Differential responses of human tumor cell lines to anti-p185HER2 monoclonal antibodies

The HER2 protooncogene encodes a receptor tyrosine kinase, p185^HER2. The overexpression of p185^HER2 has been associated with a worsened prognosis in certain human cancers. In the present work we have screened a variety of different tumor cell lines for p185^HER2 expression using both enzyme-linked immunosorbent and fluorescence-activated cell sorting assays employing murine monoclonal antibodies directed against the extracellular domain of the receptor. Increased levels of p185^HER2 were found in breast (5/9), ovarian (1/6), stomach (2/3) and colorectal (5/16) carcinomas, whereas all kidney and submaxillary adenocarcinoma cell lines tested were negative. Some monoclonal antibodies directed against the extracellular domain of p185^HER2 inhibited growth in monolayer culture of breast and ovarian tumor cell lines overexpressing p185^HER2, but had no effect on the growth of colon or gastric adenocarcinomas expressing increased levels of this receptor. The most potent growth-inhibitory anti-p185^HER2 monoclonal antibody in monolayer culture, designated mumAb 4D5 (a murine IgG1 antibody), was also tested in soft-agar growth assays for activity against p185^HER2-overexpressing tumor cell lines of each type, with similar results. In order to increase the spectrum of tumor types potentially susceptible to monoclonal antibody-mediated anti-p185^HER2 therapies, to decrease potential immunogenicity 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 4D5 (rhu)mAb 4D5 HER2 antibody were constructed. Both engineered antibodies, in combination with human peripheral blood mononuclear cells, elicited antibody-dependent cytotoxic responses in accordance with the level of p185^HER2 expression. Since this cytotoxic activity is independent of sensitivity to mumAb 4D5, the engineered monoclonal antibodies expand the potential target population for antibody-mediated therapy of human cancers characterized by the overexpression of p185^HER2.