The histone deacetylase (HDAC) inhibitor valproic acid as monotherapy or in combination with all-trans retinoic acid in patients with acute myeloid leukemia

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.

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.

Panobinostat enhances cytarabine and daunorubicin sensitivities in AML cells through suppressing the expression of BRCA1, CHK1, and Rad51

Acute myeloid leukemia (AML) remains a challenging disease to treat and urgently requires new therapies to improve its treatment outcome. In this study, we investigated the molecular mechanisms underlying the cooperative antileukemic activities of panobinostat and cytarabine or daunorubicin (DNR) in AML cell lines and diagnostic blast samples in vitro and in vivo. Panobinostat suppressed expression of BRCA1, CHK1, and RAD51 in AML cells in a dose-dependent manner. Further, panobinostat significantly increased cytarabine- or DNR-induced DNA double-strand breaks and apoptosis, and abrogated S and/or G2/M cell cycle checkpoints. Analogous results were obtained by shRNA knockdown of BRCA1, CHK1, or RAD51. Cotreatment of NOD-SCID-IL2Rγ^null mice bearing AML xenografts with panobinostat and cytarabine significantly increased survival compared to either cytarabine or panobinostat treatment alone. Additional studies revealed that panobinostat suppressed the expression of BRCA1, CHK1, and RAD51 through downregulation of E2F1 transcription factor. Our results establish a novel mechanism underlying the cooperative antileukemic activities of these drug combinations in which panobinostat suppresses expression of BRCA1, CHK1, and RAD51 to enhance cytarabine and daunorubicin sensitivities in AML cells.

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).

Novel insights into histone modifiers in adipogenesis

Recently, it has been progressively recognized that gene expression is regulated by histone methylation status, which is dynamically modulated by histone methyltransferases (HMTs) and histone demethylases (HDMs). In the past decade, many HMTs and HDMs were identified and their biological and biochemical functions have been characterized. As with other cells, several HMTs and HDMs are known to be indispensable for appropriate differentiation of adipocytes from mesenchymal stem cells. Phf2 is a recently identified dimethylated histone H3 lysine 9 (H3K9me2) demethylase that has a significant function in hepatocytes and macrophages in vitro; however, the in vivo significance of Phf2 remains unclear. To determine the physiological role of Phf2, we recently generated Phf2 knockout mice. Our analyses of these mice revealed that Phf2 has a positive role in adipogenesis by coactivating CEBPA, one of the master regulators of adipogenesis, through its demethylation activity toward H3K9me2. In this commentary, we discuss several remaining questions that underlie phenotypic abnormalities seen in our investigations of Phf2 knockout mice. These studies are related to novel functions of histone modifiers and may help identify new therapeutic targets for metabolic syndrome.

Panobinostat synergistically enhances the cytotoxic effects of cisplatin, doxorubicin or etoposide on high-risk neuroblastoma cells

High-risk neuroblastoma remains a therapeutic challenge with a long-term survival rate of less than 40%. Therefore, new agents are urgently needed to overcome chemotherapy resistance so as to improve the treatment outcome of this deadly disease. Histone deacetylase (HDAC) inhibitors (HDACIs) represent a novel class of anticancer drugs. Recent studies demonstrated that HDACIs can down-regulate the CHK1 pathway by which cancer cells can develop resistance to conventional chemotherapy drugs. This prompted our hypothesis that combining HDACIs with DNA damaging chemotherapeutic drugs for treating neuroblastoma would result in enhanced anti-tumor activities of these drugs. Treatment of high-risk neuroblastoma cell lines with a novel pan-HDACI, panobinostat (LBH589), resulted in dose-dependent growth arrest and apoptosis in 4 high-risk neuroblastoma cell lines. Further, the combination of panobinostat with cisplatin, doxorubicin, or etoposide resulted in highly synergistic antitumor interactions in the high-risk neuroblastoma cell lines, independent of the sequence of drug administration. This was accompanied by cooperative induction of apoptosis. Furthermore, panobinostat treatment resulted in substantial down-regulation of CHK1 and its downstream pathway and abrogation of the G2 cell cycle checkpoint. Synergistic antitumor interactions were also observed when the DNA damaging agents were combined with a CHK1-specific inhibitor, LY2603618. Contrary to panobinostat treatment, LY2603618 treatments neither resulted in abrogation of the G2 cell cycle checkpoint nor enhanced cisplatin, doxorubicin, or etoposide-induced apoptosis in the high-risk neuroblastoma cells. Surprisingly, LY2603618 treatments caused substantial down-regulation of total CDK1. Despite this discrepancy between panobinostat and LY2603618, our results indicate that suppression of the CHK1 pathway by panobinostat is at least partially responsible for the synergistic antitumor interactions between panobinostat and the DNA damaging agents in high-risk neuroblastoma cells. The results of this study provide a rationale for clinical evaluation of the combination of panobinostat and cisplatin, doxorubicin, or etoposide for treating children with high-risk neuroblastoma.

Inhibitory effect of valproic acid on bladder cancer in combination with chemotherapeutic agents in vitro and in vivo

Histone deacetylase inhibitors (HDACIs) are a promising class of drugs that act as antiproliferative agents by promoting differentiation and inducing apoptosis. Valproic acid (VPA) is an HDACI that has been widely used as an anti-convulsant and shows promise as a chemotherapeutic drug for a number of tumor cells. The present study aimed to investigate the inhibitory effect of VPA on the viability of bladder cancer cells and its synergistic effect with chemotherapeutic agents in vitro and in vivo. The cell viability of human bladder cancer cell lines following treatment with VPA and/or VPA in combination with mitomycin C, cisplatin (DDP) and adriamycin were determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Hoechst staining was used to observe the morphology of the apoptotic cells. Survivin protein and acetylated histone H3 levels were quantified using western blot analysis. The in vivo tumor growth inhibition of VPA was determined in rats with N-methyl-N-nitrosourea-induced bladder cancer. VPA significantly inhibited the growth of the bladder cancer cells in a concentration- and time-dependent manner. Furthermore, improved results were achieved for tumor inhibition when VPA was combined with chemotherapeutic agents in vitro and in vivo. Survivin expression decreased and acetylated histone H3 expression increased in the bladder cancer cells following the treatment with VPA. Intravesical injections of VPA were able to inhibit tumor progression when combined with DDP. In conclusion, VPA acts as an HDACI that has a direct anticancer effect and markedly enhances the action of several chemotherapy agents. VPA may sensitize bladder cancer to anticancer drugs by downregulating survivin expression.

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.

Whole-body pharmacokinetics of HDAC inhibitor drugs, butyric acid, valproic acid and 4-phenylbutyric acid measured with carbon-11 labeled analogs by PET

The fatty acids, n-butyric acid (BA), 4-phenylbutyric acid (PBA) and valproic acid (VPA, 2-propylpentanoic acid) have been used for many years in the treatment of a variety of CNS and peripheral organ diseases including cancer. New information that these drugs alter epigenetic processes through their inhibition of histone deacetylases (HDACs) has renewed interest in their biodistribution and pharmacokinetics and the relationship of these properties to their therapeutic and side effect profiles. In order to determine the pharmacokinetics and biodistribution of these drugs in primates, we synthesized their carbon-11 labeled analogues and performed dynamic positron emission tomography (PET) in six female baboons over 90 min. The carbon-11 labeled carboxylic acids were prepared by using (11)CO2 and the appropriate Grignard reagents. [(11)C]BA was metabolized rapidly (only 20% of the total carbon-11 in plasma was parent compound at 5 min post injection) whereas for VPA and PBA 98% and 85% of the radioactivity were the unmetabolized compound at 30 min after their administration respectively. The brain uptake of all three carboxylic acids was very low (<0.006%ID/cc, BA>VPA>PBA), which is consistent with the need for very high doses for therapeutic efficacy. Most of the radioactivity was excreted through the kidneys and accumulated in the bladder. However, the organ biodistribution between the drugs differed. [(11)C]BA showed relatively high uptake in spleen and pancreas whereas [(11)C]PBA showed high uptake in liver and heart. Notably, [(11)C]VPA showed exceptionally high heart uptake possibly due to its involvement in lipid metabolism. The unique biodistribution of each of these drugs may be of relevance in understanding their therapeutic and side effect profile including their teratogenic effects.

Novel therapies for children with acute myeloid leukaemia

Significant improvements in survival for children with acute myeloid leukaemia (AML) have been made over the past three decades, with overall survival rates now approximately 60-70%. However, these gains can be largely attributed to more intensive use of conventional cytotoxics made possible by advances in supportive care, and although over 90% of children achieve remission with frontline therapy, approximately one third in current protocols relapse. Furthermore, late effects of therapy cause significant morbidity for many survivors. Novel therapies are therefore desperately needed. Early-phase paediatric trials of several new agents such as clofarabine, sorafenib and gemtuzumab ozogamicin have shown encouraging results in recent years. Due to the relatively low incidence of AML in childhood, the success of paediatric early-phase clinical trials is largely dependent upon collaborative clinical trial design by international cooperative study groups. Successfully incorporating novel therapies into frontline therapy remains a challenge, but the potential for significant improvement in the duration and quality of survival for children with AML is high.

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.

Preincubation of pituitary tumor cells with the epidrugs zebularine and trichostatin A are permissive for retinoic acid-augmented expression of the BMP-4 and D2R genes

Retinoic acid (RA)-induced expression of bone morphogenetic protein-4 (BMP-4) inhibits in vitro and in vivo cell proliferation and ACTH synthesis in corticotroph-derived tumor cells. Reduced expression of BMP-4 in this adenoma subtype is associated with epigenomic silencing, and similar silencing mechanisms are also associated with the RA-responsive dopamine D2 receptor (D2R) in somatolactotroph cells. We now show that preincubation with the epidrugs zebularine and trichostatin A is obligate and permissive for RA-induced expression of the BMP-4 and the D2R genes in pituitary tumor cells. Combined epidrug challenges are associated with marginal reduction in CpG island methylation. However, significant change to histone tail modifications toward those associated with expression-competent genes is apparent, whereas RA challenge alone or in combined incubations does not have an impact on these modifications. Epidrug-mediated and RA-augmented expression of endogenous BMP-4 increased or decreased cell proliferation and colony-forming efficiency in GH3 and AtT-20 pituitary tumor cells, respectively, recapitulating recent reports of challenges of these cells with exogenous ligand. The specificity of the BMP-4-mediated effects was further supported by knock-down experiments of the BMP-4 antagonist noggin (small interfering RNA [siRNA]). Knock-down of noggin, in the absence and the presence of epidrugs, induced and augmented BMP-4 expression, respectively. In cell proliferation assays, challenge with either epidrugs or siRNA led to significant increase in cell numbers at the 72-hour time point; however, in siRNA-treated cells coincubated with epidrugs, a significant increase was apparent at the 48-hour time point. These studies show the potential of combined drug challenges as a treatment option, where epidrug renders silenced genes responsive to conventional therapeutic options.

New therapeutic approaches to acute myeloid leukemia

BACKGROUND

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the pathogenesis and treatment of patients with AML. Understanding the basic cellular and molecular pathogenesis of leukemic cells is vital to the development of new treatment approaches.

OBJECTIVE/METHODS

To review progress until now with agents that are showing promise in the treatment of AML, we summarize the published preclinical and clinical trials that have been completed.

RESULTS

Based on recent progress of investigations, more specifically targeted agents have been developed for the treatment of AML such as tyrosine kinase inhibitors, monoclonal antibodies, epigenetic agents, antiangiogenic agents, and farnesyl transferase inhibitors.

CONCLUSION

In the future, in addition to performing therapeutic trials of these agents, it will be important to identify other highly specific therapeutic agents based on our evolving understanding of the biology of AML.

Translational phase I trial of vorinostat (suberoylanilide hydroxamic acid) combined with cytarabine and etoposide in patients with relapsed, refractory, or high-risk acute myeloid leukemia

PURPOSE

To determine the maximum-tolerated dose (MTD) of the histone deacetylase inhibitor vorinostat combined with fixed doses of cytarabine (ara-C or cytosine arabinoside) and etoposide in patients with poor-risk or advanced acute leukemia, to obtain preliminary efficacy data, describe pharmacokinetics, and in vivo pharmacodynamic effects of vorinostat in leukemia blasts.

EXPERIMENTAL DESIGN

In this open-label phase I study, vorinostat was given orally on days one to seven at three escalating dose levels: 200 mg twice a day, 200 mg three times a day, and 300 mg twice a day. On days 11 to 14, etoposide (100 mg/m(2)) and cytarabine (1 or 2 g/m(2) twice a day if ≥65 or <65 years old, respectively) were given. The study used a standard 3+3 dose escalation design.

RESULTS

Eighteen of 21 patients with acute myelogenous leukemia (AML) treated on study completed planned therapy. Dose-limiting toxicities [hyperbilirubinemia/septic death (1) and anorexia/fatigue (1)] were encountered at the 200 mg three times a day level; thus, the MTD was established to be vorinostat 200 mg twice a day. Of 21 patients enrolled, seven attained a complete remission (CR) or CR with incomplete platelet recovery, including six of 13 patients treated at the MTD. The median remission duration was seven months. No differences in percentage S-phase cells or multidrug resistance transporter (MDR1 or BCRP) expression or function were observed in vivo in leukemia blasts upon vorinostat treatment.

CONCLUSIONS

Vorinostat 200 mg twice a day can be given safely for seven days before treatment with cytarabine and etoposide. The relatively high CR rate seen at the MTD in this poor-risk group of patients with AML warrants further studies to confirm these findings.

Time- and residue-specific differences in histone acetylation induced by VPA and SAHA in AML1/ETO-positive leukemia cells

We analyzed the activity of the histone deacetylase inhibitor (HDACi) suberoyl-anilide hydroxamic acid (SAHA) on Kasumi-1 acute myeloid leukemia (AML) cells expressing AML1/ETO. We also compared the effects of SAHA to those of valproic acid (VPA), a short-chain fatty acid HDACi. SAHA and VPA induced histone H3 and H4 acetylation, myeloid differentiation and massive early apoptosis. The latter effects were not determined by either drug in AML cell lines, such as NB4 or THP-1, not expressing AML1/ETO. SAHA was more rapid and effective than VPA in increasing H3 and H4 acetylation in total Kasumi-1 cell lysates and more effective than VPA in inducing acetylation of H4K8, H4K12, H4K16 residues. At the promoter of IL3, a transcriptionally-silenced target of AML1/ETO, SAHA was also more rapid than VPA in inducing total H4, H4K5, H4K8 and H3K27 acetylation, while VPA was more effective than SAHA at later times in inducing acetylation of total H4, H4K12, H4K16, as well as total H3. Consistent with these differences, SAHA induced the expression of IL3 mRNA more rapidly than VPA, while the effect of VPA was delayed. These differences might be exploited to design clinical trials specifically directed to AML subtypes characterized by constitutive HDAC activation. Our results led to include SAHA, an FDA-approved drug, among the HDACi active in the AML1/ETO-expressing AML cells.

Valproic acid inhibits proliferation of EB virus-infected natural killer cells

There is no recognized treatment for Epstein-Barr virus (EBV)-associated natural killer (NK) cell lymphoproliferative disorders (LPDs). To determine the possibility of histone deacetylase inhibitors as a therapeutic tool for such disorders, we investigated the anti-proliferative effects of valproic acid (VPA) on two EBV-infected NK cell lines (KAI3 and NKED). VPA inhibited the growth of both lines in a dose- and time-dependent manner by inducing histone hyperacetylation. G1 cell cycle arrest was induced at 24 hours and was associated with increased expression of p21(WAF1), p27(Kip1), and cyclin E and decreased expression of cyclin D2, CDK4, and c-myc. Sub-G1 fractions were not significantly changed at 24 hours, whereas cleaved caspase-3 and cleaved PARP were already detected, and the extrinsic apoptotic pathway, determined by cleaved caspase-8, was activated. Finally, sub-G1 accumulation was increased after 72 hours following stimulation. These findings indicate that VPA might be a therapeutic option for EBV-associated NK-cell LPDs.

HDAC inhibitor-based therapies: can we interpret the code?

Abnormal epigenetic control is a common early event in tumour progression, and aberrant acetylation in particular has been implicated in tumourigenesis. One of the most promising approaches towards drugs that modulate epigenetic processes has been seen in the development of inhibitors of histone deacetylases (HDACs). HDACs regulate the acetylation of histones in nucleosomes, which mediates changes in chromatin conformation, leading to regulation of gene expression. HDACs also regulate the acetylation status of a variety of other non-histone substrates, including key tumour suppressor proteins and oncogenes. Histone deacetylase inhibitors (HDIs) are potent anti-proliferative agents which modulate acetylation by targeting histone deacetylases. Interest is increasing in HDI-based therapies and so far, two HDIs, vorinostat (SAHA) and romidepsin (FK228), have been approved for treating cutaneous T-cell lymphoma (CTCL). Others are undergoing clinical trials. Treatment with HDIs prompts tumour cells to undergo apoptosis, and cell-based studies have shown a number of other outcomes to result from HDI treatment, including cell-cycle arrest, cell differentiation, anti-angiogenesis and autophagy. However, our understanding of the key pathways through which HDAC inhibitors affect tumour cell growth remains incomplete, which has hampered progress in identifying malignancies other than CTCL which are likely to respond to HDI treatment.

Autophagy is differentially induced in prostate cancer LNCaP, DU145 and PC-3 cells via distinct splicing profiles of ATG5

Autophagic responses to chemotherapeutic agents may vary greatly among different prostate cancer cells and have not been well characterized. In this study, we showed that valproic acid (VPA) induced conversion of LC3-I to LC3-II and formation of LC3 puncta, the typical markers of autophagy, in LNCaP and PC-3 cells. However, these markers were undetectable in DU145 cells upon autophagic stimulation, indicating a defect of autophagy in this cell line. Among several critical autophagy-related proteins, ATG5 and ATG12-ATG5 conjugates, which are essential for autophagy induction, were absent in DU145 cells. No canonical transcripts for full-length ATG5 but only two alternatively spliced ATG5 transcripts were identified in DU145 cells. These alternative transcripts lack one or two exons, leading to premature termination of ATG5 translation. Transfection of the wild-type ATG5 gene into DU145 cells rescued the production of ATG5 and ATG12-ATG5 conjugates, resulting in formation of LC3-II conjugates and LC3 puncta. Moreover, the levels of the SQSTM1 protein, which should be degradable as an autophagy adaptor, were much higher in DU145 than in LNCaP and PC-3 cells, but were significantly decreased after ATG5 restoration in DU145 cells. However, expression of wild-type ATG5 in DU145 or knockdown of ATG5 in LNCaP and PC-3 cells did not change the inhibitory effects of VPA on these cells. Collectively, these results indicated that VPA-induced autophagy in prostate cancer cells depended on ATG5 and more importantly, that the autophagy pathway was genetically impaired in DU145 cells, suggesting caution in interpreting autophagic responses in this cell line.

Gene signature critical to cancer phenotype as a paradigm for anticancer drug discovery

Malignant cell transformation commonly results in the deregulation of thousands of cellular genes, an observation that suggests a complex biological process and an inherently challenging scenario for the development of effective cancer interventions. To better define the genes/pathways essential to regulating the malignant phenotype, we recently described a novel strategy based on the cooperative nature of carcinogenesis that focuses on genes synergistically deregulated in response to cooperating oncogenic mutations. These so-called 'cooperation response genes' (CRGs) are highly enriched for genes critical for the cancer phenotype, thereby suggesting their causal role in the malignant state. Here, we show that CRGs have an essential role in drug-mediated anticancer activity and that anticancer agents can be identified through their ability to antagonize the CRG expression profile. These findings provide proof-of-concept for the use of the CRG signature as a novel means of drug discovery with relevance to underlying anticancer drug mechanisms.

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.

Preclinical cancer chemoprevention studies using animal model of inflammation-associated colorectal carcinogenesis

Inflammation is involved in all stages of carcinogenesis. Inflammatory bowel disease, such as ulcerative colitis and Crohn’s disease is a longstanding inflammatory disease of intestine with increased risk for colorectal cancer (CRC). Several molecular events involved in chronic inflammatory process are reported to contribute to multi-step carcinogenesis of CRC in the inflamed colon. They include over-production of free radicals, reactive oxygen and nitrogen species, up-regulation of inflammatory enzymes in arachidonic acid biosynthesis pathway, up-regulation of certain cytokines, and intestinal immune system dysfunction. In this article, firstly I briefly introduce our experimental animal models where colorectal neoplasms rapidly develop in the inflamed colorectum. Secondary, data on preclinical cancer chemoprevention studies of inflammation-associated colon carcinogenesis by morin, bezafibrate, and valproic acid, using this novel inflammation-related colorectal carcinogenesis model is described.

Prostaglandin E2 induces growth inhibition, apoptosis and differentiation in T and B cell-derived acute lymphoblastic leukemia cell lines (CCRF-CEM and Nalm-6)

Despite advances in the treatment of ALL, in most patients long-term survival rates remain unsatisfactory. The objective of the present study was to investigate the anti-cancer effects of Prostaglandin E2 (PGE2) in two different ALL cell lines (CCRF-CEM (T-ALL) and Nalm-6 (B-ALL)). The anti-leukemic effects of PGE2 were also compared with two epigenetic compounds (trichostatin A and 5-aza-2'-deoxycytidine). MTT assay was used to assess growth inhibition by anti-cancer drugs in these cells. All three compounds were shown to induce apoptosis in both ALL cell lines using flow cytometry and Western blotting. To evaluate the differentiation induction by these agents, the expressions of CD19 and CD38 markers on Nalm-6 cell line and CD7 marker on CCRF-CEM cell line were assayed. Surprisingly, the flow cytometric analysis showed a significant increase in CD markers expression in response to PGE2 treatments. We, for the first time, provide evidences that PGE2 has anti-leukemic effects and induces differentiation at micromolar ranges in both T- and B-cell derived ALL cell lines. Since T-ALL cells are insensitive to current chemotherapies, these findings may help the designing of new protocols for T-ALL differentiation therapy in the future.

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.

A mutation in the thyroid hormone receptor alpha gene

Thyroid hormones exert their effects through alpha (TRα1) and beta (TRβ1 and TRβ2) receptors. Here we describe a child with classic features of hypothyroidism (growth retardation, developmental retardation, skeletal dysplasia, and severe constipation) but only borderline-abnormal thyroid hormone levels. Using whole-exome sequencing, we identified a de novo heterozygous nonsense mutation in a gene encoding thyroid hormone receptor alpha (THRA) and generating a mutant protein that inhibits wild-type receptor action in a dominant negative manner. Our observations are consistent with defective human TRα-mediated thyroid hormone resistance and substantiate the concept of hormone action through distinct receptor subtypes in different target tissues.

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.

Effect of valproic acid on cell proliferation and cell cycle progression in human hepatoma cell line SMMC-7721

AIM: To investigate the effect of valproic acid (VPA) on cell proliferation, cell cycle progression and expression of p21^WAF1/CIP1 mRNA in human hepatoma cell line SMMC-7721 in vitro.

METHODS: SMMC-7721 cells were treated with different concentrations (0.2, 1.0 and 5.0 mmol/L) of VPA for different durations (24, 48 and 72 h). Cell growth was measured by MTT assay. Cell cycle analysis was performed by flow cytometry. The expression of p21^WAF1/CIP1 mRNA in SMMC-7721 cells treated with VPA for 72 h was detected by RT-PCR.

RESULTS: Compared to the control group and PBS group, treatment with different concentrations of VPA for different durations significantly reduced cell growth to a varying extent (all P < 0.05). VPA administration suppressed cell proliferation in a time- and dose-dependent manner. After treatment with VPA, the percentage of cells in G₁ phase increased significantly and that of cells in S phase decreased, suggesting an arrest in G₀/G₁ phrase. Significant up-regulation of p21^WAF1/CIP1 mRNA was observed in SMMC-7721 cells 72 h after treatment with VPA.

CONCLUSION: VPA could significantly suppress cell proliferation in a time- and dose-dependent manner, and result in a cell cycle arrest in G₀/G₁ phase by inducing elevated expression of p21^WAF1/CIP1 mRNA in SMMC-7721 cells.

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.

Epigenetics in myeloid malignancies

Myeloid hematological malignancies are among the epigenetically best characterized neoplasms. The comparatively low number of recurring balanced and unbalanced chromosomal abnormalities as well as common genetic mutations has enabled scientists to relate epigenetic states to these. The ease of accessing malignant cells through bone marrow aspiration has certainly contributed to the fast expansion of knowledge. Even so, the clinical and pathogenetic relevance of epigenetic changes is still not known, and the field will certainly evolve very fast with the development of new analytic techniques. The first example of successful epigenetic therapy is seen in myeloid malignancies, in the high-risk myelodysplastic syndromes (MDS) which are routinely treated with the demethylating agent azacytidine.This chapter will concentrate on describing the epigenetic changes in acute myeloid leukemia (AML), chronic myeloid leukemia (CML) and MDS. An overview of clinical relevance and epigenetic therapeutic approaches is also made.

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.

HDAC inhibitors in cancer biology: emerging mechanisms and clinical applications

Reversible acetylation mediated by histone deacetylases (HDACs) influences a broad repertoire of physiological processes, many of which are aberrantly controlled in tumor cells. As HDAC inhibition prompts tumor cells to enter apoptosis, small-molecule HDAC inhibitors have been developed as a new class of mechanism-based anti-cancer agent, many of which have entered clinical trials. Although the clinical picture is evolving and the precise utility of HDAC inhibitors remains to be determined, it is noteworthy that certain tumor types undergo a favorable response, in particular hematological malignancies. Vorinostat and romidepsin have been approved for treating cutaneous T-cell lymphoma in patients with progressive, persistent or recurrent disease. Here, we discuss developments in our understanding of molecular events that underlie the anti-cancer effects of HDAC inhibitors and relate this information to the emerging clinical picture for the application of these inhibitors in the treatment of cancer.

Predictive biomarkers: a paradigm shift towards personalized cancer medicine

Advances in our understanding of the intricate molecular mechanisms for transformation of a normal cell to a cancer cell, and the aberrant control of complementary pathways, have presented a much more complex set of challenges for the diagnostic and therapeutic disciplines than originally appreciated. The oncology field has entered an era of personalized medicine where treatment selection for each cancer patient is becoming individualized or customized. This advance reflects the molecular and genetic composition of the tumors and progress in biomarker technology, which allow us to align the most appropriate treatment according to the patient's disease. There is a worldwide acceptance that advances in our ability to identify predictive biomarkers and provide them as companion diagnostics for stratifying and subgrouping patients represents the next leap forward in improving the quality of clinical care in oncology. As such, we are progressing from a population-based empirical 'one drug fits all' treatment model, to a focused personalized approach where rational companion diagnostic tests support the drug's clinical utility by identifying the most responsive patient subgroup.

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.

Retinoids, retinoic acid receptors, and cancer

Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells. Nuclear retinoic acid receptors mediate most but not all of the effects of retinoids. Retinoid signaling is often compromised early in carcinogenesis, which suggests that a reduction in retinoid signaling may be required for tumor development. Retinoids interact with other signaling pathways, including estrogen signaling in breast cancer. Retinoids are used to treat cancer, in part because of their ability to induce differentiation and arrest proliferation. Delivery of retinoids to patients is challenging because of the rapid metabolism of some retinoids and because epigenetic changes can render cells retinoid resistant. Successful cancer therapy with retinoids is likely to require combination therapy with drugs that regulate the epigenome, such as DNA methyltransferase and histone deacetylase inhibitors, as well as classical chemotherapeutic agents. Thus, retinoid research benefits both cancer prevention and cancer treatment.

Treatment of poor-risk myelodysplastic syndromes and acute myeloid leukemia with a combination of 5-azacytidine and valproic acid

5-azacytidine (AZA) has become standard treatment for patients with higher-risk myelodysplastic syndrome (MDS). Response rate is about 50% and response duration is limited. Histone deactylase (HDAC) inhibitors are attractive partners for epigenetic combination therapy. We treated 24 patients with AZA (100 mg/m², 5 days) plus valproate (VPA; continuous dosing, trough serum level 80–110 μg/ml). According to WHO classification, 5 patients had MDS, 2 had MDS/MPD, and 17 had acute myeloid leukemia (AML). Seven patients (29%) had previously received intensive chemotherapy, and five had previous HDAC inhibitor treatment. The overall response rate was 37% in the entire cohort but significantly higher (57%) in previously untreated patients, especially those with MDS (64%). Seven (29%) patients achieved CR (29%) and two PR (8%), respectively. Hematological CR was accompanied by complete cytogenetic remission according to conventional cytogenetics in all evaluable cases. Some patients also showed complete remission according to FISH on bone marrow mononuclear cells and CD34⁺ peripheral blood cells, as well as by follow-up of somatic mitochondrial DNA mutations. Four additional patients achieved at least marrow remissions. Factors influencing response were AML (vs. MDS), marrow blast count, pretreatment, transfusion dependency, concomitant medication with hydroxyurea, and valproic acid (VPA) serum level. This trial is the first to assess the combination of AZA plus VPA without additional ATRA. A comparatively good CR rate, relatively short time to response, and the influence of VPA serum levels on response suggest that VPA provided substantial additional benefit. However, the importance of HDAC inhibitors in epigenetic combination therapy can only be proven by randomized trials.

The histone deacetylase inhibitor vorinostat selectively sensitizes fibrosarcoma cells to chemotherapy

Soft tissue sarcoma (STS) is a rare malignancy that is generally resistant to chemotherapy. We investigated the ability of the histone deacetylase inhibitor vorinostat to sensitize STS cells versus normal fibroblasts to chemotherapy. Fibrosarcoma, leiomyosarcoma, and liposarcoma cells and normal fibroblasts were treated with vorinostat to determine effects on proliferation and basal apoptosis as measured by total cell number and cleaved caspase 3 staining. Effects on histone deacetylases (HDAC) activity were confirmed by Western blotting for acetylated histone H3. A clinically relevant dose of vorinostat that had no effect on basal apoptosis was selected to examine altered sensitivity to doxorubicin. The effects of vorinostat, doxorubicin, or the combination on fibrosarcoma growth in vivo were determined in a xenograft model. Tumor volume was measured biweekly and HDAC activity and cell death were assessed by immunohistochemical analysis of acetylated histone H3, cleaved caspase 3, and TUNEL staining. Vorinostat inhibited proliferation and induced histone acetylation without affecting basal apoptosis levels. Combined treatment with vorinostat and doxorubicin synergistically induced apoptosis in vitro in fibrosarcoma but not leiomyosarcoma, liposarcoma, or normal fibroblasts. In nude mice, the combination of vorinostat and doxorubicin inhibited fibrosarcoma xenograft growth further than either agent alone. Cell death, as measured by cleaved caspase 3 and TUNEL staining, was greatest in xenografts from mice treated with vorinostat and doxorubicin. Vorinostat inhibits growth and induces chemosensitivity in fibrosarcoma cells in vitro and in vivo, suggesting that the combination of vorinostat and chemotherapy may represent a novel treatment option for this STS subtype. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:623-632, 2011.

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

Disease-stabilizing therapy with the histone deacetylase inhibitor valproic acid and all-trans retinoic acid (ATRA) has been investigated in acute myelogenous leukemia (AML) in a number of trials. Experimental studies suggest that valproic acid induces a broad chemoresistant phenotype in human AML cells; however, clinical observations combining valproic acid with conventional therapy in a disease-stabilizing setting have not been reported that would confirm this as a clinical issue. We describe five patients receiving oral treatment with low-dose oral 6-mercaptopurin and/or hydroxyurea together with ATRA+valproric acid+theophylline. Hyperleukocytosis was controlled by low doses of the cytotoxic drugs, no unexpected toxicity appeared and the increases in normal peripheral blood cell counts induced by ATRA+valproic acid+theophylline were maintained during therapy. In two patients increasing blast counts later occurred during chemotherapy; a change to the alternative cytotoxic drug was then effective in controlling hyperleukocytosis. We conclude that valproic acid+ATRA+theophylline combined with 6-mercaptopurin or hydroxyurea can be safe and effective in palliative treatment of human AML.

Histone deacetylase inhibitors for the treatment of myelodysplastic syndrome and acute myeloid leukemia

Epigenetic changes have been identified in recent years as important factors in the pathogenesis of myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Histone deacetylase inhibitors (HDACIs) regulate the acetylation of histones as well as other non-histone protein targets. Treatment with HDACIs results in chromatin remodeling that permits re-expression of silenced tumor suppressor genes in cancer cells, which, in turn, can potentially result in cellular differentiation, inhibition of proliferation and/or apoptosis. Several classes of HDACIs are currently under development for the treatment of patients with MDS and AML. Although modest clinical activity has been reported with the use of HDACIs as single-agent therapy, marked responses have been observed in selected subsets of patients. More importantly, HDACIs appear to be synergistic in vitro and improve response rates in vivo when combined with other agents, such as hypomethylating agents. Furthermore, HDACIs are also being investigated in combination with non-epigenetic therapies. This article synthesizes the most recent results reported with HDACIs in clinical trials conducted in patients with MDS and other myeloid malignancies.

Vorinostat in acute myeloid leukemia and myelodysplastic syndromes

INTRODUCTION

the results of conventional treatment for acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) remain poor and innovative strategies are warranted. With this aim, epigenetic modulation became a promising approach over the last years. Vorinostat is an epigenetic targeted drug belonging to the histone deacetylase (HDAC) inhibitors family. It is the second-generation HDAC inhibitor that has been more extensively studied in AML and MDS.

AREAS COVERED

in this review, we will present the rationale for its use in AML and MDS, describe the drug pharmacologic properties and review the current data available from clinical trials. The data presented here will allow the reader to overview the common mechanisms of action of this class of compounds in AML and MDS, as well as to better understand the biological specificities of vorinostat, and its current and future clinical development in the field.

EXPERT OPINION

vorinostat has shown an acceptable toxicity profile with mainly gastrointestinal and constitutional side effects. Efficacy as a single agent is limited in that group of patients, but promising results are currently observed with combinations of vorinostat and either conventional chemotherapy or investigational agents, including demethylating agents.