title: Double EGFR mutants containing rare EGFR mutant types show reduced in vitro response to gefitinib compared with common activating missense mutations.
abstract: Epidermal growth factor receptor (EGFR) mutations are common in lung adenocarcinomas, especially from nonsmoking women of Asian descent. We have previously shown EGFR mutations occur in >70% of lung adenocarcinoma from nonsmokers in our population with a complex mutational profile, including 13% of EGFR double mutations. In this study, we investigated the in vitro gefitinib response of four EGFR double mutants identified in untreated patients, including Q787R+L858R, E709A+G719C, T790M+L858R, and H870R+L858R. The phosphorylation profiles of EGFR and downstream effectors AKT, STAT3/5, and ERK1/2 were compared by immunoblot analyses among the single and double mutants transfected into H358 cells. Results showed that mutants responded to in vitro gefitinib treatment with different sensitivities. The G719C and L858R single mutants showed the highest gefitinib sensitivity compared with the corresponding coexisting single mutants E709A, Q787R, H870R, and T790M. The double mutants E709A+G719C, Q787R+L858R, and H870R+L858R showed attenuated responses to gefitinib in the EGFR and downstream effector phosphorylation profiles compared with G719C or L858R alone. T790M+L858R showed strong resistance to gefitinib. Clinically, the patient whose tumor contained H870R+L858R showed tumor stabilization by 250 mg oral gefitinib daily but cerebral metastasis developed 6 months later. Correlation with the in vitro phosphorylation profile of H870R+L858R suggested that treatment failure was probably due to inadequate suppression of EGFR signaling by the drug level attainable in the cerebrospinal fluid at the given oral dosage. Overall, the findings suggested that rare types of EGFR substitution mutations could confer relative gefitinib resistance when combined with the common activating mutants.
authors: Department of Pathology, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
authors: Issan Yee-San
authors: IY
authors: Tam
authors: Elaine Lai-Han
authors: EL
authors: Leung
authors: Vicky Pui-Chi
authors: VP
authors: Tin
authors: Daniel Tsin-Tien
authors: DT
authors: Chua
authors: Alan Dart-Loon
authors: AD
authors: Sihoe
authors: Lik-Cheung
authors: LC
authors: Cheng
authors: Lap-Ping
authors: LP
authors: Chung
authors: Maria Pik
authors: MP
authors: Wong
mesh_terms: D000368:Aged; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D005260:Female; D000077156:Gefitinib; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D010766:Phosphorylation; D011799:Quinazolines / Q000494:pharmacology*; D014443:Tyrosine
chemical_list: D000970:Antineoplastic Agents; D011799:Quinazolines; D014443:Tyrosine; D066246:ErbB Receptors; D000077156:Gefitinib