Histone deacetylase inhibitors are the potent inducer/enhancer of differentiation in acute myeloid leukemia: a new approach to anti-leukemia therapy

Chaetocin: A review of its anticancer potentials and mechanisms

Chaetocin is a natural metabolite product with various biological activities and pharmacological functions isolated from Chaetomium species fungi belonging to the thiodiketopyrazines. Numerous studies have demonstrated a wide range of antitumor activities of chaetocin in vitro and in vivo. Several studies have demonstrated that chaetocin suppresses the growth and proliferation of various tumour cells by regulating multiple signalling pathways related to tumour initiation and progression, inducing cancer cell apoptosis (intrinsic and extrinsic), enhancing autophagy, inducing cell cycle arrest, and inhibiting tumour angiogenesis, invasion, and migration. The antitumor effects and molecular mechanisms of chaetocin are reviewed and analysed in this paper, and the prospective applications of chaetocin in cancer prevention and therapy are also discussed. This review aimed to summarize the recent advances in the antitumor activity of chaetocin and to provide a rationale for further exploring the potential application of chaetocin in overcoming cancer in the future.

Current Understandings of Myeloid Differentiation Inducers in Leukemia Therapy

Differentiation therapy using all-trans retinoic acid for acute promyelocytic leukemia (APL) is well established. Several attempts have been made to treat non-APL, AML patients by employing differentiation inducers, such as hypomethylating agents (HMAs), and low-dose cytarabine (Ara-C) (LDAC), with encouraging results. Other than HMAs and LDAC, various inducers of myeloid cell differentiation have been identified. This review describes and categorizes these inducers, which include glycosylation modifiers, epigenetic modifiers, vitamin derivatives, cytokines, and chemotherapeutic agents. Some of these inducers are currently being used in clinical trials. I highlight the potential applications of glycosylation modifiers and epigenetic modifiers, which are attracting increasing attention in their use as differentiation therapy against AML. Among the agents described in this review, epigenomic modifiers seem particularly promising, and particular attention should also be paid to glycosylation modifiers. These drugs may signal a new era for AML differentiation therapy.

HDAC Inhibitors in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a hematological malignancy characterized by uncontrolled proliferation, differentiation arrest, and accumulation of immature myeloid progenitors. Although clinical advances in AML have been made, especially in young patients, long-term disease-free survival remains poor, making this disease an unmet therapeutic challenge. Epigenetic alterations and mutations in epigenetic regulators contribute to the pathogenesis of AML, supporting the rationale for the use of epigenetic drugs in patients with AML. While hypomethylating agents have already been approved in AML, the use of other epigenetic inhibitors, such as histone deacetylases (HDAC) inhibitors (HDACi), is under clinical development. HDACi such as Panobinostat, Vorinostat, and Tricostatin A have been shown to promote cell death, autophagy, apoptosis, or growth arrest in preclinical AML models, yet these inhibitors do not seem to be effective as monotherapies, but rather in combination with other drugs. In this review, we discuss the rationale for the use of different HDACi in patients with AML, the results of preclinical studies, and the results obtained in clinical trials. Although so far the results with HDACi in clinical trials in AML have been modest, there are some encouraging data from treatment with the HDACi Pracinostat in combination with DNA demethylating agents.

Ultimate Precision: Targeting Cancer but Not Normal Self-replication

Self-replication is the engine that drives all biologic evolution, including neoplastic evolution. A key oncotherapy challenge is to target this, the heart of malignancy, while sparing the normal self-replication mandatory for health and life. Self-replication can be demystified: it is activation of replication, the most ancient of cell programs, uncoupled from activation of lineage-differentiation, metazoan programs more recent in origin. The uncoupling can be physiologic, as in normal tissue stem cells, or pathologic, as in cancer. Neoplastic evolution selects to disengage replication from forward-differentiation where intrinsic replication rates are the highest, in committed progenitors that have division times measured in hours versus weeks for tissue stem cells, via partial loss of function in master transcription factors that activate terminal-differentiation programs (e.g., GATA4) or in the coactivators they use for this purpose (e.g., ARID1A). These loss-of-function mutations bias master transcription factor circuits, which normally regulate corepressor versus coactivator recruitment, toward corepressors (e.g., DNMT1) that repress rather than activate terminal-differentiation genes. Pharmacologic inhibition of the corepressors rebalances to coactivator function, activating lineage-differentiation genes that dominantly antagonize MYC (the master transcription factor coordinator of replication) to terminate malignant self-replication. Physiologic self-replication continues, because the master transcription factors in tissue stem cells activate stem cell, not terminal-differentiation, programs. Druggable corepressor proteins are thus the barriers between self-replicating cancer cells and the terminal-differentiation fates intended by their master transcription factor content. This final common pathway to oncogenic self-replication, being separate and distinct from the normal, offers the favorable therapeutic indices needed for clinical progress.

Epigenetic Modifiers in Myeloid Malignancies: The Role of Histone Deacetylase Inhibitors

Myeloid hematological malignancies are clonal bone marrow neoplasms, comprising of acute myeloid leukemia (AML), the myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML), the myeloproliferative neoplasms (MPN) and systemic mastocytosis (SM). The field of epigenetic regulation of normal and malignant hematopoiesis is rapidly growing. In recent years, heterozygous somatic mutations in genes encoding epigenetic regulators have been found in all subtypes of myeloid malignancies, supporting the rationale for treatment with epigenetic modifiers. Histone deacetylase inhibitors (HDACi) are epigenetic modifiers that, in vitro, have been shown to induce growth arrest, apoptotic or autophagic cell death, and terminal differentiation of myeloid tumor cells. These effects were observed both at the bulk tumor level and in the most immature CD34⁺38⁻ cell compartments containing the leukemic stem cells. Thus, there is a strong rationale supporting HDACi therapy in myeloid malignancies. However, despite initial promising results in phase I trials, HDACi in monotherapy as well as in combination with other drugs, have failed to improve responses or survival. This review provides an overview of the rationale for HDACi in myeloid malignancies, clinical results and speculations on why clinical trials have thus far not met the expectations, and how this may be improved in the future.

Recent studies on cellular and molecular mechanisms in Alzheimer’s disease: focus on epigenetic factors and histone deacetylase

Alzheimer’s disease (AD) is one of the most common neurodegenerative disorders mainly affecting elderly people. It is characterized by progressive loss of memory and cognitive function. More than 95% of AD cases are related to sporadic or late-onset AD (LOAD). The etiology of LOAD is still unclear. It has been reported that environmental factors and epigenetic alterations play a significant role in AD pathogenesis. Furthermore, recently, genome-wide association studies (GWAS) identified 10 novel risk genes:ABCA7,APOE,BIN1,CD2AP,CD33,CLU,CR1,MS4A6A,MS4A4E, andPICALM, which play an important role for LOAD. In this review, the therapeutic approaches of AD by epigenetic modifications have been discussed. Nowadays, HDAC inhibitors have clinically proven its activity for epigenetic modifications. Furthermore, we try to establish the relationship between HDAC inhibitors and above mentioned LOAD risk genes. Finally, we are hoping that this review may open new area of research for AD treatment.

Higher-Level Pathway Objectives of Epigenetic Therapy: A Solution to the p53 Problem in Cancer

Searches for effective yet nontoxic oncotherapies are searches for exploitable differences between cancer and normal cells. In its core of cell division, cancer resembles normal life, coordinated by the master transcription factor MYC. Outside of this core, apoptosis and differentiation programs, which dominantly antagonize MYC to terminate cell division, necessarily differ between cancer and normal cells, as apoptosis is suppressed by biallelic inactivation of the master regulator of apoptosis, p53, or its cofactor p16/CDKN2A in approximately 80% of cancers. These genetic alterations impact therapy: conventional oncotherapy applies stress upstream of p53 to upregulate it and causes apoptosis (cytotoxicity)-a toxic, futile intent when it is absent or nonfunctional. Differentiation, on the other hand, cannot be completely suppressed because it is a continuum along which all cells exist. Neoplastic evolution stalls advances along this continuum at its most proliferative points-in lineage-committed progenitors that have division times measured in hours compared with weeks for tissue stem cells. This differentiation arrest is by mutations/deletions in differentiation-driving transcription factors or their coactivators that shift balances of gene-regulating protein complexes toward corepressors that repress instead of activate hundreds of terminal differentiation genes. That is, malignant proliferation without differentiation, also referred to as cancer "stem" cell self-renewal, hinges on druggable corepressors. Inhibiting these corepressors (e.g., DNMT1) releases p53-independent terminal differentiation in cancer stem cells but preserves self-renewal of normal stem cells that express stem cell transcription factors. Thus, epigenetic-differentiation therapies exploit a fundamental distinction between cancer and normal stem cell self-renewal and have a pathway of action downstream of genetic defects in cancer, affording favorable therapeutic indices needed for clinical progress.

Bioinformatic identification of candidate genes induced by trichostatin A in BGC-823 gastric cancer cells

The aim of the present study was to identify the candidate genes induced by trichostatin A (TSA) in BGC-823 gastric cancer (GC) cells and to explore the possible inhibition mechanism of TSA in GC. Gene expression data were obtained through chip detection, and differentially expressed genes (DEGs) between GC cells treated with TSA and untreated GC cells (control group) were identified. Gene ontology analysis of the DEGs was performed using the database for annotation, visualization and integrated discovery. Then sub-pathway enrichment analysis was performed and a microRNA (miRNA) regulatory network was constructed. We selected 76 DEGs, among which 43 were downregulated genes and 33 were upregulated genes. By sub-pathway enrichment analysis of the DEGs, the propanoate metabolism pathway was selected as the sub-pathway. By constructing a miRNA regulatory network, we identified that DKK1 and KLF13 were the top hub nodes. The propanoate metabolism pathway and the genes DKK1 and KLF13 may play significant roles in the inhibition of GC induced by TSA. These genes may be potential therapeutic targets for GC. However, further experiments are still required to confirm our results.

Upregulation of CD54 and downregulation of HLA‑ABC contribute to the novel enhancement of the susceptibility of HL-60 cells to NK cell-mediated cytolysis induced by ATRA plus VPA

Enhancement of the susceptibility of HL-60 cells to NK cell-mediated cytolysis induced by all-trans-retinoic acid (ATRA) plus valproate (VPA) was evaluated. In addition to the synergistic effect of ATRA plus VPA on HL-60 cells, the optimal concentration of 1 mM VPA plus 0.5 µM ATRA increased the cytotoxic sensitivity of HL-60 cells to NK cells. The expression of the activated receptors NKp30 and NKG2D on NK-92 cells was higher compared with the levels noted for the other receptors, and the expression of NKG2D ligands MICA/B on HL-60 cells was not significantly upregulated in the ATRA plus VPA goup compared with the control. Moreover, it was observed that the ligands of NKp30 on HL-60 cells presented the same variation trend. As to the co-stimulatory and adhesion molecules on NK-92 and their ligands on HL-60 cells post exposure to ATRA and VPA alone or their combination, there was no obvious change in the expression of CD112, CD48 and CD70 on the HL-60 cells. However, the expression of CD54 on HL-60 cells was significantly upregulated. In contrast, the expression of NKG2A ligands HLA-ABC on HL-60 cells was obviously downregulated. In addition, the expression of HLA-E on the HL-60 cells in the group treated with ATRA plus VPA was not significantly increased. In conclusion, the combination of VPA and ATRA not only induced the differentiation of HL-60 cells, but also induced enhancement of the sensitivity of HL-60 cells to NK cells by downregulating the expression of HLA-ABC and upregulating the expression of CD54, but not MICA/MICB. The results provide experimental and theoretical basis for the clinical combination of a low-dose of ATRA plus VPA for the treatment of leukemia.

Integrated Drug Expression Analysis for leukemia: an integrated in silico and in vivo approach to drug discovery

Screening for drug compounds that exhibit therapeutic properties in the treatment of various diseases remains a challenge even after considerable advancements in biomedical research. Here, we introduce an integrated platform that exploits gene expression compendia generated from drug-treated cell lines and primary tumor tissue to identify therapeutic candidates that can be used in the treatment of acute myeloid leukemia (AML). Our framework combines these data with patient survival information to identify potential candidates that presumably have a significant impact on AML patient survival. We use a drug regulatory score (DRS) to measure the similarity between drug-induced cell line and patient tumor gene expression profiles, and show that these computed scores are highly correlated with in vitro metrics of pharmacological activity. Furthermore, we conducted several in vivo validation experiments of our potential candidate drugs in AML mouse models to demonstrate the accuracy of our in silico predictions.

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.

Runx1 regulation of Pu.1 corepressor/coactivator exchange identifies specific molecular targets for leukemia differentiation therapy

Gene activation requires cooperative assembly of multiprotein transcription factor-coregulator complexes. Disruption to cooperative assemblage could underlie repression of tumor suppressor genes in leukemia cells. Mechanisms of cooperation and its disruption were therefore examined for PU.1 and RUNX1, transcription factors that cooperate to activate hematopoietic differentiation genes. PU.1 is highly expressed in leukemia cells, whereas RUNX1 is frequently inactivated by mutation or translocation. Thus, coregulator interactions of Pu.1 were examined by immunoprecipitation coupled with tandem mass spectrometry/Western blot in wild-type and Runx1-deficient hematopoietic cells. In wild-type cells, the NuAT and Baf families of coactivators coimmunoprecipitated with Pu.1. Runx1 deficiency produced a striking switch to Pu.1 interaction with the Dnmt1, Sin3A, Nurd, CoRest, and B-Wich corepressor families. Corepressors of the Polycomb family, which are frequently inactivated by mutation or deletion in myeloid leukemia, did not interact with Pu.1. The most significant gene ontology association of Runx1-Pu.1 co-bound genes was with macrophages, therefore, functional consequences of altered corepressor/coactivator exchange were examined at Mcsfr, a key macrophage differentiation gene. In chromatin immunoprecipitation analyses, high level Pu.1 binding to the Mcsfr promoter was not decreased by Runx1 deficiency. However, the Pu.1-driven shift from histone repression to activation marks at this locus, and terminal macrophage differentiation, were substantially diminished. DNMT1 inhibition, but not Polycomb inhibition, in RUNX1-translocated leukemia cells induced terminal differentiation. Thus, RUNX1 and PU.1 cooperate to exchange corepressors for coactivators, and the specific corepressors recruited to PU.1 as a consequence of RUNX1 deficiency could be rational targets for leukemia differentiation therapy.

Prohibitin 2 represents a novel nuclear AKT substrate during all-trans retinoic acid-induced differentiation of acute promyelocytic leukemia cells

The AKT/PKB kinase is essential for cell survival, proliferation, and differentiation; however, aberrant AKT activation leads to the aggressiveness and drug resistance of many human neoplasias. In the human acute promyelocytic leukemia cell line NB4, nuclear AKT activity increases during all-trans retinoic acid (ATRA)-mediated differentiation. As nuclear AKT activity is associated with differentiation, we sought to identify the nuclear substrates of AKT that were phosphorylated after ATRA treatment. A proteomics-based search for nuclear substrates of AKT in ATRA-treated NB4 cells was undertaken by using 2D-electrophoresis/mass spectrometry (MS) in combination with an anti-AKT phospho-substrate antibody. Western blot analysis, an in vitro kinase assay, and/or site-directed mutagenesis were performed to further characterize the MS findings. MS analysis revealed prohibitin (PHB)-2, a multifunctional protein involved in cell cycle progression and the suppression of oxidative stress, to be a putative nuclear substrate of AKT. Follow-up studies confirmed that AKT phosphorylates PHB2 on Ser-91 and that forced expression of the PHB2(S91A) mutant results in a rapid loss of viability and apoptotic cell death. Activation of nuclear AKT during ATRA-mediated differentiation results in the phosphorylation of several proteins, including PHB2, which may serve to coordinate nuclear-mitochondrial events during differentiation.

Evaluation of the antitumor effects of BPR1J-340, a potent and selective FLT3 inhibitor, alone or in combination with an HDAC inhibitor, vorinostat, in AML cancer

Overexpression or/and activating mutation of FLT3 kinase play a major driving role in the pathogenesis of acute myeloid leukemia (AML). Hence, pharmacologic inhibitors of FLT3 are of therapeutic potential for AML treatment. In this study, BPR1J-340 was identified as a novel potent FLT3 inhibitor by biochemical kinase activity (IC₅₀ approximately 25 nM) and cellular proliferation (GC₅₀ approximately 5 nM) assays. BPR1J-340 inhibited the phosphorylation of FLT3 and STAT5 and triggered apoptosis in FLT3-ITD⁺ AML cells. The pharmacokinetic parameters of BPR1J-340 in rats were determined. BPR1J-340 also demonstrated pronounced tumor growth inhibition and regression in FLT3-ITD⁺ AML murine xenograft models. The combination treatment of the HDAC inhibitor vorinostat (SAHA) with BPR1J-340 synergistically induced apoptosis via Mcl-1 down-regulation in MOLM-13 AML cells, indicating that the combination of selective FLT3 kinase inhibitors and HDAC inhibitors could exhibit clinical benefit in AML therapy. Our results suggest that BPR1J-340 may be further developed in the preclinical and clinical studies as therapeutics in AML treatments.

Turning T cells on: epigenetically enhanced expression of effector T-cell costimulatory molecules on irradiated human tumor cells

BACKGROUND

Sub-lethal doses of radiation can alter the phenotype of target tissue by modulating gene expression and making tumor cells more susceptible to T-cell-mediated immune attack. We have previously shown that sub-lethal tumor cell irradiation enhances killing of colorectal carcinoma cells by tumor-specific cytotoxic T cells by unknown mechanisms. Recent data from our lab indicates that irradiation of tumor cells results in the upregulation of OX40L and 41BBL, and that T cells incubated with irradiated tumor cells displayed improved CTL survival, activation and effector activity. The objective of this current study was to determine the mechanism of enhanced OX40L and 41BBL expression in human colorectal tumor cells.

METHODS

Two colorectal carcinoma cell lines, HCT116 and SW620, were examined for changes in the expression of 41BBL and OX40L in response to inhibition of histone deacetylases (using TSA) and DNA methyltransferases (using 5-Aza-2'-deoxycytidine) to evaluate if epigenetic mechanisms of gene expression can modulate these genes. Tumor cells were treated with radiation, TSA, or 5-Aza-dC, and subsequently evaluated for changes in gene expression using RT-qPCR and flow cytometry. Moreover, we assessed levels of histone acetylation at the 41BBL promoter using chromatin immunoprecipitation assays in irradiated HCT116 cells.

RESULTS

Our data indicate that expression of 41BBL and OX40L can indeed be epigenetically regulated, as inhibition of histone deacetylases and of DNA methyltransferases results in increased OX40L and 41BBL mRNA and protein expression. Treatment of tumor cells with TSA enhanced the expression of these genes more than treatment with 5-Aza-dC, and co-incubation of T cells with TSA-treated tumor cells enhanced T-cell survival and activation, similar to radiation. Furthermore, chromatin immunoprecipitation experiments revealed significantly increased histone H3 acetylation of 41BBL promoters specifically following irradiation.

CONCLUSIONS

Full understanding of specific mechanisms of immunogenic modulation (altered expression of immune relevant genes) of irradiated tumor cells will be required to determine how to best utilize radiation as a tool to enhance cancer immunotherapy approaches. Overall, our results suggest that radiation can be used to make human tumors more immunogenic through epigenetic modulation of genes stimulatory to effector T-cells.

The evolving landscape in the therapy of acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal disorder of myeloid precursors arrested in their maturation, creating a diverse disease entity with a wide range of responses to historically standard treatment approaches. While significant progress has been made in characterizing and individualizing the disease at diagnosis to optimally inform those affected, progress in treatment to reduce relapse and induce remission has been limited thus far. In addition to a brief summary of the factors that shape prognostication at diagnosis, this review attempts to expand on the current therapies under investigation that have shown promise in treating AML, including hypomethylating agents, gemtuzumab ozogamicin, FLT3 tyrosine kinase inhibitors, antisense oligonucleotides, and other novel therapies, including aurora kinases, mTOR and PI3 kinase inhibitors, PIM kinase inhibitors, HDAC inhibitors, and IDH targeted therapies. With these, and undoubtedly many others in the future, it is the hope that by combining more accurate prognostication with more effective therapies, patients will begin to have a different, and more complete, outlook on their disease that allows for safer and more successful treatment strategies.

Improved therapeutic effect against leukemia by a combination of the histone methyltransferase inhibitor chaetocin and the histone deacetylase inhibitor trichostatin A

SUV39H1 is a histone 3 lysine 9 (H3K9)-specific methyltransferase that is important for heterochromatin formation and the regulation of gene expression. Chaetocin specifically inhibits SUV39H1, resulted in H3K9 methylation reduction as well as reactivation of silenced genes in cancer cells. Histone deacetylase (HDAC) inhibitors inhibit deacetylases and accumulate high levels of acetylation lead to cell cycle arrest and apoptosis. In this study, we demonstrated that treatment with chaetocin enhanced apoptosis in human leukemia HL60, KG1, Kasumi, K562, and THP1 cells. In addition, chaetocin induced the expression of cyclin-dependent kinase inhibitor 2B (p15), E-cadherin (CDH1) and frizzled family receptor 9 (FZD9) through depletion of SUV39H1 and reduced H3K9 methylation in their promoters. Co-treatment with chaetocin and HDAC inhibitor trichostatin A (TSA) dramatically increased apoptosis and produced greater activation of genes. Furthermore, this combined treatment significantly increased loss of SUV39H1 and reduced histone H3K9 trimethylation responses accompanied by increased acetylation. Importantly, co-treatment with chaetocin and TSA produced potent antileukemic effects in leukemia cells derived from patients. These in vitro findings suggest that combination therapy with SUV39H1 and HDAC inhibitors may be of potential value in the treatment of leukemia.

p53-Independent, normal stem cell sparing epigenetic differentiation therapy for myeloid and other malignancies

Cytotoxic chemotherapy for acute myeloid leukemia (AML) usually produces only temporary remissions, at the cost of significant toxicity and risk for death. One fundamental reason for treatment failure is that it is designed to activate apoptosis genes (eg, TP53) that may be unavailable because of mutation or deletion. Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors. Mutations in these transcription factors (eg, CEBPA) or their cofactors (eg., RUNX1) affect transactivation function and produce epigenetic repression of late-differentiation genes that antagonize MYC. Importantly, this aberrant epigenetic repression can be redressed clinically by depleting DNA methyltransferase 1 (DNMT1, a central component of the epigenetic network that mediates transcription repression) using the deoxycytidine analogue decitabine at non-cytotoxic concentrations. The DNMT1 depletion is sufficient to trigger upregulation of late-differentiation genes and irreversible cell cycle exit by p53-independent differentiation mechanisms. Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors. The biological rationale for this approach to therapy appears to apply to cancers other than MDS/AML also. Decitabine or 5-azacytidine dose and schedule can be rationalized to emphasize this mechanism of action, as an alternative or complement to conventional apoptosis-based oncotherapy.

Phase II study of the histone deacetylase inhibitor belinostat (PXD101) for the treatment of myelodysplastic syndrome (MDS)

The inhibition of histone deacetylase (HDAC) can induce differentiation, growth arrest, and apoptosis in cancer cells. This phase II multicenter study was undertaken to estimate the efficacy of belinostat, a potent inhibitor of both class I and class II HDAC enzymes, for the treatment of myelodysplastic syndrome (MDS). Adults with MDS and ≤2 prior therapies were treated with belinostat 1,000 mg/m(2) IV on days 1-5 of a 21-day cycle. The primary endpoint was a proportion of confirmed responses during the first 12 weeks of treatment. Responding patients could receive additional cycles until disease progression or unacceptable toxicity. Twenty-one patients were enrolled, and all were evaluable. Patients were a median 13.4 months from diagnosis, and 14 patients (67%) had less than 5% bone marrow blasts. Seventeen patients (81%) were transfusion dependent. Prior therapy included azacytidine (n = 7) and chemotherapy (n = 8). The patients were treated with a median of four cycles (range, 1-8) of belinostat. There was one confirmed response-hematologic improvement in neutrophils-for an overall response rate of 5% (95% CI, 0.2-23). Median overall survival was 17.9 months. Grades 3-4 toxicities considered at least to be possibly related to belinostat were: neutropenia (n = 10), thrombocytopenia (n = 9), anemia (n = 5), fatigue (n = 2), febrile neutropenia (n = 1), headache (n = 1), and QTc prolongation (n = 1). Because the study met the stopping rule in the first stage of enrollment, it was closed to further accrual.

CpG methylation patterns and decitabine treatment response in acute myeloid leukemia cells and normal hematopoietic precursors

The DNA hypomethylating drug decitabine maintains normal hematopoietic stem cell (HSC) self-renewal but induces terminal differentiation in acute myeloid leukemia (AML) cells. The basis for these contrasting cell-fates, and for selective CpG hypomethylation by decitabine, is poorly understood. Promoter CpGs, with methylation measured by microarray, were classified by the direction of methylation change with normal myeloid maturation. In AML cells, the methylation pattern at maturation-responsive CpG suggested at least partial maturation. Consistent with partial maturation, in gene expression analyses, AML cells expressed high levels of the key lineage-specifying factor CEBPA, but relatively low levels of the key late-differentiation driver CEBPE. In methylation analysis by mass-spectrometry, CEBPE promoter CpG that are usually hypomethylated during granulocyte maturation were significantly hypermethylated in AML cells. Decitabine treatment induced cellular differentiation of AML cells, and the largest methylation decreases were at CpG that are hypomethylated with myeloid maturation, including CEBPE promoter CpG. In contrast, decitabine-treated normal HSC retained immature morphology, and methylation significantly decreased at CpG that are less methylated in immature cells. High expression of lineage-specifying factor and aberrant epigenetic repression of some key late-differentiation genes distinguishes AML cells from normal HSC and could explain the contrasting differentiation and methylation responses to decitabine.

p53 independent epigenetic-differentiation treatment in xenotransplant models of acute myeloid leukemia

Suppression of apoptosis by TP53 mutation contributes to resistance of acute myeloid leukemia (AML) to conventional cytotoxic treatment. Using differentiation to induce irreversible cell cycle exit in AML cells could be a p53-independent treatment alternative, however, this possibility requires evaluation. In vitro and in vivo regimens of the deoxycytidine analogue decitabine that deplete the chromatin-modifying enzyme DNA methyl-transferase 1 without phosphorylating p53 or inducing early apoptosis were determined. These decitabine regimens but not equimolar DNA-damaging cytarabine upregulated the key late differentiation factors CCAAT enhancer-binding protein ɛ and p27/cyclin dependent kinase inhibitor 1B (CDKN1B), induced cellular differentiation and terminated AML cell cycle, even in cytarabine-resistant p53- and p16/CDKN2A-null AML cells. Leukemia initiation by xenotransplanted AML cells was abrogated but normal hematopoietic stem cell engraftment was preserved. In vivo, the low toxicity allowed frequent drug administration to increase exposure, an important consideration for S phase specific decitabine therapy. In xenotransplant models of p53-null and relapsed/refractory AML, the non-cytotoxic regimen significantly extended survival compared with conventional cytotoxic cytarabine. Modifying in vivo dose and schedule to emphasize this pathway of decitabine action can bypass a mechanism of resistance to standard therapy.

RUNX1 regulates corepressor interactions of PU.1

The transcription factor (TF) RUNX1 cooperates with lineage-specifying TFs (eg, PU.1/SPI1) to activate myeloid differentiation genes, such as macrophage and granulocyte macrophage colony-stimulating factor receptors (MCSFR and GMCSFR). Disruption of cooperative gene activation could contribute to aberrant repression of differentiation genes and leukemogenesis initiated by mutations and translocations of RUNX1. To investigate the mechanisms underlying cooperative gene activation, the effects of Runx1 deficiency were examined in an in vitro model of Pu.1-driven macrophage differentiation and in primary cells. Runx1 deficiency decreased Pu.1-mediated activation of Mcsfr and Gmcsfr, accompanied by decreased histone acetylation at the Mcsfr and Gmcsfr promoters, and increased endogenous corepressor (Eto2, Sin3A, and Hdac2) coimmunoprecipitation with Pu.1. In cotransfection experiments, corepressors were excluded from a multiprotein complex containing full-length RUNX1 and PU.1. However, corepressors interacted with PU.1 if wild-type RUNX1 was replaced with truncated variants associated with leukemia. Histone deacetylase (HDAC) enzyme activity is a major component of corepressor function. HDAC inhibition using suberoylanilide hydroxamic acid or MS-275 significantly increased MCSFR and GMCSFR expression in leukemia cell lines that express PU.1 and mutated or translocated RUNX1. RUNX1 deficiency is associated with persistent corepressor interaction with PU.1. Thus, inhibiting HDAC can partly compensate for the functional consequences of RUNX1 deficiency.

Increased HDAC1 deposition at hematopoietic promoters in AML and its association with patient survival

Epigenetic changes play a crucial role in leukemogenesis. HDACs are frequently recruited to target gene promoters by balanced translocation derived oncogenic fusion proteins. As important epigenetic effector mechanisms, histone deacetylases (HDAC) have emerged as potential therapeutic targets. However, the patterns of HDAC1 localization and the role of HDACs in leukemia pathogenesis remain to be elucidated. Using ChIP-Chip analyses we analyzed HDAC1 deposition patterns at more than 10,000 gene promoters in a large cohort of leukemia patients and CD34+ controls. HDAC1 binding was significantly increased in AML blasts compared to CD34+ progenitor cells at 130 gene promoters whereas decreased binding was observed at 66 gene promoters. Distinct HDAC1 binding patterns occurred in AML subtypes with balanced translocations t(15;17), t(8;21) and inv(16). In addition, a more generalized signature was established, that revealed an AML specific pattern of HDAC1 distribution. Many of the HDAC1-binding altered promoters regulate genes involved in hematopoiesis, transcriptional regulation and signal transduction. HDAC1 binding patterns were associated with patients' event free survival. This is the first study to determine HDAC1 modification patterns in a large number of AML and ALL specimens. Our findings suggest that dyslocalization of HDAC1 is a common feature in AML. Importantly, HDAC1 modifications possess prognostic power for patient survival. Our findings suggest that altered HDAC1 localization is an explanation for the observed benefit of HDAC inhibitors in AML therapy.

C/EBPα and PU.1 are involved in distinct differentiation responses of acute promyelocytic leukemia HL-60 and NB4 cells via chromatin remodeling

C/EBPα and PU.1 are the basic transcription factors that control differentiation-related genes, including granulocyte- colony-stimulating factor (G-CSFR) and human neutrophil elastase (HNE). Here, we analyzed a role of C/EBPα and PU.1 in human acute leukemia cell lines, HL-60 and NB4, in association with a modified chromatin structure by histone deacetylase inhibitors, FK228, sodium phenyl butyrate and vitamin B3. We found that sodium phenyl butyrate alone and 6h-pretreatment with phenyl butyrate or FK228 before the induction of differentiation with all-trans-retinoic acid in the presence of vitamin B3 effectively accelerated and enhanced differentiation to granulocytes in HL-60 but not in NB4 cells as detected by NBT test and the expression of CD11b and CD114 (G-CSFR) using flow cytometric analysis. HDACIs induced a time- and dose-dependent accumulation of hyper-acetylated histone H4 in both cell lines with the delay in NB4 cells. Time-dependent different induction of HL-60 and NB4 cell differentiation was paralleled by the activation of C/EBPα and PU.1 binding to the G-CSFR and the HNE promoters in electrophoretic mobility shift assay. Chromatin immunoprecipitation analysis revealed histone H4 acetylation in the G-CSF receptor promoter at the C/EBPα binding site in HL-60 but not in NB4 cells under the combined treatment. The results indicate that epigenetic events, such as histone acetylation, are involved in the activity modulation of the key transcription factors responsible for the induction of granulocytic differentiation in promyelocytic leukemia cells.

Decitabine maintains hematopoietic precursor self-renewal by preventing repression of stem cell genes by a differentiation-inducing stimulus

The cytosine analogue decitabine alters hematopoietic differentiation. For example, decitabine treatment increases self-renewal of normal hematopoietic stem cells. The mechanisms underlying decitabine-induced shifts in differentiation are poorly understood, but likely relate to the ability of decitabine to deplete the chromatin-modifying enzyme DNA methyltransferase 1 (DNMT1), which plays a central role in transcription repression. HOXB4 is a transcription factor that promotes hematopoietic stem cell self-renewal. In hematopoietic precursors induced to differentiate by the lineage-specifying transcription factor Pu.1 or by the cytokine granulocyte-colony stimulating factor, there is rapid repression of HOXB4 and other stem cell genes. Depletion of DNMT1 using shRNA or decitabine prevents HOXB4 repression by Pu.1 or granulocyte-colony stimulating factor and maintains hematopoietic precursor self-renewal. In contrast, depletion of DNMT1 by decitabine 6 hours after the differentiation stimulus, that is, after repression of HOXB4 has occurred, augments differentiation. Therefore, DNMT1 is required for the early repression of stem cell genes, which occurs in response to a differentiation stimulus, providing a mechanistic explanation for the observation that decitabine can maintain or increase hematopoietic stem cell self-renewal in the presence of a differentiation stimulus. Using decitabine to deplete DNMT1 after this early repression phase does not impair progressive differentiation.

SelSA, selenium analogs of SAHA as potent histone deacetylase inhibitors

Cancer treatment and therapy has moved from conventional chemotherapeutics to more mechanism-based targeted approach. Disturbances in the balance of histone acetyltransferase (HAT) and deacetylase (HDAC) leads to a change in cell morphology, cell cycle, differentiation, and carcinogenesis. In particular, HDAC plays an important role in carcinogenesis and therefore it has been a target for cancer therapy. Structurally diverse group of HDAC inhibitors are known. The broadest class of HDAC inhibitor belongs to hydroxamic acid derivatives that have been shown to inhibit both class I and II HDACs. Suberoylanilide hydroxamic acid (SAHA) and Trichostatin A (TSA), which chelate the zinc ions, fall into this group. In particular, SAHA, second generation HDAC inhibitor, is in several cancer clinical trials including solid tumors and hematological malignancy, advanced refractory leukemia, metastatic head and neck cancers, and advanced cancers. To our knowledge, selenium-containing HDAC inhibitors are not reported in the literature. In order to find novel HDAC inhibitors, two selenium based-compounds modeled after SAHA were synthesized. We have compared two selenium-containing compounds; namely, SelSA-1 and SelSA-2 for their inhibitory HDAC activities against SAHA. Both, SelSA-1 and SelSA-2 were potent HDAC inhibitors; SelSA-2 having IC50 values of 8.9 nM whereas SAHA showed HDAC IC(50) values of 196 nM. These results provided novel selenium-containing potent HDAC inhibitors.

2-(1-Hydroxethyl)-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-4,8-dione (BTP-11) enhances the ATRA-induced differentiation in human leukemia HL-60 cells

2-(1-Hydroxethyl)-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-4,8-dione (BTP-11) is a potent enhancer for all-trans retinoic acid (ATRA)-induced differentiation in HL-60 cells. Combination of BTP-11 and ATRA cut down the concentration of ATRA significantly, and that BTP-11 promoted the progression of ATRA-induced into the terminal granulocytic differentiation. Further, Western blot analysis revealed that combination of BTP-11 and ATRA decreased cyclin D/CDK4 and increased C/EBPvarepsilon protein expression to arrest the cells into G0/G1 phase leading to granulocytic maturation. These results confirmed that BTP-11 is a potent enhancer for ATRA-induced differentiation of HL-60 cells, and the great developmental potential of BTP-11 will be expected.

Novel inhibitor of Plasmodium histone deacetylase that cures P. berghei-infected mice

Histone deacetylases (HDAC) are potential targets for the development of new antimalarial drugs. The growth of Plasmodium falciparum and other apicomplexans can be suppressed in the presence of potent HDAC inhibitors in vitro and in vivo; however, in vivo parasite suppression is generally incomplete or reversible after the discontinuation of drug treatment. Furthermore, most established HDAC inhibitors concurrently show broad toxicities against parasites and human cells and high drug concentrations are required for effective antimalarial activity. Here, we report on HDAC inhibitors that are potent against P. falciparum at subnanomolar concentrations and that have high selectivities; the lead compounds have mean 50% inhibitory concentrations for the killing of the malaria parasite up to 950 times lower than those for the killing of mammalian cells. These potential drugs improved survival and completely and irreversibly suppressed parasitemia in P. berghei-infected mice.

Drug delivery in acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia was among the first malignancies to be cured by drug therapy alone, but overall survival rates remain unsatisfactory and have changed little over the past 20 years. Conventional chemotherapeutic regimens, which almost invariably include cytarabine and anthracyclines, are untargeted, and more specific therapies are needed.

OBJECTIVE

We have chosen acute myeloid leukemia as a disease prototype to review established and novel targeted approaches in leukemia treatment.

METHODS

Our selection of the reviewed literature focused on drug delivery aspects.

CONCLUSION

While the toxicity profile of chemotherapeutics has been improved by liposomal formulations and antibody conjugation for leukemia-directed uptake, their efficacy has probably not changed significantly. Drugs with an alternative mode of action, including kinase inhibitors, hold great promise. Further improvements may result from the characterization of novel acute myeloid leukemia (AML) cell surface receptors and of leukemic stem cells, as well as from the design of leukemia-targeted gene therapy vectors.

Induction of neural stem cell-like cells (NSCLCs) from mouse astrocytes by Bmi1

Recently, Bmi1 was shown to control the proliferation and self-renewal of neural stem cells (NSCs). In this study, we demonstrated the induction of NSC-like cells (NSCLCs) from mouse astrocytes by Bmi1 under NSC culture conditions. These NSCLCs exhibited the morphology and growth properties of NSCs, and expressed NSC marker genes, including nestin, CD133, and Sox2. In vitro differentiation of NSCLCs resulted in differentiated cell populations containing astrocytes, neurons, and oligodendrocytes. Following treatment with histone deacetylase inhibitors (trichostatin A and valproic acid), the potential of NSCLCs for proliferation, dedifferentiation, and self-renewal was significantly inhibited. Our data indicate that multipotent NSCLCs can be generated directly from astrocytes by the addition of Bmi1.

Histone hyperacetylation occurs on promoters of lytic cycle regulatory genes in Epstein-Barr virus-infected cell lines which are refractory to disruption of latency by histone deacetylase inhibitors

Activation of the Epstein-Barr virus (EBV) lytic cycle is mediated through the combined actions of ZEBRA and Rta, the products of the viral BZLF1 and BRLF1 genes. During latency, these two genes are tightly repressed. Histone deacetylase inhibitors (HDACi) can activate viral lytic gene expression. Therefore, a widely held hypothesis is that Zp and Rp, the promoters for BZLF1 and BRLF1, are repressed by chromatin and that hyperacetylation of histone tails, by allowing the access of positively acting factors, leads to transcription of BZLF1 and BRLF1. To investigate this hypothesis, we used chromatin immunoprecipitation (ChIP) to examine the acetylation and phosphorylation states of histones H3 and H4 on Zp and Rp in three cell lines, Raji, B95-8, and HH514-16, which differ in their response to EBV lytic induction by HDACi. We studied the effects of three HDACi, sodium butyrate (NaB), trichostatin A (TSA), and valproic acid (VPA). We also examined the effects of tetradecanoyl phorbol acetate (TPA) and 5-aza-2'-deoxycytidine, a DNA methyltransferase inhibitor, on histone modification. In Raji cells, TPA and NaB act synergistically to activate the EBV lytic cycle and promote an increase in histone H3 and H4 acetylation and phosphorylation at Zp and Rp. Surprisingly, however, when Raji cells were treated with NaB or TSA, neither of which is sufficient to activate the lytic cycle, an increase of comparable magnitude of hyperacetylated and phosphorylated histone H3 at Zp and Rp was observed. In B95-8 cells, NaB inhibited lytic induction by TPA, yet NaB promoted hyperacetylation of H3 and H4. In HH514-16 cells, NaB and TSA strongly activated the EBV lytic cycle and caused hyperacetylation of histone H3 on Zp and Rp. However, when HH514-16 cells were treated with VPA, lytic cycle mRNAs or proteins were not induced, although histone H3 was hyperacetylated as measured by immunoblotting or by ChIP on Zp and Rp. Taken together, our data suggest that open chromatin at EBV BZLF1 and BRLF1 promoters is not sufficient to activate EBV lytic cycle gene expression.

Predictors of response to reinduction chemotherapy for patients with acute myeloid leukemia who do not achieve complete remission with frontline induction chemotherapy

Eighty-one patients with acute myeloid leukemia who had persistent leukemia following standard induction therapy with cytarabine plus daunorubicin (7+3 regimen) underwent reinduction therapy with a combination of mitoxantrone, etoposide, and high-dose cytarabine (HiDAC). Patients achieving complete remission (CR) then received consolidation therapy with HiDAC plus mitoxantrone. Patients with matched sibling donors were referred for allogeneic bone marrow transplantation (BMT) in CR-1. The overall response rate to reinduction was 53%. The major adverse predictors of CR on multivariate analysis were poor risk cytogenetics, a higher % bone marrow blasts prior to reinduction therapy and increased age. The median relapse-free survival (RFS) was 9 months and the estimated 2-year RFS was 30%. No significant predictors of RFS or overall survival (OS) were found among the patients achieving CR. Patients undergoing allogeneic BMT in CR-1 after double induction had a 50% 2-year OS. Patients relapsing after achieving CR with double induction had a poor outcome with a 4% 1-year OS. The results indicate that patients with poor risk cytogenetics or marrow blast percentage >or= 60% following 7+3 induction have a low probability of achieving CR with reinduction and should be considered for novel approaches to improve CR rates. Patients achieving CR are at high risk of relapse and should be considered for allogeneic BMT or novel strategies to attempt to reduce relapse rates.

Histone deacetylases: target enzymes for cancer therapy

Epigenic regulation of gene transcription has recently been the subject of a fast growing interest particularly in the field of cancer. Enzymatic acetylation and deacetylation of the epsilon-amino groups of lysine residues from nucleosomal histones, represents major molecular epigenic mechanisms controlling gene expression. Histone deacetylases (HDACs) and histone acetyl transferases (HAT) represent the two families of enzymes in charge of the control of the level of acetylation of the histone tails. By removing the acetyl groups that abrogate the positive charge of the lysine residues that maintain the histone tails attached to DNA, HDACs repress transcription. In mammals, these latter enzymes form three groups of related enzymes based on their sequence homology and are classified as HDACs I, II and III. Global inhibition of the HDACs I and II groups results in cell growth arrest and apoptosis of cancer cells and alters tumor growth in in vivo experimental models. Their surprisingly low general toxicity and their impressive efficiency in preclinical cancer models has led to consider HDAC inhibitors as very promising new anticancer pharmacological agents. In this review, we attempt to give a comprehensive overview of the role and the involvement of HDAC in carcinogenesis as well as the current progress on the development of HDAC general and specific inhibitors as new cancer therapies.

Zebularine inhibits human acute myeloid leukemia cell growth in vitro in association with p15INK4B demethylation and reexpression

OBJECTIVE

The p15INK4B tumor suppressor is frequently silenced by promoter hypermethylation in myelodysplastic syndrome and acute myeloid leukemia (AML). Clinically approved DNA methylation inhibitors, such as 5-aza-2'-deoxycytidine, can reverse p15INK4B promoter methylation, but widespread clinical use of these inhibitors is limited by their toxicity and instability in aqueous solution. The cytidine analog zebularine is a stable DNA methylation inhibitor that has minimal toxicity in vitro and in vivo. We evaluated zebularine effects on p15INK4B reactivation and cell growth in vitro to investigate a potential role for zebularine in treating myeloid malignancies.

METHODS

We examined the specific effects of zebularine on reexpression of transcriptionally silenced p15INK4B and its global effects on cell cycle and apoptosis in AML cell lines and primary patient samples.

RESULTS

Zebularine treatment of AML193, which has a densely methylated p15INK4B promoter, results in a dose-dependent increase in p15INK4B expression that correlates with CpG island promoter demethylation and enrichment of local histone acetylation. We observed enhanced p15INK4B induction following co-treatment with zebularine and the histone deacetylase inhibitor Trichostatin A. Zebularine inhibits cell proliferation, arrests cells at G(2)/M, and induces apoptosis at dosages that effectively demethylate the p15INK4B promoter. Zebularine treatment of KG-1 cells and AML patient blasts with hypermethylated p15INK4B promoters also reactivates p15INK4B reexpression and induces apoptosis.

CONCLUSION

Zebularine is an effective inhibitor of p15INK4B methylation and cell growth in human AML in vitro. Our results extend the spectrum of zebularine effects to nonepithelial malignancies and provide a strong rationale for evaluating its clinical utility in the treatment of myeloid malignancies.

Mechanisms of HDAC inhibitor-induced thrombocytopenia

Histone deacetylase inhibitors (HDAC inhibitors) are an emerging class of anticancer agents. To elucidate the mechanism of HDAC inhibitor-induced thrombocytopenia, we focused on the effects of HDAC inhibitors on megakaryocyte differentiation and performed Affymetrix GeneChip analysis of human megakaryocytic HEL cells treated with or without HDAC inhibitors. Here, we report that GATA-1 and 10 haematopoietic factors (SCL, NF-E2, EKLF, Pleckstrin, Thrombin-R, LMO2, PU.1, Fli-1, AML1, and TCF11) are transcriptionally repressed by HDAC inhibitors in a similar pattern (R>0.98), and putative GATA-1-binding sites are found in almost all promoters of these genes. In addition, luciferase reporter assays reveal that mutations of GATA-1-binding sites in the GATA-1 promoter abolish its sensitivity to HDAC inhibitor-mediated down-regulation in HEL cells. Further, this report also asserts that HDAC inhibitor increases megakaryocyte counts and inhibits GATA-1 gene expression in rat spleen. Together, these results suggest that HDAC inhibitors inhibit GATA-1 gene expression by decreasing the transactivation function of GATA-1 itself, and that this may in turn lead to a delay in megakaryocyte maturation and finally cause thrombocytopenia. Our findings may help our understanding of the molecular mechanism of HDAC inhibitor-mediated GATA-1 transcriptional repression and to reduce the risk of HDAC inhibitor-induced thrombocytopenia.

Novel targeted therapies for non-small cell lung cancer

Targeted therapies will advance the treatment of NSCLC as we improve our understanding of the underlying biology of NSCLC and enhance our ability to clinically target the optimal therapy to an individual's cancer. Ongoing translational research including tissue arrays, genomic, and proteomic studies will help to identify clinically useful biomarkers that will allow further classification of NSCLC and may allow accurate prediction of response to specific chemotherapeutic regimens. Advances in targeted therapy in NSCLC are already yielding exciting results, and promises to become an increasingly important adjunct to surgical management of NSCLC.

The design of selective and non-selective combination therapy for acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is an unique subtype of acute myeloid leukemia typically carrying a specific reciprocal chromosome translocation, t(15;17), leading to the expression of a leukemia-generating fusion protein, PML-RARalpha. APL patients are responsive to APL-selective reagents such as all-trans retinoic acid (ATRA) or arsenic trioxide and non-selective cytotoxic chemotherapy. Nearly all de novo APL patients undergo clinical remission when treated with ATRA plus chemotherapy or with the combinational selective therapy, ATRA plus As2O3. Combining ATRA with As2O3 as an induction followed by chemotherapy consolidation results in more profound clinical remissions compared to treatment with any agent alone or any of the other possible combinations. The mechanism of action of each of these agents differs. ATRA induces APL cell differentiation and PML-RARalpha proteolysis. As2O3 induces APL cell partial differentiation, PML-RARalpha proteolysis, and apoptosis. Chemotherapy, mainly using anthracyclines, induces APL cell death. The combined effects of selective APL therapy (ATRA and As2O3) and/or non-selective chemotherapy in APL cells in vitro and their mechanisms in relation to clinical protocol design are discussed.

Leukemia-targeting ligands isolated from phage-display peptide libraries

Ligands specifically binding to leukemia cells may be used for drug targeting, resulting in more effective treatment with less side effects. Little is known about receptors specifically expressed on acute myeloid leukemia (AML) cells or ligands thereof. We selected random phage display peptide libraries on Kasumi-1 AML cells. A peptide with the sequence CPLDIDFYC was enriched. Phage displaying this peptide strongly bound to Kasumi-1 and SKNO-1 cells and binding could be inhibited by the cognate peptide. Both, Kasumi-1 and SKNO-1 cells carry the chromosomal translocation t(8;21), leading to aberrant expression of the fusion protein AML1/ETO. CPLDIDFYC also strongly and specifically bound primary AML1/ETO-positive AML blasts as well as U-937 cells with forced AML1/ETO expression, suggesting that the CPLDIDFYC receptor may be upregulated upon AML1/ETO expression. Gene expression profiling comparing a panel of CPLDIDFYC-binding and CPLDIDFYC-nonbinding cell lines identified a set of potential receptors for the CPLDIDFYC peptide. Further analysis suggested that alpha4beta1 integrin (VLA-4) is the CPLDIDFYC receptor. Finally, we showed that the CPLDIDFYC-phage is internalized upon receptor binding, suggesting that the CPLDIDFYC-receptor-ligand interaction may be exploitable for targeting drugs or gene therapy vectors to leukemia cells carrying the suitable receptor.

Boric acid inhibits embryonic histone deacetylases: a suggested mechanism to explain boric acid-related teratogenicity

Histone deacetylases (HDAC) control gene expression by changing histonic as well as non histonic protein conformation. HDAC inhibitors (HDACi) are considered to be among the most promising drugs for epigenetic treatment for cancer. Recently a strict relationship between histone hyperacetylation in specific tissues of mouse embryos exposed to two HDACi (valproic acid and trichostatin A) and specific axial skeleton malformations has been demonstrated. The aim of this study is to verify if boric acid (BA), that induces in rodents malformations similar to those valproic acid and trichostatin A-related, acts through similar mechanisms: HDAC inhibition and histone hyperacetylation. Pregnant mice were treated intraperitoneally with a teratogenic dose of BA (1000 mg/kg, day 8 of gestation). Western blot analysis and immunostaining were performed with anti hyperacetylated histone 4 (H4) antibody on embryos explanted 1, 3 or 4 h after treatment and revealed H4 hyperacetylation at the level of somites. HDAC enzyme assay was performed on embryonic nuclear extracts. A significant HDAC inhibition activity (compatible with a mixed type partial inhibition mechanism) was evident with BA. Kinetic analyses indicate that BA modifies substrate affinity by a factor alpha=0.51 and maximum velocity by a factor beta=0.70. This work provides the first evidence for HDAC inhibition by BA and suggests such a molecular mechanism for the induction of BA-related malformations.

Treatment of acute promyelocytic leukemia by retinoids

We review the role of all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). The combination of ATRA and conventional anthracycline-ARA-C chemotherapy (CT) has clearly demonstrated its superiority over CT alone (in terms of relapse and survival) in newly diagnosed APL. Combination treatment probably also reduces the incidence of initial failures, and complete remission (CR) rates greater than 90% are now regularly reported in large multicenter trials. Some randomized studies strongly suggest that prolonged maintenance treatment (for 1 or 2 years) with ATRA and low-dose CT, and possibly very early introduction of anthracycline CT during induction treatment, may reduce the incidence of relapse. With those treatments, the relapse risk appears to be only 10%-15%, although it remains greater in patients who initially have high white blood cell counts (often associated with variant M3 morphology, short bcr3 isoform, etc.) and patients with residual disease detectable by RT-PCR at the end of consolidation courses. In those patients, addition of arsenic derivatives to induction or consolidation treatment (or both treatments together) may prove useful and is currently being tested. ATRA syndrome (now generally called APL differentiation syndrome, as it is also seen with arsenic derivatives) remains the major side effect of ATRA treatment. It occurs in 10%-15% of patients and is currently fatal in at least 10% of them. Rapid onset of CT or high dose steroids (or both) should improve its outcome. A sizeable proportion of APL patients who relapse after ATRA and CT can be durably salvaged by the same treatment followed by allogeneic or autologous stem cell transplantation, provided the transplant (in the autologous setting) is RT-PCR-negative. However, in relapsing APL arsenic derivatives (mainly arsenic trioxide) are now considered to be the reference treatment. Some of the current issues with ATRA treatment in newly diagnosed APL include whether ATRA has a role during consolidation treatment and whether arabinoside (AraC) is required in addition to anthracyclines in the chemotherapy combined to ATRA.

The Histone Deacetylase Inhibitor FK228 Distinctly Sensitizes the Human Leukemia Cells to Retinoic Acid-Induced Differentiation

FK228 (depsipeptide) is a novel histone deacetylase inhibitor (HDACI) that has shown therapeutical efficacy in clinical trials for malignant lymphoma. In this article, we examined in vitro effects of FK228 on human leukemia cell lines, NB4 and HL-60. FK228 alone (0.2-1 ng/mL) inhibited leukemia cell growth in a dose-dependent manner and induced death by apoptosis. FK228 had selective differentiating effects on two cell lines when used for 6 h before induction of granulocytic differentiation by retinoic acid (RA) or in combination with RA. These effects were accompanied by a time- and dose-dependent histone H4 hyper-acetylation or histone H3 dephosphorylation and alterations in DNA binding of NF-kappaB in association with cell death and differentiation. Pifithrin-alpha (PFT), an inhibitor of p53 transcriptional activity, protected only NB4 cells with functional p53 from FK228-induced apoptosis and did not interfere with antiproliferative activity in p53-negative HL-60 cells. In NB4 cells, PFT inhibited p53 binding to the p21 (Waf1/Cip1) promotor and induced DNA binding of NF-kappaB leading to enhanced cell survival. Thus, beneficial effects of FK228 on human promyelocytic leukemia may be exerted through the induction of differentiation or apoptosis via histone modification and selective involvement of transcription factors, such as NF-kappaB and p53.

Effectiveness of trichostatin A as a potential candidate for anticancer therapy in non-small-cell lung cancer

BACKGROUND

A well-known histone deacetylase inhibitor, trichostatin A, was applied to non-small-cell lung cancer cells to determine whether inhibition of histone deacetylase leads to the production of proteins that either arrest tumor cell growth or lead to tumor cell death.

METHODS

Trichostatin A (0.01 to 1.0 micromol/L) was applied to one normal lung fibroblast and four non-small-cell lung cancer lines, and its effect was determined by flow cytometry, annexin-V staining, immunoprecipitation, and Western blot analysis.

RESULTS

Trichostatin A demonstrated tenfold greater growth inhibition in all four non-small-cell lung cancer lines compared with normal controls, with a concentration producing 50% inhibition ranging from 0.01 to 0.04 micromol/L for the tumor cell lines and 0.7 micromol/L for the normal lung fibroblast line. Trichostatin A treatment reduced the percentage of cells in S phase (10% to 23%) and increased G1 populations (10% to 40%) as determined by flow cytometry. Both annexin-V binding assay and upregulation of the protein, gelsolin (threefold to tenfold), demonstrated that the tumor cells were apoptotic, whereas normal cells were predominantly in cell cycle arrest. Trichostatin A increased histone H4 acetylation and expression of p21 twofold to 15-fold without significant effect on p16, p27, CDK2, and cyclin D1.

CONCLUSIONS

Collectively, these data suggest that inhibition of histone deacetylation may provide a valuable approach for lung cancer treatment. We evaluated trichostatin A as a potential candidate for anticancer therapy in non-small-cell lung cancer.