Activity of small molecule inhibitors of the epidermal growth factor receptor (EGFR) kinase, on EGFR kinase domain mutants

5288 It was recently suggested that epidermal growth factor receptor (EGFR) mutations may predict sensitivity to small molecule tyrosine kinase inhibitors (TKIs), as several somatic mutations in the EGFR gene have been identified in certain patients with non-small-cell lung cancer (NSCLC). We characterized the activation state of four different EGFR receptors bearing mutations in the kinase domain (G719C, L858R, L861Q, del747-753) and studied their sensitivity to small molecule TKIs. We found two mutants (L858R, L861Q) to be ligand-independent, constitutively activate kinases. Activation of the G719 mutant was found to be ligand-dependent, and the deletion mutant (del747-753) exhibited reduced kinase activity (20-fold less as compare to wild type EGFR). In the present study we determined the inhibitory activity of gefitinib and IM092214 against three EGFR mutants (G719C, L858R, L861Q) and wild type EGFR using enzymatic and cell-based phosphorylation assays. IM092214 is a structurally novel benzoxazepine that potently inhibits the EGFR kinase activity (cell-based IC50 = 60 nM). We found that gefitinib and IM092214 inhibited wild-type and mutant EGFR activity to similar extent in both the enzymatic assay (gefitinib IC50 = 15 nM, IM092214 IC50 = 60 nM) and the cell-based phosphorylation assay (gefitinib IC50 = 20 nM, IM092214 IC50 = 50 nM). Importantly, we did not observe hypersensitivity of any of the tested mutants to gefitinib or IM092214. Our data suggest that there may be other mechanisms responsible for the observed favorable response of certain lung cancer patients with EGFR mutations to TKIs.