Spontaneous Mammary Tumor Development Research Articles

Abstract IA017: An oncogenic histone reader promotes metaplastic TNBC

Abstract Human carcinosarcomas or metaplastic breast cancers (MpBC) are a rare, chemorefractory subclass of triple-negative breast cancers (TNBC). Conditional overexpression of histone reader Tripartite motif containing protein 24 (TRIM24) in mouse mammary epithelia (Trim24COE) led to spontaneous development of mammary carcinosarcoma tumors, lacking ER, PR and HER2, comprising 70% of all mammary tumors that developed with 40% penetrance. We saw strong correlation of Trim24COE carcinosarcoma tumors with human MpBC tumors and derived a conserved Trim24COE gene signature of Glycolysis, EMT and mTORC1 signaling pathways. Global and single-cell tumor profiling revealed Met as a direct oncogenic target of TRIM24, leading to aberrant PI3K/mTOR activation. To assess TRIM24-dependent metabolic alterations, we developed Trim24COE carcinosarcoma spheroid cultures. Tumor-derived Trim24COE carcinosarcoma spheroids exhibit TRIM24-dependent EMT and repressed cellular and mitochondrial ROS levels. We found that TRIM24 expression increased c-myc, NADPH and NRF2 levels to drive ROS repression and TRIM24-dependent cell survival under oxidative stress. TRIM24 mediates NRF2 activation at the level of chromatin structure activation, as shown by ATAC-seq of Trim24COE and shTrim24 carcinosarcoma spheroids. These in vivo and ex vivo models of metaplastic TNBC offer a platform for mechanistic discovery and nomination of potential therapeutic avenues for this highly malignant TNBC subtype. Citation Format: Vrutant V. Shah, Shucheng Miao, Patrick M. Krause, Sabrina A. Stratton, Lalit R. Patel, Michelle C. Barton. An oncogenic histone reader promotes metaplastic TNBC [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr IA017.

MUC1 triggers lineage plasticity of Her2 positive mammary tumors.

Aberrant overexpression of mucin 1 (MUC1) and human epidermal growth factor receptor 2 (HER2) are often observed in breast cancer. However, the role of concomitant MUC1/HER2 in the development of breast cancer has not been fully illustrated. Following analysis of public microarray datasets that revealed a correlation between double MUC1 and HER2 positivity and a worse clinical outcome, we generated a mouse model overexpressing both Her2 and MUC1 cytoplasmic domain (MUC1-CD) to investigate their interaction in mammary carcinogenesis. Coexpression of Her2 and MUC1-CD conferred a growth advantage and promoted the development of spontaneous mammary tumors. Genomic analysis revealed that enforced expression of MUC1-CD and Her2 induces mammary tumor lineage plasticity, which is supported by gene reprogramming and mammary stem cell enrichment. Through gain- and loss-of-function strategies, we show that coexpression of Her2 and MUC1-CD is associated with downregulation of tricarboxylic acid (TCA) cycle genes in tumors. Importantly, the reduction in TCA cycle genes induced by MUC1-CD was found to be significantly connected to poor prognosis in HER2+ breast cancer patients. In addition, MUC1 augments the Her2 signaling pathway by inducing Her2/Egfr dimerization. These findings collectively demonstrate the vital role of MUC1-CD/Her2 collaboration in shaping the mammary tumor landscape and highlight the prognostic and therapeutic implications of MUC1 in patients with HER2+ breast cancer.

CHIP-associated mutant ASXL1 in blood cells promotes solid tumor progression.

Clonal hematopoiesis of indeterminate potential (CHIP) is an age‐associated phenomenon characterized by clonal expansion of blood cells harboring somatic mutations in hematopoietic genes, including DNMT3A, TET2, and ASXL1. Clinical evidence suggests that CHIP is highly prevalent and associated with poor prognosis in solid‐tumor patients. However, whether blood cells with CHIP mutations play a causal role in promoting the development of solid tumors remained unclear. Using conditional knock‐in mice that express CHIP‐associated mutant Asxl1 (Asxl1‐MT), we showed that expression of Asxl1‐MT in T cells, but not in myeloid cells, promoted solid‐tumor progression in syngeneic transplantation models. We also demonstrated that Asxl1‐MT–expressing blood cells accelerated the development of spontaneous mammary tumors induced by MMTV‐PyMT. Intratumor analysis of the mammary tumors revealed the reduced T‐cell infiltration at tumor sites and programmed death receptor‐1 (PD‐1) upregulation in CD8+ T cells in MMTV‐PyMT/Asxl1‐MT mice. In addition, we found that Asxl1‐MT induced T‐cell dysregulation, including aberrant intrathymic T‐cell development, decreased CD4/CD8 ratio, and naïve‐memory imbalance in peripheral T cells. These results indicate that Asxl1‐MT perturbs T‐cell development and function, which contributes to creating a protumor microenvironment for solid tumors. Thus, our findings raise the possibility that ASXL1‐mutated blood cells exacerbate solid‐tumor progression in ASXL1‐CHIP carriers.

Mammary-specific expression of Trim24 establishes a mouse model of human metaplastic breast cancer

Conditional overexpression of histone reader Tripartite motif containing protein 24 (TRIM24) in mouse mammary epithelia (Trim24COE) drives spontaneous development of mammary carcinosarcoma tumors, lacking ER, PR and HER2. Human carcinosarcomas or metaplastic breast cancers (MpBC) are a rare, chemorefractory subclass of triple-negative breast cancers (TNBC). Comparison of Trim24COE metaplastic carcinosarcoma morphology, TRIM24 protein levels and a derived Trim24COE gene signature reveals strong correlation with human MpBC tumors and MpBC patient-derived xenograft (PDX) models. Global and single-cell tumor profiling reveal Met as a direct oncogenic target of TRIM24, leading to aberrant PI3K/mTOR activation. Here, we find that pharmacological inhibition of these pathways in primary Trim24COE tumor cells and TRIM24-PROTAC treatment of MpBC TNBC PDX tumorspheres decreased cellular viability, suggesting potential in therapeutically targeting TRIM24 and its regulated pathways in TRIM24-expressing TNBC.

NetH2pan: A Computational Tool to Guide MHC Peptide Prediction on Murine Tumors.

With the advancement of personalized cancer immunotherapies, new tools are needed to identify tumor antigens and evaluate T-cell responses in model systems, specifically those that exhibit clinically relevant tumor progression. Key transgenic mouse models of breast cancer are generated and maintained on the FVB genetic background, and one such model is the mouse mammary tumor virus-polyomavirus middle T antigen (MMTV-PyMT) mouse-an immunocompetent transgenic mouse that exhibits spontaneous mammary tumor development and metastasis with high penetrance. Backcrossing the MMTV-PyMT mouse from the FVB strain onto a C57BL/6 genetic background, in order to leverage well-developed C57BL/6 immunologic tools, results in delayed tumor development and variable metastatic phenotypes. Therefore, we initiated characterization of the FVB MHC class I H-2q haplotype to establish useful immunologic tools for evaluating antigen specificity in the murine FVB strain. Our study provides the first detailed molecular and immunoproteomic characterization of the FVB H-2q MHC class I alleles, including >8,500 unique peptide ligands, a multiallele murine MHC peptide prediction tool, and in vivo validation of these data using MMTV-PyMT primary tumors. This work allows researchers to rapidly predict H-2 peptide ligands for immune testing, including, but not limited to, the MMTV-PyMT model for metastatic breast cancer. Cancer Immunol Res; 6(6); 636-44. ©2018 AACR.

Abstract P2-08-01: Loss of function of Brca1 or Gata3 induces basal-like breast cancer

Abstract BACKGROUND: Breast cancer is mainly divided into estrogen receptor (ER)-positive luminal and ER-negative basal-like tumors. Luminal-type tumors are associated with better survival and respond to hormone therapies whereas basal-like tumors are more aggressive and associated with a poor prognosis. Mammary epithelia are mainly composed of luminal and basal cells that are maintained by luminal and basal progenitors, respectively. The maintenance of luminal cell fate is orchestrated by networks of transcription factors, including BRCA1 and GATA3. Functional loss of BRCA1 by germline or somatic mutation or by promoter methylation is associated with more than one third of basal-like breast cancers. GATA3 expression is reduced in basal-like breast cancers and cancers that metastasize. Overexpression of GATA3 in cancer cells inhibits tumor formation. Deletion of Brca1 or Gata3 in mice results in early lethality or growth defects. How BRCA1 and GATA3 suppress breast cancer remains elusive. METHODS: We generated mice lacking Brca1 or Gata3 in mammary epithelia. Due to the proliferative defects and induction of p18Ink4c (p18), an inhibitor of CDK4/6, in mammary epithelial cells of these mice, we then generated mice lacking Brca1 or Gata3 in p18 deficient mammary epithelia. We determined spontaneous mammary tumor development in mutant mice and the mechanisms underlying the role of Brca1 and Gata3 in suppressing tumorigenesis and progression. RESULTS: Depletion of Brca1 or Gata3 led to growth defects of mammary epithelial cells, which was rescued by loss of p18. Depletion of Brca1 or Gata3 in a p18 null background induced heterogeneous mammary tumors with less luminal and more basal-like features and accelerated metastasis. Deletion of Brca1 eliminated Gata3 expression in human and mouse mammary tissues and cells. How Brca1 interacts with Gata3 to control mammary tumor development and progression is currently under investigation. CONCLUSION: Our results suggest that loss of function of either Brca1 or Gata3 induces basal-like mammary tumors in p18 deficient background. Citation Format: Pei X-H, Chan HL, Zhang L, Wang C, Robbins DJ, Capobianco T, Bai F. Loss of function of Brca1 or Gata3 induces basal-like breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-08-01.

Abstract P5-09-07: Impact of germinalcenter-associated nuclear protein polymorphisms on breast cancer risk and prognosis in a Japanese population

Abstract Background: Germinal center-associated nuclear protein (GANP) is a phosphoprotein which is involved in mRNA export and the regulation of DNA recombination. We have previously demonstrated that deficiency of GANP led to spontaneous development of mammary gland tumors in a mouse model. In addition, we found that decreased GANP expression in human breast cancer tissue was an independent prognostic factor. Here, we conducted a case-control study and a retrospective cohort study to investigate whether single nucleotide polymorphisms (SNPs) of GANP are associated with sporadic breast cancer risk and prognosis in a Japanese population. Subjects and Methods: Six hundred-ninety-four breast cancer cases and 1,376 age- and menopausal status-matched controls were selected within the framework of the Hospital-based Epidemiologic Research Program at Aichi Cancer Center. Cases and controls were genotyped using an Infinium iSelect custom array (iCOGS, Illumina Inc., San Diego, CA, USA). We assessed 13 SNPs at the GANP locus, 2 SNPs (rs2839178 and rs11702450) were selected for further analysis by considering linkage disequilibrium. Conditional logistic regression methods were used to estimate odds ratios (ORs) and 95% confidence intervals. In addition, the survival impact of the two SNPs was retrospectively analyzed using the 694 breast cancer cases. To evaluate the effect of SNPs on overall survival (OS) and disease-free survival (DFS), multivariate Cox proportional hazards modeling was applied. Results: Compared to the AA genotype of rs2839178, the GG genotype showed statistically significant associations with breast cancer risk (OR: 0.48, 95%CI:0.30–0.76, P = 0.002). In prognostic analysis, compared to those with the genotype AA at rs2839178, patients with AG or GG showed longer DFS (HR: 0.71, 95%CI: 0.49–1.04 and 0.42, 0.13–1.42, respectively, P for trend = 0.04). The GG genotype of rs2839178 also showed a positive tendency for longer OS although it was not statistically significant (HR: 0.69, 95%CI: 0.44–1.08, P = 0.11). We did not find that rs11702450 was associated with either breast cancer risk or prognosis. Conclusion: This is the first study to investigate the association between GANP SNPs and breast cancer risk and prognosis. The direction of association with DFS was consistent with that of susceptibility. These results demonstrate that GANP SNPs presumably prevent the occurrence and malignant advancement of sporadic breast cancers. Citation Format: Kotani H, Ito H, Kuwahara K, Kuzushima K, Iwata H, Tsunoda N, Nagino M, Tanaka H, Matsuo K. Impact of germinalcenter-associated nuclear protein polymorphisms on breast cancer risk and prognosis in a Japanese population [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-09-07.

Spirulina lipopolysaccharides inhibit tumor growth in a Toll-like receptor 4-dependent manner by altering the cytokine milieu from interleukin-17/interleukin-23 to interferon-γ.

Th17 cells and the cytokine they produce, interleukin (IL)-17, play an important role in tumor progression in humans and in mice. IL-6 and IL-23 are critical cytokines for the differentiation and propagation of Th17 cells, respectively. Bacterial lipopolysaccharides (LPS) are known to stimulate immune cells to produce such inflammatory cytokines. Contrary to Escherichia coli (E. coli) LPS, LPS from Spirulina has low toxicity and barely induces in vivo production of IL-6 and IL-23 in mice. We examined the antitumor effects of Spirulina LPS compared to E. coli LPS in an MH134 hepatoma model. Administration of Spirulina LPS suppressed tumor growth in C3H/HeN mice, but not in Toll-like receptor 4 (TLR4)-mutant C3H/HeJ mice, by reducing serum levels of IL-17 and IL-23, while increasing interferon (IFN)-γ levels. The antitumor activity and IFN-γ production were mediated by T cells. Moreover, in vitro experiments showed that Spirulina LPS impaired the antigen-presenting function that supports the generation of IL-17-producing cells in a toll-like receptor (TLR)4-dependent manner. Of note, injection of anti-IL-17 antibody in tumor-bearing C3H/HeN mice in the absence of Spirulina LPS markedly suppressed tumor growth and augmented IFN-γ responses. Thus, our results support the notion that IFN-γ and IL-17/IL-23 mutually regulate Th17 and Th1 responses in tumor-bearing hosts, and Spirulina LPS modulates the balance of the IFN-γ-IL-17/IL-23 axis towards IFN-γ production, which leads to tumor inhibition. Furthermore, Spirulina LPS effectively inhibited the spontaneous development of mammary tumors. This study has important implications for the exploitation of TLR-based immunomodulators for cancer immunotherapy.

Abstract B29: Maintenance of a lean phenotype is associated with increased ERβ expression and ERβ gene intron methylation in murine MMTVneu luminal mammary cancer

Abstract Background: Obesity is associated with increased breast cancer mortality in premenopausal women, who predominately develop estrogen receptor (ER)-α negative breast tumors. New mechanism-based targets and intervention strategies for offsetting the procancer effects of obesity are urgently needed given the rising rates of obesity in women throughout the world and the lack of effective targeted therapies for ER-negative breast cancer. Unfortunately, the mechanisms by which obesity impacts ER-negative breast cancer prognosis remain unclear. Methods: In this study, we utilized the MMTV-neu transgenic mouse model of Her2+ breast cancer to test the hypothesis that dietary energy balance modulation alters mammary tumor development and progression through epigenetic regulation of ER in the mammary epithelium of these mice. MMTV-neu transgenic mice form spontaneous mammary tumors that progress from an ERα-positive hyperplasia to aggressive ERα-negative ductal adenocarcinomas. Female MMTV-neu transgenic mice were randomized to 3 diet regimens (30/regimen), resulting in either an obese, overweight or lean phenotype. A subset of mice were killed at baseline, 1, 3, and 5 months following diet initiation, and tissues were collected for analysis; remaining animals were followed for up to a 22 month survival study. Results: Gene and protein expression analysis revealed that mammary ERα expression, known to be lost by 8 weeks of age in normoweight MMTV-neu transgenic mice, was maintained in lean mice but lost in the overweight and obese mice (which did not statistically differ in any parameter studied). Additionally, we found lean mice had significantly increased mammary ERβ gene expression and delayed onset of hyperplasia relative to the overweight/obese mice. ERα and ERβ gene intron methylation increased from 5 months to 12 months on diet in lean mice and conversely decreased in overweight/obese mice, which parallels the ER gene expression data. After 22 months of feeding, lean mice had significantly increased tumor-free survival in relative to the overweight/obese mice. Interestingly, human and mouse HER2+ (but not but not HER2-) breast cancer cell lines, when treated with serum from obese (BMI>30), women resulted in a significant down-regulation of ERβ gene expression. Conclusions: In MMTV-neu transgenic mice, dietary energy balance modulation impacts spontaneous mammary tumor development and ERα and ERβ levels in normal and tumor tissue, possibly through epigenetic mechanisms. Moreover, increased mammary ERβ expression may represent a novel target for interventions to offset the enhancing effects of obesity on breast cancer. Citation Format: Emily L. Rossi, Sarah M. Dunlap, Nikki A. Ford, Laura W. Bowers, Stephen D. Hursting. Maintenance of a lean phenotype is associated with increased ERβ expression and ERβ gene intron methylation in murine MMTVneu luminal mammary cancer. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr B29.

Abstract 33: Mammary gland-specific deletion of Sirt1 delays mammary tumor growth and progression

Abstract SIRT1, a type III HDAC, is involved in regulation of several cellular processes including longevity, inflammatory response, energy metabolism and stem cell maintenance. SIRT1 first emerged as a potential anti-aging factor but now it is implicated in a number of age-related diseases including carcinogenesis and also in cancer stem cell maintenance. SIRT1 is over-expressed and/or catalytically activated in a variety of human cancers, including breast cancer. Several lines of evidence suggest that SIRT1 plays an important role in the activation of oncogenic signalling in mammary epithelial cells and that inhibition of SIRT1 has a direct effect on tumor cell growth and apoptosis. Despite the fact that SIRT1 is mainly involved in the promotion of oncogenic signaling, it can also function as a tumor suppressor via deacetylation and subsequent destabilization of various oncoproteins such as c-Myc, β-catenin, NF-κB, and HIF1α. Further, SIRT1 activation by resveratrol protects BRCA1 mutation-associated breast cancer. Thus, the precise role of SIRT1 in cancer is still unclear and remains debatable; it is likely that SIRT1 function in cancer is tissue/context-dependent. Therefore, understanding the precise role of SIRT1 in mammary tumorigenesis is essential for the rational design of SIRT1-based novel therapeutic drugs to combat breast cancer. To understand the functional implications of SIRT1 in breast cancer, we generated mammary gland-specific Sirt1-conditional knockout mice. Sirt1 deletion is associated with reduced mammary gland outgrowth and terminal end bud development, leading to significant reduction in mammary stem and progenitor cell formation. This perturbed mammary gland outgrowth and reduced mammary stem and progenitor cell formation recovers either by puberty or by exogenous administration of estrogen, suggesting that Sirt1 plays a key role in mediating estrogen signalling in mammary gland. To assess the functional role of SIRT1 in mammary tumor growth and progression, we crossed Sirt1-knockout mice with MMTV-PyMT-Tg mice and C3(1)-SV40-Tg mice, two spontaneous murine mammary tumor models. Sirt1 deletion significantly reduces the development and growth of spontaneous mammary tumors in both mouse models. This phenomenon is associated with significant reduction in cancer stem cell (CSC) formation with dramatic reduction in CSC markers Slug and Sox2 expression. We also found that Sirt1 deletion reactivates tumor suppressor proteins p53 and Foxo3a. In conclusion, our study provides direct evidence that SIRT1 plays a key role in breast cancer growth and progression by maintaining cancer stem cells via stabilization of CSC drivers and inactivation of tumor suppressors in mammary gland. Thus, pharmacological agents targeted to disrupt SIRT1 function and signalling might have potential in breast cancer treatment. Citation Format: Sabarish Ramachandran, Rajneesh Pathania, Selvakumar Elangovan, Ganapathy Vadivel, Muthusamy Thangaraju. Mammary gland-specific deletion of Sirt1 delays mammary tumor growth and progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 33. doi:10.1158/1538-7445.AM2015-33

Abstract P1-06-03: Maintenance of a lean phenotype is associated with increased ERβ expression and ERβ gene intron methylation in murine MMTVneu luminal mammary cancer

Abstract Background: Obesity is associated with increased breast cancer mortality in premenopausal women, who predominately develop estrogen receptor (ER)-α negative breast tumors. New mechanism-based targets and intervention strategies for offsetting the procancer effects of obesity are urgently needed given the rising rates of obesity in women throughout the world and the lack of effective targeted therapies for ER-negative breast cancer. Unfortunately, the mechanisms by which obesity impacts ER-negative breast cancer prognosis remain unclear. Methods: In this study, we utilized the MMTV-neu transgenic mouse model of Her2+ breast cancer to test the hypothesis that dietary energy balance modulation alters mammary tumor development and progression through epigenetic regulation of ER in the mammary epithelium of these mice. MMTV-neu transgenic mice form spontaneous mammary tumors that progress from an ERα-positive hyperplasia to aggressive ERα-negative ductal adenocarcinomas. Female MMTV-neu transgenic mice were randomized to 3 diet regimens (30/regimen), resulting in either an obese, overweight or lean phenotype. A subset of mice were killed at baseline, 1, 3, and 5 months following diet initiation, and tissues were collected for analysis; remaining animals were followed for up to a 22 month survival study. Results: Gene and protein expression analysis revealed that mammary ERα expression, known to be lost by 8 weeks of age in normoweight MMTV-neu transgenic mice, was maintained in lean mice but lost in the overweight and obese mice (which did not statistically differ in any parameter studied). Additionally, we found lean mice had significantly increased mammary ER gene expression and delayed onset of hyperplasia relative to the overweight/obese mice. ERα and ERβ gene intron methylation increased from 5 months to 12 months on diet in lean mice and conversely decreased in overweight/obese mice, which parallels the ER gene expression data. After 22 months of feeding, lean mice had significantly increased tumor-free survival in relative to the overweight/obese mice. Interestingly, human and mouse HER2+ (but not but not HER2-) breast cancer cell lines, when treated with serum from obese (BMI>30), women resulted in a significant down-regulation of ERβ gene expression. Conclusions: In MMTV-neu transgenic mice, dietary energy balance modulation impacts spontaneous mammary tumor development and ERα and ERβ levels in normal and tumor tissue, possibly through epigenetic mechanisms. Moreover, increased mammary ERβ expression may represent a novel target for interventions to offset the enhancing effects of obesity on breast cancer. Citation Format: Emily L Rossi, Sarah M Dunlap, Nikki A Ford, Laura W Bowers, Stephen D Hursting. Maintenance of a lean phenotype is associated with increased ERβ expression and ERβ gene intron methylation in murine MMTVneu luminal mammary cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-06-03.

Decreased mitochondrial SIRT3 expression is a potential molecular biomarker associated with poor outcome in breast cancer.

SIRT3 is a genomically expressed, mitochondrial localized tumor suppressor protein where it directs multiple metabolic processes by deacetylating downstream protein substrates. Genetic deletion of Sirt3 in mice leads to the spontaneous development of mammary tumors starting at 1 year, and decreased SIRT3 messenger RNA has been observed in several human tumors including breast malignancies. In this investigation, we assessed SIRT3 expression in human breast cancer tissue microarray and examined the relationship between SIRT3 expression and outcome in patients with breast cancer. SIRT3 protein expression is significantly lower in neoplastic compared with normal breast epithelium, including normal epithelium adjacent to tumors. Patients with breast cancer in the lowest quartile of SIRT3 expression had a significantly shorter locoregional relapse-free survival (hazard ratio, 0.53 [0.47-0.61]; log-rank P = 0). Notably, low SIRT3 expression was associated with reduced locoregional relapse-free survival in all breast cancer subtypes analyzed, including ER+, ER-, HER2+, and basal subtypes (hazard ratios, 0.44-0.65; log-rank P = 0-.0019). These results highlight the importance of the SIRT3 as a tumor suppressor protein in breast cancer and suggest that SIRT3 may be a potential molecular biomarker to identify high-risk patients across all molecular subtypes of breast cancer.

Impact of Obesity on Development and Progression of Mammary Tumors in Preclinical Models of Breast Cancer

Overweight and/or obesity are known risk factors for postmenopausal breast cancer. More recently increased body weight has also been associated with poor prognosis for premenopausal breast cancer. This relationship has primarily been identified through epidemiological studies. Additional information from in vitro studies has also been produced in attempts to delineate mechanisms of action for the association of obesity and body weight and breast cancer. This approach has identified potential growth factors such as insulin, leptin, estrogen and IGF-I which are reported to be modulated by body weight changes. However, in vitro studies are limited in scope and frequently use non-physiological concentrations of growth factors, while long follow-up is needed for human studies. Preclinical animal models provide an intermediary approach to investigate the impact of body weight and potential growth factors on mammary/breast tumor development and progression. Here results of a number of studies addressing this issue are presented. In the majority of the studies either genetically-obese or diet-induced obese rodent models have been used to investigate spontaneous, transgenic and carcinogen-induced mammary tumor development. To study tumor progression the major focus has been allograft studies in mice with either genetic or dietary-induced obesity. In general, obesity has been demonstrated to shorten mammary tumor latency and to impact tumor pathology. However, in rodents with defects in leptin and other growth factors the impact of obesity is not as straightforward. Future studies using more physiologically relevant obesity models and clearly distinguishing diet composition from body weight effects will be important in continuing to understand the factors associated with body weight's impact on mammary/breast cancer development and progression.

Abstract 174: Calorie restriction decreases spontaneous mammary tumorigenesis and upregulates ER-β in MMTV-neu transgenic mice.

Abstract Obesity increases postmenopausal breast cancer risk and increases mortality in pre- and postmenopausal women. While the majority of breast cancers in obese women are estrogen receptor (ERα)-positive, ERα-negative tumors confer a much worse prognosis. The mechanism by which obesity affects ER-negative breast cancer risk and prognosis is not clear, and strategies for offsetting the negative effects of obesity are urgently needed. In this study, we utilized the MMTV-neu mouse model of luminal-type breast cancer to test the hypothesis that energy balance modulation, through diet-induced obesity (DIO) or calorie restriction (CR) regimens, alters mammary tumor development and progression through regulation of ER in the mammary epithelium. MMTV-neu mice form spontaneous mammary tumors that progress from an ERα-positive hyperplasia to aggressive ERα-negative ductal adenocarcinomas. Female MMTV-neu transgenic mice and non-transgenic host strain (FVB) mice (6-8 weeks old; n=90/genotype) were randomized (30/group) to receive: control diet (modified AIN-76A); a 30% CR regimen (isonutrient); or a DIO regimen. A subset of mice (n=4 per group) was killed at 1, 3, and 5 months following diet initiation, and tissues were collected for analysis; remaining animals were followed for a 60-week survival study. We found that, relative to control diet, the DIO regimen significantly increased body weight, percent body fat (p<0.0001), and obesity-associated serum hormones and growth factors (IGF-I, insulin, leptin, and estradiol; p<0.01 for all) in both MMTV-neu and FVB controls. Conversely, CR significantly decreased body weight, percent body fat (p<0.0001) and decreased serum hormones/ growth factors, while increasing adiponectin (each at p<0.01). Gene expression (qRT-PCR) and protein expression (immunohistochemistry) analysis revealed that loss of mammary ERα expression, known to occur by 8 weeks of age in control MMTV-neu mice, was accelerated by DIO and delayed by CR. Additionally, we found that CR (relative to control diet) significantly increased mammary ERβ expression (p<0.0001) and delayed the onset of hyperplasia (p<0.001) in both MMTV-neu and FVB mice. Importantly, we found that after 60 weeks of feeding, CR significantly increased tumor-free survival of MMTV-neu mice (p=0.01). CR tumor samples showed a decrease in vascularity and presence of mitotic figures. In conclusion, dietary energy balance modulation impacts spontaneous MMTV-neu mammary tumor development and ERα and ERβ levels in normal and tumor tissue. In addition, increased mammary ERβ expression may represent a novel mechanism underlying the anticancer effects of CR. Citation Format: Sarah M. Dunlap, Nikki A. Ford, Laura W. Bowers, Emily L. Rossi, Samantha Miller, Lucia J. Chiao, Powel H. Brown, Stephen D. Hursting. Calorie restriction decreases spontaneous mammary tumorigenesis and upregulates ER-β in MMTV-neu transgenic mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 174. doi:10.1158/1538-7445.AM2013-174

Prevention of Mammary Tumor Development through Neuroimmunomodulation in the Spleen and Lymph Nodes of Old Female Sprague-Dawley Rats by L-Deprenyl

Background: Development of mammary tumors is an age-associated phenomenon that is likely due to deficits in the neuroendocrine-immune interactions. Previously, we demonstrated that <smlcap>L</smlcap>-deprenyl, a monoamine oxidase-B (MAO-B) inhibitor, can enhance immune responses and restore noradrenergic (NA) innervation in the spleens of rats with carcinogen-induced and spontaneously developing mammary tumors. Objectives: To investigate whether (1) treatment of early middle-aged female rats would prevent the spontaneous development of mammary tumors accompanied by restoration of immunity in the spleen and draining lymph nodes (DLN) and sympathetic NA innervation in the spleen and (2) deprenyl can influence the proliferation of estrogen receptor (ER)-positive (MCF-7 and T47D) and ER-negative (MDA-MB-231 and Hs 578T) human breast cancer cells. Methods: Early middle-aged (8- to 9-month-old) female Sprague-Dawley rats were treated with 0, 1.0 or 2.5 mg of deprenyl/kg body weight (BW) daily i.p. for 12 months. Cells of ER-positive (ER+) and ER-negative (ER-) human breast cancer cell lines were incubated with media or 10^-3 to 10^-8<smlcap>M</smlcap> deprenyl for 1, 2, 4 or 6 days to examine the proliferation of cells. Results: Tumor incidence increased in saline-treated old female rats, while deprenyl treatment significantly reduced the incidence of mammary tumors in these rats. Saline-treated tumor-bearing rats exhibited reduced splenic NA innervation and norepinephrine (NE) content, splenic interleukin (IL)-2 and interferon (IFN)-γ levels and NK cell activity as well as DLN IL-2 and IFN-γ levels compared to young female rats without tumors. In contrast, treatment with 2.5 mg/kg of deprenyl enhanced IL-2 and IFN-γ production in both the spleen and DLN as well as splenic natural killer (NK) cell activity. Deprenyl treatment also increased concanavalin A (Con A)-induced proliferation of T lymphocytes in the DLN. Deprenyl-induced changes in immune responses were accompanied by enhanced NA innervation and NE content in the spleen. In vitro incubation of various concentrations of deprenyl with ER+ human breast cancer cell lines partly inhibited the proliferation of cells, while it had no effect on the ER- breast cancer cells. Conclusions: These results suggest that (1) development of mammary tumors is mediated through the loss of immunity and sympathetic NA nerve fibers accompanied by reduced NE levels in the spleen, (2) the prevention of mammary tumor development by deprenyl may involve the reversal of the tumor-associated decline in sympathetic NA activity and cell-mediated immune responses in the spleen and DLN and (3) the antitumor effects of deprenyl may be partially mediated through ER-dependent intracellular signaling pathways.

Effect of annatto-tocotrienols supplementation on the development of mammary tumors in HER-2/neu transgenic mice

Tocotrienols (T3), the lesser known isomers of vitamin E, have been reported to possess anticancer activity both in in vitro and in vivo experimental models of rodents transplanted with parental tumors or treated with carcinogens. We investigated the effects of dietary supplementation with annatto-T3 (90% δ-T3 and 10% γ-T3) on the spontaneous development of mammary tumors in HER-2/neu transgenic mice. Underlying mechanisms of the antitumor effect were evaluated by studying apoptosis, senescent-like growth arrest, immune modulation, oxidative effect and the expression of HER-2/neu in tumoral mammary glands of transgenic mice and in vitro in human and mice tumor cell lines. Annatto-T3 supplementation delayed the development of mammary tumors, reducing the number and size of mammary tumor masses and those of lung metastases. In annatto-T3-supplemented mice, both apoptosis and senescent-like growth arrest of tumor cells were increased in mammary glands while no immune modulation was observed. In vitro, a dose-dependent inhibition of cell growth, increased apoptosis and senescent-like growth arrest and a time-dependent accumulation of reactive oxygen species were observed in tumor cells treated with annatto-T3 or purified δ-T3. Annatto-T3 reduced both HER-2/neu mRNA and p185(HER-2/neu) protein in tumors and in tumor cell lines. The results show that the antitumor effect of annatto-T3 supplementation in HER-2/neu transgenic mice is mainly related to the direct induction of oxidative stress, senescent-like growth arrest and apoptosis of tumor cells rather than to an immune modulation.

Abstract B102: A comparison of metformin treatment and moderate calorie restriction on mammary tumor development in obese mice

Abstract There has been increasing interest in metformin as an anticancer agent particularly for breast cancer prevention. Support for metformin in this capacity includes that this compound is considered to be a calorie restriction mimetic. Calorie restriction is well known to prevent the development of spontaneous, carcinogen-induced and transgenic mammary tumor development in rodent models of breast cancer. However, few studies have addressed how calorie restriction impacts the development of mammary tumors in obese animals despite the fact that initial application of this intervention in humans would likely be in overweight and obese women whose postmenopausal breast cancer risk is elevated by their body weight status. Further, direct comparisons of metformin to calorie restriction have rarely been reported. The goal of the present investigation is to compare the effect of metformin treatment and moderate calorie restriction on mammary tumor development in an obese mouse model of breast cancer. MMTV-TGF-α/C57BL6 female mice which develop mammary tumors in the second year of life will be used. Previous studies have shown that calorie restriction delays mammary tumor detection and reduces incidence (CEBP 11:836,2002; Exp.Biol.Med.232:70,2007) while obesity shortens latency and results in detection of high grade adenocarcinomas (Int.J.Obesity 28:956,2004; Breast Cancer Res. 9:R21,2007) in MMTV-TGF-α mice. At 10 weeks of age 3/4 of the experimental mice are fed a moderately high fat diet (33% by calories) and the other 1/4 maintained on AIN-93M diet until 30 weeks of age. Then high fat diet mice are divided into Obesity-Prone, Overweight and Obesity-Resistant groups based on weight gain. Within each weight group mice are further divided into ad libitum-fed, ad libitum-fed+metformin (250 mg/kg bw/day in the diet) or calorie restricted by 25%. These same interventions are applied to the Control AIN-93M mice. Final group sizes are ∼32 mice. Daily food intakes are measured and mice monitored weekly for mammary tumor status and to obtain body weights. Blood samples will be obtained at specified time points until 90 weeks of age. Two weeks prior to euthanasia mice will be given a bolus of deuterated water followed by inclusion of deuterated water in their drinking water until death. This will allow determination of in vivo cell proliferation in mammary tissues and tumors. Serum will be analyzed for insulin, IGF-I and glucose responses to these interventions. Also liver and mammary tissues will be obtained to compare the effects of metformin and calorie restriction on putative mechanistic pathways related to AMPK. Results of this study will clarify aspects of both metformin's and calorie restriction's effects on mammary tumor prevention with respect to body weight status. Supported by NIH-NCICA157012 and The Hormel Foundation. Citation Format: Michael E. Grossmann, Nancy K. Mizuno, Margot P. Cleary. A comparison of metformin treatment and moderate calorie restriction on mammary tumor development in obese mice. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B102.

Effect of annatto-tocotrienols supplementation on the Development of Mammary Tumors in HER-2/neu Transgenic Mice

Tocotrienols (T3), the lesser known isomers of vitamin E, have been reported to possess anticancer activity both in in vitro and in vivo experimental models of rodents transplanted with parental tumors or treated with carcinogens. We investigated the effects of dietary supplementation with annatto-T3 (90% δ-T3 and 10% γ-T3) on the spontaneous development of mammary tumors in HER-2/neu transgenic mice. Underlying mechanisms of the antitumor effect were evaluated by studying apoptosis, senescent-like growth arrest, immune modulation, oxidative effect and the expression of HER-2/neu in tumoral mammary glands of transgenic mice and in vitro in human and mice tumor cell lines. Annatto-T3 supplementation delayed the development of mammary tumors, reducing the number and size of mammary tumor masses and those of lung metastases. In annatto-T3-supplemented mice, both apoptosis and senescent-like growth arrest of tumor cells were increased in mammary glands while no immune modulation was observed. In vitro, a dose-dependent inhibition of cell growth, increased apoptosis and senescent-like growth arrest and a time-dependent accumulation of reactive oxygen species were observed in tumor cells treated with annatto-T3 or purified δ-T3. Annatto-T3 reduced both HER-2/neu mRNA and p185(HER-2/neu) protein in tumors and in tumor cell lines. The results show that the antitumor effect of annatto-T3 supplementation in HER-2/neu transgenic mice is mainly related to the direct induction of oxidative stress, senescent-like growth arrest and apoptosis of tumor cells rather than to an immune modulation.

Abstract 597: Response of reactive oxygen species to eicosapentaenoic and calorie restriction in relation to mammary tumor prevention

Abstract Exposure of lipid biomembranes to reactive oxygen species (ROS) results in the generation of a wide variety of lipid peroxidation products. Some of these products, including 4-hydroxy-2-nonenal (4HNE) can form protein adducts which may impact pathways associated with tumorigenesis. We have reported that calorie restriction protects against spontaneous mammary tumor development in mice and have recently shown that this is accompanied by a decrease in serum levels of lipid peroxidation products. Eicosapentaenoic acid (EPA) is known to inhibit mammary tumorigenesis; however, this type of highly unsaturated omega-3 fatty acid has also been shown to increase in vivo levels of lipid peroxidation products. In the present study, the interaction of calorie restriction and dietary EPA was investigated with respect to mammary tumor formation. Lipid peroxidation products of ROS were also measured. From 10 weeks of age MMTV-Her2/neu mice were fed a modified AIN-93M diet (10.2% kcal from fat) which had either 100% soybean oil (SO) as the fat source or a blend of EPA (72%) and SO (18%). Mice were further divided into groups which were ad libitum-fed, (AL); chronic calorie restricted (CCR, received 75% of AL) or intermittently calorie restricted (ICR, received 50% of AL for 3 weeks followed by 3 weeks at 100% of AL) until 60 weeks of age or until mammary tumor size required euthanasia. Mice were weighed and examined for mammary tumors weekly. Serum thiobarbituric acid reactive substances (TBARS) and 4-hydroxy-2-nonenal (4HNE)-protein adducts in mammary tissues were measured to assess the extent of lipid peroxidation. In both diet groups, mammary tumor incidence was highest in the AL group (SO 87%, EPA 63%). These groups also had the highest levels of serum TBARS and the AL-SO group had the highest level of mammary tissue 4HNE-protein adducts. The calorie restricted mice had lower levels of mammary tumor incidence (CCR-SO 47%, CCR-EPA 40%, ICR-SO 59%) with the lowest level in the ICR-EPA group (15%). The ICR-SO group had serum TBARS and mammary tissue 4HNE-protein adduct levels that were significantly lower than the AL-SO group (p&amp;lt;0.05 for both). In the EPA groups, there was no difference between the AL, CCR, and ICR groups in either serum TBARS or mammary tissue 4HNE-protein adducts. These results suggest that higher levels of lipid peroxidation products are associated with a higher incidence of mammary tumors. However, although the dietary combination of ICR and EPA resulted in the greatest amount of mammary tumor inhibition, this combination was not associated with the lowest level of lipid peroxidation products. The relationship between EPA, calorie restriction, and reactive oxygen species appears to be quite complex. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 597. doi:1538-7445.AM2012-597

Dysfunctional telomeres promote genomic instability and metastasis in the absence of telomerase activity in oncogene induced mammary cancer

Telomerase is a ribonucleoprotein that maintains the ends of chromosomes (telomeres). In normal cells lacking telomerase activity, telomeres shorten with each cell division because of the inability to completely synthesize the lagging strand. Critically shortened telomeres elicit DNA damage responses and limit cellular division and lifespan, providing an important tumor suppressor function. Most human cancer cells express telomerase which contributes significantly to the tumor phenotype. In human breast cancer, telomerase expression is predictive of clinical outcomes such as lymph node metastasis and survival. In mouse models of mammary cancer, telomerase expression is also upregulated. Telomerase overexpression resulted in spontaneous mammary tumor development in aged female mice. Increased mammary cancer also was observed when telomerase deficient mice were crossed with p53 null mutant animals. However, the effects of telomerase and telomere length on oncogene driven mammary cancer have not been completely characterized. To address these issues we characterized neu proto-oncogene driven mammary tumor formation in G1 Terc-/- (telomerase deficient with long telomeres), G3 Terc-/- (telomerase deficient with short telomeres), and Terc+/+ mice. Telomerase deficiency reduced the number of mammary tumors and increased tumor latency regardless of telomere length. Decreased tumor formation correlated with increased apoptosis in Terc deficient tumors. Short telomeres dramatically increased lung metastasis which correlated with increased genomic instability, and specific alterations in DNA copy number and gene expression. We concluded that short telomeres promote metastasis in the absence of telomerase activity in neu oncogene driven mammary tumors.