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A Novel Mechanism of Resistance to Epidermal Growth Factor Receptor Antagonism In vivo

Departments of ¹ Surgical Oncology and ² Pharmacology and Therapeutics, Roswell Park Cancer Institute, ³ Department of Surgery, The State University of New York at Buffalo, Buffalo, New York; ⁴ Department of Medicine, University of Michigan, Ann Arbor, Michigan; ⁵ Department of Surgery, The University of Texas at San Antonio, San Antonio, Texas; ⁶ Department of Surgery, Creighton University, Omaha, Nebraska; and ⁷ Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas

Requests for reprints: Michael G. Brattain, Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263. Phone: 716-845-3044; Fax: 716-845-4437; E-mail: michael.brattain{at}roswellpark.org.

Epidermal growth factor receptor (EGFR) is widely expressed in a number of solid tumors including colorectal cancers. Overexpression of this receptor is one means by which a cell can achieve positive signals for survival and proliferation; another effective means is by constitutive activation of EGFR. We have elucidated the role of constitutive EGFR signaling in malignant progression by stably transfecting colon cancer cells with a human transforming growth factor- cDNA (a ligand for EGFR) under repressible control by tetracycline. We show that constitutive expression of transforming growth factor- and its subsequent constitutive activation of EGFR allows for cancer cell survival in response to environmental stress in vitro and in vivo as well. The reversal of constitutive EGFR activation results in the loss of downstream mitogen-activated protein kinase and Akt activation, and a reduction in xenograft size that is associated with decreased proliferation and increased apoptosis. We used CI-1033, a small molecule antagonist of EGFR, to dissect an activation pathway that shows the ability of ERBb2 to activate Akt, but not Erk in the face of EGFR antagonism. This novel escape mechanism is a possible explanation of why anti-EGFR therapies have shown disappointing results in clinical trials. [Cancer Res 2007;67(2):665–73]

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