Coumarin-derived Hydroxamic Acids as Histone Deacetylase Inhibitors: A Review of Anti-cancer Activities

Since coumarin and hydroxamic acid compounds are well-known in medicinal chemistry, a variety of their derivatives have been highlighted due to their potential uses for plentiful treatments. Different compounds of their derivatives acting through diverse activities, such as anti-tumor, anti-cancer, anti-inflammation, and histone deacetylase inhibition, have been comprehensively investigated by many researchers over the years. This present review provides the latest literature and knowledge on hydroxamic acids derived from coumarin. Overall, some recent advancements in biological activities of hybrid derivatives of hydroxamic acids containing coumarin moieties in medicinal chemistry are discussed.

Novel trans-caffeate hydrazide derivatives: synthesis, inhibition of nitric oxide (NO) production and molecular docking studies

Eight new caffeyl hydrazide derivatives (4a-4h) were synthesised via a convenient esterification of caffeic acid with some substituted aryl acid hydrazides. The synthesised caffeyl derivatives were evaluated for their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 macrophages. The fluorobenzoylhydrazide derivatives 4f, 4 g and 4h were found to be the most powerful anti-inflammatory compounds with IC50 values ranging from 11.90 to 24.17 μM, which were more potent than the reference compound L-NMMA (IC50 32.8 μM). Additionally, synthesised compounds have been rationalised by using molecular docking studies which were performed in order to understand insights on the action mechanism of newly synthesised inhibitors against inflammatory mediator (iNOS). Obtained data indicate that compounds 4f, 4h, 4a and 4 g were observed to effectively bind to iNOS receptor with dock score values of -11.62, -10.81, -10.78 and -10.51 kcal/mol, respectively.

Design, Synthesis and In vitro Cytotoxic Evaluation of Novel Hybrids of Artemisinin and Quinazolinone

Background:

In this study, two novel hybrid series of artemisinin and quinazolinones were synthesized and evaluated in vitro cytotoxicity against two human cancer cell lines, including SKLu-1 (lung cancer), MCF- 7 (breast cancer). The bio-assay results indicated that most of the target compounds exhibited cytotoxic activities against both human cancer cell lines tested and seemed to be more cytotoxic toward the breast (MCF-7) cancer cells than lung (SKLu-1) cancer cells. Among the synthesized artemisinin hybrids, the compound 13d containing a quinazolinone conjugated system exhibited the most potent cytotoxicity against the SKLu-1 and MCF-7 cell lines with IC50 values of 1.62 and 0.77 μM, respectively.

Objective:

This study aims at developing novel hybrids of artemisinin and quinazolinones as anticancer agents.

Method:

A series of novel hybrids were designed, synthesized, and evaluated for cytotoxicity against two human cancer cell lines, including SKLu-1 and MCF-7, using the SRB method.

Results:

All thirteen hybrids of artemisinin with quinazolinone exhibited cytotoxic activity against two tested cancer cell lines, in which the compound 13d exhibited the most potent cytotoxicity against the SKLu-1 and MCF-7 cell lines with IC50 values of 1.62 and 0.77 μM, respectively.

Conclusion:

The research results suggest that some compounds could be considered as leads for future design of hybrids and have the potential for further studies in the field of anti-cancer agent development.

Novel Derivatives Based on Zerumbone Scaffold as Potential Anticancer Inhibitors

Abstract:

A two-steps procedure was applied to couple zerumbone, a natural sesquiterpene, with thiols 8a-k to yield a small library of ten novel zerumbone derivatives 9a-k with full data of spectra including 1H-, 13C-NMR, and HRMS. The tautomerization of 9a, 9b, and 9c was found in DMSO and discussed in the case of 9c. The series of 9a-k together with zerumbone 1 were evaluated for their in vitro cytotoxic activity using three human cancer cell lines HepG2, A549, and HeLa. The results showed that all zerumbone derivatives expressed the cytotoxic activity against HepG2, A549, and HeLa cells stronger than that of zerumbone from 4-20 folds.

Novel Conjugated Quinazolinone-Based Hydroxamic Acids: Design, Synthesis and Biological Evaluation

BACKGROUND

The target-based approach to drug discovery currently attracts a great deal of interest from medicinal chemists in anticancer drug discovery and development. Histone deacetylase (HDAC) inhibitors represent an extensive class of targeted anti-cancer agents. Among the most explored structure moieties, hydroxybenzamides and hydroxypropenamides have been demonstrated to have potential HDAC inhibitory effects. Several compounds of these structural classes have been approved for clinical uses to treat different types of cancer, such as vorinostat and belinostat.

AIMS

This study aims at developing novel HDAC inhibitors bearing conjugated quinazolinone scaffolds with potential cytotoxicity against different cancer cell lines.

METHODS

A series of novel N-hydroxyheptanamides incorporating conjugated 6-hydroxy-2 methylquinazolin- 4(3H)-ones (15a-l) was designed, synthesized and evaluated for HDAC inhibitory potency as well as cytotoxicity against three human cancer cell lines, including HepG-2, MCF-7 and SKLu-1. Molecular simulations were finally performed to gain more insight into the structureactivity relationships.

RESULTS

It was found that among novel conjugated quinazolinone-based hydroxamic acids synthesized, compounds 15a, 15c and 15f were the most potent, both in terms of HDAC inhibition and cytotoxicity. Especially, compound 15f displayed up to nearly 4-fold more potent than SAHA (vorinostat) in terms of cytotoxicity against MCF-7 cell line with IC₅₀ value of 1.86 μM, and HDAC inhibition with IC₅₀ value of 6.36 μM. Docking experiments on HDAC2 isozyme showed that these compounds bound to HDAC2 with binding affinities ranging from -10.08 to -14.93 kcal/mol compared to SAHA (-15.84 kcal/mol). It was also found in this research that most of the target compounds seemed to be more cytotoxic toward SKLu-1than MCF-7 and HepG-2.

CONCLUSION

The resesrch results suggest that some hydroxamic acids could emerge for further evaluation and the results are well served as basics for further design of more potent HDAC inhibitors and antitumor agents.

Nucleoside-Based Phospholipids and Their Liposomes Formed in Water

Phospholipids and liposomes have been the subjects of considerable attention because of their importance in biological systems. We have efficiently synthesized novel nucleoside-based phospholipids in six-step sequences starting from their corresponding nucleosides. These nucleoside-based phospholipids self-assemble into liposome-like structures in aqueous solutions. We have analyzed the structures of these liposomes by dynamic light scattering, transmission electron microscopy, and confocal microscopy.

Tissue inhibitor of metalloproteinase-3 expression is upregulated during human cytotrophoblast invasion in vitro

Surprisingly, a successful human pregnancy requires cells from the fetal portion of the placenta (cytotrophoblasts) to adopt tumor-like properties. Cytotrophoblasts attach the conceptus to the endometrium by invading the uterus, and they initiate blood flow to the placenta by breaching maternal vessels. But unlike tumor metastasis, cytotrophoblast invasion is highly regulated both spatially and temporally. Our previous work showed that matrix metalloproteinase-9 (MMP-9) expression is upregulated during cytotrophoblast differentiation along the invasive pathway, and that activity of this proteinase specifies the cells' ability to degrade extracellular matrix (ECM) substrates in vitro. Here we tested the hypothesis that invading cytotrophoblasts express an unusual tissue inhibitor of metalloproteinase (TIMP) repertoire that allows them to regulate their MMP-9 proteolytic activity. By using protease-substrate gel electrophoresis, we found that human cytotrophoblasts express primarily TIMP-3. We showed that the cells' TIMP-3 expression is regulated in accord with that of MMP-9. The highest levels of protein and mRNA for both these molecules were detected after differentiation to a fully invasive phenotype and during early gestation, when invasion peaks, rather than at term, when invasion has stopped. Our results suggest that coexpression of MMP-9 and TIMP-3 by invading cytotrophoblasts plays an important role in regulating the depth of uterine invasion.

Gelatinase A expression in endothelial cells is regulated by at least two cis-acting promoter elements

Increased expression of gelatinase A is associated with both angiogenesis and alterations in blood vessel structure. Heart-derived endothelial cells derived from spontaneously hypertensive rats (SHR) were found to express significantly more gelatinase A in culture, both at the protein and mRNA level, than endothelial cells from normotensive Wistar-Kyoto (WKY) rats. Other matrix metalloproteinases, as well as their tissue inhibitors, were not differentially regulated. A 1683 bp gelatinase A promoter fragment linked to a luciferase reporter demonstrated up to 40-fold more activity when transfected into SHR-derived cells versus WKY-derived cells. The promoter region between -1324 and -1272, previously termed RE1, contributed up to a five-fold increase in basal promoter activity in both cells, but contributed only 12% of the promoter activity in SHR-derived cells compared to 85% in WKY-derived cells. In SHR-derived cells, but not in WKY-derived cells, a second region between -1435 and -1375, termed RE2, contributed 60% of the total activity of the 1683 bp promoter fragment. Both electrophoretic mobility shift assays and Southwestern blots demonstrated differences in RE2-specific binding factors in nuclear extracts derived from the two cell types. SHR-derived endothelial cells thus represent a new model system to study the regulation of gelatinase A expression, which itself may contribute to the abnormal vascular structure seen in the SHR.

Identification and cloning of the membrane-associated serine protease, hepsin, from mouse preimplantation embryos

Previous studies have suggested the existence of a membrane-associated serine protease expressed by mammalian preimplantation embryos. In this study, we have identified hepsin, a type II transmembrane serine protease, in early mouse blastocysts. Mouse hepsin was highly homologous to the previously identified human and rat cDNAs. Two isoforms, differing in their cytoplasmic domains, were detected. The tissue distribution of mouse hepsin was similar to that seen in humans, with prominent expression in liver and kidney. In mouse embryos, hepsin expression was observed in the two-cell stage, reached a maximal level at the early blastocyst stage, and decreased subsequent to blastocyst hatching. Expression of a soluble form of hepsin revealed its ability to autoactivate in a concentration-dependent manner. Catalytically inactive soluble hepsin was unable to autoactivate. These results suggest that hepsin may be the first serine protease expressed during mammalian development, making its ability to autoactivate critical to its function.

Gelatinase A activation is regulated by the organization of the polymerized actin cytoskeleton

Gelatinase A (GL-A) is a matrix metalloproteinase (MMP) involved in both connective tissue remodeling and tumor invasion. GL-A activation is mediated by a membrane-type MMP (MT-MMP) that cleaves the GL-A propeptide. In this study, we examined the role of the actin cytoskeleton in regulating GL-A activation and MT-MMP-1 expression. Human palmar fascia fibroblasts and human fetal lung fibroblasts were cultured on a planar substratum or within different types of collagen lattices. Fibroblasts that formed stress fibers, either on a planar substratum or within an attached collagen lattice, showed reduced GL-A activation compared with fibroblasts lacking stress fibers, within either floating or stress-released collagen lattices. To determine whether changes in the organization of the actin cytoskeleton could promote GL-A activation, fibroblasts with stress fibers were treated with cytochalasin D. Within 24 h after treatment, GL-A activation was dramatically increased. Associated with this GL-A activation was an increase in MT-MMP-1 mRNA as determined by Northern blot analysis. Treatment with nocodazole, which induced microtubule depolymerization and cell shape changes without affecting stress fibers, did not promote GL-A activation. These results suggest that the extracellular matrix and the actin cytoskeleton transduce signals that modulate GL-A activation and regulate tissue remodeling.

Specificity of the thrombin receptor for agonist peptide is defined by its extracellular surface

G-protein-coupled receptors for catecholamines and some other small ligands are activated when agonists bind to the transmembrane region of the receptor. The docking interactions through which peptide agonists activate their receptors are less well characterized. The thrombin receptor is a specialized peptide receptor. It is activated by binding its tethered ligand domain, which is unmasked upon receptor cleavage by thrombin. Human and Xenopus thrombin receptor homologues are each selectively activated by the agonist peptide representing their respective tethered ligand domains. Here we identify receptor domains that confer this agonist specificity by replacing the Xenopus receptor's aminoterminal exodomain and three extracellular loops with the corresponding human structures. This switches receptor specificity from Xenopus to human. The specificity of these thrombin receptors for their respective peptide agonists is thus determined by their extracellular surfaces. Our results indicate that agonist interaction with extracellular domains is important for thrombin receptor activation.

The cloned platelet thrombin receptor couples to at least two distinct effectors to stimulate phosphoinositide hydrolysis and inhibit adenylyl cyclase

Thrombin both stimulates phosphoinositide hydrolysis and inhibits adenylyl cyclase in a variety of cell types. Whether the cloned human platelet thrombin receptor accounts for both of these signaling events is unknown. We report that thrombin receptor agonist peptide causes both phosphoinositide hydrolysis and inhibition of adenylyl cyclase in naturally thrombin-responsive CCL-39 cells. To exclude the possibility that the agonist peptide or thrombin itself may activate these pathways via distinct receptors and to circumvent a lack of suitable thrombin receptor-null cells, we utilized a designed "enterokinase receptor," a thrombin receptor with its thrombin cleavage recognition sequence LDPR replaced by DDDDK, the enterokinase cleavage recognition sequence. Transfection of enterokinase-unresponsive cells with this construct conferred both enterokinase-sensitive phosphoinositide hydrolysis and inhibition of adenylyl cyclase. The phosphoinositide hydrolysis response was largely insensitive to pertussis toxin, whereas the adenylyl cyclase response was completely blocked by pertussis toxin. These data show that the cloned thrombin receptor can effect both phosphoinositide hydrolysis and inhibition of adenylyl cyclase via at least two distinct effectors, most likely Gq-like and Gi-like G-proteins.

Thrombin receptor expression in normal and atherosclerotic human arteries

Thrombin is a multifunctional serine protease generated at sites of vascular injury. A host of thrombin actions on vascular endothelial cells, smooth muscle cells, and macrophages has been defined in cell culture systems, but the in vivo significance of these activities is unknown. We have defined the expression of the recently identified receptor for thrombin in human arteries by both in situ hybridization and immunohistochemistry. In normal-appearing arteries, thrombin receptor was expressed almost exclusively in the endothelial layer. By contrast, in human atheroma, the receptor was widely expressed, both in regions rich in macrophages and in regions rich in vascular smooth muscle cells and mesenchymal-appearing intimal cells of unknown origin. Thrombin receptor was expressed by human vascular endothelial cells and smooth muscle cells in culture and by macrophages obtained by bronchioalveolar lavage, thus demonstrating that all three cell types are indeed capable of expressing the thrombin receptor. These results establish thrombin receptor activation as a candidate for contributing to sclerotic and inflammatory processes in the human vasculature, such as those that occur in atherosclerosis and restenosis.

Tethered ligand agonist peptides. Structural requirements for thrombin receptor activation reveal mechanism of proteolytic unmasking of agonist function

The human platelet thrombin receptor is activated when thrombin cleaves its receptor's amino-terminal extension to reveal a new amino terminus that functions as a tethered peptide ligand. Exactly how this "agonist peptide domain" remains cryptic within the uncleaved receptor and becomes functional after receptor cleavage is unknown. In this report we define the structural features of the thrombin receptor's agonist peptide domain important for receptor activation. Studies with mutant thrombin receptors have suggested that agonist peptide domain residues 2-6 contained determinants critical for receptor activation, and the synthetic peptide SFLLR-NH2 representing the 1st 5 amino-terminal residues of the agonist peptide domain was sufficient to specify agonist activity. Acetylating or removing the agonist peptide's amino-terminal ammonium group greatly attenuated agonist activity. Agonist peptide residue Phe2 was vital for agonist function; residues Leu4 and Arg5 individually played less important roles. These structure-function relationships held for both platelet activation and activation of the cloned receptor expressed in transfected mammalian cells. Our studies suggest that structures at the extreme amino terminus of the thrombin receptor's agonist peptide domain, in particular the free ammonium group of Ser1 and the phenyl ring of Phe2, are critical for receptor activation and that the agonist function of this domain is expressed when receptor proteolysis unmasks such determinants. In addition to revealing details of the thrombin receptor's proteolytic triggering mechanism, these studies open avenues to the development of drugs targeting the thrombin receptor and to further definition for the role of the thrombin receptor in cellular regulation.

Cloned platelet thrombin receptor is necessary for thrombin-induced platelet activation

Platelet activation by thrombin is critical for hemostasis and thrombosis. Structure-function studies with a recently cloned platelet thrombin receptor suggest that a hirudin-like domain in the receptor's extracellular amino terminal extension is a thrombin-binding determinant important for receptor activation. We now report that a peptide antiserum to this domain is a potent and specific antagonist of thrombin-induced platelet activation. This study demonstrates that the cloned platelet thrombin receptor is necessary for platelet activation by thrombin, and provides a strategy for developing blocking monoclonal antibodies of potential therapeutic value.

"Mirror image" antagonists of thrombin-induced platelet activation based on thrombin receptor structure

Platelet activation by thrombin plays a critical role in hemostasis and thrombosis. Based on structure-activity studies of a cloned platelet thrombin receptor, we designed two "mirror image" antagonists of thrombin and thrombin receptor function. First, "uncleavable" peptides mimicking the receptor domain postulated to interact with thrombin were found to be potent thrombin inhibitors. Second, proteolytically inactive mutant thrombins designed to bind but not cleave the thrombin receptor were found to be specific antagonists of receptor activation by thrombin. The effectiveness of these designed antagonists in blocking thrombin-induced platelet activation suggests a model for thrombin-receptor interaction and possible strategies for the development of novel antithrombotic agents.

Domains specifying thrombin-receptor interaction

Platelet activation by the coagulation protease thrombin is central to arterial thrombosis, a major cause of morbidity and mortality. We recently isolated a complementary DNA encoding the platelet thrombin receptor. The extracellular amino-terminal extension of this seven transmembrane domain receptor contains the putative thrombin cleavage site LDPR/S which is critical for receptor activation. By replacing this cleavage site with the cleavage site for enterokinase, we have created a functional enterokinase receptor. This result demonstrates that all information necessary for receptor activation is provided by receptor proteolysis. Nanomolar enterokinase concentrations are required to activate this new receptor, in contrast to the picomolar thrombin concentrations that activate wild-type thrombin receptor. We identified a receptor domain critical for thrombin's remarkable potency at its receptor. This domain resembles the carboxyl tail of the leech anticoagulant hirudin and functions by binding to thrombin's anion-binding exosite. Our studies thus define a model for thrombin-receptor interaction. The utility of this model was demonstrated by the design of novel thrombin inhibitors based on receptor peptides.

The region of the thrombin receptor resembling hirudin binds to thrombin and alters enzyme specificity

A thrombin receptor has recently been cloned and the sequence deduced. The sequence reveals a thrombin cleavage site that accounts for receptor activation. The receptor also has an acidic region with some similarities to the carboxyl-terminal region of the leech thrombin inhibitor, hirudin. Synthetic peptides corresponding to the receptor cleavage site (residues 38-45), the hirudin-like domain (residues 52-69), and the covalently associated domains (residues 38-64) were evaluated for their ability to bind to thrombin. Peptides 38-45 and 38-64 were competitive inhibitors of thrombin's chromogenic substrate activity (Ki = 0.96 mM and 0.6 microM, respectively. Residues 52-69 altered the chromogenic substrate specificity, resulting in accelerated cleavage of some substrates and inhibited cleavage of others. The same peptide binds to thrombin and alters the fluorescence emission intensity of 5-dimethylaminonaphthalene-1-sulfonyl (dansyl)-thrombin in which the dansyl is attached directly to the active site serine (Kd = 32 +/- 7 microM). Residues 52-69 displace the carboxyl-terminal peptide of hirudin, indicating that they share a common binding site in the anion exosite of thrombin. These data suggest that the thrombin receptor has high affinity for thrombin due to the presence of the hirudin-like domain and that this domain alters the specificity of thrombin. This change in specificity may account for the ability of the receptor to serve as an excellent thrombin substrate despite the presence of an Asp residue in the P3 site, which is normally inhibitory to thrombin activity.

Molecular cloning of a functional thrombin receptor reveals a novel proteolytic mechanism of receptor activation

We isolated a cDNA encoding a functional human thrombin receptor by direct expression cloning in Xenopus oocytes. mRNA encoding this receptor was detected in human platelets and vascular endothelial cells. The deduced amino acid sequence revealed a new member of the seven transmembrane domain receptor family with a large amino-terminal extracellular extension containing a remarkable feature. A putative thrombin cleavage site (LDPR/S) resembling the activation cleavage site in the zymogen protein C (LDPR/I) was noted 41 amino acids carboxyl to the receptor's start methionine. A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. "Uncleavable" mutant thrombin receptors failed to respond to thrombin but were responsive to the new amino-terminal peptide. These data reveal a novel signaling mechanism in which thrombin cleaves its receptor's amino-terminal extension to create a new receptor amino terminus that functions as a tethered ligand and activates the receptor.

The in vitro biological effect of nerve growth factor is inhibited by synthetic peptides

Nerve growth factor (NGF)1 is a neurotrophic polypeptide that acts via specific receptors to promote the survival and growth of neurons. To delineate the NGF domain(s) responsible for eliciting biological activity, we synthesized small peptides corresponding to three regions in NGF that are hydrophilic and highly conserved. Several peptides from mouse NGF region 26-40 inhibited the neurite-promoting effect of NGF on sensory neurons in vitro. Inhibition was sequence-specific and could be overcome by increasing the concentration of NGF. Moreover, peptide actions were specific for NGF-mediated events in that they failed to block the neurotrophic activity of ciliary neuronotrophic factor (CNTF) or phorbol 12-myristate 13-acetate (PMA). In spite of the inhibition of NGF activity, peptides did not affect the binding of radiolabeled NGF. These studies define one region of NGF that may be required for neurotrophic activity.