A phase I and pharmacodynamic study of the histone deacetylase inhibitor belinostat plus azacitidine in advanced myeloid neoplasia

Do histone deacytelase inhibitors and azacitidine combination hold potential as an effective treatment for high/very-high risk myelodysplastic syndromes?

INTRODUCTION

Myelodysplastic syndrome (MDS) is a clonal hematopoietic stem cell disorder, predominantly seen in elderly patients with variable clinical outcome and high tendency for leukemic transformation. Allogeneic hematopoietic stem cell transplantation (alloHCT) is the only potential curative option but limited to a selected group of patients, for the rest, disease control is the goal and enrollment in clinical trial is always encouraged. Mechanistically, azacitidine (AZA) and histone deacetylase inhibitors (HDACi) is a promising combination for patient with high-risk MDS to improve clinical outcome, but the combination has yet to demonstrate its efficacy in randomized clinical trials.

AREAS COVERED

In this review the authors discuss the salient features, pharmacokinetics, safety, and efficacy data of AZA and HDACi combination in patients with MDS. Future strategies on how to possibly improve clinical outcome of patients with MDS using AZA and HDACi combination are discussed.

EXPERT OPINION

Pre-clinical and clinical data demonstrated synergistic activity of AZA and HDACi in patients with MDS. So far, the efficacy of this combination is undermined by toxicity; mainly gastrointestinal. Careful patient selection and alternative dosing schedule is needed in future clinical trials to evaluate clinical outcome.

Epigenetic Regulation of Multidrug Resistance Protein 1 and Breast Cancer Resistance Protein Transporters by Histone Deacetylase Inhibition

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) and breast cancer resistance protein (BCRP, ABCG2) are key efflux transporters that mediate the extrusion of drugs and toxicants in cancer cells and healthy tissues, including the liver, kidneys, and the brain. Altering the expression and activity of MDR1 and BCRP influences the disposition, pharmacodynamics, and toxicity of chemicals, including a number of commonly prescribed medications. Histone acetylation is an epigenetic modification that can regulate gene expression by changing the accessibility of the genome to transcriptional regulators and transcriptional machinery. Recently, studies have suggested that pharmacological inhibition of histone deacetylases (HDACs) modulates the expression and function of MDR1 and BCRP transporters as a result of enhanced histone acetylation. This review addresses the ability of HDAC inhibitors to modulate the expression and the function of MDR1 and BCRP transporters and explores the molecular mechanisms by which HDAC inhibition regulates these transporters. While the majority of studies have focused on histone regulation of MDR1 and BCRP in drug-resistant and drug-sensitive cancer cells, emerging data point to similar responses in nonmalignant cells and tissues. Elucidating epigenetic mechanisms regulating MDR1 and BCRP is important to expand our understanding of the basic biology of these two key transporters and subsequent consequences on chemoresistance as well as tissue exposure and responses to drugs and toxicants. SIGNIFICANCE STATEMENT: Histone deacetylase inhibitors alter the expression of key efflux transporters multidrug resistance protein 1 and breast cancer resistance protein in healthy and malignant cells.

Incorporating novel approaches in the management of MDS beyond conventional hypomethylating agents

In the last decade, the treatment of higher-risk myelodysplastic syndromes (MDS) has revolved around the azanucleosides, azacitidine and decitabine, which at lower doses are postulated to work predominantly via their effects on inhibition of DNA methyltransferases and consequent DNA hypomethylation. For patients who relapse after, or do not respond to, hypomethylating agent therapy, the outcome is dismal, and new agents and approaches that have the potential to alter the natural history of these diseases are desperately needed. Allogeneic stem cell transplant is the only known potentially curative approach in MDS, but its applicability has been limited by the advanced age of patients and attendant comorbidities. There is now an increasing array of new agents under clinical investigation in MDS that aim to exploit our expanding understanding of molecular pathways that are important in the pathogenesis of MDS. This review focuses on a critical appraisal of novel agents being evaluated in higher-risk MDS that go beyond the conventional hypomethylating agent therapies approved by the US Food and Drug Administration.

The role of the extracellular matrix in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm that arises from clonal proliferation of hematopoietic stem cells and leads to progressive bone marrow (BM) fibrosis. While cellular mutations involved in the development of PMF have been heavily investigated, noteworthy is the important role the extracellular matrix (ECM) plays in the progression of BM fibrosis. This review surveys ECM proteins contributors of PMF, and highlights how better understanding of the control of the ECM within the BM niche may lead to combined therapeutic options in PMF.

Defining and Treating Older Adults with Acute Myeloid Leukemia Who Are Ineligible for Intensive Therapies

Although acute myeloid leukemia (AML) is primarily a disease of older adults (age ≥60 years), the optimal treatment for older adults remains largely undefined. Intensive chemotherapy is rarely beneficial for frail older adults or those with poor-risk disease, but criteria that define fitness and/or appropriateness for intensive chemotherapy remain to be standardized. Evaluation of disease-related and patient-specific factors in the context of clinical decision making has therefore been largely subjective. A uniform approach to identify those patients most likely to benefit from intensive therapies is needed. Here, we review currently available objective measures to define older adults with AML who are ineligible for intensive chemotherapy, and discuss promising investigational approaches.

Targeting Suppressor of Variegation 3-9 Homologue 2 (SUV39H2) in Acute Lymphoblastic Leukemia (ALL)

Although recent progress in understanding the biology and optimizing the treatment of acute lymphoblastic leukemia (ALL) has improved cure rates of childhood ALL to nearly 90%, the cure rate in adult ALL remains less than 50%. The poor prognosis in adult ALL has in part been attributed to larger proportion of high-risk leukemia showing drug resistance. Thus, identifying novel therapeutic targets in ALL is needed for further improvements in treatment outcomes of adult ALL. Genetic aberration of chromatin-modifying molecules has been recently reported in subtypes of ALL, and targeting components of chromatin complexes has shown promising efficacy in preclinical studies. Suppressor of variegation 3-9 homologue 2 (SUV39H2), also known as KMT1B, is a SET-domain–containing histone methyltransferase that is upregulated in solid cancers, but its expression is hardly detectable in normal tissues. Here, we show that SUV39H2 is highly expressed in ALL cells but not in blood cells from healthy donors and also that SUV39H2 mRNA is expressed at significantly higher levels in bone marrow or blood cells from patients with ALL obtained at diagnosis compared with those obtained at remission (P = .007). In four ALL cell lines (Jurkat and CEM derived from T-ALL and RS4;11 and REH derived from B-ALL), SUV39H2 knockdown resulted in a significant decrease in cell viability (~ 77%, P < .001), likely through induction of apoptosis. On the other hand, SUV39H2 overexpression made cells more resistant to chemotherapy. We conclude that SUV39H2 is a promising therapeutic target and further investigation of this therapeutic approach in ALL is warranted.

Functional-genetic dissection of HDAC dependencies in mouse lymphoid and myeloid malignancies

Histone deacetylase (HDAC) inhibitors (HDACis) have demonstrated activity in hematological and solid malignancies. Vorinostat, romidepsin, belinostat, and panobinostat are Food and Drug Administration-approved for hematological malignancies and inhibit class II and/or class I HDACs, including HDAC1, 2, 3, and 6. We combined genetic and pharmacological approaches to investigate whether suppression of individual or multiple Hdacs phenocopied broad-acting HDACis in 3 genetically distinct leukemias and lymphomas. Individual Hdacs were depleted in murine acute myeloid leukemias (MLL-AF9;Nras(G12D); PML-RARα acute promyelocytic leukemia [APL] cells) and Eµ-Myc lymphoma in vitro and in vivo. Strikingly, Hdac3-depleted cells were selected against in competitive assays for all 3 tumor types. Decreased proliferation following Hdac3 knockdown was not prevented by BCL-2 overexpression, caspase inhibition, or knockout of Cdkn1a in Eµ-Myc lymphoma, and depletion of Hdac3 in vivo significantly reduced tumor burden. Interestingly, APL cells depleted of Hdac3 demonstrated a more differentiated phenotype. Consistent with these genetic studies, the HDAC3 inhibitor RGFP966 reduced proliferation of Eµ-Myc lymphoma and induced differentiation in APL. Genetic codepletion of Hdac1 with Hdac2 was pro-apoptotic in Eµ-Myc lymphoma in vitro and in vivo and was phenocopied by the HDAC1/2-specific agent RGFP233. This study demonstrates the importance of HDAC3 for the proliferation of leukemia and lymphoma cells, suggesting that HDAC3-selective inhibitors could prove useful for the treatment of hematological malignancies. Moreover, our results demonstrate that codepletion of Hdac1 with Hdac2 mediates a robust pro-apoptotic response. Our integrated genetic and pharmacological approach provides important insights into the individual or combinations of HDACs that could be prioritized for targeting in a range of hematological malignancies.