LAUSR

Epidermal growth factor receptor (EGFR) mutations occur in 15-50% of patients worldwide with lung adenocarcinoma (LUAD). While tyrosine kinase inhibitors (TKIs) that directly target activating EGFR mutations prolong the survival of these LUAD patients, most tumors inevitably develop acquired resistance to TKI therapy. The second most frequent cause of such acquired TKI resistance is the amplification of the MET oncogene, which occurs in about 20% of EGFR-mutated LUAD samples with acquired TKI resistance. Our prior study showed that Vorinostat (VS), a potent HDAC inhibitor, induced cell death in NSCLC cell lines, and its sensitivity was correlated with MET levels in these cells. Therefore, we hypothesize that VS can re-sensitize EGFR-mutant LUAD with MET amplification-induced acquired TKI resistance to TKI treatment. The human LUAD cells HCC827 parental (EGFRExon19Del) and HCC827-R (Osimertinib resistant with MET amplification) were used to test our hypothesis. To confirm if VS induced cell death in a MET-dependent manner, we conducted cell viability assays in HCC827 and HCC827-R cells after treatment with escalating doses of VS. Next, to explore the mechanism(s) through which VS enhances MET-dependent cell death, we performed several experiments including 1) real-time RT-PCRs and western blots to discern if VS regulates the expression of MET at transcriptional or translational level; 2) cycloheximide chase assays to examine the impact of VS on MET protein stability; 3) treatment with RGFP109, a HDAC1/HDAC3 selective inhibitor, to specify which HDAC(s) may be involved in this process. Finally, cell viability assays and clonogenic assays were performed using HCC827 and HCC827-R cells treated with VS alone, Osimertinib alone, or both, to investigate if VS re-sensitizes TKI-resistant cells to the treatment of Osimertinib. Our results showed that VS inhibited the viability of both HCC827 and HCC827-R cells in a dose-dependent manner with an IC50 of ∼3µM. Unexpectedly, VS failed to affect MET mRNA, but significantly reduced the protein level of MET, compared to DMSO treatment. Moreover, the treatment with VS induced MET protein degradation in a MET level-dependent manner. Treatment with RGFP109 also induced MET protein degradation, suggesting that HDAC1 and/or HDAC3 might be involved in VS induced MET degradation. Interestingly, we observed that VS rescued sensitivity to Osimertinib in both HCC827 cells pre-treated with HGF and HCC827-R cells. Our study suggests that VS promotes cell death of LUAD cells with amplification of MET via inducing HDAC1/3-mediated MET protein degradation. In combination with Osimertinib, VS reverses the amplification of MET-induced TKI resistance in LUAD cells. This combination might be therapeutically exploitable to overcome acquired TKI resistance caused by MET amplification in NSCLC patients. Choudhary Harsha, Yuan Liu, Whitney S. Brandt, Di He, Manendra B. Lankadasari, Stella Tsui, Nanruoyi Zhou, Brooke Mastrogiacomo, Tetsuhiko Asao, David R. Jones. Histone deacetylase inhibitor, Vorinostat, reverses EGFR-TKI resistance in lung adenocarcinoma via degradation of MET [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 548.