title: Low plasma levels of matrix metalloproteinase 9 permit increased tumor angiogenesis.
abstract: Angiogenesis is essential for tumor growth and blocking this process might be a valid tool for the control of cancer growth. We showed previously that tumor angiogenesis in integrin alpha1-null mice is reduced compared to that of wild type animals and that over-expression of matrix metalloproteinase 9 (MMP-9) in the alpha1-null and consequent generation of angiostatin (an inhibitor of endothelial cell growth) from circulating plasminogen was implicated in the mechanism of tumor inhibition. Our findings suggested that secretion of excess MMPs generates inhibitors of endothelial cell proliferation, including but not necessarily limited to angiostatin, resulting ultimately in auto-inhibition of angiogenesis. Thus MMP inhibitors used as anti-tumor drugs might in fact cause a paradoxical increase in tumor angiogenesis and tumor growth. In order to determine whether MMP-9 expression was directly involved in the regulation of tumor growth, we specifically inhibited or enhanced MMP-9 synthesis in vitro and in vivo, and subsequently analysed primary endothelial cell proliferation and angiostatin synthesis, as well as tumor vascularization and development. We provide evidence that reduction of plasma levels of MMP-9 in either normal or integrin alpha1-null mice leads to decreased synthesis of angiostatin and consequent increased tumor growth and vascularization. In contrast, specifically enhancing MMP-9 expression in vivo caused a reduction in tumor vascularization. These findings are the opposite to other studies suggesting a pro-tumorigenic role for MMP-9, and may account for some of the recently observed failures of anti MMP therapy in tumor treatment.
authors.affiliation: Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California, CA 92037, USA. ambra.pozzi@mcmail.vanderbilt.edu
authors.forename: Ambra
authors.initials: A
authors.lastname: Pozzi
authors.forename: Wendy F
authors.initials: WF
authors.lastname: LeVine
authors.forename: Humphrey A
authors.initials: HA
authors.lastname: Gardner
mesh_terms: D043168:Angiostatins; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000502:physiology; D000970:Antineoplastic Agents / Q000494:pharmacology; D002292:Carcinoma, Renal Cell / Q000098:blood supply / Q000235:genetics / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000098:blood supply / Q000235:genetics / Q000473:pathology; D004318:Doxycycline / Q000097:blood / Q000633:toxicity; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology; D006133:Growth Substances / Q000097:blood; D039423:Integrin alpha1; D007680:Kidney Neoplasms / Q000098:blood supply / Q000235:genetics / Q000473:pathology; D020780:Matrix Metalloproteinase 9 / Q000097:blood*; D051379:Mice; D008807:Mice, Inbred BALB C; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009389:Neovascularization, Pathologic / Q000097:blood*; D010446:Peptide Fragments / Q000494:pharmacology; D010958:Plasminogen / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D015703:Antigens, CD; D000970:Antineoplastic Agents; D006133:Growth Substances; D039423:Integrin alpha1; D010446:Peptide Fragments; D043168:Angiostatins; D010958:Plasminogen; D020780:Matrix Metalloproteinase 9; D004318:Doxycycline