title: Effects of angiopoietin-2-blocking antibody on endothelial cell-cell junctions and lung metastasis.
abstract: BACKGROUND
  Angiopoietin-2 (Ang2), a ligand for endothelial TEK (Tie2) tyrosine kinase receptor, is induced in hypoxic endothelial cells of tumors, where it promotes tumor angiogenesis and growth. However, the effects of Ang2 on tumor lymphangiogenesis and metastasis are poorly characterized.
  
  
  METHODS
  We addressed the effect of Ang2 on tumor progression and metastasis using systemic Ang2 overexpression in mice carrying tumor xenografts, endothelium-specific overexpression of Ang2 in VEC-tTA/Tet-OS-Ang2 transgenic mice implanted with isogenic tumors, and administration of Ang2-blocking antibodies to tumor-bearing immunodeficient mice. Fisher's exact test was used for analysis of metastasis occurrence, and repeated measures one-way analysis of variance was used for the analysis of primary tumor growth curves. Unpaired t test was used for all other analyses. All statistical tests were two-sided.
  
  
  RESULTS
  Adenoviral expression of Ang2 increased lymph node and lung metastasis in tumor xenografts. The metastatic burden in the lungs was increased in transgenic mice in which Ang2 expression was induced specifically in the vascular endothelium (tumor burden per grid, VEC-tTA/Tet-OS-Ang2 mice [n = 5] vs control mice [n = 4]: 45.23 vs 12.26 mm(2), difference = 32.67 mm(2), 95% confidence interval = 31.87 to 34.07, P < .001). Ang2-blocking antibodies reduced lymph node and lung metastasis, as well as tumor lymphangiogenesis, and decreased tumor cell homing to the lungs after intravenous injection. In the lung metastases, Ang2 overexpression decreased endothelial integrity, whereas the Ang2-blocking antibodies improved endothelial cell-cell junctions and basement membrane contacts of metastasis-associated lung capillaries. At the cellular level, the Ang2-blocking antibodies induced the internalization of Ang2-Tie2 receptor complexes from endothelial cell-cell junctions in endothelial-tumor cell cocultures.
  
  
  CONCLUSIONS
  Our results indicate that blocking Ang2 inhibits metastatic dissemination in part by enhancing the integrity of endothelial cell-cell junctions.
authors.affiliation: Molecular/Cancer Biology Laboratory, Biomedicum Helsinki, Haartmaninkatu 8 (PO Box 63), FI-00014 University of Helsinki, Helsinki, Finland.
authors.forename: Tanja
authors.initials: T
authors.lastname: Holopainen
authors.forename: Pipsa
authors.initials: P
authors.lastname: Saharinen
authors.forename: Gabriela
authors.initials: G
authors.lastname: D'Amico
authors.forename: Anita
authors.initials: A
authors.lastname: Lampinen
authors.forename: Lauri
authors.initials: L
authors.lastname: Eklund
authors.forename: Raija
authors.initials: R
authors.lastname: Sormunen
authors.forename: Andrey
authors.initials: A
authors.lastname: Anisimov
authors.forename: Georgia
authors.initials: G
authors.lastname: Zarkada
authors.forename: Marja
authors.initials: M
authors.lastname: Lohela
authors.forename: Hanna
authors.initials: H
authors.lastname: Heloterä
authors.forename: Tuomas
authors.initials: T
authors.lastname: Tammela
authors.forename: Laura E
authors.initials: LE
authors.lastname: Benjamin
authors.forename: Seppo
authors.initials: S
authors.lastname: Ylä-Herttuala
authors.forename: Ching Ching
authors.initials: CC
authors.lastname: Leow
authors.forename: Gou Young
authors.initials: GY
authors.lastname: Koh
authors.forename: Kari
authors.initials: K
authors.lastname: Alitalo
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D042702:Angiopoietin-2 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000818:Animals; D019138:Antibodies, Blocking / Q000378:metabolism / Q000494:pharmacology; D015687:Cell Hypoxia; D018920:Coculture Techniques; D042783:Endothelial Cells / Q000187:drug effects / Q000473:pathology; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000473:pathology; D005260:Female; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D007365:Intercellular Junctions / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D008175:Lung Neoplasms / Q000098:blood supply* / Q000556:secondary; D042583:Lymphangiogenesis; D008207:Lymphatic Metastasis; D008545:Melanoma / Q000098:blood supply / Q000556:secondary; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism* / Q000517:prevention & control*; D042787:Receptor, TIE-2 / Q000378:metabolism; D012171:Retinal Vessels / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D014183:Transplantation, Heterologous; D015854:Up-Regulation
chemical_list: D020533:Angiogenesis Inhibitors; D042702:Angiopoietin-2; D019138:Antibodies, Blocking; D042787:Receptor, TIE-2