MUC1-C Is a Common Driver of Acquired Osimertinib Resistance in NSCLC

Introduction: Osimertinib is an irreversible EGFR tyrosine kinase inhibitor approved for the first -line treatment of patients with metastatic NSCLC harboring EGFR exon 19 deletions or L858R mutations. Patients treated with osimertinib invariably develop acquired resistance by mechanisms involving additional EGFR mutations, MET amplification, and other pathways. There is no known involvement of the oncogenic MUC1-C protein in acquired osimertinib resistance. Methods: H1975/EGFR (L858R/T790M) and patientderived NSCLC cells with acquired osimertinib resistance were investigated for MUC1-C dependence in studies of EGFR pathway activation, clonogenicity, and self -renewal capacity. Results: We reveal that MUC1-C is up -regulated in H1975 osimertinib drug -tolerant persister cells and is necessary for activation of the EGFR pathway. H1975 cells selected for stable osimertinib resistance (H1975 -OR) and MGH700-2D cells isolated from a patient with acquired osimertinib resistance are found to be dependent on MUC1-C for induction of (1) phospho (p)-EGFR, p-ERK, and p-AKT, (2) EMT, and (3) the resistant phenotype. We report that MUC1-C is also required for p-EGFR, p-ERK, and p-AKT activation and self -renewal capacity in acquired osimertinib-resistant (1) MET -amplified MGH170-1D #2 cells and (2) MGH121 Res#2/ EGFR (T790M/C797S) cells. Importantly, targeting MUC1-C in these diverse models reverses osimertinib resistance. In support of these results, high MUC1 mRNA and MUC1-C protein expression is associated with a poor prognosis for patients with EGFR-mutant NSCLCs. Conclusions: Our findings reveal that MUC1-C is a common effector of osimertinib resistance and is a potential target for the treatment of osimertinib-resistant NSCLCs. (c) 2023 International Association for the Study of Lung Cancer. Published by Elsevier Inc. This is an open access article under the CC BY -NC -ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).