Acquired resistance to epidermal growth factor receptor (EGFR) kinase inhibitors associated with a novel T854A mutation in a patient with EGFR-mutant lung adenocarcinoma

Abstract

8056 Background: Somatic mutations in exons encoding the tyrosine kinase domain of EGFR are associated with increased sensitivity of lung adenocarcinomas to the EGFR tyrosine kinase inhibitors (TKIs), gefitinib and erlotinib. In almost half of cases examined, acquired drug resistance is associated with a specific secondary somatic mutation in exon 20 that leads to substitution of methionine for threonine at position 790 (T790M). We aimed to identify additional second-site EGFR kinase domain mutations associated with acquired resistance. Methods: Tumor samples were obtained from patients with acquired resistance. Tumor cell DNA was analyzed for EGFR kinase domain mutations. Molecular analyses were then performed to characterize biological properties of a novel secondary mutation. Results: We have analyzed tumor samples from 48 patients with acquired resistance. 23 samples were found to contain the T790M mutation and 1 harbored the previously characterized D761Y mutation. A novel mutation, which leads to substitution of alanine for threonine at position 854 (T854A) in exon 21 of EGFR, was identified in a patient with a drug-sensitive EGFR L858R-mutant lung adenocarcinoma after long-term treatment with TKIs. The T854A mutation was not detected in the patient’s pre-treatment tumor sample. A substitution analogous to T854A has not yet been observed in other tyrosine kinases, but published crystal structure analyses of EGFR suggest that the T854 side chain is within contact distance of gefitinib and erlotinib. Surrogate kinase assays using cells transiently expressing different alleles of EGFR demonstrate that the EGFR T854A mutation abrogates inhibition of tyrosine phosphorylation by erlotinib. Such resistance appears to be overcome by a new irreversible dual EGFR/HER2 inhibitor, BIBW 2992. Conclusions: The T854A mutation is the second reported second-site acquired resistance mutation (along with T790M) that is within contact distance of gefitinib and erlotinib. These data suggest that acquired resistance to ATP-mimetic EGFR kinase inhibitors may often be associated with amino acid substitutions that alter drug contact residues in the EGFR ATP-binding pocket. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Boehringer Ingelheim Boehringer Ingelheim