title: Specific inhibition of fibroblast activation protein (FAP)-alpha prevents tumor progression in vitro.
abstract: OBJECTIVE
  Solid tumors modulate their environment to keep non-malignant stromal cells in a tumor-promoting state. The main cells in the stroma of epithelial derived tumors are cancer associated fibroblasts (CAF) that are critical to tumorigenesis and angiogenesis. CAFs also supply the tumor cells with growth factors and extracellular matrix (ECM) degrading enzymes. They are thus essential for tumor initiation as well as tumor progression and metastasis, suggesting that they represent an ideal cellular target of an integrative tumor therapy. Fibroblast activation protein (FAP) is a well-defined marker, expressed at high levels on the cell surface of CAFs. FAP, a constitutively active serine peptidase with both dipeptidyl peptidase IV (DPP IV) and collagenase/gelatinase activity, promotes malignant and invasive behavior of epithelial cancers. High stromal expression levels of FAP correlate with poor prognosis. FAP is difficult to detect in non-diseased adult tissue, but it is generally expressed at sites of tissue remodeling.
  
  
  METHODS
  In our experiments, we aimed for a reduction of the pro-tumorigenic activities of CAFs by depleting FAP from fibroblasts growing in a composite environment with epithelial tumor cells.
  
  
  RESULTS
  FAP depletion was achieved by two therapeutically relevant approaches: a novel internalizing anti-FAP IgG1 antibody and FAP gene knock-down by siRNA delivery. The antibody effectively removed FAP from the cell surface and was capable of reversing the FAP mediated migratory and invasive capacity. FAP RNA interference was equally effective when compared to the antibody.
  
  
  CONCLUSIONS
  Thus, targeting FAP on CAF suppresses pro-tumorigenic activities and may result in a clinically effective reduction of tumor progression and dissemination.
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany. Electronic address: volker.teichgraeber@nct-heidelberg.de.
authors.forename: Volker
authors.initials: V
authors.lastname: Teichgräber
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Carmen
authors.initials: C
authors.lastname: Monasterio
authors.affiliation: Division of Oncology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Krishna
authors.initials: K
authors.lastname: Chaitanya
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Regina
authors.initials: R
authors.lastname: Boger
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Gordon
authors.affiliation: Kantonsspital Liestal, Department of Medicine and Clinical Research, University Hospital Basel, Liestal, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dieterle
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Jäger
authors.affiliation: National Center for Tumor Diseases, Department of Medical Oncology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bauer
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000502:physiology; D010450:Endopeptidases; D005347:Fibroblasts / Q000378:metabolism*; D018093:Gelatinases / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D018613:Microscopy, Confocal; D012697:Serine Endopeptidases / Q000378:metabolism*; D000099167:Fibroblast Activation Protein Alpha
chemical_list: D010450:Endopeptidases; D018093:Gelatinases; D008565:Membrane Proteins; D012697:Serine Endopeptidases; D000099167:Fibroblast Activation Protein Alpha
keywords: Activated fibroblasts; Cancer associated fibroblasts; FAP; Invasion; Migration; Proliferation; Tumor stroma