CD200 is overexpressed in the pancreatic tumor microenvironment and predictive of overall survival

Pancreatic cancer is an aggressive disease with a 5 year survival rate of 13%. This poor survival is attributed, in part, to limited and ineffective treatments for patients with metastatic disease, highlighting a need to identify molecular drivers of pancreatic cancer to target for more effective treatment. CD200 is a glycoprotein that interacts with the receptor CD200R and elicits an immunosuppressive response. Overexpression of CD200 has been associated with differential outcomes, depending on the tumor type. In the context of pancreatic cancer, we have previously reported that CD200 is expressed in the pancreatic tumor microenvironment (TME), and that targeting CD200 in murine tumor models reduces tumor burden. We hypothesized that CD200 is overexpressed on tumor and stromal populations in the pancreatic TME and that circulating levels of soluble CD200 (sCD200) have prognostic value for overall survival. We discovered that CD200 was overexpressed on immune, stromal, and tumor populations in the pancreatic TME. Particularly, single-cell RNA-sequencing indicated that CD200 was upregulated on inflammatory cancer-associated fibroblasts. Cytometry by time of flight analysis of PBMCs indicated that CD200 was overexpressed on innate immune populations, including monocytes, dendritic cells, and monocytic myeloid-derived suppressor cells. High sCD200 levels in plasma correlated with significantly worse overall and progression-free survival. Additionally, sCD200 correlated with the ratio of circulating matrix metalloproteinase (MMP) 3: tissue inhibitor of metalloproteinase (TIMP) 3 and MMP11/TIMP3. This study highlights the importance of CD200 expression in pancreatic cancer and provides the rationale for designing novel therapeutic strategies that target this protein.

TLE3 Sustains Luminal Breast Cancer Lineage Fidelity to Suppress Metastasis

Breast cancer subtypes and their phenotypes parallel different stages of the mammary epithelial cell developmental hierarchy. Discovering mechanisms that control lineage identity could provide novel avenues for mitigating disease progression. Here we report that the transcriptional corepressor TLE3 is a guardian of luminal cell fate in breast cancer and operates independently of the estrogen receptor. In luminal breast cancer, TLE3 actively repressed the gene-expression signature associated with highly aggressive basal-like breast cancers (BLBC). Moreover, maintenance of the luminal lineage depended on the appropriate localization of TLE3 to its transcriptional targets, a process mediated by interactions with FOXA1. By repressing genes that drive BLBC phenotypes, including SOX9 and TGFβ2, TLE3 prevented the acquisition of a hybrid epithelial-mesenchymal state and reduced metastatic capacity and aggressive cellular behaviors. These results establish TLE3 as an essential transcriptional repressor that sustains the more differentiated and less metastatic nature of luminal breast cancers. Approaches to induce TLE3 expression could promote the acquisition of less aggressive, more treatable disease states to extend patient survival.

SIGNIFICANCE

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.

BCL-xL inhibition potentiates cancer therapies by redirecting the outcome of p53 activation from senescence to apoptosis

Cancer therapies trigger diverse cellular responses, ranging from apoptotic death to acquisition of persistent therapy-refractory states such as senescence. Tipping the balance toward apoptosis could improve treatment outcomes regardless of therapeutic agent or malignancy. We find that inhibition of the mitochondrial protein BCL-xL increases the propensity of cancer cells to die after treatment with a broad array of oncology drugs, including mitotic inhibitors and chemotherapy. Functional precision oncology and omics analyses suggest that BCL-xL inhibition redirects the outcome of p53 transcriptional response from senescence to apoptosis, which likely occurs via caspase-dependent down-modulation of p21 and downstream cytostatic proteins. Consequently, addition of a BCL-2/xL inhibitor strongly improves melanoma response to the senescence-inducing drug targeting mitotic kinase Aurora kinase A (AURKA) in mice and patient-derived organoids. This study shows a crosstalk between the mitochondrial apoptotic pathway and cell cycle regulation that can be targeted to augment therapeutic efficacy in cancers with wild-type p53.

Stromal p53 Regulates Breast Cancer Development, the Immune Landscape, and Survival in an Oncogene-Specific Manner

Coevolution of tumor cells and adjacent stromal elements is a key feature during tumor progression; however, the precise regulatory mechanisms during this process remain unknown. Here, we show stromal p53 loss enhances oncogenic KrasG12D, but not ErbB2, driven tumorigenesis in murine mammary epithelia. Stroma-specific p53 deletion increases both epithelial and fibroblast proliferation in mammary glands bearing the KrasG12D oncogene in epithelia, while concurrently increasing DNA damage and/or DNA replication stress and decreasing apoptosis in the tumor cells proper. Normal epithelia was not affected by stromal p53 deletion. Tumors with p53-null stroma had a significant decrease in total, cytotoxic, and regulatory T cells; however, there was a significant increase in myeloid-derived suppressor cells, total macrophages, and M2-polarized tumor-associated macrophages, with no impact on angiogenesis or connective tissue deposition. Stroma-specific p53 deletion reprogrammed gene expression in both fibroblasts and adjacent epithelium, with p53 targets and chemokine receptors/chemokine signaling pathways in fibroblasts and DNA replication, DNA damage repair, and apoptosis in epithelia being the most significantly impacted biological processes. A gene cluster in p53-deficient mouse fibroblasts was negatively associated with patient survival when compared with two independent datasets. In summary, stroma-specific p53 loss promotes mammary tumorigenesis in an oncogene-specific manner, influences the tumor immune landscape, and ultimately impacts patient survival.

IMPLICATIONS

Expression of the p53 tumor suppressor in breast cancer tumor stroma regulates tumorigenesis in an oncogene-specific manner, influences the tumor immune landscape, and ultimately impacts patient survival.

Abstract 11: Prophylactic use of tamoxifen could reduce the risk of breast cancer in women who do not breast feed postpartum

Background: Triple negative breast cancer (TNBC) is associated with poor survival, particularly affecting African American women (AAW). Epidemiological studies indicate prolonged breast feeding reduces breast cancer (BC) risk, including TNBC. AAW have significantly lower rates of breast feeding compared to Caucasian women. To understand this link we developed a mouse model mimicking abrupt (AI) and gradual involution (GI). AI led to increased estrogen signaling, cell proliferation and chronic inflammation, which was followed by hyperplasia and squamous metaplasia in mammary glands1. There was an increase in the luminal progenitor (LP) cell population, the cells of origin of TNBC, and a decrease in mature luminal (ML) cells in AI glands. In this study, we sought to determine if blocking estrogen signaling with tamoxifen (TAM) could revert the negative effects of AI, and if so, could be a prophylactic option to reduce BC risk in women who do not breast feed.

Methods: Uniparous FVB/N mice (~8 weeks) were allowed to nurse six pups per dam at partum. To induce AI, all pups were removed on postpartum (PP) day 7 (d7). For TAM treatment, 5mg sustained release TAM citrate pellet or placebo was implanted in the subscapular region on PP d8. Mammary glands were harvested on PP d28 and d120. FFPE sections were used for histology and immunohistochemistry. Single cell suspensions were analyzed for mammary epithelial subpopulations using Fluorescence Activated Cell Sorting. Affymetrix and qPCR were used for gene expression analysis. Mass cytometry was performed on mammary glands harvested at PP d120.

Results: TAM treatment for 21 days completely abrogated hyperplastic and metaplastic changes in AI glands harvested on d120. Treatment initiation on PP d8, d15 and d35 had the same effect. TAM treatment reduced the cell proliferation and collagen deposition in AI glands. De-enrichment of estrogen signaling pathways and decrease in Elf5 expression, a luminal progenitor marker, were observed upon TAM treatment in d28 glands. Mass cytometry revealed a marked reduction in LP population and a significant increase in ML population in TAM treated AI glands on d120, restoring to the levels in age matched virgin mice. Significant increases in progenitor-like markers TSPAN8, Ly6D, CD200 and decreases in CD49f and CD47 expression in LP cells were observed, indicating return to a normal uniparous LP state. Expression of Ly-6D in ML cells, a ML cell marker, was also rescued upon TAM treatment.

Conclusion: Using our mouse model of AI and GI, we show that suppression of estrogen signaling after initiation of AI offered marked protection against precancerous changes. TAM restored the balance of epithelial lineages and normalized the LP and basal cells in AI glands to the post-involution phenotype. Our data provide a rationale for considering short-term TAM treatment for women who do not breastfeed to reduce risk of BC. 1. Basree et.al. PMID 31315645

Citation Format: Bhuvaneswari Ramaswamy, Neelam Shinde, Gary K. Gray, Resham Mawalkar, Allen Zhang, Mustafa Basree, Xiaoli Zhang, Ramesh Ganju, Gina M. Sizemore, Joan S. Brugge, Sarmila Majumder. Prophylactic use of tamoxifen could reduce the risk of breast cancer in women who do not breast feed postpartum [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 11.

Abstract P5-08-17: Small G protein RALA is a driver and potential therapeutic target in triple negative breast cancer

Triple Negative Breast Cancer (TNBC) is the leading cause of cancer mortality in women, mostly due to the lack of targeted treatment for this subtype of breast cancer (BC). RALA and RALB are small GTPases implicated in tumor proliferation, survival, and metastasis in a variety of cancers. However, little is known of their roles in breast cancer. Utilizing 3D spheroid invasion assays, we identified that knockout (KO) of RALA greatly reduced the invasion of MDA-MB-231 spheroids in basement membrane extract (BME). Conversely, RALB-KO significantly increased 3D invasion of MDA-MB-231 cells. We further investigated roles for RALA and RALB in TNBC with cell viability assays, transwell assays, and 3D growth assays. Results indicate that KO or depletion of RALA in TNBC cell lines MDA-MB-231 and MDA-MB-468 reduces cell viability and cell migration capabilities in vitro. On the contrary, loss of RALB increased cell migration and viability. Treating TNBC cells with a small molecule inhibitor of both RAL isoforms (BQU57) reduced cell growth in vitro as well as tumor growth and metastasis in vivo. Furthermore, RALA expression, but not RALB expression, was predictive of response to chemotherapy in TNBC patients and RAL inhibitor sensitized TNBC cells to paclitaxel. Combined, these results highlight the importance of the RALs, particularly RALA, as a therapeutic targets in TNBC.

Citation Format: Dillon S. Richardson, Matthew W. Cole, Rachel E. Schafer, Jonathan M. Spehar, Sarah A. Steck, Manjusri Das, Arthur W. Lian, Alo Ray, Reena Shakya, Sue E. Knoblaugh, Cynthia D. Timmers, Gina M. Sizemore, Steven T. Sizemore. Small G protein RALA is a driver and potential therapeutic target in triple negative breast cancer [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 P5-08-17.

Abstract PD3-05: The paradoxical role of RalA and RalB in triple negative breast cancer

Background: Breast Cancer (BC) is the most common cancer and leading cause of cancer associated mortality in women worldwide. TNBC patients have the highest mortality mainly due to lack of receptors for targeted therapies. RalA and RalB are small GTPases that are known to regulate growth and metastasis in several cancers. However, roles for these GTPases in BC is poorly understood. The goal of this study was to investigate the contributions of RalA and RalB in TNBC. Methods: Control, RalA or RalB CRISPR knockout (KO) MDA-MB-231 cells were injected into the mammary gland of nod-skid-gamma (NSG) mice. Tumor growth was monitored and groups were taken as they met early removal criteria. Tumors and lungs were formalin-fixed and paraffin embedded. Tumors underwent immunohistochemical staining for Ki-67 and Cleaved caspase-3 and lungs were stained for hematoxylin and eosin and imaged on a Leica Aperio ScanScope XT to calculate lung metastasis. RalA or RalB were also depleted in MDA-MB-231 and MVT1 cells by shRNA. In addition, RalA depleted MDA-MB-231 cells were labeled with luciferase and injected into the tail vein of NSG mice and imaged on an IVIS spectrum to test seeding and lung colonization. Immunohistochemistry of patient TMAs was preformed on a Bond RX autostainer using RalA (Abcam, ab126627, 1:2000). Immunohistochemical stains were imaged on a PerkinElmer’s Vectra® Automatic Imaging System and quantified using inForm® Advanced Image Analysis software. Statistical significance of Kaplan-Meier survival curves were determined by log rank. Results: RalA knockout and depletion slowed primary orthotopic tumor growth in MDA-MB-231 and MVT1 cells. RalB KO had the opposite effect and increased growth rate compared to controls and RalA KO cells. Ki67 and cleaved caspase 3 IHC staining of tumors indicate KO of RalA decreased proliferation, whereas KO RalB increased proliferation with no change in apoptosis. RalA KO decreased the number and area of lung metastasis in both spontaneous and experimental metastasis assays. RalB KO or depletion caused an increase in the area and number of metastasis. Utilizing data from the METABRIC and TCGA BC datasets, elevated RALA, but not RALB, was prognostic of worse outcome in the overall BC populations and the TNBC populations specifically. RALA was shown to be more highly expressed in BC, particularly TNBC, relative to normal mammary tissue whereas RalB was decreased in BC and TNBC. IHC staining of a TMA comprised of all BC subtypes and a TMA of only TNBC samples confirmed RalA as a prognostic marker of patient outcome. Conclusions: RalA and RalB have important but paradoxical roles in TNBC.

Citation Format: Jonathan M. Spehar, Katie A. Thies, Matthew W. Cole, Rachel E. Schafer, Dillon S. Richardson, Sarah A. Steck, Manjusri Das, Arthur W. Lian, Alo Ray, Sue E. Knoblaugh, Cynthia D. Trimmers, Gina M. Sizemore, Steven T. Sizemore. The paradoxical role of RalA and RalB in triple negative breast cancer [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 PD3-05.

Fibroblast pyruvate carboxylase is required for collagen production in the tumour microenvironment

The aberrant production of collagen by fibroblasts is a hallmark of many solid tumours and can influence cancer progression. How the mesenchymal cells in the tumour microenvironment maintain their production of extracellular matrix proteins as the vascular delivery of glutamine and glucose becomes compromised remains unclear. Here we show that pyruvate carboxylase (PC)-mediated anaplerosis in tumour-associated fibroblasts contributes to tumour fibrosis and growth. Using cultured mesenchymal and cancer cells, as well as mouse allograft models, we provide evidence that extracellular lactate can be utilized by fibroblasts to maintain tricarboxylic acid (TCA) cycle anaplerosis and non-essential amino acid biosynthesis through PC activity. Furthermore, we show that fibroblast PC is required for collagen production in the tumour microenvironment. These results establish TCA cycle anaplerosis as a determinant of extracellular matrix collagen production, and identify PC as a potential target to inhibit tumour desmoplasia.

The small G-protein RalA promotes progression and metastasis of triple-negative breast cancer

Background

Breast cancer (BC) is the most common cancer in women and the leading cause of cancer-associated mortality in women. In particular, triple-negative BC (TNBC) has the highest rate of mortality due in large part to the lack of targeted treatment options for this subtype. Thus, there is an urgent need to identify new molecular targets for TNBC treatment. RALA and RALB are small GTPases implicated in growth and metastasis of a variety of cancers, although little is known of their roles in BC.

Methods

The necessity of RALA and RALB for TNBC tumor growth and metastasis were evaluated in vivo using orthotopic and tail-vein models. In vitro, 2D and 3D cell culture methods were used to evaluate the contributions of RALA and RALB during TNBC cell migration, invasion, and viability. The association between TNBC patient outcome and RALA and RALB expression was examined using publicly available gene expression data and patient tissue microarrays. Finally, small molecule inhibition of RALA and RALB was evaluated as a potential treatment strategy for TNBC in cell line and patient-derived xenograft (PDX) models.

Results

Knockout or depletion of RALA inhibited orthotopic primary tumor growth, spontaneous metastasis, and experimental metastasis of TNBC cells in vivo. Conversely, knockout of RALB increased TNBC growth and metastasis. In vitro, RALA and RALB had antagonistic effects on TNBC migration, invasion, and viability with RALA generally supporting and RALB opposing these processes. In BC patient populations, elevated RALA but not RALB expression is significantly associated with poor outcome across all BC subtypes and specifically within TNBC patient cohorts. Immunohistochemical staining for RALA in patient cohorts confirmed the prognostic significance of RALA within the general BC population and the TNBC population specifically. BQU57, a small molecule inhibitor of RALA and RALB, decreased TNBC cell line viability, sensitized cells to paclitaxel in vitro and decreased tumor growth and metastasis in TNBC cell line and PDX models in vivo.

Conclusions

Together, these data demonstrate important but paradoxical roles for RALA and RALB in the pathogenesis of TNBC and advocate further investigation of RALA as a target for the precise treatment of metastatic TNBC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01438-3.

Genomic features of rapid versus late relapse in triple negative breast cancer

Background

Triple-negative breast cancer (TNBC) is a heterogeneous disease and we have previously shown that rapid relapse of TNBC is associated with distinct sociodemographic features. We hypothesized that rapid versus late relapse in TNBC is also defined by distinct clinical and genomic features of primary tumors.

Methods

Using three publicly-available datasets, we identified 453 patients diagnosed with primary TNBC with adequate follow-up to be characterized as ‘rapid relapse’ (rrTNBC; distant relapse or death ≤2 years of diagnosis), ‘late relapse’ (lrTNBC; > 2 years) or ‘no relapse’ (nrTNBC: > 5 years no relapse/death). We explored basic clinical and primary tumor multi-omic data, including whole transcriptome (n = 453), and whole genome copy number and mutation data for 171 cancer-related genes (n = 317). Association of rapid relapse with clinical and genomic features were assessed using Pearson chi-squared tests, t-tests, ANOVA, and Fisher exact tests. We evaluated logistic regression models of clinical features with subtype versus two models that integrated significant genomic features.

Results

Relative to nrTNBC, both rrTNBC and lrTNBC had significantly lower immune signatures and immune signatures were highly correlated to anti-tumor CD8 T-cell, M1 macrophage, and gamma-delta T-cell CIBERSORT inferred immune subsets. Intriguingly, lrTNBCs were enriched for luminal signatures. There was no difference in tumor mutation burden or percent genome altered across groups. Logistic regression mModels that incorporate genomic features significantly outperformed standard clinical/subtype models in training (n = 63 patients), testing (n = 63) and independent validation (n = 34) cohorts, although performance of all models were overall modest.

Conclusions

We identify clinical and genomic features associated with rapid relapse TNBC for further study of this aggressive TNBC subset.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08320-7.

Ablation of the Brca1-Palb2 Interaction Phenocopies Fanconi Anemia in Mice

Heterozygous mutations in the BRCA1 gene predispose women to breast and ovarian cancer, while biallelic BRCA1 mutations are a cause of Fanconi anemia (FA), a rare genetic disorder characterized by developmental abnormalities, early-onset bone marrow failure, increased risk of cancers, and hypersensitivity to DNA-crosslinking agents. BRCA1 is critical for homologous recombination of DNA double-strand breaks (DSB). Through its coiled-coil domain, BRCA1 interacts with an essential partner, PALB2, recruiting BRCA2 and RAD51 to sites of DNA damage. Missense mutations within the coiled-coil domain of BRCA1 (e.g., L1407P) that affect the interaction with PALB2 have been reported in familial breast cancer. We hypothesized that if PALB2 regulates or mediates BRCA1 tumor suppressor function, ablation of the BRCA1-PALB2 interaction may also elicit genomic instability and tumor susceptibility. We generated mice defective for the Brca1-Palb2 interaction (Brca1 L1363P in mice) and established MEF cells from these mice. Brca1 ^{L1363P/L1363P} MEF exhibited hypersensitivity to DNA-damaging agents and failed to recruit Rad51 to DSB. Brca1 ^{L1363P/L1363P} mice were viable but exhibited various FA symptoms including growth retardation, hyperpigmentation, skeletal abnormalities, and male/female infertility. Furthermore, all Brca1 ^{L1363P/L1363P} mice exhibited macrocytosis and died due to bone marrow failure or lymphoblastic lymphoma/leukemia with activating Notch1 mutations. These phenotypes closely recapitulate clinical features observed in patients with FA. Collectively, this model effectively demonstrates the significance of the BRCA1-PALB2 interaction in genome integrity and provides an FA model to investigate hematopoietic stem cells for mechanisms underlying progressive failure of hematopoiesis and associated development of leukemia/lymphoma, and other FA phenotypes. SIGNIFICANCE: A new Brca1 mouse model for Fanconi anemia (FA) complementation group S provides a system in which to study phenotypes observed in human FA patients including bone marrow failure.See related commentary by Her and Bunting, p. 4044.

Modeling Brain Metastases Through Intracranial Injection and Magnetic Resonance Imaging

Metastatic spread of cancer is an unfortunate consequence of disease progression, aggressive cancer subtypes, and/or late diagnosis. Brain metastases are particularly devastating, difficult to treat, and confer a poor prognosis. While the precise incidence of brain metastases in the United States remains hard to estimate, it is likely to increase as extracranial therapies continue to become more efficacious in treating cancer. Thus, it is necessary to identify and develop novel therapeutic approaches to treat metastasis at this site. To this end, intracranial injection of cancer cells has become a well-established method in which to model brain metastasis. Previously, the inability to directly measure tumor growth has been a technical hindrance to this model; however, increasing availability and quality of small animal imaging modalities, such as magnetic resonance imaging (MRI), are vastly improving the ability to monitor tumor growth over time and infer changes within the brain during the experimental period. Herein, intracranial injection of murine mammary tumor cells into immunocompetent mice followed by MRI is demonstrated. The presented injection approach utilizes isoflurane anesthesia and a stereotactic setup with a digitally controlled, automated drill and needle injection to enhance precision, and reduce technical error. MRI is measured over time using a 9.4 Tesla instrument in The Ohio State University James Comprehensive Cancer Center Small Animal Imaging Shared Resource. Tumor volume measurements are demonstrated at each time point through use of ImageJ. Overall, this intracranial injection approach allows for precise injection, day-to-day monitoring, and accurate tumor volume measurements, which combined greatly enhance the utility of this model system to test novel hypotheses on the drivers of brain metastases.

Stromal Platelet-Derived Growth Factor Receptor-β Signaling Promotes Breast Cancer Metastasis in the Brain

Platelet-derived growth factor receptor-beta (PDGFRβ) is a receptor tyrosine kinase found in cells of mesenchymal origin such as fibroblasts and pericytes. Activation of this receptor is dependent on paracrine ligand induction, and its preferred ligand PDGFB is released by neighboring epithelial and endothelial cells. While expression of both PDGFRβ and PDGFB has been noted in patient breast tumors for decades, how PDGFB-to-PDGFRβ tumor-stroma signaling mediates breast cancer initiation, progression, and metastasis remains unclear. Here we demonstrate this paracrine signaling pathway that mediates both primary tumor growth and metastasis, specifically, metastasis to the brain. Elevated levels of PDGFB accelerated orthotopic tumor growth and intracranial growth of mammary tumor cells, while mesenchymal-specific expression of an activating mutant PDGFRβ (PDGFRβ^D849V) exerted proproliferative signals on adjacent mammary tumor cells. Stromal expression of PDGFRβ^D849V also promoted brain metastases of mammary tumor cells expressing high PDGFB when injected intravenously. In the brain, expression of PDGFRβ^D849V was observed within a subset of astrocytes, and aged mice expressing PDGFRβ^D849V exhibited reactive gliosis. Importantly, the PDGFR-specific inhibitor crenolanib significantly reduced intracranial growth of mammary tumor cells. In a tissue microarray comprised of 363 primary human breast tumors, high PDGFB protein expression was prognostic for brain metastases, but not metastases to other sites. Our results advocate the use of mice expressing PDGFRβ^D849V in their stromal cells as a preclinical model of breast cancer-associated brain metastases and support continued investigation into the clinical prognostic and therapeutic use of PDGFB-to-PDGFRβ signaling in women with breast cancer. SIGNIFICANCE: These studies reveal a previously unknown role for PDGFB-to-PDGFRβ paracrine signaling in the promotion of breast cancer brain metastases and support the prognostic and therapeutic clinical utility of this pathway for patients.See related article by Wyss and colleagues, p. 594.

Abstract P3-01-15: Targeting small G proteins in triple negative breast cancer

Breast Cancer (BC) is the most common cancer in women and second leading cause of cancer-associated mortality in women world-wide. Treatment for women with BC is complicated by the molecular heterogeneity of the disease which can be classified by expression of three key receptors: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Those BCs expressing none of these receptors are known as triple negative (TNBC). Importantly, TNBC patients have the highest mortality among BC subtypes. This inequity is due in large part to the lack of targeted treatment options for TNBC patients. While women with ER-positive or HER2-positive BC benefit from therapeutic advances that target these receptors, treatment options for women with TNBC have changed little since the 1960’s with toxic chemotherapy as the primary systemic treatment option. Thus, there is an urgent need to identify new molecular targets and innovative treatment strategies to improve outcome for women with TNBC. RalA and RalB are small GTPases implicated in tumor proliferation, survival, and metastasis in a variety of cancers. However, little is known of their roles in breast cancer. Utilizing publicly available BC patient gene expression datasets, we identified RALA as a potential prognostic biomarker and therapeutic target in TNBC. RALA expression is significantly elevated in TNBC relative to normal mammary tissue or other BC subtypes. Furthermore, RALA expression is highly prognostic of overall and distant metastasis-free survival in the greater BC patient population and specifically in patients with TNBC. Importantly, RALA remains an independent prognostic factor in TNBC when other clinicopathological variables are considered. BC patient tissue microarrays revealed RalA immunohistochemical (IHC) staining is also prognostic of worse overall survival in the ER-negative and TNBC populations but not in BC patients with ER-positive disease. Surprisingly, expression of RALB, which is highly homologous to RALA and has also been implicated as pro-tumorigenic/pro-metastatic in a number of solid tumor types, is decreased in TNBC relative to normal mammary tissue and is not prognostic of TNBC outcome. These data suggest RalA may have a unique and important role in the pathogenesis of TNBC. To determine the necessity of RalA in TNBC growth and metastasis, RalA was depleted in MVT1 cells, a murine TNBC cell line. Knockdown of RalA inhibited MVT1 orthotopic primary tumor growth and metastasis in immunocompetent mice. Similarly, knockdown of RalA in the human TNBC cell line MDA-MB-231 decreased orthotopic primary tumor growth and growth of spontaneous or experimental lung metastases in NOD scid gamma mice. Conversely, stable knockdown of RalB in MDA-MB-231 cells did not impair their tumor growth or metastatic capability in vivo. Recently, BQU57, an experimental small molecule inhibitor of both Ral isoforms was reported to slow growth of lung cancer cell lines in vitro and in vivo. We report BQU57 inhibits RalA and RalB GTP-binding and anchorage independent growth of MDA-MB-231 cells in vitro.In vivo, BQU57 treatment of mice bearing palpable MDA-MB-231 tumors significantly decreased both primary orthotopic tumor growth and spontaneous lung metastasis. BQU57 also slowed the growth of a PDX model derived from a TNBC lung metastasis. Combined, these results demonstrate an important role for RalA in the pathogenesis of TNBC that is not redundant with RalB and warrant further investigation of RalA as a target for the precise treatment of advanced TNBC.

Citation Format: Rachel E Schafer, Katie A. Thies, Reena Shakya, Sue Knoblaugh, Gina M Sizemore, Steven T Sizemore. Targeting small G proteins in triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-01-15.

Abstract P6-06-06: Platelet derived growth factor-b (PDGFB) promotes breast cancer progression

Objectives of the Study: Platelet-derived growth factor (PDGF) mediated signaling is pro-tumorigenic in many types of cancer, including breast cancer. However, the requirement of individual PDGF ligands in mediating breast cancer progression remains unclear. Our evaluation of publicly available breast cancer patient datasets shows that high primary tumor expression of PDGFB correlates with reduced overall survival (OS) and reduced metastasis free survival (MFS). This is in contrast to the lack of prognostic power of PDGFA and PDGFC and the association with improved OS and MFS for PDGFD. Based on our analysis of patient datasets, we set out to test the requirement of PDGFB in mammary tumor growth.

Methods Used: Gain-of-function and loss-of-function experiments were performed wherein PDGFB was either overexpressed or knocked-down in mammary tumor cells. Manipulated tumor cells were injected directly into the mammary fat pads of adult female mice, and tumor growth was monitored over time. PDGFB is produced by tumor cells whereas the corresponding receptor, PDGFRβ, is expressed by mesenchymal cells in the stroma. As another way to mimic oncogenic PDGFB-to-PDGFRβ signaling in the breast, we developed a mouse model of stroma-specific PDGFRβ activation using the Fsp-cre transgene. We evaluated changes mammary gland development upon mesenchymal specific PDGFRβ activation, and performed orthotopic injections with mammary tumor cells in these animals to test the functional role of receptor activation in mammary tumor growth.

Results and Conclusions: We evaluated expression of PDGF ligands in FVB/N murine mammary tumor cell lines and found that the PDGFB is dramatically higher in DB7 tumor cells compared to other syngeneic cell lines. In the high-PDGFB expressing DB7 cells, we used shRNA technology to knockdown the ligand. At the same time, we overexpressed the ligand in an isogenic cell line that expresses low levels of PDGFB. These cells were injected orthotopically into the mammary fat pads of adult female mice, and in both cases, expression of PDGFB dictated tumor growth. There was a significant reduction in tumor growth with shRNA-mediated knockdown of PDGFB whereas overexpression of the ligand accelerated tumor growth.

In our mouse model of mesenchymal-specific PDGFRβ activation, we reveal that activation of the receptor exerts pro-proliferative signals on adjacent mammary epithelial cells and accelerates orthotopic tumor growth of PDGFB-expressing cells. These findings indicate that PDGFB-to-PDGFRβ signaling is a viable therapeutic target for breast cancer. In fact, treatment with the PDGFR inhibitor, imatinib, impedes tumor cell proliferation when mouse mammary fibroblasts are co-injected orthotopically with DB7 cells.

Significance: The requirement of other PDGF ligands in breast cancer remains to be evaluated, but our data support a pro-tumorigenic role for PDGFB in the breast. Importantly, PDGFR inhibitors are being used in clinical trials for several cancer types. Our data advocate for (1) the potential utility of PDGFB as a prognostic biomarker and (2) the pre-clinical evaluation of PDGFR inhibitors in breast cancer models.

Citation Format: Katie A Thies, Anisha M Hammer, Sarah A Steck, Manjusri Das, Raleigh D Kladney, Steven T Sizemore, Michael C Ostrowski, Gina M Sizemore. Platelet derived growth factor-b (PDGFB) promotes breast cancer progression [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-06-06.

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 P1-09-06: Gene-set enrichment analysis (GSEA) of breast tissue from healthy women with less than six months history of breastfeeding shows enrichment in Hedgehog signaling, notch signaling and luminal progenitor gene signatures

Introduction: Multiple epidemiological studies have shown that prolonged breastfeeding is associated with a reduced risk of developing triple negative/basal-like breast cancer (TN/BLBC). We have modeled abrupt involution (AI) due to lack of breastfeeding and gradual involution (GI) of the mammary gland that occurs over time upon prolonged breastfeeding in wild-type FVB/N mice and discovered prominent histological and molecular changes in the AI glands over time. Our studies revealed for the first time a clear and persistent expansion of mammary luminal progenitor (LP) epithelial cells in AI glands (AACR abstract#2242, 2018). Here, we corroborate animal studies using normal human breast tissue obtained from a reduction mammoplasty tissue collection study (OSU-2011C0094).

Methods: Breast tissue obtained from parous premenopausal women with no history of breast cancer who breastfed for ≥6 months (GI, n=16) versus those who breastfed for &lt;6 months (AI, n=16) (OSU-2011C0094) was used for gene expression analysis. RNA isolated from these normal mammary tissues was analyzed using Affymatrix Gene ChIP Human Transcriptome array 2.0; Gene Set Enrichment Analysis (GSEA) was used to analyze the microarray data. Molecular Signatures Database was used in GSEA querying C2 curated gene sets, Hallmark gene sets, and Lim-Mammary-Luminal-Progenitor gene sets. H&E sections of the breast tissue were used to assess lobular type by counting number of ductules per terminal ductal lobular unit (TDLU). False discovery rate (FDR) q-values and p-values were used for multiple comparison adjustment.

Results: GSEA revealed that breast tissue obtained from women in the AI cohort exhibited strong positive enrichment for Notch and Hedgehog Signaling (Hhg) pathways (FDR q-value= 0.20 and 0.12, respectively). In GI women, GSEA showed an overall trend towards enrichment in metabolic pathways and immune system functions. Moreover, there was non-significant trend towards positive enrichment of mouse LP gene signature in AI women only (FDR q-value= 0.30). Age and BMI were not statistically different between AI and GI cohorts. Analysis of TDLU, the primary anatomical source of most breast cancers, revealed that breast tissue from AI women had proportionally higher lobular type 1 only epithelium than GI women who exhibited more differentiated lobular epithelium (p-value= 0.049).

Conclusion: We report here for the first time that mammary glands from women who breastfed &lt;6 months were enriched for stem-cell signaling pathways and LP gene signature. This reflects some similarity to BRCA1 mutation carriers, who demonstrate expanded luminal progenitor population. In addition, higher Type 1 TDLU's are seen in breast tissue from parous women who breastfed &lt;6 months. Together, these data demonstrate features for TN/BLBC precursors enriched in patients who breastfed for &lt;6 months. Understanding this mechanistic link will help in developing prevention strategies, particularly for African-American women who have lower prevalence of breastfeeding and higher incidence of TN/BLBC.

Citation Format: Basree MM, Shinde N, Palettas M, Weng D, Stover DG, Sizemore GM, Shields P, Majumder S, Ramaswamy B. Gene-set enrichment analysis (GSEA) of breast tissue from healthy women with less than six months history of breastfeeding shows enrichment in Hedgehog signaling, notch signaling and luminal progenitor gene signatures [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 P1-09-06.

Abstract PD9-11: Platelet derived growth factor receptor-β signaling: A novel therapeutic target for breast cancer associated brain metastasis

PDGFRβ is a receptor tyrosine kinase found in cells of mesenchymal origin such as fibroblasts and pericytes. Activation of this receptor is dependent on paracrine ligand induction, and its preferred ligand, PDGFB, is released by neighboring epithelial and endothelial cells. While expression of both PDGFRβ and PDGFB has been noted in patient breast tumors for decades, how PDGFB-to-PDGFRβ tumor-stromal signaling mediates breast cancer initiation, progression, and metastasis remains unclear. To test this important research question, we developed a mouse model of mesenchymal-specific PDGFRβ hyper-activation. PDGFRβ mutant mammary glands exhibit increased tertiary side-branching and epithelial proliferation confirming a stromal-specific PDGFRβ effect on neighboring epithelium during normal development. To test the effect of hyper-active mesenchymal PDGFRβ on disease progression, experimental tail vein metastasis assays were performed where we observed prominent brain metastases in 50% of the PDGFRβ mutantmice (n=5/10) with no brain lesions seen in controls (n=0/19). There was no difference in the incidence of lung or liver metastases in the mutant mice suggesting a pro-metastatic function for PDGFRβ in the brain metastatic niche. To rule out dysfunction of the blood brain barrier contributing to the observed metastatic spread, we then intracranially injected mammary tumor cells, and as expected based on our metastasis assay, found that larger tumors formed in the brains of PDGFRβ mutant mice versus controls. To our knowledge, these combined findings are the first example where genetic manipulation of the stroma increases breast cancer associated brain metastases (BCBM). Given that these pre-clinical data suggest that primary breast tumors expressing high PDGFB could preferentially metastasize to the brain, we analyzed PDGFB protein expression in a tissue microarray comprised of HER2-positive and triple negative breast cancer (TNBC) primary tumors (total n=425). While high PDGFB did not correlate with site-independent metastatic recurrence, it was prognostic of brain metastasis, mirroring our mouse data. Evaluation of PDGFB in a small cohort of matched primary breast tumors with associated brain (n=5) and lung metastases (n=2) revealed intense PDGFB staining in 100% of the brain metastases, but only 50% of the lung metastases. These findings further suggest that high primary tumor PDGFBexpression defines a subset of breast cancer patients predisposed to brain metastases and that these patients may benefit from therapeutic inhibition 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 to date (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. Ongoing studies are evaluating how the PDGFRβ-expressing mesenchymal cells within the brain promote a pro-metastatic niche.

Citation Format: Sizemore GM, Hammer AM, Thies KA, Hildreth BE, Russell LO, Sizemore ST, Trimboli AJ, Kladney RD, Steck SA, Das M, Bolyard CM, Pilarski R, Schoenfield L, Otero J, Chakravarti A, Ringel M, Kaur B, Leone G, Ostrowski MC. Platelet derived growth factor receptor-β signaling: A novel therapeutic target for breast cancer associated brain metastasis [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 PD9-11.

Stromal PTEN Regulates Extracellular Matrix Organization in the Mammary Gland

The organization of the extracellular matrix has a profound impact on cancer development and progression. The matrix becomes aligned throughout tumor progression, providing “highways” for tumor cell invasion. Aligned matrix is associated with breast density and is a negative prognostic factor in several cancers; however, the underlying mechanisms regulating this reorganization remain poorly understood. Deletion of the tumor suppressor Pten in the stroma was previously shown to promote extracellular matrix expansion and tumor progression. However, it was unknown if PTEN also regulated matrix organization. To address this question, a murine model with fibroblast-specific Pten deletion was used to examine how PTEN regulates matrix remodeling. Using second harmonic generation microscopy, Pten deletion was found to promote collagen alignment parallel to the mammary duct in the normal gland and further remodeling perpendicular to the tumor edge in tumor-bearing mice. Increased alignment was observed with Pten deletion in vitro using fibroblast-derived matrices. PTEN loss was associated with fibroblast activation and increased cellular contractility, as determined by traction force microscopy. Inhibition of contractility abrogated the increased matrix alignment observed with PTEN loss. Murine mammary adenocarcinoma cells cultured on aligned matrices derived from Pten^−/− fibroblasts migrated faster than on matrices from wild-type fibroblasts. Combined, these data demonstrate that PTEN loss in fibroblasts promotes extracellular matrix deposition and alignment independently from cancer cell presence, and this reorganization regulates cancer cell behavior. Importantly, stromal PTEN negatively correlated with collagen alignment and high mammographic density in human breast tissue, suggesting parallel function for PTEN in patients.

Pyruvate kinase M2 regulates homologous recombination-mediated DNA double-strand break repair

Resistance to genotoxic therapies is a primary cause of treatment failure and tumor recurrence. The underlying mechanisms that activate the DNA damage response (DDR) and allow cancer cells to escape the lethal effects of genotoxic therapies remain unclear. Here, we uncover an unexpected mechanism through which pyruvate kinase M2 (PKM2), the highly expressed PK isoform in cancer cells and a master regulator of cancer metabolic reprogramming, integrates with the DDR to directly promote DNA double-strand break (DSB) repair. In response to ionizing radiation and oxidative stress, ATM phosphorylates PKM2 at T328 resulting in its nuclear accumulation. pT328-PKM2 is required and sufficient to promote homologous recombination (HR)-mediated DNA DSB repair through phosphorylation of CtBP-interacting protein (CtIP) on T126 to increase CtIP's recruitment at DSBs and resection of DNA ends. Disruption of the ATM-PKM2-CtIP axis sensitizes cancer cells to a variety of DNA-damaging agents and PARP1 inhibition. Furthermore, increased nuclear pT328-PKM2 level is associated with significantly worse survival in glioblastoma patients. Combined, these data advocate the use of PKM2-targeting strategies as a means to not only disrupt cancer metabolism but also inhibit an important mechanism of resistance to genotoxic therapies.

Disruption of stromal hedgehog signaling initiates RNF5-mediated proteasomal degradation of PTEN and accelerates pancreatic tumor growth

Disrupting paracrine Hedgehog signaling in pancreatic cancer stroma through genetic deletion of fibroblast Smoothened leads to proteasomal degradation of fibroblast PTEN and accelerates tumor growth.

The contribution of the tumor microenvironment to pancreatic ductal adenocarcinoma (PDAC) development is currently unclear. We therefore examined the consequences of disrupting paracrine Hedgehog (HH) signaling in PDAC stroma. Herein, we show that ablation of the key HH signaling gene Smoothened (Smo) in stromal fibroblasts led to increased proliferation of pancreatic tumor cells. Furthermore, Smo deletion resulted in proteasomal degradation of the tumor suppressor PTEN and activation of oncogenic protein kinase B (AKT) in fibroblasts. An unbiased proteomic screen identified RNF5 as a novel E3 ubiquitin ligase responsible for degradation of phosphatase and tensin homolog (PTEN) in Smo-null fibroblasts. Ring Finger Protein 5 (Rnf5) knockdown or pharmacological inhibition of glycogen synthase kinase 3β (GSKβ), the kinase that marks PTEN for ubiquitination, rescued PTEN levels and reversed the oncogenic phenotype, identifying a new node of PTEN regulation. In PDAC patients, low stromal PTEN correlated with reduced overall survival. Mechanistically, PTEN loss decreased hydraulic permeability of the extracellular matrix, which was reversed by hyaluronidase treatment. These results define non-cell autonomous tumor-promoting mechanisms activated by disruption of the HH/PTEN axis and identifies new targets for restoring stromal tumor-suppressive functions.

Stromal PTEN determines mammary epithelial response to radiotherapy

The importance of the tumor-associated stroma in cancer progression is clear. However, it remains uncertain whether early events in the stroma are capable of initiating breast tumorigenesis. Here, we show that in the mammary glands of non-tumor bearing mice, stromal-specific phosphatase and tensin homolog (Pten) deletion invokes radiation-induced genomic instability in neighboring epithelium. In these animals, a single dose of whole-body radiation causes focal mammary lobuloalveolar hyperplasia through paracrine epidermal growth factor receptor (EGFR) activation, and EGFR inhibition abrogates these cellular changes. By analyzing human tissue, we discover that stromal PTEN is lost in a subset of normal breast samples obtained from reduction mammoplasty, and is predictive of recurrence in breast cancer patients. Combined, these data indicate that diagnostic or therapeutic chest radiation may predispose patients with decreased stromal PTEN expression to secondary breast cancer, and that prophylactic EGFR inhibition may reduce this risk.

Abstract 49: Stromal platelet derived growth factor receptor (PDGFRβ) signaling: A novel therapeutic target for breast cancer brain metastasis (BCBM)

Stromal 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 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 (PDGFRβ mutant). PDGFRβ mutant mammary glands exhibit increased tertiary side-branching and epithelial proliferation confirming a stromal-specific PDGFRβ effect on neighboring epithelium. To evaluate the functional relevance of PDGFRβ activation on metastatic progression, we performed tail vein injection of PDGFB expressing murine mammary tumor cells and, surprisingly, observed brain metastases in 50% of the PDGFRβ mutant mice while no brain lesions were seen in controls. There was no difference in the incidence of lung, liver or bone metastases. Mammary tumor cells expressing low PDGFB did not exhibit a similar increase in brain metastases in mutant mice. While there is no observable difference in blood brain barrier permeability in the mutant mice, we bypassed this variable by intracranially injecting mammary tumor cells and found that larger tumors formed in the brains of PDGFRβ mutant mice versus controls. To our knowledge, this is the first example where genetic manipulation of the stroma leads to an increased incidence of BCBM. Also, 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 breast cancer (TNBC) primary tumors. While high PDGFB did not correlate with site-independent metastatic recurrence, it was prognostic of brain metastasis, mirroring our mouse data. Evaluation of PDGFB in a small cohort of matched primary breast tumors with associated brain (n=5) and lung metastases (n=2) revealed intense PDGFB staining in 100% of the brain metastases, but only 50% of the lung metastases. Our findings suggest high primary tumor PDGFB expression defines a subset of breast cancer 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.

Citation Format: Katie A. Thies, Anisha M. Hammer, B. Eason Hildreth, Luke O. Russell, Steven T. Sizemore, Anthony J. Trimboli, Raleigh D. Kladney, Chelsea M. Bolyard, Robert Pilarski, Lynn Schoenfield, Jose Otero, Arnab Chakravarti, Matthew Ringel, Balveen Kaur, Gustavo Leone, Michael C. Ostrowski, Gina M. Sizemore. Stromal platelet derived growth factor receptor (PDGFRβ) signaling: A novel therapeutic target for breast cancer brain metastasis (BCBM) [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 49.

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.

Synthetic Lethality of PARP Inhibition and Ionizing Radiation is p53-dependent

PARP inhibitors (PARPi) are potentially effective therapeutic agents capable of inducing synthetic lethality in tumors with deficiencies in homologous recombination (HR)-mediated DNA repair such as those carrying BRCA1 mutations. However, BRCA mutations are rare, the majority of tumors are proficient in HR repair, and thus most tumors are resistant to PARPi. Previously, we observed that ionizing radiation (IR) initiates cytoplasmic translocation of BRCA1 leading to suppression of HR-mediated DNA repair and induction of synthetic PARPi lethality in wild-type BRCA1 and HR-proficient tumor cells. The tumor suppressor p53 was identified as a key factor that regulates DNA damage-induced BRCA1 cytoplasmic sequestration following IR. However, the role of p53 in IR-induced PARPi sensitization remains unclear. This study elucidates the role of p53 in IR-induced PARPi cytotoxicity in HR-proficient cancer cells and suggests p53 status may help define a patient population that might benefit from this treatment strategy. Sensitization to PARPi following IR was determined in vitro and in vivo utilizing human breast and glioma tumor cells carrying wild-type BRCA1 and p53, and in associated cells in which p53 function was modified by knockdown or mutation. In breast and glioma cells with proficient HR repair, IR-induced BRCA1 cytoplasmic sequestration, HR repair inhibition, and subsequent PARPi sensitization in vitro and in vivo was dependent upon functional p53.Implications: Implications: p53 status determines PARP inhibitor sensitization by ionizing radiation in multiple BRCA1 and HR-proficient tumor types and may predict which patients are most likely to benefit from combination therapy. Mol Cancer Res; 16(7); 1092-102. ©2018 AACR.

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 1354: The role of RALA in soft tissue sarcoma tumor growth and metastasis

Soft tissue sarcomas (STS) are a diverse collection of cancers of mesenchymal origin arising from the connective and supportive tissues of the body. While localized STS are well managed by surgery and radiation; metastasis, particularly to the lung, is frequent. More than 30% of adult STS patients develop lung metastases and the 5-year survival for these patients is a dismal 16%. Treatment options for metastatic STS are limited, thus there is an urgent unmet need for a better understanding of the key molecular pathways that drive metastatic spread in STS and identification of inhibitors of these pathways for clinical application. Through analysis of gene expression data from metastatic STS patient samples, we identified decreased expression of PPP2R1B as a hallmark of metastatic STS. To directly test its function as a suppressor of tumor growth and metastasis in STS, PPP2R1B was stably over-expressed in HT1080 cells, a model of metastatic STS. PPP2R1B expression almost completely abolished HT1080 tumor growth in nude mice. PPP2R1B is a subunit of the PP2A protein phosphatase complex that negatively regulates numerous cancer signaling pathways. However, the functional consequences of decreased PPP2R1B expression in STS are unknown. A combination of high-throughput and targeted approaches were utilized to identify 37 phosphoproteins that are significantly dephosphorylated following PPP2R1B expression in HT1080 cells. One of these phosphoproteins, the small GTPase RALA, exhibited decreased phosphorylation on Ser194 following PPP2R1B expression. RALA is significantly prognostic of STS metastasis and is elevated in more aggressive STS subtypes relative to less aggressive subtypes and normal tissue. RALA knockdown in HT1080 significantly slowed tumor growth and decreased the incidence of pulmonary metastasis, mirroring PPP2R1B overexpression. Importantly, RALA is an actionable therapeutic target for improved treatment of STS. Aurora A inhibitors indirectly inhibit RALA function by preventing RALA Ser194 phosphorylation by aurora A. We found that RALA expression and activity predicted response of STS cell lines to aurora A inhibition. Excitingly, the aurora A inhibitor alisertib nearly eradicated growth of HT1080 tumors in vivo. Exploration of the biological mechanisms through which RALA regulates STS metastasis identified regulation of vesicular traffic as a likely critical function of RALA in this process. These findings identify PPP2R1B, RALA, and aurora A as members of a key molecular pathway that drives STS progression and advocate the use of treatments targeting this pathway to improve outcome for STS patients with advanced disease.

Citation Format: Steven T. Sizemore, Gina M. Sizemore, Reena Shakya, Peter Amaya, Anisha M. Hammer, Alexander H. Rice, Jeffrey J. Chalmers, Michael C. Ostrowski, Arnab Chakravarti. The role of RALA in soft tissue sarcoma tumor growth and metastasis [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 1354. doi:10.1158/1538-7445.AM2017-1354

Abstract 3911: Stromal platelet derived growth factor receptor-beta (PDGFRbeta) promotes breast brain metastasis

The platelet derived growth factor (PDGF) pathway is a prime example of tumor-stroma signaling in a number of cancer types. Others have shown that PDGF receptors are expressed in breast fibroblasts and pericytes while PDGF ligands are often expressed in breast cancer cells and tumor-associated endothelium; however, how PDGF signaling mediates breast cancer initiation, progression and metastasis remains unclear. Importantly, our evaluation of publicly available datasets revealed that PDGFB expression correlates with breast cancer patient metastatic recurrence leading to the hypothesis that PDGF-B to PDGFR signaling promotes metastatic progression of breast cancer. Given that PDGF-B preferentially activates PDGFRβ, we established an in vivo system to investigate this pathway during breast cancer progression. We utilized a mesenchymal-specific promoter to drive Cre recombinase and conditionally activate PDGFRβ by way of the endogenous Pdgfrb promoter (hereafter “PDGFRβ mutant”). A murine mammary tumor cell line which expresses high levels of PDGF-B was injected either by tail vein or intracranially to evaluate metastatic seeding and distant tumor growth. Following tail vein injection of tumor cells, we observed 50% incidence of brain metastases in the PDGFRβ mutant mice while no brain lesions were seen in the controls. There was no difference in incidence of lung, liver or bone metastases (other common sites of breast cancer metastasis). Not surprisingly, larger tumors formed in the brains of PDGFRβ mutant mice when cells were injected intracranially. Brains were stained for phospho-PLCγ as a way to confirm activation of PDGFRβ. To our knowledge, this is the first example where genetic manipulation of the stroma leads to an increased incidence of breast brain metastases. Furthermore, this study highlights a role for stromal activation of PDGFRβ in the brain microenvironment and during metastatic progression. For the 20-30% of patients that develop breast cancer brain metastases, the one-year survival rate is sadly less than 20%, and how the brain microenvironment contributes to metastatic seeding and subsequent growth of tumor cells remains poorly understood. To confirm translational relevance, we analyzed a small cohort of matched primary breast tumors and brain metastases for PDGFRβ expression observing strong stromal staining in fibroblasts and pericytes within and around all of the primary tumors similar to previous studies. Importantly, high PDGFRβ expression was found in the perivasculature of all associated brain metastases suggesting a functional role in the establishment or growth at this site. Combined, our findings strongly suggest that high primary tumor expression of PDGF-B/PDGFRβ might define a subset of breast cancer patients predisposed to brain metastases. These patients may benefit from therapeutic targeting of PDGFR signaling as a means to thwart metastatic seeding in the brain.

Citation Format: Katie A. Thies, Anisha M. Hammer, Anthony J. Trimboli, B. Eason Hildreth, Luke O. Russell, Chelsea M. Bolyard, Raleigh D. Kladney, Steven T. Sizemore, Robert Pilarski, Lynn Schoenfield, Jose Otero, Arnab Chakravarti, Balveen Kaur, Gustavo Leone, Michael C. Ostrowski, Gina M. Sizemore. Stromal platelet derived growth factor receptor-beta (PDGFRbeta) promotes breast brain metastasis [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 3911. doi:10.1158/1538-7445.AM2017-3911

Abstract 2966: Stromal platelet derived growth factor receptor-beta (PDGFRbeta) promotes breast cancer progression

Over the past decade it has become evident that the tumor microenvironment (TME) actively participates in carcinogenesis. Tumor-associated fibroblasts, for example, modulate neighboring tumor epithelium through growth factor secretion to initiate and promote tumor growth. The platelet derived growth factor receptors (PDGFRs), PDGFRalpha and PDGFRbeta, are receptor tyrosine kinases activated by PDGF that may be critical and actionable mediators of breast tumor-stromal communication. PDGFRs are predominately expressed in breast tumor stroma while their cognate ligands are specifically expressed in tumor epithelium and associated endothelium. In some cancers, tumor-derived PDGFs act on the TME to recruit tumor associated fibroblasts; however, this role has not been described in breast cancer. To begin to evaluate a role for PDGFRbeta, we utilized publicly available gene expression data to confirm upregulation in tumor stroma compared to tumor epithelium. Importantly, PDGFRB is increased in tumor stroma compared to normal stroma. To directly test whether stromal PDGFR activation promotes tumor growth, we co-injected murine mammary tumor cells with or without PDGFR-expressing mouse mammary fibroblasts (MMFs) orthotopically in FVB/N mice. MMF inclusion increased tumor cell proliferation as well as associated angiogenesis while systemic treatment with imatinib mesylate, a small molecule inhibitor for PDGFR, restored both proliferation and angiogenesis back to baseline. These findings indicated the importance of PDGFR signaling in tumor initiation leading us to develop a mouse model of stromal-specific PDGFRbeta activation using the Fsp-cre transgene previously published by our group (henceforth referred to as “PDGFRbeta mutant”). PDGFRbeta mutant mammary glands exhibit increased tertiary side-branching and epithelial proliferation confirming a stromal-specific PDGFRbeta effect on neighboring epithelium during development. Further, MMFs isolated from the PDGFRbeta mutant mice exhibit increased motility towards PDGF-B expressing tumor cells in vitro, which implies increased response and recruitment of the mutant MMFs towards an expanding tumor. To test whether PDGFRbeta mutant mice harbor a mammary TME supportive of increased tumor growth, we injected murine mammary tumor cells orthotopically into either control or PDGFRbeta mutant mice finding that the time required to meet early removal criteria (tumor &gt1.2cm3) was shorter in the mutant mice compared to controls. Ongoing studies are evaluating whether systemic PDGFR inhibition will abrogate this observed increase in tumorigenesis. In summary, our data suggest that stromal PDGFRbeta signaling is pro-tumorigenic in breast cancer and that inhibition using well-described PDGFR inhibitors could be a valid therapeutic approach for women whose tumors express increased PDGF-to-PDGFR tumor-stromal signaling.

Citation Format: Gina M. Sizemore, Anisha M. Hammer, Katie A. Thies, Steven T. Sizemore, Anthony J. Trimboli, B. Eason Hildreth, Raleigh D. Kladney, Arnab Chakravarti, Gustavo Leone, Michael C. Ostrowski. Stromal platelet derived growth factor receptor-beta (PDGFRbeta) promotes breast cancer progression [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 2966. doi:10.1158/1538-7445.AM2017-2966

The ETS family of oncogenic transcription factors in solid tumours

Findings over the past decade have identified aberrant activation of the ETS transcription factor family throughout all stages of tumorigenesis. Specifically in solid tumours, gene rearrangement and amplification, feed-forward growth factor signalling loops, formation of gain-of-function co-regulatory complexes and novel cis-acting mutations in ETS target gene promoters can result in increased ETS activity. In turn, pro-oncogenic ETS signalling enhances tumorigenesis through a broad mechanistic toolbox that includes lineage specification and self-renewal, DNA damage and genome instability, epigenetics and metabolism. This Review discusses these different mechanisms of ETS activation and subsequent oncogenic implications, as well as the clinical utility of ETS factors.

Stromal PDGFR-α Activation Enhances Matrix Stiffness, Impedes Mammary Ductal Development, and Accelerates Tumor Growth

The extracellular matrix (ECM) is critical for mammary ductal development and differentiation, but how mammary fibroblasts regulate ECM remodeling remains to be elucidated. Herein, we used a mouse genetic model to activate platelet derived growth factor receptor-alpha (PDGFRα) specifically in the stroma. Hyperactivation of PDGFRα in the mammary stroma severely hindered pubertal mammary ductal morphogenesis, but did not interrupt the lobuloalveolar differentiation program. Increased stromal PDGFRα signaling induced mammary fat pad fibrosis with a corresponding increase in interstitial hyaluronic acid (HA) and collagen deposition. Mammary fibroblasts with PDGFRα hyperactivation also decreased hydraulic permeability of a collagen substrate in an in vitro microfluidic device assay, which was mitigated by inhibition of either PDGFRα or HA. Fibrosis seen in this model significantly increased the overall stiffness of the mammary gland as measured by atomic force microscopy. Further, mammary tumor cells injected orthotopically in the fat pads of mice with stromal activation of PDGFRα grew larger tumors compared to controls. Taken together, our data establish that aberrant stromal PDGFRα signaling disrupts ECM homeostasis during mammary gland development, resulting in increased mammary stiffness and increased potential for tumor growth.

Stromal PTEN inhibits the expansion of mammary epithelial stem cells through Jagged-1

Fibroblasts within the mammary tumor microenvironment are active participants in carcinogenesis mediating both tumor initiation and progression. Our group has previously demonstrated that genetic loss of PTEN in mammary fibroblasts induces an oncogenic secretome that remodels the extracellular milieu accelerating ErbB2-driven mammary tumor progression. While these prior studies highlighted a tumor suppressive role for stromal PTEN, how the adjacent normal epithelium transforms in response to PTEN loss was not previously addressed. To identify these early events, we have evaluated both phenotypic and genetic changes within the pre-neoplastic mammary epithelium of mice with and without stromal PTEN expression. We report that fibroblast-specific PTEN deletion greatly restricts mammary ductal elongation and induces aberrant alveolar side-branching. These mice concomitantly exhibit an expansion of the mammary epithelial stem cell (MaSC) enriched basal/myoepithelial population and an increase in in vitro stem cell activity. Further analysis revealed that NOTCH signaling, specifically through NOTCH3, is diminished in these cells. Mechanistically, JAGGED-1, a transmembrane ligand for the NOTCH receptor, is downregulated in the PTEN-null fibroblasts leading to a loss in the paracrine activation of NOTCH signaling from the surrounding stroma. Reintroduction of JAGGED-1 expression within the PTEN-null fibroblasts was sufficient to abrogate the observed increase in colony forming activity implying a direct role for stromal JAGGED-1 in regulation of mammary stem cell properties. Importantly, breast cancer patients whose tumors express both low stromal JAG1 and low stromal PTEN exhibit a shorter time to recurrence than those whose tumors express low levels of either alone suggesting similar stromal signaling in advanced disease. Combined, these results unveil a novel stromal PTEN-to-JAGGED-1 axis in maintaining the mammary epithelial stem cell niche, and subsequently inhibiting breast cancer initiation and disease progression.

Genetic ablation of Smoothened in pancreatic fibroblasts increases acinar-ductal metaplasia

Liu et al. show that disruption of paracrine Hedgehog signaling via genetic ablation of Smoothened (Smo) in stromal fibroblasts in a Kras^G12D mouse model increased acinar-to-ductal metaplasia (ADM). Smo-deleted fibroblasts had higher expression of transforming growth factor-α (Tgfα) mRNA and secreted higher levels of TGFα, leading to activation of EGFR signaling in acinar cells and increased ADM.

The contribution of the microenvironment to pancreatic acinar-to-ductal metaplasia (ADM), a preneoplastic transition in oncogenic Kras-driven pancreatic cancer progression, is currently unclear. Here we show that disruption of paracrine Hedgehog signaling via genetic ablation of Smoothened (Smo) in stromal fibroblasts in a Kras^G12D mouse model increased ADM. Smo-deleted fibroblasts had higher expression of transforming growth factor-α (Tgfa) mRNA and secreted higher levels of TGFα, leading to activation of EGFR signaling in acinar cells and increased ADM. The mechanism involved activation of AKT and noncanonical activation of the GLI family transcription factor GLI2. GLI2 was phosphorylated at Ser230 in an AKT-dependent fashion and directly regulated Tgfa expression in fibroblasts lacking Smo. Additionally, Smo-deleted fibroblasts stimulated the growth of Kras^G12D/Tp53^R172H pancreatic tumor cells in vivo and in vitro. These results define a non-cell-autonomous mechanism modulating Kras^G12D-driven ADM that is balanced by cross-talk between Hedgehog/SMO and AKT/GLI2 pathways in stromal fibroblasts.

GABA(A) receptor pi (GABRP) stimulates basal-like breast cancer cell migration through activation of extracellular-regulated kinase 1/2 (ERK1/2)

Breast cancer is a heterogeneous disease comprised of distinct subtypes predictive of patient outcome. Tumors of the basal-like subtype have a poor prognosis due to inherent aggressiveness and the lack of targeted therapeutics. Basal-like tumors typically lack estrogen receptor-α, progesterone receptor and HER2/ERBB2, or in other words they are triple negative (TN). Continued evaluation of basal-like breast cancer (BLBC) biology is essential to identify novel therapeutic targets. Expression of the pi subunit of the GABA(A) receptor (GABRP) is associated with the BLBC/TN subtype, and herein, we reveal its expression also correlates with metastases to the brain and poorer patient outcome. GABRP expression in breast cancer cell lines also demonstrates a significant correlation with the basal-like subtype suggesting that GABRP functions in the initiation and/or progression of basal-like tumors. To address this postulate, we stably silenced GABRP in two BLBC cell lines, HCC1187 and HCC70 cells. Decreased GABRP reduces in vitro tumorigenic potential and migration concurrent with alterations in the cytoskeleton, specifically diminished cellular protrusions and expression of the BLBC-associated cytokeratins, KRT5, KRT6B, KRT14, and KRT17. Silencing GABRP also decreases phosphorylation of extracellular regulated kinase 1/2 (ERK1/2) in both cell lines and selective inhibition of ERK1/2 similarly decreases the basal-like cytokeratins as well as migration. Combined, these data reveal a GABRP-ERK1/2-cytokeratin axis that maintains the migratory phenotype of basal-like breast cancer. GABRP is a component of a cell surface receptor, thus, these findings suggest that targeting this new signaling axis may have therapeutic potential in BLBC.

Hypomethylation of the MMP7 promoter and increased expression of MMP7 distinguishes the basal-like breast cancer subtype from other triple-negative tumors

Identification of novel targets for the treatment of basal-like breast cancer is essential for improved outcomes in patients with this disease. This study investigates the association of MMP7 expression and MMP7 promoter methylation with subtype and outcome in breast cancer patient cohorts. Immunohistochemical analysis was performed on a breast cancer tissue microarray and validated in independent histological samples. MMP7 expression significantly correlated with patient age, tumor size, triple-negative (TN) status, and recurrence. Analysis of publically available datasets confirmed MMP7 gene expression as a prognostic marker of breast cancer metastasis, particularly metastasis to the brain and lungs. Methylation of the MMP7 promoter was assessed by methylation-specific PCR in a panel of breast cancer cell lines and patient tumor samples. Hypomethylation of the MMP7 promoter significantly correlated with TN status in DNA from patient tumor samples, and this association was confirmed using The Cancer Genome Atlas (TCGA) dataset. Evaluation of a panel of breast cancer cell lines and data from the Curtis and TCGA breast carcinoma datasets revealed that elevated MMP7 expression and MMP7 promoter hypomethylation are specific biomarkers of the basal-like molecular subtype which shares considerable, but not complete, overlap with the clinical TN subtype. Importantly, MMP7 expression was identified as an independent predictor of pathological complete response in a large breast cancer patient cohort. Combined, these data suggest that MMP7 expression and MMP7 promoter methylation may be useful as prognostic biomarkers. Furthermore, MMP7 expression and promoter methylation analysis may be effective mechanisms to distinguish basal-like breast cancers from other triple-negative subtypes. Finally, these data implicate MMP7 as a potential therapeutic target for the treatment of basal-like breast cancers.

Protein kinase C Beta in the tumor microenvironment promotes mammary tumorigenesis

Protein kinase C beta (PKCβ) expression in breast cancer is associated with a more aggressive tumor phenotype, yet the mechanism for how PKCβ is pro-tumorigenic in this disease is still unclear. Interestingly, while it is known that PKCβ mediates angiogenesis, immunity, fibroblast function and adipogenesis, all components of the mammary tumor microenvironment (TME), no study to date has investigated whether stromal PKCβ is functionally relevant in breast cancer. Herein, we evaluate mouse mammary tumor virus–polyoma middle T-antigen (MMTV–PyMT) induced mammary tumorigenesis in the presence and absence of PKCβ. We utilize two model systems: one where PKCβ is deleted in both the epithelial and stromal compartments to test the global requirement for PKCβ on tumor formation, and second, where PKCβ is deleted only in the stromal compartment to test its role in the TME. MMTV–PyMT mice globally lacking PKCβ live longer and develop smaller tumors with decreased proliferation and decreased macrophage infiltration. Similarly, when PKCβ is null exclusively in the stroma, PyMT-driven B6 cells form smaller tumors with diminished collagen deposition. These experiments reveal for the first time a tumor promoting role for stromal PKCβ in MMTV–PyMT tumorigenesis. In corroboration with these results, PKCβ mRNA (Prkcb) is increased in fibroblasts isolated from MMTV–PyMT tumors. These data were confirmed in a breast cancer patient cohort. Combined these data suggest the continued investigation of PKCβ in the mammary TME is necessary to elucidate how to effectively target this signaling pathway in breast cancer.

FOXC1 is enriched in the mammary luminal progenitor population, but is not necessary for mouse mammary ductal morphogenesis

Expression of FOXC1, a forkhead box transcription factor, correlates with the human basal-like breast cancer (BLBC) subtype, and functional analyses have revealed its importance for in vitro invasiveness of BLBC cells. Women diagnosed with this breast tumor subtype have a poorer outcome because of the lack of targeted therapies; thus, continued investigation of factors driving these tumors is critical to uncover novel therapeutic targets. Several processes that dictate normal mammary morphogenesis parallel cancer progression, and enforced expression of FOXC1 can induce a progenitor state in more-differentiated mammary epithelial cells. Consequently, evaluating how FOXC1 functions in the normal gland is critical to further understand BLBC biology. Although FOXC1 is well known to control normal development of a number of tissues, its role in the mammary gland has not yet been investigated. Herein, we describe FOXC1 expression patterning in the normal breast, where it is localized to the basal/myoepithelium, suggesting that FOXC1 would be required for normal development. However, mammary glands lacking Foxc1 have no overt defect in ductal outgrowth, alveologenesis, or lineage specification. Of significant interest, we found that expression of FOXC1 is enriched in the normal luminal progenitor population, which is the postulated cell of origin of BLBC. These results indicate that FOXC1 is unnecessary for mammary morphogenesis and that its role in BLBC likely involves processes that are unrelated to cell lineage specification.

The effects of acutely administered cocaine on responding maintained by a progressive-ratio schedule of food presentation

Lever pressing in rats (N=5) was reinforced under a progressive-ratio (PR) schedule of food presentation, in which the number of responses required increased exponentially. The session was terminated when 1 h passed without completion of the scheduled ratio. Doses of cocaine (5.6-42.0 mg/kg; one subject received a dose of 56.0 mg/kg) as well as saline were administered i.p. prior to the session. Under non-drug conditions, breakpoints were typically less than 100, and substantial responding usually occurred only during about the first 10 min of the session. The rate of responding usually increased over the first 2-8 reinforcers and then decreased for the last few reinforcers obtained. For four of five rats, breakpoint, overall rate of response, and session duration were first increased above control and vehicle levels by increasing doses of cocaine. Larger doses produced smaller increases, no effect, or decreases. Cocaine, in the range of doses near the apex of the breakpoint dose-effect functions, suppressed rates of responding at the small ratios present at the beginning of the session. It is suggested that cocaine increases low rates of response if: (1). rates are low due to extinction; and (2). the stimuli present are those present when the response is reinforced.

Toward a mathematical description of dose-effect functions for self-administered drugs in laboratory animal models

RATIONALE

The interpretation of dose-effect functions for self-administered drugs remains elusive. Since, for self-administered drugs, the amount of drug in an animal depends on its behavior, a mathematical theory of drug self-administration must include terms relevant to receptor theory, as well as a description of how an organism's behavior affects the amount of drug in the animal over time.

OBJECTIVE

A theory was constructed in which the ability of a dose to maintain responding was described in terms of receptor theory and the function relating rate of responding to amount of drug self-administered. The main predictions of the theory were that: 1) there should be no ascending limb for drugs self-administered under ratio schedules, 2) running rate of response should not change as a function of dose and, 3) pause duration should be an exponential function of dose.

RESULTS

Low doses of cocaine were either self-administered at high rates, or not at all. Run rates, though somewhat variable, did not change as an orderly function of dose. Pause duration could be well described by an exponential function.

CONCLUSIONS

The theory provides an acceptable, though no doubt preliminary, description of drug self-administration.

Antagonism of delta(2)-opioid receptors by naltrindole-5'-isothiocyanate attenuates heroin self-administration but not antinociception in rats

delta-Opioid receptors have been implicated in reinforcement processes and antagonists are available that produce long-lasting and selective antagonism of delta-opioid receptors in vivo. This experiment assessed the contribution of delta-opioid receptors to the antinociceptive and reinforcing properties of heroin. The effects of the irreversible delta-antagonist naltrindole-5'-isothiocyanate (5'-NTII) were evaluated on heroin self-administration and hot-plate antinociception in rats. 5'-NTII (10 nmol i.c.v.) shifted the dose-response curve for heroin self-administration downward, increasing the A(50) values on the ascending and descending limbs by approximately 0.5 log units and decreasing the maximum by 33%. 5'-NTII (40 nmol i.c.v.) shifted both limbs of the heroin self-administration dose-effect curve 1.2 log units to the right and decreased the maximum by 90%. Heroin self-administration gradually returned to baseline levels over 7 or 17 days after administration of 10 or 40 nmol 5'-NTII, respectively. 5'-NTII (40 nmol i.c.v.) decreased the self-administration of 0.17 mg/infusion cocaine by 40% while having no effect on responding maintained by 0.33 or 0.67 mg/infusion. 5'-NTII attenuated the antinociceptive effects of deltorphin (delta(2)) in a dose-dependent manner while having no effect on antinociception elicited after i.c. v. administration of [D-Pen(2),D-Pen(5)]-enkephalin (delta(1)) or [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (mu). In addition, the antinociceptive effects of heroin were not significantly affected by 5'-NTII (40 nmol i.c.v.). Therefore, 5'-NTII can attenuate the reinforcing effects of heroin at doses that do not affect its antinociceptive effects. Long-acting delta(2)-opioid antagonists may be beneficial in the treatment of heroin dependence or as adjuncts to reduce the abuse liability of opioid analgesics.

Ventral pallidal extracellular fluid levels of dopamine, serotonin, gamma amino butyric acid, and glutamate during cocaine self-administration in rats

RATIONALE

Dopamine innervation of the nucleus accumbens is thought to have a major role in the biological processes underlying cocaine self-administration. Recent data suggest that dopamine innervation of the ventral pallidum (VP) may also play an important role.

OBJECTIVES

This experiment was initiated to assess extracellular fluid levels of dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and glutamate (Glu) in the VP of rats self-administering cocaine using in vivo microdialysis.

METHODS

Rats were implanted with intravenous jugular catheters and a microdialysis probe guide cannula into the VP and trained to self-administer (SA) three different doses of cocaine during each daily session. Other rats (yoked rats) were surgically prepared in identical fashion and received vehicle infusions during microdialysis sessions when the SA rat to whom they were yoked produced cocaine infusions. When stable baselines of self-administration were obtained, microdialysates were collected during two consecutive daily self-administration sessions. Neurotransmitter levels were measured using HPLC with electrochemical (DA and 5-HT) or fluorescence detection (GABA and Glu).

RESULTS

In SA rats, extracellular fluid levels of DA [DA]e and 5-HT [5-HT]e were elevated throughout the session and levels of Glu [Glu]e showed small increases at a few isolated time points during the session. The increases in [DA]e and 15-HT]e were dose-dependent. Extracellular fluid levels of GABA [GABA]e were unchanged, as were levels of all four neurotransmitters in the yoked rats.

CONCLUSIONS

These data support a potential role for DA and 5-HT innervations of the VP in intravenous cocaine self-administration.

Effects of beta-funaltrexamine on dose-effect curves for heroin self-administration in rats: comparison with alteration of [3H]DAMGO binding to rat brain sections

These studies were undertaken to determine the effects of mu-opioid receptor depletion through irreversible alkylation on the dose-effect curve for heroin self-administration. Heroin maintained responding in rats with an inverted U-shaped dose-effect curve and administration of 10 nmol of beta-funaltrexamine i.c.v. (beta-FNA) significantly increased the ED50 on the ascending limb from 1.9 to 5.3 micrograms/infusion, and from 24.3 to 211.8 micrograms/infusion on the descending limb. Administration of saline i.c.v. produced no effect on heroin self-administration. Administration of 40 nmol of beta-FNA increased the ED50S from 5.1 to 33.9 and from 14.4 to 502.8 micrograms/infusion on the ascending and descending portions of heroin's dose-effect curve, respectively. beta-FNA (40 nmol, i.c.v.) had no effect on cocaine self-administration. [3H]DAMGO binding density was decreased in the caudate and nucleus accumbens by 29 or 54% 24 h after administration of 10 or 40 nmol of beta-FNA i.c.v., respectively. The effects of beta-FNA on heroin self-administration were completely overcome by increasing the dose of heroin however, as the shape and slope of the self-administration dose-effect curve was not different when higher doses of heroin were made available for self-administration compared to control data or saline administration. Therefore, there appear to be spare mu-opioid receptors for heroin for the production of its reinforcing effects in rats. Furthermore, the self-administration dose-effect curves returned to control values prior to the return of [3H]DAMGO binding, further suggesting that the full complement of mu-opioid receptors is not necessary for heroin to produce its reinforcing effects. These findings support the existence of spare mu-opioid receptors for heroin in maintaining self-administration in rats.

RTI-113 administration reduces cocaine self-administration at high occupancy of dopamine transporter

RTI-113 [3beta-(4-chlorophenyl)tropan-2beta carboxylic acid phenyl ester hydrochloride], one of many phenyltropanes potent at and selective for DAT, inhibited self-administration of cocaine in rat at doses that did not alter responding maintained by food. The doses that inhibited cocaine intake produced significant levels of occupancy of DAT.

Dose-effect functions for cocaine self-administration: effects of schedule and dosing procedure

Research related to determining how procedural variables can alter dose-effect functions for cocaine self-administration is limited. Toward clarifying the role of procedural variables, responding was maintained in rats under either variable-interval (VI) or fixed-ratio (FR) schedules of cocaine infusion. In addition to free-operant FR schedules, discrete-trial FR schedules were evaluated. The dose-effect functions were obtained by either substituting a dose for the usual daily dose, instituting a particular dose for several sessions, or making all doses available within a session. Dose-effect functions for response rate (or number of trials with infusions for the discrete-trial FR) were bitonic for the VI and discrete-trial FR schedules but tended to be strictly decreasing for the free-operant FR schedules. Responding was maintained under FR schedules by a low dose (0.083 mg/infusion) if the dose was substituted for a higher daily dose but not when made available daily. Rate of response was higher under ratio schedules at 0.17 mg/infusion when this dose occurred within the context of other higher doses within a session than when the dose was simply substituted for a higher daily dose. These data indicate that procedural variables can alter dose-response curves for cocaine self-administration.

Within-session determination of dose-response curves for heroin self-administration in rats: Comparison with between-session determination and effects of naltrexone

A procedure was employed in the present study to obtain dose-response curves for heroin self-administration within each experimental session. The data generated using this procedure were compared to dose-response data obtained using between-session dose manipulations. The dose of heroin (18, 30, 60 or 100 micrograms/kg/inf) was varied across 4-hourly segments separated by a 20-min time-out period during which heroin was not available. The within-session dose-response procedure yielded data similar to those obtained using between-session dose manipulations when the order of dose presentation was increasing or random. However, the dose-response curve for total drug-intake was flat when the doses were presented in decreasing order. Further analysis of the dose-response curves in the within-session procedure demonstrated that the rate of heroin intake increased in the third and fourth hourly components compared to the first component, suggesting acute tolerance to the reinforcing and/or rate-suppressive effects of heroin. Furthermore, using a random order of dose presentation, administration of 3.0 mg/kg of naltrexone prior to the session shifted the dose-response curve for heroin self-administration 5-fold to the right in the within-session procedure. The data indicate that the within-session dose-response procedure can be used to investigate the pharmacology of heroin self-administration in rodents.

Behavioral tolerance to cocaine in squirrel monkeys: acute and chronic effects on complex operant behavior

Four food-deprived squirrel monkeys were trained to emit complex sequences of responses. The sequences involved pressing lighted response keys in orders dictated by colors that illuminated the keys, and ranged in length from two to five responses. Appropriate completion of these behavioral chains could be followed by food presentation. Acute administration of a range of doses (0.1-1.7 mg/kg) of cocaine hydrochloride produced dose-related decreases in the rate of completing chains and in accuracy of performance during chains. There was little evidence that the drug's effects on overall accuracy were related to the length of the chain. Three of the monkeys were exposed to daily administration of a large dose of cocaine, first after daily sessions and then prior to sessions. Daily postsession administration did not alter the dose-effect curves, but daily presession injection did, indicating the development of behavioral or "contingent" tolerance. In all cases, tolerance was accompanied by an increase in reinforcement frequency relative to the frequency observed following acute administration. Omission of the daily dose during presession drug administration resulted in performance near original control levels indicating essentially no withdrawal effect. The findings illustrate the importance of behavioral factors in the development of tolerance to cocaine in a primate.

Cocaine tolerance: acute versus chronic effects as dependent upon fixed-ratio size

The effects of cocaine on operant behavior were studied by examining fixed-ratio value as a factor in the development of tolerance. Pigeons pecked a response key under a three-component multiple schedule, with each bird being exposed to fixed-ratio values that were categorized as small, medium, or large. Administered acutely, cocaine (1.0 to 10.0 mg/kg) produced dose-related decreases in overall rate of responding. Responding maintained by the largest ratio was decreased by lower doses than those required to reduce rates of responding maintained by the other two ratio schedules. Following repeated daily administration of 5.6 mg/kg of cocaine, dose-effect functions (obtained from sessions during the chronic regimen by making substitutions for the daily dose) indicated tolerance under the smaller ratios, but no tolerance or less tolerance under the largest ratio. Thus, whether tolerance developed, and the degree to which it developed, depended on the ratio value. The results are partially consistent with the notion that tolerance to drug effects on schedule-controlled behavior will develop if drug administration initially reduces reinforcement frequency, but they indicate that reinforcement loss alone is not a sufficient condition for the generation of tolerance under such conditions. The findings suggest that amount of responding required for reinforcement, or "effort," may contribute to the development of tolerance to effects of cocaine.