Lung cancers harboring common EGFR mutations respond to EGFR
tyrosine kinase inhibitors (TKI). We previously reported that
tumors with exon 18 mutations are particularly sensitive to irreversible second-generation (2G)
afatinib compared with first-generation TKIs (1G-TKI). However, data on the mechanisms of acquired resistance to
afatinib are limited. We established
afatinib-resistant cells by transfecting Ba/F3 cells with common or exon 18 (G719A and Del18) mutations and subjecting them to chronic exposure to increasing concentrations of
afatinib.
Afatinib-resistant clones were separately established through
N-ethyl-N-nitrosourea (ENU) mutagenesis and exposure to fixed concentrations of
afatinib. Rebiopsy samples from patients whose
tumors acquired resistance to
afatinib were analyzed.
Afatinib-resistant cells 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. In addition, subsets of Del18 clones acquired L792F. C797S-acquired cells were sensitive to 1G
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. T790M was detected in one of four clinical samples. In conclusion, L792F and C797S, in addition to the major T790M, can develop in
afatinib-resistant cells particularly using a low dose of
afatinib, and these minor mutations appear to exhibit sensitivity to
dacomitinib and
erlotinib, respectively. These secondary mutations should be tested in clinical practice. Mol
Cancer Ther; 16(2); 357-64. ©2016 AACRSee related article by Talbert et al., p. 344.