DIFFERENTIAL RESPONSES OF HUMAN TUMOR-CELL LINES TO ANTI-P185(HER2) MONOCLONAL-ANTIBODIES

The HER2 protooncogene encodes a receptor tyrosine kinase, p185HER2. T he overexpression of p185HER2 has been associated with a worsened prog nosis in certain human cancers. In the present work we have screened a variety of different tumor cell lines for p185HER2 expression using b oth enzyme-linked immunosorbent and fluorescence-activated cell sortin g assays employing murine monoclonal antibodies directed against the e xtracellular domain of the receptor. Increased levels of p185HER2 were found in breast (5/9), ovarian (1/6), stomach (2/3) and colorectal (5 /16) carcinomas, whereas all kidney and submaxillary adenocarcinoma ce ll lines tested were negative. Some monoclonal antibodies directed aga inst the extracellular domain of p185HER2 inhibited growth in monolaye r culture of breast and ovarian tumor cell lines overexpressing p185HE R2, but had no effect on the growth of colon or gastric adenocarcinoma s expressing increased levels of this receptor. The most potent growth -inhibitory anti-p185HER2 monoclonal antibody in monolayer culture, de signated mumAb 4D5 (a murine IgG1kappa antibody), was also tested in s oft-agar growth assays for activity against p185HER2-overexpressing tu mor cell lines of each type, with similar results. In order to increas e the spectrum of tumor types potentially susceptible to monoclonal an tibody-mediated anti-p185HER2 therapies, to decrease potential immunog enicity issues with the use of murine monoclonal antibodies for human therapy, and to provide the potential for antibody-mediated cytotoxic activity, a mouse/human chimeric 4D5 (chmAb 4D5) and a ''humanized'' 4 D5 (rhu)mAb 4D5 HER2 antibody were constructed. Both engineered antibo dies, in combination with human peripheral blood mononuclear cells, el icited antibody-dependent cytotoxic responses in accordance with the l evel of p185HER2 expression. Since this cytotoxic activity is independ ent of sensitivity to mumAb 4D5, the engineered monoclonal antibodies expand the potential target population for antibody-mediated therapy o f human cancers characterized by the overexpression of p185HER2.