Increase in Ara-C cytotoxicity in the presence of valproate, a histone deacetylase inhibitor, is associated with the concurrent expression of cyclin D1 and p27Kip1 in acute myeloblastic leukemia cells

SKLB316, a novel small-molecule inhibitor of cell-cycle progression, induces G2/M phase arrest and apoptosis in vitro and inhibits tumor growth in vivo

Benzothiazole derivatives have received considerable attentions for their potencies in cancer therapy. In the present study, we reported that SKLB316, a novel synthesized benzothiazole derivative, exhibits activities to inhibit colorectal and pancreatic cancer in vitro and in vivo by inducing G2/M cell cycle arrest and apoptosis. In vitro, it exhibited significant anti-proliferative activities against human cancer cells derived from different histotypes including the colorectal cancer cell line HCT116 and pancreatic cancer cell line CFPAC-1. We chose these cell lines to study the possible anti-tumor mechanism because they are sensitive to SKLB316 treatment. Flow cytometry assays showed that SKLB316 could induce G2/M cell cycle arrest. Mechanistically, SKLB316 could decrease the activities of cdc2/cyclin B1 complex, including decreasing the synthesis of cyclin B1, cdc2 and cdc25c, while accumulating the levels of phosphorylated cdc2 (Tyr15) and checkpoint kinase 2. SKLB316 could also decrease the level of cyclin E and A2. Moreover, SKLB316 could induce cancer cell apoptosis, which was associated with activation of caspase 9, downregulation of Bcl-2 and upregulation of Bax. SKLB316 could also decrease the mitochondrial membrane potential and induce the generation of reactive oxygen species in cells. The results implied that SKLB316 may induce apoptosis via the mitochondria-mediated apoptotic pathway. Moreover, SKLB316 could suppress the growth of established colorectal and pancreatic cancer tumors in nude mice without causing obvious side effects. TUNEL assays confirmed that SKLB316 could also induce tumor cell apoptosis in vivo. Taken together, these findings demonstrate the potential value of SKLB316 as a novel anti-tumor drug candidate.

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.

Interpreting clinical assays for histone deacetylase inhibitors

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

The role of HDACs inhibitors in childhood and adolescence acute leukemias

Acute leukemia is the most common type of childhood and adolescence cancer, characterized by clonal proliferation of variably differentiated myeloid or lymphoid precursors. Recent insights into the molecular pathogenesis of leukemia have shown that epigenetic modifications, such as deacetylation of histones and DNA methylation, play crucial roles in leukemogenesis, by transcriptional silencing of critical genes. Histone deacetylases (HDACs) are potential targets in the treatment of leukaemia, and, as a consequence, inhibitors of HDACs (HDIs) are being studied for therapeutic purposes. HDIs promote or enhance several different anticancer mechanisms, such as apoptosis, cell cycle arrest, and cellular differentiation and, therefore, are in evidence as promising treatment for children and adolescents with acute leukemia, in monotherapy or in association with other anticancer drugs. Here we review the main preclinical and clinical studies regarding the use of HDIs in treating childhood and adolescence leukemia.

Combination of sapacitabine and HDAC inhibitors stimulates cell death in AML and other tumour types

Background:

Alternative treatments are needed for elderly patients with acute myeloid leukaemia, as the disease prognosis is poor and the current treatment is unsuitable for many patients.

Methods:

In this study, we investigated whether combining the nucleoside analogue sapacitabine with histone deacetylase (HDAC) inhibitors could be an effective treatment. Synergy and mode-of-action analysis were studied in cultured cell lines and the efficacy of the combination was confirmed in a xenograft model.

Results:

CNDAC (1-(2-C-cyano-2-deoxy-β-D-arabino-pentofuranosyl)-cytosine), the active component of sapacitabine, synergised with vorinostat in cell lines derived from a range of tumour types. Synergy was not dependent on a specific sequence of drug administration and was also observed when CNDAC was combined with an alternative HDAC inhibitor, valproate. Flow cytometry and western blot analysis confirmed that the combination induced a significant increase in apoptosis. Mode-of-action analysis detected changes in Bcl-xl, Mcl-1, Noxa, Bid and Bim, which are all regulators of the apoptotic process. The sapacitabine/vorinostat combination demonstrated significant benefit compared with the single-agent treatments in an MV4-11 xenograft, in the absence of any observed toxicity.

Conclusion:

Sapacitabine and HDAC inhibitors are an effective drug combination that is worthy of clinical exploration.

Mechanisms of synergistic antileukemic interactions between valproic acid and cytarabine in pediatric acute myeloid leukemia

PURPOSE

To determine the possibility of synergistic antileukemic activity and the underlying molecular mechanisms associated with cytarabine combined with valproic acid (VPA; a histone deacetylase inhibitor and a Food and Drug Administration-licensed drug for treating both children and adults with epilepsy) in pediatric acute myeloid leukemia (AML).

EXPERIMENTAL DESIGN

The type and extent of antileukemic interactions between cytarabine and VPA in clinically relevant pediatric AML cell lines and diagnostic blasts from children with AML were determined by MTT assays and standard isobologram analyses. The effects of cytarabine and VPA on apoptosis and cell cycle distributions were determined by flow cytometry analysis and caspase enzymatic assays. The effects of the two agents on DNA damage and Bcl-2 family proteins were determined by Western blotting.

RESULTS

We showed synergistic antileukemic activities between cytarabine and VPA in four pediatric AML cell lines and nine diagnostic AML blast samples. t(8;21) AML blasts were significantly more sensitive to VPA and showed far greater sensitivities to combined cytarabine and VPA than non-t(8;21) AML cases. Cytarabine and VPA cooperatively induced DNA double-strand breaks, reflected in induction of γH2AX and apoptosis, accompanied by activation of caspase-9 and caspase-3. Further, VPA induced Bim expression and short hairpin RNA knockdown of Bim resulted in significantly decreased apoptosis induced by cytarabine and by cytarabine plus VPA.

CONCLUSIONS

Our results establish global synergistic antileukemic activity of combined VPA and cytarabine in pediatric AML and provide compelling evidence to support the use of VPA in the treatment of children with this deadly disease.

Histone deacetylase inhibitors: a new perspective for the treatment of leukemia

Histone deacetylase inhibitors (HDIs) promote or enhance several different anticancer mechanisms and therefore are in evidence as potential antileukemia agents. Studies on leukemia have provided examples for their functional implications in cancer development and progression, as well as their relevance for therapeutic targeting. A number of HDIs have been tested in clinical trials and have been proven safe with significant clinical activity. The use of HDIs in association with other molecules, such as classical chemotherapeutic drugs and DNA demethylating agents, has been implied as a promising treatment alternative for leukemia patients in the future. Here we describe the histone deacetylase inhibitors that have been tested in clinical trials for the treatment of leukemia and lymphoma. We conclude that further clinical trials involving a broader number of HDIs used either alone or in combination with other agents are needed to consolidate the use of these epigenetic modulators on leukemia therapy.

Antileukemic activity of valproic acid in chronic lymphocytic leukemia B cells defined by microarray analysis

Epigenetic code modifications by histone deacetylase inhibitors have recently been proposed as potential new therapies for hematological malignancies. Chronic lymphocytic leukemia (CLL) remains incurable despite the introduction of new treatments. CLL B cells are characterized by an apoptosis defect rather than excessive proliferation, but proliferation centers have been found in organs such as the bone marrow and lymph nodes. In this study, we analyzed gene expression modifications in CLL B cells after treatment with valproic acid (VPA), a well-tolerated anti-epileptic drug with HDAC inhibitory activity. CLL B cells obtained from 14 patients were treated in vitro with a concentration of 1 mM VPA for 4 h. VPA effects on gene expression were thereafter studied using Affymetrix technology, and some identified genes were validated by real-time PCR and western blot. We observed that VPA induced apoptosis by downregulating several anti-apoptotic genes and by upregulating pro-apoptotic genes. Furthermore, VPA significantly increased chemosensitivity to fludarabine, flavopiridol, bortezomib, thalidomide and lenalidomide. VPA inhibited the proliferation of CpG/IL2-stimulated CLL B cells and modulated many cell cycle messenger RNAs. In conclusion, exposure of CLL B cells to VPA induced apoptosis, potentiated chemotherapeutic agent effects and inhibited proliferation. These data strongly suggest the use of VPA in CLL treatment, particularly in combination with antileukemia agents.

Anti-leukemic activity of valproic acid and imatinib mesylate on human Ph+ ALL and CML cells in vitro

The armamentarium of anti-leukemic drugs has increased substantially since anti-leukemic activities were recently found for a variety of non-classical cytostatic drugs, among them the histone deacetylase (HDAC) inhibitor valproic acid (VPA). This study investigated the effect of VPA on proliferation and apoptosis of human Philadelphia chromosome-positive (Ph+) acute lymphatic (ALL) and chronic myeloid leukemia (CML) cells and on colony formation of human chronic-phase CML progenitor cells. Strong anti-proliferative and pro-apoptotic effects of VPA were observed on human ALL and CML cell lines at concentrations achievable in vivo. These effects were most pronounced in ALL cell lines as well as in primary ALL cells. Notably, VPA revealed enhanced activity with imatinib mesylate, nilotinib, the farnesyl transferase inhibitor SCH66336, interferon-alpha and cytosine arabinoside. VPA inhibited the growth of colony-forming cells from 12 Ph+ chronic-phase CML patients but also of those from normal healthy controls in a dose-dependent fashion. HDAC-inhibiting activity of VPA was confirmed on ALL and CML cells. In conclusion, VPA, whether alone or in combination with other non-classical anti-leukemic compounds, exerts significant anti-leukemic effects on human ALL and CML cells.

Emerging treatment strategies for acute myeloid leukemia (AML) in the elderly

Acute myeloid leukemia (AML) is more prevalent in older adults, with an incidence in the United States of 17.6 per 100,000 for those 65 years of age, compared with an incidence of 1.8 per 100,000 for those <65 years of age. While there have been improvements in survival during the last decade for younger patients, prognosis in elderly patients is still poor; approximately 50% achieve complete responses, but many of them relapse. With increasing age, more patients are suboptimal candidates for standard induction chemotherapy due to poor performance status, pre-existing myelodysplasia, unfavorable cytogenetics, treatment-related AML, multidrug resistance protein expression, and CD34 positivity, which are often characteristic of this patient population. In addition, the presence of comorbid conditions make many treatment options less tolerable for elderly patients. Several investigators have described subgroups showing no benefit after intensive treatment approaches in recent years. However, several novel agents have been developed to treat elderly AML patients. These include new chemotherapeutic agents, such as nucleoside analogs, as well as targeted therapies like farnesyltransferase inhibitors, tyrosine kinase inhibitors, epigenetic drugs, and antibodies. On the other hand new insights into the biology of the disease lead to a better understanding of its heterogeneity. Thus, with a variety of novel substances at hand it is increasingly important to introduce a risk-adapted approach for the optimal management of patients. This review will identify subgroups not likely to benefit from intensive chemotherapy and highlight the efficacy and tolerability of new agents in the treatment of AML.

Sodium butyrate enhances the cytotoxic effect of antineoplastic drugs in human lymphoblastic T-cells

Sodium butyrate (NaB), a potent histone deacetylase inhibitor, induces cell cycle arrest and apoptosis in malignant cells. We investigated the effects on cellular proliferation in vitro when combining NaB with antineoplastic drugs commonly used to treat leukemias. Our results demonstrate that NaB increases the cytotoxic effects of cytarabine and etoposide, but not of bleomycin, doxorubicin, vincristine or methotrexate. These data suggest that NaB is a promising adjuvant therapeutic agent for the treatment of lymphoblastic leukemias, and provides a basis for further studies in this field.

Valproic acid for the treatment of myeloid malignancies

Valproic acid (VPA) has been used as an anticonvulsant for decades. Recently, it was demonstrated that VPA also acts as a histone deacetylase inhibitor and induces differentiation and apoptosis in a variety of malignant cells in vitro. The effect of VPA on tumor cells differs according to cell type, degree of differentiation, and underlying genetic alterations. Clinical trials with VPA have focused on acute myeloid leukemia and the myelodysplastic syndromes. When it was used as monotherapy or in combination with all-trans retinoic acid, which synergizes in vitro, VPA achieved hematologic improvement in a subset of patients. Similar to other inhibitors of histone deacetylases, complete or partial remissions rarely were observed. In this report, the authors reviewed the in vitro and in vivo data obtained with VPA, and they considered possible combination regimens aimed at improving therapeutic efficacy.