Conversion from the "oncogene addiction" to "drug addiction" by intensive inhibition of the EGFR and MET in lung cancer with activating EGFR mutation.

Emergence of acquired resistance is virtually inevitable in patients with a mutation in the epidermal growth factor receptor gene (EGFR) treated with EGFR tyrosine kinase inhibitors (TKIs). Several novel TKIs that may prevent or overcome the resistance mechanisms are now under clinical development. However, it is unknown how tumor cells will respond to intensive treatment using these novel TKIs. We previously established HCC827EPR cells, which are T790M positive, through combined treatment with erlotinib and a MET-TKI from erlotinib-hypersensitive HCC827 cells. In this study, we treated HCC827EPR cells sequentially with an irreversible EGFR-TKI, CL-387,785, to establish resistant cells (HCC827CLR), and we analyzed the mechanisms responsible for resistance. In HCC827CLR cells, PTEN expression was downregulated and Akt phosphorylation persisted in the presence of CL-387,785. Akt inhibition restored CL-387,785 sensitivity. In addition, withdrawal of CL-387,785 reduced cell viability in HCC827CLR cells, indicating that these cells were "addicted" to CL-387,785. HCC827CLR cells overexpressed the EGFR, and inhibition of the EGFR or MEK-ERK was needed to maintain cell proliferation. Increased senescence was observed in HCC827CLR cells in the drug-free condition. Through long-term culture of HCC827CLR cells without CL-387,785, we established HCC827-CL-387,785-independent cells, which exhibited decreased EGFR expression and a mesenchymal phenotype. In conclusion, PTEN downregulation is a newly identified mechanism underlying the acquired resistance to irreversible EGFR-TKIs after acquisition of T790M against erlotinib. This series of experiments highlights the flexibility of cancer cells that have adapted to environmental stresses induced by intensive treatment with TKIs.

Suda K ，Tomizawa K ，Osada H ，Maehara Y ，Yatabe Y ，Sekido Y ，Mitsudomi T ... -  《-》

Hepatocyte growth factor reduces susceptibility to an irreversible epidermal growth factor receptor inhibitor in EGFR-T790M mutant lung cancer.

Yamada T ，Matsumoto K ，Wang W ，Li Q ，Nishioka Y ，Sekido Y ，Sone S ，Yano S ... -  《-》

Acquired resistance mechanisms to tyrosine kinase inhibitors in lung cancer with activating epidermal growth factor receptor mutation--diversity, ductility, and destiny.

Suda K ，Mizuuchi H ，Maehara Y ，Mitsudomi T ... -  《-》

The role of MET activation in determining the sensitivity to epidermal growth factor receptor tyrosine kinase inhibitors.

Rho JK ，Choi YJ ，Lee JK ，Ryoo BY ，Na II ，Yang SH ，Lee SS ，Kim CH ，Yoo YD ，Lee JC ... -  《-》

CRKL amplification is rare as a mechanism for acquired resistance to kinase inhibitors in lung cancers with epidermal growth factor receptor mutation.

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) often provide dramatic responses in lung cancer patients with somatic EGFR mutation. However, acquired resistance to the drugs usually emerges within a few years. EGFR T790M secondary mutation, MET gene amplification, and transformation to small cell lung cancer are well-validated mechanisms that underlie acquisition of resistance to EGFR-TKIs. In addition, many molecular aberrations have been reported as candidates for mechanisms of acquired resistance to EGFR-TKIs. Amplification of the CRKL gene was reportedly observed in 1 of 11 lung cancer patients with EGFR mutations who acquired resistance to EGFR-TKI. This study is the first report, to our knowledge, that validated the role of CRKL gene amplification as a mechanism for acquisition of resistance to EGFR-TKIs. We analyzed CRKL gene copy numbers, using a quantitative real-time PCR method, in 2 in vitro acquired-resistance cell-line models: 11 clinical samples from patients who developed acquired resistance to EGFR-TKIs, and 39 tumor specimens obtained from 7 autopsy patients whose cancers acquired resistance to EGFR-TKIs. Mutational status of EGFR codon 790 and copy numbers for the MET gene were also determined. In analysis for in vitro models, CRKL gene copy numbers were identical between EGFR-TKI-sensitive parental cells and their acquired resistant descendant cells. In addition, we found no clinical tumor specimens with acquired EGFR-TKI resistance to harbor amplified CRKL genes. These results indicate that CRKL gene amplification is rare in acquisition of resistance to EGFR-TKIs in lung cancer patients with EGFR mutations.

Suda K ，Mizuuchi H ，Murakami I ，Uramoto H ，Tanaka F ，Sato K ，Takemoto T ，Iwasaki T ，Sekido Y ，Yatabe Y ，Mitsudomi T ... -  《-》