Publications by authors named "Christopher J Ott"

42 Publications

Selective targeting of MYC mRNA by stabilized antisense oligonucleotides.

Oncogene 2021 Oct 14. Epub 2021 Oct 14.

Broad Institute of MIT & Harvard, Cambridge, MA, 02142, USA.

MYC is a prolific proto-oncogene driving the malignant behaviors of numerous common cancers, yet potent and selective cell-permeable inhibitors of MYC remain elusive. In order to ultimately realize the goal of therapeutic MYC inhibition in cancer, we have initiated discovery chemistry efforts aimed at inhibiting MYC translation. Here we describe a series of conformationally stabilized synthetic antisense oligonucleotides designed to target MYC mRNA (MYCASOs). To support bioactivity, we designed and synthesized this focused library of MYCASOs incorporating locked nucleic acid (LNA) bases at the 5'- and 3'-ends, a phosphorothioate backbone, and internal DNA bases. Treatment of MYC-expressing cancer cells with MYCASOs leads to a potent decrease in MYC mRNA and protein levels. Cleaved MYC mRNA in MYCASO-treated cells is detected with a sensitive 5' Rapid Amplification of cDNA Ends (RACE) assay. MYCASO treatment of cancer cell lines leads to significant inhibition of cellular proliferation while specifically perturbing MYC-driven gene expression signatures. In a MYC-induced model of hepatocellular carcinoma, MYCASO treatment decreases MYC protein levels within tumors, decreases tumor burden, and improves overall survival. MYCASOs represent a new chemical tool for in vitro and in vivo modulation of MYC activity, and promising therapeutic agents for MYC-addicted tumors.
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http://dx.doi.org/10.1038/s41388-021-02053-4DOI Listing
October 2021

BET bromodomain protein inhibition reverses chimeric antigen receptor extinction and reinvigorates exhausted T cells in chronic lymphocytic leukemia.

J Clin Invest 2021 Aug;131(16)

Center for Cellular Immunotherapies.

Chimeric antigen receptor (CAR) T cells have induced remarkable antitumor responses in B cell malignancies. Some patients do not respond because of T cell deficiencies that hamper the expansion, persistence, and effector function of these cells. We used longitudinal immune profiling to identify phenotypic and pharmacodynamic changes in CD19-directed CAR T cells in patients with chronic lymphocytic leukemia (CLL). CAR expression maintenance was also investigated because this can affect response durability. CAR T cell failure was accompanied by preexisting T cell-intrinsic defects or dysfunction acquired after infusion. In a small subset of patients, CAR silencing was observed coincident with leukemia relapse. Using a small molecule inhibitor, we demonstrated that the bromodomain and extra-terminal (BET) family of chromatin adapters plays a role in downregulating CAR expression. BET protein blockade also ameliorated CAR T cell exhaustion as manifested by inhibitory receptor reduction, enhanced metabolic fitness, increased proliferative capacity, and enriched transcriptomic signatures of T cell reinvigoration. BET inhibition decreased levels of the TET2 methylcytosine dioxygenase, and forced expression of the TET2 catalytic domain eliminated the potency-enhancing effects of BET protein targeting in CAR T cells, providing a mechanism linking BET proteins and T cell dysfunction. Thus, modulating BET epigenetic readers may improve the efficacy of cell-based immunotherapies.
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http://dx.doi.org/10.1172/JCI145459DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8363276PMC
August 2021

Screening and Validation of Molecular Targeted Radiosensitizers.

Int J Radiat Oncol Biol Phys 2021 Jul 31. Epub 2021 Jul 31.

OncoRay-National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany; German Cancer Research Center, Heidelberg, Germany; German Cancer Consortium, Dresden, Germany; Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiooncology-OncoRay, Dresden, Germany; Department of Radiotherapy and Radiation Oncology`, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; National Center for Tumour Diseases, Dresden, Germany.

The development of molecular targeted drugs with radiation and chemotherapy is critically important for improving the outcomes of patients with hard-to-treat, potentially curable cancers. However, too many preclinical studies have not translated into successful radiation oncology trials. Major contributing factors to this insufficiency include poor reproducibility of preclinical data, inadequate preclinical modeling of intertumoral genomic heterogeneity that influences treatment sensitivity in the clinic, and a reliance on tumor growth delay instead of local control (TCD50) endpoints. There exists an urgent need to overcome these barriers to facilitate successful clinical translation of targeted radiosensitizers. To this end, we have used 3-dimensional (3D) cell culture assays to better model tumor behavior in vivo. Examples of successful prediction of in vivo effects with these 3D assays include radiosensitization of head and neck cancers by inhibiting epidermal growth factor receptor or focal adhesion kinase signaling, and radioresistance associated with oncogenic mutation of KRAS. To address the issue of tumor heterogeneity, we leveraged institutional resources that allow high-throughput 3D screening of radiation combinations with small-molecule inhibitors across genomically characterized cell lines from lung, head and neck, and pancreatic cancers. This high-throughput screen is expected to uncover genomic biomarkers that will inform the successful clinical translation of targeted agents from the National Cancer Institute Cancer Therapy Evaluation Program portfolio and other sources. Screening "hits" need to be subjected to refinement studies that include clonogenic assays, addition of disease-specific chemotherapeutics, target/biomarker validation, and integration of patient-derived tumor models. The chemoradiosensitizing activities of the most promising drugs should be confirmed in TCD50 assays in xenograft models with or without relevant biomarker and using clinically relevant radiation fractionation. We predict that appropriately validated and biomarker-directed targeted therapies will have a higher likelihood than past efforts of being successfully incorporated into the standard management of hard-to-treat tumors.
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http://dx.doi.org/10.1016/j.ijrobp.2021.07.1694DOI Listing
July 2021

A hotspot mutation in transcription factor IKZF3 drives B cell neoplasia via transcriptional dysregulation.

Cancer Cell 2021 03;39(3):380-393.e8

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA; Harvard Medical School, Boston, MA, USA; Broad Institute of MIT and Harvard, Cambridge, MA, USA; Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA. Electronic address:

Hotspot mutation of IKZF3 (IKZF3-L162R) has been identified as a putative driver of chronic lymphocytic leukemia (CLL), but its function remains unknown. Here, we demonstrate its driving role in CLL through a B cell-restricted conditional knockin mouse model. Mutant Ikzf3 alters DNA binding specificity and target selection, leading to hyperactivation of B cell receptor (BCR) signaling, overexpression of nuclear factor κB (NF-κB) target genes, and development of CLL-like disease in elderly mice with a penetrance of ~40%. Human CLL carrying either IKZF3 mutation or high IKZF3 expression was associated with overexpression of BCR/NF-κB pathway members and reduced sensitivity to BCR signaling inhibition by ibrutinib. Our results thus highlight IKZF3 oncogenic function in CLL via transcriptional dysregulation and demonstrate that this pro-survival function can be achieved by either somatic mutation or overexpression of this CLL driver. This emphasizes the need for combinatorial approaches to overcome IKZF3-mediated BCR inhibitor resistance.
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http://dx.doi.org/10.1016/j.ccell.2021.02.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8034546PMC
March 2021

Targeting oncoproteins with a positive selection assay for protein degraders.

Sci Adv 2021 Feb 5;7(6). Epub 2021 Feb 5.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA.

Most intracellular proteins lack hydrophobic pockets suitable for altering their function with drug-like small molecules. Recent studies indicate that some undruggable proteins can be targeted by compounds that can degrade them. For example, thalidomide-like drugs (IMiDs) degrade the critical multiple myeloma transcription factors IKZF1 and IKZF3 by recruiting them to the cereblon E3 ubiquitin ligase. Current loss of signal ("down") assays for identifying degraders often exhibit poor signal-to-noise ratios, narrow dynamic ranges, and false positives from compounds that nonspecifically suppress transcription or translation. Here, we describe a gain of signal ("up") assay for degraders. In arrayed chemical screens, we identified novel IMiD-like IKZF1 degraders and Spautin-1, which, unlike the IMiDs, degrades IKZF1 in a cereblon-independent manner. In a pooled CRISPR-Cas9-based screen, we found that CDK2 regulates the abundance of the ASCL1 oncogenic transcription factor. This methodology should facilitate the identification of drugs that directly or indirectly degrade undruggable proteins.
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http://dx.doi.org/10.1126/sciadv.abd6263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7864573PMC
February 2021

Functional Genomics Identify Distinct and Overlapping Genes Mediating Resistance to Different Classes of Heterobifunctional Degraders of Oncoproteins.

Cell Rep 2021 01;34(1):108532

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA; Harvard Medical School, Boston, MA, USA; Broad Institute of MIT and Harvard, Cambridge, MA, USA.

Heterobifunctional proteolysis-targeting chimeric compounds leverage the activity of E3 ligases to induce degradation of target oncoproteins and exhibit potent preclinical antitumor activity. To dissect the mechanisms regulating tumor cell sensitivity to different classes of pharmacological "degraders" of oncoproteins, we performed genome-scale CRISPR-Cas9-based gene editing studies. We observed that myeloma cell resistance to degraders of different targets (BET bromodomain proteins, CDK9) and operating through CRBN (degronimids) or VHL is primarily mediated by prevention of, rather than adaptation to, breakdown of the target oncoprotein; and this involves loss of function of the cognate E3 ligase or interactors/regulators of the respective cullin-RING ligase (CRL) complex. The substantial gene-level differences for resistance mechanisms to CRBN- versus VHL-based degraders explains mechanistically the lack of cross-resistance with sequential administration of these two degrader classes. Development of degraders leveraging more diverse E3 ligases/CRLs may facilitate sequential/alternating versus combined uses of these agents toward potentially delaying or preventing resistance.
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http://dx.doi.org/10.1016/j.celrep.2020.108532DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8485877PMC
January 2021

Targeted degradation of the enhancer lysine acetyltransferases CBP and p300.

Cell Chem Biol 2021 04 4;28(4):503-514.e12. Epub 2021 Jan 4.

Massachusetts General Hospital Cancer Center, Charlestown, MA 02129, USA; Department of Medicine, Harvard Medical School, Boston, MA 02115, USA; Broad Institute of MIT & Harvard, Cambridge, MA 02142, USA. Electronic address:

The enhancer factors CREB-binding protein (CBP) and p300 (also known as KAT3A and KAT3B) maintain gene expression programs through lysine acetylation of chromatin and transcriptional regulators and by scaffolding functions mediated by several protein-protein interaction domains. Small molecule inhibitors that target some of these domains have been developed; however, they cannot completely ablate p300/CBP function in cells. Here we describe a chemical degrader of p300/CBP, dCBP-1. Leveraging structures of ligand-bound p300/CBP domains, we use in silico modeling of ternary complex formation with the E3 ubiquitin ligase cereblon to enable degrader design. dCBP-1 is exceptionally potent at killing multiple myeloma cells and can abolish the enhancer that drives MYC oncogene expression. As an efficient degrader of this unique class of acetyltransferases, dCBP-1 is a useful tool alongside domain inhibitors for dissecting the mechanism by which these factors coordinate enhancer activity in normal and diseased cells.
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http://dx.doi.org/10.1016/j.chembiol.2020.12.004DOI Listing
April 2021

Circles with a Point: New Insights into Oncogenic Extrachromosomal DNA.

Cancer Cell 2020 02;37(2):145-146

Massachusetts General Hospital Center for Cancer Research, Boston, MA 02114, USA; Harvard Medical School, Boston, MA 02115, USA; Broad Institute of MIT & Harvard, Cambridge, MA 02142, USA. Electronic address:

For decades, scientists have observed small extrachromosomal DNA fragments in tumor cells, yet comprehensive examination of their structure and function has remained difficult. Three recent studies, published in Nature, Cell, and Nature Genetics, have now shed important light on the architecture, regulatory capacity, and oncogenic nature of tumor-associated extrachromosomal DNA.
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http://dx.doi.org/10.1016/j.ccell.2020.01.008DOI Listing
February 2020

Mitochondrial Reprogramming Underlies Resistance to BCL-2 Inhibition in Lymphoid Malignancies.

Cancer Cell 2019 10 19;36(4):369-384.e13. Epub 2019 Sep 19.

Department of Medical Oncology, Dana-Farber Cancer Institute, 450 Brookline Avenue, Dana Building, Room DA-520, Boston MA 02215-02115, USA; Harvard Medical School, Boston, MA 02215, USA; Department of Medicine, Brigham and Women's Hospital, Boston, MA 02215, USA.

Mitochondrial apoptosis can be effectively targeted in lymphoid malignancies with the FDA-approved B cell lymphoma 2 (BCL-2) inhibitor venetoclax, but resistance to this agent is emerging. We show that venetoclax resistance in chronic lymphocytic leukemia is associated with complex clonal shifts. To identify determinants of resistance, we conducted parallel genome-scale screens of the BCL-2-driven OCI-Ly1 lymphoma cell line after venetoclax exposure along with integrated expression profiling and functional characterization of drug-resistant and engineered cell lines. We identified regulators of lymphoid transcription and cellular energy metabolism as drivers of venetoclax resistance in addition to the known involvement by BCL-2 family members, which were confirmed in patient samples. Our data support the implementation of combinatorial therapy with metabolic modulators to address venetoclax resistance.
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http://dx.doi.org/10.1016/j.ccell.2019.08.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6801112PMC
October 2019

Cohesin Members Stag1 and Stag2 Display Distinct Roles in Chromatin Accessibility and Topological Control of HSC Self-Renewal and Differentiation.

Cell Stem Cell 2019 11 5;25(5):682-696.e8. Epub 2019 Sep 5.

Human Oncology and Pathogenesis Program and Center for Hematologic Malignancies, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA; Department of Medicine, Leukemia Service, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA; Center for Epigenetics Research, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA. Electronic address:

Transcriptional regulators, including the cohesin complex member STAG2, are recurrently mutated in cancer. The role of STAG2 in gene regulation, hematopoiesis, and tumor suppression remains unresolved. We show that Stag2 deletion in hematopoietic stem and progenitor cells (HSPCs) results in altered hematopoietic function, increased self-renewal, and impaired differentiation. Chromatin immunoprecipitation (ChIP) sequencing revealed that, although Stag2 and Stag1 bind a shared set of genomic loci, a component of Stag2 binding sites is unoccupied by Stag1, even in Stag2-deficient HSPCs. Although concurrent loss of Stag2 and Stag1 abrogated hematopoiesis, Stag2 loss alone decreased chromatin accessibility and transcription of lineage-specification genes, including Ebf1 and Pax5, leading to increased self-renewal and reduced HSPC commitment to the B cell lineage. Our data illustrate a role for Stag2 in transformation and transcriptional dysregulation distinct from its shared role with Stag1 in chromosomal segregation.
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http://dx.doi.org/10.1016/j.stem.2019.08.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6842438PMC
November 2019

Small-molecule targeting of brachyury transcription factor addiction in chordoma.

Nat Med 2019 02 21;25(2):292-300. Epub 2019 Jan 21.

Broad Institute of Harvard and MIT, Cambridge, MA, USA.

Chordoma is a primary bone cancer with no approved therapy. The identification of therapeutic targets in this disease has been challenging due to the infrequent occurrence of clinically actionable somatic mutations in chordoma tumors. Here we describe the discovery of therapeutically targetable chordoma dependencies via genome-scale CRISPR-Cas9 screening and focused small-molecule sensitivity profiling. These systematic approaches reveal that the developmental transcription factor T (brachyury; TBXT) is the top selectively essential gene in chordoma, and that transcriptional cyclin-dependent kinase (CDK) inhibitors targeting CDK7/12/13 and CDK9 potently suppress chordoma cell proliferation. In other cancer types, transcriptional CDK inhibitors have been observed to downregulate highly expressed, enhancer-associated oncogenic transcription factors. In chordoma, we find that T is associated with a 1.5-Mb region containing 'super-enhancers' and is the most highly expressed super-enhancer-associated transcription factor. Notably, transcriptional CDK inhibition leads to preferential and concentration-dependent downregulation of cellular brachyury protein levels in all models tested. In vivo, CDK7/12/13-inhibitor treatment substantially reduces tumor growth. Together, these data demonstrate small-molecule targeting of brachyury transcription factor addiction in chordoma, identify a mechanism of T gene regulation that underlies this therapeutic strategy, and provide a blueprint for applying systematic genetic and chemical screening approaches to discover vulnerabilities in genomically quiet cancers.
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http://dx.doi.org/10.1038/s41591-018-0312-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6633917PMC
February 2019

Non-overlapping Control of Transcriptome by Promoter- and Super-Enhancer-Associated Dependencies in Multiple Myeloma.

Cell Rep 2018 12;25(13):3693-3705.e6

Jerome Lipper Multiple Myeloma Center, Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02215, USA; VA Boston Healthcare System, Boston, MA, USA. Electronic address:

The relationship between promoter proximal transcription factor-associated gene expression and super-enhancer-driven transcriptional programs are not well defined. However, their distinct genomic occupancy suggests a mechanism for specific and separable gene control. We explored the transcriptional and functional interrelationship between E2F transcription factors and BET transcriptional co-activators in multiple myeloma. We found that the transcription factor E2F1 and its heterodimerization partner DP1 represent a dependency in multiple myeloma cells. Global chromatin analysis reveals distinct regulatory axes for E2F and BETs, with E2F predominantly localized to active gene promoters of growth and/or proliferation genes and BETs disproportionately at enhancer-regulated tissue-specific genes. These two separate gene regulatory axes can be simultaneously targeted to impair the myeloma proliferative program, providing an important molecular mechanism for combination therapy. This study therefore suggests a sequestered cellular functional control that may be perturbed in cancer with potential for development of a promising therapeutic strategy.
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http://dx.doi.org/10.1016/j.celrep.2018.12.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6407615PMC
December 2018

Enhancer Architecture and Essential Core Regulatory Circuitry of Chronic Lymphocytic Leukemia.

Cancer Cell 2018 12 29;34(6):982-995.e7. Epub 2018 Nov 29.

Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, 450 Brookline Avenue, Boston, MA 02115, USA; Department of Medicine, Harvard Medical School, Boston, MA 02115, USA; Broad Institute of MIT & Harvard, Cambridge, MA 02142, USA; Novartis Institutes for Biomedical Research, 250 Massachusetts Avenue, Cambridge, MA 02139, USA. Electronic address:

Enhancer profiling is a powerful approach for discovering cis-regulatory elements that define the core transcriptional regulatory circuits of normal and malignant cells. Gene control through enhancer activity is often dominated by a subset of lineage-specific transcription factors. By integrating measures of chromatin accessibility and enrichment for H3K27 acetylation, we have generated regulatory landscapes of chronic lymphocytic leukemia (CLL) samples and representative cell lines. With super enhancer-based modeling of regulatory circuits and assessments of transcription factor dependencies, we discover that the essential super enhancer factor PAX5 dominates CLL regulatory nodes and is essential for CLL cell survival. Targeting enhancer signaling via BET bromodomain inhibition disrupts super enhancer-dependent gene expression with selective effects on CLL core regulatory circuitry, conferring potent anti-tumor activity.
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http://dx.doi.org/10.1016/j.ccell.2018.11.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6298230PMC
December 2018

Opportunities for targeting gene regulatory factors in B-cell acute lymphoblastic leukemia.

Int J Hematol Oncol 2017 Nov 20;6(3):57-59. Epub 2017 Nov 20.

Dana-Farber Cancer Institute, Harvard Medical School, 450 Brookline Avenue, Boston, MA 02215, USA.

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http://dx.doi.org/10.2217/ijh-2017-0018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6171982PMC
November 2017

Epigenetic regulation of NFE2 overexpression in myeloproliferative neoplasms.

Blood 2018 05 8;131(18):2065-2073. Epub 2018 Mar 8.

Division of Molecular Hematology.

The transcription factor "nuclear factor erythroid 2" (NFE2) is overexpressed in the majority of patients with myeloproliferative neoplasms (MPNs). In murine models, elevated NFE2 levels cause an MPN phenotype with spontaneous leukemic transformation. However, both the molecular mechanisms leading to NFE2 overexpression and its downstream targets remain incompletely understood. Here, we show that the histone demethylase constitutes a novel NFE2 target gene. JMJD1C levels are significantly elevated in polycythemia vera (PV) and primary myelofibrosis patients; concomitantly, global H3K9me1 and H3K9me2 levels are significantly decreased. JMJD1C binding to the promoter is increased in PV patients, decreasing both H3K9me2 levels and binding of the repressive heterochromatin protein-1α (HP1α). Hence, JMJD1C and NFE2 participate in a novel autoregulatory loop. Depleting JMJD1C expression significantly reduced cytokine-independent growth of an MPN cell line. Independently, NFE2 is regulated through the epigenetic JAK2 pathway by phosphorylation of H3Y41. This likewise inhibits HP1α binding. Treatment with decitabine lowered H3Y41ph and augmented H3K9me2 levels at the locus in HEL cells, thereby increasing HP1α binding, which normalized NFE2 expression selectively in JAK2-positive cell lines.
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http://dx.doi.org/10.1182/blood-2017-10-810622DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5934799PMC
May 2018

Functional TRIM24 degrader via conjugation of ineffectual bromodomain and VHL ligands.

Nat Chem Biol 2018 04 5;14(4):405-412. Epub 2018 Mar 5.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.

The addressable pocket of a protein is often not functionally relevant in disease. This is true for the multidomain, bromodomain-containing transcriptional regulator TRIM24. TRIM24 has been posited as a dependency in numerous cancers, yet potent and selective ligands for the TRIM24 bromodomain do not exert effective anti-proliferative responses. We therefore repositioned these probes as targeting features for heterobifunctional protein degraders. Recruitment of the VHL E3 ubiquitin ligase by dTRIM24 elicits potent and selective degradation of TRIM24. Using dTRIM24 to probe TRIM24 function, we characterize the dynamic genome-wide consequences of TRIM24 loss on chromatin localization and gene control. Further, we identify TRIM24 as a novel dependency in acute leukemia. Pairwise study of TRIM24 degradation versus bromodomain inhibition reveals enhanced anti-proliferative response from degradation. We offer dTRIM24 as a chemical probe of an emerging cancer dependency, and establish a path forward for numerous selective yet ineffectual ligands for proteins of therapeutic interest.
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http://dx.doi.org/10.1038/s41589-018-0010-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5866761PMC
April 2018

HDAC Inhibitors Finally Open Up: Chromatin Accessibility Signatures of CTCL.

Cancer Cell 2017 07;32(1):1-3

Department of Medical Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA. Electronic address:

In this issue of Cancer Cell, Qu et al. describe the chromatin accessibility profiles of cutaneous T cell lymphoma, with dynamic assessments of response and resistance to histone deacetylase inhibitor therapy. Their "personal regulome" analysis framework reveals chromatin features that may be predictive of clinical response to epigenetic therapy.
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http://dx.doi.org/10.1016/j.ccell.2017.06.008DOI Listing
July 2017

BET Bromodomain Proteins Function as Master Transcription Elongation Factors Independent of CDK9 Recruitment.

Mol Cell 2017 Jul 29;67(1):5-18.e19. Epub 2017 Jun 29.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Novartis Institutes for Biomedical Research, Cambridge, MA 02139, USA. Electronic address:

Processive elongation of RNA Polymerase II from a proximal promoter paused state is a rate-limiting event in human gene control. A small number of regulatory factors influence transcription elongation on a global scale. Prior research using small-molecule BET bromodomain inhibitors, such as JQ1, linked BRD4 to context-specific elongation at a limited number of genes associated with massive enhancer regions. Here, the mechanistic characterization of an optimized chemical degrader of BET bromodomain proteins, dBET6, led to the unexpected identification of BET proteins as master regulators of global transcription elongation. In contrast to the selective effect of bromodomain inhibition on transcription, BET degradation prompts a collapse of global elongation that phenocopies CDK9 inhibition. Notably, BRD4 loss does not directly affect CDK9 localization. These studies, performed in translational models of T cell leukemia, establish a mechanism-based rationale for the development of BET bromodomain degradation as cancer therapy.
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http://dx.doi.org/10.1016/j.molcel.2017.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5663500PMC
July 2017

BET-Bromodomain Inhibitors Engage the Host Immune System and Regulate Expression of the Immune Checkpoint Ligand PD-L1.

Cell Rep 2017 02;18(9):2162-2174

Peter MacCallum Cancer Centre, Melbourne, VIC 3000, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC 3010, Australia. Electronic address:

BET inhibitors (BETi) target bromodomain-containing proteins and are currently being evaluated as anti-cancer agents. We find that maximal therapeutic effects of BETi in a Myc-driven B cell lymphoma model required an intact host immune system. Genome-wide analysis of the BETi-induced transcriptional response identified the immune checkpoint ligand Cd274 (Pd-l1) as a Myc-independent, BETi target-gene. BETi directly repressed constitutively expressed and interferon-gamma (IFN-γ) induced CD274 expression across different human and mouse tumor cell lines and primary patient samples. Mechanistically, BETi decreased Brd4 occupancy at the Cd274 locus without any change in Myc occupancy, resulting in transcriptional pausing and rapid loss of Cd274 mRNA production. Finally, targeted inhibition of the PD-1/PD-L1 axis by combining anti-PD-1 antibodies and the BETi JQ1 caused synergistic responses in mice bearing Myc-driven lymphomas. Our data uncover an interaction between BETi and the PD-1/PD-L1 immune-checkpoint and provide mechanistic insight into the transcriptional regulation of CD274.
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http://dx.doi.org/10.1016/j.celrep.2017.02.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5340981PMC
February 2017

A chemical probe toolbox for dissecting the cancer epigenome.

Nat Rev Cancer 2017 02;17(3):160-183

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02215, USA.

Cancer cell hallmarks are underpinned by transcriptional programmes operating in the context of a dynamic and complicit epigenomic environment. Somatic alterations of chromatin modifiers are among the most prevalent cancer perturbations. There is a pressing need for targeted chemical probes to dissect these complex, interconnected gene regulatory circuits. Validated chemical probes empower mechanistic research while providing the pharmacological proof of concept that is required to translate drug-like derivatives into therapy for cancer patients. In this Review, we describe chemical probe development for epigenomic effector proteins that are linked to cancer pathogenesis. By annotating these reagents, we aim to share our perspectives on an informative 'epigenomic toolbox' of broad utility to the research community.
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http://dx.doi.org/10.1038/nrc.2016.148DOI Listing
February 2017

Assessment of Bromodomain Target Engagement by a Series of BI2536 Analogues with Miniaturized BET-BRET.

ChemMedChem 2016 Dec 15;11(23):2575-2581. Epub 2016 Nov 15.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, 02215, USA.

Evaluating the engagement of a small molecule ligand with a protein target in cells provides useful information for chemical probe optimization and pharmaceutical development. While several techniques exist that can be performed in a low-throughput manner, systematic evaluation of large compound libraries remains a challenge. In-cell engagement measurements are especially useful when evaluating compound classes suspected to target multiple cellular factors. In this study we used a bioluminescent resonant energy transfer assay to assess bromodomain engagement by a compound series containing bromodomain- and kinase-biasing polypharmacophores based on the known dual BRD4 bromodomain/PLK1 kinase inhibitor BI2536. With this assay, we discovered several novel agents with bromodomain-selective specificity profiles and cellular activity. Thus, this platform aids in distinguishing molecules whose cellular activity is difficult to assess due to polypharmacologic effects.
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http://dx.doi.org/10.1002/cmdc.201600502DOI Listing
December 2016

ATAD2 is an epigenetic reader of newly synthesized histone marks during DNA replication.

Oncotarget 2016 10;7(43):70323-70335

Drug Discovery, Bayer Pharma AG, Berlin, Germany.

ATAD2 (ATPase family AAA domain-containing protein 2) is a chromatin regulator harboring an AAA+ ATPase domain and a bromodomain, previously proposed to function as an oncogenic transcription co-factor. Here we suggest that ATAD2 is also required for DNA replication. ATAD2 is co-expressed with genes involved in DNA replication in various cancer types and predominantly expressed in S phase cells where it localized on nascent chromatin (replication sites). Our extensive biochemical and cellular analyses revealed that ATAD2 is recruited to replication sites through a direct interaction with di-acetylated histone H4 at K5 and K12, indicative of newly synthesized histones during replication-coupled chromatin reassembly. Similar to ATAD2-depletion, ectopic expression of ATAD2 mutants that are deficient in binding to these di-acetylation marks resulted in reduced DNA replication and impaired loading of PCNA onto chromatin, suggesting relevance of ATAD2 in DNA replication. Taken together, our data show a novel function of ATAD2 in cancer and for the first time identify a reader of newly synthesized histone di-acetylation-marks during replication.
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http://dx.doi.org/10.18632/oncotarget.11855DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5342555PMC
October 2016

Spiclypeus shipporum gen. et sp. nov., a Boldly Audacious New Chasmosaurine Ceratopsid (Dinosauria: Ornithischia) from the Judith River Formation (Upper Cretaceous: Campanian) of Montana, USA.

PLoS One 2016 18;11(5):e0154218. Epub 2016 May 18.

Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada.

This study reports on a new ceratopsid, Spiclypeus shipporum gen et sp. nov., from the lower Coal Ridge Member of the Judith River Formation in Montana, USA, which dates to ~76 Ma (upper Campanian). The species is distinguished by rugose dorsal contacts on the premaxillae for the nasals, laterally projecting postorbital horncores, fully fused and anteriorly curled P1 and P2 epiparietals, and a posterodorsally projecting P3 epiparietal. The holotype specimen is also notable for its pathological left squamosal and humerus, which show varied signs of osteomyelitis and osteoarthritis. Although the postorbital horncores of Spiclypeus closely resemble those of the contemporaneous 'Ceratops', the horncores of both genera are nevertheless indistinguishable from those of some other horned dinosaurs, including Albertaceratops and Kosmoceratops; 'Ceratops' is therefore maintained as a nomen dubium. Cladistic analysis recovers Spiclypeus as the sister taxon to the clade Vagaceratops + Kosmoceratops, and appears transitional in the morphology of its epiparietals. The discovery of Spiclypeus adds to the poorly known dinosaur fauna of the Judith River Formation, and suggests faunal turnover within the formation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0154218PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4871577PMC
July 2017

Dose-dependent role of the cohesin complex in normal and malignant hematopoiesis.

J Exp Med 2015 Oct 5;212(11):1819-32. Epub 2015 Oct 5.

Human Oncology and Pathogenesis Program, Leukemia Service, Department of Medicine, Department of Pathology, Molecular Cytology Core Facility, and Center for Epigenetics Research, Memorial Sloan Kettering Cancer Center, New York, NY 10065 Human Oncology and Pathogenesis Program, Leukemia Service, Department of Medicine, Department of Pathology, Molecular Cytology Core Facility, and Center for Epigenetics Research, Memorial Sloan Kettering Cancer Center, New York, NY 10065 Human Oncology and Pathogenesis Program, Leukemia Service, Department of Medicine, Department of Pathology, Molecular Cytology Core Facility, and Center for Epigenetics Research, Memorial Sloan Kettering Cancer Center, New York, NY 10065

Cohesin complex members have recently been identified as putative tumor suppressors in hematologic and epithelial malignancies. The cohesin complex guides chromosome segregation; however, cohesin mutant leukemias do not show genomic instability. We hypothesized that reduced cohesin function alters chromatin structure and disrupts cis-regulatory architecture of hematopoietic progenitors. We investigated the consequences of Smc3 deletion in normal and malignant hematopoiesis. Biallelic Smc3 loss induced bone marrow aplasia with premature sister chromatid separation and revealed an absolute requirement for cohesin in hematopoietic stem cell (HSC) function. In contrast, Smc3 haploinsufficiency increased self-renewal in vitro and in vivo, including competitive transplantation. Smc3 haploinsufficiency reduced coordinated transcriptional output, including reduced expression of transcription factors and other genes associated with lineage commitment. Smc3 haploinsufficiency cooperated with Flt3-ITD to induce acute leukemia in vivo, with potentiated Stat5 signaling and altered nucleolar topology. These data establish a dose dependency for cohesin in regulating chromatin structure and HSC function.
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http://dx.doi.org/10.1084/jem.20151317DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4612085PMC
October 2015

An epigenetic mechanism of resistance to targeted therapy in T cell acute lymphoblastic leukemia.

Nat Genet 2014 Apr 2;46(4):364-70. Epub 2014 Mar 2.

1] Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA. [2] Broad Institute of MIT and Harvard, Cambridge, Massachusetts, USA. [3] Center for Cancer Research, Massachusetts General Hospital, Boston, Massachusetts, USA. [4] Howard Hughes Medical Institute, Chevy Chase, Maryland, USA.

The identification of activating NOTCH1 mutations in T cell acute lymphoblastic leukemia (T-ALL) led to clinical testing of γ-secretase inhibitors (GSIs) that prevent NOTCH1 activation. However, responses to these inhibitors have been transient, suggesting that resistance limits their clinical efficacy. Here we modeled T-ALL resistance, identifying GSI-tolerant 'persister' cells that expand in the absence of NOTCH1 signaling. Rare persisters are already present in naive T-ALL populations, and the reversibility of their phenotype suggests an epigenetic mechanism. Relative to GSI-sensitive cells, persister cells activate distinct signaling and transcriptional programs and exhibit chromatin compaction. A knockdown screen identified chromatin regulators essential for persister viability, including BRD4. BRD4 binds enhancers near critical T-ALL genes, including MYC and BCL2. The BRD4 inhibitor JQ1 downregulates expression of these targets and induces growth arrest and apoptosis in persister cells, at doses well tolerated by GSI-sensitive cells. Consistently, the GSI-JQ1 combination was found to be effective against primary human leukemias in vivo. Our findings establish a role for epigenetic heterogeneity in leukemia resistance that may be addressed by incorporating epigenetic modulators in combination therapy.
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http://dx.doi.org/10.1038/ng.2913DOI Listing
April 2014

The myeloma drug lenalidomide promotes the cereblon-dependent destruction of Ikaros proteins.

Science 2014 Jan 29;343(6168):305-9. Epub 2013 Nov 29.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA.

Thalidomide-like drugs such as lenalidomide are clinically important treatments for multiple myeloma and show promise for other B cell malignancies. The biochemical mechanisms underlying their antitumor activity are unknown. Thalidomide was recently shown to bind to, and inhibit, the cereblon ubiquitin ligase. Cereblon loss in zebrafish causes fin defects reminiscent of the limb defects seen in children exposed to thalidomide in utero. Here we show that lenalidomide-bound cereblon acquires the ability to target for proteasomal degradation two specific B cell transcription factors, Ikaros family zinc finger proteins 1 and 3 (IKZF1 and IKZF3). Analysis of myeloma cell lines revealed that loss of IKZF1 and IKZF3 is both necessary and sufficient for lenalidomide's therapeutic effect, suggesting that the antitumor and teratogenic activities of thalidomide-like drugs are dissociable.
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http://dx.doi.org/10.1126/science.1244917DOI Listing
January 2014

Nucleosome mapping across the CFTR locus identifies novel regulatory factors.

Nucleic Acids Res 2013 Mar 15;41(5):2857-68. Epub 2013 Jan 15.

Human Molecular Genetics Program, Children's Memorial Research Center, Department of Pediatrics, Northwestern University Feinberg School of Medicine Chicago, IL 60614, USA.

Nucleosome positioning on the chromatin strand plays a critical role in regulating accessibility of DNA to transcription factors and chromatin modifying enzymes. Hence, detailed information on nucleosome depletion or movement at cis-acting regulatory elements has the potential to identify predicted binding sites for trans-acting factors. Using a novel method based on enrichment of mononucleosomal DNA by bacterial artificial chromosome hybridization, we mapped nucleosome positions by deep sequencing across 250 kb, encompassing the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR shows tight tissue-specific regulation of expression, which is largely determined by cis-regulatory elements that lie outside the gene promoter. Although multiple elements are known, the repertoire of transcription factors that interact with these sites to activate or repress CFTR expression remains incomplete. Here, we show that specific nucleosome depletion corresponds to well-characterized binding sites for known trans-acting factors, including hepatocyte nuclear factor 1, Forkhead box A1 and CCCTC-binding factor. Moreover, the cell-type selective nucleosome positioning is effective in predicting binding sites for novel interacting factors, such as BAF155. Finally, we identify transcription factor binding sites that are overrepresented in regions where nucleosomes are depleted in a cell-specific manner. This approach recognizes the glucocorticoid receptor as a novel trans-acting factor that regulates CFTR expression in vivo.
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http://dx.doi.org/10.1093/nar/gks1462DOI Listing
March 2013

BET bromodomain inhibition targets both c-Myc and IL7R in high-risk acute lymphoblastic leukemia.

Blood 2012 Oct 17;120(14):2843-52. Epub 2012 Aug 17.

Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA.

We investigated the therapeutic potential of JQ1, an inhibitor of the BET class of human bromodomain proteins, in B-cell acute lymphoblastic leukemia (B-ALL). We show that JQ1 potently reduces the viability of B-ALL cell lines with high-risk cytogenetics. Among the most sensitive were lines with rearrangements of CRLF2, which is overexpressed in ~ 10% of B-ALL. CRLF2 heterodimerizes with the IL7 receptor (IL7R) and signals through JAK2, JAK1, and STAT5 to drive proliferation and suppress apoptosis. As previously observed, JQ1 induced the down-regulation of MYC transcription, the loss of BRD4 at the MYC promoter, and the reduced expression of c-Myc target genes. Strikingly, JQ1 also down-regulated IL7R transcription, depleted BRD4 from the IL7R promoter, and reduced JAK2 and STAT5 phosphorylation. Genome-wide expression profiling demonstrated a restricted effect of JQ1 on transcription, with MYC and IL7R being among the most down-regulated genes. Indeed, IL7R was the only cytokine receptor in CRLF2-rearranged B-ALL cells significantly down-regulated by JQ1 treatment. In mice xenografted with primary human CRLF2-rearranged B-ALL, JQ1 suppressed c-Myc expression and STAT5 phosphorylation and significantly prolonged survival. Thus, bromodomain inhibition is a promising therapeutic strategy for B-ALL as well as other conditions dependent on IL7R signaling.
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http://dx.doi.org/10.1182/blood-2012-02-413021DOI Listing
October 2012

A genome-wide analysis of open chromatin in human tracheal epithelial cells reveals novel candidate regulatory elements for lung function.

Thorax 2012 May 14;67(5):385-91. Epub 2011 Dec 14.

Human Molecular Genetics Program, Children's Memorial Research Center, 2300 Children's Plaza, Box 211, Chicago, IL 60614, USA.

Background: Distal cell-type-specific regulatory elements may be located at very large distances from the genes that they control and are often hidden within intergenic regions or in introns of other genes. The development of methods that enable mapping of regions of open chromatin genome wide has greatly advanced the identification and characterisation of these elements.

Methods: Here we use DNase I hypersensitivity mapping followed by deep sequencing (DNase-seq) to generate a map of open chromatin in primary human tracheal epithelial (HTE) cells and use bioinformatic approaches to characterise the distribution of these sites within the genome and with respect to gene promoters, intronic and intergenic regions.

Results: Genes with HTE-selective open chromatin at their promoters were associated with multiple pathways of epithelial function and differentiation. The data predict novel cell-type-specific regulatory elements for genes involved in HTE cell function, such as structural proteins and ion channels, and the transcription factors that may interact with them to control gene expression. Moreover, the map of open chromatin can identify the location of potentially critical regulatory elements in genome-wide association studies (GWAS) in which the strongest association is with single nucleotide polymorphisms in non-coding regions of the genome. We demonstrate its relevance to a recent GWAS that identifies modifiers of cystic fibrosis lung disease severity.

Conclusion: Since HTE cells have many functional similarities with bronchial epithelial cells and other differentiated cells in the respiratory epithelium, these data are of direct relevance to elucidating the molecular basis of normal lung function and lung disease.
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http://dx.doi.org/10.1136/thoraxjnl-2011-200880DOI Listing
May 2012
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