title: Claudin-containing exosomes in the peripheral circulation of women with ovarian cancer.
abstract: BACKGROUND
  The absence of highly sensitive and specific serum biomarkers makes mass screening for ovarian cancer impossible. The claudin proteins are frequently overexpressed in ovarian cancers, but their potential as prognostic, diagnostic, or detection markers remains unclear. Here, we have explored the possible use of these proteins as screening biomarkers for ovarian cancer detection.
  
  
  METHODS
  Claudin protein shedding from cells was examined by immunoblotting of conditioned culture media. The presence of claudins in exosomes released from ovarian cancer cells was demonstrated by sucrose gradient separation and immunogold electron microscopy experiments. Claudin-4-containing exosomes in the plasma of ovarian cancer patients were evaluated in a pilot panel of 63 ovarian cancer patients and 50 healthy volunteers. The CA125 marker was also assessed in these samples and compared with claudin-4 positivity.
  
  
  RESULTS
  We show that full-length claudins can be shed from ovarian cancer cells in culture and found in the media as part of small lipid vesicles known as exosomes. Moreover, 32 of 63 plasma samples from ovarian cancer patients exhibited the presence of claudin-4-containing exosomes. In contrast, only one of 50 samples from individuals without cancer exhibited claudin-4-positive exosomes. In our small panel, at a specificity of 98%, the claudin-4 and CA125 tests had sensitivities of 51% and 71%, respectively. The two tests did not appear to be independent and were strongly correlated.
  
  
  CONCLUSIONS
  Our work shows for the first time that claudin-4 can be released from ovarian cancer cells and can be detected in the peripheral circulation of ovarian cancer patients. The development of sensitive assays for the detection of claudin-4 in blood will be crucial in determining whether this approach can be useful, alone or in combination with other screening methods, for the detection of ovarian cancer.
authors.affiliation: Laboratory of Cellular and Molecular Biology, National Institute on Aging, Baltimore, MD, USA. lijiang@grc.nia.nih.gov
authors.forename: Jianghong
authors.initials: J
authors.lastname: Li
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Sherman-Baust
authors.forename: Miyun
authors.initials: M
authors.lastname: Tsai-Turton
authors.forename: Robert E
authors.initials: RE
authors.lastname: Bristow
authors.forename: Richard B
authors.initials: RB
authors.lastname: Roden
authors.forename: Patrice J
authors.initials: PJ
authors.lastname: Morin
mesh_terms: D045744:Cell Line, Tumor; D062506:Claudin-4; D003470:Culture Media / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D055354:Exosomes / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission / Q000379:methods; D010051:Ovarian Neoplasms / Q000097:blood* / Q000175:diagnosis* / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D012680:Sensitivity and Specificity; D013395:Sucrose / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: C568157:CLDN4 protein, human; D062506:Claudin-4; D003470:Culture Media; D017077:Culture Media, Conditioned; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C549756:NBR1 protein, human; D011506:Proteins; D013395:Sucrose