Characterization of monoclonal antibody PAM4 reactive with a pancreatic cancer mucin

Abstract

A monoclonal antibody (MAb), PAM4, having reactivity with pancreatic carcinoma has been developed. PAM4 is an IgG1 immunoglobulin produced by immunization of mice with mucin purified from the xenografted RIP1 human pancreatic carcinoma. An immunohistochemical study of normal adult tissues showed the PAM4 reactive epitope to be restricted to the gastrointestinal tract and absent from normal pancreas. In neoplastic tissue, PAM4 was reactive with 85% of the pancreatic carcinomas, approximately half of the colon cancers and none of the breast, ovarian, prostate, renal and liver cancers. PAM4 was, in general, non-reactive with pancreatitis specimens whereas CA19.9 and DUPAN2 were strongly reactive with each one. Treatment of the mucin antigen by heating, reduction of disulfide bonds, or protease digestion abolished immunoreactivity with PAM4. Treatment of the mucin by neuraminidase or periodate oxidation reduced immunoreactivity but did not completely abolish it. Our data are consistent with the proposal that the PAM4 epitope is a conformationally dependent peptide epitope and that certain carbohydrate structures are necessary in order to maintain the correct peptide conformation. The high specificity and intense reactivity of PAM4 with pancreatic carcinoma tissue suggests that the antibody may prove useful for in vitro diagnostic assays as well as in vivo targeting of diagnostic and therapeutic agents.

Combined 90Yttrium‐DOTA‐labeled PAM4 antibody radioimmunotherapy and gemcitabine radiosensitization for the treatment of a human pancreatic cancer xenograft

“…2,61 MAb PAM4 is reactive with the MUC1 antigen as produced by the majority of pancreatic adenocarcinomas. 26 Clinical studies have demonstrated specific targeting of radiolabeled PAM4 to pancreatic tumors within an initial group of patients. 27,28 In preclinical studies, PAM4 targeted primary subcutaneous and orthotopic sites as well as metastatic tumors.…”

“…Conjugation of DOTA did not alter the immunoreactivity of the PAM4 antibody as determined by enzyme immunoassay with MUC1 antigen. 26 The specific activities for the 90 Y-DOTA-cPAM4 were in the range of 2.64 -3.21 Ci/g with less than 6% unbound material, while the specific activities for the 90 Y-DOTA-hLL2 were in the range of 3.39 -4.43 Ci/g with less than 12.5% unbound material. The final labeled antibody product was placed in a dose calibrator (Capintec CRC15R, Ramsey, NJ) and the time and activity recorded.…”

“…Animal studies were approved by the Garden State Cancer Center's Institutional Animal Care and Use Committee and performed in accordance with the American Association of Laboratory Animal Care (AALAC), United States Department of Agriculture (USDA) and Department of Health and Human Services (DHHS) regulations. 90 Y The purification and characterization of chimeric PAM4 (cPAM4) and isotype-matched, control, humanized LL2 (hLL2) anti-CD22, B-cell lymphoma MAb have been described; 26,32 hLL2 was provided by Immunomedics, Inc. (Morris Plains, NJ). DOTA (Macrocyclics, Inc., Richardson, TX) was conjugated to cPAM4 IgG by a previously described method that provides for prolonged, stable chelation of 90 yttrium.…”

“…We have developed MAb PAM4 that recognizes the MUC1 glycoprotein expressed selectively by human pancreatic cancer. 26 By immunohistology, PAM4 was shown to be reactive with 85% of pancreatic cancer specimens examined. Except for a weak reactivity within the normal gastrointestinal tract, the antibody was not reactive with normal tissues, including normal pancreas.…”

Pretargeted Radioimmunotherapy for Hematologic and Other Malignancies

“…The anti-mucin 1 glycoprotein (MUC1) monoclonal antibody, PAM4, recognizes an epitope that is accessible in the majority of invasive pancreatic adenocarcinomas, including early stage disease, but not in normal pancreas or pancreatitis, suggesting its potential value as a tumor-targeting antibody. 129,130 However, although PAM4 has been successfully used to image pancreatic cancers, and preclinical models of RIT using PAM4 appeared promising, early clinical results from a phase 1 trial with conventional 90 Y-labeled RIT were relatively modest. 131,132 PRIT approaches with PAM4, using a bivalent and, subsequently, a trivalent bispecific antibody that binds the HSG hapten (TF10), have recently demonstrated improved imaging abilities relative to conventional RIT.…”