Epigenetic-based treatments emphasize the biologic differences of core-binding factor acute myeloid leukemias

Hypomethylating agent monotherapy in core binding factor acute myeloid leukemia: a French multicentric retrospective study

Very few data are available about hypomethylating agent (HMA) efficiency in core binding factor acute myeloid leukemias (CBF-AML). Our main objective was to evaluate the efficacy and safety of HMA in the specific subset of CBF-AML. Here, we report the results of a multicenter retrospective French study about efficacy of HMA monotherapy, used frontline or for R/R CBF-AML. Forty-nine patients were included, and received a median of 5 courses of azacitidine (n = 46) or decitabine (n = 3). ORR was 49% for the whole cohort with a median time to response of 112 days. After a median follow-up of 72.3 months, median OS for the total cohort was 10.6 months. In multivariate analysis, hematological relapse of CBF-AML at HMA initiation was significantly associated with a poorer OS (HR: 2.13; 95%CI: 1.04-4.36; p = 0.038). Responders had a significantly improved OS (1-year OS: 75%) compared to non-responders (1-year OS: 15.3%; p < 0.0001). Hematological improvement occurred for respectively 28%, 33% and 48% for patients who were red blood cell or platelet transfusion-dependent, or who experienced grade 3/4 neutropenia at HMA initiation. Adverse events were consistent with the known safety profile of HMA. Our study highlights that HMA is a well-tolerated therapeutic option with moderate clinical activity for R/R CBF-AML and for patients who cannot handle intensive chemotherapy.

Epigenetic mechanisms in leukemia

Focal organization of regulatory machinery within the interphase nucleus is linked to biological responsiveness and perturbed in cancer. Lineage determinant Runx proteins organize and assemble multi-protein complexes at sites of transcription within the nucleus and regulate both RNA polymerase II- and I-mediated gene expression. In addition, Runx proteins epigenetically control lineage determining transcriptional programs including: 1) architectural organization of macromolecular complexes in interphase, 2) regulation of gene expression through bookmarking during mitosis, and 3) microRNA-mediated translational control in the interphase nucleus. These mechanisms are compromised with the onset and progression of cancer. For example, the oncogenic AML1-ETO protein, which results from a chromosomal translocation between chromosomes 8 and 21, is expressed in nearly 25% of all acute myelogenous leukemias, disrupts Runx1 subnuclear localization during interphase and compromises transcriptional regulation. Epigenetically, the leukemic protein redirects the Runx1 DNA binding domain to leukemia-specific nuclear microenvironments, modifies regulatory protein accessibility to Runx1 target genes by imprinting repressive chromatin marks, and deregulates the microRNA (miR) profile of diseased myeloid cells. Consequently, the entire Runx1-dependent transcriptional program of myeloid cells is deregulated leading to onset and progression of acute myeloid leukemia and maintenance of leukemic phenotype. We discuss the potential of modified epigenetic landscape of leukemic cells as a viable therapeutic target.

Spectrin isoforms: differential expression in normal hematopoiesis and alterations in neoplastic bone marrow disorders

Spectrins are large, rod-like, multifunctional molecules that participate in maintaining cell structure, signal transmission, and DNA repair. Because little is known about the role of spectrins in normal hematopoiesis and leukemogenesis, we immunohistochemically stained bone marrow biopsy specimens from 81 patients for αI, αII, βI, and βII spectrin isoforms in normal reactive marrow (NRM), myelodysplastic syndrome, myeloproliferative neoplasm, acute myeloid leukemia (AML) with well-characterized cytogenetic abnormalities, acute erythroid leukemia (EryL), and acute megakaryoblastic leukemia (MegL). In NRM, spectrin isoforms were differentially expressed according to cell lineage: αI and βI in erythroid precursors; αII and βII in granulocytes; and βI and βII in megakaryocytes. In contrast, 18 (44%) of 41 AMLs lacked αII spectrin and/or aberrantly expressed βI spectrin (P = .0398; Fisher exact test) and 5 (100%) of 5 EryLs expressed βII spectrin but lacked βI spectrin. The frequent loss and/or gain of spectrin isoforms in AMLs suggests a possible role for spectrin in leukemogenesis.

Dynamic single-cell network profiles in acute myelogenous leukemia are associated with patient response to standard induction therapy

PURPOSE

Complete response to induction chemotherapy is observed in approximately 60% of patients with newly diagnosed non-M3 acute myelogenous leukemia (AML). However, no methods exist to predict with high accuracy at the individual patient level the response to standard AML induction therapy.

EXPERIMENTAL DESIGN

We applied single-cell network profiling (SCNP) using flow cytometry, a tool that allows a comprehensive functional assessment of intracellular signaling pathways in heterogeneous tissues, to two training cohorts of AML samples (n = 34 and 88) to predict the likelihood of response to induction chemotherapy.

RESULTS

In the first study, univariate analysis identified multiple signaling "nodes" (readouts of modulated intracellular signaling proteins) that correlated with response (i.e., AUC(ROC) > or = 0.66; P < or = 0.05) at a level greater than age. After accounting for age, similar findings were observed in the second study. For patients <60 years old, complete response was associated with the presence of intact apoptotic pathways. In patients > or =60 years old, nonresponse was associated with FLT3 ligand-mediated increase in phosphorylated Akt and phosphorylated extracellular signal-regulated kinase. Results were independent of cytogenetics, FLT3 mutational status, and diagnosis of secondary AML.

CONCLUSIONS

These data emphasize the value of performing quantitative SCNP under modulated conditions as a basis for the development of tests highly predictive for response to induction chemotherapy. SCNP provides information distinct from other known prognostic factors such as age, secondary AML, cytogenetics, and molecular alterations and is potentially combinable with the latter to improve clinical decision making. Independent validation studies are warranted.

Histone deacetylases and epigenetic therapies of hematological malignancies

Histone deacetylase inhibitors (HDACi) represent a novel class of targeted drugs which alter the acetylation status of several cellular proteins. These agents, modulating both chromatin structure through histone acetylation, and the activity of several non-histone substrates, are at the same time able to determine changes in gene transcription and to induce a plethora of biological effects ranging from cell death induction, to differentiation, angiogenesis inhibition or modulation of immune responses. The impressive anticancer activity observed in both in vitro and in vivo cancer models, together with their preferential effect on cancer cells, have led to a huge effort into the identification and development of HDACi with different characteristics. To date, several clinical trials of HDACi conducted in solid tumors and hematological malignancies have shown a preferential clinical efficacy of these drugs in hematological malignancies, and in particular in cutaneous T-cell lymphoma (CTCL), peripheral T-cell lymphoma (PTCL), Hodgkin lymphoma (HL) and myeloid malignancies. Several agents are also beginning to be tested in combination therapies, either as chemo sensitizing agents in association with standard chemotherapy drugs or in combination with DNA methyltransferase inhibitors (DNMTi) in the context of the so-called "epigenetic therapies", aimed to revert epigenetic alterations found in cancer cells. Herein, we will review HDACi data in hematological malignancies questioning the molecular basis of observed clinical responses, and highlighting some of the concerns raised on the use of these drugs for cancer therapy.