Fig. 5

Effects of pemetrexed or cisplatin on PC9T790M osimertinib-resistant clones or on cell lines derived from osimertinib-resistant tumors. The osimertinib-resistant clones generated from PC9T790M (osi-R clA and osi-R clC) and the parental cells were treated with increasing concentrations of osimertinib (a), cisplatin (b) or pemetrexed (c). After 72 h cell proliferation was assessed by MTT assay. Results represent the mean ± standard deviation (SD) of at least three independent experiments. *p < 0.05, ***p < 0.001, ****p < 0.0001 vs osi-R clA; #p < 0.05, ##p < 0.01, ###p < 0.001 vs osi-R clC; Student’s t-test. d Thymidylate Synthase (TS) protein expression in PC9T790M, PC9T790M osi-R clA (clA), PC9T790 M osi-R clC (clC) cells evaluated by western blot analysis. Representative blot of two independent experiments is shown. PC9T790M cells and cells isolated from two osimertinib-resistant tumors (2 and 4) were treated with increasing concentrations of osimertinib (e) or pemetrexed (f). After 72 h cell proliferation was assessed by MTT assay. Results represent the mean (± standard deviation SD) of two independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.001 vs 2; #p < 0.05, ##p < 0.01, ###p < 0.001 vs 4; Student’s t-test)