Hydroxamic Acid-based Histone Deacetylase Research Articles

Diversified applications and synthesis of hydroxamic acids

Owing to the ability to form coordination complexes with several metal ions, hydroxamic acids have been widely used in the fields of medicinal chemistry, mineral flotation, metal–organic frameworks (MOFs), remediation of metal contamination and more. Since three hydroxamic acid-based histone deacetylase (HDAC) inhibitors were approved by the US Food and Drug Administration (FDA) for the treatment of haematologic malignancies, such functional groups have acquired even more attention in synthetic medicinal chemistry. However, application of hydroxamic acids for ore beneficiation is a unique area and has attracted the attention of few researchers. In order to provide insights for chemists in drug development, chelating mineral collector selection, remediation of metal pollution and preparation of MOFs, we summarize the applications of hydroxamic acids in the above-mentioned fields, and then introduce some related synthesis strategies including microwave synthesis, use of continuous flow reactors, solid-phase synthesis and enzymatic synthesis as supplements to classical synthetic methods.

Target Design of Novel Histone Deacetylase 6 Selective Inhibitors with 2-Mercaptoquinazolinone as the Cap Moiety.

Epigenetic alterations found in all human cancers are promising targets for anticancer therapy. In this sense, histone deacetylase inhibitors (HDACIs) are interesting anticancer agents that play an important role in the epigenetic regulation of cancer cells. Here, we report 15 novel hydroxamic acid-based histone deacetylase inhibitors with quinazolinone core structures. Five compounds exhibited antiproliferative activity with IC50 values of 3.4–37.8 µM. Compound 8 with a 2-mercaptoquinazolinone cap moiety displayed the highest antiproliferative efficacy against MCF-7 cells. For the HDAC6 target selectivity study, compound 8 displayed an IC50 value of 2.3 µM, which is 29.3 times higher than those of HDAC3, HDAC4, HDAC8, and HDAC11. Western blot assay proved that compound 8 strongly inhibited tubulin acetylation, a substrate of HDAC6. Compound 8 also displayed stronger inhibition activity against HDAC11 than the control drug Belinostat. The inhibitory mechanism of action of compound 8 on HDAC enzymes was then explored using molecular docking study. The data revealed a high binding affinity (−7.92 kcal/mol) of compound 8 toward HDAC6. In addition, dock pose analysis also proved that compound 8 might serve as a potent inhibitor of HDAC11.

HDACi protects against vascular cognitive impairment from CCH injury via induction of BDNF-related AMPA receptor activation.

We previously showed a hydroxamic acid‐based histone deacetylase inhibitor (HDACi), compound 13, provides neuroprotection against chronic cerebral hypoperfusion (CCH) both in vitro under oxygen‐glucose deprivation (OGD) conditions and in vivo under bilateral common carotid artery occlusion (BCCAO) conditions. Intriguingly, the protective effect of this HDACi is via H3K14 or H4K5 acetylation–mediated differential BDNF isoform activation. BDNF is involved in cell proliferation and differentiation in development, synaptic plasticity and in learning and memory related with receptors or synaptic proteins. B6 mice underwent BCCAO and were randomized into 4 groups; a sham without BCCAO (sham), BCCAO mice injected with DMSO (DMSO), mice injected with HDACi‐compound 13 (compound 13) and mice injected with suberoylanilide hydroxamic acid (SAHA). The cortex and hippocampus of mice were harvested at 3 months after BCCAO, and levels of BDNF, AMPA receptor and dopamine receptors (D1, D2 and D3) were studied using Western blotting analysis or immunohistochemistry. We found that the AMPA receptor plays a key role in the molecular mechanism of this process by modulating HDAC. This protective effect of HDACi may be through BDNF; therefore, activation of this downstream signalling molecule, for example by AMPA receptors, could be a therapeutic target or intervention applied under CCH conditions.

Appraisal of pyrrole as connecting unit in hydroxamic acid based histone deacetylase inhibitors: Synthesis, anticancer evaluation and molecular docking studies

Pyrrole is a biologically active scaffold, which itself possess noticeable anticancer activity against several types of cancer specially leukemia, lymphoma, and myelofibrosis. SAHA and its synthetic analogs has demonstrated potent antitumor activity against numerous human cancer lines and different classes of HDACs. The HDAC inhibitor possessing pyrrole as linker moiety has been developed for anticancer property. The objective of present studies was to incorporate pyrrole as connecting unit in hydroxamic acid based HDAC inhibitors for their anticancer evaluation and molecular docking studies. A series of novel 4-substituted methyl 6-(3-acetyl-2-methyl-1H-pyrrol-1-yl)hexanoate [3(a-z)] and 4-substituted 6-(3-acetyl-2-methyl-1H-pyrrol-1-yl)-N-hydroxyhexanamide [4(a-z)] were synthesized. These analogs were evaluated for their anticancer activity using in-vitro method against leukemia (K-562), lung (A-549), breast (MCF-7), and cervical (HeLa) human cancer cell lines using Sulforhodamine B (SRB) assay method, HDAC1 and HDAC6 inhibitory assay and binding mode analysis using molecular docking studies. The in-vitro studies of 3(a-z) indicated that substitution with electron donating groups produces active or moderately active compounds. Interestingly, p-nitro-substituted molecule produced a most active derivative in the series. The in-vitro anticancer study of 4(a-z) indicated that the unsubstituted phenyl derivative, 6-(3-acetyl-2-methyl-4-phenyl-1H-pyrrol-1-yl)-N-hydroxy-hexanamide (4a) have moderate antitumor activity against K-562 human leukemia cell line. Substitution at 4-phenyl ring with weak and moderate electron withdrawing groups, such as fluoro, chloro, and bromo potentiated the cytotoxic activity. The 4(a-z)] were docked against different HDAC proteins to determine the exact binding mode and orientation. These synthetic analogs have similar binding mode as SAHA on the active pocket. The pyrrole based novel SAHA analogs 3(a-z) and 4(a-z) displayed promising anticancer activity. These studies can be further employed for the design and development of novel SAHA analogs with promising anticancer activity.

Hydroxamic acid hybrids as the potential anticancer agents: An Overview.

Hydroxamic acid derivatives are potential histone deacetylase inhibitors, and several hydroxamic acid-based histone deacetylase inhibitors have already been used clinically as potent anticancer agents, so hydroxamic acid derivatives are useful scaffolds for the development of novel anticancer agents. Hybridization of hydroxamic acid moiety with other anticancer pharmacophores can overcome drug resistance and improve the specificity, so rational design of hydroxamic acid hybrids may provide valuable therapeutic interventions for the treatment of cancers. The purpose of the present review article is to update the current developments in hydroxamic acid hybrids with an emphasis on anticancer activity, structure-activity relationships, and mechanisms of action.

Synthesis and biological evaluation of a novel photo-activated histone deacetylase inhibitor

Hydroxamic acid-based histone deacetylase inhibitors (HDACi) are a class of epigenetic agents with potentially broad therapeutic application to several disease states including post angioplasty mediated neointimal hyperplasia (NIH). Precise spatiotemporal control over the release of HDACi at the target blood vessel site is required for the safe and successful therapeutic use of HDACi in the setting of drug eluting balloon catheter (DEBc) angioplasty treatment of NIH. We aimed to develop and characterise a novel photoactive HDACi, as a potential coating agent for DEBc.Metacept-3 1 was caged with a photo-labile protecting group (PPG) to synthesise a novel UV365nm active HDACi, caged metacept-3 15. Conversion of caged metacept-3 15 to active/native metacept-3 1 by UV365nm was achievable in significant quantities and at UV365nm power levels in the milliwatt (mW) range.In vitro evaluation of the biological activity of pre and post UV365nm activation of caged metacept-3 15 identified significant HDACi activity in samples exposed to short duration, mW range UV365nm. Toxicity studies performed in human umbilical vein endothelial cells (HUVEC’s) identified significantly reduced toxicity of caged metacept-3 15 pre UV365nm exposure compared with native metacept-3 1 and paclitaxel (PTX).Taken together these findings identify a novel photo-activated HDACi, caged metacept-3 15, with pharmacokinetic activation characteristics and biological properties which may make it suitable for evaluation as a novel coating for targeted DEBc angioplasty interventions.

Novel histone deacetylase inhibitors bearing a 4-piperidin-4-yl-triazole scaffold as antitumor agents.

Histone deacetylases have proven to be promising targets for the development of anticancer drugs. In this work, we reported the design and synthesis of a series of 20 novel hydroxamic acid-based histone deacetylase inhibitors with 4-piperidin-4-yl-triazole as the core structure. Five newly obtained compounds displayed excellent HDAC6 inhibitory activities. Among them, compounds WY-12 and WY-15 also exhibited excellent antiproliferative activities against six human tumor cell lines. WY-15 could increase the level of acetylated histone H3 in a dose-dependent manner. Furthermore, WY-15 remarkably induced cell cycle arrest of Sy5y cancer cells in G0 /G1 phase. Finally, the high potency of compound WY-15 toward HDAC6 was rationalized by molecular docking study.

Design, synthesis and biological evaluation of 4-piperidin-4-yl-triazole derivatives as novel histone deacetylase inhibitors.

Histone deacetylase is an important member of epigenetics and a well validated target for anti-cancer drug discovery. In this study, we designed and synthesized a series of twenty-one novel hydroxamic acid-based histone deacetylase inhibitors with 4-piperidin-4-yl-triazole as the core skeleton. Most target compounds displayed excellent inhibition rates toward histone deacetylases at the concentration of 1 μM. Among them, the inhibition rates of two compounds MH1-18 and MH1-21 exceeded 90%. Furthermore, these two compounds selectively inhibited the activity of histone deacetylase 6 with low IC50 values. The high potency of them toward histone deacetylase 6 was rationalized by molecular docking studies. We found that MH1-18 and MH1-21 moderately inhibited the proliferation of four human cancer cell lines SGC-7901, NCI-H226, MCF-7, and HL-60. However, MH1-21 showed potent efficacy in suppressing the migration of MCF-7 cells. Results obtained in the current study shed light on designing potent HDAC6 inhibitors as anti-cancer agents.

HDAC Inhibitors Induce BDNF Expression and Promote Neurite Outgrowth in Human Neural Progenitor Cells-Derived Neurons.

Besides its key role in neural development, brain-derived neurotrophic factor (BDNF) is important for long-term potentiation and neurogenesis, which makes it a critical factor in learning and memory. Due to the important role of BDNF in synaptic function and plasticity, an in-house epigenetic library was screened against human neural progenitor cells (HNPCs) and WS1 human skin fibroblast cells using Cell-to-Ct assay kit to identify the small compounds capable of modulating the BDNF expression. In addition to two well-known hydroxamic acid-based histone deacetylase inhibitors (hb-HDACis), SAHA and TSA, several structurally similar HDAC inhibitors including SB-939, PCI-24781 and JNJ-26481585 with even higher impact on BDNF expression, were discovered in this study. Furthermore, by using well-developed immunohistochemistry assays, the selected compounds were also proved to have neurogenic potential improving the neurite outgrowth in HNPCs-derived neurons. In conclusion, we proved the neurogenic potential of several hb-HDACis, alongside their ability to enhance BDNF expression, which by modulating the neurogenesis and/or compensating for neuronal loss, could be propitious for treatment of neurological disorders.

Hydroxamic Acid-Based Histone Deacetylase (HDAC) Inhibitors Bearing a Pyrazole Scaffold and a Cinnamoyl Linker

Genetic abnormalities have been conventionally considered as hallmarks of cancer. However, recent studies have demonstrated that epigenetic mechanisms are also implicated in the insurgence and development of cancer. Patterns of the epigenetic component include DNA methylation and histone modifications. Acetylation of histones is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). Imbalance of these two enzymatic systems is known to be a key factor in tumor progression. Because HDACs have been found to function incorrectly in cancer, various HDAC inhibitors (HDACIs) are being investigated to act as cancer chemotherapeutics. Herein, we report the synthesis, docking studies and biological activity of a series of hydroxamic acid-based HDACIs bearing an N1-aryl or N1-H pyrazole nucleus as surface recognition motif and a cinnamoyl group as a linker to the hydroxamic acid zinc-binding group (ZBG). Some of the tested compounds exhibited inhibitory properties towards HDACs and antiproliferative activity against neuroblastoma SH-SY5Y tumor cell line both at micromolar concentrations.

Design, synthesis and biological evaluation of novel hydroxamic acid based histone deacetylase 6 selective inhibitors bearing phenylpyrazol scaffold as surface recognition motif

In recent years, inhibition of HDAC6 became a promising therapeutic strategy for the treatment of cancer and HDAC6 inhibitors were considered to be potent anti-cancer agents. In this work, celecoxib showed moderate degree of HDAC6 inhibition activity and selectivity in preliminary enzyme inhibition activity assay. A series of hydroxamic acid derivatives bearing phenylpyrazol moiety were designed and synthesized as HDAC6 inhibitors. Most compounds showed potent HDAC6 inhibition activity. 11i was the most selective compound against HDAC6 with IC50 values of 0.020µM and selective factor of 101.1. Structure-activity relationship analysis indicated that locating the linker group at 1′ of pyrazol gave the most selectivity. The most compounds 11i (GI50=3.63μM) exhibited 6-fold more potent than vorinostat in HepG2 cells. Considering of the high selectivity against HDAC6 and anti-proliferation activity, such compounds have potential to be developed as anti-cancer agents.

Correction: Sleiman et al., Hydroxamic Acid-Based Histone Deacetylase (HDAC) Inhibitors Can Mediate Neuroprotection Independent of HDAC Inhibition

Correction: Sleiman et al., Hydroxamic Acid-Based Histone Deacetylase (HDAC) Inhibitors Can Mediate Neuroprotection Independent of HDAC Inhibition

Hydroxamic acid based histone deacetylase inhibitors with confirmed activity against the malaria parasite

Recent studies have highlighted a key role in regulating gene transcription, in both eukaryotes and prokaryotes, by enzymes that control the acetylation and deacetylation of histones. In particular, inhibitors of histone deacetylases (HDAC-Is) have been shown effective in controlling the development of many parasites, such as the plasmodium of malaria. Here we report the results of a study aimed at evaluating antiparasitic effect of two classes of HDAC-Is bearing different zinc binding group (hydroxamic acid vs thiol). The study showed that only the hydroxamic acid based HDAC inhibitors were active, with Plasmodium falciparum being the most sensitive parasite, having from low double-digit to single-digit nanomolar range in vitro activities. Among three derivatives evaluated also in vivo, ST8086AA1 (8) effectively inhibited 88% of the development of Plasmodium falciparum.

Hydroxamic acid-based histone deacetylase (HDAC) inhibitors can mediate neuroprotection independent of HDAC inhibition.

Histone deacetylase (HDAC) inhibition improves function and extends survival in rodent models of a host of neurological conditions, including stroke, and neurodegenerative diseases. Our understanding, however, of the contribution of individual HDAC isoforms to neuronal death is limited. In this study, we used selective chemical probes to assess the individual roles of the Class I HDAC isoforms in protecting Mus musculus primary cortical neurons from oxidative death. We demonstrated that the selective HDAC8 inhibitor PCI-34051 is a potent neuroprotective agent; and by taking advantage of both pharmacological and genetic tools, we established that HDAC8 is not critically involved in PCI-34051's mechanism of action. We used BRD3811, an inactive ortholog of PCI-34051, and showed that, despite its inability to inhibit HDAC8, it exhibits robust neuroprotective properties. Furthermore, molecular deletion of HDAC8 proved insufficient to protect neurons from oxidative death, whereas both PCI-34051 and BRD3811 were able to protect neurons derived from HDAC8 knock-out mice. Finally, we designed and synthesized two new, orthogonal negative control compounds, BRD9715 and BRD8461, which lack the hydroxamic acid motif and showed that they stably penetrate cell membranes but are not neuroprotective. These results indicate that the protective effects of these hydroxamic acid-containing small molecules are likely unrelated to direct epigenetic regulation via HDAC inhibition, but rather due to their ability to bind metals. Our results suggest that hydroxamic acid-based HDAC inhibitors may mediate neuroprotection via HDAC-independent mechanisms and affirm the need for careful structure-activity relationship studies when using pharmacological approaches.

RuvBL2 Is Involved in Histone Deacetylase Inhibitor PCI-24781-Induced Cell Death in SK-N-DZ Neuroblastoma Cells

Neuroblastoma is the second most common solid tumor diagnosed during infancy. The survival rate among children with high-risk neuroblastoma is less than 40%, highlighting the urgent needs for new treatment strategies. PCI-24781 is a novel hydroxamic acid-based histone deacetylase (HDAC) inhibitor that has high efficacy and safety for cancer treatment. However, the underlying mechanisms of PCI-24781 are not clearly elucidated in neuroblastoma cells. In the present study, we demonstrated that PCI-24781 treatment significantly inhibited tumor growth at very low doses in neuroblastoma cells SK-N-DZ, not in normal cell line HS-68. However, PCI-24781 caused the accumulation of acetylated histone H3 both in SK-N-DZ and HS-68 cell line. Treatment of SK-N-DZ with PCI-24781 also induced cell cycle arrest in G2/M phase and activated apoptosis signaling pathways via the up-regulation of DR4, p21, p53 and caspase 3. Further proteomic analysis revealed differential protein expression profiles between non-treated and PCI-24781 treated SK-N-DZ cells. Totally 42 differentially expressed proteins were identified by MALDI-TOF MS system. Western blotting confirmed the expression level of five candidate proteins including prohibitin, hHR23a, RuvBL2, TRAP1 and PDCD6IP. Selective knockdown of RuvBL2 rescued cells from PCI-24781-induced cell death, implying that RuvBL2 might play an important role in anti-tumor activity of PCI-24781 in SK-N-DZ cells. The present results provide a new insight into the potential mechanism of PCI-24781 in SK-N-DZ cell line.

A Structural Insight into Hydroxamic Acid Based Histone Deacetylase Inhibitors for the Presence of Anticancer Activity

Histone deacetylase inhibitors (HDACi) have been actively explored as anti-cancer agents due to their ability to prevent deacetylation of histones, resulting in uncoiling of chromatin and stimulation of a range of genes associated in the regulation of cell survival, proliferation, differentiation and apoptosis. During the past several years, many HDACi have entered pre-clinical or clinical research as anti-cancer agents with satisfying results. Out of these, more than 8 novel hydroxamic acid based HDACi i.e., belinostat, abexinostat, SB939, resminostat, givinostat, quisinostat, pentobinostat, CUDC-101 are in clinical trials and one of the drug vorinostat (SAHA) has been approved by US FDA for cutaneous T-cell lymphoma (CTCL). It is clear from the plethora of new molecules and the encouraging results from clinical trials that this class of HDAC inhibitors hold a great deal of promise for the treatment of a variety of cancers. In this review, we classified the hydroxamic acid based HDACi on the basis of their structural features into saturated, unsaturated, branched, un-branched and 5, 6-membered cyclic ring linker present between zinc binding group and connecting unit. The present article enlists reports on hydroxamic acid based HDACi designed and developed using concepts of medicinal chemistry, demonstrating that hydroxamate derivatives represent a versatile class of compounds leading to novel imaging and therapeutic agents. This article will also provide a complete insight into various structural modifications required for optimum anticancer activity.

Histone deacetylase inhibitors modulate miRNA and mRNA expression, block metaphase, and induce apoptosis in inflammatory breast cancer cells

To develop new therapies for inflammatory breast cancer (IBC) we have compared the effects of two hydroxamic acid-based histone deacetylase (HDAC) inhibitors, CG-1521 and Trichostatin A (TSA) on the biology of two IBC cell lines: SUM149PT and SUM190PT. CG-1521 and TSA induce dose (0−10 µM) and time-dependent (0−96 h) increases in the proportion of cells undergoing cell cycle arrest and apoptosis in the presence or absence of 17β-estradiol. In SUM 149PT cells, both CG-1521 and TSA increase the levels of acetylated α-tubulin; however the morphological effects are different: CG-1521 blocks mitotic spindle formation and prevents abscission during cytokinesis while TSA results in an increase in cell size. In SUM190PT cells CG-1521 does not cause an increase in acetylated-α-tubulin and even though TSA significantly increases the levels of acetylated tubulin, neither inhibitor alters the morphology of the cells. Microarray analysis demonstrates that CG-1521 modulates the expression of 876 mRNAs and 63 miRNAs in SUM149PT cells, and 1227 mRNAs and 35 miRNAs in SUM190PT cells. Only 9% of the genes are commonly modulated in both cell lines, suggesting that CG-1521 and TSA target different biological processes in the two cell lines most likely though the inhibition of different HDACs in these cell lines. Gene ontology (GO) analysis reveals that CG-1521 affects the expression of mRNAs that encode proteins associated with the spindle assembly checkpoint, chromosome segregation, and microtubule-based processes in both cell lines and has cell-type specific effects on lipid biosynthesis, response to DNA damage, and cell death.

Suppression of T cell functions by hydroxamic acid-based histone deacetylase inhibitors

Histone deacetylase inhibitors (HDACis) have recently been shown to suppress inflammatory responses at much lower concentrations than that the concentrations that produce an antitumor effect. In the current study, the inhibitory activity of T cell functions by three different HDACis was compared, and the mechanisms underlying the inhibitory activity were demonstrated. Trichostatin-A (TSA) and scriptaid (ST) had potent inhibitory effects on the proliferation of T cells. TSA suppressed the synthesis of the T cell-activating cytokine, interleukin (IL)-2, and the T cell-derived cytokines, interferon (IFN)-γ, IL-4, and IL-13. In addition, TSA induced inhibition of cell cycle progression and IL-2 receptor expression. On the whole, TSA had a stronger effect on T cell functions than other HDACis. Similarly, a longer duration of hyperacetylation was observed in the cells that had been exposed to TSA. Thus, the inhibition of histone deacetylation appears to be related to the inhibitory effect of TSA. These results are expected to serve as a guide for future studies on the ability of HDACis to inhibit acute and chronic inflammatory diseases provoked by T cells.

2,5-Disubstituted-1,3,4-oxadiazoles/thiadiazole as surface recognition moiety: Design and synthesis of novel hydroxamic acid based histone deacetylase inhibitors

The enzymatic inhibition of histone deacetylase activity has come out as a novel and effectual means for the treatment of cancer. Two novel series of 2-[5-(4-substitutedphenyl)-[1,3,4]-oxadiazol/thiadiazol-2-ylamino]-pyrimidine-5-carboxylic acid (tetrahydro-pyran-2-yloxy)-amides were designed and synthesized as novel hydroxamic acid based histone deacetylase inhibitors. The antiproliferative activities of the compounds were investigated in vitro using histone deacetylase inhibitory assay and MTT assay. The synthesized compounds were also tested for antitumor activity against Ehrlich ascites carcinoma cells in Swiss albino mice. The efforts were also made to establish structure-activity relationships among synthesized compounds. The results of the present studying indicates 2,5-disubstituted 1,3,4-oxadiazole/thiadiazole as promising surface recognition moiety for development of newer hydroxamic acid based histone deacetylase inhibitor.

Anti-Tumor Effect in Human Lung Cancer by a Combination Treatment of Novel Histone Deacetylase Inhibitors: SL142 or SL325 and Retinoic Acids

Histone deacetylase (HDAC) inhibitors arrest cancer cell growth and cause apoptosis with low toxicity thereby constituting a promising treatment for cancer. In this study, we investigated the anti-tumor activity in lung cancer cells of the novel cyclic amide-bearing hydroxamic acid based HDAC inhibitors SL142 and SL325. In A549 and H441 lung cancer cells both SL142 and SL325 induced more cell growth inhibition and cell death than the hydroxamic acid-based HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). Moreover, the combination treatment using retinoid drugs ATRA or 9-cis RA along with SL142 or SL325 significantly induced more apoptosis and suppressed colony formation than the single use of either. The expression of the retinoic acid receptors RARα, RARβ, RXRα and RXRβ were unchanged with the treatment. However a luciferase reporter construct (pGL4. RARE 7x) containing seven tandem repeats of the retinoic acid responsible element (RARE) generated significant transcriptional activity after the combination treatment of retinoic acids and SL142 or SL325 in H441 lung cancer cells. Moreover, apoptosis-promoting Bax expression and caspase-3 activity was increased after the combination treatment. These results suggest that the combination treatment of SL142 or SL325 with retinoic acids exerts significant anti-tumor activity and is a promising therapeutic candidate to treat human lung cancer.