Tabara et al. have shown that complete loss of the activating EGFR mutant gene results in the gain of a novel addiction to HER2/HER3 signaling and the acquisition of EGFR-TKI resistance in vitro [22]. In our resistant cells (4D8 and B10), cell proliferation was partially blocked buy Navitoclax by HER2 or HER3

knockdown (Supplementary Fig. 6). These findings indicate that the EGFR-unamplified resistant cells partially depend on not only EGFR but also HER2/HER3 signaling for survival. Compared with other solid tumors, NSCLC is well known for the heterogeneity of the cell populations in individual lesions [23]. Heterogeneous distribution of EGFR mutations in individual tumors has also been reported [24], [25] and [26]. In addition, loss of an EGFR mutation is reported in 3 out of 11 EGFR-mutated NSCLC patients with progressive disease after gefitinib treatment [22]. These findings indicate that some NSCLCs are genetically heterogeneous and concurrently have tumor cell populations

with either mutant or wild-type EGFR, and that the EGFR genetic heterogeneity might contribute to acquired resistance to EGFR-TKIs. Our results strongly support this mechanism of resistance, because we have clearly shown that the genetic heterogeneity of EGFR is constantly maintained by the loss of an EGFR-ampch7 in NSCLC cells with EGFR EX 527 cost mutations. In conclusion, we demonstrated that loss of amplified EGFR-mutated genes causes acquired resistance in HCC827 cells when the cells are exposed to a relatively low concentration of erlotinib, whereas high concentration of erlotinib

prevents the emergence of resistance. In addition Fenbendazole to the major known mechanisms of acquired resistance to EGFR-TKIs, including secondary mutation of T790M, amplification of MET, mutations of PIK3CA, EMT, and transformation to SCLC [8], our findings propose a novel acquired resistant mechanism, namely, the selection of preexisting EGFR-unamplified cells, which are generated by the loss of an amplified EGFR-mutated gene, may contribute to the acquired resistance to EGFR-TKIs. Further studies are needed to identify alternative addictive signal pathway(s) after the loss of amplified EGFR with mutation and to lead to the development of a novel molecular targeted therapy against EGFR-TKI-refractory NSCLC. None. The authors thank Kumiko Kondoh, Hiromi Sawamura and Masako Takahashi for technical assistance in the experiments, and also thank Kazushige Mori, Naohito Inagaki, Masamichi Sugimoto and Keiji Kosaka for support and special advice in this study. “
“Lung cancer currently causes more deaths from cancer in the world than any other tumor type, and projections over the next 20 years indicate this is likely to continue unless substantial progress is made in areas such as screening, early detection, treatment and prevention.