P2.05-010 SEVERAL RECEPTOR TYROSINE KINASE IS ACTIVATED BUT ORCHESTRATED BY EGFR IN EGFR-TKI ACQUIRED RESISTANT LUNG ADENOCARCINOMA CELLS WITH EGFR MUTATION
Background: Lung adenocarcinomas with EGFR mutation initially show good responses to EGFR- tyrosine kinase inhibitors (TKIs). However, emergence of acquired resistance is almost inevitable.
To analyze molecular mechanisms underlying acquired resistance, we established a cell line from a patient who acquired resistance to geftinib/erlotinib.
Methods: A 64-year-old woman underwent a pulmonary resection for lung adenocarcinoma in February 2009 (pT2aN0M0, EGFR L858R mutation). In April 2010, pulmonary metastases, mediastinal lymph node metastases, and right pleural effusion were identifed. Geftinib was started and this led to a complete response. However, despite continuous treatment with geftinib, pleural effusion and serum carcinoembryonic antigen (CEA) levels gradually increased. In December 2010, geftinib was switched to erlotinib but the serum CEA level continued to increase, and erlotinib was stopped on March, 2011. Even though she received no treatment after erlotinib withdrawal, interestingly, the serum CEA level was decreased signifcantly (from 89.5ng/ml on March 2011 to 19.2ng/ml on April 2011), and erlotinib was re-started on April 2011. The serum CEA level increased after re-administration of erlotinib (55.7ng/ml on May 2011). Therefore the regimen was switched to cisplatin/pemetrexed and she responded to this combination chemotherapy (CEA 9.1ng/ml on July 2011). This clinical experience may be an actual case of “drug addiction phenomenon” that we and others have observed in preclinical acquired resistance models (Suda K, et al. Lung Cancer 2012; Das Thakur M, et al. Nature 2013). We established a cell line from her pleural effusion obtained on March 2011 in drug-free condition (designated as ACC-GR1 cells). We analyzed this cell line to evaluate the effcacy of erlotinib and dacomitinib, an irreversible EGFR-TKI. In addition, we examined phosphorylation status of 42 receptor tyrosine kinase (RTK) of ACC-GR1 cells using Human Phospho-RTK Array Kit (R&D Systems) with/without erlotinib or dacomitinib. We also examined PC9 lung adenocarcinoma cell line for phosphorylation status of RTKs with/without erlotinib.
Results: ACC-GR1 cells harbored the T790M mutation, in addition to the original L858R mutation in the EGFR gene. ACC-GR1 cells do not have amplifcation of MET proto-oncogene. IC50 values for erlotinib and dacomitinib were 2.9 uM and 0.05 uM, respectively. Phospho-RTK array analysis revealed marked activation of EGFR and MET, in addition, activation of ERBB2, ERBB3, RET, and AXL in a culture condition without EGFR-TKI. Treatment with 1 uM of erlotinib led to mild inhibition of EGFR and MET phosphorylation (71% and 58%, respectively, compared with control), and phosphorylation of other RTKs fell below detectable limits. Treatment with 1 uM of dacomitinib led to further inhibition of EGFR phosphorylation (35% compared with control). In PC9 cells, phosphorylation of EGFR and MET were also observed in drug-free condition, and remarkably inhibited by 1 uM erlotinib treatment (10% and 64%, respectively, compared with control).
Conclusion: A cell line model established from pleural effusion of a patient who acquired resistance to geftinib/erlotinib harbored T790M mutation and responded to dacomitinib in vitro. The acquired resistant cells showed activation of several RTKs in drug free condition, and these are remarkably inhibited by EGFR-TKI treatment.
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