Fig. 6

Effect of osimertinib and T-DM1 on HER-2 overexpressing PC9/HER2c1 cells in vitro and in xenograft models. a HER-2 protein levels on cell surface was quantified by flow-cytometry and expressed as MEF as described in the Methods section. Mean values of two independent measurements (±SD) are shown (***p < 0.001 versus PC9 cells, Student’s t test). b PC9 and PC9/HER2c1 cells were treated with increasing concentrations of osimertinib for 72 h and then cell proliferation was assessed using MTT assay. c PC9/HER2c1 cells were treated with increasing concentrations of osimertinib in absence or in presence of 1 μg/ml T-DM1. After 72 h cell proliferation was assessed by MTT assay and the effect of drug combination was evaluated using the Bliss interaction model. Data in b e c are expressed as percent inhibition of cell proliferation versus control cells and are means ±SD of three separate experiments. d Cells were treated with 100 nM osimertinib, with 2 μg/ml T-DM1 or with their combination, and after 24 h cells were lysed and Western blot analysis was performed to detect the indicated proteins. e PC9/HER2c1 cells were subcutaneously inoculated into Balb/c-Nude female mice and after tumors have reached an average size of about 200 mm³ the animals were randomized into four different groups. Osimertinib was administered at a dosage of 10 mg/Kg/die orally and T-DM1 at a dosage of 15 mg/kg twice per week intraperitoneally for 2 weeks. Tumor sizes were measured every 3–4 days and data are expressed as percent change in tumor volume ± SEM (n = 8 tumors per treatment group). (* < 0.05, **p < 0.01, ***p < 0.001 vs ctrl; ###p < 0.001 vs osimertinib; $$p < 0.01 vs T-DM1; two-way ANOVA followed by Bonferroni’s post-test)