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S.S. Kobayashi



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    MO16 - Prognostic and Predictive Biomarkers IV (ID 97)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Medical Oncology
    • Presentations: 1
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      MO16.06 - Clinical, structural and biochemical characterization of EGFR exon 20 insertion mutations in lung cancer (ID 745)

      16:15 - 17:45  |  Author(s): S.S. Kobayashi

      • Abstract
      • Presentation
      • Slides

      Background
      Epidermal growth factor receptor (EGFR) exon 20 insertion mutations account for ~10% of EGFR-mutated non-small-cell lung cancer (NSCLC), for the most part occur at the N-lobe of EGFR after its C-helix (after amino-acid M766) and have unsolved patterns of response to ATP-mimetic EGFR tyrosine kinase inhibitors (TKIs).

      Methods
      To understand the patterns of resistance or response to EGFR TKIs of EGFR exon 20 insertion mutations, we decided to study representative mutations using in vitro systems, structural models and also NSCLCs with these specific EGFR mutations.

      Results
      We selected three mutations located within the C-helix (A763_Y764insFQEA [identical to D761_E762insEAFQ], Y764_V765insHH and M766_A767insAI) and four mutations following the C-helix (A767_V769dupASV [identical to V769_D770insASV], D770_N771insNPG, D770_N771insSVD [identical to S768_D770dupSVD] and H773_V774insH [identical to P772_H773insH]) mutations. Our data indicates almost all EGFR exon 20 insertions are resistant to submicromolar concentrations of gefitinib or erlotinib; data that mirrors the lack of clinical response of NSCLCs with these mutations. The crystal structural and enzyme kinetic studies of a prototypical post C-helix EGFR TKI-resistant insertion, between residues D770_N771 (D770_N771insNPG), highlight that these mutations favor the active conformation (i.e., are activating), don’t alter EGFR’s ATP-binding pocket and are less sensitive than TKI-sensitive mutations. D770_N771insNPG is predicted to be 7.66 fold less sensitive than the TKI-sensitive EGFR-L858R. Unexpectedly, we identified the atypical EGFR-A763_Y764insFQEA as the only EGFR exon 20 insertion hypersensitive to EGFR TKIs using enzyme kinetic and cell line models. In patients with EGFR exon 20 mutated NSCLCs, the response rates to gefitinib or erlotinib were significantly higher for A763_Y764insFQEA (2/3; 66.6%) when compared to all other mutations within or following the C-helix (0/17, 0%; p=0.0158). The unorthodox homology model of A763_Y764insFQEA suggests a mechanism of activation (by shifting the register of the C-helix N-terminal) related to TKI-sensitive mutations (such as L858R or L861Q).

      Conclusion
      Our findings not only explain the intricate interplay between different EGFR mutations and their response to EGFR TKIs, but also have clinical implications for the treatment of EGFR exon 20 insertion mutated NSCLCs. Therefore, based on our data and previously published reports the aforementioned mutations affecting amino acids V765 to V774 should be classified as non-sensitizing to the reversible EGFR TKIs gefitinib and erlotinib. Our models may usher the development of EGFR TKIs specific for EGFR exon 20 insertion mutations.

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