Aggressive Basal-like Breast Cancer Research Articles

Cancer and lymphatic marker FOXC2 drives wound healing and fibrotic tissue formation.

The FOXC2 transcription factor has been tied to a wide range of disease states, serving as a promising prognostic biomarker associated with aggressive basal-like human breast cancers (increased cancer invasion and metastasis). Dysregulation of FOXC2 expression has also been found to promote defects in lymphatic remodeling and hyperplastic lymphedema-distichiasis (LD). Since chronic lymphedema is a forerunner of several malignancies and cancers have been known to arise from poorly healing chronic wounds (e.g., Marjolin ulcers), we examined the effect of Foxc2 dysfunction on skin wound healing. We used our splinted excisional wounding model that mimics human-like wound healing on wildtype and Foxc2+/- mice (n = 4), which demonstrate incomplete lymphatic vasculature and lymphatic dysfunction. Wound size was measured over the course of 18days. Tissue was explanted from both groups at post-operative day (POD) 14 and 18 and stained with Masson's Trichrome to assess scar formation, Picrosirius Red for dermal integrity, or immunofluorescence to assess lymphatic (LYVE1) cell populations. Wildtype mice completely healed by POD 14, while Foxc2+/-mice did not completely heal until POD18. Scar area of healed Foxc2+/-mice (POD 18) was larger than that of healed wild-type mice (POD 14; p = 0.0294). At POD 14, collagen "bers in the scars of Foxc2+/-mice to be narrower (p = 0.0117) and more highly aligned (p = 0.0110), indicating signi"cantly more "brosis in these mice. Collagen "bers in both groups became longer (p = 0.0116) and wider (p = 0.0020) from POD 14 to 18, indicating a temporal evolution of "brosis. Foxc2+/-mice also had lower numbers of LYVE1+, F4/80+ and CD4+ cells compared to wildtype mice. Individuals over 65 years old are more likely to develop cancer and are highly susceptible to developing chronic wounds. Here, we found that FOXC2, which is tied to cancer metastasis and lymphatic dysregulation, also impairs wound healing and promotes "brotic tissue architecture. With FOXC2 proposed as a potential therapeutic target for cancer metastasis, its downstream systemic effects should be considered against the increased chance of developing nonhealing wounds. Further delineation of the microenvironment, cellular events, and molecular signals during normal and Foxc2-associated abnormal wound healing will improve clinical therapies targeting this important marker.

Abstract PO2-16-04: Proteogenomic characterization of non-luminal A versus luminal A breast cancer tumor cells enriched by laser microdissection

Abstract Introduction: Breast cancer (BC) is classified into four widely-accepted intrinsic subtypes based on PAM (Prediction Analysis of Microarray) 50 gene expression profiles: Luminal A (LumA), Luminal B (LumB), Her2-enriched (Her2) and basal-like (Basal). Recent multi-omic studies of human BC have identified many potential therapeutic biomarkers for these subtypes and have also revealed the extensive molecular heterogeneity of the disease. Patients with LumA tumors generally have better outcomes because these tumors are typically slower-growing and responsive to hormone therapy. However, there is still considerable variation in the clinical outcomes of patients with non-LumA tumors. Here, we strive to understand the proteogenomic characteristics of intrinsically-defined non-LumA tumors in reference to LumA tumors. Methods: A total of 117 retrospectively-collected, untreated primary breast tumor specimens, with a focus on non-LumA subtypes, were selected from the Clinical Breast Care Project and consented using a HIPAA-compliant, IRB-approved protocol. The study cohort had a median patient follow-up of 9.3 years, enabling clinical outcome-related analyses. Immunohistochemistry (IHC) subtyping was used to enrich the cohort with non-LumA subtypes. Breast tumors were embedded in OCT (Optimal Cutting Temperature) compound and processed by laser microdissection (LMD) to enrich for tumor cells. DNA, RNA, and protein were simultaneously extracted from each tumor using the illustra triplePrep kit. Paired-end RNA sequencing and whole genome sequencing (WGS) were performed for 117 and 99 tumors, respectively, using the Illumina HiSeq platform. Quantitative global proteomics and phosphoproteomic analyses were performed on 112 and 50 tumors, respectively, using isobaric TMT 6-plex labeling with the “universal reference” strategy. Results: We observed significantly lower stromal, immune and microenvironment scores in non-basal-like tumors, especially the LumA subtype from LMD-processed samples, compared to that of the same tumors but bulk-processed in TCGA-breast cancer study. There was also significantly lower stromal gene expression in LMD LumA compared to TCGA LumA. Unlike a recent report on proteomics clustering of bulk-processed tumors, we did not observe a stromal-enriched cluster, probably because the use of LMD minimized stromal components. Many common patterns of somatic mutations were observed among non-LumA tumors, such as dominant TP53 mutations and 5q deletion, suggesting a potentially common cell-of-origin for non-LumA tumors, such as an ER negative cancer stem cell or progenitor cell for these tumor subtypes. Cell proliferation-associated genes were amplified and proliferation pathways strongly enriched in non-LumA tumors. In addition to this, we identified two distinct phosphoproteomic profiles for relapsed and relapse-free basal-like BC. Moreover, we also identified 17 differentially expressed phosphopeptides that could identify cases of relapsed and relapse-free basal-like BC with a significant difference in progression-free interval of surviving cases. Conclusion: This study provides an integrated proteogenomic characterization of non-LumA vs LumA tumor specimens enriched for cancer cells. We identified many common features of non-LumA tumors and also identified phosphopeptides that could serve as potential biomarkers for less aggressive basal-like BC and possibly guide treatment selections. Disclaimer: The contents of this publication are the sole responsibility of the author(s) and do not necessarily reflect the views, opinions or policies of USUHS, HJF, the DoD or the Departments of the Army, Navy or Air Force or the DOE or PNNL. Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Government. Citation Format: Praveen Kumar Raj Kumar, Xiaoying Lin, Tao Liu, Lori Sturtz, Marina Gritsenko, Vladislav Petyuk, Tyler Sagendorf, Brenda Deyarmin, Jianfang Liu, Anupama Praveen-Kumar, Guisong Wang, Jason McDermott, Anil Shukla, Ronald Moore, Matthew Monroe, Bobbie-Jo Webb-Robertson, Jeffrey Hooke, Leigh Fantacone-Campbell, Brad Mostoller, Leonid Kvecher, Jennifer Kane, Jennifer Melley, Stella Somiari, Patrick Soon-Shiong, Richard Smith, Richard Mural, Karin Rodland, Craig Shriver, Albert Kovatich, Hai Hu. Proteogenomic characterization of non-luminal A versus luminal A breast cancer tumor cells enriched by laser microdissection [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-16-04.

TLE3 Sustains Luminal Breast Cancer Lineage Fidelity to Suppress Metastasis.

Transcriptional corepressor TLE3 actively suppresses SOX9 and TGFβ transcriptional programs to sustain the luminal lineage identity of breast cancer cells and to inhibit metastatic progression.

Abstract 5847: Normal mammary epithelium of BRCA1 mutation carriers demonstrates increased susceptibility to cell plasticity

Abstract Background: Epithelial-mesenchymal transition (EMT) in breast cancer drives tumor invasion, metastasis and drug resistance. BRCA1 mutation carriers have a high risk for developing aggressive basal-like triple-negative breast cancers with EMT characteristics. It has been described that normal mammary epithelium of BRCA1-mutation carriers is comprised of aberrant luminal progenitor cell population resembling basal-like breast cancer cells. Yet, the role of BRCA1 in regulating epithelial cell plasticity in normal mammary gland remains largely obscure. Aim: Here, we used patient-derived normal and cancer organoid cultures from BRCA1-mutation carriers and noncarriers, to examine the effect of the BRCA1 mutation background on epithelial cell plasticity and the susceptibility to EMT. Methods and results: Mammary organoids were established from normal or cancer mammary tissues obtained from consenting patients undergoing lumpectomy or mastectomy. Isolated cells were plated in adherent basement membrane extract (BME) drops and overlaid with optimized organoid culture medium. EMT regulation in breast cancer is usually studied using cell lines and murine models. To determine the possibility to study EMT on patient-derived organoids, organoid culture media was optimized and established organoids were exposed to TGFβ to induce EMT. Morphological and phenotypic alterations were characterized using immunolabeling and visualization with confocal microscopy. Breast cancer organoids induced with TGFβ demonstrated EMT-like changes including the downregulation of E-Cadherin and upregulation of N-Cadherin. Moreover, breast cancer organoids showed typical cytoskeleton rearrangements. Here, the transformation from cortical actin into stress fibers formed in dedifferentiated mesenchymal cells, was visualized with actin staining. However, normal mammary organoids behaved differently. The cytoskeleton of BRCA-wild type (noncarriers) normal mammary organoids was not affected by the treatment. Curiously, normal mammary organoids derived from BRCA1-mutation carriers demonstrated EMT like changes upon exposure to TGFβ. To further determine mechanisms facilitating cell plasticity in BRCA1-mutation carriers, single cell RNA sequencing analysis on BRACA1-mutation carriers and noncarriers derived organoids is ongoing. Conclusion: The results suggest that BRCA1 germline mutation predisposes normal mammary epithelium dedifferentiation due to increased susceptibility to EMT. Citation Format: Rakefet Ruth Ben-Yishay, Naama Herman, Vered Noy, Eyal Mor, Aiham Mansur, Dana Ishay-Ronen. Normal mammary epithelium of BRCA1 mutation carriers demonstrates increased susceptibility to cell plasticity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5847.

Abstract 2918: Characterization of a novel transplantable C3TAg breast cancer model in C57BL/6J mice

Abstract Introduction: In women in the United States, breast cancer (BC) is the second leading cause of cancer-related death. BC is a heterogeneous disease, characterized by several subtypes based on molecular markers including several hormone receptors. Transcriptomic analysis further stratifies the disease. The basal-like subtype, often triple-negative for hormone receptors, has the poorest prognosis partially due to the absence of targeted therapies. Obesity, a preventable cause of cancer, is an established risk factor for breast cancer, including basal-like breast cancers. Mouse models to study the interaction of BC and obesity, particularly the more aggressive basal-like BC, are crucial. The C3(1)/SV40 large T-antigen (TAg) transgenic mouse model is an established model of basal-like mammary cancer that recapitulates several key features of human breast cancer. However, this model was generated in FVB mice, which is not an ideal genetic background for studying obesity, immunology and other aspects of cancer research. The goal of this study was to develop and characterize a C3TAg transgenic mouse model on a C57BL/6 background. Therefore, the current study backcrossed C3TAg transgenic FVB mice with C57BL/6 mice, a model most commonly used to study obesity, for 10 generations to create a transplantable C3TAg model in C57BL/6 mice. Methods: Cell Line Generation: C3TAg transgenic FVB mice were backcrossed with C57BL/6 mice for 10 generations. Tumors from 6-month-old heterozygous female mammary tissue were harvested, dissociated, and subcloned by limited dilution. A total of 156 clonal lines were established from which a subset of 12 lines displaying differences in morphology, growth and expression of metabolic and EMT genes (by qPCR). In vivo: 96 female C57BL/6J mice were randomized into 12 groups (n=8/group) and orthotopically injected with three different cell densities (5*104, 1.5*105, 5*105 cells/mouse) from one of the four selected lines. Mice tumor growth was assessed using electronic calipers. In vitro: Proliferation and cellular respiration were assessed and molecular subtyping was conducted using Affymetrix microarray data. Results: All tested cell lines formed tumors in vivo, with macroscopic characteristics of basal-like tumors including central necrosis. In vitro growth and metabolism of tested lines showed modest dissimilarity; in contrast, tumor growth rates and metastatic outgrowth were starkly dissimilar among the tested lines. Transcriptomic data clustered these cell lines with human BC tumors. Conclusions: Here we report for the first time a transplantable C3TAg model in C57BL/6 mice with highly effective tumor engraftment and growth, and with variable phenotypes for tumor growth and metastasis. Thus, this model may serve as an attractive model for the study of the interactions of basal-like breast cancer and obesity. This work was supported by R35CA197627 to SH. Citation Format: Meredith S. Carson, Michael F. Colman, Daniel Roth, Jody Albright, Melissa VerHague, John E. French, Stephen D. Hursting. Characterization of a novel transplantable C3TAg breast cancer model in C57BL/6J mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2918.

M1 Polarization Markers Are Upregulated in Basal-Like Breast Cancer Molecular Subtype and Associated With Favorable Patient Outcome.

BackgroundBreast cancer heterogeneity is an essential element that plays a role in the therapy response variability and the patient’s outcome. This highlights the need for more precise subtyping methods that focus not only on tumor cells but also investigate the profile of stromal cells as well as immune cells.ObjectivesTo mine publicly available transcriptomic breast cancer datasets and reanalyze their transcriptomic profiling using unsupervised clustering in order to identify novel subsets in molecular subtypes of breast cancer, then explore the stromal and immune cells profile in each subset using bioinformatics and systems immunology approaches.Materials and MethodsTranscriptomic data from 1,084 breast cancer patients obtained from The Cancer Genome Atlas (TCGA) database were extracted and subjected to unsupervised clustering using a recently described, multi-step algorithm called Iterative Clustering and Guide-gene Selection (ICGS). For each cluster, the stromal and immune profile was investigated using ESTIMATE and CIBERSORT analytical tool. Clinical outcomes and differentially expressed genes of the characterized clusters were identified and validated in silico and in vitro in a cohort of 80 breast cancer samples by immunohistochemistry.ResultsSeven unique sub-clusters showed distinct molecular and clinical profiles between the well-known breast cancer subtypes. Those unsupervised clusters identified more homogenous subgroups in each of the classical subtypes with a different prognostic profile. Immune profiling of the identified clusters showed that while the classically activated macrophages (M1) are correlated with the more aggressive basal-like breast cancer subtype, the alternatively activated macrophages (M2) showed a higher level of infiltration in luminal A and luminal B subtypes. Indeed, patients with higher levels of M1 expression showed less advanced disease and better patient outcomes presented as prolonged overall survival. Moreover, the M1 high basal-like breast cancer group showed a higher expression of interferon-gamma induced chemokines and guanylate-binding proteins (GBPs) involved in immunity against microbes.ConclusionAdding immune profiling using transcriptomic data can add precision for diagnosis and prognosis and can cluster patients according to the available modalities of therapy in a more personalized approach.

Abstract 3833: Epigenetic regulation of cell state transitions and the therapeutic implications in breast cancer

Abstract During cancer progression, cells would reversibly transit among different cell states that differ in their competence to contribute towards tumor growth, survival, and metastasis. The activation of epithelial-mesenchymal transition (EMT) program in cancer cells has often been attributed to enhanced tumorigenic potential and a gain of therapeutic resistance. We hypothesized that by promoting mesenchymal-epithelial transition (MET), the reverse process of EMT, it could induce a loss of tumorigenic potential and increase susceptibility to standard chemotherapeutics. As EMT is a dynamic and reversible process, epigenetic regulations such as histone modifications and DNA methylation are important in regulating and reprogramming the expression of EMT-responsive genes. Hence, we seek to understand how the epigenetic landscape is altered during transitions between cell states. To understand the molecular link between epigenetic regulations and cell state transitions in cancer cells, a high-throughput library screen on epigenetic modifiers was performed. Epigenetic modifying compounds that can induce MET in basal-like breast cancer cells were uncovered. In vitro and in vivo data demonstrate that compounds targeting the non-BET bromodomains were able to promote MET, induce a loss of stem-like properties, and decrease the tumorigenicity of basal-like breast cancer cells. Using various next-generation sequencing approaches, we also elucidated the mechanisms of how targeting non-BET bromodomains would regulate cell state transitions in breast cancers. While epigenetic therapies are effective in the treatment of hematological malignancies, its application in solid tumors is still limited. Here, we propose the possible use of an epigenetic MET inducer for differentiation therapy of the aggressive basal-like breast cancers. Citation Format: Li Ping Toh, Ser Yue Loo, Wai Leong Tam. Epigenetic regulation of cell state transitions and the therapeutic implications in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3833.

Abstract 5107: DDR1 and MT1-MMP expression levels are major determinants of 3D type I collagen-induced apoptosis in basal-like breast carcinoma

Abstract Type I collagen is the major adhesive component in breast interstitial stroma, which represents the first barrier against tumor cell invasion after basement-membrane degradation. Among cellular receptors, type I collagen is able to activate discoidin domain receptors DDR1 and DDR2. We have previously shown that in 3D collagen matrix, DDR1 plays a key role as it promotes cell growth suppression and apoptosis through the upregulation of the pro-apoptotic mediator BIK in noninvasive luminal-like breast carcinoma cells. We have also shown that MT1-MMP is able to rescue these cells and protect them against the effects induced by collagen/DDR1/BIK axis. Our data suggested that the protective effect of MT1-MMP might be mediated through the degradation of type I collagen and/or DDR1 cleavage. Decreased DDR1 expression has been associated with the epithelial to mesenchymal transition process in breast cancer, and its overexpression in aggressive basal-like breast cancer cells reduces their invasiveness in 3D cultures and in vivo. In the present work, we propose to study the role of MT1-MMP in the resistance against collagen-induced apoptosis in basal-like breast carcinoma MDA-MB-231 cells. We aimed to investigate whether MT1-MMP depletion is able to restore apoptosis mediated by collagen/DDR1/BIK axis and to verify if such depletion is able to restore full-length DDR1 expression and phosphorylation. ShRNA strategy against MT1-MMP mRNA was able to partially restore full length DDR1 expression and phosphorylation. This was accompanied by a decrease in cell growth and an upregulation of BIK expression. This suggested that MT1-MMP expression in basal-like breast carcinoma cells, in addition to a low basal level of DDR1 expression, protects these cells against collagen-induced apoptosis via DDR1 cleavage. Since DDR1 was moderately expressed in MDA-MB-231 cells, we then investigated whether overexpression of DDR1 could be able to increase its ability to suppress cell growth and to induce apoptosis. Data showed that overexpression of DDR1 induced a decrease in cell growth and an increase in BIK expression, suggesting that moderate expression level of full length DDR1 in basal-like breast carcinoma provides them with a capacity to resist to collagen-induced cell growth suppression and apoptosis. Finally, the combined overexpression of DDR1 and depletion of MT1-MMP in MDA-MB-231 cells synergistically increased collagen-induced cell growth suppression and apoptosis to a level similar to that observed in luminal breast carcinoma. Taken together, our data suggest that during the acquisition of mesenchymal features, the low level of DDR1 expression should be considered as an important biomarker in the prognosis of basal-like breast carcinoma, conferring them a high rate of cell growth and resistance to BIK-mediated apoptosis induced by the stromal collagen. Citation Format: Charles Saby, Guillaume Collin, Maha Sinane, Emilie Buache, Laurence Van Gulick, Frédéric Saltel, Erik Maquoi, Hamid Morjani. DDR1 and MT1-MMP expression levels are major determinants of 3D type I collagen-induced apoptosis in basal-like breast carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5107.

Diverse Roles of Annexin A6 in Triple-Negative Breast Cancer Diagnosis, Prognosis and EGFR-Targeted Therapies.

The calcium (Ca2+)-dependent membrane-binding Annexin A6 (AnxA6), is a multifunctional, predominantly intracellular scaffolding protein, now known to play relevant roles in different cancer types through diverse, often cell-type-specific mechanisms. AnxA6 is differentially expressed in various stages/subtypes of several cancers, and its expression in certain tumor cells is also induced by a variety of pharmacological drugs. Together with the secretion of AnxA6 as a component of extracellular vesicles, this suggests that AnxA6 mediates distinct tumor progression patterns via extracellular and/or intracellular activities. Although it lacks enzymatic activity, some of the AnxA6-mediated functions involving membrane, nucleotide and cholesterol binding as well as the scaffolding of specific proteins or multifactorial protein complexes, suggest its potential utility in the diagnosis, prognosis and therapeutic strategies for various cancers. In breast cancer, the low AnxA6 expression levels in the more aggressive basal-like triple-negative breast cancer (TNBC) subtype correlate with its tumor suppressor activity and the poor overall survival of basal-like TNBC patients. In this review, we highlight the potential tumor suppressor function of AnxA6 in TNBC progression and metastasis, the relevance of AnxA6 in the diagnosis and prognosis of several cancers and discuss the concept of therapy-induced expression of AnxA6 as a novel mechanism for acquired resistance of TNBC to tyrosine kinase inhibitors.

FOXF2 deficiency accelerates the visceral metastasis of basal-like breast cancer by unrestrictedly increasing TGF-β and miR-182-5p.

The mesenchymal transcription factor forkhead box F2 (FOXF2) is a critical regulator of embryogenesis and tissue homeostasis. Our previous studies demonstrated that FOXF2 is ectopically expressed in basal-like breast cancer (BLBC) cells and that FOXF2 deficiency promotes the epithelial-mesenchymal transition and aggressiveness of BLBC cells. In this study, we found that FOXF2 controls transforming growth factor-beta (TGF-β)/SMAD signaling pathway activation through transrepression of TGF-β-coding genes in BLBC cells. FOXF2-deficient BLBC cells adopt a myofibroblast-/cancer-associated fibroblast (CAF)-like phenotype, and tend to metastasize to visceral organs by increasing autocrine TGF-β signaling and conferring aggressiveness to neighboring cells by increasing paracrine TGF-β signaling. In turn, TGF-β silences FOXF2 expression through upregulating miR-182-5p, a posttranscriptional regulator of FOXF2 and inducer of metastasis. In addition to mediating a reciprocal repression loop between FOXF2 and TGF-β through direct transrepression by SMAD3, miR-182-5p forms a reciprocal repression loop with FOXF2 that directly transrepresses MIR182 expression. Therefore, FOXF2 deficiency accelerates the visceral metastasis of BLBC through unrestricted increases in autocrine and paracrine TGF-β signaling, and miR-182-5p expression. Our findings provide novel mechanisms underlying the roles of TGF-β, miR-182-5p, and FOXF2 in accelerating BLBC dissemination and metastasis, and may facilitate the development of therapeutic strategies for aggressive BLBC.

ITGA2 promotes expression of ACLY and CCND1 in enhancing breast cancer stemness and metastasis

Cancer metastasis is largely incurable and accounts for 90% of breast cancer deaths, especially for the aggressive basal-like or triple negative breast cancer (TNBC). Combining patient database analyses and functional studies, we examined the association of integrin family members with clinical outcomes as well as their connection with previously identified microRNA regulators of metastasis, such as miR-206 that inhibits stemness and metastasis of TNBC. Here we report that the integrin receptor CD49b-encoding ITGA2, a direct target of miR-206, promotes breast cancer stemness and metastasis. ITGA2 knockdown suppressed self-renewal related mammosphere formation and pluripotency marker expression, inhibited cell cycling, compromised migration and invasion, and therefore decreased lung metastasis of breast cancer. ITGA2 overexpression reversed miR-206-caused cell cycle arrest in G1. RNA sequencing analyses revealed that ITGA2 knockdown inhibits genes related to cell cycle regulation and lipid metabolism, including CCND1 and ACLY as representative targets, respectively. Knockdown of CCND1 or ACLY inhibits mammosphere formation of breast cancer cells. Overexpression of CCND1 rescues the phenotype of ITGA2 knockdown-induced cell cycle arrest. ACLY-encoded ATP citrate lyase is essential to maintain cellular acetyl-CoA levels. CCND1 knockdown further mimics ITGA2 knockdown in abolishing lung colonization of breast cancer cells. We identified that the low levels of miR-206 as well as high expression levels of ITGA2, ACLY and CCND1 are associated with an unfavorable relapse-free survival of the patients with estrogen receptor-negative or high grade breast cancer, especially basal-like or TNBC, possibly serving as potential biomarkers of cancer stemness and therapeutic targets of breast cancer metastasis.

DDR1 and MT1-MMP Expression Levels Are Determinant for Triggering BIK-Mediated Apoptosis by 3D Type I Collagen Matrix in Invasive Basal-Like Breast Carcinoma Cells.

Type I collagen is the major adhesive component in breast interstitial stroma, which represents the first barrier against tumor cell invasion after basement-membrane degradation. Among cellular receptors, type I collagen is able to activate discoidin domain receptors DDR1 and DDR2. We have previously shown that in 3D collagen matrix, DDR1 plays a key role as it promotes cell growth suppression and apoptosis through the upregulation of the pro-apoptotic mediator BIK in noninvasive luminal-like breast carcinoma cells. We have also shown that MT1-MMP is able to rescue these cells and protect them against the effects induced by collagen/DDR1/BIK axis. Our data suggested that the protective effect of MT1-MMP might be mediated through the degradation of type I collagen and/or DDR1 cleavage. Decreased DDR1 expression has been associated with the epithelial to mesenchymal transition process in breast cancer, and its overexpression in aggressive basal-like breast cancer cells reduces their invasiveness in 3D cultures and in vivo. In the present work, we propose to study the role of MT1-MMP in the resistance against collagen-induced apoptosis in basal-like breast carcinoma MDA-MB-231 cells. We aimed to investigate whether MT1-MMP depletion is able to restore apoptosis mediated by collagen/DDR1/BIK axis and to verify if such depletion is able to restore full-length DDR1 expression and phosphorylation. ShRNA strategy against MT1-MMP mRNA was able to partially restore full length DDR1 expression and phosphorylation. This was accompanied by a decrease in cell growth and an upregulation of BIK expression. This suggested that MT1-MMP expression in basal-like breast carcinoma cells, in addition to a low basal level of DDR1 expression, protects these cells against collagen-induced apoptosis via DDR1 cleavage. Since DDR1 was moderately expressed in MDA-MB-231 cells, we then investigated whether overexpression of DDR1 could be able to increase its ability to suppress cell growth and to induce apoptosis. Data showed that overexpression of DDR1 induced a decrease in cell growth and an increase in BIK expression, suggesting that moderate expression level of full length DDR1 in basal-like breast carcinoma provides them with a capacity to resist to collagen-induced cell growth suppression and apoptosis. Finally, the combined overexpression of DDR1 and depletion of MT1-MMP in MDA-MB-231 cells synergistically increased collagen-induced cell growth suppression and apoptosis to a level similar to that observed in luminal breast carcinoma. Taken together, our data suggest that during the acquisition of mesenchymal features, the low level of DDR1 expression should be considered as an important biomarker in the prognosis of basal-like breast carcinoma, conferring them a high rate of cell growth and resistance to BIK-mediated apoptosis induced by the stromal collagen.

Abstract P4-05-01: Limb-Bud-and-Heart (LBH), a novel WNT effector in promoting basal-like breast cancer

Abstract BACKGROUND: Clinically aggressive basal-like breast cancers (BLBC) disproportionally contribute to cancer deaths, but lack effective treatment options due to absence of expression of key therapeutic targets (i.e. ER, PR, HER2). New evidence suggests BLBC may originate from luminal breast epithelial cells through luminal-to-basal cell lineage conversion and dedifferentiation. However, the factors that reprogram cell fate and differentiation states during BLBC development remain poorly understood. Our laboratory has identified a novel WNT/β-Catenin target transcriptional regulator, Limb-Bud-and-Heart (LBH), and shown LBH is majorly over expressed in aggressive BLBC harboring WNT hyperactivation. We previously showed in genetic mouse models in vivo that LBH is a key mammary stem cell and basal cell lineage regulator essential for normal mammary gland development. Using crosses between MMTV-Wnt1 transgenic mice and conditional LBH knockout mice, we tested if LBH is a critical effector of WNT-driven basaloid breast cancer, and whether its inhibition may prevent and/or attenuate BLBC formation and progression. RESULTS: In our in vivo mouse model, LBH inactivation in the basal mammary epithelium using a Keratin 14/K14-Cre deleter strain significantly attenuated MMTV-Wnt1-induced mammary gland hyperplasia and led to a delay in tumor onset. Surprisingly, tumor burden and tumor volumes were not changed, indicating that LBH is not required for WNT-driven tumorigenesis. However, LBH-deficient MMTV-Wnt1-transgenic tumors exhibited pronounced histopathological differences compared to LBH WT MMTV-Wnt1-transgenic tumors. Whereas MMTV-Wnt1+;K14CreLbh WT tumors were highly vascularized, disorganized, with mixed basal and luminal cell identity; tumors from MMTV-Wnt1+;K14CreLbh KO mice were more organized, differentiated, and predominantly luminal Keratin 8 positive. Since attenuation of mammary gland hyperplasia and tumor onset in this model suggests that LBH deficiency may negatively affect WNT-induced stem cell expansion, we next investigated the LBH effects on the tumor stem cell compartment. MMTV-Wnt1+;K14CreLbh KO mice were crossed with two different stem cell reporter lines: Lgr5-eGFP mice, which specifically mark WNT-responsive epithelial stem cells; and SHIP-GFP reporter mice, which mark activated, proliferating mammary stem cells but not quiescent or slow-cycling stem cells. These studies are ongoing and the latest findings will be discussed. CONCLUSION: Our data indicate that LBH is an essential cell fate regulator downstream of oncogenic WNT signaling that maintains basal lineage identity in baseloid breast cancers. LBH inhibition may be a potential novel strategy to treat basal subtype triple negative breast cancer patients through differentiation therapy. Citation Format: Briegel K, Ashad-Bishop K. Limb-Bud-and-Heart (LBH), a novel WNT effector in promoting basal-like breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-05-01.

Activin A Signaling Regulates IL13Rα2 Expression to Promote Breast Cancer Metastasis.

Metastatic dissemination of cancer cells to distal organs is the major cause of death for patients suffering from the aggressive basal-like breast cancer (BLBC) subtype. Recently, we have shown that interleukin 13 receptor alpha 2 (IL13Rα2) is a critical gene that is overexpressed in a subset of BLBC primary tumors associated with poor distant metastasis-free survival (DMFS) and can promote extravasation and metastasis of breast cancer cells to the lungs. However, the upstream signaling mechanisms that promote aberrant IL13Rα2 expression during tumor progression remain unknown. Driven by our previously published gene expression microarray data derived from a well-characterized cell line model for BLBC progression, we show that both Inhibin βA (INHBA) and IL13Rα2 genes exhibit similarly higher expression levels in metastatic compared to non-metastatic cells and that overexpression of both genes predicts worse metastasis-free survival of patients with high grade tumors. Activin A, a member of the TGFβ superfamily comprising two INHBA subunits, has been shown to play context-depended roles in cancer progression. Here, we demonstrate that INHBA depletion downregulates IL13Rα2 expression in metastatic breast cancer cells, whereas treatment with Activin A in non-metastatic cells increases its expression levels. We also find that Activin A predominantly induces Smad2 phosphorylation and to a lesser extent activates Smad3 and Akt. Interestingly, we also show that Activin A-mediated upregulation of IL13Rα2 is Smad2-dependent since knocking down Smad2 or using the ALK4/ALK5 inhibitors EW-7197 and SB-505124 abolishes this effect. Most importantly, our data indicate that knocking down INHBA levels in breast cancer cells delays primary tumor growth, suppresses migration in vitro and inhibits the formation of lung metastases in vivo. Conclusively, our findings presented here suggest that the development of therapeutic interventions employing small molecule inhibitors against Activin receptors or neutralizing antibodies targeting Activin A ligand, could serve as alternative approaches against breast tumors overexpressing INHBA and/or IL13Rα2.

<i>ITGA2</i> Promotes Breast Cancer Stemness and Metastasis Through Enhanced <i>ACLY</i> and <i>CCND1</i> Expression

Background: Cancer metastasis is largely incurable and accounts for 90% of breast cancer deaths, especially for the aggressive basal-like or triple negative breast cancer (TNBC). Accumulating evidence demonstrates that integrins are essential for normal development and malignancies; however, the molecular functions and clinical relevance for each integrin subunit in cancer metastasis have yet to be fully elucidated. Methods: Combining patient database analyses and functional studies, we examined the association of integrin family members with clinical outcomes as well as their connection with previously identified microRNA regulators of metastasis, such as miR-206 that inhibits stemness and metastasis of TNBC. Findings: Here we report that the integrin receptor CD49b-encoding ITGA2, a direct target of miR-206, promotes breast cancer stemness and metastasis through maintaining ACLY and CCND1 levels. ITGA2 knockdown suppressed self-renewal related mammosphere formation and pluripotency marker expression, inhibited cell cycling, compromised migration and invasion, and therefore decreased lung metastasis of breast cancer. RNA sequencing analyses revealed that ITGA2 knockdown inhibits genes related to cell cycle regulation and lipid metabolism such as CCND1 and ACLY. ACLY-encoded ATP citrate lyase is essential to maintain cellular acetyl-CoA levels and mammosphere formation of breast cancer cells. Overexpression of CCND1 rescues the phenotype of ITGA2 knockdown-induced cell cycle arrest. Interpretation: We identified that the miR-206/ITGA2/ACLY/CCND1 axis is associated with relapse-free survival of the patients with high grade breast cancer, especially basal-like breast cancer, possibly serving as potential biomarkers and therapeutic targets of breast cancer stemness and metastasis. Funding Statement: This manuscript has been partially supported by NIH/NCI grants R00CA160638 (H.L. & V.A.) and R01CA213843 (R.A.K), American Cancer Society grant ACS127951-RSG-15-025-01-CSM (H.L.); the Susan G. Komen Foundation CCR15332826 (H.L.) and CCR18548501 (X.L); the Department of Defense W81XWH-16-1-0021 (H.L.); the Lynn Sage Cancer Research Foundation (X.L. and H. L.); Northwestern University's Endocrinology Training Grant T32DK007169-39 (A.H.). Declaration of Interests: There is no conflict of interest for the authors of this manuscript. Ethics Approval Statement: All animal procedures complied with the NIH Guidelines for the Care and Use of Laboratory Animals and were approved by the respective Institutional Animal Care and Use Committees.

Induction of N-Ras degradation by flunarizine-mediated autophagy

Ras GTPases are powerful drivers for tumorigenesis, but directly targeting Ras for treating cancer remains challenging. The growth and transforming activity of the aggressive basal-like breast cancer (BLBC) are driven by N-Ras. To target N-Ras in BLBC, this study screened existing pharmacologically active compounds for the new ability to induce N-Ras degradation, which led to the identification of flunarizine (FLN), previously approved for treating migraine and epilepsy. The FLN-induced N-Ras degradation was not affected by a 26S-proteasome inhibitor. Rather, it was blocked by autophagy inhibitors. Furthermore, N-Ras can be seen co-localized with active autophagosomes upon FLN treatment, suggesting that FLN alters the autophagy pathway to degrade N-Ras. Importantly, FLN treatment recapitulated the effect of N-RAS silencing in vitro by selectively inhibiting the growth of BLBC cells, but not that of breast cancer cells of other subtypes. In addition, in vivo FLN inhibited tumor growth of a BLBC xenograft model. In conclusion, this proof-of-principle study presents evidence that the autophagy pathway can be coerced by small molecule inhibitors, such as FLN, to degrade Ras as a strategy to treat cancer. FLN has low toxicity and should be further investigated to enrich the toolbox of cancer therapeutics.

LncRNA BLAT1 is Upregulated in Basal-like Breast Cancer through Epigenetic Modifications

Long-noncoding RNAs (lncRNAs) have been shown to participate in oncogenesis across a variety of cancers and may represent novel therapeutic targets. However, little is known about the role of lncRNAs in basal-like breast cancer (BLBC), the aggressive form of breast cancer with no molecularly defined therapeutic target. To examine whether altered lncRNA expression contributes to the aggressive phenotype characteristic of BLBC, we performed a comparative analysis of BLBC versus non-BLBC using microarray profiling and RNA sequencing of primary breast cancer. We identified RP11-19E11.1 as a significantly up-regulated lncRNA in BLBC tumors and named it Basal-Like breast cancer Associated Transcript 1 (BLAT1). Analysis of pan-cancer datasets showed the highest expression of BLAT1 in BLBC tumors compared to all other cancers. Depletion of BLAT1 in breast cancer cells led to significantly increased apoptosis, partly because of accumulation of DNA damage. Mechanistically, BLAT1 expression is regulated at the epigenetic level via DNA methylation at CpG islands in the promoter. Concordantly, patients harboring tumors with BLAT1 hypomethylation showed decreased overall survival. Our results suggest that increased expression of BLAT1 via CpG site hypomethylation may contribute to the aggressive phenotype of BLBC, raising a possibility of new biomarkers for prognosis of aggressive BLBC tumors.

Abstract 1138: LBH, a novel WNT effector in promoting basal-like breast cancer

Abstract BACKGROUND: Clinically aggressive basal-like breast cancers (BLBC) disproportionally contribute to cancer deaths, but lack effective treatment options due to absence of expression of key therapeutic targets (ER, PR, HER2). New evidence suggests BLBC may originate from luminal breast epithelial cells through luminal-to-basal cell lineage conversion and dedifferentiation. However, the factors that reprogram cell fate and differentiation states during BLBC development remain poorly understood. Our laboratory has identified a novel WNT/β-Catenin target transcriptional regulator, Limb-Bud-and-Heart (LBH), which is majorly overexpressed in aggressive BLBC harboring WNT hyperactivation. We previously showed in a conditional LBH knockout mouse model in vivo that LBH is a key stem cell and basal lineage regulator in normal mammary gland development. However, it's role in breast cancer remains elusive. Here, we crossed conditional LBH knockout (KO) mice with a mouse model for WNT-driven breast cancer (MMTV-Wnt1) to test if LBH is a critical effector of WNT-driven basaloid breast cancer, and whether its inhibition may affect BLBC tumorigenesis. RESULTS: In our in vivo mouse model, epithelial-specific LBH inactivation using a Keratin 14/K14-Cre significantly attenuated Wnt1-induced mammary gland hyperplasia and delayed tumor onset. Yet, tumor volumes and burden were not changed, indicating that LBH is not essential for WNT-induced tumorigenesis. However, LBH-deficient MMTV-Wnt1-transgenic tumors exhibited pronounced histopathological differences compared to LBH WT MMTV-Wnt1-transgenic tumors. Whereas Wnt1+;K14CreLbh WT tumors were highly vascularized, disorganized, with mixed basal and luminal cell identity; tumors from Wnt1+;K14CreLbh KO mice were more organized, differentiated, and predominantly luminal Keratin 8 positive. We are currently investigating if the attenuated hyperplasia and tumor onset caused by LBH loss may be due to a deficiency in cancer stem cells in this breast cancer model. CONCLUSION: Our data indicate that LBH is an essential cell fate regulator downstream of WNT signaling that maintains basal lineage identity and the undifferentiated nature of BLBC. Thus, LBH inhibition may be a novel strategy to reduce the high mortality of BLBC patients through differentiation therapy. Citation Format: Kilan C. Ashad-Bishop, Karoline J. Briegel. LBH, a novel WNT effector in promoting basal-like breast cancer [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 1138.

Assessment of cytosolic free calcium changes during ceramide-induced cell death in MDA-MB-231 breast cancer cells expressing the calcium sensor GCaMP6m

Alterations in Ca2+ signaling can regulate key cancer hallmarks such as proliferation, invasiveness and resistance to cell death. Changes in the regulation of intracellular Ca2+ and specific components of Ca2+ influx are a feature of several cancers and/or cancer subtypes, including the basal-like breast cancer subtype, which has a poor prognosis. The development of genetically encoded calcium indicators, such as GCaMP6, represents an opportunity to measure changes in intracellular free Ca2+ during processes relevant to breast cancer progression that occur over long periods (e.g. hours), such as cell death. This study describes the development of a MDA-MB-231 breast cancer cell line stably expressing GCaMP6m. The cell line retained the key features of this aggressive basal-like breast cancer cell line. Using this model, we defined alterations in relative cytosolic free Ca2+ ([Ca2+]CYT) when the cells were treated with C2-ceramide. Cell death was measured simultaneously via assessment of propidium iodide permeability. Treatment with ceramide produced delayed and heterogeneous sustained increases in [Ca2+]CYT. Where cell death occurred, [Ca2+]CYT increases preceded cell death. The sustained increases in [Ca2+]CYT were not related to the rapid morphological changes induced by ceramide. Silencing of the plasma membrane Ca2+ ATPase isoform 1 (PMCA1) was associated with an augmentation in ceramide-induced increases in [Ca2+]CYT and also cell death. This work demonstrates the utility of GCaMP6 Ca2+ indicators for investigating [Ca2+]CYT changes in breast cancer cells during events relevant to tumor progression, which occur over hours rather than minutes.

Discoidin domain receptor 1 (DDR1) ablation promotes tissue fibrosis and hypoxia to induce aggressive basal-like breast cancers.

The discoidin domain receptor 1 (DDR1) is overexpressed in breast carcinoma cells. Low DDR1 expression is associated with worse relapse-free survival, reflecting its controversial role in cancer progression. We detected DDR1 on luminal cells but not on myoepithelial cells of DDR1+/+ mice. We found that DDR1 loss compromises cell adhesion, consistent with data that older DDR1-/- mammary glands had more basal/myoepithelial cells. Basal cells isolated from older mice exerted higher traction forces than the luminal cells, in agreement with increased mammary branches observed in older DDR1-/- mice and higher branching by their isolated organoids. When we crossed DDR1-/- mice with MMTV-PyMT mice, the PyMT/DDR1-/- mammary tumors grew faster and had increased epithelial tension and matricellular fibrosis with a more basal phenotype and increased lung metastases. DDR1 deletion induced basal differentiation of CD90+CD24+ cancer cells, and the increase in basal cells correlated with tumor cell mitoses. K14+ basal cells, including K8+K14+ cells, were increased adjacent to necrotic fields. These data suggest that the absence of DDR1 provides a growth and adhesion advantage that favors the expansion of basal cells, potentiates fibrosis, and enhances necrosis/hypoxia and basal differentiation of transformed cells to increase their aggression and metastatic potential.