Safety and clinical activity of the combination of 5-azacytidine, valproic acid, and all-trans retinoic acid in acute myeloid leukemia and myelodysplastic syndrome

5-Azacytidine/5-Azacitidine

The hypomethylating agent 5-Azacytidine epigenetically modulates various genes, including tumor suppressor genes. For many years, the "new agent", which was first discovered in the 1960s, remained fairly unobtrusive in the rank of salvage treatment options for myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). When the significance of epigenetics in tumorigenesis became clear, 5-Azacytidine attracted new attention. Finally, it was the first drug approved for the treatment of all categories of MDS, and its survival benefit over best conventional care was confirmed. Today, in many clinical situations, when aggressive therapies including allogeneic hematopoietic cell transplantation are not an option, 5-Azacytidine is the first treatment of choice. Preliminary data on combinations of the hypomethylating agent with other new drugs are promising, and innovative strategies involving immune modulation and regenerative tissue repair hold a broad potential for future developments.

Expression of PD-L1, PD-L2, PD-1 and CTLA4 in myelodysplastic syndromes is enhanced by treatment with hypomethylating agents

Blockade of immune checkpoints is emerging as a new form of anticancer therapy. We studied the expression of programmed death ligand 1 (PD-L1), PD-L2, programmed death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA4) mRNA in CD34+ cells from myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML) patients (N=124). Aberrant upregulation (⩾2-fold) was observed in 34, 14, 15 and 8% of the patients. Increased expression of these four genes was also observed in peripheral blood mononuclear cells (PBMNCs) (N=61). The relative expression of PD-L1 from PBMNC was significantly higher in MDS (P=0.018) and CMML (P=0.0128) compared with AML. By immunohistochemical analysis, PD-L1 protein expression was observed in MDS CD34+ cells, whereas stroma/non-blast cellular compartment was positive for PD-1. In a cohort of patients treated with epigenetic therapy, PD-L1, PD-L2, PD-1 and CTLA4 expression was upregulated. Patients resistant to therapy had relative higher increments in gene expression compared with patients who achieved response. Treatment of leukemia cells with decitabine resulted in a dose-dependent upregulation of above genes. Exposure to decitabine resulted in partial demethylation of PD-1 in leukemia cell lines and human samples. This study suggests that PD-1 signaling may be involved in MDS pathogenesis and resistance mechanisms to hypomethylating agents. Blockade of this pathway can be a potential therapy in MDS and AML.

The role of hypomethylating agents in myelodysplastic syndrome: changing the management paradigm

Modern treatment of myelodysplastic syndromes (MDS) with hypomethylating agents (HMAs) such as azacitidine (Vidaza) and decitabine (Dacogen) has changed the clinical landscape of these disorders. Novel drug combinations of HMAs with histone deacetylase inhibitor therapy may synergistically target different dysregulated molecular mechanisms within MDS clones. This article reviews current trial data concerning the use of the main HMAs in MDS patients where intensive chemotherapy and allogeneic stem cell transplantation is generally not an option. Collated data are presented of the clinical response outcomes, toxicity profiles and prognostic response criteria. Vidaza use in low-risk MDS cases, the selected place of allogeneic stem cell transplantation in older patients with significant comorbidity and the novel drug combination strategies for the future are discussed.

Hypomethylating agents and chemotherapy in MDS

Until recently, the treatment of higher risk myelodysplastic syndrome was based on [1] Intensive chemotherapy using anthracycline-AraC combinations, leading to a lower complete remission rates and a shorter CR duration compared with de novo AML [2], low dose chemotherapy with limited CR rate mainly restricted to patients with normal karyotype. Azacitidine was the first drug to significantly improve survival in higher risk MDS, although it is not curative. Thus, the survival improvement obtained with azacitidine must be the starting point for combination studies, and for utilization of this drug in other situations (before allo SCT, or after chemotherapy or allo SCT as maintenance treatment).

Imatinib induces demethylation of miR-203 gene: an epigenetic mechanism of anti-tumor effect of imatinib

MicroRNA (miRNA) is an important regulator of cellular proliferation, differentiation and death. Leukemia-specific signature of miRNAs suggests that epigenetic dysregulation of miRNAs is important for leukemogenesis. We focused on the role of DNA methylation of miR-203 which targets BCR-ABL1 mRNA. The microarray analysis showed that 48 miRNAs of CpG-rich 212 miRNAs were upregulated over 2-fold after imatinib treatment. Imatinib induced the demethylation of the miR-203 promoter region, resulting in low expression of targeted BCR-ABL1 gene, and loss of proliferation of leukemic cells. In conclusion, demethylation of miR-203 is one of the molecular mechanisms of imatinib-induced inhibition of BCR-ABL1-positive leukemic cells.

Phase I study of azacitidine and bortezomib in adults with relapsed or refractory acute myeloid leukemia

We previously reported that bortezomib indirectly modulates transcription of DNA methyltransferase 1 (DNMT). We designed a phase I study of azacitidine (a direct DNMT inhibitor) plus bortezomib in acute myeloid leukemia (AML) to determine safety and tolerability. Twenty-three adults with relapsed/refractory AML received azacitidine 75 mg/m(2) daily on days 1-7. Bortezomib was dose escalated from 0.7 mg/m(2) on days 2 and 5 to 1.3 mg/m(2) on days 2, 5, 9 and 12. The target dose was reached without dose limiting toxicities. Infection and/or febrile neutropenia were frequent. Patients received a median of 2 cycles of therapy (range, 1-12+). Five of 23 patients achieved remission, including two with morphologic and cytogenetic complete response (CR) and three with CR and incomplete count recovery (CRi). Of CR/CRi responders with cytogenetic abnormalities at baseline, three of four achieved cytogenetic CR. The combination of azacitidine and bortezomib was tolerable and active in this cohort of poor-risk previously treated patients with AML.

Methylation and histone deacetylase inhibition in combination with platinum treatment in patients with advanced malignancies

PURPOSE

The combination of DNA methylation inhibitors and histone deacetylase inhibitors is synergistic in gene expression activation and may overcome platinum resistance. Sequential treatment with azacitidine and valproic acid (VPA) in combination with carboplatin may overcome resistance to platinum-based therapy, and we conducted a phase I trial to assess safety, maximum tolerated dose (MTD), and clinical correlates. Experimental Design Patients with advanced solid tumors refractory to standard therapy were eligible. In cohorts of escalating doses, patients received azacitidine for 5 days from days 1 to 5, VPA for 7 days from days 5 to 11, and carboplatin starting in the second cycle on days 3 and 10. Clinical correlates included evaluation of epigenetic changes, methylation patterns, and histone acetylation levels in peripheral blood mononuclear cells.

RESULTS

Thirty-two patients were treated. The MTD was 75 mg/m(2) azacitidine, 20 mg/kg VPA, and AUC 3.0 carboplatin. Minor responses or stable disease lasting ≥ 4 months were achieved by six patients (18.8 %), including three with platinum-resistant or platinum-refractory ovarian cancer. The most common adverse events grade ≥ 3 were fatigue (81 %) and neutropenia (69 %). Dose-limiting toxicity occurred in six patients (18.8 %), including four patients with grade 3 altered mental status. Death receptor 4 (DR4) methylation was shown to decrease in a subset of patients, but there was no relationship with tumor response or number of cycles received.

CONCLUSIONS

Combination of azacitidine, VPA, and carboplatin demonstrates decreased DR4 methylation and modest evidence of antitumor activity in patients with heavily treated advanced malignancies.

The combination of valproic acid, all-trans retinoic acid and low-dose cytarabine as disease-stabilizing treatment in acute myeloid leukemia

Background

A large proportion of patients with acute myeloid leukemia (AML) are not fit for intensive and potentially curative therapy due to advanced age or comorbidity. Previous studies have demonstrated that a subset of these patients can benefit from disease-stabilizing therapy based on all-trans retinoic acid (ATRA) and valproic acid. Even though complete hematological remission is only achieved for exceptional patients, a relatively large subset of patients respond to this treatment with stabilization of normal peripheral blood cell counts.

Methods

In this clinical study we investigated the efficiency and safety of combining (i) continuous administration of valproic acid with (ii) intermittent oral ATRA treatment (21.5 mg/m² twice daily) for 14 days and low-dose cytarabine (10 mg/m² daily) for 10 days administered subcutaneously. If cytarabine could not control hyperleukocytosis it was replaced by hydroxyurea or 6-mercaptopurin to keep the peripheral blood blast count below 50 × 10⁹/L.

Results

The study included 36 AML patients (median age 77 years, range 48 to 90 years) unfit for conventional intensive chemotherapy; 11 patients responded to the treatment according to the myelodysplastic syndrome (MDS) response criteria and two of these responders achieved complete hematological remission. The most common response to treatment was increased and stabilized platelet counts. The responder patients had a median survival of 171 days (range 102 to > 574 days) and they could spend most of this time outside hospital, whereas the nonresponders had a median survival of 33 days (range 8 to 149 days). The valproic acid serum levels did not differ between responder and nonresponder patients and the treatment was associated with a decrease in the level of circulating regulatory T cells.

Conclusion

Treatment with continuous valproic acid and intermittent ATRA plus low-dose cytarabine has a low frequency of side effects and complete hematological remission is seen for a small minority of patients. However, disease stabilization is seen for a subset of AML patients unfit for conventional intensive chemotherapy.

Histone deacetylase inhibition in the treatment of acute myeloid leukemia: the effects of valproic acid on leukemic cells, and the clinical and experimental evidence for combining valproic acid with other antileukemic agents

Several new therapeutic strategies are now considered for acute myeloid leukemia (AML) patients unfit for intensive chemotherapy, including modulation of protein lysine acetylation through inhibition of histone deacetylases (HDACs). These enzymes alter the acetylation of several proteins, including histones and transcription factors, as well as several other proteins directly involved in the regulation of cell proliferation, differentiation and apoptosis. Valproic acid (VPA) is a HDAC inhibitor that has been investigated in several clinical AML studies, usually in combination with all-trans retinoic acid (ATRA) for treatment of patients unfit for intensive chemotherapy, for example older patients, and many of these patients have relapsed or primary resistant leukemia. The toxicity of VPA in these patients is low and complete hematological remission lasting for several months has been reported for a few patients (<5% of included patients), but increased peripheral blood platelet counts are seen for 30 to 40% of patients and may last for up to 1 to 2 years. We review the biological effects of VPA on human AML cells, the results from clinical studies of VPA in the treatment of AML and the evidence for combining VPA with new targeted therapy. However, it should be emphasized that VPA has not been investigated in randomized clinical studies. Despite this lack of randomized studies, we conclude that disease-stabilizing treatment including VPA should be considered especially in unfit patients, because the possibility of improving normal blood values has been documented in several studies and the risk of clinically relevant toxicity is minimal.

Current therapy of myelodysplastic syndromes

After being a neglected and poorly-understood disorder for many years, there has been a recent explosion of data regarding the complex pathogenesis of myelodysplastic syndromes (MDS). On the therapeutic front, the approval of azacitidine, decitabine, and lenalidomide in the last decade was a major breakthrough. Nonetheless, the responses to these agents are limited and most patients progress within 2 years. Allogeneic stem cell transplantation remains the only potentially curative therapy, but it is associated with significant toxicity and limited efficacy. Lack or loss of response after standard therapies is associated with dismal outcomes. Many unanswered questions remain regarding the optimal use of current therapies including patient selection, response prediction, therapy sequencing and combinations, and management of resistance. It is hoped that the improved understanding of the underpinnings of the complex mechanisms of pathogenesis will be translated into novel therapeutic approaches and better prognostic/predictive tools that would facilitate accurate risk-adaptive therapy.

The promise and failures of epigenetic therapies for cancer treatment

Genetic mutations and gross structural defects in the DNA sequence permanently alter genetic loci in ways that significantly disrupt gene function. In sharp contrast, genes modified by aberrant epigenetic modifications remain structurally intact and are subject to partial or complete reversal of modifications that restore the original (i.e. non-diseased) state. Such reversibility makes epigenetic modifications ideal targets for therapeutic intervention. The epigenome of cancer cells is extensively modified by specific hypermethylation of the promoters of tumor suppressor genes relative to the extensive hypomethylation of repetitive sequences, overall loss of acetylation, and loss of repressive marks at microsatellite/repeat regions. In this review, we discuss emerging therapies targeting specific epigenetic modifications or epigenetic modifying enzymes either alone or in combination with other treatment regimens. The limitations posed by cancer treatments elicit unintended epigenetic modifications that result in exacerbation of tumor progression are also discussed. Lastly, a brief discussion of the specificity restrictions posed by epigenetic therapies and ways to address such limitations is presented.

Epigenetic therapy in allogeneic hematopoietic stem cell transplantation

DNA methylation and other epigenetic phenomena appear to be relevant in the pathogenesis of several malignant disorders. DNA methyltransferases add methyl groups to cytosine-phosphate-guanine (CpG) islandsleading to gene promoter silencing. The DNA methyltransferases inhibitors azacitidine and decitabine have anti-tumor activity against a broad range of malignancies, but have been investigated mostly in myelodysplastic syndrome. In addition, these agents have immunomodulatory effects that are under investigation in the allogeneic stem cell transplantation scenario. Both drugs have been used in the perioperative period of allogeneic transplantations with varying degrees of success. It has been hypothesized that low dose azacitidine may increase the graft-versus-leukemia effect and have a role in the maintenance of remission after allogeneic transplantation for myeloid leukemias. It is also intriguing that this favorable effect might occur while mitigating graft-versus-host disease. Here we present a review of the rapidly growing field of epigenetic manipulation using hypomethylating agents in allogeneic transplantation.

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

5-Azacytidine for the treatment of myelodysplastic syndromes

INTRODUCTION

5-Azacytidine is a pyrimidine nucleoside analog of cytidine that undergoes incorporation into DNA and blocks DNA methyltransferase leading to hypomethylation and potentially beneficial re-expression of abnormally silenced genes. It is the first agent approved for use in patients with myelodysplastic syndromes (MDSs) based on its improvement in overall survival as monotherapy. Evidence of efficacy in combination with other agents is also accumulating.

AREAS COVERED

Key information on mechanisms of action is presented. Development, synthesis, and pharmacokinetics are also outlined. Key safety, tolerability, and efficacy data from clinical trials of 5-azacytidine as monotherapy as well as in combination are also presented.

EXPERT OPINION

Our understanding of the molecular basis and pathogenesis of MDS continues to evolve rapidly. 5-Azacytidine has been shown to improve both overall survival and quality of life in patients with high-risk MDS. Currently, the oral route of administration is undergoing evaluation in clinical trials. Used as a monotherapy and also in novel combinations, 5-azacytidine has the potential to further improve the prognosis of some patients with MDS.

Cancer epigenetics: new therapies and new challenges

Cancer is nowadays considered to be both a genetic and an epigenetic disease. The most well studied epigenetic modification in humans is DNA methylation; however it becomes increasingly acknowledged that DNA methylation does not work alone, but rather is linked to other modifications, such as histone modifications. Epigenetic abnormalities are reversible and as a result novel therapies that work by reversing epigenetic effects are being increasingly explored. The biggest clinical impact of epigenetic modifying agents in neoplastic disorders thus far has been in haematological malignancies, and the efficacy of DNMT inhibitors and HDAC inhibitors in blood cancers clearly attests to the principle that therapeutic modification of the cancer cell epigenome can produce clinical benefit. This paper will discuss the most well studied epigenetic modifications and how these are linked to cancer, will give a brief overview of the clinical use of epigenetics as biomarkers, and will focus in more detail on epigenetic drugs and their use in solid and blood cancers.

Histone deacetylase inhibitors (HDACIs): multitargeted anticancer agents

Histone deacetylase (HDAC) inhibitors are an emerging class of therapeutics with potential as anticancer drugs. The rationale for developing HDAC inhibitors (and other chromatin-modifying agents) as anticancer therapies arose from the understanding that in addition to genetic mutations, epigenetic changes such as dysregulation of HDAC enzymes can alter phenotype and gene expression, disturb homeostasis, and contribute to neoplastic growth. The family of HDAC inhibitors is large and diverse. It includes a range of naturally occurring and synthetic compounds that differ in terms of structure, function, and specificity. HDAC inhibitors have multiple cell type-specific effects in vitro and in vivo, such as growth arrest, cell differentiation, and apoptosis in malignant cells. HDAC inhibitors have the potential to be used as monotherapies or in combination with other anticancer therapies. Currently, there are two HDAC inhibitors that have received approval from the US FDA for the treatment of cutaneous T-cell lymphoma: vorinostat (suberoylanilide hydroxamic acid, Zolinza) and depsipeptide (romidepsin, Istodax). More recently, depsipeptide has also gained FDA approval for the treatment of peripheral T-cell lymphoma. Many more clinical trials assessing the effects of various HDAC inhibitors on hematological and solid malignancies are currently being conducted. Despite the proven anticancer effects of particular HDAC inhibitors against certain cancers, many aspects of HDAC enzymes and HDAC inhibitors are still not fully understood. Increasing our understanding of the effects of HDAC inhibitors, their targets and mechanisms of action will be critical for the advancement of these drugs, especially to facilitate the rational design of HDAC inhibitors that are effective as antineoplastic agents. This review will discuss the use of HDAC inhibitors as multitargeted therapies for malignancy. Further, we outline the pharmacology and mechanisms of action of HDAC inhibitors while discussing the safety and efficacy of these compounds in clinical studies to date.

Can we improve outcomes in patients with acute myelogenous leukemia? Incorporating HDAC inhibitors into front-line therapy

There is a need for improvements on the results of current therapies for patients with acute myelogenous leukemia (AML). A number of strategies are being used to achieve this goal. Here we present data that indicate that the addition of a histone deacetylase (HDAC) inhibitor, such as vorinostat, to idarubicin and cytarabine results in a very high response rate and can be safely administered to patients with leukemia. These results form the bases of the next SWOG front-line trial in AML. Here, we present the rationale for such combination and the studies that led to the support of this concept including both in vitro models and initial phase 1 trials.

Azacitidine fails to eradicate leukemic stem/progenitor cell populations in patients with acute myeloid leukemia and myelodysplasia

Epigenetic therapies demonstrate significant clinical activity in acute myeloid leukemia (AML) and myelodysplasia (MDS) and constitute an important new class of therapeutic agents. However hematological responses are not durable and disease relapse appears inevitable. Experimentally, leukemic stem/progenitor cells (LSC) propagate disease in animal models of AML and it has been postulated that their relative chemo-resistance contributes to disease relapse. We serially measured LSC numbers in patients with high-risk AML and MDS treated with 5'-azacitidine and sodium valproate (VAL-AZA). Fifteen out of seventy-nine patients achieved a complete remission (CR) or complete remission with incomplete blood count recovery (CRi) with VAL-AZA therapy. There was no significant reduction in the size of the LSC-containing population in non-responders. While the LSC-containing population was substantially reduced in all patients achieving a CR/CRi it was never eradicated and expansion of this population antedated morphological relapse. Similar studies were performed in seven patients with newly diagnosed AML treated with induction chemotherapy. Eradication of the LSC-containing population was observed in three patients all of whom achieved a durable CR in contrast to patients with resistant disease where LSC persistence was observed. LSC quantitation provides a novel biomarker of disease response and relapse in patients with AML treated with epigenetic therapies. New drugs that target this cellular population in vivo are required.

Epigenetic therapy is associated with similar survival compared with intensive chemotherapy in older patients with newly diagnosed acute myeloid leukemia

We reviewed the outcome of 671 patients 65 years of age or older with newly diagnosed acute myeloid leukemia (AML) treated at our institution between 2000 and 2010 with intensive chemotherapy (n = 557) or azacitidine- or decitabine-based therapy (n = 114). Both groups were balanced according to cytogenetics and performance status. The complete response rates with chemotherapy and epigenetic therapy were 42% and 28%, respectively (P = .001), and the 8-week mortality 18% and 11%, respectively (P = .075). Two-year relapse-free survival rates (28% vs 39%, P = .843) and median survival (6.7 vs 6.5 months, P = .413) were similar in the 2 groups. Multivariate analysis identified older age, adverse cytogenetics, poor performance status, elevated creatinine, peripheral blood and BM blasts, and hemoglobin, but not type of AML therapy, as independent prognostic factors for survival. No outcome differences were observed according to cytogenetics, FLT3 mutational status, age, or performance status by therapy type. Decitabine was associated with improved median overall survival compared with azacitidine (5.5 vs 8.8 months, respectively, P = .03). Survival after failure of intensive chemotherapy, azacitidine, or decitabine was more favorable in patients who had previously received decitabine (1.1 vs 0.9 vs 3.1 months, respectively, P = .109). The results of the present study show that epigenetic therapy is associated with similar survival rates as intensive chemotherapy in older patients with newly diagnosed AML. The studies reviewed are registered at www.clinicaltrials.gov as 2009-0172 (NCT00926731) and 2009-0217 (NCT00952588).

The DNA demethylating agent decitabine activates the TRAIL pathway and induces apoptosis in acute myeloid leukemia

Although epigenetic drugs have been approved for use in selected malignancies, there is significant need for a better understanding of their mechanism of action. Here, we study the action of a clinically approved DNA-methyltransferase inhibitor - decitabine (DAC) - in acute myeloid leukemia (AML) cells. At low doses, DAC treatment induced apoptosis of NB4 Acute Promyelocytic Leukemia (APL) cells, which was associated with the activation of the extrinsic apoptotic pathway. Expression studies of the members of the Death Receptor family demonstrated that DAC induces the expression of TNF-related apoptosis-inducing ligand (TRAIL). Upregulation of TRAIL, upon DAC treatment, was associated with specific epigenetic modifications induced by DAC in the proximity of the TRAIL promoter, as demonstrated by DNA demethylation, increased DNaseI sensitivity and histone acetylation of a non-CpG island, CpG-rich region located 2kb upstream to the transcription start site. Luciferase assay experiments showed that this region behave as a DNA methylation sensitive transcriptional regulatory element. The CpG regulatory element was also found methylated in samples derived from APL patients. These findings have been confirmed in the non-APL, AML Kasumi cell line, suggesting that this regulatory mechanism may be extended to other AMLs. Our study suggests that DNA methylation is a regulatory mechanism relevant for silencing of the TRAIL apoptotic pathway in leukemic cells, and further elucidates the mechanism by which epigenetic drugs mediate their anti-leukemic effects.

Acute myeloid leukemia in the elderly

SUMMARY Acute myeloid leukemia in older patients is of poor outcome, characterized by a specific biology of acute myeloid leukemia and factors related to the patient’s physical condition. Aggressive therapy results in improved survival and quality of life when compared with palliative care. However, not all patients are candidates for such therapy. Disease often demonstrates resistance related to poor-risk cytogenetics, and patients are often unable to tolerate intensive chemotherapy. For those patients, novel agents are being investigated. Understanding of the disease biology, as well as the prognostic factors associated with the host, allows the better estimation of which patients are likely to benefit from standard therapy and which require alternative approaches.

Enantioselective apoptosis induction in histiocytic lymphoma cells and acute promyelocytic leukemia cells

The aim of this study was to identify valproic acid (VPA) analogs with a broad spectrum of anti-cancer activities and an increased apoptosis-inducing potential compared with the parent VPA, which is enrolled as histone deacetylase (HDAC) inhibitor in a large number of clinical trials. We identified a chiral VPA derivative, (S)-2-pentyl-4-pentynoic acid, previously characterized as HDAC inhibitor that induced massive programmed cell death in a strongly enantioselective manner in U937 histiocytic lymphoma cells and NB4 acute promyelocytic leukemia cells. By performing fluorescence-activated cell sorting and Western blotting analyses, we established that enantiomer (S)-2-pentyl-4-pentynoic acid has higher apoptosis-inducing potential than VPA itself. The optic antipode (R)-2-pentyl-4-pentynoic acid and VPA caused under the same conditions only a weak growth inhibition without inducing cell differentiation and apoptosis. (S)-2-pentyl-4-pentynoic acid is more apoptogenic than VPA and displays enantioselective anti-cancer properties that warrant further research regarding the mechanistic basis of its activity and its potential use in cancer therapy.

DNA methyltransferase inhibitors in acute myeloid leukemia: discovery, design and first therapeutic experiences

INTRODUCTION

DNA methylation is an epigenetic change mediated by DNA methyltranferases (DNMTs), which are promising epigenetic targets for the treatment of acute myeloid leukemia (AML). This is evidenced by the two DNMT inhibitors (azacitidine and decitabine) approved by the Food and Drug Administration of the United States for the treatment of high-risk myelodysplastic syndromes and the first clinical data available in AML.

AREAS COVERED

This paper reviews data from the international literature regarding the design, sites of impact and pharmacodynamic characteristics of DNMT inhibitors, and their first clinical experiences in AML.

EXPERT OPINION

The strongest advances in epigenetic therapy have been in the treatment of AML. There are now an increasing number of DNMT inhibitors. These agents may be potentially administered at different times of leukemia therapy: before or instead of chemotherapy, as maintenance therapy, prior to allogeneic stem cell transplant (SCT) or after relapse following SCT.

ING1 and 5-azacytidine act synergistically to block breast cancer cell growth

BACKGROUND

Inhibitor of Growth (ING) proteins are epigenetic "readers" that recognize trimethylated lysine 4 of histone H3 (H3K4Me3) and target histone acetyl transferase (HAT) and histone deacetylase (HDAC) complexes to chromatin.

METHODS AND PRINCIPAL FINDINGS

Here we asked whether dysregulating two epigenetic pathways with chemical inhibitors showed synergistic effects on breast cancer cell line killing. We also tested whether ING1 could synergize better with chemotherapeutics that target the same epigenetic mechanism such as the HDAC inhibitor LBH589 (Panobinostat) or a different epigenetic mechanism such as 5-azacytidine (5azaC), which inhibits DNA methyl transferases. Simultaneous treatment of breast cancer cell lines with LBH589 and 5azaC did not show significant synergy in killing cells. However, combination treatment of ING1 with either LBH589 or 5azaC did show synergy. The combination of ING1b with 5azaC, which targets two distinct epigenetic mechanisms, was more effective at lower doses and enhanced apoptosis as determined by Annexin V staining and cleavage of caspase 3 and poly-ADP-ribose polymerase (PARP). ING1b plus 5azaC also acted synergistically to increase γH2AX staining indicating significant levels of DNA damage were induced. Adenoviral delivery of ING1b with 5azaC also inhibited cancer cell growth in a murine xenograft model and led to tumor regression when viral concentration was optimized in vivo.

CONCLUSIONS

These data show that targeting distinct epigenetic pathways can be more effective in blocking cancer cell line growth than targeting the same pathway with multiple agents, and that using viral delivery of epigenetic regulators can be more effective in synergizing with a chemical agent than using two chemotherapeutic agents. This study also indicates that the ING1 epigenetic regulator may have additional activities in the cell when expressed at high levels.

Valproic acid decreases urothelial cancer cell proliferation and induces thrombospondin-1 expression

Background

Prevention of bladder cancer recurrence is a central challenge in the management of this highly prevalent disease. The histone deacetylase inhibitor valproic acid (sodium valproate) has anti-angiogenic properties and has been shown to decrease bladder cancer growth in model systems. We have previously shown reduced expression of thrombospondin-1 in a mouse model and in human bladder cancer relative to normal urothelium. We speculated that inhibition of angiogenesis by valproate might be mediated by this anti-angiogenic protein.

Methods

Bladder cancer cell lines UMUC3 and T24 were treated with valproate or another histone deacetylase inhibitor, vorinostat, in culture for a period of three days. Proliferation was assessed by alamar blue reduction. Gene expression was evaluated by reverse transcription of RNA and quantitative PCR.

Results

Proliferation assays showed treatment with valproate or vorinostat decreased proliferation in both cell lines. Histone deacetylase inhibition also increased relative expression of thrombospondin-1 up to 8 fold at 5 mM valproate.

Conclusions

Histone deacetylase inhibitors warrant further study for the prevention or treatment of bladder cancer.

Concomitant inhibition of DNA methyltransferase and BCL-2 protein function synergistically induce mitochondrial apoptosis in acute myelogenous leukemia cells

DNA methylation and BLC-2 are potential therapeutic targets in acute myeloid leukemia (AML). We investigated pharmacologic interaction between the DNA methyltransferase inhibitor 5-azacytidine (5-AZA) and the BCL-2 inhibitor ABT-737. Increased BCL-2 expression determined by reverse phase protein analysis was associated with poor survival in AML patients with unfavorable cytogenetics (n = 195). We found that 5-AZA, which itself has modest apoptotic activity, acts synergistically with ABT-737 to induce apoptosis. The 5-AZA/ABT-737 combination enhanced mitochondrial outer membrane permeabilization, as evidenced by effective conformational activation of BAX and ∆ψ(m) loss. Although absence of p53 limited apoptotic activities of 5-AZA and ABT-737 as single agents, the combination synergistically induced apoptosis independent of p53 expression. 5-AZA down-regulated MCL-1, known to mediate resistance to ABT-737, in a p53-independent manner. The 5-AZA/ABT-737 combination synergistically induced apoptosis in AML cells in seven of eight patients. 5-AZA significantly reduced MCL-1 levels in two of three samples examined. Our data provide a molecular rationale for this combination strategy in AML therapy.

Valproic acid triggers erythro/megakaryocyte lineage decision through induction of GFI1B and MLLT3 expression

Histone deacetylase inhibitors represent a family of targeted anticancer compounds that are widely used against hematological malignancies. So far little is known about their effects on normal myelopoiesis. Therefore, in order to investigate the effect of histone deacetylase inhibitors on the myeloid commitment of hematopoietic stem/progenitor cells, we treated CD34(+) cells with valproic acid (VPA). Our results demonstrate that VPA treatment induces H4 histone acetylation and hampers cell cycle progression in CD34(+) cells sustaining high levels of CD34 protein expression. In addition, our data show that VPA treatment promotes erythrocyte and megakaryocyte differentiation. In fact, we demonstrate that VPA treatment is able to induce the expression of growth factor-independent protein 1B (GFI1B) and of mixed-lineage leukemia translocated to chromosome 3 protein (MLLT3), which are crucial regulators of erythrocyte and megakaryocyte differentiation, and that the up-regulation of these genes is mediated by the histone hyperacetylation at their promoter sites. Finally, we show that GFI1B inhibition impairs erythroid and megakaryocyte differentiation induced by VPA, while MLLT3 silencing inhibits megakaryocyte commitment only. As a whole, our data suggest that VPA sustains the expression of stemness-related markers in hematopoietic stem/progenitor cells and is able to interfere with hematopoietic lineage commitment by enhancing erythrocyte and megakaryocyte differentiation and by inhibiting the granulocyte and mono-macrophage maturation.

Phase II trial of vorinostat with idarubicin and cytarabine for patients with newly diagnosed acute myelogenous leukemia or myelodysplastic syndrome

PURPOSE

To evaluate the safety and efficacy of the combination of the histone deacetylase inhibitor vorinostat with idarubicin and ara-C (cytarabine) in patients with acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS).

PATIENTS AND METHODS

Patients with previously untreated AML or higher-risk MDS age 15 to 65 years with appropriate organ function and no core-binding factor abnormality were candidates. Induction therapy was vorinostat 500 mg orally three times a day (days 1 to 3), idarubin 12 mg/m(2) intravenously (IV) daily × 3 (days 4 to 6), and cytarabine 1.5 g/m(2) IV as a continuous infusion daily for 3 or 4 days (days 4 to 7). Patients in remission could be treated with five cycles of consolidation therapy and up to 12 months of maintenance therapy with single-agent vorinostat. The study was designed to stop early if either excess toxicity or low probability of median event-free survival (EFS) of more than 28 weeks was likely.

RESULTS

After a three-patient run-in phase, 75 patients were treated. Median age was 52 years (range, 19 to 65 years), 29 patients (39%) were cytogenetically normal, and 11 (15%) had FLT-3 internal tandem duplication (ITD). No excess vorinostat-related toxicity was observed. Induction mortality was 4%. EFS was 47 weeks (range, 3 to 134 weeks), and overall survival was 82 weeks (range, 3 to 134 weeks). Overall response rate (ORR) was 85%, including 76% complete response (CR) and 9% in CR with incomplete platelet recovery. ORR was 93% in diploid patients and 100% in FLT-3 ITD patients. Levels of NRF2 and CYBB were associated with longer survival.

CONCLUSION

The combination of vorinostat with idarubicin and cytarabine is safe and active in AML.

Promises and challenges of anticancer drugs that target the epigenome

The occurrence of epigenetic aberrations in cancer and their role in promoting tumorigenesis has led to the development of various small molecule inhibitors that target epigenetic enzymes. In preclinical settings, many epigenetic inhibitors demonstrate promising activity against a variety of both hematological and solid tumors. The therapeutic efficacy of those inhibitors that have entered the clinic however, is restricted predominantly to hematological malignancies. Here we outline the observed epigenetic aberrations in various types of cancer and the clinical responses to epigenetic drugs. We furthermore discuss strategies to improve the responsiveness of both hematological and solid malignancies to epigenetic drugs.

Optimizing hypomethylating agents in myelodysplastic syndromes

PURPOSE OF REVIEW

Hypomethylating agents (HMAs) improve the outcome of higher-risk myelodysplastic syndromes (MDS) and provide multilineage response in lower-risk patients but their results must be optimized, especially as the poor outcome of patients after HMA failure is now established.

RECENT FINDINGS

Current efforts include evaluation of novel outpatient administration schedules and routes, improving compliance and drug exposure to reach continuous hypomethylation. Novel combination strategies are emerging, with histone deacetylase inhibitors or immunomodulatory compounds, but none has proven superior to HMA single-agent therapy so far. Improved understanding of the epigenetic deregulation of MDS and of HMA's mode of action has allowed putative biomarkers to emerge, including multiple gene methylation patterns, and gene mutations, notably TET2 mutations. As HMAs may elicit antileukemic immune responses, they are also being evaluated in patients eligible for allogeneic stem cell transplantation.

SUMMARY

The indication and practical use of HMAs in MDS so far remain those of phase III registration studies, but will hopefully be modified with future results of ongoing clinical and translational research.

Valproic acid combined with cytosine arabinoside in elderly patients with acute myeloid leukemia has in vitro but limited clinical activity

Elderly patients with acute myeloid leukemia (AML) have a poor prognosis. The authors examined the in vitro and clinical activity of the histone deacetylase inhibitor valproic acid (VA) combined with cytosine arabinoside (AraC) in elderly patients with AML unsuited to intensive therapy. For the in vitro studies, primary AML cells from 11 patients were treated with AraC and VA and analyzed for apoptosis, cytostatic effects, differentiation and acetyl histone H3 induction. VA (alone and with AraC) enhanced apoptosis and induced acetyl histone H3. VA inhibited cell proliferation. For the clinical trial, 15 patients were treated with VA and subcutaneous AraC and assessed for toxicity and response. No complete or partial remissions were achieved. In conclusion, VA has in vitro activity against AML and has additional activity with AraC. However, in this study, this combination demonstrated limited clinical activity in elderly patients with AML.

Combination strategies in myelodysplastic syndromes

The myelodysplastic syndromes (MDS) consist of an array of clonal hematological malignancies resulting from disorders of pluripotent hematopoietic stem cells. MDS is associated with a poor overall prognosis and patients are categorized as higher risk and lower risk on the basis of the International Prognostic Scoring System. Currently, lenalidomide, azacitidine, and decitabine are the only three FDA-approved drugs for MDS. Traditional therapies for MDS involve the administration of single agents providing either supportive measures or disease-modifying effects directed to slowing progression to acute myeloid leukemia (AML) and improving survival. Recently, however, there has been increasing evidence suggesting that the combination of drugs with different mechanisms of action offers substantial benefit in the form of diminished side effects, improved overall survival, and delayed progression to AML. Multiple studies indicate that when compared with traditional monotherapies, combining various medications with non-overlapping mechanisms of action and toxicities may result in significant benefit for patients with MDS. A variety of combination therapies with growth factors, DNA methytransferase inhibitors, histone deacetylase inhibitors, and immunosuppressant treatments provide encouraging data indicating that the successful future of MDS treatment rests in the combination of multiple treatments modalities to achieve improved clinical outcomes.

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.

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.

Genome-wide analysis of histone H3 acetylation patterns in AML identifies PRDX2 as an epigenetically silenced tumor suppressor gene

With the use of ChIP on microarray assays in primary leukemia samples, we report that acute myeloid leukemia (AML) blasts exhibit significant alterations in histone H3 acetylation (H3Ac) levels at > 1000 genomic loci compared with CD34(+) progenitor cells. Importantly, core promoter regions tended to have lower H3Ac levels in AML compared with progenitor cells, which suggested that a large number of genes are epigenetically silenced in AML. Intriguingly, we identified peroxiredoxin 2 (PRDX2) as a novel potential tumor suppressor gene in AML. H3Ac was decreased at the PRDX2 gene promoter in AML, which correlated with low mRNA and protein expression. We also observed DNA hypermethylation at the PRDX2 promoter in AML. Low protein expression of the antioxidant PRDX2 gene was clinically associated with poor prognosis in patients with AML. Functionally, PRDX2 acted as inhibitor of myeloid cell growth by reducing levels of reactive oxygen species (ROS) generated in response to cytokines. Forced PRDX2 expression inhibited c-Myc-induced leukemogenesis in vivo on BM transplantation in mice. Taken together, epigenome-wide analyses of H3Ac in AML led to the identification of PRDX2 as an epigenetically silenced growth suppressor, suggesting a possible role of ROS in the malignant phenotype in AML.

Epigenetic cancer therapy: rationales, targets and drugs

The fundamental role of altered epigenetic modification patterns in tumorigenesis establishes epigenetic regulatory enzymes as important targets for cancer therapy. Over the past few years, several drugs with an epigenetic activity have received approval for the treatment of cancer patients, which has led to a detailed characterization of their modes of action. The results showed that both established drug classes, the histone deacetylase (HDAC) inhibitors and the DNA methyltransferase inhibitors, show substantial limitations in their epigenetic specificity. HDAC inhibitors are highly specific drugs, but the enzymes have a broad substrate specificity and deacetylate numerous proteins that are not associated with epigenetic regulation. Similarly, the induction of global DNA demethylation by non-specific inhibition of DNA methyltransferases shows pleiotropic effects on epigenetic regulation with no apparent tumor-specificity. Second-generation azanucleoside drugs have integrated the knowledge about the cellular uptake and metabolization pathways, but do not show any increased specificity for cancer epigenotypes. As such, the traditional rationale of epigenetic cancer therapy appears to be in need of refinement, as we move from the global inhibition of epigenetic modifications toward the identification and targeting of tumor-specific epigenetic programs. Recent studies have identified epigenetic mechanisms that promote self-renewal and developmental plasticity in cancer cells. Druggable somatic mutations in the corresponding epigenetic regulators are beginning to be identified and should facilitate the development of epigenetic therapy approaches with improved tumor specificity.

Chromatin remodeling, cell proliferation and cell death in valproic acid-treated HeLa cells

Background

Valproic acid (VPA) is a potent anticonvulsant that inhibits histone deacetylases. Because of this inhibitory action, we investigated whether VPA would affect chromatin supraorganization, mitotic indices and the frequency of chromosome abnormalities and cell death in HeLa cells.

Methodology/Principal Findings

Image analysis was performed by scanning microspectrophotometry for cells cultivated for 24 h, treated with 0.05, 0.5 or 1.0 mM VPA for 1–24 h, and subjected to the Feulgen reaction. TSA-treated cells were used as a predictable positive control. DNA fragmentation was investigated with the TUNEL assay. Chromatin decondensation was demonstrated under TSA and all VPA treatments, but no changes in chromosome abnormalities, mitotic indices or morphologically identified cell death were found with the VPA treatment conditions mentioned above, although decreased mitotic indices were detected under higher VPA concentration and longer exposure time. The frequency of DNA fragmentation identified with the TUNEL assay in HeLa cells increased after a 24-h VPA treatment, although this fragmentation occurred much earlier after treatment with TSA.

Conclusions/Significance

The inhibition of histone deacetylases by VPA induces chromatin remodeling in HeLa cells, which suggests an association to altered gene expression. Under VPA doses close to the therapeutic antiepileptic plasma range no changes in cell proliferation or chromosome abnormalities are elicited. The DNA fragmentation results indicate that a longer exposure to VPA or a higher VPA concentration is required for the induction of cell death.

DNA methylation topology: potential of a chromatin landmark for epigenetic drug toxicology

Targeting chromatin and its basic components through epigenetic drug therapy has become an increased focus in the treatment of complex diseases. This boost calls for the implementation of high-throughput cell-based assays that exploit the increasing knowledge about epigenetic mechanisms and their interventions for genotoxicity testing of epigenetic drugs. 3D quantitative DNA methylation imaging is a novel approach for detecting drug-induced DNA demethylation and concurrent heterochromatin decondensation/reorganization in cells through the analysis of differential nuclear distribution patterns of methylcytosine and gDNA visualized by fluorescence and processed by machine-learning algorithms. Utilizing 3D DNA methylation patterns is a powerful precursor to a series of fully automatable assays that employ chromatin structure and higher organization as novel pharmacodynamic biomarkers for various epigenetic drug actions.