Fig. 3

MDM2 drives resistance to Osimertinib independent of the canonical MDM2-p53 regulatory loop. (A) Representative fluorescent images of TUNEL assay. PC-9 NC and PC-9 MDM2 cells were treated with 1 µmol/L Osimertinib or equal amount of DMSO for 24 h. Cell apoptosis was visualized and calculated by TUNEL assay. NS: not significant. Scale bar = 200 μm. ***P < 0.001. (B-E) The Osimertinib resistant PC-9 OR cells were transfected with siRNA targeting p53 to deplete endogenous p53 expression and evaluated for the sensitivity to Osimertinib by MTT assay, colony formation assay, and TUNEL assay, respectively. Scale bar = 200 μm. NS: not significant. (F-I) The Osimertinib sensitive PC-9 cells were engineered to stably express the MDM2 ΔPBD mutant that was unable to interact with p53. The resultant cells were treated with Osimertinib or DMSO. Therapeutic response to Osimertinib was determined by cytotoxic assays, including MTT, colony formation and TUNEL assay. Scale bar = 200 μm. NS: not significant. **P < 0.01. ***P < 0.001