Cyclin D1-dependent induction of luminal inflammatory breast tumors by activated notch3

A tumor-suppressive function for Notch3 in the parous mammary gland

Notch3 promotes mammary luminal cell specification and forced Notch3 activation can induce mammary tumor formation. However, recent studies suggest a tumor-suppressive role for Notch3. Here, we report on Notch3 expression and functional analysis in the mouse mammary gland. Notch3 is expressed in the luminal compartment throughout mammary gland development, but switches to basal cells with initiation of post-lactational involution. Deletion of Notch3 caused a decrease of Notch activation in luminal cells and diminished luminal progenitors at puberty, as well as reduced alveolar progenitors during pregnancy. Parous Notch3−/− mammary glands developed hyperplasia with accumulation of CD24hiCD49flo cells, some of which progressed to invasive tumors with luminal features. Notch3 deletion abolished Notch activation in basal cells during involution, accompanied by altered apoptosis and reduced brown adipocytes, leading to expansion of parity-identified mammary epithelial cells (PI-MECs). Interestingly, the postpartum microenvironment is required for the stem cell activity of Notch3−/− PI-MECs. Finally, high expression of NOTCH3 is associated with prolonged survival in patients with luminal breast cancer. These results highlight an unexpected tumor-suppressive function for Notch3 in the parous mammary gland through restriction of PI-MEC expansion.

Aberrations of Chromosomes 1 and 16 in Breast Cancer: A Framework for Cooperation of Transcriptionally Dysregulated Genes

Derivative chromosome der(1;16), isochromosome 1q, and deleted 16q-producing arm-level 1q-gain and/or 16q-loss-are recurrent cytogenetic abnormalities in breast cancer, but their exact role in determining the malignant phenotype is still largely unknown. We exploited The Cancer Genome Atlas (TCGA) data to generate and analyze groups of breast invasive carcinomas, called 1,16-chromogroups, that are characterized by a pattern of arm-level somatic copy number aberrations congruent with known cytogenetic aberrations of chromosome 1 and 16. Substantial differences were found among 1,16-chromogroups in terms of other chromosomal aberrations, aneuploidy scores, transcriptomic data, single-point mutations, histotypes, and molecular subtypes. Breast cancers with a co-occurrence of 1q-gain and 16q-loss can be distinguished in a "low aneuploidy score" group, congruent to der(1;16), and a "high aneuploidy score" group, congruent to the co-occurrence of isochromosome 1q and deleted 16q. Another three groups are formed by cancers showing separately 1q-gain or 16q-loss or no aberrations of 1q and 16q. Transcriptome comparisons among the 1,16-chromogroups, integrated with functional pathway analysis, suggested the cooperation of overexpressed 1q genes and underexpressed 16q genes in the genesis of both ductal and lobular carcinomas, thus highlighting the putative role of genes encoding gamma-secretase subunits (APH1A, PSEN2, and NCSTN) and Wnt enhanceosome components (BCL9 and PYGO2) in 1q, and the glycoprotein E-cadherin (CDH1), the E3 ubiquitin-protein ligase WWP2, the deubiquitinating enzyme CYLD, and the transcription factor CBFB in 16q. The analysis of 1,16-chromogroups is a strategy with far-reaching implications for the selection of cancer cell models and novel experimental therapies.

NOTCH and DNA repair pathways are more frequently targeted by genomic alterations in inflammatory than in non-inflammatory breast cancers

Inflammatory breast cancer (IBC) is the most pro‐metastatic form of breast cancer. Better understanding of its pathophysiology and identification of actionable genetic alterations (AGAs) are crucial to improve systemic treatment. We aimed to define the DNA profiles of IBC vs noninflammatory breast cancer (non‐IBC) clinical samples in terms of copy number alterations (CNAs), mutations, and AGAs. We applied targeted next‐generation sequencing (tNGS) and array‐comparative genomic hybridization (aCGH) to 57 IBC and 50 non‐IBC samples and pooled these data with four public datasets profiled using NGS and aCGH, leading to a total of 101 IBC and 2351 non‐IBC untreated primary tumors. The respective percentages of each molecular subtype [hormone receptor‐positive (HR+)/HER2−, HER2+, and triple‐negative] were 68%, 15%, and 17% in non‐IBC vs 25%, 35%, and 40% in IBC. The comparisons were adjusted for both the molecular subtypes and the American Joint Committee on Cancer (AJCC) stage. The 10 most frequently altered genes in IBCs were TP53 (63%), HER2/ERBB2 (30%), MYC (27%), PIK3CA (21%), BRCA2 (14%), CCND1 (13%), GATA3 (13%), NOTCH1 (12%), FGFR1 (11%), and ARID1A (10%). The tumor mutational burden was higher in IBC than in non‐IBC. We identified 96 genes with an alteration frequency (p < 5% and q < 20%) different between IBC and non‐IBC, independently from the molecular subtypes and AJCC stage; 95 were more frequently altered in IBC, including TP53, genes involved in the DNA repair (BRCA2) and NOTCH pathways, and one (PIK3CA) was more frequently altered in non‐IBC. Ninety‐seven percent of IBCs displayed at least one AGA. This percentage was higher than in non‐IBC (87%), notably for drugs targeting DNA repair, NOTCH signaling, and CDK4/6, whose pathways were more frequently altered (DNA repair) or activated (NOTCH and CDK4/6) in IBC than in non‐IBC. The genomic landscape of IBC is different from that of non‐IBC. Enriched AGAs in IBC may explain its aggressiveness and provide clinically relevant targets.

A phase I, dose-escalation study of PF-06650808, an anti-Notch3 antibody-drug conjugate, in patients with breast cancer and other advanced solid tumors

Background PF-06650808 is a novel anti-Notch3 antibody-drug conjugate (ADC) able to deliver an auristatin-based cytotoxic payload to target cells. In this first-in-human, dose-finding, phase I study (NCT02129205), we investigated safety, pharmacokinetics, immunogenicity, and preliminary antitumor activity of single-agent PF-06650808 in 40 patients with advanced breast cancer (BC) and other solid tumors unselected for Notch3 expression. Primary endpoint was dose-limiting toxicity (DLT). PF-06650808 was administered intravenously every 3 weeks at a starting dose of 0.2 mg/kg, escalated up to 6.4 mg/kg following the modified continual reassessment method. An additional dose level, 2.0 mg/kg, was evaluated in patients with advanced, estrogen receptor-positive (ER⁺) BC. Results The majority of patients had advanced BC (60%) and almost all (90%) had received ≥3 prior lines of anticancer therapy. Treatment with PF-06650808 was generally well tolerated at dose levels ≤2.0 mg/kg with no DLTs. The maximum tolerated dose (MTD) was estimated to be 2.4 mg/kg. The most common treatment-related AEs in all patients were fatigue (40.0%), decreased appetite (37.5%), nausea (35.0%), alopecia (32.5%), abdominal pain (25.0%), pruritus (25.0%), and vomiting (25.0%). Five patients achieved a partial response (PR), including 2 unconfirmed PRs; 4 of the responders had ER⁺/PR⁺/HER2^- BC. Sixteen (51.6%) patients achieved stable disease, including 8 (57.1%) of 14 patients with ER⁺ BC. Tumor samples from all responders tested positive for NOTCH3 expression in a retrospective, exploratory analysis. Conclusions The anti-Notch3 ADC PF-06650808 has demonstrated a manageable safety profile and early signs of antitumor activity in patients with advanced BC.

Function of Integrin-Linked Kinase in Modulating the Stemness of IL-6-Abundant Breast Cancer Cells by Regulating γ-Secretase-Mediated Notch1 Activation in Caveolae

Interleukin-6 (IL-6) and Notch signaling are important regulators of breast cancer stem cells (CSCs), which drive the malignant phenotype through self-renewal, differentiation, and development of therapeutic resistance. We investigated the role of integrin-linked kinase (ILK) in regulating IL-6–driven Notch1 activation and the ability to target breast CSCs through ILK inhibition. Ectopic expression/short hairpin RNA-mediated knockdown of ILK, pharmacological inhibition of ILK with the small molecule T315, Western blot analysis, immunofluorescence, and luciferase reporter assays were used to evaluate the regulation of IL-6–driven Notch1 activation by ILK in IL-6–producing triple-negative breast cancer cell lines (MDA-MB-231, SUM-159) and in MCF-7 and MCF-7^IL-6 cells. The effects of ILK on γ-secretase complex assembly and cellular localization were determined by immunofluorescence, Western blots of membrane fractions, and immunoprecipitation. In vivo effects of T315-induced ILK inhibition on CSCs in SUM-159 xenograft models were assessed by mammosphere assays, flow cytometry, and tumorigenicity assays. Results show that the genetic knockdown or pharmacological inhibition of ILK suppressed Notch1 activation and the abundance of the γ-secretase components presenilin-1, nicastrin, and presenilin enhancer 2 at the posttranscriptional level via inhibition of caveolin-1-dependent membrane assembly of the γ-secretase complex. Accordingly, knockdown of ILK inhibited breast CSC-like properties in vitro and the breast CSC subpopulation in vivo in xenograft tumor models. Based on these findings, we propose a novel function of ILK in regulating γ-secretase–mediated Notch1 activation, which suggests the targeting of ILK as a therapeutic approach to suppress IL-6–induced breast CSCs.

Form and function: how estrogen and progesterone regulate the mammary epithelial hierarchy

The mammary gland undergoes dramatic post-natal growth beginning at puberty, followed by full development occurring during pregnancy and lactation. Following lactation, the alveoli undergo apoptosis, and the mammary gland reverses back to resemble the nonparous gland. This process of growth and regression occurs for multiple pregnancies, suggesting the presence of a hierarchy of stem and progenitor cells that are able to regenerate specialized populations of mammary epithelial cells. Expansion of epithelial cell populations in the mammary gland is regulated by ovarian steroids, in particular estrogen acting through its receptor estrogen receptor alpha (ERα) and progesterone signaling through progesterone receptor (PR). A diverse number of stem and progenitor cells have been identified based on expression of cell surface markers and functional assays. Here we review the current understanding of how estrogen and progesterone act together and separately to regulate stem and progenitor cells within the human and mouse mammary tissues. Better understanding of the hierarchal organization of epithelial cell populations in the mammary gland and how the hormonal milieu affects its regulation may provide important insights into the origins of different subtypes of breast cancer.

HIV-1 reprograms the migration of macrophages

Macrophages are motile leukocytes, targeted by HIV-1, thought to play a critical role in host dissemination of the virus. However, whether infection impacts their migration capacity remains unknown. We show that 2-dimensional migration and the 3-dimensional (3D) amoeboid migration mode of HIV-1-infected human monocyte-derived macrophages were inhibited, whereas the 3D mesenchymal migration was enhanced. The viral protein Nef was necessary and sufficient for all HIV-1-mediated effects on migration. In Nef transgenic mice, tissue infiltration of macrophages was increased in a tumor model and in several tissues at steady state, suggesting a dominant role for mesenchymal migration in vivo. The mesenchymal motility involves matrix proteolysis and podosomes, cell structures constitutive of monocyte-derived cells. Focusing on the mechanisms used by HIV-1 Nef to control the mesenchymal migration, we show that the stability, size, and proteolytic function of podosomes are increased via the phagocyte-specific kinase Hck and Wiskott-Aldrich syndrome protein (WASP), 2 major regulators of podosomes. In conclusion, HIV-1 reprograms macrophage migration, which likely explains macrophage accumulation in several patient tissues, which is a key step for virus spreading and pathogenesis. Moreover, Nef points out podosomes and the Hck/WASP signaling pathway as good candidates to control tissue infiltration of macrophages, a detrimental phenomenon in several diseases.

A synthetic triterpenoid CDDO-Im inhibits tumorsphere formation by regulating stem cell signaling pathways in triple-negative breast cancer

Triple-negative breast cancer is associated with poor prognosis because of a high rate of tumor recurrence and metastasis. Previous studies demonstrated that the synthetic triterpenoid, CDDO-Imidazolide (CDDO-Im) induced cell cycle arrest and apoptosis in triple-negative breast cancer. Since a small subpopulation of cancer stem cells has been suggested to be responsible for drug resistance and metastasis of tumors, our present study determined whether the effects of CDDO-Im in triple-negative breast cancer are due to the inhibition of a cancer stem cell subpopulation. CDDO-Im treatment markedly induced cell cycle arrest at G2/M-phase and apoptosis in the triple-negative breast cancer cell lines, SUM159 and MDA-MB-231. Because SUM159 cells were more sensitive to CDDO-Im than MDA-MB-231 cells, the effects of CDDO-Im on the cancer stem cell subpopulation were further investigated in SUM159 cells. SUM159 cells formed tumorspheres in culture, and the cancer stem cell subpopulation, CD24−/EpCAM+ cells, was markedly enriched in SUM159 tumorspheres. The CD24−/EpCAM+ cells in SUM159 tumorspheres were significantly inhibited by CDDO-Im treatment. CDDO-Im also significantly decreased sphere forming efficiency and tumorsphere size in both primary and secondary sphere cultures. PCR array of stem cell signaling genes showed that expression levels of many key molecules in the stem cell signaling pathways, such as Notch, TGF-β/Smad, Hedgehog and Wnt, were significantly down-regulated by CDDO-Im in SUM159 tumorspheres. Protein levels of Notch receptors (c-Notch1, Notch1 and Notch3), TGF-β/Smad (pSmad2/3) and Hedgehog downstream effectors (GLI1) also were markedly reduced by CDDO-Im. In conclusion, the present study demonstrates that the synthetic triterpenoid, CDDO-Im, is a potent anti-cancer agent against triple-negative breast cancer cells by targeting the cancer stem cell subpopulation.

Bringing androgens up a NOTCH in breast cancer

While it has been known for decades that androgen hormones influence normal breast development and breast carcinogenesis, the underlying mechanisms have only been recently elucidated. To date, most studies have focused on androgen action in breast cancer cell lines, yet these studies represent artificial systems that often do not faithfully replicate/recapitulate the cellular, molecular and hormonal environments of breast tumours in vivo. It is critical to have a better understanding of how androgens act in the normal mammary gland as well as in in vivo systems that maintain a relevant tumour microenvironment to gain insights into the role of androgens in the modulation of breast cancer development. This in turn will facilitate application of androgen-modulation therapy in breast cancer. This is particularly relevant as current clinical trials focus on inhibiting androgen action as breast cancer therapy but, depending on the steroid receptor profile of the tumour, certain individuals may be better served by selectively stimulating androgen action. Androgen receptor (AR) protein is primarily expressed by the hormone-sensing compartment of normal breast epithelium, commonly referred to as oestrogen receptor alpha (ERa (ESR1))-positive breast epithelial cells, which also express progesterone receptors (PRs) and prolactin receptors and exert powerful developmental influences on adjacent breast epithelial cells. Recent lineage-tracing studies, particularly those focussed on NOTCH signalling, and genetic analysis of cancer risk in the normal breast highlight how signalling via the hormone-sensing compartment can influence normal breast development and breast cancer susceptibility. This provides an impetus to focus on the relationship between androgens, AR and NOTCH signalling and the crosstalk between ERa and PR signalling in the hormone-sensing component of breast epithelium in order to unravel the mechanisms behind the ability of androgens to modulate breast cancer initiation and growth.

Runx2 is a novel regulator of mammary epithelial cell fate in development and breast cancer

Regulators of differentiated cell fate can offer targets for managing cancer development and progression. Here, we identify Runx2 as a new regulator of epithelial cell fate in mammary gland development and breast cancer. Runx2 is expressed in the epithelium of pregnant mice in a strict temporally and hormonally regulated manner. During pregnancy, Runx2 genetic deletion impaired alveolar differentiation in a manner that disrupted alveolar progenitor cell populations. Conversely, exogenous transgenic expression of Runx2 in mammary epithelial cells blocked milk production, suggesting that the decrease in endogenous Runx2 observed late in pregnancy is necessary for full differentiation. In addition, overexpression of Runx2 drove epithelial-to-mesenchymal transition-like changes in normal mammary epithelial cells, whereas Runx2 deletion in basal breast cancer cells inhibited cellular phenotypes associated with tumorigenesis. Notably, loss of Runx2 expression increased tumor latency and enhanced overall survival in a mouse model of breast cancer, with Runx2-deficient tumors exhibiting reduced cell proliferation. Together, our results establish a previously unreported function for Runx2 in breast cancer that may offer a novel generalized route for therapeutic interventions. Cancer Res; 74(18); 5277-86. ©2014 AACR.

Cellular senescence checkpoint function determines differential Notch1-dependent oncogenic and tumor-suppressor activities

Notch activity regulates tumor biology in a context-dependent and complex manner. Notch may act as an oncogene or a tumor suppressor gene even within the same tumor type. Recently, Notch signaling has been implicated in cellular senescence. Yet, it remains unclear as to how cellular senescence checkpoint functions may interact with Notch-mediated oncogenic and tumor suppressor activities. Herein, we used genetically engineered human esophageal keratinocytes and esophageal squamous cell carcinoma cells to delineate the functional consequences of Notch activation and inhibition along with pharmacological intervention and RNA interference (RNAi) experiments. When expressed in a tetracycline-inducible manner, the ectopically expressed activated form of Notch1 (ICN1) displayed oncogene-like characteristics inducing cellular senescence corroborated by the induction of G0/G1 cell-cycle arrest, Rb dephosphorylation, flat and enlarged cell morphology and senescence-associated β-galactosidase activity. Notch-induced senescence involves canonical CSL/RBPJ-dependent transcriptional activity and the p16^INK4A-Rb pathway. Loss of p16^INK4A or the presence of human papilloma virus (HPV) E6/E7 oncogene products not only prevented ICN1 from inducing senescence, but permitted ICN1 to facilitate anchorage-independent colony formation and xenograft tumor growth with increased cell proliferation and reduced squamous-cell differentiation. Moreover, Notch1 appears to mediate replicative senescence as well as TGF-β-induced cellular senescence in non-transformed cells and that HPV E6/E7 targets Notch1 for inactivation to prevent senescence, revealing a tumor suppressor attribute of endogenous Notch1. In aggregate, cellular senescence checkpoint functions may influence dichotomous Notch activities in the neoplastic context.