RT Journal Article SR Electronic T1 A Novel Mechanism of Resistance to Epidermal Growth Factor Receptor Antagonism In vivo JF Cancer Research JO Cancer Res FD American Association for Cancer Research SP 665 OP 673 DO 10.1158/0008-5472.CAN-06-2773 VO 67 IS 2 A1 Rajput, Ashwani A1 Koterba, Alan P. A1 Kreisberg, Jeffrey I. A1 Foster, Jason M. A1 Willson, James K.V. A1 Brattain, Michael G. YR 2007 UL http://cancerres.aacrjournals.org/content/67/2/665.abstract AB 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-α cDNA (a ligand for EGFR) under repressible control by tetracycline. We show that constitutive expression of transforming growth factor-α 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] ©2007 American Association for Cancer Research.