Abstract P5-01-08: Mechanistic differences between abrupt and gradual involution of mouse mammary gland

Objective: Epidemiological studies indicate a direct relation between length of breast feeding and protection against risk of triple negative breast cancer (TNBC), an aggressive subtype. While prolonged breastfeeding allows gradual involution (GI) of the breast, short-term or no breast feeding leads to abrupt involution (AI). We modelled AI and GI of breast in mice, and showed that mice subjected to GI have better protection from tissue remodeling associated injuries in the mammary gland. Our data revealed late development of ductal hyperplasia aided by pro-tumorigenic microenvironment in the AI glands1. Detailed mechanism of mammary gland involution immediately following cessation of lactation has been studied in the past, but only in the AI setting, that is after abrupt removal of pups at the peak of lactation2,3. The goal of this study is to conduct stepwise comparison of the mechanism of GI vs. AI early on to understand the protective effect of GI against breast cancer risk.Methods: Wild-type FVB mice were used in all our studies. Females were mated at 8 weeks of age and uniparous mice were allowed to nurse (6 pups/dam) for 7 days. Females were then assigned randomly to AI or GI cohort. All pups were removed from the AI dams on postnatal day7 (PND7). Three pups each were removed from GI dams on day28 and 31. Mammary glands were harvested intermittently between PND7 and PND35. H&E stained sections were used for histological studies. Unstained FFPE sections were used for immunohistochemistry and TUNEL assay. Total RNA and protein from whole mammary gland was used for qPCR and western blot respectively. Results: GI glands transitioned from fully active lactating to near involuted glands over a period of 8 days (PND17- PND25), while for AI glands it took < 4 days (PND8.5-PND12). The shrinkage and flattening of tall epithelia and loss of acini was gradual in GI glands as opposed to rapid breakdown of acini and adipocyte repopulation in AI gland. Apoptotic cell count peaked on PND11 (5%) in AI vs. PND25 (3%) in GI glands. The pStat3Y705+ cells were highest on PND8.5 (25%) in AI vs. on PND25 (11%) in GI glands. Macrophage infiltration (F4/80+) peaked on PND11 (35%) and remained elevated at ~24% till PND25, while in GI glands increase was gradual from PND17 through PND25 (27%). Expression of key genes identified in AI mice2,3 have markedly different expression pattern in GI mice (Table). While some peaked at a later time point in GI vs. AI coinciding with maximum cell death, expression of some are significantly low or undetectable in GI glands at both RNA and protein level. Conclusions: We show for the first time that kinetics of cell death, adipocyte repopulation, immune cell infiltration and inflammatory state of glands undergoing abrupt vs. gradual involution are markedly different. Several genes known to play a key role during AI are either not expressed or barely detectable in the GI glands at any time point during involution. These data suggests that not only the kinetics, but mechanism of GI and AI are not identical. We conclude that orchestrated cell death in GI protects from drastic lysosomal, and immune cell activities that predisposes mammary glands to higher risk of neoplastic changes.Significance: Epidemiological data highlights the benefits of prolonged breastfeeding in protecting against breast cancer, particularly, TNBC, an aggressive subtype prevalent in the African American women. Our study highlights the mechanism underlying the benefits of gradual involution of breast.

GeneFold Change compared to PND7 (GI vs. AI) Peaked on (GI vs. AI)Stat34.0 vs. 5.9PND25 vs. PND8.5Ctsb2.8 vs. 3.4PND25 vs. PND8.5CD143.4 vs. 20PND25 vs. PND8.5Orm11.7 vs. 10PND25 vs. PND12Lrg130 vs. 216PND25 vs. PND12MMP215.8 vs. 27PND25 vs. PND12Chi3L11350 vs. 572, 859PND28 vs. PND11, 28Cebpδnone vs. 4.4None vs. PND8.5CtsLnone vs. 5.7None vs. PND8.5Orm2none vs. 370None vs. PND12Slpinone vs. 92None vs. PND8.5

Citation Format: Bhuvaneswari Ramaswamy, Neelam Shinde, Morgan Bauer, Maria Cuitino, Saba Mehra, Resham Mawalkar, Mustafa Basree, Allen Zhang, Kirti Kaul, Xiaoli Zhang, Ramesh Ganju, Sarmila Majumder. Mechanistic differences between abrupt and gradual involution of mouse mammary gland [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-01-08.

BSCI-11. STROMAL PLATELET DERIVED GROWTH FACTOR RECEPTOR-β (PDGFRβ) PROMOTES BREAST CANCER BRAIN METASTASIS

Stromal platelet-derived growth factor receptor-beta (PDGFRβ) has emerged as an actionable mediator of breast tumor-stromal communication. As a receptor tyrosine kinase, PDGFRβ is activated by its ligand, PDGFB, which is released by neighboring tumor epithelium and endothelium. However, how PDGF signaling mediates breast cancer (BC) initiation, progression, and metastasis remains unclear. To evaluate PDGFRβ in this disease, we developed a mouse model of stromal-specific PDGFRβ activation using the Fsp-cre transgene previously published by our group. Mesenchymal-specific activation of PDGFRβ promotes preferential experimental brain metastasis of PDGFB-expressing mammary tumor cells when injected intravenously and accelerates intracranial tumor growth of these cells. Mammary tumor cells expressing low levels of PDGFB do not exhibit a similar increase in brain metastases in PDGFRβ mutant mice. To our knowledge, this is the first example where genetic manipulation of the stroma leads to an increased incidence of BCBM. Our pre-clinical data suggests that primary breast tumors that express high PDGFB could preferentially metastasize to the brain. To test this in patients, we analyzed PDGFB protein expression in a tissue microarray comprised of HER2-positive and triple negative BC primary tumors. While high PDGFB did not correlate with site-independent metastatic recurrence, it was prognostic of brain metastasis, mirroring our mouse data. Our findings suggest that high primary tumor PDGFB expression defines a subset of BC patients predisposed to brain metastases. These patients may benefit from therapeutic intervention of PDGFRβ signaling. To test this pre-clinically, we treated mice harboring intracranial tumors with the PDGFR-specific inhibitor, crenolanib. Excitingly, crenolanib treatment significantly inhibited the brain tumor burden in these mice. Combined, our findings (1) advocate that primary tumor expression of PDGFB is a novel prognostic biomarker for the development of BCBM and (2) support clinical trial evaluation of PDGFR inhibitors for the prevention and treatment of BCBM.

Abrupt involution induces inflammation, estrogenic signaling, and hyperplasia linking lack of breastfeeding with increased risk of breast cancer

Background

A large collaborative analysis of data from 47 epidemiological studies concluded that longer duration of breastfeeding reduces the risk of developing breast cancer. Despite the strong epidemiological evidence, the molecular mechanisms linking prolonged breastfeeding to decreased risk of breast cancer remain poorly understood.

Methods

We modeled two types of breastfeeding behaviors in wild type FVB/N mice: (1) normal or gradual involution of breast tissue following prolonged breastfeeding and (2) forced or abrupt involution following short-term breastfeeding. To accomplish this, pups were gradually weaned between 28 and 31 days (gradual involution) or abruptly at 7 days postpartum (abrupt involution). Mammary glands were examined for histological changes, proliferation, and inflammatory markers by immunohistochemistry. Fluorescence-activated cell sorting was used to quantify mammary epithelial subpopulations. Gene set enrichment analysis was used to analyze gene expression data from mouse mammary luminal progenitor cells. Similar analysis was done using gene expression data generated from human breast samples obtained from parous women enrolled on a tissue collection study, OSU-2011C0094, and were undergoing reduction mammoplasty without history of breast cancer.

Results

Mammary glands from mice that underwent abrupt involution exhibited denser stroma, altered collagen composition, higher inflammation and proliferation, increased estrogen receptor α and progesterone receptor expression compared to those that underwent gradual involution. Importantly, when aged to 4 months postpartum, mice that were in the abrupt involution cohort developed ductal hyperplasia and squamous metaplasia. Abrupt involution also resulted in a significant expansion of the luminal progenitor cell compartment associated with enrichment of Notch and estrogen signaling pathway genes. Breast tissues obtained from healthy women who breastfed for < 6 months vs ≥ 6 months showed significant enrichment of Notch signaling pathway genes, along with a trend for enrichment for luminal progenitor gene signature similar to what is observed in BRCA1 mutation carriers and basal-like breast tumors.

Conclusions

We report here for the first time that forced or abrupt involution of the mammary glands following pregnancy and lack of breastfeeding results in expansion of luminal progenitor cells, higher inflammation, proliferation, and ductal hyperplasia, a known risk factor for developing breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1163-7) contains supplementary material, which is available to authorized users.

Abstract 2242: Breastfeeding protects against pro-tumorigenic changes in the mammary gland by limiting epithelial luminal progenitor cell expansion

Introduction: Multiple epidemiological studies have shown that prolonged breastfeeding is associated with a reduced risk of developing triple-negative/basal-like breast cancers (TN/BLBC). However, no preclinical models that delineate the mechanism of this link exist. This understanding is critical not only to prevent TN/BLBC, but also to address disparity in breast cancer outcomes, as African-American women have a higher incidence of TN/BLBC and lower prevalence of breastfeeding. We present our data using mouse models that provides new insights into this link.

Experimental procedure: We modeled gradual involution (GI) and abrupt involution (AI) of mammary glands (MGs) in wild type FVB/N mice. Uniparous mice were assigned to AI or GI cohorts either by removal of all pups on day7 postpartum (AI) or allowing the pups to naturally wean (GI). MGs were harvested for analysis on postpartum day28, day56 and day120. We assessed MG morphology/histology using whole mounts and H&E stained sections, collagen deposition using Trichrome and PicroSirus red staining, inflammatory markers and immune cell infiltration using immunohistochemistry. Mammary epithelial cell hierarchy was analyzed by Fluorescence-Activated Cell Sorting of a single cell suspension prepared from the MGs. Gene expression was analyzed in mouse mammary epithelial cells using Affymatrix Gene ChIP Mouse Transcriptome array 1.0 and Gene Set Enrichment Analysis (GSEA) was used to analyze gene expression data.

Summary: Abruptly involuted MGs exhibited altered morphology including denser stroma, increased collagen deposition with higher levels of Type I collagen, increased inflammation (pStat3-Y705), increased immune cell infiltration and proliferation compared to GI glands. The mammary epithelial cell hierarchy was disrupted with marked expansion of the luminal progenitor (LP) population in the AI glands but not in the GI glands, a trend frequently observed in women heterozygous for BRCA1 mutation at higher risk of developing BLBC. Enrichment of an LP gene signature and Notch pathway was observed in mouse LP cells isolated from the AI glands. Most strikingly, the AI glands developed alveolar hyperplasia, and squamous metaplasia within 4 months of removal of the pups.

Conclusion: Involution leading to a pro-inflammatory milieu in the MG is well established. Whether involution that happens gradually after prolonged breastfeeding differs in its effect on MGs has not been well studied. Using novel animal modeling to study the differences in MGs following abrupt vs gradual involution, we report a distinct morphology in the mammary tissue favoring pro-carcinogenic changes following AI. Furthermore, we show for the first time, expansion of the LP population in AI glands, which is known to be cell of origin for TN/BLBC potentially linking the risk of TN/BLBC with lack of breastfeeding. Further studies are ongoing.

Citation Format: Mustafa M. Basree, Neelam Shinde, Christopher Koivisto, Maria Cuitino, Raleigh Kladney, Allen Zhang, Hee Kyung Kim, Anthony Trimboli, Jianying Zhang, Gustavo W. Leone, Gina M. Sizemore, Sarmila Majumder, Bhuvaneswari Ramaswamy. Breastfeeding protects against pro-tumorigenic changes in the mammary gland by limiting epithelial luminal progenitor cell expansion [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 2242.

Abstract 4337: PDGFR-α induced stiffness abrogates mammary ductal development and enhances tumorigenesis in vivo

Breast cancer is a leading cause of mortality in women worldwide, in part due to the tumor microenvironment which increases tumor heterogeneity and abets tumor growth. Fibroblasts are cells of mesenchymal origin that are an important component of normal and tumor stroma. Genetic alterations in these cells were shown by several groups including our own to cause fibroblast activation and fuel tumor progression giving rise to more aggressive disease. Platelet-Derived Growth Factor Receptor (PDGFR) alpha is a receptor tyrosine kinase that is chiefly expressed in mesenchymal cells such as fibroblasts. Ligand binding (PDGFAA) activates this receptor. PDGFRα signaling plays critical roles in development and aberrant signaling is seen in several types of cancer, such as lung, pancreas, GI and brain. The central goal of this study was to elucidate the role of stromal PDGFRα in breast cancer development and metastasis, where its role remains largely unknown. To address this goal, we developed a genetic mouse model of stromal activation of PDGFRα in the mammary gland by crossing an auto-activating Pdgfra mutant allele with a mesenchymal specific Cre recombinase. We found that stromal PDGFRα activation completely abrogated postnatal mammary gland ductal formation, with significantly reduced terminal end bud formation. PDGFRα activation also led to progressive fibrosis in the mouse mammary fat pad. As early as four weeks of age, mammary collagen (trichrome staining; second harmonic generation) and hyaluronan deposition (Alcian Blue) was greatly increased in vivo. In fact, this increase in collagen and hyaluronan deposition in mutant animals is believed to be responsible for the observed increased in stiffness of mutant mammary tissue (atomic force microscopy {AFM}). pFAK, which can be activated due to mechanical stress, was increased in mammary epithelia of the mutant mice in vivo corroborating the AFM results. Further, when tumor cells were injected into the mammary glands of the PDGFRα mutants, tumors grew faster as compared to controls. Importantly, we found that mRNA expression of PDGFRA correlates with worsened patient outcomes in HER2+ disease, while expression of both the ligand (PDGFA) and the receptor were found to correlate with increased incidence of lung metastases. We further discovered that in HER2+ patients, PDGFRA levels correlate with breast density. Breast density is the third strongest risk factor for breast cancer, and is directly related to collagen deposition and breast stiffness, thus suggesting a novel predictive role of PDGFRA as a molecular readout of stiffness and density. Studies are underway to utilize mouse models of HER2+ breast cancer to study both primary tumor growth and metastases. Taken together, our mouse studies and paralleling human data analyses suggest that the stromal PDGFRα signaling provides a novel theranostic window in breast cancer treatment and prognosis.

Citation Format: Anisha Mathur Hammer, Gina M. Sizemore, Vasudha Shukla, Steven T. Sizemore, Maria Cuitino, Cynthia J. Timmers, Quinn Verfurth, Arnab Chakravarti, Gustavo W. Leone, Samir N. Ghadiali, Michael C. Ostrowski. PDGFR-α induced stiffness abrogates mammary ductal development and enhances tumorigenesis in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4337. doi:10.1158/1538-7445.AM2017-4337

Abstract B01: Ets-2 acts as a novel oncogene in cancer associated fibroblasts and promotes pancreatic tumor initiation and development

Purpose of Study:Pancreatic cancer remains an overwhelmingly fatal disease with approximately 95% of patients dying within 5 years of diagnosis. Many recent reports have highlighted the emerging role that stromal cells’fibroblasts in particular’have on pancreatic tumor cell biology. It has become apparent that new models of pancreatic cancer that accurately portray the tumor microenvironment (TME) are necessary to move the field forward. Advances in genetic tools to modulate the TME developed in our lab have allowed us the unique opportunity to manipulate specific stromal cell compartments. Our overarching hypothesis is: Ets-2 in the pancreatic tumor-associated stroma promotes tumor initiation and development by regulating essential signaling pathways in fibroblasts and is critical for tumor-stroma co-evolution.

Research Method: In this study we use a previously validated and well-studied genetically engineered mouse model of pancreatic cancer that relies on constitutive activation of the Kras oncogene tumor cell lineage. We simultaneously employ lox-cre technology to conditionally delete our gene of interest exclusively in the fibroblast compartment of the pancreas. For this study we delete the transcription factor Ets-2, which has previously been shown to effect tumor initiation and growth in mammary stroma.

Novel Findings: Here we show that Ets-2 in pancreatic tumor-associated stroma promotes tumor formation by regulating essential signaling pathways in stromal fibroblasts and is critical for tumor-stroma co-evolution. We conditionally deleted Ets-2 in cancer associated fibroblasts (CAFs), thus altering stroma-tumor crosstalk and resulting in delayed tumor initiation. Specifically, we saw a decrease in pre-cancerous acinar-to-ductal metaplasic (ADM) and pancreatic intraepithelial neoplastic (PanIN) lesions in mice null for Ets-2 in the fibroblast compartment. In order to investigate the mechanism by which Ets-2 is able to effect progression of tumors from the fibroblast compartment, we developed a method for harvesting and purifying primary pancreatic CAFs. We performed microarray and gene expression analysis on Ets-2 deleted CAFs and saw significantly decreased expression of secreted factors. The altered secretome upon Ets-2 deletion in fibroblasts was crucially lacking tumor necrosis factor alpha (TNFα), a known pro-tumor ligand in pancreatic carcinogenesis. Furthermore, we found evolutionarily conserved Ets-2 transcription factor binding sites in the proximal promoter of TNFα, suggesting that Ets-2 directly regulates TNFα transcription. Thus we have shown that Ets-2 ablation in pancreatic fibroblasts delays pancreatic tumor initiation through the pro-tumor ligand TNFα.

Conclusions and Implications:This report shows that deleting a gene in pancreatic fibroblasts causes a change in tumor-stroma co-evolution and that Ets-2 is able to act as a novel oncogene in cancer associated fibroblasts to promote pancreatic carcinogenesis. We have shown that Ets-2 deletion significantly changed the biological role of the CAFs and negatively effects tumor growth. This finding is relevant to the field of pancreatic cancer because it shows that the pancreatic TME can play a driver role in overall tumor initiation and development. These collective findings contribute to our lab’s overall hypothesis that the tumor microenvironment is not a mere bystander or byproduct of tumor development, but rather that it can drive tumor evolution amongst a variety of cancers.

Citation Format: Jason R. Pitarresi, Jinghai Wu, Sarah Woelke, Raleigh Kladney, Maria Cuitino, Lianbo Yu, Ostrowski C. Michael. Ets-2 acts as a novel oncogene in cancer associated fibroblasts and promotes pancreatic tumor initiation and development. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B01.