Expression of HER2 in human gastric cancer cells directly correlates with antitumor activity of a recombinant disulfide-stabilized anti-HER2 immunotoxin

Abstract Background. Amplification of the human epidermal growth factor receptor 2 (HER2) gene and overexpression of the HER2 protein have been associated with an unfavorable prognosis. We determined the efficacy of an anti-HER2 immunotoxin, erb-38 [e23(dsFv)PE38], against human gastric cancer cells. Methods. Immunotoxin was made by fusing the disulfide-stabilized Fv fragments (dsFv) of a monoclonal antibody e23 to a truncated mutant of M r 38 Pseudomonas exotoxin (PE38) that lacks its cell-binding domain. Results. The immunotoxin-mediated cytotoxicity directly correlated with the expression levels of the HER2 gene and protein in human gastric cancer cells. Interestingly, MKN-45P cells, a variant line of MKN-45 producing peritoneal dissemination and ascites in vivo, expressed a higher level of HER2 and were more sensitive to erb-38 than MKN-45 cells. RFB-4, a control anti-CD22 immunotoxin, was cytotoxic against none of the tested human gastric cancer cells, also suggesting that the lysis mediated by erb-38 was specific for HER2 expression. Three consecutive iv injections of erb-38 at doses of 0.5 or 5 μg/body eradicated experimental liver metastases and peritoneal disseminations produced by MKN-45P in a dose-dependent manner. Conclusions. We conclude that an erb-38 anti-HER2 immunotoxin has specific antitumor activities against human gastric cancer cells overexpressing HER2.