title: Mapping PAM4 (clivatuzumab), a monoclonal antibody in clinical trials for early detection and therapy of pancreatic ductal adenocarcinoma, to MUC5AC mucin.
abstract: BACKGROUND
  PAM4, an antibody that has high specificity for pancreatic ductal adenocarcinoma (PDAC), compared to normal pancreas, benign lesions of the pancreas, and cancers originating from other tissues, is being investigated as a biomarker for early detection, as well as antibody-targeted imaging and therapy. Therefore, the identity of the antigen bound by this monoclonal antibody (MAb) can provide information leading to improved use of the antibody. Prior results suggested the antigen is a mucin-type glycoprotein rich in cysteine disulfide bridges that provide stable conformation for the PAM4-epitope.
  
  
  METHODS
  Indirect and sandwich enzyme immunoassays (EIA) were performed to compare and contrast the reactivity of PAM4 with several anti-mucin antibodies having known reactivity to specific mucin species (e.g., MUC1, MUC4, MUC5AC, etc.). Studies designed to block reactivity of PAM4 with its specific antigen also were performed.
  
  
  RESULTS
  We demonstrate that MAbs 2-11 M1 and 45 M1, each reactive with MUC5AC, are able to provide signal in a heterologous sandwich immunoassay where PAM4 is the capture antibody. Further, we identify MAbs 21 M1, 62 M1, and 463 M1, each reactive with MUC5AC, as inhibiting the reaction of PAM4 with its specific epitope. MAbs directed to MUC1, MUC3, MUC4, MUC16 and CEACAM6 are not reactive with PAM4-captured antigen, nor are they able to block the reaction of PAM4 with its antigen.
  
  
  CONCLUSIONS
  These data implicate MUC5AC as a specific mucin species to which PAM4 is reactive. Furthermore, this realization may allow for the improvement of the current PAM4 serum-based immunoassay for detection of early-stage PDAC by the application of anti-MUC5AC MAbs as probes in this sandwich EIA.
authors.affiliation: Garden State Cancer Center, Center for Molecular Medicine and Immunology, Morris Plains, NJ, USA. dvgold@gscancer.org.
authors.forename: David V
authors.initials: DV
authors.lastname: Gold
authors.forename: Guy
authors.initials: G
authors.lastname: Newsome
authors.forename: Donglin
authors.initials: D
authors.lastname: Liu
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
mesh_terms: D000818:Animals; D055910:Antibodies, Immobilized / Q000737:chemistry*; D000911:Antibodies, Monoclonal / Q000737:chemistry*; D021441:Carcinoma, Pancreatic Ductal / Q000175:diagnosis* / Q000188:drug therapy; D002986:Clinical Trials as Topic; D055088:Early Detection of Cancer; D018604:Epitope Mapping; D006801:Humans; D007118:Immunoassay; D051379:Mice; D008819:Mice, Nude; D055271:Mucin 5AC / Q000276:immunology / Q000378:metabolism*; D009368:Neoplasm Transplantation; D010190:Pancreatic Neoplasms / Q000175:diagnosis* / Q000188:drug therapy
chemical_list: D055910:Antibodies, Immobilized; D000911:Antibodies, Monoclonal; C524678:MUC5AC protein, human; D055271:Mucin 5AC; C000589320:clivatuzumab