Submicroscopic alterations and gene expression profiles of human colon cancer cell lines in response to cetuximab, gefitinib and EGF

Epidermal growth factor receptor (EGFR), one of the most important cell membrane receptors expressed in normal cells, is frequently overexpressed in colon cancer. EGFR is a pleiotropic signaler and the integrated biological response to EGFR activation varies from mitogenesis to apoptosis, to differentiation and to dedifferentiation even in the same cell, depending on the context. We have investigated the effect of cetuximab or gefitinib (EGFR target therapy molecules) alone and in combination with EGF, the natural ligand binding to EGFR, on human colon cancer cell lines (Caco-2 and HT-29). The aim of the study is to detect changes in gene expression profiles induced with these drug treatments, and to correlate them with the associated cell behaviors. Both drugs affect differentiation and apoptosis. HT-29 and Caco-2 displayed an important reduction of the microvilli (which also lose their erect position in Caco-2), possibly invalidating microvilli absorption function. HT-29 treated with cetuximab lost their boundary contacts and showed filipodi; on the other hand, when treated with gefitinib, they acquired cytoplasmic vesicles, and displayed reshape of the cellular membrane. Both cell lines showed a similar behavior in terms of on/off switched genes upon treatment with cetuximab. The gefitinib global gene expression pattern was different for the 2 cell lines, and directly correlated with EGF treatment. We found interesting cyto-morphological features closely related to gene expression profile. The EGFR inhibitors had a weaker effect in the presence of EGF. Our data show interesting cyto-morphological features possibly correlated to the clinical effects of cetuximab and gefitinib, and these could have implications for cancer therapy, especially as concerns the cellular microenvironment.