Understanding the signaling pathways that drive aggressive breast cancers is critical to the development of effective therapeutics. The oncogene MET is associated with decreased survival in breast cancer, yet the role that MET plays in the various breast cancer subtypes is unclear. We describe a knockin mouse with mutationally activated Met (Met(mut)) that develops a high incidence of diverse mammary tumors with basal characteristics, including metaplasia, absence of progesterone receptor and ERBB2 expression, and expression of cytokeratin 5. With gene expression and tissue microarray analysis, we show that high MET expression in human breast cancers significantly correlated with estrogen receptor negative/ERBB2 negative tumors and with basal breast cancers. Few treatment options exist for breast cancers of the basal or trastuzumab-resistant ERBB2 subtypes. We conclude from these studies that MET may play a critical role in the development of the most aggressive breast cancers and may be a rational therapeutic target.
<div>Abstract<p>The conventional practice of analyzing overall age-adjusted cancer mortality rates heavily emphasizes the experience of older, higher mortality age groups. This may conceal shifts in lifetime cancer mortality experience emerging first in younger age groups. We examined age-specific cancer mortality rates and birth cohort–specific cancer mortality rates in U.S. mortality data recorded since 1955 to assess the effects of age, period, and cohort in secular mortality trends. Cancer mortality and population data were obtained from WHO Statistical Information System. Age-specific cancer mortality rates have been steadily declining in the United States since the early 1950s, beginning with children and young adults and now including all age groups. During the second half of the 20th century, each successive decade of births from 1925 to 1995 experienced a lower risk of cancer death than its predecessor at virtually every age for which such a comparison can be made. A major decline in cancer mortality has been occurring in the United States for the past 50 years, affecting birth cohorts born as long as 80 years ago. Excepting lung cancer, much of this decline has occurred despite relatively stable cancer incidence. These findings suggest that improvements in cancer detection, treatment, and/or prevention have reduced the risk of cancer death across the life span for individuals born in the last three quarters of the 20th century. [Cancer Res 2009;69(16):6500–5]</p></div>
Abstract Due to its invasive nature, glioblastoma (GBM) is the most aggressive brain cancer. Hepatocyte growth factor (HGF) binds to MET tyrosine kinase receptor and induces invasive tumor growth. As MET inhibitors are entering clinical trials against several types of cancer including GBM, it is compelling to identify therapeutic determinants which could indicate which patient subsets are suitable for this therapy. We investigated in vivo four types of GBM models for their sensitivity to MET (SGX523*) or EGFR (erlotinib*) inhibitors: 1) Tumors sustained by an HGF-autocrine loop; 2) tumors displaying paracrine HGF tumor growth; and 3) tumors with polysomy MET amplification. 4) In addition, GBM tumors with epidermal growth factor receptor (EGFR) amplification were included, as this occurs frequently in GBM patients and often in association with MET aberrancy. Of the four tumor types, we observed that HGF-autocrine loop expression correlates with p-MET levels in the HGF autocrine cell lines, which in turn are extremely sensitive to MET inhibition in vivo. Moreover, serum HGF levels in HGF-autocrine loop GBM xenografts correlate with MET inhibition. Paracrine HGF can enhance GBM growth in vivo, but they were not significantly sensitive to MET inhibition. In type 4, EGFR VIII amplification predicted sensitivity to erlotinib, but MET polysomy in the same tumor did not display MET activity and the cells did not show sensitivity to MET inhibition. We conclude that HGF-autocrine loop GBM tumors bear an activated MET signaling pathway that may be used to predict sensitivity to MET inhibitors in GBM patients. However, targeting MET alone may not be sufficient for treating GBM and the combination of MET with other RTK inhibitors, especially EGFR inhibitors should be considered. *SGX523, a selective small molecule MET inhibitor, was obtained from Eli Lilly and Company, Indianapolis IN. *Erlotinib inhibits EGFR and was a generous gift from OSI Pharmaceuticals, Long Island N.Y. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-223. doi:10.1158/1538-7445.AM2011-LB-223
CENP-E, a kinesin-like protein that is known to associate with kinetochores during all phases of mitotic chromosome movement, is shown here to be a component of meiotic kinetochores as well. CENP-E is detected at kinetochores during metaphase I in both mice and frogs, and, as in mitosis, is relocalized to the midbody during telophase. CENP-E function is essential for meiosis I because injection of an antibody to CENP-E into mouse oocytes in prophase completely prevented progression of those oocytes past metaphase I. Beyond this, CENP-E is modified or masked during the natural, Mos-dependent, cell cycle arrest that occurs at metaphase II, although it is readily detectable at the kinetochores in metaphase II oocytes derived from mos -deficient (MOS −/− ) mice that fail to arrest at metaphase II. This must reflect a masking of some CENP-E epitopes, not the absence of CENP-E, in meiosis II because a different polyclonal antibody raised to the tail of CENP-E detects CENP-E at kinetochores of metaphase II-arrested eggs and because CENP-E reappears in telophase of mouse oocytes activated in the absence of protein synthesis.
We have begun characterizing the signal transduction pathways used by the c-met receptor in cells in which ligand (HGF-SF) stimulates motogenesis in the absence of mitogenesis. Primary targets (within 10-15 minutes) were identified as PI-3 kinase, GAP, PLC gamma, src, and MAP kinase, substrates which are also activated upon growth factor activation of mitogenic receptor systems. Following HGF-SF treatment, the 85 kD subunit of PI-3 kinase is phosphorylated on tyrosine and PI-3 kinase activity rapidly associates with the c-met receptor. A number of these substrates are implicated in cytoskeletal rearrangements and may be important in the motogenic response to the factor. We have also identified a number of colon carcinoma lines which express unamplified levels of constitutively tyrosine phosphorylated c-met protein. In these and other (gastric) cell lines which express amplified levels of activated receptor protein, we have determined that receptor activation is not due to the autocrine production of ligand.
A search of the National Cancer Institute's Anti‐Neoplastic Drug Screen for compounds with an inhibitory profile similar to that of the mitogen‐activated protein kinase kinase (MAPKK) inhibitor PD098059 yielded anthrax lethal toxin. Anthrax lethal factor was found to inhibit progesterone‐induced meiotic maturation of frog oocytes by preventing the phosphorylation and activation of mitogen‐activated protein kinase (MAPK). Similarly, lethal toxin prevented the activation of MAPK in serum stimulated, ras‐transformed NIH3T3 cells. In vitro analyses using recombinant proteins indicated that lethal factor proteolytically modified the NH2‐terminus of both MAPKK1 and 2, rendering them inactive and hence incapable of activating MAPK. The consequences of this inactivation upon meiosis and transformed cells are also discussed.
Abstract Hepatocyte growth factor/scatter factor-Met signaling has been implicated in tumor growth, invasion, and metastasis. Suppression of this signaling pathway by targeting the Met protein tyrosine kinase may be an ideal strategy for suppressing malignant tumor growth. Using RNA interference technology and adenovirus vectors carrying small-interfering RNA constructs (Ad Met small-interfering RNA) directed against mouse, canine, and human Met, we can knock down c-met mRNA. We show a dramatic dependence on Met in both ligand-dependent and ligand-independent mouse, canine, and human tumor cell lines. Mouse mammary tumor (DA3) cells and Met-transformed NIH3T3 (M114) cells, as well as both human and canine prostate cancer (PC-3 and TR6LM, human sarcoma (SK-LMS-1), glioblastoma (DBTRG), and gastric cancer (MKN45) cells, all display a dramatic reduction of Met expression after infection with Ad Met small-interfering RNA. In these cells, we observe suppression of tumor cell growth and viability in vitro as well as inhibition of hepatocyte growth factor/scatter factor-mediated scattering and invasion in vitro, whether Met activation was ligand dependent or not. Importantly, Ad Met small-interfering RNA led to apoptotic cell death in many of the tumor cell lines, especially DA3 and MKN45, but did not adversely affect MDCK canine kidney cells. Met small-interfering RNA also abrogated downstream Met signaling to molecules such as Akt and p44/42 mitogen-activated protein kinase. We further show that intratumoral infection with c-met small-interfering RNA adenovirus results in a substantial reduction in tumor growth. Thus, Met small-interfering RNA adenoviruses are reliable tools for studying Met function and raise the possibility of their application for cancer therapy.
We studied the frequencies and types of excision events which can occur with a retroviral shuttle vector containing the simian virus 40 origin of DNA replication. Analysis of the recloned vector plasmids by size and restriction enzyme mapping indicated that most contain one long terminal repeat. By hybridizing the plasmids to a mouse genomic repetitive DNA probe, we also determined that approximately 1 to 3% contain transduced cellular DNA sequences.
The relationship between the mos protooncogene protein and cAMP-dependent protein kinase (PKA) during the maturation of Xenopus oocytes was investigated. Microinjection of the PKA catalytic subunit (PKAc) into Xenopus oocytes inhibited oocyte maturation induced by the mos product but did not markedly affect the autophosphorylation activity of injected mos protein. By contrast, PKAc did not inhibit maturation promoting factor (MPF) activation or germinal vesicle breakdown (GVBD) that was initiated by injecting crude MPF preparations. In addition, inhibiting endogenous PKA activity by microinjecting the PKA regulatory subunit (PKAr) induced oocyte maturation that was dependent upon the presence of the endogenous mos product. Moreover, PKAr potentiated mos protein-induced MPF activation in the absence of progesterone and protein synthesis. These data are consistent with the hypothesis that progesterone-induced release from G2/M is regulated via PKAc and that PKAc negatively regulates a downstream target that is positively regulated by mos.
