Global gene expression analysis between cetuximab-sensitive and cetuximab-resistant colorectal cancer cells

Cetuximab is an epidermal growth factor receptor (EGFR)-blocking antibody approved for treatment of metastatic colorectal cancer. We examined differences in global gene expression between the syngeneic DiFi colorectal cancer cells, and a subline of DiFi cells with acquired resistance to cetuximab (DiFi5). We used Affymetrix HG-U133A array to compare the expression pattern of genes that are up-regulated or down-regulated between the parental DiFi colorectal cancer cells and the cetuximab-resistant DiFi5 cells. We generated a cetuximab-resistant DiFi subline, termed DiFi5, by chronic exposure of parental DiFi cells to serially increased doses of cetuximab (from 0.5 nM to 5 nM) for over 1 year. The resulting DiFi5 subline exhibits significant resistance to cetuximab-induced apoptosis. After we confirmed that the phenotype was stable over a period of time of more than 6 months, the RNA from DiFi and DiFi5 cells were extracted and hybridized to an Affymetrix HG-U133A array according to the manufacturer’s instructions. Following the hybridization, the array was scanned using a laser confocal scanner, and microarray image data were analyzed using DNA-Chip Analyzer (dChip), version 1.3, by the Sequencing and Microarray Facility at MD Anderson Cancer Center.