Mammary tumor-derived transplants as breast cancer models to evaluate tumor-immune interactions and therapeutic responses

In breast cancer, the type and distribution of infiltrating immune cells are associated with clinical outcome. Moreover, infiltrated cancers with abundant tumor infiltrating lymphocytes (TIL) are more likely to respond to immunotherapy, while those in which CD8+ T cells are completely absent (deserts) or excluded are less likely to respond. Detailed understanding of this biology is limited by a lack of preclinical breast cancer models that recapitulate TIL distributions and their associated biology. Here we established mammary tumor-derived transplants (mTDT) from 12 Trp53 null mammary tumors in syngeneic BALB/cJ mice and examined the stability of their growth rate, TIL distribution, and transcriptomic profiles. All mTDT were estrogen receptor negative. Half of the parental tumors were classified as infiltrated, and the rest were divided between excluded and desert phenotypes. After two orthotopic passages, most (70%) mTDT from infiltrated parents recapitulated this pattern, whereas the desert or excluded parental patterns were maintained in about half of daughter mTDT. Approximately 30% of mTDT gave rise to lung or liver metastases, but metastasis was not associated with a TIL phenotype. Unsupervised transcriptomic analysis clustered mTDT according to their TIL spatial patterns. Infiltrated mTDT transplanted subcutaneously and orthotopically were resistant to anti-PD-L1. Profiling implicated prolonged antigen stimulation and loss of effector function of lymphocytes rather than T cell exhaustion in the lack of response of infiltrated mTDT to checkpoint blockade. In summary, the molecular diversity and immune complexity of mTDT will facilitate the dissection of mechanisms of breast cancer response to immunotherapies.

Macrophages unlock progression of breast cancer cells experiencing matrigel-segregation in transplantation models

Basement membrane matrix proteins, such as matrigel, are able to improve the efficiency of tumour transplantation. This assay represents the gold standard to measure tumour initiation potential in vivo of a limited number of cancer cells. However, in culture conditions, matrigel directly signals to cancer cells altering their phenotype. We here investigate how matrigel influences the tumour reconstitution dynamics of breast cancer cells in vivo. This is particularly relevant in the setting of limiting dilution assay where cells are transplanted in a relatively high amount of Matrigel. We show that matrigel initially induces a normalized growth of transplanted MMTV-PyMT breast tumours cells. This occurs in the context of a matrigel-segregation effect where cancer cells are transiently isolated from host tissue. We identify macrophages as gatekeepers of the cancer-host cell interaction: depriving transplants from macrophages locked cancer cells in this isolated environment where they fail to form tumours despite retaining their intrinsic tumorigenic potential. This is a decisive proof of concept that cancer cells' malignant behaviour can be dominated by their microenvironment. Moreover, considering that diverse breast cancer cells are differently subjected to a segregation effect, this needs to be considered when comparing tumour initiation potential of different cancer cells.

Characterization of Breast Cancer Preclinical Models Reveals a Specific Pattern of Macrophage Polarization

Drug discovery efforts have focused on the tumor microenvironment in recent years. However, few studies have characterized the stroma component in patient-derived xenografts (PDXs) and genetically engineered mouse models (GEMs). In this study, we characterized the stroma in various models of breast cancer tumors in mice. We performed transcriptomic and flow cytometry analyses on murine populations for a series of 25 PDXs and the two most commonly used GEMs (MMTV-PyMT and MMTV-erBb2). We sorted macrophages from five models. We then profiled gene expression in these cells, which were also subjected to flow cytometry for phenotypic characterization. Hematopoietic cell composition, mostly macrophages and granulocytes, differed between tumors. Macrophages had a specific polarization phenotype related to their M1/M2 classification and associated with the expression of genes involved in the recruitment, invasion and metastasis processes. The heterogeneity of the stroma component of the models studied suggests that tumor cells modify their microenvironment to satisfy their needs. Our observations suggest that such models are of relevance for preclinical studies.

Biophysical and morphological effects of nanodiamond/nanoplatinum solution (DPV576) on metastatic murine breast cancer cells in vitro

Nanoparticles have recently gained increased attention as drug delivery systems for the treatment of cancer due to their minute size and unique chemical properties. However, very few studies have tested the biophysical changes associated with nanoparticles on metastatic cancer cells at the cellular and sub-cellular scales. Here, we investigated the mechanical and morphological properties of cancer cells by measuring the changes in cell Young's Modulus using AFM, filopodial retraction (FR) by time lapse optical light microscopy imaging and filopodial disorganization by high resolution AFM imaging of cells upon treatment with nanoparticles. In the current study, nanomechanical changes in live murine metastatic breast cancer cells (4T1) post exposure to a nanodiamond/nanoplatinum mixture dispersed in aqueous solution (DPV576), were monitored. Results showed a decrease in Young's modulus at two hours post treatment with DPV576 in a dose dependent manner. Partial FR at 20 min and complete FR at 40 min were observed. Moreover, analysis of the retraction distance (in microns) measured over time (minutes), showed that a DPV576 concentration of 15%v/v yielded the highest FR rate. In addition, DPV576 treated cells showed early signs of filopodial disorganization and disintegration. This study demonstrates the changes in cell stiffness and tracks early structural alterations of metastatic breast cancer cells post treatment with DPV576, which may have important implications in the role of nanodiamond/nanoplatinum based cancer cell therapy and sensitization to chemotherapy drugs.

Caveolin-1 and accelerated host aging in the breast tumor microenvironment: chemoprevention with rapamycin, an mTOR inhibitor and anti-aging drug

Increasing chronological age is the most significant risk factor for human cancer development. To examine the effects of host aging on mammary tumor growth, we used caveolin (Cav)-1 knockout mice as a bona fide model of accelerated host aging. Mammary tumor cells were orthotopically implanted into these distinct microenvironments (Cav-1(+/+) versus Cav-1(-/-) age-matched young female mice). Mammary tumors grown in a Cav-1-deficient tumor microenvironment have an increased stromal content, with vimentin-positive myofibroblasts (a marker associated with oxidative stress) that are also positive for S6-kinase activation (a marker associated with aging). Mammary tumors grown in a Cav-1-deficient tumor microenvironment were more than fivefold larger than tumors grown in a wild-type microenvironment. Thus, a Cav-1-deficient tumor microenvironment provides a fertile soil for breast cancer tumor growth. Interestingly, the mammary tumor-promoting effects of a Cav-1-deficient microenvironment were estrogen and progesterone independent. In this context, chemoprevention was achieved by using the mammalian target of rapamycin (mTOR) inhibitor and anti-aging drug, rapamycin. Systemic rapamycin treatment of mammary tumors grown in a Cav-1-deficient microenvironment significantly inhibited their tumor growth, decreased their stromal content, and reduced the levels of both vimentin and phospho-S6 in Cav-1-deficient cancer-associated fibroblasts. Since stromal loss of Cav-1 is a marker of a lethal tumor microenvironment in breast tumors, these high-risk patients might benefit from treatment with mTOR inhibitors, such as rapamycin or other rapamycin-related compounds (rapalogues).

In utero exposure to bisphenol A shifts the window of susceptibility for mammary carcinogenesis in the rat

BACKGROUND

Bisphenol A (BPA) is a ubiquitous environmental chemical with reported endocrine-disrupting properties.

OBJECTIVE

Our goal in this study was to determine whether prenatal exposure to BPA predisposes the adult rat mammary gland to carcinogenesis.

METHODS

Pregnant rats were treated orally with 0, 25, or 250 microg BPA/kg body weight (BW) from gestation day (GD) 10 to GD21. For tumorigenesis experiments, prenatally exposed female offspring received a single gavage of 7,12-dimethylbenz(a)anthracene (DMBA; 30 mg/kg BW) on postnatal day (PND) 50, or PND100.

RESULTS

Prenatal exposure of the dam to 250 microg BPA/kg BW combined with a single exposure of female offspring to DMBA on PND100, but not on PND50, significantly increased tumor incidence while decreasing tumor latency compared with the control group. Prenatal exposure of the dam to 250 microg BPA/kg BW, in the absence of DMBA to the female offspring, increased cell proliferation and elicited differential effects at the protein level at PND100 compared with PND50. Differentially regulated proteins in the mammary gland included estrogen receptor-alpha, progesterone receptor-A, Bcl-2, steroid receptor coactivators, epidermal growth factor receptor, phospho-insulinlike growth factor 1 receptor, and phospho-Raf.

CONCLUSIONS

Our study demonstrates that oral prenatal exposure to BPA increases mammary cancer susceptibility in offspring and shifts the window of susceptibility for DMBA-induced tumorigenesis in the rat mammary gland from PND50 to PND100. These changes are accompanied by differential effects of prenatal BPA exposure on the expression of key proteins involved in cell proliferation.

Radiation-induced mammary carcinogenesis in rodent models: what's different from chemical carcinogenesis?

Ionizing radiation is one of a few well-characterized etiologic factors of human breast cancer. Laboratory rodents serve as useful experimental models for investigating dose responses and mechanisms of cancer development. Using these models, a lot of information has been accumulated about mammary gland cancer, which can be induced by both chemical carcinogens and radiation. In this review, we first list some experimental rodent models of breast cancer induction. We then focus on several topics that are important in understanding the mechanisms and risk modification of breast cancer development, and compare radiation and chemical carcinogenesis models. We will focus on the pathology and natural history of cancer development in these models, genetic changes observed in induced cancers, indirect effects of carcinogens, and finally risk modification by reproductive factors and age at exposure to the carcinogens. In addition, we summarize the knowledge available on mammary stem/progenitor cells as a potential target of carcinogens. Comparison of chemical and radiation carcinogenesis models on these topics indicates certain similarities, but it also indicates clear differences in several important aspects, such as genetic alterations of induced cancers and modification of susceptibility by age and reproductive factors. Identification of the target cell type and relevant translational research for human risk management may be among the important issues that are addressed by radiation carcinogenesis models.JRRS Incentive Award in 2009.

Role of autophagy in mammary gland development

Autophagy is a highly conserved catabolic process responsible for degradation and recycling of long-lived proteins and organelles by lysosomes. This degradative pathway, together with proteasome system is particularly important during development and under certain environmental stress conditions. This review summarizes the latest achievements of studies aiming to explore the role of autophagy in development and differentiation of eukaryotic cells. It shows the importance of this process in the development of lower eukaryotic organisms such as Dicyostelium discoideum, and Caenorhabditis elegans, as well as functions of autophagy and autophagy related genes (Atg) in development and differentiation of higher eukaryotic organisms. The review is focused on the results of studies conducted on mammary gland, as it is a good model for studying the mechanisms controlling higher eukaryotic organisms' development. Studies have shown that autophagy is involved in the removal of epithelial cells during formation of alveolar structures, indicating its role in mammogenesis. There are also evidences of involvement of Atg's in epithelial tumors development. Context dependent manipulations of autophagic pathways may create more effective anticancer therapies in the future.

Crosstalk between GH/IGF-I axis and steroid hormones (progesterone, 17beta-estradiol) in canine mammary tumours

Growth hormone (GH), insulin-like growth factor I (IGF-I), progesterone (P4) and 17beta-estradiol (17-E2) concentrations have been studied in 84 mammary tumours (44 dysplasias and benign tumours and 40 malignant neoplasias) from 33 female dogs. Thirteen normal mammary glands from 80 healthy female dogs were also analysed as controls. GH concentrations were determined in mammary homogenates by radio-immunoassay. IGF-I, P4 and 17-E2 tissue levels were determined by enzyme-immunoassay (EIA) techniques. The potential correlations between GH/IGF-I concentrations and P4 and 17-E2 mammary tissue levels were investigated. Tissue GH (p<0.01) and IGF-I concentrations (p<0.01) were significantly higher in malignant tumours than in benign neoplasms. Likewise, malignant tumours were the mammary lesions that displayed the highest P4 and 17-E2 tissue levels. Strong correlations between GH/IGF-I (n=84; r=0.436; p<0.001), P4/GH (n=84; r=0.562; p<0.001) and 17-E2/IGF-I (n=84; r=0.638; p<0.001) were observed in tumoral tissue homogenates. Our study provides evidence that P4 might increase autocrine GH production which might directly stimulate local or systemic IGF-I secretion. Additionally, the IGF-I effect might be influenced by local levels of 17-E2. These results suggest that all these hormones and factors might act as local growth factors stimulating the development and/or maintenance of canine mammary tumours in an autocrine/paracrine manner.

Human chorionic gonadotropin (hCG) up-regulates wnt5b and wnt7b in the mammary gland, and hCGbeta transgenic female mice present with mammary Gland tumors exhibiting characteristics of the Wnt/beta-catenin pathway activation

Transgenic (TG) mice expressing human chorionic gonadotropin (hCG) beta-subunit under the ubiquitin C promoter, presenting with a moderately elevated level of LH/hCG bioactivity develop multiple neoplasms secondary to the endocrine abnormalities, including mammary gland tumors after the age of 9 months. The increased levels of circulating estradiol, progesterone, and prolactin of the TG females after puberty boost the lobuloalveolar development in the mammary gland resulting ultimately in the formation of estrogen and progesterone receptor-negative, malignant tumors. These tumors have a similar histopathology with those observed in TG mice with activated wnt/beta-catenin pathway, showing increased expression of beta-catenin, also a common finding in human breast tumors. Transdifferentiation is observed in mammary tumors of the hCGbeta TG mice, accompanied by abnormal expression of the Wnt genes in the tumorous and nontumorous mammary gland tissue. Specifically we found increased expression of Wnt5b in the TG mammary glands at the age of 3 months and up-regulation of Wnt7b and -5b in the subsequently appearing tumors. Importantly, hCG was found to up-regulate these wnt ligands in mouse mammary gland, independent of the changes in ovarian steroidogenesis. Thus, the hCGbeta-overexpressing TG mice represent a novel model that links enhanced hCG action to dysregulated wnt signaling in the mammary gland, resulting in beta-catenin-stabilizing mammary tumorigenesis. The novel finding of hCG up-regulating wnt7b and wnt5b could contribute to pregnancy-induced breast cancer in humans.

Opposing effects of retinoic acid on cell growth result from alternate activation of two different nuclear receptors

Transcriptional activation of the nuclear receptor RAR by retinoic acid (RA) often leads to inhibition of cell growth. However, in some tissues, RA promotes cell survival and hyperplasia, activities that are unlikely to be mediated by RAR. Here, we show that, in addition to functioning through RAR, RA activates the "orphan" nuclear receptor PPARbeta/delta, which, in turn, induces the expression of prosurvival genes. Partitioning of RA between the two receptors is regulated by the intracellular lipid binding proteins CRABP-II and FABP5. These proteins specifically deliver RA from the cytosol to nuclear RAR and PPARbeta/delta, respectively, thereby selectively enhancing the transcriptional activity of their cognate receptors. Consequently, RA functions through RAR and is a proapoptotic agent in cells with high CRABP-II/FABP5 ratio, but it signals through PPARbeta/delta and promotes survival in cells that highly express FABP5. Opposing effects of RA on cell growth thus emanate from alternate activation of two different nuclear receptors.

Occludin-mediated premature senescence is a fail-safe mechanism against tumorigenesis in breast carcinoma cells

We have previously demonstrated that epigenetic silencing of occludin, a tight junction-associated membrane protein, results in the acquisition of apoptotic resistance to various apoptogenic stimuli, causally contributing to the enhanced tumorigenicity of cancer cells. However, it remains to be examined whether occludin expression in transformed cells has an alternative impact that is important for cancer progression. Here we show that forced expression of occludin induces anoikis and promotes oxidative stress-induced premature senescence in breast carcinoma cells, which is accompanied by upregulation of negative cell cycle regulators such as p16(INK4A), p21(Waf1/Cip1) and p27(Kip1) but not p53. The senescent phenotype is reversed by specific inhibition of mitogen-activated protein kinase. Endogenous reexpression of occludin mediated by a synergistic effect with a demethylator and histone deacetylase inhibitor or retinoids that stimulate retinoic acid receptor alpha is also sufficient for provoking the senescent phenotype. In addition, tumors that developed from occludin-expressing cells in mice showed a feature of cellular senescence that has not been described as a consequence of occludin signaling. These findings suggest that the loss of occludin expression is at least partially involved in the senescence-escape program during mammary tumorigenesis.

RCAS-TVA in the Mammary Gland: An in vivo Oncogene Screen and a High Fidelity Model for Breast Transformation?

Mouse models of breast cancer are traditionally made by introducing genetic alterations to the entire mammary epithelium using transgenic or knockout approaches. In contrast, we have adapted the RCAS-TVA method to introduce genes into a small subset of somatic mammary cells in developmentally normal mammary glands. This new method allows the testing of the carcinogenic potential of candidate oncogenes In Vivo without the need to create individual transgenic lines. Moreover, since models created by this approach closely recapitulate evolution of human breast cancer, they may help understand human breast cancer initiation and progression, and may be useful for preclinical testing of therapeutic compounds. Finally, this approach may provide an opportunity to target oncogenes into mammary cells at different differentiation stages, providing a tool to study the relationship between cell origin and cancer phenotype.

Mammary development, carcinomas and progesterone: role of Wnt signalling

The mammary gland begins development during embryogenesis but after exposure to hormonal changes during puberty and pregnancy undergoes extensive further development. Hormonal changes are key regulators in the cycles of proliferation, differentiation, apoptosis and remodelling associated with pregnancy, lactation and involution following weaning. These developmental processes within the breast epithelium can be explained by the presence of a long-lived population of tissue-specific stem cells. The longevity of these stem cells makes them susceptible to accumulating genetic change and consequent transformation. The ovarian steroid progesterone, acting via the secreted factor Wnt4, is known to be essential for side branching of the mammary gland. One function of Wnt proteins is self-renewal of adult tissue stem cells, suggesting that progesterone may exert its effects within the breast, at least partly, by regulating the mammary stem cell population.

Infant temperament predicts life span in female rats that develop spontaneous tumors

In a recent study, we found that male rats that minimally explored a novel environment as infants died significantly faster than their more exploratory brothers. At death, these males had various complex pathologies, precluding identification of specific hormonal mechanisms underlying adult disease progression and mortality. To minimize the variance of disease processes at the end of life, we conducted a longitudinal study with female Sprague-Dawley rats prone to high rates of spontaneous mammary and pituitary tumors. For females that developed either mammary or pituitary tumors, those that had been neophobic (least exploratory) as infants died approximately 6 months earlier than their neophilic (most exploratory) sisters. In the case of mammary tumors, both benign and malignant, neophobic females developed palpable tumors earlier than neophilic females, whereas the interval between first palpation and death was the same for all females, indicating psychosocial regulation of early rather than later stages of the disease. Neophobic females' ovarian function aged more rapidly than their neophilic sisters. Concomitantly, they had lower corticosterone responses to restraint in late adulthood, ruling out high estrogen or corticosterone levels during senescence as causal factors in their accelerated mortality. During puberty, when mammary tissue is proliferating and differentiating, neophobic females experienced more irregular cycles with prolonged "luteal" phases, suggesting a role for prolactin, prolonged progesterone and fewer estrogen surges during this sensitive period for mammary tumor risk. Thus, we identified prolactin, estrogen, progesterone and possibly corticosterone dynamics as candidates for neuroendocrine mechanisms linking infant temperament with onset of adult neoplastic disease.

E-cadherin and beta-catenin reduction influence invasion but not proliferation and survival in canine malignant mammary tumors

E-Cadherin and beta-catenin are known for their role in tumor invasion, but both proteins also exert an influence on tumor proliferation. This study, performed on canine mammary tumors, aimed to analyze the influence of E-cadherin (E-cad) and beta-catenin (beta-cat), immunohistochemically assessed singly and in combination (E-cad/beta-cat), on survival and their relationship with several proliferation indices (AgNOR index, MIB1 index, mitotic index). Immunohistochemistry was carried out on 60 formalin-fixed, paraffin wax-embedded specimens of canine mammary malignancies. The labeling was defined as preserved when prevalent on cell membranes of more than 75% of cells and reduced in other forms of expression (i.e., membranous less than 75%, cytoplasmic, and negative). E-cad, beta-cat, and E-cad/beta-cat were preserved respectively in 22, 12, and 11 out of 60 cases. Immunohistochemical expression of the two proteins in the same tumors was significantly correlated (P = 0.0001; R = 0.57). Survival analysis revealed no difference in outcome comparing the preserved versus reduced cases (E-cad, P = 0.31; beta-cat, P = 0.29; E-cad/beta-cat P = 0.36). Grouping cases for histologic invasiveness, the expression of E-cad or beta-cat and E-cad/beta-cat showed a progressive reduction that paralleled an increase in invasiveness from noninfiltrating to stage-II tumors (E-cad, P < 0.001; beta-cat, P < 0.05; E-cad/beta-cat, P < 0.05). No significant difference was obtained comparing mitotic index, MIB 1 index, and AgNOR index by analysis of variance between the cases grouped for preserved or reduced E-cad, beta-cat, and E-cad/beta-cat variables. In conclusion, reduced expression of E-cad, beta-cat, or E-cad/beta-cat was significantly associated with the progression from noninfiltrating to highly infiltrating tumors but not with proliferation or survival.

The Lymph Drainage of the Neoplastic Mammary Glands in the Bitch: A Lymphographic Study

The purpose of this investigation was to study the lymph drainage of the neoplastic mammary glands in the bitch using indirect lymphography. The main conclusions drawn from the study of 41 natural cases were as follows: the first or cranial thoracic and second or caudal thoracic neoplastic mammary glands usually drain into the ipsilateral axillary lymph nodes and rarely into the ipsilateral axillary and sternal lymph nodes, simultaneously. The third or cranial abdominal neoplastic mammary gland usually drains into the ipsilateral axillary and superficial inguinal lymph nodes simultaneously, but sometimes only cranially into the ipsilateral axillary lymph nodes. Rarely, it drains only caudally into the ipsilateral superficial inguinal and medial iliac lymph nodes, simultaneously. The fourth or caudal abdominal neoplastic mammary gland usually drains only caudally into the ipsilateral superficial inguinal lymph nodes. Rarely, it drains into the ipsilateral axillary and superficial inguinal lymph nodes simultaneously. The fifth or inguinal neoplastic mammary gland usually drains into the ipsilateral superficial inguinal lymph nodes but rarely, does it also drain into the ipsilateral popliteal lymph node and into a lymphatic plexus at the medial aspect of the ipsilateral thigh. Lymphatic connections between the neoplastic and adjacent normal mammary glands were demonstrated in only one case. The lymph drainage pattern of the neoplastic mammary glands is slightly different to that described in normal glands using the same radiographic method.

Monitoring the effect of mild hyperthermia on tumour hypoxia by Cu-ATSM PET scanning

PURPOSE

Mild hyperthermia can improve tumour oxygenation and enhance radiosensitivity. Imaging the hypoxic fraction of a tumour can guide hyperthermia treatment planning and facilitate treatment optimization. 64Cu-ATSM (Copper-diacetyl-bis(N4-methylthiosemicarbazone)) is a positron emitting compound that has been demonstrated to have rapid uptake and selective retention in hypoxic cells and has been used for imaging human and animal tumours. The purpose of the present report is to establish methodology that will allow one to use Cu-ATSM PET scanning to detect the impact of hyperthermia on tumour physiology in as little time as possible.

MATERIALS AND METHODS

EMT6 tumours (mouse mammary carcinoma) were implanted into the subcutaneous tissue of both thighs of 10 BALB/c mice (one heated, one control tumour per animal). The target thermal dose was 41.5 degrees C x 45 min. Without interrupting heating, 64Cu-ATSM (mean activity 1.8 mCi) was then injected and serial PET scans were obtained. In a sub-group of four animals, a low administered activity (approximately 0.3 mCi) 64Cu-ATSM scan was also conducted before heating to permit a direct comparison of the effects of hyperthermia on the same tumours. In another sub-group of five animals, a low activity (approximately 0.3 mCi) 64Cu-PTSM (pyruvaldehyde-bis(N*-methylthiosemicarbazone)) scan was conducted before heating, to confirm a posited correlation between perfusion and early 64Cu-ATSM uptake.

RESULTS

This study corrected for perfusion differences by dividing tumour uptake by the average early (first minute) uptake ('self-normalized uptake'). The 10 heated tumours showed a significantly (p = 0.007) lower self-normalized uptake than control tumours by 2 min. For the four mice with low activity Cu-ATSM scans performed before hyperthermia, the tumours to be heated demonstrated self-normalized uptake consistent with the unheated control tumours and which departed significantly (p < or = 0.02) from their post-hyperthermia scans by 5 min. Comparisons between scans and needle electrode surveys were performed in an additional four animals with eight tumours. For technical reasons electrode surveys were done after the end of hyperthermia-and, therefore, these animals also had comparison scans taken after hyperthermia. Reduced self-normalized uptake on scans was associated with increased pO2 on electrode surveys. These data also suggested a substantial degradation of the effect on tumour hypoxia by approximately 15-45 min after the end of mild hyperthermia.

CONCLUSION

Short imaging times of approximately 5 min with modest (approximately 4-10) numbers of mice can discriminate the effects of mild hyperthermia on tumour physiology. The long-term objective is to use this tool to identify as short and mild a hyperthermia session as possible.

Of Mice and Women: Light as a Circadian Stimulus in Breast Cancer Research

OBJECTIVE

Nocturnal rodents are frequently used as models in human breast cancer research, but these species have very different visual and circadian systems and, therefore, very different responses to optical radiation or, informally, light. Because of the impact of light on the circadian system and because recent evidence suggests that cancer risk might be related to circadian disruption, it is becoming increasingly clear that optical radiation must be properly characterized for both nocturnal rodents and diurnal humans to make significant progress in unraveling links between circadian disruption and breast cancer. In this paper, we propose a quantitative framework for comparing radiometric and photometric quantities in human and rodent studies.

METHODS

We reviewed published research on light as a circadian stimulus for humans and rodents. Both suppression of nocturnal melatonin and phase shifting were examined as outcome measures for the circadian system.

RESULTS

The data were used to develop quantitative comparisons regarding the absolute and spectral sensitivity for the circadian systems of humans and nocturnal rodents.

CONCLUSIONS

Two models of circadian phototransduction, for mouse and humans, have been published providing spectral sensitivities for these two species. Despite some methodological variations among the studies reviewed, the circadian systems of nocturnal rodents are approximately 10,000 times more sensitive to optical radiation than that of humans. Circadian effectiveness of different sources for both humans and nocturnal rodents are offered together with a scale relating their absolute sensitivities. Instruments calibrated in terms of conventional photometric units (e.g., lux) will not accurately characterize the circadian stimulus for either humans or rodents.

Relationship between radiobiological hypoxia in a C3H mouse mammary carcinoma and osteopontin levels in mouse serum

PURPOSE

To investigate the possible relationship between radiobiological hypoxia in a C3H mouse mammary carcinoma and osteopontin (OPN) levels measured in mouse serum.

MATERIAL AND METHODS

Experiments were performed in CDF1 mice that were either non-tumour bearing or with different sized tumours implanted in the right rear foot. Osteopontin levels in extracted mouse blood serum and tissue from the transplanted tumours were measured using an ELISA assay. The tumour oxygenation status was estimated using the Eppendorf Histograph and the fraction of oxygen partial pressure (pO2) values =5 mm Hg (HF5) was calculated. Necrosis was measured in haematoxylin and eosin-stained sections. Tumour hypoxia was increased by placing animals in a low-oxygen (10%) environment. Single radiation doses (240 kV x-rays) were given locally to tumours under ambient or clamped conditions and response assessed using a tumour control assay.

RESULTS

Serum OPN levels increased linearly with increasing tumour volume and this increase correlated with tumour OPN. HF5 and necrosis also increased with increasing tumour volume, but this increase was non-linear. Converting the HF5 results into equivalent tumour volume gave results that were directly correlated to OPN serum levels. Placing mice in a 10% oxygen environment for 12 hours significantly increased HF5. However, serum OPN only increased if reoxygenation occurred before measurement. Radiobiological hypoxic fraction in this tumour model did not change with increasing tumour size, but the total number of hypoxic cells did increase.

CONCLUSIONS

These findings suggest that serum OPN measurement may predict the proportion of hypoxic cells in this tumour model, although increased serum OPN levels simply resulting from an increased tumour burden can not be ruled out.

Analysis of dystroglycan regulation and functions in mouse mammary epithelial cells and implications for mammary tumorigenesis

Abnormalities in the interactions of cells with the extracellular matrix (ECM) play an important role in the development and progression of many types of cancer and are a hallmark of malignant transformation. The dystroglycan (DG) complex is a transmembrane glycoprotein that forms a continuous link from the ECM to the actin cytoskeleton, providing structural integrity and perhaps transducing signal, in a manner similar to integrins. Deregulated expression of DG has been reported in a variety of human malignancies and related to tumor differentiation and aggressiveness. In breast cancer, reduced DG expression has been associated with patient survival and with loss of differentiation of tumor cells. Limited data are available on DG physiology in epithelial cells. In this study, we used the HC11 spontaneously immortalized murine mammary epithelial cells to study DG function(s) and regulation in normal cells. We found that expression of DG protein and mRNA is cell-cycle and cell-density regulated in these cells. Moreover, expression of both DG subunits increased upon lactogenic differentiation of the HC11 cells. The turnover of cell-surface-expressed DG was evaluated in the same cells and half-life of DG subunits was evaluated to be about 12 h. DG-specific small inhibitory RNAs were used to analyze the effects of a reduced expression of DG in these cells. Cells in which DG expression was suppressed were growth inhibited, accumulated in the S-phase of the cell cycle, failed to undergo lactogenic differentiation, and displayed an increase in the percentage of apoptotic cells. Moreover, changes were observed in the expression and/or activity of several molecules involved in cell growth control. These results demonstrate that DG expression is tightly regulated in normal mammary epithelial cells and support the hypothesis that DG is involved in several functions other than structural integrity in these cells. This finding provides new insight into the roles played by DG in epithelial cell physiology and will contribute to our understanding of its involvement in the process of epithelial cell transformation.

Enhancement by acrylamide of N-methyl-N-nitrosourea-induced rat mammary tumor development—possible application for a model to detect co-modifiers of carcinogenesis

Acrylamide (AA) has recently been reported to be spontaneously formed in fried and baked foods with various concentrations. Although carcinogenicity in humans is as yet equivocal, numerous positive genotoxicity data in vitro and in vivo and results of rat long-term carcinogenicity studies demonstrating tumor induction at multiple sites, like the mammary gland, thyroid and testes, suggest the risk with dietary exposure may not be negligible. In the present study, to establish a medium-term carcinogenesis model for screening of agents with the potential to modify AA effects on the mammary gland and thyroid, we pretreated rats with 7,12-dimethylbenz(a)anthracene (DMBA), in combination with N-bis(2-hydroxypropyl)nitrosamine (DHPN), or N-methyl-N-nitrosourea (MNU) alone and then administered AA at 20 and 40 ppm in the drinking water for 30 weeks. The incidence and multiplicity of mammary tumors were increased at the high dose (P<0.05) in MNU- but not DMBA+DHPN-treated rats. No thyroid tumors were induced in any case. The results indicate that the MNU model is suitable for detection of modifiers of AA actions.

Diurnal rhythmicity of thiobarbituric acid reactive substances and antioxidants in experimental mammary carcinogenesis

AIM

Circadian rhythms of reactive oxygen species and antioxidants have been the subject of considerable interest in recent years due to their crucial role in the development of malignant tumors. Our aim was to analyze the circadian pattern of lipid peroxidation by-products (TBARS) and antioxidants status in 7,12-dimethylbenz(a)anthracene (DMBA) induced rat mammary carcinogenesis.

METHODS

Mammary tumors were developed in Wistar rats, blood samples were collected at a regular interval of 4 h throughout the 24 h period and TBARS content and antioxidant enzymes activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)) were estimated by colorimetric methods. The Cosinorwin computer software program was used to analyze the characteristics of biochemical rhythms.

RESULTS

In mammary carcinogenesis, the acrophase of thiobarbituric acid reactive substances and antioxidant enzymes (SOD, CAT, GPx) in blood were found to be delayed, whilst mesor values for TBARS level - increased, and values for SOD, CAT, GPx activities - decreased. Significant r-values indicate the disruption of lipid peroxidation-antioxidants rhythms in mammary carcinogenesis.

CONCLUSION

The present investigation suggests that the circadian pattern of blood lipid peroxidation and antioxidants in rats with mammary carcinoma are markedly desynchronized as compared to normal rats.

Overexpression of cyclins D1 and D3 during estrogen-induced breast oncogenesis in female ACI rats

A common feature of human breast oncogenesis is cell cycle deregulation. The expression of cyclins D1 and D3 was examined during estradiol-17beta (E(2))-induced mammary tumorigenesis in female August Copenhagen Irish (ACI) rats. Low serum E(2) levels ( approximately 60-120 pg/ml) were sufficient to induce mammary gland tumors (MGTs) that remarkably resemble human ductal breast cancer (BC) at the histopathologic and molecular levels. Western blot analysis of the E(2)-induced MGTs revealed a marked rise in cyclins D1 (24-fold), D3 (9-fold) and cdk4 (3-fold) expression compared with age-matched untreated controls. Small focal dysplasias with large, pale staining nuclei were commonly seen at 3-3.6 months, large focal dysplasias, including atypical ductal hyperplasia at 3.6-4.3 months, ductal carcinoma in-situ (DCISs) at 4.3-5.0 months, and 100% incidence of invasive ductal BC/frank tumors at 5-6 months were detected after E(2) treatment. Immunohistochemical analysis of serial sections of focal dysplasias, DCISs and invasive ductal carcinomas showed overexpression of cyclins D1, D3, estrogen receptor-alpha (ERalpha) and progesterone receptor (PR). However, cyclin D3 expression, unlike D1, was confined essentially to early pre-malignant lesions (focal dysplasias and DCISs) and primary MGTs with <1-5% of resting and normal hyperplastic breast cells staining positive. The kinase activity for cyclins D1 and D3, using retinoblastoma (Rb) as a substrate, in E(2)-induced MGTs and their binding to cdk4 was significantly elevated. Semi-quantitative reverse transcriptase PCR analysis of the E(2)-induced MGTs exhibited increased expression of cyclins D1 (2.9-fold) and D3 (1.4-fold) mRNA, indicating that their elevated protein expression was due in part to an increase in mRNA transcription. However, when analyzed by quantitative real-time Q-PCR, these genes were not amplified. These data indicate that in female ACI rat mammary glands, E(2)-induced pre-malignant lesions differentially and selectively express cyclins D1 and D3, thus contributing to a distinct growth advantage of these pre-neoplasias relative to E(2)-elicited normal hyperplasia.

The role of human prolactin and its antagonist, G129R, in mammary gland development and DMBA-initiated tumorigenesis in transgenic mice

Human prolactin (hPRL) has been implicated to have a pathological role in breast cancer and play a critical role in mammary gland development. The hPRL antagonist, G129R, has been shown to induce breast cancer cell apoptosis. 9,10-Dimethyl-1,2-benzanthracene (DMBA), a potent mammary gland carcinogen, induces hormone responsive mammary tumor formation in rodents. To investigate the effects of hPRL and its counterpart, G129R, on mammary gland development and tumorigenesis, transgenic mice that express hPRL or G129R under the regulation of the metallothionein (Mt) promoter were generated. Mammary glands from virgin female transgenic mice at the ages of 12, 24, and 36 weeks were used to compare the effect of hPRL and G129R in various developmental stages. Mammary gland whole mount comparisons between transgenic mice and their littermates revealed a significant increase in ductal branching and lobular bud formation in hPRL transgenic mice; whereas a drastic decrease in ductal branching and lobular bud formation was observed in the mammary glands of G129R transgenic mice. In addition, total RNA isolated from the mammary glands of transgenic mice at the three different ages was analyzed on Affymetrix GeneChip Mouse Expression 430A chips (MOE430A). Microarray data revealed alteration to the gene expression levels, greatest at 12 and 36 weeks. Furthermore, hPRL and G129R transgenic mice, as well as their littermates, were treated with multiple doses of DMBA and the rate of mammary tumor formation and survival were compared. The tumor rates in the G129R transgenic mice were significantly reduced (18% at 28 weeks) as compared to that of either NTG (39%) or hPRL (40%). On the other hand, the tumor appearance is significantly earlier in the PRL transgenic group as compared to that of controls. Taken together, the data further confirmed the inhibitory effects of G129R in mammary gland development, which translates to a resistance to DMBA-initiated breast tumorigenesis.

Effects of tamoxifen and soluble tumor-associated antigens on ovarian structure in mammary tumor-bearing rats

Previously, we showed that the 66 and 51 kDa soluble tumor-associated antigens (sTAAs) have distinct suppressive effects on chemically induced mammary cancer in rats, both alone and in combination with the hormone-related anticancer drug tamoxifen. Here, we describe the effects of both sTAA and tamoxifen on the histological structure of ovaries in mammary tumor-bearing 30- to 34-week-old rats. Central ovary sections were pooled, the number of the healthy and degenerated follicles were counted, and the size of the corpora lutea was estimated. In follicular development primordial, primary, preantral and antral stages were recognized. Only healthy follicles with visible nuclei were counted. Follicular degeneration was estimated as the number of atretic follicles with follicular remnants. Treatment with tamoxifen alone or in combination with sTAA significantly increased the number of primordial follicles and atretic follicles in the ovaries, and promoted the formation of small follicular cysts. Total area of the corpora lutea decreased. sTAA participated in this process by increasing apoptosis in degenerated follicles.

Dual role of AP-2gamma in ErbB-2-induced mammary tumorigenesis

A causative role of the membrane-bound tyrosine kinase ErbB-2 in breast tumorigenesis has been well established. MMTV/neu transgenic mice which overexpress ErbB-2 consistently develop mammary carcinomas with a high incidence. In human breast cancer, ErbB-2 is overexpressed in 25-30 of all cases and is representing a clinical marker of a poor prognosis. Besides to gene amplification, ErbB-2 overexpression has been attributed to transcription factors of the AP-2 family which were shown to control the ErbB-2 gene promoter in cell culture studies. Particularly AP-2alpha and gamma are often coexpressed in ErbB-2-positive breast carcinomas. However, LTRgamma transgenic mice which overexpress AP-2gamma in their mammary epithelium display only a very weak upregulation of the erbB-2 gene and do not develop mammary carcinoma. These findings therefore raise the possibility of functional cooperativity between both genes in breast cancer. To experimentally address the impact of AP-2gammaon ErbB-2-induced breast carcinogenesis we crossed MMTV/neu transgenic mice with LTRgamma transgenic mice and monitored tumor development in bitransgenic female progeny. AP-2gamma overexpression negatively influenced tumor incidence, as reflected by a reduced tumor number and a prolonged tumor latency. Histological analysis revealed three major types of tumors corresponding to different stages of tumor progression. Interestingly, an increased proportion of advanced stage carcinomas was observed in bitransgenic mice. Moreover, the AP-2gamma transgene differentially affected proliferation rates between the different progression stages: proliferation was enhanced at early stages but reduced in advanced stages in comparison to control tumors. Therefore, AP-2gamma while reducing the incidence of mammary tumors is promoting tumor progression.

Effect of perductal paclitaxel exposure on the development of MNU-induced mammary carcinoma in female S-D rats

BACKGROUND

Breast carcinoma and precancer are thought to start in the lining of the milk duct or lobule.

METHODS

At 5weeks of age, rats received a intraperitoneal (ip) injection of MNU for carcinogenesis. After mammary tumors were identified macroscopically using fiberscope, the rats were treated with perductal (pd) or ip injection of paclitaxel tri-weekly. At 36 weeks after MNU injection, tumor burden (No. of >1cm palpable mammary tumors/rat), total number of mammary carcinoma, apoptosis (AI), and microvessel density (MVD) were measured.

RESULTS

The administration of paclitaxel through the duct did not produce any toxic side effect. The tumor burden and total number of mammary carcinoma in the pd paclitaxel-treated group were significantly reduced compared to those seen in the ip paclitaxel-treated group. In addition, in the pd paclitaxel-treated group, AI was also increased and MVD was decreased, compared to those in the ip paclitaxel-treated group.

CONCLUSION

Local administration of paclitaxel may be useful for treatment of breast cancer.

Gamma-tocotrienol inhibits neoplastic mammary epithelial cell proliferation by decreasing Akt and nuclear factor kappaB activity

Tocotrienols, a subgroup within the vitamin E family of compounds, have been shown to display potent anticancer activity and inhibit preneoplastic and neoplastic mammary epithelial cell proliferation at treatment doses that have little or no effect on normal cell growth and function. However, the specific intracellular mechanisms mediating the antiproliferative effects of tocotrienols are presently unknown. Because Akt and nuclear factor kappaB (NFkappaB) are intimately involved in mammary tumor cell proliferation and survival, studies were conducted to determine the effects of gamma-tocotrienol on Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells in vitro. Treatment with 0-8 microM gamma-tocotrienol for 0-3 days caused a dose-responsive inhibition in +SA cell growth and mitotic activity, as determined by MTT colorimetric assay and proliferating cell nuclear antigen immunocytochemical staining, respectively. Studies also showed that treatment with 4 microM gamma-tocotrienol, a dose that inhibited +SA cell growth by more than 50% compared with that of untreated control cells, decreased intracellular levels of activated phosphotidylinositol 3-kinase-dependent kinase (PI3K)-dependent kinase 1 (phospho-PDK-1) and Akt, and reduced phospho-Akt kinase activity. Furthermore, these effects were not found to be associated with an increase in either phosphatase and tensin homologue deleted from chromosome 10 (PTEN) or protein phosphatase type 2A phosphatase activity. In addition, gamma-tocotrienol treatment was shown to decrease NFkappaB transcriptional activity, apparently by suppressing the activation of IkappaB-kinase-alpha/beta, an enzyme associated with inducing NFkappaB activation. In summary, these findings demonstrate that the antiproliferative effects of gamma-tocotrienol result, at least in part, from a reduction in Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells.

Rnd3/RhoE induces tight junction formation in mammary epithelial tumor cells

Glucocorticoid hormones stimulate adherens and tight junction formation in Con8 mammary epithelial tumor cells through a multistep process in which the membrane organization of structural apical junction proteins and tight junction sealing is controlled by specific signal transduction components. We have previously shown that dexamethasone stimulation of apical junction formation requires down-regulation of the small GTPase RhoA. Here we identified Rnd3/RhoE, a GTPase-deficient Rho family member and RhoA antagonist, as a key regulator of apical junction dynamics. Exogenously expressed Rnd3/RhoE co-localized with actin at the cell periphery and induced the localization of the adherens junction protein beta-catenin and the tight junction protein ZO-1 to sites of cell-cell contact, and led to the formation of highly sealed tight junctions. Treatment with glucocorticoids was not required to achieve complete apical junction remodeling. Consistent with Rnd3/RhoE acting as an antagonist of RhoA, expression of Rnd3/RhoE rescued the disruptive effects of constitutively active RhoA on apical junction organization. Our results demonstrate a new role for the Rho family member Rnd3/RhoE in regulating the assembly of the apical junction complex and tight junction sealing.

Alterations of DNA Copy Number and Expression in Genes Involved in Cell Cycle Regulation and Apoptosis Signal Pathways in γ-Radiation-Sensitive SX9 Cells and -Resistant SR-1 Cells

In the present study, genomic differences related to sensitivity to radiation were examined by comparative genomic hybridization and GeneChip 45K microarray in SX9 cells (radiation-sensitive) and their parental line, SR-1 (radiation-resistant). SX9 cells have defective DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity. DNA-PKcs is a DNA double-strand break repair protein that maintains chromosomal stability through nonhomologous end joining. However, the molecular basis of the radiation sensitivity of SX9 cells is unclear. Flow cytometry analysis showed that SR-1 and SX9 cells had a larger G2/M-phase population at 12 h after 4 Gy gamma irradiation, while only SR-1 cells progressed to G1/S at 24-36 h. SX9 and SR-1 cells had similar patterns of DNA copy number alteration, but the gains were observed on chromosome 9 (cent-E2), 11 (cent-A3), and 12 (C1-E) only in SX9 cells. Expression of genes located on those regions is higher in SX-9 cells than in SR1 cells, and the regions include genes associated with apoptosis and cell cycle regulation. Time-course data for gene expression at 0, 1, 3, 6 and 12 h after 4 Gy gamma irradiation revealed that the genes whose expression was altered in SX9 cells but not in SR-1 cells are in 16 clusters. Three of these clusters included genes for cell cycle regulation: JNK, PKC (PRKC) and ceramide cascade protein. These results suggest that amplification and altered expression of genes associated with cell cycle and apoptosis regulators in DNA-PK-deficient SX9 cells affect the differences in response to gamma radiation between SX9 and SR-1 cells.

Muscarinic receptors participation in angiogenic response induced by macrophages from mammary adenocarcinoma-bearing mice

Introduction

The role of macrophages in tumor progression has generated contradictory evidence. We had previously demonstrated the ability of peritoneal macrophages from LMM3 murine mammary adenocarcinoma-bearing mice (TMps) to increase the angiogenicity of LMM3 tumor cells, mainly through polyamine synthesis. Here we investigate the ability of the parasympathetic nervous system to modulate angiogenesis induced by TMps through the activation of the muscarinic acetylcholine receptor (mAchR).

Methods

Peritoneal macrophages from female BALB/c mice bearing a 7-day LMM3 tumor were inoculated intradermally (3 × 10⁵ cells per site) into syngeneic mice. Before inoculation, TMps were stimulated with the muscarinic agonist carbachol in the absence or presence of different muscarinic antagonists or enzyme inhibitors. Angiogenesis was evaluated by counting vessels per square millimeter of skin. The expression of mAchR, arginase and cyclo-oxygenase (COX) isoforms was analyzed by Western blotting. Arginase and COX activities were evaluated by urea and prostaglandin E₂ (PGE₂) production, respectively.

Results

TMps, which stimulate neovascularization, express functional mAchR, because carbachol-treated TMps potently increased new blood vessels formation. This response was completely blocked by preincubating TMps with pirenzepine and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), M₁ and M₃ receptor antagonists, and partly by the M₂ receptor antagonist methoctramine. M₁ receptor activation by carbachol in TMps triggers neovascularization through arginase products because N^ω-hydroxy-L-arginine reversed the agonist action. Preincubation of TMps with methoctramine partly prevented carbachol-stimulated urea formation. In addition, COX-derived liberation of PGE₂ is responsible for the promotion of TMps angiogenic activity by M₃ receptor. We also detected a higher expression of vascular endothelial growth factor (VEGF) in TMps than in macrophages from normal mice. Carbachol significantly increased VEGF expression in TMps, and this effect was totally reversed by methoctramine and pirenzepine. Arginase and COX inhibitors partly decreased VEGF derived from TMps.

Conclusion

TMps themselves induce a potent angiogenic response that is augmented by carbachol action. mAchR activation triggers arginine metabolism, PGE₂ synthesis and VEGF production, promoting neovascularization.

Salicylate inhibition of rat mammary carcinogenesis and angiogenesis in female rat compatible with misoprostol administration

Epidemiological data suggest that non-steroidal anti-inflammatory drugs prevent colon cancer. The evidence for other types of tumour is less conclusive, though animal and in vitro studies indicate that they may be effective against mammary cancer cells. We assessed the effect of dietary acetylsalicylic and salicylic acid against dimethylbenzanthracene-induced rat tumours. Tumour angiogenesis was also investigated to explore the mechanism responsible for salicylate effect. Mammary tumours were induced in female Sprague-Dawley rats fed with different amounts of acetylsalicylic and salicylic acid. Serum vascular endothelial growth factor concentrations were measured and vascularization of basement membrane proteins injected in vivo (Matrigel) was determined by evaluation of haemoglobin content to assess the extent to which angiogenesis was inhibited. Dimethylbenzanthracene-induced carcinogenesis was inhibited by both acids and there was a log-dose/response correlation between the tumour diameter and salicylate concentration. Salicylic acid seems more effective than acetylsalicylic acid. Vascular endothelial growth factor was less concentrated in treated animals than in the controls and so was Matrigel haemoglobin. The mechanism involved, however, is still uncertain, though concomitant inhibition of tumour angiogenesis may be an important component. The documented salicylate serum VEGF modulation is interesting also for presence of the flk-1 receptor in mammary tumour cells of our model. Although misoprostol is a prostaglandin analogous its concomitant administration did not compromise the salicylate anti-tumour effect.

Role of steroid hormones and prolactin in canine mammary cancer

In several animal studies, prolactin has been found to be essential for mammary epithelial development, and its administration has been consistently shown to increase the rate of mammary tumours. High levels of steroid hormones have also been suggested to enhance mammary cancer development. The present study investigates the levels of the following hormones in serum and in tissue homogenates in dogs bearing canine mammary tumours: prolactin (PRL), progesterone (P4), dehydroepiandrosterone (DHEA), androstenedione (A4), testosterone (T), 17beta-estradiol (17beta-E2) and estrone sulfate (S04E1). Eighty mammary tumours (40 dysplasias and benign and 40 malignant tumours) from 32 female dogs, and 10 normal mammary glands from eight female dogs without history of mammary tumours, were analysed. Prolactin and steroid hormones in serum and tissue homogenates, were analysed by enzyme immunoassays (EIA) techniques, previously validated for this animal species. Levels of prolactin in tissue homogenates were significantly different between malignant and benign mammary tumours (p<0.01). Serum prolactin concentrations were lower in the control group as compared with the group of dogs with benign tumours and in dogs with malignant tumours (p=0.01). Serum prolactin levels in dogs with benign lesions were not significantly different than those obtained from dogs with malignant tumours. Levels of steroid hormones were significantly higher in malignant tumours compared with the benign tumours and normal mammary glands (p<0.01) both in serum and homogenate determinations. Our results suggest that the canine neoplastic mammary gland could be a source of prolactin. Our hypothesis is that both prolactin and steroid hormones are involved in the growth of canine mammary cancer, and that they might have an autocrine/paracrine role in the maintenance of this disease.

Atm heterozygous deficiency enhances development of mammary carcinomas in p53 heterozygous knockout mice

Introduction

Ataxia-telangiectasia is an autosomal-recessive disease that affects neuro-immunological functions, associated with increased susceptibility to malignancy, chromosomal instability and hypersensitivity to ionizing radiation. Although ataxia-telangiectasia mutated (ATM) heterozygous deficiency has been proposed to increase susceptibility to breast cancer, some studies have not found excess risk. In experimental animals, increased susceptibility to breast cancer is not observed in the Atm heterozygous deficient mice (Atm^+/-) carrying a knockout null allele. In order to determine the effect of Atm heterozygous deficiency on mammary tumourigenesis, we generated a series of Atm^+/- mice on the p53^+/- background with a certain predisposition to spontaneous development of mammary carcinomas, and we examined the development of the tumours after X-irradiation.

Methods

BALB/cHeA-p53^+/- mice were crossed with MSM/Ms-Atm^+/- mice, and females of the F₁ progeny ([BALB/cHeA × MSM/Ms]F₁) with four genotypes were used in the experiments. The mice were exposed to X-rays (5 Gy; 0.5 Gy/min) at age 5 weeks.

Results

We tested the effect of haploinsufficiency of the Atm gene on mammary tumourigenesis after X-irradiation in the p53^+/- mice of the BALB/cHeA × MSM/Ms background. The singly heterozygous p53^+/- mice subjected to X-irradiation developed mammary carcinomas at around 25 weeks of age, and the final incidence of mammary carcinomas at 39 weeks was 31% (19 out of 61). The introduction of the heterozygous Atm knockout alleles into the background of the p53^+/- genotype significantly increased the incidence of mammary carcinoma to 58% (32 out of 55) and increased the average number of mammary carcinomas per mouse. However, introduction of Atm alleles did not change the latency of development of mammary carcinoma.

Conclusion

Our results indicate a strong enhancement in mammary carcinogenesis by Atm heterozygous deficiency in p53^+/- mice. Thus, doubly heterozygous mice represent a useful model system with which to analyze the interaction of heterozygous genotypes for p53, Atm and other genes, and their effects on mammary carcinogenesis.

Deregulation of Stat5 expression and activation causes mammary tumors in transgenic mice

Members of the signal transducers and activators of transcription (Stat) family regulate essential cellular growth and survival functions in normal cells and have also been implicated in tumorigenesis. We have studied the potential role of Stat5 in mammary tumorigenesis by targeting Stat5 variants to the mammary gland of transgenic mice using regulatory sequences of the beta-lactoglobulin gene. Mammary-directed expression of the wild-type Stat5, constitutively activated Stat5 and carboxyl-terminally truncated dominant negative Stat5 forms resulted in mammary tumors with incidence rates of up to 22% and latency periods of 8-12 months. Undifferentiated carcinomas most frequently occurred in mice expressing the carboxyl-terminally truncated Stat5. The more differentiated papillary and micropapillary adenocarcinomas were primarily found in mice overexpressing the native and constitutively active transgenes. Higher levels of translation initiation factor 4E (eIF4E) and cyclin D1 expression but lower levels of activated Stat3 were found in tumors of mice expressing the constitutively active Stat5 when compared to mice expressing the wild-type or truncated forms. A higher expression of the estrogen receptor (ERalpha) was observed in carcinomas compared to other phenotypes. The ability of both forms of Stat5, the transactivating form and the dominant negative form, to participate in oncogenesis indicates that there is more than one mechanism by which Stat5 contributes to this process. The transactivation function of Stat5 is involved in the determination of tumors with a more differentiated phenotype.

Bax regulates c-Myc-induced mammary tumour apoptosis but not proliferation in MMTV-c-myc transgenic mice

The expression of the proto-oncogene c-myc is frequently deregulated, via multiple mechanisms, in human breast cancers. Deregulated expression of c-myc contributes to mammary epithelial cell transformation and is causally involved in mammary tumorigenesis in MMTV-c-myc transgenic mice. c-Myc is known to promote cellular proliferation, apoptosis, genomic instability and tumorigenesis in several distinct tissues, both in vivo and in vitro. Expression of the proapoptotic regulatory gene bax is reduced or absent in human breast cancers, and c-Myc has been shown to regulate the expression of Bax, as well as cooperate with Bax in controlling apoptosis in a fibroblast model. Additionally, loss of bax reduces c-Myc-induced apoptosis in lymphoid cells and increases c-Myc-mediated lymphomagenesis in vivo. In order to assess whether loss of bax could influence c-Myc-induced apoptosis and tumorigenesis in the mammary gland in vivo, we generated MMTV-c-myc transgenic mice in which neither, one, or both wild-type alleles of bax were eliminated. Haploid loss of bax in MMTV-c-myc transgenic mice resulted in significantly reduced mammary tumour apoptosis. As anticipated for an apoptosis-regulatory gene, loss of the wild-type bax alleles did not significantly alter cellular proliferation in either mammary adenocarcinomas or dysplastic mammary tissues. However, in contrast to c-Myc-mediated lymphomagenesis, loss of one or both alleles of bax in MMTV-c-myc transgenic mice did not significantly enhance mammary tumorigenesis, despite evidence that haploid loss of bax might modestly increase mammary tumour multiplicity. Our results demonstrate that Bax contributes significantly to c-Myc-induced apoptosis in mammary tumours. In addition, they suggest that in contrast to c-Myc-induced lymphomagenesis, mammary tumorigenesis induced by deregulated c-myc expression requires some amount of Bax expression.

High-Fat Corn Oil Diet Promotes the Development of High Histologic Grade Rat DMBA-Induced Mammary Adenocarcinomas, While High Olive Oil Diet Does Not

Effects of a high corn oil and a high olive oil diet on the histopathologic characteristics of rat dimethylbenz(alpha)anthracene-induced mammary adenocarcinomas were investigated in comparison with those of a control low-fat diet. Two experimental series (A and B) studied the influence of a high corn oil diet on the initiation and the promotion of mammary carcinogenesis, while another one (C) assessed the effects of the two dietary lipids on the promotion. Nine parameters have been analyzed and a new histologic grading method, adapted to rat tumors, has been applied in each carcinoma. High corn oil diets, particularly when acting as promoters, associated with higher-grade carcinomas than control (p < 0.05) and high olive oil groups. Stromal invasion and tumoral necrosis were more prominent and a prevailing cribriform pattern was observed (p < 0.05). High olive oil diet adenocarcinomas exhibited a predominantly low histologic grade and few necrotic and invasive areas, similar to the control, and they presented the highest percentage of papillary areas. Lymphoplasmacytic and mast cell infiltration were also influenced by the dietary lipids. Thus, high corn oil diet adenocarcinomas presented a higher degree of morphological malignancy than control and high olive oil tumors, which is in line with the greater clinical malignancy described in rats from the former group and the non-promoting effect of the high olive oil diet. As far as we are concerned, a similar histopathologic approach of the effects of the dietary lipids on experimental breast cancer has not been carried out up to now.

Involvement of TGF-beta(s)/T(beta)Rs system in tumor progression of murine mammary adenocarcinomas

We studied the expression of TGF-beta/T(beta)R system and its biological role in tumor development, in M3 and MM3 murine mammary adenocarcinomas with different metastasizing capability and in LM3 and LMM3 derived cell lines. All the studied cells secreted TGF-beta(s) and expressed T(beta)Rs. While the proliferation of the poorly metastatic M3 cells was significantly inhibited by 4 ng/ml TGF-beta(s), the highly metastatic MM3 cells were only slightly inhibited in response to the highest dose used. LM3 and LMM3 cells, highly invasive and metastatic, were totally refractory to TGF-beta antiproliferative effect. The role of TGF-beta in modulating key proteolytic cascades in tumor progression was also studied. TGF-beta(s) enhanced metalloproteinases production in all the studied cells while induced a stimulatory net effect on plasmin system activity only in the more metastatic cells. Our results in this murine mammary tumor lineage support the concept that dissociation of TGF-beta regulated growth control versus proteolytic enzyme pathways promotes tumor dissemination.

Role of CXCR4 and SDF-1 in mammary tumor metastasis in the cat

It has recently been suggested that the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12) promote metastasis of various cancers in humans. Since feline mammary tumors also metastasize to distant organs frequently, we used real-time quantitative PCR to examine the expression of feline CXCR4 (fCXCR4) in ten feline mammary tumor cell lines and seven feline mammary tumor tissues, and also the expression of feline SDF-1 (fSDF-1) in various organs. Cell lines derived from metastatic regions expressed more fCXCR4 than those derived from primary tumors. Mammary tumor tissues overexpressed more fCXCR4 than normal mammary tissues. Organs with high levels of fSDF-1 expression represent common sites of metastasis. Migration assays using the feline mammary tumor cell line NAC were also performed to test the activity of TN14003 and TC14012, antagonists of human CXCR4, to antagonize fCXCR4 expressed on NAC cells. TN14003 and TC14012 inhibited migration of NAC cells. We conclude that fCXCR4 may be a therapeutic target for feline mammary tumors.

Role of the CDK inhibitor p27 (Kip1) in mammary development and carcinogenesis: insights from knockout mice

The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis. Some investigations of its role in mammary development have demonstrated reduced cyclin D1 expression and consequent lack of lobuloalveolar development, but others have found increased cyclin E-Cdk2 activity and increased proliferation balanced by increased apoptosis. It is unclear at present why these apparently divergent results have been obtained. Mice with reduced p27 gene dosage alone do not develop mammary carcinomas but do display substantially shorter tumor latency upon overexpression of erbB2, consistent with a role for p27 as a mammary tumor suppressor gene. In this review we summarize these and other data addressing the role of p27 in normal mammary epithelium and experimental models of mammary carcinogenesis.

Cell cycle genes in a mouse mammary hyperplasia model

Human mammary epithelial cells emerge spontaneously from senescence, exhibiting eroding telomeric sequences, and ultimately enter crisis to generate the type of chromosomal abnormalities seen in early stages of breast cancer. In a mouse mammary tumor model, the spontaneous escape of senescence can be observed as an increase in DNA synthesis that is reflected by alterations in the cell cycle profile and increases in the expression levels and activities of cell cycle molecular components. This review provides an overview of gene alterations in the cell cycle components in mouse mammary hyperplasia.

Cyclins and breast cancer

The D-type and E-type cyclins control the G(1) to S phase transition during normal cell cycle progression and are critical components of steroid- and growth factor-induced mitogenesis in breast epithelial cells. Mammary epithelial cell-specific overexpression of these genes leads to mammary carcinoma, while in cyclin D1-deficient mice mammary gland development is arrested prior to lobuloalveolar development. Cyclin D1 null mice are resistant to mammary carcinoma induced by the neu and ras oncogenes, indicating an essential role for cyclin D1 in the development of some mammary cancers. Cyclin D1 and E1 are commonly overexpressed in primary breast cancer, with some evidence of an association with an adverse patient outcome. This observation may result in part from their ability to confer resistance to endocrine therapies. The functional consequences of cyclin E overexpression in breast cancer are likely related to its role in cell cycle progression, whereas that of cyclin D1 may also be a consequence of a more recently defined role in transcriptional regulation.

Of mice and Myc: c-Myc and mammary tumorigenesis

The proto-oncogene c- myc is involved in regulating proliferation and apoptosis, and its deregulation via genomic and postgenomic mechanisms, contributes to the development and progression of multiple human cancers, including those of the breast. Deregulated expression of c-Myc also contributes to neoplastic transformation by altering cellular differentiation pathways and by facilitating mutagenesis through induction of genomic instability. Transgenic and gene-knockout mice are frequently utilized to resolve the mechanisms through which specific genes influence the development and progression of malignancies. In this review, we discuss how research findings obtained from various c- myc transgenic mammary tumor models help to improve our resolution of c-Myc's role both in tumorigenesis of the murine mammary gland and cancer of the human breast.

Lymphatic drainage on healthy and neoplasic mammary glands in female dogs: can it really be altered?

The purpose of this research was to study the mammary lymphatic drainage under a macroscopic and mesoscopic view, comparing the vascular pattern of healthy and neoplasic mammary glands injected with drawing ink alcoholic and fluorescein solutions, in 46 mongrel female dogs. The results pointed out that the thoracic gland is drained by the axillary lymph centre, but in mammary neoplasia either superficial cervical or ventral thoracic lymph centres can be involved. Cranial and caudal abdominal glands may be drained by the axillary, inguinofemoral and popliteal lymph centres. However, the popliteal drainage is specific for the healthy caudal abdominal mammary gland. The inguinal gland can be drained by both inguinofemoral and popliteal lymph centres in both neoplasic and healthy conditions. Regarding the mammary lymphatic communications, this research demonstrated that neoplasic glands present more types of anastomosis (40.9%), than healthy glands (33.33%), and an increase in contralateral anastomosis (50%) compared with healthy ones (33%). Given the data, the mammary neoplasia can change the lymphatic drainage pattern in terms of lymph centres and vascular arborization, thus forming new drainage channels and recruiting a larger number of lymph nodes. Lastly, some comments were made about the severity of a specific neoplasic mammary gland and conditions to be considered before making a decision in terms of the most adequate operative procedure, and suggestions for further investigations.

Transcriptional regulators in mammary gland development and cancer

The mammary gland represents a remarkable developmental system for the study of genetic programs underlying proliferation, differentiation and inductive tissue interactions. Mammary gland ontogeny occurs predominantly in the adult and involves a complex cycle of morphogenesis, with the continuous production, differentiation and apoptosis of mammary epithelial cells occurring with each pregnancy. Perturbations in pathways controlling any of these processes may lead to neoplasia. Substantial progress has been made in defining signaling pathways important for mammopoiesis, in particular those that mediate the effects of peptide and steroid hormones. However, much less is known about the transcriptional regulators that dictate cell specificity, proliferation and differentiation within the mammary gland. This review will discuss recent insights into the transcriptional networks important for mammary gland development and consider how deregulation of specific transcription factors contributes to the pathogenesis of breast cancer.

Long term inhibition by estradiol or progesterone of melatonin secretion after administration of a mammary carcinogen, the dimethyl benz(a)anthracene, in Sprague-Dawley female rat; inhibitory effect of Melatonin on mammary carcinogenesis

A single intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA) has been shown to induce mammary tumors in young cycling female Sprague-Dawley rats. The appearance of the tumors is preceded by a series of neuroendocrine disturbances, including attenuation of the preovulatory Luteinizing Hormone surge and Gonadotropin-Releasing Hormone release and amplification of the preovulatory 17beta-Estradiol (E2) surge. In this study, we examined the hypothesis that a single administration of DMBA increases the E2 and Progesterone inhibition of the spontaneous and Isoproterenol-induced Melatonin (MT) secretion from the pineal gland, during the latency phase. Also, the incidence of mammary tumors, as well as the possible preventive effect of various doses of Melatonin, were recorded up to 6 months after daily administration. For all studies, Sprague-Dawley rats, 55-60 days of age, received, on the Estrous day of the Estrous cycle, a single dose of 15 mg DMBA delivered by intragastric intubation. For the study on ovarian steroids, they were ovariectomized 5 days later and then sacrificed by decapitation at 10 a.m., one month later. Pineal glands were removed and placed in perifusion chambers containing Hanks 199 medium. The medium was saturated with O2/CO2 (95%/5%) and its pH was 7.4. Ten independent chambers were immersed in a water bath at 37 degrees C. Each pineal gland received medium (flow rate: 0.16 ml/min) through a system of input lines. The fractions were collected every 10 min, and immediately frozen at -20 degrees C until Melatonin RIA. Experiments were repeated to obtain up to five experimental points for each treatment. E2 (10(-11)-10(-9) M) and Progesterone (10(-9)-10(-7) M) were applied during the entire perifusion period (7 h). Isoproterenol (10(-6) M) was applied for 20 min after 2.5 h in perifusion. Melatonin concentrations and Areas Under the Curves were compared using two-factor ANOVA as well as parametric or nonparametric two-sample methods after testing sample normality. For the study on the possible preventive effect of Melatonin, they were daily treated, by the intragastric route, with increasing doses of Melatonin for 6 months. The percentage of female rats having at least one mammary carcinoma were compared using the Fischer exact t-test. During the latency phase, in vehicle-treated rats, E2 and Progesterone treatments lead an almost significant inhibition of the Isoproterenol-induced stimulation of Melatonin secretion. In DMBA-treated rats, E2 treatment leads to a complete blunting of the Isoproterenol-induced stimulation of Melatonin and Progesterone treatment leads to a cyclic inhibition of the Isoproterenol-induced Melatonin secretion. During the promotion phase, there was a dose-dependent inhibitory effect (up to 65% inhibition) of the daily administration of Melatonin, on mammary tumors occurrence. In conclusion, the long term inhibition of DMBA upon Melatonin secretion from the pineal gland might accelerate the promotion of mammary tumors induced by the mammary carcinogen. Inversely, the daily administration of Melatonin for 6 months induces a long lasting protective effect against the formation of mammary tumors.

An expression study of hormone receptors in spontaneously developed, carcinogen-induced and hormone-induced mammary tumors in female Noble rats

The Noble (Nb) rat model has been used in the study of hormonal carcinogenesis of mammary and prostate glands, as this rat strain is susceptible to tumor induction in these glands by hormonal treatments. Recently, we demonstrated that this rat strain can develop spontaneously mammary tumors at high incidence in aged animals and also show high sensitivity to chemical carcinogens (DMBA and MNU) and combined treatments with sex hormones in mammary tumor induction. In the present study, we examined and compared the expression of hormone receptors [including estrogen receptors (ERalpha and ERbeta), androgen receptor (AR), progesterone receptor (PR), prolactin receptor (PRLR)] and prolactin (PRL) by immunohistochemistry, Western blotting and RT-PCR in spontaneous mammary tumors, and mammary tumors induced by sex hormones (T+E2 and T+DES for 8-10 months) and DMBA in Nb rat model. Immunohistochemistry and Western blotting showed that both the spontaneously developed and hormone-induced carcinomas exhibited strong immunoreactivity of ERalpha, ERbeta, AR, PR and PRLR, while the spontaneous fibroadenomas showed weak to moderate immunoreactivity of ERalpha and PRLR, whereas the DMBA-induced carcinomas exhibited weak to moderate immunoreactivity of ERalpha, AR, PR and PRLR, and sporadic weak ERbeta immunoreactivity. RT-PCR analyses showed that mRNA expression pattern of these markers resembled that of proteins. In addition, weak mRNA expression of PRL was detected in spontaneous carcinomas and carcinomas induced by DMBA and hormones, suggesting that PRL could be produced locally within the tumors. The results showed that the expression status of hormone receptors and PRL was different in spontaneous mammary tumors and tumors induced by carcinogen or hormones, suggesting that the extent of involvement of steroid hormones and their receptors in the spontaneous, carcinogen- or hormone-induced mammary carcinogenesis might be different.

The role of prolactin in mammary carcinoma

The contribution of prolactin (PRL) to the pathogenesis and progression of human breast cancer at the cellular, transgenic, and epidemiological levels is increasingly appreciated. Acting at the endocrine and autocrine/paracrine levels, PRL functions to stimulate the growth and motility of human breast cancer cells. The actions of this ligand are mediated by at least six recognized PRL receptor isoforms found on, or secreted by, human breast epithelium. The PRL/PRL receptor complex associates with and activates several signaling networks that are shared with other members of the cytokine receptor superfamily. Coupled with the recently identified intranuclear function of PRL, these networks are integrated into the in vitro and in vivo actions induced by ligand. These findings indicate that antagonists of PRL/PRL receptor interaction or PRL receptor-associated signal transduction may be of considerable utility in the treatment of human breast cancer.