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: Donglin Liu, Chien-Hsing Chang, David V Gold, David M Goldenberg
• Journal: Oncotarget (Oncotarget) Vol. 6 Issue 6 Pg. 4274-85 (Feb 28 2015) ISSN: 1949-2553 [Electronic] United States
• PMID: 25595893 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Antibodies, Monoclonal
• Antigens, Neoplasm
• Biomarkers, Tumor
• Epitopes
• MUC5AC protein, human
• Mucin 5AC
• clivatuzumab

Topics

• Antibodies, Monoclonal (pharmacology)
• Antigens, Neoplasm (analysis, chemistry)
• Biomarkers, Tumor (analysis)
• Blotting, Western
• Carcinoma, Pancreatic Ductal (metabolism)
• Cell Line, Tumor
• Epitopes (analysis, chemistry)
• Humans
• Microscopy, Fluorescence
• Mucin 5AC (chemistry, metabolism)
• Pancreatic Neoplasms (metabolism)