Abstract 320: Met/Ror1-β-catenin-Bcl-xL Axis Contributes to the Emergence of Drug-Tolerant Cells That Evolve into Resistant Tumors in EGFR-mutant Lung Cancer

Despite of the success of targeted therapy with tyrosine kinase inhibitors (TKI) in epidermal growth factor receptor (EGFR) -mutant lung cancer, the duration of response is limited due to the inevitable development of acquired resistance. Previous studies have revealed that TKIs may induce survival in drug-tolerant cells (DTC) following initial treatment, leading to acquired resistance from further evolution over time. Moreover, recent studies have also shown that Bcl-xL is involved in the survival of DTC; however, little is known about the mechanism of how Bcl-xL regulates DTC in the presence of EGFR TKIs. Therefore, it is crucial to elucidate pathways which promote DTC emergence in order to develop more effective therapeutic protocols. In this study, we found that the Met/Ror1-β-catenin-Bcl-xL axis may contribute to the emergence of DTC in the presence of EGFR TKIs. We previously demonstrated that β-catenin has an essential role in lung tumorigenesis driven by EGFR-mutants, particularly EGFR-T790M. We found that genetic deletion of β-catenin gene reduced Bcl-xL expression both in vitro and in vivo. Secondly, in the presence of EGFR TKI, we found that Met-induced Ror1 activation led to tyrosine phosphorylation of β-catenin via Src. Our experiments further suggested tyrosine phosphorylation of β-catenin by EGFR and the Met-Ror1-Src cascade, whose sites were identified by mass spectrometry, plays a critical role in the interaction between β-catenin and a transcriptional factor, TBX5. Contrary to known transcriptional interaction with TCF/LEF, tyrosine phosphorylated β-catenin was found to form a complex with TBX5 and the transcriptional regulator, YAP1. This complex may regulate anti-apoptotic genes such as BCL2L1, which encodes Bcl-xL. Combination treatment with osimertinib and stable knockdown of Ror1 (or TBX5) effectively reduced Bcl-xL expression. Furthermore, treatment with osimertinib in lung cancer mouse model in which Bcl2l1 can be conditionally knocked out inhibited completely the emergence of resistant tumors compared to Bcl2l1 wild-type mouse model treated with osimertinib. These observations suggest that the Met/Ror1-β-catenin-Bcl-xL axis may serve to explain the underlying mechanism for the emergence of DTC. Our findings thus identify this axis as a promising target for EGFR-mutant lung cancer.Citation Format: Masanori Fujii, Sohei Nakayama, Naoki Akanuma, Gilbert Pan, Ikei S. Kobayashi, Hisashi Takei, Kohei Shimizu, Mariko Ando, Eunyoung Heo, Carol Gergis, Hiroyuki Inuzuka, Wenyi Wei, Daniel B. Costa, Susumu S. Kobayashi. Met/Ror1-β-catenin-Bcl-xL axis contributes to the emergence of drug-tolerant cells that evolve into resistant tumors in EGFR-mutant lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 320.