Side-by-side analysis of five clinically tested anti-EpCAM monoclonal antibodies

We recombinantly produced all antibodies but murine edrecolomab and investigated them for binding affinity, EpCAM epitope recognition, ADCC and CDC, and inhibition of breast cancer cell proliferation.ING-1 and 3622W94 bound to EpCAM with much higher affinity than adecatumumab and edrecolomab. Edrecolomab, ING-1, and 3622W94 all recognized epitopes in the exon 2-encoded N-terminal domain of EpCAM, while adecatumumab recognized a more membrane proximal epitope encoded by exon 5. All antibodies induced lysis of EpCAM-expressing cancer cell lines by both ADCC and CDC with potencies that correlated with their binding affinities. The chimeric version of edrecolomab with a human Fcγ1 domain was much more potent in ADCC than the murine IgG2a version. Only adecatumumab showed a significant inhibition of MCF-7 breast cancer cell proliferation in the absence of complement and immune cells.A moderate binding affinity and recognition of a distinct domain of EpCAM may best explain why adecatumumab showed a larger therapeutic window in cancer patients than the two high-affinity IgG1 antibodies ING-1 and 3622W94, both of which caused acute pancreatitis.Epithelial cell adhesion molecule EpCAM (CD326; 17-1A antigen) was among the first human tumor-associated antigens discovered [1]. It was initially identified by the monoclonal antibody (mAb) 17-1A after immunization of mice with human colorectal cancer cells [2]. Using a similar approach, the EpCAM antigen has been identified many more times and each time given the name of the respective monoclonal antibody [3,4]. For a long time, EpCAM was considered a mere cell surface protein mediating homotypic cell adhesion [5-7]. This function did not well explain its frequent and high expression in primary tumors and metastases [1,3], correlation of expression with poor survival prognosis [1,8], and its expression on tumor-initiating or cancer stem cells [9-12]. Only recently, EpCAM was shown to play a role in cell proliferation, signal trans