title: Tumor escape from endogenous, extracellular matrix-associated angiogenesis inhibitors by up-regulation of multiple proangiogenic factors.
abstract: OBJECTIVE
  Thrombospondin-1 (Tsp1), endostatin, and tumstatin are extracellular matrix-associated proteins that inhibit angiogenesis. We examined the mechanisms by which tumor cells may bypass the antiangiogenic effects of these endogenous regulators.
  
  
  METHODS
  CT26 colon and RenCa renal carcinoma cells were stably transfected with Tsp1, endostatin, or tumstatin cDNA. Subcutaneous and metastatic tumor growth in syngeneic mice was analyzed. Expression of proangiogenic factors in resulting tumors was measured by quantitative real-time PCR. The combination of Tsp1 and vascular endothelial growth factor (VEGF) receptor-2 inhibition was also examined.
  
  
  RESULTS
  There was significant suppression of angiogenesis in flank tumors and liver metastases formed from cells overexpressing Tsp1, endostatin, or tumstatin. However, all tumors ultimately escaped angiogenesis inhibition. The combination of all three angiogenesis inhibitors had no additive effect beyond overexpression of a single inhibitor. Using quantitative real-time PCR, we found that VEGF and platelet-derived growth factor (PDGF)-A levels were routinely up-regulated at least 5-fold in all CT26 tumors overexpressing any antiangiogenic protein, and there were variable increases in angiopoietin 2 (Ang2), basic fibroblast growth factor, and PDGF-B. In contrast, RenCa tumors, which have high baseline levels of VEGF and PDGF-B, relied on basic fibroblast growth factor, Ang1, and PDGF-A up-regulation to counteract Tsp1 overexpression. Growth of CT26 cells with Tsp1 overexpression was suppressed when anti-VEGFR-2 treatment was added.
  
  
  CONCLUSIONS
  Cancer cells with overexpression of three different endogenous angiogenesis inhibitor eventually escape angiogenesis inhibition by up-regulation of various proangiogenic factors. Tsp1, endostatin, and tumstatin may be functionally redundant in this system. These endogenous angiogenesis inhibitors are likely best used in combination with the blockade of proangiogenic pathways or with traditional chemotherapy or radiation therapy.
authors.affiliation: Division of Surgical Oncology, Department of Surgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Namali T
authors.initials: NT
authors.lastname: Fernando
authors.forename: Moritz
authors.initials: M
authors.lastname: Koch
authors.forename: Courtney
authors.initials: C
authors.lastname: Rothrock
authors.forename: Lila K
authors.initials: LK
authors.lastname: Gollogly
authors.forename: Patricia A
authors.initials: PA
authors.lastname: D'Amore
authors.forename: Sandra
authors.initials: S
authors.lastname: Ryeom
authors.forename: Sam S
authors.initials: SS
authors.lastname: Yoon
mesh_terms: D020533:Angiogenesis Inhibitors / Q000502:physiology*; D042501:Angiogenic Proteins / Q000378:metabolism*; D000818:Animals; D001324:Autoantigens / Q000502:physiology; D015153:Blotting, Western; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation; D002478:Cells, Cultured; D024141:Collagen Type IV / Q000502:physiology; D017931:DNA Primers; D043169:Endostatins / Q000502:physiology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008113:Liver Neoplasms / Q000098:blood supply* / Q000556:secondary; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009389:Neovascularization, Pathologic / Q000378:metabolism*; D010957:Plasmids; D010982:Platelet-Derived Growth Factor / Q000235:genetics; D020574:Proto-Oncogene Proteins c-sis / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012878:Skin Neoplasms / Q000098:blood supply* / Q000473:pathology; D019700:Thrombospondin 1 / Q000502:physiology; D014162:Transfection; D019139:Tumor Escape / Q000502:physiology*; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics
chemical_list: D020533:Angiogenesis Inhibitors; D042501:Angiogenic Proteins; D001324:Autoantigens; D024141:Collagen Type IV; D017931:DNA Primers; D043169:Endostatins; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D019700:Thrombospondin 1; D042461:Vascular Endothelial Growth Factor A; C075278:platelet-derived growth factor A; C057112:type IV collagen alpha3 chain; D040301:Vascular Endothelial Growth Factor Receptor-2