title: Systemic administration of anti-urokinase plasminogen activator receptor monoclonal antibodies induces hepatic fibrin deposition in tissue-type plasminogen activator deficient mice.
abstract: BACKGROUND
  Degradation of extracellular matrix proteins, such as fibrin, is pivotal to tumor invasion. Inhibition of the interaction between urokinase plasminogen activator (u-PA) and its receptor (u-PAR), and hence pro-u-PA activation, is an attractive approach to anti-invasive cancer therapy. A number of inhibitors exist for the human system, but because of species specificity none of these are efficient in mice. We have recently generated an inhibitory monoclonal antibody (mAb) against mouse u-PAR (mR1) by immunization of u-PAR-deficient mice.
  
  
  OBJECTIVE
  To evaluate the effect of mR1 in vivo in a physiological setting sensitive to deregulated fibrinolysis, we have administered mR1 systemically and quantitated the effect on liver fibrin accumulation.
  
  
  METHODS
  Wild-type and tissue-type plasminogen activator (t-PA) deficient mice were administered with mR1, or control antibody, during 6 weeks. Thereafter, the livers were retrieved and the amount of liver fibrin measured by unbiased morphometrical analysis of immunofluorescence signal.
  
  
  RESULTS
  Systemic administration of mR1 caused significantly increased fibrin signal in anti-u-PAR treated t-PA-deficient mice compared to mock-treated, which mimics the phenotype of u-PAR;t-PA double-deficient mice. Fibrin and fibronectin accumulated within the sinusoidal space and was infiltrated by inflammatory cells. Analysis of small and rare hepatic fibrin plaques observed in t-PA-deficient mice showed infiltrating macrophages that, contrary to surrounding Kuppfer cells, expressed u-PAR.
  
  
  CONCLUSIONS
  We show that u-PAR-expressing macrophages are involved in cell-mediated fibrinolysis of liver fibrin deposits, and that the antimouse-u-PAR mAb is effective in vivo and thus suited for studies of the effect of targeting the u-PA/u-PAR interaction in mouse cancer models.
authors.affiliation: Finsen Laboratory, Rigshospitalet, Copenhagen Biocenter, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Jögi
authors.forename: J
authors.initials: J
authors.lastname: Pass
authors.forename: G
authors.initials: G
authors.lastname: Høyer-Hansen
authors.forename: L R
authors.initials: LR
authors.lastname: Lund
authors.forename: B S
authors.initials: BS
authors.lastname: Nielsen
authors.forename: K
authors.initials: K
authors.lastname: Danø
authors.forename: J
authors.initials: J
authors.lastname: Rømer
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage* / Q000494:pharmacology; D005337:Fibrin / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011956:Receptors, Cell Surface / Q000276:immunology*; D055293:Receptors, Urokinase Plasminogen Activator; D010959:Tissue Plasminogen Activator / Q000235:genetics*
chemical_list: D000911:Antibodies, Monoclonal; C524898:PLAUR protein, human; C524899:Plaur protein, mouse; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D005337:Fibrin; D010959:Tissue Plasminogen Activator