Acquired Resistance Mechanisms to Combination Met-TKI/EGFR-TKI Exposure in Met-Amplified EGFR-TKI-Resistant Lung Adenocarcinoma Harboring an Activating EGFR Mutation.

Met-amplified EGFR-tyrosine kinase inhibitor (TKI)-resistant non-small cell lung cancer (NSCLC) harboring an activating EGFR mutation is responsive to concurrent EGFR-TKI and Met-TKI treatment in a preclinical model. Here, we determined that Met-amplified gefitinib-resistant cells acquire dual resistance to inhibition of EGFR and Met tyrosine kinase activities. PC-9 lung adenocarcinoma cells harboring 15-bp deletions (Del E746_A750) in EGFR exon 19 were treated with increasing concentrations of the Met-TKI PHA665752 and 1 μmol/L gefitinib for 1 year; three resistant clones were established via Met amplification. The three dual-resistance cell lines (PC-9DR2, PC-9DR4, and PC-9DR6, designated as DR2, DR4, and DR6, respectively) exhibited different mechanisms for evading both EGFR and Met inhibition. None of the clones harbored a secondary mutation of EGFR T790M or a Met mutation. Insulin-like growth factor (IGF)/IGF1 receptor activation in DR2 and DR4 cells acted as a bypass signaling pathway. Met expression was attenuated to a greater extent in DR2 than in PC-9 cells, but was maintained in DR4 cells by overexpression of IGF-binding protein 3. In DR6 cells, Met was further amplified by association with HSP90, which protected Met from degradation and induced SET and MYND domain-containing 3 (SMYD3)-mediated Met transcription. This is the first report describing the acquisition of dual resistance mechanisms in NSCLC harboring an activating EGFR mutation to Met-TKI and EGFR-TKI following previous EGFR-TKI treatment. These results might inform the development of more effective therapeutic strategies for NSCLC treatment. Mol Cancer Ther; 15(12); 3040-54. ©2016 AACR.

Yamaoka T ，Ohmori T ，Ohba M ，Arata S ，Kishino Y ，Murata Y ，Kusumoto S ，Ishida H ，Shirai T ，Hirose T ，Ohnishi T ，Sasaki Y ... -  《-》

Establishing Dual Resistance to EGFR-TKI and MET-TKI in Lung Adenocarcinoma Cells In Vitro with a 2-step Dose-escalation Procedure.

Yamaoka T ，Ohba M ，Arata S ，Ohmori T ... -  《Jove-Journal of Visualized Experiments》

Distinct Afatinib Resistance Mechanisms Identified in Lung Adenocarcinoma Harboring an EGFR Mutation.

EGFR tyrosine kinase inhibitors (TKI) are associated with significant responses in non-small cell lung cancer (NSCLC) patients harboring EGFR-activating mutations. However, acquired resistance to reversible EGFR-TKIs remains a major obstacle. In particular, although the second-generation irreversible EGFR-TKI afatinib is currently used for treating NSCLC patients, the mechanisms underlying acquired afatinib resistance remain poorly understood. Here, heterogeneous mechanisms of acquired resistance were identified following long-term exposure to increasing doses of afatinib in EGFR-mutant lung adenocarcinoma PC-9 cells. Notably, three resistant cell lines, PC-9AFR1, PC-9AFR2, and PC-9AFR3 (AFR1, AFR2, and AFR3, respectively) employed distinct mechanisms for avoiding EGFR inhibition, with increased EGFR expression being detected in all resistant cell lines. Moreover, an activating EGFR mutation was partially lost in AFR1 and AFR2 cells. AFR1 cells exhibited afatinib resistance as a result of wild-type KRAS amplification and overexpression; however, these cells showed a progressive decrease and eventual loss of the acquired KRAS dependence, as well as resensitization to afatinib, following a drug holiday. Meanwhile, AFR2 cells exhibited increased expression of insulin-like growth factor-binding protein 3 (IGFBP3), which promoted insulin-like growth factor 1 receptor (IGF1R) activity and subsequent AKT phosphorylation, thereby indicating a potential bypass signaling pathway associated with IGFR1. Finally, AFR3 cells harbored the secondary EGFR mutation T790M. Our findings constitute the first report showing acquired wild-type KRAS overexpression and attenuation of afatinib resistance following a drug holiday.Implications: The heterogeneous mechanisms of afatinib resistance should facilitate the development of more effective therapeutic strategies for NSCLC patients. Mol Cancer Res; 15(7); 915-28. ©2017 AACR.

Yamaoka T ，Ohmori T ，Ohba M ，Arata S ，Murata Y ，Kusumoto S ，Ando K ，Ishida H ，Ohnishi T ，Sasaki Y ... -  《-》

Clinicopathologic and molecular features of epidermal growth factor receptor T790M mutation and c-MET amplification in tyrosine kinase inhibitor-resistant Chinese non-small cell lung cancer.

Chen HJ ，Mok TS ，Chen ZH ，Guo AL ，Zhang XC ，Su J ，Wu YL ... -  《-》

MET Copy Number Gain Is Associated with Gefitinib Resistance in Leptomeningeal Carcinomatosis of EGFR-mutant Lung Cancer.

Leptomeningeal carcinomatosis occurs frequently in EGFR-mutant lung cancer, and develops acquired resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs). This study aimed to clarify the mechanism of EGFR-TKI resistance in leptomeningeal carcinomatosis and seek for a novel therapeutic strategy. We examined EGFR mutations, including the T790M gatekeeper mutation, in 32 re-biopsy specimens from 12 leptomeningeal carcinomatosis and 20 extracranial lesions of EGFR-mutant lung cancer patients who became refractory to EGFR-TKI treatment. All the 32 specimens had the same baseline EGFR mutations, but the T790M mutation was less frequent in leptomeningeal carcinomatosis specimens than in extracranial specimens (8% vs. 55%, P < 0.01). To study molecular mechanisms of acquired EGFR-TKI resistance in leptomeningeal carcinomatosis, we utilized our previously developed mouse model of leptomeningeal carcinomatosis with the EGFR-mutant lung cancer cell line PC-9/ffluc cells, in which acquired resistance to gefitinib was induced by continuous oral treatment. Compared with subcutaneously inoculated gefitinib-resistant tumors, the T790M mutation was less frequent in leptomeningeal carcinomatosis that acquired resistance to gefitinib. PC-9/LMC-GR cells were established from the gefitinib-resistant leptomeningeal carcinomatosis model, and they were found to be intermediately resistant to gefitinib and osimertinib (third-generation EGFR-TKI). Although EGFR-T790M was negative, gefitinib resistance of PC-9/LMC-GR cells was related to MET copy number gain with MET activation. Moreover, combined use of EGFR-TKI and crizotinib, a MET inhibitor, dramatically regressed leptomeningeal carcinomatosis with acquired resistance to gefitinib or osimertinib. These findings suggest that combination therapy with MET inhibitors may be promising for controlling leptomeningeal carcinomatosis that acquires resistance to EGFR-TKIs. Mol Cancer Ther; 16(3); 506-15. ©2017 AACR.

Nanjo S ，Arai S ，Wang W ，Takeuchi S ，Yamada T ，Hata A ，Katakami N ，Okada Y ，Yano S ... -  《-》