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.