MYC Target Research Articles

Abstract 1463: Characterizing inflammation-induced epigenetic and transcriptomic alterations driving NSCLC using lung organoid models

Abstract Chronic inflammation is a major driver of lung cancer and contributes to its pathogenesis by inducing genetic and epigenetic alterations. These, in turn, modulate the microenvironment to facilitate emergence of tumor promoting immune evasive mechanisms. The evolution of epigenetic events and their role, both alone, and in association with lung cancer specific genetic drivers in initiation of lung cancer is not well delineated. Specific pathological subtypes of non-small cell lung cancer (NSCLC) have distinct cells of origin, suggestive of cell type-specific changes in driving their development. We employed lung organoid models with chronic exposure to cigarette smoke condensate (CSC) to elucidate sequential, cell type-specific epigenetic and transcriptomic alterations and their role in co-operating with genetic events to drive development of NSCLC. We examined epigenomic and transcriptomic alterations over a 6-month exposure period by DNA methylation arrays, ATAC-seq, and RNA-seq. We observe that CSC exposure causes distinct morphological changes in organoid structure and composition, accompanied by an increase in proliferative potential. Using flow cytometry and immunofluorescent staining approaches, we demonstrate a chronic inflammation-driven shift in stem cell populations accompanied by reduction in differentiated cell types. Bulk and single-cell RNA sequencing approaches identified distinct temporal changes in transcriptional signatures in CSC exposed organoids suggestive of evolution of an immune evasive and pro-tumorigenic phenotype. Gene set enrichment analysis revealed a downregulation of interferon signaling and upregulation of Myc targets and oxidative phosphorylation pathways in CSC treated organoids. Notably, co-culturing organoids with key immune cell populations, demonstrate the ability of the CSC exposed organoids to modulate shifts in immune cells from a pro- to anti- inflammatory state. In accordance with this shift in immune cell phenotype, CSC treated organoids secreted decreased levels of pro-inflammatory cytokines as measured by multiplex ELISA assays. Genome wide DNA methylation analysis reveal that CSC methylated genes were associated with differentiation and cell fate commitment as well as transcription factor activity. Finally, we demonstrate that introduction of key NSCLC-specific driver events at the 6-month time point sensitize only CSC treated organoids to tumor formation in vivo, leading to the development of distinct genetic driver-specific subtypes of NSCLC. Altogether, our results demonstrate the ability of chronic inflammation to drive key cell type-specific transcriptomic and epigenetic changes leading to the development of distinct subtypes of NSCLC. Our findings will help identify molecular correlates for early detection and aid development of novel therapeutic strategies for disease interception. Citation Format: Na Wang, Kara Lombardo, Raksha Padaki, Ray-Whay Chiu Yen, Malcolm V. Brock, Leslie Cope, Hariharan Easwaran, Stephen B. Baylin, Michelle Vaz. Characterizing inflammation-induced epigenetic and transcriptomic alterations driving NSCLC using lung organoid models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1463.

Abstract 7065: AMBRA1 coordinates mitochondrial function to regulate cancer stemness and tumorigenesis in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is a prevalent and aggressive cancer, with emerging evidence highlighting the role of cancer stem cells (CSCs) in its progression. AMBRA1 has been implicated to exert both tumor-promoting and tumor-suppressive roles through regulating cell cycle and mitophagy in various solid tumors. However, the functional roles of AMBRA1 in modulating cancer stemness and tumorigenesis in HCC remain elusive. Initial analysis of The Cancer Genome Atlas data revealed a significant inverse correlation between AMBRA1 expression and stemness indices (TSS) in HCC patients, with low AMBRA1 levels associated with an upregulated oxidative phosphorylation (OXPHOS) gene signature. To elucidate the functional consequences of AMBRA1 modulation in liver tumor development and stemness maintenance, we exploited both hydrodynamic mouse models and human HCC cell lines. Our findings indicate that hepatic AMBRA1 deletion enhances cancer stemness and tumorigenesis both in vivo and in vitro. Moreover, HCC cells with reduced AMBRA1 expression demonstrated heightened mitochondrial activity, characterized by increased oxygen consumption, respiration, mitochondrial membrane potential, and intracellular ATP levels. Apart from OXPHOS, we also observed a concomitant up-regulation and enrichment of MYC targets in TSS-high and AMBRA1-low HCC patients, pointing towards a deregulated c-MYC signaling to promote cancer stemness under AMBRA1 regulation in HCC. Collectively, our results demonstrate that AMBRA1 loss enhances mitochondrial function to support hepatic tumorigenesis in HCC. Citation Format: Yan Liu, Yunong Xie, Yimiao He, Stephanie Ma, Man Tong. AMBRA1 coordinates mitochondrial function to regulate cancer stemness and tumorigenesis in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7065.

Abstract 2570: Gastric cancer with high neuron infiltration was associated with enhanced epithelial-to-mesenchymal transition, angiogenesis and poor clinical outcomes

Abstract Introduction: Neurons within the tumor microenvironment of gastric cancer (GC), as identified through immunohistochemistry, have been reported to be associated with worse overall survival (OS) of GC patients. However, histology-based analyses have limitations in quantifying nerve cells and investigating the underlying biology. Thus, we aim to study the clinical significance of intratumoral nerve cells in GC using computational deconvolution of transcriptomes from bulk tumors. Methods: Total of 807 GC patients from two independent cohorts (TCGA; n = 375, GSE84437; n = 432) were included, encompassing both clinical and transcriptomic profiles. The neuron infiltration fraction was determined using the xCell algorithm. Results: GC with high neuron infiltration was associated with high expressions of neurotransmitter receptors; beta-adrenaline, dopamine, muscarinic acetylcholine, and neurokinin receptors in TCGA cohort (all p < 0.02). It was associated with reduced mutation rate and increased intratumoral heterogeneity (all p ≦ 0.002), as well as less immune response; interferon-alpha and interferon-gamma, and with low infiltration of immune cells; CD4 memory, T-helper 1, M1 and M2 macrophages, and NK cells (all p ≦ 0.02). Further, neuron highly infiltrated GC enriched Epithelial-to-Mesenchymal Transition and Angiogenesis gene sets and had higher lymphatic and microvessel endothelial cells and pericyte infiltrations (all p ≦ 0.001). Conversely, GC with high neuron infiltration showed an inverse relationship with cell proliferation-related gene sets; E2F Targets, G2M Checkpoint, and MYC Targets v1 and v2, and had lower Ki67 gene expression (FDR < 0.25 and p < 0.001, respectively). High neuron infiltration in GC was associated with worse patient OS in TCGA cohort, which was validated in GSE84437 cohort (both p < 0.05). It was an independent prognostic factor of OS in both univariate and multivariate Cox-regression analysis in the TCGA cohort (hazard ratio [HR]: 1.46; 95% confidence interval [CI]: 1.01 to 2.12; p = 0.045 and [HR]:1.54; 95% CI: 1.05 to 2.26; p = 0.026). Conclusion: Our research indicates that high infiltration of neurons in GC correlates with high expressions of neurotransmitter receptors, high intratumoral heterogeneity, less immune response and immune cell infiltrations, and less cell proliferation. It enriched EMT and angiogenesis which may explain its association with worse patient survival. Citation Format: Kohei Chida, Masanori Oshi, Arya Mariam Roy, Jun Arima, Pia Sharma, Gabriella Kim Mann, Itaru Endo, Kenichi Hakamada, Kazuaki Takabe. Gastric cancer with high neuron infiltration was associated with enhanced epithelial-to-mesenchymal transition, angiogenesis and poor clinical outcomes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2570.

Abstract 6253: Single-cell RNA sequencing reveals metastatic site-specific biomarkers for predicting response to CDK4/6 inhibition in advanced HR+/HER2- breast cancer

Abstract Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), in combination with endocrine therapy, are established as standard treatment for advanced HR+/HER2- breast cancer (BC). However, response heterogeneity is observed, with approximately one-third of patients exhibiting intrinsic resistance. This study investigates the mechanisms of variable responses to CDK4/6i through single-cell RNA sequencing of metastatic site biopsies, revealing distinct biomarkers for predicting CDK4/6i response. Methods: Single-cell RNA sequencing analyzed metastatic tumors from advanced HR+/HER2- BC patients pre-CDK4/6i treatment at baseline (BL) and/or at disease progression. BL samples were from CDK4/6i responders (n = 8, median progression-free survival [mPFS] = 17 months), while progressors were categorized as early-progressors (EP, n = 3, mPFS = 3 months) and late-progressors (LP, n = 8, mPFS = 10 months). Metastatic sites included liver (10), pleural effusions (6), ascites (2), and bone (1). InferCNV distinguished tumor cells, and functional analysis utilized the Molecular Signatures Database. Results: Both EP and LP tumor cells exhibited reduced estrogen response and increased IFN-γ pathways compared to BL tumors. LP tumors displayed enhanced Myc targets, EMT, TNF-α, and inflammatory pathways compared to EP tumors, revealing differential mechanisms of early versus late progression. Predictive signatures, including TFF3 and MGP, were significantly upregulated in BL tumor cells across different metastatic sites. Metastasis-specific markers included APOA and SERPINA1 (liver), and AGR2 (pleural effusion). BL and LP responders showed increased tumor infiltrating CD8+ T cell and NK cells compared to EP non-responders. Notably, despite a high CD8+ T frequency in responder tumors, functional analysis revealed a significant upregulation of genes associated with stress/apoptosis and exhaustion in proliferative CD4+ and CD8+ T cells from BL compared to LP tumors, including HSP90 and HSPA8, associated with poor response to immune checkpoint inhibitors. These findings suggest potential benefits of immunotherapy for CDK4/6i late progressors. Longitudinal biopsies further revealed dynamic NK cell expansion and enhanced cytotoxic T cell activity alongside the downregulation of stress/apoptosis gene expression at progression compared to BL tumors. Conclusion: This study underscores the significance of metastatic site-specific biomarkers in predicting outcomes to CDK4/6i. Tumor-infiltration lymphocytes may also serve as baseline predictors, while stress/apoptosis gene signatures suggest checkpoint inhibitor usage in CDK4/6i late progressors. These potentially actionable findings emphasize the need to optimize therapeutic approaches based on microenvironment-specific changes following disease progression. Citation Format: Linjie Luo, Peng Yang, Sofia Mastoraki, Yan Wang, Nicole M. Kettner, Akshara Singareeka Raghavendra, Debasish Tripathy, Senthil Damodaran, Kelly K. Hunt, Ziyi Li, Khandan Keyomarsi. Single-cell RNA sequencing reveals metastatic site-specific biomarkers for predicting response to CDK4/6 inhibition in advanced HR+/HER2- breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6253.

Abstract 4599: A novel small molecule inhibitor targeting MYC oncogenic signaling as an enhancer of HDAC inhibitors for the treatment of high-risk medulloblastoma

Abstract Background: Medulloblastoma (MB) is the most prevalent malignant childhood brain tumour. Although prognosis has improved over time, 95% of children with high-risk or relapsed MB eventually succumb to the disease. A key driver gene in high-risk MB is the c-MYC oncogene, for which there are currently no approved inhibitors. Histone deacetylases (HDACs) are transcriptional repressors that are dysregulated in many cancers, making them an attractive therapeutic target. Although several HDAC inhibitors have been FDA-approved for cancer treatment, they have been associated with high toxicity and limited efficacy as single agents. Therefore, simultaneously targeting c-MYC and HDACs may result in synergistic effects that could overcome drug resistance in high-risk MB. Methods and Results: We previously reported a novel pyrido-benzimidazole analogue, SE486-11, which enhanced the therapeutic effect of HDAC inhibitors in MYCN-driven cancers. We recently developed analogues (UNSW-SC compounds) with more potent activity (IC50: 0.017 to 3.70 µM). Here, we showed that these compounds significantly reduced cell viability and induced apoptosis in MB cells. MYC status was a key determinant of sensitivity of UNSW-SC compounds, with more than 3-fold higher cytotoxicity in high MYC compared to low MYC MB cells. The lead compound, UNSW-SC-22, was shown to reduce MYC protein expression and was found to be highly synergistic in enhancing the efficacy of HDAC inhibitors in MB cells. Most importantly, we demonstrated that UNSW-SC-22 was able to freely cross the blood brain barrier, reaching a concentration of 10.8 μM, with a half-life of 1.22 hours. UNSW-SC-22 directly bound to c-MYC and MYCN proteins at low micromolar equilibrium dissociation constant (KD) values which was demonstrated by surface plasmon resonance assay. In a MYCN-driven MB mouse model, we found that UNSW-SC-22 as a single agent at 90 mg/kg decreased tumor growth and prolonged survival. Through RNA-sequencing, we identified 512 differentially expressed genes after in vitro treatment with UNSW-SC-22. Importantly, GSEA analysis revealed MYC targets and cell cycle pathways as highly downregulated pathways, and upregulation in the p53 pathway. Several genes, such as MELK and USP1 were validated as down-stream targets of UNSW-SC-22. As UNSW-SC-22 is a first-in-class anticancer drug, which we are currently testing extensively in other MYC-driven MB mice models. Conclusion: Collectively, our data strongly suggest that c-Myc and MYCN are the molecular targets of UNSW-SC compounds, and these compounds have strong potential to serve as specific targeted therapy to treat subgroup 3 and 4 of MB patients with c-Myc and MYCN overexpression and amplification. Citation Format: Sin Wi Ng, Satyanarayana Gadde, Qian Wang, Belamy B. Cheung, Glenn M. Marshall. A novel small molecule inhibitor targeting MYC oncogenic signaling as an enhancer of HDAC inhibitors for the treatment of high-risk medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4599.

Abstract 4001: Monocyte transcriptome profiles associated with clinical response in patients with B-cell non-Hodgkin’s lymphoma receiving CD19-directed CAR-T therapy

Abstract Background Although CAR T-cell therapy has achieved remarkable response in patients (pts) with B-cell non-Hodgkin’s lymphoma (NHL), 20-30% of pts still have primary refractory disease (PD1), and another 30-40% relapse (PD2). We and others have shown that monocytes can modulate T-cell functions and impact clinical response to chemoimmunotherapy in NHL. Given that monocytes nadir and recovery kinetics differ from lymphocytes post lymphodepletion chemotherapy, we hypothesize that monocyte phenotype at peak CAR-T expansion and in the early month post CAR-T can modulate immune responses. Methods scRNAseq were performed on peripheral blood mononuclear cells of NHL pts prior to lymphodepletion chemotherapy (pre), at peak CAR-T expansion (peak), and one month following CAR-T (M1). Seurat v4.3.0 was used for unsupervised hierarchical clustering analysis. Lugano criteria was used to determine clinical responses which were categorized as CR (complete remission), PD1, or PD2. Results We analyzed 129,981 monocytes from 77 samples of 32 pts (16 CR, 4 PD1, 12 PD2) and 5 healthy controls. Unsupervised hierarchical clustering analysis identified 13 monocyte clusters: 4 classical monocyte (CM) clusters with transcriptome profiles for enriched signaling in IL-6, TGFβ, EMT, and p53; 2 intermediate monocyte (IM) clusters enriched for IL-1 or CD38 signaling; 2 non-classical monocytes (NM), one with increased CD36 expression; 3 monocytic MDSC clusters with enrichment of TGFβ, SIRPα, and HIF1α signaling; and 2 lymphoma-associated monocytes, expressing CD163 or CD169. At Pre and Peak, the distribution of the monocyte clusters was similar in pts with CR, PD2, or PD1, with only a slight decrease in the percent of NM in the PD2 group at Pre and slight increase of CD36 NM in PD1 at Peak. Compared to Pre, all pts had increased percent of CD36 NM and IL-1 IM at Peak. Interestingly, while the distribution of monocyte clusters was similar at Pre and Peak across clinical responses, GSEA showed that monocytes in CR pts, compared to PD1 and PD2, had gene expression enrichment of MYC target V2 pathway at Pre and TGFβ pathway at Peak. At M1, pts in PD1 had increased percent of p53 and TGFβ CM and decreased percent of NM. In contrast, pts with CR had decreased percent of IL-6 CM, p53 CM, TGFβ CM, IL-1 IM and increased percent of NM. Notably, as pts with CR and PD2 may appear similar clinically at M1, pts with PD2, compared to CR, have increased IL-6 CM, IL-1 IM, and decreased NM. In addition, GSEA showed that PD2 pts had increased IFNα response. Our results demonstrate that monocyte phenotype differences at Pre and Peak could be associated with CAR-T clinical response, and that persistent inflammatory monocyte signaling at M1 in pts with clinical response is associated with relapse. These data suggest a role for development of monocyte biomarkers to predict response and therapeutic targeting. Citation Format: Andre de Menezes Silva Corraes, Panwen Wang, Radhika Bansal, Henan Zhang, Zuoyi Shao, Kevin Regan, Eider Moreno Cortes, Arushi Khurana, Nora Bennani, Yucai Wang, Paul Hampel, Jonas Paludo, Patrick Johnston, Hemant Murthy, Madiha Iqbal, Stephen Ansell, Javier Munoz, Allison Rosenthal, Mohamed Kharfan-Dabaja, Januario Castro, Saad Kenderian, Haidong Dong, Ying Li, Yi Lin. Monocyte transcriptome profiles associated with clinical response in patients with B-cell non-Hodgkin’s lymphoma receiving CD19-directed CAR-T therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4001.

Abstract 6234: Single-cell analysis of state-transition from health to leukemia and the leukemic cell heterogeneities in inv(16) acute myeloid leukemia (AML)

Abstract AML is an aggressive hematological malignancy with heterogeneous genetic abnormalities. Using a conditional knock-in mouse model (Cbfb56M/+/Mx1-Cre) to mimic the somatic acquisition of fusion gene CBFB-MYH11 (CM), created in the recurrent chromosome translocation inv(16)(p13q22) of AML, we previously reported that the blood transcriptome undergoes state-transition from health to leukemia. In this study, we analyze the transcriptomic alterations and leukemic cell heterogeneities in a leukemia state-space using single-cell RNA sequencing (scRNA-seq). CM expression was induced in Cbfb56M/+/Mx1-Cre mice by poly (I:C) injection, and scRNA-seq analysis was performed on peripheral blood mononuclear cells (PBMC) and bone marrow (BM) cells from leukemic mice and age-matched wild-type (WT) controls. More than 105,000 cells were subjected to the following dimensionality reduction and cell type annotation. By performing principal component analysis (PCA), we observed a Y-shape cell distribution with emergence of a divergent branch occupied by leukemic cells which can be mapped to a leukemic state. The principal components 1 and 2 (PC1 and PC2) clearly distinguish the leukemic cells from normal cell types such as myeloid cells and lymphocytes. By accessing the eigenvalue of genes for PC1 and PC2, we quantified the crucial genes and pathways related to leukemia progression at a single-cell level. We characterized cKit+ leukemic cell clusters by transcriptome-based correlation and gene expression pattern and found that they resembled stem cells and megakaryocytic-erythroid progenitors (MEP) with dysregulated pathways, including upregulated "inflammatory response" and downregulated pathways related to Myc targets, oxidative phosphorylation, mitochondrial protein translation, and ribosomal biogenesis/assembly. Examining the 31 clusters (C0-C30) seen in cKit+ BM cells, we identified 9 leukemic clusters exhibiting distinct features, including high heme-metabolism (C0, C1, and C2), high proliferation (C1, C8), S phase (C4, C10), low oxidative phosphorylation (C2, C5, C17), high Cd9 (C10), high Egfl7 (C7, C8). In conclusion, our study unveils state-transition from health to leukemia at single-cell resolution, and uncovers diverse biological heterogeneities associated with the inv(16) AML state. Further refinement of transcriptome state-transition and single-cell analysis will provide an analytical framework for modeling the dynamic changes during disease evolution at the single-cell level. Citation Format: Yu-Hsuan Fu, Lianjun Zhang, Ying-Chieh Chen, David E. Frankhouser, Lisa Uechi, Denis O'Meally, Sergio Branciamore, Guido Marcucci, Russell Rockne, Ya-Huei Kuo. Single-cell analysis of state-transition from health to leukemia and the leukemic cell heterogeneities in inv(16) acute myeloid leukemia (AML) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6234.

Abstract 6601: Menin drives oncogenesis in Ewing sarcoma cells by activating transcription of key metastatic factors

Abstract Ewing sarcoma (EwS) is a bone and soft tissue tumor that is driven by the fusion of FET and ETS genes, most commonly resulting in creation of the EWS::FLI1 chimeric oncoprotein. The scaffolding protein Menin regulates transcription through interactions with transcription factors and chromatin modifying enzymes and has both oncogenic and tumor suppressive roles, depending on the cellular context. The half-life of Menin is prolonged in EwS cells leading to high levels of the protein that is dependent on EWS::FLI1 expression. To investigate tumorigenic functions of Menin in EwS, we used CRISPR/Cas9 to generate clonal A673 and TC32 Menin knockout cells. Consistent with our earlier studies using shRNA-mediated knockdown, loss of Menin had little effect on proliferation in 2-D culture but resulted in reduced anchorage-independent growth in soft agar assays. When MEN1-KO cells were injected into NSG mice, either subcutaneously or by tail vein, tumor formation was delayed. Injection of MEN1-KO cells into the renal subcapsule of NSG mice resulted in locally invasive tumors but their capacity to metastasize to the liver was reduced compared to control cells. To elucidate how loss of Menin led to diminished tumorigenic and metastatic potential, we performed RNA-seq of control and MEN1-KO cells. This analysis revealed significant and reproducible down-regulation of MYC target genes and up-regulation of the epithelial to mesenchymal transition pathway and extracellular matrix protein-encoding genes in MEN1-KO cells. To determine if genes altered in MEN1-KO cells were dependent on the role of Menin in Menin/MLL methyltransferase complexes, we analyzed transcriptomes of EwS cells that had been exposed to the Menin/MLL interaction inhibitor, VTP-50469. Only a subset of genes altered by the MEN1-KO were also altered by the Menin/MLL inhibitor, suggesting that Menin regulates gene expression in EwS cells by both MLL-dependent and MLL-independent mechanisms. To test this, we performed CUT&RUN to define Menin binding sites and discovered that Menin binds not only at H3K4me3-marked gene promoters but also at intragenic enhancers marked by H3K27Ac. Importantly, comparison of RNA-seq data revealed substantial overlap between Menin-regulated and established EWS::FLI1 target genes and we identified that a subset of EWS::FLI1-bound intragenic enhancers are also bound by Menin. Significantly, these co-bound, co-regulated loci encode for pro-metastatic genes, including IL1RAP, STEAP1, and CAV1. Finally, we found that Menin and EWS::FLI1 co-immunoprecipitate in EwS nuclear extracts suggesting that they may exist in complex with one another at sites of shared gene regulation. Taken together, these data indicate that Menin promotes EwS metastasis and that this is achieved by its function as a scaffolding protein that augments the transcriptional activity of EWS::FLI1 at intragenic enhancers of pro-metastasis genes. Citation Format: Katherine A. Braun, Aya Miyaki, Nicolas M. Garcia, Darleen Tu, Feinan Wu, Jay F. Sarthy, Elizabeth R. Lawlor. Menin drives oncogenesis in Ewing sarcoma cells by activating transcription of key metastatic factors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6601.

Abstract 515: Endocycling cancer cells undergo multiple S phases while repressing myc activity

Abstract Chemotherapy resistance remains a major challenge when treating patients with metastatic cancer. While intrinsic resistance to therapy has been well studied, phenotypic plasticity that drives entry and exit of resistant cell states is poorly understood. One of these plastic cell states used by cancer cells under chemotherapy treatment is characterized by the reprogramming of the mitotic cell cycle to enter a non-proliferative endocycle. Cells in this endocycling state decouple DNA synthesis from cell division by actively progressing through G1, S, and G2 phases of the cell cycle while repeatedly skipping mitosis. After a dormant period, cells can switch back to a mitotic cell cycle to repopulate a tumor. The underlying mechanisms that drive this cell cycle reprogramming remain unknown. C-myc is an oncogenic transcription factor that is dysregulated in ~70% of human cancers. C-myc is responsible for the activation of several cell cycle drivers, including cyclins and CDKs, and represses cell cycle inhibitors, such as CDK inhibitors. High levels of myc activity allow cells to move through the cell cycle quickly with a rapid doubling time. Documented endocycles in polyploid cells rely on high c-myc activity; however, our data shows that endocycling cancer cells have repressed levels of c-myc protein and transcriptional activity. Transcriptomic data shows that myc target genes are expressed at very low levels compared to the mitotic parental cells, and complementary data shows low protein levels. While myc downregulation is expected in non-proliferative cells, the compensatory mechanisms mediating the G1/S transition in the cancer endocycle remain unknown. Recent data has shown that myc suppression alone is not sufficient to induce a sustained endocycle at a population level, despite premature APCCdh1 activation during G2 in a subset of cells. We hypothesize that restoring myc activity to the levels of mitotic parental cells will drive endocycling cells to resume a proliferative mitotic cell cycle and produce mitotic progeny cells. Understanding the mechanisms that govern this transition is crucial to generate next-generation cancer therapeutics to disrupt endocycling cells, blocking acquired resistance and disease recurrence. Citation Format: Michael A. Loycano, Kenneth J. Pienta, Sarah R. Amend. Endocycling cancer cells undergo multiple S phases while repressing myc activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 515.

EIF2Ss, a Novel c-Myc-Correlated Gene Family, is Associated with Poor Prognosis and Immune Infiltration in Pancreatic Adenocarcinoma.

Pancreatic adenocarcinoma (PAAD) is a highly malignant tumor in urgent need of novel diagnostics, prognostic markers, and treatments. Eukaryotic translation initiation factor 2 subunits (EIF2Ss), comprising Eukaryotic translation initiation factor 2 subunit alpha (EIF2S1), Eukaryotic translation initiation factor 2 subunit beta (EIF2S2), and Eukaryotic translation initiation factor 2 subunit gamma (EIF2S3), is a family of eukaryotic initiation factors that participate in early protein synthesis and are crucial for tumor initiation and progression. However, the role of EIF2Ss in PAAD has yet to be reported. The aim of this study was therefore to analyze EIF2Ss in relation to the diagnosis, prognosis, and treatment of PAAD. The cancer genome atlas (TCGA) database was used to investigate gene expression and patient survival. Gene alterations, immune cell infiltration, and immune checkpoints in PAAD were also evaluated. Univariate and multivariate analysis, nomograms, calibration curves, and Decision Curve Analysis (DCA) diagrams were used to develop and evaluate a prediction model for patient outcome. Single-cell RNA-seq (scRNA) analysis, functional enrichment, co-IP assay, mass spectrometry, and western blot were used to study the relationship between EIF2Ss and c-myc in PAAD. EIF2Ss are over-expressed in PAAD tissue and are associated with poor prognosis. The frequency of EIF2S1, EIF2S2, and EIF2S3 gene alteration in PAAD was 0.2%, 0.4%, and 0.2%, respectively. High EIF2Ss expression was associated with Th2 cell infiltration, whereas low expression was associated with pDC infiltration. Moreover, EIF2Ss expression was positively correlated with the expression of the NT5E, ULBP1, PVR, CD44, IL10RB, and CD276 checkpoints. A prediction model developed using EIF2Ss and important clinicopathologic features showed good predictive value for the overall survival of PAAD patients. ScRNA-Seq data showed that EIF2Ss was associated with enrichment for endothelial cells, fibroblasts, malignant cells, and ductal cells. EIF2Ss expression was also correlated with adipogenesis, interferon-alpha response, epithelial-mesenchymal transition, myc targets, G2M checkpoint, oxidative phosphorylation, and hypoxia. Functional enrichment analysis of EIF2Ss showed a close correlation with the myc pathway, and interactions between EIF2Ss and c-myc were confirmed by co-IP assay and mass spectrometry. Importantly, knockdown of c-myc decreased the expression of EIF2S1, EIF2S2, and EIF2S3 in PAAD cells. EIF2Ss were found to have significant clinical implications for the prognosis and treatment of PAAD. Inhibition of c-myc caused the downregulation of EIF2S1, EIF2S2, and EIF2S3 expression.

Inhibition of PTPRE suppresses tumor progression and improves sorafenib response in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a poor prognosis, and the efficacy of current therapeutic strategies is extremely limited in advanced diseases. Our previous study reported that protein tyrosine phosphatase receptor epsilon (PTPRE) is a promoting factor in HCC progression. In this study, our objective was to evaluate the treatment effect of PTPRE inhibitors in different HCC preclinical models. Our results indicated that the PTPRE inhibitory compound 63 (Cpd-63) inhibited tumor cell proliferation, migration, and HCC organoid growth. Mechanism research revealed that Cpd-63 could inhibit the expression of MYC and MYC targets by inhibiting the activation of SRC. Additionally, we found that Cpd-63 could improve the response of sorafenib in HCC cells. In conclusion, we demonstrated that the PTPRE inhibitors represented a potential therapeutic agent for HCC management.

Functional characterization of cooperating MGA mutations in RUNX1::RUNX1T1 acute myeloid leukemia

MGA (Max-gene associated) is a dual-specificity transcription factor that negatively regulates MYC-target genes to inhibit proliferation and promote differentiation. Loss-of-function mutations in MGA have been commonly identified in several hematological neoplasms, including acute myeloid leukemia (AML) with RUNX1::RUNX1T1, however, very little is known about the impact of these MGA alterations on normal hematopoiesis or disease progression. We show that representative MGA mutations identified in patient samples abolish protein-protein interactions and transcriptional activity. Using a series of human and mouse model systems, including a newly developed conditional knock-out mouse strain, we demonstrate that loss of MGA results in upregulation of MYC and E2F targets, cell cycle genes, mTOR signaling, and oxidative phosphorylation in normal hematopoietic cells, leading to enhanced proliferation. The loss of MGA induces an open chromatin state at promoters of genes involved in cell cycle and proliferation. RUNX1::RUNX1T1 expression in Mga-deficient murine hematopoietic cells leads to a more aggressive AML with a significantly shortened latency. These data show that MGA regulates multiple pro-proliferative pathways in hematopoietic cells and cooperates with the RUNX1::RUNX1T1 fusion oncoprotein to enhance leukemogenesis.

Narrow-band UVB radiation triggers diverse changes in the gene expression and induces the accumulation of M1 macrophages in human skin

BackgroundThe underlying molecular mechanisms that determine the biological effects of UVB radiation exposure on human skin are still only partially comprehended. ObjectivesOur goal is to examine the human skin transcriptome and related molecular mechanisms following a single exposure to UVB in the morning versus evening. MethodsWe exposed 20 volunteer females to four-fold standard erythema doses (SED4) of narrow-band UVB (309–313 nm) in the morning or evening and studied skin transcriptome 24 h after the exposure. We performed enrichment analyses of gene pathways, predicted changes in skin cell composition using cellular deconvolution, and correlated cell proportions with gene expression. ResultsIn the skin transcriptome, UVB exposure yielded 1384 differentially expressed genes (DEGs) in the morning and 1295 DEGs in the evening, of which the most statistically significant DEGs enhanced proteasome and spliceosome pathways. Unexposed control samples showed difference by 321 DEGs in the morning vs evening, which was related to differences in genes associated with the circadian rhythm. After the UVB exposure, the fraction of proinflammatory M1 macrophages was significantly increased at both timepoints, and this increase was positively correlated with pathways on Myc targets and mTORC1 signaling. In the evening, the skin clinical erythema was more severe and had stronger positive correlation with the number of M1 macrophages than in the morning after UVB exposure. The fractions of myeloid and plasmacytoid dendritic cells and CD8 T cells were significantly decreased in the morning but not in the evening. ConclusionsNB-UVB-exposure causes changes in skin transcriptome, inhibiting cell division, and promoting proteasome activity and repair responses, both in the morning and in the evening. Inflammatory M1 macrophages may drive the UV-induced skin responses by exacerbating inflammation and erythema. These findings highlight how the same UVB exposure influences skin responses differently in morning versus evening and presents a possible explanation to the differences in gene expression in the skin after UVB irradiation at these two timepoints.

Hypermethylated Colorectal Cancer Tumours Present a Myc-Driven Hypermetabolism with a One-Carbon Signature Associated with Worsen Prognosis.

Colorectal cancer (CRC) is the second cause of cancer-related death; the CpG-island methylation pathway (CIMP) is associated with KRAS/BRAF mutations, two oncogenes rewiring cell metabolism, worse prognosis, and resistance to classical chemotherapies. Despite this, the question of a possible metabolic rewiring in CIMPs has never been investigated. Here, we analyse whether metabolic dysregulations are associated with tumour methylation by evaluating the transcriptome of CRC tumours. CIMP-high patients were found to present a hypermetabolism, activating mainly carbohydrates, folates, sphingolipids, and arachidonic acid metabolic pathways. A third of these genes had epigenetic targets of Myc in their proximal promoter, activating carboxylic acid, tetrahydrofolate interconversion, nucleobase, and oxoacid metabolisms. In the Myc signature, the expression of GAPDH, TYMS, DHFR, and TK1 was enough to predict methylation levels, microsatellite instability (MSI), and mutations in the mismatch repair (MMR) machinery, which are strong indicators of responsiveness to immunotherapies. Finally, we discovered that CIMP tumours harboured an increase in genes involved in the one-carbon metabolism, a pathway critical to providing nucleotides for cancer growth and methyl donors for DNA methylation, which is associated with worse prognosis and tumour hypermethylation. Transcriptomics could hence become a tool to help clinicians stratify their patients better.

Abstract P14: Efficacy of FHD-286 monotherapy and combinations against Menin inhibitor sensitive and resistant AML cells

Abstract BRG1 (SMARCA4) and BRM (SMARCA2) are the core ATPase within the BAF chromatin remodeler complexes. FHD-286 (Foghorn Therapeutics) is a potent, selective, oral inhibitor of BRG1/BRM in clinical development in AML. Present studies show that FHD-286 induces marked in vitro differentiation and loss of viability in AML cell lines and patient-derived (PD) AML cells with MLLr or mutant (mt) NPM1. FHD-286 treatment concordantly reduced genome-wide ATAC-Seq and RNA-Seq peaks, with negative enrichment at the gene-sets of MYC and E2F targets, mTORC1 signaling, translation initiation/elongation and DNA replication. FHD-286 reduced the occupancy of BRG1 and H3K27Ac on the chromatin. Mass spectrometry revealed FHD-286 reduced protein levels of c-Myc (and its targets), PLK1, BCL2, PU.1 and CDK4, but increased HEXIM1, CDKN1A/1B, CEBPα and CD11b levels. CyTOF analysis in the phenotypically characterized, PD, AML stem/progenitor cells with MLL1r or mtNPM1 showed decline in the protein levels of c-Myc, PU.1, BRG1, MEF2C, PBX3, BCL2 and MCL1, but increase in cleaved PARP and caspase-3 levels. In a PD xenograft (PDX) model of MLL1r AML, monotherapy with FHD-286 (oral gavage) for 4 to 6-weeks reduced AML burden and improved survival. FHD-286 treatment also significantly inhibited the AML-initiating potential, by reducing AML burden and improving survival of the re-engrafted mice with the FHD-286-treated PDX cells. Co-treatment with FHD-286 and BET inhibitor (OTX015), Menin inhibitor (MI, SNDX-50469), decitabine or venetoclax, exerted synergistic lethality in AML cell lines and PD AML cells with MLL1r or mtNPM1. Importantly, co-treatment with FHD-286 and OTX015, SNDX-5613 (oral gavage), venetoclax or decitabine vs each drug alone significantly reduced AML burden and improved survival in the PDX models of AML cells with MLLr or with mtNPM1, without significant toxicity. Notably, FHD-286 also induced significant lethality in MI-resistant AML cell lines and PD AML cells. Through repeated shocks with LD90 dosing of MI, followed by drug washout and recovery, we have generated MLL1r (MV4-11-MITR) and mtNPM1 (OCI-AML3-MITR) AML cell lines that are tolerant/resistant (TR) to MI (without exhibiting Menin mutations) with LD50 values greater than 1 µM. A domain-specific CRISPR screen in MV4-11-MITR cells identified several druggable co-dependencies (e.g., EP300 and MOZ) and co-enrichments (SMARCA4, CREBBP and BRD4) with MI. Accordingly, co-treatment with FHD-286 and OTX015, SNDX-50469 or CBP/p300 inhibitor GNE781 exerted synergistic lethality in MV4-11-MITR and OCI-AML3-MITR cells as well as in PD MITR AML cells with MLL1r or mtNPM1. FHD-286 and OTX015 or SNDX-5613 treatment also reduced AML burden in mice bearing OCI-AML3-MITR xenografts. These findings demonstrate pre-clinical efficacy of FHD-286-based rational combinations and underscore their promise against MI-sensitive or resistant AML with MLL1r or mtNPM1. Citation Format: Warren C Fiskus, Jessica Piel, Murphy Hentemann, Mike Collins, Christopher P Mill, Branko Cuglievan, Courtney D DiNardo, Kapil N Bhalla. Efficacy of FHD-286 monotherapy and combinations against Menin inhibitor sensitive and resistant AML cells [abstract]. In: Proceedings of the Blood Cancer Discovery Symposium; 2024 Mar 4-6; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(2_Suppl):Abstract nr P14.

Recurrent UBE3C-LRP5 translocations in head and neck cancer with therapeutic implications

Head and neck cancer is a major cause of morbidity and mortality worldwide. The identification of genetic alterations in head and neck cancer may improve diagnosis and treatment outcomes. In this study, we report the identification and functional characterization of UBE3C-LRP5 translocation in head and neck cancer. Our whole transcriptome sequencing and RT-PCR analysis of 151 head and neck cancer tumor samples identified the LRP5-UBE3C and UBE3C-LRP5 fusion transcripts in 5.3% of patients of Indian origin (n = 151), and UBE3C-LRP5 fusion transcripts in 1.2% of TCGA-HNSC patients (n = 502). Further, whole genome sequencing identified the breakpoint of UBE3C-LRP5 translocation. We demonstrate that UBE3C-LRP5 fusion is activating in vitro and in vivo, and promotes the proliferation, migration, and invasion of head and neck cancer cells. In contrast, depletion of UBE3C-LRP5 fusion suppresses the clonogenic, migratory, and invasive potential of the cells. The UBE3C-LRP5 fusion activates the Wnt/β-catenin signaling by promoting nuclear accumulation of β-catenin, leading to upregulation of Wnt/β-catenin target genes, MYC, CCND1, TCF4, and LEF1. Consistently, treatment with the FDA-approved drug, pyrvinium pamoate, significantly reduced the transforming ability of cells expressing the fusion protein and improved survival in mice bearing tumors of fusion-overexpressing cells. Interestingly, fusion-expressing cells upon knockdown of CTNNB1, or LEF1 show reduced proliferation, clonogenic abilities, and reduced sensitivity to pyrvinium pamoate. Overall, our study suggests that the UBE3C-LRP5 fusion is a promising therapeutic target for head and neck cancer and that pyrvinium pamoate may be a potential drug candidate for treating head and neck cancer harboring this translocation.

Activation of astrocytes by ANXA2-derived extracellular vesicles from lung cancer cells affects aggressiveness, immunotherapy response and microenvironment of lung cancer

BackgroundANXA2 has been extensively documented in relation to cancer. Nevertheless, the involvement of ANXA2 in lung carcinoma remains uncertain. MethodsData from The Cancer Genome Atlas (TCGA) database was downloaded using open-access methods. The examination of publicly available data was conducted utilizing the R software. The mRNA level of specific molecules was detected using Real-time Quantitative PCR (qPCR). The protein level of specific molecules was detected using the Western blot assay. The cell proliferation ability of cancer cells was assessed using the CCK8 assay. The invasion and migration capability of cancer cells was assessed using the Transwell assay. Validation of exosomes extraction was conducted using electron microscopy and particle size analysis. ResultsIn this study, based on series experiments, we found that ANXA2 can promote the activation of neuroastrocytes cells CP-H122 through the exosome pathway. Also, we found that ANXA2 can be transmitted from A549 cells to CP-H122 through the exosomes pathway and further promote the activation of CP-H122. Activated CP-H122 cells further enhance the proliferation, invasion and metastasis of A549 cells. Meanwhile, we performed transcriptome sequencing to explore the downstream genes of ANXA2 to screen potential targets for follow-up studies. Analysis based on public data showed that ANXA2 was related to the worse survival performance and clinical features of lung cancer. Gene set enrichment analysis based on the Hallmark gene set indicated that the patient with high ANXA2 expression might have a higher activity of the apical surface, reactive oxygen species pathway, angiogenesis, TGF-β signaling, MYC target, but lower activity of pancreas-β cells. More important, our results showed that ANXA2 can affects immunotherapy response and reshape immune microenvironment of lung cancer. ConclusionsThis study demonstrates that ANXA2 activates CP-H122 cells, affects A549 cell behavior, and impacts lung cancer prognosis and immunotherapy response.

Abstract PR006: ARID1A/B mutations retarget mSWI/SNF chromatin remodeler activity and define a spectrum of dedifferentiation in endometrial carcinoma

Abstract Dedifferentiated/undifferentiated endometrial carcinoma (DEC/UEC) is a highly aggressive histologic subtype of uterine cancer with a higher incidence among non-Hispanic Black women. Recent exome-wide sequencing studies have revealed frequent and often concomitant mutations in the ARID1A and ARID1B genes in over 50% of DEC/UEC cases and 30% of all endometrial carcinomas. The mSWI/SNF family of chromatin remodelers are critical regulators of cell type-specific chromatin accessibility and gene expression, existing in three distinct forms: canonical BAF (cBAF), Poly bromodomain-associated BAF (PBAF), and non-canonical BAF (ncBAF). The paralog subunits, ARID1A and ARID1B, specifically nucleate the assembly of cBAF complexes. However, the precise role ARID1A/ARID1B mutations (cBAF loss) play in the development of dedifferentiated endometrial carcinoma remains unclear. In this study, we define an expression signature associated with endometrial “dedifferentiation” by profiling the well-differentiated and dedifferentiated components of cBAF loss DEC cases through laser capture microdissection followed by RNA sequencing. Introduction of ARID1A or ARID1B in cBAF loss DEC cell lines demonstrated the restoration of cBAF assembly, confirmed by glycerol gradient and IP mass spectrometry. Upon the expression of ARID1A or ARID1B, we observed widespread chromatin occupancy and DNA accessibility at distinct paralog-specific sites, along with common sites associated with epithelial lineage differentiation, estrogen receptor, and PI3K/AKT pathway signaling. These findings align with the differentiation signature, defined in DEC cases demonstrating downregulation of genes associated with Myc targets, cell cycle checkpoint pathways, and DNA repair, suggesting these pathways represent potential therapeutic avenues for targeting DEC/UEC. Collectively, these data establish that well-differentiated endometrial carcinoma and DEC/UEC with mSWI/SNF mutations represent a spectrum of cBAF loss, defining the unique roles of ARID1A and ARID1B in endometrial carcinoma development. Furthermore, these findings imply that cBAF loss drives the widespread changes in DEC morphology, gene expression, and clinical behavior, enhancing our understanding of the etiology and therapeutic options for these cancers. Citation Format: Jessica D. St. Laurent, Grace Xu, Kasey Cervantas, Ajinkya Patil, Akshay Sankar, Shary Chen, David Kolin, Yemin Wang, David G. Huntsman, Cigall Kadoch. ARID1A/B mutations retarget mSWI/SNF chromatin remodeler activity and define a spectrum of dedifferentiation in endometrial carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr PR006.

Bioinformatics-Assisted Extraction of All PCa miRNAs and their Target Genes.

To retrieve, and classify PCa miRNAs and identify the functional relationship between miRNAs and their targets through literature collection with computational analysis. MicroRNAs play a role in gene regulation, which can either repress or activate the gene. Hence, the functions of miRNAs are dependent on the target gene. This study will be the first of its kind to combine computational analysis with corpus PCa data. Effectively, our study reported the huge number of miRNAs associated with PCa along with functional information. The identification and classification of previously known full PCa miRNAs and their targets were made possible by mining the literature data. Systems Biology and curated data mining assisted in identifying optimum miRNAs and their target genes for PCa therapy. PubMed database was used to collect the PCa literature up to December 2021. Pubmed. mineR package was used to extract the microRNAs associated articles and manual curation was performed to classify the microRNAs based on the function in PCa. PPI was constructed using the STRING database. Pathway analysis was performed using PANTHER and ToppGene Suite Software. Functional analysis was performed using ShinyGO software. Cluster analysis was performed using MCODE 2.0, and Hub gene analysis was performed using cytoHubba. The genemiRNA network was reconstructed using Cytoscape. Unique PCa miRNAs were retrieved and classified from mined PCa literature. Six hundred and five unique miRNAs from 250 articles were considered as oncomiRs to trigger PCa. One hundred and twenty unique miRNAs from 118 articles were considered Tumor Suppressor miRNAs to suppress the PCa. Twenty-four unique miRNAs from 22 articles were utilized as treatment miRNAs to treat PCa. miRNAs target genes and their significant pathways, functions and hub genes were identified. miR-27a, miR-34b, miR-495, miR-23b, miR-100, miR-218, Let-7a family, miR-27a- 5p, miR-34c, miR-34a, miR-143/-145, miR-125b, miR-124 and miR-205 with their target genes AKT1, SRC, CTNNB1, HRAS, MYC and TP53 are significant PCa targets.

A germline point mutation in the MYC-FBW7 phosphodegron initiates hematopoietic malignancies.

Oncogenic activation of MYC in cancers predominantly involves increased transcription rather than coding region mutations. However, MYC-dependent lymphomas frequently acquire point mutations in the MYC phosphodegron, including at threonine 58 (T58), where phosphorylation permits binding via the FBW7 ubiquitin ligase triggering MYC degradation. To understand how T58 phosphorylation functions in normal cell physiology, we introduced an alanine mutation at T58 (T58A) into the endogenous c-Myc locus in the mouse germline. While MYC-T58A mice develop normally, lymphomas and myeloid leukemias emerge in ∼60% of adult homozygous T58A mice. We found that primitive hematopoietic progenitor cells from MYC-T58A mice exhibit aberrant self-renewal normally associated with hematopoietic stem cells (HSCs) and up-regulate a subset of MYC target genes important in maintaining stem/progenitor cell balance. In lymphocytes, genomic occupancy by MYC-T58A was increased at all promoters compared with WT MYC, while genes differentially expressed in a T58A-dependent manner were significantly more proximal to MYC-bound enhancers. MYC-T58A lymphocyte progenitors exhibited metabolic alterations and decreased activation of inflammatory and apoptotic pathways. Our data demonstrate that a single point mutation stabilizing MYC is sufficient to skew target gene expression, producing a profound gain of function in multipotential hematopoietic progenitors associated with self-renewal and initiation of lymphomas and leukemias.