关系模型的非交叉验证系数R2分别为0.82和0.80,表明具有一定的统计学意义.利用所建模型对已设计合成的化合物进行了预测,预测结果对HDAC1、HDAC8选择性抑制剂的优化改造提供了一定的指导意义.     

Design,synthesis, and biological evaluation of largazole derivatives: alteration of the zinc-binding domain

A new series of largazole analogues in which the side chain was replaced with disulfide groups were synthesized, and their biological activities were evaluated. Compound 8 bearing an octyl moiety showed much better selectivity for HDAC1 over HDAC7 than largazole (320-fold). Structure–activity relationships suggested that the length in the disulfide chain of largazole is important for the selectivity toward HDAC1 over HDAC7.