Identification of type-specific anticancer histone deacetylase inhibitors: road to success

The Human Genetic Differences in the Outcomes of mRNA Vaccination against COVID-19: A Prospective Cohort Study

BACKGROUND

This study aimed to explore how genetic variations in individuals impact neutralization activity post-mRNA vaccination, recognizing the critical role vaccination plays in curbing COVID-19 spread and the necessity of ensuring vaccine efficacy amidst genetic diversity.

METHODS

In a 4-week clinical pilot study, 534 healthy subjects received their first COVID vaccine dose, followed by the second dose. Antibody levels were evaluated thrice. From this pool, 120 participants were selected and divided into high- and low-antibody groups based on their levels. Genomic DNA was isolated from peripheral blood mononuclear cells for pilot genome-wide association studies (GWAS) conducted on a single platform. Real-time PCR was used to confirm differences in gene expression identified via GWAS analysis.

RESULTS

Three SNPs exceeded the level of p < 1.0 × 10-3. The rs7795433 SNP of the HDAC9 gene (7q21.1) showed the strongest association with COVID-19 vaccination under the additive model (OR = 5.63; p = 3 × 10-5). In the PCR experiments, the AA genotype group showed that the gene expression level of HDAC9 was likely to be decreased in the low-antibody-formation group at the time of vaccination.

CONCLUSION

We found that AA genotype holders (rs7795433 SNP of the HDAC9 gene) have a high probability of having a higher antibody count when vaccinated, and GG type holders have a high probability of the opposite. These findings show that the genetic characteristics of vaccinated people may affect antibody production after COVID vaccination.

Progress in discovery and development of natural inhibitors of histone deacetylases (HDACs) as anti-cancer agents

The study of epigenetic translational modifications had drawn great interest for the last few decades. These processes play a vital role in many diseases and cancer is one of them. Histone acetyltransferase (HAT) and histone deacetylases (HDACs) are key enzymes involved in the acetylation and deacetylation of histones and ultimately in post-translational modifications. Cancer frequently exhibits epigenetic changes, particularly disruption in the expression and activity of HDACs. It includes the capacity to regulate proliferative signalling, circumvent growth inhibitors, escape cell death, enable replicative immortality, promote angiogenesis, stimulate invasion and metastasis, prevent immunological destruction, and genomic instability. The majority of tumours develop and spread as a result of HDAC dysregulation. As a result, HDAC inhibitors (HDACis) were developed, and they today stand as a very promising therapeutic approach. One of the most well-known and efficient therapies for practically all cancer types is chemotherapy. However, the efficiency and safety of treatment are constrained by higher toxicity. The same has been observed with the synthetic HDACi. Natural products, owing to many advantages over synthetic compounds for cancer treatment have always been a choice for therapy. Hence, naturally available molecules are of particular interest for HDAC inhibition and HDAC has drawn the attention of the research fraternity due to their potential to offer a diverse array of chemical structures and bioactive compounds. This diversity opens up new avenues for exploring less toxic HDAC inhibitors to reduce side effects associated with conventional synthetic inhibitors. The review presents comprehensive details on natural product HDACi, their mechanism of action and their biological effects. Moreover, this review provides a brief discussion on the structure activity relationship of selected natural HDAC inhibitors and their analogues which can guide future research to discover selective, more potent HDACi with minimal toxicity.

The expression of HDAC9 and P300 in papillary thyroid carcinoma cell line

PURPOSE

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer and accounts for 85-90% of all thyroid cancers. Metastatic differentiated thyroid cancer, radioiodine-refractory thyroid cancer, and anaplastic thyroid cancer still lack effective therapeutic options. Here, we aimed to assess HDAC9 and P300 expression in the papillary thyroid carcinoma cell line and compare them with normal thyroid cells.

METHODS

Nthy-ori-3-1, a normal thyroid cell line, and BCPAP, a PTC cell line, were cultured for 24 and 48 h and immunofluorescence staining was used to determine the levels of HDAC9 and P300 protein expression. HDAC9 paracrine release was assessed using an ELISA assay.

RESULTS

HDAC9 protein expression was higher in both cell groups at the 48th hour than at the 24th hour; however, P300 protein expression was lower in BCPAP cells at the 48th hour than at the 24th hour. In comparison to Nthy-ori-3-1, BCPAP expressed more HDAC9 and P300 proteins. HDAC9 secretion slightly increased in Nthy-ori-3-1 cells from 24 to 48 h. Furthermore, HDAC9 secretion in BCPAP cells dramatically decreased from 24 to 48 h.

CONCLUSION

Our findings revealed that the expression of HDAC9 and P300 was higher in the PTC cell line than in normal thyroid cells. This indicates that the acetylation mechanism in thyroid cancer cells is not the same as it is in healthy cells. Epigenetic studies may reveal the mechanisms underlying PTC with further analysis.

The Histone Acetyltransferase MOF Regulates SIRT1 Expression to Suppress Renal Cell Carcinoma Progression

BACKGROUND

Renal cell carcinoma (RCC) is one of the most common and lethal human urological malignancies around the world. Although many advancements in diagnostic and therapeutic strategies have been acquired, the prognosis of patients with metastatic RCC was poor. Thus, there is an urgent need to understand the molecular mechanism of RCC.

METHODS

The quantitative real-time PCR (qRT-PCR) was used to detect the RNA expression of MOF in human RCC tissues and cell lines. The protein expression of MOF was analyzed with immunohistochemistry (IHC) and Western blot. To understand the regulatory mechanism of MOF in liver cancer, ChIP-qPCR assay and dual-luciferase assay were performed. Moreover, a series of in vivo and in vitro experiments were conducted to evaluate the effect of MOF on renal cell carcinoma progression.

RESULTS

In the present study, we found that Males absent on the first (MOF), a histone acetyltransferase involved in transcription activation, was significantly decreased in both RCC tissues and RCC cells compared to normal tissues and non-cancer cells. Moreover, MOF downregulation was associated with advanced histological grade, pathologic stage and distant metastasis of RCC patients. Ectopic expression of MOF could significantly attenuate cell proliferation and promote cell apoptosis. Besides, MOF overexpression also suppressed migration of RCC cells through inhibiting epithelial-mesenchymal transition (EMT). Importantly, the inhibition of tumor growth by MOF was further confirmed by in vivo studies. Mechanism dissection revealed that MOF could transcriptionally upregulate the expression of SIRT1, leading to attenuated STAT3 signaling, which was involved in cell proliferation and migration. Moreover, SIRT1 knockdown could restore the biological function induced by MOF overexpression.

CONCLUSIONS

Our findings indicated that MOF serves as a tumor suppressor via regulation of SIRT1 in the development and progression of RCC, and MOF might be a potent biomarker for diagnosis and prognosis prediction of RCC patients.

Apoptotic Effects of N-(2-Hydroxyphenyl)-2-Propylpentanamide on U87-MG and U-2 OS Cells and Antiangiogenic Properties

BACKGROUND AND OBJECTIVE

Histone Deacetylases (HDACs) are important therapeutic targets for many types of human cancers. A derivative of valproic acid, N-(2-hydroxyphenyl)-2-propylpentanamide (HOAAVPA), has antiproliferative properties on some cancer cell lines and inhibits the HDAC1 isoform.

MATERIALS AND METHODS

In this work, HO-AAVPA was tested as an antiproliferative agent in U87-MG (human glioblastoma) and U-2 OS cells (human osteosarcoma), which are types of cancer that are difficult to treat, and its antiangiogenic properties were explored.

RESULTS

HO-AAVPA had antiproliferative effects at 48h with an IC₅₀=0.655mM in U87-MG cells and an IC₅₀=0.453mM in U-2 OS cells. Additionally, in the colony formation assay, HO-AAVPA decreased the number of colonies by approximately 99% in both cell lines and induced apoptosis by 31.3% in the U-2 OS cell line and by 78.2% in the U87-MG cell line. Additionally, HO-AAVPA reduced the number of vessels in Chorioallantoic Membranes (CAMs) by approximately 67.74% and IL-6 levels in both cell lines suggesting that the biochemical mechanism on cancer cell of HO-AAVPA is different compared to VPA.

CONCLUSION

HO-AAVPA has antiproliferative effects on glioblastoma and osteosarcoma and antiangiogenic properties.

Pharmacological targeting of TNS3 with histone deacetylase inhibitor as a therapeutic strategy in esophageal squamous cell carcinoma

Histone acetylation which regulates about 2-10% of genes has been demonstrated to be involved in tumorigenesis of esophageal squamous cell carcinoma (ESCC). In this study, we investigated the treatment response of ESCC to selective histone deacetylase inhibitor (HDACi) LMK-235 and potential biomarker predicting the treatment sensitivity. We identified tensin-3 (TNS3) which was highly over-expressed in ESCC as one of the down-regulated genes in response to LMK-235 treatment. TNS3 was found positively correlated with the tumor malignancy and poor prognosis in the patients. Silencing TNS3 significantly inhibited ESCC cell proliferation both in vitro and in vivo, sensitizing the treatment response to LMK-235. Our findings provide an insight into understanding the oncogenic role of TNS3 in ESCC and its clinical application for HDAC targeted therapy of ESCC.

Latency Reversing Agents: Kick and Kill of HTLV-1?

Human T-cell leukemia virus type 1 (HTLV-1), the cause of adult T-cell leukemia/lymphoma (ATLL), is a retrovirus, which integrates into the host genome and persistently infects CD4⁺ T-cells. Virus propagation is stimulated by (1) clonal expansion of infected cells and (2) de novo infection. Viral gene expression is induced by the transactivator protein Tax, which recruits host factors like positive transcription elongation factor b (P-TEFb) to the viral promoter. Since HTLV-1 gene expression is repressed in vivo by viral, cellular, and epigenetic mechanisms in late phases of infection, HTLV-1 avoids an efficient CD8⁺ cytotoxic T-cell (CTL) response directed against the immunodominant viral Tax antigen. Hence, therapeutic strategies using latency reversing agents (LRAs) sought to transiently activate viral gene expression and antigen presentation of Tax to enhance CTL responses towards HTLV-1, and thus, to expose the latent HTLV-1 reservoir to immune destruction. Here, we review strategies that aimed at enhancing Tax expression and Tax-specific CTL responses to interfere with HTLV-1 latency. Further, we provide an overview of LRAs including (1) histone deacetylase inhibitors (HDACi) and (2) activators of P-TEFb, that have mainly been studied in context of human immunodeficiency virus (HIV), but which may also be powerful in the context of HTLV-1.

Characterizing binding intensity and energetic features of histone deacetylase inhibitor pracinostat towards class I HDAC isozymes through futuristic drug designing strategy

Pracinostat, an emerging hydroxamate histone deacetylase (HDAC) inhibitor has shown better efficacy than approved inhibitor suberoylanilide hydroxamic acid (SAHA). Apart from haematological malignancies, this inhibitor has shown promising results in preclinical models of solid tumours. Being pan-inhibitor pracinostat targets various classical HDACs and has demonstrated antiproliferative properties in a series of cancer cell lines. Currently, no energetic and structural studies are available about the pracinostat against four HDAC isozymes of Class I. Taking this into account, the current study involved flexible molecular docking for gaining insights regarding pracinostat-HDAC isozyme interactions, molecular mechanics generalized born surface area (MM-GBSA) for estimating binding affinity of this inhibitor towards these isozymes and energetically optimized pharmacophores (e-Pharmacophores) technique for delineating the critical e-pharmacophoric features of pracinostat in its least energy state in the binding pocket of these HDACs. The outcome from this study will help in further optimization of pracinostat towards better therapeutic and the e-Pharmacophores generated will serve as queries in e-Pharamcophores guided virtual screening.

MOF Regulates TNK2 Transcription Expression to Promote Cell Proliferation in Thyroid Cancer

MOF is a well-known histone acetyltransferase to catalyze acetylation of histone H4 lysine 16 (K16), and it is relevant to diverse biological processes, such as gene transcription, cell cycle, early embryonic development and tumorigenesis. Here, we identify MOF as an oncogene in most thyroid cancer. It is found that expression level of MOF was significantly upregulated in most thyroid cancer tissue samples and cell lines. MOF-deficient in both BHP-10-3 and TT2609 cell lines inhibited cell proliferation by blocking the cell cycle in G1 phase and enhanced cell apoptosis. Mechanistically, MOF bound the TNK2 promoter to activate TNK2 transcription. Furthermore, the expression level of TNK2 was decreased with the histone acetyltransferase inhibitor. Besides, MOF promoted proliferation of thyroid cancer cells through increased phosphorylation of AKT, thus activating the PI3K/AKT pathway. Ultimately, our findings indicated that MOF played an oncogene role in development and progression of thyroid cancer and may be a potential novel target for the treatment of thyroid cancer.

Recent Update of HDAC Inhibitors in Lymphoma

Modulating epigenetic modification has been recognized for over a decade as an effective therapeutic approach to cancer and many studies of histone deacetylase (HDAC), one of the best known epigenetic modulators, have been published. HDAC modulates cell proliferation and angiogenesis and plays an essential role in cell growth. Research shows that up-regulated HDACs are present in many cancer types and synthetic or natural HDAC inhibitors have been used to silence overregulated HDACs. Inhibiting HDACs may cause arrest of cell proliferation, angiogenesis reduction and cell apoptosis. Recent studies indicate that HDAC inhibitors can provide a therapeutic effect in various cancers, such as B-cell lymphoma, leukemia, multiple myeloma and some virus-associated cancers. Some evidence has demonstrated that HDAC inhibitors can increase the expression of immune-related molecules leading to accumulation of CD8 + T cells and causing unresponsive tumor cells to be recognized by the immune system, reducing tumor immunity. This may be a solution for the blockade of PD-1. Here, we review the emerging development of HDAC inhibitors in various cancer treatments and reduction of tumor immunity.

HDAC5 Inhibitors as a Potential Treatment in Breast Cancer Affecting Very Young Women

Background: Breast cancer in very young women (BCVY) defined as <35 years old, presents with different molecular biology than in older patients. High HDAC5 expression has been associated with poor prognosis in breast cancer (BC) tissue. We aimed to analyze HDAC5 expression in BCVY and older patients and their correlation with clinical features, also studying the potential of HDAC5 inhibition in BC cell lines. Methods: HDAC5 expression in 60 BCVY and 47 older cases were analyzed by qRT-PCR and correlated with clinical data. The effect of the HDAC5 inhibitor, LMK-235, was analyzed in BC cell lines from older and young patients. We performed time and dose dependence viability, migration, proliferation, and apoptosis assays. Results: Our results correlate higher HDAC5 expression with worse prognosis in BCVY. However, we observed no differences between HDAC5 expression and pathological features. Our results showed greatly reduced progression in BCVY cell lines and also in all triple negative subtypes when cell lines were treated with LMK-235. Conclusions: In BCVY, we found higher expression of HDAC5. Overexpression of HDAC5 in BCVY correlates with lower survival rates. LMK-235 could be a potential treatment in BCVY.

Trichostatin A decreases the levels of MeCP2 expression and phosphorylation and increases its chromatin binding affinity

MeCP2 binds to methylated DNA in a chromatin context and has an important role in cancer and brain development and function. Histone deacetylase (HDAC) inhibitors are currently being used to palliate many cancer and neurological disorders. Yet, the molecular mechanisms involved are not well known for the most part and, in particular, the relationship between histone acetylation and MeCP2 is not well understood. In this paper, we study the effect of the HDAC inhibitor trichostatin A (TSA) on MeCP2, a protein whose dysregulation plays an important role in these diseases. We find that treatment of cells with TSA decreases the phosphorylation state of this protein and appears to result in a higher MeCP2 chromatin binding affinity. Yet, the binding dynamics with which the protein binds to DNA appear not to be significantly affected despite the chromatin reorganization resulting from the high levels of acetylation. HDAC inhibition also results in an overall decrease in MeCP2 levels of different cell lines. Moreover, we show that miR132 increases upon TSA treatment, and is one of the players involved in the observed downregulation of MeCP2.

Epigenetic Modifications: Novel Therapeutic Approach for Thyroid Cancer

The incidence of thyroid cancer is growing the fastest among all cancers in the United States, especially in women. The number of patients with thyroid neoplasm is part of an even larger number of patients who often need to undergo an operation to exclude a cancer diagnosis. While differentiated thyroid cancer (papillary thyroid cancer and follicular thyroid cancer) accounts for most cases of thyroid cancer and has a relatively good prognosis, effective treatments for patients with de-differentiated and anaplastic thyroid cancer are still gravely needed. Despite progress in the identification of genetic changes in thyroid cancer, the impact of aberrant epigenetic alterations on thyroid cancer remains to be fully elucidated. Understanding of the roles of epigenetic changes in thyroid cancer could open new opportunities for the identification of innovative molecular targets for novel treatment modalities, especially for anaplastic thyroid cancer for which treatment is very limited. This article briefly reviews the studies that exemplify the potential for and promise of using epigenetic regulators in the treatment of thyroid cancer.

Assessment of Interactions between Cisplatin and Two Histone Deacetylase Inhibitors in MCF7, T47D and MDA-MB-231 Human Breast Cancer Cell Lines - An Isobolographic Analysis

Histone deacetylase inhibitors (HDIs) are promising anticancer drugs, which inhibit proliferation of a wide variety of cancer cells including breast carcinoma cells. In the present study, we investigated the influence of valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA, vorinostat), alone or in combination with cisplatin (CDDP) on proliferation, induction of apoptosis and cell cycle progression in MCF7, T47D and MDA-MB-231 human breast carcinoma cell lines. The type of interaction between HDIs and CDDP was determined by an isobolographic analysis. The isobolographic analysis is a very precise and rigorous pharmacodynamic method, to determine the presence of synergism, addition or antagonism between different drugs with using variety of fixed dose ratios. Our experiments show that the combinations of CDDP with SAHA or VPA at a fixed-ratio of 1:1 exerted additive interaction in the viability of MCF7 cells, while in T47D cells there was a tendency to synergy. In contrast, sub-additive (antagonistic) interaction was observed for the combination of CDDP with VPA in MDA-MB-231 “triple-negative” (i.e. estrogen receptor negative, progesterone receptor negative, and HER-2 negative) human breast cancer cells, whereas combination of CDDP with SAHA in the same MDA-MB-231 cell line yielded additive interaction. Additionally, combined HDIs/CDDP treatment resulted in increase in apoptosis and cell cycle arrest in all tested breast cancer cell lines in comparison with a single therapy. In conclusion, the additive interaction of CDDP with SAHA or VPA suggests that HDIs could be combined with CDDP in order to optimize treatment regimen in some human breast cancers.

Trichostatin A, a histone deacetylase inhibitor, suppresses proliferation and promotes apoptosis of esophageal squamous cell lines

Histone deacetylase (HDAC)‑mediated epigenetic modification plays crucial roles in numerous biological processes, including cell cycle regulation, cell proliferation and apoptosis. HDAC inhibitors demonstrate antitumor effects in various cancers, including glioblastoma and breast cancer. HDAC inhibitors are therefore promising antitumor drugs for these tumors. The tumorigenesis and development of esophageal squamous cell carcinoma (ESCC) involve genetic and epigenetic mechanisms. However, the effects of the HDAC inhibitor on ESCC are not fully investigated. In the present study, ESCC cells were treated with trichostatin A (TSA) and its antitumor effects and related mechanisms were investigated. The results indicated that TSA suppressed the proliferation of ESCCs and caused G1 phase arrest by inducing the expression of p21 and p27. TSA also induced cell apoptosis by enhancing the expression of pro‑apoptotic protein Bax and decreasing the expression of anti‑apoptotic protein Bcl‑2. Furthermore, TSA inhibited the expression of phosphatidylinositol‑3‑kinase (PI3K) and reduced the phosphorylation of Akt and extracellular signal‑regulated kinase (ERK)1/2 in EC9706 and EC1 cell lines. High levels of acetylated histone H4 were detected in TSA‑treated ESCC cell lines. Overall, these results indicate that TSA suppresses ESCC cell growth by inhibiting the activation of the PI3K/Akt and ERK1/2 pathways. TSA also promotes cell apoptosis through epigenetic regulation of the expression of apoptosis‑related protein.

Design, synthesis, and biological evaluation of 1, 3-disubstituted-pyrazole derivatives as new class I and IIb histone deacetylase inhibitors

A novel series of HDAC inhibitors demonstrating class I and IIb subtype selectivity have been identified using a scaffold-hopping strategy. Several designed compounds showed better selectivity for class I and IIb over class IIa HDAC isoforms comparing to the FDA approved HDAC targeting drug SAHA. A representative lead compound 22 bearing a biphenyl moiety demonstrated promising class I and IIb HDAC isoforms selectivity and in vitro anticancer activities against several cancer cell lines. This work could serve as a fundamental platform for further exploration of selective HDAC inhibitors using designed molecular scaffold.

Histone deacetylase inhibitors suppress mutant p53 transcription via histone deacetylase 8

Mutation of the p53 gene is the most common genetic alteration in human cancer and contributes to malignant process by enhancing transformed properties of cells and resistance to anticancer therapy. Mutant p53 is often highly expressed in tumor cells at least, in part, due to its increased half-life. However, whether mutant p53 expression is regulated by other mechanisms in tumors is unclear. Here we found that histone deacetylase (HDAC) inhibitors suppress both wild-type and mutant p53 transcription in time- and dose-dependent manners. Consistent with this, the levels of wild-type and mutant p53 proteins are decreased upon treatment with HDAC inhibitors. Importantly, we found that upon knockdown of each class I HDAC, only HDAC8 knockdown leads to decreased expression of wild-type and mutant p53 proteins and transcripts. Conversely, we found that ectopic expression of wild-type, but not mutant HDAC8, leads to increased transcription of p53. Furthermore, we found that knockdown of HDAC8 results in reduced expression of HoxA5 and consequently, attenuated ability of HoxA5 to activate p53 transcription, which can be rescued by ectopic expression of HoxA5. Because of the fact that HDAC8 is required for expression of both wild-type and mutant p53, we found that targeted disruption of HDAC8 expression remarkably triggers proliferative defect in cells with a mutant, but not wild-type, p53. Together, our data uncover a regulatory mechanism of mutant p53 transcription via HDAC8 and suggest that HDAC inhibitors and especially HDAC8-targeting agents might be explored as an adjuvant for tumors carrying a mutant p53.

Histone deacetylase (HDAC) inhibitors with a novel connecting unit linker region reveal a selectivity profile for HDAC4 and HDAC5 with improved activity against chemoresistant cancer cells

The synthesis and biological evaluation of new potent hydroxamate-based HDAC inhibitors with a novel alkoxyamide connecting unit linker region are described. Biological evaluation includes MTT and cellular HDAC assays on sensitive and chemoresistant cancer cell lines as well as HDAC profiling of selected compounds. Compound 19i (LMK235) (N-((6-(hydroxyamino)-6-oxohexyl)oxy)-3,5-dimethylbenzamide) showed similar effects compared to vorinostat on inhibition of cellular HDACs in a pan-HDAC assay but enhanced cytotoxic effects against the human cancer cell lines A2780, Cal27, Kyse510, and MDA-MB231. Subsequent HDAC profiling yielded a novel HDAC isoform selectivity profile of 19i in comparison to vorinostat or trichostatin A (TSA). 19i shows nanomolar inhibition of HDAC4 and HDAC5, whereas vorinostat and TSA inhibit HDAC4 and HDAC5 in the higher micromolar range.

Epigenetic mechanisms in Alzheimer's disease: progress but much to do

The interesting review from Mastroeni and colleagues highlights recent progress on epigenetic analysis of Alzheimer's disease, but it also illustrates how much we still need to do.

Chidamide (CS055/HBI-8000): a new histone deacetylase inhibitor of the benzamide class with antitumor activity and the ability to enhance immune cell-mediated tumor cell cytotoxicity

PURPOSE

Chidamide (CS055/HBI-8000) is a new histone deacetylase (HDAC) inhibitor of the benzamide class currently under clinical development in cancer indications. This study reports the in vitro and in vivo antitumor characteristics of the compound.

METHODS

Selectivity and potency of chidamide in inhibition of HDAC isotypes were analyzed by using a panel of human recombinant HDAC proteins. Tumor cell lines either in culture or inoculated in nude mice were used for the evaluation of the compound's antitumor activity. To investigate the immune cell-mediated antitumor effect, isolated peripheral blood mononuclear cells from healthy donors were treated with chidamide, and cytotoxicity and expression of relevant surface proteins were analyzed. Microarray gene expression studies were performed on peripheral white blood cells from two T-cell lymphoma patients treated with chidamide.

RESULTS

Chidamide was found to be a low nanomolar inhibitor of HDAC1, 2, 3, and 10, the HDAC isotypes well documented to be associated with the malignant phenotype. Significant and broad spectrum in vitro and in vivo antitumor activity, including a wide therapeutic index, was observed. Chidamide was also shown to enhance the cytotoxic effect of human peripheral mononuclear cells ex vivo on K562 target cells, accompanied by the upregulation of proteins involved in NK cell functions. Furthermore, the expression of a number of genes involved in immune cell-mediated antitumor activity was observed to be upregulated in peripheral white blood cells from two T-cell lymphoma patients who responded to chidamide administration.

CONCLUSIONS

The results presented in this study provide evidence that chidamide has potential applicability for the treatment of a variety of tumor types, either as a single agent or in combination therapies.

Models for anti-tumor activity of bisphosphonates using refined topochemical descriptors

An in silico approach comprising of decision tree (DT), random forest (RF) and moving average analysis (MAA) was successfully employed for development of models for prediction of anti-tumor activity of bisphosphonates. A dataset consisting of 65 analogues of both nitrogen-containing and non-nitrogen-containing bisphosphonates was selected for the present study. Four refinements of eccentric distance sum topochemical index termed as augmented eccentric distance sum topochemical indices 1-4 [formula: see text] have been proposed so as to significantly augment discriminating power. Proposed topological indices (TIs) along with the exiting TIs (>1,400) were subsequently utilized for development of models for prediction of anti-tumor activity of bisphosphonates. A total of 43 descriptors of diverse nature, from a large pool of molecular descriptors, calculated through E-Dragon software (version 1.0) and an in-house computer program were selected for development of suitable models by employing DT, RF and MAA. DT identified two TIs as most important and classified the analogues of the dataset with an accuracy of 97% in training set and 90.7% in tenfold cross-validated set. Random forest correctly classified the analogues with an accuracy of 89.2%. Four independent models developed through MAA predicted the activity of analogues of the dataset with an accuracy of 87.6% to 89%. The statistical significance of proposed models was assessed through intercorrelation analysis, specificity, sensitivity and Matthew's correlation coefficient. The proposed models offer a vast potential for providing lead structures for development of potent anti-tumor agents for treatment of cancer that has spread to the bone.

Metabolism as a key to histone deacetylase inhibition

There is growing interest in the epigenetic mechanisms that are dysregulated in cancer and other human pathologies. Under this broad umbrella, modulators of histone deacetylase (HDAC) activity have gained interest as both cancer chemopreventive and therapeutic agents. Of the first generation, FDA-approved HDAC inhibitors to have progressed to clinical trials, vorinostat represents a "direct acting" compound with structural features suitable for docking into the HDAC pocket, whereas romidepsin can be considered a prodrug that undergoes reductive metabolism to generate the active intermediate (a zinc-binding thiol). It is now evident that other agents, including those in the human diet, can be converted by metabolism to intermediates that affect HDAC activity. Examples are cited of short-chain fatty acids, seleno-α-keto acids, small molecule thiols, mercapturic acid metabolites, indoles, and polyphenols. The findings are discussed in the context of putative endogenous HDAC inhibitors generated by intermediary metabolism (e.g. pyruvate), the yin-yang of HDAC inhibition versus HDAC activation, and the screening assays that might be most appropriate for discovery of novel HDAC inhibitors in the future.

HDAC6 α-tubulin deacetylase: a potential therapeutic target in neurodegenerative diseases

Histone deacetylases (HDACs), or lysine deacetylases (KDAC), are epigenetic regulators that catalyze the removal of acetyl moieties from the tails of lysine residues of histones and other proteins. To date, eighteen HDAC family members (HDAC1-11 and SIRT1-7) have been identified and grouped into four classes according to their homology to yeast histone deacetylases. HDACs play an important role in regulating gene transcription as well as a variety of cellular functions. Recent studies have found that HDAC6 (α-tubulin deacetylase) has the novel ability to capture α-tubulin as a substrate and regulate the physiological level of its acetylated form. In addition, a growing body of evidence suggests that α-tubulin deacetylase plays a critical role in the cellular response to the accumulation of misfolded and aggregated proteins, which are a prominent pathological feature common to many age-related neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases. Therefore, the role of α-tubulin deacetylase and its potential as a therapeutic target for neurodegenerative diseases are areas of rapidly expanding investigation. Here we review the research of the role played by HDAC6 in the regulation of tubulin modification and aggresome formation. We also summarize the specific inhibitors of HDAC6 and address reports that implicate HDAC6 in various neurodegenerative disorders.

The synthesis and evaluation of N1-(4-(2-[18F]-fluoroethyl)phenyl)-N8-hydroxyoctanediamide ([18F]-FESAHA), a PET radiotracer designed for the delineation of histone deacetylase expression in cancer

INTRODUCTION

Given the significant utility of suberoylanilide hydroxamic acid (SAHA) in chemotherapeutic protocols, a PET tracer that mimics the histone deacetylase (HDAC) inhibition of SAHA could be a valuable tool in the diagnosis, treatment planning and treatment monitoring of cancer. Here, we describe the synthesis, characterization and evaluation of N(1)-(4-(2-[(18)F]-fluoroethyl)phenyl)-N(8)-hydroxyoctanediamide ([(18)F]-FESAHA), a PET tracer designed for the delineation of HDAC expression in cancer.

METHODS

FESAHA was synthesized and biologically characterized in vivo and in vitro. [(18)F]-FESAHA was then synthesized in high radiochemical purity, and the logP and serum stability of the radiotracer were determined. In vitro cellular uptake experiments and acute biodistribution and small-animal PET studies were performed with [(18)F]-FESAHA in mice bearing LNCaP xenografts.

RESULTS

[(18)F]-FESAHA was synthesized in high radiochemical purity via an innovative one-pot procedure. Enzymatic inhibition assays illustrated that FESAHA is a potent HDAC inhibitor, with IC(50) values from 3 nM to 1.7 μM against the 11 HDAC subtypes. Cell proliferation experiments revealed that the cytostatic properties of FESAHA very closely resemble those of SAHA in both LNCaP cells and PC-3 cells. Acute biodistribution and PET imaging experiments revealed tumor uptake of [(18)F]-FESAHA and substantially higher values in the small intestine, kidneys, liver and bone.

CONCLUSION

The significant non-tumor background uptake of [(18)F]-FESAHA presents a substantial obstacle to the use of the radiotracer as an HDAC expression imaging agent. The study at hand, however, does present a number of lessons critical to both the synthesis of hydroxamic acid containing PET radiotracers and imaging agents aimed at delineating HDAC expression.