Contraceptive progestins with androgenic properties stimulate breast epithelial cell proliferation

Hormonal contraception exposes women to synthetic progesterone receptor (PR) agonists, progestins, and transiently increases breast cancer risk. How progesterone and progestins affect the breast epithelium is poorly understood because we lack adequate models to study this. We hypothesized that individual progestins differentially affect breast epithelial cell proliferation and hence breast cancer risk. Using mouse mammary tissue ex vivo, we show that testosterone-related progestins induce the PR target and mediator of PR signaling-induced cell proliferation receptor activator of NF-κB ligand (Rankl), whereas progestins with anti-androgenic properties in reporter assays do not. We develop intraductal xenografts of human breast epithelial cells from 36 women, show they remain hormone-responsive and that progesterone and the androgenic progestins, desogestrel, gestodene, and levonorgestrel, promote proliferation but the anti-androgenic, chlormadinone, and cyproterone acetate, do not. Prolonged exposure to androgenic progestins elicits hyperproliferation with cytologic changes. Androgen receptor inhibition interferes with PR agonist- and levonorgestrel-induced RANKL expression and reduces levonorgestrel-driven cell proliferation. Thus, different progestins have distinct biological activities in the breast epithelium to be considered for more informed choices in hormonal contraception.

Abstract 2993: Intraductal xenografts model ERα-positive invasive lobular carcinoma of the breast

Invasive lobular carcinoma (ILC) is the most frequent special histological subtype of breast cancer, typically characterized by loss of E-cadherin. It has clinical features distinct from other estrogen receptor-positive (ER+) breast cancers but the molecular mechanisms underlying its characteristic biology are poorly understood because we lack experimental models to study them. By xenografting lobular cells to the milk ducts, we recapitulate the human disease, including invasion and metastasis to clinically relevant organs. Using patient-derived intraductal xenografts from lobular and non-lobular ER+ HER2- tumors to compare global gene expression we identify extracellular matrix modulation as a lobular carcinoma cell-intrinsic trait. Analysis of TCGA patient datasets shows matrisome signature is enriched in lobular carcinomas with overexpression of elastin, collagens, and the collagen modifying enzyme LOXL1. Pharmacological treatment and silencing of LOXL1 expression decrease tumor growth, invasion, and metastasis by disrupting ECM structure resulting in decreased ER signaling. We conclude that LOXL1 inhibition is a promising therapeutic strategy for ILC. This is the first study of a hormone-responsive ER+ preclinical lobular model that mimics their clinical counterparts and opens opportunities for the development and evaluation of therapies.

Citation Format: George Sflomos , Laura Battista, Patrick Aouad, Fabio De Martino, Valentina Scabia, Athina Stravodimou, Ayyakkannu Ayyanan, Assia Ifticene-Treboux, RLS, Philipp Bucher, Maryse Fiche, Giovanna Ambrosini, Cathrin Brisken. Intraductal xenografts model ERα-positive invasive lobular carcinoma of the breast [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 2993.

Intraductal xenografts show lobular carcinoma cells rely on their own extracellular matrix and LOXL1

Invasive lobular carcinoma (ILC) is the most frequent special histological subtype of breast cancer, typically characterized by loss of E-cadherin. It has clinical features distinct from other estrogen receptor-positive (ER+ ) breast cancers but the molecular mechanisms underlying its characteristic biology are poorly understood because we lack experimental models to study them. Here, we recapitulate the human disease, including its metastatic pattern, by grafting ILC-derived breast cancer cell lines, SUM-44 PE and MDA-MB-134-VI cells, into the mouse milk ducts. Using patient-derived intraductal xenografts from lobular and non-lobular ER+ HER2- tumors to compare global gene expression, we identify extracellular matrix modulation as a lobular carcinoma cell-intrinsic trait. Analysis of TCGA patient datasets shows matrisome signature is enriched in lobular carcinomas with overexpression of elastin, collagens, and the collagen modifying enzyme LOXL1. Treatment with the pan LOX inhibitor BAPN and silencing of LOXL1 expression decrease tumor growth, invasion, and metastasis by disrupting ECM structure resulting in decreased ER signaling. We conclude that LOXL1 inhibition is a promising therapeutic strategy for ILC.

IL6/STAT3 Signaling Hijacks Estrogen Receptor α Enhancers to Drive Breast Cancer Metastasis

The cytokine interleukin-6 (IL6) and its downstream effector STAT3 constitute a key oncogenic pathway, which has been thought to be functionally connected to estrogen receptor α (ER) in breast cancer. We demonstrate that IL6/STAT3 signaling drives metastasis in ER+ breast cancer independent of ER. STAT3 hijacks a subset of ER enhancers to drive a distinct transcriptional program. Although these enhancers are shared by both STAT3 and ER, IL6/STAT3 activity is refractory to standard ER-targeted therapies. Instead, inhibition of STAT3 activity using the JAK inhibitor ruxolitinib decreases breast cancer invasion in vivo. Therefore, IL6/STAT3 and ER oncogenic pathways are functionally decoupled, highlighting the potential of IL6/STAT3-targeted therapies in ER+ breast cancer.

90 YEARS OF PROGESTERONE: Progesterone receptor signaling in the normal breast and its implications for cancer

Progesterone is considered as the pregnancy hormone and acts on many different target tissues. Progesterone receptor (PR) signaling is important for normal development and the physiologic function of the breast and impinges on breast carcinogenesis. Both systemically and locally, in the breast epithelium, there are multiple layers of complexity to progesterone action, many of which have been revealed through experiments in mice. The hormone acts via its receptor expressed in a subset of cells, the sensor cells, in the breast epithelium with different signaling outcomes in individual cells eliciting distinct cell-intrinsic and paracrine signaling involving different mediators for different intercellular interactions. PR expression itself is developmentally regulated and the biological outcome of PR signaling depends on the developmental stage of the mammary gland and the endocrine context. During both puberty and adulthood PR activates stem and progenitor cells through Wnt4-driven activation of the myoepithelium with downstream Adamts18-induced changes in extracellualr matrix (ECM) / basal membrane (BM). During estrous cycling and pregnancy, the hormone drives a major cell expansion through Rankl. At all stages, PR signaling is closely tied to estrogen receptor α (ER) signaling. As the PR itself is a target gene of ER, the complex interactions are experimentally difficult to dissect and still poorly understood. Ex vivo models of the human breast and studies on biopsy samples show that major signaling axes are conserved across species. New intraductal xenograft models hold promise to provide a better understanding of PR signaling in the normal breast epithelium and in breast cancer development in the near future.

C/EBPα mediates the growth inhibitory effect of progestins on breast cancer cells

Steroid hormones are key gene regulators in breast cancer cells. While estrogens stimulate cell proliferation, progestins activate a single cell cycle followed by proliferation arrest. Here, we use biochemical and genome-wide approaches to show that progestins achieve this effect via a functional crosstalk with C/EBPα. Using ChIP-seq, we identify around 1,000 sites where C/EBPα binding precedes and helps binding of progesterone receptor (PR) in response to hormone. These regions exhibit epigenetic marks of active enhancers, and C/EBPα maintains an open chromatin conformation that facilitates loading of ligand-activated PR. Prior to hormone exposure, C/EBPα favors promoter-enhancer contacts that assure hormonal regulation of key genes involved in cell proliferation by facilitating binding of RAD21, YY1, and the Mediator complex. Knockdown of C/EBPα disrupts enhancer-promoter contacts and decreases the presence of these architectural proteins, highlighting its key role in 3D chromatin looping. Thus, C/EBPα fulfills a previously unknown function as a potential growth modulator in hormone-dependent breast cancer.

Intraductal patient-derived xenografts of estrogen receptor α-positive breast cancer recapitulate the histopathological spectrum and metastatic potential of human lesions

Estrogen receptor α‐positive (ER‐positive) or ‘luminal’ breast cancers were notoriously difficult to establish as patient‐derived xenografts (PDXs). We and others recently demonstrated that the microenvironment is critical for ER‐positive tumor cells; when grafted as single cells into milk ducts of NOD Scid gamma females, >90% of ER‐positive tumors can be established as xenografts and recapitulate many features of the human disease in vivo. This intraductal approach holds promise for personalized medicine, yet human and murine stroma are organized differently and this and other species specificities may limit the value of this model. Here, we analyzed 21 ER‐positive intraductal PDXs histopathologically. We found that intraductal PDXs vary in extent and define four histopathological patterns: flat, lobular, in situ and invasive, which occur in pure and combined forms. The intraductal PDXs replicate earlier stages of tumor development than their clinical counterparts. Micrometastases are already detected when lesions appear in situ. Tumor extent, histopathological patterns and micrometastatic load correlate with biological properties of their tumors of origin. Our findings add evidence to the validity of the intraductal model for in vivo studies of ER‐positive breast cancer and raise the intriguing possibility that tumor cell dissemination may occur earlier than currently thought. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Patient-derived xenograft (PDX) models in basic and translational breast cancer research

Patient-derived xenograft (PDX) models of a growing spectrum of cancers are rapidly supplanting long-established traditional cell lines as preferred models for conducting basic and translational preclinical research. In breast cancer, to complement the now curated collection of approximately 45 long-established human breast cancer cell lines, a newly formed consortium of academic laboratories, currently from Europe, Australia, and North America, herein summarizes data on over 500 stably transplantable PDX models representing all three clinical subtypes of breast cancer (ER+, HER2+, and "Triple-negative" (TNBC)). Many of these models are well-characterized with respect to genomic, transcriptomic, and proteomic features, metastatic behavior, and treatment response to a variety of standard-of-care and experimental therapeutics. These stably transplantable PDX lines are generally available for dissemination to laboratories conducting translational research, and contact information for each collection is provided. This review summarizes current experiences related to PDX generation across participating groups, efforts to develop data standards for annotation and dissemination of patient clinical information that does not compromise patient privacy, efforts to develop complementary data standards for annotation of PDX characteristics and biology, and progress toward "credentialing" of PDX models as surrogates to represent individual patients for use in preclinical and co-clinical translational research. In addition, this review highlights important unresolved questions, as well as current limitations, that have hampered more efficient generation of PDX lines and more rapid adoption of PDX use in translational breast cancer research.

Abstract P2-05-11: miR363-3p mediates maintenance and resistance of breast cancer stem cells (BCSC)

Background

BCSC are considered to be involved in the recurrence of breast cancer and its resistance to the systemic therapies. Their detection and targeting remain challenging.

Patients and methods:

The study was conducted in vitro, in xenografted immunecompromised mice and samples of 38 patients with early stage BC having biopsies and blood samples before and after anthraycycline + taxane-based neoadjuvant chemotherapy (NAC). All patients gave written informed consent before inclusion. 1) MCF7 cells grown as mammospheres (MS) for BCSC enrichment were treated with 5FU or paclitaxel (Pac) to select chemo-resistant BCSC. miRNA microarray was performed to identify specific miRNAs for chemo-resistant BCSC. The results were compared to miRNAs found in immortalized non-tumorigenic MCF10A cells to exclude miRNAs related to normal stem cells. 2) The correlation between the most highly expressed miRNA and the BCSC was confirmed by RT-qPCR in ALDH+ and ALDH- cells sorted from MCF7 and MDA-MB-231 cells by flow cytometry. 3) The impact of the miRNA on MS and colony development was assessed by up- and down-regulating its expression. MCF7 cells transfected with ectopic expression of miRNA, anti-miRNA or miRNA control were grown in MS before being injected in mice using a mouse INtraDuctal xenograft Model (MIND). In vivo tumor growth was assessed by luciferase imaging, then measured and quantified with human GAPDH ex vivo at 6 weeks. 4) The miRNA was quantified by RT-qPCR in tumor samples and sera of the patients before and after treatment, and its levels were correlated with pathological complete response and patients' outcomes.

Results:

379 miRNAs out of 2006 were altered in chemo-resistant versus untreated MCF7 MS. Thirteen were specific for 5FU and 5 for Pac. Three were common for both drugs. Of these, miR-363-3p was overexpressed specifically in BCSC-enriched chemo-resistant MCF7 cells and all the other tested BC cell lines, but not in non-tumorigenic MCF10A cells. Compared to adherent MCF7 cells, miR-363-3p was 12-, 60-, and 10-folds more expressed in BCSC-enriched MS treated with 5FU, Pac, or without treatment, respectively. miR-363-3p was 20- and 100-folds higher in ALDH+ compared to ALDH- in MCF7 and MDA-MB-231 cells. Anti-miR-363-3p reduced MS size and decreased their number 50%. A significant decrease of the number of colonies was also observed in soft agar. Consistently, miR-363-3p downregulation decreased tumor growth and metastasis by MCF7 cells transplanted in mice. In patients' sera with lower baseline level (n=15), miR-363-3p appeared decreased upon NAC. Patients with high miR-363-3p serum levels (n=22) had more risk to maintain higher level after chemotherapy. Triple-negative and HER2+ BC were more frequent in this second group. No significant difference was observed in term of pCR between the 2 groups. However 3 patients relapsed with distant metastases and all were in the second group with high baseline level and no decrease after NAC.

Conclusions:

miR363-3p appeared to be a mediator of chemo-resistant BCSC. Its measurement in the serum of BC patients may predict resistance to neo-/adjuvant chemotherapy and higher risk of distant recurrence. Further investigations are warranted to confirm its role as biomarker and potential therapeutic target against BCSC.

Citation Format: Renaud S, Fiche M, Stravodimou A, Scabia V, Dormoy VM, Galmiche Rindisbacher M, Brisken C, Mermod N, Zaman K. miR363-3p mediates maintenance and resistance of breast cancer stem cells (BCSC) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-05-11.

A Preclinical Model for ERα-Positive Breast Cancer Points to the Epithelial Microenvironment as Determinant of Luminal Phenotype and Hormone Response

Seventy-five percent of breast cancers are estrogen receptor α positive (ER⁺). Research on these tumors is hampered by lack of adequate in vivo models; cell line xenografts require non-physiological hormone supplements, and patient-derived xenografts (PDXs) are hard to establish. We show that the traditional grafting of ER⁺ tumor cells into mammary fat pads induces TGFβ/SLUG signaling and basal differentiation when they require low SLUG levels to grow in vivo. Grafting into the milk ducts suppresses SLUG; ER⁺ tumor cells develop, like their clinical counterparts, in the presence of physiological hormone levels. Intraductal ER⁺ PDXs are retransplantable, predictive, and appear genomically stable. The model provides opportunities for translational research and the study of physiologically relevant hormone action in breast carcinogenesis.