The histone deacetylase inhibitor MS-275 induces caspase-dependent apoptosis in B-cell chronic lymphocytic leukemia cells

Advances in epigenetic alterations of chronic lymphocytic leukemia: from pathogenesis to treatment

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease with alterations in genetic expression and epigenetic modifications. In recent years, the new insight into epigenetics in the pathogenesis of CLL has been developed considerably, including DNA methylation, histone modification, RNA methylation, non-coding RNAs as well as chromatin remodeling. Epigenetic modification regulates various processes such as stem cell biology, cell growth, and tumorigenesis without altering gene sequence. Growing evidence indicates that the disturbance of gene expression profiles which were regulated by epigenetic modifications exerts vital roles in the development and progress in CLL, which provides novel perspectives to explore the etiology of CLL. In addition, the integration with epigenetic therapeutic targets and the in-depth understanding of epigenetic therapy contribute to develop new therapeutic strategies for CLL. Herein, the present review discusses the advances of epigenetic alterations in the pathogenesis, diagnosis, and prognostic assessment of CLL patients and also highlights existing and emerging agents targeting epigenetic regulators.

HDAC inhibitors: Promising agents for leukemia treatment

The essential role of epigenetic modification in the pathogenesis of a series of cancers have gradually been recognized. Histone deacetylase (HDACs), as well-known epigenetic modulators, are responsible for DNA repair, cell proliferation, differentiation, apoptosis and angiogenesis. Studies have shown that aberrant expression of HDACs is found in many cancer types. Thus, inhibition of HDACs has provided a promising therapeutic approach alternative for these patients. Since HDAC inhibitor (HDACi) vorinostat was first approved by the Food and Drug Administration (FDA) for treating cutaneous T-cell lymphoma (CTCL) in 2006, the combination of HDAC inhibitors with other molecules such as chemotherapeutic drugs has drawn much attention in current cancer treatment, especially in hematological malignancies therapy. Up to now, there have been more than twenty HDAC inhibitors investigated in clinic trials with five approvals being achieved. Indeed, Histone deacetylase inhibitors promote or enhance several different anticancer mechanisms and therefore are in evidence as potential antileukemia agents. In this review, we will focus on possible mechanisms by how HDAC inhibitors exert therapeutic benefit and their clinical utility in leukemia.

Glioma Stem Cells Are Sensitized to BCL-2 Family Inhibition by Compromising Histone Deacetylases

Glioblastoma (GBM) remains an incurable disease with an extremely high five-year recurrence rate. We studied apoptosis in glioma stem cells (GSCs) in response to HDAC inhibition (HDACi) combined with MEK1/2 inhibition (MEKi) or BCL-2 family inhibitors. MEKi effectively combined with HDACi to suppress growth, induce cell cycle defects, and apoptosis, as well as to rescue the expression of the pro-apoptotic BH3-only proteins BIM and BMF. A RNAseq analysis of GSCs revealed that HDACi repressed the pro-survival BCL-2 family genes MCL1 and BCL-XL. We therefore replaced MEKi with BCL-2 family inhibitors and observed enhanced apoptosis. Conversely, a ligand for the cancer stem cell receptor CD44 led to reductions in BMF, BIM, and apoptosis. Our data strongly support further testing of HDACi in combination with MEKi or BCL-2 family inhibitors in glioma.

Cancer Resistance to Immunotherapy: Comprehensive Insights with Future Perspectives

Cancer immunotherapy is a type of treatment that harnesses the power of the immune systems of patients to target cancer cells with better precision compared to traditional chemotherapy. Several lines of treatment have been approved by the US Food and Drug Administration (FDA) and have led to remarkable success in the treatment of solid tumors, such as melanoma and small-cell lung cancer. These immunotherapies include checkpoint inhibitors, cytokines, and vaccines, while the chimeric antigen receptor (CAR) T-cell treatment has shown better responses in hematological malignancies. Despite these breakthrough achievements, the response to treatment has been variable among patients, and only a small percentage of cancer patients gained from this treatment, depending on the histological type of tumor and other host factors. Cancer cells develop mechanisms to avoid interacting with immune cells in these circumstances, which has an adverse effect on how effectively they react to therapy. These mechanisms arise either due to intrinsic factors within cancer cells or due other cells within the tumor microenvironment (TME). When this scenario is used in a therapeutic setting, the term “resistance to immunotherapy” is applied; “primary resistance” denotes a failure to respond to treatment from the start, and “secondary resistance” denotes a relapse following the initial response to immunotherapy. Here, we provide a thorough summary of the internal and external mechanisms underlying tumor resistance to immunotherapy. Furthermore, a variety of immunotherapies are briefly discussed, along with recent developments that have been employed to prevent relapses following treatment, with a focus on upcoming initiatives to improve the efficacy of immunotherapy for cancer patients.

What we have learnt from Drosophila model organism: the coordination between insulin signaling pathway and tumor cells

Cancer development is related to a variety of signaling pathways which mediate various cellular processes including growth, survival, division and competition of cells, as well as cell-cell interaction. The insulin signaling pathway interacts with different pathways and plays a core role in the regulations of all these processes. In this study, we reviewed recent studies on the relationship between the insulin signaling pathway and tumors using the Drosophila melanogaster model. We found that on one hand, the insulin pathway is normally hyperactive in tumor cells, which promotes tumor growth, and on the other hand, tumor cells can suppress the growth of healthy tissues via inhibition of their insulin pathway. Moreover, systematic disruption in glucose homeostasis also facilitates cancer development by different mechanisms. The studies on how the insulin network regulates the behaviors of cancer cells may help to discover new therapeutic treatments for cancer.

Regulation of extrinsic apoptotic signaling by c-FLIP: towards targeting cancer networks

The extrinsic pathway is mediated by death receptors (DRs), including CD95 (APO-1/Fas) or TRAILR-1/2. Defects in apoptosis regulation lead to cancer and other malignancies. The master regulator of the DR networks is the cellular FLICE inhibitory protein (c-FLIP). In addition to its key role in apoptosis, c-FLIP may exert other cellular functions, including control of necroptosis, pyroptosis, nuclear factor κB (NF-κB) activation, and tumorigenesis. To gain further insight into the molecular mechanisms of c-FLIP action in cancer networks, we focus on the structure, isoforms, interactions, and post-translational modifications of c-FLIP. We also discuss various avenues to target c-FLIP in cancer cells for therapeutic benefit.

Phase 1 study of the histone deacetylase inhibitor entinostat plus clofarabine for poor-risk Philadelphia chromosome-negative (newly diagnosed older adults or adults with relapsed refractory disease) acute lymphoblastic leukemia or biphenotypic leukemia

PURPOSE

Despite advances in immunotherapies, the prognosis for adults with Philadelphia chromosome-negative, newly diagnosed (ND) or relapsed/refractory (R/R) acute lymphoblastic leukemia/acute biphenotypic leukemia (ALL/ABL) remains poor. The benzamide derivative entinostat inhibits histone deacetylase and induces histone hyperacetylation. The purine nucleoside analogue clofarabine is FDA-approved for R/R ALL in children 1-21 years of age. Low doses of clofarabine have been reported to induce DNA hypomethylation. We conducted a phase 1 study of low dose clofarabine with escalating doses of entinostat in adults with ND or R/R ALL/ABL.

EXPERIMENTAL DESIGN

Adults ≥60 years with ND ALL/ABL or ≥21 years with R/R ALL/ABL received repeated cycles every 3 weeks of entinostat (4 mg, 6 mg or 8 mg orally days 1 and 8) and clofarabine (10 mg/m²/day IV for 5 days, days 3-7) (Arm A). Adults aged 40-59 years with ND ALL/ABL or age ≥21 years in first relapse received entinostat and clofarabine prior to traditional chemotherapy on day 11 (Arm B). Changes in DNA damage, global protein lysine acetylation, myeloid-derived suppressor cells and monocytes were measured in PBMCs before and during therapy.

RESULTS

Twenty-eight patients were treated at three entinostat dose levels with the maximum administered dose being entinostat 8 mg. The regimen was well tolerated with infectious and metabolic derangements more common in the older population versus the younger cohort. There was no severe hyperglycemia and no peripheral neuropathy in this small study. There were 2 deaths (1 sepsis, 1 intracranial bleed). Overall response rate was 32 %; it was 50 % for ND ALL/ABL. Entinostat increased global protein acetylation and inhibited immunosuppressive monocyte subpopulations, while clofarabine induced DNA damage in all cell subsets examined.

CONCLUSION

Entinostat plus clofarabine appears to be tolerable and active in older adults with ND ALL/ABL, but less active in R/R patients. Further evaluation of this regimen in ND ALL/ABL appears warranted.

Anticancer Therapy with HDAC Inhibitors: Mechanism-Based Combination Strategies and Future Perspectives

The increasing knowledge of molecular drivers of tumorigenesis has fueled targeted cancer therapies based on specific inhibitors. Beyond "classic" oncogene inhibitors, epigenetic therapy is an emerging field. Epigenetic alterations can occur at any time during cancer progression, altering the structure of the chromatin, the accessibility for transcription factors and thus the transcription of genes. They rely on post-translational histone modifications, particularly the acetylation of histone lysine residues, and are determined by the inverse action of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Importantly, HDACs are often aberrantly overexpressed, predominantly leading to the transcriptional repression of tumor suppressor genes. Thus, histone deacetylase inhibitors (HDACis) are powerful drugs, with some already approved for certain hematological cancers. Albeit HDACis show activity in solid tumors as well, further refinement and the development of novel drugs are needed. This review describes the capability of HDACis to influence various pathways and, based on this knowledge, gives a comprehensive overview of various preclinical and clinical studies on solid tumors. A particular focus is placed on strategies for achieving higher efficacy by combination therapies, including phosphoinositide 3-kinase (PI3K)-EGFR inhibitors and hormone- or immunotherapy. This also includes new bifunctional inhibitors as well as novel approaches for HDAC degradation via PROteolysis-TArgeting Chimeras (PROTACs).

The Histone Deacetylase Inhibitor (MS-275) Promotes Differentiation of Human Dental Pulp Stem Cells into Odontoblast-Like Cells Independent of the MAPK Signaling System

The role of dental pulp stem cells (DPSCs) in dental tissue regeneration is gaining attention because DPSCs can differentiate into odontoblasts and other specialized cell types. Epigenetic modification has been found to play an important role in cell differentiation and regulation, among which histone deacetylase (HDAC) is involved in suppressing genes by removing histone acetyl groups. The use of HDAC inhibitor to control this is increasing and has been widely studied by many researchers. This study aimed to induce differentiation by causing epigenetic changes in odontoblast-related genes and the MAPK signaling pathway in human dental pulp stem cells. Western blot and immunofluorescence staining showed increased expression of DMP-1, ALP, DSPP, and RUNX2 compared to the control. However, activation of the MAPK signaling system was similar to but slightly different from the expression of odontoblast-related proteins. After 3 days, as shown by MTT and LDH assays, proliferation decreased overall, but cytotoxicity decreased at only a specific concentration. We confirmed that there was no change in mRNA expression of caspase 3 or 9 using real-time PCR. In addition, flow cytometry analysis confirmed that differentiation occurred due to the decrease in the expression of the CD73 and CD146. Although overall proliferation was reduced due to the G2/M inhibition of the cell cycle, the expression of BCL-2 protected the cells from cell death. Overall, cell proliferation decreased in response to MS-275, but it did not induce cytotoxicity in 5 nM and 10 nM concentration and induces differentiation into odontoblast-like cells.

The application of histone deacetylases inhibitors in glioblastoma

The epigenetic abnormality is generally accepted as the key to cancer initiation. Epigenetics that ensure the somatic inheritance of differentiated state is defined as a crucial factor influencing malignant phenotype without altering genotype. Histone modification is one such alteration playing an essential role in tumor formation, progression, and resistance to treatment. Notably, changes in histone acetylation have been strongly linked to gene expression, cell cycle, and carcinogenesis. The balance of two types of enzyme, histone acetyltransferases (HATs) and histone deacetylases (HDACs), determines the stage of histone acetylation and then the architecture of chromatin. Changes in chromatin structure result in transcriptional dysregulation of genes that are involved in cell-cycle progression, differentiation, apoptosis, and so on. Recently, HDAC inhibitors (HDACis) are identified as novel agents to keep this balance, leading to numerous researches on it for more effective strategies against cancers, including glioblastoma (GBM). This review elaborated influences on gene expression and tumorigenesis by acetylation and the antitumor mechanism of HDACis. Besdes, we outlined the preclinical and clinical advancement of HDACis in GBM as monotherapies and combination therapies.

HDAC inhibitors overcome immunotherapy resistance in B-cell lymphoma

Immunotherapy has been applied successfully to treat B-cell lymphomas in preclinical models or clinical settings. However, immunotherapy resistance is a major challenge for B-cell lymphoma treatment. To overcome this issue, combinatorial therapeutic strategies have been pursued to achieve a better efficacy for treating B-cell lymphomas. One of such strategies is to combine immunotherapy with histone deacetylase (HDAC) inhibitors. HDAC inhibitors can potentially increase tumor immunogenicity, promote anti-tumor immune responses, or reverse immunosuppressive tumor environments. Thus, the combination of HDAC inhibitors and immunotherapy has drawn much attention in current cancer treatment. However, not all HDAC inhibitors are created equal and their net effects are highly dependent on the specific inhibitors used and the HDACs they target. Hence, we suggest that optimal treatment efficacy requires personalized design and rational combination based on prognostic biomarkers and unique profiles of HDAC inhibitors. Here, we discuss the possible mechanisms by which B-cell lymphomas acquire immunotherapy resistance and the effects of HDAC inhibitors on tumor cells and immune cells that could help overcome immunotherapy resistance.

The Histone Deacetylase Inhibitor Entinostat/Syndax 275 in Osteosarcoma

The prognosis for metastatic osteosarcoma (OS) is poor and has not changed in several decades. Therapeutic paradigms that target and exploit novel molecular pathways are desperately needed. Recent preclinical data suggests that modulation of the Fas/FasL pathway may offer benefit in the treatment of refractory osteosarcoma. Fas and FasL are complimentary receptor-ligand proteins. Fas is expressed in multiple tissues, whereas FasL is restricted to privilege organs, such as the lung. Fas expression has been shown to inversely correlate with the metastatic potential of OS cells; tumor cells which express high levels of Fas have decreased metastatic potential and the ones that reach the lung undergo cell death upon interaction with constitutive FasL in the lung. Agents such as gemcitabine and the HDAC inhibitor, entinostat/Syndax 275, have been shown to upregulate Fas expression on OS cells, potentially leading to decreased OS pulmonary metastasis and improved outcome. Clinical trials are in development to evaluate this combination as a potential treatment option for patients with refractory OS.

Histone Deacetylase Inhibitors in Tumor Immunotherapy

BACKGROUND

With an increasing understanding of the antitumor immune response, considerable progress has been made in the field of tumor immunotherapy in the last decade. Inhibition of histone deacetylases represents a new strategy in tumor therapy and histone deacetylase inhibitors have been recently developed and validated as potential antitumor drugs. In addition to the direct antitumor effects, histone deacetylase inhibitors have been found to have the ability to improve tumor recognition by immune cells that may contribute to their antitumor activity. These immunomodolutory effects are desirable, and their in-depth comprehension will facilitate the design of novel regimens with improved clinical efficacy.

OBJECTIVE

Our goal here is to review recent developments in the application of histone deacetylase inhibitors as immune modulators in cancer treatment.

METHODS

Systemic compilation of the relevant literature in this field.

RESULTS & CONCLUSION

In this review, we summarize recent advances in the understanding of how histone deacetylase inhibitors alter immune process and discuss their effects on various cytokines. We also discuss the challenges to optimize the use of these inhibitors as immune modulators in cancer treatment. Information gained from this review will be valuable to this field and may be helpful for designing tumor immunotherapy trials involving histone deacetylase inhibitors.

Entinostat combined with Fludarabine synergistically enhances the induction of apoptosis in TP53 mutated CLL cells via the HDAC1/HO-1 pathway

TP53 mutation is an indicator of poor prognostic in chronic lymphocytic leukemia (CLL). Worse still, CLL patients with TP53 mutation are associated with poor efficacy to current chemotherapeutic, such as Fludarabine. Here, we confirmed that high expression of HDAC1 in CLL patients with TP53 mutation, which is closely related to poor prognosis and drug-resistance. Subsequently, we demonstrated Entinostat (HDAC1 inhibitor) combination with Fludarabine significantly induced apoptosis in TP53 mutations CLL cells. Its mechanism was associated with up-regulation of the pro-apoptotic protein Bax and the down-regulation of HDAC1, HO-1 and BCL-2 proteins. More importantly, we also confirmed that upregulation of HDAC1 could resistant Entinostat-induced apoptosis in TP53 mutations CLL cells by activating the HDAC1/P38/HO-1 pathway. In vivo, we found that Entinostat combination with Fludarabine significantly induced tumor cells apoptosis and prolong survival time in xenograft mouse model. Finally, combining vitro and vivo experiments, we presented the first demonstration that Entinostat combination with Fludarabine had a synergistic effect on the induction of apoptosis in TP53 mutations CLL cells. In conclusion, we provide valuable pre-clinical experimental evidence for the treatment of CLL patients with poor prognosis, especially for TP53 mutations.

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

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

Epigenetic mechanisms of tumor resistance to immunotherapy

The recent impact of cancer immunotherapies has firmly established the ability and importance of the immune system to fight malignancies. However, the intimate interaction between the highly dynamic tumor and immune cells leads to a selection process driven by genetic and epigenetic processes. As the molecular pathways of cancer resistance mechanisms to immunotherapy become increasingly known, novel therapeutic targets are being tested in combination with immune-stimulating approaches. We here review recent insights into the molecular mechanisms of tumor resistance with particular emphasis on epigenetic processes and place these in the context of previous models.

Combination Effect of Silver Nanoparticles and Histone Deacetylases Inhibitor in Human Alveolar Basal Epithelial Cells

Although many treatment strategies have been reported for lung disease, the mechanism of combination therapy using silver nanoparticles (AgNPs) and histone deacetylases inhibitors (HDACi) remains unclear. Therefore, innovative treatment strategies are essential for addressing the therapeutic challenges of this highly aggressive lung cancer. AgNPs and HDACi seem to be the best candidates for anticancer therapy because of their anti-proliferative effect in a variety of cancer cells. First, we synthesized AgNPs using wogonin as a reducing and stabilizing agent, following which the synthesized AgNPs were characterized by various analytical techniques. The synthesized AgNPs exhibited dose- and size-dependent toxicity towards A549 cells. Interestingly, the combination of AgNPs and MS-275 significantly induces apoptosis, which was accompanied by an increased level of reactive oxygen species (ROS); leakage of lactate dehydrogenase (LDH); secretion of TNFα; dysfunction of mitochondria; accumulation autophagosomes; caspase 9/3 activation; up and down regulation of pro-apoptotic genes and anti-apoptotic genes, respectively; and eventually, induced DNA-fragmentation. Our findings suggest that AgNPs and MS-275 induce cell death in A549 lung cells via the mitochondrial-mediated intrinsic apoptotic pathway. Finally, our data show that the combination of AgNPs and MS-275 is a promising new approach for the treatment of lung cancer and our findings contribute to understanding the potential roles of AgNPs and MS-275 in pulmonary disease. However, further study is warranted to potentiate the use of this combination therapy in cancer therapy trials.

Cladribine in combination with entinostat synergistically elicits anti-proliferative/anti-survival effects on multiple myeloma cells

Cladribine (2CdA), a synthetic purine analog interfering with DNA synthesis, is a medication used to treat hairy cell leukemia (HCL) and B-cell chronic lymphocytic leukemia. Entinostat, a selective class I histone deacetylase (HDAC) inhibitor, shows antitumor activity in various human cancers, including hematological malignancies. The therapeutic potential of cladribine and entinostat against multiple myeloma (MM) remains unclear. Here we investigate the combinatorial effects of cladribine and entinostat within the range of their clinical achievable concentrations on MM cells. While either agent alone inhibited MM cell proliferation in a dose-dependent manner, their combinations synergistically induced anti-proliferative/anti-survival effects on all MM cell lines (RPMI8226, U266, and MM1.R) tested. Further studies showed that the combinations of cladribine and entinostat as compared to either agent alone more potently induced mitotic catastrophe in the MM cells, and resulted in a marked increase of the cells at G1 phase associated with decrease of Cyclin D1 and E2F-1 expression and upregulation of p21waf-1. Apoptotic ELISA and western blot analyses revealed that the combinations of cladribine and entinostat exerted a much more profound activity to induce apoptosis and DNA damage response, evidenced by enhanced phosphorylation of histone H2A.X and the DNA repair enzymes Chk1 and Chk2. Collectively, our data demonstrate that the combinations of cladribine and entinostat exhibit potent activity to induce anti-proliferative/anti-survival effects on MM cells via induction of cell cycle G1 arrest, apoptosis, and DNA damage response. Regimens consisting of cladribine and/or entinostat may offer a new treatment option for patients with MM.

ABBREVIATIONS

MM, multiple myeloma; HCL, hairy cell leukemia; HDAC, histone deacetylase; Ab, antibody; mAb, monoclonal Ab; FBS, fetal bovine serum; CI, combination index; PAGE, polyacrylamide gel electrophoresis; ELISA, enzyme-linked immunosorbent assay; PARP, poly(ADP-ribose) polymerase; MTS, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium,inner salt.

Proteomics Profiling of CLL Versus Healthy B-cells Identifies Putative Therapeutic Targets and a Subtype-independent Signature of Spliceosome Dysregulation

Chronic lymphocytic leukemia (CLL) is a heterogeneous B-cell cancer exhibiting a wide spectrum of disease courses and treatment responses. Molecular characterization of RNA and DNA from CLL cases has led to the identification of important driver mutations and disease subtypes, but the precise mechanisms of disease progression remain elusive. To further our understanding of CLL biology we performed isobaric labeling and mass spectrometry proteomics on 14 CLL samples, comparing them with B-cells from healthy donors (HDB). Of 8694 identified proteins, ∼6000 were relatively quantitated between all samples (q<0.01). A clear CLL signature, independent of subtype, of 544 significantly overexpressed proteins relative to HDB was identified, highlighting established hallmarks of CLL (e.g. CD5, BCL2, ROR1 and CD23 overexpression). Previously unrecognized surface markers demonstrated overexpression (e.g. CKAP4, PIGR, TMCC3 and CD75) and three of these (LAX1, CLEC17A and ATP2B4) were implicated in B-cell receptor signaling, which plays an important role in CLL pathogenesis. Several other proteins (e.g. Wee1, HMOX1/2, HDAC7 and INPP5F) were identified with significant overexpression that also represent potential targets. Western blotting confirmed overexpression of a selection of these proteins in an independent cohort. mRNA processing machinery were broadly upregulated across the CLL samples. Spliceosome components demonstrated consistent overexpression (p = 1.3 × 10-21) suggesting dysregulation in CLL, independent of SF3B1 mutations. This study highlights the potential of proteomics in the identification of putative CLL therapeutic targets and reveals a subtype-independent protein expression signature in CLL.

A novel heterogeneous network-based method for drug response prediction in cancer cell lines

An enduring challenge in personalized medicine lies in selecting a suitable drug for each individual patient. Here we concentrate on predicting drug responses based on a cohort of genomic, chemical structure, and target information. Therefore, a recently study such as GDSC has provided an unprecedented opportunity to infer the potential relationships between cell line and drug. While existing approach rely primarily on regression, classification or multiple kernel learning to predict drug responses. Synthetic approach indicates drug target and protein-protein interaction could have the potential to improve the prediction performance of drug response. In this study, we propose a novel heterogeneous network-based method, named as HNMDRP, to accurately predict cell line-drug associations through incorporating heterogeneity relationship among cell line, drug and target. Compared to previous study, HNMDRP can make good use of above heterogeneous information to predict drug responses. The validity of our method is verified not only by plotting the ROC curve, but also by predicting novel cell line-drug sensitive associations which have dependable literature evidences. This allows us possibly to suggest potential sensitive associations among cell lines and drugs. Matlab and R codes of HNMDRP can be found at following https://github.com/USTC-HIlab/HNMDRP.

Combinatorial effects of histone deacetylase inhibitors (HDACi), vorinostat and entinostat, and adaphostin are characterized by distinct redox alterations

PURPOSE

Amongst the epigenetically targeted therapies, targeting of the histone deacetylases (HDACs) has yielded numerous drugs for clinical use in hematological malignancies, but none as yet for acute lymphocytic leukemia (ALL). Single agent activity of HDAC inhibitors (HDACi) has been elusive in ALL, and has prompted study of combinatorial strategies. Because several HDACi raise levels of intracellular oxidative stress, we evaluated combinations of two structurally distinct HDACi with the redox active compound adaphostin in ALL.

METHODS

The HDACi vorinostat and entinostat were tested in combination with adaphostin in human ALL cell lines. DNA fragmentation, caspase activation, mitochondrial disruption and levels of  intracellular peroxides, superoxide and glutathione were measured in cells treated with the HDACi/adaphostin combinations. Antioxidant blockade of cell death induction and gene expression profiling of cells treated with vorinostat/adaphostin versus entinostat/adaphostin combinations were evaluated.

RESULTS

Both combinations synergistically induced apoptotic DNA fragmentation, which was preceded by an increase in superoxide levels, a reduction in mitochondrial membrane potential, and an increase in caspase-9 activation. The antioxidant N-acetylcysteine (NAC) blocked superoxide generation and prevented reduction of mitochondrial membrane potential. NAC decreased DNA fragmentation and caspase activity in cells treated with adaphostin and vorinostat, but not in those treated with adaphostin and entinostat. Gene expression arrays revealed differential regulation of several redox genes prior to cell death induction.

CONCLUSIONS

A redox modulatory agent, adaphostin, enhances efficacy of two HDACi, vorinostat or entinostat, but via different mechanisms indicating a point of divergence in the mechanisms of synergy between the two distinct HDACi and adaphostin.

Scriptaid improves the reprogramming of donor cells and enhances canine-porcine interspecies embryo development

Histone methylation, histone acetylation, and DNA methylation are the important factors for somatic cell nuclear transfer (SCNT). Histone deacetylase inhibitors (HDACi) and DNA methyltransferase inhibitors (DNMTi) have been used to improve cloning efficiency. In particular, scriptaid, an HDACi, has been shown to improve SCNT efficiency. However, no studies have been performed on canines. Here, we evaluated the effects of scriptaid on histone modification in canine ear fibroblasts (cEFs) and cloned canine embryos derived from cEFs. The early development of cloned canine-porcine interspecies SCNT (iSCNT) embryos was also examined. cEFs were treated with scriptaid (0, 100, 250, 500, 750, and 1000nM) in a medium for 24h. Scriptaid treatment (all concentrations) did not significantly affect cell apoptosis. Treatment with 500nM scriptaid caused a significant increase in the acetylation of H3K9, H3K14, and H4K5. cEFs treated with 500nM scriptaid showed significantly decreased Gcn5, Hat1, Hdac6, and Bcl2 and increased Oct4 and Sox2 expression levels. After SCNT with canine oocytes, H3K14 acetylation was significantly increased in the one- and two-cell cloned embryos from scriptaid-treated cEFs. In iSCNT, the percentage of embryos in the 16-cell stage was significantly higher in the scriptaid-treated group (21.6±2.44%) than in the control (7.5±2.09%). The expression levels of Oct4, Sox2, and Bcl2 were significantly increased in 16-cell iSCNT embryos, whereas that of Hdac6 was decreased. These results demonstrated that scriptaid affected the reprogramming of canine donor and cloned embryos, as well as early embryo development in canine-porcine iSCNT, by regulating reprogramming and apoptotic genes.

Functional characterization of NAD dependent de-acetylases SIRT1 and SIRT2 in B-Cell Chronic Lymphocytic Leukemia (CLL)

Sirtuins (SIRT) are nicotinamide adenine dinucleotide (NAD+) dependent deacetylases or ADP- ribosyl transferases (ARTs) that deacetylate lysine residues on various proteins regulating a variety of cellular and metabolic processes. These enzymes regulate metabolism, cell survival, differentiation and DNA repair. SIRT proteins play an important role in the survival and drug resistance of cancer cells. The purpose of the present study was to investigate the expression and role of SIRT in chronic lymphocytic leukemia (CLL). We analyzed the expression of SIRT1 and SIRT2 in CLL and normal B cells using the Oncomine database as well as by Western blotting of fresh CLL cells from patients and pro-lymphocytic leukemia (PLL) cell lines, JVM-3 and MEC-2. We showed that both primary CLL cells and JVM-3 and MEC-2 cell lines overexpress high levels of functional SIRT1 and SIRT2. SIRT inhibitors EX-527 and sirtinol impair cell growth, induce ROS production, loss of mitochondrial membrane potential and apoptosis in primary CLL cells and cell lines. Using shRNA knock down of SIRT1 and SIRT2 in JVM-3 and MEC-2 cell lines, we showed that expression of both proteins is crucial for the survival of these cells. Furthermore, studies in nutrient deprived conditions suggest a role of SIRT in metabolism in CLL. These results demonstrate that the inhibition of SIRT1 and SIRT2 activity may be a new therapeutic approach for CLL.

Molecular mechanisms of apoptosis and roles in cancer development and treatment

Programmed cell death (PCD) or apoptosis is a mechanism which is crucial for all multicellular organisms to control cell proliferation and maintain tissue homeostasis as well as eliminate harmful or unnecessary cells from an organism. Defects in the physiological mechanisms of apoptosis may contribute to different human diseases like cancer. Identification of the mechanisms of apoptosis and its effector proteins as well as the genes responsible for apoptosis has provided a new opportunity to discover and develop novel agents that can increase the sensitivity of cancer cells to undergo apoptosis or reset their apoptotic threshold. These novel targeted therapies include those targeting anti-apoptotic Bcl-2 family members, p53, the extrinsic pathway, FLICE-inhibitory protein (c-FLIP), inhibitor of apoptosis (IAP) proteins, and the caspases. In recent years a number of these novel agents have been assessed in preclinical and clinical trials. In this review, we introduce some of the key regulatory molecules that control the apoptotic pathways, extrinsic and intrinsic death receptors, discuss how defects in apoptotic pathways contribute to cancer, and list several agents being developed to target apoptosis.

Efficacy of Combined Histone Deacetylase and Checkpoint Kinase Inhibition in a Preclinical Model of Human Burkitt Lymphoma

Checkpoint kinase inhibition has been studied as a way of enhancing the effectiveness of DNA-damaging agents. More recently, histone deacetylase inhibitors have shown efficacy in several cancers, including non-Hodgkin lymphoma. To evaluate the effectiveness of this combination for the treatment of lymphoma, we examined the combination of AR42, a histone deacetylase inhibitor, and checkpoint kinase 2 (CHEK2) inhibitor II in vitro and in vivo. The combination resulted in up to 10-fold increase in potency in five Burkitt lymphoma cell lines when compared with either drug alone. Both drugs inhibited tumor progression in xenograft models, but the combination was more effective than either agent alone, resulting in regression of established tumors. No toxicity was observed. These results suggest that the combination of histone deacetylase inhibition and checkpoint kinase inhibition represent an effective and nontoxic treatment option that should be further explored in preclinical and clinical studies.

Bilberry extract (Antho 50) selectively induces redox-sensitive caspase 3-related apoptosis in chronic lymphocytic leukemia cells by targeting the Bcl-2/Bad pathway

Defect in apoptosis has been implicated as a major cause of resistance to chemotherapy observed in B cell chronic lymphocytic leukaemia (B CLL). This study evaluated the pro-apoptotic effect of an anthocyanin-rich dietary bilberry extract (Antho 50) on B CLL cells from 30 patients and on peripheral blood mononuclear cells (PBMCs) from healthy subjects, and determined the underlying mechanism. Antho 50 induced concentration- and time-dependent pro-apoptotic effects in B CLL cells but little or no effect in PBMCs. Among the main phenolic compounds of the bilberry extract, delphinidin-3-O-glucoside and delphinidin-3-O-rutinoside induced a pro-apoptotic effect. Antho 50-induced apoptosis is associated with activation of caspase 3, down-regulation of UHRF1, a rapid dephosphorylation of Akt and Bad, and down-regulation of Bcl-2. Antho 50 significantly induced PEG-catalase-sensitive formation of reactive oxygen species in B CLL cells. PEG-catalase prevented the Antho 50-induced induction of apoptosis and related signaling. The present findings indicate that Antho 50 exhibits strong pro-apoptotic activity through redox-sensitive caspase 3 activation-related mechanism in B CLL cells involving dysregulation of the Bad/Bcl-2 pathway. This activity of Antho 50 involves the glucoside and rutinoside derivatives of delphinidin. They further suggest that Antho 50 has chemotherapeutic potential by targeting selectively B CLL cells.

You eat what you are: autophagy inhibition as a therapeutic strategy in leukemia

A deeper understanding of the role of autophagy, literally 'self-eating', in normal and cancer cell biology has emerged over the last few years. Autophagy serves as a vehicle for cells to respond to various stressors including genomic, hypoxic and nutrient stress, and to oppose mechanisms of 'programmed' cell death. Here, we review not only mechanisms of cell death and cell survival but also the early successes in applying autophagy inhibition strategies in solid tumors using the only currently available clinical inhibitor, oral hydroxychloroquine. In acute leukemia, currently available chemotherapy drugs promote cell death and demonstrate clinical benefit, but relapse and subsequent chemotherapy resistance is common. Increasing preclinical data suggest that autophagy is active in leukemia as a means of promoting cell survival in response to chemotherapy. We propose coupling autophagy inhibition strategies with current cytotoxic chemotherapy and discuss synergistic combinations of available anti-leukemic therapies with autophagy inhibition. Furthermore, novel autophagy inhibitors are in development and promise to provide new therapeutic opportunities for patients with leukemia.

Targeting the histone orthography of cancer: drugs for writers, erasers and readers

Gene expression is dynamically controlled by epigenetics through post-translational modifications of histones, chromatin-associated proteins and DNA itself. All these elements are required for the maintenance of chromatin structure and cell identity in the context of a normal cellular phenotype. Disruption of epigenetic regulation is a common event in human cancer. Here, we review the key protein families that control epigenetic signalling through writing, erasing or reading specific post-translational modifications. By exploiting the leading role of epigenetics in tumour development and the reversibility of epigenetic modifications, promising novel epigenetic-based therapies are being developed. In this article, we highlight the emerging low MW inhibitors targeting each class of chromatin-associated protein, their current use in preclinical and clinical trials and the likelihood of their being approved in the near future.

The histone deacetylase inhibitor, MS-275 (entinostat), downregulates c-FLIP, sensitizes osteosarcoma cells to FasL, and induces the regression of osteosarcoma lung metastases

The purpose of this study was to determine the effects of the histone deacetylase inhibitor, MS-275, on the Fas signaling pathway and susceptibility of osteosarcoma (OS) to Fas ligand (FasL)-induced cell death. OS metastasizes almost exclusively to the lungs. We have shown that Fas expression in OS cells is inversely correlated with their metastatic potential. Fas(+) cells are rapidly eliminated when they enter the lungs via interaction with FasL, which is constitutively expressed in the lungs. Fas(-) OS cells escape this FasL-induced apoptosis and survive in the lung microenvironment. Moreover, upregulation of Fas in established OS lung metastases results in tumor regression. Therefore, agents that upregulate Fas expression or activate the Fas signaling pathway may have therapeutic potential. Treatment of Fas(-) metastatic OS cell lines with 2 µM MS-275 sensitized cells to FasL-induced cell death in vitro. We found that MS-275 did not alter the expression of Fas on the cell surface; rather it resulted in the downregulation of the anti-apoptotic protein, c-FLIP (cellular FLICE-inhibitory protein), by inhibiting c-FLIP mRNA. Downregulation of c- FLIP correlated with caspase activation and apoptosis induction. Treatment of nu/nu-mice with established OS lung metastases with oral MS-275 resulted in tumor regression, increased apoptosis and a significant inhibition of c-FLIP expression in tumors. Histopathological examination of mice showed no evidence of significant toxicity. Overall, these results suggest that the mechanism by which MS-275 sensitizes OS cells and lung metastases to FasL-induced cell death may be by a direct reduction in the expression of c-FLIP.

Effect of histone deacetylase inhibitor valproic acid treatment on donor cell growth characteristics, cell cycle arrest, apoptosis, and handmade cloned bovine embryo production efficiency

In this study, we tested the effects of valproic acid (VPA), a known histone deacetylase inhibitor (HDACi), on the growth characteristics, apoptosis, and cell cycle stages distribution of donor cells, as well as cloning efficiency, embryo development, and histone methylation. Our results showed that treatment of donor cells with VPA (2.5 mM, 5.0 mM, 7.5 mM, or 10 mM) for 24 h resulted in altered cell proliferation, extent of apoptosis and necrosis, and cell cycle stage distribution, whereas no changes in cell viability and chromosomal complements were observed. Measurement of relative gene expression using real-time PCR of a few developmentally important genes in treated donor cells showed decreased expression of HDAC1 and increased expression of BAX (p<0.05). No change in relative expression of HDAC2 and Bcl2 was noticed. Treatment of donor cells with VPA for 24 h before electrofusion significantly (p<0.05) increased the blastocyst formation rate of somatic cell nuclear transfer (SCNT) embryos compared to the control embryos. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive nuclei in SCNT blastocysts derived from VPA-treated donor cells were significantly decreased compared to the control blastocysts (p<0.05). Immunolocalization studies revealed that the levels of histone H3 at lysine 9 (H3K9me3) were lower in VPA-treated donor cells derived cloned blastocysts than nontreated cloned embryos, and was at the level of in vitro fertilization (IVF) counterparts, although no effects of treatments were found in donor cells. Our study demonstrates that the use of VPA in SCNT has been beneficial for efficient reprogramming of donor cells. Its effect on histone methylation in cloned embryos correlates with their developmental potential and may be a useful epigenetic marker to predict the efficiency of SCNT.

Synergistic apoptotic response between valproic acid and fludarabine in chronic lymphocytic leukaemia (CLL) cells involves the lysosomal protease cathepsin B

Fludarabine, a nucleoside analogue, is commonly used in combination with other agents for the treatment of chronic lymphocytic leukaemia (CLL). In previous studies, valproic acid (VPA), an inhibitor of histone deacetylases, combined with fludarabine to synergistically increase apoptotic cell death in CLL cells. In the present study, we found that the combination of fludarabine and VPA decreases the level of the anti-apoptotic proteins Mcl-1 and XIAP in primary CLL cells. Treatment with fludarabine alone, or in combination with VPA, led to the loss of lysosome integrity, and chemical inhibition of the lysosomal protease cathepsin B, using CA074-Me, was sufficient to reduce apoptosis. VPA treatment increased cathepsin B levels and activities in primary CLL cells, thereby priming CLL cells for lysosome-mediated cell death. Six previously treated patients with relapsed CLL were treated with VPA, followed by VPA/fludarabine combination. The combined therapy resulted in reduced lymphocyte count in five out of six and reduced lymph node sizes in four out of six patients. In vivo VPA treatment increased histone-3 acetylation and cathepsin B expression levels. Thus, the synergistic apoptotic response with VPA and fludarabine in CLL is mediated by cathepsin B activation leading to a decrease in the anti-apoptotic proteins.

Histone deacetylase inhibitors induce apoptosis in myeloid leukemia by suppressing autophagy

Histone deacetylase (HDAC)-inhibitors (HDACis) are well characterized anti-cancer agents with promising results in clinical trials. However, mechanistically little is known regarding their selectivity in killing malignant cells while sparing normal cells. Gene expression-based chemical genomics identified HDACis as being particularly potent against Down syndrome associated myeloid leukemia (DS-AMKL) blasts. Investigating the anti-leukemic function of HDACis revealed their transcriptional and posttranslational regulation of key autophagic proteins, including ATG7. This leads to suppression of autophagy, a lysosomal degradation process that can protect cells against damaged or unnecessary organelles and protein aggregates. DS-AMKL cells exhibit low baseline autophagy due to mTOR activation. Consequently, HDAC inhibition repressed autophagy below a critical threshold, which resulted in accumulation of mitochondria, production of reactive oxygen species, DNA-damage and apoptosis. Those HDACi-mediated effects could be reverted upon autophagy activation or aggravated upon further pharmacological or genetic inhibition. Our findings were further extended to other major acute myeloid leukemia subgroups with low basal level autophagy. The constitutive suppression of autophagy due to mTOR activation represents an inherent difference between cancer and normal cells. Thus, via autophagy suppression, HDACis deprive cells of an essential pro-survival mechanism, which translates into an attractive strategy to specifically target cancer cells.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

Trials with 'epigenetic' drugs: an update

Epigenetic inactivation of pivotal genes involved in correct cell growth is a hallmark of human pathologies, in particular cancer. These epigenetic mechanisms, including crosstalk between DNA methylation, histone modifications and non-coding RNAs, affect gene expression and are associated with disease progression. In contrast to genetic mutations, epigenetic changes are potentially reversible. Re-expression of genes epigenetically inactivated can result in the suppression of disease state or sensitization to specific therapies. Small molecules that reverse epigenetic inactivation, so-called epi-drugs, are now undergoing clinical trials. Accordingly, the Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for cancer treatment have approved some of these drugs. Here, we focus on the biological features of epigenetic molecules, analyzing the mechanism(s) of action and their current use in clinical practice.

P38 MAP kinase functions as a switch in MS-275-induced reactive oxygen species-dependent autophagy and apoptosis in human colon cancer cells

MS-275 is a synthetic benzamide derivative of the histone deacetylase inhibitor and is currently in phase I/II clinical trials. Many reports have shown that the anti-tumor activity of MS-275 in several types of cancer is mainly attributable to its capacity to induce the apoptotic death of tumor cells. It remains unclear if autophagy is involved in MS-275 treatment of cancer cells. Here, we first show that MS-275 induces human colon cancer cell HCT116 autophagy as well as apoptosis. Short-term treatment (24h) induced HCT116 cells to undergo autophagy with dependence on intracellular reactive oxygen species production and ERK activation. The activated reactive oxygen species/ERK signal promoted Atg7 protein expression, which triggered MS-275-induced cancer cell autophagy. However, after prolonged treatment with MS-275 (over 48h), autophagic cells turned apoptotic, which was also dependent on reactive oxygen species generation. Interestingly, we found that p38 MAP kinase played a vital role in the switch from autophagy to apoptosis in MS-275-induced human colon cancer cells. High expression of p38 induced cell autophagy, but low expression resulted in apoptosis. In addition, observations in vivo are strongly consistent with the in vitro results. Therefore, these findings extend our understanding of the action of MS-275 in inducing cancer cell death and suggest that it may be a promising clinical chemotherapeutic agent with multiple effects.

Dual targeting of the cyclin/Rb/E2F and mitochondrial pathways in mantle cell lymphoma with the translation inhibitor silvestrol

PURPOSE

During cell-cycle progression, D-cyclins activate cyclin-dependent kinases (CDKs) 4/6 to inactivate Rb, permitting E2F1-mediated S-phase gene transcription. This critical pathway is typically deregulated in cancer, and novel inhibitory strategies would be effective in a variety of tumors. The protein synthesis inhibitor silvestrol has potent activity in B-cell leukemias via the mitochondrial pathway of apoptosis, and also reduces cyclin D1 expression in breast cancer and lymphoma cell lines. We hypothesized that this dual activity of silvestrol would make it especially effective in malignancies driven by aberrant cyclin D1 expression.

EXPERIMENTAL DESIGN

Mantle cell lymphoma (MCL), characterized by elevated cyclin D1, was used as a model to test this approach. The cyclin D/Rb/E2F1 pathway was investigated in vitro using MCL cell lines and primary tumor cells. Silvestrol was also evaluated in vivo using an aggressive model of MCL.

RESULTS

Silvestrol showed low nanomolar potency both in MCL cell lines and primary MCL tumor cells. D-cyclins were depleted with just 10 nmol/L silvestrol at 16 hours, with subsequent reductions of phosphorylated Rb, E2F1 protein, and E2F1 target transcription. As showed in other leukemias, silvestrol caused Mcl-1 depletion followed by mitochondrial depolarization and caspase-dependent apoptosis, effects not related to inhibition of CDK4/6. Silvestrol significantly (P < 0.0001) prolonged survival in a MCL xenograft model without detectable toxicity.

CONCLUSIONS

These data indicate that silvestrol effectively targets the cyclin/CDK/Rb pathway, and additionally induces cytotoxicity via intrinsic apoptosis. This dual activity may be an effective therapeutic strategy in MCL and other malignancies.

Small-molecule chromatin-modifying agents: therapeutic applications

Suberoylanilide hydroxamic acid (vorinostat) was the first of the histone deacetylase inhibitors (HDACi) to be entered as therapy for the treatment of cutaneous T-cell lymphoma. Since then, a number of HDACi belonging to the short-chain fatty acid, hydroxamate, cyclic peptide or benzamide classes have been investigated in Phase II or III clinical trials (alone or in combination) for the treatment of many kinds of tumors. In addition, HDACi can be useful in antimalarial and antifungal therapies, and can reactivate HIV-1 expression in latent cellular reservoirs, thus suggesting that they could be used in combination with highly active antiretroviral therapy. Moreover, they have also proved their efficacy in neurodegenerative diseases, such as Huntington's disease, Parkinson's disease and Friedreich's ataxia. In particular, a new series of bis-anilides demonstrating a peculiar mechanism of action displayed highly beneficial effects against Huntington's disease and Friedreich's ataxia. In addition, a number of sirtuin inhibitors demonstrated antiproliferative effects in cell assays as well as in mouse tumor models, thus suggesting a role of such compounds in therapy against cancer. Furthermore, the SIRT2-selective AGK-2 has been reported to have protective effects against Parkinson's disease, and resveratrol and other sirtuin activators can be useful for the treatment of Alzheimer's disease.

Histone deacetylase in chronic lymphocytic leukemia

BACKGROUND

Elevated histone deacetylase (HDAC) isoenzyme levels have been described in patients with carcinomas and leukemias. HDAC inhibitors (HDACi) have shown promise in the treatment of carcinomas and are currently under intense research. To make better use of HDACi in treating chronic lymphocytic leukemia (CLL), HDAC isoenzyme levels were studied.

METHODS

Quantitative reverse transcriptase polymerase chain reaction for HDAC isoenzyme was measured in 32 patients with CLL and compared with 17 normal volunteer controls. ZAP-70, CD38 and CD44 were also assayed and correlated to HDAC isoenzyme levels.

RESULTS

The results showed: (1) HDAC isoenzyme levels in CLL were significantly increased in class I including HDAC1 and HDAC3, in class II including HADC6, HDAC7, HDAC9 and HDAC10, and in class III including SIRT1 and SIRT6; (2) higher expression of HDAC isoenzyme levels was found in ZAP-70+ compared to ZAP-70- patients, and CD44 expression levels were correlated with HDAC isoenzyme expression levels in the majority of HDAC classes.

CONCLUSIONS

These results suggest: (1) in CLL, elevated HDAC isoenzyme activity is not restricted to one class, and therefore, HDACi therapy may need to be directed to more than one specific class of HDAC; (2) higher HDAC expression activity may indicate a poor prognosis and more advanced disease stage (through indirect evidence), since higher values were found in patients with ZAP-70+ and higher CD44 expression levels.

Mechanisms of resistance to histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are a new class of anticancer agents. HDAC inhibitors induce acetylation of histones and nonhistone proteins which are involved in regulation of gene expression and in various cellular pathways including cell growth arrest, differentiation, DNA damage and repair, redox signaling, and apoptosis (Marks, 2010). The U.S. Food and Drug Administration has approved two HDAC inhibitors, vorinostat and romidepsin, for the treatment of cutaneous T-cell lymphoma (Duvic & Vu, 2007; Grant et al., 2010; Marks & Breslow, 2007). Over 20 chemically different HDAC inhibitors are in clinical trials for hematological malignancies and solid tumors. This review considers the mechanisms of resistance to HDAC inhibitors that have been identified which account for the selective effects of these agents in inducing cancer but not normal cell death. These mechanisms, such as functioning Chk1, high levels of thioredoxin, or the prosurvival BCL-2, may also contribute to resistance of cancer cells to HDAC inhibitors.

Bortezomib-induced sensitization of malignant human glioma cells to vorinostat-induced apoptosis depends on reactive oxygen species production, mitochondrial dysfunction, Noxa upregulation, Mcl-1 cleavage, and DNA damage

Glioblastomas are invasive tumors with poor prognosis despite current therapies. Histone deacetylase inhibitors (HDACIs) represent a class of agents that can modulate gene expression to reduce tumor growth, and we and others have noted some antiglioma activity from HDACIs, such as vorinostat, although insufficient to warrant use as monotherapy. We have recently demonstrated that proteasome inhibitors, such as bortezomib, dramatically sensitized highly resistant glioma cells to apoptosis induction, suggesting that proteasomal inhibition may be a promising combination strategy for glioma therapeutics. In this study, we examined whether bortezomib could enhance response to HDAC inhibition in glioma cells. Although primary cells from glioblastoma multiforme (GBM) patients and established glioma cell lines did not show significant induction of apoptosis with vorinostat treatment alone, the combination of vorinostat plus bortezomib significantly enhanced apoptosis. The enhanced efficacy was due to proapoptotic mitochondrial injury and increased generation of reactive oxygen species. Our results also revealed that combination of bortezomib with vorinostat enhanced apoptosis by increasing Mcl-1 cleavage, Noxa upregulation, Bak and Bax activation, and cytochrome c release. Further downregulation of Mcl-1 using shRNA enhanced cell killing by the bortezomib/vorinostat combination. Vorinostat induced a rapid and sustained phosphorylation of histone H2AX in primary GBM and T98G cells, and this effect was significantly enhanced by co-administration of bortezomib. Vorinostat/bortezomib combination also induced Rad51 downregulation, which plays an important role in the synergistic enhancement of DNA damage and apoptosis. The significantly enhanced antitumor activity that results from the combination of bortezomib and HDACIs offers promise as a novel treatment for glioma patients.

Salvage therapy for relapsed chronic lymphocytic leukemia

Chronic lymphocytic leukemia is a common hematologic malignancy with a highly variable clinical course. While the median age at diagnosis is 72 years of age and fewer than 10% of patients are diagnosed before the age of 60 years, the majority of patients who require therapy will ultimately relapse. Advances in upfront therapy and supportive care have dramatically improved initial responses compared with traditional akylator-based chemotherapy. However, comparable results are not generally observed in the salvage setting. Careful planning that takes into account the duration of the initial response, patient age and/or comorbidities, and cytogenetic and molecular profiles are critical for the successful management of patients with relapsed chronic lymphocytic leukemia.

The histone deacetylase inhibitor entinostat (SNDX-275) induces apoptosis in Hodgkin lymphoma cells and synergizes with Bcl-2 family inhibitors

OBJECTIVE

Based on promising in vitro and in vivo activity of several histone deacetylase inhibitors in Hodgkin lymphoma (HL), we investigated SNDX-275, an oral class 1 isoform-selective histone deacetylase inhibitors in HL-derived cell lines.

MATERIALS AND METHODS

Proliferation and cell death were examined by MTS assay, Annexin V/propidium iodide, and fluorescence-activated cell sorting analysis. Gene and protein expression were measured by reverse transcriptase polymerase chain reaction, Western blotting, and immunohistochemical analysis. A multiplex assay was used to determine cytokines and chemokines.

RESULTS

SNDX-275 induced cell death in a dose- and time-dependent manner with an IC(50) at the sub- and lower micromolar range at 72 hours. At the molecular level, SNDX-275 increased histone H3 acetylation, upregulated p21 expression, and activated the intrinsic apoptosis pathway by downregulating the X-linked inhibitor of apoptosis protein. SNDX-275 downregulated expression of antiapoptotic Bcl-2 and Bcl-xL proteins without altering Mcl-1 or Bax levels. Combination studies demonstrated that two Bcl-2 inhibitors (ABT-737 and obatoclax) significantly enhanced the effect of SNDX-275. SNDX-275 modulated the level of several cytokines and chemokines, including interleukin-12 p40-70, interferon-inducible protein-10, RANTES (regulated on activation, normal T expressed and secreted), interleukin-13, interleukin-4, and thymus and activation-regulated chemokine and variably induced the cancer/testis antigen expression of MAGE-A4 and survivin in HL cell lines.

CONCLUSIONS

SNDX-275 has antiproliferative activity in HL cell lines, involving several mechanisms: induction of apoptosis, regulation of cytokines and chemokines, and alteration of cancer/testis antigens. Clinical investigation of SNDX-275 alone or in combination with Bcl-2 inhibitors is warranted in patients with HL. Phase 2 studies with SNDX-275 in HL are ongoing, and future clinical studies should investigate combinations with SNDX-275.

Interpreting clinical assays for histone deacetylase inhibitors

As opposed to genetics, dealing with gene expressions by direct DNA sequence modifications, the term epigenetics applies to all the external influences that target the chromatin structure of cells with impact on gene expression unrelated to the sequence coding of DNA itself. In normal cells, epigenetics modulates gene expression through all development steps. When "imprinted" early by the environment, epigenetic changes influence the organism at an early stage and can be transmitted to the progeny. Together with DNA sequence alterations, DNA aberrant cytosine methylation and microRNA deregulation, epigenetic modifications participate in the malignant transformation of cells. Their reversible nature has led to the emergence of the promising field of epigenetic therapy. The efforts made to inhibit in particular the epigenetic enzyme family called histone deacetylases (HDACs) are described. HDAC inhibitors (HDACi) have been proposed as a viable clinical therapeutic approach for the treatment of leukemia and solid tumors, but also to a lesser degree for noncancerous diseases. Three epigenetic drugs are already arriving at the patient's bedside, and more than 100 clinical assays for HDACi are registered on the National Cancer Institute website. They explore the eventual additive benefits of combined therapies. In the context of the pleiotropic effects of HDAC isoforms, more specific HDACi and more informative screening tests are being developed for the benefit of the patients.