Preferential activation of the epidermal growth factor receptor in human colon carcinoma liver metastases in nude mice.

Increased epidermal growth factor receptor (EGF-R) gene expression and functional protein levels correlate with the metastatic potential of human colon carcinoma (HCC) cells in nude mice. The purpose of this study was to determine whether the production of liver metastases by HCC cells depends on the EGF-R activation status and whether different organ microenvironments influence this activation. Using two independent monoclonal antibodies specific for the activated (i.e., tyrosine-phosphorylated) EGF-R, increased immunoreactivity was observed in HCC cells growing as metastatic lesions in the livers of athymic nude mice. Staining was observed throughout these lesions, both peripherally and centrally. In contrast, little or no immunoreactivity for activated EGF-R was observed in primary tumors growing orthotopically in the cecum or ectopically in the subcutis of nude mice. Immunohistochemistry for total EGF-R levels (irrelevant of activation status) demonstrated similar levels of immunoreactivity in HCC tumors growing in the cecum, subcutis, or liver of nude mice, indicating that total EGF-R levels are not altered after growth in these different microenvironments. Controls included immunohistochemistry for total and activated EGF-R levels in HCC cells growing in vitro under serum-free or EGF-stimulated conditions and A431-epidermoid carcinoma growing in nude mice. Western blot analyses confirmed the specificity of the antibodies for the activated EGF-R. These results suggest that the production of liver metastasis by HCC cells depends in part on the response of tumor cells to organ-derived growth factors and hence the activation of specific cell surface tyrosine kinase receptors.