Treatment of myelodysplastic syndromes with valproic acid alone or in combination with all-trans retinoic acid

All-trans retinoic acid in hematologic disorders: not just acute promyelocytic leukemia

All-trans retinoic acid (ATRA) plays a role in tissue development, neural function, reproduction, vision, cell growth and differentiation, tumor immunity, and apoptosis. ATRA can act by inducing autophagic signaling, angiogenesis, cell differentiation, apoptosis, and immune function. In the blood system ATRA was first used with great success in acute promyelocytic leukemia (APL), where ATRA differentiated leukemia cells into mature granulocytes. ATRA can play a role not only in APL, but may also play a role in other hematologic diseases such as immune thrombocytopenia (ITP), myelodysplastic syndromes (MDS), non-APL acute myeloid leukemia (AML), aplastic anemia (AA), multiple myeloma (MM), etc., especially by regulating mesenchymal stem cells and regulatory T cells for the treatment of ITP. ATRA can also increase the expression of CD38 expressed by tumor cells, thus improving the efficacy of daratumumab and CD38-CART. In this review, we focus on the mechanism of action of ATRA, its role in various hematologic diseases, drug combinations, and ongoing clinical trials.

Efficacy and Safety of Valproic Acid in Myelodysplastic Syndrome and Acute Myeloid Leukemia; a Narrative Review

Loads of new therapeutic regimes have been turned up to manage Myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), particularly in elderly patients who are unfit for intensive chemotherapy. Despite accumulating research, the best MDS and AML management approach is indeterminate. Myelodysplastic syndrome implies a group of various hematopoietic stem cell disorders that may progress to acute myeloid leukemia. These disorders are more frequent in older adults. To the high rate of morbidity and abundant toxicities related to the therapeutic approaches, also, the treatment would be challenging. The clinical effectiveness of valproic acid, a histone deacetylase inhibitor, in MDS and AML patients is unknown, even though it has demonstrated positive activities to promote differentiation and apoptosis in cancer cells. We investigated the clinical research on the effects of valproic acid in conjunction with various drugs, including low-dose cytarabine, all-trans retinoic acid, DNA-hypomethylating agents, hydrazine, and theophylline. We conclude that VPA is a safe and effective treatment option for MDS and AML patients, particularly when used in conjunction with all-trans retinoic acid, DNA-hypomethylating drugs, and hydralazine. However, more randomized clinical studies are required to identify an ideal regimen.

The epigenetic regulation of cancer cell recovery from therapy exposure and its implications as a novel therapeutic strategy for preventing disease recurrence

The ultimate goal of cancer therapy is the elimination of disease from patients. Most directly, this occurs through therapy-induced cell death. Therapy-induced growth arrest can also be a desirable outcome, if prolonged. Unfortunately, therapy-induced growth arrest is rarely durable and the recovering cell population can contribute to cancer recurrence. Consequently, therapeutic strategies that eliminate residual cancer cells reduce opportunities for recurrence. Recovery can occur through diverse mechanisms including quiescence or diapause, exit from senescence, suppression of apoptosis, cytoprotective autophagy, and reductive divisions resulting from polyploidy. Epigenetic regulation of the genome represents a fundamental regulatory mechanism integral to cancer-specific biology, including the recovery from therapy. Epigenetic pathways are particularly attractive therapeutic targets because they are reversible, without changes in DNA, and are catalyzed by druggable enzymes. Previous use of epigenetic-targeting therapies in combination with cancer therapeutics has not been widely successful because of either unacceptable toxicity or limited efficacy. The use of epigenetic-targeting therapies after a significant interval following initial cancer therapy could potentially reduce the toxicity of combination strategies, and possibly exploit essential epigenetic states following therapy exposure. This review examines the feasibility of targeting epigenetic mechanisms using a sequential approach to eliminate residual therapy-arrested populations, that might possibly prevent recovery and disease recurrence.

Clinical Utility of Azacitidine in the Management of Acute Myeloid Leukemia: Update on Patient Selection and Reported Outcomes

Acute myeloid leukemia (AML) is predominantly a disease of the elderly, and a significant proportion of these patients are not candidates for intensive, curative-intent therapies. Epigenetic dysregulation resulting in abnormal DNA hypermethylation is one of the hallmarks of AML pathogenesis. For the past two decades, hypomethylating agents including azacitidine (AZA) have been the mainstay of treatment for AML patients who are ineligible to receive intensive chemotherapies. As our understanding of AML disease biology has improved, several novel treatment combinations have been developed to improve the outcome of AML patients, with remarkable success. A considerable proportion of these novel combinations have utilized AZA as the backbone of their treatment scheme. In this review, we have highlighted the evolution of AML treatment, focusing on novel AZA-based treatment combinations and their clinical efficacy.

Sensitization of Drug Resistant Cancer Cells: A Matter of Combination Therapy

Cancer drug resistance is an enormous problem. It is responsible for most relapses in cancer patients following apparent remission after successful therapy. Understanding cancer relapse requires an understanding of the processes underlying cancer drug resistance. This article discusses the causes of cancer drug resistance, the current combination therapies, and the problems with the combination therapies. The rational design of combination therapy is warranted to improve the efficacy. These processes must be addressed by finding ways to sensitize the drug-resistant cancers cells to chemotherapy, and to prevent formation of drug resistant cancer cells. It is also necessary to prevent the formation of cancer progenitor cells by epigenetic mechanisms, as cancer progenitor cells are insensitive to standard therapies. In this article, we emphasize the role for the rational development of combination therapy, including epigenetic drugs, in achieving these goals.

Zinc binding groups for histone deacetylase inhibitors

Zinc binding groups (ZBGs) play a crucial role in targeting histone deacetylase inhibitors (HDACIs) to the active site of histone deacetylases (HDACs), thus determining the potency of HDACIs. Due to the high affinity to the zinc ion, hydroxamic acid is the most commonly used ZBG in the structure of HDACs. An alternative ZBG is benzamide group, which features excellent inhibitory selectivity for class I HDACs. Various ZBGs have been designed and tested to improve the activity and selectivity of HDACIs, and to overcome the pharmacokinetic limitations of current HDACIs. Herein, different kinds of ZBGs are reviewed and their features have been discussed for further design of HDACIs.

ATRA attenuate proteinuria via downregulation of TRPC6 in glomerulosclerosis rats induced by adriamycin

Objective: In this research, we explored the molecular mechanism of proteinuria in glomerulosclerosis rats and the protective effects of ATRA.

Methods: This research set up three groups: SHO group, GS group, and ATRA group (15 mg/(kg d), Sigma, St. Louis, MO). The serum creatinine (Scr), urea nitrogen (BUN), and 24-h proteinuria were detected 12 weeks after administration of ATRA. The pathological and ultrastructure changes were observed under light microscope and transmission electron microscope. The protein expression of TGF-β₁ and Col-IV in glomerulus was detected by immunohitochemistry method. The mRNA and the protein expression of glomerular TRPC6 were detected by RT-PCR and Western blot.

Results: In the rat model of GS, the expressions of TRPC6 were significantly elevated compared with the normal rat group; however, the use of ATRA down-regulated the expression of TRPC6 in the glomeruli and attenuated glomerulosclerosis and proteinuria. Scr and BUN were also improved by the treatment of ATRA.

Conclusions: Our results demonstrated that ATRA could ameliorate glomerulosclerosis and proteinuria in GS, which may be related to suppressed expression of TRPC6.

Epimutational profile of hematologic malignancies as attractive target for new epigenetic therapies

In recent years, recurrent somatic mutations in epigenetic regulators have been identified in patients with hematological malignancies. Furthermore, chromosomal translocations in which the fusion protein partners are themselves epigenetic regulators or where epigenetic regulators are recruited/targeted by oncogenic fusion proteins have also been described. Evidence has accumulated showing that "epigenetic drugs" are likely to provide clinical benefits in several hematological malignancies, granting their approval for the treatment of myelodysplastic syndromes and cutaneous T-cell lymphomas. A large number of pre-clinical and clinical trials evaluating epigenetic drugs alone or in combination therapies are ongoing. The aim of this review is to provide a comprehensive summary of known epigenetic alterations and of the current use of epigenetic drugs for the treatment of hematological malignancies.

Hydroxyurea synergizes with valproic acid in wild-type p53 acute myeloid leukaemia

Palliative care in acute myeloid leukaemia (AML) is inadequate. For elderly patients, unfit for intensive chemotherapy, median survival is 2–3 months. As such, there is urgent demand for low-toxic palliative alternatives. We have repositioned two commonly administered anti-leukaemia drugs, valproic acid (VPA) and hydroxyurea (HU), as a combination therapy in AML.

The anti-leukemic effect of VPA and HU was assessed in multiple AML cell lines confirming the superior anti-leukemic effect of combination therapy. Mechanistic studies revealed that VPA amplified the ability of HU to slow S-phase progression and this correlated with significantly increased DNA damage. VPA was also shown to reduce expression of the DNA repair protein, Rad51. Interestingly, the tumour suppressor protein p53 was revealed to mitigate cell cycle recovery following combination induced arrest. The efficacy of combination therapy was validated in vivo. Combination treatment increased survival in OCI-AML3 and patient-derived xenograft mouse models of AML. Therapy response was confirmed by optical imaging with multiplexed near-infrared labelled antibodies.

The combination of HU and VPA indicates significant potential in preclinical models of AML. Both compounds are widely available and well tolerated. We believe that repositioning this combination could significantly enhance the palliative care of patients unsuited to intensive chemotherapy.

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.

Paclitaxel plus valproic acid versus paclitaxel alone as second- or third-line therapy for advanced gastric cancer: a randomized Phase II trial

Background

Weekly paclitaxel (wPTX) is the preferred second-line chemotherapy for gastric cancer in Japan. Histone deacetylase inhibitors have been shown to decrease proliferation through cell-cycle arrest, differentiation, and apoptosis in gastric cancer cells. One histone deacetylase inhibitor, valproic acid (VPA), also inhibits tumor growth by inducing apoptosis and enhances the efficacy of paclitaxel (PTX), shown in a murine gastric cancer model. This Phase II trial was designed to evaluate the benefits of adding VPA to wPTX in patients with gastric cancer refractory to first-line treatment with fluoropyrimidine.

Patients and methods

The patients were randomly assigned in a 1:1 ratio to receive PTX 80 mg/m² intravenously on days 1, 8, and 15, every 4 weeks, or a dose of PTX plus VPA taken everyday at 7.5 mg/kg twice daily. Random assignment was carried out at the data center with a minimization method adjusted by the Eastern Cooperative Oncology Group performance status (0–1 vs 2), prior chemotherapy (first-line vs second-line), and measurable lesions (presence vs absence). The primary end point was the overall survival (OS) rate, and the secondary end points were the progression-free survival rate and safety analysis.

Results

Sixty-six patients were randomly assigned to receive wPTX (n=33) or wPTX plus VPA (n=33). The median OS was 9.8 months in the wPTX group and 8.7 months in the wPTX plus VPA group (hazard ratio 1.19; 95% CI 0.702–2.026; P=0.51). The median progression-free survival was 4.5 months in the wPTX group and 3.0 months in the wPTX plus VPA group (hazard ratio 1.29; 95% CI 0.753–2.211; P=0.35). Grade 3–4 adverse events were neutropenia (3.1%), pneumonia (1.6%), liver injury (1.6%), brain infarction (1.6%), and rupture of aorta (1.6%).

Conclusion

No statistically significant difference was observed between wPTX and wPTX plus VPA for OS.

Valproic acid enhances the antileukemic effect of cytarabine by triggering cell apoptosis

Acute myeloid leukemia (AML) is an aggressive clonal malignancy of hematopoietic progenitor cells with a poor clinical outcome. The resistance of leukemia cells to contemporary chemotherapy is one of the most formidable obstacles to treating AML. Combining valproic acid (VPA) with other anti-leukemic agents has previously been noted as a useful and necessary strategy which can be used to specifically induce anticancer gene expression. In the present study, we demonstrated the synergistic antileukemic activities between VPA and cytarabine (Ara‑C) in a retrovirus-mediated murine model with MLL-AF9 leukemia, three leukemia cell lines (THP-1, K562 and HL-60) and seven primary human AML samples. Using RT-qPCR, we noted that the combination of VPA and Ara‑C significantly upregulated Bax expression and led to the arrest of leukemia cell proliferation, sub-G1 DNA accumulation and cell apoptosis, as demonstrated by flow cytometric analysis. Significantly, further experiments revealed that knockdown of Bax expression prevented VPA and Ara‑C‑induced cell apoptosis in THP-1 cells. The results of our present study demonstrated the synergistic antileukemic effect of combined VPA and Ara‑C treatment in AML, and thus we suggest that VPA be used an alternative treatment for AML.

DNA Methylation and Chromatin Remodeling: The Blueprint of Cancer Epigenetics

Epigenetics deals with the interactions between genes and the immediate cellular environment. These interactions go a long way in shaping up each and every person's individuality. Further, reversibility of epigenetic interactions may offer a dynamic control over the expression of various critical genes. Thus, tweaking the epigenetic machinery may help cause or cure diseases, especially cancer. Therefore, cancer epigenetics, especially at a molecular level, needs to be scrutinised closely, as it could potentially serve as the future pharmaceutical goldmine against neoplastic diseases. However, in view of its rapidly enlarging scope of application, it has become difficult to keep abreast of scientific information coming out of various epigenetic studies directed against cancer. Using this review, we have attempted to shed light on two of the most important mechanisms implicated in cancer, that is, DNA (deoxyribonucleic acid) methylation and histone modifications, and their place in cancer pathogenesis. Further, we have attempted to take stock of the new epigenetic drugs that have emerged onto the market as well as those in the pipeline that offer hope in mankind's fight against cancer.

Quantitative Analysis of Global Proteome and Lysine Acetylome Reveal the Differential Impacts of VPA and SAHA on HL60 Cells

Valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA) are both HDAC inhibitors (HDACi). Previous studies indicated that both inhibitors show therapeutic effects on acute myeloid leukaemia (AML), while the differential impacts of the two different HDACi on AML treatment still remains elusive. In this study, using 3-plex SILAC based quantitative proteomics technique, anti-acetyllysine antibody based affinity enrichment, high resolution LC-MS/MS and intensive bioinformatic analysis, the quantitative proteome and acetylome in SAHA and VPA treated AML HL60 cells were extensively studied. In total, 5,775 proteins and 1,124 lysine acetylation sites were successfully obtained in response to VAP and SAHA treatment. It is found that VPA and SAHA treatment differently induced proteome and acetylome profiling in AML HL60 cells. This study revealed the differential impacts of VPA and SAHA on proteome/acetylome in AML cells, deepening our understanding of HDAC inhibitor mediated AML therapeutics.

Chronic myelomonocytic leukemia: Forefront of the field in 2015

Chronic myelomonocytic leukemia (CMML) includes components of both myelodysplastic syndrome and myeloproliferative neoplasms and is associated with a characteristic peripheral monocytosis. CMML is caused by the proliferation of an abnormal hematopoietic stem cell clone and may be influenced by microenvironmental changes. The disease is rare and has undergone revisions in its classification. We review the recent classification strategies as well as diagnostic criteria, focusing on CMML's genetic alterations and unique pathophysiology. We also discuss the latest molecular characterization of the disease, including how molecular factors affect current prognostic models. Finally, we focus on available treatment strategies, with a special emphasis on experimental and forthcoming therapies.

Deacetylase inhibitors for the treatment of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a diverse group of myeloid disorders, with patients being at risk for cytopenias or progression to acute myeloid leukemia. Several classification and prognostic scoring systems have been developed. High-intensity treatments are not appropriate for all patients. Two demethylating agents, azacitidine and decitabine, are approved for the treatment of MDS, although many patients do not derive long-term benefit and eventually progress. Deacetylase inhibitors have emerged as novel treatment candidates based on mechanistic rationale and preliminary data. This article reviews existing data on MDS treatment and discusses the rationale and potential for combination with deacetylase inhibitors.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Antagonism between granulocytic maturation and deacetylase inhibitor-induced apoptosis in acute promyelocytic leukaemia cells

Background:

Transcriptional repression is a key mechanism driving leukaemogenesis. In acute promyelocytic leukaemia (APL), the fusion protein promyelocytic leukaemia-retinoic acid receptor-α fusion (PML-RARα) recruits transcriptional repressors to myeloid differentiation genes. All-trans-retinoic acid (ATRA) induces the proteasomal degradation of PML-RARα and granulocytic differentiation. Histone deacetylases (HDACs) fall into four classes (I–IV) and contribute to the transcription block caused by PML-RARα.

Methods:

Immunoblot, flow cytometry, and May-Grünwald–Giemsa staining were used to analyze differentiation and induction of apoptosis.

Results:

A PML-RARα- and ATRA-dependent differentiation programme induces granulocytic maturation associated with an accumulation of the myeloid transcription factor CCAAT/enhancer binding protein (C/EBP)ɛ and of the surface protein CD11b. While this process protects APL cells from inhibitors of class I HDAC activity, inhibition of all Zinc-dependent HDACs (classes I, II, and IV) with the pan-HDACi (histone deacetylase inhibitor(s)) LBH589 induces apoptosis of immature and differentiated APL cells. LBH589 can eliminate C/EBPɛ and the mitochondrial apoptosis regulator B-cell lymphoma (BCL)-xL in immature and differentiated NB4 cells. Thus, BCL-xL and C/EBPɛ are newly identified molecular markers for the efficacy of HDACi against APL cells.

Conclusions:

Our results could explain the therapeutic limitations occurring with ATRA and class I HDACi combinations. Pro-apoptotic effects caused by pan-HDAC inhibition are not blunted by ATRA-induced differentiation and may provide a clinically interesting alternative.

Results of phase 2 randomized study of low-dose decitabine with or without valproic acid in patients with myelodysplastic syndrome and acute myelogenous leukemia

BACKGROUND

Hypomethylating agents have demonstrated activity in patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Preclinical and single-arm trials have suggested that adding histone deacetylase (HDAC) inhibitors may synergize the epigenetic modulation of hypomethylating agents and improve treatment results.

METHODS

The objective of this study was to evaluate the possible benefit of adding valproic acid, an HDAC inhibitor, to decitabine in the treatment of MDS and AML.

RESULTS

Patients with higher risk MDS or with AML aged ≥60 years were eligible. Patients were randomized in a Bayesian response-adaptive design to receive intravenous decitabine 20 mg/m(2) daily for 5 days or decitabine plus oral valproic acid 50 mg/kg daily for 7 days. Courses were repeated every 4 to 6 weeks. A maximum of 150 patients were to be treated. In total, 149 patients were treated on study, including 87 patients with MDS and 62 patients with AML. The median patient age was 69 years (range, 20-89 years; 42% of patients were aged ≥70 years). Overall, 34% of patients achieved complete remission, and 55% had an objective response. The median survival was 11.9 months, and the estimated 2-year survival rate was 27%. Outcome was not different with the addition of valproic acid to decitabine versus decitabine alone in relation to the rates of complete remission, overall response, or survival. Subset analyses did not demonstrate a benefit within the MDS or AML categories. Toxicities-particularly neurotoxicities-were higher with the combination arm.

CONCLUSIONS

Adding valproic acid to decitabine was not associated with improved outcome in the treatment of patients with MDS or elderly patients with AML. Future therapies may consider combining hypomethylating agents with better HDAC inhibitors and using different schedules.

A phase 2 study of belinostat (PXD101) in patients with relapsed or refractory acute myeloid leukemia or patients over the age of 60 with newly diagnosed acute myeloid leukemia: a California Cancer Consortium Study

We performed a phase II study of belinostat in patients with acute myeloid leukemia (AML). In this open label phase II study (NCT00357032), patients with relapsed/refractory AML, or newly diagnosed patients with AML over the age of 60, were eligible. Belinostat was administered intravenously (IV) at a dose of 1000 mg/m(2) daily on days 1-5 of a 21-day cycle until progression or unacceptable toxicity. The primary endpoint was complete response (CR) rate, with secondary endpoints of overall response rate (CR + partial response [PR]), time to treatment failure (TTF), overall survival and safety. Twelve eligible patients with AML were enrolled, of whom six had received at least one prior line of therapy. No CR or PR was seen. Four patients had stable disease for at least five cycles. Grade 3 non-hematological toxicities occurred in four patients. Belinostat as monotherapy has minimal single-agent effect in AML on this dosing schedule.

Valproic acid in combination with all-trans retinoic acid and intensive therapy for acute myeloid leukemia in older patients

The outcome of patients with acute myeloid leukemia who are older than 60 years has remained poor because of unfavorable disease characteristics and patient-related factors. The randomized German-Austrian AML Study Group 06-04 protocol was designed on the basis of in vitro synergistic effects of valproic acid (VPA) and all-trans retinoic acid with chemotherapy. Between 2004 and 2006, 186 patients were randomly assigned to receive 2 induction cycles with idarubicin, cytarabine, and all-trans retinoic acid either with VPA or without (STANDARD). In all patients, consolidation therapy was intended. Complete remission rates after induction tended to be lower in VPA compared with STANDARD (40% vs 52%; P = .14) as a result of a higher early death rate (26% vs 14%; P = .06). The main toxicities attributed to VPA were delayed hematologic recovery and grade 3/4 infections, observed predominantly during the second induction cycle. After restricting VPA to the first induction cycle and reducing the dose of idarubicin, these toxicities dropped to rates observed in STANDARD. After a median follow-up time of 84 months, event-free and overall survival were not different between the 2 groups (P = .95 and P = .57, respectively). However, relapse-free-survival was significantly superior in VPA compared with STANDARD (24.4% vs 6.4% at 5 years; P = .02). Explorative subset analyses revealed that AML with mutated Nucleophosmin 1 (NPM1) may particularly benefit from VPA. This trial was registered at www.clinicaltrials.gov as #NCT00151255.

Development of histone deacetylase inhibitors for cancer treatment

Histone deacetylase (HDAC) inhibitors are an exciting new addition to the arsenal of cancer therapeutics. The inhibition of HDAC enzymes by HDAC inhibitors shifts the balance between the deacetylation activity of HDAC enzymes and the acetylation activity of histone acetyltransferases, resulting in hyperacetylation of core histones. Exposure of cancer cells to HDAC inhibitors has been associated with a multitude of molecular and biological effects, ranging from transcriptional control, chromatin plasticity, protein-DNA interaction to cellular differentiation, growth arrest and apoptosis. In addition to the antitumor effects seen with HDAC inhibitors alone, these compounds may also potentiate cytotoxic agents or synergize with other targeted anticancer agents. The exact mechanism by which HDAC inhibitors cause cell death is still unclear and the specific roles of individual HDAC enzymes as therapeutic targets has not been established. However, emerging evidence suggests that the effects of HDAC inhibitors on tumor cells may not only depend on the specificity and selectivity of the HDAC inhibitor, but also on the expression patterns of HDAC enzymes in the tumor tissue. In this review, the recent advances in the understanding and clinical development of HDAC inhibitors, as well as their current role in cancer therapy, will be discussed.

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.

The gene signature in CCAAT-enhancer-binding protein α dysfunctional acute myeloid leukemia predicts responsiveness to histone deacetylase inhibitors

C/EPBα proteins, encoded by the CCAAT-enhancer-binding protein α gene, play a crucial role in granulocytic development, and defects in this transcription factor have been reported in acute myeloid leukemia. Here, we defined the C/EBPα signature characterized by a set of genes up-regulated upon C/EBPα activation. We analyzed expression of the C/EBPα signature in a cohort of 525 patients with acute myeloid leukemia and identified a subset characterized by low expression of this signature. We referred to this group of patients as the C/EBPα dysfunctional subset. Remarkably, a large percentage of samples harboring C/EBPα biallelic mutations clustered within this subset. We hypothesize that re-activation of the C/EBPα signature in the C/EBPα dysfunctional subset could have therapeutic potential. In search for small molecules able to reverse the low expression of the C/EBPα signature we applied the connectivity map. This analysis predicted positive connectivity between the C/EBPα activation signature and histone deacetylase inhibitors. We showed that these inhibitors reactivate expression of the C/EBPα signature and promote granulocytic differentiation of primary samples from the C/EBPα dysfunctional subset harboring biallelic C/EBPα mutations. Altogether, our study identifies histone deacetylase inhibitors as potential candidates for the treatment of certain leukemias characterized by down-regulation of the C/EBPα signature.

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).

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.

A focus on the preclinical development and clinical status of the histone deacetylase inhibitor, romidepsin (depsipeptide, Istodax(®))

Romidepsin (Istodax(®), depsipeptide, FR901228, FK228, NSC 630176) is a cyclic peptide, broad-spectrum, potent histone deacetylase inhibitor, with activity mainly against class I histone deacetylase enzymes. In this article, we give an overview of the putative modes of action, such as effects on gene expression, cell cycle regulation, apoptosis induction, DNA repair, protein acetylation and induction of autophagy. Romidepsin has mainly been developed as a therapy for hematologic malignancies and is approved by the US FDA for the treatment of cutaneous T-cell lymphomas. This report outlines the laboratory and clinical development of the compound as a single agent that has more recently been evaluated in combination with other anticancer therapeutics, such as proteasome inhibitors.

Epigenetics and miRNAs in the diagnosis and treatment of multiple sclerosis

The risk of developing multiple sclerosis (MS) depends on both genetic and environmental factors. Although the genetic susceptibility to MS has been investigated in great detail, reports describing epigenetic changes in the context of MS have only recently appeared. Epigenetic changes to DNA influence gene expression without altering the underlying DNA sequence. DNA methylation, histone modification, and miRNA-associated silencing are the three most important epigenetic mechanisms that influence gene expression. In this review, we summarize recent studies investigating epigenetic changes and miRNA as biomarkers for diagnosing MS and predicting disease course or treatment response. We also discuss how the current studies address important clinical questions and how future studies could be designed to best inform clinical practice.

Regulation of self-renewal in normal and cancer stem cells

Mutations can confer a selective advantage on specific cells, enabling them to go through the multistep process that leads to malignant transformation. The cancer stem cell hypothesis postulates that only a small pool of low-cycling stem-like cells is necessary and sufficient to originate and develop the disease. Normal and cancer stem cells share important functional similarities such as 'self-renewal' and differentiation potential. However, normal and cancer stem cells have different biological behaviours, mainly because of a profound deregulation of self-renewal capability in cancer stem cells. Differences in mode of division, cell-cycle properties, replicative potential and handling of DNA damage, in addition to the activation/inactivation of cancer-specific molecular pathways confer on cancer stem cells a malignant phenotype. In the last decade, much effort has been devoted to unravel the complex dynamics underlying cancer stem cell-specific characteristics. However, further studies are required to identify cancer stem cell-specific markers and targets that can help to confirm the cancer stem cell hypothesis and develop novel cancer stem cell-based therapeutic approaches.

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.

Understanding histone deacetylases in the cancer development and treatment: an epigenetic perspective of cancer chemotherapy

Cancer is a pathologic condition that involves genetic and epigenetic events culminating in neoplastic transformation. Alteration in epigenetic events that regulate the transcriptional activity of genes associated with various signaling pathways can influence multiple stages of tumorigenesis. In cancer cells, an imbalance often exists between histone acetyl transferase and histone deacetylase (HDAC) activities, and current research focuses actively on seeking competitive HDAC inhibitors (HDACi) for chemotherapeutic intervention. HDACi are proving useful for cancer prevention and therapy by virtue of their ability to reactivate the expression of epigenetically silenced genes, including those involved in differentiation, cell cycle regulation, apoptosis, angiogenesis, invasion, and metastasis. Furthermore, epidemiological studies suggest that different diets such as intake of cruciferous vegetables may lower the risk of different cancers, and there is growing interest in identifying the specific chemoprotective constituents and mechanistic insights of their action. Interestingly, it has been observed that cancer cells are more sensitive than nontransformed cells to apoptotic induction by some HDACi. Although the mechanistic basis for this sensitivity is unclear, yet HDACi have emerged as important epigenetic target for single and combinatorial chemotherapy. HDACi derived from diverse sources such as microbial, dietary, and synthetic increase acetylation level of cells and bring about anti-proliferative and apoptotic effects specific to cancer cells by way of their role in cell cycle regulation and expression of epigenetically silenced genes.

Epigenetic-based therapies in cancer: progress to date

Epigenetic gene silencing is a hallmark of cancer cells. Two important types of epigenetic changes are DNA methylation and histone modification. These modifications are catalysed by DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), resulting in chromatin structure changes and gene inactivation. Interestingly, inhibition of these enzymes is known to induce differentiation or apoptosis of cancer cells. Therefore, DNMTs and HDACs have become attractive therapeutic targets. In recent years, many different DNMT and HDAC inhibitors have been developed, and multiple molecular mechanisms through which these agents exert anti-cancer effects have been identified. While a large number of clinical trials are ongoing, hypomethylating agents and HDAC inhibitors seem to be promising for treating several types of cancer. Moreover, developing effective strategies of combining epigenetic therapy with conventional chemotherapy will be one of the major challenges in the future. We briefly review current advances in epigenetic therapies with a focus on recently reported clinical trials.

Valproic acid induces differentiation and transient tumor regression, but spares leukemia-initiating activity in mouse models of APL

Aberrant histone acetylation was physiopathologically associated with the development of acute myeloid leukemias (AMLs). Reversal of histone deacetylation by histone deacetylase inhibitor (HDACis) activates a cell death program that allows tumor regression in mouse models of AMLs. We have used several models of PML-RARA-driven acute promyelocytic leukemias (APLs) to analyze the in vivo effects of valproic acid, a well-characterized HDACis. Valproic acid (VPA)-induced rapid tumor regression and sharply prolonged survival. However, discontinuation of treatment was associated to an immediate relapse. In vivo, as well as ex vivo, VPA-induced terminal granulocytic differentiation. Yet, despite full differentiation, leukemia-initiating cell (LIC) activity was actually enhanced by VPA treatment. In contrast to all-trans retinoic acid (ATRA) or arsenic, VPA did not degrade PML-RARA. However, in combination with ATRA, VPA synergized for PML-RARA degradation and LIC eradication in vivo. Our studies indicate that VPA triggers differentiation, but spares LIC activity, further uncouple differentiation from APL clearance and stress the importance of PML-RARA degradation in APL cure.

Valproic acid triggers differentiation and apoptosis in AML1/ETO-positive leukemic cells specifically

Valproic acid (VPA) has extensive effects on leukemic blasts through its inhibition of histone deacetylases. The main goal of this study was to identify the subgroup of patients who may benefit most from VPA treatment. We examined the significance of t(8;21) chromosomal aberration for VPA treatment response among acute myeloid leukemia (AML) patients by direct comparison of AML1/ETO-negative vs. positive leukemic cell-lines as well as bone marrow blasts from AML patients. In t(8;21) AML, leukemogenesis is supposed to be induced via aberrant recruitment of histone deacetylases. AML cell lines of different genotypes (Kasumi-1, Kasumi-6, MV4;11, K562) and diagnostic bone marrow samples from patients were treated with VPA. VPA induced apoptosis in AML1/ETO-positive and MLL-AF4-positive cells in a dose-dependent manner. Differentiation, as indicated by changes in immunophenotype, was observed only in AML1/ETO-positive cells. VPA increased the expression of AML1 target genes - PU.1, C/EBPa, BPI and IGFBP7 only in AML1/ETO-positive cells. This AML1/ETO-specific effect was confirmed also using patient blasts isolated at the time of diagnosis. AML1/ETO-positive leukemia shows specific mechanism of VPA residing from differentiation followed by apoptosis that is accompanied by an increase in the expression of repressed AML1 target genes. Our data suggest that AML1/ETO-positive patients might derive the greatest benefit from VPA treatment.

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.

Phase 2 clinical trial of 5-azacitidine, valproic acid, and all-trans retinoic acid in patients with high-risk acute myeloid leukemia or myelodysplastic syndrome

In this Phase 2 study, we evaluated the efficacy of combination of 5-azacitidine (AZA), valproic acid (VPA), and all-trans retinoic acid (ATRA) in patients with high-risk acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Treatment consisted of six cycles of AZA and VPA for 7 days, followed by ATRA for 21 days. Sixty-five patients were enrolled (median age, 72 years; 55 AML including 13 relapsed/refractory patients, 10 MDS; 30 unfavorable karyotypes). Best responses included 14 CR and 3 PR (26%), 75% of the responders and 36% of the non-responders achieving an erythroid response. Median overall survival (OS) was 12.4 months. Untreated patients had a longer OS than relapsed/refractory patients. In patients who fulfilled the 6 planned cycles, OS did not appear to depend on CR/PR achievement, suggesting that stable disease while on-treatment would be a surrogate for survival with this approach. During therapy, early platelet response and demethylation of the FZD9, ALOX12, HPN, and CALCA genes were associated with clinical response. Finally, there was no evidence for the restoration of an ATRA-induced differentiation during therapy. Epigenetic modulation deserves prospective comparisons to conventional care in patients with high-risk AML, at least in those presenting previously untreated disease and low blast count.

Myelodysplastic syndrome and histone deacetylase inhibitors: "to be or not to be acetylated"?

Myelodysplastic syndrome (MDS) represents a heterogeneous group of diseases with clonal proliferation, bone marrow failure and increasing risk of transformation into an acute myeloid leukaemia. Structured guidelines are developed for selective therapy based on prognostic subgroups, age, and performance status. Although many driving forces of disease phenotype and biology are described, the complete and possibly interacting pathogenetic pathways still remain unclear. Epigenetic investigations of cancer and haematologic diseases like MDS give new insights into the pathogenesis of this complex disease. Modifications of DNA or histones via methylation or acetylation lead to gene silencing and altered physiology relevant for MDS. First clinical trials give evidence that patients with MDS could benefit from epigenetic treatment with, for example, DNA methyl transferase inhibitors (DNMTi) or histone deacetylase inhibitors (HDACi). Nevertheless, many issues of HDACi remain incompletely understood and pose clinical and translational challenges. In this paper, major aspects of MDS, MDS-associated epigenetics and the potential use of HDACi are discussed.