Abstract B27: Osimertinib (AZD9291) is sensitive and bound with affinity to EGFR exon 20 insertion mutant models

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Abstract Background: Although EGFR exon 20 insertion mutation is the third most common among EGFR-mutant NSCLC, this mutation has not been well studied and the first-generation EGFR TKIs are ineffective. In addition, the efficacy of the third-generation EGFR TKIs is controversial. Methods: Various EGFR exon 20 insertion mutation models were developed using Ba/F3 system as follows: C-helix (n=1, A763_Y764insFQEA) and loop following C-helix (n=7). In addition, SNU-3173 cell line was derived from NSCLC patient with EGFR exon 20 insertion mutation. Cell viability assays were performed using EGFR TKIs (gefitinib, erlotinib, dacomitinib, afatinib, rociletinib, olmutinib, nazartinib, and osimertinib). Immunoblotting was performed to evaluate the downstream signals of EGFR pathway. Additionally, the docking homology models of EGFR exon 20 insertion mutations with osimertinib were developed with SWISS-Model and SwissDock for estimation of the structural appropriateness. Results: Cell viability assay showed that EGFR exon 20 insertion mutants are resistant to the first-generation EGFR TKIs, except for A763_Y764insFQEA mutant Ba/F3 cells. IC50 values of second-generation EGFR TKIs are five- to hundreds-folds lower than gefitinib and erlotinib. Dacomitinib and afatinib have good efficacy for the most of them, and regulated down signaling pathways. The third-generation TKIs showed moderate efficacy against EGFR exon 20 insertion mutants. Overall, osimertinib has the most successful inhibition of EGFR exon 20 insertion mutants (IC50 values for C-helix and loop following C-helix mutants for afatinib, <0.1nM and 16.7-352.5nM; rociletinib 1022.1nM and 288.0-3034.6nM; olmutinib, 351.8nM and 30.4-626.7nM; osimertinib 131.6nM and 14.7-65.7nM; and nazartinib, 351.8nM and 36.3-509.9nM, respectively). Ribbon diagram with in silico homology docking simulations showed how exon 20 insertion mutations change the structures of kinase domain and the suitable binding values with various EGFR exon 20 insertion mutant subtypes with osimertinib. Conclusions: Osimertinib showed an outstanding effectiveness against various EGFR exon 20 insertion mutations. In addition, docking simulation of in silico homology models corresponded with the in vitro results. Consequently, osimertinib is effective against EGFR exon 20 insertion mutant models. Citation Format: Yusoo Lee, Tae Min Kim, Dong-Wan Kim, Yong-Oon Ahn, Soyeon Kim, Bhumsuk Keam, Miso Kim, Dae Seog Heo. Osimertinib (AZD9291) is sensitive and bound with affinity to EGFR exon 20 insertion mutant models [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr B27.