a Evaluation of cell proliferation by CCK8 assay in H1975-OR cells treated with PI-103, osimertinib, or a combination of PI-103 and osimertinib for 72 h. The combination index (CI) and CI curve were calculated by Calcusyn software. A value <1 indicates synergy. b Evaluation of cell proliferation by CCK8 assay in H1975-OR cells treated with NU7441, osimertinib, or a combination of NU7441 and osimertinib for 72 h. The combination index (CI) and CI curve were calculated by Calcusyn software. A value <1 indicates synergy. c Crystal violet staining of H1975-OR cells after treatment with osimertinib, NU7441, or a combination of osimertinib and NU7441. d Western blot analysis of DNA-PKcs expression in H1975-OR cells with or without DNA-PK knockdown. e Evaluation of cell proliferation by CCK8 assay in osimertinib-treated H1975-OR cells with or without DNA-PK knockdown. The IC50 for each cell line is indicated in parentheses. All data are presented as the mean ± SD from at least three independent experiments.