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2007 Scientific Report

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VARI |

VARI | 2007 Research Interests A mouse model of mutationally activated Met Signaling through Met and its ligand, HGF/SF, has been implicated in most types of human cancer. Compelling genetic evidence for the role of Met stems from the discovery that activating gain-of-function mutations are found in human kidney cancers and in other cancer types (http://www.vai.org/met/). To study how Met-activating mutations are involved in tumor development, we generated mice bearing mutations in the endogenous Met locus representative of both the inherited and the sporadic mutations found in human cancers. On a C57BL/6 background, the different mutant Met lines developed unique tumor profiles, including carcinomas, sarcomas, and lymphomas. We have found that the differences in tumor types and latency may be due to signaling differences triggered by the specific mutation in a tissue- or stem cell–specific pattern. Cytogenetic analysis of all tumor types shows frequent trisomy of the Met locus. Moreover, it is the mutant met allele that is amplified and likely to be required for tumor progression. When mutant Met was transferred to the FVB/N mouse background, these animals developed aggressive mammary tumors. Therefore, understanding the signaling specificity of these mutations is essential for developing successful cancer therapeutics. Our mutant mice provide a valuable model for testing Met inhibitors and for understanding the molecular events crucial for Met-mediated tumorigenesis. A novel mouse model for preclinical studies 67 We have generated a severe combined immune deficiency (SCID) mouse strain carrying a human HGF/SF transgene. This mouse provides a species-compatible ligand for propagating human tumor cells expressing human Met. The growth of Met-expressing human tumor xenografts can be significantly enhanced in this transgenic mouse relative to growth in nontransgenic hosts. This immunocompromised strain is vital for examining the role of Met in human tumor malignancy. We are developing metastasis models and generating orthotopic xenografts of human tumor cells. This model is being used for preclinical testing of drugs or compounds targeting the HGF/SF-Met complex and downstream signaling pathways. Understanding the “multiple personalities” of cancer cells Several years ago, we asked whether tumor cells can switch between proliferative and invasive phenotypes. We discovered that tumor cells can indeed switch, and they can do so rapidly; they may also express both proliferative and invasive features. We have established in vitro methods for selecting highly proliferative or highly invasive tumor cell populations that may mimic the in vivo process of clonal selection during tumor progression. We have determined that chromosomal instability correlates with the proliferative and invasive phenotypes. Using spectral karyotyping (SKY) and M-Fish, we observe significant changes in chromosome content with each phenotype, and the changes show remarkable concordance with changes in gene expression. Regional gene expression changes appear to favor the expression of specific genes appropriate for the invasive or proliferative phenotype. Moreover, the ratio of chromosomal changes closely parallels the ratio of gene expression in the chromosome. These results show that chromosome instability and the resulting heterogeneous chromosome composition provide the diversity in gene expression to allow tumor cell clonal evolution.

Van Andel Research Institute | Scientific Report Examining how geldanamycin inhibits tumor cell invasion Our lab has been studying the mechanism by which geldanamycin (GA) inhibits urokinase activation of plasmin from plasminogen (uPA). Previously, we have shown that a subset of GA-related drug derivatives inhibits HGF/SF-induced activation of plasmin in canine MDCK cells. We found that such inhibition also occurs in several human glioblastoma tumor cell lines. Curiously, these GA drugs inhibit HGF/SF-induced uPA activation and block MDCK cell scattering and glioblastoma tumor cell invasion in vitro at concentrations below that required to exhibit a measurable effect on Met degradation through HSP90. This inhibition is observed only with HGF/SF-mediated activation and only when the magnitude of HGF/SF-uPA induction is 1.5 times basal uPA-plasmin activity. Inhibition of MAPK in melanoma 68 Extracellular signals activate mitogen-activated protein kinase (MAPK) cascades, potentiating biological activities such as cell proliferation, differentiation, and survival. Constitutive activation of MAPK signaling pathways is implicated in the development and progression of many human cancers, including melanoma. Mutually exclusive activating mutations in NRas or BRAF are found in about 85% of all melanomas, resulting in constitutive activation of the MAPK pathway (Ras-BRaf-MEK-Erk-Rsk). We have previously demonstrated that inhibition of this pathway with small-molecule MEK inhibitors selectively induces apoptosis in human melanoma cells but not in normal melanocytes both in vitro and in vivo. These results support the concept that the MAPK pathway represents a tumor-specific survival signaling pathway in melanoma cells and that targeting members of this pathway may be an effective therapeutic strategy. Understanding the mechanisms by which constitutive MAPK promotes survival and defining the minimal vital MAPK pathway components required for the development and progression of melanoma may have direct translational implications. Preliminary data suggest that MAPK activation actively suppresses several pro-apoptotic Bcl-2 family members. We are currently using the specific small-molecule MEK inhibitor PD184352 together with molecular biological approaches to selectively modulate the expression and function of these molecules in order to validate and develop them as novel therapeutic targets for treating melanoma and other MAPK-associated cancers. External Collaborators Francesco DeMayo, Baylor College of Medicine, Houston, Texas Ermanno Gherardi, MRC Center, Cambridge, England Nadia Harbeck, Technische Universität, Munich, Germany Beatrice Knudsen, Fred Hutchinson Cancer Research Center, Seattle, Washington Ernest Lengyel, University of Chicago, Illinois Patricia LoRusso, Karmanos Cancer Institute, Detroit, Michigan Benedetta Peruzzi, National Cancer Institute, Bethesda, Maryland Alnawaz Rehemtulla, Brian Ross, and Richard Simon, University of Michigan, Ann Arbor Ilan Tsarfaty, Tel Aviv University, Israel Robert Wondergem, East Tennessee State University, Johnson City

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