EGFR Antagonism using ZD1839 (Iressa) Results in Increased Cytoxic Response to 5-FU in Colon Cancer Cells
University of Tennessee Health Science Center
Aim Adenocarcinoma of the colon and rectum is common in the United States with approximately 155,000 patients diagnosed annually. It is the second leading cause of cancer-related deaths. Significant improvement in disease control has been seen when 5-Fluorouracil (5-FU) is used as a component of systemic chemotherapy for node-positive and metastatic colon cancer. The frequent overexpression of Epidermal Growth Factor Receptor (EGFR) suggest that inhibition of the signal transduction pathway, through receptor antagonism, might be a novel approach to enhance tumor response. This investigation seeks to define the role of EGFR antagonism, using a selective small molecule tyrosine kinase inhibitor (ZD1839), in augmenting cytotoxicity to adjuvant chemotherapy for adenocarcinoma of the colon and rectum. Methods Human colon cancer cells, SW480 were grown in Leibovitz’s L-15 w/L-Glutamine medium supplemented with 10% fetal bovine serum (FBS), 5ml 100X vitamin solution and 5 ml 100X no-essential amino acid solution. Cells were cultured in 37°C, 5% CO2 humidified atmosphere incubator. 5000 cells per well were planted in 96 well cell culture, plate with dose titration for ZD1839 and 5-FU (0.1,0.5,1,5,10ug/ml). MTT assay was performed to assess cytotoxicity. Results There was dose-dependent inhibition of SW480 cells using 5-FU with an IC50 of 1ug/ml (P<0.0001) (Figure 1). ZD1839 resulted in similar dose – dependent inhibition with IC50 of 10μM (P>0.0001). The combination of ZD1839 (Iressa) and 5-FU resulted in a synergistic effect (P>0.0001) (Figure 2, 3). Conclusion ZD1839 resulted in enhanced cytotoxicity in SW480 cell when added to 5FU. EGFR antagonism may provide a novel mechanism for improved response to chemotherapy in the treatment of colon cancers.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 895 (Chemotherapy response).