Mixed Lineage Leukemia Research Articles

Targeting cytohesin-1 suppresses acute myeloid leukemia progression and overcomes resistance to ABT-199.

Adhesion molecules play essential roles in the homeostatic regulation and malignant transformation of hematopoietic cells. The dysregulated expression of adhesion molecules in leukemic cells accelerates disease progression and the development of drug resistance. Thus, targeting adhesion molecules represents an attractive anti-leukemic therapeutic strategy. In this study, we investigated the prognostic role and functional significance of cytohesin-1 (CYTH1) in acute myeloid leukemia (AML). Analysis of AML patient data from the GEPIA and BloodSpot databases revealed that CYTH1 was significantly overexpressed in AML and independently correlated with prognosis. Functional assays using AML cell lines and an AML xenograft mouse model confirmed that CYTH1 depletion significantly inhibited the adhesion, migration, homing, and engraftment of leukemic cells, delaying disease progression and prolonging animal survival. The CYTH1 inhibitor SecinH3 exerted in vitro and in vivo anti-leukemic effects by disrupting leukemic adhesion and survival programs. In line with the CYTH1 knockdown results, targeting CYTH1 by SecinH3 suppressed integrin-associated adhesion signaling by reducing ITGB2 expression. SecinH3 treatment efficiently induced the apoptosis and inhibited the growth of a panel of AML cell lines (MOLM-13, MV4-11 and THP-1) with mixed-lineage leukemia gene rearrangement, partly by reducing the expression of the anti-apoptotic protein MCL1. Moreover, we showed that SecinH3 synergized with the BCL2-selective inhibitor ABT-199 (venetoclax) to inhibit the proliferation and promote the apoptosis of ABT-199-resistant leukemic cells. Taken together, our results not only shed light on the role of CYTH1 in cell-adhesion-mediated leukemogenesis but also propose a novel combination treatment strategy for AML.

Childhood B-lymphoblastic leukemia: Integrating cytogenetics with other prognostic parameters and correlation with post-induction remission

BackgroundCytogenetics is irrefutably one of the most significant prognostic markers which have imparted ease and feasibility in the classification of acute leukemia. It is an essential prognostic tool in major treatment protocols for all hematological malignancies. This study aimed to note the frequency of different cytogenetic aberrations in children with B-ALL, their association with risk factors, and impact on post-induction remission status. MethodsA retrospective study was conducted in the Hematology department of The Indus Hospital, Karachi. All newly diagnosed patients of B-ALL (aged 1–17 years) from October 2, 2020 to October 13, 2021 were included. They were treated with modified Children's Oncology Group (COG) protocol. Cytogenetic studies including conventional karyotyping and fluorescence in situ hybridization (FISH) for BCR::ABL1, ETV6::RUNX1, and MLL gene rearrangement were performed on semi-automated cell imaging. ResultsAmong 238 patients, cytogenetic abnormalities were identified in 146 (61.3%) cases. A normal karyotype was observed in 92 (38.7%), high hyperdiploidy in 56 (24%), random structural abnormalities in 22 (9.2%), t (1:19) in 21 (8.8%), t (9; 22) in 12 (5.0%), complex karyotype in 10 (4.2%), 11q abnormalities in 5 (2.1%) and monosomy 7 in 1 (0.4%) case(s). FISH positivity for MLL, BCR::ABL1 and ETV6::RUNX1 was observed in 6 (2.5%), 18 (7.5%), and 20 (8.4%), cases, respectively. Post induction morphological remission was observed in 98.3% of cases. ConclusionThe overall frequency of cytogenetic abnormalities in the current cohort is comparable to previously reported studies. Our data also suggest the value of combining the karyotype and FISH techniques to increase the likelihood of detection of recurrent cytogenetic abnormalities. Even though there was a lack of correlation between genetic abnormalities and early outcome, a follow-up may be useful to ascertain the correlation with long-term survival.

The MLL-Menin Interaction is a Therapeutic Vulnerability in NUP98-rearranged AML.

Chromosomal translocations involving the NUP98 locus are among the most prevalent rearrangements in pediatric acute myeloid leukemia (AML). AML with NUP98 fusions is characterized by high expression of HOXA and MEIS1 genes and is associated with poor clinical outcome. NUP98 fusion proteins are recruited to their target genes by the mixed lineage leukemia (MLL) complex, which involves a direct interaction between MLL and Menin. Here, we show that therapeutic targeting of the Menin-MLL interaction inhibits the propagation of NUP98-rearrranged AML both ex vivo and in vivo. Treatment of primary AML cells with the Menin inhibitor revumenib (SNDX-5613) impairs proliferation and clonogenicity ex vivo in long-term coculture and drives myeloid differentiation. These phenotypic effects are associated with global gene expression changes in primary AML samples that involve the downregulation of many critical NUP98 fusion protein-target genes, such as MEIS1 and CDK6. In addition, Menin inhibition reduces the expression of both wild-type FLT3 and mutated FLT3-ITD, and in combination with FLT3 inhibitor, suppresses patient-derived NUP98-r AML cells in a synergistic manner. Revumenib treatment blocks leukemic engraftment and prevents leukemia-associated death of immunodeficient mice transplanted with NUP98::NSD1 FLT3-ITD-positive patient-derived AML cells. These results demonstrate that NUP98-rearranged AMLs are highly susceptible to inhibition of the MLL-Menin interaction and suggest the inclusion of AML patients harboring NUP98 fusions into the clinical evaluation of Menin inhibitors.

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.

Korean Red Ginseng Attenuates Particulate Matter-Induced Senescence of Skin Keratinocytes.

Skin is a direct target of fine particulate matter (PM2.5), as it is constantly exposed. Herein, we investigate whether Korean red ginseng (KRG) can inhibit PM2.5-induced senescence in skin keratinocytes. PM2.5-treated human keratinocyte cell lines and normal human epidermal keratinocytes showed characteristics of cellular senescence, including flat and enlarged forms; however, KRG suppressed them in both cell types. Moreover, while cells exposed to PM2.5 showed a higher level of p16INK4A expression (a senescence inducer), KRG inhibited its expression. Epigenetically, KRG decreased the expression of the ten-eleven translocation (TET) enzyme, a DNA demethylase induced by PM2.5, and increased the expression of DNA methyltransferases suppressed by PM2.5, resulting in the decreased methylation of the p16INK4A promoter region. Additionally, KRG decreased the expression of mixed-lineage leukemia 1 (MLL1), a histone methyltransferase, and histone acetyltransferase 1 (HAT1) induced by PM2.5. Contrastingly, KRG increased the expression of the enhancer of zeste homolog 2, a histone methyltransferase, and histone deacetyltransferase 1 reduced by PM2.5. Furthermore, KRG decreased TET1, MLL1, and HAT1 binding to the p16INK4A promoter, corresponding with the decreased mRNA expression of p16INK4A. These results suggest that KRG exerts protection against the PM2.5-induced senescence of skin keratinocytes via the epigenetic regulation of p16INK4A.

Mixed-Lineage Leukemia 1 Inhibition Enhances the Differentiation Potential of Bovine Embryonic Stem Cells by Increasing H3K4 Mono-Methylation at Active Promoters.

Mixed-lineage leukemia 1 (MLL1) introduces 1-, 2- and 3-methylation into histone H3K4 through the evolutionarily conserved set domain. In this study, bovine embryonic stem cells (bESCs, known as bESCs-F7) were established from in vitro-fertilized (IVF) embryos via Wnt signaling inhibition; however, their contribution to the endoderm in vivo is limited. To improve the quality of bESCs, MM-102, an inhibitor of MLL1, was applied to the culture. The results showed that MLL1 inhibition along with GSK3 and MAP2K inhibition (3i) at the embryonic stage did not affect bESCs' establishment and pluripotency. MLL1 inhibition improved the pluripotency and differentiation potential of bESCs via the up-regulation of stem cell signaling pathways such as PI3K-Akt and WNT. MLL1 inhibition decreased H3K4me1 modification at the promoters and altered the distribution of DNA methylation in bESCs. In summary, MLL1 inhibition gives bESCs better pluripotency, and its application may provide high-quality pluripotent stem cells for domestic animals.

Clinically Defined Mutations in MEN1 Alter Its Tumor-suppressive Function Through Increased Menin Turnover.

We examined the function of somatic and germline mutations and a variant of MEN1 sequenced from gastroenteropancreatic NETs. We report that these mutations and variant promote tumor cell growth and gastrin expression by rendering menin protein unstable and prone to increased degradation. We demonstrate that the menin-MLL (mixed lineage leukemia) inhibitor MI-503 restores menin protein expression and function in vitro and in vivo, suggesting a potential novel therapeutic approach to target MEN1 GEP-NETs.

Epigenetic Modulation of Inflammatory Pathways in Myometrial Stem Cells and Risk of Uterine Fibroids.

The period during which tissue and organ development occurs is particularly vulnerable to the influence of environmental exposures. However, the specific mechanisms through which biological pathways are disrupted in response to developmental insults, consequently elevating the risk of hormone-dependent diseases, such as uterine fibroids (UFs), remain poorly understood. Here, we show that developmental exposure to the endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), activates the inflammatory pathways in myometrial stem cells (MMSCs), which are the origin of UFs. Significantly, the secretome of reprogrammed MMSCs enhances the expression of critical inflammation-related genes in differentiated myometrial cells through the paracrine mechanism, which amplifies pro-inflammatory and immune suppression signaling in the myometrium. The expression of reprogrammed inflammatory responsive genes (IRGs) is driven by activated mixed-lineage leukemia protein-1 (MLL1) in MMSCs. The deactivation of MLL reverses the reprogramming of IRG expression. In addition, the inhibition of histone deacetylases (HDACs) also reversed the reprogrammed IRG expression induced by EDC exposure. This work identifies the epigenetic mechanisms of MLL1/HDAC-mediated MMSC reprogramming, and EDC exposure epigenetically targets MMSCs and imparts an IRG expression pattern, which may result in a "hyper-inflammatory phenotype" and an increased hormone-dependent risk of UFs later in life.

CircR-looping the leukemic translocations: The cause of MLL translocations explained

Conn etal.1 identify circular RNAs (circRNAs) derived from mixed lineage leukemia (MLL) breakpoint cluster regions, demonstrating a causal role of circRNAs in MLL translocations. CircRNAs:DNA hybrids (circR-loops) trigger RNA polymerase pausing, driving oncogenic gene fusions via endogenous RNA-directed DNA damage.

Circular RNAs drive oncogenic chromosomal translocations within the MLL recombinome in leukemia.

The first step of oncogenesis is the acquisition of a repertoire of genetic mutations to initiate and sustain the malignancy. An important example of this initiation phase in acute leukemias is the formation of a potent oncogene by chromosomal translocations between the mixed lineage leukemia (MLL) gene and one of 100 translocation partners, known as the MLL recombinome. Here, we show that circular RNAs (circRNAs)-a family of covalently closed, alternatively spliced RNA molecules-are enriched within the MLL recombinome and can bind DNA, forming circRNA:DNA hybrids (circR loops) at their cognate loci. These circR loops promote transcriptional pausing, proteasome inhibition, chromatin re-organization, and DNA breakage. Importantly, overexpressing circRNAs in mouse leukemia xenograft models results in co-localization of genomic loci, de novo generation of clinically relevant chromosomal translocations mimicking the MLL recombinome, and hastening of disease onset. Our findings provide fundamental insight into the acquisition of chromosomal translocations by endogenous RNA carcinogens in leukemia.

Mechanisms of Secondary Leukemia Development Caused by Treatment with DNA Topoisomerase Inhibitors.

Leukemia is a blood cancer originating in the blood and bone marrow. Therapy-related leukemia is associated with prior chemotherapy. Although cancer therapy with DNA topoisomerase II inhibitors is one of the most effective cancer treatments, its side effects include development of secondary leukemia characterized by the chromosomal rearrangements affecting AML1 or MLL genes. Recurrent chromosomal translocations in the therapy-related leukemia differ from chromosomal rearrangements associated with other neoplasias. Here, we reviewed the factors that drive chromosomal translocations induced by cancer treatment with DNA topoisomerase II inhibitors, such as mobility of ends of double-strand DNA breaks formed before the translocation and gain of function of fusion proteins generated as a result of translocation.

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.

Examination of in vitro and in vivo antitumor activity of Menin-MLL inhibitor, D0060-319.

e15119 Background: Rearrangements of the mixed-lineage leukemia (MLL) gene result in the production of MLL fusion proteins, which occurs in 5-10% of acute leukemia in adults and > 70% of infant leukemia, respectively. Menin protein, encoded by the MEN1 gene, interacts with MLL fusion proteins to induce leukemia. D0060-319, a Menin-MLL inhibitor, shows a significant antitumor effect in vivo and in vitro. Methods: The fluorescence polarization (FP) binding assay to assess inhibition of D0060-319 to Menin-MLL interaction. The cross reactivity of 44 molecular targets was tested to assess their off-target binding potential. The anti-proliferative ability of D0060-319 was evaluated by CCK-8 in different cell lines. The in vivo anti-tumor effect of D0060-319 was evaluated in a human MV4-11 and MOLM-13 cell mouse xenograft tumor model. Briefly, five million MV4-11 cells or 500 thousand MOLM-13 cells were subcutaneously implanted the right flank of CB-17 SCID mice to establish cell mouse xenograft tumor model. When tumor volume reached 100-120mm3, the animals were grouped and administrated with D0060-319 at the dose of 25, 50, 75, 100 mg/kg or vehicle at twice daily for 21days. Tumor measurements and body weights were performed twice weekly to assess the antitumor efficacy and tolerability of D0060-319. Results: D0060-319 competitively binds Menin to inhibit the interaction with MLL fusion protein with IC50 of 7.46nM, has high antiproliferative activity in MV4-11 and MOLM-13 cell lines containing MLL fusion proteins with IC50 values of 4.0nM and 1.7nM, respectively. However, in Kasumi-1, K562, HL-60 and KG-1 cell lines lacking MLL rearrangement, D0060-319 antiproliferative activity with IC50 > 10 μM, indicating selectivity for leukemia cell lines containing MLL fusion proteins active. In the MV4-11 cell mouse xenograft tumor model, D0060-319 significantly inhibited tumor growth at the dose of 25mg/kg, with a tumor growth inhibition (TGI) rate of 82.97%, and other doses (50, 75 and 100mg/kg) tumor completely regressed. In the MOLM-13 cell mouse xenograft tumor model, a dose-dependent anti-tumor effect was observed after 14 days of administration, with TGIs of 81.08%, 88.47% and 90.26% at the dose of 50, 75 or 100 mg/kg, respectively. In both CDX models, no bodyweight loss was observed, suggesting that D0060-319 was well tolerated. Furthermore, off-target screening assays showed that D0060-319 did not cross-react with any of the 44 molecular targets at 10 μM, indicating that D0060-319 is highly selective, high-affinity for the MLL-binding pocket on Menin. Conclusions: In MLL-rearranged leukemia, D0060-319 showed high antitumor activity and good tolerability both in vitro and in vivo.

MLL3 regulates the CDKN2A tumor suppressor locus in liver cancer.

Mutations in genes encoding components of chromatin modifying and remodeling complexes are among the most frequently observed somatic events in human cancers. For example, missense and nonsense mutations targeting the mixed lineage leukemia family member 3 (MLL3, encoded by KMT2C) histone methyltransferase occur in a range of solid tumors, and heterozygous deletions encompassing KMT2C occur in a subset of aggressive leukemias. Although MLL3 loss can promote tumorigenesis in mice, the molecular targets and biological processes by which MLL3 suppresses tumorigenesis remain poorly characterized. Here, we combined genetic, epigenomic, and animal modeling approaches to demonstrate that one of the mechanisms by which MLL3 links chromatin remodeling to tumor suppression is by co-activating the Cdkn2a tumor suppressor locus. Disruption of Kmt2c cooperates with Myc overexpression in the development of murine hepatocellular carcinoma (HCC), in which MLL3 binding to the Cdkn2a locus is blunted, resulting in reduced H3K4 methylation and low expression levels of the locus-encoded tumor suppressors p16/Ink4a and p19/Arf. Conversely, elevated KMT2C expression increases its binding to the CDKN2A locus and co-activates gene transcription. Endogenous Kmt2c restoration reverses these chromatin and transcriptional effects and triggers Ink4a/Arf-dependent apoptosis. Underscoring the human relevance of this epistasis, we found that genomic alterations in KMT2C and CDKN2A were associated with similar transcriptional profiles in human HCC samples. These results collectively point to a new mechanism for disrupting CDKN2A activity during cancer development and, in doing so, link MLL3 to an established tumor suppressor network.

Ruxolitinib inhibits the proliferation and induces the apoptosis of MLL-r ALL cells through inactivating JAK/STAT signaling pathway.

The childhood patients with mixed-lineage leukemia rearrangement (MLL-r) gene have worse outcome than non-MLL, and thus often treated with high-risk chemotherapy regimens, so targeted therapy is important for this type of leukemia. This purpose of study was to explore the effects of ruxolitinib on the proliferation, apoptosis, and cell cycle of Nalm-6 cells. In this study, human acute lymphoblastic leukemia (ALL) cell line Nalm-6 was used as the research object. By constructing an MLL overexpression vector to transfect Nalm-6 cells, exogenous JAK2/STAT3 signal pathway inhibitor ruxolitinib was applied to observe the proliferation, apoptosis, and cell cycle changes of the transfected Nalm-6 cells. Western blot was performed to determine the proteins (MLL-BP, JAK, STAT) involved in the mechanism of action of MLL-r leukemia. CCK8 assay and flow cytometry (FCM) were used for testing the proliferation and apoptosis among MLL-BP transfected Nalm-6 cells. Firstly, we determine the IC50 of ruxolitinib on Nalm-6 cells. Secondly, FCM and CCK8 showed that ruxolitinib dosedependentlyinhibits proliferation of Nalm-6 cells by blocking the cell cycle at G0/G1 phase. In addition, FCM showed that ruxolitinib promoted the apoptosis of MLL-BP transfected Nalm-6 cells. Mechanistically, ruxolitinib inactivated JAK/STAT signaling pathway in MLL-BP transfected Nalm-6 cells, mediating ruxolitinib's inhibition of cell proliferation, and inducing apoptosis. Finally, ruxolitinib significantly inhibited the proliferation of MLL-r ALL cells and promoted their apoptosis. These data provide compelling evidence that ruxolitinib is a promising agent against MLL-r leukemia cell line. However, it needs going through multiple more steps to confirm before it can be an option in clinical practice.

Association of MLL3 and TGF-β signaling gene polymorphisms with the susceptibility and prognostic outcomes of Stanford type B aortic dissection

ObjectiveThis study aims to investigate the association of lysine methyltransferase 2 C (MLL3) and transforming growth factor β (TGF-β) signaling-related gene polymorphisms with the susceptibility of Stanford type B aortic dissection (AD) and its clinical prognostic outcomes. The methods involved investigating the MLL3 (rs10244604, rs6963460, rs1137721), TGFβ1 (rs1800469), TGFβ2 (rs900), TGFR1 (rs1626340) and TGFR2 (rs4522809) gene polymorphisms. Logistic regression was performed to investigate the association between 7 single nucleotide gene polymorphisms (SNPs) and Stanford type B aortic dissection. The GMDR software was used to analyze gene-gene and gene-environment interactions. The odds ratio (OR) with a 95% confidence interval (CI) was employed to evaluate the association of genes and Stanford type B AD risk.ResultsGenotypes and allele distributions in the case and control groups showed significant differences (P < 0.05). Logistic regression has shown that the Stanford Type B AD risk was highest in individuals with the rs1137721 CT genotype (OR = 4.33, 95% CI = 1.51–12.40). Additionally, WBC, drinking, hypertension, triglycerides (TG), and low-density lipoprotein (LDL-C) were independent risk factors for Stanford Type B AD. Logistic regression showed that the Stanford Type B AD risk was highest in individuals with the MLL3 (rs1137721)-TT + CT and TGFβ1 (rs4522809)-AA genotype (OR = 6.72, 95% CI = 1.56–29.84), and lowest in those with the MLL3 (rs1137721)-CC and TGFβ1 (rs4522809)-AA + GG genotype (OR = 4.38, 95% CI = 0.92–20.83). However, the 55-month median long-term follow-up did not show statistical significance.ConclusionCarriers of both TT + CT of MLL3 (rs1137721) and AA of TGFβ1 (rs4522809) polymorphisms may be closely related to the development of Stanford type B AD. MLL3 (rs1137721), WBC, and TG/TC were found to be associated with the morbidity of Stanford type B AD. MLL3 (KMT2C) is associated with the TGF-β signaling pathway protein. The risk of Stanford type B AD is related to the interactions of gene-gene and gene-environment.

Forkhead box protein D2 suppresses colorectal cancer by reprogramming enhancer interactions.

Somatic stem cells contribute to normal tissue homeostasis, and their epigenomic features play an important role in regulating tissue identities or developing disease states. Enhancers are one of the key players controlling chromatin context-specific gene expression in a spatial and temporal manner while maintaining tissue homeostasis, and their dysregulation leads to tumorigenesis. Here, epigenomic and transcriptomic analyses reveal that forkhead box protein D2 (FOXD2) is a hub for the gene regulatory network exclusive to large intestinal stem cells, and its overexpression plays a significant role in colon cancer regression. FOXD2 is positioned at the closed chromatin and facilitates mixed-lineage leukemia protein-4 (MLL4/KMT2D) binding to deposit H3K4 monomethylation. De novo FOXD2-mediated chromatin interactions rewire the regulation of p53-responsive genes and induction of apoptosis. Taken together, our findings illustrate the novel mechanistic details of FOXD2 in suppressing colorectal cancer growth and suggest its function as a chromatin-tuning factor and a potential therapeutic target for colorectal cancer.

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 7months. 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.

RNA binding induces an allosteric switch in Cyp33 to repress MLL1-mediated transcription

Mixed-lineage leukemia 1 (MLL1) is a transcription activator of the HOX family, which binds to specific epigenetic marks on histone H3 through its third plant homeodomain (PHD3) domain. Through an unknown mechanism, MLL1 activity is repressed by cyclophilin 33 (Cyp33), which binds to MLL1 PHD3. We determined solution structures of Cyp33 RNA recognition motif (RRM) free, bound to RNA, to MLL1 PHD3, and to both MLL1 and the histone H3 lysine N6-trimethylated. We found that a conserved α helix, amino-terminal to the RRM domain, adopts three different positions facilitating a cascade of binding events. These conformational changes are triggered by Cyp33 RNA binding and ultimately lead to MLL1 release from the histone mark. Together, our mechanistic findings rationalize how Cyp33 binding to MLL1 can switch chromatin to a transcriptional repressive state triggered by RNA binding as a negative feedback loop.

The Chromatin Regulator Mll1 Supports T Follicular Helper Cell Differentiation by Controlling Expression of Bcl6, LEF-1, and TCF-1.

T follicular helper (TFH) cells are essential for developing protective Ab responses following vaccination. Greater understanding of the genetic program leading to TFH differentiation is needed. Chromatin modifications are central in the control of gene expression. However, detailed knowledge of how chromatin regulators (CRs) regulate differentiation of TFH cells is limited. We screened a large short hairpin RNA library targeting all known CRs in mice and identified the histone methyltransferase mixed lineage leukemia 1 (Mll1) as a positive regulator of TFH differentiation. Loss of Mll1 expression reduced formation of TFH cells following acute viral infection or protein immunization. In addition, expression of the TFH lineage-defining transcription factor Bcl6 was reduced in the absence of Mll1. Transcriptomics analysis identified Lef1 and Tcf7 as genes dependent on Mll1 for their expression, which provides one mechanism for the regulation of TFH differentiation by Mll1. Taken together, CRs such as Mll1 substantially influence TFH differentiation.