Monoclonal antibody 425 inhibits growth stimulation of carcinoma cells by exogenous EGF and tumor-derived EGF/TGF-alpha.

Carcinoma cells frequently coexpress transforming growth factor (TGF)-alpha and its receptor, the epidermal growth factor (EGF) receptor, implicating an autocrine function of carcinoma-derived TGF-alpha. Using a monoclonal antibody (425) to the EGF-receptor, we investigated the role of exogenous and tumor cell-derived EGF/TGF-alpha mitogenic activities in proliferation of cell lines derived from solid tumors. Monoclonal antibody 425 was chosen for these studies because it inhibits binding of EGF/TGF-alpha to the EGF-receptor and effectively blocks activation of the EGF-receptor by EGF/TGF-alpha. Seven malignant cell lines originating from carcinomas of colon, pancreas, breast, squamous epithelia, and bladder expressed surface EGF-receptor and secreted EGF/TGF-alpha-like mitogenic activities into their tissue culture media. All cell lines were maintained in a defined medium free of exogenous EGF/TGF-alpha. EGF and TGF-alpha added to the culture medium stimulated proliferation of five cell lines to comparable levels. EGF/TGF-alpha-dependent proliferation was significantly reduced by addition of MAb 425 to culture media. In addition, monoclonal antibody 425 reduced proliferation of the five EGF/TGF-alpha responsive cell lines in the absence of exogenous EGF/TGF-alpha. Antiproliferative effects induced by monoclonal antibody 425 were reversible and could be overcome by addition of EGF to culture media. Our results indicate that tumor-derived EGF-receptor-reactive mitogens can promote proliferation of carcinoma cells in an autocrine fashion.