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Alterations in the expression of the epidermal growth factor (EGF) receptor ErbB family are frequently encountered in a number of human cancers. Two of these receptors, ErbB3 and ErbB4, are known to bind a family of related proteins termed heregulins (HRGs) or neu differentiation factors. In biologically relevant systems, interaction of HRG with ErbB3 or ErbB4 results in the transactivation of ErbB2. In this report, we show that ErbB2 is a critical component in mediating HRG responsiveness in a panel of human breast and ovarian tumor cell lines. Because HRGs have been reported to elicit diverse biological effects on cultured cells, including growth stimulation, growth inhibition, and induction of differentiation, we systematically examined the effect of rHRG beta 1 on tumor cell proliferation. HRG binding studies were performed with a panel of breast and ovarian tumor cell lines expressing a range of levels of ErbB2. The biological responses to HRG were also compared to EGF and to the growth-inhibitory anti-ErbB2 antibody, 4D5. In most cases, HRG stimulation of DNA synthesis correlated with positive effects on cell cycle progression and cell number and with enhancement of colony formation in soft agar. On each cell line tested, the HRG effects were distinguishable from EGF and 4D5. Our findings indicate that HRG induces cell proliferation in a number of tumor cell lines. In addition, we show that methods for measuring cell proliferation, as well as experimental conditions, are critical for determining HRGs effect on tumor cell growth in vitro.

The proto-oncogene HER2/neu encodes a protein tyrosine kinase (p185HER2) that is homologous to the human epidermal growth factor receptor. Amplification and/or overexpression of HER2/neu occurs in multiple human malignancies and appears to be integrally involved in progression of some breast and ovarian cancers. Because of this fact, HER2/neu is an intriguing target for specific cancer therapeutic strategies. One such strategy is active specific immunotherapy, in which the immune system is targeted at specific antigens expressed by tumor cells. We have employed a transfected cell line that secretes the extracellular domain of p185HER2 as a source of HER2-derived immunogen in a guinea pig model. The immunized animals developed a cellular immune response, as monitored by delayed-type hypersensitivity, and antisera derived from immunized animals specifically inhibited the in vitro growth of human breast tumor cells overexpressing p185HER2. These data provide support for an immunotherapeutic approach to cancers characterized by overexpression of the HER2/neu proto-oncogene.

The HER2/c-erbB-2 gene encodes the epidermal growth factor receptorlike human homolog of the rat neu oncogene. Amplification of this gene in primary breast carcinomas has been show to correlate with poor clinical prognosis for certain cancer patients. We show here that a monoclonal antibody directed against the extracellular domain of p185HER2 specifically inhibits the growth of breast tumor-derived cell lines overexpressing the HER2/c-erbB-2 gene product and prevents HER2/c-erbB-2-transformed NIH 3T3 cells from forming colonies in soft agar. Furthermore, resistance to the cytotoxic effect of tumor necrosis factor alpha, which has been shown to be a consequence of HER2/c-erbB-2 overexpression, is significantly reduced in the presence of this antibody.