Cbf beta-SMMHC induces distinct abnormal myeloid progenitors able to develop acute myeloid leukemia

Targeting a lineage-specific PI3Kɣ-Akt signaling module in acute myeloid leukemia using a heterobifunctional degrader molecule

Dose-limiting toxicity poses a major limitation to the clinical utility of targeted cancer therapies, often arising from target engagement in nonmalignant tissues. This obstacle can be minimized by targeting cancer dependencies driven by proteins with tissue-restricted and/or tumor-restricted expression. In line with another recent report, we show here that, in acute myeloid leukemia (AML), suppression of the myeloid-restricted PIK3CG/p110γ-PIK3R5/p101 axis inhibits protein kinase B/Akt signaling and compromises AML cell fitness. Furthermore, silencing the genes encoding PIK3CG/p110γ or PIK3R5/p101 sensitizes AML cells to established AML therapies. Importantly, we find that existing small-molecule inhibitors against PIK3CG are insufficient to achieve a sustained long-term antileukemic effect. To address this concern, we developed a proteolysis-targeting chimera (PROTAC) heterobifunctional molecule that specifically degrades PIK3CG and potently suppresses AML progression alone and in combination with venetoclax in human AML cell lines, primary samples from patients with AML and syngeneic mouse models.

Single-Cell Chromatin Accessibility Analysis Reveals the Epigenetic Basis and Signature Transcription Factors for the Molecular Subtypes of Colorectal Cancers

Colorectal cancer is a highly heterogeneous disease, with well-characterized subtypes based on genome, DNA methylome, and transcriptome signatures. To chart the epigenetic landscape of colorectal cancers, we generated a high-quality single-cell chromatin accessibility atlas of epithelial cells for 29 patients. Abnormal chromatin states acquired in adenomas were largely retained in colorectal cancers, which were tightly accompanied by opposite changes of DNA methylation. Unsupervised analysis on malignant cells revealed two epigenetic subtypes, exactly matching the iCMS classification, and key iCMS-specific transcription factors (TFs) were identified, including HNF4A and PPARA for iCMS2 tumors and FOXA3 and MAFK for iCMS3 tumors. Notably, subtype-specific TFs bind to distinct target gene sets and contribute to both interpatient similarities and diversities for both chromatin accessibilities and RNA expressions. Moreover, we identified CpG-island methylator phenotypes and pinpointed chromatin state signatures and TF regulators for the CIMP-high subtype. Our work systematically revealed the epigenetic basis of the well-known iCMS and CIMP classifications of colorectal cancers.

SIGNIFICANCE

Our work revealed the epigenetic basis of the well-known iCMS and CIMP classifications of colorectal cancers. Moreover, interpatient minor similarities and major diversities of chromatin accessibility signatures of TF target genes can faithfully explain the corresponding interpatient minor similarities and major diversities of RNA expression signatures of colorectal cancers, respectively. This article is featured in Selected Articles from This Issue, p. 897.

Targeting PRMT9-mediated arginine methylation suppresses cancer stem cell maintenance and elicits cGAS-mediated anticancer immunity

Current anticancer therapies cannot eliminate all cancer cells, which hijack normal arginine methylation as a means to promote their maintenance via unknown mechanisms. Here we show that targeting protein arginine N-methyltransferase 9 (PRMT9), whose activities are elevated in blasts and leukemia stem cells (LSCs) from patients with acute myeloid leukemia (AML), eliminates disease via cancer-intrinsic mechanisms and cancer-extrinsic type I interferon (IFN)-associated immunity. PRMT9 ablation in AML cells decreased the arginine methylation of regulators of RNA translation and the DNA damage response, suppressing cell survival. Notably, PRMT9 inhibition promoted DNA damage and activated cyclic GMP-AMP synthase, which underlies the type I IFN response. Genetically activating cyclic GMP-AMP synthase in AML cells blocked leukemogenesis. We also report synergy of a PRMT9 inhibitor with anti-programmed cell death protein 1 in eradicating AML. Overall, we conclude that PRMT9 functions in survival and immune evasion of both LSCs and non-LSCs; targeting PRMT9 may represent a potential anticancer strategy.

N-MYC regulates cell survival via eIF4G1 in inv(16) acute myeloid leukemia

N-MYC (encoded by MYCN) is a critical regulator of hematopoietic stem cell function. While the role of N-MYC deregulation is well established in neuroblastoma, the importance of N-MYC deregulation in leukemogenesis remains elusive. Here, we demonstrate that N-MYC is overexpressed in acute myeloid leukemia (AML) cells with chromosome inversion inv(16) and contributes to the survival and maintenance of inv(16) leukemia. We identified a previously unknown MYCN enhancer, active in multiple AML subtypes, essential for MYCN mRNA levels and survival in inv(16) AML cells. We also identified eukaryotic translation initiation factor 4 gamma 1 (eIF4G1) as a key N-MYC target that sustains leukemic survival in inv(16) AML cells. The oncogenic role of eIF4G1 in AML has not been reported before. Our results reveal a mechanism whereby N-MYC drives a leukemic transcriptional program and provides a rationale for the therapeutic targeting of the N-MYC/eIF4G1 axis in myeloid leukemia.

PML/RARa leukemia induced murine model for immunotherapy evaluation

Even though leukemia murine models are valuable tools for new drug therapy studies, most of these models consist of immunocompromised mice, which do not exhibit immune responses. In order to obtain an adequate leukemia model, we established an acute promyelocytic leukemia transplantation-based model (PML/RARa) in immunocompetent BALB/c mice, thus making it possible to study drug-induced cellular immune responses in leukemia. The development of PML/RARa leukemia was confirmed by leukocytosis (76.27 ± 21.8 vs. 3.40 ± 1.06; P < 0.0001), anemia (7.46 ± 1.86 vs. 15.10 ± 0.96; P < 0.0001), and thrombocytopenia (131.85 ± 39.32 vs. 839.50 ± 171.20; P < 0.0001), and the presence of blasts in the peripheral blood of mice (approximately 50% blasts; P < 0.0001), 15 days after the transplants. These findings were corroborated through differential counts, flow cytometry, and in vivo imaging, which indicated increased number of immature cells in the bone marrow (15.75 ± 3.30 vs 6.69 ± 0.55; P < 0.001), peripheral blood (7.88 ± 2.67 vs 1.22 ± 0.89; P < 0.001), and spleen (35.21 ± 4.12 vs 1.35 ± 0.86; P < 0.0001), as well as promyelocytes in the bone marrow (41.23 ± 4.80 vs 5.73 ± 1.50; P < 0.0001), peripheral blood (46.08 ± 7.52 vs 1.10 ± 0.59; P < 0.0001) and spleen (35.31 ± 8.26 vs 2.49 ± 0.29; P < 0.0001) of PML/RARa mice. Compared to basal conditions of untransplanted mice, the PML/RARa mice exhibited frequencies of T lymphocytes CD4 helper = 14.85 ± 2.91 vs 20.77 ± 2.9 in the peripheral blood (P < 0.05); 12.75 ± 1.33 vs 45.90 ± 2.02 in the spleen (P < 0.0001); CD8 cytotoxic = 11.27 ± 3.44 vs 11.05 ± 1.22 in the peripheral blood (P > 0.05); 10.48 ± 1.16 vs 30.02 ± 1.80 in the spleen (P < 0.0001); natural killer (NK) cells = 3.68 ± 1.35 vs 6.84 ± 0.52 in the peripheral blood (P < 0.001); 4.43 ± 0.57 vs 6.40 ± 1.14 in the spleen (P < 0.05); B cells 2.50 ± 0.60 vs 15.20 ± 5.34 in the peripheral blood (P < 0.001); 17.77 ± 4.39 vs 46.90 ± 5.92 in the spleen (P < 0.0001); neutrophils = 5.97% ± 1.88 vs 31.57 ± 9.14 (P < 0.0001); and monocytes = 6.45 ± 2.97 vs 15.85 ± 2.57 (P < 0.001), selected as classical (3.33 ± 3.40 vs 57.80 ± 16.51, P < 0.0001), intermediate (57.42 ± 10.61 vs 21.75 ± 5.90, P < 0.0001), and non-classical monocytes (37.51 ± 10.85 vs 18.08 ± 7.13, P < 0.05) in the peripheral blood; and as classically activated (M1) within in the bone marrow (3.70 ± 0.94 vs 1.88 ± 0.39, P < 0.05) and spleen 15.19 ± 3.32 vs 9.47 ± 1.61, P < 0.05), in addition to alternatively activated (M2) macrophages within the bone marrow (23.06 ± 5.25 vs 1.76 ± 0.74, P < 0.0001) and spleen (46.51 ± 11.18 vs 30.58 ± 2.64, P < 0.05) compartments. All-trans retinoic acid (ATRA) treatment of PML/RARa mice reduced blast (immature cells) in the bone marrow (8.62 ± 1.81 vs 15.76 ± 1.25; P < 0.05) and spleen (8.75 ± 1.31 vs 35.21 ± 1.55; P < 0.0001) with no changes in the peripheral blood (10.13 ± 3.33 vs 7.88 ± 1.01; P > 0.05), as well as reduced promyelocytes in the bone marrow (19.79 ± 4.84 vs 41.23 ± 1.81; P < 0.05), peripheral blood (31.65 ± 3.92 vs 46.09 ± 2.84; P < 0.05) and spleen (24.84 ± 2.03 vs 41.46 ± 2.39; P < 0.001), and increased neutrophils of the peripheral blood (35.48 ± 7.24 vs 7.83 ± 1.40; P < 0.05) which was corroborated by reducing of immature cells and increase of neutrophil in the stained smears from PML/RARa mice, thus confirming that this model can be used in drug development studies. Our results show the effective induction of PML/RARa leukemia in BALB/c mice, thus producing a low-priced and reliable tool for investigating cellular immune responses in leukemia.

Regulation and signaling pathways in cancer stem cells: implications for targeted therapy for cancer

Cancer stem cells (CSCs), initially identified in leukemia in 1994, constitute a distinct subset of tumor cells characterized by surface markers such as CD133, CD44, and ALDH. Their behavior is regulated through a complex interplay of networks, including transcriptional, post-transcriptional, epigenetic, tumor microenvironment (TME), and epithelial-mesenchymal transition (EMT) factors. Numerous signaling pathways were found to be involved in the regulatory network of CSCs. The maintenance of CSC characteristics plays a pivotal role in driving CSC-associated tumor metastasis and conferring resistance to therapy. Consequently, CSCs have emerged as promising targets in cancer treatment. To date, researchers have developed several anticancer agents tailored to specifically target CSCs, with some of these treatment strategies currently undergoing preclinical or clinical trials. In this review, we outline the origin and biological characteristics of CSCs, explore the regulatory networks governing CSCs, discuss the signaling pathways implicated in these networks, and investigate the influential factors contributing to therapy resistance in CSCs. Finally, we offer insights into preclinical and clinical agents designed to eliminate CSCs.

Characterization of leukemia progression in the Cbfb-MYH11 knockin mice by single cell RNA sequencing

A recurrent inversion of chromosome 16 fuses the genes CBFB and MYH11 and the resultant CBFβ-SMMHC fusion protein acts as a driver of the M4Eo subtype of acute myeloid leukemia (AML). This study utilized single cell RNA-sequencing (scRNA-seq) to assess gene expression changes during the disease progression from normal to pre-leukemic to overt leukemia in the conditional Cbfb-MYH11 knock-in mouse model. The study investigated dynamic shifts in cell types as disease progresses, and gene expression differences between normal and diseased cells. The study identified a novel cell population in the pre-leukemic state with expression of genes involved in immune activation. Overall, this study discovered hematopoietic cells first affected by the expression of CBFβ-SMMHC and identified unique signature genes for the pre-leukemic cells that separate them from the normal hematopoietic cellular milieu.

Acute Myeloid Leukemia Stem Cells in Minimal/Measurable Residual Disease Detection

Acute myeloid leukemia (AML) is a hematological malignancy characterized by an abundance of incompletely matured or immature clonally derived hematopoietic precursors called leukemic blasts. Rare leukemia stem cells (LSCs) that can self-renew as well as give rise to leukemic progenitors comprising the bulk of leukemic blasts are considered the cellular reservoir of disease initiation and maintenance. LSCs are widely thought to be relatively resistant as well as adaptive to chemotherapy and can cause disease relapse. Therefore, it is imperative to understand the molecular bases of LSC forms and functions during different stages of disease progression, so we can more accurately identify these cells and design therapies to target them. Irrespective of the morphological, cytogenetic, and cellular heterogeneity of AML, the uniform, singularly important and independently significant prognosticator of disease response to therapy and patient outcome is measurable or minimal residual disease (MRD) detection, defined by residual disease detection below the morphology-based 5% blast threshold. The importance of LSC identification and frequency estimation during MRD detection, in order to make MRD more effective in predicting disease relapse and modifying therapeutic regimen is becoming increasingly apparent. This review focuses on summarizing functional and cellular composition-based LSC identification and linking those studies to current techniques of MRD detection to suggest LSC-inclusive MRD detection as well as outline outstanding questions that need to be addressed to improve the future of AML clinical management and treatment outcomes.

Neoantigen-specific TCR-T cell-based immunotherapy for acute myeloid leukemia

Neoantigens derived from non-synonymous somatic mutations are restricted to malignant cells and are thus considered ideal targets for T cell receptor (TCR)-based immunotherapy. Adoptive transfer of T cells bearing neoantigen-specific TCRs exhibits the ability to preferentially target tumor cells while remaining harmless to normal cells. High-avidity TCRs specific for neoantigens expressed on AML cells have been identified in vitro and verified using xenograft mouse models. Preclinical studies of these neoantigen-specific TCR-T cells are underway and offer great promise as safe and effective therapies. Additionally, TCR-based immunotherapies targeting tumor-associated antigens are used in early-phase clinical trials for the treatment of AML and show encouraging anti-leukemic effects. These clinical experiences support the application of TCR-T cells that are specifically designed to recognize neoantigens. In this review, we will provide a detailed profile of verified neoantigens in AML, describe the strategies to identify neoantigen-specific TCRs, and discuss the potential of neoantigen-specific T-cell-based immunotherapy in AML.

Comparison of cell state models derived from single-cell RNA sequencing data: graph versus multi-dimensional space

Single-cell sequencing technologies have revolutionized molecular and cellular biology and stimulated the development of computational tools to analyze the data generated from these technology platforms. However, despite the recent explosion of computational analysis tools, relatively few mathematical models have been developed to utilize these data. Here we compare and contrast two cell state geometries for building mathematical models of cell state-transitions with single-cell RNA-sequencing data with hematopoeisis as a model system; (i) by using partial differential equations on a graph representing intermediate cell states between known cell types, and (ii) by using the equations on a multi-dimensional continuous cell state-space. As an application of our approach, we demonstrate how the calibrated models may be used to mathematically perturb normal hematopoeisis to simulate, predict, and study the emergence of novel cell states during the pathogenesis of acute myeloid leukemia. We particularly focus on comparing the strength and weakness of the graph model and multi-dimensional model.

Multi-omics reveals mitochondrial metabolism proteins susceptible for drug discovery in AML

Acute myeloid leukemia (AML) is a devastating cancer affecting the hematopoietic system. Previous research has relied on RNA sequencing and microarray techniques to study the downstream effects of genomic alterations. While these studies have proven efficacious, they fail to capture the changes that occur at the proteomic level. To interrogate the effect of protein expression alterations in AML, we performed a quantitative mass spectrometry in parallel with RNAseq analysis using AML mouse models. These combined results identified 34 proteins whose expression was upregulated in AML tumors, but strikingly, were unaltered at the transcriptional level. Here we focus on mitochondrial electron transfer proteins ETFA and ETFB. Silencing of ETFA and ETFB led to increased mitochondrial activity, mitochondrial stress, and apoptosis in AML cells, but had little to no effect on normal human CD34+ cells. These studies identify a set of proteins that have not previously been associated with leukemia and may ultimately serve as potential targets for therapeutic manipulation to hinder AML progression and help contribute to our understanding of the disease.

Dynamic patterns of microRNA expression during acute myeloid leukemia state-transition

MicroRNAs (miRNAs) have been shown to hold prognostic value in acute myeloid leukemia (AML); however, the temporal dynamics of miRNA expression in AML are poorly understood. Using serial samples from a mouse model of AML to generate time-series miRNA sequencing data, we are the first to show that the miRNA transcriptome undergoes state-transition during AML initiation and progression. We modeled AML state-transition as a particle undergoing Brownian motion in a quasi-potential and validated the AML state-space and state-transition model to accurately predict time to AML in an independent cohort of mice. The critical points of the model provided a framework to align samples from mice that developed AML at different rates. Our mathematical approach allowed discovery of dynamic processes involved during AML development and, if translated to humans, has the potential to predict an individual's disease trajectory.

Targeting key proteins involved in transcriptional regulation for cancer therapy: Current strategies and future prospective

The key proteins involved in transcriptional regulation play convergent roles in cellular homeostasis, and their dysfunction mediates aberrant gene expressions that underline the hallmarks of tumorigenesis. As tumor progression is dependent on such abnormal regulation of transcription, it is important to discover novel chemical entities as antitumor drugs that target key tumor-associated proteins involved in transcriptional regulation. Despite most key proteins (especially transcription factors) involved in transcriptional regulation are historically recognized as undruggable targets, multiple targeting approaches at diverse levels of transcriptional regulation, such as epigenetic intervention, inhibition of DNA-binding of transcriptional factors, and inhibition of the protein-protein interactions (PPIs), have been established in preclinically or clinically studies. In addition, several new approaches have recently been described, such as targeting proteasomal degradation and eliciting synthetic lethality. This review will emphasize on accentuating these developing therapeutic approaches and provide a thorough conspectus of the drug development to target key proteins involved in transcriptional regulation and their impact on future oncotherapy.

Murine Models of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a phenotypically and genetically heterogeneous hematologic malignancy. Extensive sequencing efforts have mapped the genomic landscape of adult and pediatric AML revealing a number of biologically and prognostically relevant driver lesions. Beyond identifying recurrent genetic aberrations, it is of critical importance to fully delineate the complex mechanisms by which they contribute to the initiation and evolution of disease to ultimately facilitate the development of targeted therapies. Towards these aims, murine models of AML are indispensable research tools. The rapid evolution of genetic engineering techniques over the past 20 years has greatly advanced the use of murine models to mirror specific genetic subtypes of human AML, define cell-intrinsic and extrinsic disease mechanisms, study the interaction between co-occurring genetic lesions, and test novel therapeutic approaches. This review summarizes the mouse model systems that have been developed to recapitulate the most common genomic subtypes of AML. We will discuss the strengths and weaknesses of varying modeling strategies, highlight major discoveries emanating from these model systems, and outline future opportunities to leverage emerging technologies for mechanistic and preclinical investigations.

Targeting miR-126 in inv(16) acute myeloid leukemia inhibits leukemia development and leukemia stem cell maintenance

Acute myeloid leukemia (AML) harboring inv(16)(p13q22) expresses high levels of miR-126. Here we show that the CBFB-MYH11 (CM) fusion gene upregulates miR-126 expression through aberrant miR-126 transcription and perturbed miR-126 biogenesis via the HDAC8/RAN-XPO5-RCC1 axis. Aberrant miR-126 upregulation promotes survival of leukemia-initiating progenitors and is critical for initiating and maintaining CM-driven AML. We show that miR-126 enhances MYC activity through the SPRED1/PLK2-ERK-MYC axis. Notably, genetic deletion of miR-126 significantly reduces AML rate and extends survival in CM knock-in mice. Therapeutic depletion of miR-126 with an anti-miR-126 (miRisten) inhibits AML cell survival, reduces leukemia burden and leukemia stem cell (LSC) activity in inv(16) AML murine and xenograft models. The combination of miRisten with chemotherapy further enhances the anti-leukemia and anti-LSC activity. Overall, this study provides molecular insights for the mechanism and impact of miR-126 dysregulation in leukemogenesis and highlights the potential of miR-126 depletion as a therapeutic approach for inv(16) AML.

miR-126 is highly expressed in inv(16) Acute myeloid leukemia (AML) but its role is unclear. Here, the authors show that the aberrant expression of miR-126 in inv(16) AML is directly due to the CBFB-MYH11 fusion gene and that it can promote AML development and leukemia stem cell maintenance, highlighting miR-126 as a therapeutic target for inv(16) AML patients

Preleukemic and leukemic evolution at the stem cell level

Hematological malignancies are an aggregate of diverse populations of cells that arise following a complex process of clonal evolution and selection. Recent approaches have facilitated the study of clonal populations and their evolution over time across multiple phenotypic cell populations. In this review, we present current concepts on the role of clonal evolution in leukemic initiation, disease progression, and relapse. We highlight recent advances and unanswered questions about the contribution of the hematopoietic stem cell population to these processes.

Emerging therapies for inv(16) AML

The core binding factor composed of CBFβ and RUNX subunits plays a critical role in most hematopoietic lineages and is deregulated in acute myeloid leukemia (AML). The fusion oncogene CBFβ-SMMHC expressed in AML with the chromosome inversion inv(16)(p13q22) acts as a driver oncogene in hematopoietic stem cells and induces AML. This review focuses on novel insights regarding the molecular mechanisms involved in CBFβ-SMMHC-driven leukemogenesis and recent advances in therapeutic approaches to target CBFβ-SMMHC in inv(16) AML.

MDMX acts as a pervasive preleukemic-to-acute myeloid leukemia transition mechanism

MDMX is overexpressed in the vast majority of patients with acute myeloid leukemia (AML). We report that MDMX overexpression increases preleukemic stem cell (pre-LSC) number and competitive advantage. Utilizing five newly generated murine models, we found that MDMX overexpression triggers progression of multiple chronic/asymptomatic preleukemic conditions to overt AML. Transcriptomic and proteomic studies revealed that MDMX overexpression exerts this function, unexpectedly, through activation of Wnt/β-Catenin signaling in pre-LSCs. Mechanistically, MDMX binds CK1α and leads to accumulation of β-Catenin in a p53-independent manner. Wnt/β-Catenin inhibitors reverse MDMX-induced pre-LSC properties, and synergize with MDMX-p53 inhibitors. Wnt/β-Catenin signaling correlates with MDMX expression in patients with preleukemic myelodysplastic syndromes and is associated with increased risk of progression to AML. Our work identifies MDMX overexpression as a pervasive preleukemic-to-AML transition mechanism in different genetically driven disease subtypes, and reveals Wnt/β-Catenin as a non-canonical MDMX-driven pathway with therapeutic potential for progression prevention and cancer interception.

RUNX1 and CBFβ-SMMHC transactivate target genes together in abnormal myeloid progenitors for leukemia development

Inversion of chromosome 16 is a consistent finding in patients with acute myeloid leukemia subtype M4 with eosinophilia, which generates a CBFB-MYH11 fusion gene. It is generally considered that CBFβ-SMMHC, the fusion protein encoded by CBFB-MYH11, is a dominant negative repressor of RUNX1. However, recent findings challenge the RUNX1-repression model for CBFβ-SMMHC-mediated leukemogenesis. To definitively address the role of Runx1 in CBFB-MYH11-induced leukemia, we crossed conditional Runx1 knockout mice (Runx1f/f) with conditional Cbfb-MYH11 knockin mice (Cbfb+/56M). On Mx1-Cre activation in hematopoietic cells induced by poly (I:C) injection, all Mx1-CreCbfb+/56M mice developed leukemia in 5 months, whereas no leukemia developed in Runx1f/fMx1-CreCbfb+/56M mice, and this effect was cell autonomous. Importantly, the abnormal myeloid progenitors (AMPs), a leukemia-initiating cell population induced by Cbfb-MYH11 in the bone marrow, decreased and disappeared in Runx1f/fMx1-CreCbfb+/56M mice. RNA-seq analysis of AMP cells showed that genes associated with proliferation, differentiation blockage, and leukemia initiation were differentially expressed between Mx1-CreCbfb+/56M and Runx1f/fMx1-CreCbfb+/56M mice. In addition, with the chromatin immunocleavage sequencing assay, we observed a significant enrichment of RUNX1/CBFβ-SMMHC target genes in Runx1f/fMx1-CreCbfb+/56M cells, especially among downregulated genes, suggesting that RUNX1 and CBFβ-SMMHC mainly function together as activators of gene expression through direct target gene binding. These data indicate that Runx1 is indispensable for Cbfb-MYH11-induced leukemogenesis by working together with CBFβ-SMMHC to regulate critical genes associated with the generation of a functional AMP population.

CBFB-MYH11 fusion neoantigen enables T cell recognition and killing of acute myeloid leukemia

Proteins created from recurrent fusion genes like CBFB-MYH11 are prevalent in acute myeloid leukemia (AML), often necessary for leukemogenesis, persistent throughout the disease course, and highly leukemia specific, making them attractive neoantigen targets for immunotherapy. A nonameric peptide derived from a prevalent CBFB-MYH11 fusion protein was found to be immunogenic in HLA-B*40:01+ donors. High-avidity CD8+ T cell clones isolated from healthy donors killed CBFB-MYH11+ HLA-B*40:01+ AML cell lines and primary human AML samples in vitro. CBFB-MYH11-specific T cells also controlled CBFB-MYH11+ HLA-B*40:01+ AML in vivo in a patient-derived murine xenograft model. High-avidity CBFB-MYH11 epitope-specific T cell receptors (TCRs) transduced into CD8+ T cells conferred antileukemic activity in vitro. Our data indicate that the CBFB-MYH11 fusion neoantigen is naturally presented on AML blasts and enables T cell recognition and killing of AML. We provide proof of principle for immunologically targeting AML-initiating fusions and demonstrate that targeting neoantigens has clinical relevance even in low-mutational frequency cancers like fusion-driven AML. This work also represents a first critical step toward the development of TCR T cell immunotherapy targeting fusion gene-driven AML.

State-Transition Analysis of Time-Sequential Gene Expression Identifies Critical Points That Predict Development of Acute Myeloid Leukemia

Temporal dynamics of gene expression inform cellular and molecular perturbations associated with disease development and evolution. Given the complexity of high-dimensional temporal genomic data, an analytic framework guided by a robust theory is needed to interpret time-sequential changes and to predict system dynamics. Here we model temporal dynamics of the transcriptome of peripheral blood mononuclear cells in a two-dimensional state-space representing states of health and leukemia using time-sequential bulk RNA-seq data from a murine model of acute myeloid leukemia (AML). The state-transition model identified critical points that accurately predict AML development and identifies stepwise transcriptomic perturbations that drive leukemia progression. The geometry of the transcriptome state-space provided a biological interpretation of gene dynamics, aligned gene signals that are not synchronized in time across mice, and allowed quantification of gene and pathway contributions to leukemia development. Our state-transition model synthesizes information from multiple cell types in the peripheral blood and identifies critical points in the transition from health to leukemia to guide interpretation of changes in the transcriptome as a whole to predict disease progression. SIGNIFICANCE: These findings apply the theory of state transitions to model the initiation and development of acute myeloid leukemia, identifying transcriptomic perturbations that accurately predict time to disease development.See related commentary by Kuijjer, p. 3072 GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/15/3157/F1.large.jpg.

IL-33/IL1RL1 axis regulates cell survival through the p38 MAPK pathway in acute myeloid leukemia

Acute myeloid leukemia (AML) is often characterized by the presence of specific and recurrent chromosomal abnormalities. Current treatments have greatly increased remission rate, but relapse still occurs. Therefore, novel therapeutic approaches are required. Previously, using a conditional Cbfb-MYH11 knockin mouse model, we showed that Cbfb-MYH11 induces the expression of a cytokine receptor, IL1RL1. Treatment with IL-33, the only known ligand of IL1RL1, promotes leukemia cell survival in vitro. We further found that IL1RL1⁺ cells survive better with chemotherapy than IL1RL1^- population. However, the mechanism is not clear. Here, we show that IL-33 treatment decreased drug sensitivity in the human inv(16) AML cell line ME-1. By RT-PCR, we found that IL-33 increased the expression of IL-4 and IL-6 and led to the activation of both p38 MAPK and NF-κB. We also showed that IL-33 decreased apoptosis with increased phosphorylation of p38 MAPK. Moreover, pre-treatment with MAPK inhibitor attenuated the phosphorylation of p38 enhanced by IL-33 and reversed the anti-apoptotic effect by IL-33. Taken together, our findings give news insights into the potential mechanism of the anti-apoptotic effect by IL-33/IL1RL1 axis in AML which will help in future drug development.

Acute myeloid leukemia with inv(16)(p13.1q22) and deletion of the 5'MYH11/3'CBFB gene fusion: a report of two cases and literature review

Background

Abnormalities of chromosome 16 are found in about 5–8% of acute myeloid leukemia (AML). The AML with inv(16)(p13.1q22) or t (16;16)(p13.1;q22) is associated with a high rate of complete remission (CR) and favorable overall survival (OS) when treated with high-dose Cytarabine. At the inversion breakpoints, deletion of 3’CBFB has been reported, but most of them were studied by chromosome and fluorescence in situ hybridization (FISH) analyses. The genomic characteristics of such deletions remain largely undefined, hindering further understanding of the clinical significance of the deletions.

Case presentation

We report here two AML cases with inv(16) and deletion of the 5’MYH11/3’CBFB gene fusion, which were characterized by chromosome, FISH, and single nucleotide polymorphism (SNP) microarray analyses. Both cases have achieved CR for more than three years.

Conclusions

Deletion of 3’CBFB in AML with inv(16) is also accompanied with deletion of 5’MYH11 in all the cases studied by SNP microarray, suggesting that 3’CBFB and 5’MYH11 were most likely deleted together as a fusion product of inv(16) instead of occurring separately. In concert with the findings of other published studies of similar patients, our study suggests that deletion of 5’MYH11/3’CBFB in AML with inv(16) may not have negative impact on the prognosis of the disease.

Targeting Immunophenotypic Markers on Leukemic Stem Cells: How Lessons from Current Approaches and Advances in the Leukemia Stem Cell (LSC) Model Can Inform Better Strategies for Treating Acute Myeloid Leukemia (AML)

Therapies targeting cell-surface antigens in acute myeloid leukemia (AML) have been tested over the past 20 years with limited improvement in overall survival. Recent advances in the understanding of AML pathogenesis support therapeutic targeting of leukemia stem cells as the most promising avenue toward a cure. In this review, we provide an overview of the evolving leukemia stem cell (LSC) model, including evidence of the cell of origin, cellular and molecular disease architecture, and source of relapse in AML. In addition, we explore limitations of current targeted strategies utilized in AML and describe the various immunophenotypic antigens that have been proposed as LSC-directed therapeutic targets. We draw lessons from current approaches as well as from the (pre)-LSC model to suggest criteria that immunophenotypic targets should meet for more specific and effective elimination of disease-initiating clones, highlighting in detail a few targets that we suggest fit these criteria most completely.

Targeted Delivery of miRNA Antagonists to Myeloid Cells In Vitro and In Vivo

Elevated levels of microRNAs in cancer cells are often associated with oncogenic effects and thus provide potential therapeutic targets. However, the lack of efficient delivery methods for synthetic miRNA inhibitors, antagomiR, or anti-miR oligonucleotides hindered clinical translation of such strategies. We recently developed an approach for targeted delivery of synthetic, 2'-O-methyl-modified antagomiR molecules to normal and malignant myeloid cells and B cells by tethering to the single-stranded, phosphorothioate oligodeoxynucleotides (PSO). The PSO-antagomiR are rapidly internalized through scavenger receptor-mediated endocytosis by human monocytes, dendritic cells, B cells, as well as myeloid leukemia and B-cell lymphoma cells, but not by T cells. Following internalization, the unformulated PSO-antagomiR potently reduces levels of target miRNA and modulates expression of downstream protein targets, both in vitro and in vivo. The simple design of PSO-antagomiR conjugates enable adaptation of this strategy for targeting oncogenic miRNAs in nonmalignant and malignant myeloid cells and B cells.

Loss of FBXO9 Enhances Proteasome Activity and Promotes Aggressiveness in Acute Myeloid Leukemia

The hematopoietic system is maintained throughout life by stem cells that are capable of differentiating into all hematopoietic lineages. An intimate balance between self-renewal, differentiation, and quiescence is required to maintain hematopoiesis and disruption of this balance can result in malignant transformation. FBXO9, the substrate recognition component from the SCF E3 ubiquitin ligase family, is downregulated in patients with acute myeloid leukemia (AML) compared to healthy bone marrow, and this downregulation is particularly evident in patients with inv(16) AML. To study FBXO9 in malignant hematopoiesis, we generated a conditional knockout mouse model using a novel CRISPR/Cas9 strategy. Deletion of Fbxo9 in the murine hematopoietic system showed no adverse effects on stem and progenitor cell function but in AML lead to markedly accelerated and aggressive leukemia development in mice with inv(16). Not only did Fbxo9 play a role in leukemia initiation but it also functioned to maintain AML activity and promote disease progression. Quantitative mass spectrometry from primary tumors reveals tumors lacking Fbxo9 highly express proteins associated with metastasis and invasion as well as components of the ubiquitin proteasome system. We confirmed that the loss of FBXO9 leads to increased proteasome activity and tumors cells were more sensitive to in vitro proteasome inhibition with bortezomib, suggesting that FBXO9 expression may predict patients’ response to bortezomib.

Targeting transcription factors in cancer - from undruggable to reality

Mutated or dysregulated transcription factors represent a unique class of drug targets that mediate aberrant gene expression, including blockade of differentiation and cell death gene expression programmes, hallmark properties of cancers. Transcription factor activity is altered in numerous cancer types via various direct mechanisms including chromosomal translocations, gene amplification or deletion, point mutations and alteration of expression, as well as indirectly through non-coding DNA mutations that affect transcription factor binding. Multiple approaches to target transcription factor activity have been demonstrated, preclinically and, in some cases, clinically, including inhibition of transcription factor-cofactor protein-protein interactions, inhibition of transcription factor-DNA binding and modulation of levels of transcription factor activity by altering levels of ubiquitylation and subsequent proteasome degradation or by inhibition of regulators of transcription factor expression. In addition, several new approaches to targeting transcription factors have recently emerged including modulation of auto-inhibition, proteolysis targeting chimaeras (PROTACs), use of cysteine reactive inhibitors, targeting intrinsically disordered regions of transcription factors and combinations of transcription factor inhibitors with kinase inhibitors to block the development of resistance. These innovations in drug development hold great promise to yield agents with unique properties that are likely to impact future cancer treatment.

Gata2 deficiency delays leukemogenesis while contributing to aggressive leukemia phenotype in Cbfb-MYH11 knockin mice

Inversion of chromosome 16 (inv(16)) generates a fusion gene CBFB-MYH11, which is a driver mutation for acute myeloid leukemia (AML). Gene expression profiling suggests that Gata2, a hematopoietic transcription factor, is a top upregulated gene in preleukemic Cbfb-MYH11 knockin mice and is expressed in human inv(16) AML. On the other hand, we have also identified recurrent monoallelic deletions of GATA2 in relapsed human CBF-AML patients. To clarify the role of Gata2 in leukemogenesis by Cbfb-MYH11, we generated conditional Cbfb-MYH11 knockin mice with Gata2 heterozygous knockout. Gata2 heterozygous knockout reduced abnormal myeloid progenitors, which are capable of inducing leukemia in the Cbfb-MYH11 mice. Consequently, Cbfb-MYH11 mice with Gata2 heterozygous knockout developed leukemia with longer latencies than those with intact Gata2. Interestingly, leukemic cells with Gata2 heterozygous knockout gained higher number of mutations and showed more aggressive phenotype in both primary and transplanted mice. Moreover, leukemic cells with Gata2 heterozygous knockout showed higher repopulating capacity in competitive transplantation experiments. In summary, reduction of Gata2 activity affects mutational dynamics of leukemia with delayed leukemia onset in Cbfb-MYH11 knockin mice, but paradoxically results in a more aggressive leukemia phenotype, which may be correlated with leukemia relapse or poor prognosis in human patients.

A Critical Review of Animal Models Used in Acute Myeloid Leukemia Pathophysiology

Acute myeloid leukemia (AML) is one of the most frequent, complex, and heterogeneous hematological malignancies. AML prognosis largely depends on acquired cytogenetic, epigenetic, and molecular abnormalities. Despite the improvement in understanding the biology of AML, survival rates remain quite low. Animal models offer a valuable tool to recapitulate different AML subtypes, and to assess the potential role of novel and known mutations in disease progression. This review provides a comprehensive and critical overview of select available AML animal models. These include the non-mammalian Zebrafish and Drosophila models as well as the mammalian rodent systems, comprising rats and mice. The suitability of each animal model, its contribution to the advancement of knowledge in AML pathophysiology and treatment, as well as its advantages and limitations are discussed. Despite some limitations, animal models represent a powerful approach to assess toxicity, and permit the design of new therapeutic strategies.

The transcription factor CBFB suppresses breast cancer through orchestrating translation and transcription

Translation and transcription are frequently dysregulated in cancer. These two processes are generally regulated by distinct sets of factors. The CBFB gene, which encodes a transcription factor, has recently emerged as a highly mutated driver in a variety of human cancers including breast cancer. Here we report a noncanonical role of CBFB in translation regulation. RNA immunoprecipitation followed by deep sequencing (RIP-seq) reveals that cytoplasmic CBFB binds to hundreds of transcripts and regulates their translation. CBFB binds to mRNAs via hnRNPK and enhances translation through eIF4B, a general translation initiation factor. Interestingly, the RUNX1 mRNA, which encodes the transcriptional partner of CBFB, is bound and translationally regulated by CBFB. Furthermore, nuclear CBFB/RUNX1 complex transcriptionally represses the oncogenic NOTCH signaling pathway in breast cancer. Thus, our data reveal an unexpected function of CBFB in translation regulation and propose that breast cancer cells evade translation and transcription surveillance simultaneously through downregulating CBFB.

CBFB is highly mutated in breast cancers and is known to interact with RUNX proteins to regulate transcription. Here, the authors describe a non-canonical role of CBFB in translation regulation in which it binds to mRNAs through hnRNPK, facilitating translation by eIF4B.

Use of polymeric CXCR4 inhibitors as siRNA delivery vehicles for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults and is associated with poor long-term survival often owing to relapse. Current treatments for AML are associated with considerable toxicity and are frequently not effective after relapse. Thus, it is important to develop novel therapeutic strategies. Short interfering RNA (siRNA)-based therapeutics targeting key oncogenes have been proposed as treatments for AML. We recently developed novel siRNA delivery polycations (PCX) based on AMD3100 (plerixafor), an FDA-approved inhibitor of the CXC chemokine receptor 4 (CXCR4). Inhibitors of CXCR4 have been shown to sensitize leukemia cells to chemotherapy. Therefore, PCX has the potential to target leukemia cells via two mechanisms: inhibition of CXCR4 and delivery of siRNAs against critical genes. In this report, we show that PCX exerts a cytotoxic effect on leukemia cells more effectively than other CXCR4 inhibitors, including AMD3100. In addition, we show that PCX can deliver siRNAs against the transcription factor RUNX1 to mouse and human leukemia cells. Overall, our study provides the first evidence that dual-function PCX/siRNA nanoparticles can simultaneously inhibit CXCR4 and deliver siRNAs, targeting key oncogenes in leukemia cells and that PCX/siRNA has clinical potential for the treatment of AML.

CBFβ-MYH11 interferes with megakaryocyte differentiation via modulating a gene program that includes GATA2 and KLF1

The inv(16) acute myeloid leukemia-associated CBFβ-MYH11 fusion is proposed to block normal myeloid differentiation, but whether this subtype of leukemia cells is poised for a unique cell lineage remains unclear. Here, we surveyed the functional consequences of CBFβ-MYH11 in primary inv(16) patient blasts, upon expression during hematopoietic differentiation in vitro and upon knockdown in cell lines by multi-omics profiling. Our results reveal that primary inv(16) AML cells share common transcriptomic signatures and epigenetic determiners with megakaryocytes and erythrocytes. Using in vitro differentiation systems, we reveal that CBFβ-MYH11 knockdown interferes with normal megakaryocyte maturation. Two pivotal regulators, GATA2 and KLF1, are identified to complementally occupy RUNX1-binding sites upon fusion protein knockdown, and overexpression of GATA2 partly induces a gene program involved in megakaryocyte-directed differentiation. Together, our findings suggest that in inv(16) leukemia, the CBFβ-MYH11 fusion inhibits primed megakaryopoiesis by attenuating expression of GATA2/KLF1 and interfering with a balanced transcriptional program involving these two factors.

HDAC1 Is a Required Cofactor of CBFβ-SMMHC and a Potential Therapeutic Target in Inversion 16 Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a neoplastic disease characterized by the uncontrolled proliferation and accumulation of immature myeloid cells. A common mutation in AML is the inversion of chromosome 16 [inv (16)], which generates a fusion between the genes for core binding factor beta (CBFB) and smooth muscle myosin heavy chain gene (MYH11), forming the oncogene CBFB-MYH11. The expressed protein, CBFβ-SMMHC, forms a heterodimer with the key hematopoietic transcription factor RUNX1. Although CBFβ-SMMHC was previously thought to dominantly repress RUNX1, recent work suggests that CBFβ-SMMHC functions together with RUNX1 to activate transcription of specific target genes. However, the mechanism of this activity or a requirement for additional cofactors is not known. Here, we show that the epigenetic regulator histone deacetylase 1 (HDAC1) forms a complex with CBFβ-SMMHC, colocalizes with RUNX1 and CBFβ-SMMHC on the promoters of known fusion protein target genes, and that Hdac1 is required for expression of these genes. These results imply that HDAC1 is an important component of the CBFβ-SMMHC transcriptional complex, and that leukemia cells expressing the fusion protein may be sensitive to treatment with HDAC1 inhibitors. Using a knock-in mouse model expressing CBFβ-SMMHC, we found that in vivo treatment with the HDAC1 inhibitor entinostat decreased leukemic burden, and induced differentiation and apoptosis of leukemia cells. Together, these results demonstrate that HDAC1 is an important cofactor of CBFβ-SMMHC and a potential therapeutic target in inv (16) AML. IMPLICATIONS: This report describes a novel role for HDAC1 as a cofactor for the leukemogenic fusion protein CBFβ-SMMHC and shows that inhibitors of HDAC1 effectively target leukemia cells expressing the fusion protein in vivo.

IL1RL1 is dynamically expressed on Cbfb-MYH11+ leukemia stem cells and promotes cell survival

Acute myeloid leukemia (AML) is often characterized by the presence of specific, recurrent chromosomal abnormalities. One of the most common aberrations, inversion of chromosome 16 [inv(16)], generates the fusion oncogene CBFB-MYH11. Previously, we used a mouse knock-in model to show that Cbfb-MYH11 induces changes in gene expression and results in the accumulation of abnormal myeloid cells, a subset of which are enriched for leukemia stem cell (LSC) activity. One gene upregulated by Cbfb-MYH11 encodes the cytokine receptor IL1RL1 (ST2). IL1RL1 and its ligand IL-33 are known regulators of mature myeloid cells, but their roles in AML are not known. Here, we use Cbfb-MYH11 knock-in mice to show that IL1RL1 is expressed by cell populations with high LSC activity, and that the cell surface expression of IL1RL1 is dynamic, implying that the expression of IL1RL1 is not restricted to a specific stage of differentiation. We also show that treatment with IL-33 increased serial replating ability and expression of pro-survival proteins in vitro. Finally, we show that IL1RL1⁺ cells can survive chemotherapy better than IL1RL1⁻ cells in vivo. Collectively, our results indicate that IL1RL1 is dynamically expressed in Cbfb-MYH11⁺ leukemia cells and promotes their survival.

The Impact of the Cellular Origin in Acute Myeloid Leukemia: Learning From Mouse Models

Acute myeloid leukemia (AML) is a genetically heterogeneous disease driven by a limited number of cooperating mutations. There is a long-standing debate as to whether AML driver mutations occur in hematopoietic stem or in more committed progenitor cells. Here, we review how different mouse models, despite their inherent limitations, have functionally demonstrated that cellular origin plays a critical role in the biology of the disease, influencing clinical outcome. AML driven by potent oncogenes such as mixed lineage leukemia fusions often seem to emerge from committed myeloid progenitors whereas AML without any major cytogenetic abnormalities seem to develop from a combination of preleukemic initiating events arising in the hematopoietic stem cell pool. More refined mouse models may serve as experimental platforms to identify and validate novel targeted therapeutic strategies.

Murine Models of Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a rare but severe form of human cancer that results from a limited number of functionally cooperating genetic abnormalities leading to uncontrolled proliferation and impaired differentiation of hematopoietic stem and progenitor cells. Before the identification of genetic driver lesions, chemically, irradiation or viral infection-induced mouse leukaemia models provided platforms to test novel chemotherapeutics. Later, transgenic mouse models were established to test the in vivo transforming potential of newly cloned fusion genes and genetic aberrations detected in patients' genomes. Hereby researchers constitutively or conditionally expressed the respective gene in the germline of the mouse or reconstituted the hematopoietic system of lethally irradiated mice with bone marrow virally expressing the mutation of interest. More recently, immune deficient mice have been explored to study patient-derived human AML cells in vivo. Unfortunately, although complementary to each other, none of the currently available strategies faithfully model the initiation and progression of the human disease. Nevertheless, fast advances in the fields of next generation sequencing, molecular technology and bioengineering are continuously contributing to the generation of better mouse models. Here we review the most important AML mouse models of each category, briefly describe their advantages and limitations and show how they have contributed to our understanding of the biology and to the development of novel therapies.

CBFβ-SMMHC Inhibition Triggers Apoptosis by Disrupting MYC Chromatin Dynamics in Acute Myeloid Leukemia

The fusion oncoprotein CBFβ-SMMHC, expressed in leukemia cases with chromosome 16 inversion, drives leukemia development and maintenance by altering the activity of the transcription factor RUNX1. Here, we demonstrate that CBFβ-SMMHC maintains cell viability by neutralizing RUNX1-mediated repression of MYC expression. Upon pharmacologic inhibition of the CBFβ-SMMHC/RUNX1 interaction, RUNX1 shows increased binding at three MYC distal enhancers, where it represses MYC expression by mediating the replacement of the SWI/SNF complex component BRG1 with the polycomb-repressive complex component RING1B, leading to apoptosis. Combining the CBFβ-SMMHC inhibitor with the BET inhibitor JQ1 eliminates inv(16) leukemia in human cells and a mouse model. Enhancer-interaction analysis indicated that the three enhancers are physically connected with the MYC promoter, and genome-editing analysis demonstrated that they are functionally implicated in deregulation of MYC expression. This study reveals a mechanism whereby CBFβ-SMMHC drives leukemia maintenance and suggests that inhibitors targeting chromatin activity may prove effective in inv(16) leukemia therapy.

Preleukemia and Leukemia-Initiating Cell Activity in inv(16) Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a collection of hematologic malignancies with specific driver mutations that direct the pathology of the disease. The understanding of the origin and function of these mutations at early stages of transformation is critical to understand the etiology of the disease and for the design of effective therapies. The chromosome inversion inv(16) is thought to arise as a founding mutation in a hematopoietic stem cell (HSC) to produce preleukemic HSCs (preL-HSCs) with myeloid bias and differentiation block, and predisposed to AML. Studies in mice and human AML cells have established that inv(16) AML follows a clonal evolution model, in which preL-HSCs expressing the fusion protein CBFβ–SMMHC persist asymptomatic in the bone marrow. The emerging leukemia-initiating cells (LICs) are composed by the inv(16) and a heterogeneous set of mutations. In this review, we will discuss the current understanding of inv(16) preleukemia development, and the function of CBFβ–SMMHC related to preleukemia progression and LIC activity. We also discuss important open mechanistic questions in the etiology of inv(16) AML.

Targeting binding partners of the CBFβ-SMMHC fusion protein for the treatment of inversion 16 acute myeloid leukemia

Inversion of chromosome 16 (inv(16)) generates the CBFβ-SMMHC fusion protein and is found in nearly all patients with acute myeloid leukemia subtype M4 with Eosinophilia (M4Eo). Expression of CBFβ-SMMHC is causative for leukemia development, but the molecular mechanisms underlying its activity are unclear. Recently, there have been important advances in defining the role of CBFβ-SMMHC and its binding partners, the transcription factor RUNX1 and the histone deacetylase HDAC8. Importantly, initial trials demonstrate that small molecules targeting these binding partners are effective against CBFβ-SMMHC induced leukemia. This review will discuss recent advances in defining the mechanism of CBFβ-SMMHC activity, as well as efforts to develop new therapies for inv(16) AML.

Chd7 deficiency delays leukemogenesis in mice induced by Cbfb-MYH11

Inversion of chromosome 16 is a consistent finding in patients with acute myeloid leukemia subtype M4 with eosinophilia, which generates a CBFB-MYH11 fusion gene. Previous studies showed that the interaction between CBFβ-smooth muscle myosin heavy chain (SMMHC; encoded by CBFB-MYH11) and RUNX1 plays a critical role in the pathogenesis of this leukemia. Recently, it was shown that chromodomain helicase DNA-binding protein-7 (CHD7) interacts with RUNX1 and suppresses RUNX1-induced expansion of hematopoietic stem and progenitor cells. These results suggest that CHD7 is also critical for CBFB-MYH11-induced leukemogenesis. To test this hypothesis, we generated Chd7^f/fMx1-CreCbfb^+/56M mice, which expressed the Cbfb-MYH11 fusion gene and deactivated Chd7 in hematopoietic cells upon inducing Cre with polyinosinic-polycytidylic acid. The Lin^-Sca1^-c-Kit⁺ (LK) population was significantly lower in Chd7^f/fMx1-CreCbfb^+/56M mice than in Mx1-CreCbfb^+/56M mice. In addition, there were fewer 5-bromo-2'-deoxyuridine-positive cells in the LK population in Chd7^f/fMx1-CreCbfb^+/56M mice, and genes associated with cell cycle, cell growth, and proliferation were differentially expressed between Chd7^f/fMx1-CreCbfb^+/56M and Mx1-CreCbfb^+/56M leukemic cells. In vitro studies showed that CHD7 interacted with CBFβ-SMMHC through RUNX1 and that CHD7 enhanced transcriptional activity of RUNX1 and CBFβ-SMMHC on Csf1r, a RUNX1 target gene. Moreover, RNA sequencing of c-Kit⁺ cells showed that CHD7 functions mostly through altering the expression of RUNX1 target genes. Most importantly, Chd7 deficiency delayed Cbfb-MYH11-induced leukemia in both primary and transplanted mice. These data indicate that Chd7 is important for Cbfb-MYH11-induced leukemogenesis by facilitating RUNX1 regulation of transcription and cellular proliferation.

Stem and progenitor cell alterations in myelodysplastic syndromes

Recent studies have demonstrated that myelodysplastic syndromes (MDSs) arise from a small population of disease-initiating hematopoietic stem cells (HSCs) that persist and expand through conventional therapies and are major contributors to disease progression and relapse. MDS stem and progenitor cells are characterized by key founder and driver mutations and are enriched for cytogenetic alterations. Quantitative alterations in hematopoietic stem and progenitor cell (HSPC) numbers are also seen in a stage-specific manner in human MDS samples as well as in murine models of the disease. Overexpression of several markers such as interleukin-1 (IL-1) receptor accessory protein (IL1RAP), CD99, T-cell immunoglobulin mucin-3, and CD123 have begun to differentiate MDS HSPCs from healthy counterparts. Overactivation of innate immune components such as Toll-like receptors, IL-1 receptor-associated kinase/tumor necrosis factor receptor-associated factor-6, IL8/CXCR2, and IL1RAP signaling pathways has been demonstrated in MDS HSPCs and is being targeted therapeutically in preclinical and early clinical studies. Other dysregulated pathways such as signal transducer and activator of transcription 3, tyrosine kinase with immunoglobulinlike and EGF-like domains 1/angiopoietin-1, p21-activated kinase, microRNA 21, and transforming growth factor β are also being explored as therapeutic targets against MDS HSPCs. Taken together, these studies have demonstrated that MDS stem cells are functionally critical for the initiation, transformation, and relapse of disease and need to be targeted therapeutically for future curative strategies in MDSs.

Molecular Basis and Targeted Inhibition of CBFβ-SMMHC Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is characterized by recurrent chromosomal rearrangements that encode for fusion proteins which drive leukemia initiation and maintenance. The inv(16) (p13q22) rearrangement is a founding mutation and the associated CBFβ-SMMHC fusion protein is essential for the survival of inv(16) AML cells. This Chapter will discuss our understanding of the function of this fusion protein in disrupting hematopoietic homeostasis and creating pre-leukemic blasts, in its cooperation with other co-occurring mutations during leukemia initiation, and in leukemia maintenance. In addition, this chapter will discuss the current approaches used for the treatment of inv(16) AML and the recent development of AI-10-49, a selective targeted inhibitor of CBFβ-SMMHC/RUNX1 binding, the first candidate targeted therapy for inv(16) AML.

Mutant DNA methylation regulators endow hematopoietic stem cells with the preleukemic stem cell property, a requisite of leukemia initiation and relapse

Genetic mutations are considered to drive the development of acute myeloid leukemia (AML). With therapid progress in sequencing technologies, many newly reported genes that are recurrently mutated in AML have been found to govern the initiation and relapse of AML. These findings suggest the need to distinguish the driver mutations, especially the most primitive single mutation, from the subsequent passenger mutations. Recent research on DNA methyltransferase 3A (DNMT3A) mutations provides the first proof-of-principle investigation on the identification of preleukemic stem cells (pre-LSCs) in AML patients. Although DNMT3A mutations alone may only transform hematopoietic stem cells into pre-LSCs without causing the full-blown leukemia, the function of this driver mutation appear to persist from AML initiation up to relapse. Therefore, identifying and targeting preleukemic mutations, such as DNMT3A mutations, in AML is a promising strategy for treatment and reduction of relapse risk.