Many tumor-specific or tumor-associated antigens have been discovered, but only a few of them have been successfully used for cancer therapy. Not only are the pharmacological properties of therapeutic drug molecules critical to the clinical success, the biological nature of the target antigens has a big influence on the therapeutic outcome.

In searching for good drug targets for cancer, our lab discovered a cell surface protein called mesothelin in the 1990s. It is highly expressed in many tumors such as mesothelioma, ovarian cancer, pancreatic cancer and lung cancer. However, it only has minor expression in normal mesothelial cells lining the pleura, pericardium and peritoneum. This expression pattern makes it an attractive target. We designed a mesothelin targeted immunotoxin called SS1P in which the Fv portion of an anti-mesothelin antibody is fused to a truncated portion of Pseudomonas exotoxin A (PE38).