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).

The tumour suppressor C/EBPδ inhibits FBXW7 expression and promotes mammary tumour metastasis

Inflammation and hypoxia are known to promote the metastatic progression of tumours. The CCAAT/enhancer-binding protein-δ (C/EBPδ, CEBPD) is an inflammatory response gene and candidate tumour suppressor, but its physiological role in tumourigenesis in vivo is unknown. Here, we demonstrate a tumour suppressor function of C/EBPδ using transgenic mice overexpressing the Neu/Her2/ERBB2 proto-oncogene in the mammary gland. Unexpectedly, this study also revealed that C/EBPδ is necessary for efficient tumour metastasis. We show that C/EBPδ is induced by hypoxia in tumours in vivo and in breast tumour cells in vitro, and that C/EBPδ-deficient cells exhibit reduced glycolytic metabolism and cell viability under hypoxia. C/EBPδ supports CXCR4 expression. On the other hand, C/EBPδ directly inhibits expression of the tumour suppressor F-box and WD repeat-domain containing 7 gene (FBXW7, FBW7, AGO, Cdc4), encoding an F-box protein that promotes degradation of the mammalian target of rapamycin (mTOR). Consequently, C/EBPδ enhances mTOR/AKT/S6K1 signalling and augments translation and activity of hypoxia-inducible factor-1α (HIF-1α), which is necessary for hypoxia adaptation. This work provides new insight into the mechanisms by which metastasis-promoting signals are induced specifically under hypoxia.

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.