Conformational Landscapes of HER2 Exon 20 Insertions Explain Their Sensitivity to Kinase Inhibitors in Lung Adenocarcinoma

Introduction: HER2 exon 20 insertion (ex20ins) is one of the most intractable problems in lung cancer. Most ex20ins are resistant to available EGFR or pan-HER tyrosine kinase inhibitors (TKIs), with the exception of a few mutants. However, the mechanism for TKI response and resistance of HER2 ex20ins remains poorly understood. Methods: Next-generation sequencing-based genomic profiling data of 4139 patients with lung cancer were interrogated for HER2 ex20ins. Structural modeling and molecular dynamics simulations of common HER2 ex20ins were carried out to provide insights into the mechanism of activation and response heterogeneity of ex20ins. Molecular docking was performed to predict affinity to TKIs. Therapeutic decisions for patients were made on the basis of the results of genomic profiling. Results: From 155 HER2-mutant lung cancer cases, Y772_A775dup and G778_P780dup were identified in 74 (47.7%) and 18 (11.6%) cases, respectively. Molecular dynamics simulations revealed that HER2 ex20ins led to ligandindependent kinase activation by changing the conformational landscape of HER2 kinase and restricting kinase conformation in the active state. G778_P780dup had a three-amino acid extension in the aC-b4 loop and retained the HER2characteristic G776 and G778. Compared with Y772_A775dup, it had less restriction on kinase conformational sampling and higher affinity to afatinib, dacomitinib, pyrotinib, and poziotinib. Treating lung adenocarcinomas carrying G778_P780dup with these inhibitors led to sustained tumor responses in six of the 10 patients. Conclusions: The kinase conformational landscape dictated by the length of the aC-b4 loop and residues at HER2 776 and 778 position explains TKI sensitivity in ex20ins. This finding could guide therapeutic decisions with currently available therapies and future drug development strategies. (C) 2020 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved.