Epigenetic maintenance of adult neural stem cell quiescence in the mouse hippocampus via Setd1a.

Quiescence, a hallmark of adult neural stem cells (NSCs), is required for maintaining the NSC pool to support life-long continuous neurogenesis in the adult dentate gyrus (DG). Whether long-lasting epigenetic modifications maintain NSC quiescence over the long term in the adult DG is not well-understood. Here we show that mice with haploinsufficiency of Setd1a, a schizophrenia risk gene encoding a histone H3K4 methyltransferase, develop an enlarged DG with more dentate granule cells after young adulthood. Deletion of Setd1a specifically in quiescent NSCs in the adult DG promotes their activation and neurogenesis, which is countered by inhibition of the histone demethylase LSD1. Mechanistically, RNA-sequencing and CUT & RUN analyses of cultured quiescent adult NSCs reveal Setd1a deletion-induced transcriptional changes and many Setd1a targets, among which down-regulation of Bhlhe40 promotes quiescent NSC activation in the adult DG in vivo. Together, our study reveals a Setd1a-dependent epigenetic mechanism that sustains NSC quiescence in the adult DG.

NAMPT-targeting PROTAC and nicotinic acid co-administration elicit safe and robust anti-tumor efficacy in NAPRT-deficient pan-cancers.

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the biosynthesis of nicotinamide adenine dinucleotide (NAD+), making it a potential target for cancer therapy. Two challenges hinder its translation in the clinic: targeting the extracellular form of NAMPT (eNAMPT) remains insufficient, and side effects are observed in normal tissues. We previously utilized proteolysis-targeting chimera (PROTAC) to develop two compounds capable of simultaneously degrading iNAMPT and eNAMPT. Unfortunately, the pharmacokinetic properties were inadequate, and toxicities similar to those associated with traditional inhibitors arose. We have developed a next-generation PROTAC molecule 632005 to address these challenges, demonstrating exceptional target selectivity and bioavailability, improved in vivo exposure, extended half-life, and reduced clearance rate. When combined with nicotinic acid, 632005 exhibits safety and robust efficacy in treating NAPRT-deficient pan-cancers, including xenograft models with hematologic malignancy and prostate cancer and patient-derived xenograft (PDX) models with liver cancer. Our findings provide clinical references for patient selection and treatment strategies involving NAMPT-targeting PROTACs.

Hematopoietic stem cell quiescence and DNA replication dynamics maintained by the resilient ß-catenin/Hoxa9/Prmt1 axis.

ABSTRACT: Maintenance of quiescence and DNA replication dynamics are 2 paradoxical requirements for the distinct states of dormant and active hematopoietic stem cells (HSCs), which are required to preserve the stem cell reservoir and replenish the blood cell system in response to hematopoietic stress, respectively. Here, we show that key self-renewal factors, ß-catenin or Hoxa9, largely dispensable for HSC integrity, in fact, have dual functions in maintaining quiescence and enabling efficient DNA replication fork dynamics to preserve the functionality of hematopoietic stem and progenitor cells (HSPCs). Although ß-catenin or Hoxa9 single knockout (KO) exhibited mostly normal hematopoiesis, their coinactivation led to severe hematopoietic defects stemmed from aberrant cell cycle, DNA replication, and damage in HSPCs. Mechanistically, ß-catenin and Hoxa9 function in a compensatory manner to sustain key transcriptional programs that converge on the pivotal downstream target and epigenetic modifying enzyme, Prmt1, which protects the quiescent state and ensures an adequate supply of DNA replication and repair factors to maintain robust replication fork dynamics. Inactivation of Prmt1 phenocopied both cellular and molecular phenotypes of ß-catenin/Hoxa9 combined KO, which at the same time could also be partially rescued by Prmt1 expression. The discovery of the highly resilient ß-catenin/Hoxa9/Prmt1 axis in protecting both quiescence and DNA replication dynamics essential for HSCs at different key states provides not only novel mechanistic insights into their intricate regulation but also a potential tractable target for therapeutic intervention.

Dysfunction of CD169+ macrophages and blockage of erythrocyte maturation as a mechanism of anemia in Plasmodium yoelii infection.

Plasmodium parasites cause malaria with disease outcomes ranging from mild illness to deadly complications such as severe malarial anemia (SMA), pulmonary edema, acute renal failure, and cerebral malaria. In young children, SMA often requires blood transfusion and is a major cause of hospitalization. Malaria parasite infection leads to the destruction of infected and noninfected erythrocytes as well as dyserythropoiesis; however, the mechanism of dyserythropoiesis accompanied by splenomegaly is not completely understood. Using Plasmodium yoelii yoelii 17XNL as a model, we show that both a defect in erythroblastic island (EBI) macrophages in supporting red blood cell (RBC) maturation and the destruction of reticulocytes/RBCs by the parasites contribute to SMA and splenomegaly. After malaria parasite infection, the destruction of both infected and noninfected RBCs stimulates extramedullary erythropoiesis in mice. The continuous decline of RBCs stimulates active erythropoiesis and drives the expansion of EBIs in the spleen, contributing to splenomegaly. Phagocytosis of malaria parasites by macrophages in the bone marrow and spleen may alter their functional properties and abilities to support erythropoiesis, including reduced expression of the adherence molecule CD169 and inability to support erythroblast differentiation, particularly RBC maturation in vitro and in vivo. Therefore, macrophage dysfunction is a key mechanism contributing to SMA. Mitigating and/or alleviating the inhibition of RBC maturation may provide a treatment strategy for SMA.

NPM1 mutation reprograms leukemic transcription network via reshaping TAD topology.

C-terminal mutation of Nucleophosmin 1 (NPM1C+) was thought to be a primary driving event in acute myeloid leukemia (AML) that reprograms leukemic-associated transcription programs to transform hematopoietic stem and progenitor cells (HSPCs). However, molecular mechanisms underlying NPM1C+-driven leukemogenesis remain elusive. Here, we report that NPM1C+ activates signature HOX genes and reprograms cell cycle regulators by altering CTCF-driven topologically associated domains (TADs). Hematopoietic-specific NPM1C+ knock-in alters TAD topology leading to disrupted regulation of the cell cycle as well as aberrant chromatin accessibility and homeotic gene expression, which results in myeloid differentiation block. Restoration of NPM1 within the nucleus re-establishes differentiation programs by reorganizing TADs critical for myeloid TFs and cell cycle regulators that switch the oncogenic MIZ1/MYC regulatory axis in favor of interacting with coactivator NPM1/p300, and prevents NPM1C+-driven leukemogenesis. In sum, our data reveal that NPM1C+ reshapes CTCF-defined TAD topology to reprogram signature leukemic transcription programs required for cell cycle progression and leukemic transformation.

Transition of ovarian granulosa cell tumor from a solid mass to a cystic mass in two months on MR imaging in an adult woman: A case report.

Ovarian granulosa cell tumor (OGCT) is a relatively rare ovarian tumor originating from ovarian sex cord-stromal cells. It is generally believed that the tumor is mainly a solid mass in the early stage, and with the volume increasing, the tumor would undergo multiple cystic changes. But few such cases have been reported. This article reports a case of transition of ovarian granulosa cell tumor from a solid mass to a cystic mass in 2 months on MR imaging in an adult woman. In this case, a 55-year-old postmenopausal woman underwent MR imaging for irregular vaginal bleeding in March 2022, during which a 6-cm cystic-solid mass was detected in the right ovary with iso-hypo intensity on T1WI, iso-hyper intensity on T2WI, and hyper intensity on DWI. After injection of the contrast medium, the mass displayed progressive and obvious enhancement, which was diagnosed as OGCT. Due to the COVID-19 pandemic, the patient was unable to receive surgery in time. Two months later, the patient returned to the hospital and underwent MRI again, when a 20-cm cyst mass was detected in the pelvis, which contained little solid component at the edge. The patient was admitted and underwent a total abdominal hysterectomy with bilateral salpingo-oophorectomy. The postoperative pathology confirmed the diagnosis of adult type stage IC1 OGCT. This finding may be precious in that it could help understand the initiation and progression of OGCT.

Ripk3 signaling regulates HSCs during stress and represses radiation-induced leukemia in mice.

Receptor-interacting protein kinase 3 (Ripk3) is one of the critical mediators of inflammatory cytokine-stimulated signaling. Here we show that Ripk3 signaling selectively regulates both the number and the function of hematopoietic stem cells (HSCs) during stress conditions. Ripk3 signaling is not required for normal homeostatic hematopoiesis. However, in response to serial transplantation, inactivation of Ripk3 signaling prevents stress-induced HSC exhaustion and functional HSC attenuation, while in response to fractionated low doses of ionizing radiation (IR), inactivation of Ripk3 signaling accelerates leukemia/lymphoma development. In both situations, Ripk3 signaling is primarily stimulated by tumor necrosis factor-α. Activated Ripk3 signaling promotes the elimination of HSCs during serial transplantation and pre-leukemia stem cells (pre-LSCs) during fractionated IR by inducing Mlkl-dependent necroptosis. Activated Ripk3 signaling also attenuates HSC functioning and represses a pre-LSC-to-LSC transformation by promoting Mlkl-independent senescence. Furthermore, we demonstrate that Ripk3 signaling induces senescence in HSCs and pre-LSCs by attenuating ISR-mediated mitochondrial quality control.

The human ion channel TRPM2 modulates cell survival in neuroblastoma through E2F1 and FOXM1.

Transient receptor potential channel melastatin 2 (TRPM2) is highly expressed in cancer and has an essential function in preserving viability through maintenance of mitochondrial function and antioxidant response. Here, the role of TRPM2 in cell survival was examined in neuroblastoma cells with TRPM2 deletion with CRISPR technology. Viability was significantly decreased in TRPM2 knockout after doxorubicin treatment. RNA sequence analysis and RT-qPCR revealed reduced RNAs encoding master transcription regulators FOXM1 and E2F1/2 and downstream cell cycle targets including Cyclin B1, CDK1, PLK1, and CKS1. CHIP analysis demonstrated decreased FOXM1 binding to their promoters. Western blotting confirmed decreased expression, and increased expression of CDK inhibitor p21, a CKS1 target. In cells with TRPM2 deletion, cell cycle progression to S and G2/M phases was reduced after treatment with doxorubicin. RNA sequencing also identified decreased DNA repair proteins in cells with TRPM2 deletion after doxorubicin treatment, and DNA damage was increased. Wild type TRPM2, but not Ca2+-impermeable mutant E960D, restored live cell number and reconstituted expression of E2F1, FOXM1, and cell cycle/DNA repair proteins. FOXM1 expression alone restored viability. TRPM2 is a potential therapeutic target to reduce tumor proliferation and increase doxorubicin sensitivity through modulation of FOXM1, E2F1, and cell cycle/DNA repair proteins.

HOTTIP-dependent R-loop formation regulates CTCF boundary activity and TAD integrity in leukemia.

HOTTIP lncRNA is highly expressed in acute myeloid leukemia (AML) driven by MLL rearrangements or NPM1 mutations to mediate HOXA topologically associated domain (TAD) formation and drive aberrant transcription. However, the mechanism through which HOTTIP accesses CCCTC-binding factor (CTCF) chromatin boundaries and regulates CTCF-mediated genome topology remains unknown. Here, we show that HOTTIP directly interacts with and regulates a fraction of CTCF-binding sites (CBSs) in the AML genome by recruiting CTCF/cohesin complex and R-loop-associated regulators to form R-loops. HOTTIP-mediated R-loops reinforce the CTCF boundary and facilitate formation of TADs to drive gene transcription. Either deleting CBS or targeting RNase H to eliminate R-loops in the boundary CBS of ß-catenin TAD impaired CTCF boundary activity, inhibited promoter/enhancer interactions, reduced ß-catenin target expression, and mitigated leukemogenesis in xenograft mouse models with aberrant HOTTIP expression. Thus, HOTTIP-mediated R-loop formation directly reinforces CTCF chromatin boundary activity and TAD integrity to drive oncogene transcription and leukemia development.

A coordinated function of lncRNA HOTTIP and miRNA-196b underpinning leukemogenesis by targeting FAS signaling.

MicroRNAs (miRNAs) may modulate more than 60% of human coding genes and act as negative regulators, whereas long noncoding RNAs (lncRNAs) regulate gene expression on multiple levels by interacting with chromatin, functional proteins, and RNAs such as mRNAs and microRNAs. However, the crosstalk between HOTTIP lncRNA and miRNAs in leukemogenesis remains elusive. Using combined integrated analyses of global miRNA expression profiling and state-of-the-art genomic analyses of chromatin such as ChIRP-seq (HOTTIP binding in genomewide), ChIP-seq, and ATAC-seq, we found that some miRNA genes are directly controlled by HOTTIP. Specifically, the HOX cluster miRNAs (miR-196a, miR-196b, miR-10a, and miR-10b), located cis and trans, were most dramatically regulated and significantly decreased in HOTTIP-/- AML cells. HOTTIP bound to the miR-196b promoter and HOTTIP deletion reduced chromatin accessibility and enrichment of active histone modifications at HOX cluster-associated miRNAs in AML cells, whereas reactivation of HOTTIP restored miR gene expression and chromatin accessibility in the CTCF-boundary-attenuated AML cells. Inactivation of HOTTIP or miR-196b promotes apoptosis by altering the chromatin signature at the FAS promoter and increasing FAS expression. Transplantation of miR-196b knockdown MOLM13 cells in NSG mice increased overall survival of mice compared to wild-type cells transplanted into mice. Thus, HOTTIP remodels the chromatin architecture around miRNAs to promote their transcription and consequently represses tumor suppressors and promotes leukemogenesis.

Paraspeckle Protein NONO Promotes TAZ Phase Separation in the Nucleus to Drive the Oncogenic Transcriptional Program.

The Hippo pathway effector TAZ promotes cellular growth, survival, and stemness through regulating gene transcription. Recent studies suggest that TAZ liquid-liquid phase separation (LLPS) compartmentalizes key cofactors to activate transcription. However, how TAZ LLPS is achieved remains unknown. Here, it is shown that the paraspeckle protein NONO is required for TAZ LLPS and activation in the nucleus. NONO is a TAZ-binding protein. Their interaction shows temporal regulation parallel to the interaction between TAZ and TEAD as well as to the expression of TAZ target genes. NONO depletion reduces nuclear TAZ LLPS, while ectopic NONO expression promotes the LLPS. Accordingly, NONO depletion reduces TAZ interactions with TEAD, Rpb1, and enhancers. In glioblastoma, expressions of NONO and TAZ are both upregulated and predict poor prognosis. Silencing NONO expression in an orthotopic glioblastoma mouse model inhibits TAZ-driven tumorigenesis. Together, this study suggests that NONO is a nuclear factor that promotes TAZ LLPS and TAZ-driven oncogenic transcriptional program.

Long noncoding RNAs: emerging regulators of normal and malignant hematopoiesis.

Genome-wide analyses have revealed that long noncoding RNAs (lncRNAs) are not only passive transcription products, but also major regulators of genome structure and transcription. In particular, lncRNAs exert profound effects on various biological processes, such as chromatin structure, transcription, RNA stability and translation, and protein degradation and localization, that depend on their localization and interacting partners. Recent studies have revealed that thousands of lncRNAs are aberrantly expressed in various cancer types, and some are associated with malignant transformation. Despite extensive efforts, the diverse functions of lncRNAs and molecular mechanisms in which they act remain elusive. Many hematological disorders and malignancies primarily result from genetic alterations that lead to the dysregulation of gene regulatory networks required for cellular proliferation and differentiation. Consequently, a growing list of lncRNAs has been reported to be involved in the modulation of hematopoietic gene expression networks and hematopoietic stem and progenitor cell (HSPC) function. Dysregulation of some of these lncRNAs has been attributed to the pathogenesis of hematological malignancies. In this review, we summarize current advances and knowledge of lncRNAs in gene regulation, focusing on recent progress on the role of lncRNAs in CTCF/cohesin-mediated 3-dimensional genome organization and how such genome folding signals, in turn, regulate transcription, HSPC function, and transformation. This knowledge will provide mechanistic and translational insights into HSPC biology and myeloid malignancy pathophysiology.

Investigating the Barrier Activity of Novel, Human Enhancer-Blocking Chromatin Insulators for Hematopoietic Stem Cell Gene Therapy.

Despite the unequivocal success of hematopoietic stem and progenitor cell gene therapy, limitations still exist including genotoxicity and variegation/silencing of transgene expression. A class of DNA regulatory elements known as chromatin insulators (CIs) can mitigate both vector transcriptional silencing (barrier CIs) and vector-induced genotoxicity (enhancer-blocking CIs) and have been proposed as genetic modulators to minimize unwanted vector/genome interactions. Recently, a number of human, small-sized, and compact CIs bearing strong enhancer-blocking activity were identified. To ultimately uncover an ideal CI with a dual, enhancer-blocking and barrier activity, we interrogated these elements in vitro and in vivo. After initial screening of a series of these enhancer-blocking insulators for potential barrier activity, we identified three distinct categories with no, partial, or full protection against transgene silencing. Subsequently, the two CIs with full barrier activity (B4 and C1) were tested for their ability to protect against position effects in primary cells, after incorporation into lentiviral vectors (LVs) and transduction of human CD34+ cells. B4 and C1 did not adversely affect vector titers due to their small size, while they performed as strong barrier insulators in CD34+ cells, both in vitro and in vivo, shielding transgene's long-term expression, more robustly when placed in the forward orientation. Overall, the incorporation of these dual-functioning elements into therapeutic viral vectors will potentially provide a new generation of safer and more efficient LVs for all hematopoietic stem cell gene therapy applications.

HDAC1 is required for GATA-1 transcription activity, global chromatin occupancy and hematopoiesis.

The activity of hematopoietic factor GATA-1 is modulated through p300/CBP-mediated acetylation and FOG-1 mediated indirect interaction with HDAC1/2 containing NuRD complex. Although GATA-1 acetylation is implicated in GATA-1 activation, the role of deacetylation is not studied. Here, we found that the FOG-1/NuRD does not deacetylate GATA-1. However, HDAC1/2 can directly bind and deacetylate GATA-1. Two arginine residues within the GATA-1 linker region mediates direct interaction with HDAC1. The arginine to alanine mutation (2RA) blocks GATA-1 deacetylation and fails to induce erythroid differentiation. Gene expression profiling and ChIP-seq analysis further demonstrate the importance of GATA-1 deacetylation for gene activation and chromatin recruitment. GATA-12RA knock-in (KI) mice suffer mild anemia and thrombocytopenia with accumulation of immature erythrocytes and megakaryocytes in bone marrow and spleen. Single cell RNA-seq analysis of Lin- cKit+ (LK) cells further reveal a profound change in cell subpopulations and signature gene expression patterns in HSC, myeloid progenitors, and erythroid/megakaryocyte clusters in KI mice. Thus, GATA-1 deacetylation and its interaction with HDAC1 modulates GATA-1 chromatin binding and transcriptional activity that control erythroid/megakaryocyte commitment and differentiation.

Tumor size and perineural invasion predict outcome of gastric high-grade neuroendocrine neoplasms.

A new subcategory, grade 3 neuroendocrine tumors, is incorporated into the grading system of pancreatic neuroendocrine neoplasms in the 2017 WHO classification in order to differentiate grade 3 neuroendocrine tumors from neuroendocrine carcinomas. The 2019 WHO classification extends the concept of grade 3 neuroendocrine tumors to gastrointestinal high-grade neuroendocrine neoplasms. However, there is still limited study focusing on the gastric grade 3 neuroendocrine tumors and gastric neuroendocrine carcinomas. We retrospectively enrolled 151 gastric high-grade neuroendocrine neoplasms patients, who underwent radical resection from January 2007 to December 2015. Clinicopathologic and prognostic features were studied. The Surveillance, Epidemiology, and End Results (SEER) database was used to verify the prognostic determinants found in the Zhongshan cohort. Neuroendocrine carcinomas showed a higher Ki67 index and higher mitotic count than grade 3 neuroendocrine tumors. We identified 109 (72.2%) patients with neuroendocrine carcinomas, 12 (7.9%) patients with grade 3 neuroendocrine tumors, and 30 (19.9%) patients with mixed neuroendocrine-non-neuroendocrine neoplasms. Although neuroendocrine carcinomas demonstrated higher Ki67 index (P = 0.004) and mitoses (P = 0.001) than grade 3 neuroendocrine tumors, their prognosis after radical resection did not demonstrate significant differences (P = 0.709). Tumor size, perineural invasion, and TNM stage were independent prognostic factors of gastric high-grade neuroendocrine neoplasms.

Mechanistic Basis for In Vivo Therapeutic Efficacy of CK2 Inhibitor CX-4945 in Acute Myeloid Leukemia.

Protein Kinase CK2 (Casein Kinase 2 or CK2) is a constitutively active serine-threonine kinase overactive in human malignancies. Increased expression and activity of CK2 in Acute Myeloid Leukemia (AML) is associated with a poor outcome. CK2 promotes AML cell survival by impinging on multiple oncogenic signaling pathways. The selective small-molecule CK2 inhibitor CX-4945 has shown in vitro cytotoxicity in AML. Here, we report that CX-4945 has a strong in vivo therapeutic effect in preclinical models of AML. The analysis of genome-wide DNA-binding and gene expression in CX-4945 treated AML cells shows that one mechanism, by which CK2 inhibition exerts a therapeutic effect in AML, involves the revival of IKAROS tumor suppressor function. CK2 phosphorylates IKAROS and disrupts IKAROS' transcriptional activity by impairing DNA-binding and association with chromatin modifiers. Here, we demonstrate that CK2 inhibition decreases IKAROS phosphorylation and restores IKAROS binding to DNA. Further functional experiments show that IKAROS negatively regulates the transcription of anti-apoptotic genes, including BCL-XL (B cell Lymphoma like-2 like 1, BCL2L1). CX-4945 restitutes the IKAROS-mediated repression of BCL-XL in vivo and sensitizes AML cells to apoptosis. Using CX-4945, alongside the cytotoxic chemotherapeutic drug daunorubicin, augments BCL-XL suppression and AML cell apoptosis. Overall, these results establish the in vivo therapeutic efficacy of CX-4945 in AML preclinical models and determine the role of CK2 and IKAROS in regulating apoptosis in AML. Furthermore, our study provides functional and mechanistic bases for the addition of CK2 inhibitors to AML therapy.

HOXBLINC long non-coding RNA activation promotes leukemogenesis in NPM1-mutant acute myeloid leukemia.

Nucleophosmin (NPM1) is the most commonly mutated gene in acute myeloid leukemia (AML) resulting in aberrant cytoplasmic translocation of the encoded nucleolar protein (NPM1c+). NPM1c+ maintains a unique leukemic gene expression program, characterized by activation of HOXA/B clusters and MEIS1 oncogene to facilitate leukemogenesis. However, the mechanisms by which NPM1c+ controls such gene expression patterns to promote leukemogenesis remain largely unknown. Here, we show that the activation of HOXBLINC, a HOXB locus-associated long non-coding RNA (lncRNA), is a critical downstream mediator of NPM1c+-associated leukemic transcription program and leukemogenesis. HOXBLINC loss attenuates NPM1c+-driven leukemogenesis by rectifying the signature of NPM1c+ leukemic transcription programs. Furthermore, overexpression of HoxBlinc (HoxBlincTg) in mice enhances HSC self-renewal and expands myelopoiesis, leading to the development of AML-like disease, reminiscent of the phenotypes seen in the Npm1 mutant knock-in (Npm1c/+) mice. HoxBlincTg and Npm1c/+ HSPCs share significantly overlapped transcriptome and chromatin structure. Mechanistically, HoxBlinc binds to the promoter regions of NPM1c+ signature genes to control their activation in HoxBlincTg HSPCs, via MLL1 recruitment and promoter H3K4me3 modification. Our study reveals that HOXBLINC lncRNA activation plays an essential oncogenic role in NPM1c+ leukemia. HOXBLINC and its partner MLL1 are potential therapeutic targets for NPM1c+ AML.

Dual targeting of MTOR as a novel therapeutic approach for high-risk B-cell acute lymphoblastic leukemia.

Children of Hispanic/Latino ancestry have increased incidence of high-risk B-cell acute lymphoblastic leukemia (HR B-ALL) with poor prognosis. This leukemia is characterized by a single-copy deletion of the IKZF1 (IKAROS) tumor suppressor and increased activation of the PI3K/AKT/mTOR pathway. This identifies mTOR as an attractive therapeutic target in HR B-ALL. Here, we report that IKAROS represses MTOR transcription and IKAROS' ability to repress MTOR in leukemia is impaired by oncogenic CK2 kinase. Treatment with the CK2 inhibitor, CX-4945, enhances IKAROS activity as a repressor of MTOR, resulting in reduced expression of MTOR in HR B-ALL. Thus, we designed a novel therapeutic approach that implements dual targeting of mTOR: direct inhibition of the mTOR protein (with rapamycin), in combination with IKAROS-mediated transcriptional repression of the MTOR gene (using the CK2 inhibitor, CX-4945). Combination treatment with rapamycin and CX-4945 shows synergistic therapeutic effects in vitro and in patient-derived xenografts from Hispanic/Latino children with HR B-ALL. These data suggest that such therapy has the potential to reduce the health disparity in HR B-ALL among Hispanic/Latino children. The dual targeting of oncogene transcription, combined with inhibition of the corresponding oncoprotein provides a paradigm for a novel precision medicine approach for treating hematological malignancies.

Functional reconstruction of human AML reveals stem cell origin and vulnerability of treatment-resistant MLL-rearranged leukemia.

Chemoresistance remains the major challenge for successful treatment of acute myeloid leukemia (AML). Although recent mouse studies suggest that treatment response of genetically and immunophenotypically indistinguishable AML can be influenced by their different cells of origin, corresponding evidence in human disease is still largely lacking. By combining prospective disease modeling using highly purified human hematopoietic stem or progenitor cells with retrospective deconvolution study of leukemia stem cells (LSCs) from primary patient samples, we identified human hematopoietic stem cells (HSCs) and common myeloid progenitors (CMPs) as two distinctive origins of human AML driven by Mixed Lineage Leukemia (MLL) gene fusions (MLL-AML). Despite LSCs from either MLL-rearranged HSCs or MLL-rearranged CMPs having a mature CD34-/lo/CD38+ immunophenotype in both a humanized mouse model and primary patient samples, the resulting AML cells exhibited contrasting responses to chemotherapy. HSC-derived MLL-AML was highly resistant to chemotherapy and expressed elevated amounts of the multispecific anion transporter ABCC3. Inhibition of ABCC3 by shRNA-mediated knockdown or with small-molecule inhibitor fidaxomicin, currently used for diarrhea associated with Clostridium difficile infection, effectively resensitized HSC-derived MLL-AML toward standard chemotherapeutic drugs. This study not only functionally established two distinctive origins of human LSCs for MLL-AML and their role in mediating chemoresistance but also identified a potential therapeutic avenue for stem cell-associated treatment resistance by repurposing a well-tolerated antidiarrhea drug already used in the clinic.