ELISA for quantitation of the extracellular domain of p185HER2 in biological fluids.

The HER2/neu proto-oncogene encodes a receptor that belong to the tyrosine-specific protein kinase family. Amplification of the HER2 gene in patients with breast and ovarian cancer has been shown to predict poorer survival rates. In order to understand the role of HER2 in malignant and normal cells, it is necessary to devise assays that can quantitate expression levels of the HER2 gene product (p185HER2) in production samples, biopsy specimens and biological fluids. We have developed a simple, quantitative ELISA that uses two monoclonal antibodies directed against the extracellular domain of the HER2 gene product, p185HER2 (HER2 ECD). The assay has a detection range of 0.25-120 ng/ml, is precise and sensitive. The ability of this assay to detect biologically active rHER2 ECD is demonstrated by its correlation to a growth inhibitory bioassay (r = 0.92). The sandwich ELISA can also accurately quantitate rHER2 ECD in mouse and monkey serum. This assay should be useful for quantitating low levels of circulating rHER2 ECD in animals in which rHER2 ECD is being used as antigen for immunotherapy and in patients which 'shed' receptor.