ErbB2 Transgenic Mice Research Articles

Treatment of ErbB2 breast cancer by mitochondrial targeting

BackgroundErbB2 breast cancer still remains an unmet need due to primary and/or acquired resistance to current treatment strategies. MEDICA compounds consist of synthetic long-chain α,ω-dicarboxylic acids previously reported to suppress breast cancer in PyMT transgenic mice.MethodsMEDICA efficacy and mode of action in the ErbB2 context was studied in ErbB2 transgenic mice and human breast cancer cells.ResultsMEDICA treatment is shown here to suppress ErbB2 breast tumors and lung metastasis in ErbB2/neu MMTV transgenic mice, to suppress ErbB2/neu xenografts in nod/scid mice, and to suppress survival of AU565 and BT474 human ErbB2 breast cancer cells. Suppression of ErbB2 breast tumors by MEDICA is due to lipid raft disruption with loss of ErbB family members, including EGFR, ErbB2, and ErbB3. In addition, MEDICA inhibits mTORC1 activity, independently of abrogating the ErbB receptors and their signaling cascades. The double hit of MEDICA in abrogating ErbB and mTORC1 is partly accounted for by targeting mitochondria complex I.ConclusionsMitochondrial targeting by MEDICA suppresses ErbB2 breast tumors and metastasis due to lipid raft disruption and inhibition of mTORC1 activity. Inhibition of mTORC1 activity by MEDICA avoids the resistance acquired by canonical mTORC1 inhibitors like rapalogs or mTOR kinase inhibitors.

SOD1 is essential for oncogene-driven mammary tumor formation but dispensable for normal development and proliferation.

We previously reported that the dismutase SOD1 is overexpressed in breast cancer. However, whether SOD1 plays an active role in tumor formation in vivo has never been demonstrated. Further, as luminal cells of normal breast epithelial cells are enriched in SOD1, whether SOD1 is essential for normal mammary gland development has never been determined. We initiated this study to investigate the role of SOD1 in mammary gland tumorigenesis as well as in normal mammary gland development. We crossed the inducible erbB2 (MMTV-iErbB2) and Wnt (MMTV-Wnt) transgenic mice to the SOD1 heterozygote or knockout mice. Our results show that SOD1 is essential for oncogene-driven proliferation, but not normal proliferation of the mammary gland associated with pregnancy or other normal proliferative tissues such as skin and intestines. We show that activation of the oncogene ErbB2 is associated with increased ROS and that high ROS sub-population of ErbB2 cancer cells show elevated SOD1. In the same cells, decrease in SOD1 is associated with an elevation in both apoptosis as well as oncogene-induced senescence. Based on these results, we suggest that SOD1 carries a housekeeping function that maintains ROS levels below a threshold that supports oncogene-dependent proliferation, while allowing escape from oncogene-induced senescence, independently of the oncogene driving tumor formation. These results identify SOD1 as an ideal target for cancer therapy as SOD1 inhibitors hold the potential to prevent the growth of cancers cells of diverse genotypes, activate multiple modes of cell death therefore making acquired resistance more difficult, while sparing normal tissues.

Abstract P6-20-17: Targeting SHP2 for the treatment of HER2-positive breast cancer

Abstract Approximately 20% of breast cancer (BC) is caused by overexpression of the human epidermal growth factor receptor 2 (HER2). As a result, several antibody-based and small molecule-based anti-HER2 therapies have been developed. These drugs have benefited BC patients by improving overall survival and quality of life. However, development of resistance and disease recurrence have been the major clinical challenges. One way to overcome these clinical problems is to develop alternative therapeutic strategies. Multiple lines of evidence show that targeting the Src homology phosphotyrosyl phosphatase 2 (SHP2) in HER2-positive BC may prove beneficial both in treatment-naïve and anti-HER2 therapy-resistant forms of the disease. For instance, silencing SHP2 expression in HER2-positive breast cancer cells or conditional knockout in ErbB2 transgenic mice blocks HER2 overexpression and associated signaling, leading to loss of cell transformation and tumorigenesis. To test the clinical translational significance of SHP2 targeting, we have invented a specific small molecule SHP2 inhibitor named WGMDY (US 9,932,288) that has shown promising anti-cancer effects. The results obtained so far show that inhibition of SHP2 with WGMDY blocks HER2 expression, suppresses cell proliferation and anchorage independent growth, and induces regression of preformed xenograft tumors. These findings suggest that SHP2 might be an excellent drug target for HER2-positive BC and WGMDY has a promising potential to serve as a lead compound for developing anti-SHP2 drugs. Citation Format: Agazie Y, Hartman Z. Targeting SHP2 for the treatment of HER2-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-17.

Conditional knockout of SHP2 in ErbB2 transgenic mice or inhibition in HER2-amplified breast cancer cell lines blocks oncogene expression and tumorigenesis.

Overexpression of the human epidermal growth factor receptor 2 (HER2) is the cause of HER2-positive breast cancer (BC). Although HER2-inactivating therapies have benefited BC patients, development of resistance and disease recurrence have been the major clinical problems, pointing to a need for alternative therapeutic strategies. For that to happen, proteins that play critical roles in the biology of HER2-induced tumorigenesis have to be identified and characterized. Here, we show that the Src homology phosphotyrosyl phosphatase 2 (Shp2) encoded by the Ptpn11 gene is a requisite for ErbB2-induced tumorigenesis. We report that conditional knockout of Shp2 alleles in the ErbB2 BC model mice abrogates mammary tumorigenesis by blocking the expression of the ErbB2 transgene. We also show that inhibition of SHP2 encoded by the PTPN11 gene in the HER2-amplified BC cells induces a normal-like cellular phenotype and suppresses tumorigenesis and metastasis by blocking HER2 overexpression. These findings demonstrate that ErbB2-induced tumors in mice or xenograft tumors induced by transplantation of HER2-amplified BC cells are vulnerable to SHP2 inhibition since it abrogates the expression of the very oncogene that causes of the disease. This report paves the way for developing SHP2-targeting therapies for BC treatment in the future.

Abstract 400: ERBB2 Inhibition Leads to Cardiac Dysfunction

Growth factor ERBB2 inhibition is a reliable treatment for patients diagnosed with breast cancer but is known to cause cardiotoxicity, resulting in dysfunction and dilation. In our studies, we have taken a unique approach with the premise that ERBB2 inhibitors like trastuzumab or pertuzumab binding to ERBB2 may lead to a conformation that could engage/activate non-canonical signals while inhibiting classical pathways. Such non-canonical activation of signals by inhibitor may be beneficial for treating cancer, while the same pathways could be detrimental in the cardiomyocytes. Our data is further suppored by the microRNA-7 Transgenic mice developed in our lab, which downregulates ERBB2 leading to cardiac dysfunction as seen by echocardiography. These studies will lay the foundation for developing strategies that could specifically block the deleterious effect of ERBB2 inhibitors on the heart. Moreover, administration of AG825 in mice for two weeks results in significant cardiac dysfunction and dilation compared to AG1875 or vehicle controls, conferring the idea that inhibition of ERBB2 and not EGFR that mediates deleterious remodeling. Furthermore, mitochondria morphology was also affected upon ERBB2 inhibition as seen in our microRNA-7 transgenic mice hearts as well as AG825 (ERBB2 inhibtor) treated mice in the electrom micrographs. We will also discuss the proteomics analysis in the ERBB2 inhibitor treated hearts, microRNA-7 Transgenic mice hearts, ERBB2 transgenic mice hearts as compared to the C57/BL6 wildtype hearts. Our studies therefore aims to target these non-canonical signals in the heart with an idea to insulate the heart from the deleterious effects of chemotherapy.

Deregulation of the Hippo pathway in mouse mammary stem cells promotes mammary tumorigenesis.

The Hippo-YAP pathway mediates organ size control, contact inhibition, and tumorigenesis. It is a kinase cascade that inhibits the nuclear localization and transcriptional activities of YAP and TAZ. E-cadherin, cell junctions, polarity proteins, and the merlin/NF2 tumor suppressor activate the pathway to inhibit YAP/TAZ activity, while growth factor signaling inhibits the pathway to activate YAP/TAZ in the nucleus. We examined its role in the development of mouse mammary glands and tumor formation using gland reconstitution by transplantation of genetically modified mammary stem cells (MaSCs). Knockdown of YAP and TAZ with shRNA in MaSCs did not inhibit gland reconstitution. In contrast, knockdown of β-catenin blocked gland reconstitution, consistent with the known role of Wnt signaling in mammary gland development. However, we find that Hippo signaling is involved in mammary tumor formation. Expression of a constitutively active form of YAP caused rapid formation of large tumors. Moreover, knockdown of YAP/TAZ slowed the development of tumors in polyoma middle T transgenic mice, a well-studied mammary tumor model involving activation of several signaling pathways. YAP accumulated in nuclei of mammary glands in ErbB2/EGFR-transgenic mice, suggesting that EGFR signaling affects YAP in vivo similar to cell culture. ErbB2/EGFR-transgenic mice develop mammary tumors in 7-8months, but surprisingly, MaSCs from these mice did not form tumors when transplanted into host mice. Nonetheless, expression of dominant-negative Lats, which inhibits Hippo signaling, leads to tumor formation in ErbB2-transgenic mice, suggesting that Hippo signaling is involved in EGFR-induced mammary tumorigenesis.

Abstract B31: In utero exposure to bisphenol A induces reprogramming of mammary development and tumor risk in MMTV-erbB-2 transgenic mice

Abstract Increasing evidence indicates that environmental exposure plays a critical role in breast cancer etiology. Bisphenol A (BPA), the building block of polycarbonate plastics with estrogenic activity, is one of the most common chemicals exposed in daily life. Recent studies suggest a link between BPA exposure and increased breast cancer risk. However, specific conditions and the underlying mechanisms of BPA exposure associated breast cancer risk remain unclear. This study aimed to investigate the effects of in utero exposure to BPA on mammary tumor development in MMTV-erbB-2 transgenic mice, which exemplifies a scenario of gene-environmental interaction. Since erbB-2 is amplified/overexpressed in approximately 30% of breast cancer, which has been associated with poor prognosis and therapeutic resistance, use of this clinically relevant mammary tumor model is of high translational value. In this study, pregnant MMTV-erbB-2 mice were subcutaneously injected with 0, 50 ng, 500 ng and 250 μg/Kg body weight BPA daily between day 13 and day 19 of gestation. We found that in utero exposed mice in the low dose (50 and 500 ng) groups, but not the high dose group (250 μg), displayed earlier vaginal opening and prolonged estrous phase, suggesting a dose dependent pro-estrogenic effect of in utero exposure to BPA. Whole mount analysis showed that mammary glands of mice with in utero exposure to low dose BPA had a longer ductal extension at 6 weeks and increased lateral branching/alveolar structures at 10 weeks, which was more significant in the 500 ng group but less evident in the high dose group. Molecular analysis of mammary tissues at 10 weeks indicated that in utero exposure to BPA increased phosphorylation/activation of erbB-2, EGFR, erbB-3, Erk1/2 and Akt, and expression of erbB-3 and EGFR. Signaling of estrogen receptor (ER) pathway was upregulated concomitantly, as reflected by increased expression and phosphorylation of ERα and upregulation of cyclin D1 and c-myc. More importantly, mice in the 500 ng group but not in the high dose group, developed tumor earlier than the mice in the control group, suggesting that dose is a critical factor affecting the outcomes. These data demonstrated that in utero exposure to BPA may promote mammary tumor development in erbB-2 transgenic mice in a dose dependent manner. Concomitant activation of the erbB-2 and ER pathways in the premalignant tissues suggests that induction of ER-erbB-2 crosstalk may play a critical role in mammary tumorigenesis promoted by in utero exposure to BPA, which underscores the significance of gene-environment interaction in early exposure to BPA associated breast cancer risk. Citation Format: Zhikun Ma, Amanda Parris, Xiaohe Yang. In utero exposure to bisphenol A induces reprogramming of mammary development and tumor risk in MMTV-erbB-2 transgenic mice. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B31.

Protein tyrosine kinase 6 promotes ERBB2-induced mammary gland tumorigenesis in the mouse.

Protein tyrosine kinase 6 (PTK6) expression, activation, and amplification of the PTK6 gene have been reported in ERBB2/HER2-positive mammary gland cancers. To explore contributions of PTK6 to mammary gland tumorigenesis promoted by activated ERBB2, we crossed Ptk6−/− mice with the mouse mammary tumor virus-ERBB2 transgenic mouse line expressing activated ERBB2 and characterized tumor development and progression. ERBB2-induced tumorigenesis was significantly delayed and diminished in mice lacking PTK6. PTK6 expression was induced in the mammary glands of ERBB2 transgenic mice before tumor development and correlated with activation of signal transducer and activator of transcription 3 (STAT3) and increased proliferation. Disruption of PTK6 impaired STAT3 activation and proliferation. Phosphorylation of the PTK6 substrates focal adhesion kinase (FAK) and breast cancer anti-estrogen resistance 1 (BCAR1; p130CAS) was decreased in Ptk6−/− mammary gland tumors. Reduced numbers of metastases were detected in the lungs of Ptk6−/− mice expressing activated ERBB2, compared with wild-type ERBB2 transgenic mice. PTK6 activation was detected at the edges of ERBB2-positive tumors. These data support roles for PTK6 in both ERBB2-induced mammary gland tumor initiation and metastasis, and identify STAT3, FAK, and BCAR1 as physiologically relevant PTK6 substrates in breast cancer. Including PTK6 inhibitors as part of a treatment regimen could have distinct benefits in ERBB2/HER2-positive breast cancers.

Abstract 268: Myofilament Tyrosine Phosphorylation by Src Kinase is upregulated in ErbB2 Transgenic Mice

Objectives: Tyrosine (Tyr) phosphorylation of the myofilament is an emerging, and potentially important, post-translational modification in cardiomyopathy. ErbB2, a Tyr receptor kinase, was overexpressed in transgenic mice (ErbB2-Tg) resulting in significant cardiac hypertrophy. We hypothesize that the development of cardiac hypertrophy in ErbB2-Tg is associated with increased myofilament Tyr phosphorylation and may implicate myofilament Tyr phosphorylation in cardiac hypertrophy. Methods: Proteins were isolated from ErbB2-Tg and Ntg heart homogenates ( n =4 per group). Reduction/alkylation was followed by trypsinization. Resulting peptides were desalted in C 18 columns and lyophilized. Phosphorylated Tyr (p-Tyr) enrichment was performed on 20 mg of peptides using a p-Tyr Mouse mAb kit (Cell Signaling). Immuno-precipitated and desalted peptides were analyzed by LC-MS/MS (Orbitrap Elite, Thermo). Raw data were searched with Mascot 2.3. Label-free quantification with MS1 extracted ion chromatograms was performed using Skyline. Western blot analysis for total and phosphorylated Src kinase was performed per manufacturer’s protocol (Cell Signaling). Results: We found a total of 286 p-Tyr modified peptides in ErbB2-Tg compared to 226 in control NTg mice. Over 70 p-Tyr sites on myofilament protein were up-regulated in ErbB2-Tg, including troponin I, myosin heavy chain, titin, α-tropomyosin, myosin-binding protein-C3, myosin regulatory light chain-2 and myosin light chain-1. We used PhosphoMotif Finder to search the potential responsible kinase. Most of the p-Tyr sites were consistent with Src kinase motifs. Furthermore, Western blot analysis showed that total, and phospho-Src (Y416) expression was increased in ErbB2-Tg mice. Conclusion: We concluded that these novel p-Tyr sites on myofilament proteins are increased in ErbB2-Tg mice and correlate with up-regulated Src kinase activity. Thus increased tyrosine myofilament phosphorylation may be involved in the development of cardiac hypertrophy. Since ErbB2 is a therapeutic target of trastuzumab therapy this may also have translational implications to ameliorate off target effects of cancer treatment.

Abstract 2967: Metformin selectively targets tumor initiating cells in erbb-2 overexpressing breast cancer models

Abstract Metformin is an oral biguanide used for type II diabetes. Epidemiologic studies suggest a link between metformin use and reduced risk of breast and other types of cancers. erbB-2 expressing breast cancer is a subgroup of tumors with poor prognosis. Previous studies demonstrated that metformin is a potent inhibitor of erbB-2 overexpressing breast cancer cells; metformin treatment extends the life span and impedes mammary tumor development in ErbB-2 transgenic mice in vivo. However, the mechanisms of metformin associated anti-tumor activity, especially in prevention models, remain unclear. In this study, we investigated the mechanisms of metformin associated prevention/inhibition of ErbB-2 mediated breast cancer development by focusing on the potential effect of metformin on tumor initiating cells (TICs)/cancer stem cells (CSCs) in the MMTV-erbB-2 transgenic mouse model and its context with existing in vitro models. We report here for the first time that systemic administration of metformin (250 mg/kg/day, ip, between 8- and 18-week of age) selectively inhibits CD61high/CD49fhigh subpopulation, a group of TICs of MMTV-ErbB-2 mammary tumors, in preneoplastic mammary glands. Metformin also inhibited CD61high/CD49fhigh subpopulation in MMTV-erbB-2 tumor-derived cells, which was correlated with their compromised tumor initiation/development in a syngeneic tumor graft model. Molecular analysis indicated that metformin induced downregulation of erbB-2 and EGFR expression and inhibited the phosphorylation of erbB family members, IGF1R, Akt, mTOR and Stat3 in vivo. In vitro data indicate that low doses (1 mM) of metformin inhibited the self-renewal/proliferation of CSCs/TICs in ErbB-2-overexpressing breast cancer cells. We further demonstrated that the expression and activation of ErbB-2 were preferentially increased in CSC/TIC-enriched tumorsphere cells, which promoted their self-renewal/proliferation and rendered them more sensitive to metformin. Our results, especially the in vivo data, provide fundamental support for developing metformin-mediated preventive strategies targeting erbB-2-associated carcinogenesis. Citation Format: Pei Zhu, Meghan Davis, Amanda Blackwelder, Nora Bachman, Bolin Liu, Susan Edgerton, Leonard L. Williams, Ann D. Thor, Xiaohe Yang. Metformin selectively targets tumor initiating cells in erbb-2 overexpressing breast cancer models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2967. doi:10.1158/1538-7445.AM2014-2967

Metformin Selectively Targets Tumor-Initiating Cells in ErbB2-Overexpressing Breast Cancer Models

Metformin is an oral biguanide used for type II diabetes. Epidemiologic studies suggest a link between metformin use and reduced risk of breast and other types of cancers. ErbB2-expressing breast cancer is a subgroup of tumors with poor prognosis. Previous studies demonstrated that metformin is a potent inhibitor of ErbB2-overexpressing breast cancer cells; metformin treatment extends the life span and impedes mammary tumor development in ErbB2 transgenic mice in vivo. However, the mechanisms of metformin associated antitumor activity, especially in prevention models, remain unclear. We report here for the first time that systemic administration of metformin selectively inhibits CD61(high)/CD49f(high) subpopulation, a group of tumor-initiating cells (TIC) of mouse mammary tumor virus (MMTV)-ErbB2 mammary tumors, in preneoplastic mammary glands. Metformin also inhibited CD61(high)/CD49f(high) subpopulation in MMTV-ErbB2 tumor-derived cells, which was correlated with their compromised tumor initiation/development in a syngeneic tumor graft model. Molecular analysis indicated that metformin induced downregulation of ErbB2 and EGFR expression and inhibited the phosphorylation of ErbB family members, insulin-like growth factor-1R, AKT, mTOR, and STAT3 in vivo. In vitro data indicate that low doses of metformin inhibited the self-renewal/proliferation of cancer stem cells (CSC)/TICs in ErbB2-overexpressing breast cancer cells. We further demonstrated that the expression and activation of ErbB2 were preferentially increased in CSC/TIC-enriched tumorsphere cells, which promoted their self-renewal/proliferation and rendered them more sensitive to metformin. Our results, especially the in vivo data, provide fundamental support for developing metformin-mediated preventive strategies targeting ErbB2-associated carcinogenesis.

Chimeric DNA Vaccines: An Effective Way to Overcome Immune Tolerance.

The fact that cancer immunotherapy is considered to be a safe and successful weapon for use in combination with surgery, radiation, and chemotherapy treatments means that it has recently been chosen as Breakthrough of the Year 2013 by Science editors. Anticancer vaccines have been extensively tested, in this field, both in preclinical cancer models and in the clinic. However, tumor-associated antigens (TAAs) are often self-tolerated molecules and cancer patients suffer from strong immunosuppressive effects, meaning that the triggering of an effective anti-tumor immune response is difficult. One possible means to overcome immunological tolerance to self-TAAs is of course the use of vaccines that code for xenogeneic proteins. However, a low-affinity antibody response against the self-homologous protein expressed by cancer cells is generally induced by xenovaccination. This issue becomes extremely limiting when working with tumors in which the contribution of the humoral rather than the cellular immune response is required if tumor growth is to be hampered. A possible way to avoid this problem is to use hybrid vaccines which code for chimeric proteins that include both homologous and xenogeneic moieties. In fact, a superior protective anti-tumor immune response against ErbB2+ transplantable and autochthonous mammary tumors was observed over plasmids that coded for the fully rat or fully human proteins when hybrid plasmids that coded for chimeric rat/human ErbB2 protein were tested in ErbB2 transgenic mice. In principle, these findings may become the basis for a new rational means of designing effective vaccines against TAAs.

Mammary Carcinoma Cell Derived Cyclooxygenase 2 Suppresses Tumor Immune Surveillanceby Enhancing Intratumoral Immune Checkpoint Activity

IntroductionSystemic inhibition of the inflammatory enzyme cyclooxygenase (COX) 2 decreases the risk of breast cancer and its recurrence. However, the biology of COX-2 in the multicellular tumor microenvironment is poorly defined.MethodsMammary tumor onset and multiplicity were examined in ErbB2 transgenic mice that were deficient in mammary epithelial cell COX-2 (COX-2MECKO) compared to wild type (WT) mice.Tumors were analyzed, by real time PCR, immune-staining and flow cytometry, for proliferation, apoptosis, angiogenesis and immune microenvironment. Lentiviral shRNA delivery was used to knock down (KD) COX-2 in ErbB2-transformed mouse breast cancer cells (COX-2KD), and growth as orthotopic tumors was examined in syngenic recipient mice, with or without depletion of CD8+ immune cells.ResultsMammary tumor onset was delayed, and multiplicity halved, in COX-2MECKO mice compared to WT. COX-2MECKO tumors showed decreased expression of Ki67, a proliferation marker, as well as reduced VEGFA, its receptor VEGFR2, endothelial NOS and the vascular endothelial marker CD31, indicating reduced tumor vascularization. COX-2MECKO tumors contained more CD4+ T helper (Th) cells and CD8+ cytotoxic immune cells (CTL) consistent with increased immune surveillance. The ratio of Th markers Tbet (Th1) to GATA3 (Th2) was higher, and levels of Retnla, a M2 macrophage marker, lower, in COX-2MECKO tumor infiltrating leukocytes compared to WT, suggesting a prevalence of pro-immune Th1 over immune suppressive Th2 lymphocytes, and reduced macrophage polarization to the immune suppressive M2 phenotype. Enhanced immune surveillance in COX-2MECKO tumors was coincident with increased intratumoral CXCL9, a T cell chemoattractant, and decreased expression of T lymphocyte co-inhibitory receptors CTLA4 and PD-1, as well as PD-L1, the ligand for PD-1. PD-L1 was also decreased in IFNγ-treated COX-2KD mouse mammary cancer cells in vitro and, compared to control cells, growth of COX-2KD cells as orthotopic tumors in immune competent mice was markedly suppressed. However, robust growth of COX-2KD tumor cells was evident when recipients were depleted of CD8+ cells.ConclusionsThe data strongly support that, in addition to its angiogenic function, tumor cell COX-2 suppresses intratumoral cytotoxic CD8+ immune cell function, possibly through upregulation of immune checkpoints, thereby contributing to tumor immune escape. COX-2 inhibition may be clinically useful to augment breast cancer immunotherapy.

Abstract 90: Estrogen accelerates the development of estrogen receptor-negative breast cancer.

Abstract Long-term cumulative exposure to estrogen increases the breast cancer risk in women. Breast tissue must have a normal complement of estrogen receptor (ER) and progesterone receptor (PGR) for the normal development of breast tissue. Clinically, about 22% of patients with breast cancer overexpress the ERBB2 (HER2/neu) receptor tyrosine kinase. However, many HER2/neu-positive mammary tumors do not express ER or PGR by the time they are clinically recognizable. So far, the role of estrogen in the development of ER-negative breast cancers is not clearly defined. Aromatase is a key enzyme for estrogen biosynthesis and its expression pattern between human and mouse is drastically different. We generated transgenic humanized aromatase (Aromhum) mice to mimic the human aromatase distribution pattern in the mouse. Aromhum mice exhibited an increased incidence of lobuloalveolar breast hyperplasia associated with increased estrogen levels locally in mammary glands but not in the circulation. To demonstrate the important role of ER signaling in ER-negative breast tumor development and eventually to test a prevention strategy using aromatase inhibitors in this mouse model, Aromhum mice were crossed with ERBB2 transgenic mice to generate wild-type (WT), Aromhum, ERBB2 and Aromhum/ERBB2 (AE) mice. WT or Aromhum transgenic mice were free of tumors during the 26 week of follow-up. On the other hand, 56% of ERBB2 (only) mice developed mammary tumors, as expected. Interestingly, AE mice had a significantly higher (86%, p<0.05) tumor incidence compared with ERBB2 mice. Thus, it appeared that the human aromatase transgene increased the rate of ERBB2–induced mammary tumor growth. The tumors that arose in either ERBB2 or AE mice were histological adenocarcinomas as was previously reported for the ERBB2 transgenic mice. Levels of ER and PGR in benign mammary epithelial cells were higher in Aromhum and AE mice as compared to WT and ERBB2 mice. We further measured the dynamic change of sex hormone receptor status from normal mammary epithelial cells to fully developed tumors. Different stages of mammary tumors were chosen from nonpalpable microscopic visible early stage tumor to various sizes of late stage tumors. ER and PGR were present in early stage tumor but gradually decreased and eventually were absent in late stage tumors. The estrogen response gene, cyclin D1 was higher in benign and malignant mammary epithelium of Aromhum and AE mice compared with WT mice. Cell proliferation evaluated by Ki67 staining was significantly higher in benign mammary epithelium and tumors of AE mice as compared to those of ERBB2 mice. In conclusion, estrogen expedited the early development of ER-negative mammary tumors caused by a primary genetic hit (HER2/neu) via increasing cell proliferation through ER-mediated signal transduction. This study provides a fundamental mechanism for testing prevention strategies using aromatase inhibitors in this mouse model. Citation Format: Hong Zhao, John S. Coon, Robert T. Chatterton, Dolores Huberts, David Christopher Brooks, Francesco J. DeMayo, Serdar E. Bulun. Estrogen accelerates the development of estrogen receptor-negative breast cancer. [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 90. doi:10.1158/1538-7445.AM2013-90

Cardiac-Specific Over-Expression of Epidermal Growth Factor Receptor 2 (ErbB2) Induces Pro-Survival Pathways and Hypertrophic Cardiomyopathy in Mice

BackgroundEmerging evidence shows that ErbB2 signaling has a critical role in cardiomyocyte physiology, based mainly on findings that blocking ErbB2 for cancer therapy is toxic to cardiac cells. However, consequences of high levels of ErbB2 activity in the heart have not been previously explored.Methodology/Principal FindingsWe investigated consequences of cardiac-restricted over-expression of ErbB2 in two novel lines of transgenic mice. Both lines develop striking concentric cardiac hypertrophy, without heart failure or decreased life span. ErbB2 transgenic mice display electrocardiographic characteristics similar to those found in patients with Hypertrophic Cardiomyopathy, with susceptibility to adrenergic-induced arrhythmias. The hypertrophic hearts, which are 2–3 times larger than those of control littermates, express increased atrial natriuretic peptide and β-myosin heavy chain mRNA, consistent with a hypertrophic phenotype. Cardiomyocytes in these hearts are significantly larger than wild type cardiomyocytes, with enlarged nuclei and distinctive myocardial disarray. Interestingly, the over-expression of ErbB2 induces a concurrent up-regulation of multiple proteins associated with this signaling pathway, including EGFR, ErbB3, ErbB4, PI3K subunits p110 and p85, bcl-2 and multiple protective heat shock proteins. Additionally, ErbB2 up-regulation leads to an anti-apoptotic shift in the ratio of bcl-xS/xL in the heart. Finally, ErbB2 over-expression results in increased activation of the translation machinery involving S6, 4E-BP1 and eIF4E. The dependence of this hypertrophic phenotype on ErbB family signaling is confirmed by reduction in heart mass and cardiomyocyte size, and inactivation of pro-hypertrophic signaling in transgenic animals treated with the ErbB1/2 inhibitor, lapatinib.Conclusions/SignificanceThese studies are the first to demonstrate that increased ErbB2 over-expression in the heart can activate protective signaling pathways and induce a phenotype consistent with Hypertrophic Cardiomyopathy. Furthermore, our work suggests that in the situation where ErbB2 signaling contributes to cardiac hypertrophy, inhibition of this pathway may reverse this process.

Involvement of Toll-like Receptor 2 (TLR2) in self-renewal of mouse mammary cancer initiating cells (CIC) (74.8)

Abstract CIC are a subpopulation of cancer cells with stem cell properties that may be responsible for tumor progression, metastasis, resistance to therapy, and tumor recurrence. It is thus conceivable that the identification of the molecular pathway and antigens directly involved in the maintenance of the stem-cell like features of CIC could open a new and promising therapeutic opportunity for anti-cancer interventions. We enriched CIC from a mammary carcinoma cell line derived from a tumor of ErbB2 transgenic mice (TuBo cells) generating subsequent passages of mammospheres. We compared their transcriptional profiling with that of the bulk population of TUBO cells and focused our attention on a cluster of 183 up-regulated transcripts. Among them there were growth factors and immune system-related genes, including toll-like receptor 2 (TLR2). The inhibition of TLR2 signaling strongly impaired in vitro mammospheres generation and in vivo tumorigenicity, demonstrating the involvement of TLR2 in CIC self-renewal. In conclusion, this study provides a genomic characterization of mammary CIC and shows that TLR2 might have a role in initiation and progression of breast cancers.

Abstract 5452: In utero exposure to bisphenol A promotes mammary tumor development in MMTV-erbB-2 transgenic mice

Abstract Increasing evidence indicates that environmental exposure plays a critical role in breast cancer etiology. Bisphenol A (BPA), the building block of polycarbonate plastics with estrogenic activity, is one of the most common chemicals exposed in daily life. Recent studies suggest a link between BPA exposure and increased breast cancer risk. However, specific conditions and the underlying mechanisms of BPA exposure associated breast cancer risk remain unclear. This study aimed to investigate the effects of in utero exposure to BPA on mammary tumor development in MMTV-erbB-2 transgenic mice, which exemplifies a scenario of gene-environmental interaction. Since erbB-2 is amplified/overexpressed in approximately 30% of breast cancer, which has been associated with poor prognosis and therapeutic resistance, use of this clinically relevant mammary tumor model is of high translational value. In this study, pregnant MMTV-erbB-2 mice were subcutaneously injected with 0, 25 ng, 250 ng and 250 µg/Kg body weight BPA daily between day 13 and day 19 of gestation. We found that in utero exposed mice in the low dose (25 and 250 ng) groups, but not the high dose group (250 µg), displayed earlier vaginal opening and prolonged estrous phase, suggesting a dose dependent pro-estrogenic effect of in utero exposure to BPA. Whole mount analysis showed that mammary glands of mice with in utero exposure to low dose BPA had a longer ductal extension at 6 weeks and increased lateral branching/alveolar structures at 10 weeks, which was more significant in the 250 ng group but less evident in the high dose group. Molecular analysis of mammary tissues at 10 weeks indicated that in utero exposure to BPA increased phosphorylation/activation of erbB-2, EGFR, erbB-3 Erk1/2 and Akt, and expression of erbB-3 and EGFR. Signaling of estrogen receptor (ER) pathway was upregulated concomitantly, as reflected by increased expression and phosphorylation of ERα and upregulation of cyclin D1 and c-myc. More importantly, mice in the 250 ng group but not the high dose group, developed tumor earlier than the mice in the control group, suggesting that dose is a critical factor affecting the outcomes. These data demonstrated that in utero exposure to BPA may promote mammary tumor development in erbB-2 transgenic mice in a dose dependent manner. Concomitant activation of the erbB-2 and ER pathways in the premalignant tissues suggests that induction of ER-erbB-2 crosstalk may play a critical role in mammary tumorigenesis promoted by in utero exposure to BPA, which underscores the significance of gene-environment interaction in early exposure to BPA associated breast cancer risk. 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 5452. doi:1538-7445.AM2012-5452

Abstract SY37-02: Cell polarity proteins and cancer progression

Abstract The Partitioning defective protein 3 (Par3) is known to regulate asymmetric cell division, cell junction biogenesis and epithelial morphogenesis, but its role in cancer is unclear. We report that expression of Par3 is downregulated in both human breast cancers and in lung metastasis of ErbB2 transgenic mice. Downregulation of Par3 cooperated with ErbB2 to induce invasion and metastasis in vivo. Interestingly, the metastatic behavior was not associated with an overt mesenchymal phenotype. However, loss of Par3 activated a Tiam1/Rac/GTP/IRSp53/WAVE2/Arp2/3 pathway that disrupted cortical actin, blocked E-cadherin junction maturation and decreased epithelial cell-cell cohesion. Cortical actin and Arp2/3 localization were disrupted in tumor cells in vivo. Thus, we identify Par3 as a novel regulator of metastatic behavior in tumor epithelial cells. 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 SY37-02. doi:1538-7445.AM2012-SY37-02

Abstract 548: Erythropoietin promotes mammary tumor development in MMTV-erbB-2 transgenic mice

Abstract Erythropoietin (EPO), a cytokine that stimulates erythropoiesis, is frequently used to treat anemia in cancer patients. Recent clinical studies indicate that EPO administration might be associated with tumor progression and reduced overall survival rate. However, the mechanisms of EPO associated risk in cancer patients remain poorly understood. In particular, a spontaneous tumor model that allows us to test the effects of EPO on tumor development/progression and provide mechanistic insights into multifactoral interactions in a physiological context has not been established. In this study, we used the MMTV-erbB-2 transgenic mouse model to test the specific effect of EPO on erbB-2 overexpressing breast cancers and aimed to establish a spontaneous tumor model for relevant studies. Female erbB-2 transgenic mice were injected with EPO? at 2000 U/Kg body weight, twice a week for three weeks (between week 20 and 22). We found that EPO treatment during the premalignant risk window not only increased hemoglobin levels but also significantly promoted mammary tumor development. In contrast to a 36-week mean latency of tumor development in control group, the mean latency for EPO exposed mice was 30 weeks. Moreover, EPO exposure resulted in increased pulmonary metastasis. Whole mount analysis of mammary gland at 23 weeks showed that EPO exposure induced ductal branching and alveolar outgrowth, which was consistent with increased BrdU incorporation in EPO exposed mammary tissues. Molecular analysis of mammary tissues at 23 weeks showed that the protein levels of p-Jak2, p-erbB-2, p-Erk and p-Akt1 were significantly increased, which was accompanied by increased expression of EGFR, erbB-3, IGFR, Bcl-2, cyclin D1 and VEGF. These data suggest that EPO exposure induced the activation of both EPOR/Jak2 and erbB-2/EGFR/erbB-3 pathways, and had a broad impact on signal transduction and gene expression in mammary tissues. Although the difference in signal transduction and gene expression of tumor tissues between control and EPO exposed groups was less significant, tumors from EPO treated mice showed increased microvessel density as compared to controls, suggesting EPO exposure induced a long lasting proangiogenic effect. Consistently, conditioned medium extracted from EPO treated mammary tissues at 23 weeks significantly increased tube formation of endothelial cells. Taken together, our results demonstrate that EPO treatment promotes the development and metastasis of erbB-2 overexpressing mammary tumors and established the MMTV-erbB-2 mouse model for the studies of EPO associated cancer risk. The underlying mechanisms involve enhanced activation of erbB-2 pathway through EPOR/Jak2 activation and increased proangiogenic activities in EPO exposed mammary tissues. Since erbB-2 is overexpressed in about 30% of human breast cancers, these data will have significant impact on safe use of EPO in breast cancer patients with anemia. 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 548. doi:1538-7445.AM2012-548

Reciprocal repression between P53 and TCTP

Screening for genes that reprogram cancer cells for the tumor reversion switch identified TCTP (encoding translationally controlled tumor protein) as a crucial regulator of apoptosis. Here we report a negative feedback loop between P53 and TCTP. TCTP promotes P53 degradation by competing with NUMB for binding to P53-MDM2-containing complexes. TCTP inhibits MDM2 auto-ubiquitination and promotes MDM2-mediated ubiquitination and degradation of P53. Notably, Tctp haploinsufficient mice are sensitized to P53-dependent apoptosis. In addition, P53 directly represses TCTP transcription. In 508 breast cancers, high-TCTP status associates with poorly differentiated, aggressive G3-grade tumors, predicting poor prognosis (P < 0.0005). Tctp knockdown in primary mammary tumor cells from ErbB2 transgenic mice results in increased P53 expression and a decreased number of stem-like cancer cells. The pharmacological compounds sertraline and thioridazine increase the amount of P53 by neutralizing TCTP's action on the MDM2-P53 axis. This study links TCTP and P53 in a previously unidentified regulatory circuitry that may underlie the relevance of TCTP in cancer.