INTRODUCTION NSCLC with EGFR exon 20 insertion mutations is the third most common type of EGFR-mutant NSCLC and is resistant to EGFR tyrosine kinase inhibitors (TKIs). This study was conducted to evaluate the efficacies of first- to third-generation EGFR TKIs against NSCLC cells harboring EGFR exon 20 insertion mutations.

METHODS We developed seven EGFR exon 20 insertion-mutant Ba/F3 models and one patient-derived NSCLC (SNU-3173) of subtypes A763insFQEA, V769insASV, D770insSVD, D770insNPG, P772insPR, H773insH, H773insNPH, and H773insAH. Cell viability assays, immunoblotting, and N-ethyl-N-nitrosourea mutagenesis screenings were performed. EGFR exon 20 insertion-mutant structures and couplings with osimertinib, a third-generation EGFR TKI, were modeled and compared.

RESULTS EGFR exon 20 insertion-mutant NSCLC cells, excluding EGFR A763insFQEA, were resistant to first-generation EGFR TKIs (concentration that inhibits 50% [IC₅₀], 1.1 ± 0.067 to 5.4 ± 0.115 μM). Mutants were sensitive to second-generation EGFR TKIs (IC₅₀, 0.02 ± 0.0002 to 161.8 ± 18.7nM), except EGFR H773insH (IC₅₀, 46.3 ± 8.0 to 352.5 ± 22.7nM). The IC₅₀ ratios for mutant to wild-type cells were higher than those for third-generation EGFR TKIs. Third-generation EGFR TKI osimertinib was highly potent against EGFR exon 20 insertion-mutant cells (IC₅₀, 14.7-62.7 nM), including EGFR H773insH, and spared wild-type EGFR cells. N-ethyl-N-nitrosourea mutagenesis screening of EGFR exon 20 insertion-mutant Ba/F3 cells showed various second sites for EGFR mutations, mostly at exons 20 and 21, including E762K, P794S, and G796D. In addition, osimertinib-resistant cells were established by stepwise exposure to osimertinib and harbored EGFR E762K mutation.

CONCLUSIONS Osimertinib is active against EGFR exon 20 insertion-mutant NSCLC and flexibly binds within drug-binding pockets in preclinical models.