title: Soluble aminopeptidase N/CD13 in malignant and nonmalignant effusions and intratumoral fluid.
abstract: OBJECTIVE
  On the basis of the finding of marked overexpression in angiogenic microvessels, aminopeptidase N/CD13 has recently been suggested to play a prominent role in tumor angiogenesis. A soluble form of CD13 (sCD13) is present in human plasma, but its role in cancer has not been addressed. We hypothesized that sCD13 would be shed by tumor cells and/or endothelial cells lining tumor vessels, giving high levels of sCD13 in intratumoral fluid (TF) deposits and in malignant effusions. If so, sCD13 could be a convenient potential marker for tumor load and/or activated tumor endothelium.
  
  
  METHODS
  We have measured the specific sCD13 activity in effusions from 90 cancer patients and 12 patients with a nonmalignant condition, and studied its relationship with other major (anti-)angiogenic factors. In a separate group of patients (n = 41), the relationship of sCD13 activity in plasma with tumor load was studied.
  
  
  RESULTS
  The sCD13 activity was highest in plasma from cancer patients 71.9 (fmol/ml/s hydrolyzed substrate) versus 42.4 for healthy subjects. In TF, malignant effusions, and nonmalignant effusions, the activities were 52.8, 33.5, and 18.6, respectively. We further studied the relationship of sCD13 with tumor load as well as with vascular endothelial growth factor (VEGF), endostatin, matrix metalloproteinase (MMP)-2, MMP-9, urokinase-type plasminogen activator, and plasmin. A significant correlation of sCD13 activity in plasma was found with tumor load (r = 0.68; P = 0.01), suggesting that plasma sCD13 is, at least, partly originating from tumor(-endothelium). The concentrations of VEGF and endostatin and the activities of urokinase-type plasminogen activator and MMP-9, but not MMP-2, were significantly higher in TF compared with all other effusions. In TF, a correlation between sCD13 and VEGF was found (r = 0.67; P = 0.03). No correlation of sCD13 with the other protease activities was found.
  
  
  CONCLUSIONS
  The sCD13 activity is elevated in plasma and effusions of cancer patients. A strong correlation of plasma sCD13 with tumor load was found. On the basis of these results, the potential of sCD13 activity as a tumor and/or angiogenesis marker warrants further investigation.
authors.affiliation: Vrÿe Universiteit Medical Center, Department of Medical Oncology, 1081 HV Amsterdam, The Netherlands.
authors.forename: Yvette
authors.initials: Y
authors.lastname: van Hensbergen
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Broxterman
authors.forename: Roeland
authors.initials: R
authors.lastname: Hanemaaijer
authors.forename: Anita S
authors.initials: AS
authors.lastname: Jorna
authors.forename: Natascha A
authors.initials: NA
authors.lastname: van Lent
authors.forename: Henk M W
authors.initials: HM
authors.lastname: Verheul
authors.forename: Herbert M
authors.initials: HM
authors.lastname: Pinedo
authors.forename: Klaas
authors.initials: K
authors.lastname: Hoekman
mesh_terms: D000328:Adult; D001202:Ascitic Fluid / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism*; D018826:CD13 Antigens / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism; D043169:Endostatins; D016228:Endothelial Growth Factors / Q000378:metabolism; D005260:Female; D005341:Fibrinolysin / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008222:Lymphokines / Q000378:metabolism; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D008875:Middle Aged; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D010446:Peptide Fragments / Q000378:metabolism; D010996:Pleural Effusion / Q000378:metabolism* / Q000473:pathology; D011379:Prognosis; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
chemical_list: D014408:Biomarkers, Tumor; D043169:Endostatins; D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D010446:Peptide Fragments; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D016222:Fibroblast Growth Factor 2; D003094:Collagen; D018826:CD13 Antigens; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9