Current studies aim to deplete macrophages from gliomas to determine their role in tumor development and
progression. RIP1-Tag2 (RT2) transgenic mice express SV40-T-antigen under the control of the rat insulin promoter leading to the development of multiple pancreatic islet tumors. To determine the role of TAMs in the pancreatic microenvironment, RT2 mice were crossed to CSF-1 null macrophage deficient mice. There is a progressive increase in macrophage density in wild-type RT2 tumors, and in line with a tumor-promoting role of TAMs, Tariquidar molecular weight both tumor number and tumor burden are decreased in CSF-1 null RT2 mice. Histological invasion scoring has revealed a more invasive phenotype of CSF-1 null RT2 tumors relative to controls. This may be due to compensatory macrophage recruitment via a CSF-1 independent mechanism, which is under investigation. In conclusion, while the source of TAMs may be dependent on tissue context, macrophage recruitment is a critical step in cancer development and progression in both the pancreatic and brain tumor microenvironments. Poster No. 104 A Distinct Macrophage Population Determines Mammary Tumor Pulmonary Metastasis Binzhi Qian 1 , Jeffrey W. Pollard1 1 Department of Developmental and Molecular Biology,
Albert Einstein College CX-6258 concentration of Medicine, Bronx, NY, USA There is a growing appreciation of the importance of tumor-stroma interactions for tumor progression and metastasis. In the tumor stroma, macrophages are very abundant and have been shown to enhance these malignant processes. We have Linifanib (ABT-869) used an experimental metastasis assay to elucidate the significance of macrophages in promoting the two final limiting steps of metastasis: target organ seeding and persistent growth. Our data demonstrate that the pulmonary seeding and persistent growth of Polyoma virus middle T antigen induced mammary tumor cells are correlated with host colony stimulating factor 1 (the major growth factor for macrophages) gene copy number and the numbers of macrophages recruited to lung metastasis.
To further determine the macrophage contributions, liposome encapsulated Clodronate was used to deplete macrophages in vivo; this treatment reduced the efficiency of both rate-limiting steps in the pulmonary lung metastasis assay. FACS analysis revealed a recruitment of CSF-1R+CD11b+Gr1- cells in the metastasis bearing lung. CD11b+cells were deleted in vivo with diphtheria toxin (DT) treatment in mosaic animals generated by bone marrow transplant using a transgenic mouse expressing human DTR driven by the CD11b promoter as a bone marrow donor. The deletion of CD11b+cells reduced the tumor cell seeding efficiency and growth rate in lung. Further intact lung 3D imaging study revealed that tumor-macrophage interaction is critical for tumor cell extravasation. In addition, CCL2/CCR2 signaling was found to be important for the recruitment of these macrophages and critical for tumor cell seeding.