Histone deacetylase inhibitors for epigenetic therapy of cancer

Novel therapeutic agents in clinical trials: emerging approaches in cancer therapy

Novel therapeutic agents in clinical trials offer a paradigm shift in the approach to battling this prevalent and destructive disease, and the area of cancer therapy is on the precipice of a trans formative revolution. Despite the importance of tried-and-true cancer treatments like surgery, radiation, and chemotherapy, the disease continues to evolve and adapt, making new, more potent methods necessary. The field of cancer therapy is currently witnessing the emergence of a wide range of innovative approaches. Immunotherapy, including checkpoint inhibitors, CAR-T cell treatment, and cancer vaccines, utilizes the host's immune system to selectively target and eradicate malignant cells while minimizing harm to normal tissue. The development of targeted medicines like kinase inhibitors and monoclonal antibodies has allowed for more targeted and less harmful approaches to treating cancer. With the help of genomics and molecular profiling, "precision medicine" customizes therapies to each patient's unique genetic makeup to maximize therapeutic efficacy while minimizing unwanted side effects. Epigenetic therapies, metabolic interventions, radio-pharmaceuticals, and an increasing emphasis on combination therapy with synergistic effects further broaden the therapeutic landscape. Multiple-stage clinical trials are essential for determining the safety and efficacy of these novel drugs, allowing patients to gain access to novel treatments while also furthering scientific understanding. The future of cancer therapy is rife with promise, as the integration of artificial intelligence and big data has the potential to revolutionize early detection and prevention. Collaboration among researchers, and healthcare providers, and the active involvement of patients remain the bedrock of the ongoing battle against cancer. In conclusion, the dynamic and evolving landscape of cancer therapy provides hope for improved treatment outcomes, emphasizing a patient-centered, data-driven, and ethically grounded approach as we collectively strive towards a cancer-free world.

HDAC-targeting epigenetic modulators for cancer immunotherapy

HDAC inhibitors, which can inhibit the activity of HDAC enzymes, have been extensively studied in tumor immunotherapy and have shown potential therapeutic effects in cancer immunotherapy. To date, numerous small molecule HDAC inhibitors have been identified, but many of them suffer from limited clinical efficacy and serious toxicity. Hence, HDAC inhibitor-based combination therapies, and other HDAC modulators (e.g. PROTAC degraders, dual-acting agents) have attracted great attention with significant advancements achieved in the past few years due to their superior efficacy compared to single-target HDAC inhibitors. In this review, we overviewed the recent progress on HDAC-based drug discovery with a focus on HDAC inhibitor-based drug combination therapy and other HDAC-targeting strategies (e.g. selective HDAC inhibitors, HDAC-based dual-target inhibitors, and PROTAC HDAC degraders) for cancer immunotherapy. In addition, we also summarized the reported co-crystal structures of HDAC inhibitors in complex with their target proteins and the binding interactions. Finally, the challenges and future directions for HDAC-based drug discovery in cancer immunotherapy are also discussed in detail.

Targeting of the Interleukin-13 Receptor (IL-13R)α2 Expressing Prostate Cancer by a Novel Hybrid Lytic Peptide

The IL-13Rα2 cell surface receptor is highly expressed in tumours such as prostate cancer. In this report, we evaluated the hypothesis that prostate cancer cells with enhanced IL-13Rα2 expression are a suitable target for the hybrid lytic peptide (Pep-1-Phor21) peptide, which is generated by fusing the IL-13Rα2 specific ligand (Pep-1) and a cell membrane disrupting lytic peptide (Phor21). The expression of IL-13Rα2 mRNA and protein in prostate cancer tissues and cell lines was assessed via real-time PCR (RT-PCR) and immunoblotting. The effect of Pep-1-Phor21 on the viability of prostate cancer cells grown in monolayers (2D) and microtissue spheroids (3D) was assessed via CellTox green cytotoxic assay. IL-13Rα2 expression and Pep-1-Phor21-mediated killing were also determined in the cells treated with epigenetic regulators (Trichostatin A (TSA) and 5-aza-2 deoxycytidine (5-Aza-dC)). The hybrid lytic peptide cytotoxic activity correlated with the expression of IL-13Rα2 in prostate cancer cell lines cultured as monolayers (2D) or 3D spheroids. In addition, TSA or 5-Aza-dC treatment of prostate cancer cells, particularly those with low expression of IL-13Rα2, enhanced the cells' sensitivity to the lytic peptide by increasing IL-13Rα2 expression. These results demonstrate that the Pep-1-Phor21 hybrid lytic peptide has potent and selective anticancer properties against IL-13Rα2-expressing prostate cancer cells.

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

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

Histone deacetylase 3 in hippocampus contributes to memory impairment after chronic constriction injury of sciatic nerve in mice

ABSTRACT

Chronic neuropathic pain is frequently accompanied by memory impairment, yet the underlying mechanisms remain unclear. Here, we showed that mice displayed memory impairment starting at 14 days and lasting for at least 21 days after chronic constriction injury (CCI) of unilateral sciatic nerve in mice. Systemic administration of the pan histone deacetylase (HDAC) inhibitor sodium butyrate attenuated this memory impairment. More specifically, we found that hippocampus HDAC3 was involved in this process because the levels of its mRNA and protein increased significantly in the hippocampus at 14 and 21 days after CCI, but not sham surgery. Systemic administration of the selective HDAC3 antagonist RGFP966 attenuated CCI-induced memory impairment, improved hippocampal long-term potentiation impairment, and rescued reductions of dendritic spine density and synaptic plasticity-associated protein in the hippocampus. In addition, HDAC3 overexpression in the hippocampus led to memory impairment without affecting basal nociceptive responses in naive mice. Our findings suggest that HDAC3 contributes to memory impairment after CCI by impairing synaptic plasticity in hippocampus. Histone deacetylase 3 might serve as a potential molecular target for therapeutic treatment of memory impairment under neuropathic pain conditions.

The combination of histone deacetylase and p53 expressions and histological subtype has prognostic implication in uterine leiomyosarcoma

OBJECTIVE

To investigate the expression of different histone deacetylases and their association with disease characteristics and survival outcomes in uterine leiomyosarcoma patients.

METHODS

The immunohistochemical expression of different histone deacetylases and p53 by tissue microarray and histological subtypes were assessed in tumor tissue samples of 42 eligible patients.

RESULTS

Histone deacetylases 1-4, 6 and 8 showed prevalent and strong (3+) expression (88.1, 90.5, 95.2, 92.9, 83.3 and 100%, respectively). Histone deacetylases 5, 7 and 9 showed infrequent strong expression (33.3, 50 and 38.1%, respectively). There were trends of higher disease-free survival rates according to the combination of weaker expression of histone deacetylase 5, 7 or 9 with positive p53 expression or with non-epithelial subtype. The patients with triple-positive favorable prognostic factors (any of weaker histone deacetylase 5, 7 and 9 expression, p53 positive, and non-epithelioid subtype) had the better survival outcomes while the patients with other combinations had the worse survival outcomes. In multivariate analysis, histone deacetylase 5 in combination with epithelioid subtype was an independent predictor for disease-free survival.

CONCLUSIONS

Expression of histone deacetylase 5, 7 and 9 is a potential prognostic marker in uterine leiomyosarcoma when combined with pathologically relevant prognostic factors (p53 and histological subtype). This prevalent and strong histone deacetylase expression warrants further study in well-designed investigations of histone deacetylases as therapeutic targets in uterine leiomyosarcoma.

Histone deacetylase inhibitors reduce WB-F344 oval cell viability and migration capability by suppressing AKT/mTOR signaling in vitro

Histone deacetylase (HDAC) can blockDNA replication and transcription and altered HDAC expression was associated with tumorigenesis. This study investigated the effects of HDAC inhibitors on hepatic oval cells and aimed to delineate the underlying molecular events. Hepatic oval cells were treated with two different HDAC inhibitors, suberoylanilidehydroxamic acid (SAHA) and trichostatin-A (TSA). Cells were subjected to cell morphology, cell viability, cell cycle, and wound healing assays. The expression of proteins related to both apoptosis and the cell cycle, and proteins of the AKT/mammalian target of rapamycin (mTOR) signaling pathway were analyzed by Western blot. The data showed that HDAC inhibitors reduced oval cell viability and migration capability, and arrested oval cells at the G0/G1 and S phases of the cell cycle, in a dose- and time-dependent manner. HDAC inhibitors altered cell morphology and reduced oval cell viability, and downregulated the expression of PCNA, cyclinD1, c-Myc and Bmi1 proteins, while also suppressing AKT/mTOR and its downstream target activity. In conclusion, this study demonstrates that HDAC inhibitors affect oval cells by suppressing AKT/mTOR signaling.

Histone Deacetylase Inhibitors Inhibit the Proliferation of Gallbladder Carcinoma Cells by Suppressing AKT/mTOR Signaling

Gallbladder carcinoma is an aggressive malignancy with high mortality mainly due to the limited potential for curative resection and its resistance to chemotherapeutic agents. Here, we show that the histone deacetylase inhibitors (HDACIs) trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA) reduce the proliferation and induce apoptosis of gallbladder carcinoma cells by suppressing the AKT/mammalian target of rapamycin (mTOR) signaling. Gallbladder carcinoma SGC-996 cells were treated with different concentrations of TSA and SAHA for different lengths of time. Cell proliferation and morphology were assessed with MTT assay and microscopy, respectively. Cell cycle distribution and cell apoptosis were analyzed with flow cytometry. Western blotting was used to detect the proteins related to apoptosis, cell cycle, and the AKT/mTOR signaling pathway. Our data showed that TSA and SAHA reduced SGC-996 cell viability and arrested cell cycle at the G1 phase in a dose- and time-dependent manner. TSA and SAHA promoted apoptosis of SGC-996 cells, down-regulated the expression of cyclin D1, c-Myc and Bmi1, and decreased the phosphorylation of AKT, mTOR p70S6K1, S6 and 4E-BP1. Additionally, the mTOR inhibitor rapamycin further reduced the cell viability of TSA- and SAHA-treated SGC-996 cells and the phosphorylation of mTOR, whereas the mTOR activator 1,2-dioctanoyl-sn-glycero-3-phosphate (C8-PA) exerted the opposite influence. Our results demonstrate that histone deacetylase inhibitors (HDACIs) suppress the proliferation of gallbladder carcinoma cell via inhibition of AKT/mTOR signaling. These findings offer a mechanistic rationale for the application of HDACIs in gallbladder carcinoma treatment.

The HDAC Inhibitors Scriptaid and LBH589 Combined with the Oncolytic Virus Delta24-RGD Exert Enhanced Anti-Tumor Efficacy in Patient-Derived Glioblastoma Cells

Background

A phase I/II trial for glioblastoma with the oncolytic adenovirus Delta24-RGD was recently completed. Delta24-RGD conditionally replicates in cells with a disrupted retinoblastoma-pathway and enters cells via αvβ3/5 integrins. Glioblastomas are differentially sensitive to Delta24-RGD. HDAC inhibitors (HDACi) affect integrins and share common cell death pathways with Delta24-RGD. We studied the combination treatment effects of HDACi and Delta24-RGD in patient-derived glioblastoma stem-like cells (GSC), and we determined the most effective HDACi.

Methods

SAHA, Valproic Acid, Scriptaid, MS275 and LBH589 were combined with Delta24-RGD in fourteen distinct GSCs. Synergy was determined by Chou Talalay method. Viral infection and replication were assessed using luciferase and GFP encoding vectors and hexon-titration assays. Coxsackie adenovirus receptor and αvβ3 integrin levels were determined by flow cytometry. Oncolysis and mechanisms of cell death were studied by viability, caspase-3/7, LDH and LC3B/p62, phospho-p70S6K. Toxicity was studied on normal human astrocytes. MGMT promotor methylation status, TCGA classification, Rb-pathway and integrin gene expression levels were assessed as markers of responsiveness.

Results

Scriptaid and LBH589 acted synergistically with Delta24-RGD in approximately 50% of the GSCs. Both drugs moderately increased αvβ3 integrin levels and viral infection in responding but not in non-responding GSCs. LBH589 moderately increased late viral gene expression, however, virus titration revealed diminished viral progeny production by both HDACi, Scriptaid augmented caspase-3/7 activity, LC3B conversion, p62 and phospho-p70S6K consumption, as well as LDH levels. LBH589 increased LDH and phospho-p70S6K consumption. Responsiveness correlated with expression of various Rb-pathway genes and integrins. Combination treatments induced limited toxicity to human astrocytes.

Conclusion

LBH589 and Scriptaid combined with Delta24-RGD revealed synergistic anti-tumor activity in a subset of GSCs. Both HDACi moderately augmented viral infection and late gene expression, but slightly reduced progeny production. The drugs differentially activated multiple cell death pathways. The limited toxicity on astrocytes supports further evaluation of the proposed combination therapies.

HDACiDB: a database for histone deacetylase inhibitors

An histone deacetylase (HDAC) inhibitor database (HDACiDB) was constructed to enable rapid access to data relevant to the development of epigenetic modulators (HDAC inhibitors [HDACi]), helping bring precision cancer medicine a step closer. Thousands of HDACi targeting HDACs are in various stages of development and are being tested in clinical trials as monotherapy and in combination with other cancer agents. Despite the abundance of HDACi, information resources are limited. Tools for in silico experiments on specific HDACi prediction, for designing and analyzing the generated data, as well as custom-made specific tools and interactive databases, are needed. We have developed an HDACiDB that is a composite collection of HDACi and currently comprises 1,445 chemical compounds, including 419 natural and 1,026 synthetic ones having the potential to inhibit histone deacetylation. Most importantly, it will allow application of Lipinski’s rule of five drug-likeness and other physicochemical property-based screening of the inhibitors. It also provides easy access to information on their source of origin, molecular properties, drug likeness, as well as bioavailability with relevant references cited. Being the first comprehensive database on HDACi that contains all known natural and synthetic HDACi, the HDACiDB may help to improve our knowledge concerning the mechanisms of actions of available HDACi and enable us to selectively target individual HDAC isoforms and establish a new paradigm for intelligent epigenetic cancer drug design. The database is freely available on the http://hdacidb.bioinfo.au-kbc.org.in/hdacidb/website.

Assessment of the effect of trichostatin A on HeLa cells through FT-IR spectroscopy

Trichostatin A (TSA) is one of histone deacetylase (HDAC) inhibitor drugs which can suppress the enzymatic activity of deacytylases and promote the acetylation of both histone and nonhistone proteins in cells. Investigation of the effect of TSA on cellular acetylation is critical for better understanding of the antitumor drug's mechanism interacting with cancer cells. As Fourier transform infrared spectroscopy (FT-IR) is a powerful analytical tool which can detect nondestructively and quantitatively biological samples without biotagging and biolabeling, here we employed FT-IR spectroscopy to probe the chemical and structural changes of proteins in the TSA treated cells, and with the aid of fluorescent microscopy, we could scrutinize the time-dependent and dose effects on the acetylation level promoted by TSA. Our results showed that TSA caused an elevated level of cellular acetylation and conformational/structural changes of proteins in the cells, and a higher dosage of TSA caused a higher percent of α-helix structure accompanied by an increment of acetylation level in both histones and cytoskeleton proteins. This work therefore not only validates the usefulness of FT-IR spectroscopy in the quantitative assessment of cellular acetylation but also may open an avenue to the in-depth investigation of the effect of HDAC inhibitor drugs such as TSA on cancer cells.

Mechanistic Insights to the Cytotoxicity of Amaryllidaceae Alkaloids

With over 500 individual compounds, the Amaryllidaceae alkaloids represent a large and structurally diverse group of phytochemicals. Coupled to this structural diversity is the significant array of biological properties manifested by many of its members, of which their relevance in motor neuron disease and cancer chemotherapy has attracted considerable attention. To this extent, galanthamine has evolved into a successful commercial drug for Alzheimer's disease since its approval by the FDA in 2001. Concurrently, there have been several positive indicators for the emergence of an anticancer drug from the Amaryllidaceae due to the potency of several of its representatives as cell line specific antiproliferative agents. In this regard, the phenanthridones such as pancratistatin and narciclasine have offered most promise since their advancement into clinical trials, following which there has been renewed interest in the cytotoxic properties of these alkaloids. Given this background, this review seeks to highlight the various mechanisms which have been invoked to corroborate the cytotoxic effects of Amaryllidaceae alkaloids.

New therapeutic approaches to acute myeloid leukemia

BACKGROUND

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the pathogenesis and treatment of patients with AML. Understanding the basic cellular and molecular pathogenesis of leukemic cells is vital to the development of new treatment approaches.

OBJECTIVE/METHODS

To review progress until now with agents that are showing promise in the treatment of AML, we summarize the published preclinical and clinical trials that have been completed.

RESULTS

Based on recent progress of investigations, more specifically targeted agents have been developed for the treatment of AML such as tyrosine kinase inhibitors, monoclonal antibodies, epigenetic agents, antiangiogenic agents, and farnesyl transferase inhibitors.

CONCLUSION

In the future, in addition to performing therapeutic trials of these agents, it will be important to identify other highly specific therapeutic agents based on our evolving understanding of the biology of AML.

The antiepileptic drug valproic acid restores T cell homeostasis and ameliorates pathogenesis of experimental autoimmune encephalomyelitis

Maintaining a constant number and ratio of immune cells is one critical aspect of the tight regulation of immune homeostasis. Breakdown of this balance will lead to autoimmune diseases such as multiple sclerosis (MS). The antiepileptic drug valproic acid (VPA) was reported to regulate the growth, survival, and differentiation of many cells. However, its function in T cell homeostasis and MS treatment remains unknown. In this study, VPA was found to reduce spinal cord inflammation, demyelination, and disease scores in experimental autoimmune encephalomyelitis, a mouse model of MS. Further study indicated that VPA induces apoptosis in activated T cells and maintains the immune homeostasis. This effect was found to be mainly mediated by the caspase-8/caspase-3 pathway. Interestingly, this phenomenon was also confirmed in T cells from normal human subjects and MS patients. Considering the long history of clinical use and our new findings, we believe VPA might be a safe and effective therapy for autoimmune diseases, such as multiple sclerosis.

Modulation of hypoxia-inducible factors (HIF) from an integrative pharmacological perspective

Oxygen homeostasis determines the activity and expression of a multitude of cellular proteins and the interplay of pathways that affect crucial cellular processes for development, physiology, and pathophysiology. Hypoxia-inducible factors (HIFs) are transcription factors that respond to changes in available oxygen in the cellular environment and drives cellular adaptation to such conditions. Selective gene expression under hypoxic conditions is the result of an exquisite regulation of HIF, from the pre-transcriptional stage of the HIF gene to the final transcriptional activity of HIF protein. We provide a dissected analysis of HIF modulation with special focus on hypoxic conditions and HIF pharmacological interventions that can guide the application of any future HIF-mediated therapy.

Resistance to chemotherapy: short-term drug tolerance and stem cell-like subpopulations

Personalized medicine in cancer treatment has been a major goal for decades. Recently, the development of several therapies that specifically target key genetic alterations in different malignancies has dramatically improved patient outcome and brought the goal of personalized medicine closer to practicality. Despite the improved specificity of these treatment options, resistance to targeted therapy is common and remains a major obstacle to long-term management of a patient's disease. Often patient relapse is a result of the positive selection of cells with certain genetic alterations that result in a bypass of the therapeutic intervention. Once this occurs, patient relapse is inevitable and further treatment options are limited. The time to relapse is often quite rapid indicating that cancer cells may be primed for adapting to cytotoxic stimuli. Recently, it has been suggested that small subpopulations of cells allow resistance to occur more rapidly. It is thought that these cells are capable of surviving strong apoptotic stimuli until more permanent mechanisms of long-term resistance are developed. In order to decrease the rate of patient relapse, more studies are required in order to identify these subpopulations of cells, understand the mechanisms underlying their drug tolerance, and develop strategies to prevent them from evading treatment.

Anti-tumor effect in human lung cancer by a combination treatment of novel histone deacetylase inhibitors: SL142 or SL325 and retinoic acids

Histone deacetylase (HDAC) inhibitors arrest cancer cell growth and cause apoptosis with low toxicity thereby constituting a promising treatment for cancer. In this study, we investigated the anti-tumor activity in lung cancer cells of the novel cyclic amide-bearing hydroxamic acid based HDAC inhibitors SL142 and SL325. In A549 and H441 lung cancer cells both SL142 and SL325 induced more cell growth inhibition and cell death than the hydroxamic acid-based HDAC inhibitor suberoylanilide hydroxamic acid (SAHA). Moreover, the combination treatment using retinoid drugs ATRA or 9-cis RA along with SL142 or SL325 significantly induced more apoptosis and suppressed colony formation than the single use of either. The expression of the retinoic acid receptors RARα, RARβ, RXRα and RXRβ were unchanged with the treatment. However a luciferase reporter construct (pGL4. RARE 7x) containing seven tandem repeats of the retinoic acid responsible element (RARE) generated significant transcriptional activity after the combination treatment of retinoic acids and SL142 or SL325 in H441 lung cancer cells. Moreover, apoptosis-promoting Bax expression and caspase-3 activity was increased after the combination treatment. These results suggest that the combination treatment of SL142 or SL325 with retinoic acids exerts significant anti-tumor activity and is a promising therapeutic candidate to treat human lung cancer.

Histone deacetylase: a potential therapeutic target for fibrotic disorders

Histone deacetylases (HDACs) are enzymes that balance the acetylation activities of histone acetyltransferases on chromatin remodeling and play essential roles in regulating gene transcription. In the past several years, the role of HDACs in cancer initiation and progression, as well as the therapeutic effects of HDAC inhibitors in various types of cancer, has been well studied. Recent studies indicated that HDAC activity is also associated with the development and progression of some chronic diseases characterized by fibrosis, including chronic kidney disease, cardiac hypertrophy, and idiopathic pulmonary fibrosis. Here, we review what is known about HDACs in the progression of tissue fibrosis and the potential applications of HDAC inhibitors in the treatment of disorders associated with fibroblast activation and proliferation.

Inhibition of class II histone deacetylases in the spinal cord attenuates inflammatory hyperalgesia

Background

Several classes of histone deacetylases (HDACs) are expressed in the spinal cord that is a critical structure of the nociceptive pathway. HDAC-regulated histone acetylation is an important component of chromatin remodeling leading to epigenetic regulation of gene transcription. To understand the role of histone acetylation in epigenetic regulation of pathological pain, we have studied the impact of different classes of HDACs in the spinal cord on inflammatory hyperalgesia induced by complete Freund's adjuvant (CFA).

Results

We intrathecally applied inhibitors specific to different classes of HDACs and evaluated their impact on inflammatory hyperalgesia. Pre-injected inhibitors targeting class I as well as II (SAHA, TSA, LAQ824) or IIa (VPA, 4-PB) HDACs significantly delayed the thermal hyperalgesia induced by unilateral CFA injection in the hindpaw. Existing hyperalgesia induced by CFA was also attenuated by the HDAC inhibitors (HDACIs). In contrast, these inhibitors did not interfere with the thermal response either in naïve animals, or on the contralateral side of inflamed animals. Interestingly, MS-275 that specifically inhibits class I HDACs failed to alter the hyperalgesia although it increased histone 3 acetylation in the spinal cord as SAHA did. Using immunoblot analysis, we further found that the levels of class IIa HDAC members (HDAC4, 5, 7, 9) in the spinal dorsal horn were upregulated following CFA injection while those of class I HDAC members (HDAC1, 2, 3) remained stable or were slightly reduced.

Conclusions

Our data suggest that activity of class II HDACs in the spinal cord is critical to the induction and maintenance of inflammatory hyperalgesia induced by CFA, while activity of class I HDACs may be unnecessary. Comparison of the effects of HDACIs specific to class II and IIa as well as the expression pattern of different HDACs in the spinal cord in response to CFA suggests that the members of class IIa HDACs may be potential targets for attenuating persistent inflammatory pain.

Chemical regulation of epigenetic modifications: opportunities for new cancer therapy

Epigenetics is concerned about heritable changes in gene expression without alteration of the coding sequence. Epigenetic modification of chromatin includes methylation of genomic DNA as well as post-translational modification of chromatin-associated proteins, in particular, histones. The spectrum of histone and non-histone modifications ranges from the addition of relatively small groups such as methyl, acetyl and phosphoryl groups to the attachment of larger moieties such as poly(ADP-ribose) and small proteins ubiquitin or small ubiquitin-like modifier (SUMO). The combinatorial nature of DNA methylation and histone modifications constitutes a significant pathway of epigenetic regulation and considerably extends the information potential of the genetic code. Chromatin modification has emerged as a new fundamental mechanism for gene transcriptional activity control associated with many cellular processes like proliferation, growth, and differentiation. Also it is increasingly recognized that epigenetic modifications constitute important regulatory mechanisms for the pathogenesis of malignant transformations. We review here the recent progress in the development of chemical inhibitors/activators that target different chromatin modifying enzymes. Such potent natural or synthetic modulators can be utilized to establish the quantitative contributions of epigenetic modifications in DNA regulated pathways including transcription, replication, recombination and repair, as well as provide leads for developing new cancer therapeutics.

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.

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.

epigenetic multiple ligands: mixed histone/protein methyltransferase, acetyltransferase, and class III deacetylase (sirtuin) inhibitors

A number of new compounds bearing two ortho-bromo- and ortho, ortho-dibromophenol moieties linked through a saturated/unsaturated, linear/(poly)cyclic spacer (compounds 1- 9) were prepared as simplified analogues of AMI-5 (eosin), a recently reported inhibitor of both protein arginine and histone lysine methyltransferases (PRMTs and HKMTs). Such compounds were tested against a panel of PRMTs (RmtA, PRMT1, and CARM1) and against human SET7 (a HKMT), using histone and nonhistone proteins as a substrate. They were also screened against HAT and SIRTs, because they are structurally related to some HAT and/or SIRT modulators. From the inhibitory data, some of tested compounds ( 1b, 1c, 4b, 4f, 4j, 4l, 7b, and 7f) were able to inhibit PRMTs, HKMT, HAT, and SIRTs with similar potency, thus behaving as multiple ligands for these epigenetic targets (epi-MLs). When tested on the human leukemia U937 cell line, the epi-MLs induced high apoptosis levels [i.e., 40.7% ( 4l) and 42.6% ( 7b)] and/or massive, dose-dependent cytodifferentiation [i.e., 95.2% ( 1c) and 96.1% ( 4j)], whereas the single-target inhibitors eosin, curcumin, and sirtinol were ineffective or showed a weak effect.

HDAC inhibitors stimulate viral transcription by multiple mechanisms

BACKGROUND

The effects of histone deacetylase inhibitor (HDACi) treatment on SV40 transcription and replication were determined by monitoring the levels of early and late expression, the extent of replication, and the percentage of SV40 minichromosomes capable of transcription and replication following treatment with sodium butyrate (NaBu) and trichostatin A (TSA).

RESULTS

The HDACi treatment was found to maximally stimulate early transcription at early times and late transcription at late times through increased numbers of minichromosomes which carry RNA polymerase II (RNAPII) transcription complexes and increased occupancy of the transcribing minichromosomes by RNAPII. HDACi treatment also partially relieved the normal down-regulation of early transcription by T-antigen seen later in infection. The increased recruitment of transcribing minichromosomes at late times was correlated to a corresponding reduction in SV40 replication and the percentage of minichromosomes capable of replication.

CONCLUSION

These results suggest that histone deacetylation plays a critical role in the regulation of many aspects of an SV40 lytic infection.

Novobiocin and additional inhibitors of the Hsp90 C-terminal nucleotide-binding pocket

The 90 kDa heat shock proteins (Hsp90), which are integrally involved in cell signaling, proliferation, and survival, are ubiquitously expressed in cells. Many proteins in tumor cells are dependent upon the Hsp90 protein folding machinery for their stability, refolding, and maturation. Inhibition of Hsp90 uniquely targets client proteins associated with all six hallmarks of cancer. Thus, Hsp90 has emerged as a promising target for the treatment of cancer. Hsp90 exists as a homodimer, which contains three domains. The N-terminal domain contains an ATP-binding site that binds the natural products geldanamycin and radicicol. The middle domain is highly charged and has high affinity for co-chaperones and client proteins. Initial studies by Csermely and co-workers suggested a second ATP-binding site in the C-terminus of Hsp90. This C-terminal nucleotide binding pocket has been shown to not only bind ATP, but cisplatin, novobiocin, epilgallocatechin-3-gallate (EGCG) and taxol. The coumarin antibiotics novobiocin, clorobiocin, and coumermycin A1 were isolated from several streptomyces strains and exhibit potent activity against Gram-positive bacteria. These compounds bind type II topoisomerases, including DNA gyrase, and inhibit the enzyme-catalyzed hydrolysis of ATP. As a result, novobiocin analogues have garnered the attention of numerous researchers as an attractive agent for the treatment of bacterial infection. Novobiocin was reported to bind weakly to the newly discovered Hsp90 C-terminal ATP binding site ( approximately 700 M in SkBr3 cells) and induce degradation of Hsp90 client proteins. Structural modification of this compound has led to an increase of 1000-fold in activity in anti-proliferative assays. Recent studies of structure-activity relationship (SAR) by Renoir and co-workers highlighted the crucial role of the C-4 and/or C-7 positions of the coumarin and removal of the noviose moiety, which appeared to be essential for degradation of Hsp90 client proteins. Unlike the N-terminal ATP binding site, there is no reported co-crystal structure of Hsp90 C-terminus bound to any inhibitor. The Hsp90 C-terminal domain, however, is known to contain a conserved pentapeptide sequence (MEEVD) which is recognized by co-chaperones. Cisplatin is a platinum-containing chemotherapeutic used to treat various types of cancers, including testicular, ovarian, bladder, and small cell lung cancer. Most notably, cisplatin coordinates to DNA bases, resulting in cross-linked DNA, which prohibits rapidly dividing cells from duplicating DNA for mitosis. Itoh and co-workers reported that cisplatin decreases the chaperone activity of Hsp90. This group applied bovine brain cytosol to a cisplatin affinity column, eluted with cisplatin and detected Hsp90 in the eluent. Subsequent experiments indicated that cisplatin exhibits high affinity for Hsp90. Moreover Csermely and co-workers determined that the cisplatin binding site is located proximal to the C-terminal ATP binding site. EGCG is one of the active ingredients found in green tea. EGCG is known to inhibit the activity of many Hsp90-dependent client proteins, including telomerase, several kinases, and the aryl hydrocarbon receptor (AhR). Recently Gasiewicz and co-workers reported that EGCG manifests its antagonistic activity against AhR through binding Hsp90. Similar to novobiocin, EGCG was shown to bind the C-terminus of Hsp90. Unlike previously identified N-terminal Hsp90 inhibitors, EGCG does not appear to prevent Hsp90 from forming multiprotein complexes. Studies are currently underway to determine whether EGCG competes with novobiocin or cisplatin binding. Taxol, a well-known drug for the treatment of cancer, is responsible for the stabilization of microtubules and the inhibition of mitosis. Previous studies have shown that taxol induces the activation of kinases and transcription factors, and mimics the effect of bacterial lipopolysaccharide (LPS), an attribute unrelated to its tubulin-binding properties. Rosen and co-workers prepared a biotinylated taxol derivative and performed affinity chromatography experiments with lysates from both mouse brain and macrophage cell lines. These studies led to identification of two chaperones, Hsp70 and Hsp90, by mass spectrometry. In contrast to typical Hsp90-binding drugs, taxol exhibits a stimulatory response. Recently it was reported that the geldanamycin derivative 17-AAG behaves synergistically with taxol-induced apoptosis. This review describes the different C-terminal inhibitors of Hsp90, with specific emphasis on structure-activity relationship studies of novobiocin and their effects on anti-proliferative activity.

A spectrophotometric assay for histone deacetylase 8

Inhibitors for the classical protein deacetylase enzymes have been actively pursued to develop the next generation of cancer therapy. Developing a novel convenient assay platform for the classical enzyme-catalyzed reactions could thus facilitate the drug discovery process. Based on our previous studies demonstrating the functional mimicry of N(epsilon)-thioacetyl-lysine for N(epsilon)-acetyl-lysine in the reaction catalyzed by the classical enzyme histone deacetylase 8 (HDAC8) on a peptide template derived from the C terminus of the human p53 tumor suppressor protein, we have developed a spectrophotometric HDAC8 assay via quantifying thioacetate produced from the enzymatic dethioacetylation with Ellman's reagent 5,5'-dithiobis(2-nitrobenzoate). We further demonstrated that this novel assay was selective for HDAC8 versus HDAC1 and 2 and for other classical protein deacetylase enzymes present in the HeLa nuclear extracts, thus making it potentially suitable not only for screening HDAC8-selective inhibitors but also for selectively assessing HDAC8 activity under (patho)physiological conditions.

Molecular insight in cancer treatment and prevention

This article explores the impact of new insights in the biology of cancer on the treatment and the prevention of this disease. There are two types of targeted cancer treatment, afforded by the molecular profile of cancer. One concerns the use of agents targeted on a specific component of the cancer cells (e.g., CD20 in lymphoma) or on a specific survival function of the cancer cell (growth-factor-receptor interaction; transduction cascade). The other concerns the recognition of tumors that are more or less likely to benefit from cytotoxic chemotherapy according to their genomic or proteomic profile. Cancer prevention may benefit from new molecular insight in cancer biology as these processes allow early diagnosis of cancer, identification of patients at risk for cancer, and may provide intermediate markers for chemoprevention studies.