Generation of Novel Anti-CLDN18.2 Monoclonal Antibodies as Therapies for Gastric and Pancreatic Cancer

摘要

Claudin-18 (CLDN18) belongs to a large family of four span transmembrane proteins called claudin. These proteins are the essential components of the mammalian tight junctions (TJs) in the epithelial cells. Claudin-18 has two splice variants, 18.1 and 18.2. While CLDN18.1 is specifically expressed in the lung tissue, CLDN18.2 expression in normal tissue is more restricted and is only detected in small patches of stomach mucosal. CLDN18.2 expression is elevated in many types of epithelial cancers including stomach, esophagus, pancreatic and ovarian cancers. The expression of CLDN18.2 is not only detected in primary tumors, but also in the metastatic sites. Therefore, CLDN18.2 is an ideal target for monoclonal antibody-based cancer therapies. Anti-CLDN18.2 monoclonal antibody Claudiximab demonstrated promising results in the Phase II clinic trial for gastric cancers. CLDN18.2 specific antibodies are difficult to generate due to its high homology to CLDN18.1. There are only seven amino acid differences between these two splice variants in the first extra cellular loop. Using a combination of DNA, protein, and transfected cells as the immunogens, coupled with high throughput FACS-based hybridoma screening approach, we have successfully generated a panel of mouse monoclonal antibodies which are highly specific for CLDN 18.2. These antibodies had high affinities for CLDN18.2 while they did not bind to CLDN18.1. These anti-CLDN18.2 antibodies had similar or better binding affinity to CLDN18.2, compared to the IMAB 362 (Claudiximab). In addition, we demonstrated that these antibodies bind to human gastric carcinoma cell line KATO III. Currently we are analyzing by IHC the binding specificity of these antibodies for various cancer tissue samples from gastric and pancreatic cancer patients. We are also generating humanized versions of these mouse antibodies and preparing for CMC analysis.