Discovery and development of SAHA as an anticancer agent

A single supratherapeutic dose of vorinostat does not prolong the QTc interval in patients with advanced cancer

PURPOSE

This dedicated QTc phase I study, conducted in advanced-stage cancer patients, assessed the effect of a single supratherapeutic dose (800 mg) of vorinostat on the QTc interval.

EXPERIMENTAL DESIGN

A randomized, partially blind, placebo-controlled, two-period, crossover study was conducted. Patients (n = 25) received single doses of 800 mg vorinostat and placebo in the fasted state. Holter electrocardiogram monitoring was done before each treatment and for 24 h postdose. Blood samples for vorinostat concentration were collected through 24 h postdose following vorinostat treatment only. Prescribed electrocardiogram and blood sampling times were designed to capture the expected C(max) of vorinostat.

RESULTS

Twenty-four of the 25 patients enrolled in the study were included in the QTc analysis. The upper bound of the two-sided 90% confidence interval for the QTcF interval for the placebo-adjusted mean change from baseline of vorinostat was <10 ms at every time point. No patient had a QTcF change from baseline value >30 ms. One patient had QTcF values >450 ms (seen after both vorinostat and placebo administration) and none had values >480 ms. Mean AUC(0-infinity) and C(max) values attained were on the order of approximately 1.93- and approximately 1.41-fold higher, respectively, compared with the 400 mg clinical dose. Based on assessment of clinical and laboratory adverse experiences, single doses of 800 mg vorinostat were generally well tolerated.

CONCLUSIONS

Administration of a single supratherapeutic dose of the histone deacetylase inhibitor vorinostat is not associated with prolongation of the QTc interval. A dedicated QTc study in advanced cancer patients is a robust means for assessing risk for ventricular repolarization prolongation.

Design and synthesis of novel histone deacetylase inhibitor derived from nuclear localization signal peptide

We describe herein the synthesis and characterization of a new class of histone deacetylase (HDAC) inhibitors derived from conjugation of a suberoylanilide hydroxamic acid-like aliphatic-hydroxamate pharmacophore to a nuclear localization signal peptide. We found that these conjugates inhibited the histone deacetylase activities of HDACs 1, 2, 6, and 8 in a manner similar to suberoylanilide hydroxamic acid (SAHA). Notably, compound 7b showed a threefold improvement in HDAC 1/2 inhibition, a threefold increase in HDAC 6 selectivity and a twofold increase in HDAC 8 selectivity when compared to SAHA.

Study of 1,4-dihydropyridine structural scaffold: discovery of novel sirtuin activators and inhibitors

NAD(+)-dependent sirtuin deacetylases have emerged as potential therapeutic targets for treatment of human illnesses such as cancer, metabolic, cardiovascular, and neurodegenerative diseases. The benefits of sirtuin modulation by small molecules have been demonstrated for these diseases. In contrast to the discovery of inhibitors of SIRT1, -2, and -3, only activators for SIRT1 are known. Here, we rationalized the potential of the previously unexplored dihydropyridine scaffold in developing sirtuin ligands, thus we prepared a series of 1,4-dihydropyridine-based derivatives 1-3. Assessment of their SIRT1-3 deacetylase activities revealed the importance of the substituent at the N1 position of the dihydropyridine structure on sirtuin activity. Placement of cyclopropyl, phenyl, or phenylethyl groups at N1 conferred nonselective SIRT1 and SIRT2 inhibition activity, while a benzyl group at N1 conferred potent SIRT1, -2, and -3 activation. Senescence assays performed on hMSC and mitochondrial function studies conducted with murine C2C12 myoblasts confirmed the compounds' novel and unique SIRT-activating properties.

Short communication: activation of latent HIV type 1 gene expression by suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor approved for use to treat cutaneous T cell lymphoma

The ability of HIV to establish a latent infection causes life-long virus persistence, even after long-term highly active antiretroviral therapy (HAART). The role that latency is playing in preventing clearance of the virus infection has become evident in recent years. Patients who have been successfully treated with ART, having undetectable levels of viral RNA (below 50 copies/ml) in the plasma for years, experienced rapid virus rebound on withdrawal of therapy. Activation of latent proviruses from the infected cells in combination with ART is a therapeutic strategy that may lead to the complete elimination of HIV infection. We report here that suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor that has been approved for the treatment of cutaneous T cell lymphoma (CTCL), can activate an HIV-1 vector provirus in a cell model system. Treatment of cells harboring a latent, HIV-1-derived provirus caused activation of both early and late viral gene expression, acetylation of nucleosome on the 5' long terminal repeat (LTR), and remodeling of the chromatin at the 5' LTR. Several compounds, including valproic acid, have been tested for their ability to activate latent HIV-1, but have met with disappointing results. SAHA, a relatively nontoxic, FDA-approved compound, should be considered for developing a strategy to eliminate HIV from patients.

The inhibitors of histone deacetylase suberoylanilide hydroxamate and trichostatin A release nitric oxide upon oxidation

Suberoylanilide hydroxamic acid (SAHA, vorinostat, Zolinza) is the lead compound of a new class of histone deacetylase (HDAC) inhibitors used as anticancer drugs that have been shown to affect multiple proteins associated with gene expression, cell proliferation, and migration. Studies have also demonstrated the essential role of the hydroxamate moiety of SAHA in HDAC inhibition. The ability of SAHA and its structural analog trichostatin A (TSA) to generate NO upon oxidation was tested directly, by spin trapping of NO using electron paramagnetic resonance spectroscopy, and also indirectly, via the determination of nitrite using the Griess assay. H2O2/metmyoglobin was used to oxidize SAHA and TSA. These studies demonstrate, for the first time, the release of NO from SAHA and its structural analog TSA. We tested the protective effects of SAHA, TSA, and valproic acid (VPA) in mammalian Chinese hamster V79 cells exposed to a bolus of H2O2 for 1 h and monitored the clonogenic cell survival. Both SAHA and TSA afforded significant cytoprotection when co-incubated with H2O2, whereas VPA was ineffective. These studies provide evidence for the release of NO by hydroxamate-containing HDAC inhibitors and their antioxidant effects. Such roles may be an added advantage of this class of HDAC agents used for epigenetic therapies in cancer.

Proteome-wide prediction of acetylation substrates

Acetylation is a well-studied posttranslational modification that has been associated with a broad spectrum of biological processes, notably gene regulation. Many studies have contributed to our knowledge of the enzymology underlying acetylation, including efforts to understand the molecular mechanism of substrate recognition by several acetyltransferases, but traditional experiments to determine intrinsic features of substrate site specificity have proven challenging. Here, we combine experimental methods with clustering analysis of protein sequences to predict protein acetylation based on the sequence characteristics of acetylated lysines within histones with our unique prediction tool PredMod. We define a local amino acid sequence composition that represents potential acetylation sites by implementing a clustering analysis of histone and nonhistone sequences. We show that this sequence composition has predictive power on 2 independent experimental datasets of acetylation marks. Finally, we detect acetylation for selected putative substrates using mass spectrometry, and report several nonhistone acetylated substrates in budding yeast. Our approach, combined with more traditional experimental methods, may be useful for identifying acetylated substrates proteome-wide.

Vorinostat in solid and hematologic malignancies

Vorinostat (Zolinza), a histone deacetylase inhibitor, was approved by the US Food and Drug Administration in October 2006 for the treatment of cutaneous manifestations in patients with cutaneous T-cell lymphoma who have progressive, persistent or recurrent disease on or following two systemic therapies. This review summarizes evidence on the use of vorinostat in solid and hematologic malignancies and collated tolerability data from the vorinostat clinical trial program. Pooled vorinostat clinical trial data from 498 patients with solid or hematologic malignancies show that vorinostat was well tolerated as monotherapy or combination therapy. The most commonly reported drug-related adverse events (AEs) associated with monotherapy (n = 341) were fatigue (61.9%), nausea (55.7%), diarrhea (49.3%), anorexia (48.1%), and vomiting (32.8%), and Grade 3/4 drug-related AEs included fatigue (12.0%), thrombocytopenia (10.6%), dehydration (7.3%), and decreased platelet count (5.3%). The most common drug-related AEs observed with vorinostat in combination therapy (n = 157, most of whom received vorinostat 400 mg qd for 14 days) were nausea (48.4%), diarrhea (40.8%), fatigue (34.4%), vomiting (31.2%), and anorexia (20.4%), with the majority of AEs being Grade 2 or less. In Phase I trials, combinations with vorinostat were generally well tolerated and preliminary evidence of anticancer activity as monotherapy or in combination with other systemic therapies has been observed across a range of malignancies. Ongoing and planned studies will further evaluate the potential of vorinostat in combination therapy, including combinations with radiation, in patients with diverse malignancy types, including non-small-cell lung cancer, glioblastoma multiforme, multiple myeloma, and myelodysplastic syndrome.

Histone deacetylase (HDAC) inhibitors reduce the glial inflammatory response in vitro and in vivo

Histone deacetylase inhibitors (HDACi) are emerging tools for epigenetic modulation of gene expression and suppress the inflammatory response in models of systemic immune activation. Yet, their effects within the brain are still controversial. Also, whether HDACs are expressed in astrocytes or microglia is unclear. Here, we report the identification of transcripts for HDAC 1-11 in cultured mouse glial cells. Two HDACi such as SAHA and ITF2357 induce dramatic increase of histone acetylation without causing cytotoxicity of cultured cells. Of note, the two compounds inhibit expression of pro-inflammatory mediators by LPS-challenged glial cultures, and potentiate immunosuppression triggered by dexamethasone in vitro. The anti-inflammatory effect is not due to HDACi-induced transcription of immunosuppressant proteins, (including SOCS-1/3) or microRNA-146. Rather, it is accompanied by direct alteration of transcription factor DNA binding and ensuing transcriptional activation. Indeed, both HDACi impair NFkappaB-dependent IkappaBalpha resynthesis in glial cells exposed to LPS, and, among various AP1 subunits and NFkappaB p65, affect the DNA binding activity of c-FOS, c-JUN and FRA2. Importantly, ITF2357 reduces the expression of pro-inflammatory mediators in the striatum of mice iontophoretically injected with LPS. Data demonstrate that mouse glial cells have ongoing HDAC activity, and its inhibition suppresses the neuroinflammatory response because of a direct impairment of the transcriptional machinery.

Synergistic activation of HIV-1 expression by deacetylase inhibitors and prostratin: implications for treatment of latent infection

The persistence of transcriptionally silent but replication-competent HIV-1 reservoirs in Highly Active Anti-Retroviral Therapy (HAART)-treated infected individuals, represents a major hurdle to virus eradication. Activation of HIV-1 gene expression in these cells together with an efficient HAART has been proposed as an adjuvant therapy aimed at decreasing the pool of latent viral reservoirs. Using the latently-infected U1 monocytic cell line and latently-infected J-Lat T-cell clones, we here demonstrated a strong synergistic activation of HIV-1 production by clinically used histone deacetylase inhibitors (HDACIs) combined with prostratin, a non-tumor-promoting nuclear factor (NF)- κB inducer. In J-Lat cells, we showed that this synergism was due, at least partially, to the synergistic recruitment of unresponsive cells into the expressing cell population. A combination of prostratin+HDACI synergistically activated the 5′ Long Terminal Repeat (5'LTR) from HIV-1 Major group subtypes representing the most prevalent viral genetic forms, as shown by transient transfection reporter assays. Mechanistically, HDACIs increased prostratin-induced DNA-binding activity of nuclear NF-κB and degradation of cytoplasmic NF-κB inhibitor, IκBα . Moreover, the combined treatment prostratin+HDACI caused a more pronounced nucleosomal remodeling in the U1 viral promoter region than the treatments with the compounds alone. This more pronounced remodeling correlated with a synergistic reactivation of HIV-1 transcription following the combined treatment prostratin+HDACI, as demonstrated by measuring recruitment of RNA polymerase II to the 5'LTR and both initiated and elongated transcripts. The physiological relevance of the prostratin+HDACI synergism was shown in CD8⁺-depleted peripheral blood mononuclear cells from HAART-treated patients with undetectable viral load. Moreover, this combined treatment reactivated viral replication in resting CD4⁺ T cells isolated from similar patients. Our results suggest that combinations of different kinds of proviral activators may have important implications for reducing the size of latent HIV-1 reservoirs in HAART-treated patients.

Cell cycle and apoptotic effects of SAHA are regulated by the cellular microenvironment in HCT116 multicellular tumour spheroids

Using multicellular tumour spheroids (MCTS) of HCT116 colon carcinoma cells, we analysed the effects of SAHA (suberoylanilide hydroxamic acid), a histone deacetylase inhibitor (HDACi). We found that, although SAHA-induced histone acetylation and ROS level upregulation occur throughout the spheroid, inhibition of cell cycle progression and induction of apoptosis are dependent on cell microenvironment. SAHA-induced growth inhibition of HCT116 MCTS results from the inhibition of cell cycle progression and induction of apoptosis. At a low concentration SAHA decreases Ki-67 and cyclin A positive cells and increases p21 positive cells in the outer layer while it induces a ROS-dependent apoptosis in the central zone of the spheroid. Coimmunostaining of p21 and apoptotic cells confirms that SAHA effects are different depending on the position of the cells within the spheroid. At a higher dose, SAHA induces mitotic defects and survivin downregulation in the outer layer of cells resulting in an additional cytotoxic effect in this part of the spheroid. Together these findings show that SAHA-induced cytostatic and cytotoxic effects occur in different cell populations, indicating that the cellular microenvironment is an important determinant in the regulation of the effects of SAHA treatment. Consequently, the MCTS model appears to be a valuable advanced tool for evaluating the effects of SAHA treatment in combination with other anticancer agents.

New clinical developments in histone deacetylase inhibitors for epigenetic therapy of cancer

DNA methylation and histone acetylation are two well known epigenetic chromatin modifications. Epigenetic agents leading to DNA hypomethylation and histone hyperacetylation have been approved for treatment of hematological disorders. The first histone deacetylase inhibitor, vorinostat, has been licensed for cutaneous T cell lymphoma treatment. More than 11 new epigenetic agents are in various stages of clinical development for therapy of multiple cancer types. In this review we summarize novel histone deacetylase inhibitors and new regimens from clinical trials for epigenetic therapy of cancer.

Phase I and pharmacokinetic study of vorinostat (suberoylanilide hydroxamic acid) in Japanese patients with solid tumors

Vorinostat (suberoylanilide hydroxamic acid), a potent, oral histone deacetylase inhibitor, has demonstrated clinical activity in non-Japanese patients with various hematological and solid tumors. We sought to determine the maximum tolerated dose and a recommended phase II dose for 18 Japanese patients with solid tumors (median age, 58 years; range, 25-72 years) who failed standard therapy. Patients received vorinostat for 14 days followed by a 7-day rest. The initial dose was 100 mg twice daily escalating by 100 mg twice daily. Once-daily dosing was tested at 400 and 500 mg. A maximum tolerated dose could not be identified. Dose-limiting toxicities (thrombocytopenia, anorexia, and fatigue) were observed in two of six patients receiving 200 mg twice daily and in one of six patients receiving 500 mg once daily. In the 100-500 mg dose range, vorinostat area under the concentration-time curve increased in proportion to dose with a pharmacokinetic profile similar to that established in non-Japanese patients. Vorinostat doses of 200 mg twice daily or 500 mg once daily for 14 days followed by a 7-day rest were well tolerated and are candidate doses for phase II trials, although a maximum tolerated dose for vorinostat was not reached.

Transcriptional induction of GRP78/BiP by histone deacetylase inhibitors and resistance to histone deacetylase inhibitor-induced apoptosis

Histone deacetylase (HDAC) inhibitors are emerging as effective therapies in the treatment of cancer, and the role of HDACs in the regulation of promoters is rapidly expanding. GRP78/BiP is a stress inducible endoplasmic reticulum (ER) chaperone with antiapoptotic properties. We present here the mechanism for repression of the Grp78 promoter by HDAC1. Our studies reveal that HDAC inhibitors specifically induce GRP78, and the induction level is amplified by ER stress. Through mutational analysis, we have identified the minimal Grp78 promoter and specific elements responsible for HDAC-mediated repression. We show the involvement of HDAC1 in the negative regulation of the Grp78 promoter not only by its induction in the presence of the HDAC inhibitors trichostatin A and MS-275 but also by exogenous overexpression and small interfering RNA knockdown of specific HDACs. We present the results of chromatin immunoprecipitation analysis that reveals the binding of HDAC1 to the Grp78 promoter before, but not after, ER stress. Furthermore, overexpression of GRP78 confers resistance to HDAC inhibitor-induced apoptosis in cancer cells, and conversely, suppression of GRP78 sensitizes them to HDAC inhibitors. These results define HDAC inhibitors as new agents that up-regulate GRP78 without concomitantly inducing the ER or heat shock stress response, and suppression of GRP78 in tumors may provide a novel, adjunctive option to enhance anticancer therapies that use these compounds.

The paradox of autophagy and its implication in cancer etiology and therapy

Autophagy is a cellular self-catabolic process in which cytoplasmic constituents are sequestered in double membrane vesicles that fuse with lysosomes where they are degraded. As this catabolic activity generates energy, autophagy is often induced under nutrient limiting conditions providing a mechanism to maintain cell viability and may be exploited by cancer cells for survival under metabolic stress. However, progressive autophagy can be cytotoxic and autophagy can under certain settings substitute for apoptosis in induction of cell death. Moreover, loss of autophagy is correlated with tumorigenesis and several inducers of autophagy are tumor-suppressor genes. Thus, the relation of autophagy to cancer development is complex and depends on the genetic composition of the cell as well as on the extra-cellular stresses a cell is exposed to. In this review we describe the intricate nature of autophagy and its regulators, particularly those that have been linked to cancer. We discuss the multifaceted relation of autophagy to tumorigenesis and highlight studies supporting a role for autophagy in both tumor-suppression and tumor-progression. Finally, various autophagy-targeting therapeutic strategies for cancer treatment are presented.

Histone deacetylase inhibitors as a new weapon in the arsenal of differentiation therapies of cancer

Absent or altered differentiation is one of the major features of cancer cells. Histone deacetylases (HDACs) play a central role in the epigenetic regulation of gene expression. Aberrant activity of HDACs has been documented in several types of cancers, leading to the development of HDAC inhibitors (HDACi) as anti-tumor drugs. In vitro and in vivo experimental evidences show that HDACi are able to resume the process of maturation in undifferentiated cancer cells, justifying their introduction as differentiating agents in several clinical trials. Modulation of cell fate by HDACi is observed at several levels, including the stem cell compartment: HDACi can act both on cancer stem cells, and with the rest of the tumor cell mass, leading to complex biological outputs. As a note of caution, when used as single agent, HDACi show only a moderate and limited biological response, which is augmented in combinatorial therapies with drugs designed against other epigenetic targets. The optimal employment of these molecules may be therefore in combination with other epigenetic drugs acting against the set of enzymes responsible for the set-up and maintenance of epigenetic information.

Modulation of histone deacetylase activity by dietary isothiocyanates and allyl sulfides: studies with sulforaphane and garlic organosulfur compounds

Histone deacetylase (HDAC) inhibitors reactivate epigenetically-silenced genes in cancer cells, triggering cell cycle arrest and apoptosis. Recent evidence suggests that dietary constituents can act as HDAC inhibitors, such as the isothiocyanates found in cruciferous vegetables and the allyl compounds present in garlic. Broccoli sprouts are a rich source of sulforaphane (SFN), an isothiocyanate that is metabolized via the mercapturic acid pathway and inhibits HDAC activity in human colon, prostate, and breast cancer cells. In mouse preclinical models, SFN inhibited HDAC activity and induced histone hyperacetylation coincident with tumor suppression. Inhibition of HDAC activity also was observed in circulating peripheral blood mononuclear cells obtained from people who consumed a single serving of broccoli sprouts. Garlic organosulfur compounds can be metabolized to allyl mercaptan (AM), a competitive HDAC inhibitor that induced rapid and sustained histone hyperacetylation in human colon cancer cells. Inhibition of HDAC activity by AM was associated with increased histone acetylation and Sp3 transcription factor binding to the promoter region of the P21WAF1 gene, resulting in elevated p21 protein expression and cell cycle arrest. Collectively, the results from these studies, and others reviewed herein, provide new insights into the relationships between reversible histone modifications, diet, and cancer chemoprevention.

Vorinostat (NSC# 701852) in patients with relapsed non-small cell lung cancer: a Wisconsin Oncology Network phase II study

INTRODUCTION

Vorinostat is a small molecule inhibitor of histone deacetylase, and has shown preclinical activity in non-small cell lung cancer (NSCLC).

METHODS

Patients with relapsed NSCLC were eligible. Patients received oral vorinostat, 400 mg daily. The primary objective was response rate, with the goal of at least one responder in the first 14 evaluable patients, according to the two-stage minimax design. Secondary objectives included time to progression (TTP), overall survival (OS), and safety.

RESULTS

Sixteen patients enrolled from January 2006 to April 2007. The median age was 59.5 years. Thirteen patients were female. Two patients were not evaluable for response due to progressive disease within Cycle 1. No objective antitumor responses were seen in the 14 evaluable patients. Eight patients experienced stable disease (median 3.7 months, range 1.4-19.4). Median TTP was 2.3 months (range 0.9-19.4 months), median OS was 7.1 months (range 1.4-30.0+ months), and estimated 1 year OS rate was 19% (SE 10%). One patient died on study from an acute ischemic stroke; this event was deemed possibly related to treatment. Grade 3/4 adverse events possibly related to vorinostat included neutropenia, lymphopenia, fatigue, pulmonary embolus/deep vein thrombosis, dehydration, elevated alkaline phosphatase, and hypokalemia.

CONCLUSIONS

No objective antitumor activity was detected with single agent vorinostat in this setting; however, it yields TTP in relapsed NSCLC similar to that of other targeted agents. Further studies in NSCLC should focus on combining vorinostat with other antitumor agents.

Non-peptide macrocyclic histone deacetylase inhibitors

Inhibition of histone deacetylase inhibitors (HDACi) hold great promise in cancer therapy because of their demonstrated ability to arrest proliferation of nearly all transformed cell types. Of the several structurally distinct small molecule HDACi reported, macrocyclic depsipeptides have the most complex recognition cap-group moieties and present an excellent opportunity for the modulation of the biological activities of HDACi. Unfortunately, the structure-activity relationship (SAR) studies for this class of compounds have been impaired largely because most macrocyclic HDACi known to date comprise complex peptide macrocycles. In addition to retaining the pharmacologically disadvantaged peptidyl backbone, they offer only limited opportunity for side chain modifications. Here, we report the discovery of a new class of macrocyclic HDACi based on the macrolide antibiotics skeletons. SAR studies revealed that these compounds displayed both linker-length and macrolide-type dependent HDAC inhibition activities with IC(50) in the low nanomolar range. In addition, these non-peptide macrocyclic HDACi are more selective against HDACs 1 and 2 relative to HDAC 8, another class I HDAC isoform, and hence have subclass HDAC isoform selectivity.

Specific activity of class II histone deacetylases in human breast cancer cells

Although numerous studies have underlined the role of histone deacetylases (HDAC) in breast physiology and tumorigenesis, little is known on the particular contribution of the various classes of HDACs in these processes. Using estrogen receptor-alpha (ERalpha)-positive MCF-7 breast cancer cells, the effects of MC1575 and MC1568, two novel class II-specific HDAC inhibitors, were analyzed on cell proliferation, apoptosis, and estrogen signaling. The specificity of these HDAC inhibitors was validated by measuring histone and alpha-tubulin acetylation and by the specific in vitro inhibition of recombinant HDAC4 using histone and nonhistone substrates, contrasting with the lack of inhibition of class I HDACs. In addition, MC1575 did not inhibit class I HDAC gene expression, thus confirming the specific targeting of class II enzymes. Similar to trichostatin A (TSA), MC1575 displayed a dose-dependent antiproliferative effect and induced cell cycle arrest although this blockade occurred at a different level than TSA. Moreover, and in contrast to TSA, MC1575 had no effect on MCF-7 cells apoptosis. Interestingly, MC1575 was able to increase p21(waf1/CIP1) mRNA levels but did not regulate the expression of other genes such as cyclin D1, p27, p14(ARF), Bcl2, Baxalpha, Trail-R1, and Trail-R2. Finally, MC1575 strongly induced ERbeta gene expression but did not decrease ERalpha expression, nor did it switch hydroxytamoxifen to an agonist activity. Altogether, these data suggest that the class II HDAC subfamily may exert specific roles in breast cancer progression and estrogen dependence.

Expression of latent HIV induced by the potent HDAC inhibitor suberoylanilide hydroxamic acid

Histone deacetylases (HDACs) act on histones within the nucleosome-bound promoter of human immunodeficiency virus type 1 (HIV-1) to maintain proviral latency. HDAC inhibition leads to promoter expression and the escape of HIV from latency. We evaluated the ability of the potent inhibitor recently licensed for use in oncology, suberoylanilide hydroxamic acid (SAHA; Vorinostat), selective for Class I HDACs, to induce HIV promoter expression in cell lines and virus production from the resting CD4(+) T cells of antiretroviral-treated, aviremic HIV-infected patients. In J89, a Jurkat T cell line infected with a single HIV genome encoding the enhanced green fluorescence protein (EGFP) within the HIV genome, SAHA induced changes at nucleosome 1 of the HIV promoter in chromatin immunoprecipitation (ChIP) assays in concert with EGFP expression. In the resting CD4(+) T cells of antiretroviral-treated, aviremic HIV-infected patients clinically achievable exposures to SAHA induced virus outgrowth ex vivo. These results suggest that potent, selective HDAC inhibitors may allow improved targeting of persistent proviral HIV infection, and define parameters for in vivo studies using SAHA.

The many roles of histone deacetylases in development and physiology: implications for disease and therapy

Histone deacetylases (HDACs) are part of a vast family of enzymes that have crucial roles in numerous biological processes, largely through their repressive influence on transcription. The expression of many HDAC isoforms in eukaryotic cells raises questions about their possible specificity or redundancy, and whether they control global or specific programmes of gene expression. Recent analyses of HDAC knockout mice have revealed highly specific functions of individual HDACs in development and disease. Mutant mice lacking individual HDACs are a powerful tool for defining the functions of HDACs in vivo and the molecular targets of HDAC inhibitors in disease.

Caspase-8 dependent histone acetylation by a novel proteasome inhibitor, NPI-0052: a mechanism for synergy in leukemia cells

Combination studies of histone deacetylase inhibitors (HDACi) and proteasome inhibitors are providing preclinical framework to build better strategies against hematologic malignancies. Our previous work found that a novel proteasome inhibitor, NPI-0052, and HDACi synergistically induce apoptosis in leukemia cells in a caspase-8- and oxidant-dependent manner. Here we extend those observations to primary leukemia cells and identify novel mechanisms of synergy. Because the proximal targets of NPI-0052 and HDACi are inhibition of proteasome activity and histone acetylation, we initially examined those biochemical events. Increased acetylation of histone-H3 was detected in Jurkat and CLL primary cells treated with NPI-0052, alone or in combination with various HDACi (MS/SNDX-275 or vorinostat). Hyperacetylation by NPI-0052 occurred to a lesser extent in caspase-8-deficient cells and in cells treated with an antioxidant. These results indicate that NPI-0052 is eliciting caspase-8 and oxidative stress-dependent epigenetic alterations. In addition, real-time PCR revealed that MS/SNDX-275 repressed expression of the proteasomal beta5, beta2, and beta1 subunits, consequently inhibiting respective enzymatic activities. Overall, our results suggest that crosstalk by NPI-0052 and HDACi are contributing, along with caspase-8 activation and oxidative stress, to their synergistic cytotoxic effects in leukemia cells, reinforcing the potential clinical utility of combining these 2 agents.

Identification of (1H)-pyrroles as histone deacetylase inhibitors with antitumoral activity

Histone deacetylases (HDACs) play a key role in the regulation of gene expression and chromatin structure, and drugs targeting these enzymes might have an important impact in the treatment of human cancer. Herein, we report the characterization of (1H)-pyrroles as a new subfamily of HDAC inhibitors obtained by computational modeling of class-I human HDACs. From a functional standpoint, (1H)-pyrroles are powerful inductors of acetylation of histones H3 and H4, and restore the expression of growth-inhibitory genes. From a cellular view, these compounds cause a marked decrease in the viability of cancer cells in vitro and in vivo, associated with a cell-cycle arrest at G2/M and an inhibition of angiogenesis. Thus, (1H)-pyrroles emerge as a novel group of HDAC inhibitors with promising antitumoral features.

HKI 46F08, a novel potent histone deacetylase inhibitor, exhibits antitumoral activity against embryonic childhood cancer cells

Embryonic childhood cancer such as neuroblastoma and medulloblastoma are still a therapeutic challenge requiring novel treatment approaches. Here, we investigated the antitumoral effects of HKI 46F08, a novel trifluoromethyl ketone histone deacetylase (HDAC) inhibitor with a nonhydroxamic acid type structure. HKI 46F08 inhibits in-vitro HDAC activity in cell-free assays with a half maximal inhibitory concentration of 0.6 micromol/l and intracellular HDAC activity with a half maximal inhibitory concentration of 1.8 micromol/l. The compound reduces viability of both cultured neuroblastoma and medulloblastoma cells with an EC50 of 0.1-4 micromol/l. HKI 46F08 efficiently arrests tumor cell proliferation, represses clonogenic growth and induces differentiation and apoptosis in both MYCN-amplified and nonamplified neuroblastoma cells. In summary, we identified HKI 48F08 as a structural novel, potent HDAC inhibitor with strong antitumoral activity against embryonic childhood cancer cells in the low micromolar range.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

A phase II trial of vorinostat (suberoylanilide hydroxamic acid) in metastatic breast cancer: a California Cancer Consortium study

PURPOSE

The primary goal of this trial was to determine the response rate of single-agent vorinostat in patients with metastatic breast cancer. The secondary goals included assessment of time to progression, evaluation of toxicities, and overall survival.

EXPERIMENTAL DESIGN

From June 2005 to March 2006, 14 patients received vorinostat, 200 mg p.o., twice daily for 14 days of each 21 day cycle. Response and progression were evaluated using Response Evaluation Criteria in Solid Tumors (RECIST) criteria.

RESULTS

The median age for all patients was 60.5 years (range, 37-88). Eight patients were estrogen receptor and/or progesterone positive, four were Her-2 positive. Sites of metastatic disease included brain, liver, lungs, bones, pelvis, pleura, chest wall, and distant lymph nodes. Patients received a median of 1.5 prior (range, 0-2) chemotherapeutic regimens for metastatic disease. Fatigue, nausea, diarrhea, and lymphopenia were the most frequent clinically significant adverse effects. The median number of cycles delivered was 2 (range, 1-20). There were no complete or partial responses, and the study was terminated after the first stage; however, 4 patients were observed with stable disease with time to progression of 4, 8, 9, and 14 months. The median number of months that patients received treatment on this study was 1.7 (range, 0.5-14).

CONCLUSIONS

Although not meeting the RECIST response criteria for adequate single-agent activity, the observed tolerable toxicities and the potential for clinical benefit in terms of stable disease suggest that further assessment of vorinostat as a part of combination therapy with either chemotherapeutic or targeted agents in metastatic breast might be undertaken.

Salermide, a Sirtuin inhibitor with a strong cancer-specific proapoptotic effect

Sirtuin 1 (Sirt1) and Sirtuin 2 (Sirt2) belong to the family of NAD+ (nicotinamide adenine dinucleotide-positive)-dependent class III histone deacetylases and are involved in regulating lifespan. As cancer is a disease of ageing, targeting Sirtuins is emerging as a promising antitumour strategy. Here we present Salermide (N-{3-[(2-hydroxy-naphthalen-1-ylmethylene)-amino]-phenyl}-2-phenyl-propionamide), a reverse amide with a strong in vitro inhibitory effect on Sirt1 and Sirt2. Salermide was well tolerated by mice at concentrations up to 100 muM and prompted tumour-specific cell death in a wide range of human cancer cell lines. The antitumour activity of Salermide was primarily because of a massive induction of apoptosis. This was independent of global tubulin and K16H4 acetylation, which ruled out a putative Sirt2-mediated apoptotic pathway and suggested an in vivo mechanism of action through Sirt1. Consistently with this, RNA interference-mediated knockdown of Sirt1, but not Sirt2, induced apoptosis in cancer cells. Although p53 has been reported to be a target of Sirt1, genetic p53 knockdowns showed that the Sirt1-dependent proapoptotic effect of Salermide is p53-independent. We were finally able to ascribe the apoptotic effect of Salermide to the reactivation of proapoptotic genes epigenetically repressed exclusively in cancer cells by Sirt1. Taken together, our results underline Salermide's promise as an anticancer drug and provide evidence for the molecular mechanism through which Sirt1 is involved in human tumorigenesis.

Blocking TH17-polarizing cytokines by histone deacetylase inhibitors in vitro and in vivo

Histone deacetylase (HDAC) inhibitors are small molecules inducing cell-cycle arrest, differentiation, and apoptosis, currently undergoing clinical trials as anticancer drugs. In addition, emerging evidence suggests HDAC inhibitors may have anti-inflammatory and immunomodulatory properties as well, although the molecular mechanisms remain poorly defined. Given the central role of dendritic cells (DC) in the induction and maintenance of the inflammatory and immune response, we investigated the effects of HDAC inhibitors on the maturation and activation of human monocyte-derived DC in the presence of LPS and IFN-gamma. Our results show that the production of T(H)1- and T(H)17-inducing cytokines, namely IL-12 and IL-23, was inhibited by trichostatin A (72% and 52%, respectively) and suberoylanilide hydroxamic acid (86% and 83%). Strikingly, HDAC inhibitors were effective if added simultaneously as well as after the proinflammatory challenge, and their effect was not associated to a reduction of expression or function of LPS/IFN-gamma receptors. These findings were confirmed in two different murine models. In addition, HDAC inhibitors selectively blocked the production of T(H)1-attracting chemokines CXCL9, CXCL10, and CXCL11. The reduction of T(H)1- and T(H)17-inducing cytokines as well as T(H)1-attracting chemokines may represent relevant mechanisms through which HDAC inhibitors at nonproapoptotic doses exert their immunomodulatory properties.

Identification of KD5170: a novel mercaptoketone-based histone deacetylase inhibitor

We report the identification of KD5170, a potent mercaptoketone-based Class I and II-histone deacetylase inhibitor that demonstrates broad spectrum cytotoxic activity against a range of human tumor-derived cell lines. KD5170 exhibits robust and sustained histone H3 hyperacetylation in HCT-116 xenograft tumors following single oral or i.v. dose and inhibition of tumor growth following chronic dosing.

Evaluation of the effects of histone deacetylase inhibitors on cells from canine cancer cell lines

OBJECTIVE

To determine whether exposure of canine cancer cells to histone deacetylase (HDAC) inhibitors S(+)-N-hydroxy-4-(3-methyl-2-phenyl-butyrylamino)benzamide (OSU-HDAC42) or suberoylanilide hydroxamic acid (SAHA) results in increased histone acetylation and decreased cell viability and whether any changes in viability involve induction of apoptosis or alterations in progression of the cell cycle.

SAMPLE POPULATION

9 canine cancer cell lines.

PROCEDURES

Cells from 9 canine cancer cell lines were treated with dimethyl sulfoxide vehicle, OSU-HDAC42, or SAHA, then assays of cell viability were performed. Histone acetylation was assessed by use of western blot analysis. Apoptosis was assessed via ELISA to detect fragmentation of cytoplasmic nucleosomal DNA and western blot analysis to detect cleavage of caspase 3. Cell cycle analysis was performed by use of propidium iodide staining and flow cytometry. RESULTS-Concentrations of OSU-HDAC42 and SAHA required to achieve 50% inhibition of cell viability (IC(50)) were reached in cells of 6 and 4 canine cancer cell lines, respectively, and ranged from approximately 0.4 to 1.3 microM for OSU-HDAC42 and 0.6 to 4.8 microM for SAHA. Cells from T-cell lymphoma, mast cell tumor, osteosarcoma, and histiocytic sarcoma lines were most sensitive to HDAC inhibition, with IC(50)s of < 1 microM for OSU-HDAC42 and < 5 microM for SAHA. Induction of apoptosis was indicated via cleavage of caspase 3 and increases in cytoplasmic nucleosomes and the subG(1) cell population.

CONCLUSIONS AND CLINICAL RELEVANCE

Micromolar concentrations of HDAC inhibitors OSU-HDAC42 and SAHA induced histone acetylation, cytotoxicity, and apoptosis in canine cancer cells. In general, OSU-HDAC42 was more potent than SAHA.

Chemical targeting of the innate antiviral response by histone deacetylase inhibitors renders refractory cancers sensitive to viral oncolysis

Intratumoral innate immunity can play a significant role in blocking the effective therapeutic spread of a number of oncolytic viruses (OVs). Histone deacetylase inhibitors (HDIs) are known to influence epigenetic modifications of chromatin and can blunt the cellular antiviral response. We reasoned that pretreatment of tumors with HDIs could enhance the replication and spread of OVs within malignancies. Here, we show that HDIs markedly enhance the spread of vesicular stomatitis virus (VSV) in a variety of cancer cells in vitro, in primary tumor tissue explants and in multiple animal models. This increased oncolytic activity correlated with a dampening of cellular IFN responses and augmentation of virus-induced apoptosis. These results illustrate the general utility of HDIs as chemical switches to regulate cellular innate antiviral responses and to provide controlled growth of therapeutic viruses within malignancies. HDIs could have a profoundly positive impact on the clinical implementation of OV therapeutics.

Histone deacetylase inhibitors: anticancer compounds

The reversible acetylation of proteins is mediated by histone acetyltransferases which acetylate proteins and histone deacetylases that remove the acetyl groups. High levels of histone acetylation are correlated with active genes, while hypoacetylation of histones corresponds with gene repression. Importantly, acetylation also occurs on non-histone proteins and this can affect the activity and stability of these proteins. Aberrant epigenetic changes are a common hallmark of tumors and imbalances in the activities of deacetylases have been associated with cancers. Accordingly, inhibitors to the histone deacetylases are in clinical trials for the treatment of several cancer types. These drugs mediate a number of molecular changes and in turn can induce cell cycle arrest, apoptosis or differentiation of cancer cells while displaying limited toxicity in normal cells.

Histone deacetylase inhibitor panobinostat induces clinical responses with associated alterations in gene expression profiles in cutaneous T-cell lymphoma

PURPOSE

Histone deacetylase inhibitors can alter gene expression and mediate diverse antitumor activities. Herein, we report the safety and activity of the histone deacetylase inhibitor panobinostat (LBH589) in cutaneous T-cell lymphoma (CTCL) and identify genes commonly regulated by panobinostat.

EXPERIMENTAL DESIGN

Panobinostat was administered orally to patients with CTCL on Monday, Wednesday, and Friday of each week on a 28-day cycle. A dose of 30 mg was considered excessively toxic, and subsequent patients were treated at the expanded maximum tolerated dose of 20 mg. Biopsies from six patients taken 0, 4, 8, and 24 h after administration were subjected to microarray gene expression profiling and real-time quantitative PCR of selected genes.

RESULTS

Patients attained a complete response (n = 2), attained a partial response (n = 4), achieved stable disease with ongoing improvement (n = 1), and progressed on treatment (n = 2). Microarray data showed distinct gene expression response profiles over time following panobinostat treatment, with the majority of genes being repressed. Twenty-three genes were commonly regulated by panobinostat in all patients tested.

CONCLUSIONS

Panobinostat is well tolerated and induces clinical responses in CTCL patients. Microarray analyses of tumor samples indicate that panobinostat induces rapid changes in gene expression, and surprisingly more genes are repressed than are activated. A unique set of genes that can mediate biological responses such as apoptosis, immune regulation, and angiogenesis were commonly regulated in response to panobinostat. These genes are potential molecular biomarkers for panobinostat activity and are strong candidates for the future assessment of their functional role(s) in mediating the antitumor responses of panobinostat.

KD5170, a novel mercaptoketone-based histone deacetylase inhibitor that exhibits broad spectrum antitumor activity in vitro and in vivo

Histone deacetylase (HDAC) inhibitors have garnered significant attention as cancer drugs. These therapeutic agents have recently been clinically validated with the market approval of vorinostat (SAHA, Zolinza) for treatment of cutaneous T-cell lymphoma. Like vorinostat, most of the small-molecule HDAC inhibitors in clinical development are hydroxamic acids, whose inhibitory activity stems from their ability to coordinate the catalytic Zn2+ in the active site of HDACs. We sought to identify novel, nonhydroxamate-based HDAC inhibitors with potentially distinct pharmaceutical properties via an ultra-high throughput small molecule biochemical screen against the HDAC activity in a HeLa cell nuclear extract. An alpha-mercaptoketone series was identified and chemically optimized. The lead compound, KD5170, exhibits HDAC inhibitory activity with an IC50 of 0.045 micromol/L in the screening biochemical assay and an EC50 of 0.025 micromol/L in HeLa cell-based assays that monitor histone H3 acetylation. KD5170 also exhibits broad spectrum classes I and II HDAC inhibition in assays using purified recombinant human isoforms. KD5170 shows significant antiproliferative activity against a variety of human tumor cell lines, including the NCI-60 panel. Significant tumor growth inhibition was observed after p.o. dosing in human HCT-116 (colorectal cancer), NCI-H460 (non-small cell lung carcinoma), and PC-3 (prostate cancer) s.c. xenografts in nude mice. In addition, a significant increase in antitumor activity and time to end-point occurred when KD5170 was combined with docetaxel in xenografts of the PC-3 prostate cancer cell line. The biological and pharmaceutical profile of KD5170 supports its continued preclinical and clinical development as a broad spectrum anticancer agent.

MGCD0103, a novel isotype-selective histone deacetylase inhibitor, has broad spectrum antitumor activity in vitro and in vivo

Nonselective inhibitors of human histone deacetylases (HDAC) are known to have antitumor activity in mice in vivo, and several of them are under clinical investigation. The first of these, Vorinostat (SAHA), has been approved for treatment of cutaneous T-cell lymphoma. Questions remain concerning which HDAC isotype(s) are the best to target for anticancer activity and whether increased efficacy and safety will result with an isotype-selective HDAC inhibitor. We have developed an isotype-selective HDAC inhibitor, MGCD0103, which potently targets human HDAC1 but also has inhibitory activity against HDAC2, HDAC3, and HDAC11 in vitro. In intact cells, MGCD0103 inhibited only a fraction of the total HDAC activity and showed long-lasting inhibitory activity even upon drug removal. MGCD0103 induced hyperacetylation of histones, selectively induced apoptosis, and caused cell cycle blockade in various human cancer cell lines in a dose-dependent manner. MGCD0103 exhibited potent and selective antiproliferative activities against a broad spectrum of human cancer cell lines in vitro, and HDAC inhibitory activity was required for these effects. In vivo, MGCD0103 significantly inhibited growth of human tumor xenografts in nude mice in a dose-dependent manner and the antitumor activity correlated with induction of histone acetylation in tumors. Our findings suggest that the isotype-selective HDAC inhibition by MGCD0103 is sufficient for antitumor activity in vivo and that further clinical investigation is warranted.

Constitutive activation of signal transducers and activators of transcription predicts vorinostat resistance in cutaneous T-cell lymphoma

Vorinostat is a histone deacetylase inhibitor that induces differentiation, growth arrest, and/or apoptosis of malignant cells both in vitro and in vivo and has shown clinical responses in approximately 30% of patients with advanced mycosis fungoides and Sézary syndrome cutaneous T-cell lymphoma (CTCL). The purpose of this study was to identify biomarkers predictive of vorinostat response in CTCL using preclinical model systems and to assess these biomarkers in clinical samples. The signal transducer and activator of transcription (STAT) signaling pathway was evaluated. The data indicate that persistent activation of STAT1, STAT3, and STAT5 correlate with resistance to vorinostat in lymphoma cell lines. Simultaneous treatment with a pan-Janus-activated kinase inhibitor resulted in synergistic antiproliferative effect and down-regulation of the expression of several antiapoptotic genes. Immunohistochemical analysis of STAT1 and phosphorylated tyrosine STAT3 (pSTAT3) in skin biopsies obtained from CTCL patients enrolled in the vorinostat phase IIb trial showed that nuclear accumulation of STAT1 and high levels of nuclear pSTAT3 in malignant T cells correlate with a lack of clinical response. These results suggest that deregulation of STAT activity plays a role in vorinostat resistance in CTCL, and strategies that block this pathway may improve vorinostat response. Furthermore, these findings may be of prognostic value in predicting the response of CTCL patients to vorinostat.

Suberoyl bishydroxamic acid activates notch1 signaling and suppresses tumor progression in an animal model of medullary thyroid carcinoma

BACKGROUND

Medullary thyroid carcinoma (MTC) is a neuroendocrine malignancy that frequently metastasizes and has few treatments. This study was aimed at assessing the antitumor effects of suberoyl bishydroxamic acid (SBHA) in an in vivo model of MTC.

METHODS

Nude mice were injected with human MTC cells, and the groups were treated with SBHA (200 mg/kg) or vehicle (dimethyl sulfoxide) in saline injection every other day for 12 days. Tumors were measured every 4 days and collected at 12 days for Western blot analysis.

RESULTS

Treatment with SBHA resulted in an average 55% inhibition of tumor growth in the treatment group (P < .05). Analysis of SBHA-treated MTC tumors revealed a marked increase in the active form of Notch1 (NICD) with a concomitant decrease in achaete-scute complex-like 1 (ASCL1), a downstream target of Notch1 signaling, as well as the neuroendocrine tumor marker chromogranin A. Importantly, SBHA treatment resulted in an increase in protein levels of p21(CIP1/WAF1), p27(KIP1), cleaved caspase-9, cleaved caspase-3, and cleaved poly ADP-ribose polymerase and concomitant with a decrease in cyclin D1 and cyclin B1, indicating that the growth inhibition was due to both cell cycle arrest and apoptosis. Moreover, SBHA downregulated cell survival proteins Bcl-2 and Bcl-X(L), but upregulated apoptotic proteins Bax, Bad, and Bmf.

CONCLUSION

These results demonstrate that SBHA inhibits MTC growth in vivo. SBHA is a promising candidate for further preclinical and clinical studies in MTC.

Complex molecular mechanisms cooperate to mediate histone deacetylase inhibitors anti-tumour activity in neuroblastoma cells

Background

Histone deacetylase inhibitors (HDACi) are a new class of promising anti-tumour agent inhibiting cell proliferation and survival in tumour cells with very low toxicity toward normal cells. Neuroblastoma (NB) is the second most common solid tumour in children still associated with poor outcome in higher stages and, thus NB strongly requires novel treatment modalities.

Results

We show here that the HDACi Sodium Butyrate (NaB), suberoylanilide hydroxamic acid (SAHA) and Trichostatin A (TSA) strongly reduce NB cells viability. The anti-tumour activity of these HDACi involved the induction of cell cycle arrest in the G2/M phase, followed by the activation of the intrinsic apoptotic pathway, via the activation of the caspases cascade. Moreover, HDACi mediated the activation of the pro-apoptotic proteins Bid and Bim_EL and the inactivation of the anti-apoptotic proteins XIAP, Bcl-x_L, RIP and survivin, that further enhanced the apoptotic signal. Interestingly, the activity of these apoptosis regulators was modulated by several different mechanisms, either by caspases dependent proteolytic cleavage or by degradation via the proteasome pathway. In addition, HDACi strongly impaired the hypoxia-induced secretion of VEGF by NB cells.

Conclusion

HDACi are therefore interesting new anti-tumour agents for targeting highly malignant tumours such as NB, as these agents display a strong toxicity toward aggressive NB cells and they may possibly reduce angiogenesis by decreasing VEGF production by NB cells.

Histone deacetylase regulation of immune gene expression in tumor cells

Epigenetic modifications of chromatin, such as histone acetylation, are involved in repression of tumor antigens and multiple immune genes that are thought to facilitate tumor escape. The status of acetylation in a cell is determined by the balance of the activities of histone acetyltransferases and histone deacetylases. Inhibitors of histone deacetylase (HDACi) can enhance the expression of immunologically important molecules in tumor cells and HDACi treated tumor cells are able to induce immune responses in vitro and in vivo. Systemic HDACi are in clinical trails in cancer and also being used in several autoimmune disease models. To date, 18 HDACs have been reported in human cells and more than thirty HDACi identified, although only a few immune targets of these inhibitors have been identified. Here, we discuss the molecular pathways employed by HDACi and their potential role in inducing immune responses against tumors. We review data suggesting that selection of target specific HDACi and combinations with other agents and modalities, including those that activate stress pathways, may further enhance the efficacy of epigenetic therapies.

Evaluation of the pharmacodynamic effects of MGCD0103 from preclinical models to human using a novel HDAC enzyme assay

PURPOSE

The pharmacodynamic properties of MGCD0103, an isotype-selective inhibitor of histone deacetylase (HDAC), were evaluated in preclinical models and patients with a novel whole-cell HDAC enzyme assay.

EXPERIMENTAL DESIGN

Boc-Lys(epsilon-Ac)-AMC, a HDAC substrate with fluorescent readout, was found to be cell permeable and was used to monitor MGCD0103-mediated HDAC inhibition in cultured cancer cells in vitro, in peripheral WBC ex vivo, in mice in vivo, and in human patients.

RESULTS

MGCD0103 inhibited HDAC activity in several human cancer cell lines in vitro and in human peripheral WBC ex vivo in a dose-dependent manner. Unlike suberoylanilide hydroxamic acid, the HDAC inhibitory activity of MGCD0103 was time dependent and sustained for at least 24 hours following drug removal in peripheral WBC ex vivo. Inhibitory activity of MGCD0103 was sustained for at least 8 hours in vivo in mice and 48 hours in patients with solid tumors. HDAC inhibitory activity of MGCD0103 in peripheral WBC correlated with induction of histone acetylation in blood and in implanted tumors in mice. In cancer patients, sustained pharmacodynamic effect of MGCD0103 was visualized only by dose-dependent enzyme inhibition in peripheral WBC but not by histone acetylation analysis.

CONCLUSIONS

This study shows that MGCD0103 has sustained pharmacodynamic effects that can be monitored both in vitro and in vivo with a cell-based HDAC enzyme assay.