Synthesis ofN-Hydroxycinnamides Capped with a Naturally Occurring Moiety as Inhibitors of Histone Deacetylase

Molecular Diversity and Biochemical Content in Two Invasive Alien Species: Looking for Chemical Similarities and Bioactivities

The biochemical composition, molecular diversity, and two different bioactivities of Asparagopsis armata and Rugulopteryx okamurae (two alien species with different invasive patterns in the southern Iberian Peninsula) were analyzed through spectrophotometric methods and Fourier transform ion cyclotron mass spectroscopy (FT-ICR-MS). A total of 3042 molecular formulas were identified from the different extracts. The dH2O extracts were the most molecularly different. A. armata presented the highest content of nitrogenous compounds (proteins, CHON) and sulphur content, whereas R. okamurae was rich in carbonated compounds (total carbon, lipids, CHO, and CHOP). Antioxidant capacity and phenolic content were higher in R. okamurae than in A. armata. Antimicrobial activity was detected from both species. A. armata showed capacity to inhibit human and fish pathogens (e.g., Staphylococcus aureus or Vibrio anguillarum), whereas R. okamurae only showed inhibition against human bacteria (Staphylococcus aureus and Cutibacterium acnes). In R. okamurae, molecules with a great number of pharmaceutical activities (e.g., anti-inflammatory or antitumoral), antibacterial, biomaterial, and other utilities were found. The main molecules of A. armata had also pharmaceutical applications (e.g., antimalarian, antithrombotic, anti-inflammatory, or antiarthritis). The valorization of these species can help to counteract the environmental effects of the bioinvasions.

Osthole: Synthesis, Structural Modifications and Biological Properties

Abstract:

Osthole, a naturally occurring coumarin-type compound, is isolated from a Chinese herbal medicine Cnidium monnieri (L.), and exhibits a broad range of biological properties. In this review, the total synthesis and structural modifications of osthole and its analogs are described. Additionally, the progress on bioactivities of osthole and its analogs is outlined since 2016. Moreover, the structure-activity relationships and mechanisms of action of osthole and its derivatives are discussed. These can provide references for future design, development and application of osthole and its analogs as drugs or pesticides in the fields of medicine and agriculture.

From natural products to HDAC inhibitors: An overview of drug discovery and design strategy

Histone deacetylases (HDACs) play a key role in the homeostasis of protein acetylation in histones and have recently emerged as a therapeutic target for numerous diseases. The inhibition of HDACs may block angiogenesis, arrest cell growth, and lead to differentiation and apoptosis in tumour cells. Thus, HDAC inhibitors (HDACi) have received increasing attention and many of which are developed from natural sources. In the past few decades, naturally occurring HDACi have been identified to have potent anticancer activities, some of which have demonstrated promising therapeutic effects on haematological malignancies. In this review, we summarized the discovery and modification of HDAC inhibitors from natural sources, novel drug design that uses natural products as parent nuclei, and dual target design strategies that combine HDAC with non-HDAC targets.

Osthole: an overview of its sources, biological activities, and modification development

Osthole, also known as osthol, is a coumarin derivative found in several medicinal plants such as Cnidium monnieri and Angelica pubescens. It can be obtained via extraction and separation from plants or total synthesis. Plenty of experiments have suggested that osthole exhibited multiple biological activities covering antitumor, anti-inflammatory, neuroprotective, osteogenic, cardiovascular protective, antimicrobial, and antiparasitic activities. In addition, there has been some research done on the optimization and modification of osthole. This article summarizes the comprehensive information regarding the sources and modification progress of osthole. It also introduces the up-to-date biological activities of osthole, which could be of great value for its use in future research.

Exploring novel capping framework: high substituent pyridine-hydroxamic acid derivatives as potential antiproliferative agents

PURPOSE

Histone deacetylases (HDACs) play a vital role in the epigenetic regulation of gene expression due to their overexpression in several cancer forms. Therefore, these enzymes are considered as a potential anticancer drug target. Different synthetic and natural structures have been studied as HDACs inhibitors; based on available structural design information, the capping group is important for the biological activity due to the different interactions in the active site entrance. The present study aimed to analyze high substituted pyridine as a capping group, which included carrying out the synthesis, antiproliferative activity analysis, and docking studies of these novel compounds.

METHODS

To achieve the synthesis of these derivatives, four reaction steps were performed, generating desired products 15a-k. Their effects on cell proliferation and gene expression of p21, cyclin D1, and p53 were determined using the sulphorhodamine B (SRB) method and quantitative real-time polymerase chain reaction. The HDAC1, HDAC6, and HDAC8 isoforms were used for performing docking experiments with our 15a-k products.

RESULT

The products 15a-k were obtained in overall yields of 40-71%. Compounds 15j and 15k showed the highest antiproliferative activity in the breast (BT-474 and MDA-MB-231) and prostate (PC3) cancer cell lines at a concentration of 10 µM. These compounds increased p21 mRNA levels and decreased cyclin D1 and p53 gene expression. The docking study showed an increment in the strength, and in the number of interactions performed by the capping moiety of the tested molecules compared with SAHA; interactions displayed are mainly van der Waals, π-stacking, and hydrogen bond.

CONCLUSION

The synthesized compounds 2-thiophene (15j) and 2-furan (15k) pyridine displayed cell growth inhibition, regulation of genes related to cell cycle progression in highly metastatic cancer cell lines. The molecular coupling analysis performed with HDAC1, HDAC6 and HDAC8 showed an increment in the number of interactions performed by the capping moiety and consequently in the strength of the capping group interaction.

Regioselective hemisynthesis and insecticidal activity of C8-hydrazones/acylhydrazones/sulfonylhydrazones coumarin-type derivatives of osthole

Osthole, a coumarin-type natural product, is isolated from Chinese traditional herbal medicine Cnidium monnieri. In order to improve the pesticidal activity of osthole, and high value-added application of the plant Cnidium monnieri, a series of new derivatives containing hydrazone/acylhydrazone/sulfonylhydrazone skeletons at the C-8 position of osthole were regioselectively semi-prepared. The steric structure of 3c was determined by the X-ray crystal structure. Against Mythimna separata Walker, benzoylhydrazone 3b (R¹ = 4-CH₃Ph) showed 1.6 folds potent insecticidal activity of the precursor osthole. Introduction of the acylhydrazones on the 3'-methyl-2'-butylenyl fragment at the C-8 position of osthole can improve the insecticidal activity. These will provide a foundation for future structural modifications of osthole as pesticidal agents.

Strategies To Design Selective Histone Deacetylase Inhibitors

This review classifies drug-design strategies successfully implemented in the development of histone deacetylase (HDAC) inhibitors, which have many applications including cancer treatment. Our focus is on especially demanded selective HDAC inhibitors and their structure-activity relationships in relation to corresponding protein structures. The main part of the paper is divided into six subsections each narrating how optimization of one of six structural features can influence inhibitor selectivity. It starts with the impact of the zinc binding group on selectivity, continues with the optimization of the linker placed in the substrate binding tunnel as well as the adjustment of the cap group interacting with the surface of the protein, and ends with the addition of groups targeting class-specific sub-pockets: the side-pocket-, lower-pocket- and foot-pocket-targeting groups. The review is rounded off with a conclusion and an outlook on the future of HDAC inhibitor design.

Osthole extracted from a citrus fruit that affects apoptosis on A549 cell line by histone deacetylasese inhibition (HDACs)

This study aims to investigate the interactions between osthole extracted from Egyptian citrus fruits as HDACs inhibitor by theoretical study and practically. Besides, osthole was assed as anti-cancer activity. In this study, osthole was extracted from the Egyptian citrus fruit and was characterized. The role of osthole as in vitro inhibitor of HDACs was estimated and evaluated the antitumor activity against human lung cancer cells (A549), Caspase-9 activity was detected. The results obtained from GC-MS indicate that the grapefruit showed the highest osthole concentration compared to the other citrus fruits. Moreover, the grapefruit osthole competitively inhibits HDACs. The inhibition constant value, (Ki=3.36 mM), indicates that osthole exerts an inhibitory effect upon HDACs activity. In vitro study of osthole could inhibit the growth of A549 cells that depend on time and concentration. It also induces apoptosis and causes an increase of caspase-9 by osthole. In conclusion, grapefruit osthole could induce the apoptosis in A549 lung cancer cells by inhibiting the histone deacetylase.

Bioactivity and Molecular Docking Studies of Derivatives from Cinnamic and Benzoic Acids

Over the last decade, there has been a dramatic increase in the prevalence and gravity of systemic fungal diseases. This study aimed therefore at evaluating the antifungal potential of ester derivatives of benzoic and cinnamic acids from three Candida species. The compounds were prepared via Fischer esterification, and the antifungal assay was performed by the microdilution method in 96-well microplates for determining the minimal inhibitory concentrations (MICs). The findings of the antifungal tests revealed that the analogue compound methyl ferulate, methyl o-coumarate, and methyl biphenyl-3-carboxylate displayed an interesting antifungal activity against all Candida strains tested, with MIC values of 31.25-62.5, 62.5-125, and 62.5 μg/ml, respectively. A preliminary Structure-Activity Relationship study of benzoic and cinnamic acid derivatives has led to the recognition of some important structural requirements for antifungal activity. The results of molecular docking indicate that the presence of the enoate moiety along with hydroxyl and one methoxy substitution in the phenyl ring has a positive effect on the bioactivity of compound 7 against Candida albicans. These observations further support the hypothesis that the antifungal activity of compound 7 could be due to its binding to multiple targets, specifically to QR, TS, and ST-PK. Additional experiments are required in the future to test this hypothesis and to propose novel compounds with improved antifungal activity.

Synthesis and Antioxidant Activity of Caffeic Acid Derivatives

A series of caffeic acid derivatives were synthesized via a modified Wittig reaction which is a very important tool in organic chemistry for the construction of unsaturated carbon⁻carbon bonds. All reactions were performed in water medium at 90 °C. The aqueous Wittig reaction worked best when one unprotected hydroxyl group was present in the phenyl ring. The olefinations in the aqueous conditions were also conducted with good yields in the presence of two unprotected hydroxyl groups. When the number of the hydroxyl groups was increased to three, the reaction yields were worse, and the derivatives 12, 13, and 18 were obtained with 74%, 37%, and 70% yields, respectively. Nevertheless, the Wittig reaction using water as the essential medium is an elegant one-pot synthesis and a greener method, which can be a safe alternative for implementation in organic chemistry. The obtained compounds were tested for their antioxidant activity, and 12, 13, and 18 showed the highest activities. Moreover, all synthesized compounds displayed no cytotoxicity, and can therefore be used in the pharmaceutical or cosmetic industry.

Derivatives of 6-cinnamamido-quinoline-4-carboxamide impair lysosome function and induce apoptosis

Autophagy is a lysosomal degradative process that protects cancer cells from multiple types of stress. In this study, we synthesized a series of derivatives of 6-cinnamamido-quinoline-4-carboxamide (CiQ), and investigated their effects on the proliferation and autophagy of cancer cells in vitro. These derivatives effectively inhibited the proliferation of a broad spectrum of cancer cell lines. Further study revealed that CiQ derivatives may induce autophagy and result in disruption of autophagy propagation. Consequently, these derivatives triggered massive apoptosis, as evidenced by caspase-9 activation and PARP cleavage. Blockage of autophagy by depletion of autophagy related gene ATG5 or BECN1 considerably alleviated CiQ-induced cell death, indicating that autophagy may mediate CiQ-induced cell death. Furthermore, treatment with CiQ derivatives increased lysosome membrane permeability (LMP) and enhanced accumulation of ubiquitinated proteins, which collectively indicate impaired lysosome function. In addition, treatment of cells with CiQ derivatives activated extracellular signal-regulated kinase (ERK); abrogation of ERK activation, either by treating cells with U0126, an inhibitor of mitogen-activated protein/ERK kinase 1 (MEK1), or by ectopically overexpressing a dominant-negative MEK1, significantly reduced CiQ derivative-induced LMP, LC3 and p62 accumulation, and cytotoxicity. These results indicate that CiQ derivatives activate ERK and disrupt lysosome function, thereby altering autophagic flux and resulting in apoptotic cell death.

Structure–activity relationships of hydroxamate-based histone deacetylase-8 inhibitors: reality behind anticancer drug discovery

The pan-histone deacetylase (HDAC) inhibitors comprise a fish-like structural orientation where hydrophobic aryl- and zinc-binding groups act as head and tail, respectively of a fish. The linker moiety correlates the body of the fish linking head and tail groups. Despite these pan-HDAC inhibitors, selective HDAC-8 inhibitors are still in demand as a safe remedy. HDAC-8 is involved in invasion and metastasis in cancer. This review deals with the rationale behind HDAC-8 inhibitory activity and selectivity along with detailed structure–activity relationships of diverse hydroxamate-based HDAC-8 inhibitors. HDAC-8 inhibitory potency may be increased by modifying the fish-like pharmacophoric features of such type of pan-HDAC inhibitors. This review may provide a preliminary basis to design and optimize new lead molecules with higher HDAC-8 inhibitory activity. This work may surely enlighten in providing useful information in the field of target-specific anticancer therapy.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.

Natural Agents-Mediated Targeting of Histone Deacetylases

In the past few years, basic and clinical scientists have witnessed landmark achievements in many research projects, such as those conducted by the US National Institutes of Health Roadmap Epigenomics Mapping Consortium, the International Human Epigenome Consortium, The Cancer Genome Atlas Network and the International Cancer Genome Consortium, which have provided near-complete resolution of epigenetic landscape in different diseases. Furthermore, genome sequencing of tumors has provided compelling evidence related to frequent existence of mutations in readers, erasers and writers of epigenome in different cancers. Histone acetylation is an intricate mechanism modulated by two opposing sets of enzymes and deeply studied as a key biological phenomenon in 1964 by Vincent Allfrey and colleagues. The research group suggested that this protein modification contributed substantially in transcriptional regulation. Subsequently, histone deacetylases (HDACs), histone acetyltransferases and acetyl-Lys-binding proteins were identified as transcriptional mediators, which further deepened our comprehension regarding biochemical modifications. Overwhelmingly increasing high-impact research is improving our understanding of this molecularly controlled mechanism; moreover, quantification and identification of lysine acetylation by mass spectrometry has added new layers of information. We partition this multi-component review into how both activity and expression of HDAC are targeted using natural agents. We also set spotlight on how oncogenic fusion proteins tactfully utilize HDAC-associated nano-machinery to modulate expression of different genes and how HDAC inhibitors regulate TRAIL-induced apoptosis in cancer cells. HDAC inhibitors have been reported to upregulate expression of TRAIL receptors and protect TRAIL from proteasomal degradation. Deeper understanding of HDAC biology will be useful for stratification and selection of patients who are responders, non-responders and poor-responders for HDACi therapy, and for the rational design of combination studies using HDACi.

Osthole improves function of periodontitis periodontal ligament stem cells via epigenetic modification in cell sheets engineering

Inflammatory microenvironment causes the change of epigenetic modification in periodontal ligament stem cells derived from periodontitis tissues (P-PDLSCs), which results in defective osteogenic differentiation compared to cells from healthy tissues. It’s urgent to explore therapeutic strategies aimed at epigenetic targets associated with the regenerative ability of PDLSCs. Osthole, a small-molecule compound extracted from Chinese herbs, has been documented to promote osteogenesis and cell sheets formation of healthy PDLSCs. However, whether osthole shows same effect on P-PDLSCs and the mechanism of promotive effect is still unknown. The purpose of this study was to determine whether Osthole could restore defective osteogenic differentiation of P-PDLSCs via epigenetic modification. We demonstrated that 10⁻⁷ Mol/L of Osthole was the best concentration for osteogenic differentiation and proliferation of P-PDLSCs. Mechanistically, we also found that Osthole upregulated MOZ and MORF, histone acetylases that specifically catalyze acetylation of Histone3 lisine9 (H3K9) and Histone3 lisine14 (H3K14), which are key regulators in osteogenic differentiation of P-PDLSCs. Furthermore, Osthole treatment improved cell sheet formation and enhanced the bone formation of PDLSC sheets in animal models of periodontitis. Our study suggests that Osthole is a promising drug to cure periodontitis via regulating epigenetic modification in cell sheets engineering.

Inside HDACs with more selective HDAC inhibitors

Inhibitors of histone deacetylases (HDACs) are nowadays part of the therapeutic arsenal mainly against cancers, with four compounds approved by the Food and Drug Administration. During the last five years, several groups have made continuous efforts to improve this class of compounds, designing more selective compounds or compounds with multiple capacities. After a survey of the HDAC biology and structures, this review summarizes the results of the chemists working in this field, and highlights when possible the behavior of the molecules inside their targets.

Osthole: A Review on Its Bioactivities, Pharmacological Properties, and Potential as Alternative Medicine

This paper reviews the latest understanding of biological and pharmacological properties of osthole (7-methoxy-8-(3-methyl-2-butenyl)-2H-1-benzopyran-2-one), a natural product found in several medicinal plants such as Cnidium monnieri and Angelica pubescens. In vitro and in vivo experimental results have revealed that osthole demonstrates multiple pharmacological actions including neuroprotective, osteogenic, immunomodulatory, anticancer, hepatoprotective, cardiovascular protective, and antimicrobial activities. In addition, pharmacokinetic studies showed osthole uptake and utilization are fast and efficient in body. Moreover, the mechanisms of multiple pharmacological activities of osthole are very likely related to the modulatory effect on cyclic adenosine monophosphate (cAMP) and cyclic adenosine monophosphate (cGMP) level, though some mechanisms remain unclear. This review aims to summarize the pharmacological properties of osthole and give an overview of the underlying mechanisms, which showcase its potential as a multitarget alternative medicine.

Cinnamamide Derivatives for Central and Peripheral Nervous System Disorders--A Review of Structure-Activity Relationships

The cinnamamide scaffold has been incorporated in to the structure of numerous organic compounds with therapeutic potential. The scaffold enables multiple interactions, such as hydrophobic, dipolar, and hydrogen bonding, with important molecular targets. Additionally, the scaffold has multiple substitution options providing the opportunity to optimize and modify the pharmacological activity of the derivatives. In particular, cinnamamide derivatives have exhibited therapeutic potential in animal models of both central and peripheral nervous system disorders. Some have undergone clinical trials and were introduced on to the pharmaceutical market. The diverse activities observed in the nervous system included anticonvulsant, antidepressant, neuroprotective, analgesic, anti-inflammatory, muscle relaxant, and sedative properties. Over the last decade, research has focused on the molecular mechanisms of action of these derivatives, and the data reported in the literature include targeting the γ-aminobutyric acid type A (GABAA ) receptors, N-methyl-D-aspartate (NMDA) receptors, transient receptor potential (TRP) cation channels, voltage-gated potassium channels, histone deacetylases (HDACs), prostanoid receptors, opioid receptors, and histamine H3 receptors. Here, the literature data from reports evaluating cinnamic acid amide derivatives for activity in target-based or phenotypic assays, both in vivo and in vitro, relevant to disorders of the central and peripheral nervous systems are analyzed and structure-activity relationships discussed.

N-hydroxycinnamide derivatives of osthole ameliorate hyperglycemia through activation of AMPK and p38 MAPK

Our previous studies found that osthole markedly reduced blood glucose levels in both db/db and ob/ob mice. To improve the antidiabetic activity of osthole, a series of N-hydroxycinnamide derivatives of osthole were synthesized, and their hypoglycemia activities were examined in vitro and in vivo. Both N-hydroxycinnamide derivatives of osthole, OHC-4p and OHC-2m, had the greatest potential for activating AMPK and increasing glucose uptake by L6 skeletal muscle cells. In addition, OHC-4p and OHC-2m time- and dose-dependently increased phosphorylation levels of AMPK and p38 MAPK. The AMPK inhibitor, compound C, and the p38 MAPK inhibitor, SB203580, significantly reversed activation of AMPK and p38 MAPK, respectively, in OHC-4p- and OHC-2m-treated cells. Compound C and SB203580 also inhibited glucose uptake induced by OHC-4p and OHC-2m. Next, we found that OHC-4p and OHC-2m significantly increased glucose transporter 4 (GLUT4) translocation to plasma membranes and counteracted hyperglycemia in mice with streptozotocin-induced diabetes. These results suggest that activation of AMPK and p38 MAPK by OHC-4p and OHC-2m is associated with increased glucose uptake and GLUT4 translocation and subsequently led to amelioration of hyperglycemia. Therefore, OHC-4p and OHC-2m might have potential as antidiabetic agents for treating type 2 diabetes. Our previous studies found that osthole markedly reduced blood glucose levels in both db/db and ob/ob mice. To improve the antidiabetic activity of osthole, a series of N-hydroxycinnamide derivatives of osthole were synthesized, and their hypoglycemia activities were examined in vitro and in vivo. Both N-hydroxycinnamide derivatives of osthole, OHC-4p and OHC-2m, had the greatest potential for activating AMPK and increasing glucose uptake by L6 skeletal muscle cells. In addition, OHC-4p and OHC-2m time- and dose-dependently increased phosphorylation levels of AMPK and p38 MAPK. The AMPK inhibitor, compound C, and the p38 MAPK inhibitor, SB203580, significantly reversed activation of AMPK and p38 MAPK, respectively, in OHC-4p- and OHC-2m-treated cells. Compound C and SB203580 also inhibited glucose uptake induced by OHC-4p and OHC-2m. Next, we found that OHC-4p and OHC-2m significantly increased glucose transporter 4 (GLUT4) translocation to plasma membranes and counteracted hyperglycemia in mice with streptozotocin-induced diabetes. These results suggest that activation of AMPK and p38 MAPK by OHC-4p and OHC-2m is associated with increased glucose uptake and GLUT4 translocation and subsequently led to amelioration of hyperglycemia. Therefore, OHC-4p and OHC-2m might have potential as antidiabetic agents for treating type 2 diabetes.

NBM-T-L-BMX-OS01, Semisynthesized from Osthole, Is a Novel Inhibitor of Histone Deacetylase and Enhances Learning and Memory in Rats

NBM-T-L-BMX-OS01 (BMX) was derived from the semisynthesis of osthole, isolated from Cnidium monnieri (L.) Cuss., and was identified to be a potent inhibitor of HDAC8. This study shows that HDAC8 is highly expressed in the pancreas and the brain. The function of HDAC8 in the brain has not been adequately studied. Because BMX enhances neurite outgrowth and cAMP response element-binding protein (CREB) activation, the effect of BMX on neural plasticity such as learning and memory is examined. To examine declarative and nondeclarative memory, a water maze, a passive one-way avoidance task, and a novel object recognition task were performed. Results from the water maze revealed that BMX and suberoylanilide-hydroxamic-acid-(SAHA-) treated rats showed shorter escape latency in finding the hidden platform. The BMX-treated animals spent more time in the target quadrant in the probe trial performance. An analysis of the passive one-way avoidance results showed that the BMX-treated animals stayed longer in the illuminated chamber by 1 day and 7 days after footshock. The novel object recognition task revealed that the BMX-treated animals showed a marked increase in the time spent exploring novel objects. Furthermore, BMX ameliorates scopolamine-(Sco-) induced learning and memory impairment in animals, indicating a novel role of BMX in learning and memory.

Influence of natural and synthetic histone deacetylase inhibitors on chromatin

SIGNIFICANCE

Histone deacetylase inhibitors (HDACIs) have emerged as a new class of anticancer therapeutics. The hydroxamic acid, suberoylanilide hydroxamic acid (Vorinostat, Zolinza™), and the cyclic peptide, depsipeptide (Romidepsin, Istodax™), were approved by the U.S. Food and Drug Administration (FDA) for the treatment of cutaneous T-cell lymphoma in 2006 and 2009, respectively. At least 15 HDACIs are currently undergoing clinical trials either alone or in combination with other therapeutic modalities for the treatment of numerous hematological and solid malignancies.

RECENT ADVANCES

The potential utility of HDACIs has been extended to nononcologic applications, including autoimmune disorders, inflammation, diseases of the central nervous system, and malaria.

CRITICAL ISSUES

Given the promise of HDACIs, there is growing interest in the potential of dietary compounds that possess HDAC inhibition activity. This review is focused on the identification of and recent findings with HDACIs from dietary, medicinal plant, and microbial sources. We discuss the mechanisms of action and clinical potential of natural HDACIs.

FUTURE DIRECTIONS

Apart from identification of further HDACI compounds from dietary sources, further research will be aimed at understanding the effects on gene regulation on lifetime exposure to these compounds. Another important issue that requires clarification.

Insights from comprehensive multiple receptor docking to HDAC8

A systematic investigation of the available crystal structures of HDAC8 and of the influence of different receptor structures and docking protocols is presented. The study shows that the open conformation of HDAC8 may be preferred by ligands with flexible surface binding groups, as such a conformation allows the ligands to minimize their exposure to solvent upon binding. This observation allowed us to rationalize the excellent potency of pyrazole-based inhibitors compared to that of isoxazole-based inhibitors.

Isolation, identification, and biological evaluation of HIF-1-modulating compounds from Brazilian green propolis

The tumor microenvironment is characterized by hypoxia, low-nutrient levels, and acidosis. A natural product chemistry-based approach was used to discover small molecules that modulate adaptive responses to a hypoxic microenvironment through the hypoxia-inducible factor (HIF)-1 signaling pathways. Five compounds, such as baccharin (3), beturetol (4), kaempferide (5), isosakuranetin (6), and drupanin (9), that modulate HIF-1-dependent luciferase activity were identified from Brazilian green propolis using reporter assay. Compounds 3, 9 and 5 reduced HIF-1-dependent luciferase activity. The cinnamic acid derivatives 3 and 9 significantly inhibited expression of the HIF-1α protein and HIF-1 downstream target genes such as glucose transporter 1, hexokinase 2, and vascular endothelial growth factor A. They also exhibited significant anti-angiogenic effects in the chick chorioallantoic membrane (CAM) assay at doses of 300 ng/CAM. On the other hand, flavonoids 4 and 6 induced HIF-1-dependent luciferase activity and expression of HIF-1 target genes under hypoxia. The contents (g/100g extract) of the HIF-1-modulating compounds in whole propolis ethanol extracts were also determined based on liquid chromatography-electrospray ionization mass spectrometry as 1.6 (3), 14.2 (4), 4.0 (5), 0.7 (6), and 0.7 (9), respectively. These small molecules screened from Brazilian green propolis may be useful as lead compounds for the development of novel therapies against ischemic cardiovascular disease and cancer based on their ability to induce or inhibit HIF-1 activity, respectively.