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Departments of ¹ Internal Medicine, ² Radiotherapy-Radiooncology, ³ Gynaecology and Obstetrics and ⁴ Institute of Medical Chemistry and Biochemistry, Innsbruck Medical University, Innsbruck, Austria

Requests for reprints: Heinz Zwierzina, Department of Internal Medicine, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria. Phone: 43-512-504-24206; Fax: 43-512-504-24209. E-mail: Heinz.Zwierzina{at}uibk.ac.at

The monoclonal antibody C225 directed against the epidermal growth factor receptor (EGFR) blocks downstream mitogenic signaling and is effective in patients with advanced colorectal cancer. Clinical data, however, suggest the presence of primary and secondary resistance mechanisms that are hardly understood. To define proteins involved in EGFR-triggered growth regulation and potential resistance mechanisms, we characterized the proteome profile of two colorectal cancer cell lines with a high expression of functional EGFR but a different response to treatment with C225. In Caco-2 and HRT-18, a complete saturation of EGFR was achieved after incubation with C225; whereas Caco-2 showed inhibition of proliferation, growth of HRT-18 was not suppressed. Using two-dimensional electrophoresis and subsequent mass spectrometry, we identified 14 proteins differentially expressed in both cell lines. All proteins are involved in metabolic pathways and malignant growth. Expression of enzymes such as ubiquitin carboxyl-terminal hydrolase isozyme 1, glutathione S-transferase P, and chloride intracellular channel protein 1 does not seem to interfere with the antiproliferative effect of anti-EGFR antibody. On the other hand, expression of proteins such as fatty acid binding protein and heat shock protein 27 might constitute strong antiapoptotic effects contributing to the nonresponse of HRT-18 to C225 treatment. Proteome-based investigations can help us better understand the complex protein interactions involved in EGFR signaling and its blockage by therapeutic monoclonal antibodies.

Key Words: colorectal cancer • Cetuximab (C225) • resistance • proteomics

Grant support: Austrian National Bank project 10135.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 5/18/04; revised 9/ 7/04; accepted 9/28/04.