Combination of the histone deacetylase inhibitor valproic acid with oral hydroxyurea or 6-mercaptopurin can be safe and effective in patients with advanced acute myeloid leukaemia--a report of five cases

Synergistic therapeutics: Co-targeting histone deacetylases and ribonucleotide reductase for enhanced cancer treatment

The development of cancer is influenced by several variables, including altered protein expression, and signaling pathways. Cancers are inherently heterogeneous and exhibit genetic and epigenetic aberrations; therefore, developing therapies that act on numerous biological targets is encouraged. To achieve this, two approaches are employed: combination therapy and dual/multiple targeting chemotherapeutics. Two enzymes, histone deacetylases (HDACs) and ribonucleotide reductase (RR), are crucial for several biological functions, including replication and repair of DNA, division of cells, transcription of genes, etc. However, it has been noted that different cancers exhibit abnormal functions of these enzymes. Potent inhibitors for each of these proteins have been extensively researched. Many medications based on these inhibitors have been successfully food and drug administration (FDA) approved, and the majority are undergoing various stages of clinical testing. This review discusses various studies of HDAC and RR inhibitors in combination therapy and dual-targeting chemotherapeutics.

Therapeutic Use of Valproic Acid and All-Trans Retinoic Acid in Acute Myeloid Leukemia-Literature Review and Discussion of Possible Use in Relapse after Allogeneic Stem Cell Transplantation

Even though allogeneic stem cell transplantation is the most intensive treatment for acute myeloid leukemia (AML), chemo-resistant leukemia relapse is still one of the most common causes of death for these patients, as is transplant-related mortality, i.e., graft versus host disease, infections, and organ damage. These relapse patients are not always candidates for additional intensive therapy or re-transplantation, and many of them have decreased quality of life and shortened expected survival. The efficiency of azacitidine for treatment of posttransplant AML relapse has been documented in several clinical trials. Valproic acid is an antiepileptic fatty acid that exerts antileukemic activity through histone deacetylase inhibition. The combination of valproic acid and all-trans retinoic acid (ATRA) is well tolerated even by unfit or elderly AML patients, and low-toxicity chemotherapy (e.g., azacitidine) can be added to this combination. The triple combination of azacitidine, valproic acid, and ATRA may therefore represent a low-intensity and low-toxicity alternative for these patients. In the present review, we review and discuss the general experience with valproic acid/ATRA in AML therapy and we discuss its possible use in low-intensity/toxicity treatment of post-allotransplant AML relapse. Our discussion is further illustrated by four case reports where combined treatments with sequential azacitidine/hydroxyurea, valproic acid, and ATRA were used.

HDAC Inhibitors in Acute Myeloid Leukemia

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

Disease-stabilizing treatment based on all-trans retinoic acid and valproic acid in acute myeloid leukemia - identification of responders by gene expression profiling of pretreatment leukemic cells

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive malignancy only cured by intensive therapy. However, many elderly and unfit patients cannot receive such treatment due to an unacceptable risk of treatment-related morbidity and mortality. Disease-stabilizing therapy is then the only possible strategy, one alternative being treatment based on all-trans retinoic acid (ATRA) combined with the histone deacetylase inhibitor valproic acid and possibly low-toxicity conventional chemotherapy.

METHODS

Primary AML cells were derived from 43 patients included in two clinical studies of treatment based on ATRA, valproic acid and theophyllamine; low toxicity chemotherapy (low-dose cytarabine, hydroxyurea, 6-mercaptopurin) was also allowed. Pretreatment leukemic cells were analyzed by mutation profiling of 54 genes frequently mutated in myeloid malignancies and by global gene expression profiling before and during in vivo treatment.

RESULTS

Patients were classified as responders and non-responders to the treatment, however response to treatment showed no significant associations with karyotype or mutational profiles. Significance analysis of microarray (SAM) showed that responders and non-responders significantly differed with regard to the expression of 179 different genes. The differentially expressed genes encoding proteins with a known function were further classified based on the PANTHER (protein annotation through evolutionary relationship) classification system. The identified genes encoded proteins that are involved in several important biological functions, but a main subset of the genes were important for transcriptional regulation. These pretherapy differences in gene expression were largely maintained during treatment. Our analyses of primary AML cells during in vivo treatment suggest that ATRA modulates HOX activity (i.e. decreased expression of HOXA3, HOXA4 and HOXA5 and their regulator PBX3), but altered function of DNA methyl transferase 3A (DNMT3A) and G-protein coupled receptor signaling may also contribute to the effect of the overall treatment.

CONCLUSIONS

Responders and non-responders to AML stabilizing treatment based on ATRA and valproic acid differ in the pretreatment transcriptional regulation of their leukemic cells, and these differences may be important for the clinical effect of this treatment.

TRIAL REGISTRATIONS

ClinicalTrials.gov no. NCT00175812 ; EudraCT no. 2004-001663-22, registered September 9, 2005 and ClinicalTrials.gov no. NCT00995332 ; EudraCT no. 2007-2007-001995-36, registered October 14, 2009.

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.

Effects of cytarabine on activation of human T cells - cytarabine has concentration-dependent effects that are modulated both by valproic acid and all-trans retinoic acid

Background

Cytarabine is used in the treatment of acute myeloid leukemia (AML). Low-dose cytarabine can be combined with valproic acid and all-trans retinoic acid (ATRA) as AML-stabilizing treatment. We have investigated the possible risk of immunotoxicity by this combination. We examined the effects of cytarabine combined with valproic acid and ATRA on in vitro activated human T cells, and we tested cytarabine at concentrations reached during in vivo treatment with high doses, conventional doses and low doses.

Methods

T cells derived from blood donors were activated in vitro in cell culture medium alone or supplemented with ATRA (1 μM), valproic acid (500 or 1000 μM) or cytarabine (0.01-44 μM). Cell characteristics were assessed by flow cytometry. Supernatants were analyzed for cytokines by ELISA or Luminex. Effects on primary human AML cell viability and proliferation of low-dose cytarabine (0.01-0.5 μM) were also assessed. Statistical tests include ANOVA and Cluster analyses.

Results

Only cytarabine 44 μM had both antiproliferative and proapoptotic effects. Additionally, this concentration increased the CD4:CD8 T cell ratio, prolonged the expression of the CD69 activation marker, inhibited CD95L and heat shock protein (HSP) 90 release, and decreased the release of several cytokines. In contrast, the lowest concentrations (0.35 and 0.01 μM) did not have or showed minor antiproliferative or cytotoxic effects, did not alter activation marker expression (CD38, CD69) or the release of CD95L and HSP90, but inhibited the release of certain T cell cytokines. Even when these lower cytarabine concentrations were combined with ATRA and/or valproic acid there was still no or minor effects on T cell viability. However, these combinations had strong antiproliferative effects, the expression of both CD38 and CD69 was altered and there was a stronger inhibition of the release of FasL, HSP90 as well as several cytokines. Cytarabine (0.01-0.05 μM) showed a dose-dependent antiproliferative effect on AML cells, and in contrast to the T cells this effect reached statistical significance even at 0.01 μM.

Conclusions

Even low levels of cytarabine, and especially when combined with ATRA and valproic acid, can decrease T cell viability, alter activation-induced membrane-molecule expression and decrease the cytokine release.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-015-0012-2) contains supplementary material, which is available to authorized users.

Therapeutic targeting the cell division cycle 25 (CDC25) phosphatases in human acute myeloid leukemia--the possibility to target several kinases through inhibition of the various CDC25 isoforms

The cell division cycle 25 (CDC25) phosphatases include CDC25A, CDC25B and CDC25C. These three molecules are important regulators of several steps in the cell cycle, including the activation of various cyclin-dependent kinases (CDKs). CDC25s seem to have a role in the development of several human malignancies, including acute myeloid leukemia (AML); and CDC25 inhibition is therefore considered as a possible anticancer strategy. Firstly, upregulation of CDC25A can enhance cell proliferation and the expression seems to be controlled through PI3K-Akt-mTOR signaling, a pathway possibly mediating chemoresistance in human AML. Loss of CDC25A is also important for the cell cycle arrest caused by differentiation induction of malignant hematopoietic cells. Secondly, high CDC25B expression is associated with resistance against the antiproliferative effect of PI3K-Akt-mTOR inhibitors in primary human AML cells, and inhibition of this isoform seems to reduce AML cell line proliferation through effects on NFκB and p300. Finally, CDC25C seems important for the phenotype of AML cells at least for a subset of patients. Many of the identified CDC25 inhibitors show cross-reactivity among the three CDC25 isoforms. Thus, by using such cross-reactive inhibitors it may become possible to inhibit several molecular events in the regulation of cell cycle progression and even cytoplasmic signaling, including activation of several CDKs, through the use of a single drug. Such combined strategies will probably be an advantage in human cancer treatment.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

In Vitro Characterization of Valproic Acid, ATRA, and Cytarabine Used for Disease-Stabilization in Human Acute Myeloid Leukemia: Antiproliferative Effects of Drugs on Endothelial and Osteoblastic Cells and Altered Release of Angioregulatory Mediators by Endothelial Cells

The combined use of the histone deacetylase inhibitor valproic acid (VPA), the retinoic acid receptor- α agonist all-trans retinoic acid (ATRA), and the deoxyribonucleic acid polymerase- α inhibitor cytarabine (Ara-C) is now considered for disease-stabilizing treatment of acute myeloid leukemia (AML). Leukemogenesis and leukemia cell chemoresistance seem to be supported by neighbouring stromal cells in the bone marrow, and we have therefore investigated the effects of these drugs on primary human endothelial cells and the osteoblastic Cal72 cell line. The results show that VPA and Ara-C have antiproliferative effects, and the antiproliferative/cytotoxic effect of Ara-C was seen at low concentrations corresponding to serum levels found during low-dose in vivo treatment. Furthermore, in functional assays of endothelial migration and tube formation VPA elicited an antiangiogenic effect, whereas ATRA elicited a proangiogenic effect. Finally, VPA and ATRA altered the endothelial cell release of angiogenic mediators; ATRA increased levels of CXCL8, PDGF-AA, and VEGF-D, while VPA decreased VEGF-D and PDGF-AA/BB levels and both drugs reduced MMP-2 levels. Several of these mediators can enhance AML cell proliferation and/or are involved in AML-induced bone marrow angiogenesis, and direct pharmacological effects on stromal cells may thus indirectly contribute to the overall antileukemic activity of this triple drug combination.

The activity of valproic Acid in the treatment of refractory hyperleukocytosis in a child with acute lymphoblastic leukemia

Hyperleukocytosis may be associated with an early morbidity and mortality due to leukostasis. Cytoreductive therapies-such as steroids, hydroxiurea, exchange transfusion, and leukapheresis-have been used for the prevention of leukostasis. Herein, the valproic acid used for the treatment of the hyperleukocytosis did not respond to known therapies in a child; lymphoblastic lymphoma developed bone marrow relapse under the treatment is discussed.

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.

Panobinostat in lymphoid and myeloid malignancies

INTRODUCTION

Histone deacetylase inhibitors (HDACIs) are a class of antineoplastic agent targeting the epigenome, specifically chromatin remodelling, resulting in modulation of genes responsible for apoptosis and cell cycle regulation, and also hyperacetylation of many non-histone proteins. Panobinostat is a potent pan-histone inhibitor of HDAC enzymes implicated in cancer development and progression. Activity has been demonstrated in hematological diseases, such as cutaneous T-cell lymphoma (CTCL), Hodgkin lymphoma (HL), myeloma and myeloid malignancies.

AREAS COVERED

We discuss basic pharmacology, followed by early phase trial results and analyse recent large Phase II trials in HL, CTCL, myeloid malignancies and Waldenstrom's macroglobulinemia (WM). Future directions for drug development including potential predictive biomarkers are considered.

EXPERT OPINION

The results of Phase II trials prove that oral panobinostat is deliverable with dosing regimens of three times per week, either weekly or biweekly. The major hematologic side-effect of myelosuppression, in particular thrombocytopenia, is transient and manageable, as are the non-hematologic side-effects. Encouraging responses are observed in HL, CTCL, myelofibrosis and WM. The safety and efficacy results from studies of combination therapy with azacitidine in acute myeloid leukemia and myelodysplastic syndromes suggest that this agent may find a place in the management of a range of hematologic cancers.

Inhibition of Mammalian target of rapamycin in human acute myeloid leukemia cells has diverse effects that depend on the environmental in vitro stress

Effects of the mTOR inhibitor rapamycin were characterized on in vitro cultured primary human acute myeloid leukemia (AML) cells and five AML cell lines. Constitutive mTOR activation seemed to be a general characteristic of primary AML cells. Increased cellular stress induced by serum deprivation increased both mTOR signaling, lysosomal acidity, and in vitro apoptosis, where lysosomal acidity/apoptosis were independent of increased mTOR signaling. Rapamycin had antiproliferative and proapoptotic effects only for a subset of patients. Proapoptotic effect was detected for AML cell lines only in the presence of serum. Combination of rapamycin with valproic acid, all-trans retinoic acid (ATRA), and NF-κB inhibitors showed no interference with constitutive mTOR activation and mTOR inhibitory effect of rapamycin and no additional proapoptotic effect compared to rapamycin alone. In contrast, dual inhibition of the PI3K-Akt-mTOR pathway by rapamycin plus a PI3K inhibitor induced new functional effects that did not simply reflect a summary of single drug effects. To conclude, (i) pharmacological characterization of PI3K-Akt-mTOR inhibitors requires carefully standardized experimental models, (ii) rapamycin effects differ between patients, and (iii) combined targeting of different steps in this pathway should be further investigated whereas combination of rapamycin with valproic acid, ATRA, or NF-κB inhibitors seems less promising.

Analyzing gene expression profile in K562 cells exposed to sodium valproate using microarray combined with the connectivity map database

To explore the mechanism underlying antileukaemia effect of sodium valproate, the growth and survival of the K562 cell line were investigated. Global profiles of gene expression in K562 cells exposed to sodium valproate were assessed and validated. The differentially expressed genes identified were further used to query the connectivity map database to retrieve a ranked list of compounds that act on the same intracellular targets as sodium valproate. A significant increase in cell apoptosis and a change in gene expression profile were observed in valproate-exposed K562 cells. The significant enrichment analysis of gene ontology terms for the differentially expressed genes showed that these genes were involved in many important biological processes. Eight differentially expressed genes involved in apoptosis were verified by quantitative real-time PCR. The connectivity map analysis showed gene expression profile in K562 cells exposed to sodium valproate was most similar to that of HDACi and PI3K inhibitors, suggesting that sodium valproate might exert antileukaemic action by inhibiting HDAC as well as inhibiting PI3K pathway. In conclusion, our data might provide clues to elucidate the molecular and therapeutic potential of VPA in leukaemia treatment, and the connectivity map is a useful tool for exploring the molecular mechanism of drug action.

Using an exon microarray to identify a global profile of gene expression and alternative splicing in K562 cells exposed to sodium valproate

To investigate the effect of valproate treatment on the K562 cell line, a model for chronic myelogenous leukaemia, the growth and survival of the K562 cell line were investigated using the Annexin-V/PI dual staining method, and global profiles of gene expression and alternative splicing in K562 cells were assessed using exon microarrays. A significant increase in cell apoptosis was observed in valproate-exposed K562 cells using flow cytometry. A total of 628 transcripts were identified as being significantly differentially expressed. The number of genes demonstrating increased expression levels was greater than the number of genes demonstrating decreased expression levels (445 genes vs. 183 genes, respectively). The significant enrichment analysis of GO terms for the differentially expressed genes revealed that these genes are involved in many important biological processes such as apoptosis. Six of the genes observed to be differentially expressed that might be involved in apoptosis were selected to undergo qRT-PCR validation. In total, 198 candidates of alternative splicing variants were identified. Among them, three alternative splicing events were selected for validation, and CBLC and TBX1 were confirmed to be alternatively spliced by semi-nested PCR. In conclusion, valproate exposure facilitated cell apoptosis, altered mRNA expression and alternative splicing events in the K562 cell line.

Heat shock protein 90 inhibition results in altered downstream signaling of mutant KIT and exerts synergistic effects on Kasumi-1 cells when combining with histone deacetylase inhibitor

KIT mutations may be associated with a poor prognosis in t(8;21) AML. Heat shock protein 90 (Hsp90) is a molecular chaperone frequently used by cancer cells to stabilize mutant oncoproteins. Inhibition of Hsp90 by 17-allylamino-17-demethoxygeldanamycin (17-AAG) disrupted downstream signaling pathways of mutant KIT in Kasumi-1 cells. AML1-ETO fusion gene and mutated KIT act as "two-hit" factors in Kasumi-1 cells. Histone deacetylation (HDAC) inhibitors sodium phenylbutyrate (PB) and valproic acid (VPA) block AML1-ETO. Co-treatment with 17-AAG and PB or 17-AAG and VPA resulted in a synergistic effect in Kasumi-1 cells. Our results confirmed that Hsp90 and mutated KIT were valid molecular targets in the therapy of AML.