Belinostat: clinical applications in solid tumors and lymphoma

Research progress and applications of epigenetic biomarkers in cancer

Epigenetic changes are heritable changes in gene expression without changes in the nucleotide sequence of genes. Epigenetic changes play an important role in the development of cancer and in the process of malignancy metastasis. Previous studies have shown that abnormal epigenetic changes can be used as biomarkers for disease status and disease prediction. The reversibility and controllability of epigenetic modification changes also provide new strategies for early disease prevention and treatment. In addition, corresponding drug development has also reached the clinical stage. In this paper, we will discuss the recent progress and application status of tumor epigenetic biomarkers from three perspectives: DNA methylation, non-coding RNA, and histone modification, in order to provide new opportunities for additional tumor research and applications.

Rational design of supramolecular self-assembly sensor for living cell imaging of HDAC1 and its application in high-throughput screening

Supramolecular chemistry offers new insights in bioimaging, but specific tracking of enzyme in living cells via supramolecular host-guest reporter pair remains challenging, largely due to the interference caused by the complex cellular environment on the binding between analytes and hosts. Here, by exploiting the principle of supramolecular tandem assay (STA) and the classic host-guest reporter pair (p-sulfonatocalix[4]arene (SC4A) and lucigenin (LCG)) and rationally designing artificial peptide library to screen sequence with high affinity of the target enzyme, we developed a "turn-on" fluorescent sensing system for intracellular imaging of histone deacetylase 1 (HDAC1), which is a potential therapeutic target for various diseases, including cancer, neurological, and cardiovascular diseases. Based on computational simulations and experimental validations, we verified that the deacetylated peptide by HDAC1 competed LCG, freeing it from the SC4A causing fluorescence increase. Enzyme kinetics experiments were further conducted to prove that this assay could detect HDAC1 specifically with high sensitivity (the LOD value is 0.015 μg/mL, ten times lower than the published method). This system was further applied for high-throughput screening of HDAC1 inhibitors over a natural compound library containing 147 compounds, resulting in the identification of a novel HDAC1 down-regulator (Ginsenoside RK3). Our results demonstrated the sensitivity and robustness of the assay system towards HDAC1. It should serve as a valuable tool for biochemical studies and drug screening.

Perspectives and new aspects of histone deacetylase inhibitors in the therapy of CNS diseases

Many populations worldwide are suffering from central nervous system (CNS) diseases such as brain tumors, neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and Huntington's disease) and stroke. There is a shortage of effective drugs for most CNS diseases. As one of the regulatory mechanisms of epigenetics, the particular role and therapeutic benefits of histone deacetylases (HDACs) in the CNS have been extensively studied. In recent years, HDACs have attracted increasing attention as potential drug targets for CNS diseases. In this review, we summarize the recent applications of representative histone deacetylases inhibitors (HDACis) in CNS diseases and discuss the challenges in developing HDACis with different structures and better blood-brain barrier (BBB) permeability, hoping to promote the development of more effective bioactive HDACis for the treatment of CNS diseases.

Synthesis and Antitumor Evaluation of Biotin-SN38-Valproic Acid Conjugates

Despite the strong anticancer activity of SN38 (7-ethyl-10-hydroxy-camptothecin), the severe side effects and loss of anticancer activity caused by the lack of selectivity to cancer cells and hydrolysis of ring E prevent its clinical application. To address the issue, herein a multifunctional SN38 derivative (compound 9) containing biotin (tumor-targeting group) and valproic acid (histone deacetylase inhibitor, HDACi) was synthesized via click chemistry and evaluated using MTT assay. The in vitro cytotoxicity study showed that compound 9 exhibited superior cytotoxicity than irinotecan against human cervical cancer HeLa cells, albeit it was inferior to SN38. More significantly, compound 9 significantly reduced toxicity in mouse embryonic fibroblast NIH3T3 cells, indicating that compound 9 had the capacity to enhance tumor targeting due to its cell selectivity. Further studies demonstrated that, compared with irinotecan, compound 9 induced similar apoptosis of cancer cells. Consequently, compound 9 can not only improve its tumor-targeting ability mediated by biotin but also exert potent anticancer activity through the effect of SN38 and valproic acid, indicating that the design concept is an effective strategy for the structural modification of SN38.

Potential Molecular Targeted Therapy for Unresectable Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent and lethal cancers, representing a serious worldwide health concern. The recurrence incidence of hepatocellular carcinoma (HCC) following surgery or ablation is as high as 70%. Thus, the clinical applicability of standard surgery and other locoregional therapy to improve the outcomes of advanced HCC is restricted and far from ideal. The registered trials did not identify a treatment that prolonged recurrence-free survival, the primary outcome of the majority of research. Several investigator-initiated trials have demonstrated that various treatments extend patients' recurrence-free or overall survival after curative therapies. In the past decade, targeted therapy has made significant strides in the treatment of advanced HCC. These targeted medicines produce antitumour effects via specific signals, such as anti-angiogenesis or advancement of the cell cycle. As a typical systemic treatment option, it significantly improves the prognosis of this fatal disease. In addition, the combination of targeted therapy with an immune checkpoint inhibitor is redefining the paradigm of advanced HCC treatment. In this review, we focused on the role of approved targeted medicines and potential therapeutic targets in unresectable HCC.

Cysteine derivatives as acetyl lysine mimics to inhibit zinc-dependent histone deacetylases for treating cancer

Zinc-dependent histone deacetylases (HDACs) are important epigenetic regulators that have become important drug targets for treating cancer. Although five HDAC inhibitors have been approved for treating several cancers, there is still a huge demand on discovering new HDAC inhibitors to explore the therapeutic potentials for treating solid tumor cancers. Substrate mimics are a powerful rational design approach for the development of potent inhibitors. Here we describe the rational design, synthesis, biological evaluation, molecular docking and in vivo efficacy study of a class of HDAC inhibitors using N^ε-acetyl lysine mimics that are derived from cysteine. As a result, compounds 7a, 9b and 13d demonstrated pan-HDAC inhibition and broad cytotoxicity against several cancer cell lines, comparable to the approved HDAC inhibitor SAHA. Furthermore, 13d significantly inhibited tumor growth in a A549 xenograft mice model without any obvious weight loss, supporting that the cysteine-derived acetyl lysine mimics are promising HDAC inhibitors with therapeutic potentials for treating cancer.

Dual Targeting Strategies On Histone Deacetylase 6 (HDAC6) And Heat Shock Protein 90 (Hsp90)

The design of multi-target drugs acting simultaneously on multiple signaling pathways is a growing field in medicinal chemistry, especially for the treatment of complex diseases such as cancer. Histone deacetylase 6 (HDAC6) is an established anticancer drug target involved in tumor cells transformation. Being an epigenetic enzyme at the interplay of many biological processes, HDAC6 has become an attractive target for polypharmacology studies aimed at improving therapeutic efficacy of anticancer drugs. For example, the molecular chaperone Heat shock protein 90 (Hsp90) is a substrate of HDAC6 deacetylation, and several lines of evidence demonstrate that simultaneous inhibition of HDAC6 and Hsp90 promote synergistic antitumor effects on different cancer cell lines, highlighting the potential benefits of developing a single molecule endowed with multi-target activity. This review will summarize the complex interplay between HDAC6 and Hsp90, providing also useful hints for multi-target drug design and discovery approaches in this field. To this end, crystallographic structures of HDAC6 and Hsp90 complexes will be extensively reviewed in the light of discussing binding pockets features and pharmacophore requirements and providing useful guidelines for the design of dual inhibitors. The few examples of multi-target inhibitors obtained so far, mostly based on chimeric approaches, will be summarized and put into context. Finally, the main features of HDAC6 and Hsp90 inhibitors will be compared, and ligand- and structure-based strategies potentially useful for the development of small molecular weight dual inhibitors will be proposed and discussed.

Overcoming anti-cancer drug resistance via restoration of tumor suppressor gene function

The cytotoxic anti-cancer drugs cisplatin, paclitaxel, doxorubicin, 5-fluorouracil (5-FU), as well as targeted drugs including imatinib, erlotinib, and nivolumab, play key roles in clinical cancer treatment. However, the frequent emergence of drug resistance severely comprosises their anti-cancer efficacy. A number of studies indicated that loss of function of tumor suppressor genes (TSGs) is involved in the development of cancer drug resistance, apart from decreased drug influx, increased drug efflux, induction of anti-apoptosis mechanisms, alterations in tumor microenvironment, drug compartmentalization, enhanced DNA repair and drug inactivation. TSGs are involved in the pathogenesis of tumor formation through regulation of DNA damage repair, cell apoptosis, autophagy, proliferation, cell cycle progression, and signal transduction. Our increased understanding of TSGs in the past decades demonstrates that gene mutation is not the only reason that leads to the inactivation of TSGs. Loss of function of TSGs may be based on the ubiquitin-proteasome pathway, epigenetic and transcriptional regualtion, post-translation modifications like phosphorylation as well as cellular translocation of TSGs. As the above processes can constitute"druggable targets", these mechanisms provide novel therapeutic approaches in targeting TSGs. Some small molecule compounds targeting these approaches re-activated TSGs and reversed cancer drug resistance. Along this vein, functional restoration of TSGs is a novel and promising approach to surmount cancer drug resistance. In the current review, we draw a scenario based on the role of loss of function of TSGs in drug resistance, on mechanisms leading to inactivation of TSGs and on pharmacological agents acting on these mechanisms to overcome cancer drug resistance. This review discusses novel therapeutic strategies targeting TSGs and offers possible modalities to conquer cancer drug resistance.

Inhibition of histone deacetylases, topoisomerases and epidermal growth factor receptor by metal-based anticancer agents: Design & synthetic strategies and their medicinal attributes

Metal-based inhibitors of histone deacetylases (HDAC), DNA topoisomerases (Topos) and Epidermal Growth Factor Receptor (EGFR) have demonstrated their cytotoxic potential against various cancer types such as breast, lung, uterus, colon, etc. Additionally, these have proven their role in resolving the resistance issues, enhancing the affinity, lipophilicity, stability, and biocompatibility and therefore, emerged as potential candidates for molecularly targeted therapeutics. This review focusses on nature and role of metals and organic ligands in tuning the anticancer activity in multiple modes of inhibition considering HDACs, Topos or EGFR as one of the primary targets. The conceptual design and synthetic approaches of platinum and non-platinum metal complexes comprising of chiefly ruthenium, rhodium, palladium, copper, iron, nickel, cobalt, zinc metals coordinated with organic scaffolds, along with their biological activity profiles, structure-activity relationships (SARs), docking studies, possible modes of action, and their scope and limitations are discussed in detail.

A Series of Novel HDAC Inhibitors with Anthraquinone as a Cap Group

Although anthraquinone derivatives possess significant antitumor activity, most of them also displayed those side effects like cardiotoxicity, mainly owing to their inhibition of topoisomerase II of DNA repair mechanisms. Our raised design strategy by switching therapeutic target from topoisomerase II to histone deacetylase (HDAC) has been applied to the design of anthraquinone derivatives in current study. Consequently, a series of novel HDAC inhibitors with a tricylic diketone of anthraquinone as a cap group have been synthesized. After screening and evaluation, compounds 4b, 4d, 7b and 7d have displayed the comparable inhibition in enzymatic activity and cell proliferation than that of Vorinostat (SAHA). Notably, compound 4b showed certain selectivity of antiproliferative effects on cancer cell lines over non-cancer cell lines.

Structural determinants of affinity and selectivity in the binding of inhibitors to histone deacetylase 6

Histone deacetylase 6 (HDAC6) is associated with multiple neurological disorders as well as aggressive cancers, making its selective inhibition highly desirable for therapeutic purposes. The basic molecular design of an effective HDAC6 inhibitor consists of a zinc-binding group, a linker, and a capping group capable of making interactions at the mouth of the active site. To date, more than 50 high-resolution X-ray crystal structures of HDAC6-inhibitor complexes have been reported, many of which reveal intermolecular interactions that contribute to isozyme affinity and selectivity. Here, we review the key features of HDAC6 inhibitor design illuminated by these structural studies.

Post-Translational Modifications in NETosis and NETs-Mediated Diseases

Neutrophils undergo a unique form of cell death that generates neutrophil extracellular traps (NETs) that may help to neutralize invading pathogens and restore homeostasis. However, uncontrolled NET formation (NETosis) can result in numerous diseases that adversely affect health. Recent studies further elucidate the mechanistic details of the different forms of NETosis and their common end structure, as NETs were constantly found to contain DNA, modified histones and cytotoxic enzymes. In fact, emerging evidence reveal that the post translational modifications (PTMs) of histones in neutrophils have a critical role in regulating neutrophil death. Histone citrullination is shown to promote a rapid form of NET formation independent of NADPH oxidase (NOX), which relies on calcium influx. Interestingly, few studies suggest an association between histone citrullination and other types of PTMs to control cell survival and death, such as histone methylation. Even more exciting is the finding that histone acetylation has a biphasic effect upon NETosis, where histone deacetylase (HDAC) inhibitors promote baseline, NOX-dependent and -independent NETosis. However, increasing levels of histone acetylation suppresses NETosis, and to switch neutrophil death to apoptosis. Interestingly, in the presence of NETosis-promoting stimuli, high levels of HDACis limit both NETosis and apoptosis, and promote neutrophil survival. Recent studies also reveal the importance of the PTMs of neutrophils in influencing numerous pathologies. Histone modifications in NETs can act as a double-edged sword, as they are capable of altering multiple types of neutrophil death, and influencing numerous NET-mediated diseases, such as acute lung injury (ALI), thrombosis, sepsis, systemic lupus erythematosus, and cancer progression. A clear understanding of the role of different PTMs in neutrophils would be important for an understanding of the molecular mechanisms of NETosis, and to appropriately treat NETs-mediated diseases.

N ɛ -acetyl lysine derivatives with zinc binding groups as novel HDAC inhibitors

HDAC inhibitors have been developed very rapidly in clinical trials and even in approvals for treating several cancers. However, there are few reported HDAC inhibitors designed from N ɛ -acetyl lysine. In the current study, we raised a novel design, which concerns N ɛ -acetyl lysine derivatives containing amide acetyl groups with the hybridization of ZBG groups as novel HDAC inhibitors.

Zinc-dependent Deacetylase (HDAC) Inhibitors with Different Zinc Binding Groups

The state of histone acetylation plays a very crucial role in carcinogenesis and its development by chromatin remodeling and thus altering transcription of oncogenes and tumor suppressor genes. Such epigenetic regulation was controlled by zinc-dependent histone deacetylases (HDACs), one of the major regulators. Due to the therapeutic potential of HDACs as one of the promising drug targets in cancer, HDAC inhibitors have been intensively investigated over the last few decades. Notably, there are five HDAC inhibitors already approved to the market. Vorinostat (SAHA), Belinostat (PXD-101) and Romidepsin (FK228) have been approved by Food and Drug Administration (FDA) in USA for treating cutaneous T-cell lymphoma (CTCL) or peripheral T cell lymphoma (PTCL) while Panbinostat (LBH-589) has also been approved by the FDA for the treatment of multiple myeloma. Recently, Chidamide was approved by China Food and Drug Administration (CFDA) for the treatment of PTCL. The structural feature of almost all HDAC inhibitors consists of Cap group, linker, and zinc-binding group (ZBG). The binding of ZBG groups to zinc ion plays a decisive role in the inhibition of HDAC. Therefore, we will summarize the developed HDAC inhibitors according to different ZBG groups and discuss their binding mode with zinc ion.

Revisiting Histone Deacetylases in Human Tumorigenesis: The Paradigm of Urothelial Bladder Cancer

Urinary bladder cancer is a common malignancy, being characterized by substantial patient mortality and management cost. Its high somatic-mutation frequency and molecular heterogeneity usually renders tumors refractory to the applied regimens. Hitherto, methotrexate-vinblastine-adriamycin-cisplatin and gemcitabine-cisplatin represent the backbone of systemic chemotherapy. However, despite the initial chemosensitivity, the majority of treated patients will eventually develop chemoresistance, which severely reduces their survival expectancy. Since chromatin regulation genes are more frequently mutated in muscle-invasive bladder cancer, as compared to other epithelial tumors, targeted therapies against chromatin aberrations in chemoresistant clones may prove beneficial for the disease. “Acetyl-chromatin” homeostasis is regulated by the opposing functions of histone acetyltransferases (HATs) and histone deacetylases (HDACs). The HDAC/SIRT (super-)family contains 18 members, which are divided in five classes, with each family member being differentially expressed in normal urinary bladder tissues. Since a strong association between irregular HDAC expression/activity and tumorigenesis has been previously demonstrated, we herein attempt to review the accumulated published evidences that implicate HDACs/SIRTs as critical regulators in urothelial bladder cancer. Moreover, the most extensively investigated HDAC inhibitors (HDACis) are also analyzed, and the respective clinical trials are also described. Interestingly, it seems that HDACis should be preferably used in drug-combination therapeutic schemes, including radiation.

Histone Deacetylases (HDACs) Guided Novel Therapies for T-cell lymphomas

T-cell lymphomas are a heterogeneous group of cancers with different pathogenesis and poor prognosis. Histone deacetylases (HDACs) are epigenetic modifiers that modulate many key biological processes. In recent years, HDACs have been fully investigated for their roles and potential as drug targets in T-cell lymphomas. In this review, we have deciphered the modes of action of HDACs, HDAC inhibitors as single agents, and HDACs guided combination therapies in T-cell lymphomas. The overview of HDACs on the stage of T-cell lymphomas, and HDACs guided therapies both as single agents and combination regimens endow great opportunities for the cure of T-cell lymphomas.

Tetrahydroisoquinolines as novel histone deacetylase inhibitors for treatment of cancer

Histone acetylation is a critical process in the regulation of chromatin structure and gene expression. Histone deacetylases (HDACs) remove the acetyl group, leading to chromatin condensation and transcriptional repression. HDAC inhibitors are considered a new class of anticancer agents and have been shown to alter gene transcription and exert antitumor effects. This paper describes our work on the structural determination and structure-activity relationship (SAR) optimization of tetrahydroisoquinoline compounds as HDAC inhibitors. These compounds were tested for their ability to inhibit HDAC 1, 3, 6 and for their ability to inhibit the proliferation of a panel of cancer cell lines. Among these, compound 82 showed the greatest inhibitory activity toward HDAC 1, 3, 6 and strongly inhibited growth of the cancer cell lines, with results clearly superior to those of the reference compound, vorinostat (SAHA). Compound 82 increased the acetylation of histones H3, H4 and tubulin in a concentration-dependent manner, suggesting that it is a broad inhibitor of HDACs.

Histone deacetylase (HDAC)-1, -2, -4 and -6 expression in human pancreatic adenocarcinoma: associations with clinicopathological parameters, tumor proliferative capacity and patients' survival

Background

Histone deacetylases (HDACs) have been associated with malignant tumor development and progression in humans. HDAC inhibitors (HDACIs) are currently being explored as anti-cancer agents in clinical trials. The present study aimed to evaluate the clinical significance of HDAC-1, −2, −4 and −6 protein expression in pancreatic adenocarcinoma.

Methods

HDAC-1, −2, −4 and −6 protein expression was assessed immunohistochemically on 70 pancreatic adenocarcinoma tissue specimens and was statistically analyzed with clinicopathological characteristics and patients’ survival.

Results

Enhanced HDAC-1 expression was significantly associated with increased tumor proliferative capacity (p = 0.0238) and borderline with the absence of lymph node metastases (p = 0.0632). Elevated HDAC-4 expression was significantly associated with the absence of organ metastases (p = 0.0453) and borderline with the absence of lymph node metastases (p = 0.0571) and tumor proliferative capacity (p = 0.0576). Enhanced HDAC-6 expression was significantly associated with earlier histopathological stage (p = 0.0115) and borderline with smaller tumor size (p = 0.0864). Pancreatic adenocarcinoma patients with enhanced HDAC-1 and −6 expression showed significantly longer survival times compared to those with low expression (p = 0.0022 and p = 0.0113, respectively), while a borderline association concerning HDAC-2 expression was noted (p = 0.0634).

Conclusions

The present study suggested that HDACs may be implicated in pancreatic malignant disease progression, being considered of clinical utility with potential use as therapeutic targets.

Epigenetic Therapy for Solid Tumors: Highlighting the Impact of Tumor Hypoxia

In the last few decades, epigenetics has emerged as an exciting new field in development and disease, with a more recent focus towards cancer. Epigenetics has classically referred to heritable patterns of gene expression, primarily mediated through DNA methylation patterns. More recently, it has come to include the reversible chemical modification of histones and DNA that dictate gene expression patterns. Both the epigenetic up-regulation of oncogenes and downregulation of tumor suppressors have been shown to drive tumor development. Current clinical trials for cancer therapy include pharmacological inhibition of DNA methylation and histone deacetylation, with the aim of reversing these cancer-promoting epigenetic changes. However, the DNA methyltransferase and histone deacetylase inhibitors have met with less than promising results in the treatment of solid tumors. Regions of hypoxia are a common occurrence in solid tumors. Tumor hypoxia is associated with increased aggressiveness and therapy resistance, and importantly, hypoxic tumor cells have a distinct epigenetic profile. In this review, we provide a summary of the recent clinical trials using epigenetic drugs in solid tumors, discuss the hypoxia-induced epigenetic changes and highlight the importance of testing the epigenetic drugs for efficacy against the most aggressive hypoxic fraction of the tumor in future preclinical testing.

Targeting class I histone deacetylase 2 in MYC amplified group 3 medulloblastoma

Introduction

Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Four subgroups with distinct genetic, epigenetic and clinical characteristics have been identified. Survival remains particularly poor in patients with Group 3 tumors harbouring a MYC amplification. We herein explore the molecular mechanisms and translational implications of class I histone deacetylase (HDAC) inhibition in MYC driven MBs.

Material and Methods

Expression of HDACs in primary MB subgroups was compared to normal brain tissue. A panel of MB cell lines, including Group 3 MYC amplified cell lines, were used as model systems. Cells were treated with HDAC inhibitors (HDACi) selectively targeting class I or IIa HDACs. Depletion of HDAC2 was performed. Intracellular HDAC activity, cellular viability, metabolic activity, caspase activity, cell cycle progression, RNA and protein expression were analyzed.

Results

HDAC2 was found to be overexpressed in MB subgroups with poor prognosis (SHH, Group 3 and Group 4) compared to normal brain and the WNT subgroup. Inhibition of the enzymatic activity of the class I HDACs reduced metabolic activity, cell number, and viability in contrast to inhibition of class IIa HDACs. Increased sensitivity to HDACi was specifically observed in MYC amplified cells. Depletion of HDAC2 increased H4 acetylation and induced cell death. Simulation of clinical pharmacokinetics showed time-dependent on target activity that correlated with binding kinetics of HDACi compounds.

Conclusions

We conclude that HDAC2 is a valid drug target in patients with MYC amplified MB. HDACi should cover HDAC2 in their inhibitory profile and timing and dosing regimen in clinical trials should take binding kinetics of compounds into consideration.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0201-7) contains supplementary material, which is available to authorized users.

Recent advances in cancer therapeutics

In the past 20 years, cancer therapeutics has undergone a paradigm shift away from the traditional cytotoxic drugs towards the targeting of proteins intimately involved in driving the cancer phenotype. The poster child for this alternative approach to the treatment of cancer is imatinib, a small-molecule kinase inhibitor designed to target chronic myeloid leukaemia driven by the BCR-ABL translocation in a defined patient population. The improvement in survival achieved by treatment of this patient cohort with imatinib is impressive. Thus, the aim is to provide efficacy but with low toxicity. The role of the medicinal chemist in oncology drug discovery is now closely aligned with the role in most other therapeutic areas with high-throughput and/or fragment-based screening, structure-based design, selectivity, pharmacokinetic optimisation and pharmacodynamic biomarker modulation, all playing a familiar part in the process. In this chapter, we selected four areas in which compounds are either approved drugs or in clinical trials. These are chaperone inhibitors, kinase inhibitors, histone deacetylase inhibitors and inhibitors of protein-protein interactions. Even within these areas, we have been selective, particularly for kinase inhibitors, and our aim has been to exemplify newer approaches and novel aspects of medicinal chemistry.

A phase I/II trial of belinostat in combination with cisplatin, doxorubicin, and cyclophosphamide in thymic epithelial tumors: a clinical and translational study

PURPOSE

This phase I/II study sought to determine the safety and maximum tolerated dose (MTD) of a novel schedule of belinostat, a histone deacetylase inhibitor (HDAC) administered before and in combination with cisplatin (P), doxorubicin (A), and cyclophosphamide (C) in thymic epithelial tumors (TET). Antitumor activity, pharmacokinetics, and biomarkers of response were also assessed.

EXPERIMENTAL DESIGN

Patients with advanced, unresectable TET received increasing doses of belinostat as a continuous intravenous infusion over 48 hours with chemotherapy in 3-week cycles. In phase II, belinostat at the MTD was used.

RESULTS

Twenty-six patients were enrolled (thymoma, 12; thymic carcinoma, 14). Dose-limiting toxicities at 2,000 mg/m(2) belinostat were grade 3 nausea and diarrhea and grade 4 neutropenia and thrombocytopenia, respectively, in two patients. Twenty-four patients were treated at the MTD of 1,000 mg/m(2) with chemotherapy (P, 50 mg/m(2) on day 2; A, 25 mg/m(2) on days 2 and 3; C, 500 mg/m(2) on day 3). Objective response rates in thymoma and thymic carcinoma were 64% (95% confidence interval, 30.8%-89.1%) and 21% (4.7%-50.8%), respectively. Modulation of pharmacodynamic markers of HDAC inhibition and declines in regulatory T cell (Treg) and exhausted CD8(+) T-cell populations were observed. Decline in Tregs was associated with response (P = 0.0041) and progression-free survival (P = 0.021). Declines in TIM3(+) CD8(+) T cells were larger in responders than nonresponders (P = 0.049).

CONCLUSION

This study identified the MTD of belinostat in combination with PAC and indicates that the combination is active and feasible in TETs. Immunomodulatory effects on Tregs and TIM3(+) CD8(+) T cells warrant further study.

Profile of belinostat for the treatment of relapsed or refractory peripheral T-cell lymphoma

The peripheral T-cell lymphomas are a rare and heterogeneous group of mature T-cell lymphomas with limited available therapies. The outcome of frontline chemotherapy regimens has been disappointing, with a long-term survival of only 20%–30%. There is an urgent need to optimize induction therapy by incorporating novel agents that target the dysregulated pathways. Histone deacetylase inhibitors that induce acetylation of histones and enhance apoptosis have shown promising activity. In this article, we summarize the role of histone deacetylase inhibitors and specifically discuss pharmacokinetics, efficacy, and toxicity of the recently US Food and Drug Administration-approved agent belinostat for its use in patients with relapsed/refractory peripheral T-cell lymphoma.

Ginsenoside Rg3 inhibits melanoma cell proliferation through down-regulation of histone deacetylase 3 (HDAC3) and increase of p53 acetylation

Malignant melanoma is an aggressive and deadly form of skin cancer, and despite recent advances in available therapies, is still lacking in completely effective treatments. Rg3, a monomer extracted from ginseng roots, has been attempted for the treatment of many cancers. It is reported that the expressions of histone deacetylase 3 (HDAC3) and p53 acetylation correlate with tumor cell growth. However, the antitumor effect of Rg3 on melanoma and the mechanism by which it regulates HDAC3 expression and p53 acetylation remain unknown. We found high expression of HDAC3 in human melanoma tissues to be significantly correlated to lymph node metastasis and clinical stage of disease (p<0.05). In melanoma cells, Rg3 inhibited cell proliferation and induced G0/G1 cell cycle arrest. Rg3 also decreased the expression of HDAC3 and increased the acetylation of p53 on lysine (k373/k382). Moreover, suppression of HDAC3 by either siRNA or a potent HDAC3 inhibitor (MS-275) inhibited cell proliferation, increased p53 acetylation and transcription activity. In A375 melanoma xenograft studies, we demonstrated that Rg3 and HDAC3 short hairpin RNA (shHDAC3) inhibited the growth of xenograft tumors with down-regulation of HDAC3 expression and up-regulation of p53 acetylation. In conclusion, Rg3 has antiproliferative activity against melanoma by decreasing HDAC3 and increasing acetylation of p53 both in vitro and in vivo. Thus, Rg3 serves as a potential therapeutic agent for the treatment of melanoma.

Entinostat is a histone deacetylase inhibitor selective for class 1 histone deacetylases and activates HIV production from latently infected primary T cells

OBJECTIVES

To compare the potency, toxicity and mechanism of action of multiple histone deacetylase inhibitors (HDACi) in activating HIV production from latency.

DESIGN

In-vitro analysis of HDACi in a primary T-cell model of HIV latency and latently infected cell lines.

METHODS

Latently infected chemokine ligand 19 (CCL19)-treated CD4⁺ T cells and the latently infected cell lines ACH2 and J-Lat were treated with a panel of HDACi, including entinostat, vorinostat, panonbinostat and MCT3. Viral production and cell viability were compared. Expression of cellular HDACs was measured by western blot and PCR. Association of HDACs with the HIV long-terminal repeat (LTR) using latently infected CCL19-treated primary CD4⁺ T cells in the presence and absence of specific HDACi was determined by chromatin immunoprecipitation (ChIP).

RESULTS

We demonstrated considerable variation in the potency and toxicity of HDACi in latently infected primary CD4⁺ T cells and cell lines. All HDACi tested activated HIV production in latently infected primary T cells with greatest potency demonstrated with entinostat and vorinostat and greatest toxicity with panobinostat. Following the addition of HDACi in vitro, there were no changes in markers of T-cell activation or expression of the HIV coreceptors chemokine (C-X-C motif) receptor 4 (CXCR4) or chemokine (C-C motif) receptor type 5 (CCR5). ChIP analysis of latently infected CCL19-treated primary CD4⁺ T cells showed binding by HDAC1, HDAC2 and HDAC3 to the LTR with removal of HDAC1 and HDAC2 following treatment with the HDACi vorinostat and HDAC1 only following treatment with entinostat.

CONCLUSION

The HDACi entinostat, selective for inhibition of class I HDACs, induced virus expression in latently infected primary CD4⁺ T cells making this compound an attractive novel option for future clinical trials.

Clinical significance of histone deacetylase (HDAC)-1, HDAC-2, HDAC-4, and HDAC-6 expression in human malignant and benign thyroid lesions

Histone deacetylases (HDACs) have been associated with human malignant tumor development and progression, and HDAC inhibitors are currently being explored as anticancer agents in clinical trials. The present study aimed to evaluate the clinical significance of HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression in human malignant and benign thyroid lesions. HDAC-1, HDAC-2, HDAC-4, and HDAC-6 proteins' expression was assessed immunohistochemically on paraffin-embedded thyroid tissues obtained from 74 patients with benign and malignant thyroid lesions. Enhanced HDAC-2 and HDAC-6 expression was significantly more frequently observed in malignant, compared to benign, thyroid lesions (p = 0.0042 and p = 0.0069, respectively). Enhanced HDAC-2, HDAC-4, and HDAC-6 expression was significantly more frequently observed in cases with papillary carcinoma compared to hyperplastic nodules (p = 0.0065, p = 0.0394, and p = 0.0061, respectively). In malignant thyroid lesions, HDAC-1, HDAC-4, and HDAC-6 expression was significantly associated with tumor size (p = 0.0169, p = 0.0056, and p = 0.0234, respectively); HDAC-2 expression with lymphatic and vascular invasion (p = 0.0299 and p = 0.0391, respectively); and HDAC-4 expression with capsular invasion (p = 0.0464). The cellular pattern of HDAC-1 and HDAC-2 distribution (nuclear vs. nuclear and cytoplasmic) presented a distinct discrimination between malignant and benign thyroid lesions (p = 0.0030 and p = 0.0028, respectively) as well as between papillary carcinoma and hyperplastic nodules (p = 0.0036 and p = 0.0028, respectively). HDAC-1, HDAC-2, HDAC-4, and HDAC-6 may be associated with the malignant thyroid transformation and could be considered as useful biomarkers and possible therapeutic targets in this neoplasia.

[18F]FDG and [18F]FLT positron emission tomography imaging following treatment with belinostat in human ovary cancer xenografts in mice

BACKGROUND

Belinostat is a histone deacetylase inhibitor with anti-tumor effect in several pre-clinical tumor models and clinical trials. The aim of the study was to evaluate changes in cell proliferation and glucose uptake by use of 3'-deoxy-3'-[(18)F]fluorothymidine ([18F]FLT) and 2-deoxy-2-[(18)F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) following treatment with belinostat in ovarian cancer in vivo models.

METHODS

In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) were studied after treatment with belinostat. Mice were divided in 2 groups receiving either belinostat (40 mg/kg ip twice daily Day 0-4 and 6-10) or vehicle. Baseline [18F]FLT or [18F]FDG scans were made before treatment (Day 0) and repeated at Day 3, 6 and 10. Tracer uptake was quantified using small animal PET/CT.

RESULTS

Tumors in the belinostat group had volumes that were 462 ± 62% (640 mm(3)) at Day 10 relative to baseline which was significantly different (P = 0.011) from the control group 769 ± 74% (926 mm(3)). [18F]FLT SUVmax increased from baseline to Day 10 (+30 ± 9%; P = 0.048) in the control group. No increase was observed in the treatment group. [18F]FDG SUVmean was significantly different in the treatment group compared to the control group (P = 0.0023) at Day 10. Within treatment groups [18F]FDG uptake and to a lesser extent [18F]FLT uptake at Day 3 were significantly correlated with tumor growth at Day 10.

CONCLUSIONS

[18F]FDG uptake early following treatment initiation predicted tumor sizes at Day 10, suggesting that [18F]FDG may be a valuable biomarker for non-invasive assessment of anti-tumor activity of belinostat.