Molecular markers for determining Gefitinib sensitivity

1272 Gefitinib sensitivity has been associated with EGFR mutational status, yet not all tumors containing mutations are sensitive to gefitinib and some tumors lacking mutations are sensitive to gefitinib. We screened a panel of NSCLC cell lines for gefitinib sensitivity, EGFR mutational status, HER family proteins levels and ligand expression levels. Additionally, affymetrix microarray analysis was performed on these cell lines. We identified 8 EGFR mutant cell lines, 5 of which were sensitive to gefitinib. Gefitinib sensitive cell lines all express EGFR and several vastly overexpress it. The levels of HER2 and HER3 vary, while HER4 expression is very low. One cell line, HCC2935, expresses EGFR, HER2 & 3 and numerous EGFR ligands, but not Heregulin. While addition of Heregulin to HCC2935 does not effect growth, it does induce gefitinib resistance. Analysis of ligand expression shows that gefitinib sensitive lines tend to overexpress EGFR ligands, particularly Amphiregulin and Epiregulin and have relatively low levels of the HER3 ligand Heregulin. Conversely, expression of HER3 and Heregulin at levels similar to or greater than EGFR is associated with gefitinib resistance. Tumor response to gefitinib predictions can be improved by knowledge of the relative levels of EGFR to HER3 on the receptor side as well as EGFR ligand (particularly Epiregulin and Amphiregulin) to the HER3 ligand Heregulin. This suggests that the HER3 pathway signals parallel to the EGFR pathway in NSCLC and its activation is associated with gefitinib resistance. Finally we present a model that may explain EGFR family ligand receptor interactions and their role in gefitinib sensitivity/resistance.