PRMT5 is a critical regulator of breast cancer stem cell function via Histone Methylation and FOXP1 expression

Breast cancer progression, treatment resistance, and relapse are thought to originate from a small population of tumor cells, breast cancer stem cells (BCSCs). Identification of factors critical for BCSC function is therefore vital for the development of therapies. Here, we identify the argininemethyltransferase PRMT5 as a key in vitro and in vivo regulator of BCSC proliferation and self-renewal and establish FOXP1, a winged helix/forkhead transcription factor, as a critical effector of PRMT5-induced BCSC function. Mechanistically, PRMT5 recruitment to the FOXP1 promoter facilitates H3R2me2s, SET1 recruitment, H3K4me3, and gene expression. Our findings are clinically significant, as PRMT5 depletion within established tumor xenografts or treatment of patient- derived BCSCs with a pre-clinical PRMT5 inhibitor substantially reduces BCSC numbers. Together, our findings highlight the importance of PRMT5 in BCSC maintenance and suggest that small-molecule inhibitors of PRMT5 or downstream targets could be an effective strategy eliminating this cancer-causing population

Smyd3 regulates cancer cell phenotypes and catalyzes histone H4 lysine 5 methylation

Smyd3 is a lysine methyltransferase implicated in chromatin and cancer regulation. Here we show that Smyd3 catalyzes histone H4 methylation at lysine 5 (H4K5me). This novel histone methylation mark is detected in diverse cell types and its formation is attenuated by depletion of Smyd3 protein. Further, Smyd3-driven cancer cell phenotypes require its enzymatic activity. Thus, Smyd3, via H4K5 methylation, provides a potential new link between chromatin dynamics and neoplastic disease

Targeting enhancer switching overcomes non-genetic drug resistance in acute myeloid leukaemia.

Non-genetic drug resistance is increasingly recognised in various cancers. Molecular insights into this process are lacking and it is unknown whether stable non-genetic resistance can be overcome. Using single cell RNA-sequencing of paired drug naïve and resistant AML patient samples and cellular barcoding in a unique mouse model of non-genetic resistance, here we demonstrate that transcriptional plasticity drives stable epigenetic resistance. With a CRISPR-Cas9 screen we identify regulators of enhancer function as important modulators of the resistant cell state. We show that inhibition of Lsd1 (Kdm1a) is able to overcome stable epigenetic resistance by facilitating the binding of the pioneer factor, Pu.1 and cofactor, Irf8, to nucleate new enhancers that regulate the expression of key survival genes. This enhancer switching results in the re-distribution of transcriptional co-activators, including Brd4, and provides the opportunity to disable their activity and overcome epigenetic resistance. Together these findings highlight key principles to help counteract non-genetic drug resistance

Genotoxic Stress-Induced Cyclin D1 Phosphorylation and Proteolysis Are Required for Genomic Stability▿

While mitogenic induction of cyclin D1 contributes to cell cycle progression, ubiquitin-mediated proteolysis buffers this accumulation and prevents aberrant proliferation. Because the failure to degrade cyclin D1 during S-phase triggers DNA rereplication, we have investigated cellular regulation of cyclin D1 following genotoxic stress. These data reveal that expression of cyclin D1 alleles refractory to phosphorylation- and ubiquitin-mediated degradation increase the frequency of chromatid breaks following DNA damage. Double-strand break-dependent cyclin D1 degradation requires ATM and GSK3β, which in turn mediate cyclin D1 phosphorylation. Phosphorylated cyclin D1 is targeted for proteasomal degradation after ubiquitylation by SCFFbx4-αBcrystallin. Loss of Fbx4-dependent degradation triggers radio-resistant DNA synthesis, thereby sensitizing cells to S-phase-specific chemotherapeutic intervention. These data suggest that failure to degrade cyclin D1 compromises the intra-S-phase checkpoint and suggest that cyclin D1 degradation is a vital cellular response necessary to prevent genomic instability following genotoxic insult

A Phase I/II Study to Investigate the Safety and Clinical Activity of the Protein Arginine Methyltransferase 5 Inhibitor GSK3326595 in Subjects with Myelodysplastic Syndrome and Acute Myeloid Leukemia

Background Protein arginine methyltransferase 5 (PRMT5) is the primary enzyme responsible for symmetric arginine dimethylation of multiple proteins that impact cell proliferation. Its substrates include proteins involved in mRNA splicing, signal transduction, gene transcription, and DNA repair. PRMT5 overexpression occurs in many cancers and correlates with poor prognosis. GSK3326595 is a potent, specific, and reversible inhibitor of PRMT5 that inhibits proliferation and induces cell death in a broad range of solid and hematologic tumor cell lines. It also exhibits potent anti-tumor activity in vivo in animal models, including in preclinical models of myeloid malignancies. One mechanism of action of GSK3326595 is via inhibition of cellular mRNA splicing and upregulation of tumor suppressor function. Mutations in splicing factors are frequent in myeloid malignancies (including approximately 40% of patients with myelodysplastic syndrome [MDS], and over 60% of patients with chronic myelomonocytic leukemia [CMML]), and further inhibition of mRNA splicing via GSK3326595 may lead to a synthetic lethal phenotype specifically in splicing mutant disease. Study 208809 is the first trial of a PRMT5 inhibitor in participants with myeloid malignancies. Methods Study 208809 is a Phase I/II study to evaluate the safety, tolerability, and clinical activity of GSK3326595 monotherapy in participants with relapsed and refractory MDS, CMML, and hypoproliferative acute myeloid leukemia (AML) that has evolved from an antecedent MDS. Part 1 will identify a tolerated dose and establish preliminary evidence of efficacy in this population. At the end of Part 1, if pre-specified criteria are met, then the study will be expanded with three additional Parts that will be opened in parallel. Part 2A is a Phase II randomized comparison of monotherapy GSK3326595 versus investigator's choice of best available care in participants with relapsed and refractory MDS, CMML, and hypoproliferative AML. Part 2B is a single-arm investigation of safety and efficacy of GSK3326595 plus 5-azacitidine in participants with newly diagnosed high-risk MDS. Part 2C is a single-arm investigation of the safety and efficacy of monotherapy GSK3326595 in participants with relapsed or refractory AML whose tumors harbor mutations in components of the pre-mRNA splicing machinery. All participants enrolled in this study have a diagnosis of MDS, CMML, or AML, with enrollment into each cohort as defined above. Participants are adults with adequate organ function as defined in the protocol. Prior allogeneic transplant is permitted. There are no required biomarkers for enrollment to Parts 1, 2A, and 2B, though central confirmation of pre-mRNA splicing factor mutations will be performed to stratify participants for overall analysis. Enrollment to Part 2C is limited to participants with splicing factor mutations. It is estimated that a maximum of 302 participants will be enrolled in the study, divided as follows: Approximately 41 participants in Part 1, approximately 192 participants in Part 2A, approximately 41 participants in Part 2B, and approximately 28 participants in Part 2C. In Part 1, the primary endpoint is clinical benefit rate, as defined as the percentage of participants achieving a complete remission, complete marrow remission, partial remission (PR), stable disease lasting at least 8 weeks, or hematologic improvement, as per standard criteria. In Part 2A, the primary endpoint is overall survival. In Part 2B and Part 2C, the primary endpoint is overall response rate (ORR), defined as the percentage of participants achieving a PR or better. Samples are collected to evaluate symmetric dimethylated arginine (SDMA), the enzymatic product of PRMT5. This has been demonstrated to be a pharmacodynamic marker of PRMT5 inhibition in plasma and tumor tissue. In addition, participants will be stratified based on the presence or absence of spliceosome mutations and analyzed separately to evaluate the effect of these mutations on clinical activity. As of 1 August 2019, recruitment is ongoing across six centers in the United States and Canada; ten participants have been enrolled, all into Part 1. ClinicalTrials.gov identifier: NCT03614728 Study is funded by GlaxoSmithKline Disclosures Watts: Takeda: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Bradley:AbbVie: Other: Advisory Board. Brunner:Novartis: Research Funding; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Forty Seven Inc: Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Minden:Trillium Therapetuics: Other: licensing agreement. Papadantonakis:Agios: Consultancy, Honoraria. Abedin:Actinium Pharmaceuticals: Research Funding; Pfizer Inc: Research Funding; Helsinn Healthcare: Research Funding; Agios: Honoraria; Jazz Pharmaceuticals: Honoraria. Baines:GlaxoSmithKline: Employment, Equity Ownership. Barbash:GlaxoSmithKline: Employment, Equity Ownership, Patents & Royalties, Research Funding. Gorman:GlaxoSmithKline: Employment, Equity Ownership. Kremer:GlaxoSmithKline: Employment, Equity Ownership. Borthakur:Cantargia AB: Research Funding; Eisai: Research Funding; Tetralogic Pharmaceuticals: Research Funding; Argenx: Membership on an entity's Board of Directors or advisory committees; FTC Therapeutics: Membership on an entity's Board of Directors or advisory committees; BioTheryX: Membership on an entity's Board of Directors or advisory committees; Xbiotech USA: Research Funding; Novartis: Research Funding; Oncoceutics: Research Funding; Oncoceutics, Inc.: Research Funding; PTC Therapeutics: Consultancy; BioLine Rx: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Agensys: Research Funding; AstraZeneca: Research Funding; Bayer Healthcare AG: Research Funding; BMS: Research Funding; Eli Lilly and Co.: Research Funding; NKarta: Consultancy; Cyclacel: Research Funding; GSK: Research Funding; Janssen: Research Funding; Incyte: Research Funding; AbbVie: Research Funding; Merck: Research Funding; Arvinas: Research Funding; Polaris: Research Funding; Strategia Therapeutics: Research Funding

Smyd3 regulates cancer cell phenotypes and catalyzes histone H4 lysine 5 methylation

International audienc

BET Inhibition Silences Expression of <i>MYCN</i> and <i>BCL2</i> and Induces Cytotoxicity in Neuroblastoma Tumor Models

<div><p>BET family proteins are epigenetic regulators known to control expression of genes involved in cell growth and oncogenesis. Selective inhibitors of BET proteins exhibit potent anti-proliferative activity in a number of hematologic cancer models, in part through suppression of the <i>MYC</i> oncogene and downstream Myc-driven pathways. However, little is currently known about the activity of BET inhibitors in solid tumor models, and whether down-regulation of MYC family genes contributes to sensitivity. Here we provide evidence for potent BET inhibitor activity in neuroblastoma, a pediatric solid tumor associated with a high frequency of <i>MYCN</i> amplifications. We treated a panel of neuroblastoma cell lines with a novel small molecule inhibitor of BET proteins, GSK1324726A (I-BET726), and observed potent growth inhibition and cytotoxicity in most cell lines irrespective of <i>MYCN</i> copy number or expression level. Gene expression analyses in neuroblastoma cell lines suggest a role of BET inhibition in apoptosis, signaling, and N-Myc-driven pathways, including the direct suppression of <i>BCL2</i> and <i>MYCN</i>. Reversal of <i>MYCN</i> or <i>BCL2</i> suppression reduces the potency of I-BET726-induced cytotoxicity in a cell line-specific manner; however, neither factor fully accounts for I-BET726 sensitivity. Oral administration of I-BET726 to mouse xenograft models of human neuroblastoma results in tumor growth inhibition and down-regulation <i>MYCN</i> and <i>BCL2</i> expression, suggesting a potential role for these genes in tumor growth. Taken together, our data highlight the potential of BET inhibitors as novel therapeutics for neuroblastoma, and suggest that sensitivity is driven by pleiotropic effects on cell growth and apoptotic pathways in a context-specific manner.</p> </div