Simple SummaryNon-small-cell lung cancer (NSCLC) patients become resistant to targeted therapies such as tyrosine kinase inhibitors (TKIs) through mutations in the EGFR gene and by overexpression of proteins such as p120-catenin and PRMT-1. We studied EGFR wild-type and mutated EGFR in parental and Osimertinib-resistant cell lines. Our results showed overexpression of p120-catenin, PRMT-1, and Kaiso factor in Osimertinib-resistant cell lines compared to parental cell lines. We also found co-localization of PRMT-1 and Kaiso factor in resistant cell lines. Overexpression of p120-catenin and PRMT-1 was found in tumor samples recovered from smokers as compared to non-smokers. Further studies showed that inhibiting p120-catenin mediated increased Osimertinib efficiency and decreased wound healing compared to mock siRNA controls. These results indicate that p120-catenin and PRMT-1 could play a vital role in Osimertinib resistance and could be potential targets to increase TKI efficiency.AbstractOsimertinib, an irreversible tyrosine kinase inhibitor, is a first-line therapy in EGFR-mutant NSCLC patients. Prolonged treatment with Osimertinib leads to resistance due to an acquired C797S mutation in the EGFR domain and other mechanisms, such as epithelial-mesenchymal transition (EMT). In this study, we investigated the role of PRMT-1 and p120-catenin in mediating Osimertinib resistance (OR) through EMT. These studies found upregulation of gene and protein expression of PRMT-1, p120-catenin and Kaiso factor. Knockdown of p120-catenin using siRNA increased OR efficacy by 45% as compared to cells treated with mock siRNA and OR. After 24 h of transfection, the percentage wound closure in cells transfected with p120-catenin siRNA was 26.2%. However, in mock siRNA-treated cells the wound closure was 7.4%, showing its involvement in EMT. We also found high levels of p120-catenin expressed in 30% of smokers as compared to 5.5% and 0% of non-smokers and quit-smokers (respectively) suggesting that smoking may influence p120-catenin expression in NSCLC patients. These results suggest that biomarkers such as PRMT-1 may mediate EMT by methylating Twist-1 and increasing p120-catenin expression, which causes transcriptional activation of genes associated with Kaiso factor to promote EMT in Osimertinib-resistant cells.