Author of

• 18374

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  P3.02b - Poster Session with Presenters Present (ID 494)

  • Event: WCLC 2016
  • Type: Poster Presenters Present
  • Track: Advanced NSCLC
  • Presentations: 1
  • Moderators:
  • Coordinates: 12/07/2016, 14:30 - 15:45, Hall B (Poster Area)

  • 18494

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    P3.02b-120 - EGFR T790M, L792F, and C797S Mutations as Mechanisms of Acquired Resistance to Afatinib (ID 4818)

    14:30 - 14:30  |  Author(s): T. Takemoto
    • Abstract

    Background:
    Afatinib is effective for lung cancers harboring common EGFR mutations, Del19 and L858R. We reported that tumors with exon 18 mutations are especially sensitive to afatinib compared with first generation (1G) EGFR- tyrosine kinase inhibitors (TKIs). However, data on the mechanisms of acquired resistance to afatinib are limited
    
    Methods:
    We established afatinib-resistant cells from Ba/F3 cells transfected with common or exon 18 (G719A and Del18) mutations and PC9 (del E746_A750), HCC4006 (del E746_A750), and 11_18 (L858R) cell lines by chronic exposure to increasing concentrations of afatinib. Separately, afatinib-resistant clones were established from above Ba/F3 cells by exposure to fixed concentrations of afatinib using N-ethyl-N-nitrosurea (ENU) mutagenesis. Re-biopsy samples from patients whose tumors acquired resistance to afatinib were collected. EGFR secondary mutations and bypass tracks were analyzed by Sanger sequence, western blot, and real time PCR.
    
    Results:
    Afatinib-resistant cells transfected with Del19, L858R, or G719A developed T790M, whereas those with Del18 acquired novel L792F mutation. ENU mutagenesis screening established 84 afatinib-resistant clones. All Del19 clones and most of the other clones acquired only T790M. However, C797S occurred in subsets of L858R, G719A, and Del18 clones. Additionally, subsets of Del18 clones acquired L792F. C797S-acquired cells were sensitive to erlotinib. L792F demonstrated intermediate resistance between T790M and C797S to both 1G and 3G-TKIs, whereas L792F was the least resistant to 2G-TKIs, particularly dacomitinib. Chronic exposure of Del18+L792F cells to dacomitinib induced additional T790M acquisition. T790M was detected in 1 of 4 clinical samples, whereas no EGFR secondary mutations were detected in afatinib-resistant PC9, HCC4006, or 11_18 cell lines. Regarding bypass tracks, IGF1R was over expressed in all of the three afatinib-resistant cell lines compared with parental cells, whereas expression of AXL and PTEN were not changed. Neither mutations in PIK3CA and BRAF nor amplification of MET and FGFR1 were detected in clinical samples and resistant cell lines.
    
    Conclusion:
    L792F and C797S, in addition to major T790M, can develop in afatinib-resistant cells, and these minor mutations appear to exhibit sensitivity to dacomitinib and erlotinib, respectively. These secondary mutations should be tested in clinical practice. Bypass track through IGF1R may be associated with acquired resistance to afatinib.