Abstract 1098: Activation of YAP1 confers ROS1 inhibitor resistance in ROS1-rearranged lung cancer

Abstract ROS1 gene arrangements occur in approximately 1% to 2% of non-small cell lung cancers. Crizotinib, the ROS1-tyrosine kinase inhibitor (TKI), has been approved for ROS1-rearranged lung cancer based on its dramatic therapeutic effect, but cures are usually not achieved. We have been focused on relationships between Yes associated protein1 (YAP1) and resistance to molecular target drugs. YAP1, a main mediator of the Hippo pathway, promotes cell proliferation and epithelial-mesenchymal transition and is associated with drug resistance in some cancer types. We previously demonstrated that YAP1 mediates survival against alectinib therapy in anaplastic lymphoma kinase-rearranged lung cancer cells. Then, in this study, we evaluated the role of YAP1 as an initial survival mechanism from lorlatinib in ROS1-rearranged lung cancer. We established a patient-derived EZR-ROS1-rearranged lung cancer cell line (KTOR71) from pleural effusion of a patient who acquired resistance to crizotinib. Subsequently, we conducted functional analysis of YAP1 involvement in drug-resistance, using this patient-derived cell line. DNA sequencing confirmed that KTOR71 cells harbored EZR-ROS1 fusion and ROS1 S1986F mutation, which is known crizotinib resistance mutation. KTOR71 cells were sensitive to lorlatinib, while resistant to crizotinib in cell viability assay (CVA). Nuclear localization of YAP1, which is an activation marker of YAP1, was assessed using immunofluorescence staining. In KTOR71 cells, YAP1 was activated after lorlatinib exposure. Then, to evaluate functional role of YAP1 in the initial survival against lorlatinib, the genetic inhibition of YAP1 in KTOR71 cells were performed using small interfering RNA (siRNA). Silencing of YAP1 by siRNA enhanced sensitivity to lorlatinib in KTOR71 cells in CVA. Furthermore, to confirm this functional role of YAP1 in vivo, we established the KTOR71 cell-derived xenograft model. The combination therapy with lorlatinib and verteporfin, an inhibitor of YAP1-TEAD interaction, sustained tumor remission significantly compared with lorlatinib monotherapy in vivo. Finally, we found that AKT was reactivated with activation of YAP1 and silencing of YAP1 by siRNA suppressed this AKT reactivation. These results suggest that YAP1 may be a potential drug target for ROS1-rearranged lung cancer. Citation Format: Masatoshi Yamazoe, Hiroaki Ozasa, Tetsuya Ohgimoto, Kazutaka Hosoya, Hitomi Ajimizu, Tomoko Funazo, Yuto Yasuda, Takahiro Tsuji, Hironori Yoshida, Ryo Itotani, Yuichi Sakamori, Young Hak Kim, Hirai Toyohiro. Activation of YAP1 confers ROS1 inhibitor resistance in ROS1-rearranged lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1098.