title: Identification of PAM4 (clivatuzumab)-reactive epitope on MUC5AC: a promising biomarker and therapeutic target for pancreatic cancer.
abstract: PAM4 is a monoclonal antibody showing high specificity for pancreatic ductal adenocarcinoma (PDAC). Humanized PAM4 labeled with 90Y in combination with low-dose gemcitabine has shown promising therapeutic activity, and is being evaluated in a phase III clinical trial. Prior efforts have suggested that PAM4 potentially reacts with MUC5AC, a secretory mucin expressed de novo in early pancreatic neoplasia and retained throughout disease progression. In present study, we provide further evidence validating MUC5AC as the PAM4 antigen, and locate PAM4-reactive epitope within the N-terminal cysteine-rich subdomain 2 (Cys2), thus differentiating PAM4 from most anti-MUC5AC antibodies known to-date. Specifically, we show (i) PAM4-antigen and MUC5AC were co-localized in multiple human cancer cell lines, including Capan-1, BxPC-3, and CFPAC-1; (ii) MUC5AC-specific siRNA prominently reduced the expression of both MUC5AC and PAM4-antigen in CFPAC-1 cells; (iii) PAM4 preferentially binds to the void-volume fractions from Sepharose-CL2B chromatography of Capan-1 culture supernatants, which were revealed by Western blot to display the ladder pattern characteristic of oligomeric MUC5AC; and (iv) the N-terminal Cys2 within several recombinant MUC5AC fragments is essential for binding to PAM4. These findings shed light on the mechanism of PAM4-based diagnosis and treatment for pancreatic cancer, and guide further exploration of its clinical utility.
authors.affiliation: IBC Pharmaceuticals, Inc., Morris Plains, New Jersey 07950, United States of America.
authors.forename: Donglin
authors.initials: D
authors.lastname: Liu
authors.affiliation: IBC Pharmaceuticals, Inc., Morris Plains, New Jersey 07950, United States of America.|Immunomedics, Inc., Morris Plains, New Jersey 07950, United States of America.
authors.forename: Chien-Hsing
authors.initials: CH
authors.lastname: Chang
authors.affiliation: Garden State Cancer Center, Center for Molecular Medicine and Immunology, Morris Plains, New Jersey 07950, United States of America.
authors.forename: David V
authors.initials: DV
authors.lastname: Gold
authors.affiliation: IBC Pharmaceuticals, Inc., Morris Plains, New Jersey 07950, United States of America.|Immunomedics, Inc., Morris Plains, New Jersey 07950, United States of America.|Garden State Cancer Center, Center for Molecular Medicine and Immunology, Morris Plains, New Jersey 07950, United States of America.
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000032:analysis / Q000737:chemistry; D014408:Biomarkers, Tumor / Q000032:analysis*; D015153:Blotting, Western; D021441:Carcinoma, Pancreatic Ductal / Q000378:metabolism*; D045744:Cell Line, Tumor; D000939:Epitopes / Q000032:analysis / Q000737:chemistry; D006801:Humans; D008856:Microscopy, Fluorescence; D055271:Mucin 5AC / Q000737:chemistry / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D000939:Epitopes; C524678:MUC5AC protein, human; D055271:Mucin 5AC; C000589320:clivatuzumab