Epidermal growth factor receptor-related protein: a potential therapeutic agent for colorectal cancer

Abstract

Background & Aims: Epidermal growth factor receptor is frequently implicated in epithelial cancers and is, therefore, being considered as a potential target for therapy. Recently, we reported the isolation and characterization of epidermal growth factor receptor–related protein, a negative regulator of epidermal growth factor receptor. To discern whether epidermal growth factor receptor-related protein could be an effective therapeutic agent for colorectal cancer, we generated epidermal growth factor receptor–related protein fusion protein and studied its effect on the growth of colon cancer cells in vivo and in vitro. We also studied whether epidermal growth factor receptor-related protein expression is altered in colorectal cancer. Methods: A 55-kilodalton epidermal growth factor receptor–related protein fusion protein with V5 and His tags was generated in a drosophila expression system and subsequently purified by a His antibody affinity column. Rabbit polyclonal antibodies against epidermal growth factor receptor-related protein were used to examine the expression of epidermal growth factor receptor–related protein. Results: Epidermal growth factor receptor-related protein expression was found to be high in benign human colonic epithelium but low in adenocarcinoma. Exposure of the colon cancer cell lines HCT-116 and Caco-2 to purified recombinant epidermal growth factor receptor–related protein caused a marked inhibition of proliferation, as well as attenuation of basal and ligand-induced stimulation of epidermal growth factor receptor phosphorylation. Epidermal growth factor receptor-related protein-induced inhibition of proliferation of colon cancer cells was prevented by epidermal growth factor receptor–related protein antibodies. Reduced epidermal growth factor receptor phosphorylation was partly due to sequestration of epidermal growth factor receptor ligands by epidermal growth factor receptor-related protein, resulting in the formation of inactive heterodimers with epidermal growth factor receptor. Intratumoral or subcutaneous (away from the tumor site) injections of purified epidermal growth factor receptor–related protein caused regression of palpable colon cancer xenograft tumors in some severely compromised immunodeficient mice and arrested tumor growth in others. Conclusions: We propose that epidermal growth factor receptor-related protein inhibits cellular growth by attenuating epidermal growth factor receptor signaling processes and is an effective therapeutic agent for colorectal cancer.