Abstract 424: RTK inhibitor resistance in NSCLC harboring MED12 mutation is overcome by only blocking MEK signaling, not AKT due to mutated MED12-induced YAP-PTEN dysregulation

Abstract The advent of receptor tyrosine kinase inhibitors (RTKi) are important contributions to treat NSCLC patients harboring genetic aberration effectively. Nevertheless, the emergence of acquired or intrinsic RTKi resistance by other RTK activation bypass finally limits their efficacy. First of all, in this study, we identified MED12 mutation in TKI-resistant NSCLC cells based-on NGS analysis. Although MED12 was known to controls the response to multiple cancer drugs through regulation of TGF-beta receptor signaling reportedly, we additionally found that MED12 mutation activates not only TGF-beta receptor not also other ones, such as EGFR, meaning that blocking TGF-beta receptor or EGFR alone may not effective to overcome MED12 mutation-induced RTKi resistance. To overcome the RTKi resistance in NSCLC harboring MED12 mutation, we elaborated the two downstream signaling of RTK in MED12 knock-out NSCLC cells and observed that PI3K/AKT signaling is downregulated but MEK/ERK signaling is upregulated. We observed that only MEK inhibitor (MEKi), not PI3K/mTOR inhibitor, shows effective anti-cancer effect. Therefore, we explored why MEKi alone is effective in RTKi resistant NSCLC cells harboring MED12 mutation and presented that MED12 mutation directly suppressed activation of YAP via blocking a large mediator complex of MED12, MED13, CDK8 and CCNC, thereby increasing PTEN expression by inhibition of miR-29 expression. Increased PTEN inhibits reactivation of PI3K/AKT pathway. In conclusion, we first identified that MED12 mutation induces RTKi resistance though activating other RTKs, such as TGF-beta receptor or EGFR, and blocks PI3K/AKT pathway via dysregulation of YAP/PTEN/AKT interaction. Therefore, among two downstream signaling of RTK, activated MEK/ERK pathway can be a definitive target enough to overcome RTKi resistant NSCLC patients harboring MED12 mutation and MEKi could be a primary treatment option for resistant patients harboring MED12 mutation among NSCLC patients with repetitive recurrence of RTKi resistance by another RTK activation bypass. Citation Format: Hyun-Min Ryu, Deokhoon Kim, Shinkyo Yoon, Ho-Su Lee, Eunjin Lee, Chang Hoon Lee, Wanlim Kim, Seyoung Seo, Kyung Hae Jung, Sook Ryun Park, Sang-We Kim, Kang-Seo Park, Dae Ho Lee. RTK inhibitor resistance in NSCLC harboring MED12 mutation is overcome by only blocking MEK signaling, not AKT due to mutated MED12-induced YAP-PTEN dysregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 424.