Responses of Human Colorectal Tumor Cells to Treatment with the Anti–Epidermal Growth Factor Receptor Monoclonal Antibody ICR62 Used Alone and in Combination with the EGFR Tyrosine Kinase Inhibitor Gefitinib

Matthew P Cunningham,Hilary Thomas,Zhen Fan,Helmout Modjtahedi

doi:10.1158/0008-5472.can-06-1000

Abstract

The anti-epidermal growth factor receptor (EGFR) monoclonal antibody cetuximab has been approved for the treatment of patients with metastatic colorectal cancer. However, there is currently no reliable marker for response to therapy with the EGFR inhibitors. In this study, we investigated the sensitivity of 10 human colorectal tumor cell lines (DiFi, CCL218, CCL221, CCL225, CCL227, CCL228, CCL231, CCL235, CCL244, and HCT-116) to treatment with our anti-EGFR monoclonal antibody, ICR62, and/or the EGFR tyrosine kinase inhibitor, gefitinib. Of the cells examined, only DiFi contained high levels of constitutively active EGFR and were highly sensitive to treatment with both ICR62 (IC(50) = 0.52 nmol/L) and gefitinib (IC(50) = 27.5 nmol/L). In contrast, the growth of other tumor cell lines, which contained low levels of the EGFR, HER-2, and pAkt but comparable or even higher basal levels of phosphorylated mitogen-activated protein kinase (pMAPK), were relatively resistant to treatment with both inhibitors. Both ICR62 and gefitinib induced EGFR down-regulation, reduced the basal levels of pEGFR at five known tyrosine residues, pMAPK, and pAkt, and increased the sub-G(1) population in DiFi cells. However, treatment with a combination of ICR62 and gefitinib neither sensitized colorectal tumor cells that were insensitive to treatment with the single agent nor enhanced the growth-inhibitory effect of the single agent in DiFi cells. These results indicate that basal levels of pMAPK and pAkt are not good indicators of response to the EGFR inhibitors in colorectal cancer cells and dual targeting of the EGFR by a combination of ICR62 and gefitinib is not superior to treatment with a single agent.

Highlights

Colorectal cancer is one of the major types of cancer worldwide, in terms of both morbidity and mortality
The basal level of phosphorylated epidermal growth factor receptor (EGFR), phosphorylated mitogen-activated protein kinase (pMAPK), and phosphorylated Akt were determined in the panel of colorectal tumor cell lines using Western blot analysis (Fig. 1A)
In particular, those with NSCLC, the presence of activating mutations in exons 18 to 21 of the EGFR tyrosine kinase domain have been associated with improved response to therapy with the EGFR tyrosine kinase inhibitors (TKI)

Summary

Introduction

Colorectal cancer is one of the major types of cancer worldwide, in terms of both morbidity and mortality. The two most clinically advanced strategies are the monoclonal antibodies (mAb), which block the extracellular ligand-binding domain, and small molecule tyrosine kinase inhibitors (TKI), which target ATP-binding sites located in the intracellular tyrosine kinase domain of the EGFR [3, 5, 6]. Three such agents, i.e., the anti-EGFR mAb cetuximab (Erbitux), and the TKIs, gefitinib and erlotinib, have been approved for the treatment of patients with metastatic colorectal cancer and non– small cell lung cancer, respectively [5, 6]. Several studies have suggested that the expression of other growth factor receptors (e.g., HER-2, HER-3, and IGF-IR), the presence of somatic mutation in exons 18 to 21 of the EGFR gene, or increased numbers of the EGFR gene might be associated with responses to treatment with the EGFR inhibitors [3, 14,15,16,17,18,19,20,21,22]

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