Abstract 850: 32H2, a new diagnostic tool for HER2 CTFs

The tyrosine kinase receptor HER2 belongs to the Epidermal Growth Factor Receptor (EGFR) family and is amplified in 30% of breast cancer patients. These patients are currently treated with Herceptin (Trastuzumab), a monoclonal antibody against the extracellular domain of HER2. A group of HER2 positive patients express a series of carboxy terminal fragments (CTFs) of the receptor. These patients have worse prognosis and are more likely to develop metastasis. In addition, CTFs positive patients are resistant to treatment with Herceptin. Functional characterization of the different CTFs shows that only those containing the transmembrane domain are active. Furthermore, the CTF generated by alternative initiation of translation at Methionine 611, CTF-611, seems to be a hyperactive due to its ability to constitutively form dimers maintained by disulfide bonds. These hyperactive dimers specifically control the expression of genes causally involved in malignant transformation, providing a likely mechanism for the clinical observations made in patients expressing CTFs. To date, the presence of CTFs in breast tumors have been studied by Western blot or by double immunoflourescence, using two antibodies, one targeting the intracellular domain and the other the extracellular domain of the receptor. However, both techniques are not able to distinguish between active and inactive CTFs. In addition, only careful comparison of the electrophoretic migration of the species found in tumor samples with those expressed in cell lines transfected with individual CTFs allows the identification of individual CTF. Obviously these techniques cannot be used to effectively determine the presence of active CTFs in large-scale clinical studies. Furthermore, given its hyperactivity, it would be useful to have a specific antibody against 611-CTF. Here we present the generation and characterization of a monoclonal antibody that recognize specifically 611-CTFs. The low affinity of the antibody for the full-length HER2 may be explained by structural features of the antibody epitope. Using the antibody in a collection of paraffin embedded tumors, we were able to identify a subgroup in the HER2 positive tumors with worst clinical outcome. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 850.