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. Specificall... More
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.
