Effect of c-neu/ ErbB2 expression levels on estrogen receptor alpha-dependent proliferation in mammary epithelial cells: implications for breast cancer biology.

Mammary development and tumorigenesis are profoundly influenced by signaling pathways under the control of c-erbB2/c-neu and estrogen receptor alpha (ERalpha). Signaling through ERalpha is essential for ductal growth during puberty. In mice overexpressing wild-type c-neu in mammary epithelial cells, Tg (c-neu), ductal growth is impaired. An impeded signaling through ERalpha is also observed in a subset of human mammary tumors that overexpress erbB2. However, ductal growth is also impaired in the absence of c-neu in mouse mammary epithelial cells. To resolve this apparent paradox, we examined the relationship between c-neu expression and estrogen/ERalpha-dependent cell proliferation in pubertal Tg (c-neu). We report that proliferation in both terminal end buds and ducts is associated with ERalpha-positive cells, including those that coexpress c-neu, and is abolished in the absence of circulating estradiol. Tg (c-neu) contains hyperplastic mammary ducts with high proliferative index and coexpression of both ERalpha and c-neu in the dividing cells. These findings suggest that c-neu promotes ERalpha-dependent proliferation, and that this is responsible for the presence of hyperplastic ducts. Some of the hyperplastic ducts have acinar structures, indicative of morphologic differentiation. These ducts have low proliferative index and accompanied by a vast decrease in proliferation of ERalpha-positive cells, including those that express c-neu. As such, c-neu has dual but opposing effects on ERalpha-dependent proliferation in mammary epithelial cells. Therefore, depending on the physiologic setting, ductal morphogenesis will be compromised both in the absence and overexpression of c-neu, thus explaining the paradox.

Id-1 is not expressed in the luminal epithelial cells of mammary glands.

BACKGROUND: The family of inhibitor of differentiation/DNA binding (Id) proteins is known to regulate development in several tissues. One member of this gene family, Id-1, has been implicated in mammary development and carcinogenesis. Mammary glands contain various cell types, among which the luminal epithelial cells are primarily targeted for proliferation, differentiation and carcinogenesis. Therefore, to assess the precise significance of Id-1 in mammary biology and carcinogenesis, we examined its cellular localization in vivo using immunohistochemistry. METHODS: Extracts of whole mammary glands from wild type and Id-1 null mutant mice, and tissue sections from paraffin-embedded mouse mammary glands from various developmental stages and normal human breast were subjected to immunoblot and immunohistochemical analyses, respectively. In both these procedures, an anti-Id-1 rabbit polyclonal antibody was used for detection of Id-1. RESULTS: In immunoblot analyses, using whole mammary gland extracts, Id-1 was detected. In immunohistochemical analyses, however, Id-1 was not detected in the luminal epithelial cells of mammary glands during any stage of development, but it was detected in vascular endothelial cells. CONCLUSION: Id-1 is not expressed in the luminal epithelial cells of mammary glands.

Discovery of a novel class of potent and orally bioavailable sphingosine 1-phosphate receptor 1 antagonists.

A series of subtype selective sphingosine 1-phosphate receptor 1 (S1P(1)) antagonists are disclosed. Our high-throughput screening campaign revealed hit 1 for which an increase in potency and mouse oral exposure was achieved with minor modifications to the chemical scaffold. In vivo efficacy revealed that at high doses compounds 12 and 15 inhibited tumor growth. Further optimization of our lead series led to the discovery of proline derivatives 37 (XL541) and 38 which had similar efficacy as our first generation analogues at significantly lower doses. Analogue 37 displayed excellent pharmacokinetics and oral exposure in multiple species.

Cabozantinib (XL184), a novel MET and VEGFR2 inhibitor, simultaneously suppresses metastasis, angiogenesis, and tumor growth.

The signaling pathway of the receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF) is important for cell growth, survival, and motility and is functionally linked to the signaling pathway of VEGF, which is widely recognized as a key effector in angiogenesis and cancer progression. Dysregulation of the MET/VEGF axis is found in a number of human malignancies and has been associated with tumorigenesis. Cabozantinib (XL184) is a small-molecule kinase inhibitor with potent activity toward MET and VEGF receptor 2 (VEGFR2), as well as a number of other receptor tyrosine kinases that have also been implicated in tumor pathobiology, including RET, KIT, AXL, and FLT3. Treatment with cabozantinib inhibited MET and VEGFR2 phosphorylation in vitro and in tumor models in vivo and led to significant reductions in cell invasion in vitro. In mouse models, cabozantinib dramatically altered tumor pathology, resulting in decreased tumor and endothelial cell proliferation coupled with increased apoptosis and dose-dependent inhibition of tumor growth in breast, lung, and glioma tumor models. Importantly, treatment with cabozantinib did not increase lung tumor burden in an experimental model of metastasis, which has been observed with inhibitors of VEGF signaling that do not target MET. Collectively, these data suggest that cabozantinib is a promising agent for inhibiting tumor angiogenesis and metastasis in cancers with dysregulated MET and VEGFR signaling.

Mammary epithelial cells of PR-A transgenic mice exhibit distinct alterations in gene expression and growth potential associated with transformation.

Expression of the 'A' and 'B' forms of progesterone receptor (PR), in an appropriate ratio is critical for normal mammary development. As such, mammary glands of PR-A transgenic mice, carrying additional 'A' form of PR as transgene, exhibit morphological and histological characteristics associated with transformation. Accordingly, in the present studies, we analyzed these mammary glands for the presence of transformed epithelial cells by examining for alterations in gene expressions and growth potential, known to be associated with different stages of transformation. These studies reveal that, in the aberrant mammary epithelial structures, there is a decrease in p21 expression, an increase in cyclin D1 expression accompanied by an increase in cell proliferation, and a decrease in estrogen receptor alpha (ER alpha). In mammary ducts with normal histology, there is a decrease in p21 expression without an elevation in cyclin D1 expression or cell proliferation or a decrease in ER alpha expression. Treatment of PR-A transgenics with anti-progestin, mifepristone, has no effect on cell proliferation, cyclin D1 or ER alpha expression in the aberrant epithelial structures. In contrast, mifepristone restored the loss of p21 expression in the epithelial cells of both the ducts with normal histology and aberrant structures. Parallel studies reveal no apparent differences between the mammary glands of wild-type and PR-B transgenic mice, which carry additional PR 'B' form. Accordingly, we conclude that (i) mammary glands of PR-A transgenics contain at least two distinct populations of transformed epithelial cells, (ii) the epithelial cell population in the ducts with normal histology contain presumptive immortalized cells, indicative of early stages of transformation, (iii) the aberrant epithelial structures contain later stages of transformation associated with hyperplasias/pre-neoplasias and (iv) the transformation of mammary epithelial cells in PR-A transgenics might be due to a misregulation in progesterone action resulting from overexpression of PR 'A' form.