Abstract 5516: Deciphering mechanism of resistance to anti EGFR treatment regimen in a NSCLC PDX model

Abstract Acquired resistance prevents patients from long term benefits of targeted therapies in many different cancer types. Overactivation of EGFR in malignant cells is a prominent example for acquired resistance since anti-EGFR treatment in NSCLC patients often starts showing loss of activity after a certain period. We have developed three NSCLC PDX lines carrying an acquired resistance towards Gefitinib, a highly selective EGFR inhibitor. All three sublines depict a specific mutational and gene expression pattern. These PDX models were now further characterized by assessment of in vivo sensitivity versus Cetuximab, a chimeric anti-EGFR antibody. The characterization included assessment of tumor growth over time, proteomic and metabolomic analysis at different time points: 24h after treatment, in remission and at regrowth. The parental PDX line and clones 1-3 displayed distinct sensitivity patterns against Cetuximab. The parental PDX was highly sensitive showing no regrowth for >100 days post treatment. Clone2 went into full remission, with only six out of 30 tumors demonstrating regrowth by day 70 post treatment. Clone1 was completely resistant, whereas clone3 showed partial remission and regrowth of 28/30 tumors beginning 21 days after treatment. These sensitivity patterns do correlate with the molecular profile of the different lines, as Clone1 and Clone3 exhibit a downregulation of pTEN in combination with an upregulation of HER2 thereby bypassing survival signals via other RTKs than EGFR. The complete resistance of Clone1 is most likely driven by the NRAS mutation. The proteomics analysis (LC-MS) retrieved a range of 7700 - 8200 proteins per sample. The replicates (n= 4-5 per setting) displayed a Pearson’s correlation coefficient >0.95 indicating high data quality across the dataset. A PCA supported that finding with replicates grouping together. In the PCA the original PDX separated from the acquired resistant clones regardless of the treatment and time point. Within those groups samples taken when tumors were in remission separated from the other time points. A deeper analysis comparing individual groups with each other (t-test: limma package, RStudio) revealed an upregulation of proteins that are involved in EMT (TLE1), bad prognosis (UBE2D2 and MAST4), or resistance (SORL1) in the Gefitinib-resistant clone1 under treatment with Cetuximab. The upregulation of TPK1 which was observed as well might give a hint towards new treatment options as the protein is related to sensitivity towards PARP inhibitors. The full analysis of the LC-MS data will elucidate the mechanism behind those resistance mechanism and will help to identify new targets as well as favorable combination regimen for pre-treated NSCLC patients. The currently ongoing metabolomics studies will help to build a more complete picture of the cellular regulations leading to the different outcomes observed in the current study. Citation Format: Philipp Meyer, Ruzica Bago, Balasz Pograny, Kanstantsin Lashuk, Diarmuid Kenny, Blake Rushing, Eva Oswald, Julia B. Schueler. Deciphering mechanism of resistance to anti EGFR treatment regimen in a NSCLC PDX model [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 5516.