Abstract 23: Sensitivity of EGFR exon 20 insertion mutations to EGFR inhibitors is determined by their location within the tyrosine kinase domain of EGFR

Abstract

Abstract Background: Epidermal growth factor receptor (EGFR) mutations define an important subgroup of non-small-cell lung cancer (NSCLC). Most patients whose tumors harbor exon 19 deletions or L858R EGFR mutations have responses to reversible ATP-mimetic EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib. Exon 20 inframe insertion mutations comprise ∼4% of all EGFR mutations, occur at the N-lobe of EGFR after its C-helix (after AA M766; notwithstanding some C-helix exon 20 insertions have been reported affecting E762 to Y764), and most NSCLCs with EGFR exon 20 insertion mutations display lack of responses to EGFR TKIs. The reported response rate is below 5% and most patients have short intervals of disease control (Yasuda et al. Lancet Oncol 2011). Up to now, very few EGFR exon 20 insertion mutations had been studied using in vitro models and there was no available NSCLC cell line with such a mutation. Objectives: In the present study, we have attempted to: 1) study the most comprehensive panel of EGFR exon 20 insertion mutations, 2) evaluate their pattern of response/resistance to EGFR TKIs, and 3) derive a novel NSCLC cell line with an exon 20 insertion mutation. Methods: Response to EGFR TKIs of EGFR exon 20 insertion mutated NSCLCs was compiled. We generated a panel of representative exon 20 EGFR mutant constructs using site-directed mutagenesis. Vectors were introduced into Cos-7 or Ba/F3 cells for in vitro analysis. In addition, NSCLC cell lines with EGFR mutations were evaluated and compared to a novel malignant pleural effusion-derived cell line. Results: The NSCLC with EGFR-A763_Y764insFQEA (located within the C-helix of EGFR) achieved a partial response to erlotinib that lasted 18 months. Most other exon 20 insertion mutation-positive NSCLCs (15/16, p=0.11) did not respond. The cell line with EGFR-A763_Y764insFQEA had phosphorylated EGFR, ERK and AKT inhibited by nanomolar concentrations of erlotinib; and subsequently underwent upregulation of the pro-apoptotic BH3-only BIM and apoptosis. Eight different exon 20 insertion mutations were studied (including EGFR-A763_Y764insFQEA, A767_V769dupASV, D770_N771insNPG, H773_V774insH). All, but A763_Y764insFQEA, were resistant to micromolar concentrations of erlotinib/other TKIs. Ba/F3 cells with EGFR-A763_Y764insFQEA underwent apoptosis upon exposure to nanomolar concentrations of erlotinib. Detailed analysis of these exon 20 insertion mutations is ongoing. Conclusions: Not all EGFR exon 20 insertion mutations are resistant to EGFR TKIs, and in specific EGFR-A763_Y764insFQEA can be labeled an EGFR TKI-sensitive mutation. This finding has clinical implications for the care of the 10,000 cases of EGFR exon 20 insertion mutated NSCLC diagnosed yearly and points towards the need to define the molecular mechanisms that underlie the differential response to EGFR TKIs in EGFR mutated NSCLC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 23. doi:1538-7445.AM2012-23