Adult human mesenchymal stem cells enhance breast tumorigenesis and promote hormone independence

Adult human mesenchymal stem cells (hMSCs) have been shown to home to sites of breast cancer and integrate into the tumor stroma. We demonstrate here the effect of hMSCs on primary breast tumor growth and the progression of these tumors to hormone independence. Co-injection of bone marrow-derived hMSCs enhances primary tumor growth of the estrogen receptor-positive, hormone-dependent breast carcinoma cell line MCF-7 in the presence or absence of estrogen in SCID/beige mice. We also show hormone-independent growth of MCF-7 cells when co-injected with hMSCs. These effects were found in conjunction with increased immunohistochemical staining of the progesterone receptor in the MCF-7/hMSC tumors as compared to MCF-7 control tumors. This increase in PgR expression indicates a link between MCF-7 cells and MSCs through ER-mediated signaling. Taken together, our data reveal the relationship between tumor microenvironment and tumor growth and the progression to hormone independence. This tumor stroma-cell interaction may provide a novel target for the treatment of estrogen receptor-positive, hormone-independent, and endocrine-resistant breast carcinoma.     

Relationship of monoclonal antibody binding to estrogen and progesterone receptor content in breast cancer

Three monoclonal antibodies--H59, H71, and H72--which react with human breast cancers have been developed using the estrogen-dependent human breast cancer cell line, ZR-75-1, as the immunogen. H59 bound only to estrogen receptor-positive, estrogen-regulated breast cancer cells in culture, whereas H71 and H72 bound breast cancer cells irrespective of the estrogen receptor content. All three antibodies have minimal cross-reactivity with non-breast tissue culture cell lines. The three antigens appear to be glycoproteins located on the cell surface. H59 and H72 antigens bound preferentially to the apical surface of duct cells and may be secreted; H71 antigen demonstrated no evidence of an apical orientation or secretion. The binding of the antibodies to fixed cryosections from 152 breast cancer and 111 benign breast disease specimens has been evaluated using a radioimmunoassay. Eighty-five % of breast cancer and almost 100% of benign disease specimens were bound by at least one antibody. H59 bound 39%, H71 bound 51%, and H72 bound 65% of cancer specimens. Estrogen receptor and progesterone receptor analyses were obtained on 141 specimens. H59 bound almost exclusively to tumor specimens which contained estrogen and/or progesterone receptor, but not to all receptor-positive tumors. Therefore, the H59 antigen appeared to be present on a subset of estrogen receptor-positive tumors. Considering that it bound only to estrogen-regulated cells in culture, the antigen may be estrogen regulated, and its presence may predict a response to hormone therapy. H71 and H72 recognized cell surface differentiation antigens but bound tumor specimens regardless of the receptor content. These antibodies may be useful as independent variables for predicting response to therapy and prognosis of patients with breast cancer.     

Molecular classes of breast cancer and their clinical relevance

Hierarchical clustering of gene expression profiles has shown that breast cancers can be separated into subclasses characterized by distinct gene profiles. It has been known for decades that breast cancer may be classified into estrogen receptor-positive versus estrogen receptor-negative tumors and, more recently, it was discovered that breast cancer may be classified into tumors amplified versus not amplified for human epidermal growth factor receptor-2 (HER-2). Now, with the use of gene expression profiling, estrogen receptor-positive tumors can be separated into luminal A class and B class tumors, revealing different prognoses and most likely different endocrine sensitivity. Much effort has been focused on characterizing the “triple-negative” tumors (basal cell-like and normal breast cell-like classes). The finding that these tumors, similar to tumors among BRCA1/BRAC2 mutation carriers, may respond to poly(adenosine diphosphate ribose) polymerase inhibitors has led to a targeted therapy approach and suggests defects in DNA repair are also a characteristic of basal cell-like tumors in patients harboring wild-type BRCA1.     

Effects of estrogen on the proportion of stem cells in the breast

There is increasing evidence that breast cancers contain tumor-initiating cells with stem cell properties. The importance of estrogen in the development of the mammary gland and in breast cancer is well known, but the influence of estrogen on the stem cell population has not been assessed. We show that estrogen reduces the proportion of stem cells in the normal human mammary gland and in breast cancer cells. The embryonic stem cell genes NANOG, OCT4, and SOX2 are expressed in normal breast stem cells and at higher levels in breast tumor cells and their expression decreases upon differentiation. Overexpression of each stem cell gene reduces estrogen receptor (ER) expression, and increases the number of stem cells and their capacity for invasion, properties associated with tumorigenesis and poor prognosis. These results indicate that estrogen reduces the size of the human breast stem cell pool and may provide an explanation for the better prognosis of ER-positive tumors.     

Acquired tamoxifen resistance: correlation with reduced breast tumor levels of tamoxifen and isomerization of trans-4-hydroxytamoxifen

Acquired tamoxifen resistance represents a major cause of treatment failure in breast cancer. We implanted estrogen receptor-positive MCF-7 human breast cancer cells in athymic nude BALB/c mice as a model to study in vivo acquired tamoxifen resistance. After 4-6 months of tumor growth suppression by trans-tamoxifen, tumor progression was observed despite continued tamoxifen administration. Acquired resistance was not due to loss of estrogen receptors, to alterations in serum or tumor estrogen levels, or to changes in tamoxifen or its major metabolites in serum. Tamoxifen-resistant tumors remained estrogen dependent in vivo. However, resistance was also associated with the ability of tamoxifen to stimulate tumor growth. Resistant tumors were characterized by markedly lower intracellular tamoxifen levels and by isomerization of the potent antiestrogenic metabolite trans-4-hydroxy-tamoxifen to the less potent cis isomer. Metabolic tolerance, as manifested by alterations in cellular concentrations of tamoxifen and its metabolites, may thus be one mechanism for acquired tamoxifen resistance in breast cancer.     

Estrogen enhances the efficacy of an oncolytic HSV-1 mutant in the treatment of estrogen receptor-positive breast cancer

Oncolytic herpes simplex virus-1 (HSV-1) mutants selectively replicate in and lyse tumor cells. Viral replication is dependent on the cellular proliferative mechanism. Estrogen increases cellular proliferation and decreases apoptosis in estrogen receptor-positive (ER+) human breast cancer cells. We hypothesize that the cellular changes produced by estrogen may enhance oncolytic viral replication and improve the treatment of ER+ breast cancer cells. Estrogen increased proliferation and replication of the HSV-1 mutant, NV1066, in ER+ breast cancer cells. Additionally, cells grown with estrogen had lower rates of apoptosis and higher bcl-2 levels at baseline and after infection. Estrogen enhanced the oncolytic effect of NV1066, with cell kills of 95% and 97% at MOIs of 0.1 and 0.5, compared to 53 and 87% respectively without estrogen (p<0.001). Therapy of ER+ human breast cancer cells with a replication-competent HSV-1 mutant is improved in the presence of estrogen, in contrast to more standard therapies, such as chemotherapy and radiation, which demonstrate decreased efficacy in similar conditions. These data provide the mechanistic basis for the use of oncolytic HSV-1 in patients with hormone receptor-positive breast cancer, particularly if the disease progresses with conventional therapies.     

Cellular and molecular targets of estrogen in normal human breast tissue

To gain insight into the in vivo role of estrogen, we isolated estrogen receptor-positive cells fromnormal human breast tissue using a recombinant adenovirus that expresses green fluorescence protein in response to estrogen. We compared the global gene expression profile of these estrogen receptor-positive cells with that of various normal and cancerous mammary epithelial cells and identified several genes not implicated previously in estrogen signaling. One of these genes, lipocalin 2, is a putative in vivo estrogen target gene and paracrine factor that mediates the growth regulatory effects of estrogen in normal breast epithelium. These results demonstrate that normal and cancerous estrogen receptor-positive cells are distinct at the molecular level and suggest that lipocalin 2 is a new therapeutic target for breast cancer prevention and treatment.     

Role of Androgen Excess in the Development of Estrogen Receptor-positive and Estrogen Receptor-negative Breast Cancer

The androgen-excess theory posits a central role of androgens in promoting breast cancer development. At first glance, this appears to contradict the currently accepted central role of estrogens in this process, but as we will show, the apparent contradiction is not a real one. In the present article, we review the mechanisms by which androgen excess may stimulate cancer growth in different subsets of estrogen receptor-positive and estrogen receptor-negative tumors. We also propose an endocrine classification of postmenopausal breast cancer based on the simultaneous evaluation of a patient's serum testosterone levels and the estrogen receptor status of the tumor. This classification identifies several different subsets of tumors and may have important clinical implications.     

Nuclear matrix proteins associated with DNA in situ in hormone-dependent and hormone-independent human breast cancer cell lines

The nuclear matrix is a dynamic RNA-protein complex that organizes chromatin and regulates nuclear DNA metabolism. Nuclear matrix proteins informative in the diagnosis of cancer have been identified. Here, the nuclear matrix breast cancer proteins (NMBCs) cross-linked to nuclear DNA in situ with cisplatin in human breast cancer cell lines were analyzed by two-dimensional gel electrophoresis. We identified NMBCs that were differentially associated with nuclear DNA of hormone-dependent and -independent breast cancer cell lines. Three DNA cross-linked NMBCs were found to be exclusive to estrogen receptor-positive, hormone-dependent breast cancer cells, whereas two NMBCs were observed only in estrogen receptor-negative, hormone-independent breast cancer cells. Changes in these NMBCs were observed when hormone-dependent breast cancer cells became hormone independent. Furthermore, we show that the intermediate filament protein vimentin is associated with the nuclear DNA of MDA-MB-231 breast cancer cells, an estrogen receptor-negative, hormone-independent breast cancer cell line with high metastatic potential. These nuclear matrix DNA-binding proteins may play important roles in breast tumorigenesis.     

125I]17-alpha-iodovinyl 11-beta-methoxyestradiol interaction in vivo with estrogen receptors in hormone-independent MCF-7 human breast cancer transfected with the v-rasH oncogene

[125I]17-alpha-Iodovinyl 11-beta-methoxyestradiol [( 125I]MIVE2) has been evaluated as a potential radiotracer for the diagnostic imaging of estrogen receptor (ER)-positive human breast cancer. In vivo distribution experiments with athymic ovariectomized nude mice bearing human breast tumors revealed an apparent correlation between uptake of 125I-labeled compound and estrogen receptor concentration in the tumors. At 4 h after i.v. injection of [125I]MIVE2, HS578T (ER negative), ZR75-B (intermediate ER), and MCF-7ras (high ER) tumors accumulated 0.320 +/- 0.186, 0.679 +/- 0.467, and 2.6163 +/- 1.0121% injected dose/g, respectively. With coinjection of unlabeled 17-beta-estradiol, levels of radioactivity in MCF-7ras tumors were decreased to 0.4859 +/- 0.1424% injected dose/g, indicating a receptor-mediated process. Peak activity of radioligand in MCF-7ras tumors and uteri was observed at 2 h and was retained for the 8-h time course. Blood and nontarget tissue, such as muscle, revealed a rapid clearance of 125I-labeled compound by 8 h. Eight hours after injection, uterus and tumor-to-blood ratios were calculated to be 225 and 21, respectively. Also, MCF-7ras tumors were shown to accumulate 6.5-fold more radioactivity than muscle. These data suggest that [125I]MIVE2 has the capability of interacting specifically and with high affinity with estrogen receptors in human breast tumors in nude mice and may possibly be used for imaging receptor-positive tumors in breast cancer patients with very low serum estrogen levels. Selective uptake of compound in MCF-7ras tumors emphasizes the usefulness of an estrogen receptor-positive tumor model which has a unique ability to grow in a host system without circulating estrogens.     

Ski-related novel protein N (SnoN), a negative controller of transforming growth factor-beta signaling,is a prognostic marker in estrogen receptor-positive breast carcinomas

Transforming growth factor (TGF)-beta arrests the growth of breast epithelial cells, whereas breast cancer cells are highly resistant to its growth restrictive properties. To define causes for the defect in TGF-beta action, we present here the first in vivo analysis of Ski-related novel protein N (SnoN), a negative regulator of TGF-beta signaling, in human breast carcinomas. SnoN expression was analyzed by immunohistochemistry in a tissue microarray of 1122 breast carcinomas and 10 reduction mammoplasties. In the normal breast, SnoN was located predominantly in nuclei of large duct epithelial cells and the cytoplasm of terminal duct epithelial cells. Breast cancers displayed variances in both SnoN expression levels and subcellular localizations. High levels of cytoplasmic SnoN were more often observed in tumors of ductal histological type and associated with adverse prognostic features, such as lack of hormone receptors; high levels of p53, Ki-67, and cyclooxygenase-2; and amplifications of HER-2. High levels of nuclear SnoN were associated with lobular histology and favorable features, including presence of hormone receptors, low expression of p53 and Ki-67, and lack of HER-2 amplifications. Reduced expression of SnoN significantly correlated with longer distant disease-free survival in estrogen receptor-positive patients (P = 0.0027, relative risk = 3.27; 95% confidence interval = 1.44-7.41). The results suggest that the subcellular localization of SnoN may have clinical significance and that reduced expression of SnoN is associated with favorable outcome in estrogen receptor-positive breast cancer.     

Induction of transforming growth factor beta 1 in human breast cancer in vivo following tamoxifen treatment.

We have investigated the ability of tamoxifen to regulate members of the transforming growth factor beta (TGF-beta) family in human breast cancers in vivo. Using immunohistochemical techniques, we find that 3 months of tamoxifen treatment causes a consistent induction of extracellular TGF-beta 1 in breast cancer biopsies, compared with matched pretreatment samples from the same patient. The induced TGF-beta is localized between and around stromal fibroblasts and appears to be derived from these cells. Lower levels of TGF-beta 1,-beta 2, and -beta 3 seen in epithelial cells were not altered by tamoxifen treatment. The increased stromal staining of TGF-beta 1 occurred in estrogen receptor-negative as well as estrogen receptor-positive tumors. These results provide in vivo evidence for a novel, estrogen receptor-independent mechanism of action for tamoxifen, involving the stromal induction of a potent growth inhibitor for epithelial cells.     

Apigenin prevents development of medroxyprogesterone acetate-accelerated 7,12-dimethylbenz(a)anthracene-induced mammary tumors in Sprague-Dawley rats

The use of progestins as a component of hormone replacement therapy has been linked to an increase in breast cancer risk in postmenopausal women. We have previously shown that medroxyprogesterone acetate (MPA), a commonly administered synthetic progestin, increases production of the potent angiogenic factor vascular endothelial growth factor (VEGF) by tumor cells, leading to the development of new blood vessels and tumor growth. We sought to identify nontoxic chemicals that would inhibit progestin-induced tumorigenesis. We used a recently developed progestin-dependent mammary cancer model in which tumors are induced in Sprague-Dawley rats by 7,12-dimethylbenz(a)anthracene (DMBA) treatment. The flavonoid apigenin, which we previously found to inhibit progestin-dependent VEGF synthesis in human breast cancer cells in vitro, significantly delayed the development of, and decreased the incidence and multiplicity of, MPA-accelerated DMBA-induced mammary tumors in this animal model. Whereas apigenin decreased the occurrence of such tumors, it did not block MPA-induced intraductal and lobular epithelial cell hyperplasia in the mammary tissue. Apigenin blocked MPA-dependent increases in VEGF, and suppressed VEGF receptor-2 (VEGFR-2) but not VEGFR-1 in regions of hyperplasia. No differences were observed in estrogen or progesterone receptor (ER/PR) levels, or the number of estrogen receptor-positive cells, within the mammary gland of MPA-treated animals administered apigenin, MPA-treated animals, and placebo treated animals. However, the number of progesterone receptor-positive cells was reduced in animals treated with MPA or MPA and apigenin compared with those treated with placebo. These findings suggest that apigenin has important chemopreventive properties for those breast cancers that develop in response to progestins.     

A dietary pattern derived to correlate with estrogens and risk of postmenopausal breast cancer

Circulating estrogens are an established risk factor for breast cancer and some data suggest that diet may influence estrogen levels. Therefore, using a subsample (n = 550) of women from a large cohort, we applied reduced rank regression to identify a dietary pattern that was correlated with estradiol and estrone sulfate. We then adapted the pattern to be used with the full cohort (n = 67,802) and prospectively assessed its association with postmenopausal breast cancer. The estrogen food pattern, characterized by higher intakes of red meat, legumes, and pizza, but lower intakes of coffee and whole grains, was modestly but significantly correlated with estradiol (r = 0.14) and estrone sulfate (r = 0.20). During 22 years of follow-up, we ascertained 4,596 incident breast cancer, with 2,938 estrogen receptor-positive tumors and 689 estrogen receptor-negative tumors. However, after adjusting for potential confounders, we did not observe any association with overall estrogen receptor-positive or estrogen receptor-negative breast cancer. In conclusion, diet pattern appeared to only have modest association with estrogens, and was not associated with postmenopausal breast cancer risk. Although these results were null, it should be repeated in other populations as differences in food intake may yield a dietary pattern with stronger association with estrogens.     

Genistein sensitizes inhibitory effect of tamoxifen on the growth of estrogen receptor-positive and HER2-overexpressing human breast cancer cells

Although tamoxifen (TAM) is used for the front-line treatment and prevention of estrogen receptor-positive (ER+) breast tumors, nearly 40% of estrogen-dependent breast tumors do not respond to TAM treatment. Moreover, the positive response is usually of short duration, and most tumors eventually develop TAM-resistance. Overexpression of HER2 gene is associated with TAM-resistance of breast tumor, and suppression of HER2 expression enhances the TAM activity. Soy isoflavone genistein has been shown to have anti-cancer activities and suppress expression of HER2 and ERalpha. The objective of this study was to test the hypothesis that genistein may sensitize the response of ER+ and HER2-overexpressing breast cancer cells to TAM treatment. The combination treatment of TAM and genistein inhibited the growth of ER+/HER2-overexpressing BT-474 human breast cancer cells in a synergistic manner in vitro. Determination of cellular markers indicated that this synergistic inhibitory effect might be contributed in part from combined effects on cell-cycle arrest at G(1) phase and on induction of apoptosis. Further determination of the molecular markers showed that TAM and genistein combination synergistically induced BT-474 cell apoptosis in part by synergistic downregulation of the expression of survivin, one of the apoptotic effectors, and downregulation of EGFR, HER2, and ERalpha expression. Our research may provide a novel approach for the prevention and/or treatment of TAM insensitive/resistant human breast cancer, and warrants further in vivo studies to verify the efficacy of genistein and TAM combination on the growth of ER+/HER2-overexpressing breast tumors and to elucidate the in vivo mechanisms of synergistic actions.     

Phospho-serine-118 estrogen receptor-alpha expression is associated with better disease outcome in women treated with tamoxifen.

PURPOSE: The purpose of this research was to determine whether estrogen receptor alpha specifically phosphorylated at Ser(118) is associated with clinical outcome in primary breast tumors from estrogen receptor-positive and node-negative breast cancer patients. EXPERIMENTAL DESIGN: Estrogen receptor alpha specifically phosphorylated at Ser(118) was determined by immunohistochemistry in 117 primary breast tumors from node-negative patients who were subsequently treated with adjuvant tamoxifen. The relationship of estrogen receptor alpha specifically phosphorylated at Ser(118) expression to disease-free survival and overall survival was determined. RESULTS: Estrogen receptor alpha specifically phosphorylated at Ser(118) was limited to estrogen receptor alpha ligand binding assay-positive tumors and among this subset was expressed in 70 (62%) of these tumors. Estrogen receptor alpha specifically phosphorylated at Ser(118) expression was more frequently observed in progesterone receptor-positive tumors compared with progesterone receptor-negative tumors (chi(2) test, P = 0.012, n = 113). A significant correlation was also seen between estrogen receptor alpha specifically phosphorylated at Ser(118) and progesterone receptor levels (Spearman r = 0.236, P = 0.0118, n = 113). Kaplan-Meier outcome analysis showed that patients whose primary tumors expressed estrogen receptor alpha specifically phosphorylated at Ser(118) had a longer disease-free survival (P = 0.0018, n = 113) and a trend toward better overall survival, but this was not statistically significant. Among the subset of progesterone receptor-positive tumors, progesterone receptor-positive/estrogen receptor alpha specifically phosphorylated at Ser(118)-positive patients had a significantly longer disease-free survival that progesterone receptor-positive/estrogen receptor alpha specifically phosphorylated at Ser(118)-negative patients (P = 0.0041). CONCLUSIONS: Our data suggest that estrogen receptor alpha specifically phosphorylated at Ser(118) is a marker of a functional, intact ligand-dependent estrogen receptor signaling pathway in breast cancer and that estrogen receptor alpha specifically phosphorylated at Ser(118) status has the potential to provide a more precise biomarker of responsiveness to endocrine therapy in conjunction with estrogen receptor alpha and progesterone receptor status.     

PC cell-derived growth factor mediates tamoxifen resistance and promotes tumor growth of human breast cancer cells

PC cell-derived growth factor, also known as progranulin, is an M(r) 88,000 growth factor (referred as PCDGF/GP88) overexpressed in human breast cancer. Antisense inhibition of PCDGF/GP88 expression in MDA-MB-468 cells inhibited tumor formation in nude mice. In estrogen receptor-positive cells, PCDGF/GP88 was expressed in response to estradiol and shown to mediate its mitogenic effect. Pathologic studies indicated that PCDGF/GP88 was expressed in 80% of invasive ductal carcinomas in correlation with parameters of poor prognosis. In the present article, the relationship between PCDGF/GP88 expression and tamoxifen resistance was examined in MCF-7 cells. PCDGF/GP88 overexpression rendered MCF-7 cells able to proliferate in the absence of estrogen and in the presence of tamoxifen. The PCDGF/GP88-overexpressing cells formed tumors in ovariectomized nude mice in the absence of estradiol and in its presence, in contrast to MCF-7 cells. Tumor growth of the overexpressing cells was increased significantly when the mice were treated with tamoxifen. PCDGF/GP88 blocked tamoxifen-induced apoptosis by preventing down-regulation of bcl-2 expression and poly(ADP-ribose) polymerase cleavage. In addition, PCDGF/GP88-overexpressing cells presented higher level of the angiogenic factors vascular endothelial growth factor and angiopoietin-1 than MCF-7 control cells. Tamoxifen treatment additionally increased the level of vascular endothelial growth factor. These studies suggest that PCDGF/GP88 plays a critical role in breast cancer tumorigenesis and in the transition to estrogen independence and tamoxifen resistance, a hallmark of poor prognosis. On the basis of the in vivo studies, it is postulated that tamoxifen treatment of patients with estrogen receptor-positive breast tumors overexpressing PCDGF/GP88 could have adverse clinical consequences.     

Influence of obesity on breast cancer receptor status and prognosis

Pre-existing obesity and postoperative weight gain are related to a poor prognosis in breast cancer regardless of menopausal status. Delayed diagnosis may be one cause, but of more biological significance, especially in younger women, is the association of adiposity with estrogen receptor-negative tumors with a propensity for distant metastasis. After the menopause, the major mechanism for the relationship is the elevated estrogen synthesis by adipose tissue; these hormone-dependent tumors are estrogen receptor-positive. Insulin and some adipokines also stimulate breast cancer growth and metastasis, both directly and most probably by enhanced angiogenesis. Weight control is important, not only to target breast cancer progression, but also to reduce the risk of nonbreast cancer mortality risk associated with excess adiposity.