Estrogens regulate production of specific growth factors in hormone-dependent human breast cancer

Estrogen interacts with the IGF-1 system to protect nigrostriatal dopamine and maintain motoric behavior after 6-hydroxdopamine lesions

The most prominent neurochemical hallmark of Parkinson's disease (PD) is the loss of nigrostriatal dopamine (DA). Animal models of PD have concentrated on depleting DA and therapies have focused on maintaining or restoring DA. Within this context estrogen protects against 6-hydroxdopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesions of the nigrostriatal DA pathway. Present studies tested the hypothesis that neuroprotective estrogen actions involve activation of the insulin-like growth factor-1 (IGF-1) system. Ovariectomized rats were treated with either a single subcutaneous injection of 17beta-estradiol benzoate or centrally or peripherally IGF-1. All rats were infused unilaterally with 6-OHDA into the medial forebrain bundle (MFB) to lesion the nigrostriatal DA pathway. Tyrosine hydroxylase (TH) immunocytochemistry confirmed that rats injected with 6-OHDA had a massive loss of TH immunoreactivity in both the ipsilateral substantia nigra compacta (60% loss) and the striatum (>95% loss) compared to the contralateral side. Loss of TH immunoreactivity was correlated with loss of asymmetric forelimb movements, a behavioral assay for motor deficits. Pretreatment with estrogen or IGF-1 significantly prevented 6-OHDA-induced loss of substantia nigra compacta neurons (20% loss) and TH immunoreactivity in DA fibers in the striatum (<20% loss) and prevented the loss of asymmetric forelimb use. Blockage of IGF-1 receptors by intracerebroventricular JB-1, an IGF-1 receptor antagonist, attenuated both estrogen and IGF-1 neuroprotection of nigrostriatal DA neurons and motor behavior. These findings suggest that IGF-1 and estrogen acting through the IGF-1 system may be critical for neuroprotective effects of estrogen on nigrostriatal DA neurons in this model of PD.

Estrogen and its metabolites are carcinogenic agents in human breast epithelial cells

Estrogens play a crucial role in the development and evolution of human breast cancer. However, it is still unclear whether estrogens are carcinogenic to the human breast. There are three mechanisms that have been considered to be responsible for the carcinogenicity of estrogens: receptor-mediated hormonal activity, a cytochrome P450 (CYP)-mediated metabolic activation, which elicits direct genotoxic effects by increasing mutation rates, and the induction of aneuploidy by estrogen. To fully demonstrate that estrogens are carcinogenic in the human breast through one or more of the mechanisms explained above it will require an experimental system in which, estrogens by itself or one of the metabolites would induce transformation phenotypes indicative of neoplasia in HBEC in vitro and also induce genomic alterations similar to those observed in spontaneous malignancies. In order to mimic the intermittent exposure of HBEC to endogenous estrogens, MCF-10F cells that are ERalpha negative and ERbeta positive were first treated with 0, 0.007, 70 nM and 1 microM of 17beta-estradiol (E(2)), diethylstilbestrol (DES), benz(a)pyrene (BP), progesterone (P), 2-OH-E(2), 4-hydoxy estradiol (4-OH-E(2)) and 16-alpha-OH-E(2) at 72 h and 120 h post-plating. Treatment of HBEC with physiological doses of E(2), 2-OH-E(2), 4-OH-E(2) induce anchorage independent growth, colony formation in agar methocel, and reduced ductulogenic capacity in collagen gel, all phenotypes whose expression are indicative of neoplastic transformation, and that are induced by BP under the same culture conditions. The presence of ERbeta is the pathway used by E(2) to induce colony formation in agar methocel and loss of ductulogenic in collagen gel. This is supported by the fact that either tamoxifen or the pure antiestrogen ICI-182,780 (ICI) abrogated these phenotypes. However, the invasion phenotype, an important marker of tumorigenesis is not modified when the cells are treated in presence of tamoxifen or ICI, suggesting that other pathways may be involved. Although we cannot rule out the possibility, that 4-OH-E(2) may interact with other receptors still not identified, with the data presently available the direct effect of 4-OH-E(2) support the concept that metabolic activation of estrogens mediated by various cytochrome P450 complexes, generating through this pathway reactive intermediates that elicit direct genotoxic effects leading to transformation. This assumption was confirmed when we found that all the transformation phenotypes induced by 4-OH-E(2) were not abrogated when this compound was used in presence of the pure antiestrogen ICI. The novelty of these observations lies in the role of ERbeta in transformation and that this pathway can successfully bypassed by the estrogen metabolite 4-OH-E(2). Genomic DNA was analyzed for the detection of micro-satellite DNA polymorphism using 64 markers covering chromosomes (chr) 3, 11, 13 and 17. We have detected loss of heterozygosity (LOH) in ch13q12.2-12.3 (D13S893) and in ch17q21.1 (D17S800) in E(2), 2-OH-E(2), 4-OH-E(2), E(2) + ICI, E(2) + tamoxifen and BP-treated cells. LOH in ch17q21.1-21.2 (D17S806) was also observed in E(2), 4-OH-E(2), E(2)+ICI, E(2)+tamoxifen and BP-treated cells. MCF-10F cells treated with P or P+E(2) did not show LOH in the any of the markers studied. LOH was strongly associated with the invasion phenotype. Altogether our data indicate that E(2) and its metabolites induce in HBEC LOH in loci of chromosomes 13 and 17, that has been reported in primary breast cancer, that the changes are similar to those induced by the chemical carcinogen (BP) and that the genomic changes were not abrogated by antiestrogens.

17Beta-estradiol is carcinogenic in human breast epithelial cells

The association found between breast cancer development and prolonged exposure to estrogen suggests that this hormone is of etiologic importance in the causation of this disease. In order to prove this postulate, we treated the immortalized human breast epithelial cells (HBEC) MCF-10F with 17beta-estradiol (E(2)) for testing whether they express colony formation in agar methocel, or colony efficiency (CE), and loss of ductulogenesis in collagen matrix, phenotypes also induced by the carcinogen benz[a]pyrene (BP). MCF-10F cells were treated with 0.0, 0.007, 70nM, or 0.25mM of E(2) twice a week for 2 weeks. CE increased from 0 in controls to 6.1, 9.2, and 8.7 with increasing E(2) doses. Ductulogenesis was 75 +/- 4.9 in control cells; it decreased to 63.7 +/- 28.8, 41.3 +/- 12.4, and 17.8 +/- 5.0 in E(2)-treated cells, which also formed solid masses or spherical formations lined by a multilayer epithelium, whose numbers increased from 0 in controls to 18.5 +/- 6.7, 107 +/- 11.8 and 130 +/- 10.0 for each E(2) dose. MCF-10F cells were also treated with 3.7 microM of progesterone (P) and the CE was 3.39 +/- 4.05. At difference of E(2), P does not impaired the ductulogenic capacity. Genomic analysis revealed that E(2)-treated cells exhibited loss of heterozigosity in chromosome 11, as detected using the markers D11S29 and D11S912 mapped to 11q23.3 and 11q24.2-25, respectively These results also indicate that E(2), like the chemical carcinogen BP, induces in HBEC phenotypes indicative of neoplastic transformation.

Carcinogenicity of estrogens in human breast epithelial cells

Epidemiological and clinical evidences indicate that breast cancer risk is associated with prolonged ovarian function that results in elevated circulating levels of steroid hormones. Principal among these is estrogen, which is associated with two important risk factors, early onset of menarche and late menopause. However, up to now there is no direct experimental evidence that estrogens are responsible of the initiation of human breast cancer. We postulate that if estrogens are causative agents of this disease, they should elicit in human breast epithelial cells (HBEC) genomic alterations similar to those exhibited by human breast cancers, such as DNA amplification and loss of genetic material representing tumor suppressor genes. These effects could result from binding of the hormone to its nuclear receptors (ER) or from its metabolic activation to reactive metabolites. This hypothesis was tested by treating with the natural estrogen 17beta-estradiol (E2) and the synthetic steroid diethylstilbestrol (DES) MCF-10F cells, a HBEC line that is negative for ER. Cells treated with the chemical carcinogen benzo (a) pyrene (BP) served as a positive control of cell transformation. BP-, E2-, and DES-treated MCF-10F cells showed increases in survival efficiency and colony efficiency in agar methocel, and loss of ductulogenic capacity in collagen gel. The largest colonies were formed by BP-treated cells, becoming progressively smaller in DES- and E2-treated cells. The loss of ductulogenic capacity was maximal in BP-, and less prominent in E2- and DES-treated cells. Genomic analysis revealed that E2- and DES-treated cells exhibited loss of heterozygosity in chromosomes 3 and 11, at 3p21, 3p21-21.2, 3p21.1-14.2, and 3p14.2 14.1, and at 11q23.3 and 11q23.1-25 regions, respectively. It is noteworthy that these loci are also affected in breast lesions, such as ductal hyperplasia, carcinoma in situ, and invasive carcinoma. Our data are the first ones to demonstrate that estrogens induce in HBEC phenotypic changes indicative of cell transformation and that those changes are associated with significant genomic alterations that might unravel new pathways in the initiation of breast cancer.

Sequence analysis of the DNA binding domain of the estrogen receptor gene in ER (+)/PR (-) breast cancer

Estrogen stimulates the proliferation of breast cancer cells and regulates the expression of other proteins, including the progesterone receptor (PR), via interaction with a unique estrogen receptor (ER), a ligand-inducible transcription factor that binds to regulatory DNA sequences associated with target genes. The best indirect evidence of an intact ER gene signaling system in a tumor is the demonstration of both ER and PR cytosol protein. The molecular basis of the ER (+)/PR (-) phenotype is unknown and may reflect either defective PR gene expression or alterations in the ER-specifically, inability of the ligand-receptor complex to effectively bind to regulatory sequences in DNA. To test the latter possibility, we evaluated 10 ER (+)/PR (-) resected human breast cancers for small deletions and point mutations in the DNA binding domain of the ER gene. Exons 2 and 3 and their flanking intron sequences were selectively amplified using the polymerase chain reaction and then directly sequenced using the Sanger dideoxynucleotide method. A normal gene sequence was found in all cases studied. We conclude that sequence aberrations in the DNA binding domain of the ER are not a common cause of absent PR expression in ER (+)/PR (-) breast carcinomas.

The spatial and temporal expression of the alpha 2 beta 1 integrin and its ligands, collagen I, collagen IV, and laminin, suggest important roles in mouse mammary morphogenesis

To begin to determine the role of the alpha 2 beta 1 integrin and its ligands, collagen I, collagen IV, and laminin, in mammary epithelial differentiation in vivo, we determined the expression of these molecules by in situ hybridization and immunofluorescence in the developing mouse mammary gland. Expression of collagen I, collagen IV, and laminin mRNAs in the mammary gland during puberty corresponded to the period of greatest growth of the gland, 4-7 weeks postnatally. Collagen I expression preceded collagen IV expression, both of which preceded laminin expression, suggesting an important temporal sequence of extracellular matrix (ECM) production. When growth of the epithelium ceased in the adult virgin gland, expression of all three mRNAs became undetectable. Following the onset of pregnancy these molecules were re-expressed with the same chronology observed during puberty. Collagen I, collagen IV, and laminin were expressed by stromal cells immediately surrounding the developing ductal epithelium. Surprisingly, we found no expression of ECM components in the epithelial cells, suggesting the mammary epithelium does not synthesize its own basement membrane. The distribution of collagen I was consistent with a role in duct formation, since collagen I was strikingly abundant around larger mammary ducts, but was sparse around growing endbuds or alveoli. Conversely, there was abundant laminin near growing endbuds and around alveoli, and less around large ducts, suggesting its role is different than collagen I. The alpha 2 beta 1 integrin was present on the basal, lateral, and apical surfaces of the mammary epithelium throughout postnatal development and pregnancy. The alpha 2 beta 1 integrin expression was strongest at midpregnancy, suggesting a role for alpha 2 beta 1 integrin in the alveolar formation that occurs at this time. The alpha 2 beta 1 integrin expression decreased dramatically in the lactating gland. Our results suggest that alpha 2 beta 1 integrin interactions with its temporally and spatially regulated ligands, collagen I, collagen IV, and laminin, could play an important role in mammary morphogenesis in vivo.

Expression of epidermal growth factor receptor (proto-oncogene c-erbB-1) and estrogen receptor in human breast carcinoma. An immunocytochemical study of 70 cases

In vitro studies have shown that growth factors may mediate the growth stimulatory effect of estrogen in hormone-dependent human breast carcinomas while the constitutive expression of same growth factors might by-pass the need for estrogenic stimulus in hormone-independent neoplasms. We have performed immunocytochemical analysis of the expression of epidermal growth factor receptor (EGF-R or proto-oncogen c-erbB-1) and estrogen receptor (ER) in 70 cases of human breast carcinoma. We found an inverse relationship between the expression of EGF-R and ER (Kendall's tau b = -0.1997, P < 0.03), which prompts us to conclude that ER(-) breast carcinomas may grow in a hormone-independent manner through the over-expression of the proto-oncogene c-erbB-1, which is the receptor for epidermal (EGF) and alpha transforming (TGFalfa) growth factors.

Changes in the hormone dependency of epithelial cell proliferation in the genital tract of mice following neonatal oestrogen treatment

The genital tract epithelium of the female laboratory mouse has been widely studied as a model of oestrogen-dependent growth and proliferation. Perturbation of the hormonal imprinting of these tissues during neonatal development has also been used to study the development of pathological abnormalities, particularly in the cervical epithelium. This study demonstrates that mice treated neonatally from days 1-5 with supraphysiological concentrations of oestrogen are able to maintain high levels of proliferation following the removal of the ovaries later in adult life. This high level of proliferation was shown to be independent of the ovarian oestrogens and of oestrogens produced peripherally by aromatisation. These results suggest conversion of the genital tract in these mice to a fully hormonal "independent" state. However, neonatal treatment with oestrogen was not found to produce a uniform change to hormonal independence. Further challenge of the adult ovariectomised mice with oestrogen, demonstrated that a population of cells still retained the ability to respond to the mitogenic influence of this hormone.

Breast cancer

Breast cancer will affect 1 out of 10 women in the United States and cause 27 deaths per 100,000 women per year. The etiology remains unknown, but the incidence correlates with genetic as well as environmental factors. Screening programs have been shown to prolong the survival by early detection compared with control populations but remain underutilized by physicians and patients. Breast disease can be evaluated by physical examination and mammography and a definitive diagnosis made by needle aspiration, needle biopsy, or excisional biopsy. This allows the patient to participate in the decision regarding mastectomy vs. conservative surgery plus radiation therapy. These two approaches have equivalent survival in selected patients. Patients with locally advanced, nonmetastatic disease benefit from a multidisciplinary approach using preoperative chemotherapy and postoperative radiation therapy. This approach has allowed less disfiguring surgery and improved survival. Preinvasive carcinoma is diagnosed more frequently with the increased use of screening mammography. Local therapy options include simple mastectomy, local excision plus radiation, or local excision alone. The natural history and results of therapy in preinvasive disease are evolving as more data are accumulated. Systemic adjuvant therapy is recommended for all node-positive patients and most node-negative patients with invasive cancer. The specific modality (hormonal or cytotoxic) varies with the subgroup involved. Treatment of metastatic disease to palliate symptoms and prolong survival includes the use of local therapies (surgery and radiation) and hormonal and cytotoxic agents. Most patients benefit, but cure has been unobtainable. Newer approaches utilizing high-dose chemotherapy and bone marrow support with growth factors or autologous transplantation are currently being explored.

Hormone prevention of mammary carcinogenesis by norethynodrel-mestranol

The observation that the susceptibility of the mammary gland to chemical carcinogenesis is inversely related to its level of hormonally induced differentiation led us to test whether treatment of virgin rats with an estrogenic-progestagenic hormone combination protected the gland against this carcinogenesis. Virgin Sprague-Dawley rats aged 45, 55, 65, or 75 days had implanted subcutaneously for 21 days a pellet containing norethynodrel-mestranol (NM) (98.5%-1.5%) at two doses, a physiological or low dose (LD) of 0.5 mg, equivalent to the dose used in Enovid for contraception in humans, and a pharmacological or high dose (HD) of 5.0 mg. Twenty-one days after NM pellet removal, the mammary glands of 5 animals per group were examined for the number of terminal end buds (TEBs), terminal ducts (TDs), alveolar buds (ABs) and lobules, and the DNA labeling index (DNA-LI). The remaining animals received 8 mg 7,12-dimethylbenz(a) anthracene (DMBA)/100 g body weight, and tumorigenesis was evaluated at 24 weeks. The percentage of TEBs decreased with age, and further with NM treatment at both doses. Treatment did not significantly modify the percentage of TDs, but increased that of ABs in most groups. The DNA-LI of TEBs remained constant, even during aging and after treatment, whereas both aging and treatment reduced DNA-LI in TDs and ABs. Tumor incidence declined with increasing age from 75% to 44% in the 45 and 75 day-old control groups respectively. Adenocarcinoma incidence followed the same trend. NM treatment had a dose-related protective effect against development of tumors in general and of adenocarcinomas in particular. LD treatment resulted in a marginally significant reduction in adenocarcinoma incidence, whereas HD-treated animals were 0.24 times as likely as controls to develop carcinomas. There was a statistically significant correlation between the percentage of TEBs present in the gland at the time of carcinogen administration and the incidence of adenocarcinomas. It was concluded that treatment of virgin rats with the hormone combination norethynodrel-mestranol resulted in long lasting structural changes in the mammary gland which protected this organ from a subsequent carcinogenic insult.

Human trophoblast xenografts in athymic mice: a model for peripheral aromatization

A novel procedure was developed for evaluating aromatase inhibitors using human enzyme in a rodent model. Human choriocarcinoma trophoblast (JAr line) cells injected subcutaneously into athymic nude mice develop into tumor xenografts in 7-14 days which represent sites for peripheral aromatization of androgens. The rapid growth of these trophoblast tumors is estrogen independent. The tumors provide a source of nonovarian human tissue which has relatively high levels of enzyme activity (248 +/- 12 pmol estrogen/g/h) for biochemical determination of in vivo aromatase inhibition. These are major advantages for pharmacological evaluations in comparison to the slow tumor growth response of most carcinogen-induced rodent mammary cancers, which are usually devoid of aromatase activity. In addition, the hormonal dependent components of rodent mammary tumors require several weeks to regress as a result of the indirect effects of estrogen deprivation on tumor growth via inhibition of prolactin dependency, a minor component relative to the role estrogen occupies in hormonally-dependent breast cancer in humans. This model of peripheral aromatization was utilized to evaluate in vivo pharmacological parameters of MDL 18,962 (10-(2-propynyl)estr-4-ene-3,17-dione) such as bioavailability of several formulations, time course and dose responses following different routes of drug administration, pharmacokinetics and tissue distribution of [14C]MDL 18,962. Tumor aromatase activities of trophoblast xenografts were significantly (P less than or equal to 0.05) inhibited when MDL 18,962 was administered intravenously, orally, subcutaneously, or via subcutaneous silastic implants. The ED50 of MDL 18,962 for tumor aromatase inhibition at 6 h after a single treatment was 1.4 mg/kg, s.c. and 3.0 mg/kg, orally. MDL 18,962 blocked aromatase activity more effectively in human trophoblast than in mouse ovarian tissue. Human trophoblast aromatase activity was inhibited by 70% following a single oral dose of 100 mg/kg of MDL 18,962, while the host's ovarian aromatase activity exhibited only marginal inhibition. In vitro, the addition of 10 microM MDL 18,962 to trophoblast tumor cytosol or mouse ovarian cytosol resulted in 99.6 and 91.4% inhibition of aromatase activity, respectively. Tissue distribution of [14C]MDL 18,962 was predominantly associated with endocrine tissues with aromatase activity and organ systems involved in steroid metabolism and excretion. These in vivo data show that MDL 18,962 an enzyme-activated aromatase inhibitor, causes prolonged aromatase inhibition in the absence of saturating levels of inhibitor.

Receptors for epidermal growth factor and estradiol in canine mammary tumors

Both growth factors and steroid hormones are known to be associated with breast cancer. We have studied the epidermal growth factor receptor (EGFR) in canine mammary tumors and have shown the presence of a single class of 125I-EGF binding receptor sites in 9 out of 13 (70%) tumors, using Scatchard plot. The dissociation constant (KD) was 10(-9)M. An inverse correlation between EGFR and estrogen receptor (ER) was observed in 54% of the tumors. Our data suggest that EGFR might be used as a biochemical marker in canine mammary tumors.

Estrogen and oncogene mediated growth regulation of human breast cancer cells

The mechanism of growth control in estrogen-dependent and -independent human breast cancer is not completely understood. We have used both hormonally responsive and unresponsive breast cancer cells in culture to study the role of estrogens, oncogenes, and growth factors in their malignant transformation. MCF-7, an estrogen-receptor containing cell line, requires estradiol for tumor formation in vivo and is growth stimulated by estradiol and growth inhibited by antiestrogens in vitro. The growth regulation of MCF-7 cells by estrogens and antiestrogens may be linked to changes in several growth-related enzymes and polypeptide growth factors. Growth-acting polypeptides that are estradiol-inducible include IGF-I, TGF-alpha, and PDGF. Induction of at least two growth-related enzymes, thymidine kinase and dihydrofolate reductase is by transcriptional regulation of their mRNAs. To understand the natural progression of human breast cancer, we have experimentally constructed a hormone-independent fully tumorigenic cell line from the non-tumorigenic MCF-7 cells by introduction of an activated oncogene, v-rasH, into these cells by DNA-mediated gene transfer. Acquisition of the activated ras gene confers hormone autonomy on the previously hormone-dependent tumorigenicity and results in upregulation in secretion of some of the growth factors in amounts compared to estradiol stimulation. The transfected cells also become refractory to growth regulation by estradiol and antiestrogens in culture, although estrogen responses persist. Hormone-independent breast cancer cells in culture show high constitutive growth factor secretion. Direct infusion of some of the authentic growth factors and medium conditioned by estrogen-independent cells into athymic ovariectomized mice suggests a direct involvement of some of the polypeptides in the in vivo progression of tumors by these cells. Thus, aberrant production of growth factors, triggered either by activated oncogenes and estrogen stimulation in hormone-dependent cells, or by increased constitutive production in hormone-independent cells may in an autocrine, paracrine, or endocrine manner be associated with neoplastic growth of breast cancer.