Epigenetics of paediatric acute myeloid leukaemia

Epigenomic machinery regulating pediatric AML: clonal expansion mechanisms, therapies, and future perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease with a genetic, epigenetic, and transcriptional etiology mainly presenting somatic and germline abnormalities. AML incidence rises with age but can also occur during childhood. Pediatric AML (pAML) accounts for 15-20% of all pediatric leukemias and differs considerably from adult AML. Next-generation sequencing technologies have enabled the research community to "paint" the genomic and epigenomic landscape in order to identify pathology-associated mutations and other prognostic biomarkers in pAML. Although current treatments have improved the prognosis for pAML, chemoresistance, recurrence, and refractory disease remain major challenges. In particular, pAML relapse is commonly caused by leukemia stem cells that resist therapy. Marked patient-to-patient heterogeneity is likely the primary reason why the same treatment is successful for some patients but, at best, only partially effective for others. Accumulating evidence indicates that patient-specific clonal composition impinges significantly on cellular processes, such as gene regulation and metabolism. Although our understanding of metabolism in pAML is still in its infancy, greater insights into these processes and their (epigenetic) modulation may pave the way toward novel treatment options. In this review, we summarize current knowledge on the function of genetic and epigenetic (mis)regulation in pAML, including metabolic features observed in the disease. Specifically, we describe how (epi)genetic machinery can affect chromatin status during hematopoiesis, leading to an altered metabolic profile, and focus on the potential value of targeting epigenetic abnormalities in precision and combination therapy for pAML. We also discuss the possibility of using alternative epidrug-based therapeutic approaches that are already in clinical practice, either alone as adjuvant treatments and/or in combination with other drugs.

Polycomb Alterations in Acute Myeloid Leukaemia: From Structure to Function

Epigenetic dysregulation is a hallmark of many haematological malignancies and is very frequent in acute myeloid leukaemia (AML). A cardinal example is the altered activity of the Polycomb Repressive Complex 2 (PRC2) due to somatic mutations and deletions in genes encoding PRC2 core factors that are necessary for correct complex assembly. These genetic alterations typically lead to reduced histone methyltransferase activity that, in turn, has been strongly linked to poor prognosis and chemoresistance. In this review, we provide an overview of genetic alterations of PRC components in AML, with particular reference to structural and functional features of PRC2 factors. We further review genetic interactions between these alterations and other AML-associated mutations in both adult and paediatric leukaemias. Finally, we discuss reported prognostic links between PRC2 mutations and deletions and disease outcomes and potential implications for therapy.

Phase separation in epigenetics and cancer stem cells

Accumulating evidence indicates that liquid–liquid phase separation (LLPS) is the basis of the formation of membrane-less compartments in cells. This biomolecular condensate represented by phase separation may influence epigenetics in cancer stem cells (CSCs), a small subpopulation of cancer cells responding to the initiation, maintenance, metastasis, and therapy resistance of cancer. Understanding the underlying biophysical principles and the specific characteristics of biocondensates would provide insights into the precise blocking of potential tumor targets, thereby fundamentally curbing tumor occurrence, recurrence and metastasis. In this review, we summarized the key phenomenon and experimental detection of phase separation and the possibility of regulating the stemness of CSCs through phase separation. We believe that the mechanism of phase separation in CSCs will open up new avenues for the mystery of tumor formation, and modulating phase separation will be a great strategy for CSC-targeted tumor therapy.

Relapsed acute myeloid leukemia in children and adolescents: current treatment options and future strategies

Pediatric acute myeloid leukemia (AML) develops from clonal expansion of hematopoietic precursor cells and is characterized by morphologic and cytomolecular heterogeneity. Although the past 40 years have seen significant improvements in overall survival, the prevailing treatment challenges in pediatric AML are the prevention of relapse and the management of relapsed disease. Approximately 25% of children and adolescents with AML suffer disease relapse and face a poor prognosis. Our greater understanding of the genomic, epigenomic, metabolomic, and immunologic pathophysiology of relapsed AML allows for better therapeutic strategies that are being developed for pediatric clinical trials. The development of biologically rational agents is critical as conventional chemotherapeutic salvage regimens are not effective for all patients and pose risk of organ toxicity in heavily pretreated patients. Another major barrier to improvement in outcomes for relapsed pediatric AML is the historic lack of availability and participation in clinical trials. There are ongoing efforts to launch multinational clinical trials of emerging therapies. The purpose of this review is to summarize currently available and newly developed therapies for relapsed pediatric AML.

Epigenetic modifications and targeted therapy in pediatric acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematological malignancy resulting from the genetic alterations and epigenetic dysregulations of the hematopoietic progenitor cells. One-third of children with AML remain at risk of relapse even though outcomes have improved in recent decades. Epigenetic dysregulations have been identified to play a significant role during myeloid leukemogenesis. In contrast to genetic changes, epigenetic modifications are typically reversible, opening the door to the development of epigenetic targeted therapy. In this review, we provide an overview of the landscape of epigenetic alterations and describe the current progress that has been made in epigenetic targeted therapy, and pay close attention to the potential value of epigenetic abnormalities in the precision and combinational therapy of pediatric AML.

HOTAIR expression and prognostic impact in acute myeloid leukemia patients

Background

Acute myeloid leukemia (AML) is a disorder characterized by a rapid onset of symptoms attributable to bone marrow failure due to clonal proliferation of primitive hematopoietic stem cells or progenitor cells. Epigenetic abnormalities play an important role in the development and progression of acute leukemia. Long non-coding ribonucleic acid (lncRNA) plays an important role in epigenetic regulation. Homeobox (Hox) transcript antisense intergenic RNA (HOTAIR) is a lncRNA which has been determined to be a negative prognostic indicator in various solid-tumor patients. However, its role in hematopoietic tumors as AML is to be assessed. This study aimed at measuring lncRNA HOTAIR expression level on bone marrow (BM) mononuclear cells in newly diagnosed AML patients and correlating its expression with their outcome and different prognostic variables. This provides new prospective for a novel marker involved in development and progression of AML which can be used as a diagnostic marker and a target of therapy. The current study included 65 subjects divided into 35 newly diagnosed AML adult patients (before initiation of chemotherapy) and 30 non-leukemic adult patients who are candidates for BM aspiration for causes other than hematological malignancies as immune thrombocytopenic purpura and hypersplenism as controls. HOTAIR expression was measured on BM mononuclear cells by quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Results

HOTAIR expression was found to be significantly upregulated in AML patients (probability (p) value = 0.000) and it can be used as a diagnostic biomarker of AML as confirmed by a significant difference between cases and controls using receiver operating characteristic curve (ROC) analysis. However, it was not significantly correlated with event free survival (EFS) or prognostic variables.

Conclusion

This study showed that the expression of HOTAIR is upregulated in de novo AML patients and can be used as a diagnostic marker. However, highly expressed HOTAIR is not associated with poor prognosis.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Simple Summary

Immunotherapy development in pediatric AML has been slow due to the paucity of validated AML-specific targets. We recently identified mesothelin (MSLN) as a therapeutic target in pediatric AML. Mice receiving T cell engaging bispecific antibodies (BsAbs) targeting MSLN and CD3 achieved complete remission and durable responses in two MSLN-positive patient-derived xenograft (PDX) models. This is a first report showing MSLN-targeting BsAbs are a viable immunotherapy for MSLN-positive pediatric AML.

Abstract

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLN^AMA-CD3^L2K and MSLN^AMA-CD3^AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLN^AMA-CD3^AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Therapeutic Targeting of Cancer: Epigenetic Homeostasis

A large number of studies have revealed that epigenetics plays an important role in cancer development. However, the currently-developed epigenetic drugs cannot achieve a stable curative effect. Thus, it may be necessary to redefine the role of epigenetics in cancer development. It has been shown that embryonic development and tumor development share significant similarities in terms of biological behavior and molecular expression patterns, and epigenetics may be the link between them. Cell differentiation is likely a manifestation of epigenetic homeostasis at the cellular level. In this article, we introduced the importance of epigenetic homeostasis in cancer development and analyzed the shortcomings of current epigenetic treatment regimens. Understanding the dynamic process of epigenetic homeostasis in organ development can help us characterize cancer according to its differentiation stages, explore new targets for cancer treatment, and improve the clinical prognosis of patients with cancer.

New progress in the study of germline susceptibility genes of myeloid neoplasms

In 2016, the World Health Organization incorporated ‘myeloid neoplasms with germline predisposition’ into its classification of tumors of hematopoietic and lymphoid tissues, revealing the important role of germline mutations in certain myeloid neoplasms, particularly myelodysplastic syndrome and acute myeloid leukemia. The awareness of germline susceptibility has increased, and some patients with myeloid neoplasms present with a preexisting disorder or organ dysfunction. In such cases, mutations in genes including CCAAT enhancer binding protein α (CEBPA), DEAD (Asp-Glu-Ala-Asp) box polypeptide 41 (DDX41), RUNX family transcription factor 1 (RUNX1), GATA binding protein 2 (GATA2), Janus kinase 2 (JAK2) and ETS variant transcription factor 6 (ETV6) have been recognized. Moreover, with the application of advanced technologies and reports of more cases, additional germline mutations associated with myeloid neoplasms have been identified and provide insights into the formation, prognosis and therapy of myeloid neoplasms. The present review discusses the well-known CEBPA, DDX41, RUNX1, GATA2, JAK2 and ETV6 germline mutations, and other mutations including those of lymphocyte adapter protein/SH2B adapter protein 3 and duplications of autophagy related 2B, GSK3B interacting protein αnd RB binding protein 6, ubiquitin ligase, that remain to be confirmed or explored. Recommendations for the management of diseases associated with germline mutations are also provided.