The effects of histone deacetylase inhibitors on heterochromatin: implications for anticancer therapy?

Histone acetylation regulates many chromosome functions, such as gene expression and chromosome segregation. Histone deacetylase inhibitors (HDACIs) induce growth arrest, differentiation and apoptosis of cancer cells ex vivo, as well as in vivo in tumour-bearing animal models, and are now undergoing clinical trials as anti-tumour agents. However, little attention has been paid to how HDACIs function in these biological settings and why different cells respond in different ways. Here, we discuss the consequences of inhibiting histone deacetylases in cycling versus non-cycling cells, in light of the dynamics of histone acetylation patterns with a specific emphasis on heterochromatic regions of the genome.     

Synthesis of benzimidazole derivatives as potent β-glucuronidase inhibitors

Twenty five 4, 6-dichlorobenzimidazole derivatives (1–25) have been synthesized and evaluated against β-glucuronidase inhibitory activity. The compounds which actively inhibit β-glucuronidase activity have IC₅₀ values ranging between 4.48 and 46.12 μM and showing better than standard d-saccharic acid 1,4 lactone (IC₅₀ = 48.4 ± 1.25 μM). Molecular docking provided potential clues to identify interactions between the active molecules and the enzyme which further led us to identify plausible binding mode of all the benzimidazole derivatives. This study confirmed that presence of hydrophilic moieties is crucial to inhibit the human β-glucuronidase.     

Discovery of noscapine derivatives as potential β-tubulin inhibitors

Twenty novel 1,2,3-triazole noscapine derivatives were synthesized starting from noscapine by consecutive N-demethylation, reduction of lactone ring, N-propargylation and Huisgen 1,3-dipolar cycloaddition reaction. In order to select the most promising molecules to subject to further biophysical and biological evaluation, a molecular docking analysis round was performed using noscapine as reference compound. The molecules featuring docking predicted binding affinity better than that of noscapine were then subjected to MTT assay against MCF7 cell line. The obtained results disclosed that all the selected triazole derivatives exhibited a remarkably lower cell viability compared to noscapine in the range of 20 μM in 48 h. In an attempt to correlate the biological activity with the ability to bind tubulin, the surface plasmon resonance (SPR) assay was employed. Compounds 8a, 8h, 9c, 9f and 9j were able to bind tubulin with affinity constant values in the nanomolar range and higher if compared to noscapine. Integrating computational predictions and experimental evaluation, two promising compounds (8h and 9c) were identified, whose relevant cytotoxicity was supposed to be correlated with tubulin binding affinity. These findings shed lights onto structural modifications of noscapine toward the identification of more potent cytotoxic agents targeting tubulin.     

Thiadiazole derivatives as New Class of β-glucuronidase inhibitors

Thiadiazole derivatives 1–24 were synthesized via a single step reaction and screened for in vitro β-glucuronidase inhibitory activity. All the synthetic compounds displayed good inhibitory activity in the range of IC₅₀ = 2.16 ± 0.01–58.06 ± 1.60 μM as compare to standard d-saccharic acid 1,4-lactone (IC₅₀ = 48.4 ± 1.25 μM). Molecular docking study was conducted in order to establish the structure–activity relationship (SAR) which demonstrated that thiadiazole as well as both aryl moieties (aryl and N-aryl) involved to exhibit the inhibitory potential. All the synthetic compounds were characterized by spectroscopic techniques ¹H, ¹³C NMR, and EIMS.     

Synthesis and evaluation of β-carboline derivatives as inhibitors of human immunodeficiency virus

A series of β-carboline derivatives were synthesized by utilizing aromatization and chemoselective alkylation method recently reported from our laboratory. Synthesized derivatives were evaluated for anti-HIV activity in human CD4+ T cell line (CEM-GFP) infected with HIV-1 NL_4.3 virus. 1-Formyl-β-carboline-3-carbxylic acid methyl ester (15) showed inhibition of human immunodeficiency virus at IC₅₀ = 2.9 μM.     

Synthesis and evaluation of β-carboline derivatives as potential monoamine oxidase inhibitors

Previous studies have shown that harmine is a reversible inhibitor of human monoamine oxidase A (MAO-A). Moreover, the crystal structure of human MAO-A in complex with harmine has been recently solved. This crystal structure shows that close to the methoxy group of the harmine moiety, a lipophilic pocket is left vacant within the binding site of human MAO-A. Our objective was to optimize the ??-carboline series against human MAO-A in order to explore this pocket. Therefore, a series of ??-carboline derivatives has been synthesized. The compounds were evaluated for their human monoamine oxidase A and B inhibitory potency and their K_i values were estimated. The results show that O-alkylated compounds with lipophilic groups like cyclohexyl, phenyl and aliphatic chains increase the inhibition of MAO-A compared to harmine. Compound 3e, with the trifluorobutyloxy group, was the most active of this series, with a K_i against MAO-A of 3.6 nM. Molecular docking studies show that the trifluorobutyloxy chain occupies the hydrophobic pocket vacant with harmine. The O-alkylated compounds are less active on MAO-B than on MAO-A. However, several compounds show a better inhibition on MAO-B compared to harmine. Compound 3f, with the cyclohexylmethoxy chain, displayed the best inhibitory activity against MAO-B with a K_i value of 221.6 nM. This cyclohexyl bearing analogue is also a potent MAO-A inhibitor with a K_i value of 4.3 nM. Molecular docking studies show that the cyclohexyl chain also occupies a hydrophobic pocket but in different ways in MAO-A or MAO-B.     

Novel β-dicarbonyl derivatives as inhibitors of aminopeptidase N (APN)

Most zinc metalloproteases are over-expressed in tumor cells and play a critical role in the genesis, development, and metastasis of tumors. Novel zinc binding groups (ZBGs) represent a novel strategy to obtain optimal potency and selectivity for zinc metalloproteases inhibitors. Here we described the design, synthesis, and biological studies of novel β-dicarbonyl derivatives as aminopeptidase N (APN/CD13) inhibitors. The results demonstrated that some compounds exhibited moderate to good inhibitory activities against APN with compound 5c being the most potent, suggesting that 5c could serve as new lead for the future APN inhibitor development. The results further confirm our design rationale of β-dicarbonyl moiety as a new ZBG, which may provide a new direction for the design and discovery of zinc metalloproteases inhibitors as new anti-tumor agents.     

Steric structure–activity relationship of cyproheptadine derivatives as inhibitors of histone methyltransferase Set7/9

Set7/9 is a histone lysine methyltransferase, but it is also thought to be involved in a wide variety of pathophysiological functions. We previously identified cyproheptadine, which has a characteristic butterfly-like molecular conformation with bent tricyclic dibenzosuberene and chair-form N-methylpiperidine moieties, as a Set7/9 inhibitor. In this work, we synthesized several derivatives in order to examine the steric structure–inhibitory activity relationship. We found that even a small change of molecular shape due to reduction or replacement of the 10,11-olefinic bond of the tricyclic ring generally resulted in a drastic decrease of the inhibitory activity. Our results should be useful not only for development of more potent and selective inhibitors, but also for the construction of novel inhibitor scaffolds.     

Synthesis and structure–activity relationship of thiobarbituric acid derivatives as potent inhibitors of urease

A series of thiobarbituric acid derivatives 1–27 were synthesized and evaluated for their urease inhibitory potential. Exciting results were obtained from the screening of these compounds 1–27. Compounds 5, 7, 8, 11, 16, 17, 22, 23 and 24 showed excellent urease inhibition with IC₅₀ values 18.1 ± 0.52, 16.0 ± 0.45, 16.0 ± 0.22, 14.3 ± 0.27, 6.7 ± 0.27, 10.6 ± 0.17, 19.2 ± 0.29, 18.2 ± 0.76 and 1.61 ± 0.18 μM, respectively, much better than the standard urease inhibitor thiourea (IC₅₀ = 21 ± 0.11 μM). Compound 3, 4, 10, and 26 exhibited comparable activities to the standard with IC₅₀ values 21.4 ± 1.04 and 21.5 ± 0.61μM, 22.8 ± 0.32, 25.2 ± 0.63, respectively. However the remaining compounds also showed prominent inhibitory potential The structure–activity relationship was established for these compounds. This study identified a novel class of urease inhibitors. The structures of all compounds were confirmed through spectroscopic techniques such as EI-MS and ¹H NMR.     

Synthesis and biological evaluation of caffeic acid derivatives as potent inhibitors of α-MSH-stimulated melanogenesis

We have disclosed our effort to develop caffeic acid derivatives as potent and non-toxic inhibitors of α-MSH-stimulated melanogenesis to treat pigmentation disorders and skin medication including a cosmetic skin-whitening agent. The SAR studies revealed that cyclohexyl ester and secondary amide derivatives of caffeic acid showed significant inhibitory activities.     

Design and synthesis of novel β-diketo derivatives as HIV-1 integrase inhibitors

A series of novel β-diketo derivatives which combined the virtues of 1,3-diketo, 1,2,3-triazole and polyhydroxylated aromatics moieties, were designed and synthesized as potential HIV-1 integrase (IN) inhibitors and evaluated their inhibition to the strand transfer process of HIV-1 integrase. The result indicates that 3,4,5-trihydroxylated aromatic derivatives exhibit good inhibition to HIV-1 integrase, but dihydroxylated aromatic derivatives and corresponding methoxy aromatic derivatives appear little inhibition to HIV-1 integrase.     

Design,synthesis and biological evaluation of novel tripeptidyl epoxyketone derivatives constructed from β-amino acid as proteasome inhibitors

A series of novel tripeptidyl epoxyketone derivatives constructed from β-amino acid were designed, synthesized and evaluated as proteasome inhibitors. All target compounds were tested for their proteasome inhibitory activities and selected compounds were tested for their anti-proliferation activities against two multiple myeloma (MM) cell lines RPMI 8226 and NCI-H929. Among them, eleven compounds exhibited proteasome inhibitory rates of more than 50% at the concentration of 1 μg/mL and nine compounds showed anti-proliferation activities with IC₅₀ values at low micromolar level. Compound 20h displayed the most potent proteasome inhibitory activities (IC₅₀: 0.11 ± 0.01 μM) and anti-proliferation activities with IC₅₀ values at 0.23 ± 0.01 and 0.17 ± 0.02 μM against two tested cell lines. Additionally, the poly-ubiquitin accumulation in the western blot analysis supported that proteasome inhibition in a cellular system was induced by compound 20h. All these experimental results confirmed that β-amino acid can be introduced as a building block for the development of proteasome inhibitors.     

Exercise-induced oxidative stress: the effects of β-alanine supplementation in women

The purpose of this study was to evaluate the effects of β-alanine supplementation on markers of oxidative stress. Twenty-four women (age: 21.7±2.1 years; VO2max: 2.6±0.3 l min(-1)) were randomly assigned, in a double-blind fashion, to a β-alanine (BA, 2×800 mg tablets, 3× daily; CarnoSyn?; n=13) or placebo (PL, 2×800 mg maltodextrin tablets, 3× daily; n=11) group. A graded oxygen consumption test (VO2max) was performed to evaluate VO2max, time to exhaustion, ventilatory threshold and establish peak velocity (PV). A 40-min treadmill run was used to induce oxidative stress. Total antioxidant capacity, superoxide dismutase, 8-isoprostane (8ISO) and reduced glutathione were measured. Heart rate and ratings of perceived exertion were recorded during the 40 min run. Separate three- [4×2×2; acute (base vs. IP vs. 2 vs. 4 h)×chronic (pre- vs. post-)×treatment (BA vs. PL)] and two- [2×2; time (pre-supplement vs. post-supplement)×treatment (BA vs. PL)] way ANOVAs were used for analyses. There was a significant increase in VO2max (p=0.009), independent of treatment, with no significant changes in TTE (p=0.074) or VT (p=0.344). Ratings of perceived exertion values were significantly improved from pre- to post-supplementation for the BA group only at 40 min (p=0.02). The ANOVA model demonstrated no significant treatment effects on oxidative stress. The chronic effects of BA supplementation demonstrated little antioxidant potential, in women, and little influence on aerobic performance assessments.     

Preparation of triazole-linked glycosylated α-ketocarboxylic acid derivatives as new PTP1B inhibitors

The synthesis of triazole-linked glycosyl acetophenone, benzoic acid, and α-ketocarboxylic acid derivatives was readily achieved via Cu(I)-catalyzed azide–alkyne cycloaddition (‘click’ reaction) in excellent yields of 93–97%. Among the synthesized glycoconjugates, the triazolyl α-ketocarboxylic acids were identified as the most potent protein tyrosine phosphatase 1B (PTP1B) inhibitors with micromole-ranged IC₅₀ values and moderate-to-good selectivity over a panel of homologous PTPs including TCPTP (4.6-fold), LAR (>30-fold), SHP-1 (>30-fold) and SHP-2 (>30-fold). Moreover, a docking simulation was conducted to propose a plausible binding mode of the glucosyl α-ketocarboxylic acid triazole with the enzymatic target.     

Phenoxypropanolamine derivatives as selective inhibitors of the 20S proteasome β1 and β5 subunits

New series of thiophene-containing phenoxypropanolamines were synthesized and evaluated for their potency to inhibit the three proteolytic activities of the mammalian 20S proteasome. Noticeable inhibition of both ChT-L and PA activities was obtained with three compounds: one with unsubstituted phenoxypropanolamine group (7) and the two others with a p-Cl-substituted group (4 and 9). For three other compounds (3, 8 and 10), ChT-L activity alone was significantly inhibited. In silico docking performed on the β5 and β1 subunits bearing the respective ChT-L and PA catalytic sites showed features common to poses associated with active compounds. These features may constitute a selectivity criterion for structure-guided inhibitor design.     

Structure–activity relationship of boronic acid derivatives of tyropeptin: Proteasome inhibitors

The structure–activity relationship of the boronic acid derivatives of tyropeptin, a proteasome inhibitor, was studied. Based on the structure of a previously reported boronate analog of tyropeptin (2), 41 derivatives, which have varying substructure at the N-terminal acyl moiety and P2 position, were synthesized. Among them, 3-phenoxyphenylacetamide 6 and 3-fluoro picolinamide 22 displayed the most potent inhibitory activity toward chymotryptic activity of proteasome and cytotoxicity, respectively. The replacement of the isopropyl group in the P2 side chain to H or Me had negligible effects on the biological activities examined in this study.     

Structure–activity relationship investigation of tertiary amine derivatives of cinnamic acid as acetylcholinesterase and butyrylcholinesterase inhibitors: compared with that of phenylpropionic acid,sorbic acid and hexanoic acid

In the present investigation, 48 new tertiary amine derivatives of cinnamic acid, phenylpropionic acid, sorbic acid and hexanoic acid (4d–6g, 10d–12g, 16d–18g and 22d–24g) were designed, synthesized and evaluated for the effect on AChE and BChE in vitro. The results revealed that the alteration of aminoalkyl types and substituted positions markedly influences the effects in inhibiting AChE. Almost of all cinnamic acid derivatives had the most potent inhibitory activity than that of other acid derivatives with the same aminoalkyl side chain. Unsaturated bond and benzene ring in cinnamic acid scaffold seems important for the inhibitory activity against AChE. Among them, compound 6g revealed the most potent AChE inhibitory activity (IC₅₀ value: 3.64?µmol/L) and highest selectivity over BChE (ratio: 28.6). Enzyme kinetic study showed that it present a mixed-type inhibition against AChE. The molecular docking study suggested that it can bind with the catalytic site and peripheral site of AChE.     

Discovery of β-aminoacyl containing thiazolidine derivatives as potent and selective dipeptidyl peptidase IV inhibitors

A series of β-aminoacyl containing thiazolidine derivatives was synthesized and evaluated for their ability to inhibit DPP-IV. Several thiazolidine derivatives with an acid moiety were found to be potent DPP-IV inhibitors. Among them, compound 2da is the most active in this series with an IC₅₀ value of 1 nM, and it showed excellent selectivity over DPP-IV related enzymes including DPP-2, DPP-8, and DPP-9. Compound 2da is chemically and metabolically stable, and showed no CYP inhibition, hERG binding or cytotoxicity. Compound 2db, an ester prodrug of 2da, showed good in vivo DPP-IV inhibition after oral administration in rat and dog models.     

Synthesis of oxadiazole-coupled-thiadiazole derivatives as a potent β-glucuronidase inhibitors and their molecular docking study

A new series of oxadiazole with thiadiazole moiety (6–27) were synthesized, characterized by different spectroscopic techniques and evaluated for β-glucuronidase inhibitory potential. Sixteen analogs such as 6, 7, 8, 9, 10, 12, 13, 14, 17, 18, 20, 23, 24, 25, 26 and 27 showed IC₅₀ values in the range of 0.96 ± 0.01 to 46.46 ± 1.10 μM, and hence were found to have excellent inhibitory potential in comparison to standard d-saccharic acid 1,4-lactone (IC₅₀ = 48.4 ± 1.25 μM). Two analogs such as 16 and 19 showed moderate inhibitory potential while analogs 11, 15, 21 and 22 were found inactive. Our study identifies new series of potent β-glucuronidase inhibitors for further investigation. Structure activity relationships were established for all compounds which showed that the activity is varied due to different substituents on benzene ring. The interaction of the compounds with enzyme active site were confirmed with the help of docking studies, which reveals that the electron withdrawing group and hydroxy group make the molecules more favorable for enzyme inhibition.