Valproic acid ameliorates cauda equina injury by suppressing HDAC2-mediated ferroptosis.

INTRODUCTION: Persistent neuroinflammatory response after cauda equina injury (CEI) lowers nociceptor firing thresholds, accompanied by pathological pain and decreasing extremity dysfunction. Histone deacetylation has been considered a key regulator of immunity, inflammation, and neurological dysfunction. Our previous study suggested that valproic acid (VPA), a histone deacetylase inhibitor, exhibited neuroprotective effects in rat models of CEI, although the underlying mechanism remains elusive. METHODS: The cauda equina compression surgery was performed to establish the CEI model. The Basso, Beattie, Bresnahan score, and the von Frey filament test were carried out to measure the animal behavior. Immunofluorescence staining of myelin basic protein and GPX4 was carried out. In addition, transmission electron microscope analysis was used to assess the effect of VPA on the morphological changes of mitochondria. RNA-sequencing was conducted to clarify the underlying mechanism of VPA on CEI protection. RESULTS: In this current study, we revealed that the expression level of HDAC1 and HDAC2 was elevated after cauda equina compression model but was reversed by VPA treatment. Meanwhile, HDAC2 knockdown resulted in the improvement of motor functions and pathologic pain, similar to treatment with VPA. Histology analysis also showed that knockdown of histone deacetylase (HDAC)-2, but not HDAC1, remarkably alleviated cauda equina injury and demyelinating lesions. The potential mechanism may be related to lowering oxidative stress and inflammatory response in the injured region. Notably, the transcriptome sequencing indicated that the therapeutic effect of VPA may depend on HDAC2-mediated ferroptosis. Ferroptosis-related genes were analyzed in vivo and DRG cells further validated the reliability of RNA-sequencing results, suggesting HDAC2-H4K12ac axis participated in epigenetic modulation of ferroptosis-related genes. CONCLUSION: HDAC2 is critically involved in the ferroptosis and neuroinflammation in cauda equina injury, and VPA ameliorated cauda equina injury by suppressing HDAC2-mediated ferroptosis.

Histone deacetylase inhibitors inhibit lung adenocarcinoma metastasis via HDAC2/YY1 mediated downregulation of Cdh1.

Metastasis is a leading cause of mortality in patients with lung adenocarcinoma. Histone deacetylases have emerged as promising targets for anti-tumor drugs, with histone deacetylase inhibitors (HDACi) being an active area of research. However, the precise mechanisms by which HDACi inhibits lung cancer metastasis remain incompletely understood. In this study, we employed a range of techniques, including qPCR, immunoblotting, co-immunoprecipitation, chromatin-immunoprecipitation, and cell migration assays, in conjunction with online database analysis, to investigate the role of HDACi and HDAC2/YY1 in the process of lung adenocarcinoma migration. The present study has demonstrated that both trichostatin A (TSA) and sodium butyrate (NaBu) significantly inhibit the invasion and migration of lung cancer cells via Histone deacetylase 2 (HDAC2). Overexpression of HDAC2 promotes lung cancer cell migration, whereas shHDAC2 effectively inhibits it. Further investigation revealed that HDAC2 interacts with YY1 and deacetylates Lysine 27 and Lysine9 of Histone 3, thereby inhibiting Cdh1 transcriptional activity and promoting cell migration. These findings have shed light on a novel functional mechanism of HDAC2/YY1 in lung adenocarcinoma cell migration.

HDAC1/2 Control Proliferation and Survival in Adult Epidermis and Pre‒Basal Cell Carcinoma through p16 and p53.

HDAC inhibitors show therapeutic promise for skin malignancies; however, the roles of specific HDACs in adult epidermal homeostasis and in disease are poorly understood. We find that homozygous epidermal codeletion of Hdac1 and Hdac2 in adult mouse epidermis causes reduced basal cell proliferation, apoptosis, inappropriate differentiation, and eventual loss of Hdac1/2-null keratinocytes. Hdac1/2-deficient epidermis displays elevated acetylated p53 and increased expression of the senescence gene p16. Loss of p53 partially restores basal proliferation, whereas p16 deletion promotes long-term survival of Hdac1/2-null keratinocytes. In activated GLI2-driven pre-basal cell carcinoma, Hdac1/2 deletion dramatically reduces proliferation and increases apoptosis, and knockout of either p53 or p16 partially rescues both proliferation and basal cell viability. Topical application of the HDAC inhibitor romidepsin to the normal epidermis or to GLI2ΔN-driven lesions produces similar defects to those caused by genetic Hdac1/2 deletion, and these are partially rescued by loss of p16. These data reveal essential roles for HDAC1/2 in maintaining proliferation and survival of adult epidermal and basal cell carcinoma progenitors and suggest that the efficacy of therapeutic HDAC1/2 inhibition will depend in part on the mutational status of p53 and p16.

A novel HDAC1/2 inhibitor suppresses colorectal cancer through apoptosis induction and cell cycle regulation.

Colorectal cancer (CRC) is one of the leading causes of death around the world, and synthetic chemicals targeting specific proteins or various molecular pathways for tumor suppression, such as histone deacetylases (HADC) inhibitors, are under intensively studied. The target of HDAC involves in regulating critical cellular mechanisms and underpins the progression of anticancer therapy. However, little is known about the antitumor mechanisms of class I specific HDAC inhibitors in CRC. We structurally designed and synthesized benzamide-based compounds, examined their anticancer activity in several solid tumors, and identified compound 9 with high potential. Results from the in vitro enzyme and cell-based studies demonstrated that compound 9 as a selective HDAC1/2 inhibitor that possessed short-term and long-term suppression capacities against colorectal cancer cells. Investigation of molecular regulatory mechanisms of 9 in colorectal cancer cells by biological functional assays evidenced that treatment of compound 9 could activate apoptosis, induce cell cycle arrest, facilitate DNA damage process, and suppress cancer migration. A non-cancerous cell line and the in vivo zebrafish model were applied for safety evaluation. In summary, our results demonstrate that compound 9 is a promising lead drug worth further investigation for development of future cancer therapeutic agents.

Rational design of selective HDAC2 inhibitors for liver cancer treatment: computational insights into the selectivity mechanism through molecular dynamics simulations and QM/MM calculations.

The rational design of selective histone deacetylase 2 (HDAC2) inhibitors is beneficial for the therapeutic treatment of liver cancer, though HDAC2 is highly homologous to HDAC8, which may lead to undesired side effects due to the pan-inhibition towards HDAC2 and HDAC8. To clarify the structural basis of selective inhibition towards HDAC2 over HDAC8, we utilized multiple in silico strategies, including sequence alignment, structural comparison, molecular docking, molecular dynamics simulations, free energy calculations, alanine scanning mutagenesis, pharmacophore modeling, protein contacts atlas analysis and QM/MM calculations to study the binding patterns of HDAC2/8 selective inhibitors. Through the whole process described above, it is found that although HDAC2 has conserved GLY154 and PHE210 that also exist within HDAC8, namely GLY151 and PHE208, the two isoforms exhibit diverse binding modes towards their inhibitors. Typically, HDAC2 inhibitors interact with the Zn2+ ions through the core chelate group, while HDAC8 inhibitors adopt a bent conformation within the HDAC8 pocket that inclines to be in contact with the Zn2+ ions through the terminal hydroxamic acid group. In summary, our data comprehensively elucidate the selectivity mechanism towards HDAC2 over HDAC8, which would guide the rational design of selective HDAC2 inhibitors for liver cancer treatment.

Suppression of Extracellular Vesicle VEGF-C-mediated Lymphangiogenesis and Pancreatic Cancer Early Dissemination By a Selective HDAC1/2 Inhibitor.

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer characterized by early dissemination and poor drug response. Therefore, it is an unmet medical need to develop new strategies for treatment. As aberrant activation of ERK due to KRAS activating mutation is a driving force for PDAC, a brake system that can terminate ERK signaling represents an ideal druggable target. Herein, we demonstrate that forced expression of dual specificity phosphatase-2 (DUSP2), a specific ERK phosphatase, abrogated tumor formation and loss of Dusp2 facilitated Kras-driven PDAC progression. We report that a selective HDAC1/2 inhibitor (B390) has multifaceted therapeutic potential in PDAC by restoring the expression and function of DUSP2. In vitro study showed that treatment with B390 inhibited growth and migration abilities of PDAC cells, decreased extracellular vesicle-associated VEGF-C expression, and suppressed lymphatic endothelial cell proliferation. In vivo, B390 not only suppressed tumor growth by increasing tumor cell death, it also inhibited lymphangiogenesis and lymphovascular invasion. Taken together, our data demonstrate that B390 was able to alleviate loss of DUSP2-mediated pathologic processes, which provides the proof-of-concept evidence to demonstrate the potential of using selective HDAC1/2 inhibitors in PDAC treatment and suggests reinstating DUSP2 expression may be a strategy to subside PDAC progression.

A first-in-class anticancer dual HDAC2/FAK inhibitors bearing hydroxamates/benzamides capped by pyridinyl-1,2,4-triazoles.

Novel 5-pyridinyl-1,2,4-triazoles were designed as dual inhibitors of histone deacetylase 2 (HDAC2) and focal adhesion kinase (FAK). Compounds 5d, 6a, 7c, and 11c were determined as potential inhibitors of both HDAC2 (IC50 = 0.09-1.40 µM) and FAK (IC50 = 12.59-36.11 nM); 6a revealed the highest activity with IC50 values of 0.09 µM and 12.59 nM for HDAC2 and FAK, respectively. Compound 6a was superior to reference drugs vorinostat and valproic acid in its ability to inhibit growth/proliferation of A-498 and Caki-1 renal cancer cells. Further investigation proved that 6a strongly arrests the cell cycle at the G2/M phase and triggers apoptosis in both A-498 and Caki-1 cells. Moreover, the enhanced Akt activity that is observed upon chronic application of HDAC inhibitors was effectively suppressed by the dual HDAC2/FAK inhibitor. Finally, the high potency and selectivity of 6a towards HDAC2 and FAK proteins were rationalized by molecular docking. Taken together, these findings highlight the potential of 6a as a promising dual-acting HDAC2/FAK inhibitor that could benefit from further optimization.

Anchor extension: a structure-guided approach to design cyclic peptides targeting enzyme active sites.

Despite recent success in computational design of structured cyclic peptides, de novo design of cyclic peptides that bind to any protein functional site remains difficult. To address this challenge, we develop a computational "anchor extension" methodology for targeting protein interfaces by extending a peptide chain around a non-canonical amino acid residue anchor. To test our approach using a well characterized model system, we design cyclic peptides that inhibit histone deacetylases 2 and 6 (HDAC2 and HDAC6) with enhanced potency compared to the original anchor (IC50 values of 9.1 and 4.4 nM for the best binders compared to 5.4 and 0.6 µM for the anchor, respectively). The HDAC6 inhibitor is among the most potent reported so far. These results highlight the potential for de novo design of high-affinity protein-peptide interfaces, as well as the challenges that remain.

Histone deacetylase 2 selective inhibitors: A versatile therapeutic strategy as next generation drug target in cancer therapy.

Acetylation and deacetylation of histone and several non-histone proteins are the two important processes amongst the different modes of epigenetic modulation that are involved in regulating cancer initiation and development. Abnormal expression of histone deacetylases (HDACs) is often reported in various types of cancers. Few pan HDAC inhibitors have been approved for use as therapeutic interventions for cancer treatment including vorinostat, belinostat and panobinostat. However, not all the HDAC isoforms are abnormally expressed in certain cancers, such as in the case of, ovarian cancer where overexpression of HDAC1-3, lung cancer where overexpression of HDAC 1 and 3 and gastric cancer where overexpression of HDAC2 is seen. Therefore, pan-inhibition of HDAC is not an efficient way to combat cancer via HDAC inhibition. Hence, isoform-selective HDAC inhibition can be one of the best therapeutic strategies in the treatment of cancer. In this context since aberrant expression of HDAC2 largely contributes to cancer progression by silencing pro-apoptotic protein expressions such as NOXA and APAF1 (caspase 9-activating proteins) and inactivation of tumor suppressor p53, HDAC2 specific inhibitors may help to develop not only the direct targets but also indirect targets that are crucial for tumor development. However, to develop a HDAC2 specific and potent inhibitor, extensive knowledge of its structure and specific functions is essential. The present review updates details on the structural features, physiological functions, and roles of HDAC2 in different types of cancer, emphasizing the challenges and status of the development of HDAC2 selective inhibitors against various types of cancer.

Delineating binding potential, stability of Sulforaphane-N-acetyl-cysteine in the active site of histone deacetylase 2 and testing its cytotoxicity against distinct cancer lines through stringent molecular dynamics, DFT and cell-based assays.

Histone deacetylase 2 (HDAC2), an isozyme of Class I HDACs has potent imputations in actuating neurodegenerative signaling. Currently, there are sizeable therapeutic disquiets with the use of synthetic histone deacetylase inhibitors in disease management. This strongly suggests the unfulfilled medical necessity of plant substitutes for therapeutic intervention. Sulforaphane-N-acetyl-cysteine (SFN-N-acetylcysteine or SFN-NAC), a sulforaphane metabolite has shown significantly worthier activity against HDACs under in vitro conditions. However, the atomistic studies of SFN-NAC against HDAC2 are currently lacking. Thus, the present study employed a hybrid strategy including extra-precision (XP) grid-based flexible molecular docking, molecular mechanics generalized born surface area (MM-GBSA), e-Pharmacophores method, and molecular dynamics simulation for exploring the binding strengh, mode of interaction, e-Pharmacophoric features, and stability of SFN-NAC towards HDAC2. Further, the globally acknowledged density functional theory (DFT) study was performed on SFN-NAC and entinostat individually in complex state with HDAC2. Apart from this, these inhibitors were tested against three distinct cancer cell models and one transformed cell line for cytotoxic activity. Moreover, double mutant of HDAC2 was generated and the binding orientation and interaction of SFN-NAC was scrutinized in this state. On the whole, this study unbosomed and explained the comparatively higher binding affinity of entinostat for HDAC2 and its wide spectrum cytotoxicity than SFN-NAC.

Structure-based virtual screening for novel potential selective inhibitors of class IIa histone deacetylases for cancer treatment.

The fundamental cause of human cancer is strongly influenced by down- or up-regulations of epigenetic factors. Upregulated histone deacetylases (HDAC) have been shown to be effectively neutralized by the action of HDACs inhibitors (HDACi). However, cytotoxicity has been reported in normal cells because of non-specificity of several available HDACis that are in clinical use or at different phases of clinical trials. Because of the high amino acid sequence and structural similarity among HDAC enzymes, it is believed to be a challenging task to obtain isoform-selectivity. The essential aim of the present research work was to identify isoform-selective inhibitors against class IIa HDACs via structure-based drug design. Based on the highest binding affinity and isoform-selectivity, the top-ranked inhibitors were in silico tested for their absorption, distribution, metabolism, elimination, and toxicity (ADMET) properties, which were classified as drug-like compounds. Later, molecular dynamics simulation (MD) was carried out for all compound-protein complexes to evaluate the structural stability and the biding mode of the inhibitors, which showed high stability throughout the 100 ns simulation. Free binding energy predictions by MM-PBSA method showed the high binding affinity of the identified compounds toward their respective targets. Hence, these inhibitors could be used as drug candidates or as lead compounds for more in silico or in vitro optimization to design safe isoform-selective HDACs inhibitors.

HDAC2 targeting stabilizes the CoREST complex in renal tubular cells and protects against renal ischemia/reperfusion injury.

Histone/protein deacetylases (HDAC) 1 and 2 are typically viewed as structurally and functionally similar enzymes present within various co-regulatory complexes. We tested differential effects of these isoforms in renal ischemia reperfusion injury (IRI) using inducible knockout mice and found no significant change in ischemic tolerance with HDAC1 deletion, but mitigation of ischemic injury with HDAC2 deletion. Restriction of HDAC2 deletion to the kidney via transplantation or PAX8-controlled proximal renal tubule-specific Cre resulted in renal IRI protection. Pharmacologic inhibition of HDAC2 increased histone acetylation in the kidney but did not extend renal protection. Protein analysis demonstrated increased HDAC1-associated CoREST protein in HDAC2-/- versus WT cells, suggesting that in the absence of HDAC2, increased CoREST complex occupancy of HDAC1 can stabilize this complex. In vivo administration of a CoREST inhibitor exacerbated renal injury in WT mice and eliminated the benefit of HDAC2 deletion. Gene expression analysis of endothelin showed decreased endothelin levels in HDAC2 deletion. These data demonstrate that contrasting effects of HDAC1 and 2 on CoREST complex stability within renal tubules can affect outcomes of renal IRI and implicate endothelin as a potential downstream mediator.

Discovery of Ethyl Ketone-Based Highly Selective HDACs 1, 2, 3 Inhibitors for HIV Latency Reactivation with Minimum Cellular Potency Serum Shift and Reduced hERG Activity.

We describe the discovery of histone deacetylase (HDACs) 1, 2, and 3 inhibitors with ethyl ketone as the zinc-binding group. These HDACs 1, 2, and 3 inhibitors have good enzymatic and cellular activity. Their serum shift in cellular potency has been minimized, and selectivity against hERG has been improved. They are also highly selective over HDACs 6 and 8. These inhibitors contain a variety of substituted heterocycles on the imidazole or oxazole scaffold. Compounds 31 and 48 stand out due to their good potency, high selectivity over HDACs 6 and 8, reduced hERG activity, optimized serum shift in cellular potency, and good rat and dog PK profiles.

Histone deacetylase 2: A potential therapeutic target for cancer and neurodegenerative disorders.

Histone deacetylases (HDACs) have been implicated in a number of diseases including cancer, cardiovascular disorders, diabetes mellitus, neurodegenerative disorders and inflammation. For the treatment of epigenetically altered diseases such as cancer, HDAC inhibitors have made a significant progress in terms of development of isoform selective inhibitiors. Isoform specific HDAC inhibitors have less adverse events and better safety profile. A HDAC isoform i.e., HDAC2 demonstrated significant role in the development of variety of diseases, mainly involved in the cancer and neurodegenerative disorders. Discovery and development of selective HDAC2 inhibitors have a great potential for the treatment of target diseases. In the present compilation, we have reviewed the role of HDAC2 in progression of cancer and neurodegenerative disorders, and information on the drug development opportunities for selective HDAC2 inhibition.

Silencing of CREB Inhibits HDAC2/TLR4/NF-κB Cascade to Relieve Severe Acute Pancreatitis-Induced Myocardial Injury.

The purpose of the present study is to investigate the role of CREB in cardiomyocytes proliferation in regulation of HDAC2-dependent TLR4/NF-κB pathway in severe acute pancreatitis (SAP)-induced myocardial injury. The SAP rat model was developed by injecting sodium touracholate into SD rats and then infected with lentivirus vectors expressing sh-CREB in the presence/absence of LPS. The pathological alterations of rat pancreatic and cardiac tissues were observed by HE staining. TUNEL assay was used to study apoptosis of cardiomyocytes. Next, the loss- and gain-function assay was conducted in LPS-induced myocardial injury cardiomyocytes to define the roles of CREB, HDAC2, and TLR4 in cardiomyocyte proliferation, apoptosis, inflammation, and myocardial injury in vitro. ChIP assay was used to study the enrichment of CREB bound to HDAC2 promoter. RT-qPCR and Western blot analysis were used to detect the expressions of related mRNA and proteins in the NF-κB pathway, respectively. CREB was found to be overexpressed in both SAP tissues and cells. CREB directly bound to the promoter of HDAC2 and activated its expression. Overexpressed CREB or HDAC2 inhibited proliferation and promoted apoptosis of cardiomyocytes. Suppression of CREB inhibited the HDAC2/TLR4/NF-κB cascade to promote proliferation and inhibit apoptosis of cardiomyocytes. The in vitro results were validated in vivo experiments. Coherently, suppression of CREB can inhibit HDAC2/TLR4/NF-κB cascade to promote cardiomyocyte proliferation, thus ameliorating SAP-induced myocardial injury.

Ketogenic diets inhibit mitochondrial biogenesis and induce cardiac fibrosis.

In addition to their use in relieving the symptoms of various diseases, ketogenic diets (KDs) have also been adopted by healthy individuals to prevent being overweight. Herein, we reported that prolonged KD exposure induced cardiac fibrosis. In rats, KD or frequent deep fasting decreased mitochondrial biogenesis, reduced cell respiration, and increased cardiomyocyte apoptosis and cardiac fibrosis. Mechanistically, increased levels of the ketone body ß-hydroxybutyrate (ß-OHB), an HDAC2 inhibitor, promoted histone acetylation of the Sirt7 promoter and activated Sirt7 transcription. This in turn inhibited the transcription of mitochondrial ribosome-encoding genes and mitochondrial biogenesis, leading to cardiomyocyte apoptosis and cardiac fibrosis. Exogenous ß-OHB administration mimicked the effects of a KD in rats. Notably, increased ß-OHB levels and SIRT7 expression, decreased mitochondrial biogenesis, and increased cardiac fibrosis were detected in human atrial fibrillation heart tissues. Our results highlighted the unknown detrimental effects of KDs and provided insights into strategies for preventing cardiac fibrosis in patients for whom KDs are medically necessary.

miR-23b Attenuates LPS-Induced Inflammatory Responses in Acute Lung Injury via Inhibition of HDAC2.

Inflammatory responses play significant role in infectious etiology-induced acute lung injury (ALI). Histone deacetylase 2 is found to be essential and stimulated in lipopolysaccharide (LPS)-induced ALI by regulating proinflammatory cytokines. miR-23b has been demonstrated to be downregulated in LPS-induced inflammatory injury. In this study, we aimed to explore the interaction between miR-23b and HDAC2 and their function in LPS-induced ALI. LPS treatment was induced on murine alveolar macrophage cell line MH-S. Level of miR-23b and HDAC2 were determined by real-time PCR or Western blot. Proinflammatory cytokines expression and secretion were detected by real-time PCR and ELISA assay. The levels of miR-23b and HDAC2 were manipulated by transient transfection of miRNA mimics, shRNA or overexpression vector. The interaction between miR-23b and HDAC2 were tested by Luciferase reporter assay. LPS treatment inhibited miR-23b expression, while increased HDAC2 level in MH-S cells. Proinflammatory cytokines were stimulated by LPS treatment. Knockdown of HDAC2 or overexpression of miR-23b significantly repressed the expression of proinflammatory cytokines induced by LPS. miR-23b could suppress HDAC2 expression by directly targeting to its mRNA. LPS treatment stimulated the inflammatory responses in macrophages through inhibition of miR-23b, enhanced HDAC2 expression and inducing the expression of its downstream targets TNF-α, IL-6, and IL-1ß. Overexpression of miR-23b was sufficient to suppress inflammatory responses by targeting HDAC2, making it a promising therapeutic target to ALI treatment.

Involvement of histone deacetylase 1/2 in adrenocorticotropic hormone synthesis and proliferation of corticotroph tumor AtT-20 cells.

Cushing's disease is mainly caused by autonomous production of adrenocorticotropic hormone (ACTH) from pituitary adenomas. In our previous study, a histone deacetylase (HDAC) inhibitor, trichostatin A, inhibited cell proliferation and ACTH production via decreased pituitary tumor-transforming gene 1 (PTTG1) in AtT-20 mouse corticotroph tumor cells. In the present study, we examined the effects of romidepsin, a potent and selective HDAC1/2 inhibitor, on cell proliferation and ACTH synthesis. To elucidate further potential mechanisms of romidepsin, we examined the effects of HDAC1/2 on proopiomelanocortin (Pomc) and Pttg1 mRNA levels and cell proliferation. Small interfering RNA-mediated knockdown was used to decrease HDAC1 or 2. Romidepsin treatment decreased Pomc and Pttg1 mRNA levels, and cell proliferation. The drug also increased Hdac1 and decreased Hdac2 mRNA levels. Hdac1 knockdown decreased basal Pttg1 mRNA levels and cell proliferation, but not Pomc mRNA levels. Romidepsin treatment decreases ACTH synthesis in corticotroph tumor cells. Romidepsin suppresses cell proliferation via PTTG1. HDAC1 is also involved in the proliferation of corticotroph cells via PTTG1.

Design, synthesis and evaluation of novel indirubin-based N-hydroxybenzamides, N-hydroxypropenamides and N-hydroxyheptanamides as histone deacetylase inhibitors and antitumor agents.

Several novel indirubin-based N-hydroxybenzamides, N-hydropropenamides and N-hydroxyheptanamides (4a-h, 7a-h, 10a-h) were designed using a fragment-based approach with structural features extracted from several previously reported HDAC inhibitors, such as SAHA (vorinostat), MGCD0103 (mocetinostat), nexturastat A and PXD-101 (belinostat). The biological results reveal that our compounds showed excellent cytotoxicity toward three common human cancer cell lines (SW620, PC-3 and NCI-H23) with IC50 values ranging from 0.09 to 0.007 µM. The cytotoxicity of the compounds was equipotent or even up to 10-times more potent than adriamycin and up to 205-times more potent than SAHA. Among the series of N-hydroxypropenamides, compounds 10a-d were the most potent HDAC inhibitors as well as cytotoxicity toward the cell lines tested. In addition, the strong inhibitory activites toward HDAC of our compounds were observed with IC50 values of below-micromolar range. Especially, compound 4a inhibited HDAC6 with an IC50 value of 29-fold lower than that against HDAC2 isoform. Representative compounds 4a and 7a were found to significantly arrest SW620 cells at G0/G1 phase. Compounds 7a and 10a were found to strongly induce apoptosis in SW620 cells. Docking studies revealed some important features affecting the selectivity against HDAC6 isoform. The results clearly demonstrate the potential of the indirubin-hydroxamic acid hybrids and these compounds should be very promising for further development.

Gallic acid, a phenolic acid, hinders the progression of prostate cancer by inhibition of histone deacetylase 1 and 2 expression.

Gallic acid (GA) is known to possess diverse biological activities, including anticancer. Histone deacetylase (HDACs) are controlled by tumor suppressor gene transcription and are overexpressed in various tumors, resulting in tumor development, progression and poor prognosis. This study aims to demonstrate the effect of GA on inhibition of prostate cancer (PCa) progression by modulating the expression of HDAC1 and 2 in PCa cells. To prove our research rationale, we used diverse experimental methods. GA decreased the cell viability of only PCa cell lines and not normal cells (contrary to another HDAC inhibitor, suberoylanilide hydroxamic acid) and also inhibited colony and tumor spheroid formation. Exposure to GA decreased the mitochondrial membrane potential (ΔΨm), increased the number of apoptotic cells and induced DNA fragmentation. Western blot analysis revealed down-regulated expression of HDAC1 and 2, leading to up-regulation of acetyl-p53 expression at the protein level, subsequent to down-regulating the expression of cell-cycle-related genes, i.e., proliferating cell nuclear antigen (PCNA), Cyclin D1 and E1, up-regulating the expression of cell cycle arrest gene p21 and regulating the expression of apoptosis intrinsic pathway-related genes, such as Bax, Bcl-2, cleaved Caspase-3 and poly (ADP-ribose) polymerase 1 in both PCa cell lines. Furthermore, oral administration of GA for 8 weeks on PC-3 cells-derived tumor xenograft mice model decreases the tumor size, damages the tumor structure and down-regulates the expression of HDAC1 and 2 and PCNA in tumor mass, as confirmed by histological analysis. These results indicated that GA may hinder the PCa progression by inhibiting HDAC1 and 2 expression, thereby demonstrating the potential of GA to be used as HDACs inhibitor and anti-PCa therapeutics.