Spatiotemporally resolved colorectal oncogenesis in mini-colons ex vivo

Three-dimensional organoid culture technologies have revolutionized cancer research by allowing for more realistic and scalable reproductions of both tumour and microenvironmental structures1-3. This has enabled better modelling of low-complexity cancer cell behaviours that occur over relatively short periods of time4. However, available organoid systems do not capture the intricate evolutionary process of cancer development in terms of tissue architecture, cell diversity, homeostasis and lifespan. As a consequence, oncogenesis and tumour formation studies are not possible in vitro and instead require the extensive use of animal models, which provide limited spatiotemporal resolution of cellular dynamics and come at a considerable cost in terms of resources and animal lives. Here we developed topobiologically complex mini-colons that are able to undergo tumorigenesis ex vivo by integrating microfabrication, optogenetic and tissue engineering approaches. With this system, tumorigenic transformation can be spatiotemporally controlled by directing oncogenic activation through blue-light exposure, and emergent colon tumours can be tracked in real-time at the single-cell resolution for several weeks without breaking the culture. These induced mini-colons display rich intratumoural and intertumoural diversity and recapitulate key pathophysiological hallmarks displayed by colorectal tumours in vivo. By fine-tuning cell-intrinsic and cell-extrinsic parameters, mini-colons can be used to identify tumorigenic determinants and pharmacological opportunities. As a whole, our study paves the way for cancer initiation research outside living organisms.

Bcl-xL targeting eliminates ageing tumor-promoting neutrophils and inhibits lung tumor growth

Elevated peripheral blood and tumor-infiltrating neutrophils are often associated with a poor patient prognosis. However, therapeutic strategies to target these cells are difficult to implement due to the life-threatening risk of neutropenia. In a genetically engineered mouse model of lung adenocarcinoma, tumor-associated neutrophils (TAN) demonstrate tumor-supportive capacities and have a prolonged lifespan compared to circulating neutrophils. Here, we show that tumor cell-derived GM-CSF triggers the expression of the anti-apoptotic Bcl-xL protein and enhances neutrophil survival through JAK/STAT signaling. Targeting Bcl-xL activity with a specific BH3 mimetic, A-1331852, blocked the induced neutrophil survival without impacting their normal lifespan. Specifically, oral administration with A-1331852 decreased TAN survival and abundance, and reduced tumor growth without causing neutropenia. We also show that G-CSF, a drug used to combat neutropenia in patients receiving chemotherapy, increased the proportion of young TANs and augmented the anti-tumor effect resulting from Bcl-xL blockade. Finally, our human tumor data indicate the same role for Bcl-xL on pro-tumoral neutrophil survival. These results altogether provide preclinical evidence for safe neutrophil targeting based on their aberrant intra-tumor longevity.

Resistance mechanism to Notch inhibition and combination therapy in human T-cell acute lymphoblastic leukemia

Gain-of-function mutations in NOTCH1 are among the most frequent genetic alterations in T-cell acute lymphoblastic leukemia (T-ALL), highlighting the Notch signaling pathway as a promising therapeutic target for personalized medicine. Yet, a major limitation for long-term success of targeted therapy is relapse due to tumor heterogeneity or acquired resistance. Thus, we performed a genome-wide CRISPR-Cas9 screen to identify prospective resistance mechanisms to pharmacological NOTCH inhibitors and novel targeted combination therapies to efficiently combat T-ALL. Mutational loss of phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1) causes resistance to Notch inhibition. PIK3R1 deficiency leads to increased PI3K/AKT signaling, which regulates cell cycle and the spliceosome machinery, both at the transcriptional and posttranslational level. Moreover, several therapeutic combinations have been identified, in which simultaneous targeting of the cyclin-dependent kinases 4 and 6 (CDK4/6) and NOTCH proved to be the most efficacious in T-ALL xenotransplantation models.

Notch signaling drives intestinal graft-versus-host disease in mice and nonhuman primates

Notch signaling promotes T cell pathogenicity and graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (allo-HCT) in mice, with a dominant role for the Delta-like Notch ligand DLL4. To assess whether Notch's effects are evolutionarily conserved and to identify the mechanisms of Notch signaling inhibition, we studied antibody-mediated DLL4 blockade in a nonhuman primate (NHP) model similar to human allo-HCT. Short-term DLL4 blockade improved posttransplant survival with durable protection from gastrointestinal GVHD in particular. Unlike prior immunosuppressive strategies tested in the NHP GVHD model, anti-DLL4 interfered with a T cell transcriptional program associated with intestinal infiltration. In cross-species investigations, Notch inhibition decreased surface abundance of the gut-homing integrin α4β7 in conventional T cells while preserving α4β7 in regulatory T cells, with findings suggesting increased β1 competition for α4 binding in conventional T cells. Secondary lymphoid organ fibroblastic reticular cells emerged as the critical cellular source of Delta-like Notch ligands for Notch-mediated up-regulation of α4β7 integrin in T cells after allo-HCT. Together, DLL4-Notch blockade decreased effector T cell infiltration into the gut, with increased regulatory to conventional T cell ratios early after allo-HCT. Our results identify a conserved, biologically unique, and targetable role of DLL4-Notch signaling in intestinal GVHD.

Notch1 signaling is limited in healthy mature kidneys in vivo

OBJECTIVE

A Delta-Notch signaling component, Notch1, is involved in the normal development and multiple disorders of the kidney. Although the increase in Notch1 signaling is crucial to these pathogeneses, the basal signaling level in 'healthy' mature kidneys is still unclear. To address this question, we used an artificial Notch1 receptor fused with Gal4/UAS components in addition to the Cre/loxP system and fluorescent proteins in mice. This transgenic reporter mouse system enabled labeling of past and ongoing Notch1 signaling with tdsRed or Cre recombinase, respectively.

RESULTS

We confirmed that our transgenic reporter mouse system mimicked the previously reported Notch1 signaling pattern. Using this successful system, we infrequently observed cells with ongoing Notch1 signaling only in Bowman's capsule and tubules. We consider that Notch1 activation in several lines of disease model mice was pathologically significant itself.

Stromal Notch ligands foster lymphopenia-driven functional plasticity and homeostatic proliferation of naïve B cells

In lymphopenic environments, secondary lymphoid organs regulate the size of B and T-cell compartments by supporting homeostatic proliferation of mature lymphocytes. The molecular mechanisms underlying these responses and their functional consequences remain incompletely understood. To evaluate homeostasis of the mature B-cell pool during lymphopenia, we turned to an adoptive transfer model of purified follicular B-cells into Rag2-/- mouse recipients. Highly purified follicular B-cells transdifferentiated into marginal zone-like B-cells when transferred into Rag2-/- lymphopenic hosts, but not into wild-type hosts. In lymphopenic spleens, transferred B-cells gradually lost their follicular phenotype and acquired characteristics of marginal zone B-cells, as judged by cell surface phenotype, expression of integrins and chemokine receptors, positioning close to the marginal sinus, and an ability to rapidly generate functional plasma cells. Initiation of follicular to marginal zone B-cell transdifferentiation preceded proliferation. Furthermore, the transdifferentiation process was dependent on Notch2 receptors in B-cells and expression of Delta-like1 Notch ligands by splenic Ccl19-Cre+ fibroblastic stromal cells. Gene expression analysis showed rapid induction of Notch-regulated transcripts followed by upregulated Myc expression and acquisition of broad transcriptional features of marginal zone B-cells. Thus, naïve mature B-cells are endowed with plastic transdifferentiation potential in response to increased stromal Notch ligand availability during lymphopenia.

Tcf1 is essential for initiation of oncogenic Notch1-driven chromatin topology in T-ALL

NOTCH1 is a well-established lineage specifier for T cells and among the most frequently mutated genes throughout all subclasses of T cell acute lymphoblastic leukemia (T-ALL). How oncogenic NOTCH1 signaling launches a leukemia-prone chromatin landscape during T-ALL initiation is unknown. Here we demonstrate an essential role for the high-mobility-group transcription factor Tcf1 in orchestrating chromatin accessibility and topology, allowing aberrant Notch1 signaling to convey its oncogenic function. Although essential, Tcf1 is not sufficient to initiate leukemia. The formation of a leukemia-prone epigenetic landscape at the distal Notch1-regulated Myc enhancer, which is fundamental to this disease, is Tcf1-dependent and occurs within the earliest progenitor stage even before cells adopt a T lymphocyte or leukemic fate. Moreover, we discovered a unique evolutionarily conserved Tcf1-regulated enhancer element in the distal Myc-enhancer, which is important for the transition of preleukemic cells to full-blown disease.

Generation of a Gal4-dependent gene recombination and illuminating mouse

Cell labeling technologies, including the Cre/loxP system, are powerful tools in developmental biology. Although the conventional Cre/loxP system has been extensively used to label the expression of specific genes, it is less frequently used for labeling protein-protein interactions owing to technical difficulties. In the present study, we generated a new Gal4-dependent transgenic reporter mouse line that expressed Cre recombinase and a near-infrared fluorescent protein, miRFP670. To examine whether this newly generated transgenic mouse line is applicable in labeling of protein-protein interaction, we used a previously reported transgenic mouse lines that express Notch1 receptor with its intracellular domain replaced with a yeast transcription factor, Gal4. Upon the binding of this artificial Notch1 receptor and endogenous Notch1 ligands, Gal4 would be cleaved from the cell membrane to induce expression of Cre recombinase and miRFP670. Indeed, we observed miRFP670 signal in the mouse embryos (embryonic day 14.5). In addition, we examined whether our Cre recombinase was functional by using another transgenic mouse line that express dsRed after Cre-mediated recombination. We observed dsRed signal in small intestine epithelial cells where Notch1 signal was suggested to be involved in the crypt stem cell maintenance, suggesting that our Cre recombinase was functional. As our newly generated mouse line required only the functioning of Gal4, it could be useful for labeling several types of molecular activities in vivo.

A leukemia-protective germline variant mediates chromatin module formation via transcription factor nucleation

Non-coding variants coordinate transcription factor (TF) binding and chromatin mark enrichment changes over regions spanning >100 kb. These molecularly coordinated regions are named “variable chromatin modules” (VCMs), providing a conceptual framework of how regulatory variation might shape complex traits. To better understand the molecular mechanisms underlying VCM formation, here, we mechanistically dissect a VCM-modulating noncoding variant that is associated with reduced chronic lymphocytic leukemia (CLL) predisposition and disease progression. This common, germline variant constitutes a 5-bp indel that controls the activity of an AXIN2 gene-linked VCM by creating a MEF2 binding site, which, upon binding, activates a super-enhancer-like regulatory element. This triggers a large change in TF binding activity and chromatin state at an enhancer cluster spanning >150 kb, coinciding with subtle, long-range chromatin compaction and robust AXIN2 up-regulation. Our results support a model in which the indel acts as an AXIN2 VCM-activating TF nucleation event, which modulates CLL pathology.

Non-coding variants can regulate transcription factor binding and gene expression at variable chromatin modules. Here, the authors show that a germline variant induces transcription factor nucleation through chromatin compaction leading to AXIN2 up-regulation and is associated to better prognosis in chronic lymphocytic leukaemia.

Notch1 Deficiency Induces Tumor Cell Accumulation Inside the Bronchiolar Lumen and Increases TAZ Expression in an Autochthonous Kras LSL-G12V Driven Lung Cancer Mouse Model

Purpose: Abrogation of Notch signaling, which is pivotal for lung development and pulmonary epithelial cell fate decisions was shown to be involved in the aggressiveness and the differentiation of lung carcinomas. Additionally, the transcription factors YAP and TAZ which are involved in the Hippo pathway, were recently shown to be tightly linked with Notch signaling and to regulate the cell fate in epidermal stem cells. Thus, we aim to elucidate the effects of conditional Notch1 deficiency on carcinogenesis and TAZ expression in lung cancer. Methods: We investigated the effect of conditional Cre-recombinase mediated Notch1 knock-out on lung cancer cells in vivo using an autochthonous mouse model of lung adenocarcinomas driven by Kras ^LSL-G12V and comprehensive immunohistochemical analysis. In addition, we analyzed clinical samples and human lung cancer cell lines for TAZ expression and supported our findings by publicly available data from The Cancer Genome Atlas (TCGA). Results: In mice, we found induction of papillary adenocarcinomas and protrusions of tumor cells from the bronchiolar lining upon Notch1 deficiency. Moreover, the mutated Kras driven lung tumors with deleted Notch1 showed increased TAZ expression and focal nuclear translocation which was frequently observed in human pulmonary adenocarcinomas and squamous cell carcinomas of the lung, but not in small cell lung carcinomas. In addition, we used data from TCGA to show that putative inactivating NOTCH1 mutations co-occur with KRAS mutations and genomic amplifications in lung adenocarcinomas. Conclusion: Our in vivo study provides evidence that Notch1 deficiency in mutated Kras driven lung carcinomas contributes to lung carcinogenesis in a subgroup of patients by increasing TAZ expression who might benefit from TAZ signaling blockade.

A third Notch in colorectal cancer progression and metastasis

In this issue of JEM, Varga et al. (https://doi.org/10.1084/jem.20191515) describe a mouse model of invasive and metastatic colorectal cancer (CRC) closely resembling the human consensus molecular subtype (CMS) 4 associated with the poorest overall survival of the four CMSs. Transcriptomic and bioinformatic analysis combined with pharmacological and genetic studies identified Notch3 as a promoter of tumor progression and metastasis. NOTCH3 expression was up-regulated in CMS4 CRC patients and associated with tumor staging, lymph node and distant metastasis. These findings feature NOTCH3 as putative therapeutic target for advanced CMS4 CRC patients.

Canonical Notch signaling controls the early thymic epithelial progenitor cell state and emergence of the medullary epithelial lineage in fetal thymus development

Thymus function depends on the epithelial compartment of the thymic stroma. Cortical thymic epithelial cells (cTECs) regulate T cell lineage commitment and positive selection, while medullary (m) TECs impose central tolerance on the T cell repertoire. During thymus organogenesis, these functionally distinct sub-lineages are thought to arise from a common thymic epithelial progenitor cell (TEPC). However, the mechanisms controlling cTEC and mTEC production from the common TEPC are not understood. Here, we show that emergence of the earliest mTEC lineage-restricted progenitors requires active NOTCH signaling in progenitor TEC and that, once specified, further mTEC development is NOTCH independent. In addition, we demonstrate that persistent NOTCH activity favors maintenance of undifferentiated TEPCs at the expense of cTEC differentiation. Finally, we uncover a cross-regulatory relationship between NOTCH and FOXN1, a master regulator of TEC differentiation. These data establish NOTCH as a potent regulator of TEPC and mTEC fate during fetal thymus development, and are thus of high relevance to strategies aimed at generating/regenerating functional thymic tissue in vitro and in vivo.

Summary: Notch signaling regulates the initial emergence of medullary thymic epithelial sublineage, implicating Notch in the maintenance of primitive thymic epithelial progenitors and uncovering its cross-interaction with Foxn1.

GCNT1-Mediated O-Glycosylation of the Sialomucin CD43 Is a Sensitive Indicator of Notch Signaling in Activated T Cells

Notch signaling is emerging as a critical regulator of T cell activation and function. However, there is no reliable cell surface indicator of Notch signaling across activated T cell subsets. In this study, we show that Notch signals induce upregulated expression of the Gcnt1 glycosyltransferase gene in T cells mediating graft-versus-host disease after allogeneic bone marrow transplantation in mice. To determine if Gcnt1-mediated O-glycosylation could be used as a Notch signaling reporter, we quantified the core-2 O-glycoform of CD43 in multiple T cell subsets during graft-versus-host disease. Pharmacological blockade of Delta-like Notch ligands abrogated core-2 O-glycosylation in a dose-dependent manner after allogeneic bone marrow transplantation, both in donor-derived CD4⁺ and CD8⁺ effector T cells and in Foxp3⁺ regulatory T cells. CD43 core-2 O-glycosylation depended on cell-intrinsic canonical Notch signals and identified CD4⁺ and CD8⁺ T cells with high cytokine-producing ability. Gcnt1-deficient T cells still drove lethal alloreactivity, showing that core-2 O-glycosylation predicted, but did not cause, Notch-dependent T cell pathogenicity. Using core-2 O-glycosylation as a marker of Notch signaling, we identified Ccl19-Cre⁺ fibroblastic stromal cells as critical sources of Delta-like ligands in graft-versus-host responses irrespective of conditioning intensity. Core-2 O-glycosylation also reported Notch signaling in CD8⁺ T cell responses to dendritic cell immunization, Listeria infection, and viral infection. Thus, we uncovered a role for Notch in controlling core-2 O-glycosylation and identified a cell surface marker to quantify Notch signals in multiple immunological contexts. Our findings will help refine our understanding of the regulation, cellular source, and timing of Notch signals in T cell immunity.

Neutrophils suppress tumor-infiltrating T cells in colon cancer via matrix metalloproteinase-mediated activation of TGFβ

High T-cell infiltration in colorectal cancer (CRC) correlates with a favorable disease outcome and immunotherapy response. This, however, is only observed in a small subset of CRC patients. A better understanding of the factors influencing tumor T-cell responses in CRC could inspire novel therapeutic approaches to achieve broader immunotherapy responsiveness. Here, we investigated T cell-suppressive properties of different myeloid cell types in an inducible colon tumor mouse model. The most potent inhibitors of T-cell activity were tumor-infiltrating neutrophils. Gene expression analysis and combined in vitro and in vivo tests indicated that T-cell suppression is mediated by neutrophil-secreted metalloproteinase activation of latent TGFβ. CRC patient neutrophils similarly suppressed T cells via TGFβ in vitro, and public gene expression datasets suggested that T-cell activity is lowest in CRCs with combined neutrophil infiltration and TGFβ activation. Thus, the interaction of neutrophils with a TGFβ-rich tumor microenvironment may represent a conserved immunosuppressive mechanism in CRC.

Abstract 5799: Characterization and profiling of CB-103, a novel small-molecule protein-protein interaction inhibitor targeting the NOTCH transcription complex

NOTCH signalling is a key development pathway whose aberrant activation is known to play a role in multiple human cancers. In human tumors the NOTCH pathway can be activated by various genetic lesions such over expression of ligands/receptors, GOF mutations in NOTCH receptors, including protein stabilizing mutations in the PEST domain of NOTCH, chromosomal translocations, or loss-of-function mutations in the E3 ubiquitin ligase FBXW7 and other negative regulators of the pathway (SPEN, NUMB). Activation of signalling due to above mentioned mechanisms can be addressed in part using blocking antibodies against NOTCH ligands/receptors or small molecule inhibitors of the gamma secretase enzyme (GSIs). However, in human tumors where NOTCH signalling is constitutively activated due to chromosomal translocations in the NOTCH receptors (NOTCH1 and 2), none of the above-mentioned strategies will be effective. Moreover, due to on-target and off-target toxicities associated with blocking antibodies and GSIs, these anti-NOTCH agents failed to advance in clinical trials, although some of them showed signs of clinical efficacy. Given the role of NOTCH signalling in human tumors, there is a need to identify novel targets in the NOTCH pathway and develop new and more selective anti-NOTCH agents. To inhibit pan-NOTCH signalling in human tumors independently of the mechanisms of NOTCH activation, and in the most downstream part of the pathway, we have previously reported the discovery of a new class of small molecules able to target the NOTCH transcription complex enabling the specific inhibition of NOTCH target gene expression (e.g. cMYC, HES1, DTX1, CCND1). These small molecules act as protein-protein interaction inhibitors, and thereby compromise the assembly of functional NOTCH transcription complex.

Here we present further in vitro and in vivo characterization of the lead molecule CB-103. The anti-cancer activity of CB-103 was extensively profiled in several human cancer cell lines representing NOTCH positive solid tumors, leukemias and lymphomas. Moreover, CB-103 responsiveness of these cell lines correlates with a downregulation of the NOTCH signature following treatment with CB-103. Specifically, we will present data outlining the in vivo pharmacokinetic and pharmacodynamic properties of CB-103.

Citation Format: Rajwinder Lehal, Charlotte Urech, Michele Vigolo, Maximilien Murone, Freddy Radtke. Characterization and profiling of CB-103, a novel small-molecule protein-protein interaction inhibitor targeting the NOTCH transcription complex [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5799.

Notch1-WISP-1 axis determines the regulatory role of mesenchymal stem cell-derived stromal fibroblasts in melanoma metastasis

Mesenchymal stem cells-derived fibroblasts (MSC-DF) constitute a significant portion of stromal fibroblasts in the tumor microenvironment (TME) and are key modulators of tumor progression. However, the molecular mechanisms that determine their tumor-regulatory function are poorly understood. Here, we uncover the Notch1 pathway as a molecular determinant that selectively controls the regulatory role of MSC-DF in melanoma metastasis. We demonstrate that the Notch1 pathway's activity is inversely correlated with the metastasis-regulating function of fibroblasts and can determine the metastasis-promoting or -suppressing phenotype of MSC-DF. When co-grafted with melanoma cells, MSC-DFNotch1-/- selectively promote, while MSC-DFN1IC+/+ preferentially suppress melanoma metastasis, but not growth, in mouse models. Consistently, conditioned media (CM) from MSC-DFNotch1-/- and MSC-DFN1IC+/+ oppositely, yet selectively regulates migration, but not growth of melanoma cells in vitro. Additionally, when co-cultured with metastatic melanoma cells in vitro, MSC-DFNotch1-/- support, while MSC-DFN1IC+/+ inhibit melanoma cells in the formation of spheroids. These findings expand the repertoire of Notch1 signaling as a molecular switch in determining the tumor metastasis-regulating function of MSC-DF. We also identified Wnt-induced secreted protein-1 (WISP-1) as a key downstream secretory mediator of Notch1 signaling to execute the influential role of MSC-DF on melanoma metastasis. These findings reveal the Notch1-WISP-1 axis as a crucial molecular determinant in governing stromal regulation of melanoma metastasis; thus, establishing this axis as a potential therapeutic target for melanoma metastasis.

AMPK promotes survival of c-Myc-positive melanoma cells by suppressing oxidative stress

Although c-Myc is essential for melanocyte development, its role in cutaneous melanoma, the most aggressive skin cancer, is only partly understood. Here we used the Nras^Q61KINK4a^-/- mouse melanoma model to show that c-Myc is essential for tumor initiation, maintenance, and metastasis. c-Myc-expressing melanoma cells were preferentially found at metastatic sites, correlated with increased tumor aggressiveness and high tumor initiation potential. Abrogation of c-Myc caused apoptosis in primary murine and human melanoma cells. Mechanistically, c-Myc-positive melanoma cells activated and became dependent on the metabolic energy sensor AMP-activated protein kinase (AMPK), a metabolic checkpoint kinase that plays an important role in energy and redox homeostasis under stress conditions. AMPK pathway inhibition caused apoptosis of c-Myc-expressing melanoma cells, while AMPK activation protected against cell death of c-Myc-depleted melanoma cells through suppression of oxidative stress. Furthermore, TCGA database analysis of early-stage human melanoma samples revealed an inverse correlation between C-MYC and patient survival, suggesting that C-MYC expression levels could serve as a prognostic marker for early-stage disease.

Notch2 Signaling Maintains NSC Quiescence in the Murine Ventricular-Subventricular Zone

Neurogenesis continues in the ventricular-subventricular zone (V-SVZ) of the adult forebrain from quiescent neural stem cells (NSCs). V-SVZ NSCs are a reservoir for new olfactory bulb (OB) neurons that migrate through the rostral migratory stream (RMS). To generate neurons, V-SVZ NSCs need to activate and enter the cell cycle. The mechanisms underlying NSC transition from quiescence to activity are poorly understood. We show that Notch2, but not Notch1, signaling conveys quiescence to V-SVZ NSCs by repressing cell-cycle-related genes and neurogenesis. Loss of Notch2 activates quiescent NSCs, which proliferate and generate new neurons of the OB lineage. Notch2 deficiency results in accelerated V-SVZ NSC exhaustion and an aging-like phenotype. Simultaneous loss of Notch1 and Notch2 resembled the total loss of Rbpj-mediated canonical Notch signaling; thus, Notch2 functions are not compensated in NSCs, and Notch2 is indispensable for the maintenance of NSC quiescence in the adult V-SVZ.

Abstract B061: Targeting lymphomas with the novel first-in-class pan-NOTCH transcription inhibitor CB-103

Background: NOTCH pathway is recurrently activated in human cancers, including lymphomas, and overactivation of the pathway has been correlated to a worse prognosis in patients with solid tumors, leukemias, and lymphomas, making it an attractive target for treatment (Rossi et al, JEM 2012; Rossi et al, Blood 2012; Kridel et al, Blood 2012). However, so far, pharmacologic approaches to inhibit its activity are limited to the use of nonspecific gamma secretase inhibitors and blocking antibodies with limited application. None of these therapeutic agents have been approved yet for cancer treatment. CB-103 is a novel first-in-class pan-NOTCH inhibitor that blocks signaling by directly and specifically targeting the NOTCH transcription complex, and it has shown preclinical activity in a variety of solid tumor and leukemia models (Lehal et al, AACR 2017). Here, we present the very first results with CB-103 in a large panel of B and T cell lymphoma cell lines. Methods: 58 human lymphoma cell lines [27 diffuse large B cell lymphomas (DLBCL); 9 mantle cell lymphomas; 6 marginal zone lymphomas; 9 T-cell lymphomas; 7 others], 2 murine and 1 canine, were exposed to increasing doses of CB-103 for 72h. Cell proliferation was measured by using the MTT assay. Transcriptome analysis was performed using the Illumina HumanHT 12 Expression BeadChips and with the HTG EdgeSeq Oncology Biomarker Panel, a targeted RNA-Seq investigating over 2500 genes, followed by a limma moderate t-test, and GSEA. Results: CB-103 presented a median IC50 above 20 μM across the whole panel of 61 lymphoma cell lines (range from 400 nM to > 20 μM), without significant differences among lymphoma subtypes. Importantly, 13/58 cell lines had an IC50 <10 μM and were defined as sensitive. These cell lines were derived from ABC DLBCL (3/7, 43%), GCB DLBCL (5/20, 25%), MCL (3/9, 33%), marginal zone lymphoma (1/6, 17%), and canine DLBCL (1/1, 100%). The sensitive cell lines, when compared with those presenting IC50 >10 μM, presented a gene expression signature significantly enriched with genes involved in the epithelial-mesenchymal transition (FDR 0.0014), a Notch-related process. Indeed, the transcripts higher in the sensitive cell lines included, among others, DLL1 (P 0.010; Log Fold Change 2.39), BAMBI (P 0.046; Log Fold Change 0.92), MCM7 (P 0.015; Log Fold Change 1), and ULK1 (P 0.045; Log Fold Change 2.39), all connected to NOTCH pathway. Finally, 10 of the CB-103 sensitive human cell lines were also exposed to another NOTCH inhibitor, the gamma secretase inhibitor LY-3039187, which resulted active only in one MCL cell line, while it had IC50 >20 μM in the other cell lines tested. Conclusions: CB-103 presented in vitro antilymphoma activity in a restricted number of B cell lymphoma cell lines, which were characterized by a NOTCH-related gene expression signature. Further studies with the compound are ongoing and a phase I is planned to start in Q3 2017 (EUDRACT Number 2017-001491-35).

Citation Format: Filippo Spriano, Chiara Tarantelli, Alberto Arribas, Eugenio Gaudio, Luciano Cascione, Luca Aresu, Emanuele Zucca, Davide Rossi, Anastasios Stathis, Maximilien Murone, Dirk Weber, Rajwinder Lehal, Freddy Radtke, Francesco Bertoni. Targeting lymphomas with the novel first-in-class pan-NOTCH transcription inhibitor CB-103 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B061.

Notch1 haploinsufficiency causes ascending aortic aneurysms in mice

An ascending aortic aneurysm (AscAA) is a life-threatening disease whose molecular basis is poorly understood. Mutations in NOTCH1 have been linked to bicuspid aortic valve (BAV), which is associated with AscAA. Here, we describe a potentially novel role for Notch1 in AscAA. We found that Notch1 haploinsufficiency exacerbated the aneurysmal aortic root dilation seen in the Marfan syndrome mouse model and that heterozygous deletion of Notch1 in the second heart field (SHF) lineage recapitulated this exacerbated phenotype. Additionally, Notch1+/- mice in a predominantly 129S6 background develop aortic root dilation, indicating that loss of Notch1 is sufficient to cause AscAA. RNA sequencing analysis of the Notch1.129S6+/- aortic root demonstrated gene expression changes consistent with AscAA. These findings are the first to our knowledge to demonstrate an SHF lineage-specific role for Notch1 in AscAA and suggest that genes linked to the development of BAV may also contribute to the associated aortopathy.

Signalling strength determines proapoptotic functions of STING

Mammalian cells use cytosolic nucleic acid receptors to detect pathogens and other stress signals. In innate immune cells the presence of cytosolic DNA is sensed by the cGAS-STING signalling pathway, which initiates a gene expression programme linked to cellular activation and cytokine production. Whether the outcome of the STING response varies between distinct cell types remains largely unknown. Here we show that T cells exhibit an intensified STING response, which leads to the expression of a distinct set of genes and results in the induction of apoptosis. Of note, this proapoptotic STING response is still functional in cancerous T cells and delivery of small molecule STING agonists prevents in vivo growth of T-cell-derived tumours independent of its adjuvant activity. Our results demonstrate how the magnitude of STING signalling can shape distinct effector responses, which may permit for cell type-adjusted behaviours towards endogenous or exogenous insults.The cGAS/STING signalling pathway is responsible for sensing intracellular DNA and activating downstream inflammatory genes. Here the authors show mouse primary T cells and T leukaemia are hyperresponsive to STING agonist, and this strong STING signalling is associated with apoptosis induction.

The Notch Ligand Jagged1 Regulates the Osteoblastic Lineage by Maintaining the Osteoprogenitor Pool

Notch signaling is critical for osteoblastic differentiation; however, the specific contribution of individual Notch ligands is unknown. Parathyroid hormone (PTH) regulates the Notch ligand Jagged1 in osteoblastic cells. To determine if osteolineage Jagged1 contributes to bone homeostasis, selective deletion of Jagged1 in osteolineage cells was achieved through the presence of Prx1 promoter-driven Cre recombinase expression, targeting mesenchymal stem cells (MSCs) and their progeny (PJag1 mice). PJag1 mice were viable and fertile and did not exhibit any skeletal abnormalities at 2 weeks of age. At 2 months of age, however, PJag1 mice had increased trabecular bone mass compared to wild-type (WT) littermates. Dynamic histomorphometric analysis showed increased osteoblastic activity and increased mineral apposition rate. Immunohistochemical analysis showed increased numbers of osteocalcin-positive mature osteoblasts in PJag1 mice. Also increased phenotypically defined Lin^- /CD45^- /CD31^- /Sca1^- /CD51⁺ osteoblastic cells were measured by flow cytometric analysis. Surprisingly, phenotypically defined Lin^- /CD45^- /CD31^- /Sca1⁺ /CD51⁺ MSCs were unchanged in PJag1 mice as measured by flow cytometric analysis. However, functional osteoprogenitor (OP) cell frequency, measured by Von Kossa⁺ colony formation, was decreased, suggesting that osteolineage Jagged1 contributes to maintenance of the OP pool. The trabecular bone increases were not due to osteoclastic defects, because PJag1 mice had increased bone resorption. Because PTH increases osteoblastic Jagged1, we sought to understand if osteolineage Jagged1 modulates PTH-mediated bone anabolism. Intermittent PTH treatment resulted in a significantly greater increase in BV/TV in PJag1 hind limbs compared to WT. These findings demonstrate a critical role of osteolineage Jagged1 in bone homeostasis, where Jagged1 maintains the transition of OP to maturing osteoblasts. This novel role of Jagged1 not only identifies a regulatory loop maintaining appropriate populations of osteolineage cells, but also provides a novel approach to increase trabecular bone mass, particularly in combination with PTH, through modulation of Jagged1. © 2017 American Society for Bone and Mineral Research.

Fibroblastic niches prime T cell alloimmunity through Delta-like Notch ligands

Alloimmune T cell responses induce graft-versus-host disease (GVHD), a serious complication of allogeneic bone marrow transplantation (allo-BMT). Although Notch signaling mediated by Delta-like 1/4 (DLL1/4) Notch ligands has emerged as a major regulator of GVHD pathogenesis, little is known about the timing of essential Notch signals and the cellular source of Notch ligands after allo-BMT. Here, we have shown that critical DLL1/4-mediated Notch signals are delivered to donor T cells during a short 48-hour window after transplantation in a mouse allo-BMT model. Stromal, but not hematopoietic, cells were the essential source of Notch ligands during in vivo priming of alloreactive T cells. GVHD could be prevented by selective inactivation of Dll1 and Dll4 in subsets of fibroblastic stromal cells that were derived from chemokine Ccl19-expressing host cells, including fibroblastic reticular cells and follicular dendritic cells. However, neither T cell recruitment into secondary lymphoid organs nor initial T cell activation was affected by Dll1/4 loss. Thus, we have uncovered a pathogenic function for fibroblastic stromal cells in alloimmune reactivity that can be dissociated from their homeostatic functions. Our results reveal what we believe to be a previously unrecognized Notch-mediated immunopathogenic role for stromal cell niches in secondary lymphoid organs after allo-BMT and define a framework of early cellular and molecular interactions that regulate T cell alloimmunity.

Notch as a tumour suppressor

The Notch signalling cascade is an evolutionarily conserved pathway that has a crucial role in regulating development and homeostasis in various tissues. The cellular processes and events that it controls are diverse, and continued investigation over recent decades has revealed how the role of Notch signalling is multifaceted and highly context dependent. Consistent with the far-reaching impact that Notch has on development and homeostasis, aberrant activity of the pathway is also linked to the initiation and progression of several malignancies, and Notch can in fact be either oncogenic or tumour suppressive depending on the tissue and cellular context. The Notch pathway therefore represents an important target for therapeutic agents designed to treat many types of cancer. In this Review, we focus on the latest developments relating specifically to the tumour-suppressor activity of Notch signalling and discuss the potential mechanisms by which Notch can inhibit carcinogenesis in various tissues. Potential therapeutic strategies aimed at restoring or augmenting Notch-mediated tumour suppression will also be highlighted.

Corneal epithelial stem cells and their niche at a glance

The corneal epithelium acts as a protective barrier on the anterior ocular surface and is essential for maintaining transparency of the cornea and thus visual acuity. During both homeostasis and repair, the corneal epithelium is maintained by self-renewing stem cells, which persist throughout the lifetime of the organism. Importantly, as in other self-renewing tissues, the functional activity of corneal epithelial stem cells (CSCEs) is tightly regulated by the surrounding microenvironment, or niche, which provides a range of cues that maintain the stem cell population. This Cell Science at a Glance article and the accompanying poster will therefore aim to summarise our current understanding of the corneal epithelial stem cell niche and its role in regulating stem cell activity during homeostasis, repair and disease.

Myeloid DLL4 Does Not Contribute to the Pathogenesis of Non-Alcoholic Steatohepatitis in Ldlr-/- Mice

Non-alcoholic steatohepatitis (NASH) is characterized by liver steatosis and inflammation. Currently, the underlying mechanisms leading to hepatic inflammation are not fully understood and consequently, therapeutic options are poor. Non-alcoholic steatohepatitis (NASH) and atherosclerosis share the same etiology whereby macrophages play a key role in disease progression. Macrophage function can be modulated via activation of receptor-ligand binding of Notch signaling. Relevantly, global inhibition of Notch ligand Delta-Like Ligand-4 (DLL4) attenuates atherosclerosis by altering the macrophage-mediated inflammatory response. However, the specific contribution of macrophage DLL4 to hepatic inflammation is currently unknown. We hypothesized that myeloid DLL4 deficiency in low-density lipoprotein receptor knock-out (Ldlr^-/-) mice reduces hepatic inflammation. Irradiated Ldlr^-/- mice were transplanted (tp) with bone marrow from wild type (Wt) or DLL4^f/fLysMCre^+/0 (DLL4^del) mice and fed either chow or high fat, high cholesterol (HFC) diet for 11 weeks. Additionally, gene expression was assessed in bone marrow-derived macrophages (BMDM) of DLL4^f/fLysMCre^WT and DLL4^f/fLysMCre^+/0 mice. In contrast to our hypothesis, inflammation was not decreased in HFC-fed DLL4^del-transplanted mice. In line, in vitro, there was no difference in the expression of inflammatory genes between DLL4-deficient and wildtype bone marrow-derived macrophages. These results suggest that myeloid DLL4 deficiency does not contribute to hepatic inflammation in vivo. Since, macrophage-DLL4 expression in our model was not completely suppressed, it can’t be totally excluded that complete DLL4 deletion in macrophages might lead to different results. Nevertheless, the contribution of non-myeloid Kupffer cells to notch signaling with regard to the pathogenesis of steatohepatitis is unknown and as such it is possible that, DLL4 on Kupffer cells promote the pathogenesis of steatohepatitis.

Notch Signaling Regulates the Homeostasis of Tissue-Restricted Innate-like T Cells

Although Notch signaling plays important roles in lineage commitment and differentiation of multiple cell types including conventional T cells, nothing is currently known concerning Notch function in innate-like T cells. We have found that the homeostasis of several well-characterized populations of innate-like T cells including invariant NKT cells (iNKT), CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells is controlled by Notch. Notch selectively regulates hepatic iNKT cell survival via tissue-restricted control of B cell lymphoma 2 and IL-7Rα expression. More generally, Notch regulation of innate-like T cell homeostasis involves both cell-intrinsic and -extrinsic mechanisms and relies upon context-dependent interactions with Notch ligand-expressing fibroblastic stromal cells. Collectively, using conditional ablation of Notch receptors on peripheral T cells or Notch ligands on putative fibroblastic stromal cells, we show that Notch signaling is indispensable for the homeostasis of three tissue-restricted populations of innate-like T cells: hepatic iNKT, CD8ααTCRαβ small intestinal intraepithelial lymphocytes, and innate memory phenotype CD8 T cells, thus supporting a generalized role for Notch in innate T cell homeostasis.

Abstract 338: A novel small molecule inhibitor of the Notch transcription activation complex

NOTCH signaling is a developmental pathway known to play critical roles during embryonic development as well as for the regulation of self-renewing tissues. Aberrant activation of NOTCH signaling leads to deregulation of the self-renewal process resulting in sustained proliferation, evasion of cell death, loss of differentiation capacity, invasion and metastasis, all of which are hallmarks of cancer. Over activation of NOTCH in human cancers can be a consequence of over expression of NOTCH ligands/receptors, GOF mutations in NOTCH receptors as well as chromosomal translocations leading to constitutive activation of the pathway. Given the importance of Notch signaling in human cancers, several therapeutic approaches have been utilized to block NOTCH signaling. Two of these strategies are; a) the use of monoclonal blocking antibodies (Mabs) against NOTCH ligands and receptors and b) the use of small molecule γ-secretase inhibitors (GSIs). However, these approaches can only be effective if tumor cells express full-length ligand or receptor molecules. On the contrary, in human cancers harbouring NOTCH gene fusion due to chromosomal translocations, the use of Mabs and GSIs will have very limited clinical benefits. A third, yet not fully explored approach could be the blockage of NOTCH signalling by targeting the most downstream event in the NOTCH cascade i,e NOTCH transcriptional activation complex using small molecule inhibitors.

Here we report discovery and identification of a novel, orally-active small molecule inhibitor, named CB-103, of the NOTCH pathway that blocks NOTCH signaling by targeting the NOTCH transcriptional activation complex in the nucleus. CB-103 has shown the ability to block NOTCH signalling in human cancer cell lines, induce neurogenic phenotype in drosophila, induce muscle cell differentiation and inhibit NOTCH dependent cellular processes in mice. In addition, CB-103 exhibit anti-tumor efficacy in a xenograft model of human triple negative breast cancer resistant to GSIs and Mabs against NOTCH ligands/receptors. Furthermore, CB-103 has shown a remarkable activity in PDX models of human T-ALL harbouring activation of the NOTCH pathway. Additional studies are underway on several analogs of CB-103 to determine ADME/PK/PD profile and nominate a development candidate for further clinical development of this novel inhibitor of the NOTCH pathway.

Citation Format: Rajwinder Lehal, Viktoras Frismantas, Sylvain Loubéry, Viktoria Reinmuller, Gerardo Turcatti, Marcos Gonzalez-Gaitan, Jean-Pierre Bourquin, Freddy Radtke. A novel small molecule inhibitor of the Notch transcription activation complex. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 338.

Abstract LB-034: Tcf7: an essential mediator in Notch-induced T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer caused by the malignant transformation of immature thymocytes. Notch1 gain-of-function mutations are present in >50% of T-ALL cases and result in the constitutive activation of Notch1 intracellular domain (N1ICD) in mutated cells. The mechanisms by which deregulated Notch1 signalling leads to T-ALL development are currently unresolved and stringently investigated. T cell factor-1 (TCF-1) is a transcription factor encoded by Tcf7. Not only playing crucial roles in Wnt signalling, Tcf7 is (i) a direct Notch1 target gene and (ii) required for driving early T lineage commitment of hematopoietic progenitors. Together, these findings suggest that Tcf7 may play a role in Notch1-driven T-ALL. Herein, we show that the conditional loss of Tcf7 in hematopoietic progenitors prevents T-ALL development in both genetic- and retroviral-based mouse models of N1ICD over-expression. However, T-ALL development was unaffected by conditional loss of the Wnt signalling mediator, β-catenin. Interestingly, conditional Tcf7 deficiency partially restored the B lineage potential of N1ICD over-expressing bone marrow progenitors. Similar to Tcf7-/- mice, conditional Tcf7 deficiency in bone marrow progenitors abrogated T cell development in adult thymi. However, unexpectedly, Tcf7-deficient hematopoietic progenitors adopted a B cell fate in these thymi, a phenotype that was found to be comparable to conditional loss of Notch1. Overall, our results indicate that Tcf7 is an important mediator of Notch1-driven T-ALL. Furthermore, our data suggests that, in addition to promoting T lineage commitment, Tcf7 may also function as a Notch1-dependent transcriptional repressor of B lineage commitment in adult hematopoiesis. We performed RNAseq to identify the molecular players involved in Tcf7-mediated lineage repression and complement this approach with CHIP_Seq.

Citation Format: Ute Koch, Tara Sugrue, Christelle Dubey, Freddy Radtke. Tcf7: an essential mediator in Notch-induced T-ALL. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-034.

Abstract 4085: Notch1 signaling determines melanoma-regulating role of tumor stromal fibroblasts

Objectives. Tumor stromal fibroblasts are crucial in regulating tumor growth, invasion and metastasis, yet the molecular mechanisms that determine the tumor regulatory role of stromal fibroblasts remains unknown. Here, we uncover the Notch1 signaling pathway as a molecular determinant that controls the tumor regulatory role of tumor stromal fibroblasts in melanoma growth and invasion. Methods. Murine melanoma cells B16-F10, stably transduced with Luciferase 2 (Luc2)/lentivirus, were xenografted on the skin of two new mouse lines: the Gain-Of-Function of Notch1 (GOFNotch1: Fsp1.Cre+/-;ROSALSL-N1IC+/+) and Loss-Of-Function of Notch1 (LOFNotch1: Fsp1.Cre+/-;Notch1LoxP/LoxP+/+), respectively. GOFctrl (FSP1.Cre-/-;ROSALSL-N1IC+/+) and LOFctrl (FSP1.Cre-/-; Notch1LoxP/LoxP+/+) mice were used as control. Tumor growth was measured based on tumor weight and melanoma local invasion were examined by H&E staining of resected tumor tissue.

Results. Using a mouse melanoma model in which exogenous melanoma cells were grafted on the skin of two lines of mice where the genetic activation or inactivation of Notch1 signaling specifically occurs in natural host stromal fibroblasts, we demonstrated that Notch1 pathway activity could determine the tumor-promoting or tumor-suppressing phenotype in tumor stromal fibroblasts. Tumor stromal fibroblasts carrying elevated Notch1 activity significantly inhibited melanoma growth and invasion, while those with a null Notch1 promoted melanoma invasion.

Conclusions. These findings identify the Notch1 pathway as a molecular determinant that controls the regulatory role of tumor stromal fibroblasts in melanoma skin growth and invasion, unveiling Notch1 signaling as a potential therapeutic target for melanoma and potentially other solid tumors.

Citation Format: Hongwei Shao, Ranran Kong, Mecker Moller, Massimiliano L. Ferrari, Leiming Zhang, Freddy Radtke, Anthony J. Capobianco, Zhao-Jun Liu. Notch1 signaling determines melanoma-regulating role of tumor stromal fibroblasts. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4085.

Endothelial Notch1 Is Required for Proper Development of the Semilunar Valves and Cardiac Outflow Tract

Background

Congenital heart disease is the most common type of birth defect, affecting ≈2% of the population. Malformations involving the cardiac outflow tract and semilunar valves account for >50% of these cases predominantly because of a bicuspid aortic valve, which has an estimated prevalence of 1% in the population. We previously reported that mutations in NOTCH1 were a cause of bicuspid aortic valve in nonsyndromic autosomal‐dominant human pedigrees. Subsequently, we described a highly penetrant mouse model of aortic valve disease, consisting of a bicuspid aortic valve with thickened cusps and associated stenosis and regurgitation, in Notch1‐haploinsufficient adult mice backcrossed into a Nos3‐null background.

Methods and Results

Here, we described the congenital cardiac abnormalities in Notch1^+/−;Nos3^−/− embryos that led to ≈65% lethality by postnatal day 10. Although expected Mendelian ratios of Notch1^+/−;Nos3^−/− embryos were found at embryonic day 18.5, histological examination revealed thickened, malformed semilunar valve leaflets accompanied by additional anomalies of the cardiac outflow tract including ventricular septal defects and overriding aorta. The aortic valve leaflets of Notch1^+/−;Nos3^−/− embryos at embryonic day 15.5 were significantly thicker than controls, consistent with a defect in remodeling of the semilunar valve cushions. In addition, we generated mice haploinsufficient for Notch1 specifically in endothelial and endothelial‐derived cells in a Nos3‐null background and found that Notch1^fl/+;Tie2‐Cre^+/−;Nos3^−/− mice recapitulate the congenital cardiac phenotype of Notch1^+/−;Nos3^−/− embryos.

Conclusions

Our data demonstrate the role of endothelial Notch1 in the proper development of the semilunar valves and cardiac outflow tract.

Abstract IA10: Notch signaling and cancer

Cancer can be seen as disease of perturbed self-renewal. In the last decades it became clear that many of the signaling pathways known to be important during embryonic development also play important roles in regulating self-renewing tissues. Deregulation of the self-renewal process results in sustained proliferation, evasion of cell death, loss of differentiation capacity, invasion and metastasis all of which are hallmarks of cancer. The major question is how do these deregulated signaling cascades mechanistically contribute to cancer and are they suitable for targeting therapy?

The Notch pathway is one such cascade required for normal stem cell maintenance and development of different organs. Over activation of this pathway due to mutations in the Notch receptor are found in more than 50% of human T-cell leukemia and deregulated Notch signaling has been shown to promote tumor progression of various organs. The oncogenic mediators of aberrant Notch function in T-ALL and other Notch-driven cancers appear to be manifold and complex. The modulatory function of individual miRNAs in Notch driven T-ALLs has recently been established. However, whether Dicer1-processed miRNAs are essential for Notch-driven T-ALL is currently unknown. We used conditional and inducible genetic loss of function approaches to show that development and maintenance of Notch-driven T-ALL is dependent on Dicer1 function. Lineage tracing experiments revealed that Dicer1 deficiency led to the induction of apoptosis in T-ALL cells whereas cell cycle progression remained unaltered. Through microarray-based miRNA profiling, we identified miR-21 as a previously unrecognized miRNA deregulated in both mouse and human T-ALL. Herein, we demonstrate that miR-21 regulates T-ALL cell survival via repression of the tumor suppressor Pdcd4.

Moreover, we will report on the identification of a novel small molecule inhibitor (CB103) that blocks Notch signaling by interfering with the transcriptional activation complex. The compound CB103 has shown remarkable ability to block Notch signaling in human cancer cell lines as well as primary human T-ALL cells, thus abrogating their proliferative properties. In addition, compound CB103 exhibit in vivo activity as demonstrated by its ability to impinge upon Notch dependent developmental processes and by impeding tumor growth in xenograft models of human leukemia and breast cancer.

Citation Format: Fabian Junker, Rajwinder Lehal, Viktoras Frimantas, Beat C. Bornhauser, Jean-Pierre Bourquin, Ute Koch, Freddy Radtke. Notch signaling and cancer. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr IA10.

Chronic inflammation imposes aberrant cell fate in regenerating epithelia through mechanotransduction

Chronic inflammation is associated with a variety of pathological conditions in epithelial tissues, including cancer, metaplasia and aberrant wound healing. In relation to this, a significant body of evidence suggests that aberration of epithelial stem and progenitor cell function is a contributing factor in inflammation-related disease, although the underlying cellular and molecular mechanisms remain to be fully elucidated. In this study, we have delineated the effect of chronic inflammation on epithelial stem/progenitor cells using the corneal epithelium as a model tissue. Using a combination of mouse genetics, pharmacological approaches and in vitro assays, we demonstrate that chronic inflammation elicits aberrant mechanotransduction in the regenerating corneal epithelium. As a consequence, a YAP-TAZ/β-catenin cascade is triggered, resulting in the induction of epidermal differentiation on the ocular surface. Collectively, the results of this study demonstrate that chronic inflammation and mechanotransduction are linked and act to elicit pathological responses in regenerating epithelia.

Notch1 Pathway Activity Determines the Regulatory Role of Cancer-Associated Fibroblasts in Melanoma Growth and Invasion

Cancer-associated fibroblasts (CAF) play a crucial role in regulating cancer progression, yet the molecular determinant that governs the tumor regulatory role of CAF remains unknown. Using a mouse melanoma model in which exogenous melanoma cells were grafted on the skin of two lines of mice where the genetic activation or inactivation of Notch1 signaling specifically occurs in natural host stromal fibroblasts, we demonstrated that Notch1 pathway activity could determine the tumor-promoting or tumor-suppressing phenotype in CAF. CAF carrying elevated Notch1 activity significantly inhibited melanoma growth and invasion, while those with a null Notch1 promoted melanoma invasion. These findings identify the Notch1 pathway as a molecular determinant that controls the regulatory role of CAF in melanoma skin growth and invasion, unveiling Notch1 signaling as a potential therapeutic target for melanoma and potentially other solid tumors.

DLL4 promotes continuous adult intestinal lacteal regeneration and dietary fat transport

The small intestine is a dynamic and complex organ that is characterized by constant epithelium turnover and crosstalk among various cell types and the microbiota. Lymphatic capillaries of the small intestine, called lacteals, play key roles in dietary fat absorption and the gut immune response; however, little is known about the molecular regulation of lacteal function. Here, we performed a high-resolution analysis of the small intestinal stroma and determined that lacteals reside in a permanent regenerative, proliferative state that is distinct from embryonic lymphangiogenesis or quiescent lymphatic vessels observed in other tissues. We further demonstrated that this continuous regeneration process is mediated by Notch signaling and that the expression of the Notch ligand delta-like 4 (DLL4) in lacteals requires activation of VEGFR3 and VEGFR2. Moreover, genetic inactivation of Dll4 in lymphatic endothelial cells led to lacteal regression and impaired dietary fat uptake. We propose that such a slow lymphatic regeneration mode is necessary to match a unique need of intestinal lymphatic vessels for both continuous maintenance, due to the constant exposure to dietary fat and mechanical strain, and efficient uptake of fat and immune cells. Our work reveals how lymphatic vessel responses are shaped by tissue specialization and uncover a role for continuous DLL4 signaling in the function of adult lymphatic vasculature.

Bmi1 regulates murine intestinal stem cell proliferation and self-renewal downstream of Notch

Genetic data indicate that abrogation of Notch-Rbpj or Wnt-β-catenin pathways results in the loss of the intestinal stem cells (ISCs). However, whether the effect of Notch is direct or due to the aberrant differentiation of the transit-amplifying cells into post-mitotic goblet cells is unknown. To address this issue, we have generated composite tamoxifen-inducible intestine-specific genetic mouse models and analyzed the expression of intestinal differentiation markers. Importantly, we found that activation of β-catenin partially rescues the differentiation phenotype of Rbpj deletion mutants, but not the loss of the ISC compartment. Moreover, we identified Bmi1, which is expressed in the ISC and progenitor compartments, as a gene that is co-regulated by Notch and β-catenin. Loss of Bmi1 resulted in reduced proliferation in the ISC compartment accompanied by p16(INK4a) and p19(ARF) (splice variants of Cdkn2a) accumulation, and increased differentiation to the post-mitotic goblet cell lineage that partially mimics Notch loss-of-function defects. Finally, we provide evidence that Bmi1 contributes to ISC self-renewal.

Specific fibroblastic niches in secondary lymphoid organs orchestrate distinct Notch-regulated immune responses

Fasnacht et al. now show that fibroblasts in secondary lymphoid organs are responsible for the production of Notch ligands regulating the differentiation of immune cells

Fibroblast-like cells of secondary lymphoid organs (SLO) are important for tissue architecture. In addition, they regulate lymphocyte compartmentalization through the secretion of chemokines, and participate in the orchestration of appropriate cell–cell interactions required for adaptive immunity. Here, we provide data demonstrating the functional importance of SLO fibroblasts during Notch-mediated lineage specification and immune response. Genetic ablation of the Notch ligand Delta-like (DL)1 identified splenic fibroblasts rather than hematopoietic or endothelial cells as niche cells, allowing Notch 2–driven differentiation of marginal zone B cells and of Esam⁺ dendritic cells. Moreover, conditional inactivation of DL4 in lymph node fibroblasts resulted in impaired follicular helper T cell differentiation and, consequently, in reduced numbers of germinal center B cells and absence of high-affinity antibodies. Our data demonstrate previously unknown roles for DL ligand-expressing fibroblasts in SLO niches as drivers of multiple Notch-mediated immune differentiation processes.

Tumor vessel normalization by chloroquine independent of autophagy

Chloroquine (CQ) has been evaluated as an autophagy blocker for cancer treatment, but it is unknown if it acts solely by inhibiting cancer cell autophagy. We report that CQ reduced tumor growth but improved the tumor milieu. By normalizing tumor vessel structure and function and increasing perfusion, CQ reduced hypoxia, cancer cell invasion, and metastasis, while improving chemotherapy delivery and response. Inhibiting autophagy in cancer cells or endothelial cells (ECs) failed to induce such effects. CQ's vessel normalization activity relied mainly on alterations of endosomal Notch1 trafficking and signaling in ECs and was abrogated by Notch1 deletion in ECs in vivo. Thus, autophagy-independent vessel normalization by CQ restrains tumor invasion and metastasis while improving chemotherapy, supporting the use of CQ for anticancer treatment.

Alzheimer's disease mutations in APP but not γ-secretase modulators affect epsilon-cleavage-dependent AICD production

Pathological amino-acid substitutions in the amyloid precursor protein (APP) and chemical γ-secretase modulators affect the processing of APP by the γ-secretase complex and the production of the amyloid-beta peptide Aβ42, the accumulation of which is considered causative of Alzheimer's disease. Here we demonstrate that mutations in the transmembrane domain of APP causing aggressive early-onset familial Alzheimer's disease affect both γ- and ε-cleavage sites, by raising the Aβ42/40 ratio and inhibiting the production of AICD50-99, one of the two physiological APP intracellular domains (ICDs). This is in sharp contrast to γ-secretase modulators, which shift Aβ42 production towards the shorter Aβ38, but unequivocally spare the ε-site and APP- and Notch-ICDs production. Molecular simulations suggest that familial Alzheimer's disease mutations modulate the flexibility of the APP transmembrane domain and the presentation of its γ-site, modifying at the same time, the solvation of the ε-site.

Cutaneous Notch signaling in health and disease

The development and maintenance of the skin are dependent on myriad signaling pathways that regulate a variety of cellular processes. In cutaneous epithelial cells, the Notch cascade plays a central role in ensuring that proliferation and differentiation are coordinated appropriately, a function that it imparts during both ontogeny and homeostasis. Aberrations of the Notch signaling pathway result in severe abnormalities in the epidermis and its appendages and cause functional defects such as perturbed barrier function. In addition, impaired Notch signaling is associated with diseases of the skin such as atopy and cancer. The pathology associated with aberrant cutaneous Notch signaling reflects the complex mechanisms underpinning its function in this tissue and involves both cell-autonomous and nonautonomous mechanisms. This review summarizes our current knowledge of the role of Notch signaling in the skin during health and disease.