Oncogenic Notch Research Articles

Preclinical Testing Of a PI3K Inhibitor In T Lineage Leukemia: Target Validation and Notch1/Myc Down-Regulation In Drug Resistant Clones

Mutations that deregulate Notch1 and Ras/PI3K/Akt signaling are common in T-ALL and often coexist. Thus, inhibiting these pathways alone and in combination has been advocated as a rational therapeutic strategy. GDC-0941 is a pan-PI3K inhibitor that is advancing in clinical development that we evaluated for efficacy and mechanisms of drug resistance in T-ALL cell lines and primary murine T-ALLs. Cell lines are uniformly sensitive to GDC-0941; however gradual dose escalation results in resistant lines. By contrast, primary leukemia cells display variable in vivo sensitivity to treatment with GDC-0941 +/- a MEK inhibitor. Importantly, mice invariably relapse with drug resistant clones. A majority of GDC-0941-resistant T-ALL cell lines and primary leukemias unexpectedly showed reduced levels of activated Notch1 protein, down-regulate many Notch1 target genes including Myc, and display cross-resistance to gamma secretase inhibitors (GSIs). In multiple cases, Notch1 mutations that were present in drug-sensitive parental leukemias were absent at relapse. Importantly, resistant clones that emerge both in vitro and in vivo up-regulate PI3K signaling indicating an “on pathway” mechanism of resistance. Consistent with these data, inhibition of Notch1 signaling promotes GDC-0941 resistance and enhances PI3K signaling, whereas expression of activated Notch1 increases the GDC-0941 sensitivity of mouse and human T-ALL cell lines. Thus, oncogenic Notch1 mutations that promote clonal outgrowth during malignant transformation unexpectedly undergo negative selection during treatment with GDC-0941. Together, these in vivo studies: (1) validate PI3K as an important therapeutic target in T-ALL; (2) demonstrate that active Notch1 and elevated Myc expression are dispensable for T-ALL growth in vivo; and, (3) indicate that therapeutic PI3K inhibition selects for the outgrowth of leukemia cells with reduced Notch1 signaling. Importantly, our data also raise the possibility that simultaneously administering Notch1 and PI3K inhibitors will accelerate drug resistance in T-ALL, and support alternative approaches for deploying combination regimens against these dominant oncogenic “driver” pathways. Disclosures:Lee:Genentech: Employment. Aster:Cell Signaling Technology: Consultancy; Merck, Inc.: Research Funding; Pfizer, Inc.: Research Funding; Genentech, Inc.: Honoraria. Sampath:Genentech: Employment, Equity Ownership.

Abstract PR08: Loss of oncogenic Notch1 signaling contributes to PI3 kinase inhibitor resistance in T lineage leukemia.

Abstract T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer for which current therapies are toxic and frequently ineffective. Mutations that activate the Notch1 and Ras/PI3K/Akt signaling pathways are common in T-ALL and often coexist. Thus, inhibiting these pathways alone and in combination is a rational therapeutic strategy. Notch1 inhibition with a gamma-secretase inhibitor (GSI) was recently evaluated in patients with disappointing results. PI3K inhibitors are just entering Phase I clinical trials. GDC-0941 is a potent PI3K inhibitor that is currently advancing in clinical development that we evaluated for efficacy and mechanisms of drug resistance both in cell lines and primary murine T-ALLs. Cell lines are uniformly sensitive to GDC-0941, however gradual dose escalation results in resistant lines. In vivo, GDC-0941 is active against primary T-ALLs, but treated mice invariably relapse with drug resistant clones. Unexpectedly, a majority of GDC-0941-resistant cell lines and primary leukemias showed reduced levels of activated Notch1 protein, down-regulate many Notch1 target genes, and display cross-resistance to γ secretase inhibitors (GSIs). In multiple cases, Notch1 mutations that were present at enrollment were absent at relapse. Importantly, resistant clones that emerge both in vitro and in vivo up-regulate PI3K signaling indicating an “on pathway” mechanism of resistance. Consistent with these data, inhibition of Notch1 signaling promotes GDC-0941 resistance and enhances PI3K signaling, whereas expression of activated Notch1 increases the GDC-0941 sensitivity of mouse and human T-ALL cell lines. Thus, oncogenic Notch1 mutations that promote clonal outgrowth during malignant transformation unexpectedly undergo negative selection during treatment with GDC-0941. These studies validate PI3K as an important therapeutic target in T-ALL and raise the unexpected possibility that administering Notch1 and PI3K inhibitors in combination will accelerate drug resistance. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):PR08. Citation Format: Monique Dail. Loss of oncogenic Notch1 signaling contributes to PI3 kinase inhibitor resistance in T lineage leukemia. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr PR08.

Abstract A226: Identification of new synergistic compounds for the treatment of NOTCH-driven T-ALL.

Abstract T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy that accounts for 15% of childhood and 25% of adult ALLs. Constitutive activation of NOTCH signaling as result of activating mutations in the NOTCH1 gene is a hallmark of this disease and small molecule gamma-secretase inhibitors, which effectively block activation of the NOTCH1 receptor, have been proposed as targeted therapy. However, the progress of NOTCH1-blocking agents such as in the clinic has been limited. Here we hypothesized that detailed transcriptional profiling of T-ALL lymphoblasts upon inhibition of NOTCH1 signaling would uncover major effector pathways downstream of NOTCH1. Moreover, we proposed that these signatures would facilitate the identification of new drugs and drug combinations for the treatment of T-ALL. Gene expression profiling of NOTCH1 induced leukemias treated with DBZ, a highly active gamma-secretase inhibitor, identified numerous genes regulated by NOTCH1 in human leukemia. Notably these signatures were enriched in NOTCH1 direct target genes such as Hes1 and revealed a prominent role of NOTCH signaling in the control of cellular metabolic pathways. Following on these results we performed Connectiviy map analysis to identify drugs whose transcriptional effects could antagonize those of oncogenic NOTCH1 in human leukemia. This analysis identified HDAC inhibitors, anti-psychotic agents, anti-malarials and compounds targeting the PI3K and NFKB signaling pathways. Detailed analysis of the effects of these drugs alone and in combination with DBZ demonstrated strong antileukemic activity and strong synergism when combined with inhibition of NOTCH signaling with a gamma-secretase inhibitor. Moreover, biochemical and transcriptional profiling of these drugs identifies agents with unique and related mechanisms of action. Overall these results identify new antileukemic drugs with strongly synergistic activity in combination with NOTCH1 inhibition for the treatment of T-ALL Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A226. Citation Format: Marta Sanchez Martin, Alberto Ambesi, Daniel Herranz, Adolfo Ferrando. Identification of new synergistic compounds for the treatment of NOTCH-driven T-ALL. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A226.

Chemokine receptors as novel targets of the oncogene Notch1 in acute lymphoblastic leukemia.

7060 Background: Malignant cells from different cancers express different profiles of chemokine receptors (CKR). Their presence may influence site-specific spread of tumor cells, by enabling them to respond to chemokine gradient, and may increase cell sensibility to chemokine mediated proliferative and anti-apoptotic stimuli. Notch ability to positively regulate CKR has been reported: stimulation of Pax5-/- pre-B cells with the Notch ligand Delta-1 results in induction of transcripts for CCR4, CCR8 and CXCR 6; the Delta-1-dependent regulation of Langerhans cell development includes induction of CCR6 expression resulting in the activation of chemotactic response to MIP-1a; Notch controls CCR7 signaling a regulator of CNS infiltration in T-acute lymphoblastic leukemia (T-ALL). Methods: This work aims to explore the correlation between the activation of the Notch oncogenic pathway in T-ALL and multiple myeloma (MM) cells and the aberrant expression CKR. Human T-ALL cell lines were treated with the Notch activation inhibitor, DAPT, or with a potent inhibitor of the Notch target, C-MYC, and evaluated the expression and functions of CCR9, CCR5, and CXCR4. Results: Treatment of human T-ALL and MM cell lines with pharmacologic inhibitors of Notch receptor activation produced a significant reduction of CCR9, CCR5 and CXCR4 expression, at both mRNA and protein levels. Results were confirmed by chemotaxis and survival assays. We identified the product of C-MYC gene as a possible mediator of Notch effect in regulating CKR networks in T-ALL and MM. Conclusions: These results suggest that Notch receptors play a previously unknown role in cancer progression and metastasis, by maintaining the expression levels of CKR. In conclusion, the identification of the potential axis Notch/CKR could have a prognostic value and provide the rationale for a tailored approach, since both Notch and CKR are targeted by emerging drugs.

Abstract 4448: Notch1 inactivation contributes to PI3Ki resistance in T-ALL.

Abstract Tyrosine kinases inhibitors induce genotype-specific regression in advanced human cancers. However, these responses are almost invariably transient and patients ultimately relapse due to outgrowth of drug-resistant clones. Thus, increased knowledge of the mechanisms underlying de novo and acquired resistance is essential for enhancing clinical efficacy. T cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer for which current therapies are toxic and frequently ineffective. Mutations in genes encoding components of the Notch1 and Ras/PI3K/PTEN/Akt signaling networks are prevalent in T-ALL and frequently coexist in individual patients. Thus, inhibiting these pathways alone and in combination is a rational therapeutic strategy. Notch1 inhibition with a γ-secretase inhibitor (GSI) was recently evaluated in refractory T-ALL, with disappointing results that may have been due to dose-limiting gastrointestinal toxicity. We are not aware of clinical trials of Ras/PI3K/Akt/mTOR pathway inhibitors in T-ALL. Retroviral insertional mutagenesis (RIM) in mice is a robust strategy for modeling both the clonal heterogeneity that exists within individual tumors and the genetic diversity found across a population of patients with the same cancer. We generated transplantable T-ALLs by performing RIM in mice expressing oncogenic KrasG12D from its endogenous genetic locus (Mx1-Cre, KrasG12D) and in wild-type (WT) littermates. These aggressive multi-step cancers are characterized by recurring viral integrations in known oncogenes such as Ikzf1 and late occurring acquired Notch1 PEST domain mutations. We have extensively investigated patterns of response and resistance to targeted inhibitors of PI3K (PI3Ki) and MEK (MEKi) in this system. Whereas KrasWT T-ALLs respond to either PI3Ki or to a combination regimen that also include a MEKi, KrasG12D T-ALLs are largely refractory to PI3Ki, but are sensitive to the MEKi + PI3Ki combination. T-ALLs invariably relapsed despite ongoing treatment, and we verified phenotypic drug resistance in relapse leukemias by transplanting and retreating them in vivo. We unexpectedly identified multiple independent PI3Ki resistant T-ALLs with markedly reduced levels of activated Notch1, including some in which Notch1 mutations that were present at enrollment were absent at relapse. Expression of activated Notch1 increases the sensitivity of mouse and human T-ALL cells to a PI3Ki, and loss of activated Notch promotes resistance and enhances PI3K signaling. Thus, oncogenic Notch1 mutations that promote outgrowth during transformation unexpectedly “switch” to become deleterious during in vivo treatment with a PI3Ki. These data suggest that aberrant Ras/PI3K signaling plays a dominant role in T lineage leukemogenesis and also raise the unexpected possibility that administering Notch1 and PI3K inhibitors sequentially or in combination might inadvertently promote resistance. Citation Format: Monique Dail, Jason Wong, Daniel O'Connor, Joy Nakitandwe, Shann-Ching Chen, Jessica Lawrence, James R. Downing, Deepak Sampath, Kevin Shannon. Notch1 inactivation contributes to PI3Ki resistance in T-ALL. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4448. doi:10.1158/1538-7445.AM2013-4448

Selective Blockade of Transport via SERCA Inhibition: The Answer for Oncogenic Forms of Notch?

NOTCH1, which is frequently mutated in T cell acute lymphoblastic leukemia, has been an elusive therapeutic target. In this issue of Cancer Cell, Roti and colleagues demonstrate that inhibiting SERCA calcium pumps preferentially impairs the maturation of the most common class of oncogenic Notch1 mutants, thus uncovering a potential therapeutic avenue.

Distinct TCR signaling pathways drive proliferation and cytokine production in T cells

SummaryThe physiological basis and mechanistic requirement for the high immunoreceptor tyrosine activation motifs (ITAM) multiplicity of the T cell receptor (TCR)-CD3 complex remains obscure. Here we show that while low TCR-CD3 ITAM multiplicity is sufficient to engage canonical TCR-induced signaling events that lead to cytokine secretion, high TCR-CD3 ITAM multiplicity is required for TCR-driven proliferation. This is dependent on compact immunological synapse formation, interaction of the adaptor Vav1 with phosphorylated CD3 ITAMs to mediate Notch1 recruitment and activation and ultimately c-Myc-induced proliferation. Analogous mechanistic events are also required to drive proliferation in response to weak peptide agonists. Thus, the TCR-driven pathways that initiate cytokine secretion and proliferation are separable and co-ordinated by the multiplicity of phosphorylated TCR-CD3 ITAMs.

Nature of nontargeted radiation effects observed during fractionated irradiation-induced thymic lymphomagenesis in mice

Changes in the thymic microenvironment lead to radiation-induced thymic lymphomagenesis, but the phenomena are not fully understood. Here we show that radiation-induced chromosomal instability and bystander effects occur in thymocytes and are involved in lymphomagenesis in C57BL/6 mice that have been irradiated four times with 1.8-Gy γ-rays. Reactive oxygen species (ROS) were generated in descendants of irradiated thymocytes during recovery from radiation-induced thymic atrophy. Concomitantly, descendants of irradiated thymocytes manifested DNA lesions as revealed by γ-H2AX foci, chromosomal instability, aneuploidy with trisomy 15 and bystander effects on chromosomal aberration induction in co-cultured ROS-sensitive mutant cells, suggesting that the delayed generation of ROS is a primary cause of these phenomena. Abolishing the bystander effect of post-irradiation thymocytes by superoxide dismutase and catalase supports ROS involvement. Chromosomal instability in thymocytes resulted in the generation of abnormal cell clones bearing trisomy 15 and aberrant karyotypes in the thymus. The emergence of thymic lymphomas from the thymocyte population containing abnormal cell clones indicated that clones with trisomy 15 and altered karyotypes were prelymphoma cells with the potential to develop into thymic lymphomas. The oncogene Notch1 was rearranged after the prelymphoma cells were established. Thus, delayed nontargeted radiation effects drive thymic lymphomagenesis through the induction of characteristic changes in intrathymic immature T cells and the generation of prelymphoma cells.

The NOTCH signaling pathway: role in the pathogenesis of T-cell acute lymphoblastic leukemia and implication for therapy

T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) is characterized by aberrant activation of NOTCH1 in over 60% of T-ALL cases. The high prevalence of activating NOTCH1 mutations highlights the critical role of NOTCH signaling in the pathogenesis of this disease and has prompted the development of therapeutic approaches targeting the NOTCH signaling pathway. Small molecule gamma secretase inhibitors (GSIs) can effectively inhibit oncogenic NOTCH1 and are in clinical testing for the treatment of T-ALL. Treatment with GSIs and glucocorticoids are strongly synergistic and may overcome the gastrointestinal toxicity associated with systemic inhibition of the NOTCH pathway. In addition, emerging new anti-NOTCH1 therapies include selective inhibition of NOTCH1 with anti-NOTCH1 antibodies and stapled peptides targeting the NOTCH transcriptional complex in the nucleus.

Kruppel-Like Factor, Klf9, Promotes Proliferation of Notch-Independent Precursor T-Cell Lymphoblastic Lymphomas

AbstractAbstract 3496Notch1 signaling is required at multiple stages of normal T-lymphocyte development. Notch1 is a transmembrane receptor that is physiologically activated when Notch ligands induce conformational changes that allow Notch1 cleavage by the intramembranous γ-secretase complex, releasing active intracellular Notch1 (ICN1) fragment from the plasma membrane. Activating NOTCH1 mutations are very frequent in human and mouse T-cell lymphoblastic leukemia/lymphoma (T-LL). Typically, these mutations promote ligand-independent Notch1 cleavage by γ-secretase or increase ICN1 stability by truncating the C-terminal PEST domain. Understandably, much effort has focused on elucidating mechanisms of normal and oncogenic Notch1 signaling. However, some studies suggest that the absence of NOTCH1 mutations portends a worse prognosis for human T-LL. Therefore, we set out to define signals that promote proliferation and survival of T-LL cells lacking activated Notch1. We used Western blotting to detect γ-secretase cleaved ICN1 protein in a cohort of 35 primary T-LLs that developed spontaneously in mice lacking the Ataxia telangiectasia mutated (Atm) tumor suppressor. We identified 3 ICN1 subgroups: 63% expressed PEST-truncated ICN1 (T-ICN1); 17% expressed non-truncated ICN1 (NT-ICN1); and 20% had undetectable ICN1 (UD-ICN1), most lacked Notch1 mRNA. We confirmed the difference in Notch transcriptional activity and functional dependence between the UD-ICN1 and T-ICN1 subgroups and then compared their gene expression profiles to define pathways unique to the UD-ICN1 group. Gene set enrichment analyses revealed that UD-ICN1 T-LLs expressed higher levels of Klf9 and other transcription factors associated with a highly proliferative stage of normal T-cell development. siRNA knock-down studies demonstrated that Klf9 promoted proliferation of UD-ICN1 but not T-ICN1 T-LL cells. Collectively, these data demonstrate that Klf9 can regulate proliferation of Notch-independent T-LLs and suggest that Klf9 may provide a novel therapeutic target for human T-LLs lacking activating NOTCH1 mutations. Disclosures:No relevant conflicts of interest to declare.

Fetal Vs. Adult Hematopoietic Progenitors Respond Differently to NOTCH1: Implications for Pediatric Vs. Adult T-ALL.

AbstractAbstract 2381T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy of T-cell progenitors which affects both children and adults. Whereas pediatric T-ALL is curable in 80–90% of cases, only 40% of adults with T-ALL survive beyond 5 years. Fetal liver and adult bone marrow-derived hematopoietic stem/progenitor cells (HSPCs) are known to differ in terms of their gene expression programs and functional properties. Despite this work, the extent to which differential programming of fetal and adult HSPCs may impact the biology of their respective leukemias in children and adults remains unexplored.NOTCH1 is a prominent oncogene in T-ALL and activated by mutation in over 50% of cases. The retroviral NOTCH1 mouse bone marrow transplant model of T-ALL is well established; however, most investigators use 8–12 week-old adult mice as bone marrow donors for these experiments and thus these studies could be interpreted as having modeled adult disease. In order to explore the possibility that fetal program HSPCs would more accurately model pediatric disease, we transduced lineage-negative fetal liver HSPCs with activated NOTCH1 (ΔE) retrovirus, transplanted them into syngeneic (C57BL/6) recipients, and compared the behavior of the resulting leukemias to those generated from lineage-negative 8-week-old adult bone marrow HSPCs.Primary transplant recipient mice developed nearly identical T-ALL disease in terms of penetrance, latency, disease distribution/burden, and immunophenotype. Serial transplantation of these leukemias into secondary recipients, however, revealed stark differences in that whereas “adult” leukemias were readily transplantable, “fetal” leukemias were largely non-transplantable. In order to quantitate leukemia-initiating cell (LIC) frequencies in these two situations, we performed secondary transplants into highly permissive, immunodeficient (NOD/Scid/Il2rg−/−) recipients at limiting dilution and observed fetal leukemias to exhibit 500-fold lower LIC activity than adult leukemias (1 in ∼4500 cells vs. 1 in ∼9 cells, respectively).To identify potential mechanisms that might underlie this difference in LIC activity, we compared the behaviors of fetal liver vs. adult bone marrow-derived HSPCs shortly after transduction with NOTCH1(ΔE) virus. Interestingly, NOTCH1 induced fetal HSPCs to cycle rapidly whereas adult HSPCs were largely quiescent. We also noted that non-transduced cells in fetal HSPC cultures were also cycling rapidly, and through a series of fetal/adult mixing and conditioned media experiments, we determined that NOTCH1 induces an autocrine IGF1 signaling circuit in fetal, but not adult HSPCs. This observation was also confirmed to hold true for CD34+ human cord blood vs. adult bone marrow HSPCs. Expression profiling/qRT-PCR and chromatin immunoprecipitation (ChIP) studies further revealed NOTCH1 to induce IGF1 transcription and altered chromatin structure (increased H3K4me3 and decreased H3K27me3 marks) specifically in fetal, but not adult HSPCs.These findings suggest that developmental stage-specific programming in fetal vs. adult progenitors underlies their differential responses to oncogenic NOTCH1 signaling, and also the biological aggressiveness of resulting leukemias. Therapeutic targeting of adult-specific pathways may thus achieve improved clinical responses in adults with T-ALL and perhaps also the minority of pediatric patients with more aggressive, possibly “adult-like” disease. Disclosures:No relevant conflicts of interest to declare.

Loss of the Par3 Polarity Protein Promotes Breast Tumorigenesis and Metastasis

Loss of epithelial organization is a hallmark of carcinomas, but whether polarity regulates tumor growth and metastasis is poorly understood. To address this issue, we depleted the Par3 polarity gene by RNAi in combination with oncogenic Notch or Ras(61L) expression in the murine mammary gland. Par3 silencing dramatically reduced tumor latency in both models and produced invasive and metastatic tumors that retained epithelial marker expression. Par3 depletion was associated with induction of MMP9, destruction of the extracellular matrix, and invasion, all mediated by atypical PKC-dependant JAK/Stat3 activation. Importantly, Par3 expression is significantly reduced in human breast cancers, which correlates with active aPKC and Stat3. These data identify Par3 as a regulator of signaling pathways relevant to invasive breast cancer.

DDX5 is a positive regulator of oncogenic NOTCH1 signaling in T cell acute lymphoblastic leukemia

Notch signaling is a highly conserved cell-cell communication pathway regulating normal development and tissue homeostasis. Aberrant Notch signaling represents an important oncogenic mechanism for T cell acute lymphoblastic leukemia (T-ALL), an aggressive subset of the most common malignant childhood cancer ALL. Therefore, understanding the molecular regulation of Notch signaling is critical to identify new approaches to block aberrant Notch oncogenic activity. The family of three MAML transcriptional coactivators is crucial for Notch signaling activation. The prototypic member MAML1 is the major coactivator that regulates Notch oncogenic activities in leukemic cells. However, the molecular basis underlying MAML1 coactivator function that contributes to Notch signaling remains unclear. In this study, we performed proteomic studies and identified DDX5, an ATP-dependent DEAD-box RNA helicase, as a component of the MAML1 protein complex. DDX5 interacts with MAML1 in vitro and in vivo, and is associated with the endogenous NOTCH1 transcription activation complex in human T-ALL leukemic cells. Lentivirus-mediated short-hairpin RNA knock-down of DDX5 resulted in decreased expression of Notch target genes, reduced cell proliferation and increased apoptosis in cultured human leukemic cells with constitutive activation of Notch signaling. Also, DDX5 depletion inhibited the growth of human leukemia xenograft in nude mice. Moreover, DDX5 is highly expressed in primary human T-ALL leukemic cells based on the analyses of Oncomine and GEO databases, and Immunohistochemical staining. Our overall findings revealed a critical role of DDX5 in promoting efficient Notch-mediated transcription in leukemic cells, suggesting that DDX5 might be critical for NOTCH1-mediated T-ALL pathogenesis and thus is a potential new target for modulating the Notch signaling in leukemia.

C. elegans FOG-3/Tob can either promote or inhibit germline proliferation, depending on gene dosage and genetic context.

Vertebrate Tob/BTG proteins inhibit cell proliferation when overexpressed in tissue culture cells, and they can function as tumor suppressors in mice. The single Caenorhabditis elegans Tob/BTG ortholog, FOG-3, by contrast, was identified from its loss-of-function phenotype as a regulator of sperm fate specification. Here we report that FOG-3 also regulates proliferation in the germline tissue. We first demonstrate that FOG-3 is a positive regulator of germline proliferation. Thus, fog-3 null mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 null alleles. A similar decrease also occurred in fog-3/+ heterozygotes, again for both fog-3 alleles, revealing a haplo-insufficient effect on proliferation. Therefore, FOG-3 normally promotes proliferation, and two copies of the fog-3 gene are required for this function. We next overexpressed FOG-3 by removal of FBF, the collective term for FBF-1 and FBF-2, two nearly identical PUF RNA-binding proteins. We find that overexpressed FOG-3 blocks proliferation in fbf-1 fbf-2 mutants: whereas germ cells stop dividing and instead differentiate in fbf-1 fbf-2 double mutants, they continue to proliferate in fog-3; fbf-1 fbf-2 triple mutants. Therefore, like its vertebrate Tob/BTG cousins, overexpressed FOG-3 is “antiproliferative”. Indeed, some fog-3; fbf-1 fbf-2 mutants possess small tumors, suggesting that FOG-3 can act as a tumor suppressor. Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations. A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore this FOG-3 tumor-promoting effect is context-dependent. We conclude that FOG-3 can either promote or inhibit proliferation in a manner that is sensitive to both genetic context and gene dosage. The discovery of these FOG-3 effects on proliferation has implications for our understanding of vertebrate Tob/BTG proteins and their influence on normal development and tumorigenesis.

Berry anthocyanidins synergistically suppress growth and invasive potential of human non-small-cell lung cancer cells

Berry anthocyanidins (cyanidin, malvidin, peonidin, petunidin and delphinidin) have increasingly been explored for their anticancer effects; however, their combinatorial effects as a mixture, as present in blueberry, bilberry and Indian blackberry (‘Jamun’) remain untested. In this study, we demonstrate for the first time that the combination of suboptimal concentrations of equimolar anthocyanidins synergistically inhibited growth of two aggressive non-small-cell lung cancer cell lines, with minimal effects on non-tumorigenic cell viability. The induction of cell-cycle arrest, apoptosis and suppression of NSCLC cell invasion and migration were also significantly greater with the mixture than individual anthocyanidins. The superior effects of the combinatorial treatment presumably resulted from its effects on the oncogenic Notch and WNT pathways and their downstream targets (β-catenin, c-myc, cyclin D1, cyclin B1, pERK, MMP9 and VEGF proteins), enhanced cleavage of the apoptotic mediators Bcl2 and PARP and enhanced inhibition of TNFα-induced NF-kappa B activation. In vivo, both the native mixture of anthocyanidins from bilberry (0.5mg/mouse) and the most potent anthocyanidin, delphinidin (1.5mg/mouse) significantly inhibited the growth of H1299 xenografts in nude miceby ≈60%. Notably, the effective dose of delphinidin in the anthocyanidin mixture was 8-fold lower than delphinidin alone, further emphasizing synergism. Our results thus demonstrate therapeutic potential of berries rich in this mixture of diverse anthocyanidins for non-small-cell lung cancer treatment and to prevent its future recurrence and metastasis.

SOX2 Gene Regulates the Transcriptional Network of Oncogenes and Affects Tumorigenesis of Human Lung Cancer Cells

Recent studies demonstrated that cancer stem cells (CSCs) have higher tumorigenesis properties than those of differentiated cancer cells and that transcriptional factor-SOX2 plays a vital role in maintaining the unique properties of CSCs; however, the function and underlying mechanism of SOX2 in carcinogenesis of lung cancer are still elusive. This study applied immunohistochemistry to analyze the expression of SOX2 in human lung tissues of normal individuals as well as patients with adenocarcinoma, squamous cell carcinoma, and large cell and small cell carcinoma and demonstrated specific overexpression of SOX2 in all types of lung cancer tissues. This finding supports the notion that SOX2 contributes to the tumorigenesis of lung cancer cells and can be used as a diagnostic probe. In addition, obviously higher expression of oncogenes c-MYC, WNT1, WNT2, and NOTCH1 was detected in side population (SP) cells than in non-side population (NSP) cells of human lung adenocarcinoma cell line-A549, revealing a possible mechanism for the tenacious tumorigenic potential of CSCs. To further elucidate the function of SOX2 in tumorigenesis of cancer cells, A549 cells were established with expression of luciferase and doxycycline-inducible shRNA targeting SOX2. We found silencing of SOX2 gene reduces the tumorigenic property of A549 cells with attenuated expression of c-MYC, WNT1, WNT2, and NOTCH1 in xenografted NOD/SCID mice. By using the RNA-Seq method, an additional 246 target cancer genes of SOX2 were revealed. These results present evidence that SOX2 may regulate the expression of oncogenes in CSCs to promote the development of human lung cancer.

Notch-mediated repression of miR-223 contributes to IGF1R regulation in T-ALL

To identify microRNAs regulated by oncogenic Notch signaling, we performed microarray-based miRNA profiling of T-cell acute lymphoblastic leukemia (T-ALL) cells before and after treatment with γ-secretase inhibitor (GSI) to block Notch signaling. We show miR-223 levels increase after GSI treatment suggesting that active Notch signaling represses miR-223 expression. We also demonstrate that insulin-like growth factor-1 receptor (IGF1R) is regulated by miR-223 in this context, but observe no apparent effects on cell growth by overexpression or knock-down of miR-223 alone. We conclude that miR-223 contributes to IGF1R regulation, but may act in concert with other genes and/or microRNAs to alter T-ALL biology.

Genetic inactivation of the polycomb repressive complex 2 in T cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an immature hematopoietic malignancy driven mainly by oncogenic activation of NOTCH1 signaling1. In this study we report the presence of loss-of-function mutations and deletions of EZH2 and SUZ12 genes, encoding critical components of the Polycomb Repressive Complex 2 (PRC2) complex2,3, in 25% of T-ALLs. To further study the role of the PRC2 complex in T-ALL, we used NOTCH1-induced animal models of the disease, as well as human T-ALL samples, and combined locus-specific and global analysis of NOTCH1-driven epigenetic changes. These studies demonstrated that activation of NOTCH1 specifically induces loss of the repressive mark lysine-27 tri-methylation of histone 3 (H3K27me3)4 by antagonizing the activity of the Polycomb Repressive Complex 2 (PRC2) complex. These studies demonstrate a tumor suppressor role for the PRC2 complex in human leukemia and suggest a hitherto unrecognized dynamic interplay between oncogenic NOTCH1 and PRC2 function for the regulation of gene expression and cell transformation.

ETV6 Is An Early T-Cell Progenitor (ETP) Specific Tumor Suppressor Gene in Adult T-ALL

Abstract 406T-cell acute lymphoblastic leukemia (T-ALL) is a heterogeneous disease in which genetic lesions coordinately affect cell proliferation, differentiation and survival of thymocytes. Although pediatric T-ALL has been extensively studied on the genomic level during the last decade, large scale genomic studies in adult T-ALL are sparse. Importantly, significant differences in treatment outcome are present between pediatric and adult T-ALL.Here we performed integrative analysis of gene expression, copy number alterations and mutation analysis on 58 adult T-ALL samples treated in the Eastern Cooperative Oncology Group (ECOG) E2993 protocol. Unsupervised and consensus clustering of microarray gene expression data in this series revealed the presence of 2 stable gene expression clusters resembling immature/ETP (n=30) and typical (n=28) T-ALL gene signatures. Indeed, gene set enrichment analysis (GSEA) confirmed that our ETP/immature adult T-ALL signature closely resembled the previously published ETP profiles. In this adult patient cohort, the immature/ETP patient samples were associated with poor outcome (5 year OS 36% for ETP and 58% for non ETP TALL, P=0.088). Additional supervised analyses revealed differential expression of ERAP2, a gene involved in the processing of MHC peptides, between early relapse and long time survivor adult T-ALL patients. Consistently low ERAP2 expression was associated poor prognosis in adult T-ALL (OS 26%, 36% and 78% for 1st 2nd and 3rd terciles respectively, P=0.016). In addition, absence of TCR gamma deletion (p=0.013) as well as the absence of biallelic CDKN2A/CDKN2B deletion (p=0.009) were shown to be poor prognostic markers in adult T-ALL.To gain additional insight in the biology of adult ETP T-ALL, we performed GSEA analysis using the immature/ETP gene expression profiles. This analysis revealed that the adult ETP T-ALL signature is more closely related to acute myeloid leukemia (AML) profiles as compared to ALL signatures. Given this, we hypothesized that myeloid specific genetic alterations might be uniquely present in ETP adult T-ALL. Mutation analysis of AML oncogenes and tumor suppressor genes revealed the presence of myeloid mutations targeting IDH1, IDH2, DNMT3A, FLT3 and N-RAS in 13/30 (43%) of adult ETP T-ALL cases, whereas only 1/28 (3.5%) typical adult T-ALL showed a mutation in N-RAS. Although these ETP adult T-ALL samples seem to have myeloid properties, they still retain T-lymphoid characteristics including activational NOTCH1 mutations in 12/30 (40%) of ETP adult T-ALLs. Of note, the myeloid specific genetic alterations were preferentially present in NOTCH1 wild type ETP adult T-ALL samples.Next, we used a systems biology approach to identify master regulators that might be able to drive the ETP signature identified in adult T-ALL. For this, we interrogated a T-ALL interactome that was constructed from gene expression profiles of 228 human T-ALL samples. This master regulator analysis identified MN1 as the key transcription factor driving the ETP signature. The MN1 gene was initially identified as fusion partner of TEL (ETV6) in patients with AML. Notably, MN1-TEL expression in multipotent progenitors induces both AML and T-ALL and mutation analysis of ETV6 in adult T-ALL revealed the presence of 10 ETV6 mutants (9 frameshift and 1 splice site mutation) in adult T-ALL. Analysis of bone marrow remission genomic DNA confirmed the somatic origin of ETV6 mutations (3 frameshift and 1 splice site) in each of the 4 patient samples with available material. Most notably, ETV6 mutations were exclusively present in the ETP subtype of adult T-ALL. In addition, 8/10 (80%) of ETV6 mutant ETP T-ALL cases were characterized mutations in NOTCH1, suggesting a specific interaction between the oncogenic NOTCH1 programs and the mutational loss of ETV6 in early T-cell transformation.In conclusion, our integrative genomic analyses in adult T-ALL unraveled a high prevalence of immature/early T-cell progenitor (ETP) T-ALLs, associates the pathogenesis of ETP-TALL with myeloid mutations and identifies ETV6 truncating alleles as the first ETP specific gene mutation that strongly interact with NOTCH1 in T-cell transformation. Disclosures:No relevant conflicts of interest to declare.

STAT3 Is Required for Notch-Induced Leukemogenesis, and Functions As a Critical Survival Effector in T-Cell Leukemia

Abstract 920The disruption of main signaling mediators of critical leukemia cell functions represents the most promising approach for the development of more effective targeted therapies for acute lymphoblastic leukemia (ALL). Increasing evidence suggests an important combinatorial role for cell autonomous, epigenetic and extrinsic factors in tumorigenesis and tumor progression. However, little is known on how oncogenic and microenvironmental signals are integrated within leukemia T-cells and how they influence T-cell leukemogenesis. Our studies in patients’ leukemia T-cells showed that oncogenic Notch enhances their fitness by regulating the transcription of IL-7Rα, thus increasing the sensitivity of leukemia cells to IL-7, which triggers survival and mitogenic pathways. Interestingly, analysis of the Notch1/CBF-1 complex regulating IL7-Rα transcription show that it contains STAT3, but not STAT5, the main STAT molecule implicated in lymphoid cell signaling. Further analyses showed that STAT3 signaling is active in patients’ T-ALL specimens and in leukemia cells from mice with Notch-induced leukemia. We observed that IL-7 signaling triggers STAT3 phosphorylation and transcriptional activity, regulating the expression of the STAT3 target genes Bcl-xL, survivin, Cyclin D3 and miR-21.We then performed studies using a genetic model of conditional STAT3 deletion in the hematopoietic system. We observed that STAT3 loss-of-function markedly decreased the response of T-lineage cells (including thymocytes) to IL-7 stimulation, even if these cells exhibit functional STAT5 signaling. Importantly, in comparison to wild-type animals, STAT3-null mice did not exhibit defects in common lymphoid progenitors (CLP) in the bone marrow (BM) or in T-cell development, namely on DN thymocyte subsets. Also, no changes were observed in STAT3-null mice in the surface expression or transcriptional levels of IL-7Rα in CLP or thymocytes. To investigate the putative role of STAT3 in leukemia development, we performed the Notch-induced tumor model using BM primitive hematopoietic cells from STAT3-null mice, which could be effectively transduced with the constitutively-active Notch (ICN) construct. We observed that STAT3 deletion significantly inhibited the development of T-cell leukemia, with animals surviving for long periods without evidence of leukemia. Importantly, this was not due to defects in homing or in early engraftment of transplanted cells, which was further documented using intravital microscopy.Finally, pre-clinical studies were performed to evaluate the therapeutic potential of STAT3 pharmacological targeting on leukemia T-cells. STAT3 blockade by the selective inhibitors STATTIC or S3I-201 or the JAK2 inhibitor WP-1066 abrogated STAT3 phosphorylation, inhibiting the transcription of Bcl-xL and Survivin. This inhibition resulted in marked inhibition of leukemia T-cells, which was observed in primary T-ALL cells, in a IL-7-dependent T-ALL line and in leukemia cells from mice carrying ICN-induced leukemia. Mechanistically, we observed that STAT3 blockade results in and massive leukemia cell apoptosis, which is associated with activation of the pro-apoptotic p53(Ser46), and PARP cleavage. Also, STAT3 silencing by shRNA prevented leukemia cell expansion. Strong anti-leukemia synergism was observed between low doses of STATTIC and the frontline therapeutic drug Dexamethasone, or selective PI3K or mTOR inhibitors.In summary, our studies indicate that STAT3 signaling plays an important role in the integration of IL-7 and Notch signals in T-cell leukemia, and unveiled an unexpected role for STAT3 in T-cell leukemogenesis. Finally, our work suggests that the targeted disruption of STAT3 represents a valid therapeutic approach in this cancer. Disclosures:No relevant conflicts of interest to declare.