Pharmacokinetic and pharmacodynamic properties of an oral formulation of the histone deacetylase inhibitor Belinostat (PXD101)

Discovery of (S)-N-(2-Amino-4-fluorophenyl)-4-(1-(3-(4-((dimethylamino)methyl)phenyl)-6-oxopyridazin-1(6H)-yl)ethyl)benzamide as Potent Class I Selective HDAC Inhibitor for Oral Anticancer Drug Candidate

A novel series of benzamide derivatives were successively designed and synthesized prepared from the pyridazinone scaffold. Among them, (S)-17b, demonstrated potent inhibitory activity in vitro toward human class I HDAC isoforms and human myelodysplastic syndrome (SKM-1) cell line. Also, (S)-17b strongly increased the intracellular level of acetyl-histone H3 and P21 simultaneously and effectively induced G1 cell cycle arrest and apoptosis. Through oral dosing in SKM-1 xenograft models, (S)-17b exhibited excellent in vivo antitumor activity. In addition, compound (S)-17b showed better antitumor efficacy on mouse models with intact immune system than those with thymus deficiencies. Furthermore, this compound displayed a favorable pharmacokinetic profile in ICR mice and SD rat, respectively, minimal metabolic property differences among hepatocytes from five species, and a low inhibition upon the human ether-a-go-go (hERG) channel with an IC₅₀ value of 34.6 μΜ. This novel compound (S)-17b may serve as a new drug candidate for further investigation.

Unraveling the Epigenetic Role and Clinical Impact of Histone Deacetylases in Neoplasia

Histone deacetylases (HDACs) have long been implicated in tumorigenesis and tumor progression demonstrating their important participation in neoplasia. Therefore, numerous studies have been performed, highlighting the mechanism of HDACs action in tumor cells and demonstrating the potential role of HDAC inhibitors in the treatment of different cancer types. The outcome of these studies further delineated and strengthened the solid role that HDACs and epigenetic modifications exert in neoplasia. These results have spread promise regarding the potential use of HDACs as prospective therapeutic targets. Nevertheless, the clinical significance of HDAC expression and their use as biomarkers in cancer has not been extensively elucidated. The aim of our study is to emphasize the clinical significance of HDAC isoforms expression in different tumor types and the correlations noted between the clinicopathological parameters of tumors and patient outcomes. We further discuss the obstacles that the next generation HDAC inhibitors need to overcome, for them to become more potent.

Inhibition of human UDP-glucuronosyltransferase enzyme by belinostat: Implications for drug-drug interactions

Belinostat is a pan-histone deacetylase (HDAC) inhibitor which recently approved for the treatment of relapsed/refractory Peripheral T-cell lymphomas (PTCL). To assess drug-drug interactions (DDIs) potential of belinostat via inhibition of UDP-glucuronosyltransferases (UGTs), the effects of belinostat on UGTs activities were investigated using the non-selective probe substrate 4-methylumbelliferone (4-MU) and trifluoperazine (TFP) by UPLC-MS/MS. Belinostat exhibited a wide range of inhibition against UGTs activities, particularly a potent non-competitive inhibition against UGT1A3, and weak inhibition against UGT1A1, 1A7, 1A8, 2B4 and 2B7. Further, in vitro-in vivo extrapolation (IVIVE) approaches were used to predict the risk of DDI arising from inhibition of UGTs. Our data indicate that the intravenous infusion of belinostat at clinical available dose can contribute a significant increase to the AUC of co-administrated drugs primarily cleared by UGT1A3 or UGT1A1, which will result in potential DDIs. In contrast, oral administrated belinostat is unlikely to cause significant DDIs through inhibition of glucuronidation.

High-throughput screening identifies histone deacetylase inhibitors that modulate GTF2I expression in 7q11.23 microduplication autism spectrum disorder patient-derived cortical neurons

Background

Autism spectrum disorder (ASD) is a highly prevalent neurodevelopmental condition affecting almost 1% of children, and represents a major unmet medical need with no effective drug treatment available. Duplication at 7q11.23 (7Dup), encompassing 26–28 genes, is one of the best characterized ASD-causing copy number variations and offers unique translational opportunities, because the hemideletion of the same interval causes Williams–Beuren syndrome (WBS), a condition defined by hypersociability and language strengths, thereby providing a unique reference to validate treatments for the ASD symptoms. In the above-indicated interval at 7q11.23, defined as WBS critical region, several genes, such as GTF2I, BAZ1B, CLIP2 and EIF4H, emerged as critical for their role in the pathogenesis of WBS and 7Dup both from mouse models and human studies.

Methods

We performed a high-throughput screening of 1478 compounds, including central nervous system agents, epigenetic modulators and experimental substances, on patient-derived cortical glutamatergic neurons differentiated from our cohort of induced pluripotent stem cell lines (iPSCs), monitoring the transcriptional modulation of WBS interval genes, with a special focus on GTF2I, in light of its overriding pathogenic role. The hits identified were validated by measuring gene expression by qRT-PCR and the results were confirmed by western blotting.

Results

We identified and selected three histone deacetylase inhibitors (HDACi) that decreased the abnormal expression level of GTF2I in 7Dup cortical glutamatergic neurons differentiated from four genetically different iPSC lines. We confirmed this effect also at the protein level.

Limitations

In this study, we did not address the molecular mechanisms whereby HDAC inhibitors act on GTF2I. The lead compounds identified will now need to be advanced to further testing in additional models, including patient-derived brain organoids and mouse models recapitulating the gene imbalances of the 7q11.23 microduplication, in order to validate their efficacy in rescuing phenotypes across multiple functional layers within a translational pipeline towards clinical use.

Conclusions

These results represent a unique opportunity for the development of a specific class of compounds for treating 7Dup and other forms of intellectual disability and autism.

Metabolism and Pharmacokinetic Study of the Boron-Containing Prodrug of Belinostat (ZL277), a Pan HDAC Inhibitor with Enhanced Bioavailability

ZL277 is a prodrug of belinostat with enhanced bioavailability and efficacy as a pan histone deacetylase (HDAC) inhibitor. In this study, we investigated the metabolism and pharmacokinetics of ZL277 in liver S9 fractions, liver microsomes, liver cytosol, and in mice. Metabolic products were identified and quantified by a combination of liquid chromatography and tandem mass spectrometry. The in vitro metabolic profile of ZL277 includes ZL277-B(OH)₂-452, the major oxidative metabolite ZL277-OH-424, the active ingredient belinostat, belinostat amide, belinostat acid, and methylated belinostat in liver S9 fractions. Both ZL277-OH-424 and belinostat underwent further glucuronidation in liver microsome, whereas only ZL277-OH-424, but not belinostat, underwent some level of sulfation in rat liver cytosols. These metabolites were examined in plasma and in a breast tumor model in vivo. They were also examined in urine and feces from mice treated with ZL277. The pharmacokinetic study of ZL277 showed the parameters of active drug belinostat with a half-life (t_1/2) of 10.7 h, an area under curve value (AUC) of 1506.9 ng/mL*h, and a maximum plasma concentration (C_max) of 172 ng/mL, reached 3 h after a single dose of 10 mg/kg. The hydrolysis product of the prodrug, ZL277-B(OH)₂-452 showed an AUC of 8306 ng/mL*h and C_max of 931 ng/mL 3 h after drug administration.

Epigenetic Metalloenzymes

Epigenetics controls the expression of genes and is responsible for cellular phenotypes. The fundamental basis of these mechanisms involves in part the post-translational modifications (PTMs) of DNA and proteins, in particular, the nuclear histones. DNA can be methylated or demethylated on cytosine. Histones are marked by several modifications including acetylation and/or methylation, and of particular importance are the covalent modifications of lysine. There exists a balance between addition and removal of these PTMs, leading to three groups of enzymes involved in these processes: the writers adding marks, the erasers removing them, and the readers able to detect these marks and participating in the recruitment of transcription factors. The stimulation or the repression in the expression of genes is thus the result of a subtle equilibrium between all the possibilities coming from the combinations of these PTMs. Indeed, these mechanisms can be deregulated and then participate in the appearance, development and maintenance of various human diseases, including cancers, neurological and metabolic disorders. Some of the key players in epigenetics are metalloenzymes, belonging mostly to the group of erasers: the zinc-dependent histone deacetylases (HDACs), the iron-dependent lysine demethylases of the Jumonji family (JMJ or KDM) and for DNA the iron-dependent ten-eleven-translocation enzymes (TET) responsible for the oxidation of methylcytosine prior to the demethylation of DNA. This review presents these metalloenzymes, their importance in human disease and their inhibitors.

Enhanced anti-tumor efficacy of checkpoint inhibitors in combination with the histone deacetylase inhibitor Belinostat in a murine hepatocellular carcinoma model

Immune checkpoint inhibitors are currently tested in different combinations in patients with advanced hepatocellular carcinoma (HCC). Nivolumab, an anti-PD-1 agent, has gained approval in the second-line setting in the USA. Epigenetic drugs have immune-mediated antitumor effects that may improve the activity of immunotherapy agents. Our aim was to study the therapeutic efficacy of checkpoint inhibitors (anti-CTLA-4 and anti-PD-1 antibodies) in combination with the histone deacetylase inhibitor (HDACi) Belinostat. In a subcutaneous Hepa129 murine HCC model, we demonstrated that Belinostat improves the antitumor activity of anti-CTLA-4 but not of anti-PD-1 therapy. This effect correlated with enhanced IFN-γ production by antitumor T-cells and a decrease in regulatory T-cells. Moreover, the combination induced early upregulation of PD-L1 on tumor antigen-presenting cells and late expression of PD-1 on tumor-infiltrating effector T-cells, suggesting the suitability of PD-1 blockade. Indeed, Belinostat combined with the simultaneous blockade of CTLA-4 and PD-1 led to complete tumor rejection. These results provide a rationale for testing Belinostat in combination with checkpoint inhibitors to enhance their therapeutic activity in patients with HCC.

Hematologic toxicity is rare in relapsed patients treated with belinostat: a systematic review of belinostat toxicity and safety in peripheral T-cell lymphomas

Peripheral T-cell lymphomas (PTCLs) are an aggressive and diverse group of lymphomas with a T-cell origin. Most patients progress following initial treatment and require salvage therapy. The burden of symptoms is high due to its extra-nodal presentation, high rate of advanced disease, and associated cytopenias combined with its predilection for an elderly population. The disease is generally incurable at relapse in the absence of transplantation and treatment is aimed at prolonging life and reducing disease-related symptoms. Belinostat is a histone deacetylate inhibitor that was granted accelerated approval by the US Food and Drug Administration on July 3, 2014, for the treatment of relapsed PTCL. Here, a systemic review was conducted to assess the safety and efficacy of belinostat. A safety analysis involved 512 patients with relapsed malignancies, and an efficacy analysis focused on patients with relapsed PTCL and included a total of 144 patients. Common adverse events were noted including fatigue (35%), nausea (42.8%), and vomiting (28.5%), but comparatively low rates of grade 3/4 hematologic toxicity overall (6.4%). Efficacy analysis demonstrated an overall response rate of 25.7% and complete responses of 10.4% with the majority of discontinuations occurring for lack of efficacy. Ultimately, these results demonstrate that belinostat has comparable efficacy to other agents used in this setting and is well tolerated in regard to hematologic events, but there is limited data on patient-reported outcomes, reduction in disease-related symptoms, or quality of life.

Combined use of irinotecan with histone deacetylase inhibitor belinostat could cause severe toxicity by inhibiting SN-38 glucuronidation via UGT1A1

SN-38, the active metabolite of irinotecan, and histone deacetylase inhibitors (HDACis) such as belinostat, vorinostat and panobinostat, have all been shown to be deactivated by glucuronidation via UGTs. Since they all compete for UGTs for deactivation, we aimed to investigate the inhibitory effect of various HDACis on the glucuronidation of SN-38. This inhibitory effect was determined by measuring the formation rate of SN-38 glucuronide after SN-38 incubation with human recombinant UGT1A isoforms (1A1, 1A6, 1A7 and 1A9) and pooled human liver microsomes (HLM, wild type, UGT1A1*1*28 and UGT1A1*28*28 allelic variants), with and without HDACis. The data showed that belinostat at 100 and 200 µmol/L inhibited SN-38 glucuronidation via UGT1A1 in a dose-dependent manner, causing significant decrease in V_max and CL_int (p < 0.05) from 12.60 to 1.95 pmol/min/mg and 21.59 to 4.20 μL/min/mg protein respectively. Similarly, in HLMs, V_max dropped from 41.13 to 10.54, 24.96 to 3.77 and 6.23 to 3.30 pmol/min/mg, and CL_int reduced from 81.25 to 26.11, 29.22 to 6.10 and 5.40 to 1.34 µL/min/mg protein for the respective wild type, heterozygous and homozygous variants. Interestingly, belinostat at 200 µmol/L that is roughly equivalent to the average Cmax, 183 µmol/L of belinostat at a dose of 1,400 mg/m² given intravenously once per day on days 1 to 5 every 3 weeks, was able to inhibit both heterozygous and homozygous variants to same extents (~64%). This highlights the potential clinical significance, as a large proportion of patients could be at risk of developing severe toxicity if irinotecan is co-administered with belinostat.

Class I HDAC Inhibitors Display Different Antitumor Mechanism in Leukemia and Prostatic Cancer Cells Depending on Their p53 Status

Previously, we designed and synthesized a series of o-aminobenzamide-based histone deacetylase (HDAC) inhibitors, among which the representative compound 11a exhibited potent inhibitory activity against class I HDACs. In this study, we report the development of more potent hydrazide-based class I selective HDAC inhibitors using 11a as a lead. Representative compound 13b showed a mixed, slow, and tight binding inhibition mechanism for HDAC1, 2, and 3. The most potent compound 13e exhibited low nanomolar IC50s toward HDAC1, 2, and 3 and could down-regulate HDAC6 in acute myeloid leukemia MV4-11 cells. The EC50 of 13e against MV4-11 cells was 34.7 nM, which is 26 times lower than its parent compound 11a. In vitro responses to 13e vary significantly and interestingly based on cell type: in p53 wild-type MV4-11 cells, 13e induced cell death via apoptosis and G1/S cell cycle arrest, which is likely mediated by a p53-dependent pathway, while in p53-null PC-3 cells, 13e caused G2/M arrest and inhibited cell proliferation without inducing caspase-3-dependent apoptosis.

Advances and Challenges of HDAC Inhibitors in Cancer Therapeutics

Since the identification and cloning of human histone deacetylases (HDACs) and the rapid approval of vorinostat (Zolinza®) for the treatment of cutaneous T-cell lymphoma, the field of HDAC biology has met many initial successes. However, many challenges remain due to the complexity involved in the lysine posttranslational modifications, epigenetic transcription regulation, and nonepigenetic cellular signaling cascades. In this chapter, we will: review the discovery of the first HDAC inhibitor and present discussion regarding the future of next-generation HDAC inhibitors, give an overview of different classes of HDACs and their differences in lysine deacylation activity, discuss different classes of HDAC inhibitors and their HDAC isozyme preferences, and review HDAC inhibitors' preclinical studies, their clinical trials, their pharmacokinetic challenges, and future direction. We will also discuss the likely reason for the failure of multiple HDAC inhibitor clinical trials in malignancies other than lymphoma and multiple myeloma. In addition, the potential molecular mechanism(s) that may play a key role in the efficacy and therapeutic response rate in the clinic and the likely patient population for HDAC therapy will be discussed.

Sequential treatment with 5-aza-2'-deoxycytidine and deacetylase inhibitors reactivates HIV-1

Reactivation of HIV gene expression in latently infected cells together with an efficient cART has been proposed as an adjuvant therapy aimed at eliminating/decreasing the reservoir size. Results from HIV clinical trials using deacetylase inhibitors (HDACIs) question the efficiency of these latency‐reversing agents (LRAs) used alone and underline the need to evaluate other LRAs in combination with HDACIs. Here, we evaluated the therapeutic potential of a demethylating agent (5‐AzadC) in combination with clinically tolerable HDACIs in reactivating HIV‐1 from latency first in vitro and next ex vivo. We showed that a sequential treatment with 5‐AzadC and HDACIs was more effective than the corresponding simultaneous treatment both in vitro and ex vivo. Interestingly, only two of the sequential LRA combinatory treatments tested induced HIV‐1 particle recovery in a higher manner than the drugs alone ex vivo and at concentrations lower than the human tolerable plasmatic concentrations. Taken together, our data reveal the benefit of using combinations of 5‐AzadC with an HDACI and, for the first time, the importance of treatment time schedule for LRA combinations in order to reactivate HIV.

A novel combinatorial strategy using Seliciclib(®) and Belinostat(®) for eradication of non-small cell lung cancer via apoptosis induction and BID activation

With conventional anticancer agents for non-small cell lung cancer (NSCLC) reaching therapeutic ceiling, the novel combination using histone deacetylase inhibitor, PXD101 (Belinostat(®)), and CDK inhibitor, CYC202 (Seliciclib(®)), was investigated as an alternative anticancer strategy. At clinically achievable concentration of CYC202 (15 µM), combination therapy resulted in significant reduction in cell proliferation (IC50 = 3.67 ± 0.80 µM, p < 0.05) compared with PXD101 alone (IC50 = 6.56 ± 0.42 µM) in p53 wild-type A549 cells. Significant increase in apoptosis that occurred independently of cell cycle arrest was observed after concurrent treatment. This result was corroborated by greater formation of cleaved caspase-8, caspase-3 and PARP. Up-regulation of p53 and truncated BID protein levels was seen while Mcl-1 and XIAP protein levels were down-regulated upon combined treatment. Further analysis of apoptotic pathways revealed that caspase inhibitors, but not p53 silencing, significantly abrogated the cytotoxic enhancement. Moreover, the enhanced efficacy of this combination was additionally confirmed in p53 null H2444 cells, suggesting the potential of this combination for treatment of NSCLC that are not amenable to effects of conventional p53-inducing agents.

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

The prognosis of patients with relapsed/refractory peripheral T-cell lymphoma (PTCL) remains poor and current treatments are typically of limited benefit. Histone deacetylase (HDAC) inhibitors have proven effective for the treatment of relapsed/refractory PTCL. To date approved HDAC inhibitors for patients with T-cell lymphoma are vorinostat, romidepsin and, recently, belinostat. Here we review the pharmacology and the clinical activity of belinostat. Belinostat is a well-tolerated HDAC inhibitor that has shown activity in heavily pretreated patients with relapsed/refractory PTCL. Several clinical trials are currently investigating the use of belinostat in different cancers and in combination with other chemotherapeutic agents.

Epigenetic treatment of solid tumours: a review of clinical trials

Epigenetic treatment has been approved by regulatory agencies for haematological malignancies. The success observed in cutaneous lymphomas represents a proof of principle that similar results may be obtained in solid tumours. Several agents that interfere with DNA methylation-demethylation and histones acetylation/deacetylation have been studied, and some (such as azacytidine, decitabine, valproic acid and vorinostat) are already in clinical use.

The aim of this review is to provide a brief overview of the molecular events underlying the antitumour effects of epigenetic treatments and to summarise data available on clinical trials that tested the use of epigenetic agents against solid tumours. We not only list results but also try to indicate how the proper evaluation of this treatment might result in a better selection of effective agents and in a more rapid development.

We divided compounds in demethylating agents and HDAC inhibitors. For each class, we report the antitumour activity and the toxic side effects. When available, we describe plasma pharmacokinetics and pharmacodynamic evaluation in tumours and in surrogate tissues (generally white blood cells).

Epigenetic treatment is a reality in haematological malignancies and deserves adequate attention in solid tumours. A careful consideration of available clinical data however is required for faster drug development and possibly to re-evaluate some molecules that were perhaps discarded too early.

Profiling the anti-protozoal activity of anti-cancer HDAC inhibitors against Plasmodium and Trypanosoma parasites

Histone deacetylase (HDAC) enzymes work together with histone acetyltransferases (HATs) to reversibly acetylate both histone and non-histone proteins. As a result, these enzymes are involved in regulating chromatin structure and gene expression as well as other important cellular processes. HDACs are validated drug targets for some types of cancer, with four HDAC inhibitors clinically approved. However, they are also showing promise as novel drug targets for other indications, including malaria and other parasitic diseases. In this study the in vitro activity of four anti-cancer HDAC inhibitors was examined against parasites that cause malaria and trypanosomiasis. Three of these inhibitors, suberoylanilide hydroxamic acid (SAHA; vorinostat^®), romidepsin (Istodax^®) and belinostat (Beleodaq^®), are clinically approved for the treatment of T-cell lymphoma, while the fourth, panobinostat, has recently been approved for combination therapy use in certain patients with multiple myeloma. All HDAC inhibitors were found to inhibit the growth of asexual-stage Plasmodium falciparum malaria parasites in the nanomolar range (IC₅₀ 10–200 nM), while only romidepsin was active at sub-μM concentrations against bloodstream form Trypanosoma brucei brucei parasites (IC₅₀ 35 nM). The compounds were found to have some selectivity for malaria parasites compared with mammalian cells, but were not selective for trypanosome parasites versus mammalian cells. All compounds caused hyperacetylation of histone and non-histone proteins in P. falciparum asexual stage parasites and inhibited deacetylase activity in P. falciparum nuclear extracts in addition to recombinant PfHDAC1 activity. P. falciparum histone hyperacetylation data indicate that HDAC inhibitors may differentially affect the acetylation profiles of histone H3 and H4.

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Four clinically approved anti-cancer HDAC inhibitors potently inhibited P. falciparum.

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Only one, Romidepsin, was active against T. b. brucei parasites.

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All compounds hyperacetylated histone and non-histone proteins in P. falciparum.

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Some differential effects on Plasmodium histone acetylation were observed.

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All compounds inhibited Plasmodium nuclear deacetylase activity and PfHDAC1.

New developments in the treatment of peripheral T-cell lymphoma - role of Belinostat

Peripheral T-cell lymphomas (PTCL) represent a heterogeneous group of rare malignancies that with the exception of anaplastic lymphoma kinase expressing anaplastic large cell lymphoma, share a poor outcome after standard (eg, anthracycline-based) chemotherapy. Most patients are either refractory to initial therapy or eventually relapse. Randomized studies for relapsed/refractory PTCL are not available, however, recently published data show that conventional chemotherapy has very limited efficacy in the salvage setting. Thus, novel drugs are urgently needed to improve the outcome in this setting. Belinostat, a pan-histone deacetylase inhibitor, has demonstrated meaningful efficacy and a favorable toxicity profile in two single-arm Phase II trials on 153 patients with relapsed/refractory PTCL. The conclusive results led to an accelerated approval by the US Food and Drug Administration. The present review summarizes the clinical data available for belinostat, its current role, and future perspectives.

Advancements in the delivery of epigenetic drugs

INTRODUCTION

Advancements in epigenetic treatments are not only coming from new drugs, but also from modifications or encapsulation of the existing drugs into different formulations leading to greater stability and enhanced delivery to the target site. The epigenome is highly regulated and complex; therefore, it is important that off-target effects of epigenetic drugs be minimized. The step from in vitro to in vivo treatment of these drugs often requires development of a method of effective delivery for clinical translation.

AREAS COVERED

This review covers epigenetic mechanisms such as DNA methylation, chromatin remodeling and small-RNA-mediated gene regulation. There is a section in the review with examples of diseases where epigenetic alterations lead to impaired pathways, with an emphasis on cancer. Epigenetic drugs, their targets and clinical status are presented. Advantages of using a delivery method for epigenetic drugs as well as examples of current advancements and challenges are also discussed.

EXPERT OPINION

Epigenetic drugs have the potential to be very effective therapy against a number of diseases, especially cancers and neurological disorders. As with many chemotherapeutics, undesired side effects need to be minimized. Finding a suitable delivery method means reducing side effects and achieving a higher therapeutic index. Each drug may require a unique delivery method exploiting the drug's chemistry or other physical characteristic requiring interdisciplinary participation and would benefit from a better understanding of the mechanisms of action.

Autophagy induction by histone deacetylase inhibitors inhibits HIV type 1

Histone deacetylase inhibitors (HDACi) are being evaluated in a "shock-and-kill" therapeutic approach to reverse human immunodeficiency virus type-1 (HIV) latency from CD4(+) T cells. Using this approach, HDACi have induced HIV RNA synthesis in latently infected cells from some patients. The hope is that the increase in viral production will lead to killing of the infected cell either by the virus itself or by the patient's immune system, a "sterilizing cure." Although administered within the context of combination antiretroviral therapy, the infection of bystander cells remains a concern. In this study, we investigated the effect of HDACi (belinostat, givinostat, panobinostat, romidepsin, and vorinostat) on the productive infection of macrophages. We demonstrate that the HDACi tested do not alter the initial susceptibility of macrophages to HIV infection. However, we demonstrate that HDACi decrease HIV release from macrophages in a dose-dependent manner (belinostat < givinostat < vorinostat < panobinostat < romidepsin) via degradation of intracellular HIV through the canonical autophagy pathway. This mechanism involves unc-51-like autophagy-activating kinase 1 (ULK1) and the inhibition of the mammalian target of rapamycin and requires the formation of autophagosomes and their maturation into autolysosomes in the absence of increased cell death. These data provide further evidence in support of a role for autophagy in the control of HIV infection and suggest that careful consideration of off-target effects will be essential if HDACi are to be a component of a multipronged approach to eliminate latently infected cells.

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.

A phase 2 study of belinostat (PXD101) in patients with relapsed or refractory acute myeloid leukemia or patients over the age of 60 with newly diagnosed acute myeloid leukemia: a California Cancer Consortium Study

We performed a phase II study of belinostat in patients with acute myeloid leukemia (AML). In this open label phase II study (NCT00357032), patients with relapsed/refractory AML, or newly diagnosed patients with AML over the age of 60, were eligible. Belinostat was administered intravenously (IV) at a dose of 1000 mg/m(2) daily on days 1-5 of a 21-day cycle until progression or unacceptable toxicity. The primary endpoint was complete response (CR) rate, with secondary endpoints of overall response rate (CR + partial response [PR]), time to treatment failure (TTF), overall survival and safety. Twelve eligible patients with AML were enrolled, of whom six had received at least one prior line of therapy. No CR or PR was seen. Four patients had stable disease for at least five cycles. Grade 3 non-hematological toxicities occurred in four patients. Belinostat as monotherapy has minimal single-agent effect in AML on this dosing schedule.

Epigenetic mechanisms in cerebral ischemia

Treatment efficacy for ischemic stroke represents a major challenge. Despite fundamental advances in the understanding of stroke etiology, therapeutic options to improve functional recovery remain limited. However, growing knowledge in the field of epigenetics has dramatically changed our understanding of gene regulation in the last few decades. According to the knowledge gained from animal models, the manipulation of epigenetic players emerges as a highly promising possibility to target diverse neurologic pathologies, including ischemia. By altering transcriptional regulation, epigenetic modifiers can exert influence on all known pathways involved in the complex course of ischemic disease development. Beneficial transcriptional effects range from attenuation of cell death, suppression of inflammatory processes, and enhanced blood flow, to the stimulation of repair mechanisms and increased plasticity. Most striking are the results obtained from pharmacological inhibition of histone deacetylation in animal models of stroke. Multiple studies suggest high remedial qualities even upon late administration of histone deacetylase inhibitors (HDACi). In this review, the role of epigenetic mechanisms, including histone modifications as well as DNA methylation, is discussed in the context of known ischemic pathways of damage, protection, and regeneration.

Preclinical data and early clinical experience supporting the use of histone deacetylase inhibitors in multiple myeloma

Histone deacetylases (HDACs) mediate protein acetylation states, which in turn regulate normal cellular processes often dysregulated in cancer. These observations led to the development of HDAC inhibitors that target tumors through multiple effects on protein acetylation. Clinical evidence demonstrates that treatment with HDAC inhibitors (such as vorinostat, panobinostat, and romidepsin) in combination with other antimyeloma agents (such as proteasome inhibitors and immunomodulatory drugs) has promising antitumor activity in relapsed/refractory multiple myeloma patients. This mini-review highlights the role of protein acetylation in the development of cancers and the rationale for the use of HDAC inhibitors in this patient population.

Comparison of HDAC inhibitors in clinical development: effect on HIV production in latently infected cells and T-cell activation

Objective: We aimed to compare the potential for inducing HIV production and the effect on T-cell activation of potent HDAC inhibitors undergoing clinical investigation.

Design: In vitro study

Methods: The latently infected cell lines ACH2 and U1 were treated with the HDAC inhibitors panobinostat, givinostat, belinostat, vorinostat and valproic acid. Viral induction was estimated by p24 production. Peripheral blood mononuclear cells from uninfected donors were treated with the HDAC inhibitors and the expression of activation markers on T-cell phenotypes was measured using flow cytometry. Finally, the ability of givinostat, belinostat and panobinostat to reactivate latent HIV-1 expression in primary T-cells was investigated employing a CCL19-induced latent primary CD4+ T cell infection model.

Results: The various HDAC inhibitors displayed significant potency differences in stimulating HIV-1 expression from the latently infected cell lines with panobinostat > givinostat ≈belinostat > vorinostat > valproic acid. Panobinostat was significantly more potent than all other HDAC inhibitors and induced virus production even in the very low concentration range 8–31 nM. The proportion of primary T-cells expressing the early activation marker CD69 increased moderately in all HDAC inhibitor-treated cells compared with untreated cells. Finally, proof was obtained that panobinostat, givinostat and belinostat induce virus production in latently infected primary cells at therapeutic concentrations with panobinostat being the most potent stimulator.

Conclusion: At therapeutic concentrations panobinostat stimulate HIV-1 expression in latently infected cells with greater potency than other HDAC inhibitors undergoing clinical investigation. These findings warrant further investigation and panobinostat is now being advanced into clinical testing against latent HIV infection.

Toxicological and metabolic considerations for histone deacetylase inhibitors

INTRODUCTION

Vorinostat and romidepsin were the first histone deacetylase (HDAC) inhibitors (HDi) that fulfilled the preclinical promise of anticancer potential in clinical trials. Nevertheless, they merely opened a new chapter in the history of cancer therapy. Demonstration of their antitumor activity was a straightforward task in in vitro setting. Proving their efficacy in vivo was much more difficult, since the effects of an administrated drug strongly depend on its absorption, distribution, metabolism and excretion.

AREAS COVERED

This article summarizes clinical data on the pharmacokinetic properties of HDi that are currently at more advanced stages of clinical development. Specific attention is paid to the metabolic pathways. Moreover, a comprehensive overview of HDi-related adverse effects is given.

EXPERT OPINION

At this moment, HDi form one of the most interesting classes of therapeutics, yet their efficacy and safety profiles could still be improved by i) designing better formulations, ii) more extensive characterization of their disposition at the preclinical stage, iii) targeting of individual disease-related deacetylase isoforms and/or their complexes, iv) selecting a target patient population with the highest probability of response based on molecular signatures.

HDAC inhibitors for the treatment of cutaneous T-cell lymphomas

Epigenetic modification by small-molecule histone deacetylase inhibitors (HDAC-Is) has been a promising new antineoplastic approach for various solid and hematological malignancies, particularly for cutaneous T-cell lymphoma (CTCL). Vorinostat, a pan-HDAC-I and, most recently, romidepsin, a bicyclic pan-HDAC-I, have been US FDA approved for treatment of relapsed or refractory CTCL. However, because many patients do not reach the 50% partial response mark and response is not always sustainable, overcoming HDAC-I resistance by adding other agents or finding more selective molecules is an important clinical problem in realizing the full clinical potential of HDAC-Is. In this review, we discuss the molecular basis for HDAC-I function in cancer, the clinical response and side-effect profile experienced by CTCL patients, and the progress made in attempting to identify biomarkers of response and resistance, as well as synergistic combination therapies.

Novel therapeutic agents for cutaneous T-Cell lymphoma

Mycosis fungoides (MF) and Sezary Syndrome (SS) represent the most common subtypes of primary Cutaneous T-cell lymphoma (CTCL). Patients with advanced MF and SS have a poor prognosis leading to an interest in the development of new therapies with targeted mechanisms of action and acceptable safety profiles. In this review we focus on such novel strategies that have changed the treatment paradigm of this rare malignancy.

Belinostat: clinical applications in solid tumors and lymphoma

INTRODUCTION

Histone deacetylase (HDAC) inhibitors have recently emerged as a novel and active class of anticancer agents. Belinostat is one member of the class that has been tested as a single agent and in combination with other chemotherapies and biological agents in the treatment of solid tumors and lymphoma.

AREAS COVERED

A literature search of pre-clinical and clinical studies of belinostat was performed. The data from these studies were analysed to summarise the progress of belinostat from Phase I to a current pivotal trial in peripheral T-cell lymphoma. The parallel development of appropriate biomarker analysis is also discussed.

EXPERT OPINION

Belinostat has demonstrated significant clinical activity in T-cell lymphomas. Although its activity as a single agent in solid tumors has been less compelling, the emerging results from combination trials are promising. However, the basis for the activity of belinostat, like that of other HDAC inhibitors, remains to be truly defined and the identification of predictive and prognostic biomarkers of activity should be established to further progress the development of this compound.