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The protein-protein interaction between menin and mixed lineage leukemia 1 (MLL1) plays a critical role in acute leukemias with translocations of the MLL1 gene or with mutations in the nucleophosmin 1 (NPM1) gene. As a step toward clinical translation of menin-MLL1 inhibitors, we report development of MI-3454, a highly potent and orally bioavailable inhibitor of the menin-MLL1 interaction. MI-3454 profoundly inhibited proliferation and induced differentiation in acute leukemia cells and primary patient samples with MLL1 translocations or NPM1 mutations. When applied as a single agent, MI-3454 induced complete remission or regression of leukemia in mouse models of MLL1-rearranged or NPM1-mutated leukemia, including patient-derived xenograft models, through downregulation of key genes involved in leukemogenesis. We also identified MEIS1 as a potential pharmacodynamic biomarker of treatment response with MI-3454 in leukemia, and demonstrated that this compound is well tolerated and did not impair normal hematopoiesis in mice. Overall, this study demonstrates, for the first time to our knowledge, profound activity of the menin-MLL1 inhibitor as a single agent in clinically relevant PDX models of leukemia. These data provide a strong rationale for clinical translation of MI-3454 or its analogs for leukemia patients with MLL1 rearrangements or NPM1 mutations.

Key Points The histone–lysine N -methyltransferase (KMT2) family comprises a set of lysine methyltransferases that methylate the lysine 4 residue on histone H3 (H3K4). KMT2 family members demonstrate different substrate specificity in vitro and their methyltransferase activities are dependent, to varying degrees, on association with three core subunits (WD repeat protein 5, retinoblastoma binding protein 5 and ASH2L). KMT2 family members have intrinsically different biochemical properties and are recruited to different genomic regions owing to their distinct domain structures and distinct interacting proteins. KMT2 family members have important roles in transcription regulation. Among them, KMT2C and KMT2D are crucial for monomethylation of H3K4 at distal regulatory enhancers, whereas KMT2F and KMT2G are responsible for the majority of H3K4 trimethylation at transcription start sites. There is extensive interplay between KMT2-dependent H3K4 methylation and DNA methylation, underlying the potential epigenetic stability of this histone methylation. Mutations in the KMT2 family are among the most common genetic aberrations in human cancer — including haematological malignancies as well as solid tumours, such as large intestine, lung, endometrial, breast, bladder and brain cancers. Mutations in the KMT2 family frequently involve the SET domain and the plant homeotic domains. Of somatic mutations in cancers with known zygosity, heterozygous mutations predominate. These features suggest that the wild-type KMT2 allele may be required for tumour survival, similar to KMT2A -rearranged mixed lineage leukaemia. KMT2 family members may have distinct roles in cancer. Although it remains unclear whether cancer-derived KMT2 mutations are 'drivers' or 'passengers', mechanistic studies in animal models suggest that KMT2C may be a tumour suppressor and KMT2A and KMT2D may be proteins derived from proto-oncogenes. The targeting of the fusion protein and wild-type KMT2A, as well as their interacting proteins, has emerged as a promising strategy to treat mixed lineage leukaemia, and may apply more broadly to a variety of cancers. Histone–lysine N -methyltransferase 2 (KMT2) family proteins, initially named the mixed lineage leukaemia (MLL) family, are altered in many types of cancers beyond MLL. Inhibitors of KMT2 function are being developed and could work as therapeutics in a variety of cancer types. Histone–lysine N -methyltransferase 2 (KMT2) family proteins methylate lysine 4 on the histone H3 tail at important regulatory regions in the genome and thereby impart crucial functions through modulating chromatin structures and DNA accessibility. Although the human KMT2 family was initially named the mixed-lineage leukaemia (MLL) family, owing to the role of the first-found member KMT2A in this disease, recent exome-sequencing studies revealed KMT2 genes to be among the most frequently mutated genes in many types of human cancers. Efforts to integrate the molecular mechanisms of KMT2 with its roles in tumorigenesis have led to the development of first-generation inhibitors of KMT2 function, which could become novel cancer therapies.

The mixed lineage leukaemia (MLL) family of proteins (including MLL1–MLL4, SET1A and SET1B) specifically methylate histone 3 Lys4, and have pivotal roles in the transcriptional regulation of genes involved in haematopoiesis and development. The methyltransferase activity of MLL1, by itself severely compromised, is stimulated by the three conserved factors WDR5, RBBP5 and ASH2L, which are shared by all MLL family complexes. However, the molecular mechanism of how these factors regulate the activity of MLL proteins still remains poorly understood. Here we show that a minimized human RBBP5–ASH2L heterodimer is the structural unit that interacts with and activates all MLL family histone methyltransferases. Our structural, biochemical and computational analyses reveal a two-step activation mechanism of MLL family proteins. These findings provide unprecedented insights into the common theme and functional plasticity in complex assembly and activity regulation of MLL family methyltransferases, and also suggest a universal regulation mechanism for most histone methyltransferases. Crystal structures of the SET domains of MLL3 and a mutant MLL1 either unbound or complexed with domains from RBBP5 and ASH2L are determined; a combination of structural, biochemical and computational analyses reveals a two-step activation mechanism of MLL family proteins, which may be relevant for other histone methyltransferases. Activation mechanism for MLL enzymes The SET domain-containing MLL family proteins methylate histone 3 on lysine 4 (H3K4) and have key roles in transcriptional regulation. MLL proteins are catalytically inactive on their own, and have full activity only when bound in a complex with three factors: WDR5, RBBP5, and ASH2L. Yong Chen and colleagues determine crystal structures of the SET domains of MLL3 and a mutant MLL1 in unbound forms or complexed with domains from RBBP5 and ASH2L and the histone H3 substrate. Their results suggest that WDR5 is not directly involved in enzymatic stimulation, and a combination of structural, biochemical and computational analyses reveals a two-step activation mechanism which may be relevant for all histone methyltransferases.

The p30 isoform of C/EBPα associated with leukemia interacts with WDR5, a component of the SET/MLL histone methyltransferase complex. A small molecule, OICR-9429, disrupted p30-WDR5 interactions, resulting in differentiation of p30-expressing leukemia cells. The CEBPA gene is mutated in 9% of patients with acute myeloid leukemia (AML). Selective expression of a short (30-kDa) CCAAT-enhancer binding protein-α (C/EBPα) translational isoform, termed p30, represents the most common type of CEBPA mutation in AML. The molecular mechanisms underlying p30-mediated transformation remain incompletely understood. We show that C/EBPα p30, but not the normal p42 isoform, preferentially interacts with Wdr5, a key component of SET/MLL (SET-domain/mixed-lineage leukemia) histone-methyltransferase complexes. Accordingly, p30-bound genomic regions were enriched for MLL-dependent H3K4me3 marks. The p30-dependent increase in self-renewal and inhibition of myeloid differentiation required Wdr5, as downregulation of the latter inhibited proliferation and restored differentiation in p30-dependent AML models. OICR-9429 is a new small-molecule antagonist of the Wdr5-MLL interaction. This compound selectively inhibited proliferation and induced differentiation in p30-expressing human AML cells. Our data reveal the mechanism of p30-dependent transformation and establish the essential p30 cofactor Wdr5 as a therapeutic target in CEBPA -mutant AML.

Proliferative chronic myelomonocytic leukemia (pCMML), an aggressive CMML subtype, is associated with dismal outcomes. RAS pathway mutations, mainly NRAS G12D , define the pCMML phenotype as demonstrated by our exome sequencing, progenitor colony assays and a Vav-Cre - Nras G12D mouse model. Further, these mutations promote CMML transformation to acute myeloid leukemia. Using a multiomics platform and biochemical and molecular studies we show that in pCMML RAS pathway mutations are associated with a unique gene expression profile enriched in mitotic kinases such as polo-like kinase 1 ( PLK1). PLK1 transcript levels are shown to be regulated by an unmutated lysine methyl-transferase (KMT2A) resulting in increased promoter monomethylation of lysine 4 of histone 3. Pharmacologic inhibition of PLK1 in RAS mutant patient-derived xenografts, demonstrates the utility of personalized biomarker-driven therapeutics in pCMML. Chronic myelomonocytic leukaemia is classified as proliferative (pCMML) or dysplastic based on the white blood cell counts but biological differences are unclear. Here, the authors show genetic, transcriptomic and epigenomic differences between these two subtypes establishing that pCMML is RAS-pathway driven and that inhibiting RAS-driven PLK1 expression is a viable therapeutic target.

MLL fusion genes often encode leukemogenic proteins that depend on interaction with menin, a component of the MLL SET1-like histone methyltransferase complex. MI-2 and MI-3 are the first small molecules that can block menin–MLL fusion protein interaction and their oncogenic effects in cells. Translocations involving the mixed lineage leukemia ( MLL ) gene result in human acute leukemias with very poor prognosis. The leukemogenic activity of MLL fusion proteins is critically dependent on their direct interaction with menin, a product of the multiple endocrine neoplasia ( MEN1 ) gene. Here we present what are to our knowledge the first small-molecule inhibitors of the menin–MLL fusion protein interaction that specifically bind menin with nanomolar affinities. These compounds effectively reverse MLL fusion protein–mediated leukemic transformation by downregulating the expression of target genes required for MLL fusion protein oncogenic activity. They also selectively block proliferation and induce both apoptosis and differentiation of leukemia cells harboring MLL translocations. Identification of these compounds provides a new tool for better understanding MLL-mediated leukemogenesis and represents a new approach for studying the role of menin as an oncogenic cofactor of MLL fusion proteins. Our findings also highlight a new therapeutic strategy for aggressive leukemias with MLL rearrangements.

Methyltransferases of the mixed-lineage leukaemia (MLL) family—which include MLL1, MLL2, MLL3, MLL4, SET1A and SET1B—implement methylation of histone H3 on lysine 4 (H3K4), and have critical and distinct roles in the regulation of transcription in haematopoiesis, adipogenesis and development 1 – 6 . The C-terminal catalytic SET (Su(var.)3-9, enhancer of zeste and trithorax) domains of MLL proteins are associated with a common set of regulatory factors (WDR5, RBBP5, ASH2L and DPY30) to achieve specific activities 7 – 9 . Current knowledge of the regulation of MLL activity is limited to the catalysis of histone H3 peptides, and how H3K4 methyl marks are deposited on nucleosomes is poorly understood. H3K4 methylation is stimulated by mono-ubiquitination of histone H2B on lysine 120 (H2BK120ub1), a prevalent histone H2B mark that disrupts chromatin compaction and favours open chromatin structures, but the underlying mechanism remains unknown 10 – 12 . Here we report cryo-electron microscopy structures of human MLL1 and MLL3 catalytic modules associated with nucleosome core particles that contain H2BK120ub1 or unmodified H2BK120. These structures demonstrate that the MLL1 and MLL3 complexes both make extensive contacts with the histone-fold and DNA regions of the nucleosome; this allows ease of access to the histone H3 tail, which is essential for the efficient methylation of H3K4. The H2B-conjugated ubiquitin binds directly to RBBP5, orienting the association between MLL1 or MLL3 and the nucleosome. The MLL1 and MLL3 complexes display different structural organizations at the interface between the WDR5, RBBP5 and MLL1 (or the corresponding MLL3) subunits, which accounts for the opposite roles of WDR5 in regulating the activity of the two enzymes. These findings transform our understanding of the structural basis for the regulation of MLL activity at the nucleosome level, and highlight the pivotal role of nucleosome regulation in histone-tail modification. Cryo-electron microscopy structures of mixed-lineage leukaemia methyltransferases 1 and 3 associated with unmodified or mono-ubiquitinated nucleosome reveal the structural basis for the activity specificity and regulation of these enzymes.

The initiating mutations that contribute to cancer development are sometimes present in premalignant cells. Whether therapies targeting these mutations can eradicate premalignant cells is unclear. Acute myeloid leukemia (AML) is an attractive system for investigating the effect of preventative treatment because this disease is often preceded by a premalignant state (clonal hematopoiesis or myelodysplastic syndrome). In Npm1c/Dnmt3a mutant knock-in mice, a model of AML development, leukemia is preceded by a period of extended myeloid progenitor cell proliferation and self-renewal. We found that this self-renewal can be reversed by oral administration of a small molecule (VTP-50469) that targets the MLL1-Menin chromatin complex. These preclinical results support the hypothesis that individuals at high risk of developing AML might benefit from targeted epigenetic therapy in a preventative setting.

Leukaemogenesis requires enhanced self-renewal, which is induced by oncogenes. The underlying molecular mechanisms remain incompletely understood. Here, we identified C/D box snoRNAs and rRNA 2′- O -methylation as critical determinants of leukaemic stem cell activity. Leukaemogenesis by AML1-ETO required expression of the groucho-related amino-terminal enhancer of split (AES). AES functioned by inducing snoRNA/RNP formation via interaction with the RNA helicase DDX21. Similarly, global loss of C/D box snoRNAs with concomitant loss of rRNA 2′- O -methylation resulted in decreased leukaemia self-renewal potential. Genomic deletion of either C/D box snoRNA SNORD14D or SNORD35A suppressed clonogenic potential of leukaemia cells in vitro and delayed leukaemogenesis in vivo . We further showed that AML1-ETO9a, MYC and MLL-AF9 all enhanced snoRNA formation. Expression levels of C/D box snoRNAs in AML patients correlated closely with in vivo frequency of leukaemic stem cells. Collectively, these findings indicate that induction of C/D box snoRNA/RNP function constitutes an important pathway in leukaemogenesis. Zhou et al. show that in the context of AML1-ETO-driven leukaemia, AES and DDX21 induce small nucleolar RNA (snoRNA)–ribonucleoprotein (RNP) formation and this is important for self-renewal of leukaemic cells.

Balanced rearrangements involving the KMT2A gene, located at 11q23, are among the most frequent chromosome aberrations in acute myeloid leukemia (AML). Because of numerous fusion partners, the mutational landscape and prognostic impact of specific 11q23/KMT2A rearrangements are not fully understood. We analyzed clinical features of 172 adults with AML and recurrent 11q23/KMT2A rearrangements, 141 of whom had outcome data available. We compared outcomes of these patients with outcomes of 1,097 patients without an 11q23/KMT2A rearrangement categorized according to the 2017 European LeukemiaNet (ELN) classification. Using targeted next-generation sequencing, we investigated the mutational status of 81 leukemia/cancer-associated genes in 96 patients with 11q23/KMT2A rearrangements with material for molecular studies available. Patients with 11q23/KMT2A rearrangements had a low number of additional gene mutations (median, 1; range 0 to 6), which involved the RAS pathway (KRAS, NRAS, and PTPN11) in 32% of patients. KRAS mutations occurred more often in patients with t(6;11)(q27;q23)/KMT2A-AFDN compared with patients with the other 11q23/KMT2A subsets. Specific gene mutations were too infrequent in patients with specific 11q23/KMT2A rearrangements to assess their associations with outcomes. We demonstrate that younger (age 60 y) patients with t(9;11)(p22;q23)/KMT2A-MLLT3 had better outcomes than patients with other 11q23/KMT2A rearrangements and those without 11q23/KMT2A rearrangements classified in the 2017 ELN intermediate-risk group. Conversely, outcomes of older patients (age ≥60 y) with t(9;11)(p22;q23) were poor and comparable to those of the ELN adverse-risk group patients. Our study shows that patients with an 11q23/KMT2A rearrangement have distinct mutational patterns and outcomes depending on the fusion partner.