Angiopoietin decoy secreted at tumor site impairs tumor growth and metastases by inducing local inflammation and altering neoangiogenesis.
The extracellular domain of the receptor tyrosine kinase Tie2/TEK (exTEK) has been used as an angiopoietin decoy to study the role of angiopoietins in the tumor-host interactions, using a syngeneic model of experimental metastases and subcutaneous tumor. Soluble exTEK secreted by transfected tumor cells inhibited HUVECs from forming tubes in Matrigel. ExTEK-transfected C26 colon carcinoma and TS/A mammary tumor cells displayed reduced growth rate when injected subcutaneously, and reduced ability to form experimental metastases when injected intravenously. Immunohistochemical analysis of tumors and metastases showed increased leukocytes infiltration and signs of inflammation in exTEK-secreting compared to parental tumor, as well as impairment in neo-vessel growth and organization. However, while neoangiogenesis eventually rescued in the subcutis, it failed to organize in the experimental metastases of exTEK-secreting tumor, contributing to the hampering of metastatic growth and to increased mice survival. The reactive infiltrate of C26TEK contained a different percentage of leukocytes and was responsible for the tumor inhibition. In fact, leukopenia induced by gamma-irradiation of recipient mice or injection into interferon gamma (IFN-gamma) gene knockout (GKO) mice resulted in reduced mouse survival and an increased number of lung metastases. On the other hand, interleukin (IL)-12 treatment prolonged the survival of mice bearing subcutaneous C26TEK but not of those bearing lung metastases, suggesting that IL-12 could exert further antiangiogenic effects at the site where the tumor can restore neoangiogenesis. These results show in vivo that reduced angiopoietin availability at the tumor site induces a local inflammatory response and impairment of neoangiogenesis which act synergistically to limit tumor growth and metastasis.
Department of Experimental Oncology, Immunotherapy and Gene Therapy Unit, Istituto Nazionale per lo Studio e la Cura dei Tumori, via G. Venezian 1, 20133 Milan, Italy. melani@istitutotumori.mi.it
Cecilia
C
Melani
Antonella
A
Stoppacciaro
Chiara
C
Foroni
Federica
F
Felicetti
Alessandra
A
Caré
Mario P
MP
Colombo
D042683:Angiopoietin-1 / Q000378:metabolism*; D000818:Animals; D003110:Colonic Neoplasms / Q000098:blood supply / Q000378:metabolism / Q000473:pathology*; D015316:Genetic Therapy; D006801:Humans; D007124:Immunoenzyme Techniques; D007249:Inflammation / Q000209:etiology; D007371:Interferon-gamma / Q000235:genetics / Q000502:physiology; D018664:Interleukin-12 / Q000494:pharmacology; D007962:Leukocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D007970:Leukopenia / Q000209:etiology; D008175:Lung Neoplasms / Q000378:metabolism / Q000556:secondary*; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000378:metabolism / Q000517:prevention & control*; D042787:Receptor, TIE-2 / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
D042683:Angiopoietin-1; D018664:Interleukin-12; D007371:Interferon-gamma; D042787:Receptor, TIE-2