The Menin Tumor Suppressor Protein Is an Essential Oncogenic Cofactor for MLL-Associated Leukemogenesis

Combination of menin and kinase inhibitors as an effective treatment for leukemia with NUP98 translocations

Chromosomal translocations of the nucleoporin 98 (NUP98) gene are found in acute myeloid leukemia (AML) patients leading to very poor outcomes. The oncogenic activity of NUP98 fusion proteins is dependent on the interaction between Mixed Lineage Leukemia 1 and menin. NUP98-rearranged (NUP98-r) leukemia cells also rely on specific kinases, including CDK6 and/or FLT3, suggesting that simultaneous targeting of these kinases and menin could overcome limited sensitivity to single agents. Here, we found that combinations of menin inhibitor, MI-3454, with kinase inhibitors targeting either CDK6 (Palbociclib) or FLT3 (Gilteritinib) strongly enhance the anti-leukemic effect of menin inhibition in NUP98-r leukemia models. We found strong synergistic effects of both combinations on cell growth, colony formation and differentiation in patient samples with NUP98 translocations. These combinations also markedly augmented anti-leukemic efficacy of menin inhibitor in Patient Derived Xenograft models of NUP98-r leukemia. Despite inhibiting two unrelated kinases, when Palbociclib or Gilteritinib were combined with the menin inhibitor, they affected similar pathways relevant to leukemogenesis, including cell cycle regulation, cell proliferation and differentiation. This study provides strong rationale for clinical translation of the combination of menin and kinase inhibitors as novel treatments for NUP98-r leukemia, supporting the unexplored combinations of epigenetic drugs with kinase inhibitors.

MEN1 Deficiency-Driven Activation of the β-Catenin-MGMT Axis Promotes Pancreatic Neuroendocrine Tumor Growth and Confers Temozolomide Resistance

O6-methylguanine DNA methyltransferase (MGMT) removes alkyl adducts from the guanine O6 position (O6-MG) and repairs DNA damage. High MGMT expression results in poor response to temozolomide (TMZ). However, the biological importance of MGMT and the mechanism underlying its high expression in pancreatic neuroendocrine tumors (PanNETs) remain elusive. Here, it is found that MGMT expression is highly elevated in PanNET tissues compared with paired normal tissues and negatively associated with progression-free survival (PFS) time in patients with PanNETs. Knocking out MGMT inhibits cancer cell growth in vitro and in vivo. Ectopic MEN1 expression suppresses MGMT transcription in a manner that depends on β-Catenin nuclear export and degradation. The Leucine 267 residue of MEN1 is crucial for regulating β-Catenin-MGMT axis activation and chemosensitivity to TMZ. Interference with β-Catenin re-sensitizes tumor cells to TMZ and significantly reduces the cytotoxic effects of high-dose TMZ treatment, and MGMT overexpression counteracts the effects of β-Catenin deficiency. This study reveals the biological importance of MGMT and a new mechanism by which MEN1 deficiency regulates its expression, thus providing a potential combinational strategy for treating patients with TMZ-resistant PanNETs.

Roles of Menin in T cell differentiation and function: Current knowledge and perspectives

The commitment to specific T lymphocytes (T cell) lineages is governed by distinct transcription factors, whose expression is modulated through epigenetic mechanisms. Unravelling these epigenetic mechanisms that regulate T cell differentiation and function holds significant importance for understanding T cells. Menin, a multifunctional scaffolding protein, is implicated in various cellular processes, such as cell proliferation, cell cycle control, DNA repair and transcriptional regulation, primarily through epigenetic mechanisms. Existing research indicates Menin's impact on T cell differentiation and function, while a comprehensive and systematic review is currently lacking to consolidate these findings. In the current review, we have highlighted recent studies on the role of Menin in T cell differentiation and function, focusing mainly on its impact on the memory Th2 maintenance, Th17 differentiation and maintenance, CD4+ T cell senescence, and effector CD8+ T cell survival. Considering Menin's crucial function in maintaining effector T cell function, the potential of inhibiting Menin activity in mitigating inflammatory diseases associated with excessive T cell activation has also been emphasised.

Menin signaling and therapeutic targeting in breast cancer

To date, mounting evidence have shown that patients with multiple endocrine neoplasia type 1 (MEN1) may face an increased risk for breast carcinogenesis. The product of the MEN1 gene, menin, was also indicated to be an important regulator in breast cancer signaling network. Menin directly interacts with MLL, EZH2, JunD, NF-κB, PPARγ, VDR, Smad3, β-catenin and ERα to modulate gene transcriptions leading to cell proliferation inhibition. Moreover, interaction of menin-FANCD2 contributes to the enhancement of BRCA1-mediated DNA repair mechanism. Ectopic expression of menin causes Bax-, Bak- and Caspase-8-dependent apoptosis. However, despite numbers of menin inhibitors were exploited in other cancers, data on the usage of menin inhibitors in breast cancer treatment remain limited. In this review, we focused on the menin associated signaling pathways and gene transcription regulations, with the aim of elucidating its molecular mechanisms and of guiding the development of novel menin targeted drugs in breast cancer therapy.

The role of LEDGF in transcription is exploited by HIV-1 to position integration

HIV-1 integration occurs across actively transcribed genes due to the interaction of integrase with host chromatin factor LEDGF. Although LEDGF was originally isolated as a co-activator that stimulates promoter activity in purified systems, this role is inconsistent with LEDGF-mediated integration across gene bodies and with data indicating LEDGF is a histone chaperone that promotes transcriptional elongation. We found LEDGF is enriched in pronounced peaks that match the enrichments of H3K4me3 and RNA Pol II at transcription start sites (TSSs) of active promoters. Our genome-wide chromatin mapping revealed that MLL1 had a dominant role in recruiting LEDGF to promoters and the presence of LEDGF recruits RNA Pol II. Enrichment of LEDGF at TSSs correlates strongly with levels of integration across the transcribed sequences, indicating that LEDGF at TSSs contributed to integration across gene bodies. Although the N-terminal Pro-Trp-Trp-Pro (PWWP) domain of LEDGF interacts with nucleosomes containing H3K36me3, a modification thought to recruit LEDGF to chromatin, we found H3K36me3 does not contribute to gene specificity of integration. These data support a dual role model of LEDGF where it is tethered to promoters by MLL1 and recruits RNA Pol II. Subsequently, LEDGF travels across genes to effect HIV-1 integration. Our data also provides a mechanistic context for the contribution made by LEDGF to MLL1-based infant acute leukemia and acute myeloid leukemia in adults.

Combination therapy with novel agents for acute myeloid leukaemia: Insights into treatment of a heterogenous disease

The treatment landscape of acute myeloid leukaemia (AML) is evolving rapidly. Venetoclax in combination with intensive chemotherapy or doublets or triplets with targeted or immune therapies is the focus of numerous ongoing trials. The development of mutation-targeted therapies has greatly enhanced the treatment armamentarium, with FLT3 inhibitors and isocitrate dehydrogenase inhibitors improving outcomes in frontline and relapsed/refractory (RR) AML, and menin inhibitors showing efficacy in RR NPM1mut and KMT2A-rearranged AML. With so many new drugs approved, the number of potential combinatorial approaches to leverage the maximal benefit of these agents has increased dramatically, while at the same time introducing clinical challenges, such as key preclinical and clinical data supporting the development of combinatorial therapy, how to optimally combine or sequence these novel agents, how to optimise dose and duration to maintain safety while enhancing efficacy, the optimal duration of therapy and the role of measurable residual disease in decision-making in both intensive and low-intensity therapy settings. In this review, we will outline the evidence leading to the approval of key agents in AML, their on-label current approvals and how they may be optimally combined in a safe and deliverable fashion to further improve outcomes in AML.

Roles of H3K4 methylation in biology and disease

Epigenetic modifications, including posttranslational modifications of histones, are closely linked to transcriptional regulation. Trimethylated H3 lysine 4 (H3K4me3) is one of the most studied histone modifications owing to its enrichment at the start sites of transcription and its association with gene expression and processes determining cell fate, development, and disease. In this review, we focus on recent studies that have yielded insights into how levels and patterns of H3K4me3 are regulated, how H3K4me3 contributes to the regulation of specific phases of transcription such as RNA polymerase II initiation, pause-release, heterogeneity, and consistency. The conclusion from these studies is that H3K4me3 by itself regulates gene expression and its precise regulation is essential for normal development and preventing disease.

An emerging maestro of immune regulation: how DOT1L orchestrates the harmonies of the immune system

The immune system comprises a complex yet tightly regulated network of cells and molecules that play a critical role in protecting the body from infection and disease. The activity and development of each immune cell is regulated in a myriad of ways including through the cytokine milieu, the availability of key receptors, via tailored intracellular signalling cascades, dedicated transcription factors and even by directly modulating gene accessibility and expression; the latter is more commonly known as epigenetic regulation. In recent years, epigenetic regulators have begun to emerge as key players involved in modulating the immune system. Among these, the lysine methyltransferase DOT1L has gained significant attention for its involvement in orchestrating immune cell formation and function. In this review we provide an overview of the role of DOT1L across the immune system and the implications of this role on health and disease. We begin by elucidating the general mechanisms of DOT1L-mediated histone methylation and its impact on gene expression within immune cells. Subsequently, we provide a detailed and comprehensive overview of recent studies that identify DOT1L as a crucial regulator of immune cell development, differentiation, and activation. Next, we discuss the potential mechanisms of DOT1L-mediated regulation of immune cell function and shed light on how DOT1L might be contributing to immune cell homeostasis and dysfunction. We then provide food for thought by highlighting some of the current obstacles and technical limitations precluding a more in-depth elucidation of DOT1L's role. Finally, we explore the potential therapeutic implications of targeting DOT1L in the context of immune-related diseases and discuss ongoing research efforts to this end. Overall, this review consolidates the current paradigm regarding DOT1L's role across the immune network and emphasises its critical role in governing the healthy immune system and its potential as a novel therapeutic target for immune-related diseases. A deeper understanding of DOT1L's immunomodulatory functions could pave the way for innovative therapeutic approaches which fine-tune the immune response to enhance or restore human health.

HBO1, a MYSTerious KAT and its links to cancer

The histone acetyltransferase HBO1, also known as KAT7, is a major chromatin modifying enzyme responsible for H3 and H4 acetylation. It is found within two distinct tetrameric complexes, the JADE subunit-containing complex and BRPF subunit-containing complex. The HBO1-JADE complex acetylates lysine 5, 8 and 12 of histone H4, and the HBO1-BRPF complex acetylates lysine 14 of histone H3. HBO1 regulates gene transcription, DNA replication, DNA damage repair, and centromere function. It is involved in diverse signaling pathways and plays crucial roles in development and stem cell biology. Recent work has established a strong relationship of HBO1 with the histone methyltransferase MLL/KMT2A in acute myeloid leukemia. Here, we discuss functional and pathological links of HBO1 to cancer, highlighting the underlying mechanisms that may pave the way to the development of novel anti-cancer therapies.

Chromatin and aberrant enhancer activity in KMT2A rearranged acute lymphoblastic leukemia

To make a multicellular organism, genes need to be transcribed at the right developmental stages and in the right tissues. DNA sequences termed 'enhancers' are crucial to achieve this. Despite concerted efforts, the exact mechanisms of enhancer activity remain elusive. Mixed lineage leukemia (MLL or KMT2A) rearrangements (MLLr), commonly observed in cases of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia, produce novel in-frame fusion proteins. Recent work has shown that the MLL-AF4 fusion protein drives aberrant enhancer activity at key oncogenes in ALL, dependent on the continued presence of MLL-AF4 complex components. As well as providing some general insights into enhancer function, these observations may also provide an explanation for transcriptional heterogeneity observed in MLLr patients.

Pharmacological targeting of the cancer epigenome

Epigenetic dysregulation is increasingly appreciated as a hallmark of cancer, including disease initiation, maintenance and therapy resistance. As a result, there have been advances in the development and evaluation of epigenetic therapies for cancer, revealing substantial promise but also challenges. Three epigenetic inhibitor classes are approved in the USA, and many more are currently undergoing clinical investigation. In this Review, we discuss recent developments for each epigenetic drug class and their implications for therapy, as well as highlight new insights into the role of epigenetics in cancer.

The KAT module of the SAGA complex maintains the oncogenic gene expression program in MYCN-amplified neuroblastoma

Pediatric cancers are frequently driven by genomic alterations that result in aberrant transcription factor activity. Here, we used functional genomic screens to identify multiple genes within the transcriptional coactivator Spt-Ada-Gcn5-acetyltransferase (SAGA) complex as selective dependencies for MYCN-amplified neuroblastoma, a disease of dysregulated development driven by an aberrant oncogenic transcriptional program. We characterized the DNA recruitment sites of the SAGA complex in neuroblastoma and the consequences of loss of SAGA complex lysine acetyltransferase (KAT) activity on histone acetylation and gene expression. We demonstrate that loss of SAGA complex KAT activity is associated with reduced MYCN binding on chromatin, suppression of MYC/MYCN gene expression programs, and impaired cell cycle progression. Further, we showed that the SAGA complex is pharmacologically targetable in vitro and in vivo with a KAT2A/KAT2B proteolysis targeting chimeric. Our findings expand our understanding of the histone-modifying complexes that maintain the oncogenic transcriptional state in this disease and suggest therapeutic potential for inhibitors of SAGA KAT activity in MYCN-amplified neuroblastoma.

Distinct Responses to Menin Inhibition and Synergy with DOT1L Inhibition in KMT2A-Rearranged Acute Lymphoblastic and Myeloid Leukemia

Pediatric acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) exhibit favorable survival rates. However, for AML and ALL patients carrying KMT2A gene translocations clinical outcome remains unsatisfactory. Key players in KMT2A-fusion-driven leukemogenesis include menin and DOT1L. Recently, menin inhibitors like revumenib have garnered attention for their potential therapeutic efficacy in treating KMT2A-rearranged acute leukemias. However, resistance to menin inhibition poses challenges, and identifying which patients would benefit from revumenib treatment is crucial. Here, we investigated the in vitro response to revumenib in KMT2A-rearranged ALL and AML. While ALL samples show rapid, dose-dependent induction of leukemic cell death, AML responses are much slower and promote myeloid differentiation. Furthermore, we reveal that acquired resistance to revumenib in KMT2A-rearranged ALL cells can occur either through the acquisition of MEN1 mutations or independently of mutations in MEN1. Finally, we demonstrate significant synergy between revumenib and the DOT1L inhibitor pinometostat in KMT2A-rearranged ALL, suggesting that such drug combinations represent a potent therapeutic strategy for these patients. Collectively, our findings underscore the complexity of resistance mechanisms and advocate for precise patient stratification to optimize the use of menin inhibitors in KMT2A-rearranged acute leukemia.

The Menin story in acute myeloid leukaemia-The road to success

The treatment of acute myeloid leukaemia (AML) has changed fundamentally in the last decade with many new targeted therapies entering clinics. Some of the most interesting agents under development are Menin inhibitors which interfere with the interaction of Menin with wild-type (wt) KMT2A or a KMT2A-fusion protein and thereby downregulate the leukaemic gene expression (MEIS1, PBX3, HOX) in NPM1 mutant or KMT2A-rearranged leukaemia. Other HOX and MEIS1 expressing leukaemias may also be sensitive to Menin inhibition. Following the encouraging results as monotherapy in refractory and relapsed AML, the combination of Menin inhibitors with chemotherapeutic agents and other targeted drugs is being investigated clinically.

Combined deletion of MEN1, ATRX and PTEN triggers development of high-grade pancreatic neuroendocrine tumors in mice

Pancreatic neuroendocrine tumors (PanNETs) are a heterogeneous group of tumors that exhibit an unpredictable and broad spectrum of clinical presentations and biological aggressiveness. Surgical resection is still the only curative therapeutic option for localized PanNET, but the majority of patients are diagnosed at an advanced and metastatic stage with limited therapeutic options. Key factors limiting the development of new therapeutics are the extensive heterogeneity of PanNETs and the lack of appropriate clinically relevant models. In that context, genomic sequencing of human PanNETs revealed recurrent mutations and structural alterations in several tumor suppressors. Here, we demonstrated that combined loss of MEN1, ATRX, and PTEN, tumor suppressors commonly mutated in human PanNETs, triggers the development of high-grade pancreatic neuroendocrine tumors in mice. Histopathological evaluation and gene expression analyses of the developed tumors confirm the presence of PanNET hallmarks and significant overlap in gene expression patterns found in human disease. Thus, we postulate that the presented novel genetically defined mouse model is the first clinically relevant immunocompetent high-grade PanNET mouse model.

Mezigdomide is effective alone and in combination with menin inhibition in preclinical models of KMT2A-r and NPM1c AML

ABSTRACT

Small molecules that target the menin-KMT2A protein-protein interaction (menin inhibitors) have recently entered clinical trials in lysine methyltransferase 2A (KMT2A or MLL1)-rearranged (KMT2A-r) and nucleophosmin-mutant (NPM1c) acute myeloid leukemia (AML) and are demonstrating encouraging results. However, rationally chosen combination therapy is needed to improve responses and prevent resistance. We have previously identified IKZF1/IKAROS as a target in KMT2A-r AML and shown in preclinical models that IKAROS protein degradation with lenalidomide or iberdomide has modest single-agent activity yet can synergize with menin inhibitors. Recently, the novel IKAROS degrader mezigdomide was developed with greatly enhanced IKAROS protein degradation. In this study, we show that mezigdomide has increased preclinical activity in vitro as a single-agent in KMT2A-r and NPM1c AML cell lines, including sensitivity in cell lines resistant to lenalidomide and iberdomide. Further, we demonstrate that mezigdomide has the greatest capacity to synergize with and induce apoptosis in combination with menin inhibitors, including in MEN1 mutant models. We show that the superior activity of mezigdomide compared with lenalidomide or iberdomide is due to its increased depth, rate, and duration of IKAROS protein degradation. Single-agent mezigdomide was efficacious in 5 patient-derived xenograft models of KMT2A-r and 1 NPM1c AML. The combination of mezigdomide with the menin inhibitor VTP-50469 increased survival and prevented and overcame MEN1 mutations that mediate resistance in patients receiving menin inhibitor monotherapy. These results support prioritization of mezigdomide for early phase clinical trials in KMT2A-r and NPM1c AML, either as a single agent or in combination with menin inhibitors.

Therapeutic index of targeting select chromatin complexes in human cancer patients

Aberrant chromatin regulation can promote the initiation and progression of human cancer. An improved understanding of such mechanisms has resulted in the identification of cancers with an enhanced dependency on specific chromatin regulatory proteins relative to nonmalignant cell types. Hence, targeting of such complexes with small molecules has significant therapeutic potential in oncology. In recent years, several drugs have been developed and evaluated in human cancer patients, which can influence tumor biology by reprogramming of chromatin structure. In this review, we summarize several of the known mechanisms that endow cancer cells with a powerful dependency on chromatin regulation that exceeds the requirements for normal tissue homeostasis. We also summarize the remarkable small-molecule inhibitors that exploit chromatin regulator dependencies with a clear therapeutic benefit in human cancer patients.

Synergistic Effects of the RARalpha Agonist Tamibarotene and the Menin Inhibitor Revumenib in Acute Myeloid Leukemia Cells with KMT2A Rearrangement or NPM1 Mutation

Inhibition of menin in acute myeloid leukemia (AML) harboring histone-lysine-N-methyltransferase 2A rearrangement (KMT2Ar) or the mutated Nucleophosmin gene (NPM1c) is considered a novel and effective treatment approach in these patients. However, rapid acquisition of resistance mutations can impair treatment success. In patients with elevated retinoic acid receptor alpha (RARA) expression levels, promising effects are demonstrated by the next-generation RARalpha agonist tamibarotene, which restores differentiation or induces apoptosis. In this study, the combination of revumenib and tamibarotene was investigated in various KMT2Ar or NPM1c AML cell lines and patient-derived blasts, focusing on the potential synergistic induction of differentiation or apoptosis. Both effects were analyzed by flow cytometry and validated by Western blot analysis. Synergy calculations were performed using viability assays. Regulation of the relevant key mediators for the MLL complex were quantified by RT-qPCR. In MV4:11 cells characterized by the highest relative mRNA levels of RARA, highly synergistic induction of apoptosis is demonstrated upon combination treatment. Induction of apoptosis by combined treatment of MV4:11 cells is accompanied by pronounced induction of the pro-apoptotic protein BAX and a synergistic reduction in CDK6 mRNA levels. In MOLM13 and OCI-AML3 cells, an increase in differentiation markers like PU.1 or a decreased ratio of phosphorylated to total CEBPA is demonstrated. In parts, corresponding effects were observed in patient-derived AML cells carrying either KMT2Ar or NPM1c. The impact of revumenib on KMT2Ar or NPM1c AML cells was significantly enhanced when combined with tamibarotene, demonstrating synergistic differentiation or apoptosis initiation. These findings propose promising strategies for relapsed/refractory AML patients with defined molecular characteristics.

Aberrant stem cell and developmental programs in pediatric leukemia

Hematopoiesis is a finely orchestrated process, whereby hematopoietic stem cells give rise to all mature blood cells. Crucially, they maintain the ability to self-renew and/or differentiate to replenish downstream progeny. This process starts at an embryonic stage and continues throughout the human lifespan. Blood cancers such as leukemia occur when normal hematopoiesis is disrupted, leading to uncontrolled proliferation and a block in differentiation of progenitors of a particular lineage (myeloid or lymphoid). Although normal stem cell programs are crucial for tissue homeostasis, these can be co-opted in many cancers, including leukemia. Myeloid or lymphoid leukemias often display stem cell-like properties that not only allow proliferation and survival of leukemic blasts but also enable them to escape treatments currently employed to treat patients. In addition, some leukemias, especially in children, have a fetal stem cell profile, which may reflect the developmental origins of the disease. Aberrant fetal stem cell programs necessary for leukemia maintenance are particularly attractive therapeutic targets. Understanding how hijacked stem cell programs lead to aberrant gene expression in place and time, and drive the biology of leukemia, will help us develop the best treatment strategies for patients.

Discovery of novel pyrrolo[2,3-d]pyrimidines as potent menin-mixed lineage leukemia interaction inhibitors

To interfere the Menin-MLL interaction using small molecular inhibitors has been shown as new treatment of several special hematological malignancies. Herein, a series of Menin-MLL interaction inhibitors with pyrrolo[2,3-d]pyrimidine scaffold were designed, synthesized and evaluated. Among them, compound A6 exhibited potent binding affinity with an IC50 value of 0.38 μM, and strong anti-proliferative activity against MV4-11 cells with an IC50 value of 1.07 μM. Further study showed A6 reduced the transcriptional levels of HOXA9 and MEIS1 genes. Moreover, A6 induced cellular apoptosis, arrested the cell cycle in G0/G1 phase, and reversed the differentiation arrest in a concentration-dependent manner. This study suggested compound A6 was as a novel potent Menin-MLL interaction inhibitor, and it proved that introduction of 4-amino pyrrolo[2,3-d]pyrimidine to occupy the P10 hydrophobic pocket was new idea for design of novel Menin-MLL interaction inhibitors.

The future of HOXA- expressing leukemias: Menin inhibitor response and resistance

PURPOSE OF REVIEW

We provide an update on the successes and ongoing challenges of Menin inhibition as a novel approach for the treatment of patients with acute leukemias that express HOXA cluster genes including leukemias with KMT2A -rearrangements, NPM1 mutations or NUP98 -rearrangements. Initial clinical trials show promising response rates in heavily pretreated patients suggesting these inhibitors may have a significant impact on patient outcome. Furthermore, the development of resistance mutations that decrease drug binding affinity, validates Menin as a therapeutic target in human cancers. Therapeutic strategies aiming at overcoming and preventing resistance, are of high clinical relevance.

RECENT FINDINGS

Several Menin inhibitor chemotypes have entered clinical trials. Acquired point mutations have recently been described as a mechanism of resistance towards Menin inhibitors. However, resistance can develop in absence of these mutations. Combination therapies are currently being investigated in preclinical models and in early phase clinical trials.

SUMMARY

Given the remarkable overall response rates, shedding light on treatment options for patients whose leukemias develop resistance to Menin inhibitors is an imminent clinical need. Studying the underlying mechanisms to inform clinical decision making, and to potentially prevent the development of resistance is of outmost importance.

Small Molecule Menin Inhibitors: Novel Therapeutic Agents Targeting Acute Myeloid Leukemia with KMT2A Rearrangement or NPM1 Mutation

Recent advances have included insights into the clinical value of genomic abnormalities in acute myeloid leukemia (AML) and consequently the development of numerous targeted therapeutic agents that have improved clinical outcome. In this setting, various clinical trials have recently explored novel therapeutic agents either used alone or in combination with intensive chemotherapy or low-intensity treatments. Among them, menin inhibitors could represent a novel group of targeted therapies in AML driven by rearrangement of the lysine methyltransferase 2A (KMT2A) gene, previously known as mixed-lineage leukemia (MLL), or by mutation of the nucleophosmin 1 (NPM1) gene. Recent phase 1/2 clinical trials confirmed the efficacy of SNDX-5613 (revumenib) and KO-539 (ziftomenib) and their acceptable tolerability. Several small molecule menin inhibitors are currently being evaluated as a combination therapy with standard of care treatments. The current paper reviews the recent progress in exploring the inhibitors of menin-KMT2A interactions and their application prospects in the treatment of acute leukemias.

Bivalent chromatin: a developmental balancing act tipped in cancer

Bivalent chromatin is defined by the co-occurrence of otherwise opposing H3K4me3 and H3K27me3 modifications and is typically located at unmethylated promoters of lowly transcribed genes. In embryonic stem cells, bivalent chromatin has been proposed to poise developmental genes for future activation, silencing or stable repression upon lineage commitment. Normally, bivalent chromatin is kept in tight balance in cells, in part through the activity of the MLL/COMPASS-like and Polycomb repressive complexes that deposit the H3K4me3 and H3K27me3 modifications, respectively, but also emerging novel regulators including DPPA2/4, QSER1, BEND3, TET1 and METTL14. In cancers, both the deregulation of existing domains and the creation of de novo bivalent states is associated with either the activation or silencing of transcriptional programmes. This may facilitate diverse aspects of cancer pathology including epithelial-to-mesenchymal plasticity, chemoresistance and immune evasion. Here, we review current methods for detecting bivalent chromatin and discuss the factors involved in the formation and fine-tuning of bivalent domains. Finally, we examine how the deregulation of chromatin bivalency in the context of cancer could facilitate and/or reflect cancer cell adaptation. We propose a model in which bivalent chromatin represents a dynamic balance between otherwise opposing states, where the underlying DNA sequence is primed for the future activation or repression. Shifting this balance in any direction disrupts the tight equilibrium and tips cells into an altered epigenetic and phenotypic space, facilitating both developmental and cancer processes.

Acute myeloid leukemias with UBTF tandem duplications are sensitive to menin inhibitors

ABSTRACT

UBTF tandem duplications (UBTF-TDs) have recently emerged as a recurrent alteration in pediatric and adult acute myeloid leukemia (AML). UBTF-TD leukemias are characterized by a poor response to conventional chemotherapy and a transcriptional signature that mirrors NUP98-rearranged and NPM1-mutant AMLs, including HOX-gene dysregulation. However, the mechanism by which UBTF-TD drives leukemogenesis remains unknown. In this study, we investigated the genomic occupancy of UBTF-TD in transformed cord blood CD34+ cells and patient-derived xenograft models. We found that UBTF-TD protein maintained genomic occupancy at ribosomal DNA loci while also occupying genomic targets commonly dysregulated in UBTF-TD myeloid malignancies, such as the HOXA/HOXB gene clusters and MEIS1. These data suggest that UBTF-TD is a gain-of-function alteration that results in mislocalization to genomic loci dysregulated in UBTF-TD leukemias. UBTF-TD also co-occupies key genomic loci with KMT2A and menin, which are known to be key partners involved in HOX-dysregulated leukemias. Using a protein degradation system, we showed that stemness, proliferation, and transcriptional signatures are dependent on sustained UBTF-TD localization to chromatin. Finally, we demonstrate that primary cells from UBTF-TD leukemias are sensitive to the menin inhibitor SNDX-5613, resulting in markedly reduced in vitro and in vivo tumor growth, myeloid differentiation, and abrogation of the UBTF-TD leukemic expression signature. These findings provide a viable therapeutic strategy for patients with this high-risk AML subtype.

Targeting IGF2BP3 enhances antileukemic effects of menin-MLL inhibition in MLL-AF4 leukemia

ABSTRACT

RNA-binding proteins (RBPs) are emerging as a novel class of therapeutic targets in cancer, including in leukemia, given their important role in posttranscriptional gene regulation, and have the unexplored potential to be combined with existing therapies. The RBP insulin-like growth factor 2 messenger RNA-binding protein 3 (IGF2BP3) has been found to be a critical regulator of MLL-AF4 leukemogenesis and represents a promising therapeutic target. Here, we study the combined effects of targeting IGF2BP3 and menin-MLL interaction in MLL-AF4-driven leukemia in vitro and in vivo, using genetic inhibition with CRISPR-Cas9-mediated deletion of Igf2bp3 and pharmacologic inhibition of the menin-MLL interaction with multiple commercially available inhibitors. Depletion of Igf2bp3 sensitized MLL-AF4 leukemia to the effects of menin-MLL inhibition on cell growth and leukemic initiating cells in vitro. Mechanistically, we found that both Igf2bp3 depletion and menin-MLL inhibition led to increased differentiation in vitro and in vivo, seen in functional readouts and by gene expression analyses. IGF2BP3 knockdown had a greater effect on increasing survival and attenuating disease than pharmacologic menin-MLL inhibition with small molecule MI-503 alone and showed enhanced antileukemic effects in combination. Our work shows that IGF2BP3 is an oncogenic amplifier of MLL-AF4-mediated leukemogenesis and a potent therapeutic target, providing a paradigm for targeting leukemia at both the transcriptional and posttranscriptional level.

RNA-binding protein RBM5 plays an essential role in acute myeloid leukemia by activating the oncogenic protein HOXA9

BACKGROUND

The oncogenic protein HOXA9 plays a critical role in leukemia transformation and maintenance, and its aberrant expression is a hallmark of most aggressive acute leukemia. Although inhibiting the upstream regulators of HOXA9 has been proven as a significant therapeutic intervention, the comprehensive regulation network controlling HOXA9 expression in leukemia has not been systematically investigated.

RESULTS

Here, we perform genome-wide CRISPR/Cas9 screening in the HOXA9-driven reporter acute leukemia cells. We identify a poorly characterized RNA-binding protein, RBM5, as the top candidate gene required to maintain leukemia cell fitness. RBM5 is highly overexpressed in acute myeloid leukemia (AML) patients compared to healthy individuals. RBM5 loss triggered by CRISPR knockout and shRNA knockdown significantly impairs leukemia maintenance in vitro and in vivo. Through domain CRISPR screening, we reveal that RBM5 functions through a noncanonical transcriptional regulation circuitry rather than RNA splicing, such an effect depending on DNA-binding domains. By integrative analysis and functional assays, we identify HOXA9 as the downstream target of RBM5. Ectopic expression of HOXA9 rescues impaired leukemia cell proliferation upon RBM5 loss. Importantly, acute protein degradation of RBM5 through auxin-inducible degron system immediately reduces HOXA9 transcription.

CONCLUSIONS

We identify RBM5 as a new upstream regulator of HOXA9 and reveal its essential role in controlling the survival of AML. These functional and molecular mechanisms further support RBM5 as a promising therapeutic target for myeloid leukemia treatment.

HOXA9 Regulome and Pharmacological Interventions in Leukemia

HOXA9, an important transcription factor (TF) in hematopoiesis, is aberrantly expressed in numerous cases of both acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) and is a strong indicator of poor prognosis in patients. HOXA9 is a proto-oncogene which is both sufficient and necessary for leukemia transformation. HOXA9 expression in leukemia correlates with patient survival outcomes and response to therapy. Chromosomal transformations (such as NUP98-HOXA9), mutations, epigenetic dysregulation (e.g., MLL- MENIN -LEDGF complex or DOT1L/KMT4), transcription factors (such as USF1/USF2), and noncoding RNA (such as HOTTIP and HOTAIR) regulate HOXA9 mRNA and protein during leukemia. HOXA9 regulates survival, self-renewal, and progenitor cell cycle through several of its downstream target TFs including LMO2, antiapoptotic BCL2, SOX4, and receptor tyrosine kinase FLT3 and STAT5. This dynamic and multilayered HOXA9 regulome provides new therapeutic opportunities, including inhibitors targeting DOT1L/KMT4, MENIN, NPM1, and ENL proteins. Recent findings also suggest that HOXA9 maintains leukemia by actively repressing myeloid differentiation genes. This chapter summarizes the recent advances understanding biochemical mechanisms underlying HOXA9-mediated leukemogenesis, the clinical significance of its abnormal expression, and pharmacological approaches to treat HOXA9-driven leukemia.

Molecular Genetic Aspects of Sporadic Multiglandular Primary Hyperparathyroidism

Multiglandular primary hyperparathyroidism (MGD) represents a rare form of primary hyperparathyroidism (PHPT). MGD is associated with hereditary PHPT, but the sporadic MGD is more common and affects a similar patient profile as single gland parathyroid disease (SGD). The distinction between SGD and MGD is of great clinical importance, especially for the strategy of parathyroidectomy. Based on the limited knowledge available, MGD is likely to be a genetically heterogeneous disease resulting from the interaction of germline and somatic DNA mutations together with epigenetic alterations. Furthermore, these events may combine and occur independently in parathyroid tumors within the same individual with MGD. Gene expression profiling has shown that SGD and MGD may represent distinct entities in parathyroid tumorigenesis. We are waiting for studies to analyze exactly which genes are different in SGD and MGD in order to identify potential biomarkers that can distinguish between the two forms of the disease.

Emerging and Future Targeted Therapies for Pediatric Acute Myeloid Leukemia: Targeting the Leukemia Stem Cells

Acute myeloid leukemia (AML) is a rare subtype of acute leukemia in the pediatric and adolescent population but causes disproportionate morbidity and mortality in this age group. Standard chemotherapeutic regimens for AML have changed very little in the past 3-4 decades, but the addition of targeted agents in recent years has led to improved survival in select subsets of patients as well as a better biological understanding of the disease. Currently, one key paradigm of bench-to-bedside practice in the context of adult AML is the focus on leukemia stem cell (LSC)-targeted therapies. Here, we review current and emerging immunotherapies and other targeted agents that are in clinical use for pediatric AML through the lens of what is known (and not known) about their LSC-targeting capability. Based on a growing understanding of pediatric LSC biology, we also briefly discuss potential future agents on the horizon.

Therapeutic targeting in pediatric acute myeloid leukemia with aberrant HOX/MEIS1 expression

Despite advances in the clinical management of childhood acute myeloid leukemia (AML) during the last decades, outcome remains fatal in approximately one third of patients. Primary chemoresistance, relapse and acute and long-term toxicities to conventional myelosuppressive therapies still constitute significant challenges and emphasize the unmet need for effective targeted therapies. Years of scientific efforts have translated into extensive insights on the heterogeneous spectrum of genetics and oncogenic signaling pathways of AML and identified a subset of patients characterized by upregulation of HOXA and HOXB homeobox genes and myeloid ecotropic virus insertion site 1 (MEIS1). Aberrant HOXA/MEIS1 expression is associated with genotypes such as rearrangements in Histone-lysine N-methyltransferase 2A (KMT2A-r), nucleoporin 98 (NUP98-r) and mutated nucleophosmin (NPM1c) that are found in approximately one third of children with AML. AML with upregulated HOXA/MEIS1 shares a number of molecular vulnerabilities amenable to recently developed molecules targeting the assembly of protein complexes or transcriptional regulators. The interaction between the nuclear scaffold protein menin and KMT2A has gained particular interest and constitutes a molecular dependency for maintenance of the HOXA/MEIS1 transcription program. Menin inhibitors disrupt the menin-KMT2A complex in preclinical models of KMT2A-r, NUP98-r and NPM1c acute leukemias and its occupancy at target genes leading to leukemic cell differentiation and apoptosis. Early-phase clinical trials are either ongoing or in development and preliminary data suggests tolerable toxicities and encouraging efficacy of menin inhibitors in adults with relapsed or refractory KMT2A-r and NPM1c AML. The Pediatric Acute Leukemia/European Pediatric Acute Leukemia (PedAL/EUPAL) project is focused to advance and coordinate informative clinical trials with new agents and constitute an ideal framework for testing of menin inhibitors in pediatric study populations. Menin inhibitors in combination with standard chemotherapy or other targeting agents may enhance anti-leukemic effects and constitute rational treatment strategies for select genotypes of childhood AML, and provide enhanced safety to avoid differentiation syndrome. In this review, we discuss the pathophysiological mechanisms in KMT2A-r, NUP98-r and NPM1c AML, emerging molecules targeting the HOXA/MEIS1 transcription program with menin inhibitors as the most prominent examples and future therapeutic implications of these agents in childhood AML.

Treatment of Acute Myeloid Leukemia in Older Adults

Acute Myeloid Leukemia (AML) is an aggressive myeloid malignancy predominantly affecting older adults. Despite the advancements in new therapies for AML, older and medically unfit patients continue to suffer from poor outcomes due to disease-related factors such as the mutational profile and patient-related factors such as comorbidities and performance status. In this review, we discuss a spectrum of therapeutic options for older patients with AML starting with a historical perspective and ending with therapies being investigated in clinical trials. We review the standard of care treatment options including combination venetoclax and hypomethylating agents, in addition to targeted therapies such as FLT3 and IDH inhibitors. Lastly, we shed light on challenges facing the care of older adults and their representation in clinical trials.

Persistence of UBTF tandem duplications in remission in acute myeloid leukaemia

UBTF tandem duplications are recurrent in adult and paediatric acute myeloid leukaemia and have been reported to be associated with a poor prognosis. Co-mutations in WT1 and FLT3 are common while morphological dysplasia is frequent. The role of UBTF-TDs in leukemogenesis is yet to be elucidated; however they have been proposed as early initiating events, making them attractive for assessment of MRD and a potential therapeutic target. We present two cases where the UBTF-TD was observed in remission and discuss the implications of these findings in the clinicobiological understanding of this emerging entity.

The human leukemic oncogene MLL-AF4 promotes hyperplastic growth of hematopoietic tissues in Drosophila larvae

MLL-rearranged (MLL-r) leukemias are among the leukemic subtypes with poorest survival, and treatment options have barely improved over the last decades. Despite increasing molecular understanding of the mechanisms behind these hematopoietic malignancies, this knowledge has had poor translation into the clinic. Here, we report a Drosophila melanogaster model system to explore the pathways affected in MLL-r leukemia. We show that expression of the human leukemic oncogene MLL-AF4 in the Drosophila hematopoietic system resulted in increased levels of circulating hemocytes and an enlargement of the larval hematopoietic organ, the lymph gland. Strikingly, depletion of Drosophila orthologs of known interactors of MLL-AF4, such as DOT1L, rescued the leukemic phenotype. In agreement, treatment with small-molecule inhibitors of DOT1L also prevented the MLL-AF4-induced leukemia-like phenotype. Taken together, this model provides an in vivo system to unravel the genetic interactors involved in leukemogenesis and offers a system for improved biological understanding of MLL-r leukemia.

Transcription factor abnormalities in B-ALL leukemogenesis and treatment

The biological regulation of transcription factors (TFs) and repressor proteins is an important mechanism for maintaining cell homeostasis. In B cell acute lymphoblastic leukemia (B-ALL) TF abnormalities occur at high frequency and are often recognized as the major driving factor in carcinogenesis. We provide an in-depth review of molecular mechanisms of six major TF rearrangements in B-ALL, including DUX4-rearranged (DUX4-R), MEF2D-R, ZNF384-R, ETV6-RUNX1 and TCF3-PBX1 fusions, and KMT2A-R. In addition, the therapeutic options and prognoses for patients who harbor these TF abnormalities are discussed. This review aims to provide an up-to-date panoramic view of how TF-based oncogenic fusions might drive carcinogenesis and impact on potential therapeutic exploration of B-ALL treatments.

Molecular and Clinical Spectrum of Primary Hyperparathyroidism

Recent data suggest an increase in the overall incidence of parathyroid disorders, with primary hyperparathyroidism (PHPT) being the most prevalent parathyroid disorder. PHPT is associated with morbidities (fractures, kidney stones, chronic kidney disease) and increased risk of death. The symptoms of PHPT can be nonspecific, potentially delaying the diagnosis. Approximately 15% of patients with PHPT have an underlying heritable form of PHPT that may be associated with extraparathyroidal manifestations, requiring active surveillance for these manifestations as seen in multiple endocrine neoplasia type 1 and 2A. Genetic testing for heritable forms should be offered to patients with multiglandular disease, recurrent PHPT, young onset PHPT (age ≤40 years), and those with a family history of parathyroid tumors. However, the underlying genetic cause for the majority of patients with heritable forms of PHPT remains unknown. Distinction between sporadic and heritable forms of PHPT is useful in surgical planning for parathyroidectomy and has implications for the family. The genes currently known to be associated with heritable forms of PHPT account for approximately half of sporadic parathyroid tumors. But the genetic cause in approximately half of the sporadic parathyroid tumors remains unknown. Furthermore, there is no systemic therapy for parathyroid carcinoma, a rare but potentially fatal cause of PHPT. Improved understanding of the molecular characteristics of parathyroid tumors will allow us to identify biomarkers for diagnosis and novel targets for therapy.

NPM1-mutated acute myeloid leukemia: New pathogenetic and therapeutic insights and open questions

The nucleophosmin (NPM1) gene encodes for a multifunctional chaperone protein that is localized in the nucleolus but continuously shuttles between the nucleus and cytoplasm. NPM1 mutations occur in about one-third of AML, are AML-specific, usually involve exon 12 and are frequently associated with FLT3-ITD, DNMT3A, TET2, and IDH1/2 mutations. Because of its unique molecular and clinico-pathological features, NPM1-mutated AML is regarded as a distinct leukemia entity in both the International Consensus Classification (ICC) and the 5th edition of the World Health Organization (WHO) classification of myeloid neoplasms. All NPM1 mutations generate leukemic mutants that are aberrantly exported in the cytoplasm of the leukemic cells and are relevant to the pathogenesis of the disease. Here, we focus on recently identified functions of the NPM1 mutant at chromatin level and its relevance in driving HOX/MEIS gene expression. We also discuss yet controversial issues of the ICC/WHO classifications, including the biological and clinical significance of therapy-related NPM1-mutated AML and the relevance of blasts percentage in defining NPM1-mutated AML. Finally, we address the impact of new targeted therapies in NPM1-mutated AML with focus on CAR T cells directed against NPM1/HLA neoepitopes, as well as XPO1 and menin inhibitors.

Advances in acute myeloid leukemia differentiation therapy: A critical review

Acute myeloid leukemia (AML) is characterized by impaired differentiation and indefinite proliferation of abnormal myeloid progenitors. Although differentiating agents were deemed to revolutionize AML therapy, most treated non-APL AML patients are refractory or relapse. According to cancer stem cell model, leukemia-initiating cells are the root cause of relapse given their unidirectional potential to generate differentiated AML blasts. Nonetheless, accumulating evidences emphasize the de-differentiation plasticity and leukemogenic potential of mature AML blasts and the frailty of targeting leukemic stem cells per se. This review critically discusses the potential and challenges of (lessons learnt from) conventional and novel differentiating agents in AML therapy. Although differentiating agents might hold promise, they should be exploited within the context of a rationale combination regimen eradicating all maturation/differentiation states of AML cells. The results of the routinely used immunophenotypic markers and/or morphological analyses of differentiation should be carefully interpreted given their propensity to underestimate AML burden.

Phase-separated nuclear bodies of nucleoporin fusions promote condensation of MLL1/CRM1 and rearrangement of 3D genome structure

NUP98 and NUP214 form chimeric fusion proteins that assemble into phase-separated nuclear bodies containing CRM1, a nuclear export receptor. However, these nuclear bodies' function in controlling gene expression remains elusive. Here, we demonstrate that the nuclear bodies of NUP98::HOXA9 and SET::NUP214 promote the condensation of mixed lineage leukemia 1 (MLL1), a histone methyltransferase essential for the maintenance of HOX gene expression. These nuclear bodies are robustly associated with MLL1/CRM1 and co-localized on chromatin. Furthermore, whole-genome chromatin-conformation capture analysis reveals that NUP98::HOXA9 induces a drastic alteration in high-order genome structure at target regions concomitant with the generation of chromatin loops and/or rearrangement of topologically associating domains in a phase-separation-dependent manner. Collectively, these results show that the phase-separated nuclear bodies of nucleoporin fusion proteins can enhance the activation of target genes by promoting the condensation of MLL1/CRM1 and rearrangement of the 3D genome structure.

Establishment of a t(11;19), KMT2A Rearranged B-ALL Cell Line for Preclinical Evaluation and Novel Therapeutics Development for Refractory Infant Leukemia

Leukemia, diagnosed in children less than 12 months of age, is a rare condition with an aggressive disease presentation and poor response to conventional chemotherapeutic agents. In addition, the unique vulnerability of the affected population does not always permit the use of markedly intense regimens with higher doses of cytotoxic agents. However, the unique biology of these leukemic cells also provides opportunities for the identification of effective and potentially well-tolerated targeted therapeutic strategies. In this report, we describe the establishment and characterization of a cell line from the blasts of an infant diagnosed with refractory B-cell acute lymphoblastic leukemia (ALL) carrying the characteristic histone lysine methyltransferase 2A (KMT2A) gene rearrangement. This cell line consists of rapidly proliferating clones of cells with chemosensitivity patterns previously described for KMT2A rearranged leukemia cells, including relative resistance to glucocorticoids and sensitivity to cytarabine. We also show effective targetability with menin inhibitors, indicating the activity of abnormal KMT2A-related pathways and the potential utility of this cell line in comprehensive drug library screens. Overall, our findings report the establishment and in vitro validation of a cell line for research into key aspects of infant leukemia biology and targeted therapeutics development.

Acute Myeloid Leukemia Treatment in the Elderly: A Comprehensive Review of the Present and Future

BACKGROUND

Acute myeloid leukemia (AML) is a disease of the hematopoietic system that remains a therapeutic challenge despite advances in our understanding of the underlying cancer biology in the past decade. It is also an affliction of the elderly that predominantly affects patients over 60 years of age. Standard therapy involves intensive chemotherapy that is often difficult to tolerate in older populations. Fortunately, recent developments in molecular targeting have shown promising results in treating leukemia, paving the way for novel treatment strategies that are easier to tolerate.

SUMMARY

Venetoclax, a BCL-2 inhibitor, when combined with a hypomethylating agent, has proven to be a highly effective and well-tolerated drug and established itself as a new standard for treating AML in patients who are unfit for standard intensive therapy. Other targeted therapies include clinically proven and FDA-approved agents, such as IDH1/2 inhibitors, FLT3 inhibitors, and Gemtuzumab, as well as newer and more experimental drugs such as magrolimab, PI-kinase inhibitors, and T-cell engaging therapy. Some of the novel agents such as magrolimab and menin inhibitors are particularly promising, providing therapeutic options to a wider population of patients than ever before. Determining who will benefit from intense or novel low-intense therapy remains a challenge, and it requires careful assessment of individual patient's fitness and disease characteristics.

KEY MESSAGES

This article reviews past and current treatment strategies that harness various mechanisms of leukemia-targeting agents and introduces novel therapies on the horizon aimed at exploring therapeutic options for the elderly and unfit patient population. It also provides a strategy to select the best available therapy for elderly patients with both newly diagnosed and relapsed/refractory AML.

Evaluating the role of MEN1 gene expression and its clinical significance in breast cancer patients

BACKGROUND

Breast cancer is a multifactorial disease which involves number of molecular factors that are critically involved in proliferation of breast cancer cells. MEN1 gene that is traditionally known for its germline mutations in neuroendocrine tumors is associated with high risk of developing breast cancer in females with MEN1 syndrome. However, the paradoxical role of MEN1 is reported in sporadic breast cancer cases. The previous studies indicate the functional significance of MEN1 in regulating breast cells proliferation but its relevance in development and progression of breast cancer is still not known. Our study targets to find the role of MEN1 gene aberration and its clinical significance in breast cancer.

METHODS

Breast tumor and adjacent normal tissue of 142 sporadic breast cancer patients were collected at the time of surgery. The expression analysis of MEN1 mRNA and protein was done through RT-PCR, immunohistochemistry and western blotting. Further to find the genetic and epigenetic alterations, automated sequencing and MS-PCR was performed respectively. Correlation between our findings and clinical parameters was determined using appropriate statistical tests.

RESULTS

MEN1 expression was found to be significantly increased in the breast tumor tissue with its predominant nuclear localization. The elevated expression of MEN1 mRNA (63.38% cases) and protein (60.56% cases) exhibited a significant association with ER status of the patients. Most of the cases had unmethylated (53.52%) MEN1 promoter region, which can be a key factor responsible for dysregulated expression of MEN1 in breast cancer cases. Our findings also revealed the significant association of MEN1 mRNA overexpression with Age and lymph node status of the patients.

CONCLUSION

Our results indicate upregulated expression of MEN1 in sporadic breast cancer patients and it could be critically associated with development and advancement of the disease.

Insights into the New Molecular Updates in Acute Myeloid Leukemia Pathogenesis

As our understanding of the biologic basis of acute myeloid leukemia evolves, so do the classification systems used to describe this group of cancers. Early classification systems focused on the morphologic features of blasts and other cell populations; however, the explosion in genomic technologies has led to rapid growth in our understanding of these diseases and thus the refinement of classification systems. Recently, two new systems, the International Consensus Classification system and the 5th edition of the World Health Organization classification of tumors of hematopoietic and lymphoid tissues, were published to incorporate the latest genomic advances in blood cancer. This article reviews the major updates in acute myeloid leukemia in both systems and highlights the biologic insights that have driven these changes.

Biomolecular Condensates in Myeloid Leukemia: What Do They Tell Us?

Recent studies have suggested that several oncogenic and tumor-suppressive proteins carry out their functions in the context of specific membrane-less cellular compartments. As these compartments, generally referred to as onco-condensates, are specific to tumor cells and are tightly linked to disease development, the mechanisms of their formation and maintenance have been intensively studied. Here we review the proposed leukemogenic and tumor-suppressive activities of nuclear biomolecular condensates in acute myeloid leukemia (AML). We focus on condensates formed by oncogenic fusion proteins including nucleoporin 98 (NUP98), mixed-lineage leukemia 1 (MLL1, also known as KMT2A), mutated nucleophosmin (NPM1c) and others. We also discuss how altered condensate formation contributes to malignant transformation of hematopoietic cells, as described for promyelocytic leukemia protein (PML) in PML::RARA-driven acute promyelocytic leukemia (APL) and other myeloid malignancies. Finally, we discuss potential strategies for interfering with the molecular mechanisms related to AML-associated biomolecular condensates, as well as current limitations of the field.

Enhancer remodeling drives MLL oncogene-dependent transcriptional dysregulation in leukemia stem cells

Acute myeloid leukemia (AML) with mixed-lineage leukemia (MLL) gene rearrangement (MLLr) comprises a cellular hierarchy in which a subpopulation of cells serves as functional leukemia stem cells (LSCs). They are maintained by a unique gene expression program and chromatin states, which are thought to reflect the actions of enhancers. Here, we delineate the active enhancer landscape and observe pervasive enhancer malfunction in LSCs. Reconstruction of regulatory networks revealed a master set of hematopoietic transcription factors. We show that EP300 is an essential transcriptional coregulator for maintaining LSC oncogenic potential because it controls essential gene expression through modulation of H3K27 acetylation and assessments of transcription factor dependencies. Moreover, the EP300 inhibitor A-485 affects LSC growth by targeting enhancer activity via histone acetyltransferase domain inhibition. Together, these data implicate a perturbed MLLr-specific enhancer accessibility landscape, suggesting the possibility for disruption of the LSC enhancer regulatory axis as a promising therapeutic strategy in AML.

An Overview of Targeted Therapies in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most aggressive adult leukemia, characterized by clonal differentiation arrest of progenitor or precursor hematopoietic cells. Intense preclinical and clinical research has led to regulatory approval of several targeted therapeutics, administered either as single agents or as combination therapies. However, the majority of patients still face a poor prognosis and disease relapse frequently occurs due to selection of therapy-resistant clones. Hence, more effective novel therapies, most likely as innovative, rational combination therapies, are urgently needed. Chromosomal aberrations, gene mutations, and epigenetic alterations drive AML pathogenesis but concurrently provide vulnerabilities to specifically target leukemic cells. Other molecules, either aberrantly active and/or overexpressed in leukemic stem cells, may also be leveraged for therapeutic benefit. This concise review of targeted therapies for AML treatment, which are either approved or are being actively investigated in clinical trials or recent preclinical studies, provides a flavor of the direction of travel, but also highlights the current challenges in AML treatment.

Targeting the undruggable: menin inhibitors ante portas

Acute myeloid leukaemias harbouring a rearrangement of the mixed lineage leukaemia gene (MLL) are aggressive haematopoietic malignancies that relapse early and have a poor prognosis (event-free survival less than 50%). Menin is a tumour suppressor, however, in MLL-rearranged leukaemias it functions as a co-factor which is mandatory for the leukaemic transformation by interaction with the N-terminal part of MLL, which is maintained in all MLL-fusion proteins. Inhibition of menin blocks leukaemogenesis and leads to differentiation and, in turn, to apoptosis of leukaemic blasts. Furthermore, nucleophosmin 1 (NPM1) binds to specific chromatin targets, which are co-occupied by MLL, and menin inhibition has been shown to trigger degradation of mNPM1 resulting in a rapid decrease in gene expression and activating histone modifications. Therefore, disruption of the menin-MLL axis blocks leukaemias driven by NPM1 mutations for which the expression of menin-MLL target genes (e.g., MEIS1, HOX etc.) is essential. To date at least six different menin-MLL inhibitors are undergoing clinical evaluation as first- and second-line monotherapy in acute leukaemias: DS-1594, BMF-219, JNJ-75276617, DSP-5336, revumenib, and ziftomenib, however, only for revumenib and ziftomenib early clinical data have been reported. In the revumenib phase I/II AUGMENT-101 trial (N = 68) with very heavily pretreated AML patients the ORR was 53% with a CR rate of 20%. The ORR in patients harbouring MLL rearrangement of mNPM1 was 59%. Patients who achieved a response had a mOS of 7 months. Similar results have been reported for ziftomenib in the phase I/II COMET-001 trial. ORR was 40% and CRc was 35% in AML patients with mNPM1. However, outcome was worse in AML patients with a MLL rearrangement (ORR 16.7%, CRc 11%). Differentiation syndrome was a notable adverse event. The clinical development of novel menin-MLL inhibitors is well in line with the currently ongoing paradigm shift towards targeted therapies seen in the AML treatment landscape. Moreover, the clinical assessment of combinations of these inhibitors with established therapy options in AML could be the fuel for an improved outcome of MLL/NPM1 patients.

Senescent CD8+ T cells acquire NK cell-like innate functions to promote antitumor immunity

It has been suggested that aging of the immune system (immunosenescence) results in a decline in the acquired immune response, which is associated with an increase in age-related tumorigenesis. T-cell senescence plays a critical role in immunosenescence and is involved in the age-related decline of the immune function, which increases susceptibility to certain cancers. However, it has been shown that CD8⁺ T cells with the senescent T-cell phenotype acquire an natural killer (NK) cell-like function and are involved in tumor elimination. Therefore, the role of senescent CD8⁺ T cells in tumor immunity remains to be elucidated. In this study, we investigated the role of senescent CD8⁺ T cells in tumor immunity. In a murine model of transferred with B16 melanoma, lung metastasis was significantly suppressed in aged mice (age ≥30 weeks) in comparison to young mice (age 6-10 weeks). We evaluated the cytotoxic activity of CD8⁺ T cells in vitro and found that CD8⁺ T cells from aged mice activated in vitro exhibited increased cytotoxic activity in comparison to those from young mice. We used Menin-deficient effector T cells as a model for senescent CD8⁺ T cells and found that cytotoxic activity and the expression of NK receptors were upregulated in Menin-deficient senescent CD8⁺ T cells. Furthermore, Menin-deficient CD8⁺ T cells can eliminate tumor cells in an antigen-independent manner. These results suggest that senescent effector CD8⁺ T cells may contribute to tumor immunity in the elderly by acquiring NK-like innate immune functions, such as antigen-independent cytotoxic activity.

Targeting of epigenetic co-dependencies enhances anti-AML efficacy of Menin inhibitor in AML with MLL1-r or mutant NPM1

Monotherapy with Menin inhibitor (MI), e.g., SNDX-5613, induces clinical remissions in patients with relapsed/refractory AML harboring MLL1-r or mtNPM1, but most patients either fail to respond or eventually relapse. Utilizing single-cell RNA-Seq, ChiP-Seq, ATAC-Seq, RNA-Seq, RPPA, and mass cytometry (CyTOF) analyses, present pre-clinical studies elucidate gene-expression correlates of MI efficacy in AML cells harboring MLL1-r or mtNPM1. Notably, MI-mediated genome-wide, concordant, log2 fold-perturbations in ATAC-Seq and RNA-Seq peaks were observed at the loci of MLL-FP target genes, with upregulation of mRNAs associated with AML differentiation. MI treatment also reduced the number of AML cells expressing the stem/progenitor cell signature. A protein domain-focused CRISPR-Cas9 screen in MLL1-r AML cells identified targetable co-dependencies with MI treatment, including BRD4, EP300, MOZ and KDM1A. Consistent with this, in vitro co-treatment with MI and BET, MOZ, LSD1 or CBP/p300 inhibitor induced synergistic loss of viability of AML cells with MLL1-r or mtNPM1. Co-treatment with MI and BET or CBP/p300 inhibitor also exerted significantly superior in vivo efficacy in xenograft models of AML with MLL1-r. These findings highlight novel, MI-based combinations that could prevent escape of AML stem/progenitor cells following MI monotherapy, which is responsible for therapy-refractory AML relapse.